Joystick control using redundant degrees of freedom of a cooperative system consisting of three manipulators with six wires

Abstract

A method of controlling a cooperative positioning system consisting of three industrial manipulators is proposed. The positioned object is suspended with six wires each two of which are connected to each manipulator tip and remotely controlled by an operator with a joystick. In our previous study, cooperative positioning system with three manipulators has already been developed. However, positioning errors of the object inevitably remain because it is difficult to sufficiently compensate for the geometrical errors within the mechanical system. Therefore, the compensation of the object position by a joystick control is essential. For achieving the joystick control, it is necessary to keep all the tensions positive for the stable positioning. However, if the operator moves the object in arbitrary directions, some wire tensions may become zero because it is impossible to know the positioning error in advance. Therefore, a new control method for not only achieving the positioning of the object but also keeping the proper wire tensions has been developed by two joystick control modes, position control mode and tension control mode. The joystick has three degrees of freedom and control the three translational position parameters or orientation parameters by a selector switch in position control mode. In tension control mode, the minimum wire tension among six is increased by utilizing the kinematical redundancy of the system according to the joystick input. The developed control system has been applied to our experimental system and the effectiveness of the proposed method was verified.

Keywords

• joystick control
• cooperative positioning system
• kinematical redundancy
• wire susupension system