Investigation of Electrohydraulic Drive Control System with the Haptic Joystick

The term haptic is used to indicate the presence of force feedback from the manipulated object to the operator. One of the most commonly used haptic devices are joysticks. Such joysticks can be successfully applied also in communication with drive system, giving the human operator a feel of the output force. In the paper one axis joystick with force feedback used to control the electrohydraulic drive is proposed. In this joystick, a controlled brake with magnetorheological fluid and a small DC motor are applied. A beam with a strain gauge is used in a joystick arm, enabling the measurement of the force. In the joystick axis also a potentiometer is assembled, which measured the current arm position. In order to develop the control algorithms an electrohydraulic drive simulation and virtual model is worked out and then a haptic joystick is connected to it. The simulation results that have been obtained, enabled to design and test impedance and admittance control strategies for the system composed of haptic joystick and a real electrohydraulic drive. Finally the whole system is built, implemented and investigated in a laboratory environment. Investigations are conducted in conditions similar to real ones, in a situation where hydraulic piston touches an obstacle and the operator cannot observe this piston very accurately. Fifteen operators have been tested this way. The outcomes indicate that haptic control can improve the human feeling of forces between electrohydraulic drive and an obstacle and, thanks to this, the manual control is more accurate and safer.