Wolfgang Kemmetmüller

New Energy-based Nonlinear Controller for Hydraulic Piston Actuators

A new nonlinear controller for a general class of hydraulic piston actuators is derived. The controller design is founded on an energy-based formulation of the mathematical model, taking into account the fundamental relations of an isentropic fluid. The control law guarantees that the errors of the piston position, the velocity and the piston force asymptotically approach zero and that the desired equilibrium of the overall closed-loop system is stable. By means of an industrial simulation software for hydraulic systems extensive simulation tests have been performed, also considering the robustness with respect to parameter variations and measurement noise. In all cases, the results prove the feasibility and the practical usefulness of the concept being proposed.

Impedance Control of hydraulic piston actuators

Abstract This paper is devoted to the impedance control problem of a double-acting hydraulic piston actuator. Thereby, it is the task of the impedance control system to produce a response to an external force which corresponds to the response of a predefined mechanical system, with a desired (nonlinear) stiffness and a desired (nonlinear) damping characteristics around a desired operating point of the piston position. The controller design is based on a port-Hamiltonian representation of the mathematical model utilizing the fundamental thermodynamic relations of an isentropic fluid.

DESIGN, MATHEMATICAL MODELING AND CONTROL OF AN ASYMMETRICAL ELECTRORHEOLOGICAL DAMPER

Abstract This paper is concerned with the design, the mathematical modeling and the control of an electrorheological (ER) damper for automotive applications. A continuous variation and the desired asymmetrical behavior of the damping characteristics is achieved by an intelligent combination of an ER valve with a laminar damping orifice and check valves. The resulting construction is distinguished by a very compact design and its fail-safe characteristics in the case of a fault of the high-voltage amplifier. Furthermore, some design considerations for the ER damper are given. Based on a detailed mathematical model a nonlinear control strategy is developed. Finally, the feasibility and the usefulness of the proposed construction and the nonlinear control strategy is demonstrated by means of simulation studies.

Modeling and Control of an Electrorheological Actuator

Abstract This paper deals with the modeling and nonlinear control of an ER (electrorheological) actuator consisting of a double-rod cylinder and four ER valves in a full-bridge configuration. Basically, we have to face two difficulties within the controller design: First of all, the ER effect is inherently nonlinear and secondly, the ER full-bridge provides more control inputs than necessary for solving the primary control task. We will show that these additional degrees-of-freedom can be exploited to circumvent undesirable operation and to optimize the overall closed-loop performance. Furthermore, the nonlinearities of the mathematical model will be systematically included in the controller design. Measurement results performed on an experimental test-stand will demonstrate the feasibility of the proposed strategy.

Active and Semi-Active Control of Electrorheological Fluid Devices

This paper is devoted to two different applications of electrorheological (ER) fluid devices. The first application deals with the modeling and nonlinear control of an active actuator consisting of a double-rod cylinder and four ER valves arranged in a full bridge configuration. Secondly, a semi-active shock absorber system is designed by utilizing the special properties of ER valves. The latter application is also intended to demonstrate the benefits of a mechatronic design approach, where the control strategy and the system components are designed simultaneously. Measurement results prove the feasibility of the proposed ER devices.

Modeling and Nonlinear Control of an Electrohydraulic Closed-Center Power-Steering System

This paper deals with the mathematical modeling and the nonlinear control of an electrohydraulic closed-center power-steering system. The system under consideration is characterized by its high energetic efficiency at a full electric power-steering functionality. Based on a nonlinear mathematical model of the system, a flatness-based controller for the servo actuator is designed. Afterwards, an interpretation of the overall steering control system as a mechanical impedance matching problem yields a controller with good performance and robust behavior. Finally, measurement results on a test stand and in a test car show the usefulness of the proposed control approach.

Modeling and flatness-based control of a 3d of helicopter laboratory experiment

Abstract This paper deals with the modeling and control of a three-degrees-of-freedom helicopter laboratory experiment. The helicopter belongs to the class of mechanical systems underactuated by one control. The mathematical model is derived using the Lagrange formalism in combination with the concept of twists and wrenches. It can be proven that the full system is not configuration flat. Nevertheless, by a slight modification of the generalized forces, which can also be interpreted in terms of a constructive change in the experimental set-up, we are able to design a flatness-based controller. Experimental results demonstrate the effectiveness of the proposed concept.