JP2008096856A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of highly precisely measuring the position of a toner image without being affected by a noise and also highly precisely positioning respective color toner images while making the apparatus low in cost and high in operating speed. <P>SOLUTION: A solid image patch pattern formed on an intermediate transfer body is detected by an optical sensor, and the positions Mmax1 and Mmin1 on the intermediate transfer body in the conveying direction are detected, where the maximum value VSmax1 and the minimum value VSmin1 of the output voltage are respectively detected. A belt-like image patch pattern whose width in the conveying direction becomes equal to a distance difference (Mmax1-Mmin1) between the detected positions in the conveying direction is formed on the intermediate transfer body. The belt-like image patch pattern is detected by the optical sensor, and then, the center position of the belt-like image patch pattern is detected based on the output voltage of the sensor, then, the position of the toner image to be formed on the intermediate transfer body is measured. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a complex machine thereof, and more particularly, an optical image of an image patch pattern formed on an intermediate transfer body on which a color image is formed. The present invention relates to an image forming apparatus that measures with a sensor and adjusts image forming conditions and image forming timing based on the measurement result.

2. Description of the Related Art Conventionally, in an image forming apparatus such as a color copying machine, a technique for adjusting image forming conditions (process control) in order to form a color image with good image quality without color misregistration (for example, (See Patent Document 1).
More specifically, a test image patch pattern such as a solid image or a belt-like image is formed on the intermediate transfer member according to predetermined conditions in order to stabilize the image density and align each color toner image. Then, the image patch pattern is read by an optical sensor, and the state is measured by various methods, thereby controlling toner replenishment to the developing unit, image forming conditions, exposure writing timing, and the like.

Japanese Patent Application Laid-Open No. H10-260260 discloses a technique for controlling the toner adhesion amount of the solid image patch pattern by adjusting the developing bias voltage applied to the developing unit (developing roller).
Patent Document 2 and the like disclose a technique for forming a belt-like image patch pattern on an intermediate transfer belt (intermediate transfer member), measuring the position of the toner image, and aligning the toner images of the respective colors. Yes.

  Here, in order to measure the position of the toner image in order to align each color toner image, it is necessary to select an optical sensor and a measuring method according to the surface characteristics of the intermediate transfer member to be used. Optical sensors are roughly classified into a regular reflection type that receives regular reflection light and a diffuse reflection type that receives only diffuse reflection light excluding regular reflection light. In general, a regular reflection type optical sensor is used when the substrate of the photosensitive member or the intermediate transfer member has high glossiness, and a diffuse reflection type optical sensor is used when the substrate has low glossiness. However, since the diffuse reflection type optical sensor cannot measure a black toner image, a regular reflection type optical sensor is used when measuring a plurality of color toner images including black with one type of optical sensor.

However, the specular reflection type optical sensor has a specular reflection light that passes through the optical path with the same incident angle and reflection angle. The reflection point deviates from the measurement region, causing a problem that the output voltage of the optical sensor is rapidly reduced.
On the other hand, when the measurement area of the optical sensor is set large, a large amount of diffuse reflection components around the regular reflection point are included. Here, since the change in the output voltage for the toner image of the diffuse reflection component is opposite to the change in the output voltage for the toner image of the regular reflection component, the sensitivity of the optical sensor increases as the diffuse reflection component enters the optical sensor. Will get worse.

On the other hand, the measurement methods for aligning the color toner images can be broadly divided into a method of directly measuring the toner image position by reading a belt-like image patch pattern and a two-color belt-like image patch pattern. There is a method in which the relative positions of the two colors are measured by gradually shifting the relative positions of the two and measuring the average reflection amount (see, for example, Patent Document 2).
The former measurement method allows measurement even when the number of image patch patterns is relatively small. However, if the measurement area of the optical sensor is not narrowed down, the measurement accuracy cannot be increased and it is vulnerable to noise. The latter measurement method can use a diffuse reflection type optical sensor and can set a large measurement area, so it is resistant to noise and mounting errors and is not easily affected by the gloss or reflectance of the substrate. It is necessary to take a large number.

JP 2003-5465 A JP 2003-280317 A

  Conventional color image forming apparatuses have been difficult to align toner images of each color with high accuracy without being affected by noise while achieving low cost and high printing speed.

Specifically, in order to achieve cost reduction of the color image forming apparatus, it is desirable that the number of optical sensors for detecting the image patch pattern is one. Therefore, it is necessary to use a regular reflection type optical sensor capable of measuring a black toner image.
Further, in order to achieve high-speed printing of the color image forming apparatus, a measurement method with a short measurement time for alignment of each color toner image is desirable. Therefore, it is necessary to use a measurement method that reads the belt-like image patch pattern and directly measures the toner image position.

  However, when a measurement method that directly measures the toner image position using a regular reflection type optical sensor is used, a large amount of diffuse reflection components are included in addition to the regular reflection component in the output voltage of the optical sensor. Problems arise. The measurement method for directly measuring the toner image position is a voltage at which the output voltage of the optical sensor decreases most in the vicinity of the center position when the belt-shaped image patch pattern is read (hereinafter referred to as “band-shaped image minimum value output voltage Vmin”). ")" Is pushed up by the presence of a large amount of diffuse reflection components. Therefore, an appropriate threshold value that is not affected by such noise cannot be set, and the position of the toner image cannot be measured with high accuracy.

  The present invention has been made in order to solve the above-described problems, and achieves low-cost apparatus and high-speed printing while measuring the position of a toner image with high accuracy without being affected by noise. Another object of the present invention is to provide an image forming apparatus capable of aligning toner images of each color with high accuracy.

  An image forming apparatus according to a first aspect of the present invention includes a plurality of image forming units that form toner images, and toners of respective colors that move in a predetermined transport direction and are formed by the plurality of image forming units. An intermediate transfer body on which an image is transferred in an overlapping manner, and an optical sensor that outputs a voltage corresponding to the amount of reflected light including regular reflection light obtained by projecting on a predetermined measurement area on the intermediate transfer body, A solid image patch pattern having a width in the transport direction larger than the measurement area of the optical sensor is formed on the intermediate transfer member by the image forming unit, and the solid image patch pattern is detected by the optical sensor. The position in the transport direction on the intermediate transfer body where the maximum value and the minimum value are detected in the output voltage is detected, and the position in the transport direction and the minimum value where the maximum value is detected are detected. A belt-like image patch pattern having a width in the carrying direction equal to the distance difference from the carrying direction position is formed on the intermediate transfer member by the image forming means, and the belt-like image patch pattern is formed by the optical sensor. The position of the toner image formed on the intermediate transfer body is measured by detecting and detecting the center position of the belt-like image patch pattern from the output voltage.

  According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the image forming means can vary a developing bias voltage applied to the developing portion when a toner image is formed. A plurality of solid image patch patterns are formed on the intermediate transfer body by the image forming means, and the plurality of solid image patch patterns are respectively detected by the optical sensors. Then, a maximum value or a minimum value and an average value of the output voltage are read out, and the development bias voltage is varied to detect the belt-shaped image patch pattern on the intermediate transfer member, and the optical sensor detects Each of the minimum values of the strip-shaped image patch pattern calculated for each of the development bias voltages is calculated. Its minimum value is by applying a developing bias voltage to be minimized to the developing unit which forms the belt-shaped image patch pattern on the intermediate transfer body.

An image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the second aspect, wherein the output voltage of the background portion of the intermediate transfer body detected by the optical sensor is VSg and the optical sensor is used. When the maximum value of the output voltage of the solid image patch pattern to be detected is VSmax, the minimum value is VSmin, and the average value is VSave, the minimum value Vmin of the strip-shaped image patch pattern calculated for each developing bias voltage. Is
Vmin = 2 × VSmin−VSave
Or
Vmin = VSave−2 × (VSmax−VSg)
Is calculated by the following formula.

  According to a fourth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to third aspects, wherein the belt-shaped image patch pattern is detected by the optical sensor and the output voltage of the belt-shaped image patch pattern is detected. Among these, the maximum values appearing at both ends of the output waveform are detected, and the detected value of the center position of the belt-like image patch pattern is corrected based on the difference between the values.

  An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to any one of the first to fourth aspects, wherein the belt-like image is obtained when the optical sensor is mounted on or replaced with the apparatus. The center position of the patch pattern is detected to measure the position of the toner image formed on the intermediate transfer member, and the measurement result is stored.

  The present invention uses a measurement method in which the toner image position is directly measured by a specular reflection type optical sensor, and takes into account variations in the characteristics of the optical sensor itself and mounting errors of the optical sensor, and the belt-like image minimum value output voltage Vmin. The width of the belt-like image patch pattern is set so that is minimized. As a result, it is possible to measure the position of the toner image with high accuracy without being affected by noise, and to align the toner image of each color with high accuracy while achieving low cost of the apparatus and high speed printing. An image forming apparatus that can be provided can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
The first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is the main body of a color copying machine as an image forming apparatus, 2 is an exposure unit (writing unit) that emits laser light based on image information, and 20Y, 20M, 20C, and 20BK are colors (yellow, magenta, Cyan, black), 21 is a photosensitive drum (image carrier) accommodated in each of the process cartridges 20Y, 20M, 20C, and 20BK, 22 is a charging unit that charges the photosensitive drum 21, and 23Y. , 23M, 23C, and 23BK are developing units that develop the electrostatic latent image formed on the photosensitive drum 21, and 24 is a transfer bias roller that transfers the toner image formed on the photosensitive drum 21 to the intermediate transfer belt 27. And 25, a cleaning unit for collecting untransferred toner on the photosensitive drum 21.

  Reference numeral 27 denotes an intermediate transfer belt as an intermediate transfer body onto which toner images of respective colors are transferred, 28 denotes a second transfer bias roller for transferring the toner image formed on the intermediate transfer belt 27 to the recording medium P, 29 Is an intermediate transfer belt cleaning unit that collects untransferred toner on the intermediate transfer belt 27, 30 is a transfer belt that conveys a recording medium P onto which four color toner images are transferred, and 32Y, 32M, 32C, and 32BK are each A toner replenishing unit that replenishes each color toner to the developing units 23Y, 23M, 23C, and 23BK, 51 a document conveying unit that conveys the document D to the document reading unit 55, and 55 a document as a reading unit that reads image information of the document D A reading unit (scanner), 61 is a paper feeding unit that stores a recording medium P such as transfer paper, and 66 is a fixing unit that fixes an unfixed image on the recording medium P.

  Here, the process cartridges 20Y, 20M, 20C, and 20BK and the developing units 23Y, 23M, 23C, and 23BK function as image forming units that form toner images. That is, image formation of each color (yellow, magenta, cyan, black) is performed on the photosensitive drum 21 in each process cartridge 20Y, 20M, 20C, 20BK. The process cartridges 20Y, 20M, 20C, and 20BK are obtained by integrating the photosensitive drum 21, the charging unit 22, and the cleaning unit 25, respectively.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport roller of the document transport unit 51 and placed on the contact glass 53 of the document reading unit 55. Then, the document reading unit 55 optically reads the image information of the document D placed on the contact glass 53.

  Specifically, the document reading unit 55 scans the image of the document D on the contact glass 53 while irradiating light emitted from the illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, color conversion processing is performed by the image processing unit based on the intensity levels of the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information.

  Then, the color image information of yellow, magenta, cyan, and black is transmitted to the exposure unit 2 (writing unit). Then, laser light (exposure light) based on the image information of each color is emitted from the exposure unit 2 toward the corresponding photosensitive drums 21 of the process cartridges 20Y, 20M, 20C, and 20BK.

On the other hand, the four photosensitive drums 21 rotate in the clockwise direction in FIG. First, the surface of the photosensitive drum 21 is uniformly charged at a position facing the charging unit 22 (a charging process). Thus, a charged potential is formed on the photosensitive drum 21. Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of each laser beam.
In the exposure unit 2, laser light corresponding to the image signal is emitted from the light source corresponding to each color. The laser light is incident on the polygon mirror 3 and reflected, and then passes through the lenses 4 and 5. The laser light after passing through the lenses 4 and 5 passes through different optical paths for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  The laser beam corresponding to the yellow component is reflected by the mirrors 6 to 8 and then irradiated onto the surface of the photosensitive drum 21 of the first process cartridge 20Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 21 by the polygon mirror 3 that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 21 charged by the charging unit 22.

  Similarly, the laser beam corresponding to the magenta component is reflected by the mirrors 9 to 11 and then irradiated to the surface of the photosensitive drum 21 of the second process cartridge 20M from the left side of the paper, thereby causing an electrostatic latent image corresponding to the magenta component. An image is formed. The cyan component laser light is reflected by the mirrors 12 to 14 and then irradiated on the surface of the photosensitive drum 21 of the third process cartridge 20C from the left side of the paper, thereby forming an electrostatic latent image of the cyan component. The black component laser light is reflected by the mirror 15 and then irradiated on the surface of the photosensitive drum 21 of the fourth process cartridge 20BK from the left side of the paper, thereby forming an electrostatic latent image of black component.

Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent images of the respective colors are formed reaches positions facing the developing units 23Y, 23M, 23C, and 23BK, respectively. Then, each color toner is supplied onto the photosensitive drum 21 from the developing units 23Y, 23M, 23C, and 23BK, and the latent image on the photosensitive drum 21 is developed (this is a developing step).
Thereafter, the surface of the photosensitive drum 21 after the development process reaches a position facing the intermediate transfer belt 27 (intermediate transfer body). Here, the transfer bias roller 24 is installed at each facing position so as to contact the inner peripheral surface of the intermediate transfer belt 27. Then, the image of each color formed on the photosensitive drum 21 is sequentially transferred onto the intermediate transfer belt 27 at the position of the transfer bias roller 24 (first transfer step).

Then, the surface of the photosensitive drum 21 after the first transfer process reaches a position facing the cleaning unit 25. The untransferred toner remaining on the photosensitive drum 21 is collected by the cleaning unit 25 (this is a cleaning process).
Thereafter, the surface of the photosensitive drum 21 passes through a static elimination unit (not shown), and a series of image forming processes on the photosensitive drum 21 is completed.

On the other hand, the surface of the intermediate transfer belt 27 onto which the images of the respective colors on the photosensitive drum 21 have been transferred are moved in a predetermined transport direction (in the direction of the arrow in the figure), and the second transfer bias roller 28 Reach position. Then, the full color image on the intermediate transfer belt 27 is secondarily transferred onto the recording medium P at the position of the second transfer bias roller 28 (this is the second transfer step). Note that an image patch pattern (which is a solid image patch pattern or a belt-like image patch pattern for adjusting the image forming timing and image forming conditions) described later is also formed on the intermediate transfer belt 27 through the image forming process described above. The
Thereafter, the surface of the intermediate transfer belt 27 reaches the position of the intermediate transfer belt cleaning unit 29. Then, the untransferred toner on the intermediate transfer belt 27 is collected by the intermediate transfer belt cleaning unit 29, and a series of transfer processes on the intermediate transfer belt 27 is completed.

Here, the recording medium P at the position of the second transfer bias roller 28 is transported from the paper feeding unit 61 via the transport guide 63, the registration roller 64, and the like.
Specifically, the recording medium P fed by the paper feeding roller 62 from the paper feeding unit 61 that stores the recording medium P passes through the conveyance guide 63 and is guided to the registration roller 64. The recording medium P that has reached the registration roller 64 is conveyed toward the position of the second transfer bias roller 28 in synchronization with the toner image on the intermediate transfer belt 27.

Thereafter, the recording medium P on which the full-color image is transferred is guided to the fixing unit 66 by the transfer belt 30. In the fixing unit 66, the color image is fixed on the recording medium P at the nip between the heating roller 67 and the pressure roller 68.
Then, the recording medium P after the fixing process is discharged as an output image by the paper discharge roller 69 to the outside of the apparatus main body 1, and a series of image forming processes is completed.
In the image forming apparatus according to the first embodiment, a black and white output image can be formed by forming a toner image only on the photosensitive drum 21 of the black process cartridge 20BK, or yellow, magenta, and cyan. Either one color toner image can be formed to form a single color output image, or yellow, magenta, and cyan toner images can be formed to form a three color output image.

Next, the image forming unit of the image forming apparatus will be described in detail with reference to FIG. FIG. 2 is a sectional view showing the image forming means.
The four image forming units installed in the apparatus main body 1 have substantially the same structure except that the color of the toner T used in the image forming process is different. Therefore, alphabets of reference numerals in the process cartridge, the developing unit, and the toner replenishing unit. (Y, M, C, BK) is omitted for illustration.

  As shown in FIG. 2, the photosensitive drum 21, the charging unit 22, and the cleaning unit 25 are mainly housed in the case 26 in the process cartridge 20. The cleaning unit 25 is provided with a cleaning blade 25 a and a cleaning roller 25 b that are in contact with the photosensitive drum 21.

  The developing unit 23 mainly includes a developing roller 23a facing the photosensitive drum 21, a first conveying screw 23b facing the developing roller 23a, and a second conveying screw facing the first conveying screw 23b via a partition member 23e. 23c, a doctor blade 23d facing the developing roller 23a, and a magnetic permeability sensor 40 for magnetically detecting the toner concentration of the developer G accommodated in the developing unit 23. A two-component developer G composed of carrier C and toner T is accommodated in the developing unit 23. The developing roller 23a includes a magnet that is fixed inside and forms a magnetic pole on the circumferential surface of the roller, and a sleeve that rotates around the magnet.

The image forming process described above will be described in more detail.
The developing roller 23a rotates in the direction of the arrow in FIG. The developer G in the developing unit 23 is supplied from the toner replenishing unit 32 to the replenishing port 23f by the rotation of the first conveying screw 23b and the second conveying screw 23c arranged with the partition member 23e interposed therebetween. Circulates in the longitudinal direction while being agitated and mixed together with the toner T replenished via (the direction perpendicular to the paper surface of FIG. 2). Then, the toner T that is frictionally charged and adsorbed on the carrier C is carried on the developing roller 23 a together with the carrier C.

  The developer G carried on the developing roller 23a then reaches the position of the doctor blade 23d. The developer G on the developing roller 23a is adjusted to an appropriate amount at the position of the doctor blade 23d, and then reaches a position facing the photosensitive drum 21 (developing area).

Thereafter, in the development area, the toner T in the developer G adheres to the electrostatic latent image formed on the surface of the photosensitive drum 21. Specifically, an electric field (development potential) formed by a potential difference (development potential) between the latent image potential (exposure potential) of the image portion irradiated with the laser beam L and the development bias voltage applied to the development roller 23a (development portion). The toner T adheres to the latent image by the developing electric field.
Thereafter, most of the toner T adhering to the photosensitive drum 21 is transferred onto the intermediate transfer belt 27. The untransferred toner T remaining on the photosensitive drum 21 is collected in the cleaning unit 25 by the cleaning blade 25a and the cleaning roller 25b.

  Here, a toner replenishing unit 32 provided in the apparatus main body 1 includes a toner bottle 33 configured to be replaceable, and a toner hopper unit 34 that holds and rotates the toner bottle 33 and replenishes the developing unit 23 with fresh toner T. And is composed of. The toner bottle 33 contains toner T (any one of yellow, magenta, cyan, and black). In addition, a spiral protrusion is formed on the inner peripheral surface of the toner bottle 33.

  The toner T in the toner bottle 33 is appropriately replenished into the developing unit 23 from the replenishing port 23f as the toner T in the developing unit 23 is consumed. Consumption of the toner T in the developing unit 23 is detected by a magnetic permeability sensor 40 (T sensor) installed in the developing unit 23. That is, based on the detection result of the magnetic permeability sensor 40, the toner is appropriately supplied from the toner supply unit 32 into the developing unit 23.

Referring to FIG. 2, the optical sensor 41 is disposed at a position facing the intermediate transfer belt 27 (intermediate transfer member). The optical sensor 41 is a specular reflection type optical sensor, and includes a light emitting element 41a such as an infrared light source LED and a light receiving element 41b such as a photodiode (see also FIG. 3). The optical sensor 41 detects the amount of toner attached to the image patch pattern (toner image) formed on the intermediate transfer belt 27 and the amount of toner attached to the background portion on the intermediate transfer belt 27 at a predetermined timing. The
Then, the detection result of the optical sensor 41 (voltage output corresponding to the amount of received light) is signal-processed by the control unit 70, and based on the result, alignment of each color toner image and image formation on the photosensitive drum 21 are performed. Conditions, that is, image formation timing, development bias voltage, charging potential, exposure potential (exposure amount), and the like are optimally adjusted and controlled (process control). The process control can be performed every time the number of printed sheets reaches a predetermined number.

The power supply unit 82 supplies a developing bias voltage (Vb) to the developing roller 23 a of the developing unit 23. The magnitude of the developing bias voltage (Vb) can be varied by the control unit 70.
The power supply unit 81 supplies a charging voltage to the charging unit 22. The magnitude of the charging voltage can be varied by the control unit 70. Thereby, the charging potential on the photosensitive drum 21 is also varied.
The output (laser power) of the laser beam emitted from the exposure unit 2 can be varied (modulated) by the control unit 70. Thereby, the exposure potential on the photosensitive drum 21 is also varied.

Next, the optical sensor 41 will be described in more detail with reference to FIGS.
FIG. 3 is a configuration diagram showing the optical sensor 41, and is a view of the optical sensor 41 as viewed in the width direction (a direction orthogonal to the conveyance direction of the intermediate transfer belt 27). 4 is a diagram of the optical sensor 41 of FIG. 3 as viewed in the transport direction (the transport direction of the intermediate transfer belt 27).

  Referring to FIG. 3, the light emitted from the light emitting element 41a of the regular reflection type optical sensor 41 passes through a slit or a lens (not shown), and then the image patch pattern TP (or background) on the intermediate transfer belt 27. The light is condensed (projected) in the measurement area N of the portion. Since this light is infrared light, any color toner image is similarly reflected. The measurement region N is opposed to the optical sensor 41 and is formed in a circular shape having a radius r1 (about 1.0 to 3.0 mm). The normal passing through the center of the measurement region N coincides with the central axis A of the optical sensor 41, and the incident angle of light from the light emitting element 41a to the measurement region N is θ.

  The light receiving element 41b of the optical sensor 41 is disposed in a plane including the sensor central axis A and the light emitting element 41a so that the direction thereof faces the center of the measurement region N, and the angle with the sensor central axis A is θ. Are arranged as follows. The light projected from the light emitting element 41a and reflected by the area M near the center of the measurement area N and incident on the light receiving element 41b is incident and reflected with respect to the normal to the measurement area N (sensor central axis A). Are called specularly reflected light. The region is called a regular reflection measurement region M.

Since the intermediate transfer belt 27 used in the first embodiment has high glossiness, when the measurement region N is the background portion of the intermediate transfer body belt 27, the regular reflection light becomes extremely strong, and the other reflection light. (Diffuse reflected light) hardly occurs. Therefore, the output voltage of the light receiving element 41b is based only on the component of regular reflection light. The radius r2 of the regular reflection measurement region M is about 0.3 to 1.0 mm.
On the other hand, when the measurement area N is a black solid image toner image TP sufficiently developed on the intermediate transfer belt 27, the light emitted from the light emitting element 41a is almost absorbed by the toner image TP, and the light receiving element. Little light is incident on 41b.
When the measurement area N is a toner image TP of a solid color image sufficiently developed on the intermediate transfer belt 27, the light emitted from the light emitting element 41a is almost completely diffused by the toner layer and then reflected. Is done. Therefore, the output voltage VS of the light receiving element 41b is the sum of the light that is uniformly reflected from the entire measurement region N and is incident on the light receiving element 41b.

FIG. 5 is a graph showing the relationship between the toner adhesion amount of the toner image on the intermediate transfer belt 27 and the output voltage of the optical sensor 41.
Specifically, the output voltage VS of the light receiving element 41b when black toner (or color toner) is gradually adhered on the intermediate transfer belt 27 in the measurement region N is shown. This experimental result can be approximately explained by Kubelka-Munk theory.
In FIG. 5, the horizontal axis indicates the amount of toner uniformly developed on the intermediate transfer belt 27, and the vertical axis indicates the output voltage VS (V) of the optical sensor 41 (light receiving element 41b). In FIG. 5, a broken line Q1 indicates a change in the output voltage of the optical sensor 41 (light receiving element 41b) due to the reflected light of the specular reflection component, and an alternate long and short dash line Q2 indicates the optical sensor 41 (light receiving element 41b) due to the reflected light of the diffuse reflection component. ), And a solid line S indicates the output voltage VS (final output) of the optical sensor 41 (light receiving element 41b) obtained by adding the regular reflection component and the diffuse reflection component.
When the measurement region N is the background portion of the intermediate transfer belt 27, the light amount of the light emitting element 41a is adjusted so that the output voltage VS is 4V.

  As shown in FIG. 5, when the toner is not attached to the measurement region N, only the regular reflection component is the output voltage VS as described above. When the toner adheres to the measurement region N, scattering and absorption occur in the toner layer, so that the specular reflection component decreases. In the case of black toner, only absorption occurs in the toner layer, so this regular reflection component becomes the output voltage VS as it is. In the case of a color toner, scattering occurs in the toner layer and the light is reflected, so that the amount of reflection increases as the toner adhesion amount increases. Further, as described above, the reflected light due to this scattering becomes a complete diffuse reflection component, and therefore increases or decreases depending on the size (radius r1) of the measurement region N. The output voltage VS in the case of color toner is the sum of the regular reflection component and the diffuse reflection component as shown in FIG.

FIG. 6 shows an example of a belt-like image patch pattern TB formed on the intermediate transfer belt 27. The band-shaped image patch pattern TB has a width W in the transport direction (the transport direction of the intermediate transfer belt 27 and the arrow direction in FIG. 6), and the direction perpendicular to the transport direction is the longitudinal direction. Formed. The interval between the strip-shaped image patch patterns TB adjacent in the transport direction is more than the size of the measurement region N so as not to interfere with each other. The belt-like image patch pattern TB is a test image patch pattern for detecting the position by the optical sensor 41 and aligning the toner images of the respective colors.
In the first embodiment, the strip image patch pattern TB is formed so that the longitudinal direction thereof is perpendicular to the transport direction. However, the strip image patch pattern TB is formed so that the longitudinal direction is inclined with respect to the transport direction. You can also.

FIG. 7 is a diagram illustrating an output waveform of the output voltage VS of the optical sensor 41 that has detected the belt-like image patch pattern TB.
In FIG. 7, the horizontal axis indicates the conveyance direction position (mm) on the intermediate transfer belt 27, and the vertical axis indicates the output voltage VS of the optical sensor 41 (light receiving element 41 b). In FIG. 7, the broken line Q1 indicates the fluctuation of the output voltage VS due to the regular reflection component, the alternate long and short dash line Q2 indicates the fluctuation of the output voltage VS due to the diffuse reflection component, and the solid line S indicates the sum of the regular reflection component and the diffuse reflection component. The output voltage VS (the final output) is shown.

In FIG. 7, the width W of the belt-like image patch pattern TB is set to 0.8 mm (the position is −0.4 to 0.4 mm in the drawing). The measurement area N has a radius r1 of 3 mm, the regular reflection measurement area M has a radius r2 of 0.5 mm, and the centers of both areas M and N coincide.
When the band-shaped image patch pattern TB formed in this way enters the measurement region N of the optical sensor 41, the diffuse reflection component is added and the total output voltage VS increases. Then, when the entire belt-shaped image patch pattern TB enters the measurement region N, the increase in the output voltage VS stops. After that, when the strip-shaped image patch pattern TB enters the regular reflection measurement region M, the regular reflection component rapidly decreases, so that the total output voltage VS with the diffuse reflection component decreases. Further, when the belt-like image patch pattern TB passes the center Xc, the output voltage VS increases this time. Thereafter, as shown in FIG. 7, the voltage waveform is symmetrical with the voltage waveform until passing through the center. The minimum value of the voltage VS at this time is referred to as “band image minimum value output voltage Vmin”.

  As is clear from FIG. 7, when the diffuse reflection component increases, the belt-like image minimum value output voltage Vmin increases. In the first embodiment, a predetermined threshold voltage Vth is set between the output voltage VS (set to 4 V) at the background portion of the intermediate transfer belt 27 and the belt-like image minimum value output voltage Vmin. Yes. Then, the conveyance direction positions Xth1 and Xth2 that pass through the threshold voltage Vth are detected, and the center positions thereof are determined as the center position Xc of the strip-shaped image patch pattern TB. Accordingly, when the belt-like image minimum value output voltage Vmin rises, it becomes difficult to set the threshold value Vth described above, and the optical sensor 41 erroneously detects due to noise or the like. It will be convenient.

If the width W of the band-shaped image patch pattern TB is too large, a large amount of diffuse reflection components enter the light receiving element 41b and the band-shaped image minimum value output voltage Vmin becomes high. On the other hand, if the width W of the band-shaped image patch pattern TB is too small, the regular reflection component cannot be removed and the band-shaped image minimum value output voltage Vmin becomes high.
Therefore, there exists a width W of the belt-like image patch pattern TB that minimizes the belt-like image minimum value output voltage Vmin. It has been found that the width W is in principle twice the radius r2 of the regular reflection measurement region M. That is, if the band-shaped image patch pattern TB having a width W corresponding to twice the radius r2 of the regular reflection measurement region M is formed, the band-shaped image minimum value output voltage Vmin can be minimized.
However, since the radius r2 of the regular reflection measurement region M varies depending on the optical characteristics of the light emitting element 41a and how to attach the regular reflection measuring region M to the optical sensor body, the strip-shaped image minimum value output voltage Vmin also varies. In order to solve such a problem, a method of inspecting the optical sensors 41 installed in the apparatus one by one in advance can be considered, but in this case, the productivity of the apparatus is remarkably reduced.

In the first embodiment, in order to solve such a problem, the width W of the band-shaped image patch pattern TB that minimizes the band-shaped image minimum value output voltage Vmin is set by automatic measurement.
In the image forming apparatus according to the first embodiment, the toner adhesion amount is measured before the belt-shaped image patch pattern TB is formed and the position of each color toner image is measured. Specifically, a solid image patch pattern having a uniform toner adhesion amount is formed on the intermediate transfer belt 27, and the adhesion amount is detected by the optical sensor 41.

FIG. 8 shows a case where a solid image patch pattern having a width in the conveyance direction of 10 mm (position in the conveyance direction is 0 to 10 mm) is formed on the intermediate transfer belt 27 and the solid image patch pattern is read by the optical sensor 41. The output voltage VS is shown. 8 that are the same as those in FIG. 7 are not described.
In FIG. 8, the output waveform is shown continuously, but actually, the control unit 70 samples and captures the output voltage VS by AD conversion at intervals of several tens of microns.

As shown in FIG. 8, before the solid image patch pattern enters the measurement region N, the output voltage VS is the background average output voltage VSg (4 V). When the solid image patch pattern enters the measurement region N, the diffuse reflection component is added and the total output voltage VS increases. Thereafter, when the solid image patch pattern enters the regular reflection measurement region M, the regular reflection component is rapidly reduced. The maximum value at this time is referred to as a solid image maximum value output voltage VSmax1, and the conveyance direction position where the solid image maximum value output voltage VSmax1 occurs is referred to as a maximum occurrence position Mmax1.
Thereafter, when the solid image patch pattern enters the entire regular reflection measurement region M, the regular reflection component becomes the minimum and constant, and the output voltage VS rises again by the addition of the diffuse reflection component. The minimum value at this time is referred to as a solid image minimum value output voltage VSmin1, and the conveyance direction position where the solid image minimum value output voltage VSmin1 is generated is referred to as a minimum generation position Mmin1.
Thereafter, when the solid image patch pattern enters the entire measurement region N, the output voltage VS becomes constant. The output voltage at this time is called a solid image average output voltage VSave.

Here, when only the solid image average output voltage VSave is detected from the solid image patch pattern, no change appears at the edge portion of the solid image patch pattern.
In the first embodiment, the maximum occurrence position Mmax1 and the minimum occurrence position Mmin1 are detected in consideration of the change appearing at the edge portion of the solid image patch pattern. The distance difference (interval) is assumed to be twice the radius r2 of the regular reflection measurement region M. That is, the width W in the transport direction of the belt-like image patch pattern TB formed on the intermediate transfer belt 27 thereafter is
W = 2 × r2 = Mmax1-Mmin1 (Formula 1)
The band-shaped image patch pattern TB is formed so as to satisfy the following relationship. The band-shaped image minimum value output voltage Vmin is minimized by detecting the band-shaped image patch pattern TB with the width W optimized in this way by the optical sensor 41.
Then, the belt-like image patch pattern TB with the optimized width W is detected by the optical sensor 41, the center position of the belt-like image patch pattern TB is detected from the output voltage, and the toner image formed on the intermediate transfer belt 27 is detected. Measure (detect) the position of.

As described above, in the first embodiment, the maximum value of the output voltage VS (image maximum value output voltage Vsmax) and the minimum value (image minimum value output voltage VSmin) are not used, and the positions in the transport direction are set. Since the width W in the transport direction of the belt-shaped image patch pattern TB is determined using the maximum generation position Mmax and the minimum generation position Mmin, the toner image position measurement resistant to noise can be performed.
Note that the method for calculating the width W of the strip-shaped image patch pattern TB described in the first embodiment is an example, and the width W is obtained using the control table based on the measured maximum occurrence position Mmax1 and minimum occurrence position Mmin1. A method may be used.

  Further, when the optical sensor 41 is attached to the apparatus main body 1 or replaced, the toner image position measurement is performed at least once, and the measurement result (the width W in the conveyance direction of the belt-shaped image patch pattern may be used). It is preferable to control so as to memorize. Thereby, even if an attachment error of the optical sensor 41 occurs, the width W of the band-shaped image patch pattern TB is set so that the band-shaped image minimum value output voltage Vmin is minimized.

In the first embodiment, the maximum occurrence position Mmax1 and the minimum occurrence position Mmin1 of one edge portion of the solid image patch pattern are measured. However, the maximum occurrence position of the other edge portion (terminal portion) of the solid image patch pattern is measured. Mmax2 and the minimum occurrence position Mmin2 can also be measured. Also in that case, the optimum width W of the strip-shaped image patch pattern TB can be obtained by using Equation 1.
Furthermore, by measuring both maximum occurrence positions Mmax1 and Mmax2 and minimum occurrence positions Mmin1 and Mmin2 and averaging the widths W obtained respectively, it is possible to obtain a more accurate width W.
In addition, when measuring a plurality of solid image patch patterns, the width W obtained in each case is averaged, or the width W obtained in each case is averaged every time a solid image patch pattern is measured. The width W can be obtained.

  As described above, according to the first embodiment, the measurement method in which the toner image position is directly measured by the specular reflection type optical sensor 41 is used, and variations in characteristics of the optical sensor 41 itself and the optical sensor 41 are measured. The width W of the belt-like image patch pattern TB is set so that the belt-like image minimum value output voltage Vmin is minimized in consideration of the mounting error of the belt-like image. Accordingly, the position of the toner image is measured with high accuracy without being affected by noise and the alignment of the toner images of the respective colors is performed with high accuracy while achieving low cost and high printing speed of the image forming apparatus 1. be able to.

  In the first embodiment, the present invention is applied to a tandem color image forming apparatus that forms toner images of respective colors on a plurality of photosensitive drums 21. However, the application of the present invention is not limited to this. For example, a revolver system (1) in which toner images of each color are sequentially formed on one photoconductor drum, and the toner images of each color are superimposed on an intermediate transfer belt facing the photoconductor drum and then transferred onto a recording medium. Of course, the present invention can be applied to a drum type color image forming apparatus. Even in this case, the same effect as in the first embodiment can be obtained.

Embodiment 2. FIG.
Embodiment 2 of the present invention will be described in detail.
In the second embodiment, in addition to the optimization of the width W of the strip-shaped image patch pattern TB performed in the first embodiment, the toner adhesion amount of the strip-shaped image patch pattern TB is optimized by measurement.

  Here, a case where the amount of toner adhesion is measured before measuring the position of each color toner image will be considered. At this time, solid image patch patterns are sequentially formed while changing the developing bias voltage Vb. These solid image patch patterns are read by the optical sensor, the output voltage is signal-processed by the control unit, and the respective toner adhesion amounts are measured. Then, based on the result, the developing bias voltage Vb at which a predetermined amount of toner adhesion is obtained is determined and set. In such a case, only the solid image average output voltage VSave is detected from the solid image patch pattern, and the change in the voltage waveform appearing at the edge portion of the solid image patch pattern is not considered. .

  In contrast, in the second embodiment, in addition to the solid image average output voltage VSave, the background portion average output voltage VSg and the solid image maximum value output voltage VSmax1 (or the solid image minimum value output voltage VSmin1) are detected. At this time, since the control unit 70 samples the sensor output voltage VS at intervals of several tens of microns, the accuracy is sufficient, but a known peak voltage hold circuit composed of a capacitor is used to accurately measure the extreme value. Also good.

  Table 1 shows the solid image maximum value output voltage VSmax1, the solid image minimum value output voltage VSmin1, and the solid image average output voltage VSave when n solid image patch patterns are formed while changing the developing bias voltage Vb.

Next, from the background average output voltage VSg, the solid image maximum value output voltage VSmax1n (or the solid image minimum value output voltage VSmin1n), and the solid image average output voltage VSaven, which are read from a plurality of solid image patch patterns, The minimum output voltage Vmin of the output voltage of the optical sensor 41 that has read the pattern TB is calculated. Specifically, the strip image minimum output voltage Vmin is:
Vmin = 2 × VSmin−VSave (Expression 2)
Or
Vmin = VSave−2 × (VSmax−VSg) (Formula 3)
Can be obtained.

Since almost the same value is obtained from Equation 2 and Equation 3, Vmin can be calculated if either VSmin or VSmax is obtained. However, when both VSmin and VSmax can be detected, an accurate value Vmin that is more resistant to noise can be obtained by averaging Vmin obtained from each.
These detections can be performed in the same manner at the end of the solid image patch pattern. That is, the solid image average output voltage VSaven once decreases to the solid image minimum value output voltage VSmin2n, increases to the solid image maximum value output voltage VSmax2n, and then decreases to the background portion average output voltage VSg. The band-like image minimum value output voltage Vmin can be calculated using these pieces of information obtained at the end of the solid image patch pattern. When detection is possible at both edge portions of the voltage waveform, the obtained Vmin is averaged to obtain an accurate value Vmin that is more resistant to noise.

  Table 2 shows Vminn for each patch pattern obtained from Equation 2 or Equation 3 described above by varying the developing bias voltage Vb.

The minimum Vminn among the plurality of Vminn is set to the developing bias voltage Vb with a small toner adhesion amount when the optical sensor 41 in which the measurement region N is set large is used because there are many diffuse reflection components from the color toner image. It will be of time. For black toner images, since there is no diffuse reflection component, the larger the amount of toner adhesion, the better. However, the regular reflection component saturates at about 5 g / m ^{2 and} does not fall below the component amount at that time. It can also be fixed at about 6 g / m ² .

In the second embodiment, the development bias voltage Vbmin that minimizes the belt-like image minimum value output voltage Vmin is obtained from Table 2, and this development bias voltage Vbmin is applied to the developing unit (developing roller) to apply the belt-like image patch pattern TB. By forming, the belt-like image minimum value output voltage Vmin can be minimized.
In the second embodiment, since the belt-like image patch pattern TB is formed not only with the optical characteristics of the optical sensor 41 but also with the toner adhesion amount suitable for the color toner reflectance, the belt-like image minimum value output voltage Vmin can be further lowered. it can. Therefore, it is possible to accurately measure the toner image position, which is resistant to noise.

As described above, according to the second embodiment, a measurement method in which the toner image position is directly measured by the regular reflection type optical sensor 41 is used, and variations in characteristics of the optical sensor 41 itself and the optical sensor 41 are measured. The width W of the belt-like image patch pattern TB is set so that the belt-like image minimum value output voltage Vmin is minimized in consideration of the mounting error. Accordingly, the position of the toner image is measured with high accuracy without being affected by noise and the alignment of the toner images of the respective colors is performed with high accuracy while achieving low cost and high printing speed of the image forming apparatus 1. be able to.
Further, since the development bias voltage Vb is set so that the belt-like image minimum value output voltage Vmin is minimized, even when a large amount of diffusion components are introduced, the belt-like image minimum value output voltage Vmin is prevented from increasing, and high accuracy is achieved. Thus, stable toner image position measurement can be performed.

Embodiment 3 FIG.
The third embodiment of the present invention will be described in detail with reference to FIG. 9 and FIG.
The toner image position measurement method according to the third embodiment detects a toner image position measurement error amount that occurs due to poor attachment of the optical sensor 41, and enables more accurate measurement.

FIG. 9 is a diagram showing a state when the attachment failure of the optical sensor 41 occurs and the measurement area N is shifted to the upstream side in the intermediate transfer belt conveyance direction.
As shown in FIG. 9, when the optical sensor 41 is attached with a slight rotation in the clockwise direction, the central axis A of the optical sensor 41 rotates in the clockwise direction around the sensor. Then, the measurement region N moves to the upstream side (the left side in the figure) in the intermediate transfer belt conveyance direction. However, the regular reflection measurement region M that satisfies the regular reflection condition does not shift. Therefore, the position of the regular reflection measurement region M is shifted to the downstream side (right side in the figure) from the center of the measurement region N.

FIG. 10 is a diagram illustrating an output waveform of an output voltage of the optical sensor 41 that has detected the belt-like image patch pattern TB when a defective attachment of the optical sensor 41 occurs as shown in FIG. It is a figure corresponding to FIG.
The position of the strip-shaped image patch pattern TB (the width W is set to 0.8 mm) is shifted by 0.4 mm on the downstream side (the position is 0.0 to 0.8 mm in FIG. 10). The change in the output voltage waveform is basically the same as in FIG. 7, but since the regular reflection measurement region M is shifted downstream from the center of the measurement region N, the initial maximum value VSmax1 is the subsequent maximum value Vmax2. Is bigger than. For the same reason, the transport direction positions Xth1 and Xth2 corresponding to the threshold voltage Vth are downstream of the transport direction positions Xth1 and Xth2 in FIG. 7, and the detected center position Xc of the strip-shaped image patch pattern TB is also downstream. This causes measurement errors.

In the third embodiment, the maximum value voltages Vmax1 and VSmax2 are measured by a known peak voltage hold circuit composed of a capacitor, and the detected value of the center position Xc of the belt-like image patch pattern TB is corrected based on the difference between the values. is doing.
An example of the correction calculation method at this time is shown below.
Assuming that the measured center position of the strip-shaped image patch pattern TB is Xc, the corrected center position Xcc of the strip-shaped image patch pattern TB is obtained by the following equation.
Xcc = Xc-k (VSmax1-VSmax2) (Formula 4)

Here, in the above equation, k is a proportional constant, and if the maximum position (Mmax1, VSmax1) and the minimum position (Mmin1, VSmin1) described in the first embodiment are used,
k =-(Mmax1-Mmin1) / (VSmax1-VSmin1)
... (Formula 5)
Can be obtained roughly.
As described above, in the third embodiment, a more accurate toner image position measurement can be performed by detecting and correcting a toner image position measurement error amount caused by a mounting failure of the optical sensor 41 or the like. it can.

As described above, according to the third embodiment, the measurement method of directly measuring the toner image position by the specular reflection type optical sensor 41 is used, and variations in characteristics of the optical sensor 41 itself and the optical sensor 41 are used. The width W of the belt-like image patch pattern TB is set so that the belt-like image minimum value output voltage Vmin is minimized in consideration of the mounting error. Accordingly, the position of the toner image is measured with high accuracy without being affected by noise and the alignment of the toner images of the respective colors is performed with high accuracy while achieving low cost and high printing speed of the image forming apparatus 1. be able to.
Further, even when an error occurs in the sensor output voltage due to a mounting failure of the optical sensor 41, the local maximum values appearing at both ends (both edge portions) of the output waveform are detected according to the error, and the difference between the values is detected. By correcting the detection value of the center position Xc of the belt-like image patch pattern TB, it is possible to align the toner images of the respective colors with higher accuracy.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 is an overall configuration diagram illustrating an image forming apparatus. FIG. 2 is a schematic diagram illustrating image forming means in the image forming apparatus of FIG. 1. It is a block diagram which shows an optical sensor. It is the figure which looked at the optical sensor of FIG. 3 in the conveyance direction. 6 is a graph showing a relationship between a toner adhesion amount of a toner image on an intermediate transfer belt and an output voltage of an optical sensor. It is the schematic which shows a strip | belt-shaped image patch pattern. It is a figure which shows the output waveform of the output voltage of the optical sensor which detected the strip | belt-shaped image patch pattern. It is a figure which shows the output waveform of the output voltage of the optical sensor which detected the solid image patch pattern. It is the figure which showed the state when the attachment defect of an optical sensor produced. It is a figure which shows the output waveform of the output voltage of the optical sensor which detected the strip | belt-shaped image patch pattern when the attachment failure of an optical sensor arises.

Explanation of symbols

1 image forming apparatus main body (apparatus main body), 2 exposure unit (writing unit),
20, 20Y, 20M, 20C, 20BK Process cartridge,
21 photosensitive drum, 22 charging unit,
23, 23Y, 23M, 23C, 23BK Development section,
24 transfer bias roller, 25 cleaning section,
27 Intermediate transfer belt (intermediate transfer member),
41 optical sensors,
41a LED (light emitting element), 41b photodiode (light receiving element),
TP image patch pattern, TB strip image patch pattern,
M regular reflection measurement area, N measurement area.

Claims (5)

A plurality of image forming means for forming a toner image;
An intermediate transfer body that moves in a predetermined conveyance direction and onto which toner images of respective colors formed by the plurality of image forming means are transferred in an overlapping manner;
An optical sensor that outputs a voltage according to the amount of reflected light including regular reflected light obtained by projecting on a predetermined measurement region on the intermediate transfer member,
A solid image patch pattern having a width in the transport direction larger than the measurement area of the optical sensor is formed on the intermediate transfer member by the image forming unit,
The solid image patch pattern is detected by the optical sensor, and a conveyance direction position on the intermediate transfer body where a maximum value and a minimum value of the output voltage are detected is detected,
A belt-like image patch pattern having a width in the transport direction equal to a distance difference between the transport direction position where the maximum value is detected and the transport direction position where the minimum value is detected is formed by the imaging unit. Formed on the intermediate transfer member,
The belt-shaped image patch pattern is detected by the optical sensor, the center position of the belt-shaped image patch pattern is detected from the output voltage, and the position of the toner image formed on the intermediate transfer member is measured. Image forming apparatus. The image forming means is configured to change a developing bias voltage applied to the developing unit when forming a toner image,
A plurality of the solid image patch patterns are formed on the intermediate transfer member by the image forming means by varying the development bias voltage,
Each of the plurality of solid image patch patterns is detected by the optical sensor, and a maximum value or a minimum value and an average value are read out from the output voltage,
Calculating the minimum value of the output voltage detected by the optical sensor when the belt-like image patch pattern is created on the intermediate transfer member by varying the developing bias voltage;
Among the minimum values of the band-shaped image patch pattern calculated for each development bias voltage, a development bias voltage that minimizes the minimum value is applied to the developing unit, and the band-shaped image patch pattern is transferred onto the intermediate transfer member. The image forming apparatus according to claim 1, wherein the image forming apparatus is formed as follows. The output voltage of the background portion of the intermediate transfer body detected by the optical sensor is set as VSg, the maximum value of the output voltage of the solid image patch pattern detected by the optical sensor is set as VSmax, and the minimum value is set as VSmin. When VSave is set, the minimum value Vmin of the belt-like image patch pattern calculated for each developing bias voltage is
Vmin = 2 × VSmin−VSave
Or
Vmin = VSave−2 × (VSmax−VSg)
The image forming apparatus according to claim 2, wherein the image forming apparatus is calculated by the following formula.   The band-shaped image patch pattern is detected by the optical sensor, and local maximum values appearing at both ends of the output waveform of the output voltage are detected, and the center position of the band-shaped image patch pattern is detected based on the difference in the values. The image forming apparatus according to claim 1, wherein the value is corrected.   When the optical sensor is mounted on or replaced with the apparatus, the center position of the belt-like image patch pattern is detected, the position of the toner image formed on the intermediate transfer member is measured, and the measurement result is stored. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

Images