What is a torque motor – Direct drive advantages

Why adopt torque motors?

Direct drive rotary table
Direct drive rotary table

Reduced cost of ownership

Direct coupling of the payload to the rotor eliminates the need for mechanical transmission elements such as gearboxes, timing belts, speed reducers and worm gear drives. Unlike brushed rotary motors, there is no contact between rotor and stator; therefore there is no mechanical wear resulting in excellent reliability and long lifetimes. Fewer mechanical parts also minimizes maintenance and reduces the system cost. The direct drive technology intrinsic to a torque motor system results in an efficient and effective gearless assembly.

Easy integration

Conventional rotary table
Conventional rotary table

ETEL’s torque motors are available in a wide range of sizes and can be easily adapted to most applications. ETEL’s unmatched standard product offering includes motors with external diameters from 140 mm to 1'290 mm. The use of magnets and limited air gap results in a large hollow shaft or bore for easy integration of cables, cooling tubes, or other application related equipment. The ring-like configuration of a torque motor minimizes the volume required for mounting. This gives the machine designer great flexibility in locating the motor to work with bearings, feedback devices, and payload.

Dynamic performance

Timing belt

Dynamic performance is drastically improved by using direct drive due to the very high control loop bandwidth that can be achieved on the overall system. The direct coupling of the load and position feedback to the motor has the advantage of eliminating all phenomena that limit the dynamic performance on non direct driven machines. Eliminating long-time drift, elasticity, and backlash is a huge advantage for machine performance and lifetime.

Torque motor applications have a wide range of dynamic performance requirements. Depending on the specifics of a system’s duty cycle, the peak torque, continuous torque, or both will drive the selection of a motor. An application with a light duty cycle that requires high peak torque for a short period of time will typically utilize an air cooled motor like ETEL’s TML series. As the continuous torque requirement increases so will the temperature of the motor. The integrated water-cooling capability of the ETEL TMB and TMK motor provides an efficient means of temperature control ensuring high dynamic performance that can be maintained even for the most demanding applications.

Gear
Reducer

Wide torque-speed range

Direct drive torque motors deliver high torque over a wide range of speed, from a stalled or low speed condition to high angular velocities. While torque motors can achieve high velocities (up to 5'000 rpm), there is a trade-off in torque as the motor becomes limited by speed dependent losses increase. The performance of a torque motor over its velocity range can be seen in the torque/speed curve present in the corresponding data sheet.

The torque motor is part of a complete direct drive solution which includes a position controller. High-end digital controllers like the ETEL position controllers, which have been designed specifically for direct drive applications provide excellent control loop quality ensuring optimum stiffness, smooth motion, and excellent velocity control with low torque ripple.