When evaluating motors, horsepower is generally considered the primary operational feature. In the case of CNC machines, torque is the true measure of the force that drives the cutting spindle.
Think of the torque motors in CNC machines as linear motors that are “rolled” rather than “unrolled” to produce torque instead of linear force. Torque motor technology allows application of direct drive motion to the fourth and fifth axes that control spindle rotation and inclination.
What are the benefits of torque motor technology as applied to CNC machining?
Direct drive torque motors consist of two parts: an inner magnetic rotor that drives rotation and an outer stator that transmits torque via electrical coil windings. This provides a pair of advantages:
Thanks to the absence of belts, chains and gearboxes, direct drive motors can be attached directly to the load, preventing the effects of hysteresis.
Reduced Cost Of Ownership
Fewer parts means lower risk of breakage or malfunction. In addition, limited contact with the machine virtually eliminates wear and tear, so there’s little to no loss of performance over time.
A perfect match of load inertia to motor inertia is virtually impossible. The traditional goal has been a ratio somewhere from 5:1 to 10:1. Higher ratios can result in gear backlash, which causes a loss in precision.
Direct drive motors have no gearboxes, removing backlash as a factor. Some direct drive applications have been known to handle inertia ratios as high as 11,000:1.
High Torque At Low Speeds
Standard electric motors require high speed to generate high torque, which has the negative effects of reducing accuracy and increasing wear and tear. The magnetic energy used in direct drive motors lets them generate significant torque at much lower speeds.
Minimal Noise, Vibration And Torque Ripple
With fewer moving parts, direct drive motors avoid excessive vibrations and torque ripple that can affect efficiency and precision. They also produce less noise for a more pleasant shop-floor atmosphere.
If you’re looking to improve accuracy and reduce labor, five-axis CNC machines using torque motor technology will provide a positive return on investment.