JP2003015377A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device by which the defect of voltage application of an electrifying charger is easily detected. SOLUTION: When several developing material images successively fed are fed at specified intervals, it is judged whether a toner stuck amount sensor measures an off-image area existing between the developing material images or not, and in the case of measuring the off-image area, it is judged as the malfunction of the electrifying charger when toner density is equal to or above a stipulated value.

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 having an error detecting function of a charging charger that charges a photoconductor.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus for forming a toner image, the surface of a photosensitive drum is charged and an electrostatic latent image is formed by a laser beam or the like. Has been adopted. In this method, as a device for charging the surface of the photoconductor drum, a charging charger for generating corona discharge is generally used.

This charging charger has a thin wire of several k
It is generated by applying a high voltage of V, but in principle,
Since the toner, carrier, etc. tend to adhere to the wire, cleaning of the wire is absolutely necessary. Also, this wire is weak because it uses a thin wire with a diameter of about 0.1 mm. Furthermore, both ends of the charging wire are connected to the machine body by using crimp terminals or the like, and are cut by damage during cleaning or vibration from the outside. Sometimes.

Similar problems occur even when the charging charge wire is deteriorated, the high-voltage power supply is defective, or the high-voltage supply is defective (wiring is cut).

When the charging charge wire is broken, the photosensitive drum is not charged, so that toner development is performed at a high density even on a portion that should not be printed (including the outside of the paper), so that the toner and the paper are wastefully consumed. Will be done.

In order to solve these problems, JP-A-6-
Japanese Laid-Open Patent Publication No. 110295 discloses a technique in which a pulley that winds up a charging wire is used and a disconnection of the charging wire is detected from a change in the rotation speed of the pulley.

Further, Japanese Patent Laid-Open No. 5-323773 discloses a technique for detecting an abnormality of the charger by detecting the ultraviolet rays emitted from the charger.

Further, Japanese Unexamined Patent Publication No. 9-34326 discloses a technique for detecting an abnormality by measuring the surface potential of the photosensitive drum.

[0009]

[Problems to be Solved by the Invention] However, the above 3
The techniques disclosed in the two publications all add a new device for detecting an abnormality. Current,
An image forming apparatus such as a copying machine or a copying machine is indispensable for downsizing and cost reduction, and addition of the above-mentioned equipment leads to an increase in cost and an increase in size of the apparatus. As a result, for low-priced products, detection devices cannot be installed,
The user or service person must check the printing condition one by one.

[0010]

An image forming apparatus according to the present invention comprises an image bearing member carrying an image, a charging means for charging the image bearing member, and an electrostatic latent image for exposing the image bearing member. An exposure unit that forms a first developing material image by developing the electrostatic latent image with a developing material, and an exposing unit that is downstream of a developing position of the developing unit with respect to the developing material image transport direction. A density detecting unit that detects the density of the first developer image at a position, and a second developer image that is continuously conveyed following the first developer image are the first developer image. The image is conveyed at a predetermined interval, and a first judgment means for judging that the detection position of the density detection means is within the predetermined interval, and the density detection means by the first judgment means. When detecting the concentration within the predetermined interval, determines whether the concentration is abnormal It is characterized by that equipped with a second determination means.

With this image forming apparatus, it is possible to detect the abnormality of the charging charger by determining whether or not the toner adheres to the outside of the development area between the plurality of developed images.

The image forming apparatus according to the present invention further includes an image carrier for carrying an image, a charging means for charging the image carrier, and an exposure for exposing the image carrier to form an electrostatic latent image. Means, developing means for developing the electrostatic latent image with a developing material to form a developing material image having a predetermined length in the sub-scanning direction, and detecting the length of the developing material image in the sub-scanning direction. Detecting means, the data for forming the developer material image, the length of this data in the sub-scanning direction and the length of the developer image in the sub-scanning direction are compared to determine whether the operation of the charging means is abnormal. It is characterized in that it is provided with a judging means for judging whether or not.

By using this image forming apparatus, it is possible to detect the abnormality of the charging charger by judging whether or not the development is performed in the area which should not be originally developed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, FIG. 1 is a schematic view of the internal structure of the entire image forming apparatus to which the present invention can be applied.
Will be described with reference to.

The image forming apparatus is an apparatus such as a digital color copying machine which reads a color image on a document, forms a duplicate image of the color image, and outputs the duplicate image. This apparatus is roughly classified into a color scanner unit 1 as an image reading unit for reading and inputting a color input document on a document, and a color printer unit 2 as an image forming unit for forming a duplicate image of the input color input document. It has and.

The color scanner unit 1 includes a document table cover 3
And is disposed opposite to the original platen cover 3 in the closed state,
A document table 4 made of transparent glass on which an input document is placed. Below the document table 4, an exposure lamp 5 for illuminating a document placed on the document table 4, a reflector 6 for condensing light from the exposure lamp 5 onto the document, and light reflected by the document are shown in the drawing. The 1st mirror 7 etc. which bend | fold to the left direction are arrange | positioned.

The exposure lamp 5, the reflector 6, and the first mirror 7 are fixed to the first carriage 8. The first carriage 8 is provided with a toothed belt (not shown),
It is driven by a pulse motor (not shown) and moves in parallel along the lower surface of the document table 4.

The first carriage on the left side of the drawing with respect to the first carriage 8
In the direction in which the light reflected by the mirror 7 is guided, a second carriage 9 provided so as to be movable in parallel with the document table 4 via a drive mechanism (not shown) (for example, a toothed belt and a DC motor). It is arranged. The second carriage 9 includes a second mirror 11 that bends the reflected light from the document guided by the first mirror 7 downward in the figure, and a third mirror 12 that bends the reflected light from the second mirror 11 in the right direction in the figure. Are arranged at right angles to each other.

The second carriage 9 operates in accordance with the first carriage 8 and moves in parallel along the original table 4 at a speed half that of the first carriage 8.

An image forming lens 13 for forming an image of the reflected light from the third mirror 12 at a predetermined magnification is arranged in a plane including the optical axis of the light reflected by the second and third mirrors 11 and 12. ing. A CCD color image sensor (photoelectric conversion element) 15 for converting the reflected light focused by the imaging lens 13 into an electric signal is arranged in a plane substantially orthogonal to the optical axis of the light passing through the imaging lens 13. It is set up.

When the light emitted from the exposure lamp 5 is focused on the document on the document table 4 by the reflector 6, the light reflected by the document is reflected by the first mirror 7, the second mirror 11, and the like.
It is incident on the color image sensor 15 via the third mirror 12 and the imaging lens 13. The sensor 15 converts incident light into RGB signals.

The color printer unit 2 generates image signals separated into colors for each color component YMCK based on the well-known subtractive color mixing method, and the first to fourth image forming units 10y and 10y.
m, 10c, 10k.

Image forming units 10y, 10m, 10c, 1
Below 0k, a transport mechanism 20 including a transport belt 21 as a transport unit that transports the image of each color formed by each image forming unit in the direction a in the drawing is disposed. The conveyor belt 21 is wound between a driving roller 91 that rotates in the direction of arrow a by a motor (not shown) and a driven roller 92 that is separated from the driving roller 91 by a predetermined distance, and is arranged with a predetermined tension. It runs endlessly at a constant speed in the a direction. The image forming units 10y and 10
m, 10c, and 10k are arranged in series along the transport direction of the transport belt 21.

Image forming sections 10y, 10m, 10c, 1
0k is a photosensitive drum 61y, 61m, 61c, 61k as an image bearing member whose outer peripheral surface is rotatably formed in the same direction at a position in contact with the conveyor belt 21.
Have. Photosensitive drums 61y, 61m, 61c, 61k
Is rotated at a predetermined peripheral speed by a motor (not shown).

Photosensitive drums 61y, 61m, 61c, 61
The k's are arranged such that their axes are equidistant from each other, and the axes are arranged so as to be orthogonal to the direction in which an image is conveyed by the conveyor belt 21.

In the following description, each photosensitive drum 61
The axial direction of y, 61m, 61c, 61k is the main operation direction (second direction), and the photosensitive drums 61y, 61m, 61
The rotation direction of c and 61k, that is, the rotation direction of the conveyor belt 21 (direction of arrow a in the figure) is the sub-scanning direction (first direction).
And

Photosensitive drums 61y, 61m, 61c, 61
Charging chargers 62y, 62m, 62c and 62k as charging means and developing rollers 64y, 64m, 64c and 64 as developing means are provided around k along the rotation direction thereof.
k, transfer devices 93y, 93m, 93 as transfer means
c, 93k, conductive cleaning blades 65y, 65
m, 65c, 65k, respectively, and toner discharge devices 66y, 66m, 66c, 66k, and static elimination LED arrays 63y, 63m, 6 for eliminating residual charges on the photosensitive drum.
3c and 63k are arranged in order.

Transfer devices 93y, 93m, 93c, 93
k is the corresponding photosensitive drum 61y, 61m, 61c, 6
It is arranged at a position where the conveyor belt 21 is sandwiched between 1 k and 1 k, that is, inside the conveyor belt 21. The exposure points by the exposure device 50 described later are the charging devices 62y, 62m, 62c, 62k and the developing roller 64y, respectively.
64m, 64c, 64k between the photosensitive drum 61y,
It is formed on the outer peripheral surfaces of 61m, 61c, and 61k.

Below the transport mechanism 20, the image forming section 10 is provided.
Sheet cassettes 22a and 22b that accommodate a plurality of sheets P as an image forming medium (recording medium) to which the images formed by y, 10m, 10c, and 10k are transferred are arranged.

Among the end portions of the paper cassettes 22a and 22b, the end portions of the paper cassettes 22a and 22b which are closer to the driven roller 92 have the paper P accommodated in the paper cassettes 22a and 22b from the uppermost one. Pickup rollers 23a and 23b for taking out the sheets one by one are arranged. Between the pickup rollers 23a and 23b and the driven roller 92, the leading edge of the sheet P taken out from the sheet cassettes 22a and 22b and the leading edge of the y toner image formed on the photosensitive drum 61y of the image forming section 10y are provided. A registration roller 24 for alignment is arranged.

The other photosensitive drums 61y, 61m, 6
The toner image formed on 1c is supplied to each transfer position in synchronization with the transport timing of the paper P transported on the transport belt 21.

Registration roller 24 and first image forming section 1
0y, in the vicinity of the driven roller 92, that is, on the outer periphery of the driven roller 92 substantially sandwiching the conveyor belt 21, the paper P conveyed at a predetermined timing via the registration roller 24. An attraction roller 26 for providing electrostatic attraction is provided. The axis of the suction roller 26 and the axis of the driven roller 92 are set to be parallel to each other.

At the end of the conveyor belt 21, the position of the image formed on the conveyor belt 21 is near the drive roller 91, that is, substantially on the outer periphery of the drive roller 91 with the conveyor belt 21 sandwiched therebetween. A sensor group 96 including a position shift sensor and a toner adhesion amount sensor for detecting is provided.

On the outer periphery of the drive roller 91 and on the conveyor belt 21 downstream of the sensor group 96, the conveyor belt 21
A conveyor belt cleaning device 95 for removing the toner or the paper dust of the paper P adhered to the top is arranged.

The paper P conveyed through the conveyor belt 21.
Is separated from the drive roller 91, and the toner image transferred to the paper P is melted by heating the paper P to a predetermined temperature in the transport direction, and a fixing device 80 that fixes the toner image to the paper P is provided. There is. The fixing device 80 includes a heat roller pair 81, oil application rollers 82 and 83, a web winding roller 84, a web roller 85, and a web pressing roller 86.
It consists of and. The toner formed on the paper P is fixed on the paper, and the paper is discharged by the paper discharge roller pair 87.

Photosensitive drums 61y, 61m, 61c, 61
The exposure device 50 that forms color-separated electrostatic latent images on the outer peripheral surface of k is based on the image data Y, M, C, and K for each color that has been color-separated by the image processing unit 36 described later. It has a semiconductor laser oscillator 60 whose emission is controlled.
On the optical path of the semiconductor laser oscillator 60, in order to correct and focus the polygon mirror 51 rotated by the polygon motor 54 that reflects and scans the laser beam light, and the focus of the laser beam light reflected through the polygon mirror 51. Fθ lenses 52 and 53 are sequentially provided.

Fθ lens 53 and photosensitive drums 61y, 6
Between the 1 m, 61 c, and 61 k, the laser beam light of each color that has passed through the fθ lens 53 is exposed to the photosensitive drums 61 y and 6 k.
First folding mirrors 55y, 55m, 55c, 55k, which are bent toward the exposure positions of 1m, 61c, 61k,
First folding mirrors 55y, 55m, 55c, 55k
The second and third folding mirrors 56y, 56m, 56c for further bending the laser beam light bent by
57y, 57m, and 57c are arranged.

The laser beam light for black is reflected by the first folding mirror 55k and then guided onto the photosensitive drum 61k without passing through other mirrors.

The image forming process of this image forming apparatus will be described.

Printer CPU 111 for which image formation will be described later
When it is instructed by 0, the photosensitive drum 61 starts rotating by a motor (not shown), and the surface of the photosensitive drum 61 is charged to a negative potential by the charging charger 62. A charging wire (not shown) is provided in the charging charger 62, so that a negative charge is uniformly given to the surface of the photosensitive drum by negative corona discharge. Next, the exposure device 50 irradiates the image forming portion with laser light to form an electrostatic latent image on the surface of the photosensitive drum. The electrostatic latent image formed here is the developing roller 6
A toner image is attached by the method 1 to form a visible image. This visible image is transferred to a sheet by applying a positive transfer bias at the position of the transfer device.

After the transfer is completed, the residual toner remaining on the surface of the photoconductor is scraped off by the conductive cleaning blade 65 while removing the positive charge applied on the surface of the photoconductor during the transfer. Further, the negative charge remaining on the photoconductor drum is eliminated by the elimination LED array 63.

Next, the circuit configuration of this image forming apparatus will be described with reference to FIG. The control system in this circuit is composed of three CPUs: a main CPU 1091 in the main control unit 30, a scanner CPU 1100 of the color scanner unit 1, and a printer CPU 1110 of the color printer unit 2.

The main CPU 1091 is a printer CPU
Bi-directional communication is performed via 1110 and shared RAM 1035. The main CPU 1091 outputs an operation instruction, and the printer CPU 1110 outputs status information. The printer CPU 1110 and the scanner CPU 1100 perform serial communication, the printer CPU 1110 outputs an operation instruction, and the scanner CPU 1100 outputs status information.

The operation panel 1040 is provided on the liquid crystal display unit 104.
2. It has various operation keys 1043 and a panel CPU 1041 to which they are connected, and is connected to the main CPU 1091.

The main controller 1030 has a main CPU 109.
1, ROM 1032, RAM 1033, NVRAM (no
(volatile RAM) 1034, shared RAM 1035, image processing unit 1036, page memory control unit 1037, page memory 1038, printer controller 1039, printer font ROM 1121.

The main CPU 1091 performs overall control, the ROM 1032 records control processes and the like, and the RAM 1033 temporarily stores data. N
The VRAM 1034 is a non-volatile memory backed up by a battery (not shown) and can retain data even when the power supply from the power supply is cut off.

The shared RAM 1035 is the main CPU 10
It is used for bidirectional communication between the printer 91 and the printer CPU 1110.

The page memory control unit 1037 stores and reads image information in the page memory 1038. The page memory 1038 has an area capable of storing image information for a plurality of pages, compresses image information from the color scanner unit 1, and stores data in units of one page.

Photo data corresponding to print data is stored in the printer font ROM 1121. The printer controller 1039 prints the print data output from the external device 1122 such as a personal computer with a resolution corresponding to the data indicating the resolution assigned to the print data and prints the printer font RO.
Image data is generated using the font data stored in M1121.

The color scanner section 1001 includes a scanner CPU 1101 for controlling the whole, a ROM 1101 for storing control programs and the like, and a RAM 110 for storing data.
2, a CCD driver 1103 that drives a color image sensor (not shown), a scan motor driver 1104 that controls the rotation of a scan motor that moves a first carriage (not shown), and an image correction unit 1105.

The image correction unit 1105 is an A / D conversion circuit for converting R, G, B analog signals output from a color image sensor (not shown) into digital signals, variations in the characteristics of the color image sensor, or A shading correction circuit for correcting fluctuations in the threshold level with respect to the output signal from the color image sensor due to a change in ambient temperature, and a line memory for temporarily storing the corrected digital signal output from the shading correction circuit.

The color printer section 1002 has a printer CPU 1110 for overall control, a ROM 1111 for storing control programs and the like, and a RAM 111 for data storage.
2. A laser driver 1113 for driving a semiconductor laser oscillator (not shown) and a polygon motor driver 111 for driving a polygon motor of an exposure device (not shown).
4, a conveyance control unit 1115 that controls the conveyance of the paper P by a conveyance mechanism (not shown), a process control unit 1116 that controls the process of charging, developing, and transferring using a charging device, a developing roller, and a transfer device, which are illustrated. A fixing control unit 1117 that controls a fixing device that is not installed, an option control unit 1118 that controls options, a toner adhesion amount sensor 1120, which will be described later, and a position alignment sensor 1122.

Image processing unit 1036, page memory 103
8, printer controller 1039, image correction unit 110
5, the laser driver 1113, the image data bus 112
Connected by 0.

An embodiment of the present invention using the image forming apparatus having the above structure will be described below.

(First Embodiment) FIG. 3 shows a structure of a toner adhesion amount sensor for performing image quality maintenance control of the image forming apparatus. The image quality maintenance control is to change image forming conditions so as to minimize changes in image density and line width due to usage environment and life of consumables such as photoconductor drums and developing devices. The density of the test pattern developed on the transfer belt 21 is detected by the toner adhesion amount sensor, and the image forming condition is changed based on the result.

The image forming conditions mean the conditions of the image forming process such as charging voltage, laser exposure amount, developing bias and the like.

The toner adhesion amount sensor 1120 is composed of a light emitting element 100 and a light receiving element 101. CP
A light source control voltage corresponding to the light amount designated by U1091 is output from the D / A converter, and the light emitting element 100 projects light corresponding to the light amount control voltage onto the transfer belt 21. The reflected light of the transfer belt 21 and the toner image on the transfer belt 21 is received by the light receiving element 101, the output voltage corresponding to this reflected light amount is converted into a digital value by the A / D converter, and the CPU 1
Returned to 091.

Next, the flow of normal image quality maintenance control will be described with reference to FIG. This control is performed at the time of pre-run when the power of the image forming apparatus is turned on.

The CPU 1091 reads the stored reference image forming conditions and sets the conditions for each device (ST1).
The sensor light source is adjusted (ST2).

When the preparation is completed, a test pattern is formed on the conveyor belt 21 (ST3), and the density of the test pattern is read by the toner adhesion amount sensor (ST4). Here, the read density is compared with a reference value to determine whether or not it is within an allowable range value that does not hinder image formation.
It is determined by the PU 1091 (ST5). If it is determined that the value is out of the allowable range, the CPU 1091 changes the image forming condition set in step ST1 (ST
6) The test pattern is created again, and the determination is performed again. When it is finally determined in step ST5 that the density is within the allowable range, the last image forming condition before the determination is stored and reflected in the subsequent image formation.

Various phenomena when the charging charge wire of the charging charger, which is the point of the present invention, is broken will be described.

FIG. 5 shows a temporal flow of the surface potential of the photosensitive drum. As described above, after the visible image is transferred onto the paper, the negative charges remaining on the surface of the photoconductor are discharged by the discharging LED array 63 (the discharging process in the figure). After that, by the charger 62,
After being charged (charging process in the figure), the exposure device 50 irradiates the surface of the photoconductor with laser light, and the electrostatic latent image forming portion is
Surface potential rises.

The developing bias of the image forming apparatus of the present invention is -400V, and as shown in FIG. 6, if the surface potential does not rise above this bias voltage, an electrostatic latent image is not formed.

However, when the charging charge wire is broken, the surface potential of the photoconductor drum is uniformly eliminated by the electricity eliminating LED array and becomes equal to or higher than -400V.
Therefore, regardless of whether or not the laser light is applied to the portion where the toner is supplied by the developing roller,
All the toner will get on.

FIG. 7 is a diagram showing the output of the toner adhesion amount sensor when images are continuously transferred onto a sheet. When the charging charge wire is not broken, as shown in FIG. 7A, the amount of light received by the light receiving element 101 in the print area is lower than that outside the print area. Outside the print area (white background portion), there is a slight increase or decrease, but a significantly higher amount of received light can be obtained at a constant level compared to the print area.

However, when the charging charge wire is broken, solid black is always developed during the image forming process, and as shown in FIG. 7B, regardless of whether it is inside or outside the image forming area. The amount of received light is always kept low. That is, the toner adhesion amount sensor 1 is located outside the printing area.
When measured at 120, if the charging charge wire is operating normally without being broken, the same amount of light received as on a white background is detected, and if the charging charge wire is broken, only the amount of solid black light received is detected. Can not. This makes it possible to detect whether or not the charging charge wire is broken.

FIG. 8 is a flow chart for detecting an abnormality for detecting whether or not the charging charge wire is broken. When the CPU 1091 gives an instruction to start the image forming operation, the image forming operation of the photosensitive drum motor, the transfer belt motor, etc. is started (ST11). continue,
It is determined whether or not the portion currently monitored by the toner adhesion amount sensor 1120 is the image forming area (ST12), and if it is outside the image forming area, whether or not the toner density is detected outside the image forming area. Is judged (ST13).
If the toner density is not detected, the image forming operation is continued.

If it is determined that the density is a solid black or a density close to it outside the image forming area, it is determined that the charging charge wire is broken, the image forming operation is stopped, and the liquid crystal of the operation panel 1040 is stopped. An error is displayed on the display unit 1042 (ST14). The error display is not limited to the liquid crystal display unit 1042, but may be an external device 1122 (for example, a personal computer or electronic mail).

The installation position of the toner adhesion amount sensor 1120 is not limited to the position on the conveyor belt.
For example, as shown in FIG. 9, it may be a position where the surface of the photosensitive drum is detected downstream from the developing position in the rotational direction of the photosensitive drum to the transfer position.

The detection of the charging charge wire breakage is not limited to the normal continuous image formation, but may be performed when the power of the image forming apparatus is turned on or immediately after the charging charge wire is cleaned. about,
It is not limited in any way.

Further, the present embodiment has been described in the so-called four-series tandem type image forming apparatus in which images are formed on four photoconductors respectively, and the sheets are conveyed by the conveying belt to perform color superposition. The present embodiment is not limited to this method, and the present embodiment can be applied as long as the image formation is of a method capable of measuring the toner density by distinguishing the inside and outside of the image forming area.

(Second Embodiment) Next, the second embodiment of the present invention will be described.
An example of the above will be described with reference to FIGS.
In the present embodiment, a method of forming images of a plurality of colors by a plurality of photoconductors and performing color superimposition while a sheet is conveyed by a conveyor belt will be described as an example.

In this system, since a very highly accurate alignment is required for color superposition of a plurality of colors, it has an alignment control mechanism. Since the image forming apparatus is equipped with the fixing device, which is a large heat source, the temperature inside the machine body rises, and due to this, an error such as a subtle expansion of the laser optical system component of the exposure device 50 occurs. Therefore, this alignment control is performed when the power of the image forming apparatus is turned on and at regular intervals.

A method of alignment control will be described with reference to FIG. A wedge shape consisting of a straight line parallel to the main scanning direction for each of the yellow (Y), magenta (M), cyan (C), and black (K) photoreceptors, and a straight line having a predetermined angle to this straight line Transfer the test pattern of
The pitch (time) shown below is measured by the alignment sensors 1122 (a) and (b) which are formed in the vicinity of the end portion of the conveyor belt 21 and are arranged downstream of the final transfer position of the conveyor belt 21 in the conveyor belt rotation direction.

[Pk-c], [Pc-m], [Pm-y]: Parallel deviation in the sub-scanning direction [Wx-f]-[Wk-f]: Writing position deviation in the main scanning direction ([Wx-r] -[Wx-f])-([Wk-r] [Wk-f]): Main scanning direction magnification deviation [Sk]: Tilt deviation Due to the measured pitch, the sub-scanning direction parallel deviation causes Correction is performed according to the rotation speed, and the laser writing position is corrected for the writing position deviation in the main scanning direction.
In addition, the alignment is performed by correcting the polygon motor rotation speed for the magnification deviation in the main scanning direction and correcting the mirror inclination in the laser unit for the inclination deviation.

At the bottom of FIG. 10, there is shown a time chart showing the time variation of the amount of light received by the alignment sensor. As is clear from this figure, when the test pattern arrives at the measurement position of the alignment sensor, the amount of light received by the light receiving element of the alignment sensor decreases for a very short time. This is because the straight line of the test pattern is thin.

FIG. 11 shows a state of printing a test pattern when a problem occurs in the charging charge wire. If there is a problem such as disconnection of the charging charge wire, as shown in the figure, a solid black image will be transferred on the defective photoreceptor for the length of the developing time. However, the amount of received light decreases for a very long time.

By counting the time required for the amount of received light to decrease and to return to the original value, it is possible to detect a defect in the charging charge wire.

FIG. 12 shows a flow chart for detecting a charging charge wire defect by the alignment sensor 1122. When the CPU 1091 outputs the alignment control instruction, the test pattern is printed on the conveyor belt in each image forming unit (ST20). The alignment sensor counts the light reception amount reduction time of the light receiving element with reference to the normal light reception amount reduction time, and determines whether or not it is an abnormal value (ST21). If it is an abnormal value, an instruction to stop the image forming operation is issued, and an error display is displayed on the liquid crystal display unit 1042.

If normal, the alignment sensor 1122
The displacement amounts described above in (a) and (b) are measured (S
T23) Further, the calculation processing of the four color misregistration amount is performed (S
T24).

The calculated amount of deviation is compared with a specified value within an allowable range (ST25), and it is determined whether it is outside the specified value (ST26). If the value is out of the specified value, the test pattern is printed again, the predetermined operation is repeated, and if the value is not within the specified value after several times, it is judged as an error.

If it is within the specified value, various corrections such as laser writing position correction and laser beam reflection mirror angle adjustment are performed (ST27), and the determination is completed.

In the second embodiment, a four-tandem tandem type image forming apparatus using a conveyor belt is described as an example, and its detection position is on the conveyor belt. However, the present embodiment is not limited to this conveyor belt, and is applicable, for example, as long as the photosensitive member has a belt shape and can hold a plurality of images. The present invention is also applicable to an image forming apparatus of a type in which color images are overlaid with each other or a type in which a plurality of images can be held on an intermediate transfer member.

[0084]

As described above in detail, according to the image forming apparatus of the present invention, the toner adhesion amount sensor or the toner adhesion amount sensor, which has already been widespread, has the defect of the charging charge wire and the defect of the applied voltage applied to the charger. By using the alignment sensor, it can be easily realized without adding a new configuration.

[Brief description of drawings]

FIG. 1 is an apparatus cross-sectional view of an image forming apparatus according to the present invention.

FIG. 2 is a block diagram showing a system of an image forming apparatus according to the present invention.

FIG. 3 is a sectional view showing a configuration of a toner adhesion sensor.

FIG. 4 is a flowchart showing a flow of image quality maintenance control.

FIG. 5 is a diagram showing a temporal displacement of the surface potential of the photosensitive drum.

FIG. 6 is a diagram showing a relationship between a photoreceptor surface potential and a developing bias.

FIG. 7 is a time chart showing the output of the toner adhesion amount sensor.

FIG. 8 is a flowchart for detecting a charge charge wire breakage by a toner adhesion amount sensor.

FIG. 9 is a diagram showing a modification of the installation position of the toner adhesion amount sensor according to the first embodiment.

FIG. 10 is a conceptual diagram of alignment control.

FIG. 11 is an error conceptual diagram when there is a problem in the charging charge wire.

FIG. 12 is a flowchart for detecting a charging charge wire breakage by the alignment sensor.

[Explanation of symbols]

61 ... Photosensitive drum 62 ... Charger 64 ... Developing roller 96 …… Sensor County 100: Light emitting element 101 ... Light receiving element 1091 ... CPU 1120 ... Toner adhesion sensor 1122 ... Positioning sensor

Claims (7)

[Claims] 1. An image carrier for carrying an image, a charging means for charging the image carrier, an exposing means for exposing the image carrier to form an electrostatic latent image, and an electrostatic latent image for exposing the electrostatic latent image. A developing unit that develops with a developer to form a first developer image, and a density of the first developer image at a position downstream of a developing position by the developing unit with respect to the developer image carrying direction. The density detecting means for detecting, and the second developer image that is continuously conveyed after the first developer image are conveyed with a predetermined interval from the first developer image, First determining means for determining that the detection position of the concentration detecting means is within the predetermined interval, and when the concentration detecting means detects the concentration within the predetermined interval by the first determining means, A second determination means for determining whether or not the concentration is abnormal is provided. An image forming apparatus. 2. The image forming apparatus according to claim 1, further comprising a changing unit that changes an image forming condition based on a detection result of the density detecting unit. 3. The image forming apparatus according to claim 1, wherein the first developer image and the second developer image are developed by different developing means. 4. An image bearing member carrying an image, a charging unit charging the image bearing member, an exposing unit exposing the image bearing member to form an electrostatic latent image, and the electrostatic latent image Developing means for developing with a developing material to form a developing material image having a predetermined length in the sub-scanning direction; detecting means for detecting the length of the developing material image in the sub-scanning direction; And a determination unit that compares the length of the data in the sub-scanning direction of the data with the length of the developer image in the sub-scanning direction to determine whether or not the operation of the charging unit is abnormal. An image forming apparatus comprising: 5. The image forming apparatus according to claim 4, wherein there are a plurality of developing units, each of which forms a developer image having the same predetermined length in the sub-scanning direction. 6. The image forming apparatus according to claim 5, wherein a plurality of developer images formed on the image carrier and having the same length in the sub-scanning direction are transferred at predetermined intervals. . 7. A measuring device for measuring an actual interval between the plurality of developing material images, and a correcting device for correcting an image forming condition based on a measurement result of the measuring device. The image forming apparatus described.