Atsuo Kato

An EMG controlled prosthetic forearm in three degrees of freedom using ultrasonic motors

This paper discusses an EMG controlled prosthetic forearm with three degrees of freedom actuated by small size ultrasonic motors. Its weight is less than 700 g and the size is the same as the adults forearm. It produces no motion noise. In addtion, it is possible to control six kinds of motions i.e. pronation and supnation of the forearm, flection and extension of the wrist, and grasping and hand-opening.

EMG pattern classification for a prosthetic forearm with three degrees of freedom

The authors developed an EMG controlled prosthetic forearm with three degrees of freedom actuated by small size ultrasonic motors. Its weight is less than 700 g and the size is the same as the adults forearm. The interface between the amputee and the prosthetic forearm was designed on the basis of the fact that the amputee still preserves the phantom limb motor map after amputation. The paper proposes a method to estimate the motion intended by an amputee from the EMG signals using neural network. The method presented can discriminate the amputees intended motion among six kinds of limb-functions from the multi-channel EMG signals preprocessed by the bandpass and smoothing filters. The cross-information among the EMG signals can be utilized to make the electrode locations flexible, and the band-pass filters can provide the amplitude and frequency characteristics of the EMG signals. The experiments of three subjects and four electrode locations demonstrates that the method can discriminate six motions of forearm and hand from unlearned EMG signals with the accuracy above 90 %.<<ETX>>

On cooperative manipulation of dynamic object

Studies multiple-robot manipulator cooperative manipulation of an unknown dynamic object. The authors show a simple approach for each robot to identify the object dynamics through cooperation. The authors decentralize the position/internal force hybrid controller such that each robot has its controller and determines its control torque from its own feedback information. Experiments show the effectiveness of the control strategy.<<ETX>>

Limb-function discrimination using EMG signals by neural network and application to prosthetic forearm control

The authors propose a method to estimate the motion intended by an amputee from his EMG (electromyographic) signals using a backpropagation neural network. The proposed method can discriminate the amputees intended motion among six kinds of limb-functions from multichannel EMG signals preprocessed by bandpass and smoothing filters. The cross-information among the EMG signals can be utilized to make the electrode locations flexible, and the bandpass filters can provide the amplitude and frequency characteristics of the EMG signals. Experiments on three subjects and four electrode locations demonstrate that the method can discriminate six motions of the forearm and hand from unlearned EMG signals with an accuracy above 90%, and can be adapted to some dynamic variations of the EMG signals by backpropagation learning.<<ETX>>

Parametric excitation approaches to efficient dynamic bipedal walking

Traditionally, an inverted pendulum has been used as a reduced biped locomotion system, whereas this paper proposes a different approach. The essence of dynamic biped gait generation is mechanical energy restoration, and parametric excitation approach is a good idea for it. Our novel approach does not require any rotational actuation and thus enables to be free from the constraint of zero moment point (ZMP). This paper considers some basic methods of parametric excitation and shows that energy-efficient biped locomotion can achieved very easily without taking the ZMP condition into account. We then conduct parametric studies by adjusting the control and physical parameters, and determine how well the basic gait perform by introducing some performance indices.

Compliance control of an ultrasonic motor powered prosthetic forearm

The capability of a prosthetic device to mimic the response of the actual limb with respect to voluntary motor commands and to environmental loads should be addressed. This paper discusses the compliance control of an ultrasonic motor powered prosthetic forearm which utilizes cutaneously measured electromyogram (EMG) signals sensed with electrodes over the muscles as means of detecting motor commands sent by the central nervous system (CNS). Compliance control of the artificial limb was studied by implementing the bilinear model of the forearm and hand. This model emphasizes the role of the visco-elastic properties of the musculo-skeletal system of the actual limb in controlling its net configuration and movement. The flexor and extensor muscles extending over a joint influence the overall joint impedance and determines the equilibrium position of the joint. Relaxing both flexor and extensor muscles makes the joint compliant to external forces, while activating both muscles increases the impedance of the joint.<<ETX>>

Compliance control of circular traveling wave motor

Traveling wave ultrasonic motors (TWUSMs) were used as actuators for a prosthetic arm, because of their light weight, compact size, silent motion, high-speed response, and low-speed rotation. The prosthetic arm has to move in compliance with the environmental force around every joint, as in the human arm. In order to realize a compliant prosthetic arm, it is desired that the actuator have a compliant characteristic in itself, but TWUSMs have no such characteristic. The TWUSM is driven by two-phase sine-wave electric signals. Bending traveling waves which generate rotational torque on the rotor are propagated in its stator. Usually the phase difference of the driving signals is adjusted to 90 degrees to get the maximum output torque, but can be adjusted in range from 90 degrees to -90 degrees to regulate rotational torque. The authors were able to develop an adjustable compliant motion to the TWUSM using a phase difference control method of the driving signals. This controlled system acts much like a compliance adjustable spring with a minor damping characteristic.<<ETX>>

Experimental study of a parametrically excited dynamic bipedal walker with counterweights

This paper reports some interesting results on our experimental study of parametrically excited dynamic bipedal walking. We describe the details of the walking machine that has telescopic legs, semicircular feet, free hip-joint and counterweights. The walker can sustain stable dynamic walking on level ground based on mechanical energy restoration in accordance with the principle of parametric excitation utilizing the effects of semicircular feet and counterweights. Results of numerical analysis of the effect of the counterweights on the gait efficiency are also described.

Compliance Control of Direct Drive Manipulator Using Ultrasonic Motor

A compact size light weight direct drive(DD) manipulator with traveling wave ultrasonic motors (USMs) as actuators was developed. Contact tasks1) were realized by adapting an adjustable compliance control system of the USM. In the system, a torque feedback control by interaction force to environment is not used. Experiments on contact tasks like crank rotation and cooperative motion of two manipulators were observed.

Ultrasonic Motor for Direct Drive Manipulator

Abstract The direct drive manipulator must be made as low friction and no backlash in its joints. It is one solution to use the direct drive motors. But the usual direct drive motors have big size and heavy weight. As a direct motor, an ultrasonic motor has many good characteristics, but it has a little flexibility on the rotation speed and torque. So, it is developed that the speed and torque control system for the motor by a phase difference control of two-phase driving signals. Also, it is realized that the compliant motion likes an adjustable dash pot with spring.