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This paper investigates the effect of the variation of parameters of system elements on the overall performance of a generic model of a hydraulic actuation system. Specifically, this paper examines the effects on actuator performance of two issues: intrinsic compliance, the physical compliance within the actuator itself; and independent control of the actuator valve areas (e.g., supply and return areas for hydraulic fluid chambers) versus control of actuator valves with fixed area relationships. Increasing intrinsic compliance in the actuator degrades response to controller commands but improves the ability of the actuator to tolerate insults. Independent control of valve areas provides both better response to commands and better rejection of disturbances than control with valves that have fixed area relationships. The performance information provided by the model permits behavior-based design of hydraulic actuation systems. JNTRODUC TlON BackaroundA great deal of time has been spent on the design of robots, teleoperation systems, and prosthetics. These projects require actuation systems with specific groups of behavioral characteristics, such as grace, accuracy, strength, and speed. In order to achieve these desired characteristics, the systems need good actuators. However, defining a good actuator and describing how to design a good actuator are difficult problems because actuators are not completely understood [l].To address this problem, the Center for Engineering Design (CED) at the University of Utah decided to explore the issues involved in the behavior-based design of robot effectors [I]. Some issues brought up by that investigation were: 1) how well external disturbances can be tolerated; 2) how nonlinearities affect actuator performance; 3) how intrinsic qualities can be manipulated to produce desired'behaviors; 4) how additional control possibilities can be used to improve performance; and 5) how hydraulic systems fit into the behavior-based design strategies proposed for systems with electrical motors [I]. Of specific interest is the effect of intrinsic compliance on external disturbance rejection. It has also been suggested that independently controlling valves can improve actuator performance [2-41. Therefore, the effect of this added control flexibility on actuator performance is also sought.The purpose of this research is to develop and use a generic model of a hydraulic actuator to investigate the above issues. A generic model is needed so that the results of the investigation are valid for hydraulic actuation systems in general and not just for specific cases. Also, the model must include elements that have significant effects on actuator performance so that these effects may be analyzed. The model can then be used to quantify trade-offs resulting from these elements in order to permit the development of behavior-based design strategies for hydraulic actuators. In particular, an understanding of the effect on performance of intrinsic compliance, physical compliance within the actuator itself, is...

Progress in the development of Micro Electro Mechanical Systems (MEMS) has been limited by deficiencies in two broad areas: (1) a lack of knowledge of the physical behavior of interacting micro systems (phenomena such as micro-mbology, -fluid mechanics, -electrostatics, -elecmcal discharge, etc.), and (2) limitations in available fabrication methodologies (photolithography, sputtering, etching, etc.). This paper addresses the second problem by presenting specific Non-Planar Lithographic OJPL) techniques for use in fabricating both monolithic micromachines and microcomponents for use in larger systems. The emphasis here is on the use of numerically-controlled E-beam-based lithography, with the resist exposed over non-planar surfaces. Previously, non-planar, optical-mask-based approaches have been used to fabricate devices such as wobble motor rotors, but with less success than the NPL techniques due to depth-of-field problems.The specific focus is on etching cylindrically-shaped metal structures which are either (1) homogeneous or (2) layered by successive deposition, masking, and etching. Structures on the order of 80 to 500 microns in diameter have been constructed of either solid metals, or sputtered thin metallic layers on quartz shafts. A number of either deep or shallow patterns have been fabricated on and through the structures, with promising results. Examples include; helices, longitudinal lines, holes, notches, flexures, barbs, alphanumeric characters, and electrostatic field emitting patterns for use in wobble motors. Efforts are now proceeding toward generating complete systems, including transducers and actuators for industrial and medical applications.