A model of a conventional, manually driven machine tool slide which is retrofitted for Numerical Control by merely incorporating high-power stepping motor drives, is developed. This model includes the relatively large amount of stick-slip friction in the slideways, and backlash in the drive chain, which characterize the conventional slide. Simulation results obtained using this model highlight the peculiar dynamic behavior, at low speed positioning and contouring operations, of such large stepping motor drive systems under electronically damped open-loop control. The results also demonstrate the feasibility of this low-cost approach to the retrofitting problem, given adequate open- or closed-loop controllers, and provide useful insight into the design of such control systems.

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