JPS6331496A - Method for driving stepping motor and circuit therefor - Google Patents

Abstract

PURPOSE:To make current ripples smaller and also reduce overshoot, and make vibration lower at low speed, by changing the voltage of a feed circuit according to phase switching frequency. CONSTITUTION:The rotor of a stepping motor is rotated at a speed regulated by the frequency of input pulse to a phase. switching control circuit 20. The input pulse is converted to output voltage V4 via an integrating circuit 66 and a same phase voltage adder circuit 44. The output voltage V4 is applied to the input end of the error amplifier 42 of a constant-current chopper driving circuit, and a transistor 30 is ON/OFF-controlled, and to windings 22, 24, current according to the frequency of the input pulse flows. Besides, the output voltage V4 is applied to the input end of the error amplifier 90 of a feed voltage control circuit, and a transistor 80 is ON/OFF-controlled, and feed voltage is changed according to the frequency of the input pulse.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a stepping motor drive circuit.

[Conventional technology]

If a stepping motor that uses the electromagnetic force of a coil has the same structure and shape, its output torque T is proportional to the product of the number of turns W of the coil and the current 1. In other words, it is represented by a TgPOW bow.

By the way, if the pure resistance of the motor winding is R and the inductance is L, the impedance Z of the motor winding at one frequency f is Z=/V'R+ 2zfL), and when a stepping motor is used at a constant voltage, at high speed. The more you turn it, the more the impedance increases, so the current flowing decreases, and the torque decreases as shown in FIG.

In the constant voltage drive described above, a large decrease in torque at high pressure is unavoidable. To solve this problem, conventionally, a constant current chopper drive is used to prevent current and torque from decreasing at high speeds.

A diagram of the principle of constant current chopper drive is shown in FIG.

The motor current voltage V' is the rated voltage V of the stepping motor.
(usually 5 times or more). When the phase switching transistor 2 is turned on, a current (2) flows through the current detection resistor 4 through the motor winding 6. Then, due to the voltage drop across the resistor 4, a voltage v1 of vl=I·r (r is the value of the resistor 4) enters one input terminal of the error amplifier 8. The other input terminal of the error amplifier 8 is supplied with a reference voltage v2.

22, select so that v2=I'·r (I' is the motor rated current). When the amplification factor of the error amplifier 8 is A, the output voltage v3 of the error amplifier 8 is as follows: When v1-v2≦0 When v3=Ovl-v2>0, v3=A・(v
l-v2). Output voltage v3 is P, W, M, (pulse width modulation)
Enter circuit 10. In the P, W, M circuit 10, the voltage v3 is compared with a sawtooth wave as shown in FIG. 5, and when v3 is larger than the sawtooth wave, the transistor 12 is turned off.
Also, when v3 is smaller than the sawtooth wave, transistor 1
By changing the pulse width for turning on the transistor 12 at a constant cycle according to the magnitude of v3 so that the current flowing through the motor winding a6 is turned on, the current flowing through the motor winding a6 is kept constant.

14 is a flywheel diode that supplies current to the motor winding 6 when the transistor 12 is OFF. The above explanation uses an external oscillator (sawtooth wave) to
This is called a separately excited chopper that changes the N-OFF width. In addition to this, there is also a self-excited chopper in which the transistors ○N-○FF are turned on by the time constant of the motor winding. The self-excited chopper is p and w from Figure 4.

This is an example of the M circuit 10.

Constant current chopper drive makes it possible to flow a constant current through the windings of the stepping motor at a certain high speed, thereby maintaining a constant 1-lux.

However, the speed at which the current rises in the motor winding is limited by the time constant determined by L/R. For this reason, in a high speed range where sufficient current application time is not available for the rise and fall times of the current, as shown in FIG. 6, the loss becomes large and the torque of the stepping motor decreases.

As described above, in the case of a stepping motor, a reduction in high-speed torque is unavoidable. Therefore, when a stepping motor is used in a wide speed range, torque decreases at high speeds, and excessive torque is output compared to the required torque at low speeds, resulting in increased vibration and noise. This is the ninth
As shown in the figure, this is because the amount of overshoot increases due to excessive torque.

In this way, it is desirable that the output torque be constant from low speed to high speed. In particular, constant torque characteristics are desired because the required torque at each speed is constant when performing uniformly accelerated motion. Utility Model Application No. 60-135098 and No. 60-13
Japanese Patent No. 5099 discloses a pulse motor drive circuit that eliminates the above-mentioned drawbacks by passing a drive current in accordance with the drive speed of the pulse motor to a drive coil of the pulse motor.

[The problem that the invention attempts to solve]

Stepping motors require higher voltages as they become faster, so while constant current chopper drive provides a voltage that is sufficiently higher than the stepping motor's rated voltage, at low speeds the stepping motor is significantly lower than the power supply voltage. Furthermore, if a frequency-current conversion method is used that changes the drive current to the coil according to the frequency of the stepper motor's phase switching control pulse, the load will be even lighter. If switching is controlled at a high voltage to create a constant current, the fluctuations between ON and FF are large, so the current ripple (fluctuation range) becomes large, causing vibrations and reducing efficiency. In addition, since the rise is fast, the mechanical overshoot becomes large, which also causes vibration.

The present invention aims to eliminate the above-mentioned defects.

[Means to solve problems]

In order to achieve the above object, the present invention detects the magnitude of the current in the power supply circuit of the winding of a stepping motor, detects the deviation of the value of the detection signal from the set value by an error detection means, and detects the error. In the circuit, a switching element provided in the power supply circuit is controlled on and off based on an output signal of the power supply circuit so that the current in the power supply circuit changes in a direction that matches the set value, wherein the excitation phase of the winding is The power supply voltage of the power supply circuit of the winding of the stepping motor is changed according to the frequency of the input pulse for switching.

[Effect]

By changing the voltage of the power supply circuit of the stepping motor windings in accordance with the phase switching frequency, current ripple is reduced, mechanical overshoot is also reduced, and vibration is reduced at low speeds. Also, like ripple, noise is reduced and power consumption can be reduced at low speeds.

〔Example〕

The structure of the present invention will be described in detail below with reference to embodiments shown in the accompanying drawings.

In FIG. 1, 20 is a phase switching control circuit for controlling on/off switching of switching elements 26, 28 consisting of transistors, which are provided for each winding fi22 and 24 of each phase of the stepping motor, and the input terminal of this circuit is , is connected to the pulse output terminal of the CPU of the microcomputer. 30 is a switching element consisting of a transistor whose emitter and collector are connected to the power supply circuit to the windings 22 and 24, and the output terminal of the comparator 32 constituting the P, W, M circuit is connected to the base of this switching element. There is.

On one side of the power supply circuit, a positive motor power supply voltage V
M is applied, and the other side is grounded via a current detection resistor 34. The voltage VM is set to a value sufficiently larger than the rated voltage of the stepping motor. 36
゜38 is when winding 22.24 is de-energized, winding 22.2
This is a protection diode that clamps the back electromotive voltage generated in the motor to the power supply voltage of the motor to prevent the switching element from being destroyed, and each cathode side is connected to the power supply through the line L1. 40 is a flywheel diode. 42 is an error amplifier, the negative input terminal of which is connected to the cathode end (emitter) of the switching element 26, 28, and the other input terminal connected to the output terminal of the common mode voltage adding circuit 44. . The output terminal of the error amplifier 42 is connected to the input terminal of the comparator 32.6 The common mode voltage addition circuit 44 has resistors 46°48.50, 52, 54, 5.
6, 58 and an operational amplifier 60, and a resistor 54.
On one side of the line L3 to which 56 is connected, there is a positive group I?
! A voltage V Re f is applied. A current limiting circuit consisting of a Zener diode 64 is provided at the output end of the common mode voltage adding circuit 44 to cut an increase in current in the motor high speed range. 66 is an integrating circuit whose output terminal is connected to the input terminal of the common mode voltage adding circuit 44.

The input end of the integrating circuit 66 is connected to the pulse output end of the CPU via a diode 68 and a DC cut capacitor 70. The integration circuit 66 includes a capacitor 7
2, a resistor 74, and an operational amplifier 76. The anode side of the diode 78 is connected between the capacitor 70 and the diode 68, and the cathode side of the diode 78 is grounded.

A switching element 80 made of a transistor and a coil 82 are connected in series to the power supply circuit. A grounded capacitor 84 is connected to the output end of the coil 82, and the output end is grounded via a voltage dividing resistor 86 and 88, and an error amplifier is connected to the intermediate connection point between the voltage dividing resistors 86 and 88. It is connected to one input end of 90. The other input terminals, ie, inverting terminals, of the error amplifiers 90 and 42 are connected to the output terminal of the common mode voltage adding circuit 44. 94 is a sawtooth wave oscillation circuit, the output terminal of which is connected to the other input terminal of the comparators 92 and 32, and the circuit 94 and the comparator 92 and the circuit 94 and the comparator 32 are each connected to a PWM circuit (pulse width modulation circuit). ).

96 is a capacitor, L4. L6 is a line to which a reference voltage is applied, and is provided to increase the base voltage of the switching elements 80 and 30. 98 is a Schottky barrier diode.

In the above embodiment, only one phase winding [22, 24] of the four phase windings of the stepping motor is shown, but the same control circuit as above is also connected to the other one phase winding. It is something that will be done.

Next, the operation of this embodiment will be explained.

When a pulse train with a frequency corresponding to the rotation speed of the stepping motor is input from the pulse output terminal of the CPU to the phase switching control circuit 20, the control circuit 20 switches the windings 22.2 of each phase.
An on/off signal corresponding to the pulse train is supplied to the control ends (bases) of switching elements 26 and 28 corresponding to No. 4. When the switching element 26 is turned on, current flows through the switching element 30.26 to the winding 22, energizing the winding 22, and when the switching element 28 is turned on, current flows through the winding 24 through the switching element 30.28. Winding 24 is energized. The phase switching control circuit 20 is
The windings of each phase of the stepping motor are excited sequentially, and the rotor of the stepping motor is thereby controlled by the phase switching control circuit 2.
The current passing through the 0 winding 22.24, which rotates at a speed specified by the frequency of the input pulse to 0, flows to the current detection resistor 34, and the voltage drop caused by the resistor 34 causes an error in the voltage corresponding to the amount of current flowing through the winding. It is applied to one input terminal of amplifier 42.

On the other hand, when a rectangular input pulse having a peak value VS and a frequency f is applied to the capacitor 70, the DC component of the input pulse is cut by the capacitor 70, resulting in a waveform shown in FIG. 2<a). Further, since the input pulse is grounded by the diode 78, it becomes a rectangular wave of 0 to -vS as shown in FIG. 2(b). This is because even if the voltage attempts to rise above the ground potential, a forward current flows through the diode 78, and the top end of the pulse does not rise above the ground potential. Also, when the pulse voltage drops, the change in the pulse is reflected by the capacitor 7.
It passes through 0 as it is, and the change in vS of the input pulse becomes a downward change in vS. At this time, the diode 78 is reverse biased, so the waveform does not change. As the voltage v1 on the output side of the capacitor 70 changes, a charge of Q=VS-Cp (Cp is the capacitance of the capacitor 70) flows into the capacitor 72 through the diode 68, and the differential amplifier 76, the capacitor 72,
It is integrated by a resistor 74 and converted from alternating current to direct current. As a result, the integrating circuit 66 has a frequency f of the input pulse.
outputs a DC voltage v2 according to. This output voltage v2 becomes V2==f-CP/Cf·VS (Cf is the capacitance of the capacitor 72).

Op amp 60.

By setting R1=R2=R3=R4 (provided that R4 has a sufficiently high impedance with respect to V2° and dividing resistor v3), a well-known common mode voltage adding circuit is obtained. That is.

V4=V2+V3 holds true.

V3 is for ensuring torque when the motor is running at low speed, and is expressed as V3=Vre f -R6/ (R5+R6).Then, the current value IH when the motor is stopped is:

IH=V3/R8 (R8 is the resistance value of current detection resistor 34) becomes.

The output voltage v4 of the common-mode voltage addition circuit 44 is applied to the other input terminal of the error amplifier 42 of the constant current chopper drive circuit.

Assuming that the amplification factor of the error amplifier 42 is A, the output voltage v5 of the amplifier 42 is as follows: When Vl-V4≦0, v5=O When V1-V4>0(7), V5=A(Vl-V4) . vS enters a comparator 32 of the pulse width modulation circuit, and the comparator 32 outputs a pulse with a width corresponding to the input voltage v5. The output pulse of the comparator 32 is input to the base of the switching element 30, and the switching element 30 is controlled on and off, so that current flows through the windings 22 and 24 according to the frequency of the input pulse. The zener diode 64 limits the voltage v4 using the zener voltage so that the current does not increase unnecessarily at the current cut frequency fc set in the high speed range of the motor. The relationship between the motor current and the input pulse frequency is as shown in FIG. In the above embodiment, the current is changed linearly with respect to the frequency of the input pulse, but the current is not limited to a linear change, and the current is changed in accordance with the characteristics of the stepping motor to achieve low speed and high speed. The difference in torque can be reduced.

On the other hand, the voltage supplied to the emitter of switching element 30 is detected by coil 82 and resistor 86.8.
8 and applied to one input terminal of the error amplifier 90 as v6. If the amplification factor of the error amplifier 90 is A, the output voltage v7 of the error amplifier 90 is V6-V
When 4≦0, v7=O When V6-V4>0, V7=A (V6-V4). v7 enters a comparator 92 of the pulse width modulation circuit, and the comparator 92 outputs a pulse with a width corresponding to the input voltage v7. The output pulse of the comparator 92 is input to the base of the switching element 80, and the switching element 80 is controlled on and off so that the divided voltage at the point P of the power supply circuit is controlled to match v4. That is, the supply voltage of the power supply circuit of the windings 22,24 varies depending on the frequency of the input pulses. In this embodiment, the voltage at point P is changed linearly with respect to the frequency of the input pulse, but the voltage change is not limited to a linear change. You can also do it.

〔effect〕

As described above, in the stepping motor drive where the current is changed according to the constant current or the phase switching frequency of the stepping motor, the voltage applied to the power supply circuit is changed according to the frequency, so that the current ripple is small. This has the effect of reducing mechanical overshoot, resulting in lower vibration at low speeds, as well as reducing noise, similar to ripple, and reducing power consumption at low speeds.

[Brief explanation of drawings]

1 is a circuit diagram showing a preferred embodiment of the present invention, FIGS. 2(a) and 2(b) are explanatory diagrams, FIG. 3 is an explanatory diagram, FIG. 4 is a circuit diagram of the prior art, and FIG. The figure is an explanatory diagram, Figure 6 is an explanatory diagram,
Figure 7(a). (b) is an explanatory diagram, and FIG. 8 is an explanatory diagram. 2... Phase switching transistor, 4... Current detection resistor, 6... Motor winding, 8... Error amplifier, 10... Pulse width modulation circuit. 12...Transistor, 14...Flywheel diode, 20...Phase switching control circuit. 22.24...Winding, 26.28, 30°80
...Switching element, 32.92...Comparator, 34...Current detection resistor. 36.38.40...Diode, 42°90
...Error amplifier, 44...Common mode voltage addition circuit, 60...Operation amplifier, 64...Schener diode, 66...Integrator circuit. 76...Differential amplifier Fig. 2 (0) (b) Fig. 3 ■ Fig. 5 V Fig. 8 ↑ Zhou Pai (KHz)

Claims (4)

[Claims] (1) Detect the magnitude of the current in the power supply circuit of the windings of the stepping motor, detect the deviation of the value of the detection signal from the set value by error detection means, and detect the deviation of the value of the detection signal from the set value, based on the output signal of the error detection means. In a circuit in which a switching element provided in the power supply circuit is controlled to turn on and off so that the current in the power supply circuit changes in a direction that matches the set value, an input pulse for switching the excitation phase of the winding is controlled. A method for driving a stepping motor, characterized in that a power supply voltage of a power supply circuit for a winding of the stepping motor is changed according to a frequency. (2) Detect the magnitude of the current in the power supply circuit of the windings of the stepping motor, detect the deviation of the detected signal value from the set value by error detection means, and detect the deviation of the detected signal value from the set value based on the output signal of the error detection means. A switching element provided in the power supply circuit is controlled on and off so that the current in the power supply circuit changes in a direction that matches the set value, and the frequency of an input pulse for switching the excitation phase of the winding is controlled. In the circuit, the set value is changed according to the voltage of the power supply circuit of the winding of the stepping motor according to the frequency of an input pulse for switching the excitation phase of the winding. A stepping motor driving method characterized by: (3) Detecting the magnitude of the current in the power supply circuit of the winding of the stepping motor, detecting the deviation of the value of the detection signal from the set value by means of error detection means, and detecting the deviation of the value of the detection signal from the set value, based on the output signal of the error detection means. In a circuit configured to turn on and off a switching element provided in the power supply circuit so that the current in the power supply circuit changes in a direction consistent with the set value, an input pulse for switching the excitation phase of the winding is provided. A conversion means for converting the voltage into an electric signal according to the frequency is provided, and a voltage detection means for detecting the magnitude of the voltage of the power supply circuit of the winding of the stepping motor and converting it into an electric signal is provided, and the voltage detected by the voltage detection means is A stepping motor drive circuit characterized in that a constant voltage control circuit that operates in a direction in which a signal and an output electric signal of the converting means match is provided in a power supply circuit for windings of the stepping motor. (4) Detecting the magnitude of the current in the power supply circuit of the winding of the stepping motor, detecting the deviation of the detected signal value from the set value by error detection means, and detecting the deviation of the detected signal value from the set value based on the output signal of the error detection means. A switching element provided in the power supply circuit is controlled on and off so that the current in the power supply circuit changes in a direction that matches the set value, and the frequency of an input pulse for switching the excitation phase of the winding is controlled. The circuit is configured to change the set value according to the winding of the stepping motor, further comprising a conversion means for converting an input pulse for switching the excitation phase of the winding into an electric signal according to the frequency of the input pulse. A constant voltage control circuit is provided which detects the magnitude of the voltage of the power supply circuit and converts it into an electric signal, and operates in a direction in which the detected electric signal of the voltage detecting means matches the output electric signal of the converting means. A stepping motor drive circuit characterized in that it is provided in a power supply circuit for windings of a stepping motor.