Mixing is important for microfluidic systems and placing obstacles in a flow path for generating advection, or splitting/recombination flows, is a very popular method for enhancing the mixing. In this paper, we present experimental investigations on such microfluidic mixing with four different shapes of trapezoidal obstacles and tested them in a 1000-fold span of Reynolds number (Re). The obstacles have four different base ratios 1, 3, 6 and 9, which indicate the ratios between the upper and lower bases of a trapezoid. Two different dyes, yellow and blue, were used for visualizing and evaluating the performance of mixing. The results show that, when the base ratio is 1, the mixing surprisingly becomes worse with the increase of the flowrate. When the ratio is 3 or 6, the mixing performance is first reduced with the increase of Re and then went through a transition around Re of 10 before it rapidly increases. When the ratio is 9, two transition points were found around Re of 10 and 100, respectively. The work provides useful information for realizing shape-dependent mixing performance, as well as for developing an intelligent lab-on-a-chip system.

This video presents a microfluidic phenomenon called “Virtual Vortex Gear (VVG)” and an application of it. The video contains 4 parts and is described as follows: The 1st part shows an application of VVG as a controllable valve in a micro fluidic system and the on and off of the valve are controlled by different flow speeds. The valve is turned on when the flow speed is high enough, and vice versa. The 2nd part shows the generation of VVG and its mechanism. When the flow speed, which is proportional to Reynolds Number, is gradually increased, the flow pattern evolves in the order as (1)parallel streamlines, (2)one vortex, (3)two vortices and eventually (4)three vortices including the last vortex inside the circular chamber. The evolution indicates the transmission of flow energy from the main stream to the inside of the chamber when the flow speed is over a certain range. In addition, every two adjacent vortices rotate in opposite directions which is just like a set of gears, and that is why we named it “VVG”. In the 3rd part, an application of VVG for chemical injection is demonstrated. A colored liquid is represented for the chemical and is surrounded by different sheath flow for the control of injection locations. It is found that only the fluid in a particular pinpoint can be injected into the target chamber. Furthermore, the complex but stable 3D flow patterns are visualized from the video. The last part of the video shows that different amount of chemical injection can be performed in different chambers along the same main stream and the distribution of the color is gradually become uniform by spontaneous diffusing.

This paper reports an ultra-fast manipulation on micro-scale objects in a microfluidic channel. The objects are manipulated in simple harmonic motions and the manipulation speed has been achieved up to 3000 Hz. While the maximum speed was only about 130 Hz in previous works, the speed is advanced with an additional order in this work. Based on the experimental results, we find that the gain decreases along the line of -20 dB/decade in a logarithmic plot. The transfer function based on a theoretical model was employed for interpreting the results. The experimental gain and theoretical gain were well matched. Finally, experiments with red blood cells were performed and it supports the feasibility of applying such ultra-fast manipulation to cell evaluations.

An automatic system for evaluating single cell viscoelasticity is proposed and tested in this paper. The system includes three main operations, and they are the operations of catch, load and launch. In the catch operation, the system is capable of capturing a target cell by high-speed vision and high-frequency flow control. The captured cell is pushed into a narrow constriction for the load operation. Different durations of loading time are applied to cells for evaluating cell viscoelasticity. Finally, the cell is launched out from the constriction, and the recovery response of the cell is monitored for cell characterization. Human red blood cells are experimentally tested by the proposed system. The experimental results show that the system successfully perform the evaluation, and the viscoelastic characteristics of the cells are discussed.

A surprising phenomenon is observed in a microfluidic channel where suspending microbeads are spontaneously aligned into lines. Microbeads are randomly distributed in the channel at a relatively high velocity (3.27 μm/ms), but start to align into lines at a relatively low velocity (0.05 μm/ms). The alignment has been repeated with and without obstacles in the channel. The phenomenon is interpreted as an unintended acoustic wave being around the experimental environment, and the wave resulted in a standing wave which moves the microbeads towards the nodes of the standing wave. By using a frequency analyzer, it is found that a pulse-width-modulation controller in the system generated high-frequency signals, which is the most possible wave source for the alignment. The experimental results are presented, and characteristics of acoustic wave are analyzed. The phenomenon could contribute to microfluidic applications for achieving acoustic alignment without complex fabrication of interdigital transducers.

We developed a ‘hybrid actuator system’ to precisely control the position of a micro-particle at high speed in a microfluidic chip. The hybrid actuator system benefits from two actuator systems by combining an electroosmotic flow generator and pressure-driven flow induced by a piezoelectric actuator-driven syringe pump system. We also implement an image processing algorithm using a high speed vision system and design a supervisory controller for the hybrid actuator system to apply it to a microfluidic system. The proposed system can be used to overcome current limitations of conventional pump systems for microfluidic devices.

This paper proposes the method for mechanical characterization of floating cells on a microfluidic chip. We measured the reactive force of cells on the chip by applying mechanical deformation to the cells. Particularly we focused on the method to improve the sensing resolution of the probe position by using the phase detection of moiré fringe. This method realized approximately ten times higher resolution compared to the previous method. The detailed data suggest some unique characteristics of cells. We discussed the phenomenon seen on the data with a mechanical model, which is based on Heltzian contact theory in the light of stiff nucleus.

A novel method for sensing local pressure inside a microfluidic device is proposed and developed. The main advantage of the method is that the pressure can be visually seen without attaching any electrical wire or instrument. The method can also be easily integrated into applications, such as micro-robots, because of its single-layer design. The working principle is based on the deformation of Polydimethylsiloxane, a kind of polymer that is often used in microfluidic systems. The deformation in the deformation chamber causes fluid to flow in, or out, the sensing area, and consequently results in changes of color intensity in the area. As a result, the pressure can be determined based on the brightness value over the sensing area. Experimental results show a highly correlated relationship between the measured brightness and pressure with the absolute correlation of 0.986. The hysteresis and drift of the proposed sensor are investigated, and are compared with our previously proposed microbeads approach. The prototype of the proposed sensor succeeded in performing measurement on local pressure in a microfluidic device with the resolution of 3.04 kPa.

This paper discusses a dynamic nonprehensile manipulation of a deformable object, where the shape of a thin object is dynamically controlled by the plate's rapid motion. After explaining the manipulation principle, we introduce a simplified analytical model where an object is modeled by two mass points and the plate has two degrees of freedom: a translational motion and a rotational one. After categorizing jump patterns of the mass point with considering the plate's acceleration, we show that gait-like behaviors of the object are generated on the periodic plate's motion. Through simulation analysis, we show the deformation velocity transition of the object with respect to the amplitude of plate's acceleration. We reveal that the transition is characterized by particular amplitudes which govern the jump patterns of the mass point. We make clear that the optimum plate's motion leading to the maximal deformation velocity exists on one of such particular amplitudes.

We have been studying an omnidirectional driving gear mechanism that can generate thrusting force in an arbitrary direction on one surface, which may be flat or curved. This omnidirectional gear is driven by spur gears that are perpendicular. When one spur gear rotates to drive the omnidirectional gear, the other slides between the teeth of the omnidirectional gear and vice versa. In this paper, we introduce gears with passive rollers to reduce the frictional resistance with a mechanism including smooth rolling motion of conical or flat passive rollers, which can boost the power transmission efficiency of the omnidirectional driving gear system. We also confirmed another useful function of this gear with passive rollers as a worm wheel to transmit power from a worm gear with higher energy efficiency than an ordinary worm wheel.

This paper discusses the observability of cell stiffness by utilizing a micro-channel whose diameter is slightly smaller than that of a cell. By modeling each cell with distributed springs and dampers, we discuss how many sensing points are necessary and sufficient for evaluating cell stiffness. We define the observability by the velocity of each cell through a micro-channel based upon the experimental observation that the equilibrium velocity of a cell varies corresponding to its stiffness. We conclude that for evaluating cell stiffness, two points are necessary and sufficient while using an infinitely long channel, and three are necessary and sufficient for judging whether cell stiffness is observable or not. This study attempts to provide a practical guidance for developing a simpler, faster, low-cost sensor in the future.

A new concept of μ-cell fatigue test is proposed. By reciprocating a cell across the throat of a micro channel repeatedly, the dynamic deformation behavior of the cell is measured. We define a new index of fatigue characteristics of cells as the number of reciprocatory motion leading to a prescribed recovery ratio. The test system is composed of a piezoelectric (PZT) actuator, a high speed vision sensor and a micro channel with a throat. Preliminary experiments were conducted by using Red Blood Cells (RBCs). The result suggested that the activation level of a cell can be evaluated based on its fatigue characteristics.

The finger mechanism equiped with omnidirectional driving roller is shown. The omnidirectional driving roller has two active rotational axes at the touching point. The finger mechanism with this roller can manipulate the grasped object with any arbitrary directional axes. Prototype model has been developed and basic motion of the finger has been confirmed though the experiments.

In this paper, the principles and the actual configurations of the omnidirectional driving gear mechanism that was implemented by the authors were described. The validity of the proposed structure was also confirmed and its basic characteristics understood through experiments using the actual prototypes.

As ordinary dual-axis driving mechanisms in X-Y directions, for example, commercially available X-Y stages with ball screws are familiar. However, such driving mechanisms have two stages, namely both upper and lower linear actuators, the latter of which must generate sufficient thrust to carry large weights, including that of the upper actuator mechanism, which has hampered efforts to achieve suitably fast and smooth driving motion due to the inertial force effect. It is also difficult to achieve a small and slimline driving mechanism with such overlapping two-stage structure. In these ordinary two-stage driving mechanisms, the motion of the X-Y stage can be disturbed by the wires of the upper actuator. In this research, we have considered the abovementioned problems, and propose a new omnidirectional driving gear mechanism that enhances its driving area from the normal X-Y plane to convex and concave curved surfaces respectively, and even various combinations of both. The smoothness of basic omnidirectional motion and effectiveness of the driving method of this proposed omnidirectional driving gear mechanism have been confirmed with several experiments involving our setups.

In this paper, additional manipulating function for limited narrow space with omnidirectional driving gear was described. The validity and advantage of the proposed function was also confirmed through experiments using the actual prototype of the planar omnidirectional driving gear units for the parallel gripper.

A rigid plate end-effector at the tip of a high-speed manipulator can remotely manipulate an object without grasping it. This paper discusses a dynamic nonprehensile manipulation strategy to rotate thin deformable objects on a rigid plate with two degrees of freedom (DOFs). The deformation of the object due to dynamic effects is exploited to produce fast and stable rotation. By varying the frequency of the rotational component of the plate's motion, we show that the dynamic behavior of the object mimics either a sliding, walking, or running gait of a biped. We introduce a model to simulate this type of system in which the object is constructed of multiple nodes that are connected by viscoelastic joint units with three DOFs. The joint's viscoelastic parameters are estimated experimentally in order to model real food. Afterward, simulation analysis is used to investigate how the object's rotational behavior and its angular velocity change with respect to the plate's motion frequency. We show how the object's behavior during rotation is analogous to bipedal sliding, walking, and running gaits and then obtain optimal plate motions leading to the maximal angular velocity of the object. We also reveal that an appropriate angular acceleration of the plate is essential for a dynamically stable and fast object's rotation. We further show that the friction coefficient that maximizes the object's angular velocity depends on its gait.

This paper presents an experimental study of the bio-inspired artificial skin consisting of silicone and embedded strain gages, in which silicone imitates the epidermis and dermis, and strain gages mimic corpuscles. The strain gages are embedded in silicone under different configurations like corpuscle in humans skin. Both static displacement and dynamic excitations are applied in arbitrary positions, with different magnitudes and frequencies. The responses are observed by measuring the output signals from strain gages. Comparison with FEM simulation of static displacement shows intuitive agreement. The responses to dynamic excitation in typical frequency range of human somatosensors are obtained both experimentally and with simulation of dynamic modeling. We found that each configuration has advantages and disadvantages. This paper shows how strain gages embedded in silicone will behave in response to both static and dynamic excitations, and suggests modeling and fundamental concepts to design a bio-inspired artificial skin sensor.

This paper discusses a nonprehensile dynamic manipulation of a deformable object, where the object is remotely manipulated on a plate attached at the tip of a bar. We have found that the object's deformation generated by dynamic effects can drastically contribute to a fast and stable object rotation. We introduce a new simulation model for a sheet-like object, where the object is constructed of multiple nodes connected by three DOFs viscoelastic joint units. We apply the model to real food after the viscoelastic parameters are estimated. Then, simulation analysis is used to show how the object's rotation behavior changes with respect to the plate's motion frequency, similar to the motion of human legs sliding, walking, and running. Finally we obtain an optimum plate motion leading to the maximal angular velocity of the object. We also reveal that an appropriate angular acceleration of the plate is essential for a dynamically stable and fast object rotation.

A dynamic model of a flexible slewing beam in contact with the external environment is developed in this paper. The model is represented in the non-dimensional form. A definition of the percussion center of the flexible beam is introduced and its basic properties are established. It is shown that, contrary to the percussion center of rigid beam, for the flexible beam there exists infinite number of percussion centers, one for the first vibration mode, two for the second, three for the third and so on. It is also shown that the percussion centers can be considered as the points of maximal stiffness of the correspondent vibration modes. The results of our theoretical study may be interested not only for designing flexible tools but also for planning motion strategies for flexible manipulators interacting with the external environment.

This paper describes a combination mechanism of a wheeground a paddle to realize an effective movement on the border of ground and water. For the conventional mobile mechanisms on water or on ground the combination of the mechanism to the body of the robot separately, and each one can be the interruption to the other in each field. In this research, we propose a hybrid mechanism of a wheeground a paddle as drive mechanism itself to realize an effective movement on the border such as a coast with debris after a disaster like a seismic sea wave or a tanker grounding accident. A prototype robot has been built and basic experiments on its motion have been conducted.

Non-contact stiffness sensor is often utilized especially for medical fields due to its advantage of avoiding damage to tissues and keeping sanitary. However, it is hard to measure the force accurately, because the fluid jet based force much depends upon the shape after deformation of object. This paper proposes an innovative approach where the external force is adaptively calibrated based on the deformation of object so that we can evaluate the internal stiffness parameters more accurately than that of conventional approaches. It is shown that the proposed method can improve the accuracy of force application with even 100% at an extreme case.

This paper describes a dynamic nonprehensile manipulation of a deformable object, where the shape of a thin rheological object is dynamically controlled by the combination of the inertial force and the frictional one generated by the plate's rapid motion. We first introduce a one-dimensional viscous model to approximate the object deformation characteristics, focusing on the final shape of the object. Assuming that the plate has two degrees of freedom: a translational motion and a rotational one, we derive two sufficient conditions to deform the object: one to enlarge it and the other to contract it. Then, we show the plate's cyclic motion leading to the object's continuous deformation. Finally, simulation and experimental results are shown in order to verify the proposed method.

This paper describes linear load-sensitive continuously variable transmission with the spherical driving unit. This CVT mechanism consists of spherical drive, drive axis, motor housing, fixed bracket and linear sliding plate. It changes the reduction ratio continuously by inclination angle of active rotational axis. Additionally, this linear mechanism has a load-sensitive function by changing inclination of active rotational axis in response to the load. We have developed a linear load-sensitive continuously variable transmission and confirmed the effectiveness of the proposed mechanism.

This paper discusses a shaping strategy of a rheological object whose deformation characteristic includes both elasticity and plasticity. We first introduce a seven-nodes viscoelastic model for approximating the outline and the dynamic characteristics of the object. Then, we show a shaping method of the object's outline, where the ratio between the object's length in the grasping direction and that in the perpendicular one is controlled by using a parallel jaw gripper. Based on the plastic deformation distribution for the integrated input stress, the proposed method can actively manage the final object's outline. In addition to the contribution on simplifying the gripper's degree of freedom, this method has the advantage that the handling time is drastically reduced, compared with the position based passive method. We finally show the experimental results for confirming the validity of the proposed method.

This paper discusses an active shaping method for an unknown rheological object by considering the characteristics of viscoelasticity. By utilizing a four-element model for approximating the dynamic characteristics of object's deformation, we drive the deformation decomposition into the elastic response and the plastic one. For shaping the object, we then propose a two-phase strategy for controlling the resultant deformation; in the first phase the viscoelastic parameters are estimated with avoiding the over deformation, based on the elastic response; in the second phase the desired resultant deformation is generated by actively managing the integral force, based on the plastic response. This strategy has an advance that the handling time of the robot is given by a finite time, while the desired resultant deformation is theoretically completed in the infinite time. We finally show experimental results for confirming the validity of the proposed strategy.

Cell stiffness could be an index for evaluating its activity. Although various systems measuring cell stiffness have been proposed so far, they are slow for adaptively connecting to cell sorters capable of handling more than 1000 [cells/sec]. This paper proposes a new approach that can indirectly evaluate the cell stiffness by measuring the passing time for a narrow channel. When a cell passes through the channel, it receives a viscous force depending upon how much deformation is exerted on the cell. We show that the stiffness is a function of both the passing time and the initial diameter of cell. We also show that the stiffness is proportional to the passing time and inversely proportional to the initial diameter, under the assumption that the thickness of fluid film is inversely proportional to the normal force. The experimental validation is given together with the basic working principle.

We discuss an empirical based design of Active Strobe Imager (ASI) that enables us to visualize the dynamic behavior of tissue, even under a high frequency vibration that cannot be followed by the naked eye. A pneumatic actuator imparts a vibration for the target object. By flashing light with slightly different frequency, we can see the dynamics by the naked eye. We discuss an approach for determining a set of optimal parameters of ASI by considering both the uncomfortability sensation due to light flickering, the sharpness of the motion, and the amplitude of the vibration of the object. We also give an example of optimal parameter determination for human skin.

In this paper, a new category of the wheel-leg hybrid robot is presented. The proposed mechanism can compose large wheel diameter compared with the previous hybrid robot to realize a greater ability to climb obstacles. A prototype model of one Wheel-Leg module of the proposed robot mechanism has been developed to illustrate the concept. Actual design and mode changing experiment with a test mechanical module is also presented. Basic movement tests and a test of the basic properties of the rotational fingertip are also shown. The Basic configurations of wheel-leg retractable is considered well. The integrated mode is also described.

Viscoelastic materials are known to exhibit temporal response that changes force or displacement at the contact interface under position or force control, respectively. In this paper, we conduct experimental study using force control to explore and observe creep phenomenon in robotic grasping in order to better understand the nature of such contact interface, which has been widely used in soft robotic fingers, robotic feet, and contact surface of robotic arms. We found that the creep response under a constant external force exhibits the characteristics of exponentially increasing or decreasing temporal response. Such characteristics are similar in nature to those found in the relaxation response of viscoelastic materials when the grasping is under position control. Two different types of creep responses are found, depending on the state of grasping. Both Types I and II in creep response mirror the Types I and II in relaxation response. We also found that different loading rates under force control result in different elastic response, in addition to the temporal response. This is an interesting finding because the Fung's model postulates for an elastic response that is independent of, and can be separated from, the temporal response. The experimental results do not show such independence.

In this paper, a nonlinear latency model is presented to describe the relationship between the strain and strain rate of the temporal responses in robotic grasping that involves viscoelastic contact interface. The results from experiments and simulation are presented, and are found to match well with each other. The nonlinear latency model was able to adequately represent both Type I and Type II relaxation responses. For the successive loading and holding with a soft contact, the model describes the behavior of step-wise increase of equilibrium strain and a polynomial relationship between the strain rate and the strain. The nonlinear latency model can successfully predict and model the behavior of anthropomorphic soft contact interface in grasping and manipulation when the grasped object is held in certain posture of prehension with repeated loading and/or unloading.

This paper discusses the non-grasp dynamic manipulation of a deformable object inspired by the handling mechanism of pizza master. The master handles a tool where a plate is attached at the tip of a bar, and he remotely manipulates a pizza on the plate. We found that he aggressively utilizes two DOFs (degrees of freedom), such that the linear motion along the bar and the rotational one around the bar, in order to produce quick plate motions for dynamically manipulating the object. Applying this handling mechanism to the robot system, we first show how to rotate an object by using the two DOFs of plate motion. We then reveal that the deformation of the object generated by dynamic effects can drastically contribute to high-speed and stable rotation, just like human steps for turn on the floor. By both simulation and experiment, we show that there exists the optimum plate motion leading to the maximum rotational speed of the object.

For an arbitrary force impartment on tissue, the tissue color changes from red to white due to the decrease of arterial blood. The dynamics leading to (or recovering from) ischemia is a good index for evaluating the vitality of tissue. This paper discusses the ischemia dynamics by using a newly developed active sensing system composed of an air jet nozzle for imparting an air pulse to tissue and a high-speed camera for capturing the change of color of tissue with respect to time. Through experiments, we found that the ischemia dynamics is particularly characterized by the recovery phase where the time constant changes depending upon the local physical condition of tissue. We also showed a map on color changing rate conveniently utilized for quickly understanding the location of ischemia area which is a candidate replaced by regenerated tissue.

The latency model is an analytical model for describing the behavior of nonlinear viscoelastic contact interface in robotic grasping and manipulation. The latency model is based on experimental observation of viscoelastic materials which exhibit the behavior of both elastic and temporal responses when subject to external force or displacement. It is postulated that such materials display latency in response of external influence by the rearrangement of molecules, holes, and structures in order to achieve an equilibrium state corresponding to the instantaneous loading. As a result, we propose that there are temporal latent activities in progress before the material reaches the equilibrium state. In the previous study [21], the latent activity of strain re-distribution with a prescribed constant displacement was presented using both theoretical modeling and experimental results. In this paper, we build upon this latency model to study the behavior of viscoelastic materials under different loading rates with experimental results. The latency model is employed to explain the behavior of responses of hard and soft viscoelastic materials typically found in robotic contact and grasping.

This paper discusses dynamic manipulation inspired by the handling mechanism of a pizza chef. The chef handles a tool called ldquopizza peel,rdquo where a plate is attached at the tip of a bar, and he remotely manipulates a pizza on the plate. We found that he aggressively utilizes only two degrees of freedom (DOFs) from the remote handling location during manipulation: translation along the bar and rotation about the bar. From the viewpoint of a dynamic system, the inertial loads for these specific DOFs are never affected by the length of the bar. This is important for the production of quick plate motions so that the object on the plate can be dynamically and remotely manipulated. Applying this handling mechanism to a robot system, we first reveal how to make the object's motion for three DOFs by using two DOFs of plate motion. We then show that it is guaranteed to achieve an arbitrary desired set of position and orientation of the object by the proposed manipulation scheme. The proposed method has good manipulability because the translational motion of the object can be fully decoupled from the rotational motion (though notviceversa). Finally, we show a couple of experiments that confirm the basic idea.

This paper discusses a dexterous hyper plate inspired by pizza manipulation. We first discuss the necessary combinations of active degrees of freedom of the plate for manipulating an object to arbitrary position and orientation on the plate, under the gravity. While there are nine patterns for choosing two active degrees of freedom of the plate, we show one of them can satisfy a sufficient condition for manipulating the object with the weakest coupling among object’s motions and eventually leads to a simple manipulation scheme. A couple of experiments are shown to confirm the basic idea.

This paper proposes a piercing based grasping by using the self-tightening effect of objects with elasticity. We suppose a piercing hand with palm where the piercing motion by needles can be independently achieved irrespective of the palm motion. The palm first approaches and touches with the object, with a slight pushing motion. This motion produces an increase of potential energy of object. After the motion, the needles pierce the object. When the object is lifted up, the accumulated potential energy is released and the object tries to recover the original shape under the piercing condition. We found a particular mechanical configuration between the object and the needle, under which the constraint of object is tightened due to the object deformation during the release of the potential energy. In order to confirm the robustness of the proposed method, we have done a couple of experiments. The results show that the proposed method keeps an extremely high robustness compared with the other piercing methods.

In this paper, we employ Fung’s viscoelastic model discussed by Tiezzi and Kao to study the experimental data presented by Sakamoto et al. for grasping viscoelastic objects using a parallel-jaw gripper. The viscoelastic contact modeling presented in this paper is characterized by two separate responses: elastic response and temporal response. Two main and intriguing results were found in the modeling and analysis of experimental data. The first is the consistency on the normalized coefficients for the curve fitting of the temporal response during the relaxation period of the grasping. Such consistency suggests that the proposed model is applicable to the grasping task at hand. The other result is the generic pattern of the elastic response deduced from the experimental data. The pattern of elastic response represents different physical significance of grasping which involves viscoelastic contact interface.

This paper proposes dynamic capturing strategies where a 2D stick-shaped object with both translational and rotational velocities is completely stopped by two robotic fingers. We first show the fingertip position and the object orientation for generating a desired velocity of the object under the friction independent collision. Once the object results in a pure translational motion whose direction is perpendicular to the longitudinal axis of object, it is guaranteed that two fingers can always capture the object irrespective of friction coefficient. By using this nature, we show both 2-step and 3-step capturing strategies for a 2D stick-shaped object whose width is negligibly small. The 3-step capturing strategy can guide the object in an arbitrary direction, while the 2-step one can do it only in a particular direction. The 3-step capturing strategy is demonstrated by experiment for verifying our idea.

This paper newly proposes the active strobe imager (ASI) that can visualize the dynamic behaviors of internal organ to medical doctors within Human dynamic eye sight, so that they can get a hint for detecting the location of tumors in real time during operation. The ASI is composed of a nozzle for supplying a pulsated air jet to an internal organ, a strobe system for visualizing the dynamic behaviors, a camera for capturing the image at the moment of strobe flashing, and a monitor for displaying the dynamic motion of internal organ, respectively. Without the assistance of strobe, medical doctors can not see what is really happening in real time, since the frequency of air jet is even more than the range of human dynamic eye sight. After explaining the basic principle, we show a couple of experiments for both artificial and real human lungs. Through these experiments, we newly found that the ASI is really helpful for discovering tumors or other diseases hidden in internal organs. Movies are available in Website.

The contact tonometer is commonly used for measuring the internal eye pressure to diagnose glaucoma. However, the conventional eye pressure measurement is valid only under the assumption that all subjects have the same structural eye stiffness. This paper challenges to measure the contact area between the probe and the cornea in addition to the corneal deformation for considering the individual differences in the structural eye stiffness. Prior to the experiment, a spherical model of an eye is developed and the analytical eye stiffness is introduced. The experiment is conducted based on the contact method where a contact probe is pressed on an anesthetized cornea. The deformation of the cornea and the contact area are captured by cameras during the experiment. The experimental results show that the measured stiffness nicely matches the analytical solution based on the constructed model. However, some subjects have different relationships between the displacement and the contact area even with similar estimated eye pressures. This suggests that the structural eye stiffness should be considered for more precise diagnoses of glaucoma.

This paper discusses an optimum design approach for robotic hands by considering the characteristics of visco-elasticity of food. "Norimaki-sushi" is taken as an example for food. We first show that the dynamic characteristics of such food can be expressed by utilizing the Maxwell model with two layers. Based on dynamic parameters obtained by experiments, we show the relationship among the total working time, the plastic deformation of food after the grasping motion, the hand stiffness, and the operating velocity of the hand. We newly found an interesting behavior of food that allows to find an optimum set of the design parameters for achieving the minimum plastic deformation of food.

This paper proposes dynamic capturing strategies where a 2D stick-shaped object with both translational and rotational velocity is completely stopped by two robotic fingers. We first show the fingertip position and the object orientation for generating a desired velocity of the object under the friction independent collision. Once the object results in a pure translational motion whose direction is perpendicular to the longitudinal axis of object, it is guaranteed that two fingers can always capture the object irrespective of friction coefficient. By using this nature, we show both 2-step and 3-step capturing strategies for a 2D stick-shaped object whose width is negligibly small. The 3-step capturing strategy can guide the object in an arbitrary direction, while the 2-step one can do it only in a particular direction. The proposed strategies are demonstrated by experiments for verifying our idea.

This paper discusses jumping pattern generation for a serial link robot in order to maximize its jump height under torque limitation. By applying a genetic algorithm (GA) for determining torque assignment, we obtain various jumping patterns with respect to the torque limitation for a fixed mass of the robot. With the increase of the torque limitation, double-leg based jump, single-leg based jump, and spring-type jump are generated for achieving the largest jump height. Under an additional joint angle limitation, we also obtain an interesting solution where one end of the link is first lifted up and the other end finally kicks the ground strongly

The internal eye pressure is an important index for judging whether an eye suffers from glaucoma or not. The conventional eye pressure measurement is valid only under the condition that all subjects have the same structural eye stiffness. This paper challenges stiffness sensing of the human eye by pressing it with a contact probe. The displacement of the eye is captured by a camera with high resolution. Experimental results show that the stiffness is roughly constant for each subject, while it differs by up to a factor of five between subjects. The method can detect subjects whose eye stiffness is smaller than average for further careful medical examination

We discuss the optimum design issue for tracing type legged robots in the sense that it can jump as high as possible. By applying dimensional analysis techniques, we introduce four non-dimensional parameters that control the jump ratio(= h/l) for a jumping robot. An interesting observation is that there exists the optimum design point where the jump ratio becomes maximum. Through experiments, we found that the robot with the optimum design specification can achieve the jump ratio of 3.6, while the jump ratio decreases for other design points.

This paper newly proposes the four-fingered robot hand with dual turning mechanism where two and two other fingers can independently rotate inner and outer circles with the common center, respectively. Due to this mechanical configuration, it has the particular rotating axis where the manipulation around the axis can be completely decomposed into the velocity control around the axis and the internal force control in the contact plane. We achieved a manipulation task around the axis with the time of 0.8[sec] for one rotation, while it is relatively slow for another axis.

This paper challenges the dynamic based diagnosis (see Fig. 1) of human eye. Through a high speed motion capture during an air jet applied to a human eye, the eye dynamics including stiffness and damping is evaluated. By utilizing both the eye pressure and the dynamic parameters, we can increase the reliability of the eye diagnosis. We show that each subject has his (or her) own impedance parameters and that stiffness is an important index for guaranteeing the validity of eye pressure sensing.

This paper discusses 2D dynamic preshaping issue for a stick-shaped object changing both position and orientation with respect to time. We propose the two-step grasping strategy where it first stops the rotational motion by choosing an appropriate finger position, and then stops the translational motion step by step for completely making the object stationary. We confirm the basic idea by simulation.

This paper discusses the design of high speed capturing robots based on dynamic preshaping. Focusing on a wire drive robot, we obtain an optimum pulley position so that all finger links can make contact with an object simultaneously. Based on the optimum design, we also develop the hardware so that we can confirm the validity of the optimum pulley position by experiment.

Conventional non-contact impedance sensors cause an essential sensing error in principle due to the intersection angle between the line of force probing and the sensing axis of distance sensor, especially for the environment with distributed compliance. To cope with the issue, we propose the co-axis type non-contact impedance sensor that can provide us with the accurate impedance parameters of environment. The key design is that we give the common axis for both force probing and distance sensor, so that we can obtain the exact displacement of environment. Experimental results are also shown for confirming the effectiveness of the proposed sensor.

We newly propose the Non-Contact Stiffness Imager that can provide us with the pattern of stiffness distribution of environment. It is composed of a force probe and a displacement sensor capable of obtaining area information. The main application of the Stiffness Imager is diagnosis, especially for examining whether there exist tissues suffered by disease or not. In order to show the effectiveness, we implement the Stiffness Imager into an endoscope camera for obtaining inner stiffness information as well as surface information of stomach. Basic experimental results are also shown.

Dynamic preshaping is important for high speed capturing robot to catch a moving object successfully. This paper discusses dynamic preshaping for a capturing robot driven by a single wire. To control the finger posture while approaching an object, there are three essential factors, wiring, spring distribution among joints, and mass distribution in each finger link. Giving the final link posture of finger, mass distribution, and tension with respect to time, we explore hoe to determine both the wiring and the spring distribution. We first show how to find them under a quasi-static motion, where all dynamic effects are neglected. We further explore an approach to find them under a dynamic motion where the tension increases fast enough.

This paper proposes a new endoscope system with an air injection based contact probe capable of measuring the local impedance of the inner surface of stomach. By utilizing air pressure, we can produce an equivalent contact force, which is really advantageous for avoiding any damage for stomach during an examination. A big issue is that there is no way to obtain the applied force to stomach exactly. The key for solving it is the specially designed solenoid valve with the response for more than 500 Hz. The solenoid valve with such a high response allows us to estimate each impedance parameter, even with a reference value. We show experimental system with a couple of interesting results.

Dynamic preshaping is important especially for a high speed capturing robot to catch a moving object successfully. This paper discusses an issue on dynamic preshaping for a capturing robot driven by a single wire. To control the finger posture while increasing the wire tension, there are three essential factors, wiring, spring distribution among joints, and mass distribution in each finger link. Giving the final link posture of finger, mass distribution, and tension with respect to time, we explore how to determine the spring distribution. We first show how to find it under a quasi-static motion, where all dynamic effects are neglected. We further explore an approach to find it under a dynamic motion where the tension increases fast enough.

This paper proposes a new tactile sensor capable of automatically adjusting the sensitivity of each sensor unit, depending upon the contact information. Suppose a strain gauge based tactile sensor composed of multiple sub-sensor units and a single AD-DA port. For such a sensor system, we introduce two key components; the Analyzer, how to determine the contact force quickly from each sub-sensor unit, and the automatic gain controller (AGC), how to automatically change the gain for each unit, according to the sensory information. For example, the sensor can automatically cope with both the signal saturation due to an unexpectedly large input and the resolution control depending upon the contact force. The basic idea of the sensor system is verified by experiments.

In this paper we introduce a newly developed high-speed multi-fingered robotic hand. The hand has 8-joints and 3-fingers. A newly developed small harmonic drive gear and a high-power mini actuator are fitted in each finger link, and a strain gauge sensor is in each joint. The weight of the hand module is only 0.8 kg, but high-speed motion and high-power grasping are possible. The hand can close its joints at 180 deg per 0.1 s, and the fingertips have an output force of about 28 N. The hand system is controlled by a massively parallel vision system. Experimental results are shown in which a falling object was caught by the high-speed hand.

Context in time series is one of the most useful and interesting characteristics for machine learning. In some cases, the dynamic characteristic would be the only basis for achieving a possible classification. A novel neural network, which is named "a recurrent log-linearized Gaussian mixture network (R-LLGMN)," is proposed in this paper for classification of time series. The structure of this network is based on a hidden Markov model (HMM), which has been well developed in the area of speech recognition. R-LLGMN can as well be interpreted as an extension of a probabilistic neural network using a log-linearized Gaussian mixture model, in which recurrent connections have been incorporated to make temporal information in use. Some simulation experiments are carried out to compare R-LLGMN with the traditional estimator of HMM as classifiers, and finally, pattern classification experiments for EEG signals are conducted. It is indicated from these experiments that R-LLGMN can successfully classify not only artificial data but real biological data such as EEG signals.

This paper proposes a human-assisting manipulator teleoperated by electromyographic (EMG) signals and arm motions. The proposed method can realize a new master-slave manipulator system that uses no mechanical master controller. A person whose forearm has been amputated can use this manipulator as a personal assistant for desktop work. The control system consists of a hand and wrist control part and an arm control part. The hand and wrist control part selects an active joint in the manipulator's end-effector and controls it based on EMG pattern discrimination. The arm control part measures the position of the operator's wrist joint or the amputated part using a three-dimensional position sensor, and the joint angles of the manipulator's arm, except for the end-effector part, are controlled according to this position, which, in turn, corresponds to the position of the manipulator's joint. These control parts enable the operator to control the manipulator intuitively. The distinctive feature of our system is to use a novel statistical neural network for EMG pattern discrimination. The system can adapt itself to changes of the EMG patterns according to the differences among individuals, different locations of the electrodes, and time variation caused by fatigue or sweat. Our experiments have shown that the developed system could learn and estimate the operator's intended motions with a high degree of accuracy using the EMG signals, and that the manipulator could be controlled smoothly. We also confirmed that our system could assist the amputee in performing desktop work.

Discusses the manipulation of multiple objects by pushing. When manipulating ultiple objects, relative motion between two objects such as sliding and rotation may occur. We propose velocity based pushing where the region of the pusher's velocity causing the desired relative motion at each contact point is obtained as a common space of regions causing the relative motion at one of the contact points. When obtaining the velocity region, we use the equivalent center of friction (ECOF) which is an extension of the conventional COF and which is same as COF when the object translate. Experimental results are also included to show the effectiveness of our idea.

This paper newly proposes dynamic friction closure, under which a moving object is completely stopped within a predetermined length through the work due to Coulomb friction between an object and a gripper. There are two conditions for achieving it: The geometrical condition, ensuring the robot motion to meet with an object at an appropriate catching point, and frictional stopping capability, ensuring the moving distance of object is less than the predetermined distance under a limited grasping force. Through the simple analysis on catching a 2D circular object by a parallel jaw gripper, we newly found that even under the same total energy of object, the distance changes depending upon the ratio between initial rotational and translational velocity. For a 3D sphere object, the maximum moving distance is provided with the initial kinetic energy.

This paper discusses the design of a capturing system with an extremely high response. The key for achieving a quick response is the arm/gripper coupling mechanism, where the potential energy initially accumulated in the arm is transferred to the kinetic energy of the arm and, continuously, to the kinetic energy for closing the gripper at the capturing point without any time lag. The experimental results show the maximum acceleration of 91G corresponding to almost two times higher than the conventional world record, and the total capturing time of 0.03 sec. Experiments on capturing a ball are also shown.

Electromyogram (EMG) has often been used as a control signal for a prosthetic arm, which includes information on the operator's motor intentions and the mechanical impedance of joints. Most previous research adopted the control methods of the prosthetic arms based on the EMG pattern discrimination and/or the force estimation from the EMG signals, and did not utilize any knowledge on tasks performed by amputees such as object grasping and soup-spooning tasks. In this paper, a new myoelectric control method is proposed using a statistically organized neural network and an event-driven task model. The task model is represented using a Petri net to describe the task dependent knowledge, which is used to modify the neural network's output. Experimental results show that the use of the task model significantly improves the accuracy of the EMG pattern discrimination.

This paper discusses the manipulation of 3D enveloped object. By assigning all fingers as either the position controlled finger (P-finger) or the torque controlled finger (T-finger), we propose a method for letting the object to move in the desired direction along the surface of the P-fingers. For this purpose, we obtain the joint torque command for the T-fingers. The formulation of the total force/moment set can be applied to general 3D enveloping grasp. Also, we newly provide a sufficient condition for the total force/moment set of the object moving toward the desired direction, where it can be applied to general 3D contact configurations between the object and the P-fingers.

This paper discusses the determination of torque commands for always guaranteeing the body propelling motion in Hugging Walk where the environment is enveloped by legs and the body. There are two key issues, one is to obtain the sub-total force set with the function of the joint torque in each leg, and the other is to obtain the constraint space where the body propelling motion is guaranteed without the body rotating motion when the sub-total force set is put in it. The basic idea is demonstrated by simulation and experiment.

Enveloping grasp systems not in static equilibrium result in dynamical motion. In this article, we develop a method based on dynamical-balance to solve motion analysis problem for an active-external grasp, that is to determine contact forces and accelerations consistent with the dynamics and friction law for a given torque-wrench pair. Since the method is analytic in nature, it may give the chance for better efficiency and more direct insight than a relevant linear complementarity formulation, although the solutions are the same. The method is verified using two examples: one is a simple grasp system with one frictional contact, and the other is a relatively general one with all frictionless contacts.

This paper discusses a sufficient condition for the manipulation of the Envelope Family, where multiple contacts are allowed between object and chains (or the environment). All chains are assigned to either the position controlled chain (P-chain) or the torque controlled chain (T-chain). Although the object motion under multiple contacts can not be uniquely specified only by the T-chains, we are able to provide a sufficient condition ensuring that a given set of torque commands for the T-chains always moves the object within the designated direction along the surface of a P-chain (or a fixed environment). Experiments as well as simulations are shown to verify this basic idea.

In this paper, a bio-mimetic trajectory of robots for manipulating a nonholonomic car is generated with a time base generator (TBG). In order to reveal what kind of trajectories the robots should generate for the given task, experiments with human subjects were performed. It has been shown that a human generates the trajectory with a single- or double-peaked velocity profile according to the geometrical conditions of the car. Then, bio-mimetic trajectories were generated by modeling the observed primitive profiles with the TBG and also compared with the human trajectories.

This paper proposes a new trajectory generation method that allows full control of transient behavior, namely, time-to-target and velocity profile, based on the artificial potential field approach for a real-time robot motion planning problem. Little attention, in fact, has been paid to the temporal aspects of this class of path planning methods. The ability to control the motion time to the target as well as the velocity profile of the generated trajectories, however, is of great interest in real-life applications. In the paper, we argue that such transient behavior should be taken into account within the framework of the artificial potential field approach.

This paper discusses the manipulation of an object under neighborhood equilibrium (NE), where an object with rolling contact can automatically find another equilibrium state close to the original one even when the current one is broken due the change of input. For a guaranteeing NE, we newly define the contact stable region (CSR) on the object surface. By utilizing the CSR, we propose a control scheme for manipulating an object from one spot to the desired position on a plate whose posture is controllable. Numerical example is also shown to explain our idea.

This paper proposes the tactile differentiator that can enhance the edge of polygonal surface, through tracing motion. It is composed of a flexible beam anchored at the base with a moment sensor, and an actuator for moving the whole system. When the beam tip passes over the edge where two different planes are intersected with an arbitrary angle, the tactile differentiator provides a step change of output, as if it were just like a differentiator. The edge enhancement factor of sensor is introduced by the shape of beam, the intersection angle of environment, and the contact friction. By using the factor, we discuss the design of the sensor. Experimental results are also shown to verify the basic idea.

Through group experiments by human, we found an interesting grasping pattern, where the human can easily captures a small object placed on a table by changing the finger posture from upright to curved ones after each finger making contact with the object. A series of this motion is called as detaching assist motion (DAM). This paper discusses a condition for achieving DAM by taking the idea of self-posture changing motion. A sufficient condition for lifting up an object from the table is discussed. Some experiments are also shown to verify the condition.

The enveloping grasp feasibility inequality is formulated in this article using a coordinate transformation based on the concept of frictional degrees-of-freedom. Various analysis and synthesis problems pertinent to enveloping grasp of whole-limb systems can be handled within the same mathematical framework, even under the situation where statically indeterminate contact forces exists. Simulations are also shown to explain the basic idea.

In this paper, a new training method for robotic rehabilitation aids is proposed, in which only one neural network (NN) is simultaneously used in order to identify the dynamic properties of a human-robot system and give an assist to the trainee. The model used for identification of the dynamics of the human-robot system consists of the NN and a reference model which represents the main characteristic of a skilful operator. This paper explains the working principle of the training method and shows the validity of the proposed method through experiments by non-skilled operators.

The problem due to the statically indeterminate contact forces arising in indeterminate frictional enveloping grasps is addressed. First, we show that the statical model for the contact forces is incomplete in the sense that the mathematical frictional forces may have an infeasible component. To resolve this infeasibility, we directly derive the enveloping grasp infeasibility condition on the frictional forces based on the coordinate transformation developed for frictional enveloping grasps. Then the indeterminate grasp can be analyzed in cooperation with the enveloping grasp feasibility inequality, as shown in a numerical example.

Discusses the neighborhood equilibrium grasp for multiple objects. Assuming rolling contact at each contact point, we first define rolling based redundancy which means that the grasped objects have degrees of freedom through the rolling motion even if the finger posture is fixed. For the grasp having rolling based redundancy, we say that there exists the neighborhood equilibrium if the system can be shifted to another equilibrium state close to the original one even when the current equilibrium is broken. We evaluate the robustness of the equilibrium state by utilizing the rotating angle, where the system loses the neighborhood equilibrium. We show several numerical examples to verify our idea.

Discusses the manipulation of multiple objects under rolling contacts. For manipulating multiple objects, there are two key issues which do not arise in the manipulation, of a single object, (1) each object's motion is restricted by the other objects, and (2) the contact force among objects is not controlled directly. As for (1), we first formulate the motion constraint for the whole grasp system, and then provide a necessary condition for manipulating multiple objects uniquely. As for (2), we provide a condition for determining the contact forces among objects uniquely. We further show a sufficient condition for manipulating multiple objects within the object motion constraint. Under this sufficient condition, we propose a control scheme for object motion by taking the motion constraint into account. An experimental result is provided to confirm our idea.

This paper discusses a sufficient condition for manipulation of envelope family, where multiple contacts are allowed between object and chains (or environment). All chains are assigned by either position controlled chain (P-chain) or torque controlled chain (T-chain). While the object motion under multiple contacts can not be uniquely specified by T-chains only, we show a sufficient condition ensuring that a given set of torque commands for T-chains always move the object toward the goal along the surface of P-chain (or a fixed environment). Experiments as well as simulations are also shown to verify the basic idea.

Discusses a hugging walk where multiple contacts are allowed between each leg and environment during locomotion. Since an external force can be supported by multiple contact points, legged robots in this style can be expected to be even more robust against a disturbance (including gravitational force) than those in conventional gaits based on foot contact. The alternative two-legs-support gait which never exists for conventional gaits based on static balance is introduced. Two indices for stable locomotion are introduced. Experiments are also shown to confirm the basic motion of the proposed gait.

This paper discusses a whisker sensor composed of a flexible beam anchored at the base with torque sensor, and an actuator for moving it. We consider a sufficient condition for detecting the surface shape by using a whisker sensor. We show that a straight-lined whisker sensor with one axis torque sensor can achieve the requirement irrespective of contact friction, while a curved whisker can not do it. We experimentally show that a straight-lined whisker sensor can detect the surface irregularity with pretty high sensitivity (/spl les/5 /spl mu/m), even under different contact frictions.

This paper proposes a new control method of an externally powered prosthetic hand based on a skeletal muscle model. This method consists of two steps: in the first step, a joint of a prosthetic hand to be driven is selected based on the EMG pattern discrimination using a neural network. Then, muscular contraction levels of flexors and extensors are estimated using other neural networks and used for an impedance control of the prosthetic hand in the second step. In the experiments, natural feeling of the prosthetic control similar to that of a human arm is realized using the neural networks and the impedance control.

This paper discusses the manipulation of multiple objects under rolling contacts. For manipulating multiple objects, the following two key issues do not arise in the manipulation of a single object: 1) each object's motion is restricted by the other objects; and 2) the contact force among objects is not controlled directly. As for (1), we first formulate the motion constraint for the whole grasp system, and then provide a necessary condition for manipulating multiple objects uniquely. As for (2), we provide a condition for determining the contact forces among objects uniquely. We further show a sufficient condition for manipulating multiple objects within the object motion constraint. Under this sufficient condition, we propose a control scheme for object motion by taking the motion constraint into account. Simulation and experimental results are provided to confirm our idea.

The paper discusses the scale-dependent grasp. Suppose that a human approaches an object initially placed on a table and finally achieves an enveloping grasp. Under such initial and final conditions, he (or she) unconsciously changes the grasp strategy according to the size of objects, even though they have similar geometry. We call the grasp planning the scale-dependent grasp. We find that grasp patterns are also changed according to the surface friction and the geometry of cross section in addition to the scale of object. Focusing on column objects, we first classify the grasp patterns and extract the essential motions so that we can construct grasp strategies applicable to multifingered robot hands. The grasp strategies constructed for robot hands are verified by experiments. We also consider how a robot hand can recognize the failure mode and how it can switch from one to another.

Deals with the rotational stability of a rigid body under constant contact forces. For this system, the stiffness tensor is derived, and its basic properties are analyzed. Necessary and sufficient conditions of positive definiteness of the stiffness tensor are established in an analytical form. Partial cases of the contact force distribution are analyzed. For the gravity-induced stiffness, conditions for stability are presented in terms of geometric and gravity centers. The internal forces are introduced with the use of a virtual spring model. Within this representation, conditions for stability under internal force loading are formulated in terms of the stiffness of the virtual springs.

Discusses the multiple active antenna that is simply composed of two insensitive flexible beams placed in the rotational plane, one actuator, one position sensor and one axis moment sensor. The sensor system can detect the contact point between the beams and an object through a simple rotating motion even for the object placed with an inclination angle. During rotating motion, one beam first makes contact with an object. By continuously applying the rotating motion, the second beam makes contact with the same point of the object. Each contact angle is estimated by utilizing both the moment and position sensors. Finally, the contact point can be estimated by the geometrical relationship. The basic idea is verified by experiments.

Discusses an EMG based control method of a robotic manipulator as an adaptive human supporting system, which consists of an arm control part, a hand and wrist control part and a graphical feedback display. The arm control part controls joint angles of the arm according to the position of the operator's wrist joint measured by a 3D position sensor. The hand and wrist control part selects an active joint out of four joint degrees of freedom and controls if using an impedance model based on the EMG signals. A distinctive feature of our method is to use a statistical neural network for EMG pattern discrimination. This network can adapt to changes of the EMG patterns according to differences among individuals different locations of the electrodes, time variation caused by fatigue or sweat, and so on. It is shown from the experiments that the hand and wrist motions can be controlled based on the EMG signals sufficiently. It may be useful as an assistive device for a handicapped person.

Deals with the stability of a rigid body under multiple contact forces. First, the problem considered at the force planning level, and the stability of a force distribution is formulated. Analytical conditions for the stability of a force distribution, considered under unilateral frictional constraints, are studied on an illustrative example, Next, it is shown that stabilization of an unstable force distribution can be done by a simple control law. The stability conditions for this control law are formulated in terms of the force-induced stiffness tensor and the control-spring-induced stiffness tensor calculated at the stiffness center. Finally, comments on the contradiction between the Lyapunov stability and the contact stability of the objects are drawn.

The human-like trajectory of robots for manipulating a nonholonomic car is generated. In order to reveal what kind of trajectories the robots should generate on the task, experiments with subjects were performed. It is shown that a human generates the trajectories with a single-peaked and a double-peaked velocity profile. By modeling these primitive profiles with a time base generator (TBG), the human-like trajectory for the robots is generated with the TBG based trajectory generation method. Finally, simulation results are shown and compared with the trajectories.

The positioning accuracy, output torque, and the trajectory tracing property of the developed spherical stepping motor are tested. The motor is composed of two arc-shaped stepping submotors and a rotational stepping submotor. The rotational center of each submotor is identical. The following characteristics are derived from the experimental results. The positioning resolutions of the inner, middle, and outer submotors are 0.00781[deg], 0.00586[deg] and 0.00586[deg] respectively. The holding torques of the inner, middle, and outer submotors are 0.093[Nm], 0.38[Nm] and 2.06[Nm] respectively. It can trace along the circle and the radiation trajectory within 0.2[deg] error, and the star trajectory within 0.4[deg] error. In comparison with a spherical synchronous motor, the positioning resolution is better but the torque/diameter ratio is smaller.

This paper proposes a training system based on EMG signals for prosthetic control and the development of its prototype. This system aims to enhance three kinds of control ability: muscular contraction, cooperation among several muscles, and the timing of EMG generation. For EMG signal processing a statistical neural network is used which can adapt itself to changing EMG patterns according to the differences among individuals, the different locations of the electrodes, the time variation caused by fatigue or sweat, and so on. During training, EMG signal information is displayed in the feedback monitor. The experiments have been conducted using the prototype system. The subject is a 51 year old man who had his forearm amputated when he was 18 years old. After training for five days, the ability to manipulate the EMG signal of the subject has been enhanced and the effectiveness of this system is shown.

Proposes a new probabilistic neural network (NN) that can estimate the a-posteriori probability for a pattern classification problem. The structure of the proposed network is based on a statistical model composed by a mixture of log-linearized Gaussian components. However, the forward calculation and the backward learning rule can be defined in the same manner as the error backpropagation NN. In this paper, the proposed network is applied to the electroencephalogram (EEG) pattern classification problem. In the experiments described, two types of a photic stimulation, which are caused by eye opening/closing and artificial light, are used to collect the data to be classified. It is shown that the EEG signals can be classified successfully and that the classification rates change depending on the amount of training data and the dimension of the feature vectors.

This paper proposes an impedance control method for redundant manipulators, which can control not only the end-point impedance using one of the conventional impedance control methods, but the joint impedance which has no effects on the end-point impedance. First, a sufficient condition for the joint impedance controller is derived. Then, the optimal controller for a given desired joint impedance is designed using the least squares method. Finally, computer simulations and experiments using a planar direct-drive robot are performed in order to confirm the validity of the proposed method.

Proposes an impedance control method that can regulate a virtual impedance between a robot manipulator and external objects using visual information. The conventional impedance control method is not useful in some cases where no interaction force between the arm and its environment exists, although it is one of the most effective control methods for manipulators in contact with the environment. Using the proposed method, we can control the manipulator motion based on the virtual impedance before contact with the objects. The validity of the proposed method is verified through computer simulations and experiments using a direct-drive robot.

This paper proposes the concept of a human-robot interface as rehabilitation aid and develops the prototype system. The prototype system aims to be used as a controller for the robotic manipulator and as rehabilitation system for the handicapped person. In order to adapt the system to the characteristics of the operator's electromyogram (EMG) signal, the EMG pattern discrimination method using the neural network is utilized as an essential technique of our system. In the experiments, it can be seen that the robotic manipulator can be controlled with high accuracy using the operator's EMG signal, and that the adaptive learning of the neural network improves the discrimination ability of the EMG signal. The rehabilitation program and biofeedback are also discussed.

This paper discusses the enveloping grasp of multiple objects under rolling contacts. We first provide a general mathematical formulation on the kinematic relationship for multiple objects enveloped by a multifingered robot hand, and then derive a condition for judging whether the rolling condition can be satisfied at each contact point. We also show a sufficient condition for rolling up any two objects grasped by a multifingered robot hand in contact with them. Finally, an experimental result is shown to confirm how easily two cylindrical objects can be enveloped by a simple grasping motion.

This paper discusses the transition stability in sliding an object enveloped by a multi-fingered robot hand whose joints are under constant torque command. We provide a new concept on transition stability, where a transition is called stable if the object is guaranteed to reach the goal section without moving away from a virtual cylinder defined in hand working space. To evaluate the transition stability, we introduce the force-flow-diagram enabling us to confirm whether the object moves to the designated direction or not. By using the diagram, we discuss the transition stability in lifting up an object to the palm under gravitational force. Simulation results show that the transition phase for a column object with concave surface is stable, while that having convex surface tends to be unstable. We also show experimental results to confirm the basic behaviours during the transition phase.

This paper discusses a grasp scheme for a pyramidal-like object placed on a table under the gravitational field. We assume that the contact friction is small enough to ensure that any direct grasp fails in achieving an equilibrium grasp. For an idealized 2D triangle object placed vertically on a table, we first show that a planar two-fingered hand can always achieve an equilibrium grasp under frictional contact. We also extend the basic idea to a polyhedron whose face is triangle and show two possible procedures leading to equilibrium grasps. Finally, we verify our idea experimentally for the polyhedra.

Discusses the analysis of kinematics and internal force under the gravitational field in grasping multiple objects. We first provide a general, mathematical formulation on the kinematic relationships for multiple objects grasped by a multifingered hand. We show a sufficient condition for lifting up two objects toward the palm. An experimental result verifies that the sufficient condition can be easily satisfied. We also analyze the internal forces for grasped objects, and introduce an index for evaluating the degrees of freedom of internal forces. Finally, we show a couple of examples to explain the physical interpretation of internal forces in connection with the index.

This paper discusses how many fingers are necessary and sufficient for capturing a pyramidal-like object placed on a table under the gravitational field. Allowing that the contact friction is small enough to ensure that any direct grasp may fail in achieving an equilibrium grasp, we prove that a planar two-fingered hand are necessary and sufficient for achieving the task for an idealized 2D triangle object placed vertically on a table. We also consider 3D pyramidal-like objects, and prove that a spatial two-fingered hand are necessary and sufficient for achieving the task.

A trajectory generation method for the dynamic control of robots is proposed. The method is developed by introducing the combination of a time scale transformation with a time base generator into the artificial potential field approach. This method can actively control the dynamic behavior of the robot without any change of the form of the designed controller itself. Effectiveness of the proposed method is verified through computer simulations with an omnidirectional mobile robot.

This paper proposes a new active sensor system (active antenna) that can detect not only the contact location between an insensitive flexible beam and an environment but also the information of the environment's surface where the beam makes contact. The active antenna is simply composed of a flexible beam, actuators to move the beam, position sensors to measure the rotational angle of the beam, and a moment sensor. We first show that the contact distance under no lateral slip is proportional to the rotational compliance that the beam can sense at the rotational center. The lateral slip, which possibly occurs according to the pushing direction and the environment's geometry, overestimates the rotational compliance, and as a result, brings a large sensing error for the localizing contact point. The goal of this paper is to find the contact location under such conditions. We explore how to detect a lateral slip and how to determine the new pushing direction to avoid it. We show an algorithm that can search for the pushing direction which can avoid any lateral slip. The convergence of this algorithm is shown and a practical utilization of this algorithm is also discussed with a trade-off between the number of trials and the sensing accuracy.

This paper proposes a new neural adaptive control method that can perform adaptive control and identification for a class of controlled plants with linear and nonlinear uncertainties. This method uses a single neural network for both control and identification, and a sufficient condition of the local asymptotic stability is derived. Then, in order to illustrate the applicability of the proposed method, it is applied to the torque control of a flexible beam that includes linear and nonlinear structural uncertainties.

This paper discusses the 3D vision based active antenna (3D-VBAA) that can detect the contact force and the contact point between an insensitive elastic antenna and a 3D environment. The 3D-VBAA is composed of an insensitive flexible antenna, two actuators, two position sensors, a camera, and a one-axis moment sensor. By utilizing the antenna's shape mapped into the calibration, plane C, the vision sensor can provide both the contact distance and a force component on C. The moment sensor output allows us to evaluate the force component normal to C. The 3D-VBAA can work even under a compliant object, while the 3D active antenna cannot. We show that the coupling effect between vision and moment sensor depends on the implementation angle of the CCD camera. We verify our idea experimentally.

A practical procedure for achieving an, enveloping grasp is presented especially for cylindrical objects. It is composed of three phases, the approach phase, the lifting phase and the grasping phase. For the grasping phase, we introduce the natural computation mode in which a preset torque is commanded to each joint, so that both the equilibrium position and the contact forces may be determined automatically. A sufficient condition for achieving the enveloping grasps is shown for the given procedure. Experimental results are also shown to verify the effectiveness of the proposed grasping procedure.

An algorithm for detecting the shape of a 2D concave surface by utilizing a tactile probe is proposed. Pulling a tactile probe whose tip lies on an object's surface can be easily achieved, while pushing it is more difficult due to stick-slip or blocking up with an irregular surface. To cope with the difficulty of pushing motion on a frictional surface, the proposed sensing algorithm makes use of the pulling motion of a tactile probe from a local concave point to an outer direction. The algorithm is composed of three phases, local concave point search, tracing motion planning, and infinite loop escape. The proposed algorithm runs until the tactile probe detects every surface which it can reach and touch. We show some computer simulations and experimental results obtained with the proposed algorithm.

The paper deals with the rotational stability of a rigid body under the constant internal forces. For this problem, first, the stiffness tensor is constructed and its basic properties are analyzed. The internal force parameterization is done with the use of the virtual linkage/spring model. Within this parameterization, necessary and sufficient conditions of stability are obtained in the analytical form. In the space of the internal forces they form a region given by intersection of a plane and a singular quadric. Since the stability conditions guarantee only positive definiteness of the stiffness tensor, the contact friction is taken into account separately. In this paper analysis of the unilateral constraints is done under a study case, where achieving stable grasp of a convex object, with the stretching internal forces created by friction, is studied in an analytical example.

Impedance control is one of the most effective control methods for a manipulator in contact with its environment. In this method however, the manipulator does not move until an external force is exerted. The present paper proposes a non-contact impedance control which can regulate a virtual impedance between an arm and an external object using visual information. Validity of the proposed method is verified through experiments using a direct-drive robot.

A dynamic model of a flexible beam in contact with the environment is considered in this paper. The model serves as a background for a dynamic, active antenna type, contact point sensor. In its simplest realization the sensor can be implemented in the form of a flexible beam rotating in plane. The dynamic model is developed in the nondimensional form and possible sensing strategies, active and passive, are outlined. The main feature of the sensor is the use of the frequency-versus contact point curve which, for some regions, may be a multi-valued function. Basic properties of the sensing curves are formulated, and two points of interest-the point of maximal stiffness and the point of center of impact-are introduced into the analysis. Behaviour of the sensing curves is analyzed with respect to three system parameters-mass, inertia, and stiffness ratios. It is found that in some limiting, but practically attainable cases the sensing curve becomes a single-valued function within the working range of the sensor.

Proposes the self-excited dynamic active antenna (SDAA) that can detect a contact location between an insensitive flexible beam and an object through observation of the fundamental natural frequency of the beam in contact with the object. The main, part of SDAA is composed of a flexible beam, one permanent magnet and two electromagnets not only for producing the exciting motion but also for changing the boundary condition of the beam. We show that the contact position is uniquely determined by utilizing the fundamental natural frequencies before and after changing the boundary condition. We present the basic working principle of SDAA and show some experimental results to verify the idea.

A trajectory generation method for multi-arm robots through cooperative and competitive interactions among multiple end-effecters is proposed. The method can generate the trajectories of the multiple arms in a distributed manner based on a concept of a virtual interaction force which represents an interaction between an end-effector and an environment. It is shown that the method is effective not only for simple cooperative tasks such as positioning a common object, but also for more complicated tasks including relative motions among arms.

This paper proposes the vision based active antenna (VBAA) that can detect the contact force, the stiffness of the environment, and the contact location between an insensitive elastic antenna and an environment, through the observation of the antenna's shape by a camera. We show that both the contact location and the contact force can be estimated by measuring two arbitrary points on the antenna after a pushing motion; even though the exact contact point is hidden by occlusion. By considering the geometrical relationship between. The virtual (without environment) and the real (with environment) displacements of the contact point, the stiffness of the environment can also be estimated, which our conventional active antenna can not do. We present the basic working principle of the VBAA and give experimental verification.

This paper discusses scale-dependent grasp. Human beings unconsciously change their grasp strategy according to the size of objects, even though those objects have similar geometry. We first observe the grasping strategy of the human hand in wrapping around a cylindrical object placed on a table. We show that the human grasp planning can be roughly classified into three patterns according to the object's size. For a large cylindrical object, the human hand wraps around it directly without any regrasping process. As the diameter of the object decreases, a human begins to slip the object along the finger, so that the object can finally make contact with the palm. For a further smaller diameter, a human first picks it up by his/her finger tips and then makes a transition from a finger tip to a wrapping grasp. We also extract the essential motions of human grasping so that we can implement them in multifingered robot hands.

A dynamic active antenna sensor for locating a contact point is considered in this paper. In its simplest realization the sensor can be implemented in the form of a flexible beam rotating in plane. The main feature of the sensor is the use of the frequency-contact point curve which, for some regions, may be a multivalued function. One way of "improving" the curve could be concerned with the nonuniform mass and stiffness distribution of the beam which would lead to a rather complicated sensor design. Another way to remedy the situation is to change the sensing strategy by adding a proper control action at the joint of the beam. To study the sensor's response to the control, a dynamic model of the beam in contact with the external environment is developed. Analysis of the frequency equation shows how a simple proportional control law changes the sensing curve. It is found that in some limiting, but practically attainable cases the sensing curve becomes a single-valued function. Thus, the solution proposed can significantly simplify the identification procedure.

This paper discusses theoretical and experimental investigation, on dynamic active antenna which can detect the contact point between an insensitive flexible beam and an object through estimation of the oscillation frequency in contact with the object. We first prove that the contact position is uniquely determined if we consider every mode of natural frequencies of the beam in contact with the object, while the fundamental and the second order natural frequency, in most cases, satisfy the sufficient condition for providing the unique contact position. We also show a desirable mass distribution avoiding the estimation error for localizing the contact position. By utilising the maximum entropy method, we succeeded in experimental estimating the contact point from the fundamental and the second order natural frequencies.

This paper is an extended version of the vision based active antenna (VBAA) that can detect the contact force, the stiffness of the environment, and the contact location between an insensitive elastic antenna and an environment, through the observation of the antenna's shape by a camera. If measured points are on the antenna, two arbitrary points are sufficient for computing the contact location and the contact force uniquely. In a practical application of VBAA, however, the measured points are not always on the antenna. In this paper, we show the condition for uniquely obtaining both contact location and contact force under the situation that the measured points are not always on the antenna. We also show a new compensation method to improve the sensing accuracy. We further verify our idea experimentally.

This paper presents a new trajectory generation method of the artificial potential field approach to a real-time motion planning problem. In the artificial potential field approach, the goal is represented by an attractive artificial potential and the obstacles are represented by repulsive ones, so that the robot reaches the goal without colliding with obstacles by using a gradient vector of the potential field. Although this approach is simple and computationally much less expensive than other methods based on the global information on the task space, little attention has been paid to temporal behavior of the generated trajectories such as a movement time from the initial position to the goal and the velocity profile of the end-effector motion. We argue that temporal behavior of the generated arm trajectory should be taken into account within the framework of the artificial potential field approach and introduce a time base generator that determines a dynamic behavior of the arm trajectory as a part of a feedback controller. By synchronizing a time course of the potential function used as an artificial potential field with the time base generator, the temporal behavior of the generated arm trajectory can be adjusted through the time base generator without any change of the potential function to be used.

This paper proposes an adaptive regulator using neural network. For a controlled object with linear and nonlinear uncertainties, the conventional optimal regulator is designed based on a known linear part of the controlled object and the uncertainties included in the controlled object are identified using the neural network. At the same time, the neural network adaptively compensates a control input from the predesigned optimal regulator. In this paper, we show how the output of the neural network compensates the control input based on the Riccati equation, and a sufficient condition of the local asymptotic stability is derived using the Lyapunov stability technique. Then, the proposed regulator is applied to the torque control of a flexible beam. Experimental results under the proposed regulator are compared with the conventional optimal regulator in order to illustrate the effectiveness and applicability of the proposed method.

Three-axis force sensors based on the principle of a pressure pick-up device are characterized by their manufacturability, simple structure, and small size. Their use, however, has not been explored due to the incomplete force information that they provide. This paper proposes a new six-axis force sensor, composed of two three-axis force sensors and a connector, called a twin-head type six-axis force sensor (TH force sensor for short). The author first describes the theoretical basis for the operation of TH force sensors and provides the characteristic matrix connecting the load and sensor output vectors. While twenty-one types of TH force sensor are theoretically conceivable, the author proves that ten types can result in a characteristic matrix with a full rank. The author also considers an optimal design in the sense of minimum condition number.

This paper proposes an impedance control method called the multi-point impedance control (MPIC) for redundant manipulators. The method can not only control end-effector impedance, but also regulate impedances of several points on the links of the manipulator, which are called virtual end-point impedances, utilizing arm redundancy. Two approaches for realizing the MPIC are presented. In the first approach, controlling the end-effector impedance and the virtual end-point impedances are considered as the tasks with the same level, and the joint control law developed in this approach can realize the closest impedances of the multiple points, including the end-effector and the virtual end-points to the desired ones in the least squared sense. On the other hand, in the second approach, controlling the end-effector impedance is considered the most important task, and regulating the impedances of the virtual end-points is considered as a sub-task. Under the second approach, the desired end-effector impedance can be always realized since the joint control torque for the regulation of the virtual end-point impedances is designed in such a way that it has no effect on the end-effector motion of the manipulator. Simulation experiments are performed to confirm the validity and to show the advantages of the proposed method.

This paper discusses a 3-D Active Antenna that can detect the contact location between an insensitive flexible beam and a 3-D environment through the measurement of the rotational compliance of the beam in contact with the environment. The lateral slip, which possibly occurs for the 3-D Active Antenna, overestimates the rotational compliance, and as a result, brings a large sensing error for the localizing contact point. The goal of this paper is to find the contact point under such conditions. In the first step, we push the antenna to the environment. If no lateral slip is detected during this motion, the contact point can be obtained through a similar method used for the 2-D model. If a lateral slip is confirmed, the pushing direction is changed continuously until development of any lateral slip is finally avoided. The authors explore how to detect a lateral slip and how to determine the new pushing direction to avoid it. The authors show an algorithm which can search not only the contact distance but also the normal direction of the environment's surface, even under the appearance of a lateral slip during the first step. The basic idea is also verified by experiments.

This paper discusses a new control method for an ultrasonic motor (USM). An USM has the capability of generating a resistant torque against an external one even under power-off which is well known as self-locking characteristic and conveniently utilized to save energy while maintaining rotor position. The goal of the paper is to relax the self-locking characteristic and to widely change it between lock and free states. In order to achieve this, we newly propose the two d.o.f. PWM control, in which OFF command is included in addition to CW and CCW commands. By applying this, we can also control the torque of USM in open loop without using any complicated circuit. In this paper, we first demonstrate the basic structure of the two d.o.f PWM control, and then show several experimental results to verify the effectiveness of the scheme proposed.

The present paper proposes a new feedback control strategy of mobile robots with nonholonomic constraints. This method introduces a function generator called a time base generator (TBG) as a time varying feedback gain, and by synchronizing linear and angular velocities of the mobile robot with a scalar variable generated by the TBG, the mobile robot can be positioned to the origin in the state space for any initial condition. Not only the configuration of the robot but also the time behavior of the generated trajectory such as the velocity profile and the movement time from an initial to a target position can be regulated through adjusting the parameters of the TBG.

This paper discusses a new sensing strategy for the dynamic active antenna which can detect the contact point between an insensitive flexible beam and an object through the estimation of the oscillation frequency in contact with the object. The strategy is composed of two steps. In the first step, the fundamental and the second order natural frequencies of the beam in contact with the object are evaluated by utilizing an extended Kalman filter. Then by using the mapping diagram from those two frequencies into the contact point, we can uniquely obtain the contact point. We show that the use of the fundamental and the second order natural frequencies is sufficient for localizing the contact point.

This paper discusses the sensing accuracy of the active antenna that can detect the contact location between an insensitive flexible beam and an environment through the measurement of the rotational compliance of the beam in contact with the environment. During pushing motion of antenna, the contact point generally shifts on the environment's surface, which either underestimates or overestimates the rotational compliance and eventually brings a sensing error for localizing the contact point. The goal of this paper is to consider the effect of the environment's curvature on the rotational compliance. We show that the rotational compliance of the antenna being in contact with a curved environment depends on not only the contact distance but also on a new nondimensional parameter including the pushing angle and the environment's curvature where the antenna makes contact. We further show experimental results to support the theoretical analysis for various environments with different curvature.

This paper proposes a new active sensor system (Active Antenna) which is motivated by the antenna of an insect. Insects use their antennae skilfully so that they can avoid hitting objects, while they are crawling, running, and even when they are staying still. The antenna can be characterized by its "flexibility" and "active motions". Based on the observations on insect's antenna, we propose a new active sensor system which consists of only four components, an insensitive flexible beam, a position sensor, a torque sensor and an actuator. We will show that this simple sensor system can locate any contact point between the insensitive flexible beam and an object by applying an active motion to the beam. We will also show that this sensor system enables us to detect the shape of this object when it is mounted on the front part of a mobile robot. Finally, we have designed and developed an active sensor system based on our idea and have verified the working principle by experiments.>

This paper addresses the problem in detecting contact forces between link elements and an object for inner link based grasps by assuming that contact locations are not given a priori. This problem is separated into two steps, i.e., the contact point sensing and the contact force sensing. An active sensing scheme to detect all contact points simultaneously is presented. The advantages of the proposed scheme are explained in detail by comparison with conventional approaches. After the contact points are obtained the contact forces can then be evaluated by using the torque sensors mounted on the robot arm (or fingers). The concept of contact force observability is also discussed.>

This paper discusses a dynamic active sensing system, capable of detecting the contact point between a flexible beam and an object. The proposed sensing system is simply composed of an insensitive flexible beam, a torque sensor, a joint position sensor, and an actuator. The dynamics (such as moment of inertia and stiffness) of the sensing system changes when the motion phase switches from non-contact to contact. We show that the natural frequency during contact is generally a multi-valued function of the contact location, which is not desirable from the viewpoint of determining the contact location uniquely. It is also shown that by adding a proper mass at the free end of the beam, we can make the function close to a single-valued one. The additional mass also contributes to reducing the oscillation frequency, which releases us from treating high frequency signals. We design the hardware model based on this idea, and verify the basic principle experimentally.>

This paper addresses a new active sensor system (Active Antenna) motivated by insect's antenna. The antenna can be characterized by its "flexibility" and "active motions". Based on these observations on insect's antenna, the authors' discuss an active sensor system composing of only four components, an insensitive flexible antenna, a position sensor, a torque sensor, and an actuator. The authors first consider the conditions which allow localisation of any contact point between the insensitive flexible antenna and environment by applying an active motion to the antenna. The authors show that the use of a straight antenna always makes it possible to localise the contact point irrespective of friction at the point of contact. The authors also show that contact point sensing by the use of a circular shaped antenna is weakly influenced by the friction at the point of contact.>

The present paper examines spatial characteristics of human hand impedance in multi-joint arm movements. While a subject maintains a hand location, small external disturbance to his hand is applied by a manipulandum. Time changes of the hand displacements and forces caused by the disturbance are measured and the hand impedance is estimated using a second-order linear model. The estimated hand impedance in different subjects and hand locations are summarized as follows: (1) spatial variations of the estimated hand impedance ellipses approximately agree with the experimental results of other researchers (Mussa-Ivaldi et at, 1985: Dolan et al., 1993), (2) the human hand inertia characteristics can be explained from basic biomechanics of the passive inertial effects (3) the grip force of the subject increases the size of the stiffness and viscosity ellipses, and (4) spatial features of the orientation. And the shape characteristics of the stiffness and viscosity ellipses are mostly explained from the kinematics point of view of the human arm.>

Determining where the fingers of a multi-fingered robot hand touch an object of unknown shape plays an important role in achieving a stable grasp. This paper focuses on a scheme for identifying such contact points. Instead of mounting a distributed tactile sensor all over the finger links, we propose an active sensing approach using joint compliance. The proposed scheme is composed of two phases. In the first phase, the approach phase, each finger is extended to its most distal position as it approaches the object. This phase continues until any part of a finger link contacts the object. During the second phase, the detection phase, each finger's posture is strategically changed by sliding the finger over the object while maintaining contact between the object and the finger. Using two selected postures during the detection phase, we can compute an intersecting point that gives an approximate contact point. This paper develops the algorithm and provides results from an experimental implementation of the scheme on a two-fingered robot hand running a joint level compliance controller. The process of changing the posture of the finger while maintaining object-finger contact is called self posture changeability (SPC). It also develops sufficient conditions to demonstrate the robustness of the SPC technique to variations in the coefficient of friction.>

Three-axis force sensors based on the principle of the pressure pick-up device are characterized by their manufacturability, simple structure, and miniature size. Their use, however, has not been explored due to the insufficient force information they provide. To make the most of the three-axis force sensor, the authors have proposed a new six-axis force sensors composed of two three-axis force sensors and a connector [twin-head (TH) six-axis force sensor] and examined the possibility of realization for sensors using two identical three-axis force sensors. This paper discusses TH force sensors constructed from two different types of three-axis sensors. While fifteen types of combinations are theoretically conceivable, it is proved that nine types can result in a characteristic matrix with full rank.

The authors discuss active tactile sensing for detecting a contact point between a multifingered robot hand and an unknown object. They define the concept of actively sensible meaning that an active sensing motion can be planned for a sensing event. Assuming more than two sensing events, conditional-minimum-external-sensor-realization is defined, where it is shown that it is possible to reduce the number of external sensors with a well-planned sensing algorithm. Based on these definitions, an active sensing algorithm for detecting the contact point with minimum-external-sensor-realization is proposed. This approach remedies several disadvantages found in conventional approaches. The approach was tested through experiments using a single-finger model with a fingertip tactile sensor.>

The authors discuss the self-posture changeability (SPC) for a general 3-D link system. The series of motions brought about by SPC is called self-posture changing motions (SPCM). SPC and SPCM are considered assuming that the link system moves slowly enough to suppress any dynamic effects. It is shown that, according to a particular combination of link posture, joint assignment, and object shape, there exist a deadlock state, where no further angular displacement can be imparted to the position-controlled joint. It is also shown that there are two different types of deadlock states which never result in any SPCM. The authors introduce (w, omega )-posture changeability, the characteristic with which a link can change posture for every possible force within a cone of a prime axis w and a solid angle, omega . The necessary and sufficient conditions leading to (w, omega )-posture changeability are shown, for a given contact point and frictional conditions. a sufficient condition is included required to realize SPCM under the assumption that the contact point moves continuously over the object and the link-object system never results in a deadlock state.>

A finger-shaped tactile sensor previously reported in a scaled-up version was miniaturized and its signal processing speed improved. The miniaturized tactile sensor consists of a hemispherical optical waveguide with an elastic cover, a fiber-optics plate (FOP), a position-sensitive detector (PSD), and infrared light-emitting diodes (LEDs) for the light source. When an object comes in contact with the sensor, the elastic cover is depressed and light from the LEDs, which normally maintains total internal reflection within the waveguide, is scattered at the contact location of the waveguide and the cover. The scattered light is transmitted to the PSD through the FOP. The contact location and the normal to the surface of the object are determined from the output of the PSD. The sensor's fundamental characteristics were evaluated through experiments using the miniaturized version. The sensor was installed at the tip of a robotic finger to create an active touch system. By combining tactile sensing and motion control of the finger, the profile of an unseen object was successfully delineated.>

The authors discuss force control for the tendon-sheath driving system typically used to actuate robotic finger joints. For a simple tendon-sheath model, the transmission characteristics were first formulated with factors called the apparent tendon stiffness and equivalent backlash. An interesting aspect is that apparent tendon stiffness changes when the tendon is pulled or loosened, while tendon stiffness itself keeps constant under the absence of friction. This unexpected behavior is confirmed by simulations as well as experiments. The authors also consider the effect of apparent tendon stiffness on force control and show that the direction-dependent behavior of apparent tendon stiffness eventually brings about a direction-dependent response in the force control system.>

This paper discusses a design for a robotic finger with the capability of joint torque sensing. The finger joint torque around a drive pulley is proportional to the tension difference on both ends of the pulley. Using a coupling mechanism between tendons, this tension difference can be measured directly, without sensing individual tendon-tensions. The tension differential type torque sensor (TDT sensor) is based on this idea. With a single body of small size and fewer signal lines, the TDT sensor has several advantages in comparison with the conventional approach that obtains the torque by attaching tension sensors at both ends of the drive pulley and feeding sensor signals to a differential circuit.>

Input-dependent stability was observed during torque control experiments using the first joint of the Darmstadt-HAND. The friction and compliance existing in tendon-sheath driving systems bring a hysteresis characteristic into the dependence of joint torque output on actuator displacement. While this transmission characteristic is close to the well-known backlash behavior appearing for the gears situated between a motor and load shaft, input-dependent characteristics were found to exist in the backlash region of the transmission system in the case of the use of a practical tendon length. The observed characteristic shows springlike behavior even in the backlash region and it also depends on input. Through experiments, it was confirmed that there are close relationships between the input-dependent backlash characteristics and the input-dependent stability. Based on the experiments, a description is given of the transmission characteristic in simple model equations, and the system stability is explored by using the sinusoidal-input-describing-function technique. A nondimensional stability-criterion map explaining the experimental results is shown.>

The authors focus on a scheme for searching for a contact point between a multifingered hand and an unknown object. They propose an active touch approach using joint compliance from the viewpoint of considerably reduced hardware improvement. The algorithm is composed of two phases. One is the approach phase, in which each finger first is opened widely and approaches an object until a part of a finger link is in contact with the object. The other is the detection phase, in which each finger posture is changed by slip while maintaining contact between object and finger. With a suitable combination of compliant joints and position-controlled joints, a finger link has the capability of changing its posture while maintaining contact with an object over a small angular displacement at a particular joint. This is defined as self-posture changeability (SPC). The condition leading to SPC is discussed for a general n-link system. The algorithm is confirmed through simple experiments using a two-fingered robot hand with the capability of joint compliance.>

A new type of torque sensor is proposed for finger actuation with N actuators and tendons per N external degrees of freedom. The finger joint around a drive pulley is proportional to the tension difference on both ends of the pulley. Using a coupling mechanism between tendons, this tension difference can be measured directly without sensing individual tendon tensions. On the basis of this idea, a tension differential-type torque (TDT) sensor is proposed. With a single body of small size and fewer signal lines, the TDT sensor has several advantages over the conventional approach, which obtains the torque by attaching two tension sensors at both ends of the drive pulley and feeding sensor signals to a differential circuit. The basic principle of the TDT sensor is described, together with the design orientation. The dynamic and static characteristics are examined with the introduction of equivalent rotational stiffness, which is useful for examining system stability. The specially designed TDT sensors were implemented in a two-fingered robot hand, and the effectiveness of the sensor was confirmed.>

A control structure suitable for torque control using a geared DC servomotor discussed. The torque sensory feedback is advantageous for the fine torque generation by geared DC motors. However, it reduces the structural stiffness and in turn causes a low response in both the torque and position controls. To improve this, it is suggested that the natural frequency of the motor rotor position servosystem should be large. The suggestion is verified by experiments on a single-joint manipulator.>

A control algorithm is presented for a hexapod walking machine, with alternating tripod-gait, proceeding over soft ground. The control algorithm is based on a foot-force sensing and is composed of two parts. The first part, which is applied to the leg alternating phase, confirms the support of body weight and generates the ground model using internal sensors. The second, which is applied to the body-propelling phase, compensates for the additional ground-sinkage due to the change of supporting force using the generated ground model. The proposed control algorithm is incorporated into the hexapod walking machine (MELWALK-III) and some basic experiments are performed to demonstrate the effectiveness of the algorithm for three types of ground simulations.>

Because of the size of walking machines, scaled-down models having geometrical similarity can be used instead of full-scale models to measure energetic efficiency. First, to cope with this situation, five nondimensional parameters that control energetic efficiency Of walking machines are introduced for nine physical parameters by applying dimensional analysis techniques. Next, in order to check those influences on energetic efficiency, computer simulations are performed for an n-legged walking model. In these simulations, the influence on ground reaction forces is considered to satisfy the approximate balance of forces and moments when an overall walking machine assembly is assumed as a free body. Resultantly, several new facts are acquired from the viewpoint of similarity law.

Legged locomotion over irregular terrain is composed of body-propelling motion and terrain-adapting motion. Although conventional walking machines with three degrees-of-freedom for each leg can adapt their feet on irregular ground using flexible leg freedom, such machines generally require a tremendously complex control scheme for the body-propelling motion. A walking machine with decoupled freedoms is based on the idea that body-propelling motion is realized by only one degree-of-freedom, and this freedom can be perfectly decoupled from the freedoms for terrain adaptability. As an application of such a walking machine, a hexapod walking machine using an approximate straight line mechanism was developed and several basic experiments were performed to demonstrate the properties of this type of walking machine.