JP2012037546A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To specify the home position of an intermediate transfer belt by forming a cured thin film layer on the surface of the intermediate transfer belt and accurately detecting a film thickness change part formed on a part of the cured thin film layer, as a reference mark.SOLUTION: On the transfer surface of the intermediate transfer belt, the cured thin film layer comprising an inorganic oxide is formed and the film thickness change part whose thickness is different from that in other places is provided in a part of the cured thin film layer in the peripheral direction, to detect the home position based on the detection result of the surface of the intermediate transfer belt by a plurality of optical sensors arranged in positions different from each other in the width direction of the intermediate transfer belt.

Description

  The present invention relates to an image forming apparatus including an intermediate transfer rotator such as an intermediate transfer belt, and more particularly to a technique for detecting a home position of the intermediate transfer rotator.

  In an electrophotographic image forming apparatus, the surface of a photoreceptor is uniformly charged by a charger, and then the charged photoreceptor surface is scanned with a laser beam to form an electrostatic latent image. The image is visualized by supplying toner from the developing device. The toner image thus obtained is primarily transferred to an intermediate transfer rotating body such as an intermediate transfer belt, and then secondarily transferred onto a recording sheet to form an image.

In such an image forming apparatus, image stabilization processing such as automatic density control and color misregistration correction has been conventionally performed at a predetermined timing in order to maintain a good quality of a reproduced image.
For example, in the case of automatic density control, a toner pattern is formed on the intermediate transfer belt at a predetermined timing after the home position of the intermediate transfer belt is detected, and the density of the toner pattern is detected by a photoelectric sensor. When the obtained density is different from the original density, the image forming conditions such as the developing bias are controlled so that the reproduced image has an appropriate image density.

As a method for detecting the home position of such an intermediate transfer belt, usually, a reference mark is attached to a predetermined position of the intermediate transfer belt, and the reference mark is detected by a photoelectric sensor. The home position was specified.
However, the reference mark is formed by applying paint outside the image area on the surface of the intermediate transfer belt or pasting a highly reflective seal, and the width of the intermediate transfer belt is increased accordingly. This could hinder space saving. Further, since the reference mark itself cannot be cleaned by the cleaning blade, it may not be detected due to contamination by toner fumes.

On the other hand, a technique for improving the transfer rate by curing the surface of the intermediate transfer belt by forming a cured thin film layer made of an inorganic oxide such as SiO _{2 on} the surface of the intermediate transfer belt has been advanced.
FIG. 15 is a graph showing experimental results showing the relationship between the thickness of the cured thin film layer formed on the intermediate transfer belt and the transfer rate. In the graph, the horizontal axis indicates the film thickness of the cured thin film layer, and the vertical axis indicates the transfer rate of the toner image when transferred from the photosensitive drum to the intermediate transfer belt as a percentage.

As can be seen from the experimental results, the transfer rate is improved by about 7 to 8% when the cured thin film layer is present rather than when the cured thin film layer is not present, and a transfer rate close to 100% can be obtained. . In addition, even if the thickness of the cured thin film layer is changed from about 100 [nm] to 500 [nm], the transfer rate is almost constant at a high transfer rate of almost 100%.
The inventors of the present application pay attention to this point, and form a film thickness changing portion in which a part of the cured thin film layer is intentionally changed to a predetermined thickness, and use this as a reference mark for detecting the home position. I devised that.

If the thickness of the film thickness change part and the light emission main wavelength of the light source of the optical sensor are set appropriately, the reflectivity of the film thickness change part can be different from other parts by the principle of optical interference in the thin film, As a result, the position of the film thickness changing portion can be detected by the optical sensor.
According to this configuration, it is possible to dramatically increase the durability of the reference mark compared to a paint or a seal. Further, since the transfer rate at the film thickness changing portion is not different from that at other portions, the toner image can be transferred to the relevant portion, and it is necessary to provide a space for the reference mark in the width direction of the intermediate transfer belt. There is also an advantage that space saving can be achieved.

JP 2009-42473 A

However, the cured thin film layer made of an inorganic oxide is translucent, and if there is a scratch on the surface of the intermediate transfer belt substrate, the thickness of the thin film layer at this portion also changes, or the color of the scratch itself May be different from the color of other base materials, and scratches due to durability, roughening, filming, etc. may occur on the surface of the cured thin film layer, and these may be erroneously detected as reference marks.
The present invention has been made in view of the above circumstances, and changes the thickness of the thin film layer as a reference mark even if the intermediate transfer rotator on which the inorganic oxide thin film layer is formed has scratches or the like. An object of the present invention is to provide an image forming apparatus that can detect an appropriate film thickness change portion and perform an accurate home position detection operation.

  In order to achieve the above object, an image forming apparatus according to the present invention primarily transfers a toner image formed on an image carrier to a rotating intermediate transfer rotator, and then secondarily transfers the image onto a recording sheet. An image forming apparatus for forming, comprising home position detecting means for detecting a home position of the rotating intermediate transfer rotator, wherein at least one inorganic oxide thin film layer is formed on a transfer surface of the intermediate transfer rotator. And at one or a plurality of locations thereof, a film thickness changing portion having a thickness different from that of the other portions of the inorganic oxide thin film layer is provided. A plurality of optical sensors arranged at different positions in the width direction are provided, and the home position is detected based on the detection result of the surface of the intermediate transfer rotating body by the plurality of optical sensors. It is characterized in.

  According to the above configuration, since the home position detection means includes the plurality of optical sensors arranged at different positions in the width direction of the intermediate transfer rotator, the reference position is detected on the detection surface of the intermediate transfer rotator by the optical sensor. Even if there is a flaw that may be mistakenly detected as a mark, it is considered that the probability that it exists in the same positional relationship as the film thickness changing portion provided in one or a plurality of locations of the intermediate transfer rotator is extremely low. Therefore, the home position detection accuracy can be increased based on the detection values of the plurality of optical sensors.

Here, the film thickness changing portion is formed so as to extend in a band shape in the width direction of the intermediate transfer rotating body, and the plurality of detecting means are spaced apart along the width direction of the intermediate transfer body. And may be arranged in a row.
Further, each of the plurality of optical sensors is configured to detect, with a light receiving element, return light from the surface of the intermediate transfer rotating body of light emitted from the light emitting element, and the light emitting elements of all the plurality of optical sensors Irradiation of each light emitting element is such that the reflectance of the film thickness changing portion of the irradiation light is higher or lower than the reflectance of other non-film thickness changing portions due to light interference by the inorganic oxide thin film layer. Desirably, the dominant wavelength of the light is determined.

  In addition, each of the plurality of optical sensors is configured to detect, with a light receiving element, return light from the surface of the intermediate transfer rotating body of light emitted from the light emitting element, and among the plurality of optical sensors, The main wavelength of the light emitted from the light emitting element of the optical sensor and the light emitting element of the second optical sensor is different from that of the non-thickness changing portion in the thickness changing portion due to the interference of light by the inorganic oxide thin film layer. It is good also as having decided so that it may become a wavelength which becomes higher and a wavelength which becomes lower.

Further, here, the thickness of the film thickness changing portion and the non-film thickness changing portion of the inorganic oxide layer is determined by the main wavelength of the irradiation light of at least one of the plurality of optical sensors, and the surface of the cured thin film layer. It is desirable that the difference in reflectance between the film thickness changing portion and the non-film thickness changing portion is set to be the maximum in relation to the incident angle and the refractive index of the inorganic oxide layer.
The image forming apparatus further includes an image stabilization unit that forms a toner pattern on the surface of the intermediate transfer member, detects the toner pattern with one or a plurality of toner pattern detection optical sensors, and executes image stabilization processing. The optical sensor for detection may also serve as part or all of the optical sensor for home position detection.

1 is a schematic diagram illustrating an overall configuration of a printer according to an embodiment of the present invention. It is a block diagram which shows the structure of the control part of the said printer. (A) is a figure which shows the external appearance of the intermediate transfer belt before incorporating in an apparatus, (b) is an expanded sectional view of the part containing the film thickness change part. (A) is a figure for demonstrating the interference of the light in the surface part of an intermediate transfer belt, (b) is a hardening thin film layer when the main wavelength of the light emitting element of the photoelectric sensor 23 is 730 [nm]. It is a figure which shows the change of thickness and reflectance. It is a figure for demonstrating the method to determine the thickness of a cured thin film layer, and the thickness of a film thickness change part based on the data of the said FIG.4 (b). It is a figure which shows the change of the detected value by the photoelectric sensor of an intermediate transfer belt surface. FIG. 5 is a diagram illustrating an example of a detection position on an intermediate transfer belt in two photoelectric sensors, a positional relationship between a film thickness changing portion, and a scratch on the intermediate transfer belt. FIG. 8 is a diagram illustrating a change in detection value on the surface of the intermediate transfer belt by two photoelectric sensors in the case of FIG. 7. It is a flowchart which shows the content of the home position detection process. It is a figure which shows the change of the thickness of a thin film, and a reflectance when the main wavelength of the light emitting element of one photoelectric sensor is 530 [nm]. FIG. 11 is a diagram illustrating changes in detection values on the surface of the intermediate transfer belt by two photoelectric sensors in the case of FIG. 10. It is a figure which shows the example in the case of forming a film thickness change part in two places. FIG. 13 is a diagram illustrating changes in detection values of the intermediate transfer belt by two photoelectric sensors in the case of FIG. 12. It is a flowchart which shows the content of the detection process of a home position in the case of FIG. It is a graph which shows the relationship between the thickness of the surface hardening film formed in the surrounding surface of an intermediate transfer belt, and a transfer rate.

Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described by taking as an example a case where it is applied to a tandem type color digital printer (hereinafter simply referred to as “printer”).
(1) Overall Configuration of Printer FIG. 1 is a schematic diagram showing the overall configuration of the printer 1 according to the present embodiment.
The printer 1 forms an image on a recording sheet by a known electrophotographic method, and includes an image process unit 10, an intermediate transfer unit 20, a paper feeding unit 30, a fixing unit 40, and a control unit 45. Color and monochrome printing is selectively executed based on a print job received from an external terminal device (not shown) via a network (for example, LAN).

The image processing unit 10 includes image forming units 10Y to 10K corresponding to development colors of yellow (Y), magenta (M), cyan (C), and black (K).
The image forming unit 10Y includes a photosensitive drum 11, a charger 12, an exposure unit 13, a developing unit 14, a primary transfer roller 15, a cleaner 16, and the like disposed around the photosensitive drum 11.
The charger 12 charges the peripheral surface of the photosensitive drum 11 that rotates in the direction indicated by the arrow A.

The exposure unit 13 exposes and scans the charged photosensitive drum 11 with laser light to form an electrostatic latent image on the photosensitive drum 11.
The developing unit 14 contains a developer containing toner, and develops the electrostatic latent image on the photosensitive drum 11 with the toner, whereby a Y-color toner image is formed on the photosensitive drum 11. .
The developing method of the developing unit 14 may be either a one-component developing method using only toner or a two-component developing method using toner and carrier.

The primary transfer roller 15 transfers the Y color toner image on the photosensitive drum 11 onto the intermediate transfer belt 21 by electrostatic action. The cleaner 16 cleans residual toner remaining on the photosensitive drum 11Y after transfer. The other image forming units 10M to 10K have the same configuration as the image forming unit 10Y, and the reference numerals are omitted in FIG.
The intermediate transfer unit 20 includes an intermediate transfer belt 21 that is stretched around a driving roller 25 and a driven roller 26 and circulates in the direction of the arrow.

The intermediate transfer belt 21 is formed by forming a cured thin film layer 211 on the outer peripheral surface of a resin belt base 210 (see FIGS. 3A and 3B). A film thickness changing portion 21 a in which the thickness of the cured thin film layer 211 is changed to detect the home position is formed in a band shape in the width direction of the intermediate transfer belt 21. Details will be described later.
When color printing (color mode) is executed, a corresponding color toner is formed on the photosensitive drum 11 for each of the image forming units 10Y to 10K, and each of the formed toner images is intermediately transferred. Transferred onto the belt 21. The image forming operations for the respective colors Y to K are executed while shifting the timing from the upstream side to the downstream side so that the toner images of the respective colors are transferred to the same position on the traveling intermediate transfer belt 21. The

The paper feeding unit 30 feeds the sheets S from the paper feeding cassette one by one in accordance with the above image forming timing, and conveys the fed sheets S toward the secondary transfer roller 22 via the conveyance path 31. .
When the sheet S conveyed to the secondary transfer roller 22 passes between the secondary transfer roller 22 and the intermediate transfer belt 21, each color toner image formed on the intermediate transfer belt 21 is transferred to the secondary transfer roller 22. Are secondarily transferred to the sheet S by the electrostatic action.

The sheet S after the toner images of the respective colors are secondarily transferred is conveyed to the fixing unit 40, where the toner on the surface is fused and fixed to the surface of the sheet S by being heated and pressurized in the fixing unit 40. Then, the paper is discharged onto the paper discharge tray 33 by the paper discharge roller 32.
In the above, the operation in the case of executing the color mode has been described. However, in the case of executing monochrome (for example, black) printing (monochrome mode), only the black image forming unit 10K is driven, and the same as described above. With this operation, black image formation (printing) is performed on the recording sheet S through the steps of charging, exposing, developing, transferring, and fixing the black color.

The toner or toner pattern that has not been transferred onto the recording sheet S on the intermediate transfer belt 21 is removed by a cleaning blade 27 disposed at a position facing the driven roller 26 across the intermediate transfer belt 21.
Further, on the downstream side of the image forming unit 10K in the traveling direction of the intermediate transfer belt 21, for example, two photoelectric sensors 23 and 24 made of a reflective photoelectric sensor are arranged in a direction perpendicular to the paper surface (the intermediate transfer belt 21). In the image stabilization process, the density of the toner pattern formed on the intermediate transfer belt 21 or the home position of the intermediate transfer belt 21 is detected.

Each of the photoelectric sensors 23 and 24 is a reflection type composed of a light emitting element and a light receiving element that receives regular reflection light or diffused light from the intermediate transfer belt 21 and outputs a voltage corresponding to the amount of light received. is there. Usually, a light emitting diode (LED) and a photodiode (PD) are used for the light emitting element and the light receiving element, respectively.
In addition, an operation panel 35 is arranged at a position on the front side and the upper side of the apparatus main body, which is easy for the user to operate. The operation panel 35 includes buttons for receiving various instructions from the user, a touch panel type liquid crystal display unit, and the like, and transmits the received instruction content to the control unit 45 or displays information indicating the status of the printer 1 on the liquid crystal display. To display.

The control unit 45 controls each unit based on the print job data received from the external terminal device via the network to execute a smooth print operation.
(2) Configuration of Control Unit 45 FIG. 2 is a block diagram showing the configuration of the control unit 45.
As shown in the figure, the control unit 45 includes a CPU 451, a communication I / F (interface) unit 452, a RAM 453, a ROM 454, an EEPROM 455, and the like.

The communication I / F unit 452 is a LAN card or a LAN board for connecting an external client terminal to a LAN, receives print job data transmitted from the client terminal via the LAN, and sends it to the CPU 451.
The RAM 453 is a volatile memory and serves as a work area when the CPU 451 executes a program.

The ROM 454 stores a program for controlling the operation of each unit in the printer 1 and image data for printing a toner pattern used in the image stabilization process.
The EEPROM 455 is a recordable non-volatile memory, and stores an accumulated value of the number of printed sheets.

The CPU 451 reads out a necessary program from the ROM 454 based on the acquired image data and controls the operations of the image processing unit 10, the transfer unit 20, the document reading unit 30 and the fixing unit 40 in a unified manner while measuring the timing. The forming operation is executed smoothly, and image stabilization processing is executed based on the output of the photoelectric sensor 23.
(3) Configuration of Intermediate Transfer Belt 21 As described above, the intermediate transfer belt 21 is formed by laminating the cured thin film layer 211 on the outer peripheral surface of the belt base 210 (see FIG. 3B).

For example, the belt base material 210 is obtained by dispersing carbon in polyphenylene sulfide (PPS) resin to have a surface resistivity of 1 × 10 ⁷ to 1 × 10 ¹² Ω / □ and a volume resistivity of 1 × 10 ⁶ to 1 × 10. ^The one adjusted to ¹² Ω · cm is used. In addition, resistance adjustment is performed by dispersing conductive fillers such as carbon and ionic conductive materials in polycarbonate (PC) resin, polyimide (PI) resin, urethane resin, fluorine resin, nylon resin, etc. Other materials may be used.

The belt substrate 210 has a seamless belt shape, and is formed of a cylindrical substrate that is injection-molded or centrifugally molded so as to have a desired circumference determined by design, thereby reducing manufacturing costs and yield. The substrate surface smoothing step is omitted for improvement.
The cured thin film layer 211 is made of, for example, an inorganic oxide such as SiO ₂ on the surface of at least the transfer surface side of the intermediate transfer belt 21 by a known plasma CVD method proposed in Japanese Patent Application Laid-Open No. 2007-212921. Laminated to thickness.

The thickness d of the cured thin film layer 211 is preferably 10 [nm] <d <1000 [nm] from the viewpoint of preventing cracks and peeling, and the transfer rate is substantially constant and stable. It is desirable that the range is [nm] <d <500 [nm] (see FIG. 15).
As described above, by laminating the cured thin film layer 211 on the outer peripheral surface of the belt base 210, the hardness of the surface of the intermediate transfer belt 21 is increased, the transfer rate is increased, and a constant thickness is maintained within a predetermined thickness range. An excellent effect that the high transfer rate is stable is obtained.

In addition, the cured thin film layer 211 made of an inorganic oxide is generally translucent, so that it can be used for home position detection by partially changing its thickness using general optical characteristics for the transparent thin film layer. Mark.
FIG. 4A is a diagram for explaining that interference occurs in the reflected light of the light beam incident on the intermediate transfer belt 21 due to the intervention of the cured thin film layer 211.

When the light beam L0 is incident on the thin film layer 211, the first reflected light L1 reflected from the surface of the cured thin film layer 211 is refracted and transmitted through the cured thin film layer 211, and the cured thin film layer 211 and the belt base material. The second reflected light L2 reflected at the interface 210 is generated.
Depending on the optical path difference ΔL between the first reflected light L1 and the second reflected light L2, optical interference occurs between them, and the reflected light having a specific wavelength λ is emphasized or attenuated (ΔL is N times λ ( When N is a natural number), the reflectance is maximum, and when the phase is shifted by a half wavelength (N-1 / 2) times, the reflectance is minimum.

The optical path difference ΔL between the first reflected light L1 and the second reflected light L2 is determined by the thickness d of the cured thin film layer 211, its refractive index n2 / n1 with respect to the air, and the incident angle θ1 of the light beam. If constant, the intensity of the reflected light of the light beam can be changed mainly by changing the thickness d of the cured thin film layer with respect to the light beam having a specific wavelength λ.
The relationship between the reflectance R for incident light of wavelength λ and the thickness d of the thin film layer can be expressed by a reflectance function R (d), and this function is known to exhibit a waveform having periodicity. ing.

The graph of FIG. 4B shows the thickness d [nm] of the thin film layer when a light beam is incident on the cured thin film layer 211 at an incident angle of 20 ° from a light emitting element having an emission main wavelength of 730 [nm]. This shows the relationship with the reflectance R (d). Here, the incident angle of 20 ° is the same value as the incident angle of the detection light emitted from the light emitting element in the photoelectric sensors 23 and 24.
As shown in FIG. 5, the reflectivity R (d) periodically changes as the thickness d of the cured thin film layer 211 increases. As shown in FIG. 5, the desired thickness of the cured thin film layer 211 described above is obtained. Within the range of d (100 [nm] <d <500 [nm]), the reflectance is maximum when the thickness d is 260 [nm], and the reflectance is minimum when the thickness d is 390 [nm].

  Therefore, as shown in FIGS. 3A and 3B, a film thickness change 21a having a thickness of 390 [nm] is formed in a part of the thin film layer 211 formed on the peripheral surface of the belt base 210 in the circumferential direction. At the same time, the thickness of the other part (hereinafter referred to as “non-film thickness changing part”) 21b of the peripheral surface is set to 260 [nm]. The film thickness changing portion 21a is formed to extend in a strip shape parallel to the width direction (main scanning direction) of the intermediate transfer belt 21, and in the present embodiment, the film thickness changing portion 21a in the circumferential direction of the film thickness changing portion 21a. The width is set to 10 [mm].

In this way, changing the thickness of a part of the cured thin film layer 211 can be easily performed in the field of film formation by performing a mask process or the like.
When the surface of the intermediate transfer belt 21 on which the cured thin film layer 211 as described above is formed is detected by a reflective photoelectric sensor including a light emitting element having a light emission dominant wavelength of 730 [nm], a film as shown in FIG. Since the sensor output greatly decreases at the thickness changing portion 21a, this can be used as a mark for detecting the home position.

The inorganic oxide as a component of the cured thin film layer 211 may be Al ₂ O ₃ , ZrO ₂ , TiO ₂ or the like in addition to the above SiO ₂ .
(4) Home Position Detection Operation However, since the base material 210 of the intermediate transfer belt 21 is molded by injection molding or centrifugal molding as described above, the surface is scratched (hereinafter referred to as “molding scratch”) when it is punched. Is inevitable). In this embodiment, in order to reduce the cost, the step of removing the molding scratch on the belt base material (base material surface smoothing step) is omitted, and therefore the probability that the surface of the intermediate transfer belt has scratches remaining. Is expensive. In addition, the surface of the intermediate transfer belt 21 is scratched or roughened due to long-term use, and the home position is highly likely to be erroneously detected due to factors such as filming in which toner adheres to the surface of the intermediate transfer belt 21.

Therefore, in this embodiment, in order to avoid erroneous detection of the home position, the detection positions 23a and 24a of the two photoelectric sensors 23 and 24 are parallel to the width direction (main scanning direction) of the intermediate transfer belt 21. The film thickness changing portion 21a is simultaneously detected by both the photoelectric sensors 23 and 24.
FIG. 7 is a schematic view of the intermediate transfer belt 21 of FIG. 1 as viewed from below. The detection positions on the intermediate transfer belt 21 in the two photoelectric sensors 23 and 24 and the positions of the film thickness changing portion 21a. FIG. 4 is a diagram illustrating an example of a relationship and a scratch 212 on an intermediate transfer belt.

  As shown in the figure, it is assumed that there is a scratch 212 on the detection line of the photoelectric sensor 23 on the intermediate transfer belt 21. In this case, the detection values of the photoelectric sensors 23 and 24 change as shown in FIG. 8, but the photoelectric sensors 23 and 24 change at the same time, and both the detection values become lower than the predetermined threshold value h1. If the rise time is determined to be the home position detection, the scratch 212 is not erroneously detected as the home position.

FIG. 9 is a flowchart showing the contents of the home position detection process executed by the control unit 45 in order to achieve the above detection method, and is executed as a subroutine of a main flowchart (not shown) for controlling the entire apparatus.
First, it is determined whether or not the photoelectric sensors 23 and 24 are detected at the same time (step S1). If they are detected at the same time, it is determined that the home position of the intermediate transfer belt 21 is detected (step S1: YES, S2). If not, return directly.

  Even if scratches or dirt are attached to the intermediate transfer belt 21, the length thereof is not so large as the width of the two photoelectric sensors 23, 24. The edge on the front side is completely parallel to the width direction of the intermediate transfer belt 21 and is hardly detected at the same time. Therefore, the home position can be accurately detected by the above method.

(5) Image stabilization processing
Here, an example of automatic density control executed using the home position detection method will be described.
First, regarding the intermediate transfer belt 21 that is rotationally driven with no toner pattern formed on the intermediate transfer belt 21, when the film thickness changing portion 21a is simultaneously detected by the photoelectric sensors 23 and 24, it is regarded as home position detection. The CPU 451 acquires the detection value of the photoelectric sensor 23 for one round of the intermediate transfer belt 21 with a predetermined sampling clock, and stores it as a bare surface profile data in a predetermined table in the EEPROM 455 in the order of sampling.

  Next, on the detection line of the photoelectric sensor 23 on the intermediate transfer belt 21 (virtual line indicating the locus of the detection position 23a of the photoelectric sensor 23 on the intermediate transfer belt 21) based on predetermined gradation data, FIG. A density detection pattern group 220 is formed as shown in FIG. The density detection pattern group 220 includes a plurality of density detection patterns 221, 222,... Formed based on the gradation data stored in the ROM 454.

The density detection pattern group 220 is detected by a sampling clock started from the home position detection by the photoelectric sensors 23 and 24, and stored in association with the same sampling number as the bare surface profile of the table.
The actual toner density of each density detection pattern is the value of the ground color detection data (bare surface profile data) of the intermediate transfer belt 21 having the same sampling number from the detection data (pattern detection data) of the density detection pattern group 220. Is obtained based on the value obtained by subtracting. By subtracting the bare surface profile data from the pattern detection data at the same rotational position on the intermediate transfer belt 21 in this way, noise components due to molding flaws of the intermediate transfer belt 21 can be canceled together. The density data of the pattern group 220 can be acquired accurately.

  Then, when the density data acquired in this way is compared with the density value that should be originally (the density value indicated by the tone data of each density detection pattern stored in the ROM 454) and they are different. In addition, the conditions of the image process such as the output of the charger, the developing bias of the developing unit, and the gradation conversion curve (γ curve) are set so that the density data of each density detection pattern is equal to the density value that should be originally obtained Control is performed by the control unit 45.

In this way, by accurately detecting the home position, the bare surface file data having the same rotational phase can be subtracted from the detection data of the density detection pattern group 220 in the automatic density control. Appropriate density correction that is not affected by molding flaws or the like can be realized.
<Modification>
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications may be considered.

  (1) In the above embodiment, the main wavelength of the light emitting elements in the two photoelectric sensors 23 and 24 is set to the same 730 [nm], and the reflectance is reduced with respect to the film thickness changing portion 21a. Since the home position can be detected if the reflectances of the changing portion 21a and the non-thickness changing portion 21b are different, the film thickness changing portion 21a for both or one of the two photoelectric sensors 23 and 24 can be detected. This can also be implemented by using a photoelectric sensor having a light emission main wavelength such that the reflectance of the portion of this portion increases more than the reflectance of the other non-film thickness changing portion 21b.

FIG. 10 is a graph showing the change in reflectance with respect to the film thickness d when the emission main wavelength is 530 [nm] (incident angle θ1 is 20 ° as in FIG. 4B).
As shown in the graph, when the emission main wavelength is 530 [nm], the reflectance is almost the maximum reflectance when the thickness of the film thickness changing portion 21a is 390 [nm], and the non-film thickness changing portion 21b When the thickness is 260 [nm], it approaches the minimum reflectance.

FIG. 11 shows the detection of the surface of the intermediate transfer belt 21 when the main emission wavelength of the photoelectric sensor 24 remains 730 [nm] and the emission main wavelength of the photoelectric sensor 23 is 530 [nm] in the positional relationship of FIG. It shows a change in value.
The photoelectric sensor 23 detects the scratch 212 at time t1 (in this case, since the reflectance of the non-film thickness changing portion 21b is low, the detection value of the scratch 212 is also smaller than the detection value of the non-film thickness changing portion 21b. The film thickness change portion 21a is detected by both the photoelectric sensors 23 and 24 at time t2. Unlike the case of FIG. 8, the output of the photoelectric sensor 23 becomes higher than the detection level of the non-film thickness changing portion 21b and exceeds the threshold value h2.

  Even if the scratch 212 extends long in the width direction of the intermediate transfer belt 21 and both the photoelectric sensors 23 and 24 detect the scratch 211 at the same time, the detection values of both photoelectric sensors at that time are detected. Are both lower than the detection value of the non-film thickness changing portion 21b, but when the film thickness changing portion 21a is detected, the detection value is simultaneously opposite to the detection level of the non-film thickness changing portion 21b (increase and decrease directions). Therefore, the film thickness changing portion 21a can be detected more reliably.

(2) In the above embodiment, the photoelectric sensors 23 and 24 are arranged in parallel with the band-shaped film thickness changing portion 21a so that the film thickness changing portion 21a can be detected simultaneously by both photoelectric sensors. However, both do not necessarily have to be parallel.
When both are not parallel, the time difference between the time of the film thickness changing portion 21a by the photoelectric sensor 23 and the time of detection of the film thickness changing portion 21a by the photoelectric sensor 24 is obtained in advance at the shipping stage, and stored in the EEPROM 459 or the like. During the home position detection process, if the difference between the detection times of the photoelectric sensors 23 and 24 is equal to the stored time difference, it is considered that the film thickness changing portion 21a has been detected and detected later, for example. The position detected by the photoelectric sensor may be set as the home position.

FIG. 12 shows an example of the case where the film thickness changing portion 21a is separated into two and formed in a different step so that the film thickness changing portions are not detected by the photoelectric sensors 23 and 24 at the same time.
The detection positions of the photoelectric sensors 23 and 24 are arranged in a line in the width direction of the intermediate transfer belt 21, but are separated into two parts, a film thickness changing part 21a and film thickness changing parts 21c and 21d, and the intermediate transfer belt. The position of the tip in the running direction (arrow Y direction) is shifted by a distance D.

In this case, changes in the detection values of the photoelectric sensors 23 and 24 are as shown in FIG.
First, the photoelectric sensor 23 detects the scratch 212 at time t1, and then detects the film thickness changing portion 21c at time t2. Further, at time t3 after ΔT, the photoelectric sensor 24 detects the film thickness changing portion 21d.
Here, if the system speed of the apparatus is Vs, ΔT = D / Vs.

FIG. 14 is a flowchart showing the contents of the home position detection process performed by the control unit 45 when the photoelectric sensors 23 and 24 and the film thickness changing units 21c and 21d have the positional relationship n as shown in FIG.
First, in step S11, it is determined whether or not the detection value of the photoelectric sensor 23 has become the threshold value h1 or less. If it is equal to or less than the threshold value h1, the time is stored in the RAM 453, and then it is determined whether or not the detection value of the photoelectric sensor 24 is equal to or less than the threshold value h1 (step S11: YES, step S12).

In step S12, when the detection value of the photoelectric sensor 24 is also equal to or less than the threshold value h1 (step S12: YES), the detection time is stored in the RAM 453, and the detection time of the photoelectric sensor 23 and the photoelectric sensor 24 is set. The difference is obtained, and it is determined whether or not this is ΔT (step S13).
If the determination in step S13 is affirmative, both the photoelectric sensors 23 and 24 have detected the film thickness changing portions 21c and 21d, so that the photoelectric sensor 24 detects the home position of the intermediate transfer belt 21. (Step S14), the process returns to the main flowchart (not shown).

If “NO” is determined in steps S11, S12, and S13, the process directly returns to the main flowchart.
As described above, even in the case of this modification, the home position of the intermediate transfer belt 21 can be reliably detected.
(3) In the above embodiment, the thickness of the film thickness changing portion 21a is 260 [nm], the thickness of the other non-film thickness changing portion 21b is 390 [nm], and the thickness of the non-film thickness changing portion 21b is the film thickness. Although it is possible to detect the home position even if it is relatively thicker than the changing portion 21a, it is desirable to make the thickness changing portion 21a having a smaller area thicker from the viewpoint of cost reduction.

In addition, the thickness of each part can be detected by the light receiving element even if the difference in reflected light between the film thickness changing part and the non-film thickness changing part caused by the emission main wavelength of the light emitting element of the photoelectric sensor to be used is not necessarily maximized. Needless to say, the difference is not limited to the numerical values in the above embodiment.
(4) The number of photoelectric sensors for detecting the home position is two in the above embodiment, but even if there are three or more at different positions in the width direction (main scanning direction) of the intermediate transfer belt. I do not care. This is because the certainty of home position detection is increased accordingly.

(5) In the above embodiment, the photoelectric sensor 23 used for density detection in the image stabilization process is also used as the home position detection photoelectric sensor.
In addition, when color misregistration correction is performed as an image stabilization process, for example, a toner pattern for detecting a color misregistration amount is formed at both ends and the center in the width direction of the intermediate transfer belt, and the color at each position is determined. In a model in which three photoelectric sensors are arranged to detect the amount of deviation, a part or all of them may be used as a photoelectric sensor for home position detection.

On the contrary, a photoelectric sensor dedicated to home position detection may be provided separately without using any photoelectric sensor for image stabilization processing.
(6) Although the cured thin film layer 211 is a single layer in the above embodiment, it may be two or more layers in some cases. In this case, the optical path difference between the reflected light at the outermost surface, the reflected light at the interface between the cured thin film layers, and the reflected light at the interface between the lowermost cured thin film layer and the belt substrate 210 is the emission main wavelength λ. The thickness is determined according to the refractive index of each layer so as to be N times (N: natural number).

(7) Although the example in which the developing device and the image forming apparatus according to the present invention are applied to a tandem color digital printer has been described, the scope of application of the present invention is not limited thereto.
For example, even if the intermediate transfer drum is provided as an intermediate transfer member, the intermediate transfer drum is rotated four times, and CMYK toner images are sequentially superimposed and transferred onto the peripheral surface thereof, the intermediate transfer drum is scratched. The present invention can be applied as long as it may occur.

Further, the present invention can be applied to, for example, a copying machine, a facsimile machine, and a multi-function peripheral (MFP) regardless of color or monochrome image formation.
Moreover, you may combine the content of the said embodiment and modification as much as possible.

  The present invention is suitable as a technique for detecting the home position of the intermediate transfer rotator in the image forming apparatus.

DESCRIPTION OF SYMBOLS 1 Printer 10 Image process part 20 Intermediate transfer part 21 Intermediate transfer belt 21a, 21c, 21d Film thickness change part
21b Non-film thickness change part
23, 24 Photoelectric sensor 30 Paper feed unit 35 Operation panel
40 Fixing Unit 45 Control Unit 220 Density Detection Pattern Group 451 CPU
452 Communication I / F unit 453 RAM
454 ROM
455 EEPROM

Claims (6)

An image forming apparatus that primary-transfers a toner image formed on an image carrier to a rotating intermediate transfer rotator and then secondary-transfers it onto a recording sheet to form an image,
Home position detecting means for detecting a home position of the rotating intermediate transfer rotating body,
At least one or more inorganic oxide thin film layers are formed on the transfer surface of the intermediate transfer rotator, and at one or more locations, the thickness is different from the thickness of the other inorganic oxide thin film layers. There is a change section,
The home position detection means includes a plurality of optical sensors arranged at different positions in the width direction of the intermediate transfer rotator, and the home position is detected based on detection results of the surface of the intermediate transfer rotator by the plurality of optical sensors. An image forming apparatus characterized by detecting the above. The film thickness changing portion is formed to extend in a band shape in the width direction of the intermediate transfer rotating body, and the plurality of detection means are arranged at intervals along the width direction of the intermediate transfer body. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Each of the plurality of optical sensors is configured to detect, with a light receiving element, return light from the surface of the intermediate transfer rotating body of light irradiated from the light emitting element.
The reflectance at the film thickness change portion of the light emitted from the light emitting elements in all the plurality of optical sensors is higher than the reflectance at other non-film thickness change portions due to light interference by the inorganic oxide thin film layer, 3. The image forming apparatus according to claim 1, wherein the main wavelength of the irradiation light of each light emitting element is determined so as to be low. Each of the plurality of optical sensors is configured to detect, with a light receiving element, return light from the surface of the intermediate transfer rotating body of light irradiated from the light emitting element.
Among the plurality of optical sensors, the main wavelength of the irradiation light of the light emitting element of the first optical sensor and the light emitting element of the second optical sensor is changed in thickness by the interference of light by the inorganic oxide thin film layer. 3. The image forming apparatus according to claim 1, wherein the reflectance is determined to be a wavelength at which the reflectance is higher and a wavelength at which the reflectance is lower than those of the other non-film thickness changing portions.   The thickness of the film thickness changing portion and the non-film thickness changing portion of the inorganic oxide layer includes a main wavelength of irradiation light of at least one optical sensor among the plurality of optical sensors, an incident angle to the surface of the cured thin film layer, and 5. The method according to claim 3, wherein the difference in reflectance between the film thickness changing portion and the non-film thickness changing portion is set to be maximum in relation to the refractive index of the inorganic oxide layer. Image forming apparatus. An image stabilization unit that forms a toner pattern on the surface of the intermediate transfer member, detects the toner pattern by one or a plurality of toner pattern detection optical sensors, and executes image stabilization processing;
6. The image forming apparatus according to claim 1, wherein the toner pattern detection optical sensor also serves as a part or all of the home position detection optical sensor.

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