JPH11327224A - Potential control method for image forming device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of fogging and the break of the trailing edge of an image by making a potential difference between a developing bias and a dark potential become smaller as the density of a toner developing image is lowered at a dark potential part. SOLUTION: Relation between the output (sensor output) of a reflection type photosensor 5 and the potential difference ΔV between a developing bias and a dark potential is previously obtained so that the potential difference ΔV between the developing bias and the dark potential becomes smaller as the output of the sensor 5 is higher (fogging density is lower). Then, the relation between the sensor output and the potential difference ΔV is stored in a storage device as a table. When the image density is corrected, the potential difference ΔV corresponding to the sensor output is read from the table by making the output of the sensor 5 as the sensor output obtained when the density (fogging density) of the dark potential with respect to a patch is measured. Then, the developing bias and the dark potential are adjusted so that the potential difference between the developing bias and the dark potential becomes the read potential difference ΔV.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a potential control method for an image forming apparatus and an image forming apparatus.

[0002]

2. Description of the Related Art When copying is performed by a copying machine, a phenomenon in which the rear end of a halftone solid image portion is blurred (hereinafter referred to as "rear end") tends to appear.

As a method of preventing the trailing edge, it is conceivable to decrease the peripheral speed of the developing roller so as to approach the peripheral speed of the drum. However, this causes a problem that a high-density image cannot be output.

It is conceivable to reduce the absolute value of the difference between the developing bias and the dark potential. However, if the absolute value of the difference between the developing bias and the dark potential is reduced, fogging is likely to occur. .

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a potential control method for an image forming apparatus and an image forming apparatus capable of minimizing the occurrence of fogging and the occurrence of a trailing edge.

[0006]

A potential control method for an image forming apparatus according to the present invention is directed to a method of controlling a dark potential so that the lower the toner visual density in a dark potential portion, the smaller the potential difference between the developing bias and the dark potential. The first step is to obtain in advance the relationship between the value relating to the toner visual density at the image forming section and the potential difference between the developing bias and the dark potential. At the time of image density correction, the value relating to the toner visual density at the dark potential section is measured. A second step of obtaining a potential difference between a developing bias and a dark potential corresponding to a value related to a measured toner visual density in a dark potential portion based on the relationship obtained in the first step; A third step of adjusting the developing bias and / or the dark potential so that the potential difference from the dark potential becomes the potential difference obtained in the second step is provided.

As the value relating to the toner visual density at the dark potential portion, for example, the output value of a reflection type photosensor for measuring the toner visual density at the dark potential portion is used.

The developing bias is given, for example, by a pulsating voltage whose direction and magnitude periodically change around a predetermined voltage value. In this case, the potential difference between the developing bias and the dark potential is the potential difference between the average value of the developing bias and the dark potential.

In the image forming apparatus according to the present invention, the absolute value of the difference between the developing bias and the dark potential is 40 V or more and 15
It is characterized in that it is set within a range of 0 V or less.
The absolute value of the difference between the developing bias and the dark potential is set within the range of 40 V or more and 150 V or less because if the absolute value of the difference between the developing bias and the dark potential is smaller than 40 V, fog is likely to occur. This is because if the absolute value of the difference between the developing bias and the dark potential is larger than 150 V, the rear end is likely to occur.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a digital copying machine.

A contact glass 1 on which an original to be copied is placed is provided at an upper portion of the main body of the copying machine. On one side of the copying machine main body, a paper feed cassette 2 is provided. An exposing mechanism, a printing mechanism, and a recording paper transport mechanism are provided in the copying machine main body.

The exposure mechanism includes an exposure lamp 21 for exposing and scanning an image of a document (not shown) placed on the contact glass 1 and a first mirror 22 for reflecting light reflected from the document. 1 optical system traveling body 31, first mirror 2
2 for guiding the light reflected by 2 to the lens 25
And a second optical system traveling body 32 having third mirrors 23 and 24; a solid-state image sensor 26 such as a CCD for converting optical information obtained by the condenser lens 25 into an electric signal; A signal processing unit 27 for performing various image processing on the obtained image information and a laser unit 28 for converting an output signal of the signal processing unit 27 into an optical signal (laser light) are provided. The laser beam output from the laser unit 28 irradiates the photosensitive drum 11.

The first optical system running body 31 and the second optical system running body 32 are reciprocated in the left-right direction by a scan motor (not shown). The second optical system traveling body 32 moves at a speed that is half the speed of the first optical system traveling body 31 and a distance that is half the moving distance of the first optical system traveling body 31.

The printing mechanism has a photosensitive drum 11. The photosensitive drum 11 is driven to rotate in a direction indicated by an arrow by a main motor (not shown). Photoconductor drum 1
1 around the photosensitive drums 11 in the order of their rotation.
A charging device 12 for charging the photosensitive layer on the surface of the photosensitive layer, a developing device 13 for developing the electrostatic latent image formed on the photosensitive layer as a toner visible image, and a toner visible image formed on the photosensitive layer on recording paper. A transfer discharger 14 for transferring, a separation discharger 15 for separating recording paper from the photosensitive drum 11, a cleaning device 16 for removing toner remaining on the photosensitive drum 11 after transfer, and a photosensitive drum A static eliminator 17 for removing charges on the surface 11 is provided.

A surface potential sensor 4 for measuring the charged potential of the photosensitive drum 11 is provided around the photosensitive drum 11. Further, at the time of image density correction (ID correction) around the photoreceptor drum 11, the toner visual density for patches such as a bright potential and a dark potential generated by the signal processing unit 27 and the laser unit 28 is measured. Reflective photosensor 5 is disposed. The reflection type photo sensor 5 is provided on the photosensitive drum surface 1.
1 is provided with a light emitting diode (light emitting unit) for irradiating light and a phototransistor (light receiving unit) for receiving light reflected from the surface of the photosensitive drum.

The recording paper transport mechanism transports the recording paper fed by the paper feeding roller 36 to the photosensitive drum 11 at a predetermined timing. The recording paper on which the toner image formed on the resist roller 37 and the photosensitive drum 11 is transferred and peeled from the photosensitive drum 11 is fixed to the fixing roller 3.
9 is provided.

Normally, image density correction is performed each time a predetermined number of copies are made. In the image density correction, dark potential control (grid voltage control of the charger 12), bright potential control (control of the exposure amount of the exposure lamp 21), control of the developing bias, and the like are performed. In this embodiment, the absolute value of the difference between the developing bias and the dark potential (the grid voltage of the charger 12) (hereinafter referred to as developing bias) is suitable for suppressing the occurrence of fogging and trailing edge during image density correction. And a dark potential) are obtained, and one or both of the developing bias and the dark potential are controlled so as to obtain the obtained potential difference.

FIG. 2 shows an example of a bright potential, a dark potential and a developing bias. In this example, the light potential is -200
V DC voltage. The dark potential is a DC voltage of -700V. The developing bias is a square wave voltage (pulsating voltage) whose direction and magnitude periodically change around -600V. The peak-to-peak value Vpp of the developing bias is 750
V is set. The frequency f of the developing bias is set to 4 KHz.

As described above, it is conceivable to reduce the potential difference between the developing bias and the dark potential in order to keep the occurrence of the rear end portion low. However, the absolute value of the difference between the developing bias and the dark potential is reduced. Then, fog tends to occur.

The density of the toner image at the dark potential portion is called fog density, and the higher the fog density, the more easily fogging occurs. In a state where fogging is likely to occur, the potential difference between the developing bias and the dark potential cannot be reduced. On the other hand, in a state where fogging is unlikely to occur, the potential difference between the developing bias and the dark potential can be reduced in order to suppress the occurrence of the rear end portion low.

In this embodiment, the relationship between the fog density and the potential difference between the developing bias and the dark potential is determined in advance so that the lower the fog density, the smaller the potential difference between the developing bias and the dark potential. deep. Actually, the relationship between the output of the reflective photosensor 5 for detecting the fog density and the potential difference between the developing bias and the dark potential is determined in advance.

Since the output of the reflection type photosensor 5 decreases as the fog density increases, as shown in FIG. 3, as the output of the reflection type photosensor 5 increases (the fog density decreases), the developing bias and the dark potential (Sensor output) so that the potential difference ΔV from
And the relationship between the developing bias and the potential difference ΔV between the dark potential and the developing bias are obtained in advance. Then, the relationship between the sensor output and the potential difference ΔV is stored in the storage device as a table.

At the time of image density correction, the density of each patch is measured by the photo sensor 5. When the density (fog density) of a patch with dark potential was measured,
With the output of the photosensor 5 as the sensor output, the potential difference ΔV corresponding to the sensor output is read from the table. Then, one or both of the developing bias and the dark potential are adjusted so that the potential difference between the developing bias and the dark potential becomes the read potential difference ΔV.

It is preferable that the potential difference between the developing bias and the dark potential is set within a range of 40 V or more and 150 V or less. The reason is that when the absolute value of the difference between the developing bias and the dark potential is smaller than 40 V, fog tends to occur, and when the absolute value of the difference between the developing bias and the dark potential is larger than 150 V, the trailing edge is likely to occur. Because it becomes.

[0026]

According to the present invention, the occurrence of fogging and the occurrence of the rear end can be minimized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a schematic configuration of a digital copying machine.

FIG. 2 is a time chart illustrating an example of a bright potential, a dark potential, and a developing bias.

FIG. 3 is a graph showing a relationship between a sensor output obtained in advance and a potential difference ΔV.

[Explanation of symbols]

 Reference Signs List 5 reflective photosensor 21 exposure lamp 26 solid-state imaging device 27 signal processing unit 28 laser unit 11 photoconductor drum 12 charger 13 developing device 16 cleaning device 17 static eliminator

Claims (4)

[Claims] 1. The lower the toner visual density in a dark potential portion, the more
To reduce the potential difference between the development bias and the dark potential,
A first step in which the relationship between the toner visual density at the dark potential portion and the potential difference between the developing bias and the dark potential is determined in advance; Measuring, based on the relationship obtained in the first step, a second step of obtaining a potential difference between a developing bias and a dark potential corresponding to the measured value of the toner visual density in the dark potential portion; A third step of adjusting the developing bias and / or the dark potential so that the potential difference between the bias and the dark potential becomes the potential difference obtained in the second step.
A potential control method for an image forming apparatus, comprising: 2. The potential of the image forming apparatus according to claim 1, wherein the value relating to the toner visual density at the dark potential portion is an output value of a reflection type photo sensor for measuring the toner visual density at the dark potential portion. Control method. 3. The developing bias is given by a pulsating voltage whose direction and magnitude periodically change around a predetermined voltage value, and the potential difference between the developing bias and the dark potential is determined by the average value of the developing bias and the dark potential. 2. A potential difference from a dark potential.
3. The potential control method for an image forming apparatus according to claim 1, wherein 4. An image forming apparatus wherein an absolute value of a difference between a developing bias and a dark potential is set within a range of 40 V or more and 150 V or less.