JPH09163795A - Driving circuit for stepping motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce energy loss due to heat generation under the low load in a constant current driving system. SOLUTION: A switching pulse Vp is chopped by the output of a self- oscillating circuit 16 at an AND gate IC3 to turn on or off a switching element 14 connected in series to a motor winding 12. When the switch SW of a time constant circuit 18 in the oscillating circuit 16 is turned on, oscillating frequency becomes higher, and when off, it becomes lower. When chopping frequency is lowered by turning off the switch SW with the load of a stepping motor kept small, the average current of the motor winding becomes low, thus it is possible to restrain heat generation due to the motor winding.

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 particularly, to a stepping motor drive circuit for driving an optical scanner or conveying an original or a recording sheet in a PPC, a facsimile, a printer or the like or a combined device thereof. Regarding a drive circuit.

[0002]

2. Description of the Related Art In a conventional apparatus of this type, a four-phase PM (Permanent Magnet) type stepping motor or an HB (Hybrid) type is generally used to drive an optical scanner or convey an original or a recording sheet. Stepping motors are used. In addition, as the driving circuit, there are a bipolar driving circuit and a unipolar driving circuit. The former has many performance advantages as compared with the latter, but since the external circuit tends to be complicated, it is generally used. Uses a unipolar drive circuit.

Further, as a driving method, a constant voltage driving method or a constant current driving method is well known. In the latter, a voltage sufficiently higher than the motor rating is pulsed by a switching circuit and applied to the motor winding. , It is a method to keep the current constant from low speed rotation to high speed rotation. The constant current drive method tends to be more complicated than the constant voltage drive method, but recently, many dedicated ICs have been marketed,
The constant current drive method is often used for stepping motors that require high torque and high speed rotation.

[0004]

In the constant current driving type stepping motor driving circuit, energy is wasted due to heat generation. More specifically, in a 4-phase PM type stepping motor or HB type stepping motor, the winding resistance of the motor winding is large (especially, PM type stepping motors have large resistance of several tens of ohms). As a result, the heat generated by the winding itself becomes large. That is,
If the motor drive current is set at the maximum load in the constant current drive method, heat is generated similarly even when the drive load is small, and energy is wasted.

Therefore, a main object of the present invention is to provide a drive circuit for a stepping motor capable of reducing energy loss due to heat generation of a motor winding as much as possible in a constant current drive system.

[0006]

SUMMARY OF THE INVENTION The present invention provides a stepping motor control circuit for turning on or off a switching element connected in series to a motor winding of a stepping motor according to a logical sum of a switching pulse and a chopping signal. It is a drive circuit for a stepping motor, characterized in that frequency changing means for changing the frequency of the chopping signal according to the drive load of the motor is provided.

[0007]

When the frequency of the chopping signal is changed, the switching element is turned on or off by the logical sum of the switching pulse and the chopping signal, so that the on period (off period) of the switching element changes, which causes a change in the low output. The heat generation of the motor winding can be reduced.

[0008]

According to the present invention, by changing the frequency of the chopping signal, it is possible to reduce the heat generation of the motor winding when the output is low, and therefore to reduce the energy loss. Other objects and features of the present invention will become more apparent from the detailed detailed description of the embodiments below with reference to the drawings.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a drive circuit 10 of this embodiment.
Is a constant current drive type unipolar drive circuit that drives a stepping motor (not shown) having a motor winding 12 according to a switching pulse Vp. However, it should be noted in advance that although the stepping motor has four phases, only one phase is shown in FIG.

A switching element 14 is connected in series with the motor winding 12 to connect the motor winding 12 and the switching element 1 to each other.
4 is connected in series between the power supply Vcc1 and the ground, and the power supply Vcc1 such as 24 V is applied. A resistor Rs for winding current detection is connected between the switching element 14 and the ground. The voltage generated in the winding current detection resistor Rs is fed back to the oscillation circuit 16. That is, the oscillation circuit 16 includes the comparator IC1, the (+) input of the comparator IC1 is supplied with a voltage Vs1 which is substantially equal to the feedback voltage, for example, 5 V or less, and the (-) input is supplied with the feedback voltage. . The output of the comparator IC1 is added to the output of the time constant circuit 18, which is given to the (−) input of the comparator IC2. A voltage Vs2 such as 5V is applied to the (+) input of the comparator IC2.

The time constant circuit 18 includes a resistor R1 and a capacitor C connected in series, and a resistor R2 is connected in parallel to the resistor R1 via a switch SW. Series connection is power supply Vcc
It is connected between 2 and the ground, and is supplied with a power supply Vcc2 such as 5V. The switch SW is turned on or off according to the magnitude of the driving load of a stepping motor (not shown).

The output of the comparator IC2 is given to one input of the AND gate IC3, and the above-mentioned switching pulse Vp is given to the other input of the AND gate IC3. Therefore, the switching element 14 is turned on or off by the voltage obtained by chopping the switching pulse Vp with the output of the oscillation circuit 16. Such a control circuit 10 is called a constant current chopping type drive circuit.

In the embodiment shown in FIG. 1, the off time T _OFF of the switching element 14 when the switch SW is off.
Is given by the following equation (1).

[0014]

## EQU1 ## T _OFF = KCR1 where K is a coefficient, C is the capacitance of the capacitor C, and R1 is the resistance value of the resistor R1. The off time T _OFF 1 of the switching element 14 when the switch SW of FIG. 1 is turned on is given by the following equation (2).

[0015]

[Formula 2] T _OFF 1 = K · C · {R1 · R2 / (R1 + R2)} Time constant C · R1 is the time constant C · {R1 · R2 / (R1 + R
2)}, and therefore the off time T _OFF of the switching element 14 when the switch SW of FIG. 1 is turned on.
1 is shorter than the OFF time T _OFF of the switching element 14 when the switch SW is turned off (T _OFF > T
_OFF 1), the chopping frequency for chopping the switching pulse Vp becomes high.

FIGS. 2A and 2B show motor winding current waveforms when the chopping frequency is high and when the chopping frequency is low, respectively. FIG.
As shown in FIG. 2B, when the chopping frequency is low, the average current is smaller than that when the chopping frequency in FIG. , The output of the motor is reduced, and the heat generated in the motor winding is reduced. Therefore,
If the time constant of the time constant circuit 18 is switched according to the motor output, that is, the drive load as in the embodiment of FIG.
It is possible to reduce heat generation of the motor winding when the output is low.

As a concrete application example of such an embodiment, a composite machine of an analog copying machine and a facsimile can be considered. In the case of such a multifunction device, ADF (Automatic Doc)
The stepping motor is used as a motor for feeding the document of the ument Feeder) and a motor for driving the optical scanner of the analog copying machine. In the document transportation motor, since the document transportation speed differs depending on the mode, the driving load of the motor differs for each mode. Further, in the motor for driving the optical scanner, since the moving speed of the scanner is different at the time of feeding (scanning) and at the time of returning, the driving load of the motor is different.

Tables 1 and 2 show in which mode the switch SW of FIG. 1 is turned on for each of the original feeding motor and the optical scanner driving motor. In the former case, the switches are switched in the analog copy mode. S
By turning on W and turning off in the other facsimile modes, heat generation of the motor during low-speed document feeding as in the analog copy mode is reduced. In the latter,
Since the load at the time of return is smaller than the load at the time of feed, the switch SW is turned on at this time. Therefore, heat generation of the motor when the scanner returns can be reduced.

[0019]

[Table 1]

[0020]

[Table 2]

In the above embodiment, the self-excited oscillation circuit is used as the oscillation circuit 16. However, a separately excited oscillator circuit may be used. In this case, in order to change the chopping frequency, that is, the oscillation frequency, the frequency of the separately excited signal may be changed according to the motor load.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a waveform diagram showing a motor current waveform when the switch is turned off or on to increase the chopping frequency and when the chopping frequency is decreased in this embodiment.

[Explanation of symbols]

 10 Stepping motor control circuit 12 Motor winding 14 Switching element 16 Oscillation circuit 18 Time constant circuit

Claims (2)

[Claims] 1. A stepping motor drive circuit for turning on or off a switching element connected in series to a motor winding of a stepping motor in accordance with a logical sum of a switching pulse and a chopping signal. A stepping motor control circuit comprising a frequency changing means for changing the frequency of the chopping signal. 2. An oscillator for generating the chopping signal is provided, the oscillator includes a time constant circuit having different time constants, and the frequency changing means includes a switching means for switching the time constant. A stepping motor control circuit described.