JPH0338593B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides image density control in an image forming apparatus of the type that forms an electrostatic latent image of a recorded image on an image support, that is, a photoreceptor, using an optical scanning device such as a CRT and an optical fiber tube. Regarding equipment.

Conventionally, various image recording apparatuses are known that record images using a developing method using a powder developer or a liquid developer using toner or carrier. It is converted into an electrical signal, and the electrical information signal controls the exposure scanning by an optical scanning device such as a CRT and an optical fiber tube to form an electrostatic latent image of the recorded image on the photoreceptor, and performs a series of processes such as development, transfer, and fixing. There are image recording devices that form recorded images through electrophotographic processing.
It is applied to electrophotographic copiers and other printers.

FIG. 1 shows a schematic configuration of the above-mentioned type of image recording apparatus, and is an example in which a recorded image is created from an original image. In the figure, 1 is a document table on which a document M to be recorded is placed, which moves back and forth once in the direction of the arrow, 2 is a lamp that illuminates the document M, 3 is a mirror that reflects light reflected from the document M, and 4 is a lens. , 5 is a photoelectric conversion element such as a CCD that converts the intensity of reflected light into an electrical signal. On the other hand, an electrostatic recording photosensitive layer 6a is provided on the drum 6, and the electrostatic recording photoreceptor used for the photosensitive layer is made of selenium, zinc oxide, organic semiconductors, or the like. The drum 6 rotates in the direction of the arrow, and the photosensitive layer 6a is uniformly charged by the corona charger 7. For example, when the photosensitive layer 6a has selenium as its main component, it is positively charged by the charger 7. The charged photosensitive layer 6a passes through the scanning surface of the CRT and the optical fiber tube 8 as the drum 6 rotates. The scanning surfaces of the CRT and optical fiber tube 8 are placed opposite to the photosensitive layer 6a with a very narrow gap of approximately 50 to 500 μm, and the portion of the photosensitive layer that receives light from the scanning surface has a surface charge. As a result, an electrostatic latent image is formed on the photosensitive layer 6a. As the drum 6 rotates, the photosensitive layer 6a on which the electrostatic latent image is formed passes through a developing device 9, where toner adheres to the electrostatic latent image portion to form a toner image.

On the other hand, the recording paper P is transferred from the recording paper transport section to the photosensitive layer 6a.
The transfer charger 1 is transported at the same speed as the transfer speed.
The toner image contacts the photosensitive layer 6a in the vicinity of 0, and the toner image adhering to the photosensitive layer 6a is transferred onto the recording paper P. Thereafter, the recording paper P is separated from the photosensitive layer 6a by the separation charger 11, transported to the fixing device 13 by the transport section 12, fixed there, and discharged to the stored toner 14. The photosensitive layer 6a loses most of the attached toner during the transfer process, or a small amount of toner that has not been transferred remains on the photosensitive layer 6a. When the photosensitive layer 6a with this residual toner attached passes under the static eliminator 15 as the drum 6 rotates,
The residual adhering toner loses its electrostatic adhesion and is removed and cleaned when passing through the next cleaning device 16, and the thus cleaned photosensitive layer 6a passes under the charger 7 again and is used for the next recording cycle. and the cycle described above is repeated. Here, as the cleaning device 16, a fur brush, roller, blade, wave, etc. are practically used as cleaning means.

Incidentally, for development in this type of image recording apparatus, a two-component developer consisting of a carrier such as iron powder and a toner which is a colored resin powder is widely used, but as the number of recordings increases, the toner in the developer increases. To keep the recording density constant, it is necessary to maintain the toner density in the developer within a predetermined range. If the toner density becomes too high, the background of the recorded material becomes dirty, and if it becomes too low, the image density decreases and the contrast deteriorates.

Conventionally, various methods for keeping toner concentration constant have been proposed, and several methods are known for electrically, physically, or optically detecting and controlling toner concentration. Conventionally, as an image density control method in an image recording apparatus using an optical scanning device, an electrostatic latent image for image density control is formed on a non-image forming area on a photoreceptor.
This is developed by a developing device to form a toner image,
A method is known in which this toner image is irradiated with an exposure light source, the amount of reflected light is detected using a light receiving element such as a phototransistor, and toner replenishment is controlled based on this detection signal (for example,
−16199). To form such an electrostatic latent image for image density control, a signal for this purpose must be generated before outputting the electrical information signal, or if the recorded image is an original image, the original platen on which the original is placed must be A small piece (called a batch) with a standard density (usually optical density 1.0) is placed in the non-image area on the back side, and this small piece is scanned before scanning the original image to create a toner image for image density control. There is also a way to use it as a signal.

By the way, in this type of image recording device, the light emitting end surface of the optical scanning device used as the electrostatic recording head, such as an optical fiber tube, has a very narrow gap (50 to 500 μm) with respect to the photoreceptor.
Since the photoreceptors are arranged opposite to each other, any toner remaining on the photoreceptor tends to adhere electrostatically and physically to the light emitting end surface.

For this reason, in the above image density control type image recording apparatus in which a solid black area (patch toner image) for image density control is formed on the photoreceptor, even if the toner image is removed at each copying cycle, Due to the residual toner, a corresponding portion of the light emitting end face of the optical scanning device is likely to become dirty. When the light projecting end surface becomes dirty, the amount of light from the optical scanning device decreases in that area, but in the case of reversal development, which will be described later, the decrease in light amount causes an increase in the amount of toner adhesion, which further promotes the staining of the light projecting end surface. Conventionally, no particular measures have been taken to deal with this problem. Furthermore, in the image density control method described above, it is of course necessary to create a signal for forming an image for image density control and to control its output timing.
There is also the problem that the circuits and control systems for this become complex.

In view of the above points, the present invention focuses on the fact that toner can be attached to a low-potential member by reversal development. The metal drum is grounded, and toner is applied to the non-image forming area of the photosensitive drum using reversal development. is attached to the toner, and the density of this attached toner is detected by an optical detection element. In this way, it is possible to reduce dirt on the light emitting end face of the optical scanning device, and since the optical scanning device is not used to form an image for image density control, the circuit configuration and control system of the optical scanning device can be simplified. .

The present invention will be explained below based on the drawings.

FIG. 2 is a schematic diagram of the main parts of the image density control apparatus according to the present invention, and the illustrated part is the developing section of the image recording apparatus. In the figure, 6 is a drum, the surface of which is mostly covered with a photosensitive layer 6a, and a conductive member 6b is provided near one end in the axial direction. When selenium, which has been widely used in the past, is used as the photosensitive layer 6a, the drum as described above can be manufactured by masking the vicinity of one axial end of the metal drum and depositing a selenium layer.
The conductive member 6b of the drum 6 is grounded. 9
is a developing device provided opposite to the drum 6, and is, for example, a magnetic brush type developing device. The developing device 9 is provided in the axial direction of the drum 6 to cover approximately the length of the drum, that is, to cover not only the photosensitive layer 6a but also the conductive member 6b. This developing device 9 simultaneously performs reversal development.

Here, reversal development will be explained using FIG. 3.

Figure 3A shows the principle of normal development, and Figure 3B shows the principle of reversal development. In regular development, when the uniformly charged area B of the photoreceptor is exposed, its surface potential becomes as shown. Therefore, the potential of the developing electrode V
When (dashed line) is lowered, negatively charged toner is electrostatically attracted and adheres to areas A and C of the photoreceptor. In this way, positive-positive development is performed. On the other hand, in reversal development, the potential of the surface photosensitive layer 17a of the photoreceptor 17 is as shown in the figure, as in the case of FIG. If the voltage is set to a value close to the potential V of areas A and C, the developing electrode 18 and the photoreceptor 17
The electric field is as shown by the arrow, and the positively charged toner is electrostatically attracted and attached only to area B. In this way, positive-negative development is performed.

Now, after an electrostatic latent image of a recorded image is formed on the photosensitive layer 6a of the drum 6 by an optical scanning device, a developing potential is appropriately set with the grounded conductive member 6b, and reversal development is performed by the developing device 9.
It adheres to the non-charged portion of a and the conductive member 6b. Therefore, by detecting the amount of toner adhering to the conductive member 6b, that is, the density, using an optical detection element, it is possible to extract it as an image density signal. The optical detection element is located between the developing device 9 and the transfer electrode 10 or the separation charger 11 in FIG.
and the cleaning device 16. Image density signals output from the optical sensing element can be used to control toner replenishment and image density. In this case, since various toner replenishment control devices are already known, a description thereof will be omitted.

In the above example, the image for image density control was formed on a conductive member provided at one end of the drum in the axial direction, but a sheet-like photoreceptor using zinc oxide (ZnO), organic photoconductor (OPC), etc. In this case, it is also possible to form it at the center in the width direction. Moreover, the pattern of this conductive member can be selected as desired. In the present invention, metals such as aluminum can be used in addition to selenium as exemplified above as the conductor member forming the image for image density detection.

Further, in the above embodiment, an electrostatic latent image of a recorded image is formed on a photoreceptor using an optical scanning device. The present invention can be similarly applied to the case of forming an electrostatic latent image.

As explained above, the present invention provides an image recording apparatus of the type that forms an electrostatic latent image of a recorded image on a photoreceptor using an optical scanning device such as an optical fiber tube. Using a photosensitive drum made of a photosensitive material, leaving a portion corresponding to the non-image forming area nearby, the metal drum is grounded, and toner is attached to the non-image forming area of the photosensitive drum using reversal development. Since the density of adhered toner is detected by an optical detection element and the replenishment of developer is controlled based on the detection signal, it is possible to prevent the light emitting end surface of the optical scanning device from becoming dirty with toner. Since the image density detection image is not formed by the optical scanning device, the circuit configuration and control system of the optical scanning device can be simplified.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of an image recording device using an optical scanning device, Fig. 2 is a schematic diagram showing the main parts of an image density control device according to the present invention, and Fig. 3 A is an explanatory diagram of the principle of regular development. , B are explanatory diagrams of the principle of reversal development. DESCRIPTION OF SYMBOLS 1... Original table, 2... Lamp, 3... Mirror, 4... Lens, 5... Photoelectric conversion element, 6... Drum, 6a... Photosensitive layer, 6b... Conductive member, 7... Corona charger, 8...
Optical fiber tube, 9...Developing device, 10...
Transfer charger, 11... Separation charger, 12... Conveyance section, 13... Fixing device, 14... Storage tray, 15...
Static eliminator, 16... Cleaning device, 17... Photoreceptor.

Claims (1)

[Claims] 1. A metal drum of a photosensitive drum on which a photosensitive material is formed leaving a portion corresponding to a non-image forming area near one end of the drum on the metal drum is grounded, and the metal drum is placed in contact with the image forming area of the photosensitive drum. An optical scanning device for forming an electrostatic latent image of a recorded image is provided, and an optical detection means is provided close to the non-image area to measure the concentration of the developer attached to the non-image area of the photosensitive drum through reversal development by the developing unit. An image density control device characterized by detecting.