Journal of the Robotics Society of Japan

New trajectory planning method with consideration on control ability of designed robot manipulator control system is proposed. Tracking speed of robot manipulator should be changed with curvature of the given path. Systematical method for determination of the tracking speed considering the designed control system's ability has not been developed. The determination of the tracking speed is made systematically on the basis of the frequency response of the designed control system. Then, trajectory planning is finished by carrying out the procedure only once. That is, trial and error procedure is not necessary. This method is called as variable speed trajectory planning. Adaptive control with variable speed method is considered. Adaptive control method is very suitable to apply the variable speed method because each servo system of robot manipulator is decoupled by adaptive control method. Parallel drive robot manipulator is taken to be an example to show the effectiveness of the proposed method.

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A control method for multi-joint manipulator is proposed, which is based on the manipulator with slider mechanism at the base and controller which gives the bending angle command to all joints while shifting the angle commands to the adjacent joints with synchronization of the linear motion of slider. This method drives all joints of the manipulator as to always follow the same spatial trajectory, just like the motion of Moray, the fish living in the hole of rock on the ocean bed. It is thus called Moray drive. The characteristics of Moray drive are, i) possibility to use light-weight joint driving mechanism by subrogating most of the driving power to the slider, ii) simplicity of control in spite of the redundancy of the multi-joint system, iii) feasibility to make obstacle avoidance, and iv) little fluid resistance in case of the manipulation in the fluid environment. Several simulation experiments are performed as to Moray drive and basic knowledges are acquired, such as the optimal trajectory considering dynamics.

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A new approach to the teaching of manipulative skills is developed and applied to a deburring robot. Teaching data acquired from a human expert, who can perform an efficient job, are processed on a computer in order to attain his skillful manipulation strategies. The strategies are described by a group of control laws that relate sensor signals to motion commands. Sensor signals are processed by using pattern recognition techniques in order to interpret sensor information and to allow the robot to recognize the state of the process. The attained control laws designate which control action the robot should take in response to each signal pattern generated in the process. A method of deriving a compact set of discriminate functions for real-time, recognition of signal patterns is also discussed. The method is implemented on a direct-drive deburring robot. It is demonstrated that the robot can mimic the skillful manipulation of the human expert and perform the task efficiently.

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The dynamic equations of a manipulator are modeled by a system of second-order nonlinear differential equations with its kinematic and dynamic parameters. On the basis of this model, the manipulator can be controlled in a strict way by compensating all dynamic torques/forces consist of inertial, centrifugal, Coriolis, and frictional effects. However, since these dynamic torques/forces are highly complex functions of joint positions and velocities, the computational burden for evaluating these torques is significant. Further, the Cartesian-space control, in which positions and velocities are controlled directly in Cartesian work space, requires considerable amount of additional computations for inverse kinematics. Hence it has been difficult to implement the realtime model-based control with conventional commercially available microprocessors.
This paper presents a real-time implemetation scheme of Cartesian-space nonlinear feedback control based on a new parallel computation scheme called Resolved Newton-Euler algorithm. Some experiments on the basic three joints of the PUMA 560 manipulator are also reported by using a parallel processing system with multiple microprocessors. A sampling period of 0.79 msec is achieved and fairly good control performances are obtained.

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