Satoshi Komada

Disturbance observer-based motion control of direct drive motors

Simple and high-performance path tracking control and force control based on an acceleration control are proposed. To realize the acceleration control, disturbance feedback is necessary. The disturbance observer whose inputs are a current reference to the power converter and a position signal by simple computation works as if it were a disturbance detector. The control poles of the observer are varied in accordance with the velocity of the motor for precise positioning. The proposed method was applied to the linear synchronous motor, which is used for direct drive linear motor, and was tested. Results are presented. >

Design of a nonlinear disturbance observer

This paper presents a new disturbance observer based on the variable structure system theory for minimum-phase (with respect to the relationship between the disturbance and output) dynamical systems with arbitrary relative degrees. The model uncertainties and the nonlinear parts of the system are merged into the disturbance term and are regarded as a part of the disturbances. The upper and lower bounds of the disturbance are assumed to be known as a priori information. Simulation results are presented to show the robustness and effectiveness of the new disturbance observer. Experimental results show the practicality of the new observer.

Control of redundant manipulators considering order of disturbance observer

A manipulator control method using a disturbance observer with no inverse dynamics has been proposed. The order of the disturbance observer affects the performance of control system, because nominalization of plant is dependent on the control object and the order of the disturbance observer. This paper proposes a unique choice of disturbance observers of different order in joint and task space to improve system performance of hybrid position/force control of redundant manipulators. Also, it has been shown that a proper selection of a coefficient of the disturbance observer is capable to improve robust stability, while not influencing basic performance. The proposed strategy can realize acceleration control and second derivative of force control in the task space, which realizes robust and precise control of manipulators. Experimental results using a redundant manipulator show the effectiveness of the proposed strategy.

Force feedback control of robot manipulator by the acceleration tracing orientation method

The authors propose a novel approach to force and compliance control of multi-degree-of-freedom (DOF) robot manipulators. The acceleration tracing orientation method (ATOM) is applied to both controllers. The control law is described in the Cartesian space; however, the final command is the acceleration in the joint space. The interactive terms in each joint disturb and deteriorate the joint motion. The disturbance observer cancels out the total sum of these terms and enables each joint to trace the acceleration command. As a result, a robust control is possible in the force task. The testing of the proposed system in a three-DOF robot manipulator is discussed. >

Development of a Biofeedback Therapeutic-Exercise-Supporting Manipulator

Although much equipment for physical therapy has been developed, equipment to improve the quality of physical therapy is scarce. We propose a robotic biofeedback exercise device that can display human joint torque and muscle force during training without a problematic electromyogram (EMG). The purpose is to increase the therapeutic value by understanding a persons condition during exercise and to provide an incentive to improve performance. The manipulator supports lower limb rehabilitation in the sagittal plane. With its ability to adjust the maximum speed and the time constant, the manipulator provides simultaneous and safe isokinetic exercise for the knee and hip joints. This paper describes the estimation of the human joint torque and muscle force. The display of the joint torque and the muscle force is realized during exercise of the knee joint using the developed manipulator. The estimation of the muscle force from Crowninshields method and Hases method generally agrees with the EMG.

Analysis and classical control design of servo system using high order disturbance observer

In earlier papers, it has been reported that a fast and precise servo system, which has low-sensitivity to parameter variation and disturbance, can be realized with simple structure by using a high order disturbance observer. However, a clear and simple design method satisfying specifications for robust stability, influence of measurement noise, and relative stability has hardly been proposed. In this paper, we clarify the class of the robust servo system realized by adjusting the order of the disturbance observer and show design of an estimated disturbance feedback by the disturbance observer, which can represent a classical control approach. We apply this strategy to a design of a position servo system and realize the high performance robust servo system using the high order disturbance observer.

Characteristics of servo system using high order disturbance observer

It is desirable to realize a nominal system which can control acceleration in order to realize a fast and precise servo system, even if the servo system has parameter variation and suffers from disturbance. We have shown previously that compensating disturbance and parameter variation by using a disturbance observer can realize an ideal linear system which can control acceleration. In this paper, first, we transform a plant with a disturbance compensation loop by disturbance observer into a two-degrees-of-freedom control system with a feedforward controller, which indicates that the disturbance observer system includes a series compensator such as P, PI, etc. depending on the order of the disturbance observer. By clarifying the feature of the series compensator, we describe the bandwidth and the stability (the attenuation) of the system and show some simulation results, considering the influence of the measurement noise.

Robust force control based on compensation for parameter variations of dynamic environment

Force control strategies that are robust against disturbance and parameter variations are proposed. These strategies are expansions of disturbance observer-based control strategy, and require little computation. Observers are proposed that estimate parameter variations of the dynamic environment on which the force is imposed are introduced. Since the observer-based control represents a nominal system, a second derivative of force can be controlled. A force control strategy for controlling the second derivative of force is also proposed. The force response similar to the force command is realized by these strategies in spite of the disturbance and the parameter variations of the control object. The effectiveness of the proposed methods is confirmed by simulation and experimental results. >

Hybrid position/force control of robot manipulators based on acceleration controller

A simple high-performance hybrid position/force control that is based on the acceleration tracing orientation method (ATOM) is proposed. From the analysis of ATOM, it is pointed out that precise acceleration control is a key to improve the performance of the motion of the robot. The realization of a strict acceleration controller, however, is almost impossible by the conventional disturbance compensation methods. Recent research on a disturbance observed shows the realization of the acceleration controller. Compared with the inverse dynamics, the observer is simple and robust against parameter variation. Moreover, the disturbance observer can perform parallel computation in each joint by the same algorithm. ATOM was applied to a three-degrees-of-freedom robot to show the effectiveness of the ATOM experimentally.<<ETX>>

Robust force control by estimation of environment

A novel force control strategy which is robust against disturbance and parameter variation is proposed. This method is an expansion of a disturbance observer which estimates the disturbance and parameter variation of motors using simple computation. The observer also estimates the disturbance and parameters variation of the environment on which the force is imposed. Since they are compensated by the observer, a similar force response to the force command is realized. The effectiveness of the proposed method is confirmed by some experimental results.<<ETX>>