I. What is a servo?
1. What is a server? Why use a server?
Servo system definition: A control system that enables the output variable to accurately follow or reproduce the input variable. With increasingly demanding requirements for motion control, servo control has emerged.
2. What is a servo motor? What are its characteristics?
Servo motors, also known as actuator motors, are used as actuators in automatic control systems to convert received electrical signals into angular displacement or angular velocity output on the motor shaft. They are divided into two main categories: DC and AC servo motors. Their main characteristic is that they do not rotate when the signal voltage is zero, and their speed decreases uniformly as the torque increases.
II. How to implement servo control?
Servo systems primarily rely on pulses for positioning. Essentially, a servo motor receives one pulse and rotates by the angle corresponding to that pulse, thus achieving displacement. Because the servo motor itself has the function of emitting pulses, it emits a corresponding number of pulses for each rotation angle. This creates a feedback loop with the pulses received by the servo motor, or a closed loop. In this way, the system knows how many pulses were sent to the servo motor and how many were received, enabling precise control of the motor's rotation and achieving accurate positioning down to 0.001mm.
In servo drive systems, pulse-based control is generally used in simple servo applications with low requirements. As is well known, there is a certain delay in sending and receiving pulses. Only bus-type servo drives (i.e., absolute servos or EtherCAT servos) with bus control can truly achieve isochronous synchronization because bus communication is faster and can directly send speed or position setpoints. Therefore, high-end servo applications use bus control.
III. Bus-type servo vs. pulse-type servo
Bus-type servo drives offer high flexibility and cost-effectiveness, and their advantages over pulse-type servos are as follows:
1. Saves wiring costs, reduces wiring time, and decreases the chance of errors. One bus communication port of the controller can connect multiple servos, which can be connected to each other using a simple RJ45 port, shortening the construction cycle.
2. Greater information capacity: Fully digital information interaction allows for bidirectional transmission of many parameters, commands, and status data; pulse mode can only transmit position or speed information unidirectionally and cannot obtain more status or parameters of the servo.
3. High precision, digital communication: no signal drift problem, and the precision of command and feedback data can reach 32 bits.
4. Higher reliability and stronger anti-interference capability; no pulse loss occurs. Pulse/direction control becomes unreliable at high speeds.
5. Reduce the total system cost. When there are more than two servos, there is no need to adjust the controller configuration. However, pulse-type servos require the addition of pulse or axis control modules. When there are a large number of servos, it may even be necessary to use higher-level controller hardware to meet the requirements.
6. It enables the development of devices with more powerful software functions without requiring additional hardware or wiring: The controller can monitor servo motor faults in real time via the bus and display them on the teach pendant. Simultaneously, the controller can monitor the actual position and speed of the servo motor, and can automatically adjust servo parameters as needed. Servo parameters can be set in the teach pendant without modifying them on the servo panel, making it simple, intuitive, and less prone to errors.
7. Adopting a standard motion function block library improves programming and debugging efficiency: The adoption of a bus system solution avoids the problems of large programming volume and complex debugging of traditional pulse direction control methods, thereby improving efficiency and saving costs and time.
8. It can achieve remote control, which is very convenient when the production line equipment is long or the number of servos is large, and the installation cost is low.
9. Enhanced maintainability, with more status and diagnostic information. Bus control is currently very popular in Europe and America for CNC and motion control.
IV. Summary of the advantages of bus-type servos
1. Simplified wiring. Traditional controllers require approximately 13 to 16 wires per axis, and if feedback is needed, an additional 6 to 8 wires are required; while using a bus only requires 2 cables.
2. Good EMI/EMC: Traditional wiring methods have a grounding point problem for each unit's signal transmission. Due to the harsh industrial environment, the grounding point may drift and be easily interfered with.
3. Flexible and simple control mode.
4. High synchronization and real-time operation, high reliability and redundancy.
5. High-isolation electrostatic impedance device protection.
6. Small common-mode error.
7. Real-time reading of parameters and diagnostic data via the bus simplifies equipment debugging and maintenance.
