Power scaling bond graph approach to the passification of mechatronic systems - With application to electrohydraulic valves

In many applications that require physical interaction with humans or other physical environments, passivity is a useful property to have in order to improve safety and ease of use. Many mechatronic applications (e.g., teleoperators, robots that interact with humans) fall into this category. In this paper, we develop an approach to design passifying control laws for mechatronic components from a bond graph perspective. Two new bond graph elements with power scaling properties are first introduced and the passivity properties of bond graphs containing these elements are investigated. These elements are used to better model mechatronic systems that have embedded energy sources. A procedure for passifying mechatronic systems is then developed using the four-way directional electro-hydraulic flow control valve as an example. The passified valve is a two-port system that is passive with respect to the scaled power input at the command and hydraulic ports. This is achieved by representing the control valve in a suitable augmented bond graph, and then by replacing the signal bonds with power scaling elements. The procedure generalizes a previous passifying control law resulting in improved performance. Similar procedure can be applied to other mechatronic systems.