Direct Drives

GEISS LLC

A direct drive is a special type of servomotor. Modern versions are electrically equivalent to 3-phase brushless, synchronous motors with permanent magnet field excitation. The geometry of the motor has however been chosen to generate high torques (or forces) instead of high power output.   The direct drive technology applies the power to the movement directly, without previous conversion of a mostly rotary movement. In order that the copper losses and electrical time constants remain low, these motors have a higher number of magnetic poles than a conventional servo motor.   The design of these motors is optimised for torque (or force) output rather than for high efficiency. The most important selection criterion is the accelerating ability of the drive.   There are a number of advantages in using this modern drive technology - both for rotary and for linear motion control. It is not only a question of performance. Often secondary issues of mechanical assembly are of equal importance, such as:

  • high accelerating ability,
  • high dynamic performance (ratio max./min. speed),
  • better stiffness and damping,
  • better positioning repetitive accuracy,
  • high reliability,
  • high efficiency,
  • good, consistent performance over a wide temperature range,
  • no wearing parts, long life,
  • lower operational noise level,
  • hollow shaft,
  • short motor length or smaller cross-section,
  • overall size or shape.