JP2009271194A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus enabling stable adjustment of image density while suppressing increase in size and cost of the apparatus. <P>SOLUTION: The image forming apparatus for recording and printing a toner image formed on an image carrier 2 comprises an optical path shielding member 17 capable of performing opening and closing operation to block a light receiving optical path of an optical sensor 16 disposed above an intermediate transfer body 7 at an optional time; and an optical path shielding member opening and closing operation means 18 which moves the shielding member 17 between an open position and a close position, in which output of the optical sensor 16 is detected, and state check is performed according to the detection result for whether the opening and closing operation of the shielding member 17 is normal or not. The execution timing of the check for the opening and closing operation of the shielding member 17 can be varied. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus, such as a copying machine or a facsimile printer, provided with a dustproof mechanism for an optical density sensor.

As an image density control unit in a conventional image forming apparatus, an image density control method that is generally mounted generally forms a toner adhesion pattern on a toner image carrier such as a photoreceptor or a transfer belt, and the toner adhesion amount. Is detected by an optical sensor to optimize image forming conditions such as development conditions and toner density control target values (see, for example, Patent Documents 1 and 2).
As described above, in order to detect the toner adhesion amount of the toner adhesion pattern by the optical sensor, it is necessary to install the optical sensor in a close region facing the pattern image. Therefore, there is a possibility that the detection surface of the optical sensor may be contaminated with time due to toner dropping from a unit arranged above the optical sensor, toner flying from the surface of the toner image carrier or foreign matter floating in the image forming apparatus. is there.
In Patent Documents 1 and 2 relating to such a toner density control method, when the contamination state of the optical sensor is deteriorated, there is a problem that the density control accuracy is lowered. As a countermeasure, the optical sensor performs density control. It is disclosed that the dustproof shutter is closed at the time of detecting for the above or at a timing other than the initialization operation of the optical sensor.
Although not publicly known, the applicant has an optical path shielding member and an opening / closing operation means capable of opening and closing to interrupt the light receiving optical path of the optical sensor at an arbitrary timing in the prior application, and the optical path shielding member is closed. An image forming apparatus is proposed that detects the output of an optical sensor in a state where the light receiving optical path is blocked by, and determines whether or not the opening / closing operation of the optical path shielding member is normal according to the detection result. In the prior application, the present applicant can prevent the detection function of the optical sensor from being impaired due to the malfunction of the optical path shielding member.
JP 2004-110018 A JP 2006-208645 A

However, a conventional image forming apparatus employs a dust-proof shutter for avoiding contamination due to toner and foreign matter on the detection surface of the optical sensor for controlling the density of toner. However, if a malfunction occurs in the opening / closing operation of the shutter and the shutter remains in the closed state, the detection itself cannot be performed, rather than the density control accuracy decreasing due to the contamination of the detection surface.
In this regard, since the detection value of the optical sensor is extremely reduced, it is possible to easily determine a shutter operation failure, and it has conventionally been common to stop density control and warn of an abnormality. Yes.
On the other hand, if the shutter remains open due to a malfunction of the shutter, the pattern can be detected by the optical sensor, but the optical sensor is detected over time without the original effect of the shutter functioning. There is a problem in that surface contamination increases and density control accuracy decreases.
When an optical sensor adjustment patch is provided on the rear surface of the dust-proof shutter so that the initial adjustment of the optical sensor is performed in the shutter closed state, the contamination of the optical sensor detection surface is more serious.
Further, according to the above-mentioned prior application of the present applicant, it is possible to prevent the detection function of the optical sensor from being impaired due to the malfunction of the optical path shielding member, but further, the optical sensor output is detected and the detection result is obtained. Accordingly, it is more desirable that the timing for determining whether the shutter opening / closing operation is normal can be changed according to the state of the image forming apparatus.
Accordingly, an object of the present invention is to make it possible to change the timing for determining whether or not the shutter opening / closing operation is normal in accordance with the state of the image forming apparatus in consideration of the above-described actual situation. An object of the present invention is to provide an image forming apparatus capable of stably adjusting image density while suppressing an increase in price.

In order to solve the above-described problems, the invention according to claim 1 is an optical path capable of opening and closing that blocks a light receiving optical path of an optical sensor disposed above an intermediate transfer member and blocks the light receiving optical path at an arbitrary timing. In a state where the light path shielding member opening / closing operation means for moving the light shielding member and the light path shielding member between the open position and the closed position, the light path shielding member being in the closed state and the light receiving light path being blocked, Image formation that detects the output of the optical sensor and determines whether the opening / closing operation of the optical path shielding member is normal according to the detection result, and records and prints the toner image formed on the image carrier In the apparatus, the image forming apparatus is characterized in that execution timing of the open / close operation quality determination of the optical path shielding member is variable.
According to a second aspect of the present invention, there is provided an image forming apparatus according to the first aspect, wherein the execution timing of the open / close operation quality determination of the optical path shielding member is changed according to the formed image area.
According to a third aspect of the present invention, in the image forming according to the second aspect, when the image area integrated value of the formed image area is equal to or greater than a predetermined value, the pass / fail operation determination of the optical path shielding member is executed. Features the device.
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the execution timing of the pass / fail judgment of the opening / closing operation of the optical path shielding member is changed according to a change amount of the developing ability.
According to a fifth aspect of the present invention, the image forming apparatus according to the fourth aspect is characterized in that when the amount of change in the developing capacity becomes equal to or greater than a predetermined value, the quality determination of the opening / closing operation of the optical path shielding member is performed. To do.
According to a sixth aspect of the invention, there is provided the image forming apparatus according to the first aspect, wherein the opening / closing operation quality determination of the optical path shielding member is executed immediately after detection of a paper jam.

  According to the present invention, a light receiving element or an optical sensor having a light receiving / emitting element is provided, and has an optical path shielding member and an opening / closing operation means capable of opening and closing the light receiving optical path at an arbitrary timing, and the optical path shielding member is closed. The optical path is detected when the optical sensor output is detected in a state where the light receiving optical path is interrupted, and whether the opening / closing operation of the shielding member is normal or not is determined at a predetermined timing according to the detection result. Since the execution timing of the opening / closing operation quality determination of the shielding member is made variable, it is possible to prevent deterioration of the detection function of the optical sensor due to the operation failure of the optical path shielding member as necessary, and the opening / closing operation quality of the useless optical path shielding member Sensor degradation due to the determination can be prevented.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an overall layout around an image forming station of an image forming apparatus according to the present invention. This image forming apparatus A is configured such that an intermediate transfer member (hereinafter referred to as an intermediate transfer belt) 7 is disposed in the horizontal direction so as to form an image from monochromatic to full color.
In the present embodiment, the image forming stations 1Y, 1C, 1M, and 1K respectively include photosensitive drums 2Y, 2C, 2M, and 2K as image forming bodies or image carriers, and charging rollers 3Y, 3C, and the like as charging units. 3M, 3K, laser exposure device (not shown) as image writing means and developing units 4Y, 4C, 4M, 4K as developing means, cleaning units 6Y, 6C, 6M for removing transfer residual toner on the surface of the photosensitive drum , 6K at least.
The image forming stations 1Y, 1C, 1M, and 1K are configured as an image forming unit of each color of a plurality of sets (four sets in the present embodiment), and yellow (Y), magenta (M), cyan (C), and black ( K) The image forming stations for each color are arranged in the order of Y, C, M, and K from the left in the lower part of the intermediate transfer belt 7 as an intermediate transfer member that runs in a loop, facing the horizontal stretching surface. Has been. The four color image forming stations have the same configuration.

The charging rollers 3Y, 3C, 3M, and 3K charge the photosensitive drums 2Y, 2C, 2M, and 2K by charging with the same polarity as that of the toner held at a predetermined potential (in this embodiment, negative charging). ) To apply a uniform potential to the photosensitive drums 2Y, 2C, 2M, and 2K.
The laser exposure apparatus (not shown) is upstream of the developing units 4Y, 4C, 4M, and 4K on the downstream side in the rotation direction of the photosensitive drums 2Y, 2C, 2M, and 2K with respect to the charging rollers 3Y, 3C, 3M, and 3K. Placed on the side. The laser exposure apparatus is arranged in the main scanning direction in parallel with the rotation axes of the photosensitive drums 2Y, 2C, 2M, and 2K.
The laser exposure apparatus, for example, performs image exposure on the photosensitive layers of the photosensitive drums 2Y, 2C, 2M, and 2K in accordance with the image data of each color that is read by an image reading apparatus provided in a different configuration and recorded in the memory, and for each color. An electrostatic latent image is formed.
Although not shown, the photosensitive drums 2Y, 2C, 2M, and 2K are arranged in the order of the charge generation layer (lower layer) and the charge transport layer (upper layer) on the undercoat layer formed on the surface of the conductive cylindrical support. These layers are stacked in the reverse order or the reverse order.
A known surface protective layer such as an overcoat layer mainly composed of a thermoplastic or thermosetting polymer may be formed on the surface of the charge transport layer or the charge generation layer. In the present embodiment, the conductive cylindrical supports of the photosensitive drums 2Y, 2C, 2M, and 2K are grounded.

The developing units 4Y, 4C, 4M, and 4K maintain a predetermined gap with respect to the peripheral surfaces of the photosensitive drums 2Y, 2C, 2M, and 2K, and rotate in the forward direction and the rotational direction of the photosensitive drums 2Y, 2C, 2M, and 2K. Development sleeves 41Y, 41C, 41M, and 41K made of cylindrical nonmagnetic stainless steel or aluminum.
In the development units 4Y, 4C, 4M, and 4K, one-component or two-component developers of yellow (Y), magenta (M), cyan (C), and black (K) are accommodated according to the development color for each color. Yes. In the present embodiment, a two-component developer (in this embodiment, the toner is negatively charged) is stored.
The developing sleeves 41Y, 41C, 41M, and 41K of the developing units 4Y, 4C, 4M, and 4K have a predetermined gap, for example, a drum surface of the photosensitive drums 2Y, 2C, 2M, and 2K by an abutting roller (not shown). , And kept in a non-contact state between 100 to 500 μm.
By applying a developing bias in which a DC voltage and an AC voltage are superimposed on the developing sleeves 41Y, 41C, 41M, and 41K, contact or non-contact reversal development is performed, and the photosensitive drums 2Y, 2C, 2M, and 2K are drums. A toner image is formed on the surface.
The intermediate transfer member (intermediate transfer belt) 7 is stretched around the intermediate transfer belt driving roller (also serving as a secondary transfer backup roller) 8, intermediate transfer belt tension rollers 10 a and 10 b, and the intermediate transfer belt support roller 9. The intermediate transfer belt 7 is provided so that the rotation direction thereof is counterclockwise.

Further, a secondary transfer roller 13 is provided through the intermediate transfer belt 7 so as to face the secondary transfer backup roller (intermediate transfer belt drive roller) 8. A cleaning blade 12 a of the cleaning unit 12 is provided in contact with the intermediate transfer belt 7 at the position of the support roller 9 in the facing direction.
The cleaning blades B of the cleaning units 6Y, 6C, 6M, and 6K are also provided in contact with the opposing direction of the photosensitive drums 2Y, 2C, 2M, and 2K as image carriers. Similarly, primary transfer rollers 5Y, 5C, 5M, and 5K for the respective colors are provided to face the photosensitive drums 2Y, 2C, 2M, and 2K with the intermediate transfer belt 7 interposed therebetween.
The intermediate transfer belt 7 is an endless belt having a volume resistance of 106 to 1012 Ω · cm. For example, polycarbonate (PC), polyimide (PI), polyamideimide (PAI), polyvinylidene fluoride (PVDF), and etrafluoroethylene -Belts made of resin materials such as ethylene copolymer (ETFE), rubber materials such as EPDM, NBR, CR, and polyurethane with conductive fillers such as carbon dispersed or ionic conductive materials are used. It is done.
The thickness of the intermediate transfer belt 7 is preferably set to about 50 to 200 μm in the case of a resin material and about 300 to 700 μm in the case of a rubber material. A rubber layer may be provided on the resin belt, and a coating layer may be provided on the surface layer. The intermediate transfer belt 7 is driven by rotation of a drive roller (secondary transfer backup roller) 8 by a drive motor (not shown).

The drive roller (secondary transfer backup roller) 8 is made of, for example, a peripheral surface of a conductive metal core (not shown) such as stainless steel, rubber or resin material such as polyurethane, EPDM, or silicone, and a conductive filler such as carbon. A material coated with a dispersed conductive or semiconductive material (no symbol) is used.
The primary transfer rollers 5Y, 5C, 5M, and 5K are provided to face the photosensitive drums 2Y, 2C, 2M, and 2K with the intermediate transfer belt 7 interposed therebetween, and the intermediate transfer belt 7 and the photosensitive drums 2Y, 2C, and 2M are provided. A transfer zone is formed between 2K and 2K.
The primary transfer rollers 5Y, 5C, 5M, and 5K are applied with a DC voltage having a polarity opposite to that of the toner (in this embodiment, a positive polarity) to form a transfer electric field in the transfer area, thereby forming a photosensitive drum. The toner images of the respective colors formed on 2Y, 2C, 2M, and 2K are transferred onto the intermediate transfer belt 7.
The primary transfer rollers 5Y, 5C, 5M, and 5K, which are the first transfer units for the respective colors, have, for example, a conductive core bar (not shown) such as stainless steel having an outer diameter of 8 mm. Further, a semiconductive elastic rubber (not shown) having a thickness of 5 mm and a rubber hardness of about 20 to 70 ° (Asker-C) is applied to a rubber material such as EPDM or silicone on the peripheral surface of the core metal. A conductive filler such as carbon is dispersed or an ionic conductive material is contained, and the volume resistance is formed in a solid state or foamed sponge state with a volume resistance of about 105 to 109 Ω · cm.

The secondary transfer roller 13 for transferring to the surface of the transfer material S is provided opposite to the secondary transfer backup roller 8 that is grounded with the intermediate transfer belt 7 interposed therebetween, and has a polarity opposite to that of the toner (in this embodiment, plus). ) Is applied by a DC power source. The superimposed toner image carried on the intermediate transfer belt 7 is transferred onto the surface of the transfer material S via the secondary transfer roller 13.
The secondary transfer roller 13 serving as a second transfer unit that re-transfers the color toner image on the intermediate transfer belt 7 onto the transfer material S that is a recording material is, for example, a conductive core (such as stainless steel having an outer diameter of 16 mm). (Not shown) having a thickness of 7 mm and covering the same configuration as the primary transfer roller described above.
In this case, unlike the primary transfer rollers 5Y, 5C, 5M, and 5K, the secondary transfer roller 13 is in contact with toner, so that the surface is covered with a material having good releasability such as a semiconductive fluororesin or urethane resin. There is.
The secondary transfer backup roller 8 is formed by dispersing a conductive filler such as carbon in a rubber or resin material such as polyurethane, EPDM, or silicone on the peripheral surface of a conductive metal core (not shown) such as stainless steel, It is formed by coating a semiconductive material containing a conductive material with a thickness of about 0.05 to 0.5 mm.
The cleaning blades 12a and 12B in contact with the surfaces of the photosensitive drums 2Y, 2C, 2M, and 2K and the intermediate transfer belt 7 are plate-shaped urethane rubber having a thickness of 1 to 3 mm and a JIS-A hardness of 60 to 80 ° on the sheet metal holder. Are bonded so that the free length is about 5 to 12 mm.

The cleaning blades 12a and B are in contact with the photosensitive drums 2Y, 2C, 2M, and 2K and the intermediate transfer belt 7 with a load of about 5 to 50 gf. In order to prevent the cleaning blades 12a, B from rolling up, the tip of the cleaning blades 12a, B may be coated with fluorine or conductive urethane rubber may be used so that the other side is not charged.
Here, the transfer material S such as a recording material is conveyed one by one from a stacking device (not shown) and conveyed so as to be superimposed on the intermediate transfer belt 7 sandwiched between the secondary transfer roller 13 and the secondary transfer backup roller 8. Then, the secondary transfer is received and sent to a fixing unit 15 including a fixing roller 15a and a pressure roller 15b, and fixed by heat welding and recovered.
In this embodiment, charging rollers 3Y, 3C, 3M, and 3K are used as charging means for the photosensitive drums 2Y, 2C, 2M, and 2K, and primary transfer rollers 5Y, 5C, 5M, and 5K are used as primary transfer members. Is used. This is preferable from the viewpoint of suppressing the generation of harmful ozone, but is not limited to this, and a corotron discharger can be used as a charging means in a non-contact state.

After the toner images on the photosensitive drums 2Y, 2C, 2M, and 2K are transferred to the intermediate transfer belt 7 (primary transfer), the toner images are transferred from the intermediate transfer belt 7 to the transfer material S by the secondary transfer roller 13 ( Secondary transfer), and a pattern detection sensor 16 for an image adjustment pattern facing the surface of the intermediate transfer belt 7 on the downstream side in the rotation direction of the intermediate transfer belt 7 from the secondary transfer position.
Then, the image formation conditions of the next image are changed based on the detection information, and process control is performed by a control means such as a CPU so that an appropriate image can be obtained, or toner replenishment amount optimization for toner density control is performed. Yes. Further, the control means can set the timing of the contact of the secondary transfer roller 13 and the release operation (release to the dotted line position in FIG. 1) so as to efficiently ensure the copy productivity while preventing the influence on the image quality. Can be controlled.
In the present invention, the toner adhesion pattern detection of each color of Y, C, M, and K is performed in a short time as much as possible. Therefore, the light reflection type photosensor (pattern detection sensor) 16 shown in FIG. In order to avoid contamination such as toner scattering and dropping from the secondary transfer portion, a total of four colors of each color are arranged downstream of the secondary transfer roller 13 (downward) in the direction of the intermediate transfer belt 7 drive shaft (not shown). The four light-reflective photosensors (hereinafter referred to as optical sensors) can be simultaneously detected. However, even in such an arrangement, toner flying may occur during secondary transfer.

FIG. 2 is a schematic perspective view showing the positional relationship between the intermediate transfer belt and the optical sensor. Referring to FIG. 2, the optical sensors (photosensors) 16 are attached to the frame body 16a in a row, and the frame body 16a is conveyed above the intermediate transfer belt 7 (FIG. 2) by an appropriate method. It is attached to a frame of an image forming apparatus (not shown) in a direction orthogonal to the direction.
The frame body 16a to which the optical sensor 16 is attached is provided with an optical path shielding member (shutter) 17 that shields light (optical path) from the optical sensor 16, and this optical path shielding member 17 has its function, that is, on the intermediate transfer belt 7. The optical sensor 16 can be moved between a closed position and an open position in order to shield the optical path.
On the back side of the frame body 16a, a frame member 21 that houses the solenoid 20, a contact member 21a in front of the core 20a of the solenoid 20, a connecting rod 22 having one end connected to the contact member 21a, An opening / closing operation means 18 for the optical path shielding member 17 comprising a spring 23 which is an elastic member fixed to a protrusion (not shown) which is coupled to the other end and bent a part of the optical path shielding member 17 is disposed.
The opening / closing operation means 18 is configured such that the optical path shielding member 17 is interlocked with the operation of the solenoid 20. In the normal state, the optical path shielding member 17 is closed by the action of the spring 23, and in the state where the optical sensor 16 (unit including the optical path shielding member 17, the optical sensor 16, and the opening / closing operation means 18) is attached to the image forming apparatus, the optical path shielding member 17 is intermediate. Shielding is performed while being positioned between the transfer belt 7 and the detection surface of the optical sensor 16.

The opening / closing operation means 18 supplies current to the solenoid 20 according to the control timing of the printing operation and image quality adjustment operation of the image forming apparatus, and opens / closes the optical path shielding member 17 at an arbitrary timing. Although not shown in detail, the stepped screw restricts the operation of the optical path shielding member 17 in the direction of the long hole provided obliquely in the vicinity of both ends of the optical path shielding member 17, and slides in the direction along the long hole to shield the optical path. The member 17 is opened and closed.
The optical path shielding member 17 is formed in an elongated hole at both ends in the longitudinal direction of the optical path shielding member 17 so as to cover the detection surface (light emitting / receiving surface) of the optical sensor 16 on a frame body 16a having an L-shaped cross section that fixes the optical sensor 16. It is attached with a stepped screw. This long hole is a long hole having an inclined surface so that the optical path shielding member 17 can be opened and closed.
As described above, the optical path shielding member (shutter) 17 is provided between the light reflection type photosensor 16 and the intermediate transfer belt 7 and the optical path shielding member at an arbitrary timing is provided by the solenoid 20 to prevent toner flying that may occur during the secondary transfer. Can be opened and closed.
An image forming apparatus according to the present invention includes a shutter and a shutter opening / closing operation means capable of opening / closing to interrupt a light receiving optical path of an optical sensor including a light receiving element or a light receiving / emitting element at an arbitrary timing, and the shutter is closed. In the state where the light receiving optical path is interrupted, the output of the optical sensor is detected, and the timing for determining whether the shutter opening / closing operation is normal or not is determined according to the detection result. It can be changed according to.

FIG. 3 is a block diagram partially showing a control unit of the image forming apparatus according to the present invention. FIG. 4 is a graph showing the relationship between the output of the optical sensor and the opening / closing of the optical path shielding member. The control unit 26 partially shows a control unit that performs process control of the image forming apparatus, and is configured by a CPU or the like.
Connected to the control unit 26 are an optical path shielding member 17, an opening / closing operation means 18 including a solenoid 20 (FIG. 2), an optical sensor 16 which is a light reflection type photosensor, a toner concentration control unit 24, and a potential control unit 25. Yes.
Referring to FIGS. 3 and 4, the optical path shielding member 17 performs other than execution of initial calibration (Vsg (ave) adjustment) described later of the optical sensor (light reflection type photosensor) 16 and toner pattern detection timing for density control. Is closed.
As a result, scattering toner and foreign matter floating in the image forming apparatus are prevented from adhering to the detection surface of the optical sensor 16. Further, the offset voltage (Voffset) of the optical sensor 16 is detected in the closed state of the optical path shielding member 17.
The output voltage was adjusted by the offset voltage Voffset of the optical sensor 16 detected in the closed state of the optical path shielding member 17 and the open state of the optical path shielding member 17 as criteria for determining whether the open / closed state of the optical path shielding member 17 is normal. The value is set between the value Vsg (0).
Accordingly, a value set between the offset voltage Voffset of the optical sensor 16 detected in the closed state of the optical path shielding member 17 and Vsg (0) adjusted in the output voltage in the opened state of the optical path shielding member 17 is used. Therefore, the operation state of the optical path shielding member 17 can be reliably detected.

When the value of the offset voltage Voffset, which is the output of the optical sensor 16 detected when the optical path shielding member 17 is closed, is equal to or less than a predetermined value, the control unit (CPU) 26 uses the detected value as the offset voltage Voffset. Record.
In addition, as a result of adjusting the output of the optical sensor 16 to a predetermined value in a state where the optical path shielding member 17 is opened, the average value of the fluctuation range of the value detected by the optical sensor 16 is Vsg (ave), and the minimum value is Vsg (min) is recorded and used as a criterion for determining the state of the optical path shielding member 17.
When the optical sensor 16 output is detected in the closed state of the optical path shielding member 17, and the detected value is equal to or less than a predetermined value, the detected value is recorded as the offset voltage Voffset.
Further, as a result of adjusting the output of the optical sensor 16 to a predetermined value in the opened state of the optical path shielding member 17, the average value of the fluctuation range of the detection value of the optical sensor 16 is Vsg (ave), and the minimum value is Vsg ( min), and these are used as determination criteria. Therefore, the influence of individual sensitivity variations and output fluctuations of the optical sensor 16 is excluded, and the operation state of the optical path shielding member 17 is accurately and reliably detected. be able to.

The optical sensor 16 is disposed so as to face the intermediate transfer belt 7 which is an intermediate transfer body that transfers and conveys the toner image formed by the image forming unit 1 (Y, C, M, K) in FIG. It is installed so that it can be detected.
The optical path shielding member 17 that blocks the optical path of the optical sensor 16 is configured to open and close between the optical sensor 16 facing the intermediate transfer belt 7, and the detection result Vsg of the optical sensor 16 in the closed state of the optical path shielding member 17. Accordingly, the state of the optical path shielding member 17 is determined.
In this state determination, if Vsg ≦ Voffset, the optical path shielding member 17 is closed and normal, and if Voffset <Vsg ≦ Vsg (min), the optical path shielding member 17 is open and dirty. If A and then Vsg (min) <Vsg, the shutter is open, so the process is performed as an abnormality B.
The optical path shielding member 17 opens and closes between the intermediate transfer belt 7 and the optical sensor 16, and the state as described above according to the detection result Vsg of the optical sensor 16 when the optical path shielding member 17 is closed. Since the determination is made, the content to be dealt with after that can be divided into cases.
The operator is warned of the following measures according to the determination result. At the time of Vsg (ave) adjustment described above, the light-emitting element current Ifsg is also detected at the same time, and when it is determined as abnormality A, the following different warning contents are displayed according to the Ifsg value.
In other words, in the case of abnormality A, a) Ifsg <predetermined value, the current state is maintained, b) If predetermined value ≦ Ifsg <allowable maximum value, P / TM sensor cleaning instruction, and c) allowable maximum value If .ltoreq.Ifsg, the P / TM sensor use prohibition is displayed, and if it is abnormal B, the shutter operation failure is warned.

When Vsg (ave) adjustment of the optical sensor 16 is performed, the light emitting element current Ifsg is detected and recorded. When the abnormality A is determined, the above-described different warning contents are displayed according to the Ifsg value. The content to be treated thereafter can be appropriately communicated.
A dark brown flocked seal (not shown) is attached to the surface of the optical path shielding member 17 facing the detection surface of the optical sensor 16 so that the light reflectance is 10% or less. Thereby, the offset voltage of the optical sensor 16 in the closed state of the optical path shielding member 17 can be detected with high accuracy.
In addition, it is possible to prevent the detection surface of the optical sensor 16 from being worn and scratched when the optical path shielding member 17 is opened and closed, and to prevent scattered toner from entering when the optical path shielding member 17 is closed.
The initial calibration (Vsg (ave) adjustment) is performed so that the output (Vsg) of the optical sensor 16 that detects the surface of the intermediate transfer belt 7 (FIG. 2) that does not form a toner pattern is 4.0 ± 0.5 v. The current value (Ifsg) flowing through the LED is adjusted and determined.
At this time, the following data is also acquired and stored as determination reference value information for determining whether the optical path shielding member 17 is open or closed. That is,
Vsg (0) adjustment minimum (min) value ... lower limit value of Vsg fluctuation range detected during Vsg (ave) adjustment, and Ifsg (0) adjustment value ... Vsg (ave) = 4.0 ± 0.5 v The LED current value when adjusted to is stored.
Ifsg (0) recorded at the time of Vsg (ave) adjustment is the light receiving sensitivity of the optical sensor 16, the LED luminance of the light emitting element, the mounting position of the optical sensor 16, the angle variation, the sensor detection surface or the surface of the intermediate transfer belt that is the detection target. It changes depending on the fouling condition.
If the image forming apparatus, the intermediate transfer belt 7 and the optical sensor 16 are in a new state, Ifsg is usually 10 mA or less, and this value is the “predetermined value” referred to in the present invention. Even if the above-described fluctuation factors that affect Ifsg (0) excluding the contamination of the detection surface of the optical sensor 16 are worst, Ifsg (0) does not exceed 20 mA (allowable maximum value).
Therefore, when 20 mA <Ifsg (0), the shutter is not closed and Vsg is lowered due to contamination of the light reflection type photosensor detection surface, so that the density control accuracy is considerably lowered. The image density control using the light-reflective photosensor 16 is prohibited, and a warning is issued to promote cleaning of the sensor detection surface and improvement of the shutter opening / closing operation failure (FIG. 5).
If Vsg> Vsg (0) adjustment min value before that, it is determined that the shutter opening / closing operation is defective, and a warning is issued to promote the improvement (FIG. 5).

FIG. 5 is a graph showing the relationship between the optical sensor output voltage and Ifsg. FIG. 6 is a flowchart of an operation for issuing a warning so as to promote the cleaning of the optical sensor detection surface and the improvement of the opening / closing operation failure of the optical path shielding member. This flowchart is a flowchart that summarizes the operations described with reference to FIGS. 3 and 4, and will be described with reference to FIGS. 2, 3 to 6.
First, it is determined whether or not the optical path shielding member (shutter) 17 is in a closed (closed) state (S1). If it is closed, the light emitting element LED of the optical sensor 16 is caused to emit light (S2), and it is determined whether or not the initial calibration Vsg ≦ the offset voltage Voffset of the optical sensor 16 (S3).
If Vsg ≦ Voffset, it is determined that the optical path shielding member 17 is closed (S4), and the current state is maintained as normal (S5) (S6). If Vsg ≦ Voffset is not satisfied, it is determined that the light path shielding member 17 is open (S7), and it is determined whether Vsg ≦ V (0) is the minimum value (S8). If Vsg ≦ V (0) is not the minimum value, it is determined as abnormality B (S9), and the use of the optical sensor 16 is prohibited (S10).
If Vsg ≦ V (0) minimum value in step (S8), it is determined as abnormality A (S11), and it is determined whether current value Ifsg <predetermined value (S12). If Ifsg <predetermined value, the current state is maintained (S13).
If Ifsg <predetermined value, it is determined whether Ifsg <allowable maximum value (S14). If Ifsg <allowable maximum value, the optical sensor 16 needs to be cleaned (S15). If Ifsg <allowable maximum value, Use of the optical sensor 16 is prohibited (S16).
Therefore, when 20 mA <Ifsg (0), the optical path shielding member 17 is not closed and Vsg is lowered due to contamination of the detection surface of the optical sensor 16, so that the density control accuracy is high. The image density control using the optical sensor 16 is prohibited by determining that it is considerably lowered.
At the same time, a warning is issued to promote the cleaning of the detection surface of the optical sensor 16 and the improvement of the opening / closing failure of the optical path shielding member 17. If Vsg> Vsg (0) reaches the minimum adjustment value before that, it is determined that the optical path shielding member 17 is in an open / close operation failure, and a warning is issued to promote the improvement.

Referring again to FIG. 1, in the present invention, the contact type secondary transfer roller 13 is used as the secondary transfer means as described above, so that the generation of ozone is suppressed as compared with the case where the discharge type corotron is used. It is also possible to transfer the transfer material.
A toner adhesion pattern (not shown) formed on the photoreceptor 2 </ b> Y outside the normal image forming area is transferred onto the intermediate transfer belt 7, and an optical sensor (light reflection) disposed downstream of the secondary transfer roller 13. Type photosensor) 16 detects the amount of reflected light, that is, the toner adhesion amount. At this time, the secondary transfer roller 13 needs to be separated from the intermediate transfer belt 7 so as not to disturb the toner adhesion pattern on the intermediate transfer belt 7.
Further, there is a problem that the vibration when the secondary transfer roller 13 contacts and separates from the intermediate transfer member (intermediate transfer belt) 7 adversely affects the image. For this reason, the time when the secondary transfer roller 13 is brought into contact with and separated from the intermediate transfer belt 7 is selected as a time when the influence of the disturbance on the image does not occur.
That is, during the image forming operation, the secondary transfer roller 13 is separated from the intermediate transfer belt 7 before the writing operation of the first image forming unit (yellow (Y) in the present embodiment) that starts the operation first is started. Thus, in the case of forming a single pattern, it is possible to reliably execute image forming operations such as writing exposure, development, and primary transfer without being affected by vibration when the secondary transfer roller 13 is separated. it can.

On the other hand, when a plurality of patterns with different toner adhesion amounts are formed and detected by the optical sensor 16 during potential control, the time required to form and detect all the patterns becomes long.
Therefore, when the plurality of patterns cannot be completely transferred to the primary transfer even when the top of the plurality of patterns reaches the secondary transfer roller 13 in this way, the separation timing of the secondary transfer roller 13 is the same as that at the time of forming the single pattern. Perform at different times.
In this embodiment, after the yellow (Y) image forming operation is started, the secondary transfer roller 13 is separated from the intermediate transfer belt 7 before the top of the plurality of patterns reaches the secondary transfer roller 13.
At this time, vibration at the time of separation of the secondary transfer roller 13 is transmitted to the plurality of image forming units, and the image adjustment pattern may be disturbed. Since this vibration does not affect the image adjustment result, the value detected by the optical sensor 16 for the pattern transferred or exposed at the separation timing of the secondary transfer roller 13 is excluded from the input information of the image adjustment. ing.
Further, if the input information is not adopted from the beginning, in order not to form a visible image pattern at the separation timing of the secondary transfer roller 13 in order to reduce the toner consumption and the burden on the intermediate transfer belt cleaning. In addition, a plurality of write patterns are arranged so as not to execute pattern exposure.

As described above, when the secondary transfer roller 13 that is in contact with the intermediate transfer belt 7 at the time of print output is subjected to an image adjustment operation immediately after the print output operation, the image adjustment operation is performed in preparation for the next print output operation. Try to be as short and efficient as possible.
Then, by providing a detection sensor using a wide area after the secondary transfer position, the space from the final primary transfer portion to the secondary transfer portion of the image forming apparatus is reduced, and from the primary transfer position to the secondary transfer position. The first printout time is shortened by reducing the distance.
Note that the same toner adhesion amount pattern is formed on the intermediate transfer belt 7 in a line in the scanning direction, and the image density is detected by detecting the image density or the like. Reflected in formation.
The color balance and gradation of the obtained image are made appropriate along with the density. These operations are normally executed every several tens to several hundreds of prints, and the amount of toner consumed in the image adjustment pattern is suppressed to a predetermined value or less.

Next, main image adjustment operations will be briefly described. The toner density control unit 24 in FIG. 3 calculates the toner replenishment time from the toner density sensor output, the toner density control reference value, and the pixel detection data, and drives the toner replenishment motor.
The potential control unit 25 in FIG. 3 outputs a predetermined LD power and charging voltage, creates a plurality of toner adhesion patterns (10) while changing the developing bias voltage, and detects them with a light-reflective photosensor. To do. The development input / output characteristic is obtained from the light reflection type photosensor output, and the development bias is changed so that this characteristic becomes a target value.
At the time of secondary transfer, when the toner image is transferred from the intermediate transfer belt 7 shown in FIG. 2 to a transfer body such as transfer paper, the toner is slightly scattered or the intermediate transfer belt is not transferred to the transfer body at the time of secondary transfer. 7 The light-reflective photosensor 16 is easily damaged due to scattering of transfer residual toner remaining on the surface.
The toner scattering tends to increase as the image area increases and as the amount of toner adhesion per unit area increases. Accordingly, in the state where the toner scattering amount increases, the above-mentioned “determination of whether the light reflection type photosensor shutter opening / closing operation is normal” is executed, so that it is effective without causing unnecessary standby time. Thus, abnormality detection of the optical path shielding member (shutter) 17 can be performed.
In the present invention, when the image area accumulated by the printing operation becomes 300,000 cm ² or more, the above-described “state determination as to whether the opening / closing operation of the light reflection type photosensor shutter is normal” is executed. . Thereafter, the determination operation is executed every 10,000 cm ² .

FIG. 7 is a flowchart of a determination operation for determining whether or not the opening / closing operation of the optical path shielding member of the light reflection type photosensor shutter is normal. Referring to FIGS. 2 and 7, after the print job is finished, it is determined whether the image area S is greater than or equal to a predetermined value (S ≧ predetermined value) (S21).
If the image area S is greater than or equal to a predetermined value, the stored image area S 300,000 ² is greater than or equal to (S ≧ 300,000 ²⁾ determines whether (S22). If S ≧ 300,000 cm ² , the quality of the operation of the optical path shielding member (shutter) 17 of the photosensor 16 is determined (S23).
Next, the image area S is reset (S25). On the other hand, if not step (S21) in (S ≧ predetermined value), the image area S 10,000 cm ² is greater than or equal to (S ≧ 10,000 cm ²⁾ to determine whether (S26). If S ≧ 10,000 cm ² , the quality determination of the operation of the optical path shielding member (shutter) 17 of the photosensor 16 is executed (S27), and the image area S is reset (S28).
Since the execution timing of the opening / closing operation quality determination of the optical path shielding member 17 is changed according to the image area to be formed, the determination operation is performed only when necessary according to the use state of the image forming apparatus. Can be avoided.
Further, when the integrated image area value is equal to or larger than the predetermined value, the quality determination of the opening / closing operation of the optical path shielding member 17 is performed, so that the toner adhesion amount on the intermediate transfer belt 7 is large and the toner is relatively scattered. As a result, it is possible to avoid performing unnecessary operations by performing the determination operation only when there is a possibility of affecting the optical sensor output.
As described above, when a plurality of patterns having different toner adhesion amounts are formed for potential control, if the developing ability is high and the toner adhesion amount per unit area is high, the development γ detection value also becomes high.
Therefore, in the present invention, when “development γ ≧ development γ target value × 1.2” is detected, the “state determination as to whether the light reflection type photosensor shutter opening / closing operation is normal” is executed.

FIG. 8 is a flowchart for explaining the “state determination as to whether or not the light-reflective photosensor shutter opening / closing operation is normal” when development γ ≧ development γ target value × 1.2 is detected.
Referring to FIG. 2 and FIG. 8, it is determined whether the development γ is greater than or equal to the development γ target value × 1.2 (development γ ≧ development γ target value × 1.2) after the potential control is completed. (S31). Here, the development γ target value is set to 0.9 mg / cm ² · kV. Subsequently, the quality determination of the opening / closing operation | movement of the optical path shielding member (shutter) 17 of the photosensor 16 is performed (S32).
Since the execution timing of the opening / closing operation quality determination of the optical path shielding member 17 is changed according to the change amount of the developing ability, it is unnecessary to perform the determination operation only when necessary according to the use state of the image forming apparatus. The execution of the operation can be avoided.
When the change amount of the developing ability is equal to or greater than a predetermined value, the quality determination of the opening / closing operation of the optical path shielding member 17 is performed. Therefore, the developing ability is high, the toner adhesion amount on the intermediate transfer belt 7 is large, Since the toner easily scatters, the determination operation is performed only in a state where there is a possibility of affecting the output of the optical sensor, so that unnecessary operations can be avoided.
During an image forming operation, if an abnormal operation such as a transfer material such as transfer paper being jammed in the middle of the transport path occurs and the printing operation stops urgently, an unfixed toner image will be on the intermediate transfer belt or on the surface of the transfer material When the toner is moved in the image forming apparatus in a state where the unfixed toner is present, the unfixed toner scatters or directly contacts the light-reflective photosensor 16 (FIG. 2) via the transfer member. Sensors can be soiled.
At this time, if the light path shielding member (shutter) 17 (FIG. 2) of the light reflection type photosensor 16 is not closed due to malfunction, the detection output of the light reflection type photosensor 16 is also affected. It will be affected.

FIG. 9 is a flowchart for explaining the operation in the abnormal occurrence of paper jam. FIG. 10 is a flowchart for explaining a state determination operation for determining whether or not the light reflection type photosensor shutter opening / closing operation is normal in the case of a paper jam.
In FIG. 9, after the operation is started, it is determined whether or not a paper jam has occurred (S35).
If a paper jam has occurred, the paper jam flag is set to "1" (S36). Next, the paper jam is displayed on the display unit of the operation unit (not shown) (S37).
In FIG. 10, after the image forming apparatus is turned on, it is determined whether the paper jam flag is 1 (paper jam flag = 1) (S40). If the paper jam flag is 1, the recovery operation is executed (S41). Subsequently, the quality determination of the opening / closing operation | movement of the optical path shielding member (shutter) 17 (FIG. 2) of the light reflection type photosensor 16 is executed (S42).
Accordingly, when an abnormal operation such as a paper jam occurs as described above, immediately after the recovery from the abnormal operation, “whether the opening / closing operation of the light path shielding member (shutter) 17 of the light reflection type photosensor 16 is normal or not is normal. Execute state determination "operation.
Since the quality determination of the opening / closing operation of the optical path shielding member 17 is performed immediately after the paper jam is detected, the toner of the unfixed image portion adhering to the jammed transfer paper is scattered or brought into contact with the optical sensor 16, thereby When there is a possibility of affecting the output, it is possible to prevent deterioration of controllability by the optical sensor 16 by confirming the presence or absence of the above-mentioned effect at an early stage and warning as necessary.

1 is a schematic configuration diagram showing an overall layout around an image forming station of an image forming apparatus according to the present invention. It is a schematic perspective view which shows the positional relationship of an intermediate transfer belt and an optical sensor. FIG. 2 is a block diagram partially showing a control unit of the image forming apparatus according to the present invention. It is a figure which shows the relationship between the output of an optical sensor, and the opening / closing of an optical path shielding member with a graph. It is a figure which shows the relationship between an optical sensor output voltage and Ifsg with a graph. It is a flowchart of the operation | movement which issues a warning so that the cleaning of an optical sensor detection surface and improvement of the opening / closing operation | movement defect of an optical path shielding member may be promoted. It is a flowchart of the determination operation | movement of the state determination whether the opening / closing operation | movement of the optical path shielding member of a light reflection type photosensor shutter is normal. FIG. 10 is a flowchart for explaining an operation of “determination of whether or not the light reflection type photosensor shutter opening / closing operation is normal” when detecting development γ ≧ development γ target value × 1.2. 6 is a flowchart for explaining an operation in an abnormal occurrence of a paper jam. 6 is a flowchart illustrating a state determination operation for determining whether or not the light reflection type photosensor shutter opening / closing operation is normal in the case of a paper jam.

Explanation of symbols

A image forming apparatus, 2 (Y, C, M, K) image carrier (photosensitive member), 7 intermediate transfer member (intermediate transfer belt), 16 optical sensor (light reflection type photosensor), 16a frame, 17 optical path Shielding member (shutter), 18 opening / closing operation means, S22 image area determination means, S23 operation quality execution means, S26 image area determination means, S31 operation quality execution means, S40 paper jam determination means, S42 operation quality execution means, Ifsg light emitting element Value of current flowing through, Voffset offset voltage, Vsg (ave) average value of fluctuation range of detection value of optical sensor, Vsg (min) minimum value

Claims (6)

  An optical path shielding member that can be opened and closed to block the light receiving optical path of the optical sensor disposed above the intermediate transfer member and block the light receiving optical path at an arbitrary timing, and the optical path shielding member is moved between an open position and a closed position. An optical path shielding member opening / closing operation means for detecting the output of the optical sensor in a state where the optical path shielding member is closed and the light receiving optical path is blocked, and the optical path shielding member is detected according to a detection result. In an image forming apparatus that performs printing by recording a toner image formed on an image carrier that determines whether or not the opening / closing operation of the optical member is normal, the execution timing of the quality determination of the opening / closing operation of the optical path shielding member is variable An image forming apparatus.   The image forming apparatus according to claim 1, wherein the execution timing of the open / close operation quality determination of the optical path shielding member is changed according to the formed image area.   3. The image forming apparatus according to claim 2, wherein when the image area integrated value of the formed image area is equal to or greater than a predetermined value, the open / close operation of the optical path shielding member is determined to be good or bad.   The image forming apparatus according to claim 1, wherein execution timing of the opening / closing operation quality determination of the optical path shielding member is changed according to a change amount of developing ability.   The image forming apparatus according to claim 4, wherein whether or not the optical path shielding member is open / closed is determined when the change amount of the developing ability becomes a predetermined value or more.   The image forming apparatus according to claim 1, wherein the quality determination of the opening / closing operation of the optical path shielding member is performed immediately after a paper jam is detected.

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