Low Cost Cascade Controllers for Non Linear Hydraulically Driven Joints

Abstract

The usefulness of low cost cascade controllers for manipulation of hydraulically driven rotary joints was examined by measuring the controller’s effectiveness in practice using single joint control and describes the implementation across seven joints in a serial manipulator. The ideal hydraulic dynamics is examined and how non-linear kinematics of a cylinder driven joint, valve hysteresis and asymmetrical volumes of a single ended cylinder affect accurate control of the joint using a single control layer. We linearize the control problem by implementing a feed forward velocity with error loop to handle valve actuation and achieve linear joint velocity. This lower control was connected to more complex higher controllers via a standard interface implemented with ROS Control. The overall system allows the implementation of complex rate and trajectory controllers to manoeuvre the tool position of the manipulator.