introduction

In many fields such as industrial automation, robotics, and semiconductor manufacturing, high-precision torque control is the key to ensuring stable equipment operation and product quality. DD motor (Direct Drive Motor) has become an ideal choice for achieving high-precision torque control due to its characteristics of low-speed high torque, high-precision positioning, and high response speed. However, to fully utilize the performance of DD motors, effective control strategies need to be adopted.

DD motor characteristics and torque control requirements

The DD motor generates a magnetic field by exciting current, causing the rotor to rotate on a fixed stator. The rotor adopts an external rotor design, consisting of permanent magnets, while the stator is composed of an annular iron core, windings, and a three-phase power supply system. This structure enables DD motors to have the characteristics of low speed and high torque, which can output large torque at low speeds and meet some application scenarios with high torque requirements. Meanwhile, the high-precision positioning capability of DD motors is thanks to their high-resolution encoder and precise current control, which enables real-time monitoring and precise adjustment of rotor position and speed.

In practical applications, different devices have different requirements for torque control. For example, in semiconductor manufacturing equipment, wafer handling robots need to achieve high-precision torque control in a very small space to ensure safe handling and precise placement of wafers; In industrial robots, joint drive needs to achieve smooth and accurate torque output to ensure the motion accuracy and repetitive positioning accuracy of the robot. Therefore, corresponding torque control strategies need to be developed for different application requirements.

High precision torque control strategy

Current control strategy

Current control is the foundation for achieving torque control of DD motors. By precisely controlling the magnitude and waveform of the current supplied to the DD motor, the output torque of the motor can be adjusted. Common current control methods include PID control, fuzzy control, etc.

PID control is a classic control method that adjusts the deviation between the set value and the actual value according to the laws of proportionality, integration, and differentiation. In the current control of DD motors, PID controllers can adjust the current supplied to the motor based on the deviation between the set torque value and the actual output torque value, so that the output torque gradually approaches the set value. Fuzzy control is a control method based on fuzzy logic, which does not require an accurate mathematical model. Instead, it formulates fuzzy rules based on expert experience and knowledge, fuzzifies the input variables, and then obtains the fuzzy values of the output variables through fuzzy inference. After deblurring, the actual current control quantity is obtained. Fuzzy control has strong robustness and adaptability, and can better cope with system uncertainty and nonlinearity.

To further improve the accuracy of current control, current prediction control method can be adopted. By modeling and simulating the mathematical model of DD motor, this method predicts the current and torque changes in the future and adjusts the control input in advance, thus reducing the dynamic error of the system.

The combination of position control and torque control

In some application scenarios, it is necessary to achieve both position control and torque control simultaneously. For example, in the joint drive of industrial robots, it is not only necessary to control the position of the joints, but also to control the output torque of the joints to ensure the smoothness and safety of the robot's motion.

Position control usually uses encoders or absolute value encoders to monitor the actual position of the motor rotor in real time, compare it with the target position, and achieve accurate position control by adjusting the current or voltage. Torque control is achieved through current control. In order to organically combine position control and torque control, torque feedforward control method can be used. This method calculates the required torque in advance based on the output of the position controller and the dynamic model of the system, and adds it as a feedforward signal to the torque controller to improve the response speed and control accuracy of the system.

Anti interference control strategy

In practical applications, DD motor systems are subject to various interference factors, such as load changes, power fluctuations, electromagnetic interference, etc. These interference factors can cause fluctuations in output torque, affecting the control accuracy of the system. Therefore, it is necessary to adopt anti-interference control strategies to suppress the impact of interference.

A common anti-interference control strategy is to use observer technology. The observer can estimate the state variables and disturbance variables of the system in real time, and feed them back to the controller to compensate for the control input. For example, using an extended Kalman filter can simultaneously estimate the system's state and disturbances, thereby improving the system's anti-interference ability. In addition, adaptive control methods can be used to automatically adjust control parameters based on the real-time operating status of the system, so that the system can maintain stable performance under different working conditions.

The role of sensors and feedback systems in high-precision torque control

Sensors and feedback systems are key components for achieving high-precision torque control. Common sensors include Hall sensors, photoelectric sensors, and magnetic encoders. Hall sensors can detect changes in magnetic fields, thereby achieving measurements of rotor position and velocity; Photoelectric sensors use the principle of reflection or transmission of light to detect the position and motion of objects; The magnetic encoder obtains the position and velocity information of the rotor by measuring the changes in the magnetic field.

A high-resolution encoder is an important component of the DD motor feedback system, which can detect the position and speed information of the rotor in real time and feed this information back to the controller. The controller uses corresponding control algorithms based on feedback information to adjust the current supplied to the DD motor, thereby achieving precise control of torque. For example, some high-precision DD motors are equipped with encoders with a resolution of up to tens of thousands of lines, and their absolute precision control can usually reach within 15 seconds, which can meet the needs of high-precision applications.

In order to improve the reliability and accuracy of the feedback system, redundancy design methods can be adopted. Multiple sensors are used to monitor the system's status simultaneously, and the monitoring results are fused to improve the system's fault tolerance and measurement accuracy.

Practical application case analysis

Application in Semiconductor Manufacturing Equipment

In semiconductor manufacturing equipment, wafer handling robots need to achieve high-precision torque control. A certain wafer handling robot adopts a high-precision torque control strategy based on DD motors, combined with current control, position control, and anti-interference control methods. By precisely controlling the current supplied to the DD motor, precise adjustment of the joint torque of the robot has been achieved. At the same time, a high-resolution encoder is used to monitor the position and velocity information of the robot in real time, and this information is fed back to the controller, achieving precise control of the robot's motion trajectory. In practical applications, the positioning accuracy of the wafer handling robot has reached ± 1 μ m, and the torque control accuracy has reached ± 0.1N · m, meeting the high-precision requirements of semiconductor manufacturing.

Applications in Industrial Robots

In the field of industrial robots, a certain six axis industrial robot uses DD motors as joint drives and adopts a torque control strategy based on torque feedforward control and observer technology. By using torque feedforward control, the required torque for robot joint motion is calculated in advance and added as a feedforward signal to the torque controller, which improves the system's response speed and control accuracy. At the same time, observer technology is used to estimate the disturbance variables of the system in real time and compensate for the control inputs, suppressing the impact of disturbances on system performance. In practical applications, the repeated positioning accuracy of the industrial robot has reached ± 0.01mm, and the motion stability has been significantly improved, which can meet the requirements of high precision and high efficiency in industrial production.

conclusion

The high-precision torque control strategy based on DD motor is one of the key technologies for achieving industrial automation and intelligent manufacturing. By adopting strategies such as combining current control, position control, and torque control, anti-interference control, and selecting sensors and feedback systems reasonably, the torque control accuracy and stability of DD motors can be effectively improved. In practical applications, it is necessary to select appropriate control strategies and hardware devices based on different application requirements and working environments, and optimize and combine them to achieve the best control effect. With the continuous development of motor technology and control technology, high-precision torque control strategies based on DD motors will continue to be improved and innovated, providing more reliable technical support for the development of various fields.