JPH04310976A - Image forming device - Google Patents

Abstract

PURPOSE:To provide a stable image by adjusting a developing bias on a region corresponding to an original leading edge part, even in the case of a copying interval at the time of consecutive copying is short. CONSTITUTION:In an image forming device irradiating a photosensitive body uniformly electrified in advance with light after an original is exposed/scanned, to form a latent image, and forming an image by developing the latent image by means of a developing unit, a detecting means for detecting an exposure amount, that is, for detecting the exposure amount at a prescribed position before the original is scanned at the time of scanning and exposing, and an adjusting control means 400 adjusting the developing bias of the developing unit higher than a reference bias VB1 only for a prescribed time for developing an image top end part prescribed region when a detection value L obtained by the detecting means is lower than a reference value L2, are provided.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a developing device bias adjustment function.

0002

2. Description of the Related Art In copying machines, changes in the amount of exposure during exposure of an original affect the quality of the formed image. For this reason, conventionally, other conditions that affect image formation (bias voltage, etc.) are adjusted in response to changes in exposure amount. An example of such a device is a device that detects the amount of light during exposure and adjusts the developing bias of the developing device according to the detected value (Japanese Patent Laid-Open No. 6
3-28957) has been proposed.

0003

[Problems to be Solved by the Invention] By the way, in conventional copying machines, halogen lamps are used as exposure lamps, and if the lamps are turned on continuously, the life of the lamps will be shortened. When returning, the lamp is turned off. However, as the processing speed of copying machines increases, it is necessary to shorten the copying interval during continuous copying.If the copying interval is shortened and continuous copying is performed, the scanner will reach the document scanning start point during the second and subsequent scans. However, the exposure lamp may not start up completely. Conventional equipment (
In Japanese Unexamined Patent Publication No. 63-28957), the developing bias of the developing device is adjusted in response to the change (small change) in the exposure amount when the lamp is turned on, so that the change (large change) in the exposure amount when the lamp is turned on is adjusted. This resulted in insufficient exposure at the leading edge of the document, resulting in a portion of the formed image becoming dark.

An object of the present invention is to provide a stable image by adjusting the developing bias in the area corresponding to the leading edge of the document even when the copying interval during continuous copying is short.

[0005]

[Means for Solving the Problems] The image forming apparatus of the present invention forms a latent image by irradiating light obtained by exposing and scanning a document onto a photoreceptor (121) uniformly charged in advance, and In an image forming apparatus that forms an image by developing the latent image with a developing device (124), a detection unit (112a) that detects an exposure amount;
During exposure scanning, the detection means (112a) detects the exposure amount at a predetermined position before scanning the original, and the detected value (L) is determined as the reference value (L).
2) adjustment control means (400) for adjusting the developing bias of the developing device (124) to be higher than the reference bias (VB1) for a predetermined time period for developing a predetermined region at the leading edge of the image;
Equipped with Note that the symbols in parentheses are corresponding elements in the embodiment described later.

[0006]

[Operation] According to this, the adjustment control means (400) detects the amount of exposure at a predetermined position before scanning the document during exposure scanning with the detection means (112a), and the detected value (L) is set to the reference value (L2).
), the developing bias of the developing device (124) is set to the reference bias (
VB1) Adjust higher. Therefore, if the lamp does not start up at the start of exposure or if there is insufficient time to repeat the exposure, the insufficient amount of light at the leading edge of the document is determined before the document is exposed, and this is corrected by adjusting the developing bias.
It is possible to eliminate the darkness of the image due to insufficient light intensity at the leading edge of the document. Furthermore, in a preferred embodiment, the lamp light intensity for the first sheet is used as the reference light amount, and the second and subsequent sheets are compared with the reference value and the output of the developing bias is changed, so that a stable image can always be obtained.

Furthermore, a preferred embodiment of the present invention includes a standard white plate (116) at a predetermined location. Therefore, when the light amount is detected by the detection means (112a), the light amount is detected using the exposure light of the standard white plate (116), so the detection accuracy is improved and a stable image can be obtained. Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0008]

Embodiment 1 FIG. 1 shows an outline of the mechanism of a copying machine 100 as an example of the present invention. The copying machine 100 is an electrostatic transfer type copying device with a fixed original, and includes an optical system 110, an image forming system 120, a paper feeding system 130, a paper ejection system 140, and the like.

The optical system 110 includes a contact glass 111.
and an exposure lamp 112 arranged below, a light amount detection sensor 112a, a first mirror 113A, a second mirror 1
13B, third mirror 113C, fourth mirror 113D, fifth mirror 113E, sixth mirror 113F, lens 114
, a dustproof glass 115, a standard white plate 116, etc., and the image forming system 120 includes a photosensitive drum 121, a charger 122, an eraser 123, a developer 124, and a pre-transfer charger arranged around the photosensitive drum 121. 126, separation charger 127, separation claw 128, pre-cleaning static elimination charger (hereinafter referred to as PCC) 129, and cleaner 12A,
It also includes a conveyor belt 12B, a fixing device 12C, etc. arranged downstream of the photosensitive drum 121. Paper feed system 13
0 includes a manual paper feed tray 131, a paper feed tray 131A, a call roller 132, a paper feed roller 133, a reversing roller 134 provided on the paper feed tray, a registration roller 135, a guide mylar 136, and various guides and intermediate rollers. - Consists of la etc. Note that the manual paper feed tray 131 has a calling roller 132.
, the paper feed roller 133 and the reversing roller 134 are connected to the paper feed table 13.
It is shared with 1A. The paper ejection system 140 includes approach and separation rollers 142 and paper ejection rollers 14.
1st prize.

When a document is set on the contact glass 111 and a start instruction is given, the paper feed clutch is turned on and the call roller of the paper feed table selected at that time feeds the recording paper to the paper feed roller. The paper feed roller registers the recording paper.
Send it towards La 135. During this time, the optical system 110 scans the original on the contact glass 111, and the exposure lamp 1
The reflected light from the original illuminated by 12 is reflected by the first mirror 113A.
, second mirror 113B, third mirror 113C, lens 1
14, 4th mirror-113D, 5th mirror-113E, 6th mirror
The light is guided to the photosensitive surface of the photosensitive drum 121 via the mirror 113F and the dustproof glass 115.

The photosensitive drum 121 rotates clockwise in the drawing, and its photosensitive surface is uniformly charged by a charging charger 122 and erased before receiving the reflected light from the optical system 110. - A latent image area is formed by charge removal by the sensor 123. Therefore, when this latent image area is irradiated with light reflected from the original, photoconduction occurs depending on the strength of the light, and an electrostatic latent image is formed. This electrostatic latent image is developed by a developing device 124, and becomes a toner image with toner attached thereto according to the density of the document. This toner image is transferred onto the recording paper fed out from the registration roller 135, but in order to facilitate the transfer, the PTL 125 removes the charge before the transfer.

The recording paper fed out by the registration roller 135 is brought into close contact with the photosensitive surface of the photosensitive drum 121 by a guide mylar 136, and the toner is deposited directly above the transfer charger 126.
The image is transferred. Immediately after this, the recording paper is transferred to separation charger 1.
27, but if the separation is insufficient, the separation claw 128 forcibly separates the photosensitive material. After the recording paper is separated, residual toner is removed from the photosensitive surface of the photosensitive drum 121 by a cleaner 12A, and the recording paper is sent to a fixing device 12C by a conveyor belt 12B. The fixing device 12C includes a fixing roller 12C1 and a pressure roller 12C.
2, the recording paper onto which the toner image has been transferred is heated (approximately 185° C.) while applying pressure to fix the toner image. The recording paper with the toner image fixed thereon is delivered to a paper refeeding system 140. A paper discharge system 140 guides the recording paper to a paper discharge roller 141, and the recording paper is discharged from the apparatus by the paper discharge roller 141 and the contact/separation roller 142.

FIG. 2 schematically shows the electrical control system of the copying machine 100. This electrical control system includes a main control section 400, a storage section 410, an optical control section 420, and an AC control section 430.
, and an operation control unit 440.

The main control unit 400 includes various sensors 420 (exposure detection sensor 112a) provided in each part of the main body 100.
), and controls the loads of the solenoids and motors of various parts, the bias voltage of the developing device 124, etc. The optical control unit 420 controls the lens motor that drives the lens 114 and the scanner motor that performs optical scanning, and controls the AC
The control unit 430 controls AC loads such as the exposure lamp 112, the heater of the fixing device 12C, the main motor, the developing motor, the transport motor, and the paper feed motor. The operation control section 440 performs key operation reading and display control on the operation and display board 150.

By the way, in the copying machine 100, during exposure scanning, the light amount is detected at a predetermined position (scanning position of the standard white plate 116) using the light amount detection sensor 112a. FIG. 3 shows the set value of the developing bias in a predetermined area with respect to the amount of light detected at this time. Lamp 112 (lit) is 10
The light intensity when it rises to 0% is L2, and the developing device 1 at this time
The developing bias setting of No. 24 is set to VB1. Further, when the light amount is between L2 and L1 (L2>L1), the developing bias is set to VB2, and when the light amount is less than L1, the developing bias is set to VB3. In addition, VB1<VB2<VB3
It is.

FIG. 4 is a flowchart of scanner control processing by the main control section 400. This will be explained below. First, initialization is performed (Step 1: The word "step" will be omitted below in parentheses). In this initialization, each register etc. are cleared and the scanner is set at a predetermined position (home position). Next, it waits until a start instruction is given (2), and when a start instruction is given, the register N for determining the number of copies is set to 0 (3), the lamp 112 is turned on, and the scanner starts running (4). . When the scanner reaches a predetermined light amount detection position (5), the light amount at this time is read by the sensor 112a and set as L (6). Here, it is determined whether the value of N is 0 (7), and if so, it is 1
The value L read after determining that it is the first copy is set as the reference value L2,
The developing bias of the developing device 124 is set to a predetermined value VB1 (8, 9). On the other hand, if the value of N is not 0, it is determined that the copying is the second or subsequent copying of continuous copying, and the processes of steps 10 to 14 (bias adjustment process) are performed. In this process, if the read value L is less than or equal to the reference value L1, the developing bias of the developing device 124 is set to a predetermined value VB3 (10, 11), and if L is greater than or equal to the reference value L2, the developing bias of the developing device 124 is set to a predetermined value VB3 (10, 11). is set to a predetermined value VB1 (12, 13), and when L is in the range of L1 to L2, the developing bias of the developing device 124 is set to a predetermined value VB1.
Set to 2 (10, 12, 14). Note that development is performed using the adjusted development bias for a predetermined period of time, and thereafter development is performed using a normal development bias (fixed value). After that, when the scanner reaches the return position (15)
, turn off lamp 112 and drive the scanner in the reverse direction (16). When the scanner reaches the home position (17)
, if the set number of scans has not been completed, the value of N is set to 1 and the process returns to step 4 (18, 19). When the regular number of scans is completed, the scanner stops scanning, returns to step 2 (20), and waits for a start instruction.

FIG. 5 shows the timing of each of the operations described above and changes in the developing bias output. Since there is time to copy the first copy, the exposure lamp can be turned on more quickly than during continuous copying. Turn on the exposure lamp
After that, the scanner drive starts and the leading edge of the document (L.E.
．． ) The amount of light is measured at the position of the standard white plate 116 in front of. Since there is time for the first image, it is assumed that the lamp is turned on, and this value is set as the light amount L2 when the lamp 112 is turned on 100%. The developing bias value for the first sheet is VB1.

The exposure lamp is turned off at the same time as the scanner returns, and then, when the scanner returns to a predetermined position, copying of the second sheet begins. Since there is not enough time for the second and subsequent shots, I turned on the exposure lamp 11 at a later timing than for the first shot.
2 is turned on. Scanner drive is started, and the amount of light is measured at the position of the standard white plate 116 in front of the leading edge (LE) of the document. The value of this light amount is compared with the light amount of the first sheet, and the developing bias is set. The bias value set above is applied to the developing device 124 for a certain period of time from the leading edge (LE) of the document. Note that T1 in the figure is set depending on the mounting position of the standard white plate 116, and T2 is set depending on the mounting position of the standard white plate 116.
The time is set to develop an area of about 0 mm.

[0019]

As described above, according to the present invention, the adjustment control means (400) uses the detection means (112a) to detect the exposure amount at a predetermined position before scanning the document during exposure scanning, and calculates the detected value ( If L) is smaller than the reference value (L2), the developing bias of the developing device (124) is adjusted to be higher than the reference bias (VB1) for a predetermined period of time to develop a predetermined region at the leading edge of the image. Therefore, the lack of light at the leading edge of the document due to the lamp not starting up at the start of exposure or lack of time during repeat is determined before the document is exposed, and this is corrected by adjusting the developing bias. It is possible to eliminate the darkness of the image due to insufficient light intensity at the tip.

[Brief explanation of drawings]

FIG. 1 is a side view showing a schematic configuration of a copying machine that is an example of the present invention.

2 is a block diagram schematically showing a control system of the copying machine 100 shown in FIG. 1. FIG.

FIG. 3 is a graph showing the setting value of the developing bias in a predetermined area with respect to the amount of light detected by the exposure amount detection sensor 112a.

FIG. 4 is a flowchart showing the control operation of the main control section 400.

FIG. 5 is a time chart showing changes in light amount reading timing and developing bias output.

[Explanation of symbols]

100: Copy machine
110: Optical system 112a: Exposure detection sensor (detection means) 116: Standard white plate (standard white plate) 120: Image forming system
121: Photoreceptor (photoreceptor)

Claims (3)

[Claims] [Claim 1] An image in which a latent image is formed by irradiating light obtained by exposing and scanning a document onto a photoreceptor that has been uniformly charged in advance, and the latent image is developed with a developing device to form an image. In the forming apparatus, a detection means for detecting the exposure amount; during exposure scanning, the detection means detects the exposure amount at a predetermined position before scanning the document, and if the detected value is smaller than a reference value, a predetermined detection means is used to develop a predetermined area at the leading edge of the image. An image forming apparatus comprising: an adjustment control means for adjusting a developing bias of a developing device to be higher than a reference bias by an amount of time. 2. The image forming apparatus according to claim 1, further comprising a standard white plate at the predetermined position. 3. An image in which a latent image is formed by irradiating light obtained by exposing and scanning a document onto a photoreceptor that has been uniformly charged in advance, and the latent image is developed with a developing device to form an image. In the forming method, during exposure scanning, the exposure amount at a predetermined position before scanning the document is detected, and if the detected value is smaller than a reference value, the developing bias of the developing device is changed to the reference bias for a predetermined time to develop a predetermined area at the leading edge of the image. An image forming method that forms images with higher adjustment.