Dr. Thomas Pollock Profile

Dr. Thomas Pollock

Associate Professor at Texas A&M Univ

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Proceedings Article | 9 May 1997 Paper

Compensation for passive damping in a large-amplitude microgravity suspension system

Mark Anderson, Timothy Hasselman, Thomas Pollock

Proceedings Volume 3045, (1997) https://doi.org/10.1117/12.274204

KEYWORDS: Actuators, Control systems, Motion models, Heat treatments, Resistance, Linear filtering, Differential equations, Magnetism, Manufacturing, Aerospace engineering

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ACTA has developed and demonstrated a three-dimensional, large amplitude, actively-controlled, multi-cable suspension system for dynamically testing large space structures in a simulated microgravity environment. Tension in the cables is actively controlled by large amplitude rotary actuators designed and built at Texas A&M University. The actuators passively support the weight of the test article on soft spiral springs. Spring stiffness in each actuator is compensated by a torque- controlled direct current motor. Bearing and brush friction and damping are actively compensated as well as the algorithmic damping induced by the control law. Actuator stiffness properties were determined by measuring the torque- deflection characteristics of the actuator. Hysteresis loops are compared for the different spring materials Actuator friction and damping properties (velocity-dependent resistance) are determined by measuring the torque-speed characteristics of the actuator with the spring disconnected. Multiple tests were conducted to establish the degree of randomness in these characteristics for robust control design. This paper describes the characterization of actuator stiffness, kinetic friction, and damping, and describes how these characteristics are used to negate the resulting resistance torques in the suspension system. Conclusions regarding the effectiveness of the system and possible enhancements are discussed.

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