Dynamic stiffness enhancement of direct linear motor feed drives for machining

Linear motion electric motors have shown promising potential for use as next generation machine tool feed drives since they can increase machining rates and improve servo accuracy by eliminating gear related mechanical problems. To combat chatter instability, large dynamic stiffness is desirable in the servo control loop. This paper investigates the use of optimal H_∞ control to design for large stiffness. Position feedback alone is first considered, with cutting force feedback later added to augment closed loop stiffness. Optimal position feedback is experimentally seen to achieve up to a 46% stiffness improvement over that achievable with proportional derivative control. The addition of force feedback to the servo loop resulted in a further 70-100% stiffness improvement over the position feedback alone values.