How to choose servo motor for automation equipment?-Xinda Motor- electric motors and EV accessories supplier|INDEX--

How to choose servo motor for automation equipment?

Date：2024-06-03　　　Author：XINDA MOTOR

Introduction

Servo motors are widely used in the field of automation, and are usually used to drive more precise speed or position control components in projects. Designers of automation equipment often need to face the problem of motor selection for various different needs, and the motors provided by suppliers are also varied, with numerous parameters, which often confuses beginners. This article only shares some of the author's actual work experience, hoping to provide some help to those in need.

1. Application scenarios

Control motors in the automation field can be divided into servo motors, stepper motors, variable frequency motors, etc. Servo motor drives are selected for components that require more precise speed or position control.

The control method of frequency converter + variable frequency motor is a control method that changes the motor speed by changing the power frequency input to the motor. It is generally only used for motor speed control.

Servo motors compared to stepper motors:

a) The servo motor uses closed-loop control, while the stepper motor uses open-loop control;

b) Servo motors use rotary encoders to measure accuracy, while stepper motors use step angles. The accuracy of the former can be up to a hundred times that of the latter at the general product level;

c) The control method is similar (pulse or direction signal).

2. Power supply

Servo motors can be divided into AC servo motors and DC servo motors based on the power supply.

It is better to choose between the two. For general automation equipment, Party A will provide a standard 380V industrial power supply or 220V power supply. In this case, you can choose a servo motor with the corresponding power supply, eliminating the need to convert the power supply type. However, some equipment, such as shuttle boards and AGV carts in stereoscopic warehouses, use their own DC power supply due to their own mobile nature, so DC servo motors are generally used.

3. Brake

According to the design of the action mechanism, consider whether there will be a reverse trend of the motor in the power-off state or in the static state. If there is a reverse trend, you need to choose a servo motor with a brake.

4. Model selection calculation

Before selecting and calculating, the first thing to do is to determine the position and speed requirements of the end of the mechanism, and then determine the transmission mechanism. At this point, you can choose the servo system and the corresponding reducer.

During 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 the reduction ratio of the reducer usually needs to be selected in combination with the speed of the selected motor.

In the actual selection process, for example, if the load is horizontal motion, due to the uncertainty of the friction coefficient and wind load coefficient of each transmission mechanism, the formula P=T*N/9549 is often unable to be clearly calculated (the torque cannot be accurately calculated). In practice, it is also found that the maximum power required for using a servo motor is often in the acceleration and deceleration stage. Therefore, the required motor power and the reduction ratio of the reducer can be quantitatively calculated through T=F*R=m*a*R (m: load mass; a: load acceleration; R: load rotation radius).

There are a few points to note:

a) The power surplus factor of the motor;

b) Consider the transmission efficiency of the mechanism;

c) Whether the input and output torque of the reducer meet the standards and have a certain safety factor;

d) Whether there is a possibility of increasing the speed in the future.

It is worth mentioning that in traditional industries, such as cranes, ordinary induction motors are used for drive, there is no clear requirement for acceleration, and the calculation process uses empirical formulas.

Note: When the load runs vertically, be sure to take gravity acceleration into account.

4.2 Inertia Matching

To achieve high-precision control of the load, it is necessary to consider whether the inertia of the motor and the system match.

There is no unanimous explanation on the Internet as to why inertia matching is needed. My personal understanding is limited, so I will not explain it here. Interested friends can verify it by themselves and let me know. The principle of inertia matching is: consider the system inertia converted to the motor shaft, and the ratio of the inertia to the motor is not greater than 10 (Siemens); 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 study "Theoretical Mechanics" in college by yourself.

4.3 Accuracy requirements

Calculate whether the motor's control accuracy can meet the load requirements after the changes in 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 mainly involves communication and confirmation with electrical designers, such as whether the communication method of the servo controller matches the PLC, the encoder type, and whether data needs to be extracted.

5. Brand

There are many servo motor brands on the market, and their performances vary widely. Generally speaking, if you have money, choose European and American ones. If you have a little money, choose Japanese ones, and then Taiwan and mainland ones. This is not because the author is worshipping foreign things, but because of the lessons learned from actual use. According to past experience, there is no problem with the basic performance of domestic servo motors, but there is a certain gap in the control algorithm, integration and stability of the main servo controller. I hope that domestic manufacturers will continue to work hard to narrow the gap with foreign products.

If readers have used domestic brands that have worked well, please recommend them to everyone. After all, domestic products need our support to become stronger.

It is worth mentioning that when designing automation, you must learn to borrow external forces. Especially when doing non-standard automation, you are often overwhelmed by the selection and calculation of too many equipment, and working overtime is the norm. Now servo motor manufacturers will provide technical support. As long as you provide them with parameter requirements such as load, speed, acceleration, etc., they have their own software to automatically help you calculate and select the appropriate servo motor, which is very convenient.

How to choose servo motor for automation equipment?

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