Concept, Simulation Studies and Design for a Novel Concept of the Hydraulic Binary Counter

Abstract

For the realization of compact and lightweight digital hydraulic cylinder drives for exoskeleton actuation the hydraulic binary counter concept was proposed and studied previously. This counter principle is based on hydraulically piloted switching valves which feature a hysteretic response with respect to the pilot pressure. In first prototypes of that counter bistable mechanical buckling beams realized the hysteretic response. Their performance suffered from high friction in the hinges and high local stresses. Furthermore, they require tight manufacturing tolerances not only of themselves but also of their bearing structure. In this paper, hydraulic feedback from the multi-chamber cylinders is proposed and investigated to realize the reset of lower order valves when a higher order valve switches. To make the hydraulic feedback independent from the system pressure feedback to the valve is done via spring compression. This principle makes bi-stable elements obsolete. The functioning of this principle for a small drive for exoskeleton use is proven by a simple mathematical model and its numerical solution by a MATLAB program. An exemplary embodiment design of the valves with the proposed feedback mechanism shows the feasibility of its practical realization. The application of this concept is not limited to small drives but can be applied for larger drives where multi-chamber cylinders are advantageous, such as for excavators, to save cost and installation space of the many solenoid valves required otherwise.