Torque Motors for Direct Drive Applications

In order to meet customers request in terms of customised motors, CNC specialist NUM has significantly expanded its portfolio of motors for machine tool applications by launching a range of high performance brushless torque motors, ideal for applications that demand very smooth and accurate rotation.

by Sergio Soriano

Employing innovative optimised magnetics, NUM’s new TMX series direct drive motors have an extremely low cogging torque, almost half that of most motors available on the market. They are ideal for applications that demand very smooth and accurate rotation, especially at low speeds. Typical uses include direct drive machine tools, rotary tables and radial positioning units.
For direct drive applications, NUM has generally specified use of torque motors produced by IDAM, a member of the Schaeffler Group. However, as Massimiliano Menegotto, General Manager of NUM’s main manufacturing plant in Milan, explains, a growing number of customers request customised motors and prefer to deal with a single supplier for all their CNC machine tool requirements.
A range to be broadened NUM is initially launching two TMX series frameless torque motors, with stator diameters of 140 mm and 291 mm, and intends growing the range in the future. The motors’ hollow shaft rotors utilise high flux density neodymium-iron-boron (NdFeB) magnets and offer ample internal space for through-motor wiring or mechanical parts. The stator windings are fully protected against over-temperature conditions and are encapsulated within a thermally optimised enclosure that offers a choice of air-cooled and water-cooled configurations. Like all direct drive motors, the TMX series units are capable of providing continuous torque even when stalled, and are designed for direct attachment to the load. This obviates the need for gearboxes or shaft couplings, to provide highly accurate, backlash-free rotary transmission. The rotor and frameless stator are supplied as component parts and are primarily intended for applications that require total integration of the motor within the servomechanism in order to reduce weight or volume.

A choice of stator and rotor lengths to best suit the applications
NUM’s new TMX series motors can produce a very high S1 torque density and are available with a choice of stator and rotor lengths to best suit the motion requirements of the applications.
By way of example, a 140 mm diameter motor with an active length of 70 mm can produce a peak torque of approximately 82 Nm at speeds up to 1,500 rpm, and a continuous (stall) torque of approximately 50 Nm.
The motors can be driven by most industry-standard servo drives, including NUM’s MDLU3 and MDLUX drives, which form part of the company’s latest-generation Flexium+ CNC platform.