JPH09117198A - Stepping motor driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the current detecting accuracy of current detecting resistors so as to prevent the deterioration of the control of the drive of a stepping motor by means of a stepping motor driving circuit by feeding back the results of the comparison between a reference voltage which, provides for the phase current of a stepping motor and detected voltages to a control section. SOLUTION: The electric current flowing to a stepping motor M is detected by means of current detecting resistors R11-R16 and inputted to comparators C11-C16 where the currents are compared with a reference voltage having a sine waveform from a control section 11. The compared results are fed back to the section 11. The section 11 drives the motor M so that a phase current following the reference voltage having the sine waveform can flow to the motor M. Therefore, the detecting accuracy of the resistors R11-R16 can be improved and the deterioration of the control of the drive of the motor M can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stepping motor drive circuit, and more specifically, it is an object of the present invention to improve a drive circuit for microstep driving a three-phase excitation stepping motor used in a printer or a copying machine.
In recent years, the demand for a three-phase excitation stepping motor has been increasing in the market because the drive circuit can be simplified compared to the five-phase excitation stepping motor and a drive with lower vibration than that of the two-phase excitation stepping motor can be realized. The improvement of the drive circuit is required.

[0002]

2. Description of the Related Art A drive circuit of a conventional three-phase excitation stepping motor will be described below with reference to the drawings. FIG. 2 is a configuration diagram of a stepping motor drive circuit according to a conventional example, and FIG. 3 is a timing chart for explaining a drive state of a W2-3 phase stepping motor.

As shown in FIG. 2, this drive circuit includes a control section (1), a reference voltage generation section (2), MOSFET drivers (F1 to F6), current detection resistors (R1, R2, R3),
Comprising comparators (C1, C2, C3), the drive control of a three-phase excitation stepping motor (M) is performed based on a drive signal output from a CPU (not shown).

According to the above circuit, various control signals and a rotation speed designation clock (Clock) for setting the rotation speed of the stepping motor (M) are input to the control section (1) from a CPU (not shown). The control unit (1) controls the ON / OFF operation of the MOSFET drivers (F1 to F6) based on the above control signal and the outputs of comparators (C1, C2, C3) described later. Thereby, MOSF
The ET driver (F1 to F6) is turned on / off to make a coil (U,
Current is supplied / not supplied to (V, W), and the stepping motor (M) is rotationally driven.

The power supply voltage (Vdd) is applied to each coil (U, V, W) forming the stepping motor (M).
The MOSFET drivers (F1 to F6) are connected to both the side and the ground potential (GND) side, and one coil is driven by the two MOSFET drivers (F1 to F6). For example, regarding the coil (U), the MOSFET driver (F1) is connected to the power supply voltage (Vdd) side, and the MOSFET driver (F4) is connected to the ground potential (GND) side.
When 1) turns on, current flows into the coil (U),
The coil (U) is driven by using these two MOSFET drivers (F1, F4) such that when the MOSFET driver (F4) is turned on, a current flows out from the coil (U).

At this time, the phase current flowing through the coils (U, V, W) of the stepping motor (M) is the current detection resistance (R).
1, R2, R3) constantly converts the voltage, and feedback amplifiers (FA1, FA2, FA3) convert A /
After being D-converted, it is input to the non-inverting inputs of three comparators (C1, C2, C3) provided for each coil (U, V, W).

On the other hand, the inverting input of the comparators (C1, C2, C3) is supplied with a sinusoidal reference voltage as shown in FIG. 3 from the reference voltage generator (2), and the reference voltage and the feedback amplifier (FA1 , FA2, FA3) is compared with the output voltage of the control unit (1).
Will be returned to Based on the comparison result and the control signal from the CPU, the stepping motor (M) is rotationally driven so that the phase current that follows the sinusoidal reference voltage as shown in FIG. 3 flows.

[0008]

However, according to the conventional driving circuit as shown in FIG. 2, the current detecting resistor (R1) is directly connected to each coil (U, V, W) which constitutes the stepping motor (M). , R2, R3) are connected to directly detect the phase current actually flowing in the stepping motor (M) by voltage conversion.

Since the currents flowing through these coils (U, V, W) are quite large currents, these are connected to current detection resistors (R
The voltage converted by (1, R2, R3) (hereinafter referred to as a detection voltage) also becomes large. This detection voltage is finally input to the comparators (C1, C2, C3), but since the level of the detection voltage is quite large, it is lowered to the operation level of the comparators (C1, C2, C3), and then the comparator (C1, C1). C2, C3) must be entered.

In that case, a feedback amplifier (FA
1, FA2, FA3), the level of the detection voltage is lowered by the voltage division ratio using resistors connected in series.
Since it is considerably higher than the voltage of the operation level of 3), it is necessary to increase the voltage division ratio. At this time, since the above-mentioned voltage division ratio is large, there has been a problem that the rate of errors mixed in at the time of current detection increases, the detection accuracy decreases, and the drive control accuracy decreases.

[0011]

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and as shown in FIG. 1, a control unit for generating a drive signal for driving a three-phase excitation stepping motor. A switching transistor that performs ON / OFF operation based on the drive signal to supply / non-supply a phase current to the stepping motor, and a current detection unit that detects a current flowing in the stepping motor and feeds it back to the control unit. The current detection unit is provided for each of the switching transistors, a current detection resistor for converting a current flowing through the switching transistor to generate a detection voltage, and for each of the switching transistors, and the phase current And a comparator for comparing the detected voltage with a reference voltage that defines the above and feeding back the comparison result to the control unit. By, to improve the detection accuracy of the current flowing through the stepping motor, it is an object to provide a driving circuit of a stepping motor which occupies trivial possible to improve the driving control accuracy.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A drive circuit for a stepping motor according to an embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the drive circuit includes a control unit (11), MOSFET drivers (F1 to F6), current detection resistors (R11 to R16), a comparator (C11).
C16), and a three-phase excitation stepping motor (M) based on a drive signal output from a CPU (not shown).
Drive control of the.

The control unit (11) receives control signals input from a CPU (not shown) and comparators (C11 to C1) described later.
6) Based on the output result of the MOSFET driver (F1
~ F6) ON / OFF operation is controlled. M
The OSFET drivers (F1 to F6) are an example of switching transistors, and are switching transistors that drive the stepping motor (M) by supplying / not supplying current to the stepping motor (M) by ON / OFF operation. .

The current detecting resistors (R11 to R16) and the comparators (C11 to C16) constitute an example of a current detecting section. The current detection resistors (R11 to R16) are MO
The current flowing through the SFET drivers (F1 to F6) is converted into a voltage (this voltage is hereinafter referred to as a detection voltage) and output to the comparators (C11 to C16).

For example, the current detection resistor (R14) is a MOSF.
The current flowing through the ET driver (F4) is converted into a voltage and input to the comparator (C14). The comparators (C11 to C16) compare the detected voltage with a predetermined reference voltage and a sinusoidal reference voltage supplied from the control unit (11) and feed back the comparison result to the control unit (11). is there.

The general circuit operation of the above circuit will be described below. First, various control signals are input to the control unit (11) from a CPU (not shown), and the control unit (11) controls the MOSFET driver (F1) based on the above control signals and the outputs of comparators (C11 to C16) described later. ~ F
The ON / OFF operation of 6) is controlled. As a result, the coils (U, V,
Current is supplied / not supplied to W), and the stepping motor (M) is rotationally driven.

A power supply voltage (Vd
MOSFET on both the d) side and the ground potential (GND) side
The drivers (F1 to F6) are connected, and one coil is driven by two MOSFET drivers (F1 to F6). For example, regarding the coil (U), the MOSFET driver (F1) is connected to the power supply voltage (Vdd) side, and the MOSFET driver (F4) is connected to the ground potential (GND) side.
When 1) turns on, current flows into the coil (U),
The coil (U) is driven by using these two MOSFET drivers (F1, F4) such that when the MOSFET driver (F4) is turned on, a current flows out from the coil (U).

The current flowing through the stepping motor (M) is detected by using the current detecting resistors (R11 to R16). In the circuit described above, these current detecting resistors (R11 to R16) are used as in the conventional case. M) is not directly connected to 6 MOSFET drivers (F1
~ F6) connected to each of these MOSFETs
The current flowing through the drivers (F1 to F6) is converted into a voltage (hereinafter, this voltage is referred to as a detection voltage).

Taking the MOSFET driver (F6) as an example, the current flowing through it is converted into a voltage by the current detecting resistor (R16) and input to the inverting input side of the comparator (C16). The detection voltage generated in this manner is input to one input of the comparators (C11 to C16), and the other input thereof receives the sinusoidal reference voltage as shown in FIG. 3 from the control unit (11), The reference voltage and the detected voltage are compared, and the comparison result is fed back to the control section (11). Based on this comparison result and the control signal from the CPU,
The stepping motor (M) is driven so that the phase current that follows the sinusoidal reference voltage as shown in FIG. 3 flows.

The effects of the drive circuit for the stepping motor according to this embodiment will be described below. As a specific example for explaining the function and effect, current supply to the coil (U) and current detection will be described below. Since the coils (V, W) are the same as the coils (U), the description thereof will be omitted. A MOSFET driver (F1) is connected to the power supply voltage (Vdd) side of the coil (U), and an MO is connected to the ground potential (GND) side.
The SFET driver (F4) is connected to the MOSFET driver (F4) when a current is passed through the coil (U).
When 1) turns on, current flows into the coil (U),
When the MOSFET driver (F4) is turned on, a current starts to flow from the coil (U).

There are two types of current flowing through the coil (U), namely, a current flowing into the coil (U) and a current flowing out of the coil (U) as described above.
In order to detect the current flowing into the coil (U) when 1) is turned on, the voltage converted by the current detection resistor (R11) is input to the non-inverting input of the comparator (C11) and the control unit (11). ), And the level is converted by the level shift circuit (A1) and detected by comparing with a sinusoidal reference voltage.

Regarding the detection voltage at this time, not the ground potential (GND) but the power supply voltage (Vdd) is used as a reference, and the magnitude of the detection voltage is different from the high voltage power supply voltage (Vdd). Therefore, the voltage does not become so high. For example, power supply voltage (Vdd) is 20V, coil (U)
Even if the current flowing in the circuit is converted into a voltage of 19V, the detected voltage input to the comparator (C11) is about 20-19 = 1V.

On the contrary, the MOSFET driver (F4) is turned on.
In order to detect the current flowing out of the coil (U), the voltage converted by the current detection resistor (R14) is input to the non-inverting input of the comparator (C14) and output from the control unit (11). It is detected by comparing with a sinusoidal reference voltage. At this time, the current detection resistor (R1
Since 4) is connected to the ground potential (GND) side, even if a large current flows, the voltage-converted detection voltage does not become so high and is input to the comparator (C14).

Therefore, in any case, the detection voltage does not become as high as the conventional voltage. As described above, in the above circuit, the current detection resistors (R11 to R16) have six MOSFETs.
The T drivers (F1 to F6) are connected to each other, and the current flowing through the MOSFET drivers (F1 to F6) is converted into a detection voltage to generate a detection voltage. It is not necessary to divide the resistance to lower the detection voltage level with a high voltage division ratio and input the voltage to the comparators (C11 to C16) as in the conventional case.

As a result, by lowering the level of the detection voltage with a high voltage division ratio as in the prior art, the rate of errors mixed in during current detection increases, the detection accuracy decreases, and the drive control accuracy decreases. It becomes possible to suppress the problem as much as possible.

[0026]

As described above, according to the drive circuit of the stepping motor for three-phase excitation of the present invention, the current detection is provided for each switching transistor, and the current flowing through the switching transistor is converted into a voltage to generate a detection voltage. By having a resistor and a comparator that is provided for each switching transistor and that compares the reference voltage that defines the phase current with the detection voltage and feeds back the comparison result to the control unit, the detection voltage is as high as the conventional one. Therefore, unlike the conventional case, it is not necessary to divide the detection voltage with a high voltage division ratio to input it to the comparator as in the conventional case.

As a result, by lowering the level of the detection voltage with a high voltage division ratio as in the prior art, the ratio of errors mixed in during current detection increases, the detection accuracy decreases, and the drive control accuracy decreases. It becomes possible to suppress the problem as much as possible.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a drive circuit for a stepping motor according to the present invention.

FIG. 2 is a circuit diagram of a drive circuit for a conventional stepping motor.

FIG. 3 is a timing chart illustrating an operation of a drive circuit of a three-phase excitation stepping motor.

[Explanation of symbols]

 (11) Control unit (R11 to R16) Current detection resistance (F1 to F6) MOSFET driver (A1 to A3) Level shift circuit (M) Stepping motor (U, V, W) Coil (C11 to C16) Comparator

Claims (1)

[Claims] 1. A control unit that generates a drive signal for driving a three-phase excitation stepping motor, and a switching transistor that is turned on / off based on the drive signal to supply / non-supply a phase current to the stepping motor. And a current detection unit that detects a current flowing through the stepping motor and feeds it back to the control unit, the current detection unit being provided for each of the switching transistors, and converting the current flowing through the switching transistor into a voltage. A current detection resistor that generates a detection voltage by comparing the detection voltage with a reference voltage that is provided for each of the switching transistors and that defines the phase current,
A stepping motor drive circuit, comprising: a comparator for feeding back the comparison result to the control unit.