Why Don't Closed-loop Stepper Motors Lose Steps?

Reasons why open-loop stepper motors lose steps:

1. Excessive Load: If a suddenly applied load torque exceeds the motor's output torque, the motor cannot rotate, but the driver continues to send pulses. This causes the actual position to lag behind the commanded position.
2. Speed Too High: When a motor rotates at high speed, its torque decreases. If the acceleration is too rapid or the speed exceeds the motor's capability, it may fail to keep up with the pulse frequency, also resulting in lost steps.
3. Resonance Phenomenon: Stepper motors are prone to resonance within specific mid-speed ranges, causing unstable operation which can also lead to lost steps.

Reasons why closed-loop stepper motors do not lose steps:

1. Real-time Monitoring: An encoder mounted on the rear of the motor continuously monitors the actual position of the motor's rotor in real-time and feeds this information back to the driver.
2. Comparison and Error Correction: The driver's control chip constantly compares the "commanded position" with the "actual feedback position."
3. Dynamic Adjustment:

• If the actual position lags behind the commanded position (indicating an impending or already occurred step loss), the driver instantly increases the output current to provide more torque, forcing the motor to "catch up" until the positions match.
• If the actual position leads (less common but possible), the driver reduces the current to apply braking.
• If the load suddenly increases, the encoder immediately detects the slowdown or positional lag, and the driver instantly increases torque to overcome this sudden load.

The principle behind why closed-loop stepper motors do not lose steps lies in their closed-loop control system's ability to monitor and correct the motor's speed and position errors in real-time. Provided that the available torque is sufficient, the encoder monitors the motor's speed and position in real-time, sends this data to the driver, which then adjusts the motor's operation based on this data to ensure the speed and position accurately reach the preset values.

It is important to note: if the torque is insufficient or there is a mechanical transmission failure, the motor can still lose steps.

Example:

If 1000 pulses are sent to the motor but it does not reach the theoretical position, the encoder identifies this, and the driver sends additional pulses to compensate, moving the motor to the correct position. (Note: Compensation is only for fine adjustment; it is essential to ensure that the step loss is not due to insufficient torque or mechanical issues).

Updated on: 26/09/2025