JPH07271173A - Color image developing method - Google Patents

Abstract

PURPOSE:To quickly detect the abnormality of a developer and to prevent the generation of a defect in an image such as surface fogging by forming three reference patches of low, middle and high concentrations and judging the abnormality of the developer when a developing curve at each concentration of the reference patches exceeds a normal range. CONSTITUTION:In an image forming process in an image forming part, three reference patches whose input concentrations are made low, middle and high are formed in the nonimage part of a photoreceptor 1. Then, each reference patch is measured by a concentration sensor 5 and a coefficient of developing curve at each concentration of the patches is calculated and used for the control of the concentration. The value of a part where the developing curve itself is not changed as much as possible is used for controlling the concentration. However, this unchanged point (steady point) is varied according to the state of the developer. At this time, the coefficients of developing curve are obtained from three reference patch concentrations and when the coefficients exceed the normal set range, the abnormality of the development is detected, a toner supplying signal is stopped and the fact is displayed as a message.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus in which a latent image on a photoconductor is developed into a toner image by using a magnetic brush developing device, and a plurality of reference patches developed on the photoconductor surface. The present invention relates to a color image developing method for detecting abnormality of a developer based on the density of the color image.

[0002]

2. Description of the Related Art As is well known, in a magnetic brush developing device, when the developer deteriorates or the mixing ratio of toner to carrier increases, the layer thickness of the developer changes greatly. On the other hand, when the reference potential on the photoconductor is developed and the toner replenishment control is performed by the density signal, the development curve showing the relationship between the development density and the input density changes.

[0003]

If the amount of change in the developing curve is too large, the toner replenishment control mechanism will not operate normally. In particular, when the developer layer thickness starts to decrease, the development curve changes, and at a potential of medium density or higher, the developability decreases.
In this case, in the density control method at a medium density or higher, the toner replenishment amount is larger than usual, and as a result, developer charging failure or background fogging is likely to occur due to an increase in the toner mixing ratio.

The present invention has been made in view of the above points, and measures the development curve at low, medium and high densities,
An object of the present invention is to provide a color image developing method capable of promptly detecting an abnormality of a developer based on the measurement result and preventing occurrence of image defects such as background fog.

[0005]

In order to achieve the above object, a color image developing method according to the present invention develops a reference patch formed on the surface of a photoconductor with a developing device and detects the development density. In the color image developing method in which the state of the developing device is determined by using the above-mentioned reference patch, at least three low-density, medium-density, and high-density reference patches are created, and the development curve at each density of the reference patch is known. When it exceeds the normal range, it is judged that the developer is abnormal.

[0006]

[Operation] The development curve at each density of the reference patch is measured, and the abnormality of the developer is quickly detected based on the measurement result to prevent the occurrence of image defects such as background fog.

[0007]

EXAMPLES Examples of the present invention will be invented based on the drawings. FIG. 1 schematically shows an image forming section of a color copying machine. Reference numeral 1 denotes a drum-shaped photoconductor, and a charging device 2, an exposure unit 3, a rotary developing device 4, and a rotary developing device 4 in a rotating direction of the photoconductor 1. The density sensor 5, the transfer drum 6, the cleaner 7, and the static eliminator 8 are sequentially arranged to face each other. As the photoconductor 1 rotates, the surface of the photoconductor 1 is uniformly charged by the charger 2, and then the latent image of the image is formed by the exposure unit 3. Each of the developing devices 4a of the latent image rotary developing device 4 is formed. , 4b, 4c, 4d are developed into toner images, and the toner images are transferred by the transfer drum 6.
It is adapted to be transferred onto a sheet fed between the transfer drum 6 and the photoconductor 1.

In the image forming process in the image forming section, three reference patches having low, medium and high input densities are prepared in the non-image area of the photoconductor 1. Then, each of the reference patches is measured by the density sensor 5, a development curve (development characteristic) coefficient at the density of each of the reference patches is calculated, and the value is used for density control.

For the density control, as in the conventional case, the value of the portion where the development curve itself does not change is used as much as possible. However, the point where the development curve itself does not change (fixed point) is not perfect, and changes depending on the state of the developer. Therefore, the development curve coefficient is obtained from the plurality of (three) reference patch densities, and if the coefficient exceeds the set normal range, it is detected that the development is abnormal, the toner supply signal is stopped, and a message to that effect is displayed. indicate.

FIG. 2 shows a developing curve. In the figure, A shows a regular developing curve, and B shows a developing curve when the amount of developer becomes small. Then, the development curve coefficient is calculated using this development curve by selecting the point of the development curve A that does not change the most, and setting this point as the point b.
Is set in advance. The development curve coefficient is represented by the slopes of the straight line a'b 'and the straight line b'c'.

FIG. 3 shows a toner replenishment amount determination process.
The density of each of the three reference patches is detected by the density sensor, the density signal is calculated by the above-mentioned action (step 1), and the density signal is compared with the target density (step 2). If the density of the density signal is higher than the target density as a result of the comparison in step 2, a signal without toner replenishment is output (step 3).

On the other hand, the image density of the development is always detected (step 4), and when the density from the density signal is smaller than the target density as a result of the comparison in step 2, the toner is determined from this density and the image density. A supply amount and a supply time are calculated (step 5). Then, it is judged whether or not the development curve coefficient exceeds the set range (step 6), and when it does not exceed the set range, toner supply is instructed (step 7).

Note that the developer layer thickness decreases due to the deterioration of the developer or the abnormal increase of the toner concentration. In this case, the development curve also changes as the developer layer thickness changes.
The dotted line B in the figure shows the case where the amount of developer per unit area on the sleeve of the developing device, which is an alternative value of the developer layer thickness, has decreased. At this time, when the development curve coefficient is within the set range and there is no large difference, the same control as the conventional one is performed. In this method, the abnormal toner replenishment operation can be stopped by changing the algorithm of the toner replenishment amount determination process without changing the mechanism from the conventional one.

[0014]

According to the present invention, it is possible to detect an abnormality of the developer as soon as possible and prevent the occurrence of image defects such as background fog.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory diagram of an image forming unit of a color copying machine.

FIG. 2 is a diagram showing a relationship between a developer amount and a development curve.

FIG. 3 is a flowchart schematically showing a toner supply process.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive member, 2 ... Charging device, 3 ... Exposure part, 4 ... Rotary developing device, 4a, 4b, 4c, 4d ... Developing device, 5 ... Density sensor, 6 ... Transfer drum, 7 ... Cleaner, 8 ... Static eliminator .

Claims (1)

[Claims] 1. A color image developing method, wherein a reference patch formed on the surface of a photoconductor is developed by a developing device, and the developing density is detected to judge the state of a developing device.
At least three low density, medium density, and high density standard patches are created, and when the development curve at each density of this standard patch exceeds a known normal range, it is determined that the developer is abnormal. And a color developing method.