ELECTRONIC CONTROL OF PUMP PRESSURE FOR A SMALL HAPTIC BACKHOE
Keywords:
haptics, excavators, backhoes, coordinated motion, electronic load sensing, pressure controlAbstract
The use of haptic interfaces to control mobile hydraulic machinery has several enhancing features over traditional human-machine interfaces comprised of joysticks/levers. This paper presents and analyzes schemes for controlling pump pressure designed for coordinated haptic control. Typical of many small backhoes and excavators, the hydraulic system used on the test-bed is comprised of a constant displacement pump and proportional directional control valves. In this type of system, a main pressure regulator is needed to supply the other closed-centre valves with pressure and to dump the additional flow generated by the pump to tank. An energy-saving solution has a load-sensing pressure regulator that maintains the system pressure to a preset margin above the highest active load pressure. Using these valves for haptic applications requires closed-loop control. Applying closed-loop control to these valves can excite instabilities in the valve assembly due to complex interactions and nonlinearities in the load-sensing pressure regulator and proportional valves. On this setup, the hydro-mechanical pressure regulator has been replaced with one that is electronically controlled, and a non-linear filter is utilized to decouple oscillations in port pressure from the pump pressure input signal. This filter does not slow down the build up of pump pressure. Experimental results with multiple degrees-offreedom are presented.
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