Comparison of Stepping Motor and Servo Motor.
Comparison of Stepping Motor and Servo Motor.

1. Structure

The stepper motor rotates in a step-by-step manner, using a magnetic coil to gradually pull a magnet from one position to the next. To make the motor move 100 positions in any direction, the circuit needs to perform 100 steps on the motor. Stepper motors use pulses to achieve incremental motion, which can achieve precise positioning without using any feedback sensors.

The movement method of the servo motor is different. It connects a position sensor to the magnetic rotor, which will continuously detect the exact position of the motor. The servo will monitor the difference between the actual motor position and the commanded position, and adjust the current accordingly. This closed-loop system can keep the motor in the correct state of motion.

2. Simplicity and cost

Stepper motors are not only lower in cost than servo motors, but also easier to debug and maintain. The stepper motor is stable at a standstill and can maintain its position (even with dynamic loads). However, if certain applications have higher performance requirements, more expensive and more complex servo motors must be used.

3. Positioning

In applications that need to know the exact position of the machine at all times, there are important differences between stepper motors and servo motors. In an open-loop motion application controlled by a stepper motor, the control system assumes that the motor is always in the correct motion state. However, after encountering a problem, such as a motor stall due to a stuck component, the controller cannot understand the actual position of the machine, resulting in a loss of position. The closed-loop system of the servo motor itself has an advantage: if it gets stuck by an object, it will be detected immediately. The machine will stop operating and never lose its position.

4. Speed ​​and torque

The performance difference between stepper motors and servo motors stems from their different motor design schemes. The number of poles of the stepper motor is much more than that of the servo motor. Therefore, the stepper motor rotates a full circle, and the required winding current exchange times are much more, which causes its torque to drop rapidly when the speed increases. In addition, if the maximum torque is reached, the stepper motor may lose the speed synchronization function. For these reasons, in most high-speed applications, servo motors are the preferred solution. In contrast, a stepper motor with more poles has an advantage at low speeds, because a stepper motor has a torque advantage compared to a servo motor of the same size.

5. Heat and energy consumption

The open loop stepper motor uses a fixed current and emits a lot of heat. The closed-loop control only provides the current required by the speed loop, thus avoiding the problem of motor heating.

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