3. Selecting high-performance ac spindle motors
Technologies are opening new choices for machine tool spindle motors. This article will
help you make a better choice
Jul 1, 2000 JOHN MAZURKIEWICZ, Baldor Electric Co. | Motion System Design
If your spindle application calls for moderate speed regulation, and will operate at one
or two defined speeds, then a standard ac motor may be a candidate. Speed regulation would
be limited to the slip of the motor, approximately 1.5 to 3% of base speed. Some applications
use a one or two-speed motor with or without a changeable-ratio gear box.
However, for a high-performance adjustable- speed operation, a vector controller with an ac
spindle motor should be used.
Spindle motor vs. standard motor
High-peak-torque capability combined with low rotor inertia of a high-performance
spindle motor enables higher acceleration rates to base speed than are available with a standard
ac motor. Figure 1 shows the acceleration time for a standard TENV ac motor and a high- performance ac spindle motor. Both are driving a tool load with an inertia of 0.25 lb-ft2 and are
powered at their continuous rating of 10 hp. The spindle motor, with a rotor that has 24% of the
inertia of a standard ac motor, reaches the set speed in 28% of the time required for the
standard motor. This shorter acceleration time produces faster orientation capability for tool
changing, for example.