JPH02271370A - Image forming device - Google Patents

Abstract

PURPOSE:To facilitate the correction of a surface potential and to obtain a proper image density by detecting the surface potential of a photosensitive body, comparing it with a reference value, and adjusting the output of an auxiliary electrifying charger based on the result. CONSTITUTION:An electrifying charger 2 is outputted by rotating the photosensitive drum 1, and the surface potential of the drum 1 is detected by a surface potential sensor 20. When the detected potential is within a reference range, a PCU sets a copy flag to perform main routine return. When the potential is outside the range, the correction value of the auxiliary electrifying charger 4, which meets the detected value, is calculated, and the charger 4 is caused to output the correction value. The surface potential can be adjusted during the idling of the drum 1, and also during copying.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrostatic recording type image forming apparatus such as a copying machine, and more specifically to a means for adjusting the surface potential of a photoreceptor.

[Prior art]

In devices such as copying machines that expose photoreceptors to form electrostatic latent images, proper latent images may not be formed due to variations in the electrostatic properties of individual photoreceptors that are mass-produced, or due to deterioration due to long-term use. , which may lead to a decrease in image quality.

Therefore, in order to prevent this, for example,
In JP-A No. 340, the electrostatic characteristics of the photoconductor during idling are detected and the exposure amount is adjusted according to this characteristic, and in JP-A-53-47832, the surface of the photoconductor is adjusted before exposure. A device has been disclosed that detects the potential and irradiates the surface with an amount of light corresponding to the detected value to make the surface potential substantially constant.

Problem to be solved by the invention] Incidentally, the surface potential of a photoreceptor changes during a series of steps from charging to exposure to static elimination, but if the electrostatic characteristics change due to the reasons mentioned above, the surface potential will change from the ideal reference value. It changes to become higher or lower than.

As a result, as the surface potential changes higher, the image becomes darker, and conversely, as the surface potential changes lower, it becomes lighter.

Therefore, in the above-mentioned Japanese Patent Application Laid-Open No. 54-137340, correction is made by adjusting the exposure amount.
Since it does not correct the surface potential itself, there is a limit to the adjustment range of the image density, and depending on the degree of change in electrostatic characteristics, it may not be possible to adjust the density to the operator's desired density, or even the normal appropriate density may be reached at the By1 section. There is an impossible situation.

Furthermore, in JP-A-53-47832, since the surface potential is lowered by light irradiation, it can only be applied when the surface potential is higher than the reference value, and it cannot be corrected when the surface potential is low. Can not. Furthermore, even when the surface potential is high, if residual potential accumulates due to fatigue of the photoreceptor, it may not be possible to remove the charge sufficiently by light irradiation, resulting in the problem of overcharging.

The present invention has been made in view of the above circumstances, and provides an image in which the surface potential of the detected photoreceptor can be accurately corrected regardless of whether the surface potential is higher or lower than a reference value. The purpose is to provide a forming device.

[Means for Solving the Problems] An image forming apparatus according to the present invention is an image forming apparatus including a surface potential detection means for detecting the surface potential of a photoreceptor charged by a charging charger and an auxiliary charging charger,
It is characterized by comprising a comparison means for comparing the detection result of the surface potential detection means with a reference value of the surface potential, and a means for adjusting the output of the auxiliary charger based on the comparison result of the comparison means. .

[Effect]

The surface potential of the photoreceptor is detected by a surface potential detection means, and the detection result is compared with a reference value of the surface potential. Then, the output of the auxiliary charger is adjusted based on the comparison result, thereby correcting the surface potential with respect to the reference value.

〔Example〕

EMBODIMENT OF THE INVENTION Hereinafter, an embodiment in which the present invention is applied to a copying machine will be described in detail based on the drawings. FIG. 1 is a schematic diagram showing the internal structure of a copying machine according to the present invention. In the figure, 1 is a photosensitive drum having a photoconductive layer on its outer peripheral surface, and is rotatable in the direction of arrow a. A charger 2 is arranged above the photoreceptor drum 1, and applies a constant electric charge to the surface of the photoreceptor drum 1.

A surface potential sensor 20 for detecting the surface potential of the photoreceptor drum 1 and an auxiliary charger 4 for correcting the surface potential are provided in this order on the downstream side of the charger 2 in the direction of drum rotation. It is arranged at approximately the center position in the axial direction.

The scanning light of the original by the image exposure device 3 provided below the document platen 21 is guided to the surface of the photosensitive drum 1 on the downstream side of the auxiliary charger 4 in the drum rotation direction, and the image exposure device 3 is a mirror group 33 that scans in the direction of the arrow. Consists of an exposure lamp 31, a lens 32, etc.
An electrostatic latent image corresponding to the original image placed on the original platen 21 is formed on the surface of the photoreceptor drum 1.

After this electrostatic latent image is developed into a toner image in the next developing device 5, an electric field is applied by a transfer charger 6 provided below the photosensitive drum 1, and the image is conveyed in the direction of arrow C. The image is transferred onto the copy paper that comes with it. A separation charger 7 is provided downstream of the transfer charger 6 in the drum rotation direction.
The separation charger 7 applies an alternating current electric field to the copy paper immediately after transfer, thereby removing electricity from the copy paper and separating it from the surface of the photoreceptor drum 1.

A cleaning device 8 is provided downstream of the separation charger 7 in the drum rotation direction, and the cleaning device 8 uses a blade method to remove toner remaining on the surface of the photoreceptor drum 1. Cleaning device 8 and the charger 2
An eraser lamp 9 is provided between the photoreceptor drum 1 and the photoreceptor drum 1. The eraser lamp 9 removes charges remaining on the surface of the photoreceptor drum 1 by irradiating light in preparation for the next copying process.

Reference numeral 10 denotes a cassette for storing copy paper, which is removably attached to the main body of the copying machine, and is provided with a paper feed roller 11 for feeding the copy paper.

The copy paper sent out from the cassette 10 is once stopped by the timing roller 12, and then moved to the photosensitive drum 1 as shown by arrow C in synchronization with the rotation timing of the toner image.
and the transfer charger 6.

The copy paper on which the toner image has been transferred is sent to the fixing device 14 by the conveyor belt 13, and after the toner image is melted and fixed onto the copy paper by heat, the paper is transferred to the paper output tray 1 by the discharge roller 15.
6 is discharged on top.

FIG. 2 is a block diagram of the control system, mainly showing the portion related to the surface potential adjustment mechanism of the photosensitive drum. The detection signal of the surface potential sensor 20 is input to the input side of the CPU 201 that controls a series of copying operations.
2 is converted into a digital signal and given.

On the other hand, on the output side of the CPU 201, a charger 2 and an auxiliary charger 4 are connected to drive circuits 203 and 20, respectively.
4, and is also connected to a serviceman call indicator 205 that is disposed on the operation panel (not shown) and lights up when the surface potential correction is out of the adjustment range of the CPU 201. It is.

Next, the control procedure of the CPU 201 described above will be explained based on the flowcharts shown in FIGS. 3 to 6. FIG. 3 shows the main flow, and when the copying machine is powered on, cpυ 201 sets itself to the initial state (step Sl).

In the next step S2, an internal timer is started. This internal timer determines the time required for one routine of the main routine, regardless of the processing content in each subroutine described below, and is set to, for example, 10 m5ec in advance in initial setting step S1.

In step S3, input processing for the key matrix of the operation panel, various defect detectors, etc. is performed.

Step S4 is a photoreceptor surface potential adjustment routine according to the present invention, and details are shown in FIG.

Continuation (In steps 35 to S7, the trouble detection routine, copy operation routine, and other processing routines are sequentially called, respectively. When the processing of all subroutines is completed, the process waits for the internal timer to end in step S8, and then returns to step S.
Return to 2. The time length of one routine is used to count various timers used in each subroutine. The various timers determine the end of the timer depending on how many times this one routine has been counted.

Figure 4 shows the surface potential adjustment routine, starting with step 5.
When the print key is pressed in step 400, step 5401
The photosensitive drum 1 is rotated and the charger 2 is outputted. Next, in step 5402, the photosensitive drum 1 is
A surface potential sensor 20 detects the surface potential of . Then, in step 54, it is determined whether the detected surface potential is within the reference range.
If it is within the range, c is determined in step 5404.
The opy flag is set and the process returns to the main routine, and if it is outside the range, the process proceeds to step 5405.

In step 5405, it is determined whether the flag F indicating whether or not correction has been performed by the auxiliary charger 4 has been reset, and if this has been reset, step 3
In step 406, an output value of the auxiliary charger 4, that is, a correction value is calculated in accordance with the detected value of the surface potential. This correction value is calculated, for example, by the following equation.

Correction value = (V + V.)・K where ■. is the reference potential, ■1 is the detection potential, and the correction coefficient is the reference potential ■. The amount of deviation from 1v+■. How much potential should be corrected relative to 1, that is, how many V should be corrected to bring it close to the standard attenuation characteristic?This is determined experimentally in advance, and this is calculated as a value for each deviation amount. , stored in the ROM of the CPU 201.

Now, when the correction value is calculated, in the next step 5407, it is determined whether or not the correction value is within the adjustment range by the auxiliary charger 4, and if it is within the range, the correction value is outputted by the auxiliary charger 4 ( Step 5408), Step 54
At step 09, the copy flag and flag F are set and the process returns to the main routine.

On the other hand, if flag F is set in step 5405, that is, if the surface potential falls outside the standard range again even though correction by the auxiliary charger 4 has already been performed, or if the correction value is set in step 5407. If it is determined that the adjustment is outside the adjustment range, the serviceman call display 205 is turned on in step 5410 to notify that adjustment is not possible, and the copy prohibition flag is set and turned on in the next step 5411, and the main Return to routine. still,
This copy prohibition flag is reset by a switch for service personnel (not shown).

FIG. 5 shows the contents of the trouble detection routine in step S5. When the copy prohibition flag is set (step 5501), a code number indicating that the surface potential cannot be adjusted is displayed on the operation panel (not shown). It is displayed on a 7-segment display (step 5502').

FIG. 6 shows the contents of the copy operation routine in step S6. First, it is determined whether the copy prohibition flag is reset (step 5601). If this is reset, then if the copy flag is set, Step 5602), start the image forming operation (Step 5604), and when the image forming operation for the set number of sheets is completed,
After resetting the copy flag, return to the main routine (steps 5603, 5605, 5606)
).

FIG. 7 is a graph showing changes in surface potential as the photoreceptor drum rotates, and FIG. 7(a) shows the graph when no correction is performed.
FIG. 7(b) shows the case where the correction according to the present invention is performed. First, if no correction is performed, it is ideal that the surface potential changes as shown by A. However, in reality, after being charged by the charger, due to variations in the characteristics of the photosensitive drum or deterioration, A! , or as in A3, the surface potential changes higher or lower than the reference potential, resulting in a decrease in image quality.

Therefore, in the present invention, as shown in FIG. 7 (bl), Az, A, can be corrected to A2 or A2'. Here, when A is corrected to A2', the polarity of the auxiliary charger is reversed to that of the charger.

In this embodiment, the surface potential is adjusted while the photosensitive drum is idling before the copying operation, but it may also be adjusted during the copying operation.
Furthermore, the surface potential sensor is provided between the electrostatic charger and the auxiliary electrostatic charger, but instead of this position, it may be provided in front of the developing device, that is, after the auxiliary electrostatic charger, or it may be provided on both. good. In other words,
When provided in front of the developing device, even if the surface potential of the photoreceptor decreases due to dark decay, the surface potential at approximately the time of development can be detected, and its characteristics can be corrected.

〔effect〕

As described above, in the image forming apparatus according to the present invention, the detected surface potential of the photoconductor is compared with the reference surface potential, and the output value of the auxiliary charger is adjusted based on the result to correct the surface potential. Therefore, even if the surface potential before correction is lower than the reference potential, it can be easily corrected.
Furthermore, since the surface potential itself is corrected, not only can images with appropriate density be obtained, but also the image density can be changed without any problems.

Further, according to the present invention, it is possible to adjust the surface potential of the photoreceptor to a potential according to the light amount of the exposure lamp, the output of the charger, etc., and the present invention has excellent effects.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the internal structure of a copying machine to which the present invention is applied, Figure 2 is a block diagram of the control system, and Figures 3 to 6 are CPU
FIG. 7 is a flowchart showing the control procedure, and FIG. 7 is a graph showing changes in surface potential. 1... Photosensitive drum 2... Charger 4.
...Auxiliary charger 20...Surface potential sensor
201...CPU Patent Applicant Minolta Camera Co., Ltd. Agent Patent Attorney Noboru Kono Funeral map Funeral map (a) Figure

Claims (1)

[Scope of Claims] 1. An image forming apparatus comprising a surface potential detection means for detecting the surface potential of a photoreceptor charged by a charging charger and an auxiliary charger, the detection result of the surface potential detection means and the surface An image forming apparatus comprising: a comparison means for comparing a potential with a reference value; and a means for adjusting an output of the auxiliary charger based on a comparison result of the comparison means.