JP2594595B2 - Step motor drive - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for a step motor used for controlling a throttle valve of an engine, for example.

[Prior art and problems to be solved by the invention]

For example, a method of driving a step motor disclosed in Japanese Patent Application Laid-Open No. 60-200798 aims to improve the reduction in torque generated during high-speed driving of the step motor by changing (increase or decrease) the voltage applied to the step motor. It is. For example, when the applied voltage (that is, the battery voltage) is a low voltage value such as DC12V, which is a constant voltage such as an automobile or a motorcycle, and it is difficult to change the voltage, the control described in the above publication is performed. Even if it is performed, the generated torque of the step motor cannot be improved, and the reduction of the generated torque at the time of high-speed driving of the step motor still remains.In addition, since the applied voltage is low, the generated torque of the high-speed driving also decreases. It will be noticeable. Usually, when the applied voltage is low and the driving speed is high, it is common to use the constant current driving in which the generated torque is not so affected by the applied voltage.
With such an applied voltage, there is a problem that a reduction in the generated torque during high-speed driving is inevitable.

[Means for solving the problem]

According to the present invention, there is provided a pair of constant current drive circuits for supplying a current to one phase winding and another phase winding in order to drive a stepping motor in a constant current mode, The excitation phase switching timing signal for the motor drive is input, and each excitation phase of the step motor is switched at any time, and the current applied to each winding is limited by a signal from the reference current value switching circuit, and the step motor is controlled by this signal. A circuit for driving a constant current; a reference current value switching circuit for supplying a reference current value signal to the constant current drive circuit; In response to this signal, the excitation pattern of the drive current to the motor of the switching circuit corresponding to this signal is changed from a symmetrical step shape to a drive current value of the latter half of the pulse that is larger than the former half of the pulse. The switching circuit can be switched in an asymmetric stepwise manner, and the switching circuit includes a circuit configured by combining a potentiometer, a bidirectional switch, and an inverter; and a microcomputer and a clock generator that supplies a reference clock to the microcomputer. Control circuit,
The microcomputer further includes a programmable timer capable of presetting and generating an interrupt request at any time, an interrupt control circuit for performing an interrupt process, a CPU for performing a step motor drive control process, and an arithmetic operation of the CPU. ROM in which a control program or data for processing is recorded in advance, RAM for temporarily reading and writing data for arithmetic processing, a drive frequency monitor for latching the latest drive frequency information of the step motor using a part of the RAM, A control circuit comprising a constant current drive circuit and an input / output buffer for respectively outputting a drive signal and a switch signal to a reference current value switching circuit; When this happens, a signal is sent to the reference current value switching circuit to change the drive current value of the step motor, and the reference current value switching circuit follows the signal and forms a symmetrical step at low speeds and at a high speed. The present invention provides a stepping motor driving device characterized in that switching is performed in an asymmetric stepwise manner in which the driving current level in the latter half of the pulse is larger than that in the first half of the pulse.

(Operation)

In the device according to the present invention, when the drive frequency of the step motor exceeds a predetermined frequency, the applied voltage is increased by changing the distribution ratio of the phase currents unequally distributed in a stepwise manner as described above. Without reducing the generated torque during high-speed driving.

〔Example〕

FIG. 1 is a diagram showing a drive device for a step motor according to one embodiment of the present invention.

Referring to FIG. 1, the control circuit 3 includes a constant current driving circuit 2
And the control signal is sent to the reference current value switching circuit 6, and the constant current drive circuit 2 appropriately controls the step motor 1 connected to the constant current drive circuit 2 according to the signals from the reference current value switching circuit 6 and the control circuit 3. Drive control.

A drive frequency monitor 50 is connected to the constant current drive circuit 2 so that the drive frequency of the step motor 1 is sent to the control circuit 3 as needed. One of the features of the apparatus shown in FIG. 1 is that the drive frequency monitor 50 is provided, and the drive frequency of the step motor 1 is constantly monitored. Control circuit 3
Therefore, the optimum control is performed so as to improve the torque reduction of the step motor 1.

The constant current drive circuit 2 in FIG. 1 drives the step motor 1 by a constant current method. Signals from the control circuit 3 and the reference current value switching circuit 6 are input to the constant current drive circuit 2. The signal from the control circuit 3 is an excitation phase switching timing signal for driving the stepping motor 1, and the constant current driving circuit 2 switches each excitation phase of the stepping motor 1 as needed by this signal. The signal from the reference current value switching circuit 6 defines the value of the current applied to each winding of the step motor 1, and the constant current drive circuit 2 limits the current value flowing to the step motor 1 by this signal. Then, constant current driving is performed.

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

Due to the above-described operation, each winding of the motor is normally provided with a current waveform as shown in FIG. 6 (b) in accordance with the output waveform of the reference current value switching circuit 6 as shown by a solid line in FIG. 6 (a). A current is supplied to the wire to drive the step motor 1 optimally. However, the current waveform shown in FIG. 6 (b) is in a low drive frequency range, and as the drive frequency increases, the current rises as shown in FIG. 6 (c) due to the influence of the inductance of the motor winding. As a result, as shown by the solid line in FIG. 6 (d), the current does not reach the reference current value I. If the winding current does not reach the reference current value, the reference torque cannot be generated. This is the cause of the decrease in the torque generated by the motor during high-speed driving. Therefore, the above problem is solved by installing a drive frequency monitor 50 as shown in FIG.

The drive frequency monitor 50 detects the step motor excitation phase switching timing of the constant current drive circuit 2 based on the step motor 1
, And sends out data to the control circuit 3 as needed. 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 drive frequency (for example, a drive frequency at which the generated torque of the step motor 1 starts to decrease), the reference current value A signal is sent to the switching circuit 6 to change the drive current value of the step motor 1. In accordance with the signal, the reference current value switching circuit 6 changes the output waveform of FIG. 6 (a) from a waveform shown by a solid line to a waveform shown by a solid line + a dotted line. When such an output waveform is output from the reference current value switching circuit 6, the current waveform applied to the motor of the constant current drive circuit 2 is also the current waveform to which the dotted line portion in FIG. 6 (d) is added. To satisfy the reference current value even in the high driving frequency range. As a result, a decrease in the generated torque of the motor during high-speed driving can be improved.

FIG. 7 shows the torque characteristics of the motor at this time. The solid line shows the characteristics before the improvement and the broken line shows the characteristics after the improvement. Finger marks indicate set points of a predetermined drive frequency at which the reference current value is switched.

Next, the constant current drive circuit 2 will be described. In FIG.
The reference voltages of the comparators 74 and 94 are set via a reference current value switching circuit under the command of the microcomputer 5. The reference current value switching circuit is composed of potentiometers 60 and 61 and bidirectional switches 62, 63, 64 and 65. The voltage set by the potentiometers 60 or 61 and serving as the base of the reference current value is commanded by the microcomputer 5. The reference voltage of the comparators 74 and 94 is supplied. The comparators 74 and 94 compare the voltages corresponding to the currents flowing through the respective coil phases A and B in the step motor 1 with the reference voltage to generate an ON or OFF signal. The power transistor 78 or 98 is turned on or off via the gate transistor 76 or 96 in response to the on or off signal. + B in the figure
Indicates a 12V automotive battery.

On the other hand, the power transistor 84, 86, 104 or 106 is turned on / off under the command of the microcomputer 5. There are four coil phases A, B in the stepper motor 1; the power transistor 78 is connected to the two coil phases A, while the power transistor 98 is connected to the remaining phases B. In addition, each power transistor 84, 86, 104,
106 is connected to coils A, B, respectively. Thus, a current flows through each coil phase according to the on / off state of each power transistor. The resistors 88 and 108 in the figure are resistors having a small current detection value. The diodes 79 and 99 are
This is a flywheel diode for damping control.

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

The operation of the above circuit will be further described with reference to FIG. 5 which is a timing chart. The left symbols in the respective drawings in FIG. 5 correspond to the respective signal generation locations in FIG.

The signals a and b indicate periodic switching signals because a method of controlling the current flowing in each phase in two steps when the step motor 1 is driven is adopted. Signals c and d indicate the generation states of two reference voltages according to signals a and b. Between times t ₁ and t _2, beginning the torque generated by the motor is reduced, indicates a period for changing the distribution ratio of the phase current, signal a from the microcomputer 5 between times t ₁ and t _2, b
Has changed. As the signals a and b change, the signals c and d also change accordingly.

The signals i, j, k, l are on / off signals for controlling the energization of the coils A, B,. In controlling the energization of 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 signals of the transistors 76 and 96, and falls with a certain slope in accordance with the OFF signals. First, when only the power transistor 84 is on, only the coil A is energized according to the on signal of the transistor 76. In accordance with the inductance of the coil phase A, the current increases at a certain inclination angle, and the comparison side voltage input to the comparator 74 starts to exceed the reference value voltage. At this time, an off signal is generated by the operation of the comparator 74, and the transistor 76 is turned off. Also in this case, the current does not disappear immediately according to the inductance of the coil A, but decreases with a certain slope. That is, the input voltage on the comparison side of the comparator 74 also drops at a certain slope, and then starts to drop below the reference voltage. At this time the comparator
Since 74 generates an ON signal, the transistor 76 is turned ON, and the coil A is restarted. Fluctuation of the comparison side input voltage to the comparator 74 according to the energization to the coil A is schematically shown in a signal g, and the comparator according to the energization to the coil B.
The fluctuation of the comparison-side input voltage to 94 is schematically shown in a signal h. Signals e and f indicate 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
The microcomputer 5 includes a microcomputer 5 and a clock generator 72 for supplying a reference clock pulse to the microcomputer 5. Microcomputer 5
Is a programmable timer 52 that generates an interrupt request at any time preset by the CPU 54 based on a reference clock signal from the clock generator 72, and an interrupt control circuit that executes an interrupt process in response to the interrupt request. 53
And a CPU 54 that executes a drive control process of the step motor 1.
A ROM 55 in which a control program and data necessary for executing the arithmetic processing by the CPU 54 are recorded in advance; a RAM 56 for temporarily reading and writing data necessary for executing the arithmetic processing by the CPU 54; and a RAM 56 , A driving frequency monitor 50 for latching the latest driving frequency information of the step motor 1, a constant current driving circuit 2 and a reference current value switching circuit 6.
An input / output buffer 57 that outputs a drive signal and a switching signal to the
It is composed of

Hereinafter, a drive control process of the step motor 1 executed by the control circuit 3 configured as described above will be described with reference to FIGS.
This will be described in detail with reference to the flowchart shown in FIG.

The drive frequency monitor 50 uses a part of the RAM 56 inside the microcomputer 5 and uses the step motor drive frequency information calculated by the CPU 54 based on the step motor control motor recorded in the ROM 55 every time the drive frequency is changed. The drive frequency information to be latched is updated each time the drive frequency of the step motor 1 is changed in the main routine of the CPU.

The drive frequency information referred to here is a reciprocal of the drive frequency, that is, a cycle, as shown in FIG. 4, and the cycle itself is 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.

FIG. 12 shows that the step motor 1 is constantly executed repeatedly.
4 shows a target excitation pattern calculation routine for calculating an excitation pattern of the step motor 1 based on information output from the drive frequency monitor 50 of FIG.

As shown in FIG. 12, when this process is started, first, step 201 is executed, and drive frequency information RPPS is read from the drive frequency monitor 50 of the step motor 1, and step 20 is executed.
Move to 2.

In the next step 202, the drive frequency information RPPS and the reference drive frequency information BAPPS are compared in magnitude. When it is determined that RPPS> BAPPS as a result of the magnitude comparison, the process proceeds to step 203, where the flag F is set to “0” and the excitation pattern is set to the excitation pattern I shown in the upper part of FIG. calculate.

On the other hand, if it is determined in step 202 that RPPS ≦ BAPPS, the process proceeds to step 204, where the flag F is set to “1” and the excitation pattern is set to the excitation pattern II shown in the lower part of FIG. ,calculate.

Here, the reference drive frequency information BAPPS, which is compared in magnitude in step 202, is stored in the ROM in the microcomputer 5.
The data is a predetermined drive frequency at which the torque of the step motor 1 starts to decrease.

Next, FIG. 9 shows a drive control routine for outputting a drive signal to the drive circuit 2 and controlling the drive of the stepper motor 1. Under the control of the CPU 54, an arbitrary time as shown in FIG. It is executed for each pulse signal generated from the timer 52.

When the process is started, first, in step 301, it is determined whether the flag CWCCW for determining the rotation direction of the step motor 1 is “0” or “1”. If the flag CWCCW is “0”,
The process proceeds to the next step 302. Then, in step 302, “1” is added to the value of the step counter NSTEP, and the process proceeds to step 304.

On the other hand, if the value of the flag CWCCW is “1” in step 301, the process proceeds to step 303. This time, “1” is subtracted from the value of the step counter NSTEP, and the process proceeds to step 304.

In step 304, a driving / switching signal pattern to the driving circuit 2 and the reference current value switching circuit 6 is calculated based on the lower 3 bits of the step counter NSTEP using a data map as shown in FIG. Move to

In step 305, it is determined whether the flag F set in the target excitation pattern calculation routine of FIG. 12 is "0" or "1". If it is determined that the flag F is "0", the process proceeds to the next step 306. Then, the output shown in the excitation pattern I in the upper part of FIG. 3 is performed. If it is determined in step 305 that the flag F is "1", the process proceeds to step 307 to output the excitation pattern II shown in the lower part of FIG.

After performing the processing described above, this routine ends once,
It waits for the next interrupt instruction.

Here, the flag CWCCW determined as “0” or “1” in step 301 is a flag for determining the rotation direction of the step motor 1 calculated in the main routine of the CPU.

Also, the step counter N appearing after step 302
STEP is 8bit here. NSTEP in step 304
The signal pattern as shown in FIG. 3 is calculated from the lower 3 bits of the step signal 1 because the step motor 1 is driven in four phases and driven by 1-2 phase excitation. This is because the drive of the stepping motor 1 can be controlled only by the information.

FIG. 6 shows only the drive pattern of the 1-2-phase excitation drive, but other double 1-2-phase, triple 1-2-phase,
.., The torque characteristics of the step motor at the time of high-speed driving can be similarly improved by using a driving pattern such as micro-step driving.

In addition, not only the change in the reference current value waveform as shown by the broken line in FIG. 6 (a) but also the rectangular wave waveform as shown in FIG. 8 (c) has the same effect. This facilitates waveform changes.

If the current value does not exceed the upper limit, the rate of increase in the unequal distribution change of the phase current may be any number.

Generally, the relationship between the step motor torque and the phase current is
The relationship is as shown in FIG. 10. For example, in the case of two-phase excitation in which the A and B phases are simultaneously energized, torque is generated as a combined vector of the A-phase and B-phase currents. B
If the phase current of each phase should be reduced like a sine curve, 1
A difference from the torque at the time of the phase excitation occurs. Therefore, in terms of eliminating the torque pulsation of the step motor, the ratio of the unequal distribution of the phase current is preferably a sine curve distribution ratio as shown in FIG. 11 (a). If it is not used, the ratio may be unequally distributed like a triangular wave.

〔The invention's effect〕

According to the present invention, the stepping motor can be used up to the high-speed region by improving the torque reduction at the time of the high-speed driving, so that the driving can be performed without any loss of synchronism even in the high-speed region. More specifically, by unequally distributing the voltage waveform during high-speed continuous driving, the current in one phase reaches a saturation state, and a sufficient torque can be generated. Tuning can be prevented. Further, since the torque is increased by changing the current value of the constant current drive and does not depend on the power supply voltage (battery voltage), there is no need to change the applied voltage.

In addition, since a drive frequency monitor, a reference current value switching signal, and the like can all be handled by software in the control circuit, there is no need for special additional components. As a result, the configuration is simplified.

Further, since the switching parameter is only the motor drive frequency, it is only necessary to change the numerical value of the control software. As a result, even if the motor and the driving method are changed, it can be dealt with immediately.

In addition, since the current value is controlled so as not to exceed the upper limit peak current at the time of high-speed driving, there is no change in motor heat generation, and therefore, there is no increase in heat generation.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a step motor driving apparatus according to the present invention; FIG. 2 is a block diagram of a control circuit in the apparatus shown in FIG. 1; FIG. 3 is a control circuit in the apparatus shown in FIG. FIG. 4 is a diagram for explaining preset data for the drive frequency of the programmable timer of the control circuit of FIG. 2; FIG. 5 is a diagram for explaining a, b,. l Diagram showing the timing of each line output; FIG. 6 is a waveform diagram of a 1-2-phase excitation drive pattern in the apparatus of FIG. 1; FIG. 7 is a diagram showing the torque characteristics of a step motor; FIG. 9 is a waveform diagram showing another example of the excitation drive pattern in the apparatus shown in FIG. 9; FIG. 9 is a flowchart of a drive signal output routine in the apparatus shown in FIG. 1; FIG. 10 is a view showing the relationship between torque and phase current; Diagram illustrating phase current distribution; FIG. 12 shows drive Flow diagram of the excitation pattern calculation routine with wavenumber information; indicates respectively a. 1 ... step motor, 2 ... constant current drive circuit, 3 ... control circuit, 5 ... microcomputer, 6 ... reference current value switching circuit, 50 ... drive frequency monitor. 60,61… Potentiometer, 62,63,64,65… Bidirectional switch, 74,94… Comparator, 76,78,84,86,96,98,104,106 …… Transistor, 79,99 …… Diode 88,108… Resistance, 90,110 …… Buffer amplifier.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichiro Tanaka 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References JP-A-62-236386 (JP, A) JP-A-61-88799 (JP, A) Japanese Utility Model Showa 60-135098 (JP, U) Japanese Utility Model Showa 60-77300 (JP, U)

Claims (1)

(57) [Claims] 1. A pair of constant current drive circuits for supplying current to one phase winding and another phase winding to drive a step motor by a constant current method. The excitation phase switching timing signal for driving is inputted, and each excitation phase of the step motor is switched at any time, and the current applied to each winding is limited by a signal from the reference current value switching circuit, and the step motor is determined by this signal. A current driving circuit; a reference current value switching circuit for supplying a reference current value signal to the constant current driving circuit, wherein the control circuit changes the driving current value when the driving frequency at which the generated torque of the step motor starts to decrease is reached. A signal is sent, and in response to this signal, the excitation pattern of the drive current to the motor of the switching circuit is changed from a symmetrical staircase to a drive current value in the latter half of the pulse that is larger than that in the first half of the pulse. It is possible to switch in a stepwise manner, and the switching circuit includes a potentiometer, a bidirectional switch,
A control circuit comprising a microcomputer and a clock generator for supplying a reference clock to the microcomputer, the microcomputer further comprising a presettable interrupt request at any time; A programmable timer that generates an interrupt, an interrupt control circuit that performs an interrupt process, a CPU that executes a step motor drive control process, a ROM in which a control program and data for the arithmetic process of the CPU are recorded in advance, and an arithmetic process. RAM for temporarily reading and writing data, a driving frequency monitor for latching the latest driving frequency information of the step motor using a part of the RAM, a driving signal and a switching signal for a constant current driving circuit and a reference current switching circuit. And a control circuit composed of an input / output buffer for respectively outputting the driving frequency, and constantly monitors the driving frequency data so that the driving frequency becomes a predetermined driving frequency. A signal is sent to the reference current value switching circuit to change the drive current value of the step motor. A drive device for a stepping motor, characterized in that the current is switched in an asymmetric stepwise manner with a large current value.