Motors have a major impact on the accuracy and surface quality of machine tools. Key criteria include the motor’s maximum torque, the torque ripple, and the inertia ratio between the motor and its load, all of which are particularly well-matched in the motors of HEIDENHAIN and ETEL.
Disturbance resistance is a key factor in a system’s ability to resist disturbances arising from vibrations or milling forces. The larger the motor is relative to its load, the higher the system’s disturbance resistance is to fluctuating milling forces or vibrations. But if the inertia ratio between the motor and its load is high, then the loop gain must be reduced, thereby also lowering the disturbance resistance.
Motors specifically designed for machine tools enable a more balanced transmission ratio between the motor and its load. In this case, outside influences on the load have no effect on the machining results, and a high loop gain can be employed.
A motor designed with the highest possible moment of inertia, however, contradicts the objective of maximizing acceleration. Higher acceleration is delivered by a motor with a low moment of inertia. Increasing the maximum torque would make the motor more expensive since improved performance for larger or optimized motors requires more or better magnetic materials. As a result, acceleration and cost factors call for an application‑appropriate motor-to-load balance, which is what HEIDENHAIN and ETEL motors offer.
The motor itself can introduce disturbances into the system that affect machining and workpiece surface quality. A key factor is the torque ripple. Axis motors optimized for machine tools feature a low torque ripple, allowing them to produce smoothly inclined surfaces without visible shading, for example.