JPS61245173A - Reference latent image forming device of copying machine - Google Patents

Abstract

PURPOSE:To detect image density after development precisely by irradiating the part on a photosensitive body which corresponds to the operation position of a shutter member with none of light from an optical eraser or with the light weakly and forming a reference latent image which has a lower potential than a specific electrostatic charging potential. CONSTITUTION:Projection light is cut off by the shutter 1 at a specific rate to reduce the quantity of projection light reaching the photosensitive body 5 and the latent image having a lower potential than the electrostatic charging potential is formed, and an LED 10b at some part of an interimage eraser corresponding to the part is turned off to form the reference latent image. In this case, the projection light is cut off completely by the shutter 11 and then the operation part on the photosensitive drum is irradiated with weak light from the LED 10b or with less light by the LED 10 by cutting off the projection light by the shutter 11 at the specific rate to form the reference latent image which has the lower potential than the charging potential on the photosensitive body 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a reference latent image forming device for a copying machine. Equipped with an imaging device that forms a latent image and an optical eraser that is composed of a plurality of light emitting elements that erases the charge on the photoreceptor that corresponds to the part other than the original image, and detects the image density after development. The present invention relates to a reference latent image forming device for a copying machine that forms a reference latent image on a photoreceptor for use in printing.

2. Description of the Related Art Conventionally, in a reference latent image forming apparatus of such a copying machine, a reference latent image is formed on a photoreceptor as described below.

In other words, a reference pattern is provided near the original platen glass of the table on which the original is placed, and by scanning this reference pattern when scanning the original with the scanning device, the latent image of this pattern is transferred to the photoreceptor. (See, for example, Japanese Patent Laid-Open No. 54-61938).

Problems to be Solved by the Invention However, the conventional configuration described above tends to cause the following problems, and there is room for improvement.

In other words, the reference latent image is used exclusively to detect the image density after development, and it is not desirable for the reference latent image to be developed and copied together with the original. It is necessary to form the image on a portion other than the upper document latent image. Therefore, as described above, in the case of a method in which the reference pattern is provided on the document table, the reference pattern must be positioned one step away from the document in the direction of scanning by the scanning device. Follow °
The time required for scanning by the C1 scanning device is longer than when scanning only the original by the time required to scan the reference pattern portion, resulting in a reduction in copy speed.

In addition, since the reference pattern is provided on the document table, for example, when enlarging or reducing the original for copying, the reference latent image on the photoreceptor due to this reference pattern will also be created in the same way. It will be formed by being enlarged or reduced. Therefore, since the size of the reference latent image varies depending on the copying magnification, variations in detection by a photosensor or the like provided for detecting image density after development tend to occur. Therefore, for example, when controlling the toner concentration in the developer based on the detected image density, there is a risk that the control will have large fluctuations.

Therefore, in order to solve the above-mentioned inconvenience, a method can be considered in which a light shielding member is provided in the middle of the projection optical path without providing a reference pattern near the document table glass, and thereby a reference latent image is formed on the photoreceptor. In this method, the potential of the reference latent image becomes the same potential as the charging potential, resulting in the following inconvenience. That is, the curve in FIG. 8 (al) is a graph showing the relationship between the toner density and the resulting image density when the potential of the latent image on the photoreceptor is the same as the charging potential.
As is clear from this graph, the curve (al) with respect to the appropriate toner density range C%d is slightly saturated with little difference in image density, and a highly accurate photosensor is required to detect this change in image density. detection means are required.

In view of the above-mentioned circumstances, the present invention has been devised to avoid the inconvenience of a reduction in copying speed caused by scanning a reference chart, to ensure that the size of the reference latent image does not change even when copying is enlarged or reduced, and that the formed reference latent image is It is an object of the present invention to provide a reference latent image forming device for a copying machine in which, when an image is developed, the image density changes sufficiently in accordance with changes in toner density.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides the following:
an imaging device that projects and forms an electrostatic latent image on a uniformly charged photoreceptor; In a copying machine that is equipped with an optical eraser constituted by a light emitting element, and forms a reference latent image on a photoreceptor for detecting the image density after development, the projection light is blocked or the light is blocked at a predetermined ratio. a shutter member; a displacement means for displacing the shutter member between a position where it acts on projection light and a position where it does not act on the projection light; and a latent image formed on a photoreceptor when the shutter member is in the action position. an optical eraser control means for prohibiting lighting of a light emitting element of the optical eraser corresponding to a position or reducing the amount of light when the light emitting element is turned on, the shutter member, the displacement means, and the optical eraser control means; The present invention is characterized in that a reference latent image having a potential lower than the charging potential is formed by the means.

In order to form a reference latent image for detecting the image density after development, a shutter member is moved into the projection optical path by a displacement means to create a region on a part of the photoreceptor where no light is irradiated, and By lowering the potential of the reference latent image thus formed than the charging potential, this latent image is prevented from becoming saturated when developed.

Therefore, when the C1 shutter member blocks the light projected onto the photoreceptor at a predetermined rate, the shutter member blocks the light from the optical eraser to suppress wasteful adhesion of developer to areas other than the document latent image. If the light from the optical eraser is not irradiated or is weakly irradiated to the part of the photoreceptor, or if the shutter member blocks the projected light onto the photoreceptor, the light from the optical eraser is transmitted to the shutter on the photoreceptor. By irradiating a portion corresponding to a position blocked by one member with a reduced amount of light, a reference latent image having a potential lower than the charging potential is formed on the photoreceptor.

Furthermore, the shutter member is located in the projection optical path from the imaging device to the photoconductor, and the optical eraser does not directly act on the projection light from the imaging device, so the cooperation between the two is important. When forming a reference latent image by operation, the size of the reference latent image on the photoreceptor does not change even if the copying magnification changes depending on the imaging device.

Example The present invention will be described in detail below based on the drawings.

FIG. 1 is a sectional view schematically showing an electrophotographic copying machine.

A manuscript (M
) is irradiated by an exposure lamp (2), and the reflected light from the original (M) is transmitted to an imaging lens (3) and a plurality of mirrors (4).
The image is projected onto the photoreceptor drum (5) via the imaging device (11) consisting of a) to (4d), etc. The scanning device (51
The exposure lamp (2) and the first mirror (4a), which are an example, are configured to move to the right in the figure by a drive mechanism (not shown) to scan the original (M). The image of the document (M) scanned by the scanning device (S) is formed on the photosensitive drum (5) which is rotated in the direction a1 in the figure by a drive mechanism (not shown), forming an electrostatic latent image. is formed.

Around the photosensitive drum (5), there is a main charger (6), which is an example of a charging device that uniformly charges the surface of the drum.
A developing device (D) that attaches toner to an electrostatic latent image formed by projection imaging by an imaging device (11) and visualizes it, and transfers the developed image to a transfer paper (D) that is fed by a registration roller (7).
P) and the transfer paper (I) are transferred onto the photoreceptor drum (
A main eraser (8) for erasing the electric charge on the photoreceptor drum (5) after transferring the developed image onto the transfer paper (5);
) Cleaner (9) to remove excess toner from the surface.
) etc. are arranged in that order.

The developing device (D) of this copying machine is configured to develop the electrostatic latent image using a so-called regular development method in which toner is attached to the charged portion of the photoreceptor drum (5). ing.

In addition, in front of the developing device (D), a blank eraser (10) is provided as an optical eraser for erasing the charge in a portion of the photosensitive drum +51 corresponding to a portion other than the document latent image, that is, a so-called inter-image portion. It is. In other words, the main charger (6
) takes into account the rise and fall times of its operation, in order to uniformly charge the area where the document latent image is formed, it is necessary to charge the photosensitive drum (
5) It is necessary to operate the apparatus above as well, and it is preferable to keep operating the apparatus at all times, especially when performing continuous copying work at high speed.

Therefore, charges exist on the photoreceptor drum (5) in areas other than the latent image of the document, and if the photoreceptor drum (5) is passed through the developing device (D) as it is, the copy will not be processed. The result is that toner is wasted even though it is not necessary at all. Therefore, the inter-image eraser (10
This is to remove charges in areas other than the required area before passing through the developing device (D). The inter-image eraser Oα is a plurality of light emitting diodes (hereinafter abbreviated as LED) (10a) arranged in parallel along the longitudinal direction of the photoreceptor drum (5).

(job).

On the other hand, in this copying machine, a reference latent image (Ll) for detecting the image density after development is placed on the photosensitive drum (5) in the inter-image area that is not transferred onto the transfer paper (Pl). Next, the structure will be explained.

As shown in FIG. 1, in the middle of the optical path of projection onto the photoreceptor drum (5) by the imaging device (11), there is a position-changing and fixable structure that can be freely changed and fixed between a position where the projection light (Bl) is shielded and a position where it is not shielded. Shutter (ID is provided. This shutter (
Reference numeral 111 is an acrylic plate that blocks the projected light at a predetermined ratio, and as shown in FIG. 2, it is welded to a part of the rotating shaft supported by a pair of bearings (2). A collar for operation is fixed to one end of the rotating shaft (131),
The shutter (111) is biased by a spring I) attached to this collar circle so that it rotates upward in the figure around the rotation axis (Xl) and retreats from the projection optical path. It is connected to an operating rod 0 seconds opposite the solenoid aη via a link mechanism αe.

Then, by energizing the solenoid aη, the operating rod α
The mark is drawn and the shutter (11) is rotated downward in the figure around the rotation axis (X1) against the biasing force of the spring mark so as to be positioned on the path of the projection light (BJ). There is.

When the shutter (111) is activated, the shutter (111
on the photoreceptor drum (5) at a portion corresponding to the action position of
A latent image (LI/) is formed at a potential slightly lower than the potential charged by the main charger (6) and corresponding to the shape of the shutter (111). Thus, the manner in which a latent image (LI/) is formed on the C photosensitive drum (5) is schematically shown.

The latent image (Ll/) formed in this way is located in the inter-image area, and this inter-image area is connected to a plurality of LEDs (
loa), (fob) When passing through the caranal inter-image eraser (uo), the charge is eliminated by the inter-image eraser (Iα), as mentioned earlier. The inter-image eraser a
is provided very close to the surface of the photoreceptor drum (5), and has a width approximately equal to the number of LEDs (10b) to be turned off. The charge remains without disappearing. Also, the LEDs that turn off (job)
The electric charge remains without disappearing for a length that the photoreceptor drum (5) rotates for approximately the same time as the oil dissolution time. Therefore, a shapeless reference latent image (LI) is formed on the photoreceptor drum (5). FIG. 4 shows a portion of the inter-image eraser σ■.
A state in which a reference latent image (LI) is formed on the photoreceptor drum (5) by turning off the light (lQb) is schematically shown.

As described above, while the reference latent image (LI) is formed on the photoreceptor drum (5) by the cooperation of the shutter tti> and the inter-image eraser 0), the scanning device (S) performs scanning. Return to the starting position and prepare for the next scanning operation.

Therefore, the time required for scanning is the minimum necessary for only the portion corresponding to the document (M), and the copying speed can be improved.

The reference latent image (LI) formed as described above is the first
As shown in the figure, as the photoreceptor drum (5) rotates, it passes through a developing device (D), where toner is attached and visualized. A graph showing the relationship between image density and toner density at this time is curve (b) in FIG.

That is, the curve (bl) in FIG. 8 is a graph showing the relationship between image density and toner density when the potential of the reference latent image is lower than the charging potential. It can be seen that there is a noticeable change in image density compared to the charged potential.This is because when a reference latent image with a potential lower than the charging potential is developed, an image with an intermediate tone between black and white is obtained, and the image does not become saturated. It's for a reason.

Thereafter, the photoreceptor drum (5) passes through the transfer separation device (T), but since the reference latent image (Ll) is formed in the area between the images, it is not transferred onto the transfer paper (Pl) and is transferred to the photoreceptor. It remains on the drum (5).

On the other hand, the separated transfer paper (Pl) is sent to a fixing device (not shown), and the toner transferred onto it is heated by the fixing device to melt and fix it, and then is carried out of the copying machine. .

As shown in FIG.
．． A reflective 7-photo sensor (191) consisting of a light emitting part (19a) and a receiving part (19b) is provided.This photosensor U mark is in the longitudinal direction of the photoreceptor drum (5). It is provided at a position corresponding to the reference latent image (Ll) explained earlier.
Accordingly, the density of the image after developing the reference latent image (Ll) can be detected. In other words, if this image is dark, the amount of light reflected from the light emitting part (19a) is small, and the light receiving part (19a) is reflected less.
The output voltage from 9b) becomes lower. Furthermore, if this image is thinner, more light from the light emitting part (19a) is reflected and the output voltage from the light receiving part (19b) becomes higher. The reference latent image (Ll
) is lower than the charging potential, toner density fluctuations within the developing device (D) are noticeable as changes in image density when the reference latent image (LI) is developed. Therefore, concentration detection by the photosensor side becomes easy. (See Figure 8) The shutter described above (1111 inter-image eraser α0),
FIG. 5 schematically shows the positional relationship of the photosensor αS1 and the reference latent image (Ll) formed on the photosensitive drum (5) with respect to the longitudinal direction of the photosensitive drum (5).

Further, the operation of each of these parts is shown in the time chart of FIG.

As shown in FIG. 5, the center of the shutter (111 (C1
) does not coincide with the center (CO) of the reference latent image (Ll). This is because the portion where the reference latent image (LI) is formed is biased with respect to the longitudinal center of the photoreceptor drum (5). Ori,
In addition, because the shutter (111) is located away from the surface of the photoreceptor drum (5), the light projected by the imaging device (1) is enlarged in the longitudinal direction of the photoreceptor drum (5). However, this is to allow the charge to remain in the necessary area on the photoreceptor drum (5) by blocking the shutter (11J) for the previous projection.On the other hand, the inter-image eraser α■ is the photosensitive drum (5)
Since it is provided very close to the surface, this inter-image eraser (1α) L E D (loa), (ta
The center (C) of the LED (10b) part to be turned off in b) coincides with the center (Co) of the reference latent image (LI).
The width (W2) of the portion becomes the width (W) of the reference latent image (LI) in the longitudinal direction of the photosensitive drum (5). Furthermore, the center (C3) of the photosensor a is also made to coincide with the center (Co) of the reference latent image (LI).

The time chart shown in FIG. 6 corresponds to the inter-image area. Therefore, the inter-image eraser (all L E
D (10a), (tab) lights up. Also,
The exposure lamp (2) requires time to rise and fall when it is activated, and in order to stabilize the amount of irradiation when scanning the original and to increase the copying speed, it is turned on even in the areas between images. It is designed to be maintained. Then, in order to form a reference latent image (LI), the shutter (111) is operated to block the projection light for a certain period of time ((0) by energizing the lensoid surface, and the inter-image eraser (10) is
A part of L K D (10b) is turned off for a certain period of time (t2). The reference latent image (Ll) shown in FIG.
) Photoreceptor drum (5) length in the rotation direction [Yes])
will be decided.

As shown in FIGS. 5 and 6, the width (W!) of the shutter (111) corresponding to the width (W) of the reference latent image is determined from the width (W2) of the L E D (10b) portion where the light is turned off. In addition, the operating time (0) of the shutter (11) corresponding to the length of the reference latent image (L) is set to a large value.
D Set longer than the smoke extinguishing time ([2) of job].
There is C. In other words, as mentioned earlier, shutter αD
is located away from the surface of the photoreceptor drum (5), so when the latent image of the document (M) is being enlarged or reduced by the imaging device (Il), the shutter ( 11) The position of the latent image (LI/) formed by the blocking effect on the projection light (Bl) will shift slightly.

Therefore, regardless of the copying magnification, in addition to turning off some of the LEDs (fob) of the inter-image eraser (10), a standard size of one foot is always placed on the photoreceptor drum (5). A latent image (LI) is formed as described above.

As shown in FIG. 6, when the portion on which the reference latent image (LI) is formed reaches a position facing the photosensor (191) as the photosensitive drum (5) rotates, The light emitting part (191) of the light emitting part (191) is made to emit light for a certain period of time to develop the reference latent image (Ll), and then the image is irradiated [7.
19b) receives the reflected light from the image.

As shown in FIG. 7, this photosensor (191) outputs a voltage signal (Vn) according to the amount of reflected light. ■ It is configured to input.

In the toner supply control means ■, the comparator ■
The output voltage (Vo) from the photosensor (sensor) is compared with a first reference voltage (Vthl). This first reference voltage (Vth 1 ) is based on the reflection density (
ID) is set to about 0.5 to 1.0.

If the output voltage (Vo) is larger than the first reference voltage (Vtht), the output of the comparator (2) becomes "L level. At this time, the density of the image after developing the reference latent image (LI) is low, and the light receiving part (19b) of the photosensor (191)
This is the case when the amount of reflected light received by is large. That is, the developing device (
This is a case where the toner concentration in D) has decreased, and the WLII level output signal (01) from the comparator ■ is received.
[, the central control unit (hereinafter abbreviated as CPU) ■ sends a control signal (02 ) is output.

Also, the output voltage (VD) is equal to the first reference voltage (Vtht).
If it is smaller than , the output of comparator ■ becomes ``H level. At this time, the density of the image after developing the reference latent image (LI) is high, and the reflection received by the light receiving part (19b) of photosensor 4 is high. This is the case when the amount of light is small.

That is, the toner density inside the developing device mouth is higher than the required density, and the H" level output signal (0
1), the CPU II sends the control signal (02
) stops outputting.

In other words, the C1 developing device (
So that the toner density within 9 is always near the set density,
It controls toner supply from the supply device (8) to the developing device q.

As described above, in this embodiment, the shutter U
After blocking the projection light at a predetermined ratio and reducing the amount of projection light reaching the photoreceptor to form a latent image with a potential lower than the charging potential, a portion of the inter-image eraser αO corresponding to this portion is L E A reference latent image is formed by dissolving D (FOB) in oil, but the projection light is completely blocked by a shutter (ID), and then the active part of the photoreceptor drum is
By irradiating with a small amount of light using D (lQb), or by blocking the projection light at a predetermined ratio with a shutter (11J), and then emitting an even smaller amount of light using L E D (lob). too,
It is possible to form a reference latent image on the photoreceptor at a potential lower than the charging potential, and a similar effect can be achieved.

Effects of the Invention As described above, the copying machine according to the present invention uses a shutter member to block the light projected onto the photoconductor or to block the light at a predetermined ratio, and also prevents wasted developer from being applied to areas other than the latent image of the document. By not irradiating the light from the optical eraser for suppressing adhesion to a portion of the photoconductor corresponding to the position where the shutter member acts, or by irradiating it weakly, the necessary charging potential on the photoconductor is reduced. Since it forms a reference latent image with a lower potential, only the original document needs to be scanned by the scanning device, and by eliminating the need for extra scanning that was previously required, a reduction in copy speed can be avoided. became. In addition, since the reference latent image is always formed at a constant size regardless of the copying magnification, there is less variation in detection by a photosensor, etc. provided for detecting image density after development. When controlling toner density based on density, it is now possible to control with less variation, and since the potential of the reference latent image is lower than the charging potential, it is difficult to detect toner density in the developing device. It's easy. Therefore, it has become possible to provide an efficient copying machine that can improve the overall operating efficiency by 7° C. and can also accurately detect the image density after development.

[Brief explanation of drawings]

The drawings show an embodiment of an electrophotographic copying machine according to the present invention, in which FIG. 1 is a cross-sectional view showing a schematic structure of the electrophotographic copying machine, FIG. 2 is a perspective view showing a portion of the shutter, and FIG. 3 is a diagram showing the operation of the shutter. FIG. 4 is a schematic diagram showing the formation of a reference latent image by the operation of the inter-image eraser; FIG. 5 is a schematic diagram showing the positional relationship of parts involved in the formation of the reference latent image;
FIG. 6 is a time chart showing the standard latent image forming operation, and FIG.
The figure is a circuit diagram of the part that detects the density after developing the reference latent image, and Figure 8 is a curve showing the toner density and the resulting image density when the potential of the latent image on the photoreceptor is the same as the charging potential. (This is a graph showing the curve (bl) for a low case as a parameter. (5)... Photoreceptor, (6)... Charging device, αα
...Optical eraser, (1℃...Shutter mechanism,
(M)...Original, (I)...Imaging device, (5
1...Scanning device, (D)...Developing device, (Bl
... Projection light, (Ll) ... Reference latent image. Applicant: Minolta Camera Co., Ltd. Figure 1 Figure 7 Figure 5

Claims (1)

[Scope of Claims] An imaging device that forms an electrostatic latent image by projecting a document image onto a uniformly charged photoconductor, and a portion corresponding to the outside of the document latent image area on the photoconductor. In a copying machine that forms a reference latent image on a photoreceptor for detecting the image density after development, it is equipped with an optical eraser composed of a plurality of light emitting elements to eliminate the electric charge of the image. Alternatively, a shutter member that blocks light at a predetermined ratio, a displacement means that displaces the shutter member between a position where it acts on the projection light and a position where it does not work, and a means that moves the shutter member onto the photoconductor when the shutter member is in the action position. an optical eraser control means for prohibiting lighting of a light emitting element of the optical eraser corresponding to a position of a latent image to be formed or reducing the amount of light when the light emitting element is turned on, the shutter member and the displacement means; A reference latent image forming apparatus for a copying machine, characterized in that a reference latent image having a potential lower than a charging potential is formed by the optical eraser control means.