JPS61151641A - Original exposing device - Google Patents

Abstract

PURPOSE:To simplify constitution by making control of the quantity of light of a light source and measurement of the density of an original by using the same detecting device. CONSTITUTION:Irradiated light from a lamp 3 of a light source for exposure reflected by a standard white plate 6 shifted to a reflecting position is received by a photodiode 22. The quantity of light of the lamp 3 is detected, and current supply is controlled, and the quantity of light of the lamp 3 is controlled. After the standard plate 6 returned to the home position, reflected light corresponding to the density of the original is received by the diode 22 and the density of the original is measured using a detecting device for controlling the quantity of light of light source. By common use of the detecting device, constitution of the exposing device is made simple.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a document exposure device installed in a copying machine, facsimile machine, etc.

Conventionally, in copying machines, a document to be copied is exposed to light from a light source such as a halogen lamp or a fluorescent lamp.

An image forming operation is performed based on the reflected light from the original. Therefore, the density of the image formed depends on the brightness of the light source for exposing the document. Therefore, it is conceivable to detect the amount of light from a light source in order to form an image with a desired density, and to control the amount of light based on the detected value.

In addition, the original image density is measured, and according to the measurement results,
Techniques for controlling the imaging process have also recently been proposed.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an original exposure device that achieves good original exposure and is also capable of measuring original image density. a detection means for detecting the amount of reflected light from the exposed exposed portion; a means for measuring the density of the document exposed by the light source based on the output of the detection means; and a control unit for controlling the light amount of the light source based on the output of the detection means. The present invention provides a document exposure apparatus having means.

This allows the light amount control of the light source and the density measurement of the document to be performed using a common detection means, which is effective in terms of configuration and cost.

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

FIG. 1 is a block diagram of a copying machine to which the present invention is applied, and numeral 1 in the figure is a platen on which a document is placed, which is reciprocated by a drive mechanism (not shown). A standard white plate f is provided on the lower surface of the tip of the platen 1. 2 is a rotatable drum having a photosensitive layer made of a seamless organic semiconductor (OPC) around a cylindrical aluminum conductive substrate; 3 is a fluorescent lamp for exposing the original image on the platen 1 to the drum 2; 23 is a pre-exposure lamp; 5 is a primary charger that negatively charges the surface of the photoreceptor in advance; 8 is a developer that develops the electrostatic latent image formed on drum 2; 9 is a developed image on drum z; A transfer charger 11 for transferring to the transfer paper IO is a cassette storing a large number of transfer papers and is detachable from the main body. 13 is a roller that feeds the transfer paper lO one by one from the cassette; 17 is the transfer paper 10;
18 is a belt for conveying the transfer paper lO after image transfer; 20 is a fixing roller for fixing the image on the transfer paper; A discharge roller for discharging the transfer paper onto a tray 16; 15 a cleaner for removing residual toner on the drum 2 after transfer; 12 a pre-cleaning static eliminator for facilitating the removal of residual toner by the cleaner 15; 7 a drum surface. 14 is a convergence rod lens array for focusing the reflected light from the document of the lamp 3 on the drum surface; 22 is the amount of light reflected by the lamp 3 from the document or the standard white plate 6; It is a photodiode that detects.

Explain the operation. When a copy switch (not shown) is turned on, the lamp 3 is turned on, the drum 2 is rotated, and after about one revolution, the platen 1 starts moving forward and the document on the platen 1 starts slit exposure. The reflected image of the lamp 3 is slit-exposed onto the drum 2 via a rod lens array. The photoreceptor of the drum 2 is exposed from the front with a pre-exposure lamp 23, and is further charged with a primary charger 5. When the charged drum surface reaches the exposed surface, the negative charge is removed by the optical image. This forms a negative electrostatic latent image on the drum surface. The latent image is transferred onto a transfer paper 10 by a transfer charger 9 in a development transfer area where AC bias and DC bias are superimposed. One sheet of transfer paper 10 is separated from the cassette 11 by the timing operation of the paper feed roller 13. After being fed and transferred, the transfer paper is separated from the drum by the roller 1B, and transferred to the fixing roller 20 by the belt 19.
The image is fixed thereon and then discharged onto the tray 16 by the rollers 21. After the transfer is completed, the drum surface is neutralized by a pre-cleaning static eliminator 12 and then cleaned by a cleaner 15.

When making continuous copies from the same document, the platen l is reciprocated a number of times set by the ten keys on the copying machine operating section.

Next, the light amount control and automatic image density control (AE function) of the lamp (fluorescent lamp) 3 in the copying machine of this embodiment will be explained.

FIG. 2 is a block diagram of a control circuit for controlling the light amount of the lamp and the AE function. Reference numeral 22 in FIG. 2 corresponds to the photodiode 22 shown in FIG.

The photocurrent of the photodiode 22 is subjected to current-voltage conversion by the operational amplifier 32, and becomes a light amount detection output vA having a voltage value corresponding to the amount of light incident on the photodiode 22. The light amount detection output VA is an analog-to-digital (A/D) converter 33-
1, it is converted into an 8-bit digital value. In addition, the reference level vF from the variable resistor VR2 for setting the light intensity of the lamp and the A from the variable resistor VRI for setting the AE concentration are also supplied.
A/D converter 33 for A/D converting E level WE
-2.33-3, and these are converted into 8-bit digital values in the same way as the light amount detection output vA.

34 is a one-chip microcomputer having memory RAM, ROM, arithmetic section, etc. A/D converter 33
The 8-bit digital value outputted by -1 is input to the microcomputer 34. The microcomputer 34 takes in this 8-bit digital value at a predetermined timing, performs arithmetic processing based on it, and outputs control data for light amount control and AH@Simplification as described later.

Converts the 8-bit digital data output by the input controller 34 into analog data. 36 is a level shift circuit; D
/A converter 35-1 output is level shifted by a predetermined amount,
AE control voltage V9 is formed. AE control voltage vB is supplied to high voltage transformer 37. The high-voltage transformer 37 supplies a developing bias to the developing device 8 shown in the first diagram, and a high voltage to the transfer charger 9, the pre-cleaning static eliminator 12, and the primary charger 5, and supplies it in accordance with the above-mentioned AE control voltage vB. to change the developing bias to be applied to the developing device 8.

The output of the D/A converter 35-2 is a PW consisting of a sledge.
It is also printed on the M modulator 38.

A triangular wave Vc with a repetition period T is also input to the PWM modulator 38 from a pulse generator 39 consisting of an unstable multi-octabulator, and the PWM modulator 38 compares this triangular wave Vc with a threshold voltage VO. According to
A PWMI-tuned output pulse train Vp is generated according to the level of the threshold voltage Vo. FIG. 3 shows the operation of the PWM modulator 38, that is, Vp with a duty ratio τt/T corresponding to the threshold voltage Vo is generated.

41 is a converter oscillator, and 42 is an inverter transformer, which form a high frequency voltage for driving the lamp 3. 40 is a switching circuit, PW
The lamp is turned on and off by the output pulse train Vp from the M modulator 38, and the lamp current IL is supplied to the balance 3 by switching the high frequency voltage from the inverter transformer 42 as shown in FIG. Therefore, PWM'117A
The duty ratio of the high frequency voltage supplied to the lamp 3 is determined in accordance with the duty ratio of the output pulse train Vp from the device 38. still.

IP is a current for preheating the filament of the lamp 3.

A driver 42 generates operation control signals for the high voltage transformer 37, converter oscillator 41, and other AC or DC loads according to the output of the microcomputer 34. Although FIG. 2 shows details regarding the light amount control and AE function, the microcomputer 34
It also performs sequence control of other drive units and process means of the copying machine.

The operation of the circuit block diagram of FIG. 2 will be explained in more detail.

First, the 1til control of the light amount of the lamp 3 according to FIG. 2 will be explained. FIG. 4 is a flowchart showing control operations related to light amount control. Light amount control is executed before exposing the original. That is, when a copy key (not shown) is pressed at the start of am exposure, the lamp 3 is turned on at the initial current ILO, the platen 1 is moved to the left as shown in the first diagram, and the Is semi-white color plate 6 lamp is turned on. It stops at the exposed position (start position) in step 3. As a result, the light from the lamp 3 reflected by the standard white plate 6 enters the photodiode 22 . Therefore, the A/1 converter 33-1 outputs 8-bit data corresponding to the amount of light reflected by the standard white plate 6 as the light amount detection output vA.

The microcomputer 34 receives the zero-crossing pulse of the commercial electric sign, and samples the light amount detection output vA at the time of inputting this zero-crossing pulse. That is, when the commercial power source is 50H2, a sampling operation is performed every 10 ms. The sampled output vA is Σ
+vA is calculated and Σ is stored in a predetermined area of the memory RAM. Along with this, the calculation @n←n+1 is performed, and the sampling of this light amount detection output vA is repeated 5 times until n becomes 5. As a result, the predetermined area of the memory RAM is filled with 5 The sum of the sampling times is stored as Σ.

When sampling of the light amount detection output vA has been completed five times, Σ is divided by 5. As a result, an average value vA obtained by sampling five times is obtained. Also, Σ and n are cleared in preparation for the next light amount detection. The reflected light amount data TI from the standard white plate 6 obtained in this way and the A/D converter 3
3-2 is compared with the reference level vF from the variable resistor VR2. and.

The energization of the lamp 3 is controlled so that the data vA approximately matches the reference level VF.

That is, when the amount of lamp light has not reached the set level, TA is less than vF, and in this case, the threshold voltage Vo to the PWM modulator 38 is lowered and the duty ratio of the high frequency voltage to the lamp 3 is increased. As a result, the lamp current I
L increases, and the amount of light emitted from the lamp 3 increases. Conversely, if the lamp light intensity exceeds the set level, TI>V
F, and in this case, the threshold voltage Vo is increased and the duty ratio of the high frequency voltage applied to the lamp 3 is decreased. As a result, the amount of light emitted from the lamp 3 decreases.

As described above, in this embodiment, the outputs of the A/D converters 33-1 and 33-2 are 8 bits, which is data divided into 256. And IVY-VF l, iii, 2L
The light amount of the light source for exposing the document is determined based on the threshold voltage Vo when vA reaches the range of sB.

Once the light amount of the light source for exposing the original is determined in this manner, the light amount control operation of this embodiment is to start exposing the original and maintain this light amount during copying. Note that a heater may be provided to stabilize the amount of light from the light source to control the ambient temperature around the lamp 3 (fluorescent lamp).

Next, we will explain the AE function during exposure of the original after the light amount control has been completed as described above.The AE function of this embodiment is based on the amount of light reflected from the exposed original during exposure of the original. The developing bias of No. 8 is controlled to maintain the density of the copied image at an appropriate value.

When the above-mentioned light amount control is completed, the platen 1 starts moving from the start position to the right in the first diagram. As a result, reflected light from the document on the platen exposed by the lamp 3 enters the photodiode 22 . Therefore, the output of the A/D converter 33-1 is digital data corresponding to the original density. As is clear from FIG. 5, the relationship between the light amount detection output vA and the density of the original is shown in FIG.

The brighter the document density, the larger the output vA.

When the microcomputer 34 receives a document leading edge signal indicating that the leading edge of the document on the platen has reached the exposure position, it starts sampling the output of the A/D converter 33-1. This sampling is also performed when the zero-cross pulse is input to the microcomputer 34, as in the example of light amount control described above. FIG. 6 shows the relationship between the sampling timing of the light amount detection output VA by the microcomputer 34 and the developing bias control. .

The microcomputer 34 calculates the average value TI of vA of eight consecutive points sampled every time a zero-crossing pulse arrives, and determines the developing bias value Vn corresponding to the document density based on this average value TI. As is clear from FIG. 6, each sampling section consisting of 8 points of sampling overlaps with one sampling section before and after each half (4 points). This is the developing bias value V
By determining the developing bias value including the density of the areas before and after the latent image area on the drum to be developed by n, this is to prevent extreme changes in the copy density at the change point of the developing bias value. be.

In this way, the determined developing bias values are each stored in a predetermined area of the memory RAM, and the photodiode 22
After a delay of time Td until the latent image with the image density detected by the latent image reaches the development position, it is output to the D/A converter 35.

FIG. 7 shows the relationship between the original density (reflected light amount) and the developing bias DC value for the AE@ function in the microcomputer 34. As is clear from FIG. The bias value increases. Further, for document densities that are brighter than a standard document or brighter than a newspaper, a specific bias value is applied. With this type of relationship, the AE sub-control allows for dense originals to be printed without overlapping.
Further, in a thin original, characters, etc. will be clearly reproduced.

The slope of the straight line in FIG. 7 is adjusted by the AE level vE from the variable resistor VRI shown in FIG. Therefore.

Manual concentration setting can be combined with automatic concentration control using the AE function.

In this manner, the developing bias is sequentially controlled according to the density of the original, and the latent image formed on the drum is developed.

Therefore, copies can always be made with good density.

The analog output of the D/A converter 35-1 is subjected to a predetermined level shift in the level shift circuit 36, and then applied to the high voltage tolerance 37. As mentioned above, high voltage transformer 3
7 controls the developing bias of the developing machine according to the value of the AE control voltage vB from the level shift circuit 36.

FIG. 8 shows the relationship between the AE control voltage V from the level shift circuit 36 and the developing bias DC value of the high voltage transformer 37.

As described above, when exposing an original for copying, the density of the original is sampled, and according to this sampling data, the developing bias is sequentially controlled to perform copying with good density.

1. In the AE function of this embodiment, the original density was measured at the same time as the original was exposed for copying. However, before the original was exposed for copying, a briscan was performed to measure the original density, and this prescan After determining the developing bias based on the obtained data, perform the main scan (original exposure) for copying.
It may also be configured to execute.

Further, in this embodiment, a copying machine with a movable document table (platen) has been described, but the present invention can be similarly applied to a well-known copying machine with a fixed document table. Furthermore, the present invention is applicable not only to copying machines but also to light amount control and original density measurement in devices that photoelectrically read original images, such as facsimile machines and digital copying machines.

Further, in addition to a fluorescent lamp, a halogen lamp or the like can also be used as a light source for exposing the original.

As described above, according to the present invention, it is possible to stabilize the light source for exposing the original, and it is possible to always perform good exposure of the original. Moreover, not only light amount control but also process control suitable for the original density can be performed with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a copying machine to which the present invention is applied, FIG. 2 is a block diagram of a control circuit according to the present invention, FIG. 3 is a timing chart showing PWM modulation operation, and FIG. 4 is a flow chart showing light amount control. Figure 5 is a diagram showing the relationship between original density and light amount detection output, Figure 6 is a timing chart showing the relationship between sampling timing of light amount detection output and developing bias control, and Figure 7 is a diagram showing the relationship between original density and developing bias value. 8th v4 is a diagram showing the relationship between the AE control voltage and the developing bias value. 1 is the platen. 2 is a drum 3 is a lamp, 6 is a standard white plate, 22 is a photodiode 34 is a microcomputer, and 37 is a high voltage transformer. Eshi

Claims (1)

[Claims] a light source; a detection means for detecting the amount of reflected light from the exposed portion exposed by the light source; a means for measuring the density of the document exposed by the light source based on the output of the detection means; 1. A document exposure device comprising: means for controlling the amount of light from a light source.