JPS61203896A - Pulse motor drive circuit - Google Patents

Abstract

PURPOSE:To suppress a vibration at a low speed rotation time by varying the current value of an exciting current in response to the rotating speed of a pulse motor. CONSTITUTION:A motor drive circuit has current setting resistors 20a-20c, and a switch 21 is controlled by a changeover controller 22. The controller 22 receives a high and low mode set signal from a terminal of a mode flip-flop 23 and a pulse signal train of the pulse width of the prescribed time (t) from a oneshot multivibrator 24. A resistor 20c is connected at a high speed time, it is set to a current set value I3 to control the current of the pulse motor. A resistor 20a is connected only for the prescribed time (t) from the multivibrator 24 at a low speed time, 20b is then connected, a large current I1 is flowed at phase switching time, and a low current I2 is then flowed to control. The amplitude of the current set value becomes a relation of I2<I2<I3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) This invention relates to a pulse motor drive circuit, and more particularly, it is applied to a paper conveying device of an optical character reading device and a spacing mechanism of a print head of a printer. The present invention relates to a suitable pulse motor drive circuit.

(Prior Art) FIG. 3 is a diagram showing a configuration example of a paper conveyance device of an optical character reading device using a pulse motor drive circuit. In the figure, a sheet of paper 1 on which a character pattern 9 is printed is conveyed by a drive device comprising a belt 2, rollers 3, pulleys 4 and 5, and a pulse motor 6. This character pattern 9 is rung 10. The light is optically read and then converted into an electrical signal by a photoelectric conversion circuit consisting of lenses Ila and Ilb and scanning fluorescent sensors 12a and 12b.

In this type of device, a scanning fluorescent sensor 12a is used in a high-speed mode to transport the paper 1 at high speed and in character reading.

12b. This mode switching is performed by controlling the rotation speed of the pulse motor 6 by the pulse motor drive circuit 7 and control circuit 8 in FIG. Here, in order to rotate the pulse motor 6 at high speed, the pulse motor 6
In order to cancel the back electromotive force induced in the winding, it is necessary to drive it with a high voltage. Conversely, when the pulse motor 6 rotates at a low speed, the back electromotive force is small and an excessive current flows through the windings, causing problems such as overheating of the pulse motor 6.

Therefore, when the pulse motor 6 is operated in a high speed mode and a low speed mode, a pulse motor drive circuit 7 of constant current drive using chopping is generally used.

FIG. 4 shows a circuit diagram of a conventional pulse motor drive circuit 7 for a two-phase pulse motor using constant current drive of this type. In the figure, 13a and 13b are chopping transistors (hereinafter referred to as transistors), 14a to 14d are windings of the pulse motor 6, 15a to 15d are phase excitation transistors (hereinafter referred to as transistors), 16a and 16b.
is a sampling resistor that samples the current flowing through the winding; 17a and 17b are comparators; 18a and 18b
is the chopping current setting resistor (hereinafter referred to as resistor),
19 is a DC power supply. FIGS. 5(a) and 5(b) each show an example of the negative phase current and the corresponding excitation current. To explain the operation of FIG. 4, the control circuit 8
The phase current (FIG. 5(a)) supplied from the phase current (FIG. 3) is applied to the base of the transistor 15a, for example, and the transistor 15a is repeatedly turned on and off. Transistor 15a
When is on, an exciting current flows through the winding 14a from the DC power supply 19 via the transistor 13a. This excitation current is detected as a voltage by the sampling resistor 16a, and becomes one input of the comparator 17a. A voltage set by a resistor 18a is supplied to the other input of the comparator 17a. As a result of this comparison, the transistor 13a is sequentially controlled to turn on and off, and a chopping current as shown in FIG. 5(a) is supplied to the winding 14a as an excitation current. Therefore, the excitation current flowing through the winding 14a is kept constant. still,
The other windings 14b to 14d are similarly controlled.

(Problem to be Solved by the Invention) However, in the conventional pulse motor drive circuit described above, the current value I (Fig. 5) of the chopping current is constant regardless of whether the rotation speed is low or high. There is a problem in that the torque is too large during rotation and vibration occurs when switching phases. As a result, for example, in an optical character reading device, a problem arises in that distortion occurs in the reading of the character pattern 9 on the paper 1.

Therefore, it is an object of the present invention to provide a pulse motor drive circuit which eliminates the occurrence of vibration during low speed rotation and is suitable for application to spacing mechanisms of print heads of optical character reading devices and printers.

(Means for Solving the Problems) The present invention provides a pulse motor drive circuit that supplies a pulsed excitation current to the windings of a pulse motor to drive the pulse motor with a constant current. The present invention is constructed by providing means for varying the current value of the excitation current. The means mainly comprises a plurality of resistors, switching means and switching control means for controlling the switching means. Each of the plurality of resistors is used to set an excitation current corresponding to the number of rotations of the pulse motor, and is used for comparison to control on/off of the chopping transistor provided in the pulse motor drive circuit via a switching means. Supplies the reference voltage for the device. A voltage corresponding to the excitation current is supplied as the other input of the comparator. The switching control means controls the switching means based on the number of rotations of the pulse motor, and connects any one of the resistors to the comparator.

(Function) According to the present invention, the current value of the excitation current changes according to the rotation speed of the pulse motor, so that an excitation current suitable for the rotation speed can be supplied. Furthermore, for example, when the pulse motor rotates at a low speed, the switching control means controls the switching means to connect the resistor and comparator corresponding to the low speed rotation. Therefore, the reference voltage of the comparator is set so as to obtain a chopped excitation current suitable for low-speed rotation. It operates in the same way when the pulse motor rotates at high speed.

(Example) Hereinafter, the present invention will be described in detail based on an example with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention.
゛In this figure, the same reference numerals are given to the same components as in FIG. 4, and the explanations here will be omitted. Center tap portions of the current setting resistors (hereinafter referred to as resistors) 20a to 20c are connected to one input of each of the comparators 17a and 17b via a switch 21 composed of a transistor, FET, etc. Further, one end of each of the resistors 20a to 20c is grounded, and the other end of each of the resistors 20a to 20c is connected to the DC power source 1.
It is connected to the positive terminal of 9.

The switch 21 is controlled by the output of the switching control section n.

The switching control unit B has a mode flip-flop terminal t,
A high-speed mode and low-speed mode setting signal supplied from t8 and a pulse signal train composed of pulses having a pulse width of a predetermined time t supplied from the one-shot multivibrator U are supplied. This time t is the resistance 24a
It can be adjusted by The control circuit 5 supplies phase currents φ and φ4 from the terminals t and t4 to the transistors 15a and 15c, respectively, based on the input pulse input from the terminal t7.
, 15b, 15d (7) Supply to the base.

Further, the control circuit 5 outputs a control signal for mode setting to the mode flip-flop device from the terminal t.

Further, the control circuit 5 outputs a signal that triggers the one-shot multivibrator U in synchronization with the input pulse input from the terminal t.

Next, the operation of this embodiment will be explained with reference to the operation timing diagram of FIG. In Figure 2, φ1~φ4rP
I''P5 indicates signals at locations indicated by the same symbols in FIG. 1, respectively.

First, when the input pulse P shown in FIG. 2(a) is applied to the terminal t of the control circuit 5, the terminal t of the control circuit 5 is applied.

The phase currents φ and φ4 (second
Figures (b) to (e)) show transistors 15a and 15c.
, 15b, 15d, and each winding 14a of the pulse motor.

14c, 14b, and 14d are sequentially excited. Under this situation, when this embodiment is applied to the optical character reading device shown in FIG. 3, a high speed mode for rapidly feeding paper 1 and a low speed mode for character pattern 9 when read manually (when reading) is obtained. For this purpose, this embodiment drives the pulse motor 6 according to the operation described below. In the following explanation, only the phase current φ will be explained, and other phase currents φ2 to φ4 will be explained.
are similar, so the explanation will be omitted.

(A) High-speed mode In the high-speed mode, first the terminal 1 of the control circuit 5. The mode flip-flop is set to high speed mode according to a control signal provided by the controller. In this case, the mode flip-flop terminal t is at a high level, and the terminal 1a is at a low level (FIG. 2(f)).

When the switching control section n receives this mode setting signal from the mode flip-flop n, it controls the switch 21 to connect the resistor 20c and the comparators 17a and 17b. Note that in the high-speed mode, no signal is output from the one-shot multivibrator U.

As a result, the comparators 17g and 17b are supplied with a set voltage corresponding to the set current amount (2) in the high-speed mode. On the other hand, the other input of the comparator 17& is supplied with a voltage corresponding to (proportional to) the excitation current P of the winding 14a (when phase current φ is given) from the sampling resistor 16a. Comparator 17a compares these voltages. For comparison, the excitation current P is the set current value■.

When the comparator 17a turns off the transistor 13a, the comparator 17a turns off the transistor 13a. After the transistor 13a is turned off, when the excitation current P5 becomes equal to or less than the set current value I3, the transistor 13a is turned on again.

Therefore, the exciting current P is not a so-called chopping current, but is kept constant. In this case, the set current value I is set to a current value that generates the necessary torque during startup, high-speed rotation, and stopping. The excitation current P controlled in this way becomes as shown in FIG. 2(i).

Incidentally, when the pulse motor is in a stopped state with the phase current φ being applied, the heat generation of the pulse motor can be suppressed by exciting the winding 14a with a setting current generator 2, which will be described later.

(B) Low-speed mode When rotating a pulse motor in low-speed mode, if the drive torque is unnecessarily large, unnecessary vibrations will occur during phase switching. Must be set to a small value.

In the low speed mode, the mode flip-flop is set to the low speed mode by a control signal output from the terminal t of the control circuit 5. In this case, the terminal t is at a low level and the terminal t8 is at a high level. Furthermore, the one-shot multivibrator Sae generates a pulse signal P4 having a pulse width of a certain fixed time t every time the phase is switched in synchronization with the signal output from the terminal t6 of the control circuit 5 (see Fig. 2). ))
. While the pulse signal P4 is at a high level, the switch 21 is controlled by the switching control section n that receives the output signal from the mode flip-flop device and the pulse signal P4, and the resistor 20a is switched on.
and comparators 17a and 17b are connected. In addition, the resistor 20a
The set current value {circle over (1)} set by 1 is in the relationship II<I3.

As a result, each pulse of the excitation current P is a pulse signal P.

The set current value is kept constant while it is at a high level (
2nd exit)). On the other hand, while the pulse signal P4 is at a low level, the switch 21 is controlled by the switching control section ρ, and the resistor 20
b and comparators 17a and 17b are connected. This resistance 20
The set current value ■2 set by b is I2<II<I! The relationship is as follows. As a result, each pulse of the excitation current P is kept constant at the set current value while the pulse signal P4 is at a low level (FIG. 2(h)). The reason why two types of set current values are set in the low speed mode is as follows. That is, in order to suppress vibration of the pulse motor, it is preferable that the excitation current value be as small as I2.

However, in this case, torque may be insufficient during phase switching, and malfunctions such as step-out may occur. Therefore, by setting the excitation current value to a value such as <I2<II over a predetermined period of time, the shortage of torque can be compensated for. Incidentally, the set current values I, , I, and time t may be set so that the actual device operates stably and vibrations are minimized.

The present invention has been described above based on one embodiment.

The present invention is not limited to two-phase pulse motors, but can be implemented similarly to pulse motors having other numbers of phases.

(Effects of the Invention) As described above, according to the present invention, it is possible to provide a pulse motor drive circuit that can suppress the occurrence of vibrations during low speed rotation. The present invention is suitable for application to spacing means for print heads of optical character reading devices and printers.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is an operation timing diagram of this embodiment, and FIG. 3 is a diagram showing an example of the configuration of an optical character reading device using a pulse motor drive circuit.
FIG. 4 is a diagram showing a configuration example of a conventional pulse motor drive circuit, and FIG. 5 is an operation timing chart of this configuration example. 13a, 13b... Chopping transistor, 14a to 14d... Winding wire, 15a to 15d... Phase excitation transistor, 16a
, 16b...sampling resistor, 17a, 17
b - Comparator, 19... DC power supply, 20a to 20c... Current setting resistor, 21... Switch, n... Switching control unit, O... Mode flip-flop, U...・One-shot multivibrator, 5...control circuit.

Claims (1)

[Claims] In a pulse motor drive circuit that supplies a pulsed excitation current to the windings of the pulse motor to drive the pulse motor with a constant current, means is provided for varying the current value of the excitation current according to the rotational speed of the pulse motor. A pulse motor drive circuit characterized by: