Absence of inertial moderation of pump ripples and wall friction makes the design of a force-controller more challenging than a motion controller. Design and experimental validation of a novel force controller has been executed here in a setup with a pressure-compensated variable-displacement pump and a protective safety guide around a loading spring. These contrast a lower-efficiency fixed-displacement pump of lower pressure oscillations and a bare spring with no guide friction. The controller core has been developed from an order-separated feedforward model handling multiple nonlinearities in a rationalized extension of motion-to-force dynamics. Additional feedback of fractional-order proportional control together with tangent-hyperbolic type bounded integral control has been proposed. The controller parameter has been estimated by a real-coded genetic algorithm based novel two-step identification. While the first step involves the feedforward parameters for the pump flow characteristics, the second step pertains to the force dynamics of the overall system with the controller. The appropriate parametric form and the set of values have been estimated by minimizing the deviation of the simulation prediction of the proposed respective models from the experimental variation. In the second step, the demand track of a sinusoidal force demand of 0.5 Hz and amplitude of 300 N about a mean of 1000 N corresponding to an earlier study with back-stepping controller has been considered so as to accomplish a simultaneous validation. Lower IAE and ITAE errors by 30% and 36% and smoother tracking in this validation study is indeed very encouraging for achieving it in a system with a valve of 25 Hz frequency and a guided spring in comparison to an 80 Hz frequency valve and a bare spring in the earlier study. Studies with other force-tracking demand forms have clearly indicated the potential of the controller proposed in this study involving cheaper and more energy-efficient electrohydraulic system.
Naskar et al. (Sat,) studied this question.