JPH0135345B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an electrostatic recording device such as an electrophotographic copying machine or an electrostatic printer. The present invention relates to image control of an electrostatic recording device that detects the density of a visible image obtained by developing an image and controls toner supply based on the detected development characteristics.

[Prior art]

Conventionally, in order to maintain the image quality of copies obtained using electrophotographic copying machines, particularly the density of copied images, at a constant level, a part of the photoreceptor, which is an image carrier, is first exposed to a standard amount of light, and then this is developed. An image density detection device detects the amount of toner adhering to a toner image, and the toner supply amount is automatically controlled based on the amount of toner adhesion detected by the image density detection device. ing. In order to maintain a constant density of a copied image, it is necessary that the measured value by the image density detection device described above be accurate.

The detection pattern exposed and developed on the photoreceptor with a reference light amount forms a latent image of a reference target (reference density piece) placed near the document table (outside the document placement area) on the photoreceptor, and the developing section It is obtained by passing through and developing. In order to detect the image density of this detection pattern, the reflected light from the toner image is detected by a detector. Since the detection pattern is limited to a relatively small portion, in order to accurately detect this reflected light at a predetermined detection timing, a detector is provided to receive and detect the regular reflection component of the reflected light. The detector provided in this manner responds sharply to the condition of the surface of the photoreceptor, provides highly accurate detection results, and can accurately detect image density.

Conventionally, the above-mentioned detection pattern is produced by illuminating a reference target placed near the document table with a document illumination lamp, and depositing the detection pattern image on a photoreceptor whose surface potential has been brought to a constant level by charging means in advance. An image was formed to form a reference latent image.

Providing such a reference target near the document table increases the movement range of copying machines with a movable document table or a movable optical system, which reduces the copy speed and reduces the durability of the illumination lamp. This will also have a negative impact on sexuality, etc. In addition, for documents larger than the size of the document table, there is a method in which the optical system remains fixed while the document is moved and scanned. Imaging a pattern onto a photoreceptor is not easy and requires a special mechanism.

[Purpose of the invention]

The present invention provides an image forming apparatus using a detection pattern on a photoreceptor even in an electrostatic recording device that has a function of copying originals that exceed the size of the document tray as well as documents that are smaller than the size specified by the document tray. The purpose is to give you control.

[Structure of the invention]

The present invention aims to achieve the above object,
The present invention is capable of copying originals that are smaller than a specified size corresponding to a document mounting table and originals that have a length that exceeds the specified size, and scans originals that are smaller than the specified size by moving an exposure optical system, For documents whose length exceeds the specified size, the exposure optical system scans the moving document in a stopped state, forms an electrostatic latent image on the image carrier, and develops the electrostatic latent image. In the electrostatic recording device, the non-image area on the uniformly charged image carrier is provided with a reference density disposed near the document table for originals smaller than the specified size. A piece is scanned and exposed to form an electrostatic latent image, which is then developed to form a detection pattern.For originals with a length exceeding the specified size, the original is developed using a predetermined developing bias to form a detection pattern. The present invention also provides an electrostatic recording device that detects the reflection density of the detection pattern where the toner is attached, and controls the toner density based on the detection signal.

〔Example〕

FIG. 1 shows the structure of an electrophotographic copying machine taken as an example of the electrostatic recording device of the present invention, in which 1 is a photoreceptor consisting of a rotating drum installed in the machine frame;
A charging means 2 is provided on the circumferential surface of the photoreceptor drum 1 for corona charging the surface potential on the photoreceptor.

Reference numeral 3 denotes an exposure means that forms an image of a document placed on a document table 4 onto a rotating, charged photosensitive drum 1 to form a latent image. Reference numeral 5 denotes a developing device, in which the latent image on the photosensitive drum 1 is developed while passing through a developing section of the developing device 5, and toner is electrostatically attached thereto to form a toner image.

6 is a transfer device, and 7 is a separation means. The toner image on the photoreceptor drum 1 is transferred onto a transfer sheet that has been conveyed separately at a position facing the transfer device 6.
The transfer paper to which the transferred toner image is attached is separated from the photosensitive drum 1 in the separating section 7, fixed thereon, and then transported out of the copying machine.

On the other hand, the circumferential surface of the photosensitive drum 1 after the transfer is further rotated and cleaned by a cleaning device 9.
This will prepare for the next copy cycle.

The illustrated electrophotographic copying machine is structured so that it can copy both sheet originals that are smaller than the specified size and sheet originals that are longer than the specified size.
I will explain about this.

A document mounting table 4 corresponding to the size of a specified size sheet document is fixed to the upper part of the copying machine, and a conveyor belt 4a rotated clockwise by drive rollers R1 and R2 and a conveyor belt 4a on its upper surface are rotated clockwise by drive rollers R1 and R2. belt 4
A conveyor device is provided which includes a feed roller 4b for feeding a sheet document and a discharge roller 4c for discharging the sheet document from the conveyor belt 4a.

Further, an exposure optical system 3 comprising a first mirror unit 3a equipped with an exposure lamp L, a second mirror unit 3b, a projection lens 5c, and a reflection mirror 3d is arranged below the document placement glass 4. The first mirror unit 3a has a speed related to the circumferential speed of the photoreceptor drum 1, that is, the speed of the first mirror unit 3a is _V2 , the circumferential speed of the photoreceptor drum 1 is _V3 , and the copying magnification is V. ₂ = V ₃ /n, and the second mirror unit 3b moves to the right in parallel with the document placement glass 4 at 1/2·V ₂ , which is half the speed. It is now possible to move in a straight line. Furthermore, a document stopper 41 is provided at a position facing the left end of the document placement glass 4, and when copying a sheet document of the same size or shorter than the specified size, the document stopper 41 protrudes from the document placement surface to stop the sheet document. , it is possible to retract downward in response to the ejection signal, but when copying sheet originals longer than the specified size, it is possible to maintain the retracted state by special operation. It's getting old.

In such a copying apparatus, when copying a sheet document D ₁ that is equal to or shorter than the specified size, the sheet document D ₁ inserted into the feed roller 4b is moved to the document placement glass 4 by the conveyor belt 4a as shown in the figure. It moves to the left on the top and comes into contact with the document stopper 41 and stops.

Thereafter, the first mirror unit 3a and the second mirror unit 3b move to the dotted line position and perform exposure scanning, and the image on the document surface is rotated at a circumferential speed of V ₃ by the projection lens 3c via the reflection mirror 3d. An image is formed on the circumferential surface of the photoreceptor drum 1.

When the exposure scan is thus completed, the exposure lamp L is turned off and the first and second mirror units 3a and 3b return to the positions indicated by solid lines, but in conjunction with this, the document stopper 41 is retracted downward. ,
After the sheet document _D1 is again moved by the conveyor belt 4a and discharged out of the apparatus via the discharge roller 4c, it again protrudes onto the document placement surface as shown in the figure and is ready for the next sheet document. There is.

On the other hand, sheet originals whose length exceeds the specified size
When copying D ₂ , the exposure optical system 3 does not stop at a fixed position and scan;
The sheet original D ₂ inserted into the photosensitive drum 1 is moved to the left on the original placing glass 4 at a speed of V ₂ by a conveyor belt 4 a, and rotates at a circumferential speed of V ₃ . The image is formed on the circumferential surface of the In this case, since the document stopper 41 is retracted downward, the sheet document D ₂ that has been exposed to light is continuously transported to the discharge roller 4.
It is discharged from the device through c. In such a copying machine, it is not easy to provide a reference target as conventionally used.

In the above-described copying machine, in the present invention, a detector 8 for detecting the density of a detection pattern, which will be described later, is provided at the peripheral edge of the photosensitive drum 1 between the developing device 5 and the cleaning device 9. ing. Detector 8
is a reflective photocoupler consisting of a light-emitting element 8a such as a light-emitting diode and a light-receiving element 8b such as a phototransistor. It is now possible to detect the concentration of

Here, the formation of the detection pattern according to the present invention will be explained. In the present invention, a reference latent image is created on the image carrier without providing a reference target (reference density piece) outside the document placement area, and the same effect as that obtained by forming a detection pattern is obtained. It is. That is, in the copying machine shown in FIG. 1, the detection pattern area P2 provided before or after the image area G2 on which the original image is projected is the lamp L.
This is a latent image formed on the photoreceptor 1 when the light is off. On the other hand, the image area G2 is
Since the non-image area including the detection pattern area P2 is also uniformly charged under the same conditions, the detection pattern area P2 on the photosensitive drum 1 has a latent image with a constant surface potential. becomes.

As is well known, the amount of adhering toner when a latent image is developed varies depending on the developing bias applied to the developing sleeve 52. Therefore, in the present invention, as shown in FIG. Pattern area P2
When the toner passes through the developing device 5, the developing bias applied to the developing sleeve 52 is changed to a constant value, and the toner density is controlled so that the image density is at the level required for the machine.

By passing through the developing device 5, toner adheres to the detection pattern area P2, and the reflection density is measured by the detector 8 shown in FIG.

Detected by the detector 8 in this way,
The reflection density indicated by the voltage of the detection pattern region P2 is compared with the reference density indicated by a preset voltage by a known comparison circuit. When it is determined that the reflection density of the detection pattern area P2 is lower than the preset reference density, toner is replenished from the toner replenishing section 51 in the developing device 5 shown in FIG. 1, or the amount of toner replenishment is It acts to increase the toner concentration of the developer.

Figure 3 shows a basic electrical circuit diagram.
COMP is a comparator built into a circuit consisting of a light emitting element 8a, a light receiving element 8b, etc.
are the potential at point A4 and B4 generated by the reflected light from the detection pattern area when the toner standard density is reached.
Adjustments are made using a variable resistor VR so that the potentials of the points are equal, and each time a copy is made, the developed detection pattern on the photoreceptor 1 is irradiated with infrared light from the light emitting element 8a and the reflected light is emitted. The light is received by the light receiving element 8b. Then, the comparator COMP determines whether the output voltage level at point A4 due to light reception has become higher or lower than the set level B4, and based on that signal, the swinging rod 51a of the toner replenishing section 51 is stopped,
Alternatively, it is activated to control the supply of toner to the developing device 5.

〔Effect of the invention〕

The electrostatic recording device according to the present invention forms a detection pattern on an image carrier not only for copying originals of a size smaller than a specified size corresponding to a document mounting table but also for copying originals with a length exceeding a specified size, This system detects the reflection density of the detection pattern and controls the toner density based on the detection signal, eliminating the need to optically scan the reference target even when the document moves, which was previously considered difficult, and improving copy speed. This has the effect of making it possible to easily control the image while increasing the image quality.

[Brief explanation of drawings]

FIG. 1 is a front view of an electrophotographic copying machine showing an embodiment of the present invention, FIG. 2 is a graph showing an example of the developing bias according to the present invention, and FIG. 3 is a graph showing toner adhesion on the surface of a photoreceptor according to the present invention. An example of a circuit for detecting the amount is shown. 1... Photoreceptor, 2... Charging means, 3... Exposure means, 5
...Developing device, 8...Detector, 8a...Light emitting element, 8b
. . . Light receiving element, 51 . . . Toner replenishing section, 51a . . . Swinging rod, 52 .

Claims (1)

[Scope of Claims] 1. A device capable of copying originals of a size smaller than a specified size corresponding to a document mounting table and originals with a length exceeding the specified size, and for an original having a length smaller than the specified size, an exposure optical system is moved. If the length of the original exceeds the specified size, the exposure optical system stops and scans the moving original, forms an electrostatic latent image on the image carrier, and removes the electrostatic latent image. In an electrostatic recording device that has a step of developing a latent image, a non-image area on the uniformly charged image carrier, and for originals smaller than the specified size, a portion near the original platen. The placed reference density strip is scanned and exposed to form an electrostatic latent image, which is then developed to form a detection pattern.On the other hand, for originals whose length exceeds the specified size, they are developed with a predetermined developing bias and detected. An electrostatic recording device that forms a detection pattern, detects the reflection density at a place where toner of the detection pattern is attached, and controls the toner density based on the detection signal.