October 2009

TECHNICAL TIDBIT

Torque in Servo Motors

When specifying servo motors for a new machine or CNC retrofit, there are many specifications regarding servo motor performance. One of the most confusing is the differing torque specifications of the motor. Torque can be specified in Newton meters (Nm) or more commonly foot pounds (lb-ft) or inch pounds (lbf-in).

1Nm  =  0.74 lbf-ft  =  8.85 lbf-in

Torque (also called moment of force) can be defined as the mechanical work generated by the turning effect produced when force is applied to a rotational axis. Or the measure of how much a force acting on an object causes that object to rotate.

Rated Torque (MN) - The maximum continuous torque available at the rated speed that allows the motor to do the work without overheating (typically specified at a temperature). This is the working range of the motor.

Stall Torque (MO) - The torque, which is produced by a device when the output rotational speed is zero or the torque load that causes the output rotational speed of a device to become zero – i.e. to cause stalling.

Max. Torque (Mmax) - Also known as peak torque, the greatest amount of torque the motor can generate for a very short time period (typically specified in ms).

When specifying servo motors for a machine tool application, the commonly accepted specification is the Rated Torque.

 

Additional Resources

• More information about HEIDENHAIN drive technology and motors