CN116232141A

CN116232141A - Micro-step subdivision driving system of high-precision stepping motor

Info

Publication number: CN116232141A
Application number: CN202310034191.2A
Authority: CN
Inventors: 黄海滨; 马辉
Original assignee: Hangzhou Sitai Microelectronics Co ltd
Current assignee: Hangzhou Sitai Microelectronics Co ltd
Priority date: 2023-01-10
Filing date: 2023-01-10
Publication date: 2023-06-06

Abstract

The invention relates to the technical field of stepping motor driving, in particular to a high-precision stepping motor micro-step subdivision driving system which can ensure that undistorted coil current waveforms are obtained and comprises an H-bridge circuit, and is characterized in that two MOS (metal oxide semiconductor) tubes at the lower part of the H-bridge circuit are respectively connected with a tail current induction resistor and the input end of a comparator module, the input end of the comparator module is also connected with the digital waveform output end of a digital controller, and the output end of the comparator module is connected with the input end of the digital controller; the digital controller processes the comparator signals to obtain back electromotive force correction signals, and the digital controller outputs H-bridge control signals with the back electromotive force correction signals to the H-bridge circuit.

Description

Micro-step subdivision driving system of high-precision stepping motor

Technical Field

The invention relates to the technical field of stepping motor driving, in particular to a high-precision stepping motor micro-step subdivision driving system.

Background

The H-bridge driving circuit has wide application in the motor driving field, and can output current (power) through the MOS tube with the same type (N type) or the different type (P type and N type) on the upper bridge arm and the lower bridge arm, thereby being capable of efficiently driving power peripherals such as a motor. For some motor types that require precise control, such as stepper motors, precise control of the current output by the H-bridge is required to achieve less torque ripple and noise.

In the H-bridge driving circuit, as shown in FIG. 1, four MOS transistors (101-104) form an H-bridge for driving a motor coil. The driving voltage of the H bridge (the gate voltage applied to the four MOS transistors 101-104) adopts a pulse width modulation mode (also called a chopping mode), and the driving voltage is composed of pulse width modulation periods with fixed frequency: when the H-bridge works, if the MOS tube 101 and the MOS tube 104 are conducted simultaneously, the current direction is shown by a solid arrow 107 in the figure. When the H-bridge drive reaches the required current, the

MOS transistors

101 and 104 will be turned off, and since the motor load is a winding coil, it presents an inductance characteristic, and after the drive is turned off, the coil current will continue to flow according to the original direction (freewheeling characteristic):

the common freewheel mode is to turn off the

upper MOS transistors

101, 103 and turn on the

lower MOS transistors

102, 104, and the current direction is shown by the dashed arrow 106. Because of its operating characteristics, the current of this freewheel mode is smaller, so the voltage difference across the load drops more slowly, known as slow decay;

slow decay generally exhibits a smoother current waveform and a stable motor operating condition, but is susceptible to distortion when the current waveform frequency is increased due to the effects of back emf;

in a micro-step subdivision system, to ensure that the current flowing through the motor coil is sinusoidal, the current needs to be precisely controlled by controlling the H-bridge. Typically this control is achieved in two ways, open loop and closed loop:

open loop is simply the current through each point in the voltage duty cycle defined waveform. The method has the advantages that the algorithm is simple, and is not easily influenced by the system measurement error; however, the disadvantage is that the back electromotive force inside the coil can cause distortion of the coil current waveform with the increase of the motor rotation speed; the closed loop control is complex, and the voltage of the H bridge is controlled to change the duty ratio by measuring the current flowing through the coil, so that a more accurate current waveform is obtained. The method has the advantages of accurate current control, complex current and digital algorithm, and difficult control due to the problem of a measuring circuit.

Disclosure of Invention

In order to solve the problem that the waveform of coil current is distorted due to the increase of the rotating speed of a motor in the existing open-loop control mode, the invention provides a high-precision micro-step subdivision driving system of a stepping motor, which can ensure that the waveform of coil current is undistorted.

The technical scheme is as follows: the high-precision stepping motor micro-step subdivision driving system comprises an H-bridge circuit, and is characterized in that two MOS tubes at the lower part of the H-bridge circuit are respectively connected with a tail current sensing resistor and the input end of a comparator module, the input end of the comparator module is also connected with the digital waveform output end of a digital controller, and the output end of the comparator module is connected with the input end of the digital controller; the digital controller processes the comparator signals to obtain back electromotive force correction signals, and the digital controller outputs H-bridge control signals with the back electromotive force correction signals to the H-bridge circuit.

The digital waveform output end of the digital controller is connected with the two-way analog comparator through the digital-to-analog converter;

the digital controller comprises a counter electromotive force measuring module and a sinusoidal PWM waveform correcting module, wherein the counter electromotive force measuring module is used for timing a comparator signal to respectively obtain current driving time tdrive, current decay time tdecay and a complete stepping period. The waveform of the method consists of steps of current steady states, the period of each step is a micro-step subdivision period, a single micro-step subdivision period can be subdivided into a plurality of normal working periods consisting of a current charging process and a slow attenuation process, a plurality of back electromotive force detection periods are inserted into the periods, the detection periods comprise charging duration and attenuation duration, timing is carried out when the charging duration is started, the attenuation period is started after the current reaches a preset current target value, and the attenuation period is ended after the current is attenuated to the preset current attenuation target value, so that continuously-changed information is obtained; the sine PWM waveform correction module corrects a coil current target value and a detected counter electromotive force value which are controlled by a system to obtain a control waveform, and the control waveform compensates the influence of the counter electromotive force on the coil current, so that a coil current waveform close to a control target is finally obtained.

After the invention is adopted, the digital waveform signal output by the digital controller is compared with the tail current signal of the H bridge circuit, and the counter electromotive force correction signal is obtained through the processing of the digital controller, so that the undistorted coil current waveform is finally obtained.

Drawings

FIG. 1 is a schematic diagram of a prior H-bridge circuit;

FIG. 2 is a schematic diagram of the present invention;

FIG. 3 is a schematic diagram of a comparator module;

fig. 4 is a schematic diagram of a standard sine wave current, back emf waveform and actual distortion waveform;

FIG. 5 is a schematic diagram of a timing module;

fig. 6 is a schematic diagram of a back emf detection process;

fig. 7 is a schematic diagram of waveform correction.

Detailed Description

As shown in fig. 2, a high-precision stepping motor micro-step subdivision driving system comprises an H-bridge circuit, wherein two MOS tubes at the lower part of the H-bridge circuit are respectively connected with a tail current sensing resistor and an input end of a comparator module, the input end of the comparator module is also connected with a digital waveform output end of a digital controller, and the output end of the comparator module is connected with the input end of the digital controller; the digital controller processes the comparator signals to obtain back electromotive force correction signals, and the digital controller outputs H-bridge control signals with the back electromotive force correction signals to the H-bridge circuit.

See fig. 3, where 301, 302 are digital-to-analog converters and 303 are two-way comparators. 301. 302 are derived from the digital controller 200, digital-to-analog converted by digital-to-analog converters 301, 302, and then compared with the tail current of the H-bridge by a two-way comparator 303, and the comparison result is sent to the digital controller 200. Digital to analog converters and analog comparators are used instead of digital to analog converters to perform digital comparisons after conversion, because digital to analog converters are generally faster than analog to digital converters in converters of the same accuracy. In the present invention, the timely comparison result is very important for the final control accuracy.

As shown in fig. 4, the digital control system 200 converts the sine wave drive voltage (401 waveform) into a PWM waveform and drives the MOS transistors 204 to 207 on the H-bridge. The purpose of the drive at this time is that the phase current flowing through the load on the H-bridge exhibits a sinusoidal character, i.e.: a sine wave current corresponding to the driving voltage 401. However, as the motor 208 starts to rotate, its stator coils cut magnetic lines of force causing back emf to be generated, such as: the back emf equivalent power supply shown at 209 in fig. 2 has a waveform as shown by the dashed waveform 402 in fig. 3. It should be noted that, along with the rotation of the magnetic force lines inside the motor, the direction and the amplitude of the back electromotive force 209 are also continuously changed (402 waveform); just because of the existence of the back emf 209 (402 waveform), the voltage across the load on the H-bridge is not actually sinusoidal as shown by the 401 waveform, thus resulting in a waveform in which the current 403 flowing through the stepper motor coil does not correspond exactly to the sinusoidal current of the 401 waveform, but is distorted by the back emf; the precise current control strategy in the present invention is to induce the back emf in the motor coil in real time (209 in fig. 2) and then compensate in the H-bridge drive signal to obtain a more precise sinusoidal current under the condition of rotating the motor back emf. The digital control part 200 in fig. 2 receives the current comparison signal output by the comparator 303 in fig. 3.

As shown in fig. 5, in which the comparator signal is clocked 501 to obtain the current driving time tdrive and the current decay time tdecay, respectively, it should be noted that the decays of the H-bridge are all formed by slow decays, so that a relatively stable decay rate can be obtained. Since it is difficult to directly measure the back emf, it is desirable to measure the back emf indirectly through the current drive time and the current decay time. Referring to the following description, due to the existence of back electromotive force, under the same external condition, the current decay time shows different change rules: as the back emf increases/decreases, the decay time increases or decreases, wherein the polarity of the increase or decrease is related to the current decay direction of the back emf. 502, calculating the back electromotive force detected by the system and the current waveform to give a current signal with a back electromotive force correction signal, thereby obtaining a current waveform which is not influenced by the current back electromotive force.

The back emf detection process of the present invention is shown in fig. 6, where 600 is a complete stepping cycle. The waveform is composed of individual steps of current steady state, the period 601 of these steps is the period of micro-step subdivision, and the number of steps is the micro-step subdivision fraction. Taking a single micro-step subdivision period 602 as an example, it may be subdivided into several normal operating periods of current charging process 610 and slow decay process 611. In the present invention, the digital control system will insert several back emf detection periods in these periods, which are made up of 612 and 613. Unlike the normal duty cycle described above, the charge duration 612 and decay duration 613 of this detection cycle are not predefined by the system, but rather are measured: timing is started when 612, the decay period starts after the current reaches the preset current target value 603, and the decay period 613 ends after the current decays to the preset current decay target value 604. In the absence of the effect of back emf, it can be seen from fig. 1 that the rate of current decay is substantially uniform, but due to the presence of back emf, the rate of current decay in 613 and 611 varies with the magnitude and direction of back emf, due to the difference in

back emf

620 and 621. Since the detection system of the present invention detects the back emf at every micro-step subdivision period, it is possible to obtain continuously variable information, i.e., the waveform 402 of fig. 4.

After the accurate information of the counter electromotive force is obtained, the micro-step subdivision control system corrects the predefined sinusoidal PWM waveform according to the intensity of the current counter electromotive force so as to offset the influence of the counter electromotive force; this function is completed in 502. As shown in fig. 7, where 701 is the system controlled coil current target value (standard sinusoidal waveform) and 702 is the detected back emf value. If no correction is made to the control waveform, the final coil current value will be the distorted current value. But the correction of 701 is performed according to 702 to obtain a control waveform 710 that better compensates for the influence of back emf 702 on the coil current, thereby ultimately obtaining a coil current waveform that approximates the control target 701.

Claims

1. The high-precision stepping motor micro-step subdivision driving system comprises an H-bridge circuit, and is characterized in that two MOS tubes at the lower part of the H-bridge circuit are respectively connected with a tail current sensing resistor and the input end of a comparator module, the input end of the comparator module is also connected with the digital waveform output end of a digital controller, and the output end of the comparator module is connected with the input end of the digital controller; the digital controller processes the comparator signals to obtain back electromotive force correction signals, and the digital controller outputs H-bridge control signals with the back electromotive force correction signals to the H-bridge circuit.

2. The high-precision stepping motor micro-step subdivision driving system of claim 1, wherein the comparator module comprises a two-way analog comparator and two digital-to-analog converters, and the digital waveform output end of the digital controller is connected with the two-way analog comparator through the digital-to-analog converters.

3. The micro-step subdivision driving system of the high-precision stepping motor according to claim 1, wherein the digital controller comprises a counter electromotive force measuring module and a sinusoidal PWM waveform correction module, the counter electromotive force measuring module counts a comparator signal to respectively obtain a current driving time tdrive and a current attenuation time tdecay, a complete stepping period is formed by steps of current steady states, the period of each step is a micro-step subdivision period, a single micro-step subdivision period can be subdivided into a plurality of normal working periods consisting of a current charging process and a slow attenuation process, a plurality of counter electromotive force detection periods are inserted into the periods, the detection periods comprise a charging time length and an attenuation time length, the counting is performed when the charging time length is started, the attenuation period is started after the current reaches a preset current target value, and the attenuation period is ended after the current is attenuated to the preset current attenuation target value, and continuously-changed information is obtained; the sine PWM waveform correction module corrects a coil current target value and a detected counter electromotive force value which are controlled by a system to obtain a control waveform, and the control waveform compensates the influence of the counter electromotive force on the coil current, so that a coil current waveform close to a control target is finally obtained.