Some people say that stepper motor system does not need closed-loop, itself is open-loop, but not more than the use of the range can be, and this view I do not agree. I have the following is the point of view:

Closed-loop Stepper system is cheaper than the servo system, in the field of automatic control stepper system used in most of the use,But the possibility of stepping out of the stepping system, and do not know whether it has been out of step and there are step-by-step drive can subdivide and produce micro-step, but the stepper system is mainly to make the current more smooth, Although it can improve the stepping power Machine accuracy, but the micro-step is not reliable.

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Because of this, the stepping system is limited to the requirements of high precision and high risk requirements of the machine.With a closed-loop controller, the stepper system accuracy is no worse than the servo, but the speed is not comparable to the servo,If you can use the Linear Scale on the market, the positioning accuracy can exceed the servo motor, because the servo is only semi-closed loop Control, and stepper motor with closed-loop controller and the grating is fully closed-loop control, eliminating the mechanical system error,So the positioning accuracy can be more than the servo system, while the price is only 1 / N servo.

Stepper motor can not guarantee absolute accuracy, but also do not know whether it is accurate, so the workload changes or uncertain working conditions, such as CNC milling machine, engraving and milling machine cutting force changes are uncontrollable, such as In the steel layer of a deep groove milling, to the multi-layer after each cutter, close to the edge of the groove when the cutting force will increase dramatically, in order to cope with this possibility and to ensure accuracy, the only way is to reduce The entire processing speed, in exchange for local safety, and in fact most of the working hours are not in a large resistance state, so a serious reduction in the efficiency of the system.The use of closed-loop controllers can significantly improve the efficiency of the machine in this case, and you do not have to reduce the overall process and speed and efficiency for individual resistance points. The controller will automatically adjust the speed through the resistance point.

Automatically recovers the speed and accelerates the compensation back to the lost pulses, and is instantaneous to complete.If you set the alarm function, can be out of step to a certain situation, the alarm signal to the host computer servo system is the same way.

I have seen a lot of imported mechanical and electrical equipment there are some medical machines, stepper motor behind with an encoder,
To ensure the accuracy and safety of the equipment.

From the above points can be seen stepping motor closed-loop control is the existence of their own rationality and value,Of course, these are only for high demand but not on the servo of the machine, not for low-demand machines.
Its role is to fill the open loop of the stepper motor and high performance servo motor in the middle of the blank,Giving more choice.