Prevents step-out and error when stepping motor is running - Database & Sql Blog Articles

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The stepping motor is a kind of digital actuator with good performance. In the point control of the numerical control system, the stepping motor can be used as the driving motor. In open loop control, the stepper motor is controlled by pulses of a certain frequency. Directly generating pulses by plc to control the stepper motor can effectively simplify the hardware circuit of the system and further improve reliability. Since the PLC works in a cyclic scan mode, its scanning period is generally between several milliseconds and tens of milliseconds. Therefore, the stepping motor cannot work at high frequencies due to the limitation of the PLC working mode and the scanning cycle. For example, if the pulse frequency of the stepping motor is controlled to 4000HZ, the pulse period is 0.25 milliseconds, so that the pulse period is much smaller than the scan period, and the frequency is used to control the stepping motor. Then the PLC has issued many control pulses when the output refresh task has not been completed, but the stepper motor still does not move, and there is a serious out-of-step phenomenon. If the pulse frequency of the stepping motor is controlled to be 100 Hz, the pulse period is 10 milliseconds, which is about the same order of magnitude as the scanning period of the PLC, and a large error may occur when the stepping motor is running. Therefore, when using the PLC to drive the stepping motor, in order to prevent the stepping motor from running out of step and error, the stepping motor should be operated at low frequency, and the pulse signal frequency is selected to be about ten to several tens of hertz, which can be realized by programming. . The contradiction between ensuring the positioning accuracy and increasing the positioning speed The speed of the stepping motor is proportional to the frequency of its control pulse. When the stepping motor is running at very low frequency, its rotation speed must be very low. In order to ensure the positioning accuracy of the system, the pulse equivalent is the distance that the tool or the table moves when the stepping motor rotates to a step angle. The two factors together bring a prominent problem: the positioning time is too long. . For example, if the working frequency of the stepping motor is 20HZ, that is, 50ms one step, and the pulse equivalent is δ=0.01mm/step, the distance of the tool or table moving in 1 second is 20x0.01=0.2mm, 1 minute moving The distance is 60x0.2=12mm. If the positioning distance is 120mm, the positioning time takes 10 minutes. Such slow positioning speed is unbearable in actual operation.
In order to ensure the positioning accuracy, the pulse equivalent can not be too large, but it affects the positioning speed. Therefore, how to improve the positioning speed while ensuring the positioning accuracy is a problem that needs to be seriously considered and effectively solved.