JP5392156B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

In an image forming process using an electrophotographic system, the following “image density control” is performed in order to always obtain a stable image density.
That is, a test pattern is formed by a plurality of “toner density detection patches” having different toner densities by varying “image forming conditions such as exposure intensity, charging bias potential, and developing bias potential” on the photoconductor and transfer belt. .
The formed test pattern is irradiated with light, the reflected light is detected, and a calculation according to a predetermined algorithm is performed on the detected amount to obtain “toner density of each patch”.

  Development γ and development start voltage: Vk are obtained based on the relationship between the “toner density of each patch” thus obtained and the development potential under the image forming conditions on which the patch is formed.

  “Development γ” is the slope of the “γ curve” representing the relationship between the development potential and the toner density on the “development potential / toner density seat surface” with the development potential on the horizontal axis and the toner density on the horizontal axis. The “starting voltage” is a “horizontal axis intercept” of the γ curve at the development potential / toner density.

  Based on the obtained “development γ”, image forming conditions such as exposure intensity, charging bias potential, and developing bias potential are adjusted so that a developing potential with an appropriate toner density is realized.

  Various types of reflective optical sensors used for detecting the toner density of each patch of a test pattern have been proposed. For example, Patent Document 1 discloses a type in which one LED is used as a light emitting unit, light from the LED is irradiated onto a patch, and reflected light is received by a light receiving unit including two photodiodes. ing.

  In this type of reflective optical sensor, the “size of the light spot that irradiates the patch” is usually 2 to 3 mm. On the other hand, the size of each patch formed is 15 mm or more in both the moving direction of the patch and the direction orthogonal thereto. The size of the patch is “larger than the light spot”, and even if there is a relative positional error between the patch and the light spot, the patch is intended to be appropriately irradiated with the light spot.

  The toner that forms the test pattern is consumed as “non-contributing toner” that does not contribute to the original image formation. For this reason, if the area of the test pattern is increased, the consumption of non-contributing toner is increased in proportion thereto.

  In order to reduce the consumption of non-contributing toner, the area of each patch constituting the test pattern may be reduced. However, since the size of the patch needs to be larger than the light spot, the patch should be made smaller. Has a limit.

  The applicant previously proposed to use a new reflective optical sensor having three or more light emitting sections and three or more light receiving sections to detect toner density on a patch smaller than the conventional one. (Patent Document 2).

  As a specific example, Patent Document 2 discloses a case where the size of a light spot is 2 mm in diameter, the interval between adjacent light spots is 1 mm, and the size of a patch is 1 mm or more. Compared to the case described, the size of the patch can be made extremely small.

  However, in this case, since the size of the patch is smaller than the light spot, when the patch is between adjacent light spots, the area irradiated with the patch is small, and “light use efficiency” used for toner density detection. It is difficult to improve the accuracy of toner density detection.

  In view of the above-described circumstances, the present invention achieves higher accuracy of toner density detection while suppressing consumption of non-contributing toner by using a small patch, and makes it possible to perform toner density detection that is simpler, lower energy, and more efficient. The challenge is to achieve this.

  The image forming apparatus according to the present invention “forms an electrostatic latent image on a photoconductive photosensitive member, visualizes the electrostatic latent image as a toner image, transfers the obtained toner image to a sheet-like recording medium, and fixes it. Thus, an image forming apparatus that forms an image ".

  To add a little about this image forming apparatus, the “image forming apparatus part” excluding the characteristic part described below is a monochrome copier or color copier that has been widely known as an “electrophotographic image forming apparatus”. It can be a two-color copier, a multicolor copier, a color copier, a plotter, a printer, a multifunction printer, or the like.

The “photoconductive photoreceptor” is formed in a drum shape or an endless belt shape, and one or more are used.
An “electrostatic latent image” is formed by uniform charging and exposure of a photoreceptor. The exposure can be performed by optical image irradiation or optical writing. The electrostatic latent image is visualized as a toner image by development.

  The toner image is transferred to a “sheet-shaped recording medium” such as recording paper. The transfer of the toner image onto the sheet-like recording medium can be a direct transfer method in which the toner image is directly transferred onto the sheet-like recording medium from the photosensitive member, or the toner image on the photosensitive member is temporarily “on the intermediate transfer belt”. It is also possible to adopt an intermediate transfer method in which the toner image is transferred to the sheet-like recording medium from the intermediate transfer belt.

  In the direct transfer method, there is a case where the toner image is transferred while the sheet-like recording medium is conveyed to the transfer portion by the endless belt. At this time, the “endless belt” is referred to as a “direct transfer belt”.

  When a plurality of photoconductors are used, an electrostatic latent image is formed on each photoconductor, visualized as a toner image, and the plurality of visualized toner images are transferred onto the same sheet-like recording medium.

  In other words, the present invention can be applied to conventionally known “various types of electrophotographic image forming apparatuses”.

  The image forming apparatus according to the first aspect includes a test pattern forming unit, a reflective optical sensor, an image forming process control unit, and a density detection control unit.

“Test pattern forming means” is means for forming a test pattern with toner on a support member.
The “support member” is a member capable of supporting a test pattern made of toner, and specifically, the “photosensitive member” or the “direct transfer belt or intermediate transfer belt”.
When the photosensitive member is used as a support member, the test pattern is formed by charging and exposing the photosensitive member to form an “electrostatic latent image corresponding to the test pattern”, and the electrostatic latent image is developed to form a “test pattern using toner”. It becomes.

  Therefore, in this case, the “test pattern forming means” includes a charging means for charging the photosensitive member, a means for performing exposure according to the test pattern to form an “electrostatic latent image corresponding to the test pattern”, and an electrostatic latent image. And developing means for visualizing the image.

  When the direct transfer belt or the intermediate transfer belt is used as a support member, the test pattern is formed by forming an electrostatic latent image corresponding to the test pattern on the photosensitive member, and then visualizing with toner by development. It is transferred onto a “direct transfer belt or intermediate transfer belt” to form a test pattern.

  Accordingly, in this case, a charging means for charging the photosensitive member, a means for performing exposure according to the test pattern to form an “electrostatic latent image corresponding to the test pattern”, a developing means for visualizing the electrostatic latent image, and At the same time, the means for directly transferring the visualized pattern to the transfer belt or the intermediate transfer belt constitutes the test pattern forming means.

The “reflective optical sensor” is a sensor for optically detecting the toner density in a test pattern formed on a support member and moving in a predetermined sub-direction.
The “sub direction” is a direction in which the surface of the support member on which the test pattern is formed moves, and a direction orthogonal to the sub direction on the support member surface is referred to as a “main direction”.

  The “image forming process control means” determines the image forming process conditions (various conditions in the image forming process such as the charging conditions of the photosensitive member, the exposure conditions, and the developing conditions such as the developing bias voltage) based on the detection result by the reflective optical sensor. It is a means to determine.

  “Density detection control means” is means for controlling the reflective optical sensor for toner density detection and performing predetermined calculation processing on the output of the reflective optical sensor.

  The “image forming process control means” and the “density detection control means” can be specifically realized as a microcomputer or a CPU. These control means are configured by incorporating each control content into a common microcomputer. Alternatively, they can be configured separately from each other.

  Further, one or both of the image forming process control means and the density detection control means may be incorporated in a control means for comprehensively controlling the image forming apparatus.

  The reflective optical sensor has the following configuration.

That is, the reflective optical element has an illumination system and a light receiving system.
In the “illumination system”, N (≧ 3) light emitting units are arranged at equal intervals in a main direction that is parallel to the support member surface and perpendicular to the sub direction at a predetermined pitch: P, and supports light from each light emitting unit. Irradiate as a light spot on the member.

  In the “light receiving system”, N (≧ 3) light receiving portions are arranged in the main direction in the same direction as the light emitting portions at the same pitch: P corresponding to the N light emitting portions, and emitted from the irradiation system to be “supported”. The light reflected by the “member or test pattern” or “support member and test pattern (patch)” is received.

  In the test pattern forming means, the size in the main direction is “the sum of the size in the main direction of one light spot irradiated on the support member: SD and the pitch of the light emitting portion: P: SD + P”. A test pattern is formed by “patches”.

The test pattern is composed of one or more patches, but the “size in the main direction” is
Since the size of the light spot in the main direction: SD and the pitch of the light emitting parts: P is larger than the sum of the light spots, the “light spot irradiated on the patch” can surely irradiate the surface area corresponding to the patch. For this reason, the use efficiency of light at the time of patch detection is high, and highly accurate toner density detection is possible.

  In addition, since the light from a light emission part is irradiated as a "light spot" on the support member surface, the light beam from a light emission part has directivity. For example, when an LED is used as a light source for a light spot, a “microlens” integrally formed on the light emission surface (light emission source) of each LED may be referred to as “one unit of light emitting portion”. it can. Alternatively, for each LED, a microlens separate from the LED may be combined, and an array of light emitting units may be configured by the LED array and the microlens array.

  It is to be noted that a photodiode (PD) is used as the photoelectric conversion element of the light receiving unit, and the light receiving unit is combined with a microlens array for effectively allowing the reflected light from the support member and the patch to enter the light source conversion unit. It is preferable to construct an array of

The number N of the light emitting units / light receiving units is required to be 3 or more as described above, but the upper limit can be appropriately determined according to the detection range in the main direction by the reflective optical sensor.
“N = 11” is one of the preferred examples as in the example in the case where the “main direction detection range” is relatively small as in the embodiment described later, and “5 ≦ N ≦ 50”. "Is a practical range in the case of a form similar to the embodiment described later.

  The “density detection control means” executes a test pattern position recognition process, a drive system operation determination process, a reflected light acquisition process, and a toner density calculation process when toner density is detected.

The “test pattern position recognition process” is a process for recognizing the “position in the main direction” of the test pattern.
The “irradiation system operation determining step” is a step of determining the operation of the irradiation system.
The “light receiving system operation determining step” is a step of determining the operation of the light receiving system.
The “reflected light acquisition step” is a step of acquiring the “light receiving unit output” of the light receiving unit that has received the light emitted from the irradiation system and reflected by the “support member or test pattern” or “support member and test pattern”. is there.
The “toner density calculation step” is based on “divided output” obtained by dividing the light receiving unit output into “regular reflection contribution due to specular reflection light” and “diffuse reflection contribution due to diffuse reflection”. In this step, the toner concentration is calculated.

  In the image forming apparatus according to claim 1, in the test pattern position recognition step performed by the density detection control means, it is possible to "estimate the position of the test pattern based on the information when the test pattern was last detected". Item 2).

  “Information when the last test pattern is detected” is “information when the test pattern is detected” when the previous image forming process is performed. By using such information, Patent Document 2 can be used. It is not necessary to form the “toner pattern for the preliminary detection step” as in FIG.

  2. The image forming apparatus according to claim 1, wherein when the toner density is detected, the test pattern forming means “forms a test pattern position recognition patch on the upstream side of the test pattern on the support member” and density detection control means. In the test pattern position recognition step performed by the above, it is possible to "irradiate the upper test pattern position recognition patch with light from the irradiation system and estimate the position of the test pattern based on the output of the light receiving unit at this time" (claims) 3).

  In the image forming apparatus according to claim 1, in the test pattern position recognition step performed by the density detection control means, “the most upstream patch of the test pattern on the support member is irradiated with light from the irradiation system, and the light reception at this time is received. It is possible to determine the position of the test pattern based on the output of the section ”.

  In the image forming apparatus according to any one of claims 1 to 4, in the irradiation system operation determining step performed by the density detection control means, a "light emitting unit that emits light in the irradiation system of the reflective optical sensor" and the light emitting unit “At least one of the light emission pattern and the light emission mode” can be determined. As described above, since the “light emitting part” is composed of a light emitting source such as an LED and a microlens, the “light emitting part for emitting light” means a light emitting source for emitting light, but there is no possibility of confusion. Therefore, the above meaning is also referred to as “light emitting part”.

  In the image forming apparatus according to any one of claims 1 to 4, in the light receiving system operation determining step performed by the density detection control means, "the light receiving unit that acquires the light receiving unit output in the light receiving system and the light receiving unit output "At least one of the acquisition timings" can be determined (claim 6).

  4. The image forming apparatus according to claim 2, wherein the density detection control means determines whether the test pattern position estimated in the test pattern position recognition process is correct between the reflected light acquisition process and the toner density calculation process. A test pattern position correct / incorrect determination step ”.

  In the image forming apparatus according to claim 3 or 7, it is preferable that the size of the test pattern position recognition patch in the main direction is “smaller than the size of the test pattern in the main direction” (claim 8).

  The test pattern forming means in the image forming apparatus according to any one of claims 1 to 8, wherein the size in the main direction is the size SD in the main direction of one light spot irradiated on the support member; It is preferable that the test pattern is formed by a patch larger than the pitch of the light emitting portion: twice the sum of P: SD + 2P.

  10. The image forming apparatus according to claim 1, wherein the size of the light spot formed by the reflective optical sensor on the support member in the main direction: SD is “same as the pitch of the light emitting part: P”. (Claim 10). In this way, since the light spots adjacent in the main direction are not separated from each other, the light irradiation to the patch becomes more reliable, and the accuracy of toner density detection can be improved.

  The image forming apparatus according to any one of claims 1 to 10, wherein "a toner image is transferred from a photosensitive member to a sheet-like recording medium via an intermediate transfer belt, and a test pattern is formed using the intermediate transfer belt as a support member. Can be formed "(claim 11).

  The image forming apparatus according to claim 11 is a “tandem image forming apparatus that forms toner images of different colors on a plurality of photoconductors and superimposes the plurality of toner images to form a multicolor image”. Can do. Toner images formed on a plurality of photoconductors are superimposed and transferred onto a common intermediate transfer belt to form a multicolor image (including a color image), and transferred and fixed onto a common sheet-like recording medium. .

As described above, according to the present invention, a novel image forming apparatus can be realized.
In the image forming apparatus according to the present invention, the size of the light spot formed by the irradiation system of the reflective optical sensor is “SD + P” or “SD + P” or Since a test pattern with a patch larger than “SD + 2P” is formed, if the size of the patch in the main direction is reduced, the pitch: P and the size of the light spot: SD are reduced accordingly, and the patch is reduced. The accuracy of toner density detection can be improved while reducing the consumption of non-contributing toner.

  Further, by executing the above steps by the density detection control means, it is possible to realize efficient toner density detection with low energy consumption.

  Therefore, it is possible to perform good image formation by controlling the image forming process more precisely.

1 is a schematic diagram of an embodiment of an image forming apparatus. It is a figure for demonstrating the optical scanning device in embodiment of FIG. It is a figure for demonstrating the optical scanning device in embodiment of FIG. It is a figure for demonstrating the optical scanning device in embodiment of FIG. It is a figure for demonstrating the optical scanning device in embodiment of FIG. It is a figure for demonstrating the test pattern formed in the intermediate transfer belt as a supporting member, and its detection. It is a figure for demonstrating one example of implementation of a reflection type optical sensor. It is a figure for demonstrating a reflection type optical sensor. It is a figure for demonstrating a reflection type optical sensor. It is a figure for demonstrating a printer control apparatus. It is a figure for demonstrating image process control. FIG. 6 is a diagram for explaining toner density detection control. It is a figure for demonstrating the detection of a test pattern. It is a figure for demonstrating the detection of a test pattern. It is a figure for demonstrating the detection of a test pattern. It is a figure for demonstrating the detection of a test pattern. It is a figure for demonstrating the detection of a test pattern. It is a figure which shows an example of the drive timing of the light emission part in the detection of a test pattern, and a light-receiving part. It is a figure which shows an example of the drive timing of the light emission part in the detection of a test pattern, and a light-receiving part. It is a figure which shows an example of the drive timing of the light emission part in the detection of a test pattern, and a light-receiving part. It is a figure which shows an example of the drive timing of the light emission part in the detection of a test pattern, and a light-receiving part. It is a figure which shows an example of the drive timing of the light emission part in the detection of a test pattern, and a light-receiving part. It is a figure which shows an example of the drive timing of the light emission part in the detection of a test pattern, and a light-receiving part. It is a figure which shows an example of the drive timing of the light emission part in the detection of a test pattern, and a light-receiving part. It is a figure which shows an example of the drive timing of the light emission part in the detection of a test pattern, and a light-receiving part. FIG. 6 is a diagram for explaining toner density detection based on a test pattern. It is a figure for demonstrating test pattern detection. FIG. 6 is a diagram for explaining toner density detection. FIG. 6 is a diagram for explaining toner density detection. FIG. 6 is a diagram for explaining toner density detection. FIG. 6 is a diagram for explaining toner density detection. FIG. 6 is a diagram for explaining toner density detection. FIG. 6 is a diagram for explaining toner density detection. FIG. 6 is a diagram for explaining toner density detection. FIG. 6 is a diagram for explaining toner density detection. It is a figure for demonstrating the position detection by a test pattern. It is a figure for demonstrating the position detection by a test pattern. It is a figure for demonstrating the position detection by a test pattern. It is a figure for demonstrating the position detection by a test pattern. It is a figure for demonstrating the position detection of a test pattern It is a figure for demonstrating the position detection by a test pattern. It is a figure for demonstrating the position detection by a test pattern. It is a figure for demonstrating the reflection state of the light from a light emission part. It is a figure for demonstrating the position detection by a test pattern. It is a figure for demonstrating another example of a test pattern. It is a figure for demonstrating the toner density detection by another example of a test pattern. It is a figure for demonstrating the toner density detection by another example of a test pattern. It is a figure for demonstrating the toner density detection by the other example of a test pattern. It is a figure for demonstrating another example of a test pattern.

Hereinafter, embodiments will be described.
First, an outline of a “color printer” as one embodiment of an image forming apparatus will be described with reference to FIG.
The color printer 2000 shown in FIG. 1 is a “tandem multicolor printer that forms a full color image by superimposing black, cyan, magenta, and yellow toner images”.

  The color printer 2000 includes an optical scanning device 2010, four photosensitive drums 2030a, 2030b, 2030c, 2030d, four cleaning units 2031a, 2031b, 2031c, 2031d, four charging devices 2032a, 2032b, 2032c, 2032d, and four developing units. Rollers 2033a, 2033b, 2033c, 2033d, four toner cartridges 2034a, 2034b, 2034c, 2034d, transfer belt 2040, transfer roller 2042, fixing roller 2050, paper feed roller 2054, registration roller pair 2056, paper discharge roller 2058, paper feed A tray 2060, a paper discharge tray 2070, a communication control device 2080, a sensor device 2245, and a printer control device 2090 that comprehensively controls the above-described units are provided.

  In the following, as shown in FIG. 1, an “XYZ three-dimensional orthogonal coordinate system” is assumed, and the direction along the longitudinal direction of each photosensitive drum is defined as the Y-axis direction (direction orthogonal to the drawing of FIG. 1). The direction along the arrangement direction of the photosensitive drums will be described as the X-axis direction.

  The communication control device 2080 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like.

  Each of the photosensitive drums 2030a to 2030d, which is a “photosensitive body formed in a drum shape”, has a photosensitive layer formed on the surface, and the surface is a “scanned surface” of optical scanning by the optical scanning device 2010. . The photosensitive drums 2030a to 2030d are rotated in the direction of the arrow (clockwise) in the plane of FIG. 1 by a rotation mechanism (not shown).

  A charging device 2032a, a developing roller 2033a, and a cleaning unit 2031a are arranged along the rotation direction of the photosensitive drum 2030a so as to surround the photosensitive drum 2030a.

  The photosensitive drum 2030a, the charging device 2032a, the developing roller 2033a, the toner cartridge 2034a, and the cleaning unit 2031a constitute an image forming station (hereinafter also referred to as “K station”) that forms a black image.

  The charging device 2032b, the developing roller 2033b, and the cleaning unit 2031b, which are disposed so as to surround the photosensitive drum 2030b and the photosensitive drum 2030b along the rotation direction thereof, include an image forming station (hereinafter referred to as “C”) that forms a cyan image. Station)).

  The charging device 2032c, the developing roller 2033c, and the cleaning unit 2031c, which are disposed so as to surround the photosensitive drum 2030c and the rotation direction of the photosensitive drum 2030c, include an image forming station (hereinafter referred to as “M”) that forms a magenta image. Station)).

  A charging device 2032d, a developing roller 2033d, and a cleaning unit 2031d, which are disposed so as to surround the photosensitive drum 2030d and the photosensitive drum 2030d along the rotation direction thereof, are arranged in an image forming station (hereinafter, “Y”) that forms a yellow image. Station)).

  The charging devices 2032a to 2032d constitute “charging means” and, together with the optical scanning device 2010, constitute “electrostatic latent image forming means”.

  The charging devices 2032a to 2032d uniformly charge the surfaces of the corresponding photosensitive drums 2030a to 2030d, respectively.

The optical scanning device 2010 responds with a light beam modulated for each color image information based on multi-color image information (black image information, cyan image information, magenta image information, yellow image information) from the “higher-level device”. The surface of the photosensitive drum to be scanned is optically scanned in the Y direction.
As a result, “electrostatic latent images corresponding to each color image information” are formed on the respective photosensitive drums 2030a to 2030d. The formed electrostatic latent image is a so-called “negative latent image” and moves to the corresponding developing roller side as the photosensitive drum rotates.
The optical scanning device 2010 will be described later.

The black toner stored in the toner cartridge 2034a is supplied to the developing roller 2033a, and the cyan toner stored in the toner cartridge 2034b is supplied to the developing roller 2033b.
The magenta toner stored in the toner cartridge 2034c is supplied to the developing roller 2033c, and the yellow toner stored in the toner cartridge 2034d is supplied to the developing roller 2033d.

The developing rollers 2033a to 2033d rotate, and each color toner from the corresponding toner cartridge is thinly and uniformly applied to the surface.
The toner applied to the surface of each developing roller “negative develops” the electrostatic latent image formed on the surface of the corresponding photosensitive drum, and visualizes it as a toner image.
The “toner images having different colors” formed for each photoconductor drum move as the photoconductor drum rotates.

  The transfer belt 2040 is an “intermediate transfer belt”, and yellow, magenta, cyan, and black toner images are sequentially transferred from the photosensitive drums 2030a to 2030d onto the transfer belt 2040 at a predetermined timing, and are superimposed on each other. A color image is formed.

  In this embodiment, the transfer belt 2040 that is an intermediate transfer belt is a “support member on which a test pattern is formed”, and the direction in which the toner image moves along with the rotation of the transfer belt 2040 is the “sub-direction”. A direction (Y-axis direction) orthogonal to the sub direction is the “main direction”.

The recording sheets as the “sheet-like recording medium” stored in the sheet feeding tray 2060 are fed one by one from the sheet feeding tray 2060 by the sheet feeding roller 2054, and the “transfer belt” at a predetermined timing by the registration roller pair 2056. 2040 and the transfer roller 2042 ". The transfer roller 2042 transfers the color image onto the recording paper surface.
The recording sheet to which the color image has been transferred is heated and pressed by a fixing roller 2050 to fix the color image. The recording paper on which the color image has been fixed is discharged onto a discharge tray 2070 via a discharge roller 2058 and sequentially stacked.

  Residual toner on the surface of each photosensitive drum after the toner image transfer is removed by cleaning units 2031a to 2031d.

  Next, the configuration of the optical scanning device 2010 will be described.

As shown in FIGS. 2 to 5, an optical scanning device 2010 as an embodiment of the optical scanning device includes light sources 2200a, 2200b, 2200c, and 2200d, coupling lenses 2201a, 2201b, 2201c, and 2201d, an aperture plate 2202a, 2202b, 2202c, 2202d, cylindrical lenses 2204a, 2204b, 2204c, 2204d, polygon mirror 2104, fθ lenses 2105a, 2105b, 2105c, 2105d, folding mirrors 2106a, 2106b, 2106c, 2106d, 2108a, 2108b, 2108c, 2108d, toroidal lens 2107a, 2107b, 2107c, 2107d, light detection sensors 2205a, 2205b, 2205c, 2205d, light detection mirrors 2207a, 2207 Includes 2207c, 2207d, etc. (not shown) scanning control unit.
As shown in FIG. 5, these are assembled at predetermined positions of an optical housing 2300 (not shown in FIGS. 2 to 4).

  Hereinafter, the direction corresponding to the main scanning direction of the optical scanning is referred to as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is referred to as “sub scanning corresponding direction”.

  The direction along the optical axis of the coupling lens 2201a and the coupling lens 2201b is referred to as “w1 direction”, and the main scanning corresponding direction on the optical path from the light source 2200a and the light source 2200b to the polygon mirror 2104 is referred to as “m1 direction”.

The direction along the optical axis of the coupling lens 2201c and the coupling lens 2201d is “w2 direction”, and the main scanning corresponding direction on the optical path from the light source 2200c and the light source 2200d to the polygon mirror 2104 is “m2 direction”.
The sub-scanning corresponding direction on the optical path from the light source 2200a and the light source 2200b to the polygon mirror 2104 and the sub-scanning corresponding direction on the optical path from the light source 2200c and the light source 2200d to the polygon mirror 2104 are both the same as the Z-axis direction. Direction.

  The light source 2200b and the light source 2200c are arranged at positions separated from each other in the X-axis direction, the light source 2200a is arranged on the “−Z” side of the light source 2200b (see FIG. 3), and the light source 2200d is on the “−Z” side of the light source 2200c. Are arranged (see FIG. 4).

  The coupling lenses 2201a to 2201d are arranged on the optical path of the light beams emitted from the corresponding light sources 2200a to 2200d, and the incident light beams are made substantially parallel light beams.

  Each of the aperture plates 2202a to 220d has an opening, and shapes the light flux from the corresponding coupling lens 2201a to 2201d.

  The cylindrical lenses 2204a to 2204d form images of the light beams that have passed through the openings of the aperture plates 2202a to 2202d in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the “sub-scanning corresponding direction”.

The polygon mirror 2104 has a “structure in which the four-way mirrors having four deflecting reflecting surfaces are stacked in two stages in the Z direction”, and the light flux from the cylindrical lenses 2204a and 2204d in the first (lower) four-sided mirror. Are arranged so as to deflect the light beams from the cylindrical lenses 2204b and 2204c, respectively.
The first-stage tetrahedral mirror and the second-stage tetrahedral mirror are shifted from each other by 45 degrees around the rotation axis, the rotation phase is shifted by 45 °, and the deflection scanning is performed in the first and second stages. And alternately.

  The light beams from the cylindrical lenses 2204 a and 2204 b are deflected on the “−X” side of the polygon mirror 2104, and the light beams from the cylindrical lenses 2204 c and 2204 d are deflected on the “+ X” side of the polygon mirror 2104.

  Each of the fθ lenses 2105a to 2105d has optical characteristics such that the light spot moves at a constant speed in the main scanning direction on the surface (scanned surface) of the corresponding photosensitive drum 2030a to 2030d as the polygon mirror 2104 rotates. It has a non-circular arc surface shape.

  The fθ lenses 2105 a and 2105 b are arranged on the “−X” side of the polygon mirror 2104, and the fθ lenses 2105 c and 2105 d are arranged on the “+ X” side of the polygon mirror 2104.

  As shown in FIG. 5, the fθ lenses 2105a and 2105b are stacked in the Z-axis direction, the fθ lens 2105a is opposed to the first-stage tetrahedral mirror, and the fθ lens 2105b is opposed to the second-stage tetrahedral mirror. Yes. The fθ lenses 2105c and 2105d are also laminated in the Z-axis direction. The fθ lens 2105c is opposed to the second-stage four-sided mirror, and the fθ lens 2105d is opposed to the first-stage four-sided mirror.

The light beam from the cylindrical lens 2204a is deflected by the polygon mirror 2104 and forms a light spot on the photosensitive drum 2030a via the fθ lens 2105a, the folding mirror 2106a, the toroidal lens 2107a, and the folding mirror 2108a. As the polygon mirror 2104 rotates, the photosensitive drum 2030a is optically scanned in the longitudinal direction (Y direction).
The moving direction of the light spot at this time is the “main scanning direction” with respect to the photosensitive drum 2030a, and the rotational direction of the photosensitive drum 2030a is the “sub-scanning direction” with respect to the photosensitive drum 2030a.

The light beam from the cylindrical lens 2204b is deflected by the polygon mirror 2104 and forms a light spot on the photosensitive drum 2030b via the fθ lens 2105b, the folding mirror 2106b, the toroidal lens 2107b, and the folding mirror 2108b. As the mirror 2104 rotates, the photosensitive drum 2030b is optically scanned in the longitudinal direction.
The moving direction of the light spot at this time is the “main scanning direction” with respect to the photosensitive drum 2030b, and the rotational direction of the photosensitive drum 2030b is the “sub-scanning direction” with respect to the photosensitive drum 2030b.

The light beam from the cylindrical lens 2204c is deflected by the polygon mirror 2104 and forms a light spot on the photosensitive drum 2030c via the fθ lens 2105c, the folding mirror 2106c, the toroidal lens 2107c, and the folding mirror 2108c. As the mirror 2104 rotates, the photosensitive drum 2030c is optically scanned in the longitudinal direction.
The moving direction of the light spot at this time is the “main scanning direction” with respect to the photosensitive drum 2030c, and the rotational direction of the photosensitive drum 2030c is the “sub-scanning direction” with respect to the photosensitive drum 2030c.

  The light beam from the cylindrical lens 2204d is deflected by the polygon mirror 2104, and forms a light spot on the photosensitive drum 2030d via the fθ lens 2105d, the folding mirror 2106d, the toroidal lens 2107d, and the folding mirror 2108d. As the mirror 2104 rotates, the photosensitive drum 2030d is optically scanned in the longitudinal direction.

  The moving direction of the light spot at this time is the “main scanning direction” with respect to the photosensitive drum 2030d, and the rotational direction of the photosensitive drum 2030d is the “sub-scanning direction” with respect to the photosensitive drum 2030d.

  A scanning area in the main scanning direction in which image information is written on each photosensitive drum is called an “effective scanning area” or an “image forming area”, but is also called an “effective image area” in this specification.

  The folding mirrors are arranged so that the optical path lengths from the polygon mirror 2104 to the photosensitive drums coincide with each other, and the incident position and incident angle of the light flux to the photosensitive drum are “equal to each other”. Has been.

  The “fθ lens and the corresponding toroidal lens” constitute a “surface tilt correction optical system having a conjugate relationship in the sub-scanning corresponding direction” between the deflection point of the polygon mirror and the corresponding photosensitive drum surface. .

An optical system disposed on the optical path between the polygon mirror 2104 and each photosensitive drum is also referred to as a “scanning optical system”.
In the embodiment being described, the “scanning optical system of the K station” is formed by the fθ lens 2105a, the toroidal lens 2107a, and the folding mirrors 2106a and 2108a. Each of the “station scanning optical systems” is configured.
Similarly, the “M station scanning optical system” is composed of the fθ lens 2105c, the toroidal lens 2107c, and the folding mirrors 2106c and 2108c, and the fθ lens 2105d, the toroidal lens 2107d and the folding mirrors 2106d and 2108d are coupled to the “Y station scanning optical system”. Are each configured.

  Of the light beam deflected by the polygon mirror 2104 and passed through the scanning optical system of the K station, “a part of the light beam before starting writing” enters the light detection sensor 2205a via the light detection mirror 2207a.

  Of the light beam deflected by the polygon mirror 2104 and passed through the scanning optical system of the C station, “a part of the light beam before starting writing” enters the light detection sensor 2205b via the light detection mirror 2207b.

  Of the light beam deflected by the polygon mirror 2104 and passed through the scanning optical system of the M station, “a part of the light beam before starting writing” enters the light detection sensor 2205c via the light detection mirror 2207c.

  Of the light beam deflected by the polygon mirror 2104 and passed through the scanning optical system of the Y station, “a part of the light beam before starting writing” enters the light detection sensor 2205d via the light detection mirror 2207d.

  The light detection sensors 2205a to 2205d output signals (photoelectric conversion signals) corresponding to the amount of received light.

  A “scanning control device” (not shown) determines the scanning start timing of the corresponding photosensitive drum based on the output signal of each photodetection sensor, and the optical scanning device 2010 applies to each photosensitive drum at the determined timing. “Image writing by optical scanning” is started.

  Thereafter, the process of forming the electrostatic latent image, developing, transferring and fixing the toner image, and discharging the transfer paper is executed.

  With reference to FIG. 6, an outline of the test pattern, toner density detection based on the test pattern, and position detection will be described.

FIG. 6 illustrates a state in which a test pattern is formed on the transfer belt 2040 as a support member. Since it is an explanatory diagram, it is noted that the relative sizes of the respective parts are different from the actual size.
As shown in FIG. 6, the lower side of the figure is the “sub-direction”, and the surface of the transfer belt 2040 moves in the sub-direction due to belt rotation.
Reference numeral 201 denotes a “test pattern for toner density detection”. The test pattern 201 includes four types of test patterns 201K, 201M, 201C, and 201Y.

  The test pattern 201K is “a test pattern for detecting the toner density of black toner”, the test pattern 201M is “a test pattern for detecting the toner density of magenta toner”, and the test pattern 201C is “the toner density of cyan toner”. The test pattern 201Y is a “test pattern for detecting the toner density of yellow toner”.

  Each of these test patterns 201K to 201Y is composed of “five patches in which the gradation due to the toner density changes in five steps from the low density to the high density on the side reverse in the sub direction”.

  Each patch has a “long rectangular shape in the sub-direction”.

  As shown in the drawing, the test patterns 201K to 201Y are formed in a row in the sub direction in the “near the center of the main direction (left and right direction in the drawing)” of the intermediate transfer belt 2040.

  Reference numerals 201L, 201CT, and 201R in FIG. 6 indicate “test patterns for position detection”. The test pattern 201L is used for position detection on the left end side in the main direction of the transfer belt 2040, the test pattern 201CT is used for position detection in the center portion of the transfer belt 2040 in the main direction, and the test pattern 201R is used for the transfer belt. 2040 is used for position detection on the right end side in the main direction.

  The position detection by the test pattern 201L will be described later.

  The “sensor device” indicated by reference numeral 2445 in FIG. 1 includes three reflective optical sensors 2445a, 2005b, and 2445c as shown in FIG.

  Of these three reflective optical sensors 2445a to 2445c, the reflective optical sensor 2245b is used for position detection by the test pattern 201L, and the reflective optical sensor 2245c is used for position detection by the test pattern 201L.

  The reflective optical sensor 2445a is used for detection of toner density of each color toner by the test pattern 201 and position detection by the test pattern 201CT.

  In the example in the description, the reflective optical sensors 2445a to 2445c have the same structure, but the reflective optical sensors 2245b and 2245c do not detect "toner density". 2245b and 2245c may be replaced with ones having a simpler configuration, for example, those disclosed in Patent Document 1.

  The reflective optical sensor will be described with reference to FIGS.

  The reflection type optical sensor 2245a will be described as an example.

  FIG. 7A conceptually shows a state in which the reflective optical sensor 2245 is viewed from the main direction.

  The reflective optical sensor 2245a is a "light source array" in which 11 light sources E1 to E11 are arranged and integrated at equal intervals in the main direction, and 11 irradiation microlenses LE1 to LE11 are arranged and integrated in the main direction. “Irradiation microlens array”, “photoelectric conversion array” in which 11 light source conversion units D1 to D11 are arranged and integrated in the main direction, and 11 light receiving microlenses LD1 to LD11 are arranged and integrated in the main direction It has a “light-receiving microlens array” and a “processing device” (not shown).

The light emitting source array is, for example, an LED array, and the eleven light emitting sources L1 to L11 are arranged at a predetermined pitch: P in the main direction.
In the irradiation microlens array, eleven irradiation microlenses LE1 to LE11 are arranged at the same pitch as the pitch P of the light emitting source and corresponding to the light emitting sources E1 to E11.

  The photoelectric conversion unit array is, for example, a PD array, and 11 photoelectric conversion units D1 to D11 are arranged in the main direction at the same pitch as the pitch P of the light source.

  In the light receiving microlens array, 11 light receiving microlenses LD1 to LD11 are arranged in the main direction at the same pitch as the pitch P of the light emitting source.

FIG. 7B shows a correspondence relationship between the light emission sources E1 to E11 and the photoelectric conversion units D1 to D11 of the reflective optical sensor 2245a.
Any one of the light emitting sources is a light emitting source Ei, any one of the irradiation microlenses is an irradiation microlens LEi, any one of the light receiving microlenses is LDi, and any one of the photoelectric conversion units is Di Then, in these, “i = 1 to 11”.

  The upper diagram of FIG. 7C shows the light emitted from the light source Ei (i = 1 to 11) of the intermediate transfer belt 2040 via the corresponding irradiation microlens LEi (i = 1 to 11). The state of irradiating the surface is shown.

  The lower part of FIG. 7C shows the light radiated from the light emission source Ei (i = 1 to 11) (via the corresponding irradiation microlens LEi (i = 1 to 11)), the intermediate transfer belt. The surface of 2040 is shown as a light spot Si (i = 1 to 11).

  As shown in FIG. 7A, the light reflected by the intermediate transfer belt 2040 enters the photoelectric conversion unit Di (i = 1 to 11) via the light receiving micro-les LDi (i = 1 to 11). .

  That is, as shown in FIGS. 7A to 7C, the light emitting source Ei, the irradiation microlens LEi, the light receiving microlens LDi, and the photoelectric conversion unit Di are in the same position in the sub-direction with respect to i = 1 to 11. These are arranged in the main direction at a pitch: P. Therefore, the light spots Si (i = 1 to 11) are also arranged in the main direction at a pitch: P.

  Accordingly, the light emission source Ei and the irradiation microlens LEi constitute a “light emission source” in the reflective optical sensor, and the whole of these light emission sources constitutes an “irradiation system”. Further, the photoelectric conversion unit Di and the light receiving microlens LDi constitute a “light receiving unit”, and the whole of these constitutes a “light receiving system”. The light-receiving microlens LDi is effective in enhancing the light condensing property to the corresponding photoelectric conversion unit Di and enhancing the detection accuracy, but can be omitted in principle.

  A specific example of the reflective optical sensor shown in FIG. 7 will be described. Eleven light emitting sources E1 to E11 are LEDs, and are arranged at equal intervals along the main direction at a pitch of P = 0.4 mm. It has become. The size of the light emitting source Ei (the size of the light emitting surface) is 0.04 mm in both the main and sub directions, and the central emission wavelength is 850 nm.

  The irradiation microlenses LE1 to LE11 individually correspond to the light emission sources E1 to E11, respectively, and are arrayed and integrated at an array pitch of P = 0.4 mm in the main direction to form a microlens array.

  The irradiation microlens LEi (i = 1 to 11) is arranged on the “light receiving part side (left side in FIG. 7A)” with respect to the corresponding light emitting part Ei, and the light beam emitted from the light emitting part Ei is The light is condensed and directed toward the surface of the intermediate transfer belt 2040.

  In order to simplify the description, the light emitted from the light emitting unit Ei (i = 1 to 11) is collected and detected only through the corresponding irradiation microlens LEi (i = 1 to 11). It is assumed that the intermediate transfer belt 2040 is irradiated as light spots Si (i = 1 to 11).

  Further, the surface of the intermediate transfer belt 2040 is smooth, and most of the light irradiated on the surface is regularly reflected. The photoelectric conversion unit Di (i = 1 to 11) is configured such that when the “detection light” from the light source Ei (i = 1 to 11) is irradiated to the intermediate transfer belt 2040, the light receiving units D1 to D11 are Only the regular reflection light of the detection light from the light emission sources E1 to E11 is received.

  The microlens array for irradiation and the microlens array for light reception are integrated, and the integration improves the "workability when assembling these microlens arrays to the detection sensor", and "placement accuracy between microlenses" Can be increased. The lens surface of each microlens can be formed on a glass substrate or a resin substrate using a processing method such as photolithography or molding.

  Each irradiation microlens and each light-receiving microlens include a spherical lens having a condensing function in the main direction and the sub direction, a cylindrical lens having a positive power in the sub direction, and an anamorphic in which the power in the main direction and the sub direction are different. A lens or the like can be used.

  Each photoelectric conversion unit Di is a PD (photodiode), the size of the light receiving surface is 0.35 mm in both the main and sub directions, and the peak wavelength of the light receiving sensitivity is in the vicinity of 850 nm. Each photoelectric conversion unit Di outputs a photoelectric conversion signal corresponding to the amount of received light.

  By making the light emission wavelength of the light emission source Ei substantially coincide with the peak sensitivity wavelength of the photoelectric conversion unit Di, the level of the output photoelectric conversion signal can be maximized.

  The eleven irradiation microlenses LEi (i = 1 to 11) constituting the irradiation microlens array used in the reflective optical sensor shown in FIG. 7 are “a lens diameter, a lens surface curvature radius, and a lens thickness. Is the same.

  Similarly, the 11 light receiving microlenses LDi (i = 1 to 11) constituting the light receiving microlens array have “the same lens diameter, lens surface radius of curvature, and lens thickness”.

However, the lens diameter, the lens surface radius of curvature, and the lens thickness are all different between the irradiation microlens LEi and the light receiving microlens LDi.
In the specific example in the description, the lens diameter: 0.613 mm, the lens surface radius of curvature: 0.430 mm, and the lens thickness: 0.129 mm in the irradiation microlens LEi, and the lens diameter: 0 in the light receiving microlens LDi. 750 mm, lens surface radius of curvature: 0.380 mm, and lens thickness: 0.319 mm.
As shown in FIG. 7A, the optical axis of the irradiation microlens LEi (i = 1 to 11) emits light in order to effectively guide the reflected light of the detection light from the light source Ei to the light receiving unit. It is shifted by Δd = 0.035 mm toward the “light receiving system side” in parallel with the axis perpendicular to the light emitting source Ei through the center of the source Ei.

The optical axis of the light receiving microlens LDi (i = 1 to 11) passes through the center of the light receiving surface of the corresponding photoelectric conversion unit Di (i = 1 to 11) in order to receive more reflected light. Δd ′ = 0.020 mm is shifted to the “irradiation system side” parallel to the axis perpendicular to the axis.
The distance between the irradiation microlens LEi and the light receiving microlens LDi in the sub direction is 0.445 mm. Further, the “interval in the sub direction” between the light emission source Ei and the corresponding photoelectric conversion unit Di is 0.500 mm.
The distance in the optical axis direction from the light emission source Ei to the irradiation microlens LEi is 0.800 mm, and this distance is applicable in all examples shown below. Moreover, the distance of the optical axis direction from the back surface of a micro lens array to a test object is 5 mm.

  As described above, the center interval between adjacent light spots is 0.4 mm, similar to the pitch P of the light source. That is, in the optical layout described above, the size of the light spot Si (i = 1 to 11) formed on the surface of the intermediate transfer belt 2040 by each detection light is about 0.4 mm in diameter, and the pitch of the light source Is the same.

  By making the lens diameter of the light receiving microlens LDi larger than the lens diameter of the “irradiating microlens LEi”, the photoelectric conversion unit Di can receive more reflected light.

  Further, by reducing the lens surface radius of curvature of the light receiving microlens LDi as compared with the lens surface radius of curvature of the irradiating microlens LEi, total reflection inside the lens increases, so that the amount of regular reflection light received by the photoelectric conversion unit Di is increased. It is considered possible to reduce

  By reducing the radius of curvature of the lens surface of the light receiving microlens LDi, the photoelectric conversion unit Di ± 1 adjacent to the photoelectric conversion unit Di corresponding to the light emitting source Ei to be turned on passes through the corresponding light receiving microlens LDi ± 1. Later light rays can be refracted greatly, and as will be described later, it is expected that the number of photoelectric conversion units that can receive diffusely reflected light from the patch increases, and the amount of diffusely reflected light received also increases.

  In the example in the description, the individual microlenses LEi and LDi are “spherical lenses” as described above, and are “plano-convex lenses” as shown in FIG. 7A. The irradiation microlens LEi has a lens incident surface. It has condensing power and the exit surface has no condensing power. In each of the light receiving microlenses LDi, the lens incident surface does not have a condensing power, and the exit surface has a condensing power.

  FIG. 8 is a block diagram showing the electrical circuit configuration of the color printer being described.

As shown in FIG. 8, the color printer includes a printer control device 2090 that controls the above-described units of the computer in an integrated manner. As described above, the printer control device 2009 controls and controls the respective units.
A printer control unit 2090 surrounded by a broken line stores a ROM 405 that preliminarily stores fixed data such as a computer program and the like in a CPU 402 that executes various calculations and drive control of each unit via a bus line 409, and stores various data in a rewritable manner. And an A / D conversion circuit 401 that converts various analog input signals into digital signals.

  The ROM 405 stores a test pattern formation position and density information necessary for generating the test pattern, a bias condition for forming the test pattern gradation, and a reflective optical sensor output for estimating the test pattern toner density. Density conversion information is stored.

The printer controller 2090 is connected to the print controller 410, and transmits image information from a host device such as the PC 411, scanner 412, FAX 413 to the printer controller 2090 as “unified image data”.
Further, a drive circuit 415 that drives a motor and a clutch 417 and a high voltage generator 416 that generates a voltage necessary for image formation are also connected.

  For example, when printing image information from the PC 411, the image information is transmitted using the printer driver of the PC 411. The print controller 410 sends print information from the printer driver to the CPU 402, the CPU 402 drives the drive unit via the drive circuit 415, sends a signal to the image forming station 418, and the image forming station 418 receives the image forming process described above. Execute.

Next, “image process control performed based on a computer program” by the CPU 402 of the printer control apparatus 2090 will be described with reference to FIG.
FIG. 9 is a flowchart showing the flow of execution of image process control.

  “Image process control” determines whether control is necessary when the power switch of the image forming apparatus main body is powered on or when printing is started, and is executed if necessary (S502, S503). .

Immediately after the power is turned on, the heating time of the fixing heater and the preparation time of the print controller 410 are necessary, and the possibility that the image forming process has been left unexecuted up to that point and the usage environment have changed. Image process control may be performed.
Also, during printing (printing), there is a possibility that “replenishment and consumption of toner” and characteristics of the photosensitive drum and the intermediate transfer belt may change, and image process control may be performed.

Immediately after the power is turned on, the image process is performed when the rotation stop time of the photosensitive drum is 6 hours or more, the temperature in the apparatus is changed by 10 ° C. or more, and the relative humidity in the apparatus is changed by 50% or more. Execute control.
Among the above, the rotation stop time of the photosensitive drum is obtained as follows.
In FIG. 8, when the rotation of the photosensitive drum is stopped, time information is acquired from the real-time clock held by the print controller 410 and stored in the RAM 403. Similarly, at the time of power-on, time information is acquired from the real-time clock, and the photosensitive member stop time is obtained from the difference.
The temperature and humidity change can be obtained by acquiring temperature information / relative humidity information from the temperature / humidity sensor 414 when the photosensitive drum is stopped, and similarly obtaining temperature information / relative humidity information from the temperature / humidity sensor 414 at power-on. Obtain “temperature change amount, relative humidity change amount” from the difference.

  During printing, when the number of printed sheets reaches a predetermined number, the printing operation is stopped and “test pattern creation” is performed. The number of prints in this case is determined by the amount of process variation obtained in advance through experiments or the like. In addition to the number of prints, the travel distance of the developing sleeve 305 and the intermediate transfer belt 105 may be a threshold value.

  Next, when it is determined that image process control is necessary, a test pattern is formed (S504).

  That is, the CPU 402 controls the test pattern generator and the image forming station 418 to form the test pattern as shown in FIG.

  As described above, among the test patterns 201 shown in FIG. 6, the test pattern 201 for detecting the toner density is formed with “five gradation patches for each color” for four colors of black, magenta, cyan, and yellow. A test pattern 201 is composed of individual patches.

  On the downstream side of the test pattern 201, test patterns 201CT, 201L, and 201R for position detection are formed near the center and both ends in the effective image area in the main direction of the intermediate transfer belt 2040.

  Image process control includes image density control (development potential control and gradation control) for maintaining the image density, image position correction control for aligning the image position, and the like. The formation conditions are different.

In the development potential control, the development potential (development bias-solid exposure potential) is controlled in order to secure a desired image density (for example, solid density).
“Development γ and development start voltage: Vk” are obtained from the relationship between the toner density obtained by detecting the test pattern 201 and the development potential.
That is, the necessary development potential is expressed in “−kV” units, the desired image density (toner density) and development gamma are both expressed in “mg / cm ² ” units, and the development start voltage: Vk is expressed in “−kV” units. And the following formula:
[Necessary development potential] = [desired image density / development γ] + [development start voltage: Vk]
Is used to determine the “development potential necessary to ensure a desired image density”, and based on this, image forming conditions (exposure power, charging bias, development bias) are determined.

  If the toner charge amount and the development potential are constant, the development γ is “almost maintained”, but in a temperature and humidity change environment, the “toner charge amount change” cannot be avoided, and the gradation of the halftone area is Change. In order to correct this, “gradation control” is performed. The gradation control can also use the “test pattern equivalent to the development potential control”.

When the light source for optical scanning is a semiconductor laser (LD), the toner density for each patch in the test pattern can be varied by fixing the LD power and making the light emission duty variable.
In the gradation control, the “gradation correction look-up table (LUT)” is appropriately changed so that the deviation between the obtained gradation property and the “target gradation property” is eliminated. Specifically, there are a method of rewriting to a new LUT each time, a method of selecting and switching an optimum one from a plurality of LUTs prepared in advance.

  Each patch of the test pattern 201 is formed in a size of 1 mm in the main direction and 2 mm in the sub direction. The center distance between the patches arranged in the sub-direction is 3 mm. As described above, the size (1.0 mm) of each patch in the main direction is determined by the light emitting portion pitch (P = 0.4 mm) in the main direction of the reflective optical sensor and the light spot irradiated on the intermediate transfer belt 2040. It is larger than the sum (0.8 mm) with the size in the main direction (SD = 0.4 mm).

  By setting the size of the main direction of the patch to 1.0 mm, it is possible to reduce the non-contributing toner consumption by 1/15 compared to a conventional patch size of 15 mm or more.

  The “sub-direction size” of each patch of the test pattern 201 is determined according to the number of times of averaging for obtaining the light receiving unit output as will be described later, but if it is set to 2 mm as described above, the sub-direction is also determined. By including small patches, it is possible to reduce non-contributing toner consumption by about 1/100 in total.

“Control for correcting the position of the toner image” is performed as “toner position detection” shown in FIG. 9 (S506).
The test patterns for position detection for this purpose are the test patterns 201CT, 201L, and 201R in FIG. 6. These are the “same image forming conditions” described below, and the center in the effective image area of the intermediate transfer belt 2040. It is formed near the part and both ends.
The position detection test pattern 201CT or the like is preferably “high density” from the viewpoint of detection accuracy. For example, it is preferable to form them under the “image forming conditions for obtaining a solid density” obtained by the above-described development potential control.

  The position detection test patterns 201CT, 201L, and 201R are all the same pattern, and the same “line pattern” having a size of 1.0 mm in the main direction and 0.5 mm in the sub direction is the sub direction. An “oblique line pattern” inclined by 45 ° is formed in the order of K (black), M (magenta), C (cyan), and Y (yellow). The line interval in the sub direction is 1 mm.

  When the test patterns for toner density detection and position detection are formed as described above, first, the toner density of the test pattern 201 is detected using the sensor device 2445 using a reflective optical sensor (S505).

  In “toner density detection”, the toner density of each patch of the test pattern 201 is calculated from the light receiving unit output of the reflective optical sensor 2245a.

  Details of the “toner density detection process” using the reflective optical sensor 2245a will be described later.

  Next, “toner position detection” is performed using the test patterns 201CT, 201L, and 201R for position detection using the reflective optical sensors 2245a to 2245c (S506).

  The toner position detection process will be described later.

  Subsequently, “arithmetic processing for obtaining each characteristic value” is executed from the detection result of the reflective optical sensor 2245a and the like (S507).

  In the “arithmetic process”, the above-described calculation for determining “development γ and development start voltage Vk” is executed from the calculation result of the toner density of each patch. A “least-squares method” can be applied to the linear approximation for obtaining these. An arithmetic process for changing the LUT is also executed.

In addition, “calculation processing related to image position correction” is executed based on the calculated toner position. That is, correction of “registration misalignment”, scan line tilt, color misregistration, and the like of each color.
The color misregistration is defined as misregistration of other colors (M: magenta, C: cyan, Y: yellow in the example in the description) when a certain color (for example, K: black) is used as a reference.

  After the arithmetic processing, image process conditions such as an image forming condition, an LUT, and an image position correction amount are determined (S508).

  Hereinafter, the process of detecting the toner density will be described with reference to FIG.

  When toner density detection is started, first, the position of the test pattern detected by the reflective optical sensor in the main direction is recognized ("test pattern position recognition" S102).

  As shown in FIG. 7C, 11 light spots Si having a diameter of 0.4 mm emitted from the irradiation system are arranged, and the length between the light emitting portions at both ends is 4 mm. The “size in the main direction” of the patch written by the test pattern 201 is 1 mm.

  Although the “position in the main direction” of the test pattern 201 is preferably “overlapping with the center position of 11 light spots (center position of the light spot S6)”, the position error in the main direction of the patch (patch formation) This is not always the case because of misalignment, and the peripheral surface of the photosensitive drum and the meandering surface of the intermediate transfer belt.

  Therefore, “test pattern position recognition” is required in which the position of the test pattern in the main direction is recognized in advance.

  For this recognition, in claim 2, the position of the test pattern 201 in the main direction is estimated based on “last toner density detection information”, that is, information when the previous test pattern 201 was detected.

  For example, it is possible to “estimate in which position in the main direction the test pattern comes” from the “result of the light receiving unit output when the previous test pattern is detected” stored in the memory or the like.

Specifically, it can be determined from the output of the corresponding photoelectric conversion unit Di when the light emission source Ei emits light. That is, when the light emission source Ei (i = 1 to 11) emits light, the photoelectric conversion unit Di receives light “output of regular reflection light from the intermediate transfer belt 2040 and regular reflection light from patches on the intermediate transfer belt 2040. The test pattern 201 exists at the main direction position of the light emitting portion Ei having the largest difference: ΔDi ”.
The “magenta solid patch” shown in FIG. 11A is formed on the most upstream side in the sub-direction of the test pattern 202M using the magenta toner shown in FIG. .)

  FIG. 12A shows the “positional relationship between the light spot and the solid patch” when the “center position in the main direction of the magenta solid patch” is in the main direction position of the light emission source E6. At this time, the size of the solid patch in the main direction is 1 mm, “the sum of the size of the light spot Si (i = 1 to 11) in the main direction: 0.4 mm and the light emitting portion pitch in the main direction: 0.4 mm: 0.8 mm "or more.

In FIG. 11B, when the light source E6 emits light, the photoelectric conversion unit D6 receives the light receiving unit output: “D6 (V)” by “regularly reflected light from the intermediate transfer belt 2040”, and the photoelectric conversion unit D6 receives the light. The difference between the light receiving unit output and the light receiving unit output D6 (par) due to “regularly reflected light from the solid patch” is ΔD6.
In the light spot S6 formed by the light source E6, since all the light constituting the light spot is irradiated to the solid patch and scattered by the toner constituting the solid patch, the light receiving unit output: D6 (par) is the light receiving unit output: D6. Take a value smaller than (be).
In FIG. 11C, when the light emission source E7 emits light, the photoelectric conversion unit D7 receives the light receiving unit output: “D7 (B)” by the “regular reflection light from the intermediate transfer belt”, and the photoelectric conversion unit D7 receives the light. A difference between the light receiving unit output and the light receiving unit output due to “regularly reflected light from the solid patch”: ΔD7.

Light receiving unit output: D7 (Be) and D6 (Be) are “same”, but light receiving unit output: D7 (Par) is larger than the light receiving unit output: D6 (Par).
That is, as apparent from FIG. 11A, the light spot S7 formed by the light source E7 irradiates both the intermediate transfer belt and the solid patch, and therefore the reflected light component scattered by the toner is the light spot. It is smaller than the case of S6. Therefore, ΔD6> ΔD7.
Similarly, when the light source E5 emits light, the light receiving unit output D5 (be) by the regular reflection light from the intermediate transfer belt received by the photoelectric conversion unit D5 and the light receiving unit output D5 by the regular reflection light from the solid patch: D5 ( The difference between the light receiving unit outputs and ΔD5 is ΔD5 <ΔD6.

Further, as is apparent from FIG. 11, since there is no “solid patch” at positions corresponding to the light emission sources E1 to E4 and the light emission sources E8 to E11, the difference between the light receiving unit outputs: ΔD1 to ΔD4, ΔD8 to ΔD11 is zero. is there.
That is, it can be seen that the position of the test pattern (solid patch) in the main direction is a position corresponding to the light spot S6 formed by the light source E6 with i = 6 having the largest difference in light receiving unit output: ΔDi.
Of course, if the variation in detection is ignored, the light receiving unit output: Di (B) is all equal to i = 1 to 11, so that “light receiving unit output: main direction position of the light emitting unit Ei having the smallest Di (P)”. In addition, a test pattern (solid pattern) may exist.

As another example, FIG. 12A shows the light spot and the solid patch when the center position in the main direction of the test pattern “magenta solid patch” is between the light spots S6 and S7 by the light emission sources E6 and E7. The arrangement relationship is shown. At this time, the “size of the solid patch in the main direction” is 1.0 mm.
As shown in FIGS. 12B and 12C, the difference in light receiving unit output when the light emission source Ei (i = 6, 7) emits light: ΔDi is the light emission source Ej (j = 5, 8) emits light. The difference in the light receiving unit output at that time is greater than ΔDj and ΔD6≈ΔD7, so the position of the test pattern (solid patch) in the main direction corresponds to the light spots S6 and S7 formed by the light sources E6 and E7. That is, it can be seen that the light source is between E6 and E7.

  In addition, even if the result of the light receiving unit output is not seen, the position of the test pattern 201 generally changes greatly in the main direction when “the change in the elapsed time and the environmental conditions since the last detection of the test pattern 201 is small”. Therefore, it can be estimated that the position is the same as when it was last detected.

When the “position in the main direction of the test pattern 201” can be recognized as described above, the operation of the irradiation system is determined (“irradiation system operation determination” in FIG. 10) S103.
The “operation to be determined” of the irradiation system includes determination of a light emission source that emits light for detecting the toner density and determination of how the light emission source emits light (light emission pattern and light emission mode). There are two types of light sources that emit light: “several light sources emit light” and “all light sources emit light”.

When several light sources are caused to emit light, the light source to be emitted can be determined based on the “position recognition result in the main direction” of the test pattern 201 described above.
For example, in the example illustrated in FIG. 11, it is possible to determine that the light emission source to emit light is “only the light emission source E6”.
This is because even if the light emission sources E1 to E4 and the light emission sources E8 to E11 emit light, the light spots S1 to S4 and S8 to S11 do not irradiate the patch of the test pattern 201, and thus do not contribute to “toner density detection”.
Further, even if the light sources E5 and E7 are caused to emit light, a part of the light spots S5 and S7 do not irradiate the patch, so that “light utilization efficiency” is small for toner density detection, and the accuracy of toner density detection is low. Therefore, as a necessary minimum, only the light source E6 needs to emit light.

  Further, in order to prevent a problem that the light spot S6 is detached from the patch due to the main-direction position error of the patch when the test pattern 201 is moving in the sub direction, the margins on both sides of the light source E6 are taken into consideration. In addition to the light-emitting portions E5 and E7, the light-emitting sources that emit light can be determined as “three light-emitting sources E5 to E7”.

  The “margin” can be determined by the performance of the image forming apparatus (position shift performance with respect to patch formation, performance with respect to meandering of the photoconductor and intermediate transfer belt, etc.).

  As another example, in the example shown in FIG. 12, the light emission sources E6 and E7 can be determined as the light emission sources to emit light. This is because even if the light emitting sources E1 to E4 and E9 to E11 are caused to emit light, the light spots S1 to S4 and S9 to S11 do not irradiate the patch of the test pattern 201 and thus do not contribute to toner density detection.

Further, even when the light sources E5 and E8 are caused to emit light, a part of the light spots S5 and S8 does not irradiate the patch. Therefore, “light utilization efficiency” is small for toner density detection, and the accuracy of toner density detection is low. .
From this, it is understood that the two light sources E6 and E7 should be made to emit light. In this case, as will be described later, a “toner density calculation result” is obtained for one light emitting source. Therefore, by averaging the toner densities obtained for the two light emitting sources E6 and E7, “1” is obtained. Toner density detection accuracy for one patch ”can be improved.

  Moreover, it is also possible to select only one of the light emitting unit E6 and the light emitting unit E7 and cause only one light emitting unit to emit light as a necessary minimum. Furthermore, the light sources E6 and E7 are given a margin so as not to cause a problem that the light spot S6 deviates from the patch due to the main direction position error of the patch when the test pattern 201 moves in the sub direction. In addition, the light emitting parts E5 and E8 on both sides of the light source can be added, and the light emission sources for emitting light can be four, E5 to E8.

  When all of the light emitting sources E1 to E11 are caused to emit light, “all the light emitting sources of the reflective optical sensor” are used for toner density detection. In this case, regardless of the “recognition result of the main direction position of the test pattern” described above, there is a problem that the patch may be removed from the spot light even if “the main direction position of the test pattern suddenly changes”. Hateful.

  There are “light emission pattern and light emission mode” as to how the light source emits light.

As the “light emission pattern”, when there are a plurality of light emission sources, there are a case where these light sources are simultaneously emitted and a case where light is emitted sequentially.
As the “light emission mode”, there are a case where the light emission source always emits light and a case where pulse light emission is performed. Multiple light sources can cause these to “light up” or “sequentially”.

When a plurality of light sources, for example, two light sources Eα and Eβ, emit light simultaneously, irradiate one patch with the light spots Sα and Sβ, and detect the reflected light with a plurality of photoelectric conversion units, the light spot Sα When the reflected light and the reflected light with respect to Sβ are received by the same photoelectric conversion unit, the “reflected light is mixed” and cannot be separated.
However, when the light sources Eα and Eβ are “sequentially emitted”, even if the reflected light for the light spot Sα and the reflected light for the light spot Sβ are received by the same photoelectric conversion unit, depending on the sequential light emission timing. The light receiving unit output can be “time separated”.

On the other hand, when “the reflected light from the patch is not mixed”, it is possible to simultaneously emit light from a plurality of light emitting sources. Of course, the light may be emitted sequentially.
As a reflection-type optical sensor, if the period of “simultaneously or sequentially emitting” a plurality of light emitting sources once is set as a “line period”, simultaneous emission has an advantage that the line period can be increased.

  Whether or not the reflected light from the patch is mixed depends on the position of a plurality of light sources that emit light, the diffuse reflection characteristics (angle distribution of reflected light) from the patch, the lens shape of the irradiation microlens and the light receiving microlens, etc. Depends on the “layout of each part of the reflective optical sensor”.

  For example, as shown in FIG. 13, the “size in the main direction” of the patch (“magenta solid patch”) of the test pattern 201 is increased to emit light sources E3 and E9 separated in the main direction. As described above, in the case of “separating each other”, it is easy to take a layout in which the reflected light from the solid patch by the light source E3 and the reflected light from the solid patch by the light source E9 are not mixed with each other.

  That is, when the light emission source E3 emits light, the reflected light is received by the photoelectric conversion units D1 to D5, but is not received by the photoelectric conversion units D6 to D11. When the light emission source E9 emits light, the reflected light is received by the photoelectric conversion units E7 to E11, but not received by the photoelectric conversion units D1 to D6. In such a layout, the light sources E3 and E9 can emit light simultaneously.

  In the example shown in FIG. 12, in the case where the light emission sources that emit light are adjacent light emission sources such as “when light emission sources E6 and E7”, the reflected light from the solid patch when the light emission source E6 emits light is converted into a photoelectric conversion unit. Even when light is received by D6 and D7 and the light emission source E7 emits light, the reflected light from the solid patch is received by the photoelectric conversion units D6 and D7.

In such a case, the light received by the photoelectric conversion units D6 and D7 cannot be separated from the light source E6 or the light source E7.
In such a case, the light emitting sources E6 and E7 need to emit light sequentially (in this case, since they are two, alternately) to “separate in time” the light receiving unit output.

  In the example shown in FIG. 12, when the light emission sources to emit light are “four light emission sources E5 to E8”, the light emission sources E5 to E8 are sequentially changed to the light emission sources E5, E6, E7, E8, E5, E6. Repeatedly emits light in the order.

  Next, “light emission mode (when always emitting light and when emitting pulsed light)” will be described.

  In the example shown in FIG. 11, when only the light emission source E6 emits light, the light emission source E6 can always emit light or emit pulse light.

When there are a plurality of light emission sources that emit light, for example, when the light emission sources that emit light are the light emission sources E6 and E7 as in the example shown in FIG. 12, it is necessary to sequentially turn on these light sources. It is necessary to let
As shown in the example shown in FIG. 13, when the light emission sources to emit light are the light emission sources E3 and E9, these can be emitted simultaneously, and each light emission source can always emit light or pulse light. When the light sources E3 and E9 emit light sequentially, each light source needs to emit pulses.

  As described above, when there are a plurality of light emission sources that emit light and these light are emitted sequentially, each light emission source needs to emit pulses. In other cases, the light emission of each light emission source is “always light emission and pulse emission”. “Luminescence” can be selected.

“Always light emission” has an advantage that the number of “light emission / extinguishing times” of the light emission source can be reduced, and the drive circuit becomes easy.
“Pulsed light emission” has the merit of shortening the light emission time, suppressing the deterioration of the light emission source, obtaining the effect of “long life”, and suppressing the temperature rise of the light emission source.

  As described above, in the “irradiation system operation determination step (S103)” in FIG. 10, the light emission source that emits light to detect the toner density and “at least one of the light emission pattern and the light emission mode” of the light emission source are displayed. Can be determined.

  A reflection type optical sensor may be equipped with an “irradiation system drive circuit that can select any of the above”, but the light source is allowed to emit light (light emission pattern and light emission mode). A “circuit” may be built.

  In the former case, “the driving circuit is complicated”, but various operations can be performed on various image forming apparatuses. In the latter case, the “light emission pattern for emitting light from the light emission source and the light emission mode” are determined, so that the drive circuit is easy and the cost can be reduced. The light emission source that emits light is practical because it can be varied depending on “the size of the test pattern 201 in the main direction” and the performance of the image forming apparatus (patch formation position displacement performance, the meandering performance of the photoreceptor and the intermediate transfer belt, etc.). .

  Next, when the “irradiation system operation” is determined as described above, the light reception system operation is determined (“light reception system operation determination” S104 in FIG. 10).

  “Operation to be determined” for the light receiving system includes determination of “photoelectric conversion unit that acquires light receiving unit output” and determination of “light receiving unit output acquisition timing”.

  As the light receiving unit for acquiring the light receiving unit output, there are a case where the light receiving unit output is acquired by some light receiving units and a case where the light receiving unit output is acquired by all the light receiving units.

  When the light receiving unit output is acquired by several light receiving units, the photoelectric conversion unit for acquiring the light receiving unit output can be determined based on the above-described “determination result of light emitting source to emit light”.

For example, in the example shown in FIG. 11, in the case where “only the light emission source E6 emits light”, the photoelectric conversion unit that acquires the light receiving unit output is only the photoelectric conversion unit D6 corresponding to the light emission source E6 and the neighboring photoelectric conversion units. good.
FIG. 14 shows an example of “light receiving unit output distribution” when the light emission source E6 emits light. FIG. 6A shows a light receiving unit output distribution when “reflected light from the intermediate transfer belt” is received by the photoelectric conversion unit Di (i = 1 to 11), and FIG. 5B shows “from the solid patch on the intermediate transfer belt”. It is a light receiving portion output distribution when the “reflected light” is received by the photoelectric conversion portion Di (i = 1 to 11).

  In the cases shown in FIGS. 14A and 14B, five photoelectric conversion units D4 to D8 are necessary for obtaining the light receiving unit output. This is because the photoelectric conversion units D1 to D3 and D9 to D11 have “the light receiving unit output is zero”.

  Similarly, in the example shown in FIG. 12, when the light sources E6 and E7 are sequentially turned on, what is required for the light source E6 is the photoelectric conversion units D4 to D8 and the light source E7. These are photoelectric conversion units D5 to D9, and only six photoelectric conversion units D4 to D9 are necessary.

Similarly, in the example shown in FIG. 13, when two light sources E3 and E9 are turned on simultaneously or sequentially, photoelectric conversion units D1 to D5 are required for the light source E3, and the light source E9 is used. In contrast, since the photoelectric conversion units D7 to D11 are necessary, ten photoelectric conversion units Di (i = 1 to 5, i = 7 to 11) excluding the photoelectric conversion unit D6 are necessary.
Thus, “not acquiring the light receiving unit output unnecessary for toner density detection” leads to a reduction in the amount of data, and a reduction in the amount of calculation in the later-described toner density calculation.

  When all the light receiving unit outputs are acquired, all the light receiving units included in the reflective optical sensor are used to detect the toner density. In this case, all the light receiving unit outputs are acquired regardless of the above-mentioned “result of determination of the light emitting source to emit light”, and if the output is a light receiving unit output that is zero, the calculation of the toner density described later is performed. Used as “zero value”.

  Of course, if the above-described “result of determination of the light emitting sources to emit light is light emission of all the light emitting sources”, all light receiving unit outputs are acquired.

  “Acquisition timing of the light receiving unit output” includes “how much the light receiving unit output is acquired at what timing” while the light emitting source emits light.

  With reference to the example shown in FIG. 11, the case where only the light emission source E6 is allowed to emit light constantly will be described.

The light receiving unit outputs are acquired by “five photoelectric conversion elements D4 to D8”.
FIG. 15A shows a plurality of patches of magenta toner in the test pattern for toner density detection using the reflective optical sensor shown in FIG. 7 (in this case, four gradations and four patches DP1-1). To DP1-4) are formed on the intermediate transfer belt and proceed in the left direction (sub direction) of the drawing.

In this example, the light receiving unit output of the reflected light from the intermediate transfer belt in the “no patch” state is acquired in front (left side) of the four patches.
FIG. 15B shows the timing when the patch passes the position of the light spot, the timing when the light emission source E6 emits light (ON), and the timing when the light receiving unit output is acquired (ON) in accordance with FIG. 15A. It is a timing chart.

The light emission source E6 starts (ON) light emission prior to passing the patch.
Thereafter, the photoelectric conversion units D4 to D8 sample the light receiving unit output once (ON / OFF) at “the position of the intermediate transfer belt without the patch” to obtain the light receiving unit output. The first patch DP1-1 passes through the spot light position while the light source E6 emits light.

  In accordance with the timing, the light receiving unit output is sampled once at “near the center in the sub direction” of the patch DP1-1. Thereafter, in the same manner, sampling is performed once for each of the patch DP1-2, the patch DP1-3, and the patch DP1-4 while the light source E6 is made to emit light.

  After the sampling of the patch DP1-4 is completed and the patch DP1-4 has passed the light spot position, the light emission source E6 is turned off (OFF). That is, while the light emission source E6 is emitting light, sampling is performed once in accordance with the timing at which “the center in the sub direction passes through the light spot” of each of the patches DP1-1 to DP1-4, and the light receiving unit data is acquired. doing.

In FIG. 15A, the “position of the intermediate transfer belt without a patch” is surrounded by a square so as to be an area having the same size as each patch DP1-1, and the area is indicated as “BELT”. However, this area “BELT” does not have to be the same size as each patch.
The “light receiving unit output when there is no patch” can acquire the light receiving unit output at any time when there is no test pattern.

As another example, FIG. 16A shows a timing chart corresponding to FIG. In this example, while the light emission source E6 is emitting light, sampling is performed three times in accordance with the timing when the portions other than the front and rear of each patch pass the light spot, and the light receiving unit output is acquired.
As will be described later, since the toner density calculation result is obtained for one light receiving unit output, the toner density obtained for the three light receiving unit outputs is averaged in the sub-direction (patch moving direction). By doing so, “accuracy of detecting toner density for one patch” can be improved.

  As yet another example, FIG. 16B shows a timing chart corresponding to FIG. Here, the light emission source E6 emits pulses (ON / OFF) in accordance with the timing at which each patch passes the light spot position. The light receiving unit output is sampled once in accordance with the pulse light emission timing of the light emitting unit.

  FIG. 16C shows a case where the “time during which the light emission source E6 emits pulses” is shortened.

  The time during which the light emission source E6 emits a pulse may be shorter than the “time when the patch passes the light spot position”. The effect is great for reducing the amount of light emitted by the temperature rise of the light source. The light receiving unit output is sampled once in accordance with the pulse emission timing of the light source E6.

FIG. 16D shows a case where the light emission source E6 emits pulses, and the light receiving unit output is sampled three times in accordance with the pulse emission timing of the light emission source E6.
In FIG. 16 (e), the light emission source E6 emits pulses twice according to the timing when each patch passes the light spot position, and the light receiving unit output is sampled once according to each pulse emission. This is a case where sampling is performed twice for the patch.

  In FIG. 16F, the light emission source E6 “starts pulse emission” prior to passing the patch. The pulse emission continues until the light is extinguished after passing through the patch DP1-4. The light receiving unit output is always sampled in accordance with the “pulse emission timing” of the light source E6. Among these sampling results, “sampling results of several times for each patch” can be extracted.

  If “the number of times of sampling for each patch required by the image forming apparatus” is set to perform good toner density detection, various acquisition timings can be set in accordance with the irradiation system operation.

  Next, a case where a plurality of light emitting units emit light will be described.

The case where the light emission sources E6 and E7 are caused to emit light sequentially will be described with reference to the example shown in FIG.
The light receiving unit outputs are acquired by the photoelectric conversion units D4 to D9. A timing chart at this time is shown in FIG.

  The light sources E6 and E7 start to emit light sequentially before passing the patch. As described above, the light emission of each of the light emission sources E6 and E7 is pulse light emission. If the sequential light emission that the light source E7 emits / quenches after the light source E6 emits / extinguishes is called one-line light emission, here, two-line light emission is performed.

The line period, which is the line light emission period, is “T”.
The photoelectric conversion units D4 to D9 “sample the light receiving unit output” in accordance with the timing at which the light emitting sources E6 and E7 emit light pulses at the “position of the intermediate transfer belt without the patch” to obtain the light receiving unit output. That is, since the two light emitting sources E6 and E7 emit two lines, the light receiving unit output is sampled four times.
Next, in accordance with the timing when the first patch DP1-1 passes the light spot position, the light emission sources E6 and E7 emit two lines near the center in the sub-direction of the patch DP1-1. The photoelectric conversion units D4 to D9 sample the light receiving unit output four times in accordance with the timing at which each light emitting source emits pulses.
Thereafter, the same operation is performed for the patch DP1-2, the patch DP1-3, and the patch DP1-4.

  As will be described later, since the calculation result of the toner density is obtained for one output of the light receiving unit, the toner density obtained for the light emission of the two light emission sources E6 and E7 that sequentially emit light is averaged in the main direction. Can be Further, since “light receiving unit output twice for one patch” is acquired for each light emission of each light source, the obtained toner density can be averaged in the sub direction. That is, four toner density detection results can be averaged, and the toner density detection accuracy for one patch can be improved.

  Another example is shown in FIG.

Prior to the passage of the patch, the light emission sources E6 and E7 alternately and repeatedly emit light and extinguish at a line cycle: T ′. The photoelectric conversion units D4 to D9 sample the light receiving unit output in accordance with the timing at which each of the light emitting sources E6 and E7 emits pulses, and acquire the light receiving unit output.
The alternate light emission of the light emission sources E6 and E7 ends after passing through the patch DP1-4. From the obtained sampling results, “sampling results of several times for each patch” can be extracted.

  By shortening the line cycle, it is possible to increase the number of times of sampling in the sub direction, and to increase the toner density detection accuracy.

  By performing the above three steps, that is, the test pattern position recognition step, the irradiation system operation determination step, and the light reception system operation determination step, “preparation” for acquiring the light receiving unit output of reflected light for toner density detection is performed. Complete.

After the preparation is completed, the reflected light is acquired to determine the toner density.
FIG. 18 shows how reflected light from the five patches DP1-1 to DP1-5 constituting the test pattern 201M with the magenta toner shown in FIG. 6 is acquired using the reflective optical sensor shown in FIG. Is shown. The vertical direction in the figure is the “main direction”, and the left direction in the horizontal direction is the “sub direction”.

  The light emitting sources E1 to E11 of the irradiation system and the photoelectric conversion units D1 to D11 of the light receiving system are located at “the same position in the main direction”, and the arrangement pitch of the photoelectric conversion units D1 to D11 is the arrangement of the light emitting sources E1 to E11. Equal to the pitch.

  As described above with reference to FIG. 6, the test pattern 201 for detecting the toner density is formed by toner of each color of black, cyan, magenta, and yellow, but the test pattern 201M shown in FIG. “Magenta toner”.

  The test pattern 201M is formed by forming five rectangular patches DP1-1 to DP1-5 with the density changed to five gradations in the sub direction.

  That is, the test pattern 201M is a set of five “rectangular patches” having different density gradations, and these rectangular patches having different density gradations are “the emission duty of a semiconductor laser used as a light source for optical scanning”. It can be formed by “adjustment”. The density can also be changed by the “area gradation method”.

  The density of the five “rectangular patches” constituting the test pattern 201M is lowest in the rectangular patch DP1-1, and the density increases in the order of DP1-2, DP1-3, DP1-4, and DP1-5. Further, an area “BELT” for receiving the reflected light from the intermediate transfer belt without the patch is provided in front (downstream side) of the test pattern 201M.

Each rectangular patch is formed with a size of “1 mm in the main direction and 2 mm in the sub direction”.
The center distance between the patches arranged in the sub-direction is 3 mm. Note that the size of each rectangular patch in the main direction: 1.0 mm is the main direction of the light spot irradiated on the intermediate transfer belt when the pitch of the light emitting portions in the main direction of the reflective optical sensor is P = 0.4 mm. Is larger than the sum of SD = 0.4 mm.

  The light emitting part pitch: P and the size of the light spot in the main direction: SD are substantially the same.

  In the specific example shown in FIG. 18, the results obtained as the “preparation” are shown.

  By the “test pattern position recognition step”, the position of the test pattern 201 in the main direction is “estimated to be the position of the light emission source E3”.

Based on this result, only the light emission source E3 is caused to emit light by the “irradiation system operation determination step”, and the light emission mode is determined as “pulse light emission”.
Subsequently, in the “light-receiving system operation determination step”, the light-receiving unit output is acquired by “five photoelectric conversion units D1 to D5”, and the light-receiving unit output acquisition timing is of the type shown in FIG. In accordance with the timing when each rectangular patch passes the light spot position, the light emission source E3 is caused to emit light, and sampling at the photoelectric conversion units D1 to D5 is performed "once every pulse emission" to obtain the light receiving unit output. Decided to do.

  A procedure for acquiring the reflected light based on the above-mentioned preparation result will be described below.

  In FIG. 18, the test pattern 201M is formed on the surface of the intermediate transfer belt as a support member, moves in the sub direction, and approaches the light spot irradiation region from the reflective optical sensor 2245a.

  Since the timing at which the test pattern 201M is formed is known, pulse emission of the light source E3 is started at an appropriate timing approaching the irradiation area after the formation.

  First, at the intermediate transfer belt position “BELT” where there is no rectangular patch in front of the test pattern 201M, the light emission source E3 emits pulse light, and the photoelectric conversion units D1 to D5 are sampled once in accordance with the timing to output the light receiving unit output. get.

  The surface of the intermediate transfer belt is smooth, and “reflection on the surface of the intermediate transfer belt” of the light spot irradiated from the light source E3 to the belt surface can be regarded as substantially regular reflection, and photoelectric conversion corresponding to the light source E3. The light was received by a total of three parts D3 and photoelectric conversion parts D2 and D4 adjacent thereto. The remaining photoelectric conversion units D1 and D5 do not receive the reflected light.

  That is, when the light spot from the light source Ei is irradiated on the surface of the intermediate transfer belt and regularly reflected by the belt surface, the reflected light is converted into a photoelectric conversion unit Di corresponding to the light source Ei and a photoelectric conversion unit adjacent thereto. Light is received only at Di ± 1.

  The light receiving unit output distribution of the photoelectric conversion units D1 to D5 at this time is shown in FIG. In the figure, D (ALL) on the horizontal axis represents “the output sum of the five photoelectric conversion units D1 to D5”, and the vertical axis represents “a value obtained by normalizing the light receiving unit output of the photoelectric conversion unit D3 to 1.”

  The test pattern 201M moves in the sub direction, and the light emission source E3 emits a pulse at the timing when the first rectangular patch DP1-1 passes the light spot position, and the vicinity of the center in the sub direction of the rectangular patch DP1-1 is light. The photoelectric conversion units D1 to D5 are sampled once in accordance with the timing of passing the spot position, and the light receiving unit output is acquired.

The reflected light of the light spot irradiated on the rectangular patch DP1-1 formed on the intermediate transfer belt includes the diffuse reflected light scattered by the toner constituting the rectangular patch and the positive light reflected on the surface of the intermediate transfer belt. It consisted of reflected light and was received by a total of five photoelectric conversion units D1 to D5.
The light receiving unit output distribution at this time is shown in FIG. In the rectangular patch DP1-1, since the toner is present on the intermediate transfer belt, the light receiving portion output distribution is different from the light receiving portion output distribution (due to reflection on the intermediate transfer belt) in FIG.
The light receiving unit output distribution in FIG. 19B is due to “diffuse reflected light is generated by the toner constituting the rectangular patch DP1-1 and regular reflected light from the surface of the intermediate transfer belt is reduced”.

  The test pattern 201M further moves in the sub-direction, and the light emission source E3 emits a pulse at the timing when the rectangular patch DP1-2 passes the light spot position, and the vicinity of the center of the rectangular patch DP1-2 in the sub-direction is present. The light receiving parts D1 to D5 are sampled once in accordance with the timing of passing the spot light position, and the light receiving part output is acquired.

  Since the rectangular patch DP1-2 has a "higher density" toner density than the rectangular patch DP1-1, "diffuse reflected light by toner" increases compared to the rectangular patch DP1-1, and intermediate transfer is performed. The specular reflection light from the belt surface is further reduced. As a result, the light receiving portion output distribution was as shown in FIG.

  In the same manner as described above, the light receiving unit output distributions acquired for the rectangular patches DP1-3 to DP1-5 are shown in FIGS.

  In this way, the reflected light from the test pattern 201M composed of the intermediate transfer belt portion ("BELT") and the five-tone rectangular patches DP1-1 to DP1-5, that is, the light receiving unit output distribution can be acquired.

  Next, “test pattern position correct / incorrect determination (S106)” of FIG. 10 is performed based on the light receiving unit output obtained in the reflected light acquisition step.

  This determination is “can be omitted”, but it is preferable to perform the determination when the position is estimated in the test pattern position recognition step. However, as will be described later, the above determination is unnecessary when the position of the test pattern is directly detected and determined.

  When some unexpected cause acts and "the test pattern does not exist at the position estimated in the test pattern position recognition process", the acquired light receiving unit output distribution "does not include diffuse reflection light from the rectangular patch" Therefore, the result of “the same as when the intermediate transfer belt is detected” is obtained as the light receiving unit output distribution.

Thereby, it can be determined that “estimation of the test pattern position is not correct”.
In addition, if the test pattern “moves in the main direction more than the position estimated in the test pattern position recognition process” and the light spot “irradiates only a part of the rectangular patch”, diffusion from the rectangular patch Since the amount of reflected light is small, it can be determined that “estimation of the test pattern position is incorrect” by comparison with previously acquired data.

  As described above, when it is determined that the test pattern position is not correct and the test pattern detection is not normally performed, it is necessary to execute the toner density detection step again.

  When the test pattern position correct / incorrect determination is “appropriate” or “when the determination is omitted”, the toner density is calculated from the light receiving unit output obtained in the “reflected light acquisition step (S105)” of FIG. .

  Taking the case of the rectangular patch DP1-1 described above as an example, a toner density calculation method will be described.

When a test pattern does not exist on the intermediate transfer belt, as shown in a schematic diagram in FIG. 28A, almost all of the spot light irradiated on the intermediate transfer belt is regularly reflected on the surface of the intermediate transfer belt.
When the light reflected from the surface of the intermediate transfer belt is received by the five photoelectric conversion units D1 to D5 of the detection light from the light emission source E3, the light reception unit outputs in the three photoelectric conversion units D2 to D4 are not 0, but photoelectric conversion The light receiving part outputs in the parts D1 and D5 are 0 (FIG. 20A).
This is because the specularly reflected light from the intermediate transfer belt has a “beam size incident on the light receiving microlenses LD2 to LD4 corresponding to the photoelectric conversion units D2 to D4” on the light receiving microlens array of the reflective optical sensor. Because it is.

  That is, the “regular reflection light” spreads in the main direction, enters the light receiving microlens LD3 and the light receiving microlenses LD2 and LD4 adjacent to both, and enters the photoelectric conversion units D2 to D4. The light does not practically enter the microlens and does not enter the other photoelectric conversion unit.

When the test pattern (rectangular patch DP1-1) exists on the intermediate transfer belt, as shown in the schematic diagram of FIG. 28B, the light spot irradiated to the intermediate transfer belt and the toner is the surface of the intermediate transfer belt. The light is roughly divided into light that is regularly reflected from the light and scattered light that is scattered by being reflected and refracted at least once by the toner.
The latter scattered light includes light that is scattered in the same direction as the regular reflection from the surface of the intermediate transfer belt, but the amount of light is so small that it cannot be distinguished from the light that is regularly reflected from the surface of the intermediate transfer belt. Conceivable.

Reflected light resulting from the intermediate transfer belt is referred to as “regular reflection contribution”, and reflected light resulting from toner is referred to as “diffuse reflection contribution”.
Thus, since the reflected light from the intermediate transfer belt and the toner includes the regular reflection contribution and the diffuse reflection contribution, none of the light receiving unit outputs of the five photoelectric conversion units D1 to D5 becomes 0 (FIG. 20). (A)). This is because the diffusely reflected light has a beam size incident on the light receiving microlenses LD1 to LD5 corresponding to the photoelectric conversion units D1 to D5 on the light receiving microlens array of the reflective optical sensor. is there.

  When the light emission source E3 emits light, the photoelectric conversion unit D3 receives only specular reflection light. Therefore, the main part of the light reception unit includes only the “regular reflection light contribution”, but the other four light receptions except the light reception unit D3. The light receiving unit outputs in the parts D1, D2, D4, and D5 all include “diffuse reflection contribution”.

  The light receiving unit outputs in the two photoelectric conversion units D1 and D5 include only “diffuse reflection contribution”. This is a result of the regular reflection light from the intermediate transfer belt being received by only the three photoelectric conversion units D2 to D4 when the light spot irradiates only the intermediate transfer belt.

  Accordingly, the light receiving unit outputs from the two photoelectric conversion units D2 and D4 are “regular reflection contribution” and “diffuse reflection contribution” by the rectangular patch DP1-1 irradiated by the light spot from the light emission source E3. It will be mixed.

  The light receiving unit output obtained as shown in FIG. 20A can be divided into a regular reflection contribution and a diffuse reflection contribution.

  Next, a method of obtaining the mixture ratio in the photoelectric conversion units D2 and D4 in which the regular reflection contribution and the diffuse reflection contribution are mixed will be described.

The light receiving portion output distribution with respect to the intermediate transfer transfer belt is “regular reflection contribution itself” and is known as shown in FIG.
Therefore, the “light receiving portion output distribution for the intermediate transfer belt” shown in FIG. 19A is subtracted by a constant from the light receiving portion output distribution for the rectangular patch DP1-1 shown in FIG. 19B. Thus, “diffuse reflection contribution only” can be extracted from the light receiving unit outputs of the photoelectric conversion units D2 and D4 of the reflected light from the rectangular patch DP1-1. Assuming that this constant is “α1”, this is determined as follows.

Since the “light receiving unit output of the photoelectric conversion unit D3 with respect to the rectangular patch DP1-1” due to the light emission of the light emitting source E3 is a regular reflection contribution, the light receiving unit output of the photoelectric conversion unit D3 in FIG. The constant α1 may be obtained so that “a constant of the light receiving unit output of the photoelectric conversion unit D3: α1 times” in FIG.
In this way, as shown in FIG. 20A, from the “regular reflection contribution” obtained by multiplying the light receiving portion output distribution of FIG. 19A by a constant: α1, and the light receiving portion output distribution of FIG. 19B. The output distribution in FIG. 19A can be divided into “diffuse reflection contribution” obtained by subtracting the constant: contribution of regular reflection obtained by multiplying α1.

  That is, when the light receiving unit output of the photoelectric conversion unit D3 in FIG. 19A is “A” and the light receiving unit output of the photoelectric conversion unit D3 in FIG. 19B is “A1”, “A” is “regular reflection”. “Only the contribution” and “A1” are the portions that are reduced by the “diffuse reflection by the toner in the rectangular patch DP1-1” from the portion that should be the regular reflection contribution: A.

Therefore, α1 · A = A1
Then, the diffuse reflection contribution is
A-α1 · A = (1-α1) A
It becomes.
Accordingly, when the light spot from the light source E3 irradiates the rectangular patch DP1-1, the regular reflection contribution is “A1”, that is, “α1 · A”, and the diffuse reflection contribution is “(1-α1)”. A "and both contributions can be separated.

  Similarly, for the patches DP1-2 to DP1-5 having the respective densities in FIGS. 19C to 19F, as shown in FIGS. 20B to 20E, the regular reflection contribution and the diffuse reflection contribution are obtained. And can be separated. In this case, instead of the constant: α1, constants: α2 to α5 (determined in the same manner as described above) may be used.

  For each of the rectangular patches DP1-1 to DP1-5, with respect to the regular reflection contribution and the diffuse reflection contribution divided as described above, the light receiving unit output of each photoelectric conversion unit: Di (for convenience, reference numeral of the photoelectric conversion unit) 21 (a) and (b) are plotted with D (ALL) for each rectangular patch, where D (ALL) = D1 + D2 + D3 + D4 + D5.

The sum of the regular reflection contributions: D (positive) is “the light receiving unit output of the photoelectric conversion unit D 1: D 1 and the light receiving unit output of the photoelectric conversion unit D 5: D 5 are both 0”.
D (ALL) ≡D (positive) = D3 + (regular reflection contribution of D2 and D4)
It becomes.
About the sum of the diffuse reflection contribution: D (expansion), since the light receiving unit output D3 of the photoelectric conversion unit D3 is 0,
D (ALL) = D (expansion) = D1 + (diffuse reflection contribution of D2 and D4) + D5
It becomes.

The sum of regular reflection contributions D (positive) shown in FIG. 21A decreases in the order of rectangular patches DP1-1 to DP1-5 as the toner density increases.
This is because the higher the toner concentration, the more toner is attached, and the amount of specularly reflected light decreases. The toner concentration and D (positive) have a one-to-one correspondence.

  In other words, the toner density corresponding to the calculated D (positive) is obtained.

In contrast, the sum D (expansion) of the diffuse reflection contribution shown in FIG. 21B is maximal with respect to the rectangular patch DP1-3 and is not a “monotonic function”.
Therefore, it is possible but not always easy to obtain the relationship between the toner density and D (expansion) from D (expansion) shown in FIG.

  Intuitively, D (expansion) seems to be “as the density of the toner constituting the rectangular patch increases, the amount of adhering toner increases, and thus increases due to an increase in diffuse reflection light”. This is not the case in (b).

  This is due to the subtraction calculation of the light receiving unit output result using the constants α1 to α5 described above.

The result of obtaining D (expanded) / D (positive) is shown in FIG.
The vertical axis shown in FIG. 22: D (expanded) / D (positive) indicates a “monotonic function” that increases as the density of the toner forming the rectangular patch increases in the order of the patches DP1-1 to DP1-5. It has become. Therefore, by calculating “D (expanded) / D (positive)”, the toner density corresponding to each rectangular patch (horizontal axis in FIG. 22) can be obtained.

The reflective optical sensor in the description has a plurality of light emitting portions in one sensor, and the light spots by the detection light are arranged side by side in the main scanning direction, so that rectangular patches arranged in a plurality of rows in the main direction are simultaneously attached. Can be irradiated.
In addition, there are a plurality of light receiving units, and the roles (when receiving regular reflection light, when receiving diffuse reflection light, or both) change according to each light emitting unit, so Separation into regular reflection contribution and diffuse reflection contribution ”is possible. From this, it is possible to simultaneously detect “rectangular patches arranged in a plurality of rows” with one reflective optical sensor.

  When the rectangular patches arranged in a plurality of rows in the main direction are illuminated by the “light source of the light emitting unit” in sequence, strictly speaking, there is a slight time difference in the illumination time, but within one line scanning. If rectangular patches arranged in a plurality of rows can be detected, it can be regarded as simultaneous detection.

  Further, since the light emitting portion is very small, the light spot can be reduced, and the size of the rectangular patch can be reduced. Furthermore, the proximity of the light-emitting part and the light-receiving part makes it possible to reduce the incident angle and reflection angle of detection light to the intermediate transfer belt and the rectangular patch, and the intermediate transfer belt becomes a shadow of toner. It is also possible to reduce the influence of the detection error due to the influence of the “factor” and the vibrational fluctuation of the surface of the intermediate transfer belt (the fluctuation in the distance between the reflective optical sensor and the intermediate transfer belt).

  Since the patches constituting the test pattern can be reduced, the consumption of non-contributing toner that does not contribute to image formation can be reduced.

  As described above, the sum of the regular reflection contributions to the five-gradation rectangular patches DP-1 to DP1-5: D (positive) and the sum of the diffuse reflection contributions: D (expansion) can be obtained.

FIG. 23A shows “relative regular reflectance” obtained by normalizing the regular reflection contribution shown in FIG. 21A with a reference value (here, the regular reflection contribution due to the surface of the intermediate transfer belt).
FIG. 23B shows a value obtained by normalizing “D (expansion) / D (positive)” shown in FIG. 22 with a reference value (here, the diffuse reflection contribution at the maximum density).

  Thus, a new value is obtained using a value obtained by dividing the sum of the diffuse reflection contributions: D (expansion) by the sum of the regular reflection contributions: D (positive): D (expansion) / D (positive). The toner density may be obtained.

Using the calculation algorithm as described above, D (positive) or D (expanded) / D (positive) is calculated, and from this, toner concentration: [mg / cm ² ] can be obtained.

  Next, “toner position detection (S506)” in the image forming process control shown in FIG. 9 will be described. The toner position detection is performed subsequent to “toner density detection (S505)”.

  As shown in FIG. 6, the toner position detection is performed using a reflection type optical sensor 2445a and reflection type optical sensors 2245b and 2245c used for toner density detection and using test patterns 201CT, 201L and 201R for position detection.

  As described above, in the example being described, the reflection type optical sensors 2245a to 2245c have the same structure, and therefore the position detection using the reflection type optical sensor 2245a and the test pattern 201CT will be described as an example.

  The test pattern 201CT for position detection includes a “line pattern having a size of 1.0 mm in the main direction and a size of 0.5 mm in the sub direction”, and an “oblique line pattern” obtained by inclining the same 45 °, black, magenta, They are formed in the order of cyan and yellow. The line interval in the sub direction is 1 mm.

FIG. 24A schematically shows the reflective optical sensor (2245a) and the test pattern 201CT.
In the test pattern 201CT, line patterns LPK1, LPM1, LPC1, and LPY1 parallel to the main direction are formed at equal intervals from the downstream side (reflection-type optical sensor side) in the sub-direction (left-right direction in the figure) toward the upstream side. On the upstream side, oblique line patterns LPK2, LPM2, LPC2, and LPY2 inclined at 45 degrees with respect to the main direction are formed at equal intervals.

  The line pattern LPK1 and the oblique line pattern LPK2 are made of black toner, the line pattern LPM1 and the oblique line pattern LPM2 are made of magenta toner, the line pattern LPC1 and the oblique line pattern LPC2 are made of cyan toner, and the line pattern LPKY and the oblique line pattern LPKY. Are formed by yellow toner.

  In FIG. 24A, the test pattern 201CT is formed on the intermediate transfer belt so that the center position in the main direction of the line pattern LPK1 and the like matches the center position of the light emission source E3 of the reflective optical sensor. Shall.

  The printer control device 2090 (FIG. 1) measures the timing at which the position detection test pattern 201CT approaches the reflective optical sensor and causes the light emission source E3 to emit light continuously.

  The light spot from the light source E3 sequentially irradiates the line pattern LPK1 to the oblique line pattern LPY2 constituting the test pattern 201CT as the intermediate transfer belt 2040 rotates.

The printer controller 2090 temporally tracks the output signal of the photoelectric conversion unit D3 of the light receiving unit corresponding to the light emission source E3. FIG. 24B shows a schematic diagram of the output signal.
The output signal of the photoelectric conversion unit D3 is high when an intermediate transfer belt is detected, and is low when a toner test pattern patch (line pattern, diagonal line pattern) is detected.

  In this way, the time from when the light spot irradiates the line pattern LPK1 to the next line pattern LPM1: Tkm, the time from when the light spot irradiates the line pattern LPK1 to the line pattern LPC1. : Tkc, the time from when the light spot irradiates the line pattern LPK1 to the irradiation of the line pattern LPY1, Tky is detected (FIG. 24B).

  In addition, the output signal of each photoelectric conversion part shall be amplified and shall pass through the comparison circuit compared with a predetermined reference value.

If the time: Tkm, Tkc, and Tky are the same as the “reference time preset for these”, the printer control apparatus 2090 determines that “the positional relationship in the sub-direction between the toner images is appropriate”. .
Time: When Tkm, Tkc, and Tky are different from the reference time, it is determined that “the positional relationship between the toner images in the sub-direction is shifted”.
In this case, the printer control device 2090 obtains the positional relationship deviation amount from the “time difference from the reference value” of the times: Tkm, Tkc, and Tky, and notifies the scanning control device of the deviation amount. The scanning control device adjusts “light scanning start timing at the corresponding station” so that the shift amount becomes zero.

FIG. 24C shows a state of an output signal when the line pattern LPM1 is “displaced by a distance: ΔS1 in the sub direction” in the relationship between the line patterns LPK1 and LPM1 of the test pattern 201CT.
In this case, the time: Tkm is larger than the reference time by “a movement speed in the sub-direction of the intermediate transfer belt: V and a distance: ΔT1 (= ΔS1 / V) obtained from ΔS1.

  As shown in FIG. 25B, the printer control device 2090 irradiates the oblique line pattern LPK2 until the light spot light irradiates the oblique line pattern LPM2: Tkm2, until the oblique line pattern LPC2 is emitted. Time: Tkc2 and time until irradiation of the oblique line pattern LPY2: Tky2 are detected.

Then, the printer control device 2090 compares the times: Tkm2, Tkc2, and Tky with “a reference time preset for these”.
The printer control device 2090 determines that “the positional relationship in the main direction between the toner images is appropriate” if the times: Tkm2, Tkc2, and Tky2 are all the same as the set reference times, and the time: If Tkm2, Tkc2, and Tky2 are different from the respective reference times, it is determined that “the positional relationship between the toner images is different in the main direction”.

  FIG. 24D shows a state of an output signal when the name line pattern LPM2 is “displaced in the main direction by a distance: ΔS2” with respect to the oblique line pattern LPK2. In this case, the time: Tkm2 becomes larger than the reference time by “the moving speed in the sub-direction of the intermediate transfer belt: V and the distance: ΔS2 obtained from ΔS2”.

  At this time, the printer control device 2090 uses the following equation (1) to obtain a positional deviation amount ΔS2 in the main direction of the magenta toner image.

ΔS2 = V · ΔT2 · cot45 ° (1)
The positional deviation amount ΔS2 is notified to the scanning control device.

  The scanning control apparatus controls the M station so that “the positional deviation amount: ΔS2 becomes 0”.

  In exactly the same manner as described above, it is possible to detect misalignment in the vicinity of both ends of the intermediate transfer belt 2040 in the main direction using the reflective optical sensors 2235b and 2245c and the test patterns 201L and 201R shown in FIG.

  For the sake of simplicity, the case of eleven light emitting sources E1 to E11 and eleven light receiving photoelectric conversion units D1 to D11 has been described above. However, the number of light emitting units and the number of light receiving units are not limited thereto. .

In addition, the case of “transfer belt with smooth surface (reflection on the surface is regular reflection only)” has been explained above, but “transfer belt with non-smooth surface (reflection on the surface includes diffuse reflection)” It can also be applied. That is, if the “detection output distribution by the regular reflector” can be measured by using an appropriate means, it can be “separated into a regular reflection contribution and a diffuse reflection contribution” by using it.
For example, the received light output distribution can be measured in advance using a regular reflector, and the measured received light output distribution can be stored in a memory or the like. The specular reflection at this portion can be detected, and a movable specular reflector is provided in the image forming apparatus, and the specular reflector can be moved and detected as necessary. it can.

  The test pattern 201 shown in FIG. 6 is formed in one row at the substantially central portion of the effective image area. As in the conventional image forming apparatus, the test pattern 201 is arranged in the effective image area. It is also possible to arrange a plurality of test patterns by arranging a plurality of test patterns outside the effective image area.

  In the example of the image process control shown in FIG. 9, the toner density detection (S505) is performed prior to the toner position detection (S506).

  In the embodiment described above, in the “test pattern position recognition step”, the “position in the main direction is estimated” based on the information when the test pattern was last detected.

  In the embodiment described below, in order to improve the estimation accuracy of the test pattern position, by further forming and arranging a “test pattern position recognition patch” upstream of the test pattern and detecting the main direction position of this patch, The main direction position of the test pattern for density detection downstream of the test pattern position recognition patch is estimated.

FIG. 25 shows an example in which a test pattern position recognition patch TP is newly formed and arranged in the test pattern example shown in FIG.
The test pattern position recognition patch TP is a “magenta solid patch” formed and arranged upstream of the test pattern 201M for detecting toner density, and the patch size is 0.5 mm in the main direction and 1 mm in the sub direction. . This is smaller than the size in the main direction of the patch of the test pattern 201M.
The test pattern position recognition patch TP prior to the test pattern 201M is formed on the surface of the intermediate transfer belt, which is a support member, and moves in the sub direction to approach the irradiation area of the light spot from the reflective optical sensor 2245a.
Since the timing at which the test pattern position recognition patches TP are formed is known, all the light emission sources Ei (i = 1 to 11) start to emit light sequentially at an appropriate timing after passing through the irradiation region. .
For sequential light emission, one line light emission (light emission sources E1 to E11 are sequentially blinked once) or several lines light emission (the above sequential blinking is repeated a plurality of times) is sufficient. The light receiving unit output may be acquired only by the photoelectric conversion unit Di of the light receiving unit in accordance with the timing of the light emission source Ei. Since the light emission source Ei emits light and the light spot is irradiated on the intermediate transfer belt, the presence or absence of the test pattern position recognition patch TP at the spot light position can be determined by looking at the light receiving unit output of the photoelectric conversion unit Di.
That is, if the test pattern position recognition patch TP is present, the light receiving unit output is reduced by the amount of diffused light from the patch, compared with the case where there is no test pattern position recognition patch TP.

  Accordingly, at least one line is emitted to the test pattern position recognition patch TP, and the test pattern position recognition patch TP is located at a position corresponding to which light source Ei from the acquired light receiving unit output Di (i = 1 to 11). You can see if there is.

FIG. 26 shows the light-receiving unit output of the photoelectric conversion unit Di with respect to the light-emitting source Ei when the test pattern position recognition patch TP reaches the light spots S1 to S11 (FIG. 26A) and emits one line. (FIG. 26 (b)).
The photoelectric conversion unit D1 and the photoelectric conversion units D5 to D11 receive “regular reflection light from the intermediate transfer belt”, and the light receiving unit output is high. In the photoelectric conversion units D2 and D4, the light receiving unit output is slightly lower, and in the photoelectric conversion unit D3, the light receiving unit output is greatly reduced. From this, it can be seen that the test pattern position recognition patch TP is exactly at the position corresponding to the light emitting portion E3. Further, the test pattern position recognition is based on the fact that the light emitting part pitch: P = 0.4 mm, the size of the test pattern position recognition patch TP in the main direction: 0.5 mm, and the light receiving part outputs of the photoelectric conversion parts D2 and D4. It can be seen that both ends of the patch TP are “slightly irradiated by the light spots S2 and S4”.
Thus, it can be seen that the test pattern position recognition patch TP exists at the position corresponding to the photoelectric conversion unit Di having the lowest light receiving unit output.

  If the density detection test pattern 201M is formed and arranged downstream of the test pattern position recognition patch TP so that the center position in the main direction is the same, “estimation of the main direction position” of the density detection test pattern 201M is performed. It can be performed with high accuracy.

  In this embodiment, the test pattern position recognition patch TP is magenta. However, the color of the patch is not limited, and may be black, cyan, or yellow. Further, although a solid patch is illustrated, it is of course possible to use a halftone patch.

  From the viewpoint of a large decrease in output at the light emitting portion, it is preferable to use black toner or “high density if color toner”.

  The size of the test pattern position recognizing patch TP is not limited to the above size, and it is only necessary to know the position in the main direction. Therefore, in order to reduce the toner consumption, the size of the test pattern 201M in the main direction is reduced. It is preferable that the size is smaller than the size.

  Furthermore, if the light spot irradiates a “part of the test pattern position recognition patch” to determine a decrease in the light receiving unit output due to scattering by the patch, the size of the test pattern position recognition patch in the main direction can be determined. It is also possible to make the length smaller than the light emitting portion pitch.

Furthermore, another embodiment will be described.
In the two examples of the “test pattern position recognition process” described above, the position in the main direction is estimated. That is, the “position in the main direction of the test pattern for density detection” is not directly detected.

  In the embodiment described below, the position can be determined by directly detecting the position in the main direction of the test pattern for density detection.

  FIG. 27A shows a state in which the patch DP1-1 of the test pattern 201M has reached the irradiation area of the light spots S1 to S11, and photoelectric conversion for the light source Ei when “one line is emitted” by all the light sources in this state. The light receiving part output of the part Di is shown in FIG.

  Since the timing at which the test pattern 201M is formed is known, all the light emission sources Ei (i = 1 to 11) start blinking sequentially at an appropriate timing when the patch DP1-1 passes through the irradiation region.

For sequential flashing, one line light emission or several line light emission is sufficient.
The light receiving unit output may be acquired only by the corresponding photoelectric conversion unit Di according to the light emission timing of the light source Ei.
When the light emission source Ei emits light, whether or not the patch DP1-1 of the test pattern 201M is at the light spot position can be determined by looking at the light receiving unit output of the photoelectric conversion unit Di. If the patch DP1-1 is present at the “irradiation position of the light spot by the light source Ei”, the “diffuse reflection by the patch” and the light receiving unit output by the photoelectric conversion unit Di are lower than when the patch DP1-1 is not present.

When the light reception output distribution is as shown in FIG. 27B, the photoelectric conversion units D1 and D5 to D11 have high light reception unit outputs, and the photoelectric conversion units D2 and D4 have lower light reception unit outputs. D3 is even lower. From this, as shown in FIG. 27A, it can be seen that the patch DP1-1 is at a position corresponding to the light emission source E3.
Further, the light emitting portion pitch: P = 0.4 mm, the size of the patch DP1-1 in the main direction: 1 mm, and the light receiving portion outputs of the photoelectric conversion portions D2 and D4, the corresponding portions of the light spots S2, S4 are It can be seen that the patch DP1-1 was irradiated.
Thus, it can be seen that the patch DP1-1 exists at the position in the main direction corresponding to the light receiving part Di having the lowest light receiving part output.

  The patch DP1-1 is a part of the test pattern 201M, and the patches DP1-2 to DP1-5 are connected to the patch DP1-1. Therefore, in this embodiment, the main direction position of the test pattern 201M for density detection can be determined without "estimating".

  After this “test pattern position determination”, the above-mentioned “irradiation system operation determination step and light receiving system operation determination step” is performed, and the “reflected light acquisition step” is performed using the patch DP1-1.

  When “a certain amount of time is required” for performing the “test pattern position recognition process”, “irradiation system operation determination process”, and “light reception system operation determination process”, the first patch (in the example in the description, patch DP1 The “sub-direction size” of -1) can be made larger than other patches.

In FIG. 27, the “intermediate transfer belt region (BELT) without patches” shown in FIG. 18 is omitted. Since “light receiving portion output when there is no patch” can obtain the light receiving portion output at any time when there is no test pattern, the intermediate transfer belt region (BELT) is “between patches DP1-1 and DP1-2”. Between each patch "or upstream of the patch DP1-5.
As shown in FIG. 18, when the intermediate transfer belt region (BELT) is “upstream from the first patch DP1-1 of the test pattern 201M”, since the test pattern position is not determined, all the light emission sources Ei ( The light receiving unit output may be obtained by emitting i = 1 to 11).

  Next, the size of the test pattern in the main direction will be described with reference to FIG.

In the above description, the “size of the test pattern in the main direction” is 1 mm.
In the example of FIG. 29, the size of the test pattern (magenta solid patch) in the main direction is 1.2 mm.

In the state shown in FIG. 29A, the center position of the test pattern (magenta solid patch) in the main direction is at the position of the light spot S6 by the light source E6.
The size of the solid patch in the main direction is 1.2 mm, which is equal to the size of the light spot in the main direction: 0.4 mm and twice the light emitting portion pitch: 0.4 mm (0.08 mm).
In the state of FIG. 29A, since the test pattern can be irradiated in the main direction with the light spots S5 to S7 by the three light emitting sources E5 to E7, the toner density can be calculated for these three light emitting sources.

  In the state of FIG. 29 (b), the center position of the magenta solid patch in the main direction is at an intermediate position between the light spots S6 and S7 by the light emission sources E6 and E7. In this case, the solid patch is irradiated with the light spots from the two light emitting sources E6 and E7, and the toner density can be calculated for the two light emitting sources E6 and E7.

  Thus, by setting the size of the main direction of the patch to be equal to or larger than the sum (2P + SD) of the size of the main direction of the light spot: SD and the light emitting unit pitch: twice P, two or more light emitting units. The toner density can be calculated with respect to the toner density, and by averaging the plurality of toner densities, the “toner density averaged in the main direction” can be obtained, and the toner density detection accuracy is improved.

  If “three toner densities” can be calculated, an intermediate value that excludes the maximum and minimum values is adopted, or if four or more toner densities can be obtained, the remaining values excluding the maximum and minimum values are excluded. It is also possible to improve the detection accuracy by adopting an average value of, and removing abnormal values.

  As another example of the test pattern, FIG. 30 shows an embodiment in which two patches are provided in the main direction. Except for the arrangement of the test pattern, it is the same as FIG.

  30 shows a top view of the transfer belt 2040 on which a test pattern is formed in the image forming apparatus of FIG. 1, and a test pattern 201 for detecting the toner density is formed near the center in the main direction.

  In FIG. 30, “4-tone patches for each color” are formed, and the test pattern 201 is configured by a total of 16 patches. A total of four four-gradation patches are arranged, two in the main direction and two in the sub direction.

  Compared to the case of FIG. 6, the “sub-direction length” of the test pattern is halved, and the time for detecting the test pattern can be shortened to about ½. Further, toner position detection test patterns 201CT, 201L, and 201R for detecting the toner position are formed on the downstream side of the intermediate transfer belt 2040 in the center and both ends in the effective image area.

  FIG. 31 shows “a state in which reflected light from a plurality of magenta (M) patches (here, four gradations) is acquired using the reflective optical sensor shown in FIG. 7”. The up-down direction is the “main direction”, and the left-right direction is the “sub-direction”.

As shown in FIG. 30, the test patterns for toner density detection are formed by toners of black, cyan, magenta, and yellow, respectively. The test pattern 201M shown in FIG. "Pattern", two rectangular patches in which the density is changed to a plurality of gradations (4 gradations in the example in the figure) are arranged in the main direction and two in the sub direction. From low to high, patches DP1-1, DP1-2,.
On the downstream side of the patches DP1-1 and DP1-2, there is an area “BELT” for receiving reflected light from the intermediate transfer belt without the patch.

Each patch has a size of 1 mm in the main direction and 2 mm in the sub direction. The center interval between the patches arranged in the main scanning direction is 2.4 mm.
The size of each patch in the main scanning direction: 1.0 mm is the light emitting portion pitch in the main direction of the reflective optical sensor: P = 0.4 mm, and the size of the light spot irradiated on the intermediate transfer belt in the main direction. S: It is larger than the sum of SD = 0.4 mm.

  First, similarly to the example shown in FIG. 18, the result obtained as a preliminary preparation in the specific example of FIG. 31 is shown.

  By the test pattern position recognition step, the position of the test pattern in the main direction was “estimated to be the position of the light emitting part E3 and the light emitting part E9”.

  Based on the result, it was determined in the irradiation system operation determination step that the light emitting portions to emit light were E3 and E9, and the light emission mode was to emit light sequentially. Subsequently, in the light receiving system operation determining step, the light receiving units that acquire the light receiving unit output are all D1 to D11, and the acquisition timing is matched with the timing when each patch passes the spot light position as shown in FIG. The light emitting units E3 and E9 emit light sequentially, and the light receiving unit is determined to be sampled once in response to obtain the light receiving unit output.

  FIG. 32 shows a “procedure for acquiring reflected light” based on the result of the preparation.

  The test pattern 201M is formed on the surface of the intermediate transfer belt as a support member, moves in the sub direction, and approaches the spot light irradiation region from the reflective optical sensor 2245a.

  Since the timing at which the test pattern 201M is formed is known, the light emitting units E3 and E9 start to emit light at an appropriate timing approaching the irradiation area after the formation.

  First, at the position of the intermediate transfer belt where there is no patch in front of the test pattern 201M, the light emitting portions E3 and E9 emit light pulses, and the light receiving portions D1 to D11 are sampled once in accordance with the timing to obtain the light receiving portion output.

  Subsequently, the test pattern 201M moves in the sub direction, and the light emitting units E3 and E9 sequentially emit light according to the timing when the first patches DP1-1 and DP1-2 pass the spot light position, and the patches DP1-1 and DP1. The light receiving units D1 to D11 are sampled once in accordance with the timing at which −2 passes the spot light position to obtain the light receiving unit output.

  Further, the test pattern DP1 moves in the sub-direction, and the light emitting units E3 and E9 sequentially emit light according to the timing when the patches DP1-3 and DP1-4 pass the spot light position, and the patches DP1-3 and DP1-4. The light receiving parts D1 to D11 are sampled once in accordance with the timing when the light passes through the spot light position, and the light receiving part output is acquired.

  In this way, the reflected light from the test pattern 201M composed of the intermediate transfer belt portion and the four gradation patches, that is, the light receiving portion output distribution can be acquired.

  Therefore, based on the acquisition result, as described above, the toner density can be calculated arithmetically.

  By arranging the test pattern 201M in this way, it is possible to acquire the light receiving unit output for two patches at the same time (during one-line light emission) with one reflective optical sensor.

  Of course, it is possible to acquire light receiving unit outputs for two or more patches according to the number of light emitting units and the number of light receiving units of the reflective optical sensor.

  Thereby, the length of the test pattern in the sub-direction can be shortened, and the detection time can be shortened.

  Since the image forming apparatus often uses a member that rotates in the sub-direction depending on the configuration of the photosensitive member or the developing device, image density unevenness tends to occur in the sub-direction due to the variation of the member. That is, when this density unevenness occurs, it is superimposed on the test pattern.

  Therefore, if the length of the test pattern in the sub-direction is shortened, the influence of this density unevenness can be reduced.

  The arrangement of such test patterns is not limited to that shown in FIG. 31. As shown in FIG. 33, the high density patch DP1- adjacent to the low density patch DP1-1 in the sub-direction. 4 and by making the patches DP-2 and DP3 adjacent to each other, the “toner consumption of patches passing through positions in different main directions” is made as uniform as possible, thereby cleaning the patches on the intermediate transfer belt. Can also be reduced. Further, as shown in FIG. 34, the toner color is changed in the main direction, the test patterns 201M and 201Y are formed in “one row in the sub direction”, and the test patterns 201K and 201C are formed in “one row in the sub direction”. You can also

The arrangement length of the plurality of light emitting portions, that is, the light spot row irradiated on the intermediate transfer belt is made larger than the length of the plurality of patches arranged in the main direction, thereby preventing the light spots from being irradiated on the patches. .
Furthermore, the arrangement length of the plurality of light emitting units is set to the extent that the margin of misalignment in the main direction when the intermediate transfer belt is conveyed and the misalignment margin in the main scanning direction when the patch is formed is also considered. It is desirable to make it larger than the length of a plurality of patches arranged in the direction. Thereby, the magnitude | size of the main direction of a reflection type optical sensor can be set without excess and deficiency.

  In the direct transfer type image forming apparatus, a test pattern is formed on the photosensitive drum. However, as in the above-described embodiments, in the intermediate transfer method in which the support member is a (smooth) intermediate transfer belt, the test pattern is supported. A test pattern is formed on the member. In this case, since the “density unevenness in the sub-direction” described above is more likely to occur, it is preferable to apply a reflective optical sensor that can shorten the length of the test pattern in the sub-direction.

2040 Transfer belt as support member
201 Test pattern
2445a Reflective optical sensor

JP2009-216930 JP2009-258601A

Claims (12)

Image formation in which an electrostatic latent image is formed on a photoconductive photoreceptor, the electrostatic latent image is visualized as a toner image, and the obtained toner image is transferred to a sheet-like recording medium and fixed to form an image. In the device
Test pattern forming means for forming a test pattern with toner on a support member;
A reflective optical sensor for optically detecting the toner density in the test pattern formed on the support member and moving in a predetermined sub-direction;
An image forming process control means for determining an image forming process condition based on the detection result of the reflective optical sensor;
Density detection control means for controlling the reflective optical sensor for detection of the toner density and performing predetermined arithmetic processing on the output of the reflective optical sensor;
The reflective optical sensor is
N (≧ 3) light emitting portions are arranged at a predetermined pitch P in the main direction parallel to the support member surface and orthogonal to the sub direction, and light from each light emitting portion is placed on the support member. An irradiation system for irradiating as a light spot, and a light receiving system in which N (≧ 3) light receiving portions are arranged in the main direction at equal intervals corresponding to the N light emitting portions at the same pitch as the light emitting portions. The light emitted from the irradiation system and reflected by the support member or the test pattern, or the support member and the test pattern is received by the light receiving system,
In the test pattern forming means, the size in the main direction is the sum of the size in the main direction of one light spot irradiated on the support member: SD and the pitch of the light emitting portion: P: SD + P. The test pattern is formed by a large patch,
The density detection control means is configured to detect the toner density.
A test pattern position recognition step for recognizing the position of the test pattern in the main direction;
An irradiation system operation determining step for determining the operation of the irradiation system;
A light receiving system operation determining step for determining the operation of the light receiving system;
A reflected light acquisition step of acquiring a light receiving unit output received by the light receiving system, the light emitted from the irradiation system and reflected by the support member or the test pattern, or the support member and the test pattern;
Toner density calculation for calculating toner density based on the divided output obtained by dividing the light receiving unit output into a regular reflection contribution due to regular reflection light and a diffuse reflection contribution due to diffuse reflection And an image forming apparatus. The image forming apparatus according to claim 1.
An image forming apparatus characterized in that the position of a test pattern is estimated based on information when a test pattern is last detected in a test pattern position recognition step performed by a density detection control means. The image forming apparatus according to claim 1.
The test pattern forming means forms a test pattern position recognition patch on the upstream side of the test pattern on the support member when detecting the toner density,
In the test pattern position recognition step performed by the density detection control means, the test pattern position recognition patch is irradiated with light from the irradiation system, and the position of the test pattern is estimated based on the output of the light receiving unit at this time An image forming apparatus. The image forming apparatus according to claim 1.
In the test pattern position recognition process performed by the density detection control means, the most upstream patch of the test pattern on the support member is irradiated with light from the irradiation system, and the position of the test pattern is determined based on the output of the light receiving unit at this time. An image forming apparatus characterized by determining. The image forming apparatus according to any one of claims 1 to 4,
In the irradiation system operation determination step performed by the density detection control means, a light emitting unit that emits light in the irradiation system of the reflective optical sensor, and at least one of a light emission pattern and a light emission mode of the light emitting unit are determined. apparatus. The image forming apparatus according to any one of claims 1 to 4,
An image forming apparatus characterized in that, in the light receiving system operation determination step performed by the density detection control means, at least one of a light receiving unit for acquiring a light receiving unit output and an acquisition timing of the light receiving unit output in the light receiving system is determined. The image forming apparatus according to claim 2 or 3,
The density detection control means includes a test pattern position correct / incorrect determination step for determining whether the position of the test pattern estimated in the test pattern position recognition step is correct between the reflected light acquisition step and the toner concentration calculation step. Image forming apparatus. The image forming apparatus according to claim 3 or 7,
An image forming apparatus, wherein the size of the test pattern position recognition patch in the main direction is smaller than the size of the test pattern in the main direction. The image forming apparatus according to any one of claims 1 to 8,
In the test pattern forming means, the size in the main direction is larger than the sum of the size SD in the main direction of one light spot irradiated on the support member and the pitch of the light emitting part: twice P: SD + 2P. An image forming apparatus for forming a test pattern with a large patch. The image forming apparatus according to claim 1,
An image forming apparatus, wherein a size SD in a main direction of a light spot formed on a support member by a reflective optical sensor is approximately equal to a pitch P of the light emitting portions. The image forming apparatus according to any one of claims 1 to 10,
An intermediate transfer type image forming apparatus, wherein a toner image is transferred from a photosensitive member to a sheet-like recording medium via an intermediate transfer belt, and a test pattern is formed using the intermediate transfer belt as a support member. The image forming apparatus according to claim 11.
A tandem image forming apparatus that forms toner images of different colors on a plurality of photoconductors and superimposes the plurality of toner images to form a multicolor image.

Images