There are two common types of drive motors used in CNC machinery such as cutting machines and engraving machines: stepper motors and servo motors. Shenzhen Leisai, a domestic motor manufacturer, has also produced a type of drive motor known in the industry as a hybrid servo motor, which is actually a closed-loop stepper motor with an encoder.
CNC engraving machine
Often, the speed of a CNC machine depends not only on the control system but also on whether the motor used is a stepper or a servo motor.
So what are the differences between stepper motors and servo motors?
In general, the two motors have different control methods: stepper motors are driven by open-loop control, while servo motors with encoders are driven by closed-loop control.
Servo motor
In terms of control precision, the accuracy of a stepper motor depends on the number of phases and the number of steps. The higher the number of phases and the number of steps, the higher the precision. The accuracy of a servo motor depends on its built-in encoder. The more scale values of the encoder, the higher the precision.
Stepper motor
Another issue is low-frequency characteristics. Stepper motors are prone to low-frequency vibration when running at low speeds, so damping technology or adjusting the microstepping of the driver is usually used to solve this problem. Servo motors, on the other hand, run very smoothly and do not vibrate even at low speeds.
Another difference is the torque-frequency characteristics. The output torque of a stepper motor decreases as the speed increases, meaning that the higher the motor speed, the smaller the output force. In contrast, an AC servo motor outputs a constant torque and its force does not change with the speed.
In addition, the overload capacity is different. Stepper motors generally do not have overload performance, meaning they cannot exceed the output range, otherwise the motor will easily burn out. AC servo motors, on the other hand, have a strong overload capacity, can increase the output, and the encoder will automatically adjust, so the motor will not be damaged due to overload.
Another difference lies in their operating performance. Stepper motors use open-loop control, which can easily lead to missed steps, failure to rotate, or even burnout if the starting frequency is too high or the load is too heavy. Overshoot can also occur when the motor stops rotating at too high a speed. In contrast, AC servo drive systems use closed-loop control, where the motor driver directly feeds back signals from the motor encoder and samples them. This generally prevents stepper motors from experiencing missed steps or overshoot, resulting in more reliable control performance.
Finally, the speed response performance is different. Stepper motors take hundreds of milliseconds to accelerate from a standstill to the required speed, while AC servo systems have better acceleration performance, generally only requiring a few milliseconds. Therefore, they are generally used in control applications or machines that require rapid start and stop.
