In this paper, a methodology is proposed to obtain a stable control law for the manipulators which perform contact tasks. The methodology is based on unified approach of the Lyapunov direct method. The subject manipulators are varied from a simple linear manipulator to a nonlinear 3-dimensional re-dundant multi-link manipulator, which are interacting with a flexible wall with collision pheonomena at the contact of tasks. The stability and response of the system are examined by parameter studies of numerical simulations adequately. As the demands for rapid motion of robotics has been increasing in the field of industry to achieve higher efficiency, collision has become a problem to be solved, because every task includes contact when a manipulator acts on an object. The contact, or collision, is analyzed and proved to be stable on the manipulator tasks.
A docking mechanism and its control scheme ate discussed for high performance autonomous docking systems. A discussed problem is to achieve soft docking and to absorb the shock of collision when a satellite approaches to the docking mechanism with relative velocity. To solve the problem an intelligent adaptive structure is examined to use as the docking mechanism. Control strategy for the docking mechanism is discussed and a PD-impedance control, i.e., impedance control combined with PD-control, is proposed. The docking mechanism is controlled along an appropriate trajectory by using the PD-impedance control and the soft docking is achieved. Advantage of the PD-impedance control is discussed through a simple example. Finally, feasibility of the proposed scheme is verified by numerical simulations.
This paper describes a motion planning method which use an artifical potential fleld based on the solution of the Laplacian differential equation, and illustrates several simulation examples, both with mobile robots and manipulator arms. There ie no minimal point in the of the Laplacian differential equation. This mathematical nature guarantees a robot to attain to the goal and to avoid collision with the obstacles. And this method can apply 4 or more degrees of freedom maniuplators simply because of that the Laplacian differential equation is easy to expand into high-dimensional space. A robot motion plan which is in knownn environment with the given start and goal configurations is created by tracking the valley of the potential field.
A method for a task division which is needed to realize an efficient parallel processing on the inverse dynamics problem is proposed. In the preprocessing step of scheduling, calculating equations are divided into many tasks which become processing units. On dividing the given equations into a task set, if the task granularity is fine, the number of tasks which can be processed simultaneously tends to increase, whereas communication overhead between processors tends to increase. The purpose of this study is to develop a task dividing method for efficient implementation of parallel processing. The inverse dynamics equations are divided into tasks by equation level. Divided tasks are composed or divided additionally considering the precedence constraints inherent in the inverse dynamics problem.
Lowering energy consumption of space robot systems has triple fold reasoning : lighter-weight systems, longer life-time, easier heat-control. In this paper, we have studied this problem from control point of view. It has been proposed to regenerate electricity and store it when a space robot decelerate its motion. Even when we regenerate electricity, there still is energy loss due to various physical reasons such as heat loss by electric resistance of motors and mechanical friction, recharging loss of battery, and so on. The recharging efficiency is known to be 75-80% and the rest is the recharging loss. We aim at totally eliminating this loss by motion control. The main idea is to control the motion of a space robot system with the artificial constraint of kinetic energy conservation. This makes recharging unnecessary and recharging-loss zero. We utilize the redundancy of control momentum wheels to meet the scalar constraint. The simulation result shows that a three-second motion with the proposed control can save approximately 40-84 (J) .
For the problem of catching the target that has a will to flee from the chaser, an effective method using predictive control is proposed in this paper. The method is characterized by following processes. 1. Estimate the unknown behavior of the target by simple system identifying method. 2. On the linearlized behavior model, calculate the control input to the chaser (robot) to make the position of the robot equal to the postion of the target on certain time in the future. 3. The constraint of the limitation of available force (torque) of the robot is considered when control input is calculated. 4. Iterate these prosesses on every sampling time and modify the behavior model of the target and control input to the chaser. The effectiveness of this method is proved by experiments and simulations.
This paper describes a nonlinear robust control for a robot manipulator with artificial rubber muscles by applying a fuzzy compensation. A fuzzy logic controller as a compensator is added to control the trajectory of a two-link robot manipulator, in which the computed torque control method has been already assumed to be applied to the robot. It is shown that when there exist model uncertainties and/or untuned feedback gains, the fuzzy compensator with a simple adaptive scaling technique is effective for the robust control. The effectiveness of the proposed control method is illustrated by making some simulations and experiments for the robot manipulator.
This paper disusses the condition for realizing Sell-Posture Changing Motion (SPCM) . With a proper combination of a compliant joint and a position-controlled joint, a link system has the capability of changing its posture while maintaining contact between inner link and environment over an angular displacement at the position-controlled joint, The series of these motions is so-called SPCM. The condition for realizing SPCM depends on many factors, such as the object's shape where the link contacts, the frictional coefficient at the point of contact, link posture, the compliance of the system and so on. While we have obtained a sufficient condition leading to SPCM in our former works, this condition normally provides the severer condition than the actual one. After proving that a pure thcoretical approach never provides the necessary and sufficient condition, we have examined how actual SPCMs stop. Through experiments, we newly found an interesting coatact force behavior, namely, it shoots up after a particular link configuration and an SPCM stops after this force behavior. After analyzing the mechanism of this characteristic, we propose a new control strategy which suppresses the increase of contact force and contributes to extending the link posture leading to SPCM.
In this paper, we design a new pneumatic actuator using welded metal bellows. Since this actuator has no slide parts, there is no influence of friction forces. Therefore, it is expected that the actuator has good control performance for positioning and generating exact desired forces. First, we propose a positioning control law for the bellows actuator in which position and pressure of the bellows are controlled independently by dividing the control loop into two stages. It is experimentally shown that fine positioning can be easily obtained by the proposed control law. Furthermore pressure control performance is revealed through experimental results. Second, in order to use the bellows actuator as a force sensor (bellows sensor), we investigate the static and dynamic characteristics of the bellows actuator. From the experimental results, the capability of the bellows sensor becomes clear. Finally, the bellows actuator is applied to a sensing actuator and the effectiveness of the actuator is demons-trated through several experimental results.
The paper describes a force sensorless control in multi-degrees-of-fredom robot. In the active com-pliant control, force sensor is attached to the robot to detect the reaction force. However it makes a structure of the robot system complicated. To improve this problem, we propose the force sensorless control strategy based on disturbance observer. First, a basic structure of the dusturbance observer is shown. Then the calculation process of the reaction force is also introduced. Second, the force sensorless compliant controller is constructed. The experimental results are also shown to confirm the validity of the proposed method.