This paper describes current status of our effort to develop a robot system that can play Jenga game against human players. Unlike most of the previous Jenga robots that use grippers, this robot is equipped with a hand with two multiarticulated fingers covered by soft skin and does not have any major mechanical constraint in playing the game in a natural way as human players do. An experimental result of a game played between the robot and a human player is presented.

This paper proposes a novel shuffle-translating method that combines shuffle turns repeatedly for a humanoid robot. Conventionally, the walking motion of a humanoid robot is performed through a repeated foot stepping motion. However, this motion is inefficient and has low stability. Previously, we have studied the shuffle-turning method for a humanoid robot, which can perform a stepless and stable turning. In this paper, we present a precise shuffle turn with feedback control and a new shuffle translation method by repeating shuffle turns. Experiments using a humanoid robot were conducted and the results revealed that the proposed method was effective for shuffle translation.

This paper describes the theory and the simulation of an improved velocity potential approach for path planning by which a mobile robot avoids standing and/or moving obstacles by using the hydrodynamic potential. This potential function for path planning is feasible for guiding a mobile robot to avoid an arbitrarily moving obstacle and to reach the goal in real time without finding the local maximum or minimum points in all cases. In this theory, there are two problems. One is that a mobile robot accelerates rapidly when it avoids a moving obstacle. The other is that a mobile robot has a discontinuous velocity when it is passing a moving obstacle. An ellipse field, which is obtained by using the conformal transformation, and a correction function, which generates the continuous velocity field, are installed in the previous potential function to cope with the difficulty. As a result, a mobile robot can gradually avoid a moving obstacle from further away, and can be safely guided without rapid acceleration.

In this study, grasp positions of human hands are measured for planar objects for development of a reasonable grasp criterion for a two-soft-fingered robotic hand. We first propose a grasp criterion that yields the best grasping position for a robot hand with two soft fingers. To examine the properties of this criterion with respect to some weighting coefficients included in the criterion, a grasping experiment is performed by humans for planar objects with various sizes and shapes. Results show that many observed grasping positions used by humans correspond to a set of weighting coefficients that equally weigh all the factors in the criterion. A grasping experiment using a robot has also been conducted using a set of coefficients corresponding to the equal weight; the effectiveness of the criterion was confirmed.

The purpose of this paper is to establish a method of shape recognition and grasping of unknown objects using a robotic hand with two soft fingers and one omnidirectional camera. For shape recognition, we propose to use a simple 2D version of the visual volume intersection method which takes advantage of a special feature of the omnidiretional camera attached to the hand. For grasping we propose a simple grasp quality criterion to obtain the best grasping position for the two soft fingers based on a visual hull in a horizontal grasp plane. We conducted several experiments and the results show the validity of the proposed method.

This paper proposes a method for evaluating quantitatively the degree of handedness of a person by using the haptic virtual reality technology. A definition is also given of a pair of quantitative indices for handedness and dexterity of a person from the data obtained by this method using the factor analysis. A haptic display system has been developed consisting of two PHANToM OMNI haptic devices, a graphics display, and a computer for virtual space calculation and control. To observe the skillfulness of two hands of a person, three virtual tasks have been developed: positioning task, force control task, and manipulation task. Ten male subjects aged from 22 to 23 years old have taken the test. The obtained performance data from these tasks have been analyzed using the factor analysis. Since the obtained factor scores for the right and left hands of each subject can be regarded as the skillfulness of the right and left hand, it is proposed to define the degree of handedness of the subject based on the difference of these factor scores. The proposed degree of handedness and the result of conventional LQ method did not contradict to each other. The calculated degrees of handedness, however, differ largely among the subjects. From this result, it is expected that the proposed method can be useful for detailed and quantitative evaluation of handedness.

In this paper, we investigate optimal grasp points on an arbitrary-shaped grasped object using a required external force set. The required external force set is given based on a task, and consists of the external forces and moments, which must be balanced by virtue of contact forces applied by a robotic hand. When the origin is in the interior of the set, a force-closure grasp is required. When the dimension of the set is one, an equilibrium grasp is required. Therefore, we can investigate whatever the desired grasp is, such as when the desired grasp is a force closure and equilibrium grasps. Also, we only have to consider the forces contained in a given required external force set, not the whole set of possible resulting forces. Furthermore, we can avoid the frame-invariant problem (the criterion value changes with the change of the task (object) coordinate frame). We consider an optimization problem from the viewpoint of decreasing the magnitudes of the contact forces needed to balance any external force and moment contained in a given required external force set. In order to solve the problem, we present an algorithm based on a branch-and-bound method. We also present some numerical examples to show the validity of our approach. Note to Practitioners-This paper is concerned with grasping an object by a robotic hand. This article address how to grasp the object, namely, how to position every finger on the object. Recently, robots are desired to be used in housekeeping and in caring for elderly people. For this purpose, robot (multifingered) hands are equipped with the robots as general-purpose end effectors. The robot hands are required to automatically move to accomplish such tasks. In this case, the most fundamental issue for robot hands is to grasp the object. At home, there are many various-shaped objects. Consider the case where the robot (hand) is commanded to perform a certain task, such as putting the object into a box. In this case, the robot (hand) must grasp such an object (of any arbitrary shape) with appropriate grasp positions for completing the task. Therefore, the appropriate grasp positions must be calculated automatically. This article addresses a method to solve this problem. But to complete the grasping task, the following problems remain: calculation and control of the appropriate grasping forces

In Earth orbit, astronomical observations are possible free from any absorption or disturbances by the Earth's atmosphere. Therefore, some large space telescopes and large space radio telescopes are planned for the future. We discuss the design of a radio telescope reflector which can be assembled in orbit by a space robot arm, with its networks and connecting mechanisms suitable for robot tasks. The characteristics of the new end-effector of robot arm and their suitability for onboard assembly tasks were confirmed by testing using a prototype end-effector and a two dimensional ground test arm. The test results are also described in this paper

This paper discusses the whole arm manipulation allowing the contact state transition. For manipulation of an object under fully constrained, the contact state transition becomes necessary. In order to realize the object manipulation, we first derive the feasible direction of the object manipulation by analyzing the active/passive closure properties for every combination of contact states. Second, we derive the set of joint torque to move the object in the feasible direction. These analyses also provide the joint torque to realize the manipulation at the planned contact states. Effectiveness of the proposed method is confirmed by some simulation results

The purpose of this research is to develop an intuitive interface to control rescue robots. We propose a new image stabilization system for easy operation of rescue robots. A promising method to search victims in rubble, is the use of teleoperated rescue robots. In the rescue activities with such robots, operators remotely control the robots through images captured by cameras mounted on the robots. Since the orientation of the robots change intensively while they move in rubble, image stabilization is necessary so that the operators can search victims without suffering from fatigue nor motion sickness. However, the orientation changes of the rescue robots are so intensive that conventional methods may not be capable of stabilizing the camera images. In this paper, we propose a new image stabilization system which can cancel the camera motion due to the intensive changes of the robot’s orientation on an uneven terrain. After a preliminary experiment, a 3-DOF camera system was designed based on the newly proposed mechanism. To verify the performance of the camera system, we conducted three experiments. The result of the experiments confirmed that the proposed mechanism shows good performance in motion stabilization as well as good performance in tracking the commanded head motion. Finally, we verified that the camera system works properly even when it was mounted on a crawler running on an uneven terrain.

In this paper, we discuss the manipulation of an object under hybrid active/passive closure. We show the orthogonality between the directions of active and passive force closures for general grasping systems. Based on the orthogonality, we decompose the dynamics of grasping system into the” active part” and the” passive part”. By using the decomposition, we show that the grasped object can be manipulated only by considering the dynamics of the active part. We also consider how to determine the desired internal forces in order to satisfy frictional constraints during the manipulation. In order to verify the validity of our approach, some simulation results are shown.

In this paper, we discuss the directions of active and passive force closures in hybrid active/passive-closure grasps. We show the directions are orthogonal to each other. We also discuss the magnitudes of the internal forces in the manipulation of the object. In hybrid active/passive-closure grasps, there exist two kinds of magnitudes of internal forces. One is the magnitude of internal forces, which changes if the object moves and the geometry of the fingers changes. The other is the one which don't change even when the object moves. We derive these two magnitudes.

In this paper, we propose a simulation model of uneven terrains based on fractional Brownian motions (fBm) for evaluating traversatility of mobile robots. Using fBm model, one can generate various terrain models by changing only two parameters. We modeled two different terrains by using fBm and checked statistical traversability of a robot with different wheel sizes and body configurations in computer simulation. To validate the effectiveness of the fBm model, we conducted real experiments with a wheeled mobile robot. Probabilities that the robot can travel a certain distance well agreed with the simulation results.

Unlike conventional haptic devices, an encountered-type device is not held by a user all the time. Instead, the device stays at the location of a virtual object and waits for the user to encounter it. In this paper, we extend this concept to fingertip contacts and design an encountered-type haptic display for multiple fingertip contacts to simulate tasks of grasping an object with any shape and size. Before designing the device, we intensively observed human grasping behaviors. This observation was very helpful to determine the mechanism of the device. An encountered-type device for three-fingered grasping was actually prototyped based on our design. We then discuss a path planning algorithm for the designed device, once again based on the observation of human grasping behaviors. A rough sketch of the algorithm is proposed and a preliminary experimental result to support our idea is shown.

In this research, we focused on the degrees-of-freedom for robot foot mechanism. To realize the functions of human locomotion on biped robots, we should know the fundamental aspects of human foot mechanisms through intensive observations of human locomotion. We proposed a novel mechanical shoe with 2-DOF toe parts, which move independently and are able to constrain human foot in various ways. Wearing the mechanical shoes, three subjects were measured on their walking speed, toe joint angles, and center of pressure. They were walking in straight, zigzag and slalom courses. Through these observations, we show that a biped robot with the proposed toe mechanism could potentially walk faster than conventional ones.

A bilateral teleoperation experiment with Engineering Test Satellite 7 (ETS-VII) was conducted on November 22, 1999. Round-trip time for communication between the National Space Development Agency of Japan ground station and the ETS-VII was approximately seven seconds. We constructed a bilateral teleoperator that is stable, even under such a long time delay. Several experiments, such as slope-tracing task and peg-in-hole task, were carried out. Task performance was compared between the bilateral mode and the unilateral mode with force telemetry data visually displayed on a screen. All tasks were possible by bilateral control without any visual information. Experimental results showed that kinesthetic force feedback to the operator is helpful even under such a long time delay, and improves the performance of the task.

In this paper, the concept of the "robust arm configuration" is expanded by using a mode-shape compensator. This compensator improves the robustness of the arm configuration where the robustness is not high enough. The compensator consists of a constant gain matrix and acceleration of each joint. The structure is simple and easy to use. The design method for this mode-shaping matrix is presented, based on the previously proposed mode-shaping algorithm. Effect upon the manipulability is also examined. It suggests that inclining of the dynamic manipulability ellipsoid's principal axes by the compensator, resulting in changing the coupling rigid body dynamics, leads to the improvement of the robustness. The validity is confirmed by a numerical example and experiments. The experiments are performed with an experimental system consisting of a two-degree-of-freedom (DOF) planar manipulator and a 1-DOF flexible base. A high bandwidth positioning is realized with the obtained compensator.

This paper presents a force-reflecting teleoperation scheme with time delay. Considering reciprocal systems, the necessary and sufficient condition of the stability of the proposed type and several conventional types are analytically investigated. It is shown that the stability is not guaranteed under force feedback for a time-delayed system unless the ideal response is strictly realized, although wave transmission is applied. This problem is solved by signal filtering. The validity of the proposed type is confirmed by experiments in contacting a solid wall.

In this paper, the robustness of a manipulator mounted on a flexible base with a task-space feedback control to a fixed desired point is considered. We define the robust arm configuration (RAC), which is a special configuration where the linearized system is positive real. Lyapunov indirect method and the passivity theory guarantee a local asymptotic stability of the original nonlinear system. A finite but high closed-loop gain can be applied in the neighborhood of the RAC without considering the base flexibility, i.e., an additional sensor or a solution of whole inverse dynamics is not necessary. Considering the positive semidefiniteness of the residue matrices, a measure is proposed that measures the distance from the RAC. This measure represents the controllability of the manipulator itself, and does not depend on the underlying control law. The validity of the proposed approach is confirmed by a numerical example and experiments.

In this paper, we propose a passivity monitor which evaluates stability of a system based on the concept of passivity, and a software limiter which turns the system stable if it is originally unstable. It is shown that asymptotic stability will be guaranteed for arbitrary robots with arbitrary control schemes and environments, even if their properties are unknown. The validity of the passivity monitor and the software limiter is verified by numerical simulations and experiments performed on various unstable systems.

When the end-effector of a robot is slid on a flat surface, the stiffness matrix obtained by linear fitting of position and force contains information not only on the stiffness coefficient and on the normal direction, but also on the friction coefficient. This paper proposes a new method for extracting information on those properties from the stiffness matrix provided by the impedance perception, which the authors previously proposed. The proposed method can be implemented as an encapsulated module for perception, which is separated from any control and planning methodologies. Therefore, this can be used for both autonomous and remote controlled robots, and even for monitoring a manipulation tasks performed by humans. Results of preliminary experiments are presented.

In this paper, we focus on a problem of how to confirm a feasible condition of applied force to a multi-legged robot on rough terrain. The problem often appeals as a subject of walking stability criterion for a legged robot. ZMP (zero moment point) is one of the well-known criteria. It shows the condition as footprints of a legged robot, but it cannot be defined on the rough terrain. Therefore, we suggest a new criterion FSW (feasible solution of wrench), which gives the feasible condition even on the rough terrain from the viewpoint of "wrench"-a special representation of force screw. And we present two short examples of FSW for a biped robot, how to analyse the validity of ZMP on stairs and how to design a force trajectory on rough terrain.

In this paper, the concept of the 'robust arm configuration' (RAC) is expanded using a mode shape compensator. This compensator improves the robustness of the arm configuration which is far out of the RAC. The compensator consists of a constant gain matrix and acceleration of each joint. The design method for this mode shaping matrix is presented based on the mode shaping algorithm. Effect upon the manipulability is also examined. It suggests that inclining of DME's principal axes, resulting in changing the rigid body dynamics, by the compensator leads to the improvement of the robustness. The validity is confirmed by a numerical example performed with a 2 DOF planar manipulator mounted on a 1 DOF flexible base. A high bandwidth settling is realized with obtained compensator.

In this paper, we consider an optimization of grasping by using a required external force set. Using the set, we cannot only deal with whatever a desired grasp is, such as force closure or equilibrium grasp, but also evaluate the magnitudes of the resistible external forces and moments. Then, we define an optimization problem from the viewpoint of decreasing the magnitudes of the contact forces required to resist the required external force, and show that we can solve the problem by using a branch-and-bound method. Lastly we present some numerical simulations to show the validity of our approach.

In a previous paper, we proposed the impedance perception technique, by which the stiffness matrix that constrains the motion-force relation of the robot's end-effector is estimated on-line, and the uncertainties of the estimates are evaluated. Based on this technique, this paper proposes a method of extracting information on local properties of a cylindrical curved surface, including normal direction, primary directions, curvature, and stiffness and friction coefficients, from the stiffness matrix obtained under the situation where the end-effector is slid on the surface. This technique can be implemented as an encapsulated perception function independent from control strategies, and thus it can be used for both autonomous and remote-controlled robots, and for direct monitoring of human manipulations. Results of preliminary experiments are presented.

In order to search and rescue the victims in rubble effectively, a 3-D map of the rubble is required. As a part of the national project of rescue robot system, we are investigating a method for constructing a 3-D map of rubble by teleoperated mobile robots. We are also planning to build an intuitive user interface for teleoperating robots and navigating in a virtualized rubble model using the obtained 3-D model. In this paper, some preliminary research results are introduced. We did some design studies of laser range finders that can be mounted on a mobile robot and can get the range data of the rubble around the robot. Then, we formulated a 3D SLAM (Simultaneous Localization and Map Building) algorithm and conducted some simulation studies. Lastly, we proposed a novel motion canceling camera system and confirmed its validity by experiment.

Humans unconsciously use efficient algorithms when performing a manipulation task by their hands. Robots can be made more efficient by applying these same algorithms. In this paper, we focus on the mechanical impedance of the operator's fingers as a key parameter for describing such kind of algorithms. To overcome the difficulty of identifying the parameters in the real world task, we propose to use a virtual task environment based on the haptic virtual reality technology. Some preliminary experiments are presented to show the validity of the proposed approach.

In this paper, we propose a method for image overlay on the front glass of a vehicle to navigate a driver to a desired destination. By overlaying the navigation information on the front glass, the driver need not gaze at the console panel. Therefore, accidents caused by gazing at console panel could be reduced. To overlay the image accurately on the target object through the front glass, both the vehicle's position/orientation and the driver's position/information are estimated by vision-based tracking and measuring angular velocities of the vehicle's wheels. Experimental results show the validity of the proposed method.

Stability of haptic interface is an important issue in virtual reality because ail operator touches directly a haptic interface device. The stability is influenced by sampling period and discrete-time property of control system. In this paper, for decreasing the influence of sampling system, we propose a haptic device with an analog circuit, which is placed between the computer and the haptic device and works as springs and dampers. The control system can specify the stiffness and the damping coefficients and their equilibrium. For displaying virtual objects that can move in virtual environment, we propose two methods to utilize the device, continuous-time coupling impedance (CCI) method and continuous-time object impedance (COI) method. We also analyze the passivity of each method for 1-DOF display system. Finally, some experimental results in two-dimensional virtual environment are presented to show the validity of the proposed approach.

Proposes an identification technique of constraint condition that the environment imposes on the robot's end-effector, based on position and force sensing during arbitrary manipulation. In the proposed method, the impedance that constrains the motion of the end-effector is estimated on-line; the uncertainties of the estimates are evaluated; and discontinuous changes of the impedance are detected. This method can be installed on robots as human-like perception of impedance, and can be used for monitoring human demonstration. Results of preliminary experiments are presented.

We consider the robustness of a manipulator mounted on a flexible base with direct positioning error feedback control. Based on the positive realness of the transfer function matrix, we define the robust arm configuration which is a kind of singular configuration where the system is passive. We show that the system shows good robustness in the neighborhood of this robust arm configuration. We propose a measure which indicates the distance from the robust arm configuration. We also show that the robustness is closely related with the robust stability margin by the normalized coprime factor description. The validity is confirmed by numerical examples. The method is applied to a flexible assembly system consisting of a manipulator and two moving tracks.

To replace human activities by humanoid robots in hazardous environment, they should perform various motions, not only simply walking by their two legs but also passing through a narrow way, climbing a ladder and even getting in a operating machine. In such cases, humanoid robots are contacting/grasping the surrounding environment through their hands as well as their legs. In this paper, we propose a method to evaluate the postures of humanoid robots when their limbs (arms and legs) are constrained to the surrounding environment. From a given posture, a quantitative measure is calculated considering various aspects, such as joint torque limit, joint motion range, and the robustness from falling down and slipping down. Only static posture is evaluated, assuming stationary postures or quasi-static motions. Numerical examples show the validity of the proposed evaluation method. Based on the proposed evaluation, an example of optimizing a motion sequence is also shown.

A bilateral teleoperation experiment with ETS-VII was conducted on November 22, 1999. Round-trip time for communication between the NASDA ground station and ETS-VII was approximately six seconds. We constructed a bilateral teleoperator that is stable even under such a long time delay. Several experiments, such as slope tracing task and peg-in-hole task, were carried out. Experimental results showed that kinesthetic force feedback to the operator is helpful even under such long time delay and improves the performance of the task.

In this paper, we discuss displaying a virtual object with coupling impedance by a haptic interface device with long sampling period. For such system to be stable, coupling impedance has to be set low. But it means that the operator feels soft surface of the virtual object and it is not suitable for displaying a virtual object with hard surface. This is because the system is a discrete time system. So we propose a haptic interface device with analog springs and dampers that exert reaction force continuously. The method can decrease the influence of the sampling period and make haptic interface more stable. Finally we perform some experiments with two dimensional virtual environment to confirm the effect of the proposed method.

The purpose of this study is to establish a method of virtual-reality-mediated motion/force teaching from human teacher to human "teachee". For effective teaching, position and force information of the teacher's action have to be communicated to the teachee. Position information is easy to display, but force information is difficult to display by conventional haptic devices. In this paper, we propose a new type of haptic interface with fingertip presser which could make it possible to display both position and force information. The teacher's finger force of pushing a surface is displayed as a mechanical pressing force onto the teachee's fingertip, and position is displayed by active multijoint linkage. The results of basic experiments show that the proposed method is effective as a media of motion/force teaching, but reveal some limitations.

When we control a flexible manipulator based on a dynamic model, we need to estimate the state variables with accuracy. In the case of rigid manipulators, the state variables consist of joint angles and their velocities which are measured easily by encoders, potentiometers, tachometers, and so on. In the case of flexible manipulators, however, the state variables also include elastic deformations and their velocities due to flexibility. Here we focus on visual sensor to measure distributed state variables of flexible manipulators. First, we discuss a distributed state estimation method which uses discrete position information of markers attached on flexible links. Second, when we apply the virtual joint model to flexible manipulators, elastic deformations are expressed by virtual passive joint angles which are lumped. So we have to correspond the real elastic deformations to the virtual joint angles. We also discuss this transformation. Third, when we estimate the lumped state variables by the proposed method, it is possible to identify physical parameters of the dynamic model. Finally, some experiments were carried out to verify the effectiveness of the proposed method.

The flexibility of the mechanical system is one of the factors of the bandwidth limitation. Especially, it is known that an out-of-phase vibration mode makes the closed loop unstable with the negative feedback of the positioning error. In this paper, a novel mode shaping method for in-phase design of flexible structures is proposed. From the relation between the modal analysis and the state-space representation, we classify in-phase mode shaping into two types based on the boundary which is passed across during the shaping process. By the proposed method, the out-of-phase modes are shaped into in-phase in order of the natural frequencies applying a task priority based modification scheme. We also propose a method of selecting the boundary, so that the vibration mode is shaped into the arbitrary type of in-phase design.

Power grasp is a grasp that can hold objects stably without changing the joint torques of fingers. Almost all studies on power grasp deal with one object, but it is more efficient to hold multiple objects at the same time. This paper derives a condition for power grasp for multiple objects, and defines an optimal power grasp from the viewpoint of decreasing the work of joint torques. Finally, we show some numerical examples to verify the validity of our approach.

A path-planning algorithm for encountered-type haptic devices that render multiple virtual objects in 3D space is proposed. To render multiple virtual objects with a single haptic device, the following two behaviors must be realized: (i) the device should move to the target object location in advance of the user's hand so that the user can encounter it; (ii) otherwise, the device should keep away from the user's hand, avoiding an unexpected collision. To realize such a consistent encounter, the user's hand motion must be tracked. The proposed algorithm determines the device location based on the minimum distance problem between a point (the user's hand) and a convex polyhedron constructed from the reference points of multiple objects. An automobile virtual control panel was constructed using an encountered-type haptic device in which the proposed path-planning algorithm was implemented. The validity of the proposed algorithm was confirmed and the required performances, such as the device speed and the accuracy of hand tracking were evaluated.

In previous work, we (1999) have proposed a control scheme based on wave variables. Unlike other methods, the proposed method could minimize the performance degradation due to the fluctuation of time delay. With this method however the system may potentially generate infinite energy in some special situations and the system stability could not be ensured rigorously. In this paper, we modify the method by introducing an energy input/output balance monitoring mechanism, which limits the energy that the system can generate. We conducted some simulation studies with a one DOF system. Simulation results show the validity of the proposed scheme.

The state of the art of force control for robot manipulators is surveyed in this article. An overview and a unified description of the two major approaches to force control are presented. Several research topics related to force control are also surveyed.

A unified control algorithm for grasping and manipulation of rigid objects by multifingered robot hands with fixed, rolling and/or sliding point contacts is established. Control algorithms have been proposed in the past for the cases of fixed contacts, rolling contacts, or sliding contacts separately. However, force control part of these control algorithms was not given enough consideration with respect to making clear the essential force variables that can be arbitrarily controlled. Also the sliding contact case was formulated only for 2D work space. Adopting the virtual truss model characterization of the internal force, this paper formulates a dynamic control algorithm that has a clear feedback structure in a general 3D setting. Some examples of bases of internal force parameter vectors are also given that are useful for determining the desired internal force vector in the control algorithm.

This paper deals with the control of a 3-link planar underactuated manipulator whose most distal joint is unactuated. This system is known as a second order nonholonomic system. In a previous paper (1996), we proposed a control law that guarantees the convergence of its state to a given desirable trajectory and to any desired final point, and we also gave a design method of the desirable trajectory. However, this method has a limitation on the location of the initial state. In this paper, we propose a design method of a desirable trajectory that starts from any given initial point, converges to any given desired final point, and on the way passes through any given desired passing point that can be specified rather freely. By this new design method, one can derive a desirable trajectory that satisfies given requirements much better than the previous method.

In this paper, the new concept of the dynamic singular configuration of flexible manipulators using the inverse dynamics method, we need to consider this dynamic singular configuration of flexible manipulators. Without considering it, the control around the dynamic singular configuration may become unstable. As an example, we derive the dynamic singular configuration of a 2-DOF planar flexible manipulator modeled by a virtual passive joint model. The characteristics of the dynamic singular configuration and the dynamic manipulability of flexible manipulators are discussed, and its experimental verification was performed.

We discuss a haptic display for 1-DOF grasping of a virtual object by two fingers. Much research has been done on fundamental analysis for stability of haptic displays. But it is difficult to apply the results immediately to grasping situations by two fingers, since the studies deal with a single device and a single object. This is because the fingertip force in grasping situations has two components, internal and external force. The conventional methods, which calculate the coupling impedance at each contact point separately, have no other alternative but to calculate the impedance for the sum of the internal and external force components. So even if only the impedance for external force should be changed, the impedance for internal force is also changed at the same time. We propose a method, in which the coupling impedance is calculated separately for internal and external forces. Second, we discuss the stability of the proposed method and compare it with the conventional method. Finally, we perform some experiments to confirm the effects of the proposed method.

This paper is concerned with the analysis of controllability for a class of nonholonomic systems. We discuss the controllability of under-actuated planar manipulators with one unactuated joint. We show that these systems are completely controllable if the first joint (in the base side) is actuated. In order to prove this, we use a kind of bi-directional approach.

A unified hand/arm master-slave system was developed to conduct more dexterous tasks by teleoperation. Both the master and the slave consist of a two-fingered hand and a 3-DOF planer manipulator. The system is also aimed at investigating the bottleneck of autonomous robotic manipulation systems. To evaluate the performance of individual teleoperation systems all over the world in equal condition, we propose toy block assembling (LEGO) as the benchmark test for teleoperation systems. Using our hand/arm master-slave system, we announce the measured completion time for assembling some block structures, expecting other research group to try the same task in the future.

We propose a dynamic control method of soft-finger hands for pivoting an object in contact with the environment. This pivoting operation is often observed when a human moves a large or heavy object such as furniture. Different from the conventional manipulation of the object by only fingers, the characteristic of the pivoting operation is that we can use the reaction force from the environment. By using this reaction force, we can expect the magnitude of the forces applied to the object by the fingers to be smaller than the conventional manipulation of the object by only fingers. Taking this characteristic of the reaction force into consideration, we propose a dynamic control method for pivoting. To verify our approach, the simulation result is also presented.

Proposes a method for accurate image overlay on head-mounted displays (HMDs) using vision and accelerometers. The proposed method is suitable for video see-through HMDs in augmented reality applications but is not limited to them. Acceleration information is used for predicting the head motion to compensate the end-to-end system delay and to make the vision-based tracking robust. Experimental results showed that the proposed method can reduce the alignment errors within 6 pixels on average and 11 pixels at the maximum, even is the user moves his/her head quickly (with 10 m/s/sup 2/ and 49 rad/s/sup 2/ at the maximum). The viewing range was enlarged by placing additional landmarks in the environment.

Dynamic control of a three-fingered robot hand manipulating an object in 3D space, while allowing one of the three fingers to slide in order to change its grasp location on the object surface, is formulated. The static and dynamic friction between the sliding finger and the object surface are explicitly considered and their effects regarding the behavior of the finger and object are discussed. Motion equations of the whole system are derived and a dynamic control law for realizing the desired object motion, as well as the desired finger sliding and the desired grasping force, is proposed. The realizability of the given trajectories under the constraints of maximal static friction and dynamic friction at the grasp points, and of joint driving torque, are also discussed. A simulation example to demonstrate the use of the proposed control law is given. The results of this work will have useful application to a multifingered robot hand in performing certain tasks involving the re-grasping and re-orientation of an object without interrupting the grasp.

Soft fingertips can easily achieve high friction contacts but their frictional moment around the contact normals makes manipulation control difficult. We propose a control scheme to manipulate an object by a multifingered hand with soft fingertips. The proposed scheme cancels the frictional moment according to the direction of the relative rotation between the fingertip and the object. Whatever the fingertip contact type is, accurate pose measurement is very important for the object manipulation. We also propose a systematic method to estimate the object pose with a complementary use of camera images and finger joint information. The proposed control scheme and the pose estimation method were combined and implemented in an experimental system. Results of the experiment show the effectiveness of the proposed pose estimation method and the overall control system for manipulating an object by a soft-fingered hand.

We propose a method for accurate image overlay on head-mounted displays (HMDs) using vision and accelerometers. The proposed method is suitable for video see-through HMDs in, augmented reality applications but not limited to them. Acceleration information is used for predicting the head motion to compensate the end-to-end system delay and to make the vision-based tracking robust. Experimental results showed that the proposed method can reduce the alignment errors within 6 pixels on average and 11 pixels at the maximum, even if the user moves his/her head quickly (with 10 [m/s/sup 2/] and 49 [rad/s/sup 2/] at the maximum).

It is widely recognized that haptic display is one of the key elements for making the virtual reality technology more powerful, and various force and/or tactile display devices have been developed. However, many of these devices are always in touch with the fingers or hands of the operator and it is impossible for an operator to feel the difference between contact and non-contact state with a virtual object directly from sensory channel of touch in his/her fingers or hands. This paper presents a new three-dimensional haptic display device we have developed for providing both touch and force feeling to operator's fingers. This is an extension of our previous device for two-dimensional application. The control algorithm for the new device and some experimental results are also presented.

Several approaches based on wave variables have already been proposed for bilateral teleoperation control under time-varying delay. However, these approaches are too conservative for keeping the system passivity or for estimating the amount of virtually constant time delay. These conservative approaches result in too much degradation of maneuverability from the constant time delay situations. We propose a novel control scheme that is also based on wave variables, but minimizes the performance degradation due to the fluctuation of the communication time delay. The proposed method is simple and easy to implement. We conducted some simulation studies with a one DOF system. Simulation results show the validity of the proposed scheme.

It is well known that any internal force for three finger grasps with frictional point contacts can usually be decomposed into three pushing or pulling force components along the three lines joining the contact points. This paper studies the question of how far this intuitive decomposition can go for general multiple finger grasps. We propose a virtual truss model for the grasped object for characterizing the internal force and show that this characterization is valid for general multiple finger grasps under a nondegeneracy condition. We also discuss some degenerate cases and give a method of extending the virtual truss model to cope with these special cases. Based on this characterization, we give an explicit formulation of the categorization by Ponce et al. (1993) of four finger grasps into concurrent, pencil, and regulus grasps. A procedure is also given for obtaining a nonredundant expression of all possible internal forces from this characterization.

The concept of a virtual lesson is proposed for transferring a teacher's skill to a student using haptic virtual reality technology. We have developed a virtual calligraphy system as one of its applications. In this system, the position and force trajectories of the teacher's writing brush is recorded first and then these trajectories are displayed to the student. What the student can learn is the teacher's horizontal brush position trajectory, his normal pushing force against a virtual paper, and the distance between the teacher's brush and the virtual paper. Recognizing that it is impossible to display both the normal force information and the normal position information at the same time, we have implemented two methods of skill display: one is to use the haptic display device for displaying the position information, and the other is to use it for displaying the force information. The remaining information is displayed using a secondary display device, visual display in the developed system. A preliminary experimental result is also presented.

Internal force plays important roles in grasping and manipulation of objects by multiple fingers. It is well known that any internal force for three finger grasps with frictional point contacts can usually be decomposed into three pushing or pulling force components along the three lines joining the contact points. This paper studies the question of how far this intuitive decomposition can go for general multiple finger grasps. We propose a virtual truss model for the grasped object for characterizing the internal force and show that this characterization is valid for general multiple finger grasps under a non-degeneracy condition. We then discuss some degenerate cases and give a method of extending the virtual truss model to cope with these special cases. Based on this characterization, we give an explicit formulation of the categorization by Ponce et. al. (1993) of four finger grasps into concurrent, pencil, and regulus grasps. A method is also given for obtaining a non-redundant expression of all possible internal forces from this characterization.

When an object is grasped by a multifingered hand with power grasp, there are an infinite number of possible power grasp forms, provided by combinations of the hand shape, the contact positions between fingers and the object, and the joint torques of the hand. To plan a power grasp, it is necessary to know, by some prior evaluation which form is most suitable among these forms. This paper proposes a technique for automatically obtaining optimal power grasp. By analyzing the degree of freedom of the force space caused by frictional contacts between fingers and object, the conditions and mechanical properties of power grasp are described. Also, the region of feasible joint torques for power grasp is derived. Then, an optimal power grasp form is defined and its determination procedure is established.

It is well known that there are positional and geometric uncertainties in the robotic assembly operation, and that in order to perform an assembly operation by robot successfully, it is necessary to estimate the correct position and geometric information of a fixed environment. In response to these problems the authors present a technique for estimating the contact position and geometric information between the object and the environment from a number of positions and orientations of a moving object. This information is to be measured while the object is dexterously probed on the environment around the contact position. The paper considers a method for generating the probing operations automatically. First, the possibility of performing probing operations on a contact position is discussed. Then, automatic generation approaches for probing operations are described.

The importance of force and tactile display in virtual reality technology has been recognized recently and numerous researches have been done including development of various force and/or tactile display devices. However, many of them are always in touch with fingers or hands of operators and it is impossible for an operator to feel difference between contact and noncontact state with a virtual object directly from sensory channel of touch in his/her finger or hand. This paper presents a new haptic display device we have developed which provides both touch and force feeling to the operator's fingers. This device tracks the operator's finger with no contact when the finger is not in contact with any virtual object. It touches and displays force to the finger only when some virtual object is in touch with the finger. A control algorithm for the system to display dynamic virtual objects is given. Preliminary experimental results are also presented.

In assembly operations, there are various constraint states while a moving object is in contact with a fixed object. For different constraint states, the existent regions of contacting forces, geometrical constraints, possible object displacements, which can be expressed by polyhedral convex cones respectively, are different. We consider that the sizes of these regions are important characteristic of contact stability for planning assembly operations. This paper proposes an approach that can evaluate the sizes of these regions. Based on this approach, the magnitude of form constraint, the constraint maintainability and the constraint separability are defined to evaluate the contact stability and contact condition between objects. And then, their applications to planning of assembly tasks are discussed.

This paper provides a unified theoretical framework for grasping and manipulation by robotic grippers and hands as well as for fixing works by fixtures and vises. The concept of passive closure and active closure for general constraining mechanisms is introduced. Passive closure is further classified into passive form closure and passive force closure. Conditions for these closures to hold are studied. Several new conditions are given for passive force closure. Especially, it is shown that, for the existence of passive force closure by frictionless point contacts, there must be at least six fixed contact points in the case of three dimensional space, and at least three in the case of two dimensional space. Conditions for other closures, which are mostly slight modifications of known results, are also included to show that they are naturally located in proper positions in the proposed unified framework.

Recently force-feedback has been recognized to be important for virtual reality systems, and many studies have been done in this field. Although we have proposed several methods for displaying the operating feel of a virtual object by considering its dynamics, we have not dealt with cases of multiple objects or operators. In more advanced applications of haptic virtual reality, however, multiple operators and multiple objects will generally exist in the virtual world. In this paper, we propose a systematic method of constructing a virtual world by combining the dynamics modules and interaction modules, the former denoting elements of the virtual world (virtual objects or operators) and the latter denoting interactions between them. Since this method makes it possible to regard those elements as equal, we can construct a flexible and extendable virtual world to which we can easily add new elements or remove some of its elements. An experimental result using a prototype force display system shows the validity of the proposed method.

In this paper, two kinds of the degree of freedom in constraint state (CSDOF) are defined for motion of an object in contact with an immobile environment, and then their application to planning of assembly tasks is discussed. The CSDOF of the first kind is defined as the number of independent directions in which the object can move, keeping the current constraint state. The CSDOF of the second kind is defined as the number of independent directions in which the object can move bilaterally when it is allowed to break the current constraint conditions and to go away from the current constraint state. We discuss the difficulty of state transition by considering the two kinds of CSDOF as well as the degree of constraint in constraint state (CS-DOC) and give a criterion function for state transitions. Based on this criterion function, we propose an algorithm for planning the optimal procedure for assembly tasks. Some numerical examples are given to show the validity of the proposed approach.

We deal with the problem of internal stabilization in dynamic trajectory control of flexible manipulators. We compare two configurations of flexible manipulators. One is the conventional flexible manipulator, and the other is the macro-micro system that has a small rigid manipulator at the tip of the flexible manipulator. In order to preserve the stability, the precise end point tracking is impossible for the conventional flexible manipulator. On the other hand, utilizing the redundancy, the precise end point tracking with internal stabilization is available by using the macro-micro system. First, we construct a dynamic trajectory controller for the flexible manipulator considering the internal stabilization, and analyze the problems in controllers of conventional flexible manipulators. Second, we propose a controller for the macro-micro system, and show that the problems can be solved by using the macro-micro system. Lastly, simulation and experimental results are shown.

We consider the problem of making a manipulator push an object on a flat floor with point contact to a desired position. A manipulator control method for the object to follow a planned trajectory as proposed. First, using the given distribution of frictional forces between the object and the floor, we find out a particular point, named pseudo center, on which the motion of the pushed object cart be approximates by the motion of wheeled mobile robot on its center. Then, a control rule of the pushing operation is derived by applying a tracking control rule for a nonholonomic mobile robot at the pseudo center. This method makes it possible for the robot to perform the tracking control in the pushing operation. A simulation result shows the effectiveness of the proposed method. Finally, we give an, approach to use a mobile manipulator for realizing the pushing operation. Experimental verification on the proposed method is performed and its result is described.

When multiple mobile robots cooperate in carrying large objects, it is important for them to be located in appropriate positions. This paper describes optimal grasping positions of robots and regrasping procedure for carrying an object by cooperating multiple mobile robots. Regrasping action is performed by several exchanges of the robots, the number of which is more than the number of robots to be need of the load on the robots. Then, we propose a method for deciding the optimal grasping positions of them and optimal regrasping times by using the performance index. The regrasping procedure is decided in consideration of the intermediate situation between the initial situation and the optimal one. A numerical example shows the effectiveness of the proposed method.

Time delay usually makes master-slave systems unstable, even if the system is stable under no time delay. In this paper, we propose a control scheme for master-slave systems with time delay which maintains stability defined by scattering theory. We define four types of realization of the ideal response and describe control schemes which strictly realize the ideal response. Based on these schemes, we propose a practical control scheme and its stability is proven. We also discuss stability of conventional schemes, and show that they cannot maintain stability. Finally, some experimental results are presented.

Their are positional and geometric uncertainties in assembly operation. In order to perform an assembly operation by robot successfully, it is necessary to estimate the correct position and geometric information of a fixed environment. This paper describes a technique that can estimate the contact position and geometric information between the object and the environment from a number of positions and orientations of a moving object, which are measured while the object is dexterously slid and rotated on the environment around the contact position. It is assumed that the environment and object are polyhedra. There are three kinds of basic contact pairs when the two polyhedra are in contact with each other. Corresponding to these basic contact pairs, three kinds of estimation approaches are proposed. By these estimation approaches, the environment position and geometric information on contacting parts can be estimated successfully. Experimental verification on the proposed approaches is performed and its results are outlined.

In this paper, hybrid position/force control algorithms of combined flexible-macro/rigid-micro manipulator systems are proposed, In the proposed system, the micro manipulator is attached at the tip of the flexible macro manipulator. The macro manipulator can move widely, but cannot realize fast and precise motion because of its flexibility. On the contrary, the micro manipulator cannot move widely, but can move fast and precisely. By taking advantage of the macro/micro system, both the end point position and the force exerted by its end effector can be easily controlled in spite of the flexibility in the macro part. This paper first discusses trajectory planning for the macro/micro system. Second, a quasi-static hybrid control algorithm and a dynamic hybrid control algorithm are developed, In our control algorithms, the macro part is controlled roughly to realize the desired trajectory, and suppress vibration. The micro part is controlled to compensate for the position and force errors due to the elasticity in the macro part. Finally, to verify the effectiveness of the proposed control algorithms, experimental results are shown.

A control scheme for grasping and manipulation by arm-hand mechanisms is proposed. The arm-hand mechanisms, consisting of arm and multifingered hand have the same feature as that of redundant macro-micro manipulators concerning manipulation. That is: (1) manipulations are possible by both the arms and hands, (2) the hands are suitable for the compliant motions compared to the arms because of their small inertia, and the motion ranges of the arms are bigger than those of the hands. The control scheme can utilize both merits of the arms and hands. Simultaneously, it can realize the secure grasping during manipulations. Several simulation and experimental results illustrate the validity of the proposed control scheme.

In this paper, we first define the ideal response of micro-teleoperation. Then, we discuss the robust stability of bilateral control systems based on the structured singular value of scattering matrix. Finally, we propose a new control scheme which can realize the ideal response. It is shown that the proposed control scheme satisfies the robust stability condition. A prototype of 1DOF teleoperation system with a mini manipulator was developed. The validity of the proposed control scheme is confirmed by experiments and compared to the conventional control schemes, such as the symmetric position type and force reflecting type.>

A macro-micro manipulator system has been proposed with the purpose of overcoming the difficulty to realize a trajectory tracking control of a flexible manipulator. In this paper, a trajectory tracking controller of macro-micro manipulator system is proposed which takes the dynamics of the system into consideration. This control law consists of a simple PD feedback law for the macro flexible manipulator and a dynamic trajectory tracking control law for the micro rigid manipulator. Experimental results show the effectiveness of the proposed scheme.>

In this paper, to realize the hybrid position/force control of a flexible manipulator, the macro-micro manipulator system is used. The macro manipulator can move widely, but can not realize fast and precise motion because of its flexibility. To compensate the position and force errors, a micro manipulator is attached at the tip of the macro manipulator. The kinematic equations of the macro-micro manipulator system are introduced. By utilizing the redundancy and flexibility of the system, the trajectory planning is discussed. A quasi-static hybrid position/force control algorithm and a dynamic hybrid position/force control algorithm are proposed. Lastly, experimental results are shown to verify the effectiveness of the proposed control algorithms.>

An impedance control scheme of redundant macro-micro manipulators is proposed. In this control scheme, we can specify not only the desired mechanical impedance of the end effector, but also that of the macro manipulator by considering the internal force applied at the tip of the macro manipulator. This control scheme can utilize both of the merits of the macro and micro manipulators. That is, by specifying a suitable set of the desired mechanical impedance, a compliant motion can be realized without any excessive joint torque of the macro manipulator, and a wide motion range of the macro manipulator can be used effectively to compensate a small motion range of the micro manipulator. The validity of the proposed control scheme is shown by several simulation results.>

A display system for displaying feel information while manipulating dynamic virtual objects is introduced and new concept of impedance display is proposed. An unified description of the dynamics of virtual objects based on the Lagrangian formulation is derived. The detection of the grasp states, and the friction effects at the grasp points on virtual object surface, which is important to help recognize the object and handle it more dexterously, are treated explicitly. Display algorithms which create and present the dynamic operating feel of an object as well as the friction feel on the object surface to the operator is provided. Experimental verification on the proposed approaches is performed and its results are outlined.>

In this paper, a new adaptive robust control scheme for manipulators is proposed that overcomes the drawbacks of conventional adaptive robust control methods. The proposed controller has a simple structure by exploiting the special structure of the manipulator dynamics, and achieves the specified tracking precision without any a priori information on uncertainty. Furthermore, the feedback gain of the proposed method is almost necessary and minimum for the specified precision. To verify the advantages of the method, experimental results are shown for the trajectory control of a 2-DOF direct-drive arm.>

In this paper, the analysis and design of master-slave teleoperation systems are discussed. The goal of this paper is to build a superior master-slave system that can provide good maneuverability. We first analyze a one degree-of-freedom system including operator and object dynamics. Second, some ideal responses of master-slave systems are defined and a quantitative index of maneuverability is given, based on the concept of ideal responses. Third, we propose new control schemes of master-slave manipulators that provide the ideal kinesthetic coupling such that the operator can maneuver the system as though he/she were directly manipulating the remote object himself/herself. The proposed control scheme requires accurate dynamic models of the master and slave arms, but neither parameters of the remote object nor the operator dynamics is necessary. Last, the proposed control scheme is introduced to a prototype master-slave system and the experimental results show the validity of the proposed scheme.

The authors discuss how to manipulate an object in contact with the fixed environment with robot-fingers to perform a planned assembly operation successfully. First, the region of possible fingertip force to balance the reaction force from the environment (quasi-static analysis) is explicitly represented to ensure that the moving object is manipulated correctly. Next, by considering the assembly operation in quasi-dynamic way (i.e., assuming that the velocity of the motion is small enough to be neglected but its acceleration is not negligible), the region of feasible fingertip forces to operate the object is described. According to the region of possible finger forces, the corresponding feasible range of the fingertip positions on the object surface can be obtained. And the difference between the fingertip position obtained by the quasi-dynamic analysis and the fingertip position obtained by the quasi-static analysis is shown. Lastly, the validity of this quasi-dynamic method is verified by serval experiments., All discussions are on the assumptions that objects are polyhedra and their notions are planar and frictionless, and its velocity is small enough.

In this paper, a method for PTP and trajectory control of Cartesian type three DOF industrial manipulator with flexible joints are proposed. The elasticity of the manipulator is modeled using the spring-mass model. To establish the equation of motion, the Lagrangian formulation is used. The state equation is derived. Then it is linearized approximately. The PTP control system is formulated. A minimal order observer is used in this PTP control system, and the trajectory control is realized based on the optimal control theory. Furthermore, the desired trajectory is modified to improve the tracking performance. Finally, computer simulation results are given to show the validity of the proposed tracking controller.

In this paper, a quasi-static object manipulation by an articulated three-fingered robot hand with slip motion of grasping is discussed. This kind of manipulation achieves more dexterous manipulation by robot hands. The equilibrium relations of fingertip forces for grasping an object are solved in three dimensions. It is assumed that a slip happens when the fingertip forces go beyond the bound of the cone of maximum static friction. Possible directions of slip within a grasp are determined from the analysis. The fingertip force which achieves a desired slip motion is determined uniquely. Finally the set of fingertip forces is obtained, and the planning method of slip motion is discussed.

Efficient computational algorithms for the trajectory control of multiarm free-flying space robots are presented. The motion of the aircraft itself during manipulation is considered in order to obtain an accurate trajectory control. The generalized Jacobian of multiarm free-flying space robots is obtained efficiently by regarding the total multilink system as a composite system consisting of two links with a joint. The algorithm can be easily extended to any tree-structured multiarm robot with rotational as well as prismatic joints except for closed-loop structures. An efficient computational algorithm for the resolved acceleration control of the multiarm free-flying robots is also presented. The computational complexities are evaluated and compared to those of fixed-base manipulators. It is shown that the computational complexity for the generalized Jacobian is five times greater than that for fixed-base manipulators whereas the resolved acceleration control requires twice the computation for fixed-base manipulators.>

A dynamic hybrid position/force control method, which takes into consideration the manipulator dynamics and the constraints on the end-effector specified by the given task, is obtained by extending the method of M.H. Raibert and J.J. Craig (1981). One difficulty in implementing the method is that precise information on the size and position of the object with which the end-effector contacts is not usually available. To cope with this difficulty, a problem of dynamic hybrid control with unknown constraint is studied. An online algorithm is developed that estimates the local shape of the constraint surface by using measured data on the position and force of the end-effector. It is shown by experiments, using a SCARA-type robot, that the combination of this algorithm with the dynamic hybrid control method works fairly well, making the dynamic hybrid control approach more practical.>

The analysis and design of master-slave teleoperation system are discussed in order to build a superior master-slave system that can provide good maneuverability. The authors first analyze one degree-of-freedom systems considering operator and object dynamics. Secondly, they define some ideal responses of master-slave system, and a quantitative performance index is given based on the concept of the ideal responses in order to evaluate the maneuverability of the system. Thirdly, they propose new control schemes of master-slave manipulators which can provide the ideal object realities so that the operator can feel the object through the system ass though he were manipulating it himself. Lastly, the proposed control scheme is examined by a prototype master-slave system, and its validity is confirmed experimentally.>

Deals with robust control of robot manipulators in the case where joint torque sensors are available. First, the authors derive a dynamic equation of the manipulator with joint torque sensors that explicitly expresses the total nonlinear multivariable structure. This dynamic equation makes it possible to construct the control system of the manipulator with joint torque sensors using the same method as in the conventional case without the sensors. Second, based on this dynamic equation, they propose a robust trajectory control scheme which achieves the specified tracking accuracy in the presence of the modeling errors including the modeling errors of actuator systems. In the proposed method, the joint torque sensor information is fully exploited to compensate the uncertainty of link and load parameters. Furthermore, an illustrative simulation result is given to show the effectiveness of the proposed control method.>

For developing a dynamic model of a flexible manipulator, a modeling scheme using virtual rigid links and passive joints is proposed. The parameters of the model are identified by measured data of the real arm, so it is expected that the dynamic behavior of the model is similar to that of the real arm. The equations of motion of an N degree of freedom flexible arm using this model are derived to simulate its dynamic behavior. The results of simulation and experiment show the validity of this modeling scheme.>

When mobile robots convey objects on a floor by pushing them, the motion of the pushed object is closely related to the distribution of the frictional force between the object and the floor. When the pushing force vector applied to an object passes through the center of friction which is the centroid of the friction distribution, the motion of the object is a pure translation. The authors describe a method for estimating the friction distribution of an object and the position of the center of friction by pushing the object several times using a manipulator mounted on a mobile robot, which also has a visual sensor. Simulation and experimental results show the effectiveness of the approach.>

For autonomous assembly operations by a robot, it is required to build a planning function that can generate a series of operations to reach a goal state. This paper describes an automatic planning algorithm that synthesizes the assembly operation strategies. By minimizing a criterion function based on the difficulty of state transitions the method can find an optimal path in a contact state network. The degree of constraint is proposed by regarding the assembly task as a process of changing the constraint state of the object. State transition difficulty is discussed by considering the variation of the degree of constraint and the shape information from the geometric models of objects. Then, a criterion function for state transitions is defined based on the state transition difficulty. Lastly, an algorithm which plans an optimal state transition path from an initial state to a goal state is proposed. Some examples are given to show the validity of this algorithm.>

A cooperative dynamic hybrid position/force control method for a set of robot arms or a multifingered robot hand handling a single object with or without its motion being constrained by its environment is shown. The method takes the manipulator dynamics and object dynamics into consideration and controls the motion of an object under constraint as well as constraint force when the object motion constraint and the internal force occur. The motion control of an object in free space can be treated as the case of no constraint on object motion in the formulation. An unified description for accommodating various grasp types is used. Several experimental results are presented that show the validity of the proposed approach.>

A new definition of grasping and manipulating forces for multifingered robot hands is proposed. First, a short discussion of the grasping and manipulating forces for two-fingered hands with linear motion is given to explain the motivation more clearly and to give the basic idea of the new definition. Then, for three-fingered hands, based on a representation of the internal force, the grasping force is defined as an internal force that satisfies the static friction constraint. The concept of grasp mode is also introduced. The manipulating force is then defined as a fingertip force that satisfies the following three conditions: (1) it produces the specified resultant force, (2) it is not in the inverse direction of the grasping force, (3) and it is orthogonal to the grasping force component. An algorithm for decomposing a given fingertip force into manipulating and grasping forces is presented. Extensions of the result to cases of two-fingered hands with planar motion and four-fingered hands are discussed. Finally, a simple example of synthesizing fingertip force for a given manipulation task is given to illustrate the usefulness of the proposed definition.>

A cooperative dynamic hybrid control method for multimotion robotic mechanisms handling a single object whose motion is constrained by environment is discussed. This method takes the manipulator dynamics and object dynamics into consideration and is for controlling the motion of the object as well as for controlling the constraint force and the internal force. The following results are obtained: (1) the force and kinematic relations are established for arms grasping and manipulating an object using various types of end effector; and (2) using the first result, a nonlinear state feedback law for the joint driving force that linearizes and decouples the robot system with respect to the object motion, constraint force, and internal force is given. A basic structure of the dynamic hybrid control system with a servo compensator is presented. The effectiveness of the proposed approach has been examined by a simple experiment. These results are useful for the fine manipulation of an object, in the sense that one can specify the controller characteristics independently for the individual specification of the object motion, the interaction between the object and its environment, and the grasping of the object.>

A six-axis force sensor is described, which has three pairs of elastic elements aligning on three axes which are orthogonal and cross at the center of the sensor. This orthogonal structure is called a three-dimensional cross-shape structure. Each elastic element consists of a pair of thin parallel plates which form the parallel plate structure. From the outputs of strain gauges placed on the elastic elements, the six force components are obtained. The whole characteristic of the sensor is obtainable just by analyzing the force-strain relation of a pair of elastic elements on an axis, making it simpler to design a sensor for a given specification. The cross-coupling between the strain gauge outputs and the six force components can be made small. A prototype sensor has been fabricated and it has been shown that the measured characteristic coincides with the analyses based on beam theory, the cross-coupling is rather small, and the force-strain characteristics in all force directions are uniform.>

Evaluation of grasping and determination of grasping forces in manipulation by multifingered hands are discussed. Based on the definitions of manipulating and grasping forces introduced previously, the advantages of determining a grasping force beforehand for the secure grasping against an anticipated class of external forces is described. For evaluation of a given grasping force, a criterion of the remaining ability of grasping is proposed. A method of grasping for a given manipulation tasks, in which grasping forces are determined as those with the maximum value of this criterion, for the expected external forces in each step of the task, is proposed.>

An approach to designing controllers for dynamic hybrid position/force control of robot manipulators is presented, and preliminary experimental results are given. Dynamic hybrid control is an extension of an approach proposed by M.H. Raibert and J.J. Craig (1981) to the case where the full manipulator dynamics is taken into consideration and the end-effector constraint is explicitly given by the constraint hypersurfaces. This design method consists of two steps. The first step is the linearization of the manipulator dynamics by nonlinear state feedback. Formulation of the constraint by the constraint hypersurfaces plays an essential role in establishing the linearizing law. The second step is the design of position and force controllers for the linearized model using the concept of two-degrees-of-freedom servocontroller. The merit of this servocontroller is that it can take account of both the command response and the robustness of the controllers to modeling errors and disturbances. Preliminary experiments using a SCARA robot show the validity of the approach.>

This paper discusses the mechanics of coordinative manipulation by multiple robot manipulators or a multifingered robot hand. The coordinative manipulation problem is divided into two phases. One is determining the resultant force by multiple robotic mechanisms, and the other is determining the internal force between them. The resultant force is used for the manipulation of an object subjected by the external forces or the environmental constraints. The internal force is used for adapting the robotic mechanisms to uncertainty and variety of the static friction. A dynamic coordinative control scheme is proposed for determining the resultant forces. The optimal internal force is defined as the internal force that yields the minimal norm force satisfying static frictional constraints. The optimal internal force promotes the stability of prehension, while the conventional method sometimes result in too much internal force and reduce the stability. Finally, by applying a non-linear programming method, it is clarified that the optimal solution is necessarily obtained by solving, at most, 2(2m-1) (m is the number of robotic mechanisms) sets of algebraic equations if it exists.

Manipulating force and grasping force for skillful manipulation of objects by multifingered robot hands are discussed in this paper. A new representation of the internal force among the fingers is given. Based on this representation, the grasping force is defined as an internal force which satisfies the static friction constraint. The mode of grasping is also introduced. The manipulating force is then defined as a fingertip force which satisfies the following three conditions: 1) It produces the specified resultant force. 2) It is not in the inverse direction of the grasping force. 3) It does not contain any grasping force component. An algorithm for decomposing a given fingertip force into manipulating and grasping forces is presented.

An approach to designing controllers for dynamic hybrid position/force control of robot maniulators is presented and preliminary experimental results are given. Dynamic hybrid control is an extension of the hybrid control approach proposed by Raibert and Craig to the case where the full manipulator dynamics is taken into consideration. This design method consists of two steps. The first step is the linearization of the manipulator dynamics by nonlinear state feedback. The second step is the design of position and force controllers for the linearized model which takes account of both the command response and the robustness of the controllers to modeling errors and disturbances. Preliminary experiments using a SCARA robot show the validity of the approach.

For the application of robot manipulators to complex tasks, it is often necessary to control not only the position of a manipulator but also the force exerted by the hand on an object. For this purpose, Raibert and Craig have proposed the hybrid position/force control method. In this method, however, the manipulator dynamics has not been taken into account rigorously. The dynamic hybrid control method is proposed, which takes the manipulator dynamics into consideration. Constraints on the end effector are described by a set of constraint hypersurfaces. Then the basic equations for dynamic hybrid control are derived. It is shown that if the manipulator is not in a singular configuration, the desired position and force at the end effector can be simultaneously realized. Finally, a basic structure of the dynamic hybrid control system with a servo compensator is given.

For application of robot manipulators to complex tasks, it is often necessary to control not only the position of a manipulator but also the force exerted by the hand on an object. For this purpose, Raibert and Craig have proposed the hybrid position/force control method. In this method, however, the manipulator dynamics has not been taken into account rigorously. In this paper, we propose dynamic hybrid control method which takes the manipulator dynamics into consideration. Constraints on the end-effector are described by a set of constraint hypersurfaces. Then the basic equations for dynamic hybrid control are derived. Finally, a basic structure of the dynamic hybrid control system with servo compensator is given.

The concept of manipulability measure of robotic mechanisms is discussed. This is a measure of manipulating ability of robotic mechanisms in positioning and orienting the end-effectors. Some properties of this measure are established and the best postures of various types of manipulators from the viewpoint of this measure are given. A four-joint wrist mechanism is also analyzed with respect to its manipulability, and a control algorithm for this redundant mechanism is developed.

The concept of dynamic manipulability measure of robot arms is proposed as a quantitative measure of their manipulating ability in positioning and orienting the end-effectors, which takes the arm dynamics into consideration. This measure is defined on the basis of the relation between the joint driving force and the acceleration of the end-effector. Some properties of the measure are established. A two-joint link mechanism is analyzed and its best posture is obtained under certain condition from the viewpoint of this measure. A numerical example is also given to illustrate the utilization of this concept for the design of robot manipulators.