System Identification and Modelling of A High Performance Hydraulic Actuator

Detailed knowledge of actuator properties is a prerequisite for advanced manipulator design and control. This paper deals with the experimental identification and modelling of the nonlinear dynamics of a high performance hydraulic actuator. Such actuators are of interest for applications which require both high power and high bandwidth. An analytical model of the system is formulated, and a software simulator implementing the force-controlled actuator model including all the nonlinear elements is shown to predict the real system's behavior quite well. The actuator properties and performance are also discussed. 1 I n t r o d u c t i o n Hydraulic actuation used to be, and in many cases, remains the technique of choice for high performance robotic applications. However, this type of actuation is not presently receiving a great deal of attention from the robotic research community despite its often ignored advantages. This may be due, in part, to unjustified prejudice against hydraulic systems on the part of robot designers in the research community. Hydraulic actuation is often believed to be dirty, noisy, inaccurate, inadequate for force control, complicated to use, dangerous, expensive, and hard to package. These descriptions do indeed apply to certain, general purpose, hydraulic actuators. However, hydraulic actuators specifically designed for robotics and other demanding applications, such as those discussed in this paper, overcome many of these alleged shortcomings and offer a unique set of performance characteristics. As tile objectives in advanced manipulator research become increasingly demanding, the interaction among various components of the system, and the impact of this interaction on overall manipulator performance, becomes progressively more important. This necessitates an integrated approach to manipulator design: encompassing the kinematic, structural, actuation, sensing, and control aspects of the manipulator within a unified design process. Hence, detailed knowledge of actuator properties, and the nature of the