This paper describes some of the interaction effects arising between two electrohydraulic servoactuator systems operating to sustain predetermined and separate force programs on a cantilever beam load system. The work is intended to be relevant to the simultaneous multi-channel drive situations of structure fatigue testing rigs, flight simulators, industrial robots and some machine tools. Simulation and experimental responses of a single-actuator system for a few locations of the drive on the beam and of the two-actuator system for a number of location combinations are presented, compared, and discussed. Combinations of step inputs of desired force were used to excite the system. Simulation and experimental responses show reasonable agreement. Interaction and its effects are quantified in terms of dynamic characteristics of the force responses of the actuators measured from the simulation and experimental results. The model for simulation was obtained via power bond graph modeling technique. The results show that interaction modifies the responses of the actuators, and that the level of interaction, its magnitude and nature are functions of the relative positions of the actuators. Interactions and its effects are also examined using simulation for a three-actuator force control system. The results confirm the earlier observation. The relative gain array developed for steady-state analysis of interaction by Bristol and extended by Witcher and McAvoy for use in dynamic situations is developed as a measure of interaction and is designated as interaction index. Interaction index is calculated and presented for a few cases. The results show that interaction index can be used to examine the magnitude and nature of interaction for multi-actuator systems. The objective of this study was to further appreciation of the origins, nature, and effects of interaction on the response patterns of several powered actuator systems acting simultaneously on one load.

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