In the field of industrial control automation, servo motors are an indispensable product.
In this industry, every engineer is required to understand the basic usage of servos.
Today we'll talk about how to wire a servo motor.
Let's first understand what a servo motor is:
The word "servo" comes from "servus" (English: slave). A servo motor system is actually a motor that can be controlled in real time: if you tell it to move 1mm, it will move 1mm; if you tell it to go to a certain position, it will go to that position; if you tell it to go fast first and then slow down, it will go fast first and then slow down.
Three types of servo motor applications: (This will help many people understand servo motors in advance)
1. Speed mode , for example, when rapid acceleration and deceleration are required. The most typical example of this application is the light spheres suspended above the stage, which are used for rapid acceleration and deceleration.
2. Torque Mode (also known as torque output mode): This mode provides a constant output force and torque. Examples include wire EDM machines and diamond cutting machines. The spindle and feed axes of these machine tools are typically servo motors, primarily for this function. (Of course, it also incorporates the other two functions.)
3. Position Mode . This mode allows for precise position control, which essentially means controlling the rotation angle of the servo motor. The degree of rotation of a motor is counted by an encoder.
encoder
Two types of encoders
These three modes are not used independently, but often one of them stands out as the primary function.
The basic structure of a servo motor is: servo driver (also known as servo amplifier) + motor.
Servo driver, servo motor
(1) Servo driver , also called servo amplifier. Position commands sent from the host computer, PLC, or motion controller are sent to the driver. The driver converts the numerical or analog signals into speed, and then into the magnitude of the current to control the rotation of the motor.
After all, motors can only recognize current; they can't recognize any other signals.
Driver working principle
(2) Servo motor: A servo motor is actually just a regular motor + encoder + electromagnetic brake (there are motors without brakes).
The so-called servo brake is actually an electromagnetic switch. When power is cut off, the brake automatically engages the stator, preventing it from rotating. This is an essential feature on cranes. It's also indispensable on stamping presses and various machine tools. In other words, it must be able to stop the machine in the event of a power outage. (This is the rapid protection function in emergency stop situations.)
After introducing these functions, many people should have a better understanding of the application and overall structure of servo motors.
The emergence of a complete servo system always involves a servo drive and a motor working together. Current solutions include 1-to-1 (one drive drives one motor), 1-to-2 (one drive drives two motors), 1-to-3, and 1-to-6 (primarily used in industrial robots).
Let's take the most common one-to-one wiring as an example.
Host computer - Motion control - Driver - Motor (TRIO servo)
In practical servo applications, all companies have instruction manuals for their servo products. These manuals will invariably include servo wiring instructions. (Customers who don't have these manuals can download them from the manufacturer's website.)
Because each servo's interface is slightly different, especially when it comes to servo drivers that support multiple drives, it's even more difficult to distinguish them. Furthermore, if there's an error in the servo wiring, the servo will either alarm or stop working, and may even burn out the servo driver.
Drivers are the most expensive component in a server application, and replacing them can cost a significant amount of money.
A set of Yaskawa 400W bus motors costs 1800 yuan. (2020 price)
Wiring method for the drive power supply:
Since this involves actual driver wiring, we must use a product as an example. Let's take ESTUN's SUMMA driver as an example.
(1) Prepare tools (this is very important, especially for beginners)
Servo wiring preparation tools
Generally, you'll need a flathead screwdriver, wiring pliers, and cold-pressed terminals.
(2) Check the input voltage : The input power supply of the servo driver is single-phase AC100V, single-phase AC200V, single-phase/three-phase AC200V, and three-phase AC380V/400V.
Input voltage is AC400V, 3-phase
(3) When installing inside the electrical cabinet, leave a heat dissipation gap between the drives. They must be installed at intervals of about 10mm, not close together, and at least 30mm apart vertically.
(4) Wiring of the main power supply and control power supply of the driver.
Generally, the servo main power supply and control power supply each have pluggable terminals.
Normally, we would first disconnect these two terminals and then connect the wires. This is easier to do.
Disconnect the main power and control power terminals.
Note: The main power supply and control power supply of different drivers are not always together. You need to refer to the servo driver's instruction manual for details.
(5) Three-phase AC power connection method.
Many servo drives can be connected to three-phase power or mains power below 230V (i.e., household electricity). Common domestic servo drives use several voltage types, including 100V, 220V, 380V, and 400V. (There are also more specialized types, such as the large motors in stamping machines, which, if using dedicated power, can operate at voltages above 1000V, thus reducing the current draw of the equipment. This will not be discussed in detail here.)
Driver power cable wiring principle
From the circuit breaker to the driver, there are actually two power lines: one is the main power supply, and the other is the control power supply. The main power input consists of three wires, L1, L2, and L3, corresponding to the R, S, and T power lines. (This is being emphasized for the first time: the driver must be grounded.)
The final result is shown in the image below:
Actual wiring diagram of the driver (Omron servo)
Make sure to press the wiring firmly and straighten it.
Terminal wiring method
(6) AC unidirectional power connection
Similar to the three terms of AC
With the current sophisticated terminal blocks, we basically no longer need to connect wires directly.
(7) DC power connection
DC power input
DC power input simply adds a 24V or 48V AC-DC power supply to the main power supply and control power supply sections.
(8) Connection of driver and motor
Driver connected to motor
The motor has two wires: a power wire and a control wire. The control wire has two ports: one for the encoder (usually small) and the other for the signal output (with U/V/W indicators). This connection must be correct. Current designs have mitigated the risk of incorrect connection. Most servo wiring is pre-packaged.
The original factory-supplied servo cables are usually no longer than 5 meters. If they are longer than 5 meters, you will probably have to pay extra.
In some special situations, a 5-meter distance can meet about 90% of the application scenarios, but for some coordinate measuring machines or large-scale three-dimensional machines, a 5-meter servo cable is not enough.
The motor's power line is the one that connects to the power source; the power line and control cable are generally not placed together.
Interference suppression issues: wiring layout and noise filter wiring methods
1. When you find that the server is unstable and occasionally loses points, you must check if there is any interference.
The most common method to eliminate interference is to avoid placing the following cables in the same conduit or bundling them together.
2. Use of noise filters
If welding machines, electrical discharge machining (EDM) machines, ultrasonic welding machines, and similar products use the same power supply, or if there are high-frequency generators nearby, noise filters should be connected to the input side of both the main power cable and the control power cable.
The noise filter is connected at the power supply and driver connection point, closer to the power supply side. It should be placed near the driver.
