Torque Motor

The key characteristic of a torque motor is that it can run indefinitely in a stalled condition. In other words, its locked rotor current is not a large multiple of its full load current, as in squirrel cage motors. I don't yet know the differences in structural details. I suspect (again don't know) that it could run on a VFD, but I'm not sure why a VFD would be needed or considered, since the motor's design would allow it to be slowed down without overloading. We may learn more from other responders.

Please read this.

There are also AC Torque motors. They provide a relatively constant torque at any speed. The reel motors on the better reel-to-reel tape recorders were torque motors. A low torque on the supply reel kept the tape tensioned, and a higher torque on the take-up reel helped the capstan keep the speed constant in spite of changing tape diameters. They would have to spin relatively rapidly when the reel was nearly empty, and slow down as the reel filled (slower to faster for the supply reel). Cheaper machines used one or another method of slipping from a constant speed motor (much less reliable).

Hi,

any servo-motor is a torque-motor if torque is linearly dependent on current.

If at standstill there may be the necessity of additional cooling.

Most or all are now PMDC-design: modern very powerful permanent magnets provide flux and the current in the flux-gap generates the torque.

Most have the magnets in the stator and the coils in the rotor - with no iron in the coils to provide fast and accurate torque=Km * current. Km is the motor-constant and is not only the ratio of torque/current but also the ratio of voltage/(2*pi*ups) <this is true only if the friction torque is negligible or compensated>.

The rotating coils require a commutator that contributes friction, wear and speed limit by start of arcing at too high a velocity.

"Can we run the torque motor with AC Drive"

If you can control torque by current and speed by voltage, ok. Usually two servo loops nested: inner loop controlling torque, outer loop velocity.

Very small motors of this type: Faulhaber, Escap, Maxon

Medium size: Mattke

Big size: Infranor.

And many others.

Above link to Kollmorgen is ok but most useful if the free axis through-hole is important.The big diameter of the collector generates much friction.

RHABE

"Much friction" on the Kollmorgens? I suspect you must not have used many of them. Can you explain that a little more?

Hi TVP45,

the friction in Kollmorgen type torque-motors is nearly 3-times higher as in other types as Kollmorgen did locate the commutator on the outermost diameter of the rotor.

This was and is a good solution for passing optical beams through the center.

I am momentarily trying to get to life again an early x-y-z (5x5x1inch travel) machine made by Anorad (mod.35) with three axis, each driven by a Kollmorgen torque motor.

The fourth one (rotary) I did remove as a pure x-y-z grinding and milling micro-machine is to be made.

This object came to me as scrap as a nearby fire with a considerable amount of PVC burning corroded everything.

One of the linear (Schneeberger-type) ball-guides is defect, I don't know if can get enough information on the glass-scales with preamplifier at the optical head to bring these to life again. Wait and see.

I am using many types of torque motors (German makes of pancake types) in driving slow rotary motions in high precision gas-bearings (Professional-Instruments is top of the notch!) in my micro-machines for grinding micro-milling tools (down to 10 µm diameter) and micro-grinding tools the same size that are first ground then coated with nickel then coated with diamond-nickel then over-coated with nickel.

I made myself design and prototyping of two-axis torque motors for limited angular movement of near 10 to 20 mrad, 4 coils at standstill and magnet-system of radially magnetised rings at rotation: torquer fro a 2-axis gyro. Here a photo. Only the upper circumferential part of the coils is used for axial force-generation, up at left, down at right, so in total a torque. These used with one or two magnet-rings but also both circumferential parts of a single coil can be used together with two or 4 magnet rings.

RHABE

Oh, ok, I think I know what you're using now. I've only used the ones Kollmorgen got from Contraves. I forgot the other style. My bad.

We serviced some torque motors for printing machines. They were used to strech the paper.

In general the have a normal three phase squirrel cage rotor and a normal 8 pole stator winding. They always have an external cooling fan, that operates independently from the motor.

The main difference is the applied voltage. The winding of such a motor is calculated for a much bigger voltage then they actually apply to the winding.

If you take a normal 230/400V motor and you supply it with 50V AC 3 phase, you get the same construction.

Also the current did not change much when a torque was applied to the motor shaft.

The torque was adjustable by changing the applied voltage.

The biggest problems were the bearings, because in the field, the motor shaft did only turn minimal and the bearing grease did not mix and lubricated the inside of the bearing.

After a while, the bearings broke down and needed a much to high torque to turn ….