Servo motors have a wide range of applications. To understand where servo motors are used, we need to start by explaining the function of the motor in principle.
Servo motor, a rather awkward term: servo comes from the English word " servo ." The common ground between Chinese and English lies here: "server " means "to serve, to accompany," which is somewhat similar to the Chinese word "伺候" (sìhòu).
For those new to industrial automation or just getting acquainted with machinery, what exactly is a servo motor?
In simple terms, this means the motor's rotation angle can be precisely calculated, and its position can be fed back in real time. Doesn't that sound like the motor is being monitored in real time? That monitoring device is the encoder.
Therefore, the characteristics of servo motors are very distinct, and these characteristics determine which devices servo motors will be used in.
1. High precision. High precision allows for position control.
2. Fast closed-loop control response. A fast response allows for control over changes in frequency and intensity.
3. If the entire movement of the motor is controlled, then the entire motor can be programmably controlled via digital signals or pulse signals, enabling complex movements.
Still don't understand after reading this? Let's discuss it below and you'll understand. We'll translate the three main characteristics above into various actions in an industrial setting.
1. Feature 1: Position control.
Since highly precise alignment can be achieved, could we then perform tasks such as labeling, aligning and bonding two products, and creating promotional displays? Could we simultaneously control the rhythmic movement of multiple products, like the disco balls on a stage? Could we achieve high precision in printing machines and horizontal and vertical sewing? Could we then perform sawing?
Therefore, when we encounter any device that requires high precision, the first thing we should consider is using a servo motor. As for whether to use a servo motor or a stepper motor in the final product design, it depends on the cost-effectiveness and the required precision.
Servo motors are much more precise than stepper motors. A servo motor with a 17-bit encoder can achieve 600 times the precision of a regular stepper motor.
This is already present in devices that primarily demonstrate servo position modes:
Quilting and embroidery machines, printing machines, dispensing machines, laminating machines, labeling machines, stacking machines, inspection and conveying platforms in the electronics manufacturing industry, various conveyor lines, positioners, and various flying shears and tracking shears.
The servo motor used in the hottest mask-making machines in 2020 was a 750W servo motor, controlled by a PLC or motion controller. Its main function was to control the tension of the mask material strip by dragging it (you can think of it as an advanced version of position control mode).
For many newcomers to this industry, when assessing whether a device needs a servo motor, ask the manufacturer about its machining precision and whether very high precision is required. If very high precision isn't necessary, a stepper motor might suffice.
2. Feature Two: Closed-loop control related applications.
In fact, the fast response of closed-loop control is immediately apparent in the applications of various valves and switches, isn't it?
Congratulations, you got it right.
Take the ventilator, which is currently very popular, for example. When the ventilator mixes air and oxygen, it uses a servo valve.
In terms of fast response speed, the first application area we found was various machine tools. You can see that machine tools that frequently change speed or frequently change position basically use servo motors to provide power.
For example, all axes of a 5-axis machine tool are servo-driven, with several primarily providing position control. The second largest application market is the industrial robot market. An industrial robot uses six servo motors, requiring extremely high precision control and responsiveness.
Servo motors are used in rapidly responding applications such as CNC machine tools (turning, milling, planing, grinding), servo turret punches, bending machines, laser cutting machines, and various industrial robots, collaborative robots, and AGVs.
3. Feature Three: Precise control of continuous motion.
This feature is essentially an enhanced version of the first two features. For example, a servo press, such as a 2000- ton servo press, can achieve a pressure of 20000 N · m , and it can be controlled in real time. This is what servo control can do.
For example, wire cutting equipment is extremely common in the stone and polysilicon markets. This is a typical example of equipment that can achieve precise control in continuous reciprocating motion.
To put it simply, the application scenarios of servo motors can be controlled to vary in output force (technically called torque), and the force can be increased and decreased very evenly. In other words, not only the final result can be controlled, but every step of the process can also be controlled.
The following section discusses the selection of servo motors:
When discussing the applications of servo motors, many people mention the constant speed and constant power of servo motors.
In fact, the constant speed and power of a servo motor are parameters that are considered during the selection process.
Here's a more convenient approach: If you're designing a device and already have information about its production frequency and other electrical parameters, and you're unfamiliar with servo motors, simply find a servo motor manufacturer and have them handle the selection and matching for you. This saves you the effort of doing the calculations yourself.
If you really want to calculate how to select a servo motor yourself, then you need to know the basic torque required.
Generally, during the equipment design process, the required torque is roughly understood. After all, how much force you need to process the equipment can be estimated based on experience. (If you can't calculate it, then you're a blank slate; you'll learn gradually.)
In reality, it should take into account torque, motor power, and torque calculation formulas.
That is, T=9550P/n
In the formula:
P – Power, kW; n – Rated speed of the motor, r/min; T – Torque, Nm .
The output torque of a servo motor must be greater than the torque required by the working machine, and a safety factor is generally required.
Mechanical power formula: P=T*N/97500
P : Power unit W; T : Torque unit g /cm; N : Rotational speed unit r/min .
How are servo systems selected in practice?
In practice, you consult the servo manufacturer based on the equipment's parameters. The manufacturer's sales engineers will determine the most suitable motor based on speed and torque. Then, the servo motor is tested on-site. During testing, parameters are adjusted based on actual usage conditions to determine if the servo motor is suitable for the specific application. For example, if the inertia is too high, a servo motor with lower inertia needs to be used. The need for a servo motor with a holding brake or oil seal, etc., is determined during on-site evaluation. Servo selection is rarely a one-step process.
