UBC Theses and Dissertations
Monitoring and control of milling with an open architecture computer numerical controller Munasinghe, Watukarage Kamal
The importance of an Open Architecture design of a Computer Numerical Controller for integration of process monitoring and control for unmanned intelligent machining is demonstrated. The Hierarchical Open Architecture Multiprocessor Computer Numerical Controller (HOAM-CNC), which is used in this thesis has been designed and built in the Manu facturing Automation Laboratory of UBC. Basic milling process monitoring and control modules which are adaptive force control, tool breakage detection, chatter detection and suppression have been integrated to HOAM-CNC system for intelligent machining. Adaptive force control module keeps the peak cutting force at a specified reference level by manipulating the feed. The purpose of adaptive force control is to avoid shank failure of the cutter and to increase machining accuracy. Tool breakage monitoring system is based on the residuals of two first order adaptive time series filters. Filters remove the effect of geometric transients from average forces. In the event of a tool breakage the residuals simultaneously violate their own adaptive thresholds. Chatter detection and suppression algorithm uses the frequency spectrum of sound emitting from the cutting process. The presence of chatter vibrations is detected when the spectrum amplitude exceeds a predetermined threshold level. The system automatically reduces the depth of cut until chatter vibrations diminish. All three process monitoring and control functions run in parallel in the proposed open architecture system. Performance of the complete CNC system is tested by intelligent machining of a pocket.
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