TORQUEMOTORS

What is a direct drive motor? Technically speaking a direct drive is the same as a servo-drive. 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 mechanical form of the torque motor tends therefore to be short of relatively large diameter. In order that the copper losses and electical time constants remain low, these motors have a higher number of magnetic poles than a conventional servomotor.

The design of these motors is optimised for torque (or force) output rather than for high efficiency. The most important selection criterium for a torque motor alongside the acceleration capability (Nm/kg.m²) is the motor constant Km (Nm/(W)^1/2). This parameter tells the user, what energy losses can be expected from a motor at the demanded torque level - independent of speed!

 

Torquemotor in µ-ross Roboter (BGT Bodenseewerk Gerätetechnik)

There are a number of advantages in using this modern drive technology - both for rotatory 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 acceleration capability
  • high dynamic performance (ratio max./min. speed)
  • better stiffness and damping
  • better position accurarcy and repeatability
  • high reliability
  • high efficiency
  • good, consistant performance over a wide temperature range
  • no wearing parts, long life
  • lower operational noise level
  • hollow shaft
  • short motor length or smaller cross-section
  • framesize or form

The main reason to employ a direct drive still remains servo-performance. This is generally better than for a conventional servo-drive with mechanical reduction. The explanation lies in the extremely stiff connection between the motor and the load, which can be achieved in this mechanical configuration.

We offer the following torquemotor families:

  • ST(K): a cost-effective torquemotor family with torques from 15 to 2,700Nm continuous, which can be supplied as motor kit or as housed version with optional hollow shaft and various feedback options
  • KBM: modern torque motor series for operation up to 680Vdc, 14 sizes (60 to 782mm OD), each in 3 or 4 different stack length, cont. holding torque from 0.5 to 3,500Nm
  • DDR: big hollow shaft torquemotors in three different versions regarding mounting:
    • Cartridge: housed version with preinstalled feedback, but no internal bearing, with torques from 4.5 to 429Nm continuous, especially suited to drive big drums!
    • Goldline: housed version with very robust internal bearings, with torques from 5.8 to 136Nm continuous 
  • MF (Megaflux): big hollow shaft motors with torques from 3.5 to 2,000Nm continuous, extremly short length (from 10mm lamination), high torque density, frameless with preparation for axial mounting, sizes 150 / 210 / 310 also as housed versions!
  • HT: small torquemotors with torques from 0.01 to 45Nm continuous, available as motor kit (hollowshaft) and as housed version, halls standard, high torque density, very flexible regarding winding design (12 to 300Vdc) and mechanical adaptation
  • RBE: small torquemotors with torques from 0.01 to 40Nm continuous, available as motor kit (hollowshaft), halls standard, high torque density, very flexible regarding winding design (12 to 300Vdc)  
  • QT: brushed DC-torquer with torques from 0.02 to 340Nm peak, available as motor kit (hollowshaft), various winding options, suitable tacho generators available, still very good servo performance!
  • MA: outer rotor torquers and servos
  • MR: thin ring motors: very short motor length but big hollow shaft
  • ATK wind alternators: frameless, low cogging, direct drive