JPS63163841A - Exposing device - Google Patents

Abstract

PURPOSE:To suppress the generation of a flicker of a light source which projects light on a body to be read and widen dimming width, and also to simplify circuit constitution by varying a frequency according to the quantity of light from the light source. CONSTITUTION:When the output of a photodiode 51 responding to the illumination of an exposure lamp 4 is converted by a differential amplifier 51 into a voltage proportional to the quantity of light of the exposure lamp 4, the frequency of self-oscillation is determined by a ripple component which can not be cut by a capacitor C2. In this case, the ripple component from the photodiode 51 is varied according to the quantity of light of the exposure lamp 4 to vary the frequency of the oscillation. A transistor TR 1 is therefore turned on and off at the frequency determined by the output of the differential amplifier 53 corresponding to the comparison result between a reference voltage and the ripple from the differential amplifier 52, i.e. whether the ripple is larger than the reference voltage or not, thereby controlling the dimming of the exposure lamp 4. Consequently, a flicker of a fluorescent lamp is precluded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an exposure apparatus applied to, for example, an electronic copying machine.

(Prior Art) As is well known, an electronic copying machine is equipped with an exposure device having an exposure lamp (light source), and the image of the document is read by lighting the exposure lamp and exposing and scanning the surface of the document. It looks like this.

In such an exposure apparatus, a fluorescent lamp is used as an exposure lamp.

Incidentally, in an exposure apparatus using a fluorescent lamp, dimming of the fluorescent lamp is controlled by a separately excited pulse width modulation circuit. That is, to dim the fluorescent lamp, as shown in FIG. 4, a constant frequency pulse is obtained from an external triangular wave (or sawtooth wave) generating circuit 55, and the duty ratio is changed according to the light intensity of the fluorescent lamp 4. Controlled by DO
It is supposed to be done.

However, fluorescent lamps used in exposure devices have a smaller dimming range than halogen lamps. In other words, in a separately excited pulse width modulation circuit, when it is dark, that is, when the amount of light is small,
(The rising pulse of the triangular wave fluctuates without instability), so the duty ratio is limited to about 20% to 15%, and if it is lower than this, the fluorescent lamp starts to flicker.

(Problems to be Solved by the Invention) This invention has the disadvantage that fluorescent lamps have a small dimming range, so when controlled by a passive pulse width modulation circuit, they begin to flicker when the duty ratio in the dark side is reduced to 15% or less. It is an object of the present invention to provide an exposure apparatus that can increase the dimming range by suppressing the flickering of a light source, and can simplify the circuit configuration.

[Structure of the Invention] (Means for Solving the Problems) The exposure apparatus of the present invention includes a light source that irradiates light onto an object to be read, and a light source that changes the frequency according to the amount of light from the light source. , and a dimming means for dimming the light source.

(Function) According to the present invention, dimming of a light source is controlled by changing the frequency according to the amount of light from the light source.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

2 and 3 schematically show an image forming apparatus, for example, a two-color copying machine. That is, 1 is a main body of a copying machine, and a document table (transparent glass) 2 is fixed to the upper surface of the main body 1 for supporting a document (an object to be read). This document table 2 has a fixed scale 2 that serves as a reference for setting the document.
1 is provided, and a document cover 11 that can be opened and closed is provided near the document table 2.

° The original placed on the document table 2 is moved back and forth in the direction of arrow a along the lower surface of the document table 2 by an optical system consisting of an exposure lamp (fluorescent lamp) 4 as a light source and a mirror 5°6.7. By moving, exposure scanning is performed during the forward movement. In this case, mirror 6.7 moves at half the speed of mirror 5 so as to maintain the optical path length. The light reflected from the original by the scanning of the optical system, that is, the light reflected from the original by the light irradiation of the exposure lamp 4, is reflected by the mirror 5°6.
The document is further reflected by mirrors 91, 92, and 93 and guided to the photoreceptor drum (078 mm) 10, so that an image of the document is formed on the surface of the photoreceptor drum 10.

The photosensitive drum 10 rotates in the direction shown by the arrow at the same speed as the scanning speed of the original by the optical system, and the surface is first charged by the charging device 11, and then the image is exposed by slit exposure at the exposure section Ph. As a result, an electrostatic latent image is formed on the surface. This electrostatic latent image is formed by a first or second developing unit 121 or 122 which contains, for example, rarely used red toner or rarely used black toner, and is selectively driven as required. By attaching it, it becomes a visible image.

That is, the above 1. The second developing device 121° 122 is
It is designed to be selectively driven in accordance with the operation of a color change (developing unit selection) key 30a on an operation panel 30 provided on the copying machine main body 1. As a result, in normal times, for example, the electrostatic latent image formed on the photoreceptor drum 10 by the developer 122 is developed with black toner.
When specifying a color using the color change key 30a, the developer 12
1, the electrostatic latent image formed on the photoreceptor drum 10 is developed with red toner.

In this case, for example, in normal times, the toner on the exposed portion of the sleeve constituting the developing device 121 is scraped off by a blade (none of which is shown) provided on the sleeve, so that the red toner does not come into contact with the photoreceptor drum 10. When specifying a color, the toner on the exposed portion of the sleeve constituting the developing device 122 is scraped off by a blade (not shown) provided on the sleeve, and the black toner is applied to the photoreceptor drum 10. It is now considered a contactless state.

The developing units 121 and 122 are detachably attached to the copying machine main body 1, and the color of the toner contained in these developing units 121 and 122 is determined by, for example, a It is set by the connection status of multiple bins of the connector.

On the other hand, sheets of paper (material to be transferred) are taken out one by one from the selected upper paper feed cassette 131 or lower paper feed cassette 132 by the feed rollers 141 and 142 and the pair of rollers 15x and 152. The photosensitive drum 10 is guided to a pair of registration rollers 17 through which the photosensitive drum 10 is guided to a transfer section in synchronization with the rotation of the photosensitive drum 10 . here,
The paper feed cassettes 131 and 132 are detachably provided at the lower right end of the main body 1, and one of them can be selected from the operation panel 30.

Each of the paper feed cassettes 131 and 132 has a cassette size detection switch 60, respectively.

The cassette size is detected by 602. This cassette size detection switch 601.60
2 is composed of a plurality of microswitches that are turned on and off according to the insertion of cassettes of different sizes. Further, a manual feed guide 13a is provided on the upper surface of the paper feed cassette 131.
The paper manually inserted through the feed roller 14
The paper is guided to the pair of rollers 151 by the rollers a, and then transported in the same way as the paper fed from the paper feed cassette 131.

On the other hand, the paper sent to the transfer section comes into close contact with the surface of the photoreceptor drum 10 at the transfer charger 18, so that the toner image on the photoreceptor drum 10 is transferred by the action of the charger 18. . This transferred paper P is transferred to the peeling charger 1
The transferred image is electrostatically separated from the photoreceptor drum 10 by the action of step 9, is conveyed by a conveyor belt 20, and is sent to a fixing roller 21 as a fixing device provided at the end of the conveyor belt. It will be established. After fixing, the paper is discharged to a tray 25 outside the main body 1 by a pair of delivery rollers 22.

Further, after the photosensitive drum 10 has been transferred, residual toner on the surface thereof is removed by a cleaner 26, and afterimages are erased by a static elimination lamp 27, so that the photosensitive drum 10 returns to its initial state. Note that 29 is a cooling fan for preventing the temperature inside the main body 1 from rising. Further, the exposure lamp 4,
The mirror 5 is provided on the first carriage 411, and the mirror 6
．． 7 is provided in the second carriage 412.

On the other hand, the first carriage 411 includes the first carriage 41! A spot light source 131 is provided that is movable in a direction perpendicular to the direction of movement. This spot light [131
is provided with a light-emitting element that irradiates the document table 2 with a spotlight, and by means of this spotlight, it is possible to specify, for example, the erasing range of the document.

Furthermore, an erasing array 150 in which a plurality of light emitting elements are arranged along the longitudinal direction of the photosensitive drum 10 is provided between the charging charger 11 of the photosensitive drum 10 and the exposure section Ph.
is provided, and when performing partial erasure of a document image, the light emitting elements constituting the erasure array are turned on corresponding to the erasure area designated by the spot light source 131, for example, and the photoreceptor drum 10 is charged. It is designed to remove. Therefore, the part where the charge is removed is
Thereafter, in the exposure section ph, even if slit exposure is performed, an electrostatic latent image is not formed, so that the original image is erased.

FIG. 1 schematically shows the main parts of the dimming circuit. That is, the anode of the photodiode 51 that receives light from the exposure lamp 4 is connected to the non-inverting input terminal of the differential amplifier 52. A non-inverting input terminal of this differential amplifier 52 is grounded via a resistor R1 and a capacitor C1 connected in parallel. Further, the cathode of the photodiode 51 is connected to the inverting input terminal of the differential amplifier 52. Furthermore, the inverting input terminal and output terminal of this differential amplifier 52 are connected via a resistor R2 and a capacitor C2 that are connected in parallel.

On the other hand, the output terminal of the differential amplifier 52 is connected to the non-inverting input terminal of a differential amplifier 53 via a resistor R3, and the inverting input terminal of the differential amplifier 53 is connected to a voltage 1f for setting a reference voltage.
A movable contact piece of a variable resistor R4 provided between AVC1 and ground is connected via a resistor R5. This differential amplifier 5
The output terminal of the transistor Tr3 is connected to the non-inverting input terminal via the resistor R6, and is also connected to the base of the transistor Tr1.

The emitter of this transistor Tr1 is grounded, and the collector is connected to an inverter 5 that controls lighting of the exposure lamp 4.
Connected to 4. Moreover, this inverter 54 includes
It is connected to the power supply VC2 and is also grounded.

That is, the output of the photodiode 51 in response to the lighting of the exposure lamp 4 is transmitted to the exposure lamp 4 by the differential amplifier 52.
When converted into a voltage proportional to the amount of light, the capacitor C
The frequency of self-oscillation is determined by the ripple component that cannot be completely cut by 2.

In this case, the frequency of oscillation is changed by changing the ripple component from the photodiode 51 according to the amount of light from the exposure lamp 4. As a result, the transistor Tr1 is turned on and off at a frequency determined by the output from the differential amplifier 53 according to the comparison result between the reference voltage and the pulsating wave from the differential amplifier 52, that is, the magnitude of the ripple with respect to the reference voltage. This controls the dimming of the exposure lamp 4.

In the above configuration, when scanning of the exposure lamp 4 is started in response to, for example, operation of a copy key (not shown) on the operation panel 30, lighting of the exposure lamp 4 is detected by the photodiode 51.

The detection signal from the photodiode 51 is converted by a differential amplifier 52 into a voltage signal proportional to the amount of light from the exposure lamp 4, and is supplied to a differential amplifier 53. Then, the differential amplifier 53 compares the voltage signal from the differential amplifier 52 with the reference voltage, thereby determining the frequency of self-assisted oscillation. That is, the differential amplifier 53 oscillates at a frequency corresponding to the magnitude of the ripple with respect to the reference voltage, which varies depending on the amount of light from the exposure lamp 4. As a result, the transistor Tr1 is turned on and off at a frequency that corresponds to the amount of light from the exposure lamp 4. As a result, the inverter 54 is controlled by a frequency that changes depending on the amount of light, thereby controlling the dimming of the exposure lamp 4, that is, the brightness and darkness of the lighting of the exposure lamp 4.

In this state, the optical system consisting of the exposure lamp 4 and the mirror 5°6.7, the registration roller pair 17, etc. are controlled to scan the original and convey the paper, and the developer 122 and the stripping charger are controlled. 19, the above-described copying operation is performed by controlling the pair of fixing rollers 21, the cleaner 26, the neutralizing lamp 27, and the like. At this time, the exposure lamp 4 irradiates the original with the optimum amount of light for exposure scanning.

According to the above embodiment, the light from the exposure lamp is fed back and the frequency is varied according to the amount of light. This makes it possible to perform dimming control at a frequency based on self-sustained oscillation, so it is possible to prevent fluorescent lamps from flickering in the dark even when the duty ratio is lowered to about 5%. That is, since the frequency is determined by the change in ripple depending on the amount of light, that is, the noise of the circuit itself, the instability of the reference frequency does not affect the change in the amount of light. Therefore, the dimming width of the fluorescent lamp can be increased.

In addition, self-assisted oscillation eliminates the need for a triangular wave generation circuit that obtains a signal of a constant frequency, so the number of parts can be reduced and the circuit configuration can be simplified.

Note that although the above embodiment has been described using a copying machine as an example, the present invention is not limited to this and can be applied to, for example, an image scanner or a facsimile.

Further, in the above embodiment, the case where the application is applied to a copying machine with a fixed document table has been described, but the invention is not limited to this. For example, by fixing the optical system such as an exposure lamp and moving the document table, Needless to say, the present invention can also be applied to a copying machine with a movable document table that exposes and scans a document.

It goes without saying that various other modifications can be made without departing from the gist of the invention.

[Effects of the Invention] As detailed above, the present invention provides an exposure apparatus that can increase the dimming range by suppressing the flickering of the light source and can simplify the circuit configuration. can.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of a dimming circuit showing an embodiment of the present invention, FIGS. 2 and 3 each show the configuration of a two-color copying machine, and FIG. 2 is an external perspective view, FIG. 3 is a side sectional view, and FIG. 4 is a circuit configuration diagram showing a conventional example of a dimming circuit. 1... copying machine body, 4... exposure lamp (fluorescent lamp),
10... Photosensitive drum, 11... Charger for charging, 1
21...First developer, 122...Second developer,
18... Transfer charger, 30... Operation panel, 51
...Photodiode, 52.53...Differential amplifier, 54...Inverter, Trl...Transistor, C1°C2...Capacitor, R1-R6...Resistance.

Claims (3)

[Claims] (1) Exposure characterized by comprising a light source that irradiates light onto the object to be read, and a dimming means that dims the light source by changing the frequency according to the amount of light from the light source. Device. (2) The exposure apparatus according to claim 1, wherein the light adjustment means has a self-excited pulse width modulation circuit. (3) The exposure apparatus according to claim 1, wherein the light source is constituted by a fluorescent lamp.