I believe you are refering to the drive control unit for a spindle motor. On some machines the motor direct drives a small gearbox and then performs an output function. The drive or "inverter" is used to control this motion of the motor.
A spindle drive has a torque/speed performance as follows:<br><br>Constant torque from 0rpm to a base speed and constant power output above this speed.<br><br>Example,<br>0rpm to 1500rpm with 10Nm and above 1500rpm the power output (1.5kW) is constant to 6000rpm. So at 6000rpm the torque is 2.5NM. (Power output is approx = rpm/10 * Nm)<br><br>A typical application is to drill holes. Often 20,000rpm is the top speed and 3 phase asynchronous motors are used with a frequency inverter (up to 600Hz)<br><br>Special spindles are used in servo applications (C- axis) that can rotate smoothly from 1rpm to the base speed.<br>
Rotary to linear conversion. Nothing more. A motor performs a rotary motion(!) we need to sometimes drive robot arms in a 'linear' fashion.
Pretty much old hat in Robotics. ABB S2 robots used them but dropped them for far better planetary drives.
