Comparison between stepping motor and servo motor

by:V&T Technologies     2020-01-19
In more and more high-standard industrial automation applications, technological advances are changing the performance between stepping motors and servo motors-Cost ratio. After adopting the closed-loop technology, the closed-loop stepping motor provides users with excellent precision and efficiency, which can not only achieve the performance of servo motor, but also has the advantage of low price of stepping motor. Stepping motors with lower cost are gradually penetrating into the application fields originally dominated by high-cost servo motors. Compared with the servo motor, according to the traditional concept, the servo control system has better performance in applications requiring speed exceeding 800 RPM and high dynamic response. Stepper motors are more suitable for applications with lower speed, low to medium acceleration, and higher holding torque. So what is the basis of this traditional concept of stepping motor and servo motor? Let's analyze it in detail. 1 Structure: The stepping motor rotates in a stepping manner, and a magnetic coil is used to gradually pull a magnet to reach the next position from one position. In order to move the motor 100 positions in any direction, the circuit needs to perform 100 step operations on the motor. The stepping motor uses pulses to realize incremental motion, which can realize accurate positioning without using any feedback sensor. The motion method of servo motor is different. It is connected to a position sensor on the magnetic rotor-Encoder-The accurate position of the motor will be continuously detected. The servo will monitor the difference between the actual position of the motor and the command position, and adjust the current accordingly. This closed-loop system can keep the motor in the correct motion state. 2 simplicity and cost stepping motors are not only cheaper than servo motors, but also simpler to debug and maintain. The stepping motor is stable at rest and can maintain its position (Even with dynamic load). However, if some applications have higher performance requirements, more expensive and complex servo motors must be adopted. 3 positioning, there are important differences between stepping motor and servo motor in applications that need to know the accurate position of the machine at any time. In the open-loop motion application controlled by stepping motor, the control system thinks that the motor is always in the correct motion state. However, after encountering problems, such as motor stall caused by stuck parts, the controller cannot understand the actual position of the machine, resulting in misalignment. The closed-loop system of the servo motor itself has an advantage: if it is stuck by an object, it will be detected immediately. The machine will stop operating and will never lose position. 4 the performance difference between speed and torque stepping motor and servo motor comes from their different motor design schemes. The number of poles of the stepping motor is much more than that of the servo motor, so the winding current Exchange times required for the stepping motor to rotate for a full circle are much more, resulting in a rapid decrease in torque when the speed increases. In addition, if the maximum torque is reached, the stepping motor may lose the speed synchronization function. For these reasons, servo motors are the preferred solution in most high-speed applications. On the contrary, the stepping motor has more poles and has advantages at low speed, because the stepping motor has torque advantages compared with servo motors of the same size. With the increase of speed, the torque of stepping motor will decrease by 5 heat and energy consumption. Open-loop stepping motor adopts fixed current and will emit a large amount of heat. Closed-loop control only provides the current required by the speed Loop, thus avoiding the motor heating problem. Comparison and summary servo control system is most suitable for high-speed applications involving dynamic load changes, such as mechanical arms. Stepping control system is more suitable for applications that need low to speed and high holding torque, such as 3D printer, conveyor belt, auxiliary shaft, etc. Because the cost of stepping motor is lower, the cost of automation system can be reduced after use. If the motion control system needs to make use of the characteristics of servo motors, it must prove that these motors with higher cost are worth the money. Driven by the progress of closed-loop technology, stepping motors can penetrate into the high-performance and high-speed application fields that used to belong to servo motors. Stepping motors adopting closed-loop technology, if the advantages of closed-loop servo technology can be applied to stepping motors, what will be the effect? Can we achieve the same performance as servo motor while realizing the cost advantage of stepping motor? By combining closed-loop control technology, stepping motor will become a low-cost comprehensive product with both servo and stepping motor advantages. Because closed-loop stepping motors can significantly improve performance and energy efficiency, they can replace more expensive servo motors in more and more high-standard applications. TAG servo motor
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