1. Overview of Servo Motor Control Methods
Introduces common servo motor control methods, including speed control, torque control, and position control modes, as well as their characteristics and application scenarios.
(I) Speed Control Mode
Describes the speed control mode, which controls the motor speed through analog input or pulse frequency, and has a wide range of application scenarios, such as continuous speed regulation systems that require fast response.
The speed control mode has the characteristics of fast response speed and high precision. In some continuous speed regulation systems that require fast response, the speed control mode can meet the system's requirements for speed changes. For example, in an automated production line, different production links may require different speeds. The speed control mode can quickly adjust the motor speed according to production needs to improve production efficiency.
In addition, the positioning system with an upper closed loop also often adopts the speed control mode. In this system, speed control can be used as an auxiliary means of positioning control. By adjusting the speed of the motor, the motor can reach the target position quickly and accurately. At the same time, systems that require fast switching of multiple speeds are also suitable for the speed control mode. For example, some multi-functional equipment needs to switch different speeds in different working modes. The speed control mode can achieve fast switching to meet the working needs of the equipment.
(II) Torque Control Mode
DescriptionThe torque control mode is mainly used in tension control and other occasions, and the motor output torque is set by external analog input.
The torque control mode has the characteristics of precise control of torque and strict requirements on material force. In some winding and unwinding devices, such as winding devices or optical fiber pulling equipment, the torque control mode can ensure that the material force does not change with the change of winding radius. For example, in a winding device, when the winding radius changes, by adjusting the output torque of the motor, the tension of the wire can be kept constant to prevent the wire from being too loose or too tight.
In addition, in some occasions that require constant pressure, such as semiconductor wafer bonding, the torque control mode can also be used. By controlling the output torque of the motor, constant pressure control of the wafer can be achieved to ensure the bonding quality.
(III) Position Control Mode
The position control mode is commonly used in positioning occasions, and the motor running speed and angle are determined by receiving pulses.
The position control mode has the characteristics of high precision, good stability, and simple and easy-to-understand control method. Position control mode is widely used in automation equipment such as manipulators, placement machines, engraving machines, and CNC machine tools. For example, in CNC machine tools, by setting the target position, the servo motor moves to the specified position and remains stable, high-precision cutting and processing operations can be achieved.
The position control mode mainly relies on the pulse signal returned by the encoder, and determines the rotation speed and angle of the motor by controlling the frequency and number of pulses sent. In practical applications, it can be subdivided into absolute position mode and relative position mode. In absolute position mode, the motor moves directly to the specified position without being affected by the current position; in relative position mode, the motor starts from the current position and moves to the specified position relative to the current position.
2. Advantages and methods of PLC control of servo motors
(I) Advantages of PLC control
PLC control of servo motors has many advantages. First, it can implement complex control strategies. Through programming, control parameters and logic can be flexibly adjusted according to different application scenarios and needs to meet various complex motion control requirements. For example, in an automated production line, the speed, position and torque of the servo motor can be adjusted in real time according to different production processes and procedures to achieve efficient and accurate production.
Secondly, PLC can be better integrated with other automation equipment. In modern industrial automation systems, multiple devices are often required to work together. PLC can be seamlessly connected with sensors, actuators, human-machine interfaces and other devices through various communication interfaces and protocols to achieve centralized control and management of the entire system. For example, through the connection with the sensor, various parameters in the production process, such as temperature, pressure, flow, etc., can be obtained in real time. According to these parameters, the operating status of the servo motor can be adjusted to improve production quality and efficiency.
In addition, PLC has a high degree of reliability and stability. It uses advanced hardware and software technologies, and can operate stably for a long time in harsh industrial environments, reduce equipment failures and downtime, and improve production efficiency. At the same time, PLC also has rich diagnostic and alarm functions, which can detect and handle equipment failures in a timely manner to ensure the safety and stability of production.
(II) Connection method and control strategy
- Connection method
- Analog signal connection: PLC outputs analog signals through analog output modules (such as DA modules), and the driver receives the analog signals and converts them into motor operation instructions. The advantage of this connection method is that the control accuracy is high. For example, PLC outputs 0-10V or 4-20mA analog signals through analog output modules, and the driver can accurately adjust the speed and other parameters of the motor according to the size of the analog signal. However, it is susceptible to interference, which may affect the control effect in some industrial sites with complex electromagnetic environments.
- Pulse signal connection: PLC outputs pulse signals through pulse output modules (such as PWM modules), and the driver receives the pulse signals and controls the speed and direction of the motor according to the frequency and direction of the pulses. This method has strong anti-interference ability. The higher the frequency of the pulse signal, the faster the motor speed. For example, in some occasions where the speed control accuracy is not high but the anti-interference ability is high, such as step servo systems, this control method is often used.
- Communication connection: PLC communicates with the driver through a communication interface (such as RS485, CAN, etc.) to control the servo motor. Through network communication, PLC can send control instructions and receive feedback information to achieve advanced motion control functions. For example, PLC and servo system drivers are connected by buses such as EtherCAT and CANopen. PLC sends bus control instructions to the driver, the driver drives the motor to run, and the encoder feeds back the motor motion status to achieve closed-loop control. This method is suitable for complex systems and is generally suitable for high-demand projects, but the cost is also relatively high.
- Control strategy
- Point control: PLC controls the motor to run to the specified position according to the given position instruction. This method is suitable for simple positioning control, for example, in some material handling equipment, it only needs to move the material to the specified position.
- Speed control: PLC controls the motor to run at a constant speed according to the given speed command. This method is suitable for occasions that require constant speed operation, such as conveyor belt systems.
- Acceleration and deceleration control: PLC controls the motor to accelerate and decelerate according to the given acceleration and deceleration commands. This method is suitable for occasions that require smooth start and stop, such as in some equipment that requires smooth start and stop processes, such as elevators.
- Trace control: PLC controls the motor to run according to the predetermined trajectory according to the given trajectory command. This method is suitable for complex motion control, such as robot motion control.
3. Servo motor control method without PLC
(I) Multiple alternatives
In addition to PLC control of servo motors, there are many alternatives. Touch screen and driver communication is a feasible method. The touch screen sets parameters and communicates with the servo driver to control the servo motor. For example, Kunlun Tongtai touch screen can directly control the operation of servo motors and use modbus communication protocol.
Industrial computer motion module board can also be used to control servo motors. By installing the motion module board on the industrial computer, the servo motor can be controlled by software programming.
Analog signal control is also a common method. Delta servo motors can be controlled by analog signals (such as 0 - 10V or 4 - 20mA), which can be generated by various control devices, including simple relays, analog potentiometers, etc. For example, in some occasions where the speed control accuracy is not high, analog potentiometers can be used to generate analog signals to control the speed of the servo motor.
In addition, switch quantity control can also be used. If the requirements are not high, the servo motor can also be controlled directly using switch quantity. For example, the start and stop of the servo motor can be controlled by external IO to achieve simple control functions.
(II) Delta servo motor case
Delta servo motors can operate without PLC control. First, Delta servo motors are usually equipped with a controller inside, which can independently complete functions such as starting, stopping, speed and position control. The built-in control unit allows the motor to work according to preset programs or manually entered instructions even without an external controller.
Secondly, manual control is also a way. Users can start and stop the motor and adjust the speed and direction through the manual control panel or buttons on the motor.
In addition, Delta servo motors can also be used with dedicated servo drives. This drive can receive signals from various control devices, such as HMI (human-machine interface) or other controllers, but even in the absence of these devices, the drive can control the motor through built-in parameter settings.
In some simple applications, Delta servo motors can be directly connected to the power supply and operate independently with preset parameters. For example, in certain repetitive tasks on the production line, Delta servo motors can run continuously at a preset speed and direction without PLC control.
In short, Delta servo motors are designed with multiple control methods to meet different application requirements without PLC. However, in actual applications, using PLC can provide more complex and flexible control strategies, as well as better integration with other automation equipment.
4. Summary and Outlook
In summary, servo motors do not necessarily have to be controlled by PLC. In actual applications, there are many alternatives to choose from. If the control accuracy and complexity are not high, you can consider using touch screen and driver communication, industrial computer motion module board, analog signal control or switch quantity control. These methods are relatively simple, low cost, and suitable for some simple application scenarios.
However, in complex industrial automation systems, PLC control still has irreplaceable advantages. PLC can implement complex control strategies, better integrate with other automation equipment, and has high reliability and stability. Therefore, in practical applications, it is necessary to select the appropriate control method according to specific needs and application scenarios.
Looking to the future, with the continuous development of technology, the control method of servo motors will continue to innovate and improve. For example, with the development of the Internet of Things and Industry 4.0, more and more devices will realize intelligent and networked control. Servo motors will also be more intelligent, and can communicate and work with other devices through the network to achieve more efficient and precise control.
In addition, with the development of artificial intelligence and machine learning technology, the control of servo motors will become more intelligent and adaptive. For example, the operation data of servo motors can be analyzed and predicted through machine learning algorithms to achieve more accurate control and fault diagnosis.
In short, there are many ways to control servo motors. In practical applications, it is necessary to select the appropriate control method according to specific needs. In the future, with the continuous development of technology, the control method of servo motors will continue to innovate and improve, providing more powerful support for the development of industrial automation.