1.Brief introduction of closed-loop stepper motors
Closed-loop stepper motors are high-precision servo motors. By installing position sensors such as encoders or resolvers on the motor shaft, the actual position of the motor is fed back to the control system to achieve closed-loop control. This design makes the closed-loop stepper motor have the advantages of high precision, high stability and low vibration, and is suitable for occasions with high precision requirements.
2.Working principle of closed-loop stepper motors
The working principle of closed-loop stepper motors is similar to that of open-loop stepper motors. Both control the rotation angle of the motor by receiving pulse signals. The difference is that closed-loop stepper motors add a position feedback link to the control system. When the motor rotates, the position sensor detects the actual position of the motor and sends this feedback signal back to the control system. The control system adjusts the drive current and phase of the motor by comparing the input signal and the feedback signal, thereby more accurately controlling the position and speed of the motor.
3.Debugging steps of closed-loop stepper motors
1.Initialization parameters: Before wiring, the parameters need to be initialized. This includes selecting the appropriate control mode on the control card, clearing the PID parameters, ensuring that the default enable signal is off when the control card is powered on, and saving this state. Set the control mode, enable external control, encoder signal output gear ratio, and the proportional relationship between the control signal and the motor speed on the stepper motor.
2.Wiring: Power off the control card and connect the stepper motor driver and the stepper motor according to the instructions. Make sure all connections are firm and not loose.
3.Debug the stepper motor driver: Set the subdivision number, start-up speed, single-axis acceleration, and cornering acceleration of the stepper driver as needed. The higher the subdivision number, the higher the control resolution, but it will affect the maximum feed speed. The start-up speed is the highest frequency at which the stepper motor can start working directly without acceleration. Single-axis acceleration and cornering acceleration describe the acceleration and deceleration capabilities of a single feed axis and multiple feed axes when linked, respectively.
4.Use encoder feedback: In a closed-loop control system, use the encoder to feedback the real-time speed of the motor, and adjust the output of the pulse frequency after comparing it with the set value to achieve accurate speed tracking and enhance control accuracy. 5. S-type acceleration curve: Use S-type acceleration curve for smooth acceleration and deceleration control, so that the speed increases or decreases smoothly according to the set slope, and realizes smooth start and stop.
4.Optimization method of closed-loop stepper motor
1. Subdivision control: By increasing the number of teeth on the rotor, the accuracy of the stepper motor can be improved. Subdivision control can make the stepper motor move a smaller step size under each pulse, thereby improving positioning accuracy.
2.Closed-loop control: Closed-loop control is a key method to improve the accuracy and stability of stepper motors. By adding position feedback to the motor control system, the closed-loop control system can detect the actual position of the motor in real time during the motor movement and compare it with the target position. If a deviation is found, the system will send instructions for correction to ensure that the motor runs according to the expected path and speed. This method can effectively prevent step loss and vibration and improve the stability and accuracy of the system.
3.Configure a reducer: By configuring a reducer on the stepper motor, the speed of the motor can be reduced and the torque can be increased, thereby improving the stability and accuracy of the system. The function of the reducer is to reduce the rotation speed of the motor and increase the output torque. It is suitable for scenarios that require high torque and low-speed operation.
4.Use a cost-effective drive solution: For example, use the TMC4361 stepper closed-loop drive solution, which combines the TMC2130/TMC5130 (low power) or TMC2160/TMC5160 (high power) driver chip, built-in closed-loop algorithm and current control, supports S-shaped ramp acceleration and deceleration, and has the characteristics of high response, high speed and high precision.
5.Optimize current control: The performance of the stepper motor can be further improved by optimizing the current control strategy. For example, using an absolute encoder or an incremental encoder can achieve more precise position control.
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