JPS60131574A - Control method of image density - Google Patents

Abstract

PURPOSE:To obtain an accurate measured value, supply a necessary amount of toner, and maintain stable development characteristics by measuring image density without charging a photosensitive drum elecrostatically. CONSTITUTION:The photosensitive drum 1 is rotated at a zero potential in a dead cycle before a copying cycle until it faces to a developing device 3 without forming any path latent image on a platen on the drum 1 by exposure, charging the drum 1 by a charging corotron 2, and exposing the patch image. Synchronously, the bias potential of a developing roll 3' is switched from a normal potential to a negative potential and the beltlike latent image corresponding to its duration is formed on the drum 1 and developed into a visual image. The optical density is measured by a sensor 8 arranged in a successive rotational direction and its output is inputted to a comparator 9 and compared with a density reference value to send the output to a motor driving circuit 10 according to the comparison result. Consequently, the driving motor 12 of a toner supplementing device 11 is driven to supply a necessary amount of toner into a developing device 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of controlling image density in a copying machine using a two-component developer.

In the conventional technology, a patch of a certain density is placed and scanned, a patch latent image is formed on the surface of the re-drum, its optical density is measured and compared with a reference level, and toner is replenished according to the result. The toner concentration was maintained constant by operating the device.

However, with this method, the patch latent image on the photoreceptor is disturbed due to the influence of changes in the charging characteristics of the photoreceptor and/or changes in charging corotrometry over time, resulting in a high toner concentration in the developing machine.
There was fog in the background and dirt inside the machine due to toner blowing out.

To be more specific, the charging characteristics of the photoreceptor change depending on its fatigue state, and particularly in a continuous copying process, the charging potential of the photoreceptor gradually decreases as the number of copies increases. Therefore, in the conventional case, for example, if a patch image formed in the above-described manner is removed once during the decision cycle of successive copy cycles, its density will be lower than that measured during the preparation cycle before the start of the copy cycle. Therefore, based on the measured value, the toner density control circuit automatically operates to generate a toner density control circuit that indicates that the inside of the imager is higher than the reference value. The toner concentration becomes high and fogging occurs in the background.Furthermore, the suitable toner inside the developing machine is separated from the magnetic brush formed between the developing roll and the photoreceptor and floats inside the copying machine, causing dirt inside the developing machine.

Also, as the number of copies increases, dust floating inside the copier,
Toner, metal powder, etc. contaminated the charged corotron and deteriorated the charging characteristics of the charged corotron.

Therefore, there was a drawback that a satisfactory copy could not be obtained.

Purpose of the Invention Therefore, this book b"1F1A was developed in view of the above-mentioned drawbacks. It forms a patch latent image for toner placement measurement using a method different from the conventional method, and measures toner density by visualizing this. Therefore, by operating the toner replenisher, the standard toner density of the developing machine is maintained, and thus image 1# is produced without fogging in the background and without contaminating the inside of the copying machine.
The purpose is to provide a concentration control method.

Structure of the Invention The above object is to patch ff! on the surface of the photoreceptor drum! An image density control method that controls toner replenishment amount by forming an I image, measuring the optical density of the developed patch image, and comparing it with a reference level, wherein the formation of the patch latent image is controlled by The bias voltage is temporarily switched to a negative bias potential, a part of the toner band formed on the photoreceptor is detected by an optical density sensor, this value is compared with a preset reference density level, and toner is replenished. This can be achieved by controlling the amount.

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

FIG. 1 is a schematic explanatory diagram of a copying machine using the image density control method according to the present invention.
A cleaning device 6 and a static eliminating corotron 7 are shown.

In the normal copying process, the photosensitive drum 1 is charged with a charge by the charging corotron 2, and then a latent image is formed corresponding to the document placed on the document table (not shown) (see the arrow in the figure). This latent image is visualized by the developing device 3, transferred to a paper (not shown) by the transfer and paper corotron, and the static electricity is removed.

The paper is then conveyed to a fixing device, where it is fixed, and then ejected from the copying machine. On the other hand, the photoreceptor laminate 1 is cleaned by a cleaning device 6, and static electricity is removed by a static elimination corotronor.

The above is a general copy cycle, but in the dead cycle before the start of this cycle, the present invention does not form a latent image of the patch on the document table by exposure on the photoreceptor drum. The drum 1 is rotated at zero potential to a position facing the developing device 3 without being charged by the charging corotron 2 and without exposing the patch image on the platen. The bias voltage of the developing roll 3' is changed from the normal bias potential to a negative potential (40
0 to 700V), and forms a band-shaped developed image on the photoreceptor drum corresponding to the duration of that potential (11 & 1lkL3).
It is formed on the surface parallel to the direction of rotation K, and has a width corresponding to the application time of the negative bias potential. Since the latent image formed in this way does not use the charging of the photoreceptor drum or the charging corotron, the latent image is not subject to these changes and is solid black M at a density corresponding to the amount of toner in the developing machine.
It is developed and visualized in the same manner as when developing an image.

Then, without transferring this developed image onto paper, its density is measured by an optical density sensor 8 (consisting of an LE and a phototransistor) arranged in the direction of subsequent rotation. The output of this optical density sensor 8 is input to a comparison circuit 9, which compares this output signal with a concentration reference value that is set internally, and supplies an output to the motor drive circuit 1O according to the result. . The motor drive circuit energizes the drive motor 12 of the toner replenisher 11 in response to the signal from the comparison circuit to supply a desired amount of toner into the developing machine 3.

Effects of the Invention As described above, the present invention performs the image density measurement without charging the photoreceptor drum, so it is easy to measure the image density unlike the conventional method.
Since it is possible to accurately measure image density without being affected by changes in charging characteristics due to the photoreceptor drum, etc. and/or changes over time in the charging corotron, the required amount of toner can always be supplied to the developing machine. Therefore, stable development characteristics can be maintained.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of a copying machine according to the present invention, FIG. 2 is a diagram showing the Z bias voltage of the developing roll of the developing machine shown in FIG. 1, and FIG. FIG. 3 is a diagram showing the upper belt-shaped developed toner and an optical density sensor. (Symbols in the figure) 1: Photosensitive drum 2: Charging corotron 3: Developing machine 3
': Developing roll 4.5: Corotron for transfer and paper static elimination 6: Cleaning device 7; Static elimination corotron 8: Optical quality sensor 9
: Comparison circuit 10: Motor drive circuit 11: Toner replenisher 12: Drive motor (3 others)

Claims (1)

[Claims] Forming a patch latent image on the surface of a photoreceptor drum, measuring the optical density of the patch image after development, and comparing it with a reference level.
An image density control method for controlling the toner replenishment amount by controlling the formation of the patch latent image by temporarily switching the negative bias voltage of the developing roll to a negative bias potential, An image density control method comprising detecting a part of a toner band with an optical density processor, comparing this value with a preset reference density level, and controlling the amount of toner replenishment.