Motor controller has a torque knob

British firm Meliamex has developed a motor controller which it claims is unique in having two control knobs - one for speed, the other for torque. The latter control is used to adjust the torque applied by the motor from 2-100% of the available torque. The result, says Meliamex, is an "exceptionally smooth" turning motion, with no cogging.

The controller is aimed, in particular, at applications requiring a constant force rather than a constant speed. Examples include coil-winding, winch tension controls, conveyors, paper and printing machinery where the adjustable torque can reduce breakages, and plastics extrusion machines operating under adjustable pressure or tension. It can also be used to replace DC motor drives.

The controller is available for use with standard three-phase induction motors operating from 230V single-phase or 400V, three-phase, supplies.

The level of performance depends on how the motor is cooled. The best performance is achieved from motors with fixed-speed electric cooling fans. These allow the motor to deliver the full torque even at zero speed when mechanically coupled fans would be stationary.

To prevent motors with mechanical fans from overheating at low speeds, Meliamex recommends limiting the torque to 50% of its full value. It also suggests using a protective motor temperature switch.

Beta site testing of the Excal controller was completed in the third quarter of 2000, and Duncan White, Meliamex`s managing director, reports "an exceptional level of interest". He says the company had won many repeat orders even before the controller was launched officially.

"This design should greatly simplify many industrial processes and improve customers` process yields and quality," he declares.