Frameless Torque Motor

A motor sold as just a stator and rotor, with no housing or bearings, built to be mounted straight into a joint.

A frameless torque motor is a permanent-magnet motor sold as a bare component: just a stator (the coils) and a rotor (a ring of magnets), with no housing, bearings, output shaft, or encoder — the robot manufacturer mounts it directly inside a joint housing of its own design. It's typically shaped as a large-diameter, thin, flat ring with many magnetic poles, so it can deliver substantial torque even at low speed, and it leaves a large center bore for routing cables or fitting a gearbox. This design eliminates couplings and duplicate structural parts, making the joint more compact, lighter, and stiffer. A common combination in the rotary joint modules of collaborative arms and humanoid robots is a frameless torque motor paired with a harmonic or planetary gearbox, a dual encoder, and a holding brake. Kollmorgen is one of the leading manufacturers.

ExampleIn a collaborative arm's joint, the frameless motor's rotor is fitted onto a hollow shaft and its stator is pressed into the joint housing, with cables routed through the center bore.

Also called

Frameless Motor, Torque Motor

Related

Joint Actuator Module · Permanent Magnet Synchronous Motor · Hollow-Shaft Cable Routing · Strain Wave Gear (Harmonic Drive) · Direct Drive · Kollmorgen

Sources

Torque motor - Wikipedia