Ankle-foot orthoses (AFOs) are orthotic devices that support the movement of the ankles of disabled people, for example, those suffering from hemiplegia or peroneal nerve palsy. We have developed an intelligently controllable AFO (i-AFO) in which the ankle torque is controlled by a compact magnetorheological fluid brake. Gait-control tests with the i-AFO were performed for a patient with flaccid paralysis of the ankles, who has difficulty in voluntary movement of the peripheral part of the inferior limb, and physical limitations on his ankles. By using the i-AFO, his gait control was improved by prevention of drop foot in the swing phase and by forward promotion in the stance phase.

In this study, we propose a leg-robot with a Compact MR Fluid Clutch (CMRFC) to realize haptic control of abnormal spastic movements of brain-injured patients. This system can be used in the practical training for trainees of physical therapy. Additionally, we will study to figure out the physiological mechanism of spastic movements of human with the process to simulate patient-like spastic motion by this robot. In this paper, basic structure and mechanism of the leg-robot with CMRFC are explained. Finally, experimental results of some kinds of haptic control for spastic movements are described.

Force information in virtual space is important and often required for tele-operation, training, amusement, design supporting, and other virtual reality systems. While passive force display which uses only passive elements is an effective method for assuring safety, it has some directions and link postures which are hard to present force. To this problem, a method for improvement of controllability using redundant couple of brakes had been suggested. This method was able to make it possible to display various force directions and various postures of virtual objects. The purpose of this study was further improvement of controllability of systems with redundant couple of brakes. In this paper, we discussed the outline of developed redundant-type system and basic experiments with it. We also mentioned an algorithm how to use the brakes to represent various positions and orientations of virtual objects. It was confirmed by experiments in some typical cases.

Force information in virtual space is important and often required for tele-operation, training, amusement, design supporting and other virtual reality systems. While conventional force displays are active systems with actuators and therefore may become inherently dangerous, passive force displays, which use only passive elements, are an effective methods for assuring safety. However, passive type systems have some directions and link postures, which are hard to present force. To this problem, a method for improvement of controllability using redundant couple of brakes had been suggested. It was able to be considered this method made it possible to display various force directions and various postures of virtual objects. The purpose of this study was, for further improvement of controllability of systems with redundant couples of brakes, design and development of more generalized redundant mechanism by adding another element of design freedom. Moreover, improvement of force display-ability by reducing equivalent inertia was also aimed. In this paper, the developed system was outlined and basic experiments with it discussed.

A force display system is a kind of human-coexistent robot systems, which share the space with people while they are working, and which directly touch and display force-senses to their users. For such a robot system, it is important to estimate safety quantitatively and to ensure mechanical safety. In this paper, it is described that using MR (magneto-rheological) actuators, which is one clutch type actuators, can ensure safety. Moreover, the characteristics of MR actuators that are low inertia, high torque/inertia ratio and high responsibility contribute to improve the performance of force display systems. In this study, we developed an MR actuator with low inertia (2.6/spl times/10/sup -5/[kg/spl middot/ m/sup 2/]), high torque/inertia ratio (3.8/spl times/10/sup 5/[1/s/sup 2/]) and high responsibility. Torque/inertia ratio of this MR actuator is highest among MR actuators developed so far and much higher than those of conventional servo actuators. Then, a high-performance 2-D force display system using the MR actuator was developed. Maximum force displayed is 190 [N] and rigidity of the system is 5.9 [N/mm]. Moreover, backdrivability, dynamic range and collision sense are improved by using MR actuators in comparison with a system using ER actuators.

ER fluid has rheological characteristics which can be controlled by the electric field. Using particle-type ER fluid, we developed a brake device. In this study, this ER brake was used in an isokinetic exercise system for rehabilitation training under restriction of constant rotational speed of a joint during exercise. Such a passive system using a brake is basically safe for human use.

Movements of the upper limbs are complicated, various and indispensable for daily activities. It therefore is important for the aged to exercise to keep their upper limb function. When something is wrong with the upper limb function because of disease or disorder, rehabilitation along with medical treatment is needed to recover function. Application of robotics and virtual reality technology makes possible for new training methods and exercises on upper limb rehabilitation and for quantitative evaluations to enhance the qualitative effect of training. However, rehabilitation systems applying training within a three-dimensional to upper limbs have not been in practical use. The authors have involved in a project managed by NEDO (New Energy and Industrial Technology Development Organization as a semi-governmental organization under the Ministry of Economy, Trade and Industry, Japan), "Rehabilitation System for the Upper Limbs and Lower Limbs", and developed a 3-DOF exercise machine for upper limb (EMUL). In this paper, the authors report on development of EMUL which can be use as a motion guide robot or a force display device. Particularly, mechanical structure safety kept by actuators using ER fluid is mentioned.

Magnetorheological (MR) fluids are materials that change their rheological behavior in the presence of an applied magnetic field. Devices using MR fluids have an ability to provide high torque, low inertia, be a safe device and have a simple interface. We have developed an MR-fluid actuator, which consists of an input component, an output component and an MR-fluid clutch between the two. In this paper, we investigate the dynamic characteristics of an MR-fluid actuator and aim to improve its response. Transient magnetic analyses are examined and experimental results are shown in the case of the proposed approaches. Finally, we realize a much faster MR-fluid actuator.

Homogeneous electrorheological (ER) fluid damper reduce the vibration in robot joints due to the elasticity of the drive system. Also, it enlarges servo stiffness in direct-drive motor system. However, conventional research into ER fluids is based on parallel electrodes with ER fluids between them while ER fluids are used in a shear mode. Since a high voltage is required for use of ER fluids with parallel electrodes, problems of cost, safety and wiring to moving part for practical applications are of concern. In order to solve some of the above problems, we have proposed a one-sided pattern electrode, which is an electrode in a pattern arranged on only one of the two surfaces of a pair of electrodes, with an insulator arranged on the other surface. We experimentally verify the manifestation of ER effects in a homogeneous ER fluid. Moreover, the effect of disk gap upon viscosity change was investigated. The proposed configuration leads to new damping devices for robots and mechatronics systems.

Magnetorheological (MR) fluids are substances that respond to an applied magnetic field with a change in their theological behavior. Though they are functionally similar to electrorheological (ER) fluids, MR fluids exhibit much higher yield strengths for the applied magnetic fields than ER fluids for the applied electric fields. The devices using MR fluids have an ability to provide high-torque, low-inertia, a safe device and simple interface. In this study, we report on an actuator developed using the MR fluid, which consists of an input part, an output part and an MR fluid clutch between them. First, the basic experiments are examined to investigate the characteristics of the actuator. Next, the torque control system of the MR-fluid actuator is proposed. Finally, the closed-loop control experiments were carried out and it is confirmed that the torque-feedback control is effective for improving the response properties of MR actuators.

Force information is often required for tele-operation systems and virtual reality. Conventional force displays are active systems with actuators. This, however, is inherently active, so that it may become a danger. Consequently, passive force display is an effective method for assuring safety. The authors developed a brake using ER (electrorheological) fluid and passive force display using ER brakes. They discuss two degree of freedom passive force display and basic control experiments.

ER fluid is a kind of functional fluid. The ER fluids have a unique characteristic, which changes its rheology characteristic to apply the electric fields. The property of the actuator using ER fluid is different from conventional actuators such as DC or AC servomotors. In this study, we developed a new actuator using particle-type ER fluid, which is called ER actuator. The developed actuator can produce two directional torques by using two ER clutches. We derive the simple models of ER actuator from reference torque to output torque and velocity characteristics. Then, we verified the validity of the models and control performance of the actuator by conducting velocity and position control experiments.

In industrial robots, each joint is driven through a reduction gear unit such as a harmonic drive gear. The elasticity of the drive systems cannot be ignored when the high-speed and precise motion control is required for robots. Due to the elasticity of the drive systems, vibratory behaviors are caused, and the control performances of robot systems deteriorate. In this study, we develop a new actuator that consists of an AC servomotor, a harmonic drive gear and an electrorheological (ER) damper. The ER damper can change the damping coefficient by applying an electric field. Since the gap between electrodes of the ER damper is 80 /spl mu/m only the voltage of 160 V is needed for the electric field of 2 kV/mm. The ER damper consumes little electric power. The actuator is installed on a one-link robot arm. The mathematical model of the robot arm is derived, and the eigenvalues of the robot system are analyzed. Experiments were carried out, and the effectiveness of the actuator is confirmed.

Since a direct-drive (DD) motor system does not have the reduction gear, its structure is simple and has stiffness. In the DD motor system, the disturbance torque directly influences the control accuracy. The high servo stiffness is effective and important for reducing the influence of the disturbance torque. However, the high servo control often makes the system vibratory or unstable. Therefore, the servo gain must be lowered for assuring stability, and the influence of the disturbance becomes serious. In this study, the DD motor system using an electro-rheological (ER) fluid damper is developed. By applying the ER damper to the DD motor system, the gain margin of the control system is improved, so it is possible to realize the high servo control. Finally, it is experimentally shown that the proposed system is effective for high-speed and high-precision control.

We developed ER actuators with low inertia. ER actuator is a torque-controllable clutch which uses an electrorheological fluid. It is shown that this actuator has good properties for force display device, physical therapy treatment, etc. Then, we developed new force display devices for virtual reality by using the developed ER actuators.

A semiclosed-loop control which utilizes the signal of an encoder mounted on a servomotor is adopted in the control of industrial robots. In this method, the position of the end-effector is not controlled very accurately. Therefore, we aim to apply a closed-loop control which uses the positional signal measured directly at the end-effector. Because of the flexibility of the driving system, however, it is very difficult to control the arm based on this method. In this study, a robot arm is developed which has a variable damper using an electrorheological fluid (ER fluid). It is shown that the ER damper is very effective for precise position control based on a closed-loop control method.

A variable viscous damper using electrorheological (ER) fluid is developed to suppress torsional vibration of industrial robot. An integrated system consisting of drive motor, harmonic drive, arm linkage and ER damper was measured experimentally and found to be able to reduce the resonance/antiresonance phenomenon by increasing the viscosity of ER damper. A position control system, which is based on both the conventional semi-closed loop control and this new type ER damper, is analyzed and the relation between the ER damping coefficient and the bandwidth of the system is discussed using pole assignment technique. It is shown that the ER damper provides both vibration suppression and disturbance rejection.

This paper is basic study on vibration control, disturbance rejection and friction compensation in robots with flexible driving systems. Firstly, the system gain characteristic at the antiresonance frequency is introduced to evaluate the vibratory behavior of the control system. Secondly, the joint torque negative feedback which has a good effect on vibration suppression is discussed, while it is shown that the property of disturbance rejection is easily deteriorated when using high-gain joint torque feedback. Based on the assignment of pole-distribution, the relations between the vibration suppression and the disturbance rejection are analyzed. Thirdly, a feedforward compensation control based on a friction observer is proposed, it is shown that the tracking error is effectively decreased by this friction compensation. Lastly, a position control system considering the trade-off between vibration suppression and disturbance rejection is presented, and experimental results are also given.

The purpose of this study is to realize the bounce gait in articular-joint-type quadruped robots. We first develop a new robot which can realize bounce. A simulator is then made for the purpose of analyzing dynamic walking and efficiently developing its control methods. We formulate the leg-support-exchange phenomenon using Lagrangian impulsive equation. The control method is discussed, and the results of computer simulation are shown. Experimental results are also presented.

In biped locomotion systems, the angular momentum of the whole system can be taken as a good index, as seen from the law of conservation of angular momentum. A control method which divides the walking into motions in the sagittal plane and in the lateral plane has been adopted. For motion in the sagittal plane, the angular momentum is placed close to a smooth reference function given in advance by controlling the ankle torque of the supporting leg. For motion in the lateral plane, the motion control is treated as a regulator problem with two equilibrium states. The effectiveness of the proposed control method has been examined by experiments with the BLR-G2 walking robot. The BLR-G2 achieved 3-D walking at a speed of 0.35 m/s.>