JP2010091797A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of stably adjusting image density in a short time while suppressing an increase in size and price of the apparatus.
When the light emission amount adjustment value L of the image density detection means in the calibration is set to a predetermined range, the light emission amount adjustment value L is ½ of the normal calibration before the next calibration. A pre-calibration operation is performed to determine whether or not the output average value Vsg (0) of the image density detection means is a predetermined value during the following detection time, and the output average value Vsg (0) of the image density detection means. In the image forming apparatus that does not execute the calibration operation, sampling is performed to calculate the output average value Vsg (0) of the image density detection means in the pre-calibration operation. The calibration operation is executed when variations in the output values detected by the plurality of image carrier non-image parts are equal to or greater than a predetermined value. Wherein the image forming apparatus.
[Selection] Figure 3

Description

  The present invention relates to an image forming apparatus capable of calibrating an optical density sensor which is an image density control means of a copying machine, a printer, a facsimile machine or the like.

Conventionally, a forming apparatus forms a pattern by depositing toner on a toner image carrier such as a photoconductor, and detects the amount of adhesion with an optical sensor to form an image such as a development target and a control target value of toner density. We are trying to optimize the conditions. In order to detect the toner adhesion amount of the pattern whose density is controlled by the optical sensor in this way, first, calibration is performed so that the output of the optical sensor becomes a predetermined value in a region where the toner image does not exist on the toner image carrier. .
The output value of the optical sensor set at this time is Vsg, and the optical sensor output when the toner pattern image is detected is Vsp. Then, it is determined whether or not the toner adhesion amount is appropriate based on the output ratio of Vsp and Vsg. In the image forming apparatus using the intermediate transfer belt as a toner image carrier, this optical sensor calibration requires an operation time of nearly 10 seconds to obtain an average value for one rotation of the intermediate transfer belt.
Further, the detection is not performed for one rotation of the intermediate transfer belt, so that the intermediate transfer belt is not affected by the deflection of the intermediate transfer belt. It is necessary to install a sensor. In this case, in order to cancel the influence of the drive of the intermediate transfer belt or the eccentricity of the driven roller, at least an optical value with an average value equal to or more than one rotation of the drive or driven roller of the intermediate transfer belt as one light amount adjustment value As the detection output of the sensor, the light amount adjustment value of the optical sensor is adjusted until the optical sensor output becomes a predetermined value, and this adjustment is repeated until the detection value of the optical sensor becomes the optimum value.

To prevent adhesion of toner and other dust scattered on the detection surface of the optical sensor, the shutter should be closed except when a shutter is installed on the optical sensor for detection, or air is blown on the detection surface of the optical sensor. In order to prevent the detection surface from being soiled or to provide a cleaning member on the optical sensor to periodically clean the detection surface of the optical sensor, a means for removing disturbance from the optical sensor for detection has been made.
However, the toner has fallen from the unit arranged above the optical sensor on the optical sensor detection surface, and conventionally, the optical sensor is periodically calibrated.
In recent years, the performance of image forming apparatuses has been further improved, and there has been a demand for shortening the printing operation time, and the demand for maintaining stable image quality is increasing. Various sensors including the optical sensor are used in order to maintain stable image quality, and improvement in detection accuracy of various sensors is indispensable.
On the other hand, image quality adjustment operations to maintain stable image quality include disturbances such as installation conditions of the image forming apparatus, deterioration of supply such as developer over time, usage conditions by the operator of the image forming apparatus such as the number of printed sheets and image area ratio. It is necessary to optimize the image forming conditions. Many of these cannot be executed in parallel during the printing operation, resulting in factors such as increasing the waiting time for the operator of the image forming apparatus and deteriorating the productivity of the printing job.

The above-described calibration operation by the optical sensor is one of them, and it is necessary to reduce the execution frequency of the operation as much as possible.
Accordingly, a pre-calibration operation has been devised in which the optical sensor output value is confirmed in a short time before the calibration operation of the optical sensor and the necessity of the calibration operation is determined in a short time (for example, Patent Documents 1 to 3). 2).
As a result, when it is determined that the calibration of the optical sensor is unnecessary, it is possible to shorten the time of the image quality adjustment operation without performing unnecessary calibration operation.
JP 2002-296852 A JP 2007-72282 A

Pre-calibration used in an optical sensor for image density control mounted on a conventional image forming apparatus is performed to shorten the time of image quality adjustment operation. Although this shortens the detection time, it has been found that partial deterioration such as scratches and wear on the surface of the image carrier cannot be detected, and it may be difficult to detect defects during the calibration operation. .
The present invention has been made in view of such a problem, and when it is determined that the variation in detection values is large as a result of executing the pre-calibration operation, the detection by the optical sensor by the pre-calibration operation is appropriate. In other words, the calibration operation is executed, and depending on the situation, the operation of stopping the control of the image density and the operation of warning the abnormality are automatically performed. Accordingly, an object of the present invention is to provide an image forming apparatus capable of stably adjusting image density in a short time while suppressing an increase in size and price of the apparatus.

  In order to solve the above-mentioned problems, an invention according to claim 1 is directed to an image carrier, an image density detector for detecting an image density of a toner image formed on the image carrier, and the image carrier. Calibration is performed so that the output value of the image density detection unit for the upper non-image portion becomes a predetermined value, and based on the output value of the image density detection unit for the reference image formed on the image carrier. Control means for controlling toner replenishment from the toner replenishing means to the developing device, and when the light emission amount adjustment value of the image density detecting means in the calibration is set within a predetermined range, the next calibration A pre-judgment to determine whether the output average value of the image density detection means is a predetermined value or not in the detection time of 1/2 or less of the normal calibration before the light emission quantity adjustment value. In the image forming apparatus in which the calibration operation is not executed when the reblation operation is performed and the output average value of the image density detection means is a predetermined value, the image density detection is performed by the pre-calibration operation. The calibration operation is executed when the variation of the plurality of image carrier non-image portion detection output values sampled to calculate the output average value of the means becomes a predetermined value or more.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the difference between the nth output average value sequentially sampled and the previous output average value in the plurality of sampled sampling data. Of the image carrier non-image portion detection output value, the predetermined value is a first predetermined value, and the absolute value is greater than or equal to the first predetermined value. In this case, the variation of the output average value is determined to be large.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, a difference value between a maximum value and a minimum value in the plurality of sampled sampling data is calculated as the image carrier non-image portion detection output value. Variation of the output average value is determined to be large when the predetermined value is a second predetermined value and the second determination criterion is that the difference value is greater than or equal to the second predetermined value. It is characterized by.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, a third determination criterion in which it is determined that the variation in the output average value is accumulated more than a predetermined number of times. To issue a warning.
According to a fifth aspect of the present invention, in the image forming apparatus according to any of the second to fourth aspects, the predetermined value relating to the first to third determination criteria can be arbitrarily set.

  According to the present invention, when it is determined that the variation in the detected value is large as a result of executing the pre-calibration operation, it is determined that the optical sensor detection by the pre-calibration operation is not appropriate, and the calibration operation is executed. At the same time, depending on the situation, image density control is automatically stopped and warnings such as warnings are automatically issued, so that image density adjustment can be stabilized in a short time while suppressing the increase in size and price of the device. Can be done.

Hereinafter, an image forming apparatus according to the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a peripheral layout related to image formation of the image forming apparatus according to the present invention.
The image forming apparatus of the present invention is configured such that an intermediate transfer belt 7 is disposed long in the horizontal direction so that an image from monocolor to full color can be appropriately formed.
In the present embodiment, a photoreceptor 2 (2Y, 2C, 2M, 2K) as an image carrier, a charging roller 3 (3Y, 3C, 3M, 3K) as a charging unit, and a laser exposure apparatus as an image writing unit. (Not shown), a developing unit 4 (4Y, 4C, 4M, 4K) as developing means, and a unit (image) having at least cleaning 6 (6Y, 6C, 6M, 6K) for removing transfer residual toner on the surface of the photoreceptor. Forming units) are provided for each color (units for each color of four sets (Y, M, C, K) in this embodiment). As shown in FIG. 1, the image forming units of these yellow (Y), magenta (M), cyan (C), and black (K) colors are disposed below the intermediate transfer belt 7 that is an intermediate transfer member. Arranged in order of Y, C, M, K from the left. These four color image forming units have the same configuration in the four sets Y to K.
Each of the charging rollers 3 uniformly charges the photosensitive member (negatively charged in this embodiment) by charging with the same polarity as the toner held at a predetermined potential, and applies the uniform potential to the photosensitive member.

A laser exposure device (not shown) is arranged on the downstream side in the rotation direction of the photoreceptors 2Y, 2C, 2M, and 2K with respect to the charging roller and on the upstream side of the developing devices 4Y, 4C, 4M, and 4K. This laser exposure apparatus is arranged in the main scanning direction in parallel with the rotation axis of the photoconductor in each image forming unit (scanning light from each laser exposure apparatus is indicated by an arrow in FIG. 1).
The laser exposure apparatus, for example, on the photoconductors 2Y, 2C, 2M, and 2K to which a uniform potential is applied according to data recorded on a memory for each color image data read by an image reading apparatus. To form an electrostatic latent image for each color.
The photoreceptors 2Y, 2C, 2M, and 2K are, for example, on the undercoat layer formed on the conductive cylindrical support, in the order of the charge generation layer (lower layer) and the charge transport layer (upper layer), or vice versa. A photosensitive layer is laminated in this order, and a known surface protective layer (for example, an overcoat layer mainly composed of a thermoplastic or thermosetting polymer) is formed on the surface of the charge transport layer or the charge generation layer. . In the present embodiment, the support for the photosensitive member is grounded.

The developing device 4 has a cylindrical developing sleeve 41 (41Y, 41C, 41M, 41K) that maintains a predetermined gap with respect to the photoreceptor 2 and rotates in the forward direction and the rotational direction of the photoreceptor 2. The sleeve 41 contains a one-component developer or a two-component developer of yellow (Y), magenta (M), cyan (C), and black (K) according to the development color for each color. (For example, it contains a two-component developer that is negatively charged). The developing sleeve 41 is made of nonmagnetic stainless steel or aluminum.
The developing sleeve 41 of the developing device 4 is kept in non-contact with the photosensitive member 2 through a predetermined gap (for example, a gap of 100 to 500 μm) with a drum surface of the photosensitive member 2 by an abutting roller (not shown). A voltage obtained by superimposing a DC voltage and an AC voltage is applied to the developing sleeve 41, and the electrostatic latent image is developed on the drum of the photosensitive member 2 by the developing device 4 to form a toner image.
The intermediate transfer member (intermediate transfer belt) 7 circumscribes an intermediate transfer belt drive roller (also serving as a secondary transfer backup roller) 8, intermediate transfer belt tension rollers 10a and 10b, an intermediate transfer belt support roller 9 and a reverse bending roller. The intermediate transfer body (intermediate transfer belt) 8 is stretched so that the rotation direction thereof is counterclockwise.

Further, a secondary transfer roller is provided via an intermediate transfer member (intermediate transfer belt) 7 so as to face the secondary transfer backup roller (also serves as a secondary transfer backup roller) 8.
The cleaning blade 12a is provided in contact with the intermediate transfer member (intermediate transfer belt) 7 at the position of the support roller, and the cleaning blade B is provided in contact with the photosensitive member 2 as an image carrier in the counter direction. Similarly, primary transfer rollers 5Y, 5C, 5M, and 5K for each color are provided to face the photoreceptors 2Y, 2C, 2M, and 2K with an intermediate transfer body (intermediate transfer belt) 7 interposed therebetween. .
The intermediate transfer member (intermediate transfer belt) 7 is an endless belt having a volume resistance of 10 ⁶ to 10 ¹² Ω · cm. For example, this endless belt is made of a resin material such as polycarbonate (PC), polyimide (PI), polyamideimide (PAI), polyvinylidene fluoride (PVDF), tetrafluoroethylene-ethylene copolymer (ETFE), EPDM, NBR, Examples thereof include those obtained by dispersing conductive fillers such as carbon in rubber materials such as CR and polyurethane, and those containing ionic conductive materials. The thickness of the endless belt is preferably about 50 to 200 μm in the case of a resin material, and is preferably set to about 300 to 700 μm in the case of a rubber material. A rubber layer may be provided on the resin belt, or a coating layer may be provided on the surface layer.

The intermediate transfer member (intermediate transfer belt) 7 is driven by rotation of a driving roller (also serving as a secondary transfer backup roller) 8 by a driving motor (not shown).
The drive roller (also known as secondary transfer backup roller) 8 is made of, for example, a conductive core metal (not indicated) such as stainless steel, a rubber or resin material such as polyurethane, EPDM, or silicone, and a conductive filler such as carbon. A coating of dispersed conductive or semiconductive (no symbol) is used.
The primary transfer roller 5 (5Y, 5C, 5M, 5K) is provided to face the photosensitive member 2 (2Y, 2C, 2M, 2K) with an intermediate transfer member (intermediate transfer belt) 7 interposed therebetween. A transfer area is formed between the (intermediate transfer belt) 7 and the photoreceptor 2 (2Y, 2C, 2M, 2K). To each primary transfer roller 5, a DC voltage having a polarity opposite to that of the toner (in this embodiment, a positive polarity) is applied, and a transfer electric field is formed in the transfer area, thereby forming a toner image of each color formed on the photoreceptor 2. Is transferred onto an intermediate transfer member (intermediate transfer belt) 7.
The primary transfer roller 5 (5Y, 5C, 5M, 5K), which is the first transfer means for each color, is made of polyurethane, EPDM, or the like on a peripheral surface of a conductive metal core (not shown) such as stainless steel having an outer diameter of 8 mm. Solid state or foamed sponge state in which volume resistance is about 10 ⁵ to 10 ⁹ Ω · cm by dispersing conductive filler such as carbon in rubber material such as silicone or containing ionic conductive material Thus, it is formed by coating a semiconductive elastic rubber (not shown) having a thickness of 5 mm and a rubber hardness of Asker-C of about 20 to 70 °.

The secondary transfer roller 13 that performs transfer onto the surface of the transfer material S is provided opposite to the secondary transfer backup roller 8 that is grounded with an intermediate transfer member (intermediate transfer belt) 7 interposed therebetween, and has a polarity opposite to that of toner (this embodiment). In this embodiment, a positive DC voltage is applied by a DC power source. The superimposed toner image carried on the intermediate transfer member (intermediate transfer belt) 7 is transferred to the surface of the transfer material S via the secondary transfer roller 13.
The secondary transfer roller, which is a second transfer means for retransferring the color toner image on the intermediate transfer body (intermediate transfer belt) 7 onto the transfer material S, which is a recording material, is also the same half as the primary transfer roller 5 described above. It is formed by covering a conductive elastic rubber (not shown). Since the secondary transfer roller is in contact with toner unlike the primary transfer roller, the surface may be coated with a material having good releasability such as semiconductive fluorine resin or urethane resin. The secondary transfer backup roller has a conductive core such as stainless steel (not shown) with a conductive filler such as carbon dispersed in a rubber or resin material such as polyurethane, EPDM or silicone, or an ionic It is formed by covering a semiconductive material containing a conductive material with a thickness of about 0.05 to 0.5 mm.

The cleaning blades 12a and 12B that are in contact with the surface of the photosensitive member or the intermediate transfer belt are made by adhering a plate-like urethane rubber having a thickness of 1 to 3 mm and a JIS-A hardness of 60 to 80 ° on a sheet metal holder, and having a free length of 5 to 5. It is intended to be about 12 mm. The cleaning blades 12a and B are in contact with the photoreceptor and the intermediate transfer belt with a load of about 5 to 50 gf. In order to prevent the blade from rolling up, a fluorine coating may be applied to the tip of the blade, or conductive urethane rubber may be used so that the other side is not charged.
Here, the transfer material S such as recording paper is conveyed one by one from the schematically shown stacking device 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. And is subjected to secondary transfer, sent to a fixing unit 15 comprising a fixing roller 15a and a pressure roller 15b, and fixed by heat welding and collected.
In the present embodiment, the charging roller 3 (3Y, 3C, 3M, 3K) is used as the charging means for the photoreceptor 2 (2Y, 2C, 2M, 2K), and the primary transfer roller 5 (5Y) is used as the primary transfer member. 5C, 5M, 5K). This is preferable from the viewpoint of suppressing generation of harmful ozone. The present invention is not limited to this example, and a corotron discharger can be used as a charging means in a non-contact state.

After the toner image on the photoreceptor 2 is transferred (primary transfer) to an intermediate transfer member (intermediate transfer belt) 7, the toner image is transferred from the intermediate transfer member (intermediate transfer belt) 7 to a transfer paper or the like by a transfer roller 13 (secondary transfer). And an image adjustment pattern detection sensor 16 that is opposed to the surface of the intermediate transfer body on the downstream side in the rotational direction of the intermediate transfer body (intermediate transfer belt) 7 from the secondary transfer position.
Then, the process control is performed by a control means such as a CPU so that an appropriate image can be obtained by changing the image formation conditions of the next image according to the detection information, and the toner replenishment amount optimization for toner density control is also performed. ing. This control means inputs information from an optical sensor, etc., optimizes the toner replenishment amount by the toner density replenishment control unit, etc., and executes pre-calibration operations so that the optical path of the optical sensor can be blocked. The calibration operation is executed when the variation of the plurality of image carrier non-image portion detection output values sampled for calculating the output average value Vsg (0) of the image density detection means is equal to or greater than a predetermined value. To be able to.
Further, the control means prevents contact with the secondary transfer roller 13 and releases it (releases it to the dotted line position shown in FIG. 1) so as to efficiently ensure copy productivity while preventing the influence on the image quality. It is controlled so that it can be set.

In the present invention, since the toner adhesion pattern detection of each color of Y, C, M, and K is performed in a short time as much as possible, the light reflection type photosensor (pattern detection sensor) indicated by reference numeral 16 in FIG. In order to avoid contamination such as toner scattering and dropping from the secondary transfer section, a total of 4 of each color is arranged on the downstream side of the secondary transfer roller (downward) in the direction of the intermediate transfer belt drive shaft, and a light-reflective photo Detection is possible using four sensors simultaneously.
However, even in such an arrangement, toner flying may occur during the secondary transfer. Therefore, as shown in FIG. 2, an optical path shielding member (for example, a shutter) 18 is provided between the light reflection type photosensor and the intermediate transfer belt. The shutter 20 can be opened and closed by the solenoid 20 at an arbitrary timing.

As shown in FIG. 3, the shutter 18 calibrates the light-reflective photosensor, that is, calibration (Vsg adjustment (see * 1 described later)) S1 or pre-calibration (Vsg (0) detection (described later *). 2)))), except for S3 and the toner pattern detection timing for density control. This highly suppresses the detection surface of the light reflection type photosensor from adhering scattered toner and foreign matters floating in the apparatus.
Further, the offset voltage (Voffset) of the light reflection type photosensor is detected in the shutter closed state.
A dark brown flocked seal is attached to the surface of the shutter facing the detection surface of the light reflection type photosensor so that the light reflectance is 10% or less. This prevents the detection surface of the light reflecting photosensor from being worn or scratched when the shutter is opened and closed, prevents the scattered toner from entering when the shutter is closed, and the offset voltage of the light reflecting photosensor when the shutter is closed. This has the effect of detecting (Voffset) with high accuracy.

Here, the Vsg adjustment * 1 will be described.
The surface of the intermediate transfer belt 7 on which the toner pattern image is not formed is detected by the light reflection type photosensor 16 (S3), and the light emitting element LED is set so that the output Vsg becomes the adjustment target value 4.0 ± 0.5v. Is adjusted and determined (S4). At this time, the intermediate transfer belt 7 is driven to rotate at a standard speed.
In the adjustment of Ifsg (S8), first, 150 data are acquired for 600 msec when Vsg is set to the median value of the variable range, and the average value is calculated. If the calculated average value is lower than the Vsg adjustment target value, the Ifsg is increased by the two-division method so that Vsg is increased. Conversely, if it is higher than the Vsg adjustment target value, the Ifsg is lowered by the two-division method so that Vsg becomes lower. In this way, Ifsg is adjusted by the two-division method until Vsg reaches the target value (S9). When Vsg reaches the adjustment target value (S10 / Y), the Ifsg at that time is converted into a light-reflective photo The LED current of the sensor is set as Ifsg (0) (S11).
At this time, the following data is also acquired and stored in memory.
Ifsg (0) adjustment value ... LED current value when adjusted to Vsg = 4.0 ± 0.5v Should not be adjusted to Vsg = 4.0 ± 0.5v (S10 / N) The image forming apparatus issues a warning as a result of Vsg adjustment failure (S10 / N → S12), and the subsequent image quality adjustment operation is not executed (S12 → end).

Next, the Vsg (0) detection (S3) will be described below.
Similar to the Vsg adjustment operation, just before the image quality adjustment operation, the light reflection detected on the surface of the intermediate transfer belt that does not form a toner pattern image with the LED current value: Ifsg (0) set by the previous Vsg adjustment operation. The output (Vsg) of the photosensor is detected.
The sampling time of Vsg is 400 msec, the average value of 100 sampling data is calculated as Vsg (0), and the past 10 times are stored in the storage device installed in the main body (S3).
If Vsg (0) = 4.0 ± 0.5v (S4 / Y), the Vsg adjustment operation is not executed and the already set Ifsg (0) is used as the image quality adjustment pattern detection condition. If Vsg (0) ≠ 4.0 ± 0.5v is detected (S4 / N), the light reflection type photosensor calibration (Vsg adjustment * 1) execution flag is set and the Vsg adjustment operation is subsequently executed. Then, the image quality adjustment operation is executed using the newly set Ifsg (0).
Note that Vsg (n) and Vsg (n-1) are sequentially compared during sampling of 100 data, and if the following condition (Equation 1) is not satisfied, it is determined that the Vsg (0) variation is large (S13 / N → S15: see FIG.
| Vsg (n) −Vsg (n−1) | ≦ α ··· Equation 1

Further, the minimum value and the maximum value among the 100 data sampled at the time of detecting Vsg (0) are recorded in the storage device of the main body, and when the following condition (Equation 2) is not satisfied, the light Vsg (0) variation is large. (S14 / N → S15: FIG. 4).
Vsg (0) detection min value ... Vsg (n) detected at the time of Vsg (0) detection: lower limit value Vsg (0) detection max value of n = 1 to 100 ... Vsg detected at the time of Vsg (0) detection (N): Upper limit value n = 1 to 100 Vsg (0) detection max−Vsg (0) detection min ≦ β Equation 2
Ifsg (0) recorded at the time of Vsg adjustment is the light-receiving sensitivity of the light-reflective photosensor 16, the LED brightness of the light-emitting element, the mounting position of the light-reflective photosensor 16, the angle variation, the sensor detection surface, or the intermediate transfer that is the detection target. It varies depending on the contamination of the belt surface. If the image forming apparatus, the intermediate transfer belt, and the light reflection type photosensor are in a new state, Ifsg is usually 10 mA or less.

When the sensor detection surface is fouled, the Vsg output decreases as a whole, so the value of Vsg (0), which is the detection result by the pre-calibration of the reflective photosensor, also decreases. In this case, if the Vsg adjustment target value is not reached, the calibration operation (Vsg adjustment operation) of the reflection type photosensor is executed. Normally, by increasing the value of Ifsg (0), Vsg (0 0) is set as the Vsg adjustment target value.
However, when a scratch or partial fouling occurs on the surface of the intermediate transfer belt, which is a detection target of the reflective photosensor, only the Vsg that detects the portion is extremely increased or decreased, and the reflective photosensor 16 When the value of Vsg (0), which is the detection result of the pre-calibration, is present, the value is high, and when it is low, the value of Vsg (0) varies for each pre-calibration. In such a state, even when the toner pattern image formed on the intermediate transfer belt is detected, the same variation occurs in the toner pattern image detection result (Vsp), and the image density control result is also unstable. (S15).

The Vsg adjustment target value: 4.0 ± 0.5 v includes a tolerance in consideration of sensor characteristic variation, sensor mounting variation, etc., and the value of Vsg (0) of the pre-calibration result of the reflection type photosensor is also If it is the Vsg adjustment target value, OK is determined. However, even if the value of Vsg (0) is within the range of the Vsg adjustment target value, if the value fluctuates every time it is detected, it becomes a factor that makes the image density control unstable. Then, the calibration operation of the reflection type photosensor is executed again to optimize Ifsg (0).
If the Vsg (0) variation is due to temporary contamination of the intermediate transfer belt or the like, the problem is solved by executing the calibration operation of the reflective photosensor 16.
However, the Vsg (0) variation is eliminated if the cause is a permanent cause such as a scratch on the surface of the intermediate transfer belt or a random occurrence such as a malfunction of the reflective photosensor shutter. In addition, the image density controllability becomes unstable.

As shown in FIG. 4, when it is determined that the variation in Vsg (0) is large, that is, when the above (Expression 1) or (Expression 2) is not satisfied (N in S13 or S14), dedicated for each case Are added (S15), and when the total counter reaches a predetermined number of times: γ (in this embodiment, 5 times) or more (S16 / Y), a warning is displayed (S17). ) Inform the operator that a defect has occurred around the reflective photosensor.
The warning display indicates the necessity of maintenance with characters on the main body operation screen, but this warning may be a sound or sound, or blinking of light such as an LED, or these may be used in combination.
In addition, even if the above problems occur, if a change in image density does not appear noticeably for a while due to a substitute means other than the reflection type photosensor, a warning line is not displayed immediately, but a means using a telephone line or Internet line. Therefore, the maintenance contract base may be notified as service maintenance information.
In S16, if the integration counter is less than the predetermined number of times: γ (5 in the present embodiment) (S16 / N), the process proceeds to B in FIG. 3 (S16 / N → B in FIG. 3). What).
Since each of the determination reference values α, β, and γ can be arbitrarily set from an operation unit of the image forming apparatus main body (not shown), it can be set to be optimized according to a user request.
In the present embodiment, the initial setting values of α, β, and γ are 0.5 v, 0.5 v, and 5 times, respectively (FIG. 4).

In the present invention, as described above, the contact type secondary transfer roller is used as the secondary transfer unit, so that the generation of ozone can be suppressed as compared with the case where the discharge type corotron is used, and the transfer material is also transportable. preferable.
The toner adhesion pattern formed on the photoreceptor 2 outside the normal image forming region is transferred onto the intermediate transfer belt and reflected by the light reflection type photosensor 16 disposed downstream of the secondary transfer roller, that is, toner. Detect the amount of adhesion. At this time, the secondary transfer roller needs to be separated from the intermediate transfer belt 7 so as not to disturb the toner adhesion pattern on the intermediate transfer belt.
Further, there may be a problem that the vibration when the secondary transfer roller is brought into contact with or separated from the intermediate transfer member (transfer belt) 7 adversely affects the image.
For this reason, the timing when the secondary transfer roller is brought into contact with and separated from the intermediate transfer belt 7 is selected so as not to affect the image disturbance. That is, the secondary transfer roller is separated from the intermediate transfer belt before the writing operation of the first image forming unit (yellow (Y) in this embodiment) that starts the operation first during the image forming operation is started. Image forming operations such as writing exposure, development, and primary transfer can be reliably executed without being affected by vibrations when the next transfer roller is separated (in the case of single pattern formation).

On the other hand, when a plurality of patterns having different toner adhesion amounts are formed and detected by the sensor during potential control, the time required to form and detect all the patterns becomes long.
Therefore, even if the top of the plurality of patterns reaches the secondary transfer roller portion even when the plurality of patterns cannot be completely transferred to the primary transfer, the secondary transfer roller separation timing is set to the time when the single pattern is formed. Do at different times.
In the embodiment, after the yellow (Y) image forming operation is started, the secondary transfer roller is separated before the head of the plurality of patterns reaches the secondary transfer roller.
At this time, vibration when the secondary transfer roller is separated may be transmitted to the plurality of image forming units, and the image adjustment pattern may be disturbed.
In order that this vibration does not affect the image adjustment result, the value detected by the optical sensor for the pattern transferred or exposed at the secondary transfer roller separation timing is excluded from the input information of the image adjustment. ing.

If the input information is not adopted from the beginning, in order not to form a visible image pattern of the secondary transfer roller separation timing in order to reduce the toner consumption and the burden on the intermediate transfer belt cleaning, A plurality of write patterns are arranged so as not to perform pattern exposure.
As described above, for the secondary transfer roller that is in contact with the intermediate transfer belt during print output, when performing the image adjustment operation immediately after the print output operation, the next print output operation is avoided and the image adjustment operation is made as short as possible. By providing a detection sensor using a wide area after the secondary transfer position, the space from the final primary transfer part to the secondary transfer part of the image device is reduced, and from the primary transfer position. The distance to the secondary transfer position was reduced so that the first printout time was shortened.
The same toner adhesion amount pattern is formed on the intermediate transfer belt so as to be aligned in the scanning direction for both single color and multiple image adjustment patterns, and image density is detected to form an image. It is reflected in. 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.
[Toner supply control]
This is an operation for calculating the toner replenishment time from the toner density sensor output, the toner density control reference value and the pixel detection data, and controlling to drive the toner replenishment motor.
[Potential control]
This 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 reflection photosensor. In this operation, 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.
When transferring a toner image from an intermediate transfer belt to a transfer material such as transfer paper at the time of secondary transfer, toner that slightly scatters or transfer remaining on the surface of the intermediate transfer belt 7 without being transferred to the transfer member at the time of secondary transfer The light-reflective photosensor is easily damaged due to scattering of residual toner.

This toner scattering tends to increase as the image area increases and as the amount of toner adhesion per unit area increases.
Therefore, in the state where the toner scattering amount increases, the above-described “determination of whether or not the light reflection type photosensor shutter opening / closing operation is normal” is executed, so that unnecessary waiting time is not generated. The shutter abnormality can be detected effectively.
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-reflective photosensor shutter is normal” is executed. .
Thereafter, the determination operation is executed every 10,000 cm ² .
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 it is detected that development γ ≧ development γ target value × 1.2, the above-described “state determination as to whether the opening / closing operation of the light reflection type photosensor shutter is normal” is executed (development). γ target value = 0.9 mg / cm ² · kV).

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 If the unfixed toner is scattered or directly contacts the light-reflective photosensor via a transfer member, the photosensor may be contaminated. is there. At that time, if the light-reflective photosensor shutter is not closed due to malfunction, the detection output of the light-reflective photosensor is also affected.
Therefore, when an abnormal operation such as a paper jam occurs as described above, immediately after returning from the abnormal operation, the “determination of whether or not the light reflection type photosensor shutter opening / closing operation is normal” operation is executed. To do.

1 is a schematic configuration diagram showing a layout around image formation of an image forming apparatus according to the present invention. FIG. 4 is a schematic perspective view showing a positional relationship between an intermediate transfer belt and an optical sensor. It is a flowchart of the operation | movement which issues a warning so that improvement of the cleaning of an optical sensor detection surface and the opening / closing operation | movement defect of an optical path shielding member may be promoted. 4 is a flowchart showing a flow for determining the magnitude of Vsg (0) variation in the flowchart shown in FIG. 3.

Explanation of symbols

  A Image forming apparatus, 2 (Y, C, M, K) Image carrier (photosensitive member), 7 Intermediate transfer body (intermediate transfer belt), 16 Optical sensor (reflection type photo sensor, pattern detection sensor), 16a Frame body , 17 optical path shielding member (shutter), 18 opening / closing operation means, 20 solenoid of opening / closing operation means, 20a solenoid core of opening / closing operation means, 22 connecting rod of opening / closing operation means, 23 spring of opening / closing operation means, Isfg Current value, Voffset offset voltage, Vsg (ave) Average value of fluctuation range of detection value of optical sensor, Vsg (min) minimum value

Claims (5)

An image carrier, an image density detector for detecting an image density of a toner image formed on the image carrier, and an output value of the image density detector for a non-image portion on the image carrier is a predetermined value. Control means for controlling the toner supply from the toner replenishing means to the developing device based on the output value of the image density detecting means for the reference image formed on the image carrier and performing calibration so that And the light emission amount adjustment value of the image density detection means in the calibration is set to a predetermined range, the light emission amount adjustment value is ½ or less of the normal calibration before the next calibration. A pre-calibration operation is performed to determine whether the output average value of the image density detection means is a predetermined value during the detection time, and the output of the image density detection means is performed. If the average value has been a predetermined value, the image forming apparatus for the non-execution of the calibration operation,
The calibration is performed when variations in a plurality of the image carrier non-image portion detection output values sampled for calculating the output average value of the image density detection means in the pre-calibration operation become a predetermined value or more. An image forming apparatus that performs an operation.   2. The image forming apparatus according to claim 1, wherein an absolute value of a difference between an n-th output average value sequentially sampled and a previous output average value in the plurality of sampled sampling data is detected as the image carrier non-image portion detection. When the predetermined value is the first predetermined value and the first determination criterion is that the absolute value is greater than or equal to the first predetermined value, the output average value is determined to be large. An image forming apparatus.   2. The image forming apparatus according to claim 1, wherein a difference value between a maximum value and a minimum value in the plurality of sampled sampling data is set as a variation in the image carrier non-image portion detection output value, and the predetermined value is a second predetermined value. In the case where the difference value is a second determination criterion that is equal to or greater than the second predetermined value, the variation in the output average value is determined to be large.   4. The image forming apparatus according to claim 1, wherein a warning is issued according to a third determination criterion that is determined that the variation in the output average value is accumulated more than a predetermined number of times. Forming equipment.   5. The image forming apparatus according to claim 2, wherein a predetermined value relating to the first to third determination criteria can be arbitrarily set. 6.

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