The difference between servo motors and stepper motors in automation

Comparison of the performance of stepper motors and AC servo motors. A stepper motor is a device that enables discrete motion, and it is inherently linked to modern digital control technology. In current domestic digital control systems, stepper motors are widely used. With the emergence of fully digital AC servo systems, AC servo motors are also being used more and more in digital control systems. To keep up with the development trends of digital control, stepping motors or fully digital AC servo motors are commonly used as actuator motors in motion control systems. Although the two share similar control methods (pulse trains and direction signals), there are significant differences in their performance and application areas. A comparison of their performance is now made. I. Different control precisions: The step angle of two-phase hybrid stepper motors is generally 3.6° or 1.8°, while that of five-phase hybrid stepper motors is usually 0.72° or 0.36°. There are also some high-performance stepper motors with a smaller step angle. For example, a stepper motor produced by SITONG for slow-speed wire cutting machines has a step angle of 0.09° ； The three-phase hybrid stepper motors produced by the German company BERGER LAHR have a step angle that can be set to 1.8°, 0.9°, 0.72°, 0.36°, 0.18°, 0.09°, 0.072°, and 0.036° using a DIP switch; they are compatible with the step angles of both two-phase and five-phase hybrid stepper motors. The control accuracy of the AC servo motor is ensured by the rotary encoder at the rear end of the motor shaft. Taking Panasonic’s all-digital AC servo motors as an example, for motors equipped with standard 2500-line encoders, the pulse equivalent is 360°/10000=0.036°, thanks to the quadrupling technique used inside the driver. For a motor equipped with a 17-bit encoder, the driver receives 2^17=131072 pulses per revolution of the motor; thus its pulse equivalent is 360°/131072=9.89 seconds. It is 1/655 of the pulse equivalent of a stepper motor with a step angle of 1.8°. II. Different low-frequency characteristics: Stepper motors are prone to low-frequency vibration at low speeds. The vibration frequency is related to the load conditions and the performance of the driver; it is generally considered to be half of the motor’s no-load starting frequency. This low-frequency vibration phenomenon, which is determined by the working principle of stepper motors, is very detrimental to the proper operation of the machine. When a stepper motor operates at low speeds, damping techniques are generally used to overcome low-frequency vibrations, such as installing dampers on the motor or using microstepping technology in the driver. AC servo motors operate very smoothly, with no vibration even at low speeds. AC servo systems have resonance suppression capabilities that can address insufficient mechanical stiffness, and they are equipped with a frequency analysis function (FFT) that allows the detection of the machine’s resonance points, facilitating system adjustment. III. Different torque-frequency characteristics: The output torque of a stepper motor decreases as its speed increases, and this decrease becomes more significant at higher speeds; therefore, its maximum operating speed is generally between 300 and 600 RPM. AC servo motors provide constant torque output; that is, within their rated speed range (usually 2000 RPM or 3000 RPM), they can deliver the rated torque, while above the rated speed they offer constant power output. IV. Different overload capacities: Stepper motors generally do not have an overload capacity. AC servo motors have a strong overload capacity. Taking the Panasonic AC servo system as an example, it has the capability to handle speed overload and torque overload. Its maximum torque is three times the rated torque, and it can be used to overcome the inertial torque of inertial loads at the moment of startup. Since stepper motors lack such overload capacity, when selecting them to overcome this inertial torque, it is often necessary to choose motors with a higher torque. However, the machine does not require such a high torque during normal operation, resulting in waste of torque. V. Different operating performance: Stepper motors are controlled using open-loop control; excessive starting frequency or high load can lead to loss of steps or stalling, while too high a speed at the time of stopping can cause overshoot. Therefore, to ensure control accuracy, it is necessary to properly manage the acceleration and deceleration processes. AC servo drive systems operate in a closed-loop control mode; the driver can directly sample the feedback signals from the motor encoder. They consist of a position loop and a speed loop internally, and as a result, issues such as step loss or overshoot that occur in stepper motors do not arise, offering more reliable control performance. VI. Different speed response characteristics: It takes 200–400 milliseconds for a stepper motor to accelerate from rest to its operating speed (usually several hundred revolutions per minute). AC servo systems exhibit good acceleration performance; taking the Panasonic MSMA 400W AC servo motor as an example, it only takes a few milliseconds to accelerate from rest to its rated speed of 3000 RPM, making it suitable for control applications that require rapid start-up and stop-off. In summary, AC servo systems outperform stepper motors in many performance aspects. However, in some applications with lower requirements, stepper motors are also often used as actuation motors. Therefore, during the design of a control system, it is necessary to take into account various factors such as control requirements and cost in order to select an appropriate control motor. https://zhidao.baidu.com/question/21111189.html

The terminology is too academic. The more I look at it, the more confused I get.

This post was last edited by Fully Automatic Palletizer on 2018-12-10 at 13:24. It’s material I found. Easy to understand. The servo motor used in stackers is a regular motor equipped with a feedback encoder (which records the motor’s angle, speed, and acceleration; in other words, the control precision of the servo motor is ensured by the rotary feedback encoder located at the rear end of the motor shaft). If you want to enable very precise control over angle, speed, and acceleration. It can only be achieved with supporting devices, such as a servo motor + servo driver. For example, open-loop control: servo motor + servo controller + PLC for programmable control. Closed-loop control: servo motor + position sensing device + servo driver + PLC for programmable control, as shown in Figure 3. Difference between open-loop control and closed-loop control: A control system that has feedback to correct errors is called a closed-loop control system. A control system with no feedback is called an open-loop control system. As shown in the servo motor control demonstration diagram: a servo motor alone is not sufficient to complete a sequence of actions. It is necessary to have (servo motor control system: composed of a position sensor device + servo motor + servo motor driver + PLC for programmable control). ) to enable a perfect integration of the servo motor with the mechanical components, thereby carrying out various actions. (Such as the palletizing actions of palletizing robots, CNC machine tools, etc.) Stepper motor: A stepper motor is controlled by pulse signals; each time it receives a control signal, it rotates by a certain angle (one step). Moreover, it is different from servo motors, which can only rotate a certain angle, as stepper motors can rotate continuously. Differences between servo motors and stepper motors in palletizing robots: 1. Structure and working principle: In terms of motor structure, stepper motors are more complex than servo motors. Stepper motors are used in applications that require low speeds but high precision, while servo motors can reach 3000 revolutions. Then the stepping speed is low. Servo motors are more expensive than stepper motors. . Because a servo motor must be used together with a servo motor driver. Servo motor + servo motor driver. Source: http://www.tsrun.com/jishu/185.html