JPS633682A - Constant current circuit for stepping motor - Google Patents

Abstract

PURPOSE:To simplify a constant current circuit, by making a current control switching means a switching means common to coils of each phase. CONSTITUTION:Coils 31-34 of each phase of a stepping motor is connected to current detecting resistances 43-46 by means of phase excitation control switching means 35-38. The current value detected by the current detecting resistances 43-46 is inputted into a voltage comparator 39 and compared with the reference voltage V0. In answer to the result of this comparison a current control switching means 30 is ON/OFF controlled and the constant current flows through the coils 31-34 of the stepping motor. On this account, a current control switch can be enough to keep the current constant which flows through coils of each phase of the stepping motor, so that a constant current circuit can be simplified.

Description

Detailed Description of the Invention (Hereinafter in the margin) 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a constant current circuit for a stepping motor used in a copying machine or the like.

[Prior Art] Stepping motors are widely used in precision equipment because their rotational speeds and rotation angles can be precisely controlled, and the number of copying machines that use stepping motors has been increasing in recent years.

First, the basic operation of a copying machine will be explained.

Before driving the optical system drive motor, the photoreceptor consisting of a conductive layer, a photoconductive layer, and an insulating layer is charged by a wide charger as the photoreceptor drive motor rotates. Next, the document table or the optical system is moved by the rotation of the optical system driving motor, and the optical image is scanned and projected onto the photoreceptor. At the same time, the photoreceptor is discharged by a recharging device, and an electrostatic latent image is formed depending on the brightness and darkness of the optical image. After the latent image is entirely exposed to light to form a high-contrast electrostatic latent image, it is made visible by a developer in a developing device. The visible image is then facilitated by corona discharge and transferred to a transfer material. The transfer material is heated by a heater while being conveyed, and the visible image is fixed on the transfer material.

In recent years, an increasing number of such copying machines use stepping motors as optical system drive motors and photoreceptor drive motors.

As a drive circuit system for this stepping motor, the sixth
The constant voltage method shown in the figure and the constant current method shown in FIG. 7 are generally well known.

In FIG. 6, C1, C2, C3, C4 are coils of each phase, Sl, S2, . S3. S4 is coil CI,
This is a switch for supplying or cutting off current to C2, C3, and C4, and consists of a transistor or the like. In Fig. 7, R1°R2, R3, and R4 are respectively coil C
1, C2° Resistance that detects the current flowing through C3, C4, v
ci.

VC2, VC3, and VC4 are voltage comparators. Each voltage comparator has the voltage generated in the current detection resistor of each phase and the reference voltage (2) from the voltage divider circuit DC. is input, and if the current flowing through the current detection resistor is larger than the specified value, the voltage comparators VCI to VC4 turn off the switches Sll to S14, respectively, and if the current is smaller than the specified value, they are turned on to reduce the current flowing through the coil. It's in control.

A constant voltage method is used when using a stepping motor at low speeds, and a constant current method is used when using a stepping motor at high speeds. The constant voltage method has a simpler circuit and is cheaper than the constant current method. The constant current method has a complicated circuit and is expensive.

[Problems to be Solved by the Invention] Stepping motors for copying machines and the like are required to have high speed, high output, and high resolution, so they are often driven using a constant current method. However, as shown in Figure 7, this conventional method requires a current detection resistor and voltage comparator for current detection in each phase, which increases the number of circuit elements, making the device larger and increasing cost. There were drawbacks.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such conventional drawbacks and provide a constant current circuit for a stepping motor with a simple circuit configuration.

[Means for solving the problem] In order to achieve such an object, the constant current circuit for a stepping motor of the present invention has a constant current circuit for comparing the current flowing through the coils of each phase of the stepping motor with a reference current. The switching means for turning on or off the coils of each phase according to the output signal of the comparison means provided in the coils of each phase is characterized in that the switching means is one switching means common to the coils of each phase.

[Function] According to the present invention, the constant current circuit can be simplified because the number of current control switches for keeping the current flowing through the coils of each phase of the stepping motor at a constant current can be reduced to one.

[Example] The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the constant current circuit of the present invention. In the figure, 3o is a constant current control switch, 31
．． 32, 33, and 34 are coils for each phase of the stepping motor, and only four phases are shown in the figure. 35.
36, 37, and 38 are switches for supplying or cutting off current to the coils 31 to 34, respectively; 39, 4;
0, 41, 42 are voltage comparators that respectively compare the current flowing through each coil 31 to 34 with a reference current and output a signal according to the result, 43, 44, 45° 46 are current detection resistors, and 47 is a voltage comparator that outputs a signal according to the result. Based on each voltage comparator! ! Voltage dividing circuits 48, 49, and 50° 51 for manually controlling the voltage are diodes for passing transient currents when the switch 30 is turned off. In this embodiment, each switch 30.
This shows an example in which 35, 36, 37, and 38 are configured with transistors.

The operation of this embodiment will be explained with reference to FIGS. 1, 2, and 3. Figure 2 shows the case of 1-phase excitation, and Figure 3 shows the case of 1-phase excitation.
3 is a timing chart showing the states of switches 35 to 38 and the current values flowing through coils 31 to 34 in the case of two-phase excitation.

First, the constant current value of each coil is ``■'', the resistance value of the current detection resistors 43 to 46 is R, and the voltage Vo of the voltage dividing circuit 47 is ``■''.

=nRI.

First, the case of one-phase excitation will be explained. In the power-on state, when each switch 35-38 is off, no current flows through each coil 31-34, so the non-inverting input voltage of the voltage comparators 39-42 is OV, and the inverting input voltage ■
. rLOWJ than voltage comparators 39 to 42 because it is smaller.
is output, and the switch 30 is turned on. When the switch 35 is turned on in this state (FIG. 2A), the coil 31.
A current begins to flow through the current detection resistor 43, and the non-inverting input voltage RI of the voltage comparator 39 and the inverting input voltage ■. is Vo=RI
(B2 section a in Figure 2). ■. When =RI, the voltage comparator 39 outputs rHI G HJ, the switch 30 is turned off, the current in the coil 31 is cut off, and the non-inverting input voltage decreases. >R1, the voltage comparator 39 outputs rLOWJ again, and the switch 30
is turned on to supply current to the coil 31. This is repeated, and a constant current I flows through the coil 31 (section b of B1 in FIG. 2). When the switch 35 is turned off, the current to the coil 31 is cut off (sections A and E1 in Fig. 2). o When the switch 35 is turned off and the switch 36 is turned on simultaneously (the second
(B), a constant current I flows through the coil 32 as shown in FIG. 2F in exactly the same manner as described for the coil 31. Thereafter, the switch 36 is turned off and the switch 37 is turned on (second
Figure B.

C), switch 37 is turned off, switch 38 is turned on (second
Figures C and D) Then, a constant current flows through the coils 33 and 34 as shown in Figures G and H, respectively.

Next, as an example of changing the number of excited phases, one phase,
1-2 phase excitation in which two phases are alternately excited will be explained.

The switch 35 is turned on in the same way as in the case of one-phase excitation,
A state in which a constant current I is flowing through the coil 31 (Fig. 3 AI,
When the switch 36 is turned on at El), the voltage comparator 40 operates in exactly the same manner as described for the voltage comparator 39, operating the switch 30, and a constant current I flows through the coil 32.
Two phases are excited (FIG. 3 B1.El, Fl). When the switch 35 is turned off to cut off the current in the coil 31 (the third
Figure A2. E2), only the 321st phase of the coil is excited by the constant current I. Thereafter, the switch 37 is similarly turned on to excite the coils 32 and 33, the switch 36 is turned off and only the coil 33 is excited, and so on.
Two phases can be excited alternately, and the exciting current can always be kept constant.

FIGS. 4 and 5 show an example of a copying machine to which the present invention is applied.

FIG. 4 is a configuration diagram of the main body, in which 1 is the main body of the copying machine, 2 is a photoreceptor, 3 is a developing device for developing the latent image on the photoreceptor 2, and 4 is the photoreceptor 2.
A cleaner that removes the toner on the top, 5, 6, and 7 each a charger, 8 an erase lamp that removes the charge on the photoreceptor 2,
9 is a blank exposure lamp, 10 is a transfer paper 13 and a photoreceptor 2.
Registration rollers to align with the image above, J
l is a paper feed roller 12 that feeds the transfer paper 13 into the main body;
14 is a cassette for storing the transfer paper 13, 14 is a transfer paper conveyance section, 15 is an optical unit on which a halogen lamp is mounted, 16
17 is a reflection plate, 17 is a first mirror, and 18 is an optical lens.

FIG. 5 is a top view showing the drive system of the optical system, in which 1 is the main body of the copying machine, 15 is an optical unit, 19 is a halogen lamp, and 20 is a top view showing the drive system of the optical system.
is an optical system drive motor, which is a stepping motor targeted by the present invention. 21 is a transmission means such as a wire for transmitting the power of the stepping motor 20 to the optical unit 15, 22 is a stop plate for fixing the wire 21 to the optical unit 15, 23 is a guide roller for the wire 21, and 24 is a photo sensor. Home position, 2
5 is a home position detection plate, and 26 is an optical unit guide.

[Effects of the Invention] As explained above, according to the present invention, only one current control switch can be used to maintain the current flowing through the coils of each phase of the stepping motor at a constant current, thereby simplifying the constant current circuit. can.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the constant current circuit of the present invention, FIGS. 2 and 3 are timing charts showing the operation of 1-phase excitation and 1-2 phase excitation, respectively, and FIGS. 4 and 5 are FIG. 6 is a diagram of a constant voltage circuit of a conventional stepping motor, and FIG. 7 is a diagram of a constant current circuit of a conventional stepping motor. . 20...Stepping motor, 30...Current control switch, 31.32.33.34...Coil, 35.36,3
7.38... Current supply switch, 39.40, 41
．． 42...Voltage comparator, 43.44.45.46...
・Current detection resistor, 47... Voltage divider circuit. Figure 2 Figure 3 Figure 5

Claims (1)

[Claims] Switching means for turning on or off the coils of each phase according to an output signal of a comparison means provided in the coils of each phase for comparing the current flowing through the coils of each phase of the stepping motor with a reference current; A constant current circuit for a stepping motor, characterized by having one switching means common to phase coils.