A METHOD OF MACHINING A WORKPIECE, AND AN APPARATUS FOR CONTROLLING FEED RATE OF A WORKPIECE MACHINING CUTTER

摘要

A workpiece (W) is machined circumferentially by a cutter (T). The workpiece is driven by a motor so that the circumferential speed (Vc) of the workpiece (W) is maintained constant (at least until a maximum motor speed Nmax is attained during machining). Below a predetermined base speed Nb the motor exhibits a constant torque characteristic (motor power increases with motor speed). Above Nb the motor exhibits a constant power characteristic i.e. delivers a maximum power output Pmax (motor torque decreases with motor speed). A comparison of actual motor speed (Ns) and base speed Nb is effected, and feed rate is controlled so that at motor speeds (Ns) below Nb cutter feed rate (fr) is dependent upon motor speed (and hence power) and so that at motor speeds (Ns) above Nb cutter feed rate maintains a maximum value (frmax) (dependent upon circumferential speed Vc, maximum motor power output Pmax, and cutter characteristics). Thereby efficient use of the motor power can be provided, for example when machining in a lathe or other machine tool.