In modern industrial automation control system, servo valve, as a high-precision and high-response hydraulic control element, is widely used in construction machinery, aerospace, intelligent manufacturing and other fields. As an important communication protocol of field bus, CAN(Controller Area Network) bus has become one of the preferred communication methods between servo valve and controller because of its high reliability, strong real-time performance and good anti-interference ability. This paper will elaborate the basic principle of CAN bus, the communication requirements of servo valve and its implementation on CAN bus.
I. Communication Basis of CAN Bus
CAN is a serial communication protocol widely used in industrial automatic control, automotive electronics and other fields, which has the characteristics of multi-master, non-destructive arbitration mechanism and efficient data transmission. Its communication rate can reach 1 Mbps, and the communication distance can be flexibly adjusted according to the rate within 5000 meters. Because CAN bus adopts differential signal transmission mode, it has strong anti-electromagnetic interference ability and is very suitable for complex electromagnetic environment in industrial field.
The frame format of standard CAN protocol includes data frame, remote frame, error frame and overload frame, among which data frame is used to transmit effective data and is the most commonly used frame type in servo valve communication.
Second, the servo valve communication demand analysis
Servo valve usually needs to receive control instructions sent by the controller, such as target position, speed, pressure or flow rate and other parameters, and feed back the actual working state such as pressure, position, temperature and other information. The transmission of these data requires high real-time and reliability to ensure the stability and response speed of the system.
Traditional servo valves mostly adopt analog control methods, such as 10 V voltage or 4~20mA current control, but there are some problems such as poor anti-interference ability and complicated wiring. After adopting CAN bus communication, it not only improves the anti-interference ability of communication, but also realizes the efficient networking of multi-parameters and multi-devices, which greatly improves the maintainability and expansibility of the system.
Third, the realization of servo valve communication on CAN bus.
The servo valve is connected with the upper controller through the CAN communication interface, and a microcontroller (MCU) is usually embedded to analyze the CAN protocol and convert the received instructions into driving signals to control the position of the valve core. At the same time, the feedback information collected by the sensor in the valve is also fed back to the controller through CAN to realize closed-loop control.
In terms of communication protocol, servo valves usually follow high-level protocols such as CANopen or DeviceNet. Among them, CANopen, based on CAN protocol, defines mechanisms such as object dictionary, PDO (process data object) and service data objects (), which is suitable for multi-axis control and distributed systems, and is one of the most widely used protocols in servo valve communication.
For example, the controller updates the target position or speed of the servo valve by sending PDO data packets, and the servo valve periodically sends its own status information, such as current position and working current. If you need to modify the parameters, you can read and write through SDO to realize remote configuration.
Fourth, application advantages and future prospects
The servo valve system using CAN bus communication has the following obvious advantages:
1. Simplify wiring structure: reduce the use of a large number of analog signal lines and reduce system complexity;
2. Improve control accuracy and response speed: digital communication avoids analog signal drift and improves system stability;
3. Enhance the maintainability of the system: the fault CAN be quickly located through CAN diagnostic information;
4. Support multi-device networking: it is convenient to build a complex multi-axis control system.
In the future, with the development of industrial Internet of Things (IIoT) and intelligent manufacturing, CAN bus will be further integrated with Ethernet technology, and higher bandwidth protocols such as CAN FD(Flexible Data-rate) will appear, providing more efficient and intelligent communication support for servo valves.
tag
With the help of CAN bus communication technology, the servo valve not only improves the intelligence and integration level of the control system, but also injects new vitality into the development of industrial automation. With the continuous progress of related technologies, servo valve communication based on CAN bus will play an important role in more high-end application fields.