Stepping motor stalling detection system based on voltage driving

Abstract

The invention relates to an H-bridge driving circuit, in particular to a stepping motor locked-rotor detection system based on voltage driving, which can accurately detect external load change and realize locked-rotor detection on the basis of not increasing system devices, and comprises an H-bridge, a digital control unit and an analog comparator, the analog comparator is used for detecting the zero-crossing state of an H-bridge output current value, a timer is arranged in the digital control unit, the timer starts timing when receiving a zero-crossing signal, the timing is ended and the hysteresis Tdelay of the current lagging behind the voltage is obtained after the analog comparator is detected to turn over a signal, and the zero-crossing state of the H-bridge output current value is detected to be the zero-crossing state of the H-bridge output current value. After the rotating speed and the voltage duty ratio of the motor are set, the motor operates for a certain time under a normal load, a Tdelay 0 value in a normal operation state is obtained, a threshold value is set according to the Tdelay 0 value, and when Tdelay is smaller than the threshold value, it is judged that a locked-rotor signal is detected.

Description

Technical Field

[0001] The invention relates to an H-bridge driving circuit, and more specifically to a stepping motor stall detection system based on voltage driving. Background Art

[0002] Stepper motors are a widely used type of motor that features simple control and fast response. Normally, stepper motors do not require a feedback system, and accurate stepper control can be achieved using open-loop control. Without overloading, the control accuracy is high, making them particularly suitable for use in low-speed, high-torque scenarios. However, the above characteristics of stepper motors also result in low overload capacity. Once the external load suddenly increases, the stepper motor will be overloaded, which will further cause the stepper motor to heat up, lose steps, or even be damaged. In terms of H-bridge control, there are currently two main chopping methods, namely current chopping and voltage chopping. The current chopping scheme is to respond to the coil current measurement in each PWM cycle, which is suitable for use in situations where medium and high voltage motors are high-speed and the load changes dramatically. The disadvantage is that there is audible noise; the voltage chopping scheme is to indirectly control the current by controlling the voltage duty cycle. Since the current measurement and comparison units are omitted, it is a silent driving scheme and is suitable for use in low-voltage driven motors, especially in the field of consumer electronics that are sensitive to noise. The traditional approach is to use position sensors to monitor the loss of step, that is, the position and speed of the motor shaft are collected by the position sensor installed on the motor shaft, and the position and speed signals are fed back to the digital control system to avoid the occurrence of loss of step or stalling. However, the presence of the sensor will not only make the system signal chain complicated, installation and maintenance difficult, but will also greatly increase the system hardware cost. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a voltage-driven stepper motor stall detection system, which can accurately detect external load changes without adding system components to achieve stall detection.

[0004] The technical solution is as follows: a voltage-driven stepper motor stall detection system, characterized in that it includes an H-bridge, a digital control unit and an analog comparator, the analog comparator is used to detect the zero-crossing state of the H-bridge output current value, a timer is set in the digital control unit, and the timer starts timing when a zero-crossing signal is received. When the analog comparator flip signal is detected, the timing ends and the lag amount Tdelay of the current lagging behind the voltage is obtained. After setting the motor speed and voltage duty cycle, the motor is allowed to run for a certain period of time under normal load, and the Tdelay0 value under normal operation is obtained, and a threshold is set according to the Tdelay0 value. When Tdelay is less than the threshold, it is determined that a stall signal is detected.

[0005] After adopting the present invention, no additional sensors are needed, which reduces system cost and installation complexity, monitors and analyzes the motor load condition in real time, can quickly discover abnormal loads, and improves the safety and stability of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 This is a schematic diagram of the present invention. DETAILED DESCRIPTION

[0007] See Figure 1 As shown, a voltage-driven stepper motor stall detection system includes an H-bridge 110 (common stepper motors are bipolar, and for the sake of simplicity, only one coil and an H-bridge are drawn in the figure), a digital control unit 100, and an analog comparator 101. The digital control unit 100 includes a tail current sensing resistor 111. Similarly, the tail current sensing resistor may include an auxiliary filter device, which is not drawn here for the sake of simplicity. The analog comparator 101 detects when the tail current flowing through the tail current sensing resistor 111 crosses zero, and sends the zero-crossing comparison result to the digital control unit 100. Since the MOS switch has high-frequency switching noise, it has a greater impact on the current at the moment of the MOS switch. If the current is processed at this time, it is easy to misjudge. Therefore, there will be a shortest working time after the MOS tube is turned on. During this period of time, the analog comparator does not process the current. This period of time is called Tblank. During the Tblank time, the digital control 100 does not respond to the output result of the analog comparator 101.

[0008] In voltage chopping, the sine wave curve that determines the duty cycle is compared with the triangular carrier to generate a PWM signal, which further controls the switching state of the four MOS tubes of the H bridge. Due to the inductance characteristics of the motor, the current flowing through the motor coil will lag behind the voltage. When the load is small, the current lags more; when the load is large, the lag is smaller. Therefore, the load size can be indirectly detected by detecting the lag amount.

[0009] A timer is set in the digital control unit. When the sinusoidal voltage of the output current passes through zero, the timer starts timing and compares whether the current passes through zero during the period when the PWM signal is at a high level. When the analog comparator 101 flip signal is detected, the timing ends and the lag Tdelay of the current behind the voltage is obtained. It should be noted that since the digital control unit 100 does not respond to the output result of the analog comparator 101 during the Tblank time, the comparator will output the correct value only after the duty cycle reaches a certain value. Since the current has two zero-crossing signals in one electrical cycle, the two-phase stepper motor updates the Tdelay value every 1 / 4 electrical cycle, and the system can quickly obtain the signal.

[0010] When the external load of the motor remains unchanged, Tdelay is a stable value. When the external load increases, Tdelay will gradually decrease. Therefore, when implementing stall detection, the motor speed and voltage duty cycle are set, and the motor is allowed to run for a certain period of time under normal load to obtain the Tdelay0 value under normal operation. As long as the newly detected Tdelay is reduced to a certain threshold value, such as less than 0.5Tdelay0, it is considered that a stall signal is detected; similarly, if the threshold is set to 0.8Tdelay0, the system will detect motor stall more sensitively; different thresholds represent different sensitivities.

[0011] Figure 1 The detection resistor 111 for detecting the current direction can be omitted and replaced by a current mirror solution with MOS internal resistance, which can also detect the current direction and achieve the purpose of this patent.

[0012] The stepper motor load detection system disclosed in the present invention has the following advantages: no additional sensors are required, which reduces system cost and installation complexity, monitors and analyzes motor load conditions in real time, can quickly detect abnormal loads, and improves the safety and stability of the motor; after the hysteresis Tdelay or the stall signal is fed back to the host computer, the system can further optimize the working performance of the motor and improve the motor operation efficiency through intelligent adjustment, and can be widely used in various occasions that require real-time monitoring and control of motor loads, and has good application prospects and economic benefits.

Claims

1. A voltage-driven stepper motor stall detection system, characterized in that: It includes an H-bridge, a digital control unit and an analog comparator. The analog comparator is used to detect the zero-crossing state of the H-bridge output current value. A timer is set in the digital control unit. When a zero-crossing signal is received, the timer starts timing. When a flip signal of the analog comparator is detected, the timing ends and the hysteresis Tdelay of the current lagging behind the voltage is obtained. After setting the motor speed and the voltage duty cycle, the motor is allowed to run for a certain period of time under normal load, and the Tdelay0 value under normal operation is obtained. A threshold is set according to the Tdelay0 value. When Tdelay is less than the threshold, it is determined that a stall signal is detected.

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