JPH01194896A - Driving unit for stepping motor - Google Patents

Abstract

PURPOSE:To prevent generated torque from being lowered at the time of driving at a high speed without increasing applied voltage, by changing the distribution ratio of phase current distributed unequally stepwise, to drive a device, when driving frequency exceeds specified frequency. CONSTITUTION:By a constant-current driving circuit 2, a stepping motor 1 is properly driven and controlled according to a signal from a reference current value switching circuit 6 and a control circuit 3. By a driving frequency monitor 50 connected to the constant-current driving circuit 2, the driving frequency of the stepping motor 1 is always monitored, and when the driving frequency of the stepping motor 1 comes to the specified frequency, for example, when the driving frequency comes to one at which the generated torque begins to decrease, the decrease is detected by the control circuit 3, and optimum control is performed so that the lowering of the torque of the stepping motor 1 may be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a step motor drive device used for controlling a throttle valve of an engine, for example.

[Prior Art and Problems to be Solved by the Invention] For example, a step motor driving method disclosed in Japanese Patent Application Laid-Open No. 60-200798 has a method that reduces the torque generated when the step motor is driven at high speed by reducing the voltage applied to the step motor. Change (
The aim is to improve this by increasing or decreasing the

For example, in cars, motorcycles, etc., the applied voltage (
In other words, if the voltage (battery voltage) is low and constant, such as 12 V DC, and difficult to change, the torque generated by the step motor cannot be improved even if the control described in the above publication is performed. If this is not possible, the decrease in the torque generated when the steering knob motor is driven at high speed still remains, and since the applied voltage is low, the decrease in the torque generated when the steering knob motor is driven at high speed is also noticeable. usually,
When driving at high speed with a low applied voltage, it is common to use constant current driving in which the generated torque is not affected much by the applied voltage, but even if this constant current driving is used,
With an applied voltage of approximately 12 V DC, there is a problem in that a decrease in generated torque during high-speed driving is unavoidable.

[Means to solve the problem]

The present invention includes a pair of constant current drive circuits that supply current to the windings of one phase and the other phase of the step motor, a control circuit that supplies control signals to the constant current drive circuits, and A reference current value switching circuit is provided that supplies a reference current value signal to the constant current drive circuit, and the control circuit corrects the torque drop using only the drive frequency of the step motor as a parameter and sends the reference current value signal to the reference current value switching circuit. It is possible to supply a switching command signal and a drive command signal to the constant current drive circuit, respectively, so that the switching command signal and the drive command signal can be supplied to the constant current drive circuit, respectively, so that the switching command signal and the drive command signal can be supplied to the constant current drive circuit, respectively.
A step motor driving device is provided, characterized in that the proportion of phase currents that are unevenly distributed in a stepwise manner and supplied to the step motor is changed.

[For production]

In the device according to the present invention, when the drive frequency of the step motor exceeds a predetermined frequency, the step motor is driven by changing the distribution ratio of the phase current, which is unevenly distributed in the form of two steps. (Improve the decrease in generated torque during high-speed driving without increasing the voltage.)

〔Example〕

FIG. 1 is a diagram showing a step motor driving device as an embodiment of the present invention.

Referring to FIG. 1, the control circuit 3 sends control signals to the constant current drive circuit 2 and the reference current value switching circuit 6, and the constant current drive circuit 2 receives signals from the reference current value switching circuit 6 and the control circuit 3. Accordingly, the step motor 1 connected to the constant current drive circuit 2 is appropriately driven and controlled.

Further, a drive frequency monitor 50 is connected to the constant current drive circuit 2, and the drive frequency of the step motor 1 is sent to the control circuit 3 at any time. One of the features of the device shown in FIG. 1 is that it is equipped with the drive frequency monitor 50 mentioned above, and constantly monitors the drive frequency of the step motor 1 so that the drive frequency of the step motor 1 reaches a predetermined frequency (for example, the drive frequency at which the generated torque begins to decrease). frequency), the control circuit 3 detects this and performs optimal control to improve the decrease in torque of the step motor 1.

A constant current drive circuit 2 shown in FIG. 1 drives the step motor 1 using a constant current method. Signals are input to this constant current drive circuit 2 from a control circuit 3 and a reference current value switching circuit 6. The signal from the control circuit 3 is an excitation phase switching timing signal for driving the step motor 1, and based on this signal, the constant current drive circuit 2 switches each excitation phase of the step motor 1 at any time. Further, the signal from the reference current value switching circuit 6 defines the current value applied to each winding of the step motor 1, and based on this signal, the constant current drive circuit 2 limits the current value flowing through the step motor 1. The device is driven at a constant current.

The output waveform of the reference current value switching circuit 6 is shown by a solid line in FIG. 6(a). FIG. 6(a) is written according to the drive pulse order, that is, the drive sequence. The figure shows a 1-2 phase excitation drive pattern as a representative example of many drive methods.

Due to the above-mentioned effects, each winding of the motor normally follows the output waveform of the reference current value switching circuit 6 as shown by the solid line in FIG. 6(a), and the current waveform as shown in FIG. 6(b). The step motor 1 is optimally driven by passing a current through the wire. However, the current waveform shown in Figure 6(b) is in a low driving frequency range, and as the driving frequency increases, the current rises as shown in Figure 6(c) due to the influence of the inductance of the motor windings. Things got worse, and finally, Figure 6 (
As shown by the solid line in d), the reference current value ■ cannot be reached. If the winding current does not reach the reference current value,
The reference torque cannot be generated. This is the reason why the torque generated by the motor decreases during high-speed driving. Therefore, by installing a driving frequency monitor 50 as shown in FIG. 1, the above problem can be solved.

The drive frequency monitor 50 detects the step motor 1 from the step motor excitation phase switching timing of the constant current drive circuit 2.
The drive frequency is detected and data is sent to the control circuit 3 at any time. The control circuit 3 constantly monitors the drive frequency data sent from the drive frequency monitor 50, and when the drive frequency reaches a predetermined value (for example, the drive frequency at which the torque generated by the step motor 1 starts to decrease), the reference current value is changed. A signal is sent to the switching circuit 6 to change the drive current value of the step motor 1. According to the signal, the reference current value switching circuit 6 changes the output waveform of FIG. 6(a) from the waveform shown by the solid line to
Change the waveform to the one shown by the solid ten-dot line. When such an output waveform is output from the reference current value switching circuit 6, the current waveform applied to the motor by the constant current drive circuit 2 also changes as shown in FIG. 6(d).
The current waveform changes to one with a dotted line added, and the reference current value is satisfied even in the high drive frequency range. This makes it possible to improve the reduction in torque generated by the motor during high-speed driving.

The torque characteristics of the motor at this time are shown in FIG.

The solid line shows the characteristics before improvement, and the broken line shows the characteristics after improvement. The finger mark indicates a predetermined drive frequency set point at which the reference current value is switched.

Next, the constant current drive circuit 2 will be explained. In FIG. 1, the reference side voltages of the comparators 74 and 94 are set via a reference current value switching circuit under instructions from the microcomputer 5. The reference current value switching circuit includes potentiometers 60 and 6.
1 and two-way switches 62 , 63 , 64 .

65, which supplies the voltage set by the potentiometer 6o or 61, which is the base of the reference current value, to the reference side voltage of the comparators 74 and 94 according to instructions from the microcomputer 5. The comparators 74 and 94 compare each voltage corresponding to the current flowing through each coil phase A and τ or B in the step motor 1 with the reference voltage to generate an ON or OFF signal.

The power transistor 78 or 98 is connected via each gate transistor 76 or 96 depending on the on or off signal.
turn on or off. 10B in the figure indicates a 12V automobile battery.

On the other hand, the power transistors 84, 86, 104, or 106 are turned on and off under instructions from the microcomputer 5.
Turn it off. The step motor 1 has four coil phases A,
A, B, B are present, and the power transistor 78 is connected to the two coil phases A, τ, while the power transistor 98 is connected to the remaining phases B, H. Also, each power transistor 84 , 86 .

104 and 106 are connected to coils A, τ, B, and B, respectively. In this way, each power transistor turns on and off.
When turned off, current flows through each coil phase.

Resistors 88 and 108 in the figure are small-value resistors for current detection. Furthermore, the diodes 79 and 99 are flywheel diodes for damping control.

The potential (voltage) at point 89 or 109 corresponding to the current flowing through coil phases A, τ, or B, B is amplified by buffer amplifier 90 or 110, respectively, and fed back to each comparator 74 or 94. This input voltage is input to the comparator 74 or 9.
4 to generate an on/off signal by comparing each reference voltage, that is, the current flowing through each coil phase is set and controlled to be below a certain reference value.

The above circuit operation will be further explained with reference to FIG. 5 which is a timing diagram. The symbols on the left side of each figure in FIG. 5 correspond to the respective signal generation locations in FIG.

Signals a and b represent periodic switching signals since a method of switching and controlling the current flowing through each phase in two stages is adopted when driving the step motor 1. signal c, d
shows the generation states of two reference voltages according to signals a and b. Time too.

The period between t and t2 indicates a period in which the torque generated by the motor begins to decrease and the phase current distribution ratio is changed.
2, the switching pattern of the signals a and b from the microcomputer 5 is changing.

As signals a and b change, signals c and d also change accordingly.

For signals t, j, I are coil phases A, B, τ, respectively.

This is an on/off signal that controls the power supply to ■. When controlling energization to each coil phase, the current is delayed due to the inductance of each coil phase. That is, the current flowing through each coil rises with a certain slope in response to the ON signal of the transistors 76 and 96, and falls with a certain slope in response to the OFF signal. First, when only the power transistor 84 is on,
Only coil A is energized in response to the ON signal of transistor 76. Depending on the inductance of the coil phase A, its current increases at a certain slope angle, and soon the comparison side voltage input to the comparator 74 begins to exceed the reference value voltage. At this time, an off signal is generated by the action of comparator 74 to turn off transistor 76. In this case as well, the current does not disappear immediately depending on the inductance of the coil phase A;
The current decreases with a certain slope. That is, the comparison side input voltage of the comparator 74 also falls at a certain slope, and this time it begins to fall below the reference voltage. At this time, the comparator 74 generates an on signal, so the transistor 76 is turned on, and the coil A is energized again. Comparator 7 according to energization to coil A and τ
The fluctuation of the comparison side input voltage to 4 is schematically shown as signal g,
The signal diagram schematically shows the fluctuation of the comparison side input voltage to the comparator 94 according to the energization of the coils B and D. signal e,
f indicates on/off signals (chopping signals) corresponding to input voltage fluctuations of signals g and h, respectively.

FIG. 2 shows the configuration of the control circuit 3. The control circuit 3 includes a microcomputer 5 and a microcomputer 5.
A clock generator 72 supplies a reference clock pulse to the clock generator 72.

The microcomputer 5 has a clock generator 72
A programmable timer 52 that generates an interrupt request at arbitrary time intervals that can be preset by the CPU 54 based on a reference clock signal from the CPU 54, an interrupt control circuit 53 that executes interrupt processing in response to this interrupt request, and a step motor. 1
The CPU 54 executes the drive control process, and the ROM 55 stores the control programs and data necessary for executing the arithmetic processing in the CPU 54, and the data necessary for executing the arithmetic processing in the CPU 54 is temporarily stored. Using the RAM 56 that is read and written to, and a part of this RAM 56,
It consists of a drive frequency monitor 50 that latches the latest drive frequency information of the step motor 1, and an input/output buffer 57 that outputs drive signals and switching signals to the constant current drive circuit 2 and reference current value switching circuit 6.

The drive control process for the step motor l executed by the control circuit 3 configured as described above will be described below with reference to FIGS. 12 and 9.
This will be explained in detail using the flowchart shown in the figure.

The drive frequency monitor 50 is connected to the [?] inside the microcomputer 5. This is a buffer that uses a part of the AM56 to latch the step motor drive frequency information calculated by the CPU 54 based on the step motor control motor recorded in the ROM 55 as the latest information every time the drive frequency is changed. It is assumed that the latched drive frequency information is updated in the main routine of the CPU every time the drive frequency of the step motor l is changed.

The driving frequency information here refers to the reciprocal of the driving frequency, that is, the period, as shown in FIG. 4, and this period itself becomes the preset data of the programmable timer 52. Here, since 100 KHz is used as the reference clock, the data is as shown in FIG. 4.

In Fig. 12, the step motor 1 is constantly executed repeatedly.
Based on the information output from the drive frequency monitor 50 of
A target excitation pattern calculation routine for calculating the excitation pattern of the step motor 1 is shown.

As shown in FIG. 12, when this process is started, step 201 is first executed, drive frequency information RPPS is read from the drive frequency monitor 50 of the step motor 1, and the process proceeds to step 202.

In the next step 202, drive frequency information RPPS,
A comparison is made with reference drive frequency information BAPPS.

If it is determined that RPPS > BAPPS as a result of the size comparison, the process moves to step 203 and the flag F is set to "0".
'', and the excitation pattern is set to the excitation pattern ■ shown in the upper row of FIG. 3.

On the other hand, in step 202 above, the RPPS S BA
If it is determined to be PPS, the process proceeds to step 204, where the flag F is set to "1" and the excitation pattern is calculated to be the excitation pattern H shown in the lower part of FIG. 3.

Here, the reference drive frequency information BAPPS, which is compared in magnitude in step 202, is data recorded in advance in the ROM 55 in the microcomputer 5, and its value is determined at a predetermined value at which the torque of the step motor 1 starts to decrease. This is the driving frequency.

Next, FIG. 9 shows a drive control routine for outputting a drive signal to the drive circuit 2 and controlling the drive of the step motor 1.
Under the control of the CPU 54, the process is executed every time a pulse signal is generated from a programmable timer 52, which can be preset to an arbitrary time as shown in FIG.

When the process starts, first in step 301, the flag cwcch that determines the rotation direction of the step motor 1 is set to "0".
” or “1”, and if the flag CWCCW is “0”, the process moves to the next step 302. Then, in step 302, rlJ is added to the step counter N5TEPO value, and the process moves to step 3o4.

On the other hand, in step 301, if the flag CWCCWO value is "1", the process moves to step 303,
This time, rlJ is subtracted from the value of the step counter N5TEP, and the process moves to step 304.

In step 304, step counter N5TE
The drive circuit 2 and the reference current value switching circuit 6 use a data map as shown in FIG. 3 based on the value of the lower 3 bits of P.
Step 30
Move to 5.

In step 305, it is determined whether the flag F set in the target excitation pattern calculation routine of FIG. The output shown in the excitation pattern (3) in the upper part of FIG. 3 is produced. Further, if it is determined in step 305 that the flag F is "1", the process moves to step 307, and the output shown in the excitation pattern (2) in the lower part of FIG. 3 is performed.

After performing the above processing, this routine ends and waits for the next interrupt command.

Here, the flag 4CC-, which is determined to be "0" or "1" in step 301, is a flag that determines the rotational direction of the step motor I, which is calculated in the main routine of the CPU.

Further, the step counter N5TEP that appears after step 302 is set to 8 bits here. The reason why the signal pattern shown in FIG. 3 is calculated from the lower 3 bits of N5TEP in step 304 is because the step motor 1 has 4 phases and is driven by 1-2 phase excitation, so there are 8 drive signal patterns. This is because the step motor 1 can be driven and controlled using only the step position information of the lower 3 bits.

In Fig. 6, only the drive pattern of 1-2 phase excitation drive is shown, but other double 1-2 phase, triple 1-2 phase,...
・The torque characteristics of the step motor during high-speed driving can be similarly improved with a drive pattern such as microstep drive.

Furthermore, in addition to changing the reference current value waveform as shown by the broken line in FIG. 6(a), the same effect can be obtained by changing the waveform to a rectangular waveform as shown in FIG. 8(c). This makes it easier to change the waveform.

Further, as long as the upper limit current value is not exceeded, the increase rate of the phase current unequal distribution change may be any number.

Generally, the relationship between step motor torque and phase current is
The relationship is as shown in diagram O. For example, in two-phase excitation where A and B phases are energized at the same time, torque is generated as a composite vector of each phase current of A phase and B phase.
Unless each phase current of B phase is decreased like a sine curve,
A difference occurs between the torque and the torque during one-phase excitation. Therefore, in terms of eliminating the step motor's torque pulsation, it is preferable to use a sine curve distribution ratio as shown in FIG. If the method of use is such that it does not occur, a triangular wave-like unequal distribution ratio may be used.

〔Effect of the invention〕

According to the present invention, by improving the torque drop during high-speed driving, it is possible to drive with confidence without losing synchronization even in the high-speed range, so the step motor can be used up to the high-speed range.

In addition, the torque is increased by changing the current value of constant current drive, and it does not depend on the power supply voltage (battery voltage), so there is no need to change the applied voltage.

In addition, the drive frequency monitor, reference current value switching signal, etc. can all be handled by software within the control circuit, so no special additions are required. As a result, the structure becomes simple.

Furthermore, since the only parameter for switching is the motor drive frequency, all that is required is to change the numerical values in the control software. As a result, even if the motor or drive method changes, it can be adapted immediately.

Additionally, during high-speed drive, the current value is controlled so as not to exceed the upper limit peak current, so there is no change in motor heat generation.
Therefore, there is no increase in fever.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the step motor drive device of the present invention; Fig. 2 is a block diagram of a control circuit in the device shown in Fig. 1; Fig. 3 is a control circuit in the device shown in Fig. 1. 4 is a diagram illustrating preset data for the drive frequency of the programmable timer of the control circuit in FIG. 2; FIG. 5 is a diagram illustrating a, b, . . . in the device in FIG. k. l A diagram showing the timing of each line output; Figure 6 is a waveform diagram of the 1-2 phase excitation drive pattern in the device shown in Figure 1; Figure 7 is a diagram showing the torque characteristics of the step motor; Figure 8 is a diagram showing the torque characteristics of the step motor; A waveform diagram showing another example of the excitation drive pattern in the device shown in the figure; FIG. 9 is a flowchart of the drive signal output routine in the device shown in FIG. 1; FIG. 10 is a diagram showing the relationship between torque and phase current; A diagram explaining phase current distribution; FIG. 12 is a flowchart of an excitation pattern calculation routine using drive frequency information; and FIG. DESCRIPTION OF SYMBOLS 1...Step motor, 2...Constant current drive circuit, 3...Control circuit, 5
...Microcomputer, 6.Reference current value switching circuit, 50.Driving frequency monitor. 60, 61...potentiometer, 62, 63
, 64 , 65 . . . bidirectional switch, 74 , 94 .
...Comparator, 76.78,84,86.96.98,104,10
6...Transistor, 79, 99...Diode, 88, 108
...Resistance, 90, 110... Banfa amplifier. 3 Control circuit Control circuit Fig. 2 zJ? Data map of turn calculation routine Figure 3 Preset data 4th drive frequency torque characteristics Figure 7 Figure 8 Figure 9 A phase A (0) Example of sine wave curved phase current distribution (b) Triangular wave phase current distribution Example of 11th PjJ

Claims (1)

[Scope of Claims] A pair of constant current drive circuits that supply current to the windings of one phase and the other phase of a step motor, a control circuit that supplies control signals to the constant current drive circuits, and A reference current value switching circuit is provided that supplies a reference current value signal to the constant current drive circuit, and the control circuit corrects for torque reduction using only the drive frequency of the step motor as a parameter and sends the signal to the reference current value switching circuit. It is possible to supply a switching command signal and a drive command signal to the constant current drive circuit, respectively, so that the switching command signal and the drive command signal can be supplied to the constant current drive circuit, respectively, so that the switching command signal and the drive command signal can be supplied to the constant current drive circuit, respectively.
1. A step motor drive device, characterized in that the ratio of unequal distribution of stepwise phase currents supplied to the step motor is changed.