Optimum design and machining parameters of a permanent magnet brushless DC linear motor as a CNC feed drive

A new heuristic has been developed to determine optimal operating parameters applied to a permanent magnet brushless DC linear motor (PMBDCLM) as a CNC feed drive. An FEA model has been developed utilizing an electromagnetic postprocessor to provide performance output of a PMBDCLM and DC servomotor. Based on the developed FEA models, velocity results have been utilized to provide feedrate levels for design of experiments (DOE). DOE has been conducted to provide force, tolerance, and surface finish data necessary for the performance comparison of a DC servo motor/ballscrew equipped CNC vertical milling machine and a PMBDCLM equipped CNC vertical milling machine. Based on the DOE, a knowledge base has been developed using force, tolerance, and surface finish data. Relationships between force, and spindle speed and feedrate with tolerance and surface finish indices were determined. A heuristic has been developed which represents a guide of applying a set of decisions through the knowledge base to provide a set of operating parameters that will meet user specified tolerance and surface finish requirements for given surfaces. Application of the developed heuristic to a milled part is illustrated. A PMBDCLM CNC retrofit for a conventional ballscrew feed drive system has also been developed to improve machine performance and cost.