Introduction and selection of AC servo motors

1. Introduction to AC servo motors
The motor is also called a motor. As one of the most commonly used power sources, its main principle is to use the law of electromagnetic induction to convert electrical energy into mechanical energy. Among them, the servo motor is based on the ordinary motor with control and feedback added to control the torque, speed and position of the motor. The main classification and characteristics of the servo motor are shown in Figure 1.

Figure 1 Classification of servo motors

Among servo motors, AC servo motors are easy to use, maintenance-free, and cost-effective. They are widely used in industrial robots, precision machine tools, precision measuring tables, transfer arms, cable placement, and other equipment. As shown in Figure 2, AC servo motors are used in conjunction with ball screws and linear guides. The speed and position control of the servo motor can be used to accurately set the moving speed and position of the workbench.

In the mechanism of mobile phone placement, the torque control of the servo motor can prevent excessive pressure from damaging parts, and can be used in mechanisms that have upper limits on tightening torque. Similarly, AC servo motors can also be used with transmission elements such as synchronous belts, gear racks, and indexing plates to form industrial equipment with different functions.

Figure 2 Application of AC servo motor

AC servo motors are usually composed of motors (including encoders), drivers (also known as amplifiers), wiring harnesses and other accessories. The driver controls the three-phase electricity to form an electromagnetic field, and the rotor rotates under the action of the electromagnetic field; at the same time, the encoder feeds back signals to the driver, and the driver adjusts the rotor speed based on the feedback value and the target value, forming the entire drive control process. Misumi can provide separate motors or drivers, and there are also servo motor sets available.

2. Selection of AC servo motors

There are many parameters for servo motors. You can first select the rated speed, rated torque, and inertia matching, and then select other detailed parameters such as voltage, encoder, power, etc. The author briefly introduces the selection ideas of these three.

Rated speed: The speed n is mainly calculated based on the feed speed v required by the transmission element. For example, if the ball screw is used as a transmission element, then

Rated torque: Torque T needs to take into account the inertia moment (acceleration torque) and friction torque (load torque). At the same time, the appropriate safety factor should be selected according to the industry situation, generally 1.5~3.

Inertia matching: Inertia matching is an issue that is easily overlooked during design. When the load inertia is smaller, the system is easier to control; when the load inertia is larger, the system response speed is slower; when the inertia is not matched, the load cannot start normally within the specified time and stop accurately at the specified position, and sometimes even cause additional system vibration.

Generally speaking, when high response is required, the load inertia should be less than 10 times the motor inertia; for occasions with low start-stop requirements, or pure point-to-point movement, the load inertia can be considered to be about 30 times the motor inertia.