Optimal Motion Planning and Multimodal Control of MHSB for Hydraulic Manipulators

A novel hydraulic circuit, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Modular Hydraulic Servo Booster</i> (MHSB), is applied to conventional hydraulic manipulators. The MHSB uses multiple pumps and valves to drive multiple actuators, thereby enabling flow summing from multiple subpumps to supply the boosted pressure to any actuator. The resultant multimodal control greatly improves the energy efficiency compared to conventional servo-valve systems. This article presents a control strategy to drive multiple pumps and valves optimally to execute point-to-point (PTP) tasks of manipulators. This strategy incorporates energy-optimal trajectory planning and operation mode switching using a graph search algorithm making it suitable for multi-axis robots with frequent position and joint load variations. Numerical simulation and experimentally obtained results from different PTP tasks on a two-link manipulator (1-m length, 10-kg weight, 15-kg payload) validate the proposed method. For example, the experimentally obtained data show significant energy reduction of the optimized path over a shortest path using the high pressure mode.