Quad tilt rotor Unmanned Aerial Vehicle (UAV) solves the problem of underacuated system in general quadrotor UAV. The quad tilt rotor UAV can control position and attitude independently by tilting directions of propellers. However, the flight control system in a wide range of attitudes has not been discussed yet, e.g. a UAV flying and hovering with a 90 [°] pitch angle and can flip over when the range of the tilting motor rotates wide enough. In this paper, we present the attitude transition flight control system for pitch angles ranging 0 [°] to 90 [°] since flight condition with a 90 [°] pitch angle significantly differs from that in a conventional quadrotor UAV flight, and then adequate control system and sufficient experimental validation are necessary for stable flight in a wide range of attitude conditions.

This paper presents development of a quad rotor tail-sitter VTOL UAV (Vertical Takeoff and Landing Unmanned Aerial Vehicle) which is composed of four rotors and a fixed wing. The conventional VTOL UAVs have a drawback in the accuracy of the attitude control in stationary hovering because they were developed based on a fixed-wing aircraft and they used the control surfaces, such as aileron, elevator, and rudder for the attitude control. To overcome such a drawback, we developed a quad rotor tail-sitter VTOL UAV. The quad rotor tail-sitter VTOL UAV realizes high accuracy in the attitude control with four rotors like a quad rotor helicopter and achieves level flight like a fixed-wing airplane. The remarkable characteristic of the developed quad rotor tail-sitter VTOL UAV is that it does not use any control surfaces even in the level flight. This paper shows the design concept of the developed UAV and experimental verification of all flight modes including hovering, transition flight and level flight.

In this paper we propose a new method to detumble a malfunctioning satellite. Large space debris such as malfunctioning satellites generally rotates with nutational motion. Thus several researches have proposed the methods to use a space robot for capturing and deorbiting these debris. The most of the past studies considered the method to detumble an uncontrollable satellite and then capture a single spinning satellite. However these methods require physical contact with malfunctioning satellites, which has a risk of accident. Therefore, we propose a method with an eddy current brake. The eddy current brake system can produce braking force to the target without any physical contact. Thus, we can reduce the risk of critical collision between the space robot and the target object. This paper firstly reviews dynamics of a tumbling satellite and proposes a detumbling strategy with the eddy current brake. We carry out a fundamental experiment to evaluate the performance of the braking force of the developed eddy current brake system, and then we simulate detumbling operation by using the experimental data and show an effectiveness of the proposed detumbling method.

In open abdominal surgical procedures, many surgical instruments, e.g., knives, cutting shears and clamps, are generally used. Therefore, a haptic interface should display reaction force of a soft biological tissue through such a surgical instrument. Simplest solution for this difficulty is that an actual instrument is mechanically mounted on the traditional haptic interface driven by servomotors. However, operators lose a sense of reality when they change the instrument since they must perform a procedure which is not required in actual surgery for attaching/detaching the instrument to/from the haptic interface. Therefore, a novel haptic interface using MR (Magneto-Rheological) fluid is developed in this research. Rheological property of MR fluid can be changed in a short time by applied magnetic flux density. By cutting the fluid using a surgical instrument, operators can feel resistance force as if they cut tissue. However, MR fluid cannot display large deformation of soft tissues since elastic region of MR fluid is small. Therefore, a container of the fluid is moved by a motion table driven by servomotors. In this paper, concept and design of the haptic interface and performance evaluations are described.

A hybrid simulator is a simulator which embeds a hardware experiment in a numerical simulation. However, the hybrid simulator is generally subjected to an inherent problem of energy increase in collision of two hardwares in the loop because of delay times. To solve this problem, Osaki et al. proposed a compensation method of delay time that can realize a variable coefficient of restitution [1]. However, the above method has a drawback that a model error of the system degrades the accuracy of the compensation method. This paper describes the influence of the model error and proposes a new approach to improve the accuracy of delay time compensation based on the coefficient of restitution by introducing a new model of the system. A collision experiment by the hybrid simulator is carried out to validate the accuracy of the proposed compensation method compared with the conventional compensation method.

The application range of UAVs (unmanned aerial vehicles) is expanding along with performance upgrades. Vertical take-off and landing (VTOL) aircraft has the merits of both fixed-wing and rotary-wing aircraft. Tail-sitting is the simplest way for the VTOL maneuver since it does not need extra actuators. However, conventional hovering control for a tail-sitter UAV is not robust enough against large disturbance such as a blast of wind, a bird strike, and so on. It is experimentally observed that the conventional quaternion feedback hovering control often fails to keep stability when the control compensates large attitude errors. This paper proposes a novel hovering control strategy for a tail-sitter VTOL UAV that increases stability against large disturbance. In order to verify the proposed hovering control strategy, simulations and experiments on hovering of the UAV are performed giving large attitude errors. The results show that the proposed control strategy successfully compensates initial large attitude errors keeping stability, while the conventional quaternion feedback controller fails.

This paper presents a robust and efficient method of generating manipulation motion skill for non-force-feedback high speed constrained compliant robot motion. Using a non-structured teaching environment, the inherent task in the captured demonstration force and position data is estimated and reconstructed from three sets of complimentary models, including analytical mathematical modelling, empirical modelling and human skill demonstration modelling. The approach addresses task specification accuracy deficiencies, and involves outward interface simplifications, with embedded rigorous analytical methodologies that enable users to realise complex and robust constrained compliant robot motion without dealing with the low level motion generation aspects. Function based task representation supports an intuitive approach to generate robust constrained motion by skill superimposition, as exemplified by peg-in-hole with crank turning.

This paper presents an asymmetric stiffness characteristic of a human hand. In human support robotics or medical robotics, the detail comprehension of physical human body is important to develop safe and high performed robots to work cooperatively with a human and to replace human dexterous tasks. It is known that a human arm generates variable stiffness depending on tasks by coactivation of agonist and antagonist muscles. Previous related researches have been presented impedance characteristics of a human upper limb in static posture and dynamic motion. These characteristics are represented by ellipsoids. However, the above analyses are based on a simple muscle model and conventional kinematic and dynamics of an articulated body system. In this paper, perturbation-excited method is carried out for estimating the stiffness of a human hand. The experimental results demonstrate nonlinear property of the stiffness of a human hand. To illustrate the observed stiffness characteristic, this paper proposes nonlinear stiffness model of the human hand.

This paper addresses an engineering attempt of utilizing multiple robot arms in assemblies of deformable parts. The developed robot system simulates a practically existing assembly process in an automobile plant where wrapped cables (wire harness) have to be fixed on the body of a car. This operation has been performed by skilled workers and is considered to be difficult for automatization. During the development of the system, solutions are proposed for various engineering problems confronted. The problems are all due to the deformable properties of a wire harness. Many of them are general for other operations involved with deformable objects. The proposed methods in the research are verified by a successful demonstration of wire harness assembly under a condition similar to a real plant.

Miniature vertical take-off and landing unmanned aerial vehicles (VTOL UAVs) make various missions possible alone such as surveillance in partially-destroyed building and at broad hazard area where many obstacle exist. In such missions, agile turnaround using post-stall maneuvers is useful to avoid obstacles. This paper discusses agile turnaround strategies utilizing post-stall maneuvers for tail-sitter VTOL UAVs. Two agile turn strategies are studied in this paper: (1) minimum travel distance turn, and (2) minimum radius turn. The proposed strategies are formulated and optimization problems are solved. Through computer simulation, the proposed strategies are evaluated in terms of travel distance and turning radius comparing with conventional Immelmann turn strategy.

Vertical take-off and landing unmanned aerial vehicles (VTOL UAVs) are expected to perform dangerous mission such as rescue and exploring disaster site alone. As for the operation of a UAV in a rescue mission, teleoperation is preferred. This paper describes teleoperation of a miniature tail-sitter VTOL UAV. A teleoperation system is developed to navigate a tail-sitter UAV. A velocity estimation method for outdoor flight is described and a velocity control strategy based on attitude control for indoor hovering of tail-sitter VTOL UAVs is proposed. In order to verify the teleoperation system and velocity control strategy, indoor exploration and target tracking teleoperation are performed in this paper. Through the experiments, the operator successfully controlled a teleoperated tail-sitter VTOL UAV with non-line-of-sight. In addition, a preliminary obstacle avoidance system is also implemented to assist operator.

In order to exert large force on an environment, it is effective to apply impulsive force. We describe the motions that perform tasks by applying impulsive force as “impact motion.” The objective of an impact motion is to exert large force on an environment, however if the impulsive force is too large, the robot may fall down due to the reaction force. This paper presents an optimization scheme to generate impact motions for humanoid robots. The advantage of the proposed scheme is that impulsive force exerted on a target by a humanoid robot's whole body is maximized while guaranteeing the stability. A punching motion is generated by the scheme as an example and evaluated by performing simulations.

In order to exert a large force on the environment, it is effective to apply impulsive force. We describe the motions that perform tasks by applying impulsive force as ¿impact motion¿. This paper presents a contact dynamics model of a humanoid robot for such a motion. Multibody dynamics and effect of a servo controller on impulsive force are also considered in the proposed model. The proposed model can estimate impulsive force at low computation cost compared with full-featured dynamics computation methods. The estimation results of each motion are compared with simulation results by OpenHRP3. The maximum error of impulse is about 6 (%). Therefore, the proposed model is useful for estimating dynamics behavior of a humanoid robot.

In this paper, a method for displaying feeling of cutting by a micro-scissors type haptic device is described. Micro-scissors are a type of surgical instrument, which is frequently used in brain surgery under a microscope. A prototype of a micro-scissors type haptic device consists of three components: an interface, a drive member, and force sensors. The interface is designed to equip features of a pair of micro-scissors and has a blade spring on its end. The drive member is composed of two DC-motors and two crank-lever mechanisms as decelerators. The force sensors are composed of strain gauges with H-slits, and implemented into each handle of the interface. For the aid of applying the force sensors to feedback control of cutting resistance forces, compensation for influence of a blade spring on the force sensors is added. Evaluation experiment for basic performance of the device is carried out, and the device is proved to be able to generate the computed cutting resistance forces. Virtual cutting experiment by six subjects is carried out, and it is proved that the device is able to display feeling of cutting.

This paper describes a procedure of avoiding singularity for a redundantly-driven, dual-arm, master-slave robotic system. In cooperative operation, the procedure starts with a periodic check if one of the dual arms is close to a singular configuration by examining the manipulability of the arm. If it is close to a singularity, then the system stops its cooperative operation and control scheme switches to redundancy control. Then the operator manipulates the joint until the arm moves away from the singular configuration by inputing angular velocity to a redundant axis. The fact that the operator can select a new arm configuration to avoid singular configuration in teleoperation is the contribution of this research. After moving away from the singular configuration, the system can resume cooperative operation. Because this manual operation applies to a redundant axis only (in the null space of the Jacobian matrix), it does not affect the current end-effector pose and force status. Experimental examples are provided to demonstrate the proposed method.

This paper presents a MPID (Modified Proportional-Integral-Derivative) controller used to suppress vibration of flexible manipulator moving vertically. To attain the vibration suppression a vibration variable should play role in the control signal which drives the flexible manipulator. The proposed controller is based on the conventional PID control but the integral term is replaced with another one which mainly depends on the vibration of the end effector. Camera becomes an inherent part of space manipulator, using the MPID controller with the visual information recorded by the camera makes the strain measuring circuits and amplifiers unnecessary. This means reducing the hardware used in the control of flexible manipulator. The novelty of the results lies in the fact that the measurement of the rate of change in deflection, which is used as a vibration variable, has been done without the need of numerical differentiation. Experiments successfully demonstrate that using the visual data with an observer based on Kalman filer can achieve a noticeable damping of the end effector vibration of the flexible manipulator.

In order to verify orbital operations of a dual-arm space robot on the ground, a hybrid simulator (hardware in the loop simulator) is developed. The hybrid simulator includes a 14-degrees-of-freedom (14-DOF) dual-arm robot and 9-DOF motion table. A hybrid simulator has a great advantage in simulating complicated collision with multiple contacts, because it is difficult for a numerical simulation to get reliable and accurate results of such complicated phenomena. In this paper, the system architecture and the motion planning for three motion tables are presented. Two experiments are performed to confirm the basic motion and simulate a free-flying dualarm space robot colliding with a floating object. The feasibility of robot operation is discussed from showing the position and force data obtained in the motion simulation.

In this paper, a vision-based vibration control approach is proposed to deal with the vibration appearing at the end-point of a flexible-link manipulator. It is achieved by utilizing the information obtained from end-effector camera. Particularly, the image features necessary for this approach are not specified to those obtained from assumed objects like artificial markers. This property enables the approach to be applied in a completely unknown environment. In that case, end-effector camera automatically collects the visual information needed for vibration damping. This paper shows feasibility of this strategy.

When a human needs to generate a large force, the human will try to apply an impulsive force cooperating whole body. This paper proposes a way to generate impact motions for humanoid robots to exert a large force keeping a balance. In the proposed method, the Sequential Quadratic Programming (SQP) is used to solve a nonlinear programming problem in which an objective function and constraints may be nonlinear functions of the motion parameters. Impact motions are generated using SQP so that the impact force is maximized while the angular momentum is minimized to keep stability. Breaking wooden boards by Karate-chop is taken as a case study because it is a typical example of tasks that utilize impulsive force. A humanoid robot motion for the Karate-chop is generated by the proposed method. In order to validate the designed motion, experiments are carried out using a small humanoid robot Fujitsu HOAP-2. The Karate-chop motion generated by the proposed method is compared with the motion designed by a human. The results of the breaking wooden boards experiments clearly show the effectiveness of the proposed method.

Robot operation requires a succinct interface with fewer parameters to specify. This paper presents an algorithm to interface an integrated torque control law, and human task demonstration data. The data is comprised of 6 degrees of freedom, pendant force and position data, and hand posture tracking data. The aim is to automatically specify all the required parameters for the control law, which include constrained and non-constrained trajectories, reference task frames and distal end compliance. The algorithm is embedded with functions to optimise, filter, synchronise and enhance safety.

In order to exert a large force on the environment, it is effective to apply impulsive force. We describe the motions that perform tasks by applying impulsive force as ldquoimpact motionrdquo. In this research, a nailing task is taken as an example of impact motion. This paper presents a relationship between driving depth and force or impulse and analysis of impulsive force prediction model.

This paper addresses a vision-based endpoint trajectory and vibration control approach for flexible manipulators. In this approach, both the trajectory and vibration control are implemented by using an endpoint camera. In order to estimate link vibrations from the visual information, Kalman filter is used. To make the endpoint to follow a specified trajectory, image interpolation approach is introduced. The experimental results prove the effectiveness of the proposed control strategy.

Performance of a human size humanoid robot is strictly limited by performance of the motor. The progress of a motor has not been remarkable compared with the progress of electronics. Therefore, the great progress of the performance of the motor cannot be expected, at least in the present circumstances. In this paper, a gravity compensation mechanism is designed which is applicable to a general biped robot. The mechanism is expected to reduce the joint torque of the legs required to support the gravitational force of the whole body. A humanoid robot Saika-4 is equipped with the gravity compensation mechanism in the legs. To evaluate effectiveness of the gravity compensation mechanism, preliminary experiments are performed using the humanoid robot.

A purpose of this paper is to expedite onerous initial procedures when a force-controlled parallel robot is taught task motions by the off-line task teaching/playback system which we have developed to realize the motion planning suitable for tasks and playback task motions dexterously. In this teaching system, the numerical teaching method has been employed to give detailed descriptions of the motion parameters, but it brings out a trade-off between fine-tuning and complication. Therefore, new devices and functions are added to the teaching system and multiple teaching modes are implemented for solving this problem. The main feature is the use of task teaching with human demonstration data which are obtained in real and virtual human motion measurement systems. The initial teaching data are generated by the demonstration data and the robot commands are converted into them with the control parameters. Typical task is demonstrated and we verify the effectiveness of the teaching modes experimentally

Unlike wheeled robots, humanoid robots are able to overcome obstacles in the environment by stepping over or upon them. Conventional 2D methods for robot navigation fail to exploit this unique ability of humanoids and thus design trajectories only by circumventing obstacles. Recently, globalized algorithms have been presented that take into account this feature of humanoids. However, due to high computational complexity, most of them are very time consuming. In this paper we present a new approach to footstep planning in obstacle cluttered environments that employs a human-like strategy to terrain traversal. Simulation results of its implementation on a model of Saika-3 humanoid robot are also presented. The algorithm, being one of reactive nature, refutes previous claims that reactive algorithms fail to find successful paths in complex obstacle cluttered environments

This paper discusses an approach to apply visual servoing to a 3D flexible-link manipulator. The proposed approach is composed of an end-effector position control based on eye-in-hand visual servoing and a vibration suppression control. In order to decouple the end-effector position control and the vibration control, the end-effector position control is applied in a low frequency domain, while the vibration control is applied in a high frequency domain. To decouple the frequency domain, a high-pass filter and a low-pass filter are used. Stability of the whole system is analyzed by investigating the pole of the system. Using the proposed approach, the 3D flexible-link manipulator succeeds to insert a peg into a hole whose clearance is 0.5 mm. However, it is difficult for the flexible-link manipulator to insert the peg into a hole whose clearance is 0.1 mm, if there is no force control. Therefore, an impedance control is also tested together with the end-effector position control and the vibration control. Using the modified approach, the flexible-link manipulator succeeds to insert the peg into the hole whose clearance is 0.1 mm

In order to achieve human-like quick eye movements and image processing for intelligent mobile robots, a high speed vision system is developed. The vision system is composed of a binocular camera head and high speed image sensors. The camera head is originally designed to mount neuromorphic vision chips fabricated using three-dimensional integration technology. The prototype of the neuromorphic vision chip has three layers: (1) photoreceptor layer, (2) horizontal and bipolar cell layer, and (3) ganglion cell layer. An image sensor is separately developed, which corresponds to the photoreceptor layer of the layered vision chip. The image sensors are tentatively mounted on the camera head, since the resolution of the prototype of the layered vision chip is not sufficient at this stage. The camera head has an azimuth DOF for each eye and a common elevation DOF. The weight of the camera head is strictly limited, since it is mounted on a mobile robot. In order to satisfy both demands for the quick movements and light weight, the camera head is designed based upon a simple parallel mechanism. The total performance of the vision system is examined in this work. Saccadic eye movement and frequency response are experimentally reviewed

When a human needs to generate a large force, the human will try to apply an impulsive force cooperating whole body. However, exerting impulsive force is one of the most difficult tasks for humanoid robots, because a reaction force caused by the applied impulsive force may bring the humanoid robot down. This paper discusses a humanoid robot motion to generate a large force utilizing an impact. Breaking wooden boards by Karate-chop is taken as a case study because it is a typical example of tasks that utilize impulsive force. A humanoid robot motion for the Karate-chop is carefully designed to maximize the speed of a hand keeping the stability. In order to validate the designed motion, experiments are carried out using a small humanoid robot Fujitsu HOAP-2. In the experiments, three kinds of wooden boards are tested to break by the Karate-chop. The strength of wooden boards is estimated striking the boards with a free-falling plummet. Stabilizing control is also applied to the robot in order to stabilize the body after the impact. The experimentation results are reported in the paper

In order to achieve human-like quick eye movements and image processing for intelligent mobile robots, a high speed binocular camera head is developed. The aim of the binocular camera head is to provide a platform to reproduce the human brain information processing. Two neuromorphic vision chips with lenses, which are developed imitating human retinas, will be mounted on the camera head. The camera head has an azimuth DOF for each camera and a common elevation DOF, thus there are three DOF in total. The weight of the camera head is strictly limited, since it is mounted on a mobile robot. In order to satisfy both demands for the quick movements and light weight, the camera head is designed based upon a simple parallel mechanism. Consequently, all motors are mounted on the base. The characteristics of the camera head are quickness, lightweight and simple mechanism. This paper presents the design, development and evaluation of the camera head. The inverse and forward kinematics are also discussed in this paper.

When a human needs to apply a large force to an environment, the human takes an appropriate posture to produce a large manipulation force. This paper discusses appropriate working postures for a humanoid robot to apply a force effectively to an environment. An objective function is defined and the sequential quadratic programming (SQP) is used to find a solution. The pushing a wall and turning a valve are taken as examples of tasks for a humanoid robot, and simulations and experimentations are performed. The results show that the consideration of working postures clearly contributes to make the manipulation force larger.

This paper addresses a plantar H-slit force sensor for humanoid robots to detect the reaction force. The zero moment point (ZMP) is calculated from the detected reaction force balance. The H-slit force sensors are structuralized on a plantar frame. Since a H-slit beam unidirectionally deforms, only the normal force from the ground is selectively detected without being affected from the friction force between the sole and ground. The plantar H-slit force sensors are developed for a humanoid robot. A model is proposed to simulate the sensor output. The simulated outputs are compared with results of the finite element analysis (FEA) and the experimentation results.

In this paper, inverse dynamics of the H4 robot is addressed. Dynamics of parallel robots is one of a very complicated subject. Especially, for the real time control of the parallel robot, it is an important issue. The actuating torque would depend not only on a given trajectory but also on the mass properties of the arms, the rods, travelling plate, and external forces. Dynamics are useful for computer simulation, the design of suitable control equations, and the evaluation of the kinematic design of parallel robots. The detailed dynamic equations for the H4 robot are derived using Newton-Euler method. In the last section, the effect of the rod inertia is introduced using comparative study of those methods whether the inertia of the light rod can be negligible or not in the fast motion.

In order to meet the demand of a research platform for intelligent robotics, a humanoid robot named Saika-4 is developed. The Saika-4 is a self-sustained biped robot equipped with two arms and a robotics head. The Saika-4 is designed so as to be light weight, low cost and human size. The weight is about 47 kg, and the height is about 1300 mm. The Saika-4 have 30 DOF in total, that is 6 DOF for each leg, 7 DOF for each arm, 1 DOF for each hand and 2 DOF for robotics head. The Saika-4 is equipped with a PC, batteries, a wireless ethernet modem, a gyroscope, and motor drivers in the body. Furthermore, the Saika-4 is equipped with a gravity compensation mechanism using springs in the legs. This paper presents the design of a humanoid robot Saika-4 and the progress of the project. The details of the gravity compensation mechanism is also presented.

In our previous research, we developed space robot teleoperation technology to achieve control from the ground of effective manual manipulations in orbit. To solve the communication time delay in the space robot teleoperation, we propose a mixed force and motion command-based space robot teleoperation system that is a model-based teleoperation. Moreover, we have also developed a compact 6-degree-of-freedom haptic interface as a master device. The important features of our teleoperation system are its robustness against modeling errors and its ability to realize the force exerted by the operator at the remote site. We introduce a new control method, which modified our model-based teleoperation system, to control the real robotic system Engineering Test Satellite VII manipulator. Surface-tracking and peg-in-hole tasks have been performed to confirm the effectiveness of our system. The experimental results obtained with our system including the haptic interface demonstrate its ability to perform these tasks in space without any major problems. We also evaluated different master device approaches for the model-based space teleoperation system. For this purpose, we used two methods, which are a master-slave (MS) approach and a force-joystick approach. Our results show that the MS approach is the best control method for contact tasks in which the directions of motion of the slave arm and of the operator's input force are different, as in the surface-tracking task.

This paper deals with the design and dynamic control simulation of a new type and dynamic control simulation of a new type of 4-DOFs parallel mechanism providing 3 translations and 1 rotation for high-speed handling and machining. This parallel mechanism is named as H4. A model-based dynamic control scheme is developed to improve the accuracy of the trajectory tracking. A simplified dynamic model is used for the H4 robot to decrease the cost of computation. A dynamic simulation is performed using ADAMS/sup TM/. In addition, the adept motion is used as a benchmark test to evaluate the effect of the dynamic control. The simulation results show that the dynamic control dramatically improves the trajectory tracking accuracy.

This paper describes an efficient dynamic simulation of a humanoid robot. In the simulation, an order n formulation is used to solve the inverse dynamics and forward dynamics of a multi-body system. The formulation can deal with a tree structure and multiple contacts with the environment. In order to simulate a collision with friction between the foot and a floor, a virtual spring-damper contact model is proposed. By introducing this model, computation of contact becomes easier and faster compared with other method such as plastic contact. A simulation of ascending steep stairs is carried out in order to demonstrate the validity of the simulation. The results of the simulation are presented and discussed.

This paper presents the software system architecture with the dynamic reconfigurability for highly autonomous systems. The proposed architecture is based on multi-agent model, which is suitable for autonomous, open and distributed systems. Since an agent is too sophisticated as the minimal component that we handle, we define a unit as a simple component of an agent. We present the advanced capability to dynamically reconfigure autonomous systems because their goals and environments vary frequently. We determine the specification of units and agents in order to analyze the behavior of overall system and to implement the dynamic reconfiguration as easy and simple as possible. In this paper, we also discuss the method to guarantee the system behavior during the dynamic reconfiguration in order to operate the robotic system without a hitch at any time, especially while reconfiguring.

The recent developments in the space technology demand various services to the exhausted or damaged satellites such as refueling and repairing in order to extend their life spans. In this paper, an automated object capturing with a two-arm flexible manipulator is addressed, which is a basic technology for such services. This object capturing includes the symmetric cooperative control, the visual servoing, the resolution of the inverse kinematics problem and the optimization of the configuration of a two-arm redundant flexible manipulator. There have been no researches on such a practical application with the flexible manipulators so far. The effectiveness of this capturing sequence is validated with the experiment.

This paper purposes to implement fast and complicated tasks by a high-speed parallel robot, HEXA, for industrial applications and the others. Although this parallel robot does not use any force/torque sensors, it has sufficient capabilities to achieve various tasks by applying an integrated control of motion, force and compliance, which takes advantage of the back-driveability and friction compensation of the actuators. A key point is how simply and easily operators can bring out the performance. We develop an off-line task teaching system to realize the motion planning suitable for tasks. Some tasks are demonstrated by using this teaching and control system and we experimentally confirm the effectiveness of our system.

We proposed an H-slit type parallel beam, which can be effectively utilized to achieve a highly unidirectional deformable structure for force/torque sensors. The structure is an extension of the parallel beam structure. And hence, the proposed design structure will result in 4-bar link closed mechanism the joints of which are deformable, so the strain gauges are fixed at these positions. This is the basic idea and unique feature of our proposed design. The H-slit beam can be used to measure very small-generated forces. In this paper, we present above characteristics of the both beam structures with finite element method (FEM) analysis, and outline of a small force/torque sensor using H-slit beams. Moreover reported in this article is over load protection mechanism, which exhibits beam's effectiveness and its ability, to withstand overload conditions without much deformation. This is due to the protection provided in the cross section of the beam.

This paper present closed-form solutions for the forward kinematics of a 4-DOFs parallel robot H4. Many researchers have tried to obtain closed-form solutions of 3-and 6-DOFs parallel robots, i.e., planar, Delta, Stewart platform and Hexapod robots, in a single variable polynomial equation. Indeed, there are just few effort have been devoted in the past to 4-DOFs parallel robot. Therefore, we focus on the forward kinematics of a 4-DOFs parallel robot H4. Solutions of the forward kinematic yields a 16/sup th/ degree polynomial in a single variable which indicates that there may be up to 16 different configurations for the travelling plate for a given set of motor's angle. The results are presented via a numerical example.

Human beings utilize a whole body motion such as weight shift to generate a large force while doing heavy works. Momentum is harnessed to increase an action force to the object. This paper discusses whole body cooperative motions of a humanoid robot for heavy works and the static stability during the motion. Pushing a wall and twisting a valve are taken as examples of heavy works in this study. Several whole body motion patterns are examined using a dynamic simulator, which efficiently solves dynamic equations of serial rigid body system using an O(n) algorithm. Static stability is evaluated through simulation results that include external force, joint torques, position of the center of gravity and ZMP, etc.

This paper proposes an adaptive intermittent crawl gait for quadruped robots to walk on a slope. In the proposed method, the inclination of a floor is estimated in real time by the displacement of the projection of the center of gravity from the nominal position. Depending upon the estimated inclination, the gait is changed in order to gain the longitudinal stability margin. Experiments and dynamic simulations are performed to validate the proposed method. The results are presented and discussed.

In order to meet the demand for a research platform of intelligent robotics, a quadrupedal research platform JROB-2 has been developed. This paper presents the design and development of the quadrupedal walking robot JROB-2. The JROB-2 consists of five parts: a quadrupedal walking mechanism, an embedded PC, servo amplifiers, power supplies, and a high speed stereo camera head. The stereo camera head can track the sinusoidal joint trajectory of the 15' amplitude and about 30 Hz frequency. The performance of the developed camera head is high enough to imitate the human eye movement such as saccade and pursuit. Almost all components of the JROB-2 are commercially available, and thus, its development cost is reduced and its maintenance becomes much easier. It is expected that the JROB-2 will serve as a good research platform for the studies of robotics and artificial intelligence.

An analysis of the stiffness of redundant manipulators is undertaken in this paper. First, the matrix of the force-dependent stiffness is derived and its basic properties are analyzed. In particular, in the planar case the stability conditions for the force dependent stiffness (and gravity-dependent stiffness) are obtained in the analytical form. Next, dual properties of the stiffness and compliance are exploited to establish a decomposition of the joint stiffness and compliance in the form similar to the decomposition of the joint velocities and torques. Finally, a minimal, nonredundant parameterization of the joint stiffness and compliance is commented.

During teleoperation, when the operator's attention is focused on controlling the end-effector's motion, it is very difficult to recognize possible link collisions. Such collisions may damage the environment or the links seriously, because usually the links have no sensors. We propose a so-called "virtual radar" which displays the collision information related to the motion of the whole manipulator at the end-effector level. The computer checks for unreachable areas due to the presence of obstacles and displays the appropriate information mapped on the task space using 3D graphics. This would enhance the reliability of the system. When applied to a 6-DOF manipulator, the possible collision space must also be 6-dimensional. Hence it is difficult to visualized and comprehend by the operator. To tackle this problem, the virtual radar displays the collision information by means of a deformable sphere and various patterns on it. The effectiveness of this method has been verified by experiments with a real telerobotic system.

This paper discusses cooperative control of a two-arm spatial flexible manipulator with redundancy. Two different approaches are discussed to solve the kinematics of this manipulator. Moreover, several performance criteria are also discussed for this system in order to obtain an optimal kinematics solution. Some of the criteria discussed are peculiar to the cooperation of the two-arm spatial flexible manipulators, and have not been described before. Finally, the criteria and kinematics solutions are evaluated with experimental implementations.

In this paper, we present a method for analyzing parallel mechanism stiffness including elastic deformations in the structure. In our previous works, we developed a compact 6-DOF haptic interface as a master device which achieved an effective manual teleoperation. The haptic interface contains a modified Delta parallel-link positioning mechanism. Parallel mechanism is usually characterized by a high stiffness, however, it is reduced by elastic deformations of both parts and bearings. Therefore, to study such a parallel mechanism, we analyzed stiffness in a parallel mechanism, including elastic deformation of both parts and bearings. Key points of our method are a modeling of bearings, a modeling of a elasticity coefficient of a passive axis in a bearing and a modeling of a parallel mechanism. Finally, we show that our stiffness analysis method of a parallel mechanism is high reliability and precision.

This paper deals with a class of parallel mechanisms, called Gough-Stewart platforms. For these mechanisms, pre-loaded by driving forces, the stiffness matrix is derived and its basic properties are established. It is shown when the stiffness matrix becomes asymmetric, how the parametric imbalance may influence the system stability, and how the center of stiffness depends on the force pre-loading. Next, some necessary and some sufficient conditions for the stability are established in an analytical form by transforming the stiffness matrix to the center of stiffness.

In our previous works, we have proposed a mixed force and motion commands-based space robot teleoperation system and a compact 6-DOF haptic interface to achieve an effective manual teleoperation. Until now, the effectiveness of this system and the haptic interface has been confirmed by the experiments in our laboratory. The most important features of this teleoperation system are robustness against modeling errors and ability to realize the operator exerted force at a remote site. In this paper, elements of this system and the haptic interface have been employed to teleoperate the 6-DOF manipulator mounted on the Engineering Test Satellite VII (ETS-VII) which is a real space robotic system. Surface-tracking and peg-in-hole tasks with modeling errors have been executed in this experiment. The results show that our space robot teleoperation system including the haptic interface has been able to execute these tasks in real space environment without any big problems.

In a new stage of space development, collision and contact tasks under micro-gravity, such as docking, orbital servicing, and touchdown to a minor body, are now increasingly being considered. A hybrid motion simulation consisting of both physical and numerical models is an effective method to test the motions of a spacecraft under zero G on the ground. The authors have developed a hybrid zero G motion simulator based on a highspeed parallel link mechanism. A wide response bandwidth and high stiffness of the simulator have made it possible to simulate the contact motions with high precision. In this paper, they evaluate analytically the simulator characteristics and verify experimentally the impact of dynamics on the hybrid motion simulation by comparing it with a collision experiment under zero G in a drop-shaft facility. The results imply that the simulator is highly reliable for the impact dynamics simulation under zero G.

This paper discusses an object recovery with flexible manipulators. To realize a stable capture with no slips at the end-effectors on the object surface, it is necessary to reduce the rise time of the internal forces. The relationship between the approach velocity and the internal forces being developed in the object during the capturing task is analyzed. Moreover, an approach to switch between the control modes is also proposed considering the resultant mechanical compliance at the tips of the arms, so that the internal forces rise rapidly. Finally, the experimental implementations illustrate the effectiveness of this approach.

This paper deals with the stability of a class of planar parallel mechanisms, called unifunctional manipulators. For this problem the stiffness matrix of the mechanisms is derived, and its basic properties are analyzed. Necessary and sufficient conditions for the stability are established in an analytical form by transforming the stiffness matrix to the center of stiffness. Next, at the level of force planning, the problem of stable force distribution is formulated. It is shown that an unstable force distribution can be stabilized by a simple control law if the mechanism is not in a singular configuration. Finally, conditions of the feedback stabilizability in singular configurations are established and illustrated on simple examples.

This paper discusses a way of capturing a floating object by two flexible manipulators. We propose a capturing procedure using hybrid position/force control and vibration suppression control. The procedure is established so that two hands reach the object simultaneously and grasp the object exerting the desired forces/moments. The hands approach the object measuring the positions/orientations of the object and grasp it measuring the exerted forces/moments in the procedure. The effectiveness of our method is shown in experiments using two 3D manipulators, each of which has two flexible links and seven joints.

In order to meet the demand of a research platform for intelligent robotics, a humanoid robot named Saika-3 has been developed. It is a self-sustaining biped robot with dual arms and a robotic head. It is equipped with a PC (IBM PC/AT clone), batteries, a wireless ethernet modem, a gyroscope and motor drivers inside its body. Saika-3 can be teleoperated via wireless' ethernet communication. A graphic dynamic simulator is also developed to study control strategy. The paper presents an outline of the hardware of Saika-3 and a simulation result.

A new kind of motion simulation is proposed for the purpose of simulating complicated motions such as those caused by interactions between objects in special environments (e.g., those of micro-gravity). The motion simulation is based on a hybrid simulation: consisting of a combined analog-digital system. Hence it has functions of real-time numerical simulation and embedding a physical model in the simulation. In addition, the motion simulation is equipped with flexibility of modeling, effective human interface and scalability of system. Finally, as a preliminary experiment, motion caused by interactions between a chaser (space robot) and a target (nano satellite) has been simulated with a prototype of the hybrid motion simulator.

In our previous work, several system elements for space teleoperation were introduced: a Singularity Consistent (SC) teleoperation system, a mixed force and motion commands based space teleoperation system, and a 6-DOF haptic interface (Y. Tsumaki and M. Uchiyama, 1997; Y. Tsumaki et al., 1998). We introduce an advanced space teleoperation system which includes all the above elements. As a result, the system realizes safety against the singularities and excessive force, with good perception for the operator. In addition, to verify the effectiveness of this system, we conducted experiments through the Internet between DLR in Germany and Tohoku University in Japan in January 1999.

This paper discusses a way of capturing a spinning object using two flexible manipulators. We propose a capturing procedure using hybrid position/force control and vibration suppression control. The procedure is established so that the manipulators capture the object automatically measuring position and rotational velocity of the object. The motion of the two hands of the manipulators are synchronized with the rotation of the object. The hands make contact with the spinning object safely, considering link flexibility, and then brake the spin smoothly. The effectiveness of our method is shown in experiments using two 3D manipulators, each of which has two flexible links and seven joints.

In ground testing of a spacecraft system, a simulator system which emulates a micro-gravity environment is necessary. It is demanded that the simulator system has wide response frequency bandwidth when dealing with motions having contacts and collisions. The authors have been developing a hybrid micro-gravity simulator which has a wide response bandwidth. Its motion table is a high-speed parallel robot driven by powerful direct drive motors. In preliminary experiments, this robot has achieved accelerations up to 40 (G). In this paper, we report an outline of the simulator and discuss the experimental results obtained.

Most of the control schemes developed for cooperation of multiple robots use centralized approach, hence the complexity of a system increases with an increase in the number of robots or complexity of an individual robot. Distributed control and event-based control approaches have been applied to a non-mobile multiple manipulator system with robots having only two degrees of freedom, while one of them is passive. Computer simulations show the applicability of these schemes for such a simple and under-actuated system. This paper extends the same discussion to a real-life experimental implementation. The results have proved the applicability of these control schemes for the proposed systems, and hence have opened new doors towards further research.

We compare the main features of the singularity-consistent (SC) method and the damped-least-squares (DLS) method. It is shown that both methods introduce a so-called algorithmic error in the vicinity of a singular point. The direction of this error is, however, different in each method. This is shown to play an important role for system stability.

A composite control law for end-effector path tracking with a flexible structure mounted manipulator system is proposed, such that no disturbances on the flexible base are induced. The control law is based on the reaction null-space concept introduced earlier to tackle dynamic interaction problems of free-floating robots, or moving base robots in general. The control law is called composite since it ensures base vibration suppression control as well, although independently of the reactionless motion control subtask. The requirement of task independence is essential to avoid the appearance of complex dynamics expressions in the control law, such as nonlinear velocity-dependent coupling terms and dependencies of inertias on the elastic coordinates. We present experimental data from computer simulations and the experimental test bed TREP developed at Tohoku university. The experimental data is shown to agree well with theory.

Many different control procedures and task execution strategies have been developed for multiple robots cooperation. Most of them are centralized and hence become very complex with increase in number of robots or their complexity. For this reason, the distributed control approach is found very attractive and the event-based control has enhanced its effectiveness. However, they demand the robots to be autonomous in all respects, and hence have found their applications for autonomous mobile robots or manipulator arms with abundant sensors and actuators. This paper, in contrast, has used these control approaches for a immobile multiple manipulator system with robots having only two degrees of freedom, while one of them is passive and with minimal sensory informations. Computer simulations show that it is also practicable to execute these schemes for an under-actuated system.

We discuss a new type of space robot system composed of a spacecraft and a robot attached through a tether to it. The tethered robot is translated away from the spacecraft using existing tether tension control techniques in gravitational field. Link motion of the tethered robot, however, is complicated, since the momentum is not constant due to the presence of external forces. This paper especially focuses on momentum control of the tethered robot. In addition to translational momentum control, we show that angular momentum of the tethered robot can be controlled by proper motion of the tether attachment point. We propose a control law for link motion of the tethered robot composed of two subtasks: the end-effector motion subtask and the tether attachment point motion subtask.

In this paper we propose a new compact 6-DOF haptic interface with large workspace. It contains a newly developed five bar spatial gimbal mechanism for orientation, placed on a modified Delta parallel-link mechanism. The motion range of each axis of the five bar mechanism is over /spl plusmn/70 degrees. Quick motions can be realized easily due to the parallelism inherent to both the modified Delta substructure and the five bar substructure.

In this paper, we discuss the control scheme on cooperative control of two flexible manipulators handling a rigid object in 3D space. We propose a control scheme which consists of hybrid position/force control and vibration suppression control. Hybrid position/force control is extended from that for two cooperative rigid manipulators to that for flexible ones. In addition to the control, vibration suppression control based upon the dynamics of both the flexible manipulators and the object is applied. To illustrate the validity of the proposed control scheme, we show experimental results.

This work reports progress on a long-reach manipulator project. The original single-arm manipulator was complemented with an identical second arm. We introduce several noncontact motion control strategies which are based on the reaction null space concept. Experimental verification of disturbance compensation control via a single arm, and via the two arms while holding an object, is done. Also, motion feasibility on reactionless paths for a closed kinematic chain, including the two arms and the object, is examined.

In our previous work (1997, 1998) we proposed two approaches to singularity treatment: one is based on a null space notation, and the other on the adjoint Jacobian. We use the term "singularity-consistent (SC) approach" in referring to any of them. The SC approach guarantees the direction of motion in the whole work space. Thus, it becomes possible to move through singularities in teleoperated mode, without producing an infeasible joint velocity. However, a precise command direction is needed to accomplish such a specific motion. In this paper, we propose a supporting system for the operator to handle the above problem. An advanced SC teleoperation system is obtained, based on virtual reality techniques. Experimental results show that a real peg-in-hole task, including through-singularity motion, can be easily realized by the operator.

A singularity-consistent direct kinematics algorithm is a necessity for the analysis and control of parallel manipulators. The present work proposes a first order singularity consistent algorithm for a class of parallel manipulators. It is shown that the algorithm is stable, convergent and can handle the multiplicity of the direct kinematics solutions for the manipulators. The performance of the method is analyzed with the help of the numerical examples given.

This paper proposes a hybrid numerical method (HNM) to solve the inverse kinematics of a class of spatial flexible manipulators modeled by mass/spring (mass-lumped stations and massless-spring fields) modeling method. The HNM includes two parts: one is an implicit recursive numerical method (IRNM) which is used to find a better approximate solution to the inverse problem, the other is a global iterative learning compensator that can further reduce the end-effector's position errors. The stability of IRNM is also analyzed and a sufficient condition of convergence is obtained. Using this HNM numerical simulation is conducted on a spatial flexible manipulator which possesses two flexible links and three rigid joints. Results are presented to show the effectiveness of the method.

For free motions, vibration suppression of flexible manipulators has been one of the hottest research topics. However, for constrained motions, little effort has been devoted to vibration suppression control. Using the dependency of elastic deflections of links on contact force under static conditions, vibrations for constrained planar two-link flexible manipulators have been suppressed successfully by controlling the contact force. However, for constrained spatial multi-link flexible manipulators, the vibrations cannot be suppressed by only controlling the contact force. So, the aim of this paper is to clarify the vibration, mechanism of a constrained, multi-DOF, flexible manipulator and to devise the suppression method. We apply a concise hybrid position/force control scheme to control a flexible manipulator modeled by a lumped-parameter modeling method. Finally, a comparison between simulation and experimental results is presented to show the performance of our method.

This work adds some new insight into the singularity-consistent parametrization of the inverse kinematics of a nonredundant robot tracing a reference path. We show that in the general case (e.g. motion with constant end-effector velocity on the path) there is a nonintegrable motion component. When the end-effector moves with a velocity proportional to the determinant of the Jacobian, the nonintegrable motion component is removed. At the same time, the order of the equation of motion is reduced. We call this type of motion "natural". Furthermore, from the simplified equation of natural motion, we derive the mechanical power measure. This is an instantaneous-motion performance measure defined over the phase space of the system, and thus, can be useful to evaluate the dynamic performance for the specified instantaneous motion direction.

The control of a dextrous manipulator mounted on a flexible structure is discussed. Using the concept of reaction null space, the manipulator dynamics is decoupled from the base dynamics. As a consequence of the decoupling, feedback control gains for structural vibration suppression and manipulator end-point control can be determined in a straightforward manner. We examine experimentally the performance of the above control tasks, using a planar experimental setup.

In our previous study we introduced a new type of space robot system, which consists of a spacecraft and a robot attached to it via a tether. In this paper, the characteristics of the system in gravitational field are described and a path planning approach is proposed. The translational motion of the mass center of the robot is controlled by tether tension. The path planning approach ensures end-effector motion along the desired path. In addition, proper motion of the tether attachment point is obtained, such that tension control can take effect. The effectiveness of the approach is examined by computer simulations.

The singularity-consistent path-planning and motion control approach has so far been successfully tested within a teleoperation environment, but with separate control of the positioning subsystem and the wrist of the slave arm. In this paper, we show that the approach can be applied to a 6-DOF slave arm with a non-spherical wrist. The problems arising from the coupling between position and orientation are handled easily within the null-space/adjoint Jacobian framework of the singularity-consistent approach. The experiments show that the operator is able to approach the shoulder singularity smoothly, to move through it or to perform motions without leaving it.

Teleoperation with long time delay causes bilateral control to become unstable. A possible solution to the problem can be found with the help of virtual reality. Forces, reflected from the virtual world, do not depend upon the existing time delay in the system. Unfortunately, virtual reality based systems strongly depend on the accuracy of the model. In this paper we propose a teleoperation system which is robust to modeling errors, including geometric and dynamic ones. The reference force command is generated by using both force and position information simultaneously. The effectiveness of our approach is confirmed by experiments.

We analyze some aspects of human physical skill and propose a model thereof, with a view to implementing such skills in robots. We implement our model in a control scheme which makes use of impedance control in combination with low-gain force control and feedforward control. The summation results show that the model is able to achieve the reference force, and at the same time, the manipulator shows impedance-type behavior. Furthermore, with this scheme it is possible to track the reference force quickly, when the disturbance is known apriori. The experiments show that the performance of our control scheme is very close to that of the human operator.

Discusses the force control of flexible manipulators. Since the force control of flexible manipulators with one or two planar links using the distributed-parameter modeling has been the subject of a considerable number of publications, real time computations of the force control schemes are possible. But, application of those control schemes to multi-link spatial flexible manipulators is fairly complicated. In this paper the authors apply a concise hybrid position/force control scheme to a flexible manipulator using lumped-parameter modeling. Hamilton's principle is applied to deriving the equations of motion and then, a state-space model is obtained by Lagrange's method. Finally, a comparison between simulation and experimental results is presented to show the performance of the authors' method.

Proposes a new technique for closed-loop kinematic control of nonredundant robotic mechanisms, based on the adjoint matrix of the kinematic Jacobian. Using the Lyapunov direct method, the authors show that the adjoint Jacobian approach guarantees asymptotic stability at regular points, around singularities, and at so-called instantaneous self-motion singularities. The new property, as compared to previous approaches, is that direction of motion can be precisely controlled at those points. To guarantee the asymptotic stability around any singularity and at instantaneous self-motion singularities, the desired (scalar) end-effector velocity is appropriately modified, and at the same time, restriction on the joint velocity norm according to a user-specified valve is imposed. In the vicinity of a singularity an error in the position along the desired path is tolerated, which however, does not lead to deviation from the path.

In this paper we discuss the relation between the two approaches to velocity command generation for nonredundant robotic mechanisms, which the two groups of the authors proposed recently and independently of each other. It will be shown analytically that the singularity-consistent null space based approach, and the split Jacobian approach, are equivalent. Analysis of the behavior at a singularity will be presented from the viewpoint of both approaches. An analytical example will be used to demonstrate the theoretical results.

We apply our newly proposed singularity-consistent path tracking approach to nonredundant parallel-link manipulators. We analyze the singularities of such mechanisms, assuming that the output-link moves on a pre-defined and parametric path. Especially, we focus on the so-called instantaneous self-motion type singularity. We propose a closed-loop controller that guarantees asymptotic stability when tracking paths through such a singularity. As a comprehensive analytical example we use a planar five bar mechanism. A computer simulation study is also presented, using the same example, as well as the HEXA parallel robot structure.

We discuss the implementation and experimental verification of two new approaches to control of a nonredundant manipulator at and around singularities. One of the approaches is based on the adjoined matrix of the manipulator Jacobian, while the other one is a null-space based approach. The approaches share a common theoretical base described in our previous work. We focus mainly on several implementation issues and the experimental results obtained from our teleoperation system.

We consider the design of a modular hybrid functional electrical stimulation (FES) system for an injured person. We propose a system using an assistant robot to follow the FES performance, as FES control has many uncertainties in characteristics. The assistant robot used is a 3-link serial type, and attached to the injured person to actively assist the FES performance. The assistant robot must be very simple, light, and can be easily attached to the injured person. We constitute various types of human models which can be used to show the exact actions and muscle function characteristics. Furthermore, we propose a control system for the model of an injured person fitted with the assistant robot. Finally, we show that a robust performance of the injured person has been achieved in the standing motion using the modular hybrid FES system.

In this paper, we deal with the handling of a flexible object by rigid arm robots. We consider three main tasks: 1) to propose a mathematical model for a variety of flexible objects of our daily life; 2) to design a controller to achieve cooperative handling of the flexible object by the robots; and 3) to analyze the stability and robustness of the control system. In particular, demands for manipulating a large-scale structure by a space robot will be increasing. Therefore, it is important to constitute the cooperative control problem of several robots handling a flexible object, and to analyze the proposed control system.

In the past decade, a considerable amount of research has been devoted to flexible manipulators, especially to their modeling, vibration control, inverse kinematics and inverse dynamics. When a flexible manipulator is set to an environmental constraint, force control is necessary to be implemented to complete the task. In this work, we apply a concise position/force control scheme to a spatial flexible manipulator, using lumped-parameter modeling. The equations of motion, including elastic deflection and contact force, have been obtained based on Hamilton's principle. Force control has been realized, both in simulation and experimentally. A comparison between those results is also presented.

An approach to modeling flexible manipulators consisting of rotary joints and flexible kinks is proposed. In the proposed approach, flexible manipulators are modeled by lumped-masses and massless springs on the basis of Holzer's model, which is known as an approximate model for vibration analysis of flexible systems. Due to its simplicity, the constructed model is advantageous to the study of kinematics, dynamics and control strategy of complicated systems such as 3D multi-link multi-DOF flexible manipulators. Based on the model, dynamic equations of motion are derived using Lagrangean equation. Kinematics and the relationship between the dynamics of rigid manipulators and flexible manipulators are also discussed. The effectiveness of the model is evaluated by comparing the results of simulation with those of the experiment.

We develop further our singularity-consistent approach to arrive at a parameterized form of the dynamics of a nonredundant robotic mechanism tracking a desired path in Cartesian space. It is shown that this form is suitable for incorporating joint torque limits, which is an important issue for practical applications. We propose a closed-loop controller which behaves as a "conventional" resolved-acceleration type controller at regular points of the kinematic function. Around any singularity and at so-called instantaneous self-motion singularities the controller is able to truck the direction of the specified path exactly. The limit on the torque norm results in some position error, without deteriorating, however, the direction tracking ability. It is shown also that motion through the bifurcation type singularity can be easily controlled in practice as well.

For a class of parallel-link manipulators we develop a general formulation of the equation of motion, suitable for parallel computations. We analyze the torque requirement when moving through various self-motion type singularities on a path generated under the singularity-consistent framework. The formulation, contributes mainly to the analysis of a singularity which is typical for parallel robots only, known from previous studies as "overmobility". We show that if the dynamics of the system is taken, under consideration, it is possible to move through such a singularity. This analysis motivates the introduction of the concept of dynamic singularity consistency. As a comprehensive analytical example we use a five bar robotic mechanism.

We propose a new singularity-perturbed design approach to a planar five bar parallel-link manipulator. The design allows us to operate the manipulator either in parallel or in serial branch mode, and also to exchange those modes. Thus, it is possible to merge some of the well-known advantages of serial and parallel manipulators. We study two basic singularity-perturbed designs and show that one of them is preferable. A feasibility study through computer simulation, including maximum torque requirement, is also presented.

The authors previously (1996) proposed a new type of space robot system, consisting of a spacecraft and a robot attached through a tether to it. This system is called a "tethered robot system." In this paper, we clarify the characteristics of the tethered robot system, and especially focus on position control of the center of mass of the robot. Tether tension is used to control the position, taking into account the gravity gradient and the centrifugal force. The results from the trajectory planning procedure suggest that the shape of the path depends both on the direction to the destination point and the time to accomplish the mission, it does not depend on the distance. From the simulation results with feedforward control it is concluded that accurate path planning is possible only if the destination point is close to the initial point, or if the time to accomplish the mission is long enough.

It is well known that teleoperation with time delay causes force feedback control to become unstable. Therefore, bilateral control could not be used in such applications as space teleoperation with time delay. Force feedback information is, however, very important for the operator when performing contact tasks. Recently, virtual reality has been introduced to support force feedback based teleoperation with long time delay. The operator can feel the forces which are generated in the virtual world, even if there is long time delay. Unfortunately, virtual reality based teleoperation is prone to modeling errors between the real world and the virtual world. In this paper we propose such a teleoperation system which combines velocity-level commands with certain slave arm autonomy. The experimental results show that our system is robust with respect to tolerances in the geometrical model, and also, through the feedback loop from the virtual environment the operator can always feel a stable force.

Time delay reduced significantly the ability of teleoperation. This problem becomes especially serious in case of earth-to-space teleoperation, when the time delay is large. To overcome the problem, a predictive display technique has been proposed for non-contact tasks. However, the effectiveness of this technique has not been verified sufficiently. In this paper we propose a teleoperation system with time delay, based on the predictive display of a virtual beam, as well as on the concept of optimal approach velocity. The experimental results show that a peg-in-hole task, which includes a contact task, is realized very effectively by our method in spite of the long time delay. These results have been verified from various viewpoints such as task completion time, deviation of the task completion time, contact force, command, and integration of contact force and command.

Point-to-point operation of a flexible structure mounted manipulator systems (FSMS) is discussed. Four operation strategies: (1) straight-line path in joint space, (2) high-coupling path, (3) low-coupling path obtained from the coupling map concept, and (4) 3-phase motion obtained from the reactionless path are examined and compared in terms of a minimum oscillation of the supporting flexible structure, using an FSMS test bed, TREP, developed at Tohoku University.

In this paper we develop further the recently proposed null-space method for path tracking at and around kinematic singularities. We consider two types of singularities known as ordinary singularities and bifurcation/isolated-point singularities. A closed-loop kinematic control scheme is introduced, which is able to keep precisely the direction of the specified end-effector path passing arbitrary close to kinematic singularities. The desired velocity magnitude can be maintained at regular points of the kinematic mapping. In the vicinity of singularities, the maximum available joint velocity specified from hardware limits can be applied. Several advantages of the proposed singularity-consistent approach are pointed out when compared with other well-known methods.

Deals with the handling of a constrained flexible object by a robot. The authors regard the robot as a rigid manipulator and the object as having one side free and the other side fixed to the wall. The authors' purpose is for the robot, to follow up the open end of the flexible object and to suppress its vibration. As a technique to achieve their purpose, the authors propose a new numerical modeling method to handle the object by the robot. This model reveals the force relationship at the handling point. Next, the authors constitute the control system to make it possible to achieve two performances, following up the object and vibration suppression.

In this paper, we deal with the handling of a vibrating flexible object by a rigid dual-arm robot. Each arm consists of two links and an end-effector. The aim of this work is to realize the position control of the flexible object while suppressing its vibration. In particular, the problem considered is about the control system designed to realize the active handling of the flexible object. For this purpose, we propose a model for both the robot and the object in a connected position so as to guarantee the whole handling system's stability. We also express a new mathematical model of the flexible object using the model reduction theory in the same connected position. The model of the robot and the object while they are in contact is derived by the positional requirements at the handling point. We also consider the design of the controller to satisfy the constraint condition at the static equilibrium point. The design of the combined system consisting of the robot and the object is useful for the analysis of whole handling system's stability.

In order to be able to achieve intelligent action at a remote place with or without time-delay, it has been realized that the human operator has difficulty in interpreting input information (from TV cameras, virtual reality and force reflection system) and hence his performance in teleoperation decision making is clumsy. In complex environments, where every point on the slave robot is subject to a potential collision, this problem becomes even more pronounced. Thus, the burden on the operator must be decreased from active control in situations where different parts of the robot body are simultaneously interacting with the obstacles. This paper describes the authors' research in shared intelligence for incorporating local and remote intelligence for path planning and obstacle avoidance to help the operator in improving his performance and also to enable the intelligence units to take over when the operator fails to maneuver fine controls of the remote manipulator.>

Discusses the structural vibration controllability of flexible manipulators. In spatial flexible manipulators, the structural vibration controllability would be configuration-dependent. Therefore, the flexible manipulator might have some vibration uncontrollable configurations and thus a discussion on the vibration controllability is a must. In order to understand the physical interpretation of vibration uncontrollable configurations the authors propose the concept which indicates how well the actuators can affect the structural vibration modes. The configuration in which all actuators can't affect at least one of the vibration modes of the manipulator is vibration uncontrollable. To clarify this point, the authors consider an example and perform experiments on vibration suppression control of the flexible manipulator. Experimental results clarify the modal accessibility concept. >

An inverse kinematics problem of flexible manipulators is considered. The problem is of importance for compensation of tip deflections when the manipulators perform quasi-static operations. Based upon kinematic and static relationships, a definition of the inverse kinematic task of flexible manipulators is formulated. Specific features of the task are considered, and a conventional approach applicable for resolving the task is analyzed. To avoid disadvantages of the conventional approach, an implicit iterative scheme based upon step-by-step compensation for the relative elastic deflections is proposed. Corresponding convergence conditions of the scheme are derived, and applicability of the scheme is verified through simulation.>

This paper presents a systematic analysis of force sensors at the design stage. A generalized model of the sensors is developed on the basis of static and kinematic equations, and the block form of the resulting strain compliance matrix of the sensor is obtained. The model developed is then applied to the analysis of the two and three-dimensional sensor schemes corresponding to the regular polygons and polyhedrons. The condition number of the normalized strain compliance matrix of the sensor is used as the performance index. Impossibility of reaching the optimal values of this criterion is stated for the regular-polygon-form-based sensors. Partial solutions of the optimisation problem are found out for the regular-polyhedron-form-based sensors. The presentation of the material is illustrated by analytical examples.>

Research on vibration suppression control of flexible robots has concentrated mainly on the one-link and two-link planar manipulators. Most of the techniques that have been presented can not be easily extended to the case of a general 3D flexible robot. In this paper we present a general control scheme upon the basis of hardware velocity servo cards. The velocity commands to move the robot are calculated by adding a vibration suppression term to the joint position feedback employed in "rigid" robots. Two different methods are proposed to calculate this term, one based on optimum quadratic control and the other based on pseudo-inverse nonlinear decoupling. These techniques are studied numerically in the case of a real 2-link 3-joint flexible robot, by computing the values of the closed-loop poles at different configurations. Experiments of position stabilization of the robot prove the validity of our methods.>

This paper presents a dynamic model and a control strategy for N robot arms cooperating through a flexible object. The dynamic equations of the system under consideration are derived, with position and force parameters being considered in an extended 6N-dimensional space. The control strategy is based on the decomposition of the position and force parameters. The strategy includes feedforward and feedback levels, which take into account the object compliance. The force and moments applied to the object by manipulators as well as the end-point accelerations are considered to be the control inputs for the Cartesian-level control system. The feedback level includes the nonlinear decoupling control law to ensure the tracking of the object trajectories in the position and force spaces. To damp out the object oscillations, an additional control input, which is added to the prespecified internal forces, is introduced. The applicability of the control strategy is tested under a case study.>

A method of generating an optimal approach velocity, to control the collision forces properly, of a manipulator to its environment is presented. Analysis of a contact motion shows the necessity of contact control not only after the collision, but also before it. Using a model of the force-controlled end-effector and its environment, forces generated at the contact are formulated as outputs of an autonomous system of which the initial condition is determined by the approach velocity. The optimal approach velocity is defined as the velocity that minimizes a performance index. A proportional relation between the optimal approach velocity and the contact force reference is derived analytically based on a mass-damper-spring model of the force-controlled end-effector and its environment. Results of the simulation and the experiment are presented to demonstrate the effectiveness of the method.>

Adaptive load sharing of two cooperative manipulators that hold a common object is examined from the viewpoint of robust holding. Task vectors to describe the task are first summarized, and a hybrid control scheme for the simultaneous control of holding forces and carrying positions is presented. Within the framework of the hybrid control, the robust holding problem is analyzed, paying attention to the contact conditions between the manipulators and the object. The contact conditions are formulated as a set of linear inequalities with respect to the load sharing coefficients. Based on the analysis, a heuristic but very simple algorithm for online adaptation is presented. The algorithm is corroborated experimentally.>

A symmetric scheme-not a master/slave scheme-is proposed for the coordination of two robots to manipulate a single object jointly. The definition of workspace force, velocity, and position vectors as symmetric functions of the joint space force, velocity and position vectors of the two robots is essential to implementing the symmetric scheme. These workspace vectors are derived by first analyzing the statics of the closed kinematic chain consisting of the two robots and the object, and then calculating velocities using the force-velocity duality. The workspace-position vector is defined by integrating the velocities. The derived workspace vectors are used successfully to implement the symmetric scheme.>

In this paper we discuss the control of cooperating tasks being done by two robotic arms. In order to control those tasks, we extend hybrid position/force control scheme presented thus far by various researchers for a single-arm robot. The point of the extension is formulation of kinematics and statics for a two-arm robot which is new in this paper. We define a unique system of workspace coordinates and, corresponding to the unique workspace, introduce an unique jointspace vector consisting of joint-vectors of the two arms. Using these work and joint spaces, we formulate kinematics and statics. Based upon this formulation, we successfully apply the hybrid scheme to the two-arm robot. A demonstration of the theory working on a real two-arm industrial robot and experimental data of simultaneous control of position and force proves the effectiveness of our method.