Control

Closed loop control is an essential topic for embedded systems, bringing together actuators and sensors with the control algorithm in software. The central point of this chapter is to use motor feedback via encoders for velocity control and position control of motors. We will exemplify this by a stepwise introduction of PID (Proportional, Integral, Derivative) control.

In Chapter 4, we showed how to drive a motor forward or backward and how to change its speed. However, because of the lack of feedback, the actual motor speed could not be verified. This is important, because supplying the same analog voltage (or equivalent: the same PWM signal) to a motor does not guarantee that the motor will run at the same speed under all circumstances. For example, a motor will run faster when free spinning than under load (for example driving a vehicle) with the same PWM signal. In order to control the motor speed we do need feedback from the motor shaft encoders. Feedback control is called “closed loop control” (simply called “control” in the following), as opposed to “open loop control”, which was discussed in Chapter.