JPS62254692A - Stepper motor driving circuit - Google Patents

Abstract

PURPOSE:To reduce the difference of a torque from a low speed to a high speed by varying a current value to a motor in response to the frequency of an input pulse. CONSTITUTION:An integrator 66 outputs a DC voltage V2 responsive to the frequency (f) of an input pulse. A same phase voltage adder 44 adds the DC voltage V2 and a divided voltage V3, and outputs an output voltage V4. An output voltage Vr is applied to the noninverting input terminal of an error amplifier 42 of a constant-current chopper driving circuit. The output voltage V5 of an amplifier 42 is input to a pulse-width modulator 32 to control ON or OFF a switching element 30 in response to the voltage V5. Thus, a current responsive to the frequency of the input pulse flows to windings 22, 24.

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 expressed as TωW·k.

By the way, if the pure resistance of the motor winding is R and the inductance is L, then the impedance Z of the motor winding at frequency f is Z=/V'R0 (2πfL)", and when a stepping motor is used at a constant voltage. As the rotation speed increases, 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. Therefore, for this solution, conventionally constant current chopper drive is used to drive the current at high speed.

Prevents torque from decreasing.

A diagram of the principle of constant current chopper drive is shown in Figure 4.

The motor power supply 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 flows through the current detection resistor 4 via 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.

Here, v2=I'・r (I' is the motor rated current)
choose as desired. If the amplification factor of the error amplifier 8 is A, the output voltage v3 of the error amplifier 8 is v1-v2≦0
When v3=0v l −v 2 > O when v
3=A・(vl-v2), the output voltage v3 is P,
W, M, (pulse width modulation) circuit 10 is entered. P, W, M
In the 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, and when v3 is smaller than the sawtooth wave, the transistor 12 is turned on. To, v3
In order to keep the current flowing through the motor winding 6 constant by changing the pulse width that turns on the transistor 12 at a certain period according to the magnitude of the plow, the current flowing through the motor winding 6 is The flywheel diode described above is called a separately excited chopper that changes the ON-OFF width using an external oscillator (sawtooth wave). Besides this.

There is also a self-excited chopper that turns the transistor ON-OFF depending on the time constant of the motor winding. The self-excited chopper is P from Figure 4.
, W, M times 110.

[Problem that the invention seeks to solve]

Constant current chopper drive allows a certain amount of constant current to flow through the windings of a high-speed stepping motor, allowing constant torque to be maintained. However, the motor winding is L/R.
The rise speed of the current is limited by the time constant determined by . 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 9th
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. However, increasing the power supply voltage of the constant current chopper in order to obtain high-speed torque increases the cost and noise of the entire circuit.

This leads to an increase in vibration and noise due to an increase in the amount of overshoot.

A main object of the present invention is to provide a stepping motor drive circuit characterized by an analog system, which eliminates the above-mentioned defects.

[Means to solve problems]

In order to achieve the above object, the present invention provides: (1) detecting a deviation from a set value of the magnitude of current during excitation of a winding of a stepping motor by means of an error detection means; (3) controlling a switching element provided in a power supply circuit of the winding on and off based on the detection signal so that the deviation becomes zero; (4) converting the set value into an analog DC electric signal according to the frequency thereof; and (4) changing the set value in response to changes in the DC electric signal.

[Effect]

The switching element provided in the power supply circuit of the winding is controlled to be turned on and off in a direction in which the current in the power supply circuit becomes the same as a set value. This set value changes depending on the frequency of the excitation phase switching input pulse of the first winding.

Therefore, as the frequency of the input pulse increases, the current in the power supply circuit of the first winding increases, and as the frequency of the input pulse decreases, the current in the power supply circuit of the first winding decreases.

Due to the above operation, the difference in torque of the stepping motor from low speed to high speed becomes small.

〔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, reference numeral 20 denotes a phase switching control circuit for controlling on/off switching of switching elements 26.28 consisting of transistors provided for each winding 22.24 of each phase of the stepping motor; is connected to the pulse output terminal of the CPU of the microcomputer. Reference numeral 30 denotes a switching element consisting of a transistor whose emitter and collector are connected to a power supply circuit to the windings 22 and 24, and the output terminal of the P, W, M circuit 32 is connected to the base of this switching element. A positive motor power supply voltage VM is applied to one side of the power supply circuit.

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 winding 22
, 24, a protection diode 40 is a flywheel diode that clamps the back electromotive voltage generated in the windings 22, 24 to the power supply voltage of the motor to prevent the switching element from being destroyed. 42 is an error amplifier, one input terminal of which is connected to the switching element 26.
The other input terminal is connected to the output terminal of the common mode voltage adding circuit 44. The output terminal of the error amplifier 42 is the P.

W, 'M (pulse width modulation) circuit 32 is connected to its input terminal. The common mode voltage addition circuit 44 has a resistor of 46°48.5
0,52,54,56.58. and a differential amplifier 60, and a positive base voltage VRef is applied to one side of a line 62 to which resistors 54 and 56 are connected. A current limiting circuit consisting of a Zener diode 64 is provided between the output terminal of the common mode voltage adding circuit 44 and the error amplifier 42 to cut an increase in current in the motor high speed range. 66 is an integrating circuit, the output terminal of which is connected to the input terminal of the common mode voltage adding circuit 44, and the integrating circuit 6
The input terminal of 6 is connected to the pulse output terminal of the CPU via a diode 68 and a DC cut capacitor 70. The integration circuit 66 is.

Capacitor 72. Resistance 74. and a differential amplifier 76. The capacitor 70 and the diode 68
The anode side of the diode 78 is grounded between the diode 7
The cathode side of 8 is grounded.

In the above embodiment, only two phase windings 22 and 24 of the four phase windings of the stepping motor are illustrated, but the same control circuit as above is also provided for the other two phase windings. It is grounded.

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.
On/off signals corresponding to the pulse train are supplied to the control terminals (bases) of the corresponding switching elements 26 and 28.

When the switching element 26 is turned on, current flows through the switching element 30.26 to the winding 22.
is excited and the switching element 28 is turned on, current flows to the winding 24 through the switching element 30.28, and the winding 24 is excited. The phase switching control circuit 20 sequentially excites the windings of each phase of the stepping motor, whereby the rotor of the stepping motor rotates at a speed defined by the frequency of the input pulse to the phase switching control circuit 20. The current passing through the windings 22 and 24 flows through the current detection resistor 34, and due to the voltage drop caused by the resistor 34, a voltage corresponding to the amount of current flowing through one winding is applied to one input terminal of the error amplifier 42.

On the other hand, when a rectangular input pulse with peak value vS and 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 caused by the capacitor 70.
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, the voltage applied to the capacitor 72 through the diode 68 is Q=vS-Cp (Cp is the capacitance of the capacitor 70). ) flows into the differential amplifier 76, 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.
The DC voltage ■2 is output according to the voltage. This output voltage v2 is v2cof-Cp/Cf-vS (Cf is the capacitor 72
capacitance).

The differential amplifier 60 becomes a well-known common mode voltage adding circuit by setting R1=R2=R3=R4 (where R4 has a sufficiently high impedance with respect to V2. and dividing resistor 3). That is, V4=V2+V3 holds true.

vS is to ensure the torque at low speed of the motor and is expressed as V3=Vref -R6/ (R5+R6). At that time, the current value when the motor is stopped is IH=V3/R8 (R8 is the current The resistance value of the detection resistor 34) is as follows.

The output voltage v4 of the common mode voltage addition circuit 44 is applied to the other input terminal of the error amplifier A2 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≦o, V5=O; When V1-V4>C1), V5=A (Vl-V4). vS enters the pulse width modulation circuit 32, and the pulse width modulation circuit 32 outputs a pulse having a width corresponding to the input voltage v5. The output pulse of the pulse width modulation circuit 32 is input to the base of the switching element 3o, the switching element 3o is controlled on and off, and a current flows through the windings 22, 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.

〔effect〕

As described above, the present invention can reduce the difference in torque from low speed to high speed by changing the value of the current flowing through the motor windings in accordance with the frequency of the input pulse which is proportional to the speed of the stepping motor. In particular, when configured to limit the increase in current at high speeds, the difference in torque can be reduced by lowering the torque at high speeds where efficiency is low. Further, there are effects such as reduction in power consumption in a low speed range.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a preferred embodiment of the present invention, FIGS. 2(a) and (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, FIG. 6 is an explanatory diagram, FIGS. 7(a) and (b) are 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, 2
2.24...Winding, 26.28...Switching element, 32...PWM circuit, 34...
...Current detection resistor, 36, 38.40...
·diode. 42...Error amplifier, 44...Common mode voltage addition circuit. 60... Differential amplifier, 64... Zener diode, 66... Integrating circuit, 76...
... Differential amplifier Fig. 2 (Q) (b) Fig. 3 ■ Fig. 5 V Fig. 8 Frequency (in Hz)

Claims (1)

[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 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. 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 stepping motor drive circuit characterized in that a frequency/DC conversion means for converting into a DC electric signal according to the frequency is provided, and a setting value of the error detection means is changed based on an output signal of the conversion means. . (2) The stepping motor drive circuit according to item 1, further comprising a limit means for preventing the set value from increasing beyond a predetermined limit value.