This paper introduces a crawler robot equipped with a movable bending point mechanism that allows it to bend anywhere along its trunk. The robot features a movable motor unit that travels along its body, dynamically adjusting the bending initiation point. This enables the robot to move forward and backward, bend its body, and shift the bending position as needed. By integrating these capabilities, the robot enhances its ability to navigate obstacles and confined spaces. We develop three statics-based models to predict the robot’s performance in escaping narrow spaces, climbing steps, and crossing ditches. These models demonstrate that adjusting the bending point improves traversal capabilities, a finding corroborated by experiments with the physical robot.

Motion control of underactuated systems through the inverse dynamics contains configuration singularities. These limitations in configuration space mainly stem from the inertial coupling that passive joints/bodies create. In this study, we present a model that is free from singularity while the trajectory of the rotating mass has a small-amplitude sine wave around its circle. First, we derive the modified non-linear dynamics for a rolling system. Also, the singularity regions for this underactuated system is demonstrated. Then, the wave parameters are designed under certain conditions to remove the coupling singularities. We obtain these conditions from the positive definiteness of the inertia matrix in the inverse dynamics. Finally, the simulation results are confirmed by using a prescribed Beta function on the specified states of the rolling carrier. Because our algebraic method is integrated into the non-linear dynamics, the proposed solution has a great potential to be extended to the Lagrangian mechanics with multiple degrees-of-freedom.

In situations such as endoscopic surgeries, a leader cannot use their hands to instruct the other surgeons to perform a task on the monitor because he/she must use both hands to control the surgical equipment. Although there are several pointing methods such as eye gaze tracking, these methods are not suitable for endoscopic surgeries, where optical sensors (e.g. infrared sensors) cannot be used due to the existence of physical obstacles in the operating theater. Therefore, an assisting pointing device apparatus that directly measures the behavior of users and is not based on hands is specifically needed. To tackle this problem, we built a pointing device that measures the tilt angle of a user's head by gyro and acceleration sensors. Furthermore, we evaluated the performance of our device compared to that of a mouse using statistical analysis based on Fitts' law and other commonly used parameters. We considered a mouse as a benchmark to clarify the limitations and possible usage of our device. We found that, although it does not perform as good as a mouse, our device can still suitably perform as an assisting device for limited usage such as for tracking pre-defined lines.

An adaptive trajectory tracking problem for a spherical rolling robot driven by a 2DOF pendulum is considered in this paper. A feedback controller is proposed for the goal of tracking the trajectory for the full configuration of the spherical robot. To deal with time-varying uncertainty of the system dynamics, an adaptation mechanism is included in the trajectory tracking controller by parameterizing the system uncertainty with a polynomial function, weighted by unknown constant parameters adjustable by the defined update law. The constructed controller is first tested for the planar hoop-pendulum and then applied to the ball-pendulum system. The convergence to the desired trajectories under the control law is proved and then verified by simulations for tracking circular motions under perturbation.

This paper deals with motion planning and control for an underactuated system, the hoop-pendulum, a pendulum mounted at the center of a hoop. The dynamic model for this system is derived and the local controllability around the equilibrium point is established. To transfer the system from a initial configuration to a desired final configuration in rest-to-rest mode, two controllers, the feedback and feedforward ones, are constructed. The feedback controller stabilizes the system at the origin and is based on the construction of a suitable Lyapunov function. The feedforward controller is based on the representation of the motion of the pendulum by the second derivative of Beta function. The feasibility and the performance of the proposed controllers are verified under simulations.

This paper deals with a trajectory tracking problem for the ball-pendulum system, a spherical rolling robot driven by a two degree of freedom pendulum. The backstepping technique is applied and first tested on the hoop-pendulum system, a planar case of the ball-pendulum. By mimicking the backstepping process of the planar case, a feedback controller for the ball-pendulum system is then proposed, tracking motion trajectories for both the position and orientation of the spherical shell of the rolling robot. The validity of the constructed tracking controller is demonstrated by establishing the asymptotic stability of the error dynamics for the closed-loop system. The performance of the controller is verified under simulations for tracking linear and circular motions.

The paper presents an analysis of human-like reaching movements in manipulation of parallel flexible objects. To predict the trajectory of human hand, a minimum hand jerk model, based on the minimization of integral of squared hand jerk over the movement duration is established. It is shown that within this model the optimal hand trajectory is composed of a fifth order polynomial and two trigonometric terms depending on the natural frequencies of the system and the movement time. A virtual reality-based experimental setup with a haptic simulator is designed, and the prediction by the minimum hand jerk model is verified against experimental data. The theoretical prediction matches the collected data with a reasonable accuracy. The initial experimental results confirm the applicability of the minimum hand jerk model for modeling of human-like reaching movements in dynamic environments.

Conventional motion planners for wheeled vehicles often assume no-slipping and no-skidding conditions and construct motion trajectories in the context of nonholonomic motion planning. However, in some practical situations slipping and skidding cannot be ignored or can even be useful. To take them into account in the construction of planning algorithms, it is important to model the friction force between the tire and the contact plane. In this paper, we first construct a model of the friction force as an extension of the two-dimensional Coulomb model, considering both the slipping conditions and the nonholonomic constraints. Next, we formulate the motion planning problem as a drift parking problem and propose a motion planning strategy combining the nonholonomic planner and the control in the slipping mode. The feasibility and the performance of the proposed strategy are tested under simulation.

This paper deals with the dynamics and motion planning for a spherical rolling robot with a pendulum actuated by two motors. First a dynamic model for the rolling robot is established. In general, not all feasible kinematic trajectories of the rolling carrier are dynamically realizable. A notable exception is when the contact trajectories on the sphere and on the plane are geodesic lines. Based on this consideration, a motion planning strategy for complete reconfiguration of the rolling robot is proposed. The strategy consists of two trivial movements and a non-trivial maneuver that is based on tracing multiple spherical triangles. To compute the sizes and the number of triangles, a reachability diagram is constructed. To define the control torques realizing the rest-to-rest motion along the geodesic lines, two possible approaches are suggested. A computational algorithm, implementing the motion planning strategy, is developed and verified under simulation.

This paper deals with motion planning problems for spherical rolling robots driven by a two degree of freedom pendulum. A full dynamic model for this system is first introduced. Then, assuming that the contact path is specified and the sphere moves in pure rolling mode, the full dynamic model is reduced by imposing virtual constraints. A timing control law, based on the Beta function, for tracing the contact curves in rest-to-rest motion is constructed. The constructed control law is verified under simulation for tracing Viviani's curve and the Loxodrome on the sphere.

In this paper, we propose a motion control algorithm for switching between three motion strategies in unknown environment using a gradually building map. It is well known that the motion control of a coverage problem based on a global map is more efficient than local information based motion control which does not use the map. When the beginning of the coverage task, the building map is insufficient, so the motion control based on the map is not so efficient. When almost end of the coverage task, the built map is expected to be almost perfect one. Our algorithm is designed with the insufficiency of the gradually building map. In the algorithm, the robot selects one of three motion strategies depending on completeness of the map. The strategies include local motion control based on local sensing, wall following control to get environmental information and global motion control based on the built map. The robot selects mainly local motion control at an early stage. As time goes on, a global motion control using the reliable map is more selected automatically. The efficiency of the coverage problem is discussed by comparing the proposed method with a control method only by local information. Some simulations and experiments using the algorithm are shown in the paper.

Most motion planners for a vehicle often assume no-slipping and no-skidding in the context of nonholonomic motion planning. However, there actually exist slipping and skidding in practical situations and it is important to know the force between the tire and the contact plane considering slipping and skidding in the planning problem. In this paper, a Coulomb friction model of the tire friction force of vehicle is extended to nonholonomic constraints. In the modeling, the longitudinal and lateral tire friction forces are modeled corresponding to no slipping and no skidding constraints, respectively. A two directional model based on the maximum dissipation principle is also developed. Some typical movements of vehicles with the proposed friction force model are illustrated by simulations.

This paper proposes a novel set-point control method of a musculoskeletal system by combining a feedforward and feedback manner to complement each drawback each other. In our previous work, a feedforward positioning method of the musculoskeletal arm model was proposed which does not need any realtime sensory information. Its performance, however, depends on a muscular arrangement and an attitude of the arm, and thereby a large initial muscular internal force is necessary to make a good performance. On the other hand, it is well-known that a visual servoing is effective and versatile for the set-point control. However, there is a considerable time-delay due to a computational burden to acquire useful information from an image and an insufficient sampling period to capture each image when using a video frame rate camera. Thus in this paper, the feedforward and feedback signal are linearly combined into one in order to mutually complement each drawback. The combined control signal is newly designed and then numerical simulation results are shown to demonstrate the effectiveness and usefulness of the proposed method.

This paper deals with a motion planning problem for a spherical rolling robot actuated by two internal rotors that are placed on orthogonal axes. The key feature of the problem is that it can be stated only in dynamic formulation. In addition, the problem features a singularity when the contact trajectory goes along the equatorial line in the plane of the two rotors. A motion planning strategy composed of two trivial and one nontrivial maneuver is devised. The trivial maneuvers implement motion along the geodesic line perpendicular to the singularity line. The construction of the nontrivial maneuver employs the nilpotent approximation of the originally nonnilpotent robot dynamics, and is based on an iterative steering algorithm. At each iteration, the control inputs are constructed with the use of geometric phases. The motion planning strategy thus constructed is verified under simulation.

The paper deals with the problem of motion planning for a spherical rolling robot actuated by two internal rotors that are placed on orthogonal axes. To solve the problem, we employ the so-called geometric phase approach based on the fact that tracing a closed path in the space of input variables results in a non-closed path in the space of output variables. To set up the governing equations, the contact kinematic equations are modified by the condition of dynamic realizability, which constrains the component of the angular velocity of the rolling carrier and depends on the mass distribution, and parameterized. By using a motion planning strategy based on tracing two circles on the spherical surface, an exact and dynamically realizable motion planning algorithm is fabricated and verified under simulation.

A high-fidelity attitude estimation technique for wide and irregular movements is proposed, in which heterogeneous inertial sensors are combined in complementary way. Although the working frequency ranges of each sensor are not necessarily complementary, inverse sensor models are utilized in order to restore the original movements. In the case of 3D rotation, the sensor dynamics displays a highly nonlinear property. Even if it is approximated by a linear system, the inverse model of a sensor tends to be non-proper and unstable. An idea is to decouple it into the dynamics compensation part approximated by a linear transfer function and the strictly nonlinear coordinate transformation part. Bandpass filters inserted before the coordinate transformation guarantee that the total transfer function becomes proper and stable. Particularly, the differential operator of a high-pass filter cancels the integral operator included in the dynamics compensation of the rate gyroscope, which causes instability. The proposed method is more beneficial than Kalman filter in terms of the implementation since it facilitates a systematic design of the filter.

The paper deals with the dynamics and motion planning for a spherical rolling robot actuated by internal rotors that are placed on orthogonal axes. The driving principle for such a robot exploits non-holonomic constraints to propel the rolling carrier. The full mathematical model as well as its reduced version are derived, and the inverse dynamics is addressed. It is shown that if the rotors are mounted on three orthogonal axes, any feasible kinematic trajectory of the rolling robot is dynamically realizable. For the case of only two orthogonal axes of the actuation the condition of dynamic realizability of a feasible kinematic trajectory is established. The implication of this condition to motion planning in dynamic formulation is explored under a case study. It is shown there that in maneuvering the robot by tracing circles on the sphere surface the dynamically realizable trajectories are essentially different from those resulted from kinematic models.

This paper presents an improvement of our previously proposed dynamic object grasping and manipulation method. This method, which utilizes a dual-fingered hand of which each soft and hemispheric fingertip owns a torsional joint, has performed novel 3-dimensional dynamic object grasping and manipulation stably without the use of any external sensing device. However, several limitation and weakness have still remained in terms of dexterity and robustness. In order to improve it, firstly a triple-fingered hand is newly introduced instead of the dual-fingered hand to perform regrasping. Next, the previously proposed stable object grasping controller is adequately modified to perform dynamic regrasping during manipulation. Additionally, the virtual object attitude controller is also modified to improve its performance. Finally, several experiments are conducted by using a prototype, and the usefulness of proposed controller is demonstrated through these results.

The paper deals with the motion planning for a spherical rolling robot actuated by internal rotors that are placed on orthogonal axes. It is shown that if the robot is actuated by three rotors, any feasible kinematic trajectory is dynamically realizable. For the case of two rotors the conditions of controllability and dynamic realizability of a feasible kinematic trajectory are established. It is shown that in moving the robot by tracing straight lines and circles in the contact plane the dynamically realizable trajectories are not represented by the circles on the sphere, which is a feature of the kinematic model of pure rolling. The dynamic motion planning problem is then formulated in the optimal control settings, and the properties of the optimal trajectories are illustrated under simulation.

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.

Cleaning of glass windows for buildings is a dangerous work for human. Automatic cleaning for glass windows has been, thus, expected. Authors have developed an autonomous small-sized robot which can be used for glass window's cleaning even on not fully-flat walls. There are two major ways for the motion control of the autonomous cleaning mobile robot, which are reaction-based control method and model-based control method. Efficiency of the cleaning using the reaction-based method is lower than one using the model-based method. This study aims to develop a high efficiency and high reliable glass cleaning robot. Thus, we adopt the model-based method for the control of the cleaning robot. For the efficient and reliable cleaning, the robot should follow a desired path accurately. However, the trajectory tracking on a window is not so easy because of gravity and other dynamical effects. Moreover, even if the robot follows the desired path exactly, the robot can not assure a complete cleaning of the glass window. Therefore, the paper discusses a trajectory tracking control problem on the glass window, and also proposes a novel dirt detect sensor and a motion control method to guarantee the completeness of glass window cleaning. The validity of those proposed methods is confirmed by experiments using a window cleaning robot which attracts a window by magnetic force.

The paper deals with modeling of human-like reaching movements using a probabilistic minimum variance model. A continuous formulation of the minimum variance model is developed and analyzed. The model features a parameter, having the meaning of the post-movement time period, whose assignment in a systematic way is not evident. To facilitate the situation and avoid the explicit specification of this parameter, the limiting case of the post-movement period tending to infinity is analyzed for several classes of the control plant. A connection between this limiting model and the conventional minimum control effort model is also established.

This paper proposes a novel high-backdrivable parallel-link manipulator with Continuously Variable Transmission (CVT) mechanism using several shaft actuators. The backdrivability is important and necessary for robots that operate around our life space to guarantee the safety of us, themselves and environments. A rotational actuator with a high reduction ratio reducer has been commonly used in traditional robotics field, but it cannot realize the high-backdrivability without any sensory feedback. In this study, several high-backdrivable shaft actuators are used instead of it. Moreover, the CVT mechanism which is brought by a novel configuration of the parallel mechanism is employed effectively. To utilize multiple shaft actuators with the CVT mechanism is able to surmount a drawback of the shaft actuator whose output force is relatively weak. A simple 1 DOF manipulator is proposed as the first step of this study. Firstly, its kinematic and dynamic models are given. Next, a PD type feedback control signal to regulate the arm's angle and the CVT simultaneously is designed. A static relation between an output end-point force and the CVT mechanism is analyzed. Finally, several fundamental experiments are conducted to show the effectiveness of proposed mechanism.

This paper proposes a novel object manipulation method by using a dual soft-fingered robotic hand system, in which each fingertip has a torsional joint. By using the torsional motion of the fingertips, a novel 3-dimensional dynamic object manipulation without use of any external sensing can be achieved even though the hand system has only two fingers. Firstly, our proposed system, which includes contact models between each fingertip and surfaces of an object, is modeled. A rolling contact between each fingertip and the object surfaces can be allowed because our proposed system has soft and deformable hemispheric fingertips. Moreover, a torsional contact model between each fingertip and the object surfaces is newly proposed. It is based on an assumption that the torsional motion induces an elastic strain potential. Secondly, a dynamic object manipulation control method is designed. The control signal is composed of four parts, the one is for grasping the object stably, the second one is for controlling a position of the object, the third one is for controlling an attitude of the object, and the last one is for the torsional fingertip motion. A numerical simulation based on our model is performed, and a manipulation experiment by using our developed setup is performed. The usefulness of our proposed method is demonstrated through these results.

The paper deals with modeling of human-like reaching movements. Several models are under study. First, we consider a model of reaching movement that corresponds to the minimization of control effort. It is shown that this model is represented by the well-known Beta function. The representation can be used for the construction of fractional order models and also for modeling of asymmetric velocity profiles. The natural boundary conditions, defined in this part of the paper, can also be used in modeling asymmetric velocity profiles. Finally, we consider the minimum time formulation of the optimization problem and (for the n-th order integrator) find its analytical solution in the general form.

High-gain proportional-integral-derivative (PID) position control involves some risk of unsafe behaviors in cases of abnormal events, such as unexpected environment contacts and temporary power failures. This paper proposes a new position-control method that is as accurate as conventional PID control during normal operation, but is capable of slow, overdamped resuming motion without overshoots from large positional errors that result in actuator-force saturation. The proposed method, which we call proxy-based sliding mode control (PSMC), is an alternative approximation of a simplest type of sliding mode control (SMC), and also is an extension of the PID control. The validity of the proposed method is demonstrated through stability analysis and experimental results.

This article describes a computationally efficient formulation and an algorithm for tetrahedral finite-element simulation of elastic objects subject to Saint Venant-Kirchhoff (StVK) material law. The number of floating point operations required by the algorithm is in the range of 15% to 27% for computing the vertex forces from a given set of vertex positions, and 27% to 38% for the tangent stiffness matrix, in comparison to a well-optimized algorithm directly derived from the conventional Total Lagrangian formulation. In the new algorithm, the data is associated with edges and tetrahedron-sharing edge-pairs (TSEPs), as opposed to tetrahedra, to avoid redundant computation. Another characteristic of the presented formulation is that it reduces to that of a spring-network model by simply ignoring all the TSEPs. The technique is demonstrated through an interactive application involving haptic interaction, being combined with a linearized implicit integration technique employing a preconditioned conjugate gradient method.

The severely handicapped often uses breath pressure for an input method to control various instruments such as TV, motorized bed, curtain, air conditioner in everyday life. Most of the input devices are ON/OFF (digital) type for the control of equipments. Considering the application of electrically powered wheelchair, the ON/OFF type interface is not desirable. Because the control of powered wheelchair needs preciseness and quickness for safe operation. A new input device using breath pressure is proposed for such purposes. The paper examines basic performances of human breath pressure control as an analog input device. Then possibility of two-dimensional input device by the breath pressure is discussed for the control of powered wheelchair. Basic experiments to study performance of the two-dimensional analog input device by breath pressure for an operation of the powered wheelchair are shown.

This paper presents a modular architecture of simulation software that is capable of properly capturing Coulomb friction in mechanical systems. The presented architecture is built upon Kikuuwe et al.’s discrete-time friction model, which is based on the implicit Euler method. The paper reformulates the model into a form that can be integrable through the standard fourth order Runge-Kutta method. Some examples based on the presented architecture are presented.

Intraoral radiography is one of the effective diagnosis method for dental clinic, which is used to examine dental caries and gum disease. A patient needs to have a small film inserted in their mouth. The position and orientation of the film are properly adjusted by the dentist. An indicator cone which directs X-ray is set up outside the patient's mouth. The intraoral radiograph provide a dental perspective projection image of the patient's teeth, thus the individual differences of patients make it more difficult to take an appropriate radiograph regardless of the experience of dentist. Recently, the skills of intraoral radiography of Japanese dental students and intern doctors are declining. A conventional education method for intraoral radiography currently conducted does not provide enough time to master intraoral radiographic technique for the dental students, because much time to develop the roentgenogram is necessary. This paper describes the development of a training system for intraoral radiography. The system is composed of a notebook computer, two PHANToM Omni devices, and a dental arch model, where the PHANToM Omni devices are used to measure the position and orientation of a indicator cone and film of the system. We applied the computer graphics technique to draw an intraoral radiograph on the computer display, thus the system enables trainees to practice the intraoral radiography without a X-ray machine, lots of film sheets, and time for the development of roentgenogram. In this paper, we present the system structure, a simulation method for generating an intraoral radiography, and simulation results

Intraoral radiography is one of the most important techniques for dentists, which is commonly used to diagnose dental caries and gum disease. An intraoral radiograph shows a perspective projection image of the teeth of patient, so that the roentgenogram is affected by the positional relationship between film, teeth, and indicator cone which directs X-ray radiation toward the film. In order to administer intraoral radiography for a patient, he/she has to have a small X-ray film inserted in their oral cavity. The position and orientation of the film are properly adjusted by the dentist or radiologic technician. And then, the indicator cone is positioned outside the patient's mouth, and its orientation is determined depending on the teeth and film. Recently, it has been reported that the skill of intraoral radiography of dental students and interns are declining in Japan. The background of this issue is that the conventional training method needs to use an actual X-ray machine and lots of film, and much time to develop the roentgenogram. We assumed that these training inefficiencies would be improved by using virtual reality technique. In this paper, we propose a training simulator for intraoral radiography based on virtual reality, where the trainees quickly obtain a graphical image of intraoral radiograph on a computer display after the setting of film and indicator cone is finished. This paper presents a simulation algorithm for generating a graphical image of intraoral radiograph, and discusses about optimum design of an indicator cone positioning device for the simulator. Simulation results show that the proposed simulation algorithm provides realistic observations of intraoral radiograph

This paper proposes a safe emergency stop control for collision avoidance of gantry cranes. The crane mechanism is widely used for handling heavy load. A big problem is that the suspended load swings easily. This leads to possibilities of collision of load with obstacle during the crane work. Emergency stop for collision avoidance is, however, also dangerous. Because residual sways after the stop is easy to be caused by the stop. Therefore, this paper presents an anti-sway control method when the emergency stop. The method is based on inverse dynamics of the crane system. Thus the inverse dynamics problem is also discussed. Using the inverse dynamics calculation and a real time obstacle detection system, a feed-forward based emergency stop control method is proposed. Experiments of emergency stop control using the method are shown.

This paper presents a development of a cleaner robot for vertical type air conditioning duct. The air conditioning duct is used for ventilation and air conditioning. After years use of the duct without cleaning, much dust is gathered inside the duct. That leads scattering the dust into rooms. This is not desirable in the view point of sanitation or health. Thus, periodic cleaning of the duct is requested. For the cleaning work, an air hose type cleaner robot is developed. An air nozzle is attached with the tip of the hose type robot. Compressed air blows off the dust from the air nozzle, then the dust inside the duct is collected by a dust collector with a filter. The part of nozzle is manipulated by wires' constraint using two DC motors. By watching TV monitor which shows inside of the duct, the cleaning work is done remotely using a control stick operation. To control the nozzle of the hose robot, the paper discusses a relation between position of nozzle (tip of hose robot) and wire length. Discussions on wire force for the position are also given. An experiment of the motion for the hose robot is presented, then theoretical solutions and experimental results are compared.

This paper discusses parallel wire mechanisms where an end-effector of the mechanism is suspended by multiple wires. The mechanisms enable not only three-dimensional (3-D) positioning but also 3-D orienting of the end-effector, unlike typical wire suspension-type mechanisms such as overhead crane. To discuss the parallel-wire-suspended mechanisms generally, two forms of basic dynamic equations are presented. Then the parallel wire mechanisms are classified into two types based on the basic equations. Dynamical properties of the two types of wire-suspended positioning mechanism are discussed. In this paper, one of the wire-suspended mechanism, incompletely restrained-type parallel wire mechanism, is mainly discussed on its inverse dynamics problem and its trajectory control problem. The inverse dynamics problem for the incompletely restrained-type mechanism plays an important role on its control problem, because the mechanism has low stiffness based on incomplete constraints on the suspended object which is governed by its dynamics. The paper proposes an antisway control method for the suspended object. In the method, the inverse dynamics calculation is used for nonlinear dynamics compensation to control the suspended object of the incompletely restrained parallel wire mechanism.

This paper presents methods of trajectory planning for a mobile manipulator with stability considerations. The proposed trajectory planning method is to generate a trajectory for the mobile manipulator from a given path of the end-effector considering stability. Then, we derive a dynamics model of the mobile manipulator considering it as the combined system of the manipulator and the mobile platform. ZMP criterion is used as an index for the system stability. The trajectory planning problem is formulated as an optimal control problem with some constraints. To solve the problem, we use a hierarchical gradient method which synthesizes the gradient function in a hierarchical manner based on the order of priority. The simulation results of the 2-link planar nonholonomic mobile manipulator are given to show the effectiveness of the proposed algorithm.

This paper proposes a new type of two wheels caster type odometer to estimate the current position and orientation of omni-directional vehicles. The proposed odometer is composed of two passive wheels and one passive rotational axis. The two wheels rotate independently, and the rotational axis changes the odometer's orientation as the omni-directional vehicle moves. Three rotary encoders using a gear train measure angular velocities of the two wheels and rotational axis. A mechanism of the gear train is proposed to prevent the encoder from being entangled with it. Using measured values of the three encoders, the current velocity vector of an omni-directional vehicle is calculated by kinematics of the odometer. Using the velocity vector, the current position and orientation of the omni-directional vehicle are estimated by dead reckoning. Results of localization experiments by the developed odometer are shown.

In this paper, we propose the trajectory planning method of multiple mobile manipulators which carry a common object in cooperation. We derive a dynamic equation considering dynamic characteristics of mobile manipulators and the object. The dynamic equation consists of equations of motion of mobile manipulators and the object, nonholonomic constraints of mobile platforms, and geometrical constraints between end-effectors and the object. The trajectory planning problem is formulated as an optimal control problem. A simulation result is given to show the effectiveness of the proposed method.

A feedback control method of Omni-Directional Vehicles (ODV) is proposed by using a caster type odometer. The odometer which is called the Two Wheels Caster Type Odometer (TWCTOdometer) is specially designed for ODVs. Driving wheels of typical ODVs are easy to slip. When an odometer is connected directly with the shafts of driving wheels, the slip of the driving wheels causes much dead-reckoning error. Thus the TWCTOdometer is attached independently to the driving wheels of the ODV in order to avoid the influence of slips of the driving wheels. The TWCTOdometer has a characteristic of passive omni-directional motion, which is to follow the omni-directional motion of the ODV. The ODV's current position and orientation are estimated accurately from the measurement values of the TWCTOdometer. The proposed control method uses the estimated current position and orientation that allow the accurate trajectory control of the ODV along desired trajectories. Experimental results show effectiveness of the proposed control method by using the TWCTOdometer.

Proposes a feedback control method for wire-suspended mechanisms. The wire-suspended mechanisms are classified into two types, which are completely restrained type mechanisms and incompletely restrained type mechanisms. The paper discusses mainly incompletely restrained type mechanisms form the viewpoint of actual control. The incompletely restrained type wire-suspended mechanism has the merit that it enables three dimensional positioning and orientation of suspended object with simple mechanism using a small number of wires. However it also has the drawback that the manipulated object is easy to swing as seen in overhead crane which is a simple incompletely restrained type mechanism. For this reason, an anti-sway control method for incompletely restrained type mechanisms is needed. To resolve the problem of swing, inverse dynamics for general incompletely restrained type wire-suspended mechanism is discussed, then a feedback control method based on dynamics compensation is presented.

In this paper, we consider cooperative multiple manipulators with passive joints and study the effect of a combination of active and passive joints. This kind of manipulator system may restrict the direction of the end-effector's force depending on which joints are set to passive ones. In the case of operating and transferring a common object, this restriction may give a less effective force and excessive internal force to the object. To use driving force effectively, the question of which joints are set to passive ones must be considered. Therefore, we show the effect of the joint configurations by case studies.

This paper discusses a feedback control method for incompletely restrained wire-suspended mechanisms. The incompletely restrained wire-suspended mechanism has a merit that it enables three dimensional positioning and orientating of suspended object with simple mechanism using a small number of wires. However it also has a drawback that the manipulated object is easy to swing as seen in overhead crane which is one of the simplest incompletely restrained mechanism. For this reason, anti-sway control method for incompletely restrained type mechanisms is needed. A key point of our method is exact linearization using inverse dynamics of the system. Feedback control method with exact linearization and measuring method for the suspended object are presented, and effectiveness of proposed methods are shown by an experiment.

A trajectory planning method of a mobile manipulator is presented. We derive the dynamics of the mobile manipulator considering it as the combined system of the manipulator and the mobile platform. The planning problem is formulated as an optimal control problem. To solve the problem, we use the concept of the order of priority. A gradient-based iterative algorithm which synthesize the gradient function in a hierarchical manner based on the order of priority is used. The simulation results of the 2-link planar nonholonomic mobile manipulator are given to show the effectiveness of the proposed algorithm.

Discusses an inverse dynamics problem and proposes a trajectory generation method for wire-suspended mechanisms. The wire-suspended mechanisms are classified into two types, which are completely restrained type mechanisms and incomplete by restrained type mechanisms. For the incompletely restrained type mechanisms, consideration of dynamics is important, because the motion of this mechanism is governed by its dynamics and kinematics, whereas the motion of the completely restrained type mechanism is determined by only its kinematics. The paper discusses mainly the incompletely restrained type mechanisms from the viewpoint of dynamical properties. The incompletely restrained type wire-suspended mechanism has a merit that it enables three dimensional positioning and orientating of suspended object with simple mechanism using a small number of wires. However it also has a drawback that the manipulated object is easy to swing as seen in overhead crane which as a simple incompletely restrained type mechanism. To overcome the problem, inverse dynamics for general incompletely restrained type wire-suspended mechanism is discussed, then a condition on desired trajectory of manipulated object is presented on the basis of the inverse dynamics analysis. Using the desired trajectory, an online trajectory modification method for the control of manually operated overhead crane is proposed.

In this paper, a trajectory planning method of a mobile manipulator with the end-effector's specified path is presented. We derive the dynamics of the mobile manipulator considering it as the combined system of the manipulator and the mobile platform. The planning problem is formulated as an optimal control problem. To solve the problem, we use the concept of the order of priority. A gradient-based iterative algorithm which synthesize the gradient function in a hierarchical manner based on the order of priority is used. The simulation results of the 2-link planar nonholonomic mobile manipulator are given to show the effectiveness of the proposed algorithm.

Proposes a control method for a crane using inverse dynamics calculation of the system. The load of a crane is generally easy to swing and thus the work using the crane is dangerous. For preventing the unfavorable swing of the load, it is desirable to feedback the actual position of the load in a control method. As such a control law, state-feedback control based on linearization of the crane system is often used. However the method reduces control performance when rope length is changed, because of nonlinearity of the system. In the paper, a feedback control method is proposed where the inverse dynamics calculation is involved to compensate non-linear dynamics of the system. In the control system, an observer is used to get higher order derivatives of the position of load, which is needed for the inverse dynamics calculation. By using the control method, control performance is unchangeable for changing rope length. Numerical simulation and experiment are shown to verify the effectiveness of the proposed control method.

In this paper, an optimal motion planning scheme using time-axis transformation and gradient method is proposed for nonholonomic systems. The motion planning of nonholonomic systems can be formulated as a nonlinear optimal control problem. However, the optimal control problem is too difficult to solve due to peculiar difficulty in the control of the nonholonomic systems. To alleviate the difficulty, we first convert the optimal control problem to a bidirectional, fixed-domain optimal control problem by using quasi-time variable. Then, a numerical algorithm which is based on the gradient method is developed for the optimal control problem and its convergence property with respect to final state error is proved. The optimal motion planning scheme is also applied to a 2-link planar free-joint manipulator. The simulation results show the effectiveness of the proposed optimal motion planning scheme.

This paper proposes an algorithm to determine suboptimal paths and trajectories for cooperative multiple manipulators with passive joints. The problem of operating and transferring the object from a given start point to a given goal point is considered. In this case, in general, degrees of freedom of the manipulators are larger than that of the object, and thus this manipulator system involves redundancy. Several joints can be changed to passive ones. We use remaining redundant degrees of freedom to refine trajectories. We apply this algorithm to a two-manipulators system. Simulation results show the effectiveness of the algorithm.

This paper discusses the optimal trajectory planning problem of nonholonomic systems in the presence of obstacles. The problem can be formulated as an optimal control problem by incorporating final state errors and obstacle avoidance conditions in the cost function. To solve the highly nonlinear optimal control problem, we introduce the concept of the order of priority into the trajectory generation procedure. We place the first priority on the convergence of the state to a desired state. The second priority is given to obstacle avoidance and the third priority is given to trajectory optimization. Then, a gradient-based iterative algorithm which synthesizes the gradient function in a hierarchical manner considering the order of priority is proposed. The simulation results of the 3-link planar free-joint manipulator are given to show the effectiveness of the proposed algorithm.

This paper discusses parallel wire mechanisms where an end-effector of the mechanism is suspended by multiple wires. This mechanism enables not only three dimensional positioning but also three dimensional orientating of the end-effector, unlike typical wire suspension type mechanism such as overhead crane. To discuss the parallel wire mechanism, two forms of basic dynamic equations are presented. Then dynamical properties of the mechanism is described based on the basic equations. This paper mainly issues an inverse kinematics problem for general incompletely restrained type parallel wire mechanism. To distinguish some parallel wire mechanisms including the incompletely restrained type, the paper first defines constraint states of the end-effector, then parallel wire mechanisms are classified into three categories based on the definition. Each characteristic of the mechanism corresponding to the categories is described. Especially, incompletely restrained type parallel wire mechanism is mainly discussed in the view point of inverse kinematics problem. After arguing a general solution for the inverse kinematics problem of the incompletely restrained type parallel wire mechanism, an actual mechanism of the incompletely restrained type mechanism is presented and the inverse kinematics problem for this mechanism is analyzed.

This paper addresses a problem of optimal motion planning of mobile platforms amidst obstacles, considering the mobile platform dynamics. Due to nonholonomic constraints, actuator constraints, and state constraints by obstacle avoidance, the planning problem of mobile platform with two independently driven wheels is a complicated one. In this study, a dynamical model for the mobile platform is presented, including nonholonomic kinematic constraints. The idea of a path parameter is introduced to simplify the planning problem by considering the dynamics and nonholonomic constraints. Using the path parameter, the optimal motion planning problem is divided into two sub-problems: 1) time-optimization of trajectory along specified path, and 2) search for optimal path. Then two methods are proposed the solve the problems using the path parameter and parametrization by B-spline function. Finally, quasi-time-optimal solution for the original problem are planned by combining the two methods. Numerical examples show effectiveness of the motion planner.

Discusses the optimal trajectory planning problem of classical nonholonomic systems. Most conventional studies have discussed the nonholonomic motion planning problem considering only kinematics. However, when a trajectory is required to minimize the traveling time or the energy used in performing tasks, the dynamics must be taken into consideration. In this paper, a trajectory planning method that considers the full nonlinear dynamics of the system is proposed. This method is based on the concept of geometric phase and the minimum cost trajectory planning algorithm which were previously developed for motion planning of robotic manipulators. Simulation results show the effectiveness of the proposed method.

This paper discusses an inverse dynamics problem for a parallel wire mechanism with multi-degrees of freedom. Firstly, a crane-type parallel wires mechanism which has three trolleys and three wires is proposed for handling heavy objects. This handling mechanism enables not only three dimensional positioning but also orientating of objects, unlike typical crane mechanism. A dynamical model using wire force vector is derived. Based on the dynamical model with wire force vector, inverse dynamics problem is analytically solved by a linear equation in terms of the wire force vector. The trajectory of end-effector of the crane-type manipulator can be transformed into the trajectory of wire length and trolley position by the calculation method. Using the trajectory of wire length and trolley position, the end-effector of the crane-type manipulator is controlled. Two dimensional experimental crane-type manipulator is also developed to verify an effectiveness of the inverse dynamics calculation and the trajectory control method.

Feedforward control design of flexible robot can take advantage of planning algorithm. In this paper two such algorithms have been presented, one for static case and the other for dynamic case. Both the algorithms are iterative in nature and are computationally based on the minimization of position or tracking error defined at the end-effector level. The algorithms are simple but computationally expensive. The performance is tested on a planar two-link arm through simulation and the results show the capability of the methods to compensate error due to deflection of the flexible links at the time of static condition of positioning and to track a given trajectory effectively at the time of dynamic condition of tracking under end kinematic constraints.

A motion planning problem of a cooperative multiple manipulator system carrying out grinding work or similar works to the object is considered. One manipulator holds the object rigidly and the other holds the tool and works on the object's surface. At the contact point between the object and the tool there exists friction, so that interaction forces must be taken into consideration in the dynamics of manipulators and the object. We only specify the tool task on the object's surface, so the object and manipulators can move arbitrary paths in the world coordinates frame. We propose an algorithm to generate joint trajectories for cooperative multiple manipulators to accomplish the specified task effectively.

Motion planning under fixed travelling time between start and goal point along a specified path is considered in this study. The structure between the actuator and the end point of the robot arm is assumed flexible and is the main cause of positioning error because of residual vibration. An algorithm is developed to generate motion of the manipulator arm along the specified path that significantly reduces the residual vibration, at the goal point configuration. The problem also considers the full nonlinear dynamics of the manipulator arm. The dynamics are described by finite element method using Lagrange's equation and are expressed by the time scale factor. The performance index is optimized successfully through off-line computation for a two link flexible manipulator, one example of which is described in detail.

The tracking error of robot manipulators based on flexible arm models are presented in this study. The number of actuator is equal to the dimension of the task space which is usually equal to the rigid body degrees of freedom. Actuator torques required for a flexible arm to track a given trajectory are formulated and computed by an iterative algorithm which is based on path planning method. The formulation is complete in the sense that it also considers the full nonlinear dynamics of the manipulator arm. The Euler-Bernoulli beam theory is used to model the dynamics of flexible links and the resulting equations of motion are derived by Lagrange's equation using finite element discretization technique. The algorithm is simple to implement but computationally expensive. The performance and capabilities of the proposed method are tested on a two-link arm through simulation and the results show the potential use of this method not only for feedforward open-loop control but also for closed-loop control strategies.

Addresses a problem of time-optimal motion planning of skid-steer mobile robots amidst obstacles. Due to nonholonomic constraints, actuator constraints, and state constraints by obstacle avoidance, the planning problem is a complicated one. In this study, the problem is divided into two sub-problems: (1) time-optimization of trajectory along specified path, (2) search for the optimal path, to alleviate the difficulties of the original problem. Then two methods to solve the problems are proposed, using an idea of path parameter and parametrization by B-spline function. Finally, quasi-optimal solutions for the original problem are obtained by combining the two algorithms. A simulation result shows an effectiveness of the proposed motion planner.

Two methods are presented to design the joint trajectory for a two-link flexible manipulator: 1) a combined Fourier series and polynomial function; and 2) a B-spline function. In both cases, the path satisfies the start and end kinematic constraints of motion. Using the energy approach for the above two cases, the final path is generated optimizing kinetic and strain energy at the goal point that reduces the residual vibration significantly. The present study is to compare the two methods and to predict that the B-spline curve has faster convergence property and at the same time, minimizes the performance index by six-fold and thus gives further reduction of residual vibration compared to the combined Fourier series and polynomial function. The dynamics of the manipulator arm, during its motion as well as free vibration after reaching the goal, are described by finite element analysis using Lagrange's equation of motion.

Rapid end point positioning along a specified path is considered in this study. The structure between the actuator and the end point of the robot arm is assumed flexible and is the main cause of positioning error because of residual vibration. An algorithm, based on optimization of residual energy at the goal point and the fundamental property of time scaling of manipulator dynamics, is developed that iteratively determines the time optimal trajectory along the specified path under given start and end point conditions. It also considers the full nonlinear dynamics of the manipulator arm and its actuator saturation limit, The dynamics are described by finite element method using Lagrange's equation and are expressed by the time scale factor. The performance index is optimized successfully through off-line computation for a two link flexible manipulator, one example of which is described in detail.

This paper proposes a method of planning collision free joints paths for two cooperative manipulators. When two manipulators hold a common object and execute specified tasks, there are problems related to handling and collision. To move two manipulators effectively, all of them must be considered together. There are redundancy aspects peculiar to the cooperative two manipulators. We use this redundancy and the potential function method to avoid collisions between the object and the link, the link and the link, the link and the obstacle and so on. Simulation results show the effectiveness of the proposed method.

This paper proposes a method for planning the collision free trajectory of a manipulator. In this method, geometrical constraints to avoid obstacles are represented by restrictive potential functions. The dynamic equation of the manipulator is expressed by a path parameter 's' which is the generalized length along the path. The driving torque/force is improved by taking shorter travelling time and collision avoidance into considerations. Finally, the proposed method is applied to a manipulator with three links and is shown to be effective.

A method for a time optimal collision free trajectory planning problem is proposed. In this paper, the dynamics of manipulator and obstacles are considered. This type of optimal trajectory planning problem is very difficult and complicated one because of the nonlinearity of manipulator dynamics and existence of obstacles. Generally, it results in a multimodal optimization problem. The proposed method is basically an iteratively improving one based on a gradient method. Firstly, two global methods (a genetic algorithm or an exact cell decomposition method) are used to search multiple initial feasible spatial paths for the gradient method. Next, the gradient method searches the time optimal solution locally with the multiple initial feasible solutions. Simulation results show that this is an effective approach to the time optimal collision free trajectory planning problem.>

Proposes a method of planning collision-free trajectories for two manipulators considering dynamic constraints. This algorithm is composed of two planning stages. In the first stage, minimum time trajectories for two manipulators are searched with limits of input torques/forces. In the second stage, if there is interference between two obtained trajectories, motion priority is given to two manipulators in order to avoid collision. Collision-free trajectories are obtained along the paths generated in the first stage and their traveling times are shortened, too.>