Positional Feedback Loop and Velocity Feedback Loop

The robot controller needs to be able to control the speed (velocity) and the position of each axis. The robot axis controller uses a velocity feedback loop and a positional feedback loop (see ill. 1). The command signal comes from the robot program in the form of a new position and feed rate (speed) for each axis. The controller will accelerate the motor and provide the designated control signal to ensure the axis is moving at the correct speed so that all of the robot's axes are synchronized. When the encoder indicates the robot is nearing the correct position for the move, the controller will begin the deceleration process and stop the motor at just the right position.

Above: ill.1: A diagram of the velocity feedback loop and the positional feedback loop for a robot axis controller.