Meaning
Periodic disturbances in linear motors arise from the magnetic interaction between the permanent magnets and the stator teeth. The cogging force ripple represents the variation in thrust that occurs as the motor moves, even when no current flows through the coils. It defines the smoothness of motion at low speeds and limits the precision of high resolution positioning systems.
Precision Impact
Fluctuations in output force lead to velocity errors that degrade the surface finish of machined parts. Because cogging force ripple is a function of position, it creates a repeatable pattern of vibration that can be mapped and compensated for in the controller. High precision applications often require motors with skewed magnets to minimize this effect.
Control Strategy
Mechanical components such as bearings and couplings provide a small amount of passive resistance to oscillation. The cogging force ripple can excite the natural frequencies of the machine frame if the control loop is not tuned to dampen these specific periodic inputs. Effective design reduces the amplitude of these ripples before the system enters production.
Mechanical Wear
The resistance felt when moving a motor manually is a physical manifestation of the magnetic detent positions. While cogging force ripple does not consume power in the same way as friction, it requires additional current to maintain a steady speed against the varying magnetic resistance. This interaction increases the heat generated by the motor during slow, precise movements.
Increased thermal load can degrade the insulation of the motor windings and shorten the operational life of the equipment in a high duty cycle production environment.
