Servo drives are an important component of modern motion control and are widely used in automated equipment such as industrial robots and CNC machining centers. Generally, servos have three control modes: position control, torque control, and speed control.
1. Position control
Position control mode typically determines the rotation speed by the frequency of externally input pulses and the rotation angle by the number of pulses. Some servos can also directly assign speed and displacement values via communication. Because position mode can provide very strict control over both speed and position, it is generally used in positioning devices.
2. Torque Control
Torque control is achieved by setting the output torque of the motor shaft through external analog input or direct address assignment. The torque setting can be changed in real time by altering the analog input, or by changing the corresponding address value via communication.
The main applications are in winding and unwinding devices that have strict requirements on the material, such as winding devices or optical fiber drawing equipment. The torque setting must be changed at any time according to the change of the winding radius to ensure that the stress on the material does not change with the change of the winding radius.
3. Speed Mode
Rotational speed can be controlled via analog input or pulse frequency. In speed mode, positioning can also be achieved with outer-loop PID control from a higher-level control unit, but the motor position signal or the position signal from the direct load must be fed back to the higher-level unit for calculation. Position mode also supports direct load outer-loop position signal detection. In this case, the encoder at the motor shaft end only detects the motor speed, and the position signal is provided by the detection device at the direct final load end. This reduces errors in the intermediate transmission process and increases the overall positioning accuracy of the system.
If there are no requirements for the speed or position of the motor, and all that is needed is a constant torque output, then torque mode is the appropriate choice.
If you have certain accuracy requirements for position and speed, but are not very concerned about real-time torque, torque mode is not very convenient, and speed or position mode is better.
If the host controller has good closed-loop control, speed control will be more effective. If the requirements are not very high or there are basically no real-time requirements, position control can be used.
Servo drives, also known as servo controllers or servo amplifiers, are controllers used to control servo motors. Their function is similar to that of a frequency converter for a regular AC motor. They are part of a servo system and are primarily used in high-precision positioning systems. Generally, they control the servo motor through position, speed, and torque to achieve high-precision positioning of the transmission system. Currently, they represent a high-end product in transmission technology.
Servo drives are an important component of modern motion control and are widely used in automated equipment such as industrial robots and CNC machining centers. Servo drives for controlling AC permanent magnet synchronous motors, in particular, have become a research hotspot both domestically and internationally. Current AC servo drive designs commonly employ a three-loop control algorithm based on vector control, encompassing current, speed, and position. The rationality of the speed closed-loop design within this algorithm plays a crucial role in the overall performance of the servo control system, especially in terms of speed control performance.
In the speed closed loop of a servo drive, the real-time speed measurement accuracy of the motor rotor is crucial for improving the dynamic and static characteristics of the speed loop's speed control. To achieve a balance between measurement accuracy and system cost, incremental photoelectric encoders are generally used as speed sensors, and the commonly used speed measurement method is the M/T (Mean Transmission/Turning) method. While the M/T method offers a certain level of measurement accuracy and a relatively wide measurement range, it has inherent drawbacks, primarily including:
1. At least one complete encoder pulse must be detected within the speed measurement cycle, which limits the minimum measurable speed;
2. The timer switches of the two control systems used for speed measurement are difficult to keep strictly synchronized, which cannot guarantee speed measurement accuracy in situations where speed changes significantly. Therefore, traditional speed loop designs using this speed measurement method are unlikely to improve the speed tracking and control performance of the servo driver.
Currently, most mainstream servo drives use digital signal processors (DSPs) as their control core, enabling complex control algorithms and achieving digitalization, networking, and intelligence. Power devices generally employ drive circuits designed around intelligent power modules (IPMs). The IPM integrates the drive circuitry and includes fault detection and protection circuits for overvoltage, overcurrent, overheating, and undervoltage. A soft-start circuit is also added to the main circuit to reduce the impact on the driver during startup. The power drive unit first rectifies the input three-phase power or mains power through a three-phase full-bridge rectifier circuit to obtain the corresponding DC power. The rectified three-phase power or mains power is then frequency-converted by a three-phase sinusoidal PWM voltage-type inverter to drive the three-phase permanent magnet synchronous AC servo motor. The entire process of the power drive unit can be simply described as an AC-DC-AC process. The main topology of the rectifier unit (AC-DC) is a three-phase full-bridge uncontrolled rectifier circuit.
With the large-scale application of servo systems, the use, debugging, and repair of servo drives are important technical issues in servo drive technology today, and more and more industrial control technology service providers are conducting in-depth research on servo drives.
Servo drives are an important component of modern motion control and are widely used in automated equipment such as industrial robots and CNC machining centers. Servo drives for controlling AC permanent magnet synchronous motors, in particular, have become a research hotspot both domestically and internationally. Current AC servo drive designs commonly employ a three-loop control algorithm based on vector control, encompassing current, speed, and position. The rationality of the speed closed-loop design within this algorithm plays a crucial role in the overall performance of the servo control system, especially in terms of speed control performance.
