Figure 4.5 - Typical System Interconnections.................................... 4

The components of the basic indexing drive system form two information loops. The position loop is a closed-loop which consists of the controller, drive, motor, and feedback device. The controller, continually compares motor position, derived from the feedback pulses received from the drive, with the desired position calculated within the controller. Any difference between calculated position and actual position results in a corrective command signal being sent to the drive. The drive then corrects motor position by adjusting its velocity loop. The objective of the position loop is to keep the actual position equal to the commanded position.

The velocity loop is also a closed-loop system. The drive continually compares motor velocity, derived from the feedback device, with the magnitude of the command signal generated by the controller. Any difference causes the drive to alter the current to the motor, which in turn changes the motor velocity. The objective of the velocity loop is to keep actual velocity equal to commanded velocity.

The position loop and velocity loop are independent loops, but the controller uses the velocity loop to achieve movement to the desired position. When data is received by the controller specifying a movement, the controller calculates the time required to accelerate to maximum speed and to decelerate from maximum speed. It then calculates the time at maximum speed necessary to complete the movement. This information is then transmitted to the drive by the controller.