Special motors called servos are used for executing machine movements in closed loop system. The name indicates that the closed loop control system has a loop that is closed as shown in fig. A feedback device is used for this purpose. This makes the design of closed loop a little complicated and expensive. But a very high degree of accuracy is achieved in the movement of slide. This system is similar to open loop control system. But it consists of two additional devices in the form of feedback transducer and a comparator as shown in Fig. The transducer feedbacks the actual slide displacement to the comparator. The comparator compares the actually achieved slide movement with command signal. If there is any error then it is feedback to the MCU. The MCU then sends the corrective commands to the drive unit and the cycle repeats until there is no error signal from the comparator.