How does speed stability affect motor selection on printing and paper machines?

As the demand for speed stability grows, the selection is no longer about the motor alone and becomes a combination of motor, drive and feedback. An induction motor fed directly from the mains changes its speed somewhat with load because of slip: it slows down as the load increases and approaches synchronous speed as the load decreases. This is irrelevant for a fixed-speed fan, but it can make a difference for print registration or paper tension.

Why is speed deviation noticeable on these machines?

In offset or flexo printing, the colours line up only if the cylinders keep the same speed relative to one another. In unwinding and rewinding units, speed deviation shows up as a change in tension: the paper slackens, wrinkles or breaks. When the load changes suddenly, the speed of an induction motor also fluctuates slightly; on its own, the motor has no mechanism to correct this deviation.

Which solution for which application?

What must be verified on the motor side

For a motor running on a drive, bear in mind that its own fan slows down at low speed and cooling decreases; if full torque is required at low speed for long periods, a power margin or external cooling comes into consideration. If encoder feedback is required, note that DRG's standard models have no encoder or separate fan option; the suitability of such equipment should be assessed with the system integrator. DRG's standard range does not include servo motors or drive units; DRG motors can form the induction drive part of systems built with a suitable drive.

You can see how torque and power change with frequency using the frequency-torque-power calculator, and review applications close to this sector on the paper and board converting machine motors page.