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The field of automation refers to today's hot spot, in which servo motor plays an important role. It is usually used to drive more accurate speed or position control components in the project. Designers of automation equipment often need to face a variety of motor selection problems with different needs, and the motors provided by suppliers are also diverse, with many parameters, which often confuse beginners. This paper shares it according to practical work experience, hoping to provide some help to those in need.

Rexay servo motor
1. Application scenario
Control motors in the field of automation can be divided into servo motors, stepping motors, variable frequency motors, etc. Servo motor drive will be selected for components requiring more accurate speed or position control. The control mode of frequency converter + frequency conversion motor is to change the motor speed by changing the power frequency of the input motor. Generally, it is only used for speed regulation control of motor.
Compared with stepping motor, servo motor:
a) The servo motor adopts closed-loop control, and the stepping motor adopts open-loop control;
b) The servo motor uses rotary encoder to measure accuracy, and the stepper motor uses step angle. The accuracy of the former can reach the order of 100 times that of the latter;
c) The control mode is similar (pulse or direction signal).
2. Power supply
Servo motor can be divided into AC servo motor and DC servo motor from the power supply.
The two are better choices. For general automation equipment, Party A will provide standard 380V industrial power supply or 220V power supply. At this time, select the servo motor of the corresponding power supply to avoid the conversion of power type. However, for some equipment, such as shuttle board and AGV trolley in three-dimensional warehouse, due to their mobile nature, most of them use their own DC power supply, so DC servo motor is generally used.
3. Holding brake
According to the design of the action mechanism, consider whether it will cause the reverse trend of the motor in the power failure state or static state. If there is a reverse trend, it is necessary to select the servo motor with band brake.
4. Type selection calculation
Before type selection calculation, the position and speed requirements at the end of the mechanism should be determined first, and then the transmission mechanism should be determined. At this time, you can select the servo system and the corresponding reducer.
In the selection process, the following parameters are mainly considered: 4.1. Power and speed
Calculate the required power and speed of the motor according to the structural form and the speed and acceleration requirements of the final load. It is worth noting that, generally, the reduction ratio of the reducer needs to be selected in combination with the speed of the selected motor.
In the actual selection process, for example, the load is horizontal movement. Because of the uncertainty of friction coefficient and wind load coefficient of each transmission mechanism, the formula P = t * n / 9549 often cannot be clearly calculated (the torque cannot be accurately calculated). In practice, it is also found that the acceleration and deceleration stage is often the place where the maximum power required by the servo motor is used. Therefore, through t = f * r = m * a * r, the power of the required motor and the reduction ratio of the reducer can be calculated quantitatively (M: load mass; a: load acceleration; R: load rotation radius).
The following points need to be noted:
a) Power margin coefficient of motor;
b) Consider the transmission efficiency of the mechanism;
c) Whether the input and output torque of the reducer meets the standard and has a certain safety factor;
d) Whether there will be the possibility of increasing the speed in the later stage.
It is worth mentioning that in traditional industries, such as crane and other industries, ordinary induction motor drive is used, there is no clear requirement for acceleration, and empirical formula is used in the calculation process.
Note: when the load runs vertically, the gravity acceleration shall be taken into account.
4.2. Inertia matching
In order to realize the high-precision control of the load, it is necessary to consider whether the inertia of the motor and the system match.
For why inertia matching is needed, there is no unified statement on the Internet. Personal understanding is limited, so I won't explain it here.
Interested friends can make their own research and let us know. The principle of inertia matching is: consider that the system inertia is converted to the motor shaft, and the inertia ratio with the motor is not greater than 10; The smaller the ratio, the better the control stability, but a larger motor is required and the cost performance is lower. If you don't understand the specific calculation method, please make up for the "theoretical mechanics" of the University.
4.3. Accuracy requirements
Calculate whether the control accuracy of the motor can meet the load requirements after the changes of the reducer and transmission mechanism. The reducer or some transmission mechanisms have a certain return clearance, which needs to be considered.
4.4. Control matching
This aspect is mainly to communicate and confirm with electrical designers, such as whether the communication mode of servo controller matches PLC, encoder type and whether data needs to be exported, etc

Rexay servo motor
The servo motor can control the speed and position accuracy very accurately, and can convert the voltage signal into torque and speed to drive the control object. The rotor speed of the servo motor is controlled by the input signal and can respond quickly. In the automatic control system, it is used as an actuator, and has the characteristics of small electromechanical time constant and high linearity. It can convert the received electrical signal into angular displacement or angular speed output on the motor shaft. It is divided into DC and AC servo motors. Its main feature is that when the signal voltage is zero, there is no rotation, and the speed decreases at a uniform speed with the increase of torque.