A method for reliable motion control of pressure compensated hydraulic actuation with counterbalance valves

This paper is concerned with the robust handling of negative loads using counterbalance valves in hydraulically actuated equipment. Emphasis is on pressure compensated velocity control of a double acting cylinder. A linearized stability analysis of such a hydraulic circuit with hard quantities; cylinder volumes, cylinder area ratio and counterbalance valve pilot area ratio, is used prove to that without extra measures such a system will be unstable in a substantial part of the cylinder stroke. An alternative approach that guarantees stability while maintaining the counterbalance valve is put forward. The approach transfers the task of throttling the return flow from the counterbalance valve to the directional control valve. Thereby the remaining functionality of the multifunctional counterbalance valve is maintained. The practical implementation and limitation of the approach is discussed as well as the influence on overall performance.