Merits and demerits of closed loop control system

A closed-loop step motor system combines the advantages of servo motor and stepper motor technologies. Functionally, a closed-loop stepper motor system will run much more smoothly and with less resistance than a standard stepper motor setup. Since a closed-loop system provides feedback and control as well as short transient and free oscillation times, the closed-loop system will not lose or gain steps.

A closed-loop stepper motor system, such as the CL86T & , 34HS59-5004D-E1000 may be the best option when the application requires improved energy efficiency and smoothness of operation, especially at high loads. In addition, a closed-loop system has the advantage over servo motor systems of higher torque at low RPMs. Additional benefits include short transient times, less packaging, accurate/correct positioning using feedback from encoders integrated into the motor(s) to the controller, and comparatively low prices.

Open-loop vs. Closed-loop efficiency
To measure the relative efficiency of an open-loop vs. closed-loop system, assume we repeat the same test with the same two motors of equal size. This time we have the closed-loop and open-loop motors run side by side with the same inertial loads but run programming that holds the move profiles constant and equal, so that both systems perform the same amount of work.

open-loop vs. closed-loop
This is a Relative Comparison Chart for StepSERVO closed-loop systems versus open-loop systems. Note the superior performance of the closed-loop stepper system as demonstrated in the results of laboratory testing that compare two systems for acceleration (torque), efficiency (power consumption), position error (accuracy), heat generation, and noise levels.

While the two motors index the same move profile repeatedly, current draw from the dc power supply feeding the two systems is measured and power consumption is calculated. As can be seen in value plots, average power consumption of the open-loop stepper system is 43.8 watts, while that of the closed-loop system is only one third as much — 14.2 watts on average. This dramatic difference in power consumption clearly shows the higher efficiency operation of the closed-loop system. Any user looking to increase the system efficiency of their open-loop stepper system can now consider a simple upgrade to a closed-loop system and expect significantly lower consumption.

Some difference between servo motor and closed-loop stepper motors?