JPH0229668A - Image density controller - Google Patents

Abstract

PURPOSE:To enhance light receiving efficiency and to improve detection sensitivity by arranging a pair of transmissive image density sensors and controlling them so that they do not detect a toner image left on the joint of a photosensitive body belt abutting on a non-image area. CONSTITUTION:A transmissive photosensitive body is used for the photosensitive body belt 18, and a pair of transmissive image density sensors made of light emitting elements 19 and light receiving elements 20 is disposed close to the front and back of the photosensitive body belt 18 positioned between a developing unit 6 and a transfer unit 7. The image density sensors are controlled so as not to detect a toner image left on the splice of the photosensitive body belt 18 abutting on the non-image area. Namely, the image density sensors detect density after transmitting by the photosensitive body belt 18, whereby the optical path of light passing by the photosensitive layer of the photosensitive body belt can be shortened. Thus, light receiving efficiency is enhanced and detection sensitivity can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image density control device for copying machines, printers, etc.

2. Description of the Related Art Conventionally, image density control devices have been used in copying machines, printers, etc., and here, a copying machine will be used as an example and explained with reference to FIG. The surface of the photoreceptor belt 2 having the seam A charged by the charger 1 is exposed to light by the light source 3 to form an electrostatic latent image. Then, unnecessary portions other than the electrostatic latent image are erased by an eraser 4, passed through a filming removal device 5, and then developed by a developer 6 to form a toner image. The formed toner image is transferred onto a transfer paper 8 by a transfer device 7, separated by a separator 9, and sent to a fixing section IQ where it is fixed, thereby completing the copying. On the other hand, the surface of the photoreceptor belt 2 after the transfer is cleaned by the cleaning device 11, and then returns to its original position and repeats the same process again.

In this case, in order to check the amount of toner adhering to the photoreceptor belt 2 after development and control the amount of toner supplied to the developing device 6, the photoreceptor is placed between the developing device 6 and the transfer device 7. A P sensor 14 including a light emitting element 12 and a light receiving element 13 is disposed on the front side of the belt 2. This P sensor 1
Based on the signal detected by 4, the amount of toner supplied to the developing section 6 is controlled by a toner density control device (not shown).

Problems to be Solved by the Invention FIGS. 4(a) and 4(b) show how light is detected by the reflective P sensor 14 in this manner. The light emitted from the light emitting element 12 passes through the photosensitive layer 15 of the photosensitive belt 2 and is reflected by the conductive layer 16, and the light that passes through the photosensitive layer 15 again is reflected directly from the surface of the photosensitive layer 15. It can be divided into two types: In this case, the light emitting element 12 emits infrared light so as not to detect external light such as visible light, and therefore, most of the amount of light received by the light receiving element 12 comes from the light reflected by the conductive layer 16. To detect. Therefore, since the light passes through the photosensitive layer 15 twice before being detected, the amount of light is weakened, resulting in poor detection efficiency.

In addition, in such a reflective type P sensor 14, the light receiving element 13 may become contaminated due to scattering of toner 17 or carrier (not shown), and the amount of light may deteriorate, which requires frequent cleaning, which is troublesome. there were.

Furthermore, when using the photoreceptor belt 2 with seam A,
Since the image position is determined in advance, there is a difference in the degree of deterioration of the photoreceptor belt 2 between the image area and the non-image area. As a result, the photosensitive layer 15 in the image area and the non-image area
Since there is a difference in the amount of light passing through the P sensor 14, the image quality will be poor even if the control by the P sensor 14 is performed with high precision.

Means for Solving the Problems Therefore, in order to solve these problems, the present invention provides a photoreceptor belt that does not have a photoreceptor that is permeable to odor, and a photoreceptor that is located between a developing device and a transfer device. A pair of transmission-type image density sensors consisting of a light emitting element and a light receiving element are arranged close to the front and back surfaces of the body belt, and these image density sensors detect the toner image remaining at the joint of the photoreceptor belt that corresponds to the non-image area. An image density control means is provided to control the image density so that it does not occur.

Effect: Therefore, by detecting the light transmitted through the photoreceptor belt by the image density sensor, it is possible to shorten the optical path of the light passing through the photoreceptor layer of the photoreceptor belt, thereby increasing light receiving efficiency and detection sensitivity. . In addition, by arranging the light receiving element on the back side of the photoreceptor belt where toner and carrier do not scatter, dirt does not adhere to the light receiving element, so light receiving efficiency can be increased.
Moreover, there is no need for frequent cleaning as in the past. Further, the image density control means causes the image density sensor to
By detecting the toner density only in the image area without detecting the toner density in the non-image area, it is possible to supply toner according to the state of deterioration of the image area actually used, which reduces unevenness in image density. This allows you to always obtain stable images.

Example An embodiment of the present invention will be described based on FIG.

Note that the image density control device in this embodiment will be explained using a copying machine as an example, as in the prior art, and therefore a description of the same parts will be omitted.

The photoreceptor belt 18 is made of a transparent photoreceptor. The image density control device includes a P sensor 21 as a transmission type image density sensor having a light emitting element 19 and a light receiving element 20, and image density control means (not shown) connected to the P sensor 21. . Said P sensor 21
is provided between the developing device 6 and the transfer device 7, which are arranged around the photoreceptor belt 18. The light emitting element 19 of the P sensor 21 is arranged on the front side of the photoreceptor belt 18, and the light receiving element 20 is arranged on the back side of the photoreceptor belt 18 facing the light emitting element 19.

In such a configuration, first, the transmission type P sensor 21
Explain how it works. Light emitting element 19 of P sensor 21
The light emitted from the photoreceptor belt 18, which is made of a transparent photoreceptor, passes through the photoreceptor belt 18, and the light-receiving element 2 disposed on the back side thereof.
0 is detected.

In this case, if the toner 17 is present on the surface of the photoreceptor belt 18, the light from the light emitting element 19 will not pass through the light receiving element 2.
If it is 0, it will not be detected.

Next, a description will be given of how toner density control is performed using the image density control means.

The image density control means connects the P sensor 21 to the photoreceptor belt 18.
The toner image remaining in the seam A portion corresponding to the non-image area is not detected, and only the toner density in the image area is detected. Further, the image density control means performs the following control. First, as an initial setting, the output of the light-receiving element 20 is set to be approximately 4 V in a portion of the image area where there is no toner image.

Next, when a portion of the image area where a toner image exists comes, the amount of light incident on the light receiving element 20 changes according to the amount of toner, so the output also changes in the same way. This output is compared with a reference value and the amount of toner supplied to the developing device 6 is adjusted so that the toner density supplied to the image area is always constant.

By having the image density control means perform such control, it is possible to supply toner according to the state of deterioration of the image area actually used, thereby eliminating uneven image density and always obtaining a stable image. can.

The method of creating an electrostatic latent image in this embodiment is to charge the surface of the photoreceptor belt 18 with the charger 1, and erase unnecessary portions with the eraser 4 without using an exposure means, thereby forming a static latent image of a certain size. Create a latent image. Furthermore, although the image density control device in this embodiment has been described using a copying machine as an example, the present invention is not limited to this, and can also be used for controlling toner density in a printer, for example.

Effects of the Invention The present invention comprises a photoreceptor belt made of a transparent photoreceptor, and a pair of light-emitting elements and light-receiving elements located close to the front and back surfaces of the photoreceptor belt located between a developing device and a transfer device. A transmission-type image density sensor is provided, and an image density control means is provided to prevent the image density sensor from detecting the toner image remaining at the joint of the photoreceptor belt that corresponds to the non-image area. By transmitting the light through the photoreceptor belt and detecting it, it is possible to shorten the optical path of the light passing through the photosensitive layer of the photoreceptor belt, thereby increasing light receiving efficiency and detection sensitivity. In addition, by arranging the light receiving element on the back side of the photoreceptor belt where toner and carrier do not scatter, there is no possibility of dirt adhering to the light receiving element, making it possible to increase the light receiving efficiency. This eliminates the need for frequent cleaning.

Furthermore, the image density control means causes the image density sensor to detect the toner density only in the image area without detecting the toner density in the non-image area, thereby supplying toner according to the deterioration state of the image area actually used. This makes it possible to eliminate unevenness in image density and always obtain stable images.

An explanatory diagram showing the transmission state by the sensor, FIG. 2(b) is an explanatory diagram showing the transmission state by the P sensor when toner is present, and FIG. 3 is a schematic longitudinal sectional side view showing a conventional example.
FIG. 4(a) is an explanatory diagram showing the transmission state by the conventional P sensor when toner is not present, and FIG. 4(b) is an explanatory diagram showing the transmission state by the conventional P sensor when toner is present. It is a diagram.

1... Charger, 2... Photoreceptor belt, 6... Developer.

7... Transfer device, 8... Transfer paper, 18... Photoreceptor belt, 19... Light emitting element, 20... Light receiving element, 21
...Image density sensor, A...Seam applicant Ricoh Co., Ltd. -

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal sectional side view showing one embodiment of the present invention. Figure 2 (a) shows P in the absence of toner. Z diagram

Claims (1)

[Claims] The surface of the seamed photoreceptor belt is charged with a charger, and then an electrostatic latent image is formed, this electrostatic latent image is developed with a developer to form a toner image, and this toner image is transferred with a transfer device. In a copying machine that performs copying by transferring onto paper, the photoreceptor belt is not made of a transparent photoreceptor,
A pair of transmission type image density sensors including a light emitting element and a light receiving element are disposed close to the front and back surfaces of the photoreceptor belt located between the developing device and the transfer device, and this image density sensor An image density control device comprising an image density control means for controlling not to detect a toner image remaining at the seam of the photoreceptor belt corresponding to a non-image area.