Velocity Feedback

You can configure the NI motion controller for velocity feedback using the Kv (velocity feedback) gain. Using Kv creates a minor velocity feedback loop. This is very similar to the traditional analog servo control method of using a tachometer for closing the velocity loop. This type of feedback is necessary for systems where precise speed control is essential.

You can use a less expensive standard torque, or current mode, amplifier with the velocity feedback loop on NI motion controllers to achieve the same results you would get from using velocity amplifiers, as shown in the following figure.

Setting any non-zero value for Kv allows you to use the Kv term instead of or in addition to the Kd term to stabilize the system.

Velocity feedback gain (Kv) is similar to derivative gain (Kd) except that it scales the velocity estimated from encoder resources only. The derivative gain scales the derivative of the position error, which is the difference between the instantaneous trajectory position and the primary feedback position. Like the Kd term, the velocity feedback derivative is calculated every derivative sample period, and the contribution is updated every PID sample period, as shown in the following figure.