I. Stepper Motor
Moreover, it allows for open-loop position control; a single pulse signal input yields a predetermined position increment. Compared to traditional DC control systems, this incremental position control system significantly reduces costs and requires almost no system adjustments. The angular displacement of the stepper motor is strictly proportional to the number of input pulses and is synchronized with the pulses in time. Therefore, by controlling the number and frequency of pulses and the phase sequence of the motor windings, the desired angle, speed, and direction can be obtained.
my country's stepper motor industry began in the early 1970s, and the development of finished products took place from the mid-1970s to the mid-1980s, with the continuous development of new varieties and high-performance motors. Currently, with the development of science and technology, especially permanent magnet materials, semiconductor technology and computer technology, stepper motors have been widely used in many fields.
II. Servo Motor
Servo motors can control speed and position with extremely high accuracy. They convert voltage signals into torque and speed to drive the controlled object. The rotor speed of a servo motor is controlled by the input signal and can respond quickly. In automatic control systems, they are used as actuators and have characteristics such as a small electromechanical time constant and high linearity. They can convert received electrical signals into angular displacement or angular velocity output on the motor shaft. Servo motors are divided into two main categories: DC and AC servo motors. Their main characteristic is that they do not rotate when the signal voltage is zero, and their speed decreases uniformly as the torque increases.
DC servo motors can be used in EDM machines, robotic arms, and precision machinery. They can be equipped with a high-resolution 2500P/R standard encoder and tachometer, and further enhanced with a gearbox, providing reliable accuracy and high torque to the machinery. They offer excellent speed control and, for their weight and volume, deliver the highest output power, exceeding that of AC motors and far surpassing stepper motors. Their multi-stage structure minimizes torque fluctuation.
III. What are the main differences between stepper motors and servo motors?
1. Differences in working principle
Stepper motors rotate by sequentially activating each electromagnetic coil. When current flows through each coil, the electromagnetic force causes the rotor to rotate relative to gears or a transmission system. Each activation of an electromagnetic coil moves the rotor one step at a fixed angle. Therefore, the motion of a stepper motor is discrete, allowing for precise control of each step's position.
In contrast, servo motors achieve precise control and positioning through a feedback control system. The system architecture of a servo motor includes a motor, an encoder, and a feedback controller. The encoder monitors the position of the motor rotor in real time and feeds the data back to the controller. The controller adjusts the motor's speed and torque output based on the difference between the desired and actual positions to ensure precise motion control.
2. Differences in control methods
Stepper motors typically use open-loop control systems. In such systems, the controller sends commands to the motor, and the motor executes the corresponding actions according to the commands. Because each step of a stepper motor is discrete, and there is a fixed angle between any two steps, position feedback is not required under normal conditions. This makes stepper motor systems relatively simple, and the control method is also relatively simple.
Servo motors typically employ closed-loop control systems. These systems control motor rotation through real-time position feedback. An encoder monitors the actual position of the motor rotor and feeds this information back to the controller. The controller compares this information with the input position command and adjusts the motor accordingly. This type of closed-loop control system offers higher control accuracy and stability, making it suitable for applications requiring high-precision positioning.
3. Differences in output torque characteristics
Stepper motors typically have high torque output, especially at low speeds, where their torque performance surpasses that of servo motors. This makes stepper motors excellent in applications requiring heavy loads or high static torque. However, during high-speed operation or acceleration/deceleration, the output torque of a stepper motor drops significantly, resulting in poor dynamic response performance of the control system.
Servo motors, on the other hand, offer smoother and more stable torque output characteristics. Through a closed-loop control system, a servo motor can provide stable torque output across the entire speed range. This makes servo motors suitable for applications requiring high-speed operation, high acceleration/deceleration performance, and precise positioning.
4. Differences in the complexity of control systems
Because stepper motors use open-loop control, their control systems are relatively simple, requiring only appropriate pulse signals to achieve basic rotation. This makes stepper motors relatively easy to integrate into various control systems at a lower cost.
The control system of a servo motor is relatively complex, requiring components such as encoders and feedback controllers to achieve closed-loop control. This makes the integration requirements for servo motors higher, and the cost relatively higher. However, its high precision and stability are essential in some applications.
