JP2014126615A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately perform registration correction even when a non-light receiving area is generated in a light-receiving spot of a sensor.SOLUTION: A position correction unit specifies, as first reference positions, positions of a plurality of colors of patch images in a registration correction pattern 61 that is formed by a pattern forming unit when an intermediate transfer belt is in an initial state. The position correction unit also specifies, as second reference positions, positions of a plurality of colors of patch images in a registration correction pattern 62 on a black toner layer 73. The position correction unit further specifies, in performing registration correction when the intermediate transfer belt is used over time, positions of a plurality of colors of patch images in a registration correction pattern that is formed by the pattern forming unit, and corrects the correction amount of respective image forming positions of the plurality of colors specified in the registration correction, on the basis of the first reference positions and the second reference positions.

Description

  The present invention relates to an image forming apparatus.

  In a color image forming apparatus, since a color image is formed with a plurality of colors of toner by a plurality of developing devices, image quality deteriorates when a shift in image forming position (so-called color shift) occurs between colors. For this reason, in a certain image forming apparatus, a resist pattern is formed on a transfer belt, and a shift between colors is detected based on the detection timing of a patch image of each color in the resist pattern by a sensor (for example, refer to Patent Document 1). ).

JP 2003-114551 A

  The surface roughness (that is, light reflection characteristics) of the intermediate transfer belt on which the resist pattern is formed deteriorates as the printing time increases. For example, in the case of an intermediate transfer belt made of a TPU (thermoplastic polyurethane) -based elastic material, the surface roughness (that is, light reflection characteristics) is increased as compared with a polyimide-based relatively hard intermediate transfer belt, and the printing time is increased. to degrade. That is, such an image carrier has a high glossiness in the initial state, but the glossiness gradually decreases with use.

  A sensor used for detecting the amount of color misregistration causes light to enter a patch image of each color, the reflected light is detected by a light receiving element, and the position of the patch image of each color is specified at the timing of the intensity change of the reflected light. This reflected light has a regular reflection component and a diffuse reflection component, and as shown in FIG. 9A, the higher the glossiness (that is, the smoother the surface), the higher the intensity of the regular reflection component, The angular distribution of specular reflection components is narrow. Further, as shown in FIG. 9B, when the glossiness becomes low (that is, when the surface becomes rough), the intensity of the diffuse reflection component becomes high.

  Therefore, since the glossiness of the intermediate transfer belt in the initial state is high, as shown in FIG. 10A, the regular reflection component increases in the reflected light from other than the patch image (that is, the surface material of the intermediate transfer belt). The diffuse reflection component is reduced.

  Then, the glossiness of the intermediate transfer belt decreases with use, and as shown in FIG. 10B, in the reflected light from other than the patch image (that is, the surface material of the intermediate transfer belt), the regular reflection component is the initial value. Less than the state, the diffuse reflection component is greater than the initial state.

  Thus, the reflection characteristics of the intermediate transfer belt surface change with time, and as shown in FIG. 10B, the intensity of the reflected light from the patch image and the intensity of the reflected light from the surface material of the intermediate transfer belt And the position of the patch image is difficult to detect accurately.

  Therefore, the position of the patch image is detected based on the difference between the intensity of the regular reflection component and the intensity of the diffuse reflection component. By using the difference between the intensity of the regular reflection component and the intensity of the diffuse reflection component, the detected value for the patch image and the detected value for the surface of the intermediate transfer belt, as shown in FIG. Therefore, the position of the patch image can be easily detected accurately.

  On the other hand, in the sensor used for detecting the color misregistration amount, a part of the light receiving spot of the reflected light deviates from the light receiving area of the light receiving element due to a deviation of the mounting angle at the time of manufacture, etc., and becomes a non-light receiving area. May end up. When such a non-light receiving area occurs at the end of the light receiving spot in the traveling direction of the intermediate transfer belt (or the opposite direction), the timing at which the patch image is detected varies depending on the reflection characteristics of the intermediate transfer belt. End up.

  As shown in FIG. 12, in the initial state, since the angular distribution of the regular reflection component is narrow and steep as described above (FIG. 9A), the timing at which the intensity change of the regular reflection component sufficient for position detection is obtained. Become slow. On the other hand, in the time-lapse state, the angle distribution of the specular reflection component becomes wide and gentle as described above (FIG. 9B), and the timing at which the intensity change of the specular reflection component sufficient for position detection is obtained is not so late. . For this reason, the timing at which the patch image is detected fluctuates, and an error occurs in the detection position due to the temporal change in the reflection characteristics of the intermediate transfer belt.

  The present invention has been made in view of the above problems, and provides an image forming apparatus that performs registration correction accurately even when a non-light-receiving region of a light receiving spot occurs in a light receiving element of a registration correction sensor. For the purpose.

  In order to solve the above problems, the present invention is configured as follows.

  An image forming apparatus according to the present invention is an image forming apparatus that forms an image with a plurality of color toners, the image bearing member carrying a resist correction pattern having the plurality of color patch images, and the image bearing member on the image bearing member. A sensor that makes light incident on the resist correction pattern and receives reflected light; a pattern forming unit that forms the resist correction pattern on the image carrier; and a sensor that corresponds to the surface of the image carrier and the resist correction pattern. A position for specifying the position of the plurality of color patch images of the registration correction pattern based on the output, and a position for specifying the correction amount of each image forming position of the plurality of colors based on the position of the plurality of color patch images A correction unit. Then, the position correction unit specifies the positions of the patch images of the plurality of colors in the resist correction pattern formed by the pattern forming unit when the image carrier is in an initial state as a first reference position. The pattern forming unit forms a black toner layer on the image carrier, and forms the resist correction pattern on the black toner layer. The position correction unit includes the resist correction on the black toner layer. The position of the patch image of the plurality of colors in the pattern is specified as the second reference position. Further, the position correction unit may perform the registration correction when the image carrier is in a time-lapsed state after the initial state, and the plurality of colors in the registration correction pattern formed by the pattern formation unit. The position of the patch image is specified, and the correction amounts of the image forming positions of the plurality of colors specified by the registration correction are corrected based on the first reference position and the second reference position.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the sensor includes a light receiving element that receives the reflected light, and a part of the light receiving spot of the reflected light on the light receiving element is out of the light receiving region of the light receiving element.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the sensor includes a first light receiving element that receives a regular reflection component of the reflected light, and a second light receiving element that receives a diffuse reflection component of the reflected light. At least a part of the light receiving spot of the reflected light on the first light receiving element is out of the light receiving region.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the position correction unit identifies the position of the black patch image among the patch images of the plurality of colors based on the output of the sensor corresponding to the regular reflection component of the reflected light, and the plurality of colors The position of the patch image of a color other than black is specified based on the output of the sensor corresponding to the diffuse reflection component of the reflected light.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the position correction unit specifies the glossiness of the image carrier in the initial state as the first reference glossiness based on the output of the sensor, and sets the glossiness of the black toner layer as the second reference glossiness. Specifying the glossiness when performing registration correction when the time is after the initial state, specifying the glossiness when performing the registration correction, the first reference glossiness, and the Based on the second reference glossiness, the correction amounts of the image forming positions of the plurality of colors specified by the registration correction are corrected.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the sensor includes a first light receiving element that receives a regular reflection component of the reflected light, and a second light receiving element that receives a diffuse reflection component of the reflected light. The glossiness is a ratio or difference between the intensity of the regular reflection component of the reflected light and the intensity of the diffuse reflection component of the reflected light.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the image carrier is an intermediate transfer belt made of thermoplastic polyurethane.

  According to the present invention, even when a non-light-receiving region of a light receiving spot occurs in the light receiving element of the sensor for registration correction, the registration correction is accurately performed.

FIG. 1 is a side view showing a part of a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration example of the sensor in FIG. FIG. 3 is a diagram illustrating the tilt angle of the sensor in FIG. FIG. 4 is a diagram for explaining a non-light-receiving region due to the tilt angle of the sensor in FIG. FIG. 5 is a block diagram showing a part of the electrical configuration of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a diagram showing an example of a resist correction pattern in the image forming apparatus shown in FIG. FIG. 7 is a diagram illustrating patch images formed on the black toner layer in FIG. 6 and sensor output waveforms obtained from the patch images. FIG. 8 is a diagram for explaining the position detection error of the patch image corresponding to the glossiness change amount of the intermediate transfer belt in the image forming apparatus shown in FIG. FIG. 9 is a diagram for explaining the relationship between the glossiness of the intermediate transfer belt and the angular distribution and intensity of the regular reflection component and diffuse reflection component of the reflected light. FIG. 10 is a diagram for explaining the relationship between the glossiness of the intermediate transfer belt and the sensor output waveforms of the regular reflection component and diffuse reflection component of the reflected light. FIG. 11 is a diagram illustrating a waveform of a difference between the regular reflection component and the diffuse reflection component of the reflected light. FIG. 12 is a diagram for explaining a shift in the detection timing of the patch image due to the non-light receiving area in the reflected light.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a side view showing a part of a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus is an apparatus having an electrophotographic printing function, such as a printer, a facsimile machine, a copying machine, or a multifunction machine.

  The image forming apparatus of this embodiment has a tandem color developing device. The color developing device includes photosensitive drums 1a to 1d, exposure devices 2a to 2d, and developing devices 3a to 3d for the respective colors. The photoconductor drums 1a to 1d are four-color photoconductors of cyan, magenta, yellow, and black. The exposure apparatuses 2a to 2d are apparatuses that form electrostatic latent images by irradiating the photosensitive drums 1a to 1d with laser light. The exposure apparatuses 2a to 2d include a laser diode that is a light source of laser light and optical elements (lenses, mirrors, polygon mirrors, etc.) that guide the laser light to the photosensitive drums 1a to 1d.

  Further, a charging device, a cleaning device, a static eliminator, and the like are arranged around the photosensitive drums 1a to 1d. The charging device charges the photosensitive drums 1a to 1d by a scorotron method or the like. The cleaning device removes residual toner on the photosensitive drums 1a to 1d after the primary transfer, and the static eliminator neutralizes the photosensitive drums 1a to 1d after the primary transfer.

  The developing devices 3a to 3d are equipped with toner containers filled with toners of four colors, cyan, magenta, yellow and black. A developing bias is applied between the developing devices 3a to 3d and the photosensitive drums 1a to 1d, and the developing devices 3a to 3d transfer the toner supplied from the toner containers to the electrostatic on the photosensitive drums 1a to 1d. A toner image is formed by adhering to the latent image. For example, the toner constitutes a developer together with the carrier, and an external additive such as titanium oxide is further added.

  The photosensitive drum 1a, the exposure device 2a, and the developing device 3a develop magenta, and the photosensitive drum 1b, the exposure device 2b, and the developing device 3b develop cyan, the photosensitive drum 1c, and the exposure device 2c. The developing device 3c performs yellow development, and the photosensitive drum 1d, the exposure device 2d, and the developing device 3d perform black development.

  The intermediate transfer belt 4 is an endless (that is, ring-shaped) intermediate transfer body and an image carrier on which the toner images on the photosensitive drums 1a to 1d are primary transferred while being in contact with the photosensitive drums 1a to 1d. . The intermediate transfer belt 4 is stretched around the driving roller 5 and circulates in the direction from the contact position with the photosensitive drum 1d to the contact position with the photosensitive drum 1a by the driving force from the driving roller 5.

  In this embodiment, the intermediate transfer belt 4 is made of thermoplastic polyurethane.

  The transfer roller 6 brings the conveyed paper into contact with the intermediate transfer belt 4 and secondarily transfers the toner image on the intermediate transfer belt 4 to the paper. The sheet on which the toner image has been transferred is conveyed to the fixing device 9 and the toner image is fixed on the sheet.

  The roller 7 has a cleaning brush, and the cleaning brush is brought into contact with the intermediate transfer belt 4 to remove the toner remaining on the intermediate transfer belt 4 after the transfer of the toner image onto the paper.

  The sensor 8 irradiates the intermediate transfer belt 4 with light to detect the toner density and detects the reflected light. During toner density adjustment and registration correction, the sensor 8 irradiates a predetermined region through which a test pattern (toner patch image described later) formed on the intermediate transfer belt 4 passes and detects reflected light of the light beam. The electric signal according to the light quantity is output.

  FIG. 2 is a diagram illustrating a configuration example of the sensor 8 in FIG.

  As shown in FIG. 2, the sensor 8 includes a light source 11 that emits light, a beam splitter 12 on the light source side, a light receiving element 13 on the light source side, a beam splitter 14 on the light receiving side, a first light receiving element 15, A second light receiving element 16.

  The light source 11 is a light emitting diode, for example. The beam splitter 12 transmits the P-polarized component and reflects the S-polarized component of the light from the light source 11. The light receiving element 13 on the light source side is, for example, a photodiode, detects the S-polarized light component from the beam splitter 12, and outputs an electrical signal corresponding to the amount of light. This electric signal is used for stable control of the output light quantity of the light source 11.

  The P-polarized component light that has passed through the beam splitter 12 on the light source side is incident on the surface (toner pattern 21 or surface material) of the intermediate transfer belt 4 and reflected. The reflected light at this time has a regular reflection component and a diffuse reflection component, and the regular reflection component is P-polarized light.

  The beam splitter 14 transmits the P-polarized component (that is, the regular reflection component) of the reflected light and reflects the S-polarized component. The first light receiving element 15 is, for example, a photodiode, detects light of a P-polarized component (that is, a regular reflection component) that has passed through the beam splitter 14, and outputs an electric signal having a voltage corresponding to the amount of light. The second light receiving element 16 is, for example, a photodiode, has light detection characteristics similar to those of the first light receiving element 15, detects light of an S-polarized component (that is, diffuse reflection component) reflected by the beam splitter 14, An electric signal having a voltage corresponding to the amount of light is output.

  FIG. 3 is a diagram for explaining a tilt angle of the sensor 8 in FIG. FIG. 4 is a diagram for explaining a non-light-receiving region caused by the tilt angle of the sensor 8 in FIG.

  The sensor 8 is attached at a predetermined position when the image forming apparatus is assembled. The light source 11 and / or the light receiving element 15 of the sensor 8 due to the mounting accuracy at this time, the variation in the directivity of the light receiving elements 15 and 16 and the light source 11 inside the sensor 8, the behavior of the intermediate transfer belt 4 during rotation, and the like. , 16 have a tilt angle in the traveling direction of the intermediate transfer belt 4, and the incident surface of the light beam by the sensor 8 on the intermediate transfer belt 4 may not be completely perpendicular to the surface of the intermediate transfer belt 4. .

  In such a case, as shown in FIG. 4, a part of the light receiving spot 15a on the first light receiving element 15 due to the reflected light from the intermediate transfer belt 4 becomes a light receiving region 15b (that is, incident light) of the first light receiving element 15. May deviate from the area sensitive to. A region 15c that deviates from the light receiving region 15b is a non-light receiving region. Therefore, in the first light receiving element 15, the substantial shape of the light receiving spot 15a used for detecting the toner density is a shape excluding the region 15c.

  In this embodiment, at least a part of the light receiving spot 15a of the reflected light on the first light receiving element 15 is out of the light receiving region 15b.

  FIG. 5 is a block diagram showing a part of the electrical configuration of the image forming apparatus according to the embodiment of the present invention. In FIG. 5, a print engine 31 controls a toner (not shown) that drives the above-described roller, a bias circuit that applies a primary transfer bias, developing devices 3a to 3d, exposure devices 2a to 2d, and the like. A processing circuit that executes image development, transfer, and fixing, and paper feeding, printing, and paper ejection. The primary transfer bias is applied between the photosensitive drums 1 a to 1 d and the intermediate transfer belt 4.

  Further, the print engine 31 specifies the toner density, the gloss of the surface material of the intermediate transfer belt 4 and the toner layer from the output of the sensor 8, and the position of the patch image of each color in the registration pattern at the time of registration correction. Identify.

  In this embodiment, the print engine 31 specifies the position of the patch image of each color in the registration pattern at the time of registration correction based on the output of the first light receiving element 15 and the output of the second light receiving element 16. . An amplifier or the like is provided between the light receiving elements 15 and 16 and the print engine 31 as necessary.

  The toner density is calculated based on the following equation, for example.

  Toner density [percent] = {1− (PS) / (Po−So)} × 100

  Here, P is the sensor output value (voltage) of the P-polarized component, S is the sensor output value (voltage) of the S-polarized component, and Po is a portion where there is no toner image (that is, the intermediate transfer belt 4). Sensor output value (voltage) of the P-polarized component at the surface material of the S-polarized component, and So is the sensor output value (voltage) of the S-polarized component at the location where there is no toner image (that is, the surface material of the intermediate transfer belt 4). It is.

  The glossiness is a ratio or difference between the sensor output value (voltage) of the P-polarized component and the sensor output value (voltage) of the S-polarized component.

  The print engine 31 performs registration correction for adjusting the image forming position of each toner color periodically or at a predetermined timing. In registration correction, the image forming position of each toner color is set to an appropriate position by adjusting the scanning start timing, the number of scanning lines, and the like of the exposure apparatuses 2a to 2d.

  The print engine 31 includes a pattern forming unit 41 and a position correcting unit 42.

  The pattern forming unit 41 controls the exposure devices 2a to 2d, the developing devices 3a to 3d, etc., performs position control for each toner color based on the correction amount of the current image forming position, and applies the resist correction pattern to the intermediate transfer belt. 4 is formed. The resist correction pattern has a plurality of color patch images. The sensor 8 makes light incident on the resist correction pattern on the intermediate transfer belt 4 and receives reflected light.

  The position correction unit 42 specifies the positions of the patch images of a plurality of colors of the resist correction pattern based on the surface of the intermediate transfer belt 4 and the output of the sensor 8 corresponding to the resist correction pattern, and sets the positions of the patch images of the plurality of colors. Based on this, the correction amount of each image forming position of the plurality of colors is specified.

  For example, the position correction unit 42 compares the difference between the output of the first light receiving element 15 and the output of the second light receiving element 16 with a predetermined threshold, and when the difference exceeds or falls below the threshold, The position of each patch image is specified.

  When the intermediate transfer belt 4 is in an initial state (that is, when the use of the image forming apparatus is started or when the intermediate transfer belt 4 is replaced), the position correction unit 42 includes a plurality of registration correction patterns formed by the pattern forming unit 41. The position of the color patch image is specified as the first reference position.

  The pattern forming unit 41 forms a black toner layer on the intermediate transfer belt 4 and forms a resist correction pattern on the black toner layer, and the position correction unit 42 includes a plurality of resist correction patterns on the black toner layer. The position of the color patch image is specified as the second reference position. Note that the black toner layer is formed with a larger area than the resist correction pattern so that the black toner layer is exposed in a region around each patch image in the resist correction pattern.

  Further, the position correction unit 42 performs patch registration of a plurality of color patch images in the registration correction pattern formed by the pattern forming unit 41 when performing registration correction when the intermediate transfer belt 4 is in a time-lapse state after the initial state. The position is specified, and the correction amount of each image forming position of the plurality of colors specified by the registration correction is corrected based on the first reference position and the second reference position.

  Further, the position correction unit 42 specifies the glossiness of the intermediate transfer belt in the initial state as the first reference glossiness based on the output of the sensor 8, and specifies the glossiness of the black toner layer as the second reference glossiness. , Specifying the glossiness when performing registration correction in a time-lapse state after the initial state, and based on the glossiness when performing registration correction, the first reference glossiness, and the second reference glossiness Thus, the correction amounts of the image forming positions of the plurality of colors specified by the registration correction are corrected.

  For example, the first reference position and the first reference glossiness are associated with each other, and the second reference position and the second reference glossiness are associated with each other, and the glossiness at the time of registration correction is based on the association. An error from the first reference position or the second reference position corresponding to is specified, and the correction amount of the image forming position specified by the registration correction is adjusted by an amount corresponding to the error.

  Next, the operation of the image forming apparatus will be described.

  FIG. 6 is a diagram showing an example of a resist correction pattern in the image forming apparatus shown in FIG. FIG. 7 is a diagram illustrating patch images formed on the black toner layer in FIG. 6 and sensor output waveforms obtained from the patch images. FIG. 8 is a diagram for explaining the position detection error of the patch image corresponding to the glossiness change amount of the intermediate transfer belt 4 in the image forming apparatus shown in FIG.

  In the initial state, first, the pattern forming unit 41 forms a resist correction pattern 61 without a black toner layer, as shown in FIG. 6, on the first turn of the intermediate transfer belt 4. The resist correction pattern 61 includes patch images 71K, 71Y, 71C, and 71M and patch images 72K, 72Y, 72C, and 72M.

  The patch images 71K, 71Y, 71C, and 71M are black, yellow, cyan, and magenta toner patch images for correcting color misregistration in the main scanning direction (width direction of the intermediate transfer belt 4). The patch images 72K, 72Y, 72C, and 72M are black, yellow, cyan, and magenta toner patch images for correcting color misregistration in the sub-scanning direction (advancing direction of the intermediate transfer belt 4). The main scanning direction is based on the position of a patch image of a certain color in the patch images 71K, 71Y, 71C, 71M and the position of a patch image of another color in the patch images 72K, 72Y, 72C, 72M. Thus, the color misregistration is corrected, and the color misregistration is corrected based on the positions of the patch images 72K, 72Y, 72C, and 72M in the sub-scanning direction.

  The density of the patch images 71K, 71Y, 71C, 71M and the patch images 72K, 72Y, 72C, 72M is 100%.

  The position correction unit 42 specifies the positions (that is, the first reference positions) of the patch images 71K, 71Y, 71C, 71M and the patch images 72K, 72Y, 72C, 72M based on the output of the sensor 8, and in the initial state. The glossiness of the surface material of the intermediate transfer belt 4 (that is, the first reference glossiness) is specified.

  Next, in the second turn of the intermediate transfer belt 4 (after the resist correction pattern 61 formed in the first turn described above is removed), the pattern forming unit 41 is black as shown in FIGS. A resist correction pattern 62 is formed on the toner layer 73. The resist correction pattern 62 includes patch images 74K, 74Y, 74C, and 74M and patch images 75K, 75Y, 75C, and 75M.

  The patch images 74K, 74Y, 74C, and 74M are black, yellow, cyan, and magenta toner patch images for correcting color misregistration in the main scanning direction, similarly to the patch images 71K, 71Y, 71C, and 71M. Similarly to the patch images 72K, 72Y, 72C, and 72M, the patch images 75K, 75Y, 75C, and 75M are black, yellow, cyan, and magenta toner patch images for correcting color misregistration in the sub-scanning direction.

  The density of the patch images 74K, 74Y, 74C, and 74M and the density of the patch images 75K, 75Y, 75C, and 75M is 100%, and the density of the black toner layer 73 is lower than the density of the black patch images 74K and 75K. The concentration of

  The position correction unit 42 specifies the positions (that is, the second reference positions) of the patch images 74K, 74Y, 74C, and 74M and the patch images 75K, 75Y, 75C, and 75M based on the output of the sensor 8, and the black toner layer. 73 (that is, the portions where the patch images 74K, 74Y, 74C, and 74M and the patch images 75K, 75Y, 75C, and 75M are not superimposed and the black toner layer 73 is exposed) Specify the standard glossiness.

  As shown in FIG. 7, the output (regular reflection component and diffuse reflection component) of the sensor 8 by the black toner layer 73 at this time is the output of the sensor 8 by the surface material of the intermediate transfer belt 4 when the glossiness is very low. The tendency is similar to (regular reflection component and diffuse reflection component).

  In this way, in the initial state, the pattern forming unit 41 and the position correcting unit 42 specify the first reference position and the second reference position for each toner color, and the glossiness (first level) of the intermediate transfer belt 4 at that time. 1 reference glossiness) and the black toner layer glossiness (second reference glossiness) are specified.

  Then, the position correction unit 42 detects a detection error of the patch image corresponding to the glossiness of the intermediate transfer belt 4 from the relationship between the first reference glossiness and the second reference glossiness and the first reference position and the second reference position. A relational expression or table for specifying is generated and stored in a non-volatile memory or the like. For example, as shown in FIG. 8, a relational expression or table regarding the relationship of the position detection error corresponding to the amount of change from the first reference glossiness is specified.

  At this time, the relational expression or table is generated for each of the main scanning direction and the sub-scanning direction. The relational expression or table is generated only once (for example, at the time of replacement) for each intermediate transfer belt 4.

  Thereafter, at the timing of registration correction, the pattern forming unit 41 causes the intermediate transfer belt 4 to form a resist correction pattern 61 without a black toner layer, as in the first round in FIG.

  Based on the output of the sensor 8, the position correction unit 42 specifies the positions of the patch images 71K, 71Y, 71C, 71M and the patch images 72K, 72Y, 72C, 72M in the registration correction pattern 61, and at this time The glossiness of the surface material of the transfer belt 4 (that is, the glossiness after change with time) is specified.

  Then, the position correction unit 42 specifies an error in the detection position corresponding to the specified glossiness using the above-described relational expression or table, and the patch images 71K, 71Y, 71C, 71M, and the patch are determined only by the error. The positions of the images 72K, 72Y, 72C, and 72M are corrected, and the correction amount of the image forming position for each toner color by the current registration correction is specified.

  Thereafter, until the next registration correction, the print engine 11 forms an image of each toner color with the correction amount of the image forming position.

  As described above, according to the above embodiment, the position correction unit 42 positions the patch images of a plurality of colors in the resist correction pattern 61 formed by the pattern forming unit 41 when the intermediate transfer belt 4 is in the initial state. Is specified as the first reference position. Further, the position correcting unit 42 specifies the positions of the patch images of a plurality of colors in the resist correction pattern 62 on the black toner layer 73 as the second reference position. The position correction unit 42 specifies the positions of the patch images of a plurality of colors in the registration correction pattern formed by the pattern forming unit 41 when performing the registration correction when the intermediate transfer belt 4 is in the time-lapse state. Based on the first reference position and the second reference position, the correction amounts of the image forming positions of the plurality of colors specified by the registration correction are corrected.

  As a result, even if a non-light-receiving area of the light receiving spot occurs in the light receiving element 15 of the sensor 8 for registration correction, the registration correction is accurately performed.

  The above-described embodiments are preferred examples of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. is there.

  For example, in the above-described embodiment, the position correction unit 42 identifies the position of the black patch image among the multiple color patch images based on the output of the sensor 8 corresponding to the regular reflection component of the reflected light. Of the color patch images, the position of the color patch image other than black may be specified based on the output of the sensor 8 corresponding to the diffuse reflection component of the reflected light. In this case, for example, each output of the sensor 8 is compared with a threshold value, and the position of each patch image is specified from the timing when each output exceeds or falls below the threshold value.

  In the above embodiment, the density is changed to form a plurality of black toner layers. For each of the plurality of black toner layers 73, for each density, the reference glossiness of the black toner layer and the reference glossiness are set as described above. The reference position of the patch image is specified, and the correction amount of the image forming position at the time of registration correction may be adjusted using the reference glossiness and the reference position.

  The present invention is applicable to, for example, a tandem color image forming apparatus.

4 Intermediate transfer belt (an example of an image carrier)
8 sensor 15 first light receiving element 16 second light receiving element 41 pattern forming unit 42 position correcting unit 61, 62 resist correcting pattern 71K, 71Y, 71C, 71M, 72K, 72Y, 72C, 72M, 74K, 74Y, 74C, 74M, 75K, 75Y, 75C, 75M Patch image 73 Black toner layer

Claims (7)

In an image forming apparatus that forms an image with a plurality of colors of toner,
An image carrier carrying a resist correction pattern having a patch image of the plurality of colors;
A sensor for receiving light to be incident on the resist correction pattern on the image carrier and receiving reflected light;
A pattern forming portion for forming the resist correction pattern on the image carrier;
Based on the output of the sensor corresponding to the surface of the image carrier and the resist correction pattern, the position of the multiple color patch image of the resist correction pattern is specified, and based on the position of the multiple color patch image, A position correction unit that specifies a correction amount of each image forming position of the plurality of colors,
The position correction unit specifies, as a first reference position, the position of the plurality of color patch images in the resist correction pattern formed by the pattern forming unit when the image carrier is in an initial state,
The pattern forming unit forms a black toner layer on the image carrier, forms the resist correction pattern on the black toner layer,
The position correction unit specifies a position of the patch image of the plurality of colors in the resist correction pattern on the black toner layer as a second reference position;
The position correction unit, when performing registration correction when the image carrier is in a timed state after the initial state, the patch images of the plurality of colors in the registration correction pattern formed by the pattern forming unit. And correcting the correction amount of each image forming position of the plurality of colors specified by the registration correction based on the first reference position and the second reference position.
An image forming apparatus. The sensor has a light receiving element that receives the reflected light,
A part of the light receiving spot of the reflected light on the light receiving element is out of the light receiving region of the light receiving element;
The image forming apparatus according to claim 1. The sensor includes a first light receiving element that receives a regular reflection component of the reflected light, and a second light receiving element that receives a diffuse reflection component of the reflected light,
At least a part of the light receiving spot of the reflected light on the first light receiving element is out of the light receiving region;
The image forming apparatus according to claim 1.   The position correction unit identifies the position of the black patch image among the patch images of the plurality of colors based on the output of the sensor corresponding to the regular reflection component of the reflected light, and the patch image of the plurality of colors The image forming apparatus according to claim 3, wherein the position of the patch image of a color other than black is specified based on an output of the sensor corresponding to a diffuse reflection component of the reflected light.   The position correction unit specifies the glossiness of the image carrier in the initial state as a first reference glossiness based on the output of the sensor, and specifies the glossiness of the black toner layer as a second reference glossiness The glossiness when performing the registration correction when the time-lapse state is after the initial state is specified, the glossiness when performing the registration correction, the first reference glossiness and the second reference glossiness The image forming apparatus according to claim 1, wherein a correction amount of each image forming position of the plurality of colors specified by the registration correction is corrected based on the glossiness. The sensor includes a first light receiving element that receives a regular reflection component of the reflected light, and a second light receiving element that receives a diffuse reflection component of the reflected light,
The glossiness is a ratio or difference between the intensity of the regular reflection component of the reflected light and the intensity of the diffuse reflection component of the reflected light;
The image forming apparatus according to claim 5.   The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer belt made of thermoplastic polyurethane.

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