JP5106841B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and a multifunction machine.

  A widely known method is to create a test pattern outside the print area on the photoconductor or transfer belt, and to control the image process conditions related to image density, image position, etc. by inferring density and position information from the reflectance data. Yes. In the control of the image process conditions, the created test pattern is not discharged as a printed image after the completion of reading the test pattern, and therefore is discarded by a belt cleaner or the like or reused by a recycling apparatus or the like. Such image process condition control includes creating a test pattern during a preparation period from when the power is turned on until printing is possible, and creating a test pattern in a non-image area during printing.

  Incidentally, in recent years, the toner has been made smaller in size to improve the granularity, and the particle size has become spherical and uniform by a production method such as a polymerization method toner. It is generally known that it is difficult to clean these small particle warp toner and spherical toner. The toner that is not properly cleaned remains on the image carrier and is generated as an abnormal image on the transfer material.

  In order to prevent such a cleaning failure from occurring and improve the cleaning performance per time, it is necessary to increase the contact pressure in the case of a blade cleaning device, but in that case, the load on the belt and the cleaning blade increases. The blade wear due to this is promoted, resulting in misalignment and jitter.

  In the case of bias roller cleaning, it is necessary to provide a plurality of rollers, both of which have an effect on cost reduction and space saving. A method of improving the cleaning property by rotating the transfer belt a plurality of times is also used. However, this method increases the downtime of the apparatus.

  A color image forming apparatus that forms a color image by superimposing a plurality of images transfers a plurality of photosensitive member images to a transfer material on a conveying belt and a plurality of photosensitive member images once on a transfer belt. There is an intermediate transfer method in which the image is superimposed on the transfer material and then transferred to the transfer material, but since the intermediate transfer method once forms a color image on the transfer belt, the image overlay accuracy is high, and the thickness of the transfer material and the tolerance for the material are high. There are advantages such as high.

  In the intermediate transfer system, as means for performing a transfer process, (1) a primary transfer device (a primary transfer belt as an example) for superimposing images and (2) a secondary transfer device for transferring an image to a transfer material such as paper There is an intermediate transfer system using two transfer devices (second transfer roller as an example). In the intermediate transfer method using these two transfer devices, a device that enables the primary transfer belt and the secondary transfer roller to contact and separate from each other is required so that the test pattern is not transferred to the secondary transfer roller. Before reaching the transfer roller, it is necessary to separate the primary transfer belt and the secondary transfer roller.

  Therefore, since a contact / separation mechanism is required, there are problems such as high cost, large equipment, and increased layout restrictions. In particular, when it is necessary to create a test pattern during a printing operation, performing the contact / separation during the printing operation is used to change the load on an image carrier such as a transfer belt or a photoconductor or to form a latent image. Since image shift or jitter occurs due to a shock to the exposure apparatus or the like, there is a restriction that the above contact / separation operation cannot be performed from the start of exposure for printing to the end of primary transfer, and throughput is reduced.

  On the other hand, when the mechanism that does not contact and separate the secondary transfer roller is used, the test pattern is inevitably transferred to the secondary transfer roller, thereby requiring a cleaning device for the secondary transfer roller. Furthermore, since the test pattern needs to be read before being transferred to the secondary transfer roller, the layout of the reading device is limited.

In addition, as a known technique, in an image forming apparatus provided with a detection unit that detects the toner adhesion amount of a toner image for adhesion amount detection from each transferred photoreceptor, and a toner adhesion amount control unit that controls image formation conditions, Transfer where X <Z−Y, where X is the length in the axial direction of the transfer paper, Y is the length in the axial direction of the toner image for detecting the toner adhesion amount, and Z is the length in the axial direction of the printable area. 2. Description of the Related Art There is an image forming apparatus that includes a toner image creating unit that creates a toner image for toner adhesion amount detection outside a printing area when printing is performed in a paper size (see, for example, Patent Document 1).
For example, in the case of A4 longitudinal paper, since a margin is formed in the axial direction on the intermediate transfer belt, a test pattern is formed at that portion. However, a test pattern cannot be formed because there is no margin in a mode that uses the image area in the entire axial direction, such as A4 landscape paper.
Conventionally, the following methods are mainly known as density detection methods.
(1) Regular reflection light receiving type (2) Diffuse reflection light receiving type (3) Regular reflection + diffuse reflection light receiving type These density detection methods are a toner portion and an image carrier portion formed on the image carrier as test patterns, respectively. Concentration detection is performed using the difference in the reflection characteristics of (1), but the type (1) has no sensitivity to highly adhered parts, and the type (2) has changed in sensitivity due to the effects of mounting variations. In this case, since it cannot be corrected, it is necessary to use a calibration plate or increase the mounting accuracy. The type (3) is for correcting the sensitivity change of the diffused light receiving unit by the output of the regular reflection light receiving element (for example, It is possible to achieve both high sensitivity and high accuracy.
On the other hand, in the detection unit for detecting the toner portion on the image carrier, (b) a type in which the sensor S1 detects the roller R supporting the belt-like image carrier B1 as shown in FIG. A type that detects the vicinity of the roller R as shown in FIG. 23, (c) a type in which the flat plate 1 is arranged on the back surface of the image carrier B1 as shown in FIG.
As shown in FIG. 22A, when detecting on the roller R, the distance and angle of the detection surface with respect to the sensor S1 vary due to the influence of roller eccentricity. Similarly, even when the sensor S1 is arranged in the vicinity of the roller as shown in (b) of FIG. 23, or a flat plate is arranged on the back surface of the image carrier as shown in (c) of FIG. As shown in the figures, there are variations in the distance and angle between the sensor S1 and the detection surface, and it is difficult to completely eliminate them. If the distance between the sensor and the detection surface or variation in angle occurs, the correct output cannot be read when the density is detected, so that accurate density detection cannot be performed.
As shown in FIGS. 22 to 24, the direction in which the surface of the image carrier 105 fluctuates includes a traveling direction indicated by an arrow 64 and tends to swing in a virtual plane perpendicular to the surface of the image carrier 105. There is.
The reason why correct density detection cannot be performed with respect to the image carrier 105 will be described.
4 and 25 are views of the sensor and the detection surface of the sensor as viewed from the front. The sensor 109 (also described later as a P / TM sensor) contains the following elements which are sensors in a narrow sense in a sensor case. A light emitting element 602 (also described later as an infrared LED), a regular reflection light receiving element 603, a diffuse reflection light receiving element 604, and the like are provided. Reference numeral 605 denotes a lens, reference numeral 105 denotes an image carrier such as an intermediate transfer belt, and reference numeral 107 denotes toner. 4 shows the case where the angle of the detection surface has not changed, and FIG. 25 shows the case where the angle of the detection surface has changed to the right as compared with the state of FIG. Represents.
When the angle of the detection surface changes as shown in FIG. 25, the amount of light incident on the regular reflection light receiving element 603 of the light emitted from the light emitting element 602 changes. This can be expressed as a time transition as shown in FIG. In FIG. 26, (a) part is an output part on the surface of the image carrier when the angle between the sensor and the detection surface is changed, and (b) part is test patterns (c), (d), (e) parts having different densities. Shows the output.
In general, the output of the regular reflection portion is normalized by the output (Vsg) on the image carrier and the output (Vsp_n) of the test pattern portion. By performing this normalization, it is possible to absorb sensitivity variations such as sensor mounting variations. However, if there is a variation as shown in part (a) when detecting Vsg, the correct Vsg cannot be detected and an error occurs in the normalized value.
On the other hand, the diffused light output is detected based on the difference in diffuse reflectance between the image carrier surface and the toner surface. As shown in FIG. 27, sensors (light emitting element 602, regular reflection light receiving element 603, diffuse reflection light receiving element). 604) and the detection surface (image carrier 105) change more greatly than in the case of FIG. 25, and if the regular reflection output enters the diffused light receiving element 604, sensitivity variation occurs.
As described above, in any of the density detection methods (1), (2), and (3), if the output of the regular reflection light receiving element 603 or the diffused light receiving element 604 varies, the density detection accuracy deteriorates.

JP 2006-17868 A JP 2004-279664 A JP 2004-354623 A

  An object of the present invention is to obtain a stable image quality by reducing the influence of a detection surface distance and angle fluctuation with respect to a sensor in an image forming apparatus.

In order to achieve the above object, according to the first aspect of the present invention, light is emitted from a light emitting element to an image carrier and a test pattern formed on the image carrier, and the reflected light is detected by two light receiving elements. Thus, in the image forming apparatus having the density detecting device for acquiring the density information of the test pattern and the image forming condition control device for controlling the image forming conditions based on the information obtained from the density detecting device, the density detecting device is one A light-emitting unit and two light-receiving units, wherein the first light-receiving unit is disposed at a position for receiving regular reflection, and the second light-receiving unit is disposed at a position for receiving diffused light, and is irradiated from the light-emitting unit. The light emitting portion and the first light receiving portion are arranged so that the surface including the optical axis of the reflected light and the regular reflection light from the image carrier surface is parallel to the traveling direction of the image carrier, and the second light receiving portion is The surface including the optical axis of the light emitting part and the specularly reflected light Without,
Irradiation range of the light-emitting portion, the traveling direction and in the direction parallel to the range of the image carrier is a, when the traveling direction and in the vertical direction range of the image bearing member and is b, Ri a ≧ b der, and
When the distance between the second light receiving unit and the light emitting unit is L1, and the distance between the first light receiving unit and the second light receiving unit in the direction perpendicular to the traveling direction of the image carrier is L2, L1 <L2 .
According to a second aspect of the present invention, in the first aspect, the image forming apparatus is based on an electrophotographic system, and the image forming condition control apparatus controls the development potential.
According to a third aspect of the present invention, the image forming apparatus according to the first aspect is a tandem type color electrophotographic apparatus, and the image carrier is a transfer belt.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the light receiving range of the first light receiving unit is a 'in the range parallel to the traveling direction of the image carrier, and When the range between the traveling direction and the vertical direction is b ′, a ′ ≧ b ′.
According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the irradiation range of the light emitting portion is a range in the direction parallel to the traveling direction of the image carrier, and the direction perpendicular to the traveling direction of the image carrier. Where b is the range, a ≧ b, and
When the light receiving range of the first light receiving portion is a ′ in the range parallel to the traveling direction of the image carrier and b ′ in the direction perpendicular to the traveling direction of the image carrier, a ′ ≧ b ′. It was.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects,
A lens is used for at least one of the light emitting unit or the first light receiving unit .
In the invention of claim 7, wherein the image forming apparatus according to claim 1 comprising a concentration measuring apparatus is a color image forming apparatus for obtaining a color image by superimposing a plurality of colors, any one of claims 1 to 7 the concentration detecting apparatus according to was the Rukoto be combined to detect the positional deviation of the plurality of colors.

  According to the present invention, in the image forming apparatus, it is possible to reduce the influence of the detection surface distance and angle variation with respect to the sensor, and to obtain a stable image quality.

[1] Example of Density Detection Device that Acquires Density Information of Test Pattern and Image Formation Condition Control for Controlling Image Formation Conditions Based on Information Obtained from Density Detection Device First, the configuration of the printer of the present embodiment will be described. . FIG. 1 is a schematic configuration diagram showing an image forming process part (process engine part) that performs exposure, charging, development, transfer, and fixing in the printer of this embodiment.

  In addition to the components shown in FIG. 1, the printer includes a print controller (indicated by reference numeral 410 in FIG. 4 to be described later) that processes image data sent from a PC (personal computer) or the like and converts it into exposure data, and a high pressure. A high pressure generator (denoted by reference numeral 416 in FIG. 5 described later), a main body control unit (denoted by reference numeral 406 in FIG. 5 described later) for controlling the image forming operation, and a transfer material serving as a recording material. A paper supply device (not shown) for supplying the paper 115, a manual feed tray (not shown) for manually feeding the transfer paper 115, and a paper output tray (not shown) for discharging the image-formed transfer paper 115 are provided. Yes.

  In FIG. 1, the main body is provided with an endless belt-like intermediate transfer belt 105 as an intermediate transfer member and a charging device (primary transfer device 106) as a first transfer device. The intermediate transfer belt 105 has a three-layer structure including a base layer, an elastic layer, and a coat layer. The base layer is configured, for example, by combining a fluorine resin having a small elongation or a rubber material having a large elongation with a material that is difficult to stretch, such as a canvas.

  The elastic layer is made of, for example, fluorine rubber or acrylonitrile-butadiene copolymer rubber, and is formed on the base layer. The coat layer is formed by coating the surface of the elastic layer with, for example, a fluorine resin. The intermediate transfer belt 105 is rotationally driven by a support roller 112 having a function as a drive roller while being stretched around four support rollers 112, 113, 114, and 119.

There are four image forming units for each color of yellow (Y), cyan (C), magenta (M), and black (K) in the stretched portion of the intermediate transfer belt. The four image forming units for each color have the same configuration and are composed of the same constituent members. In FIG. 1, the same constituent members represent numerical parts with the same numerals, and end with color identification codes Y (yellow), C (cyan), M ( Magenta) and K (black). In each image forming unit, photoreceptor units 103Y, 103C, 103M, and 103K and developing units 102Y, 102C, 102M, and 102K are arranged side by side.
The developing units 102Y, 102C, 102M, and 102K are supplied with toner from the toner bottles 104K, 104Y, 104C, and 104M.

  Below these image forming units, an exposure apparatus 200 is provided. Based on the image information, a semiconductor laser is driven from a laser exposure unit (not shown) provided in the exposure apparatus 200 to write light. Lb is emitted to form an electrostatic latent image on the photosensitive drums 101Y, 101C, 101M, and 101K as the first image carriers provided in the respective photosensitive units. Here, the emission of the writing light is not limited to the laser, but may be, for example, an LED (light emitting diode).

  The configuration of the image forming unit will be described. Hereinafter, an image forming unit that forms a black toner image will be described as an example with reference to FIG. 2, but image forming units that form toner images of other colors also have the same configuration.

Image Forming Unit In FIG. 2, the constituent members of the image forming unit for black toner are originally provided with a symbol K at the end of the symbol, but are omitted here. In this image forming unit, a charging device 301 for charging the photosensitive drum, a developing device 102, and a photosensitive member cleaning device 308 are provided around the photosensitive drum 101. Further, a primary transfer device 106 as a charging device is provided at a position facing the photosensitive drum 101 via the intermediate transfer belt 105.

  The charging device 301 is of a contact charging type employing a charging roller, and uniformly charges the surface of the photosensitive drum 101 by applying a voltage in contact with the photosensitive drum 101. As the charging device 301, a non-contact charging type using a non-contact scorotron charger or the like can be used.

  The developing device 102 uses a two-component developer composed of a magnetic carrier and a nonmagnetic toner. As the developer, a one-component developer may be used. The developing device 102 can be roughly divided into an agitating unit 303 and a developing unit 304 provided in the developing case. In the agitation unit 303, a two-component developer (hereinafter simply referred to as “developer”) is conveyed while being agitated and supplied onto a developing sleeve 305 as a developer carrier.

  The stirring unit 303 is provided with two parallel screws. A partition plate is provided between the two screws 306 to partition the two screws 306 so as to communicate with each other. A toner density sensor 104 for detecting the toner density of the developer in the developing device 102 is attached to the developing case. On the other hand, in the developing unit 304, the toner in the developer attached to the developing sleeve 305 is transferred to the photosensitive drum 101.

  The developing unit 304 is provided with a developing sleeve 305 that faces the photosensitive drum 101 through the opening of the developing case, and a magnet (not shown) is fixedly disposed in the developing sleeve 305. A doctor blade 307 is provided so that the tip approaches the developing sleeve 305. In the present embodiment, the distance at the closest portion between the doctor blade 307 and the developing sleeve 305 is set to 0.9 mm.

  In the developing device 102, the developer is conveyed and circulated while being stirred by two screws 306, and is supplied to the developing sleeve 305. The developer supplied to the developing sleeve 305 is drawn up and held by a magnet. The developer pumped up by the developing sleeve 305 is conveyed as the developing sleeve 305 rotates, and is regulated to an appropriate amount by the doctor blade 307.

  The regulated developer is returned to the stirring unit 303. The developer transported to the developing area facing the photosensitive drum 101 in this manner is brought into a spiked state by a magnet and forms a magnetic brush. In the developing region, a developing electric field that moves the toner in the developer to the electrostatic latent image portion on the photosensitive drum 101 is formed by the developing bias applied to the developing sleeve 305.

  As a result, the toner in the developer is transferred to the electrostatic latent image portion on the photosensitive drum 101, and the electrostatic latent image on the photosensitive drum 101 is visualized to form a toner image. The developer that has passed through the developing region is transported to a portion where the magnetic force of the magnet is weak, thereby leaving the developing sleeve 305 and being returned to the stirring unit 303.

  When the toner concentration in the agitation unit 303 becomes light by repeating such operations, the toner concentration sensor 104 detects this, and toner is replenished to the agitation unit 303 based on the detection result.

  A primary transfer roller is employed as the primary transfer device 106 and is installed so as to be pressed against the photosensitive drum 101 with the intermediate transfer belt 105 interposed therebetween. Further, both ends of the primary transfer roller are in contact with each other in a range 203 corresponding to the maximum width of the transfer material in the axial width of the intermediate transfer belt 105 in FIG.

  The primary transfer device 106 may not be a roller shape, but may be a conductive brush shape, a non-contact corona charger, or the like. Further, in the axial range 203, the transfer paper 115 of the transfer paper 115 having the longest length in the direction perpendicular to the rotation direction of the intermediate transfer belt (transfer paper in a form in which the maximum used paper is laterally fed) is primarily transferred. It is set so as to be sandwiched between the apparatus 106 and the intermediate transfer belt 105.

  The photoconductor cleaning device 308 includes a cleaning blade 309 made of, for example, polyurethane rubber, which is disposed so that the front end is pressed against the photoconductor drum 101. In this embodiment, in order to improve the cleaning performance, a conductive fur brush 310 that contacts the photosensitive drum 101 is also used.

  A bias is applied to the fur brush 310 from a metal electric field roller (not shown), and the tip of a scraper (not shown) is pressed against the electric field roller. The toner removed from the photosensitive drum 101 by the cleaning blade 309 and the fur brush 310 is accommodated in the photosensitive member cleaning device 308 and collected by a waste toner collecting device (not shown).

  A specific setting of the image forming unit will be described. The diameter of the photosensitive drum 101 is 40 mm, and the photosensitive drum 101 is driven at a linear speed of 200 mm / s. The developing sleeve 305 has a diameter of 25 mm, and the developing sleeve 305 is driven at a linear speed of 564 mm / s.

  The charge amount of the toner in the developer supplied to the development area is preferably in the range of about −10 to −30 μC / g. The development gap, which is the gap between the photosensitive drum 101 and the development sleeve 305, can be set in the range of 0.5 to 0.3 mm, and the development efficiency can be improved by reducing the value.

  The thickness of the photosensitive layer of the photosensitive drum 101 is 30 μm, the beam spot diameter of the optical system of the exposure apparatus 200 is 50 × 60 μm, and the amount of light is about 0.47 mW. As an example, the surface of the photosensitive drum 101 is uniformly charged to −700 V by the charging device 301, and the potential of the electrostatic latent image portion irradiated with the laser by the exposure device 200 is −120 V. On the other hand, the developing bias voltage is set to -470V, and a developing potential of 350V is secured. Such process conditions are changed as appropriate according to the result of the potential control.

  In the image forming unit of FIG. 2 having the above configuration, first, the surface of the photosensitive drum 101 is uniformly charged by the charging device 301 as the photosensitive drum 101 rotates. Next, based on the image information from the print controller, laser beam writing light Lb is emitted from the exposure device 200 to form an electrostatic latent image on the photosensitive drum 101. Thereafter, the electrostatic latent image is visualized by the developing device 102 to form a toner image.

  The toner image is primarily transferred onto the intermediate transfer belt 105 by the primary transfer device 106. The transfer residual toner remaining on the surface of the photosensitive drum 101 after the primary transfer is removed by the photosensitive member cleaning device 308 and used for the next image formation.

  1 and 3, a secondary transfer roller 108 is provided as a second transfer device at a position facing the support roller 112 with the intermediate transfer belt 105 interposed therebetween. The secondary transfer roller 108 transfers the toner image formed on the intermediate transfer belt 105 onto the transfer paper with an electrostatic force. When the toner image on the transfer belt 105 is secondarily transferred onto the transfer paper 115, the secondary transfer roller 108 is pressed against the portion of the intermediate transfer belt 105 wound around the support roller 112 to perform secondary transfer.

The secondary transfer device may not be configured using the secondary transfer roller 108 but may be configured using, for example, a transfer belt or a non-contact transfer charger.
The axial width of the intermediate transfer belt 105 is larger than the longitudinal width (axial width) of the secondary transfer roller 108, and the maximum width of the transfer paper 115 (during lateral feed) is the longitudinal width (axial width) of the secondary transfer roller 108. ) Is the following size,
The test pattern formation region is set in a region having a dimensional difference between the axial width of the intermediate transfer belt 105 and the longitudinal width (axial width) of the secondary transfer roller 108, and the test pattern is formed in the test pattern formation region. Is formed.
Here, an example in which a roller-like secondary transfer roller 108 is used as the secondary transfer device has been described. However, when a transfer belt or a non-contact transfer charger is used instead of the secondary transfer roller 108, the same applies to the above. Similarly, a test pattern can be formed.
In the example shown in FIG. 3, the axial range 203 corresponding to the longitudinal width of the secondary transfer roller 108 is located at the center of the axial width of the intermediate transfer belt 105, and the test pattern formation region is the intermediate transfer belt 105. It is formed in a strip shape at both ends of the axial width of the.

  Since the secondary transfer roller 108 is arranged at a position shifted from the test pattern formation region by the above-described configuration, it is not in contact with the test pattern, and a transfer sheet is interposed between the secondary transfer roller 108 and the intermediate transfer belt 105 at the time of transfer. Therefore, the toner image on the intermediate transfer belt 105 is not in contact with the toner image and does not adhere to the toner, so that it is not necessary to attach a cleaning unit that is in sliding contact with the peripheral surface of the secondary transfer roller 108.

  In FIG. 1, a fixing device 111 for fixing the toner image transferred onto the transfer paper 115 is provided on the downstream side of the secondary transfer roller 108 in the conveyance direction of the transfer paper 115. The fixing device 111 has a configuration in which a pressure roller 118 is pressed against a heating roller 117.

  1 and 3, photosensors 109F (front side) and 109R (rear side) for estimating the density and relative position of the test pattern are located at positions facing the support roller 112 with the intermediate transfer belt 105 in between. Thereafter, P / TM sensors 109) are provided at two positions on the front side and the back side of the support roller 112 in the axial direction. A belt cleaning device 110 is provided at a position facing the support roller 113 with the intermediate transfer belt 105 interposed therebetween. The belt cleaning device 110 is for removing residual toner remaining on the intermediate transfer belt 105 after the toner image on the intermediate transfer belt 105 is transferred to the transfer paper 115.

  In the schematic diagram of the P / TM sensor 109 shown in FIG. 4, the P / TM sensor 109 has one light emitting element and two light receiving elements. This light emitting element is an infrared LED 602. The two light receiving elements are a specular reflection light receiving element 603 and a diffuse reflection light receiving element 604 provided at two positions, a position where the light reflected by the mirror on the intermediate transfer belt 105 can be received and a position where the specular reflection light is not received, respectively. It is. As the light emitting element, a laser light emitting element or the like may be used instead of the infrared LED.

  Phototransistors are used as the regular reflection light receiving element 603 and the diffuse reflection light receiving element 604, but photodiodes may be amplified and used. A condensing lens 605 is provided in the middle of the optical path. In this configuration, the regular reflection light receiving element 604 and the diffuse reflection light receiving element 604 are provided as the light receiving elements, but either one may be used depending on the detection target and necessary information.

  FIG. 5 is a block diagram showing an electrical connection of each unit provided in the printer of this embodiment. As shown in FIG. 5, the printer according to the present embodiment includes a main body control unit 406 having a computer configuration, and the main body control unit 406 controls driving of each unit. A main body control unit 406 includes a ROM (Read Only Memory) 405 that stores in advance fixed data such as a computer program via a bus line 409 in a CPU (Central Processing Unit) 402 that executes various calculations and drive control of each unit. A RAM (Random Access Memory) 403 that functions as a work area for storing various data in a rewritable manner is connected.

  The ROM 405 stores the test pattern formation position and density information necessary for generating the test pattern, the bias condition for forming the test pattern gradation, and the TM / P sensor 109 for estimating the test pattern adhesion amount. An output adhesion amount conversion LUT (Look up table) is stored (see FIG. 10).

  A print controller 410 is connected to the main body control unit 406, and the print controller 410 transmits image information from a PC (personal computer), a FAX (facsimile), a scanner, or the like as unified image data to the main body control unit 406. . Further, an A / D conversion circuit 401 that converts various sensor information into digital data, a drive circuit that drives a motor and a clutch, a high-voltage generator that generates a voltage necessary for image formation, and the like are also connected.

Next, the operation of the printer of this embodiment will be described with reference to FIGS.
When printing with information from a PC using a printer having the above configuration, first, image information is transmitted using a printer driver on the PC. The print controller 410 receives print information from the printer driver and sends an exposure signal to the exposure apparatus 200.

  Upon receiving the print command, the main body control unit 406 drives a drive motor (not shown) so that the support roller 112 is rotated and the intermediate transfer belt 105 is rotated. At the same time, the photosensitive drums 101Y, 101C, 101M, and 101K of each image forming unit are also rotated.

  Thereafter, based on information from the print controller, the exposure apparatus 200 irradiates the writing light Lb onto the photosensitive drums 101Y, 101C, 101M, and 101K of the respective image forming units. As a result, electrostatic latent images are formed on the respective photosensitive drums 101Y, 101C, 101M, and 101K, and are visualized by the developing devices 102Y, 102C, 102M, and 102K. Then, yellow, cyan, magenta, and black toner images are formed on the photosensitive drums 101Y, 101C, 101M, and 101K, respectively.

  The respective color toner images formed in this way are primarily transferred by the primary transfer devices 106Y, 106C, 106M, and 106K so as to sequentially overlap the intermediate transfer belt 105. As a result, a composite toner image in which the toner images of the respective colors overlap is formed on the intermediate transfer belt 105. The transfer residual toner remaining on the intermediate transfer belt 105 after the secondary transfer is removed by the belt cleaning device 110.

  In response to the image information, a paper feed roller of a paper feed device (not shown) corresponding to the transfer paper 105 selected by the user rotates, and the transfer paper 105 is sent out from one of the paper feed cassettes (not shown). The fed transfer paper 105 is separated into one sheet by a separation roller (not shown), enters a paper feed path (not shown), and is conveyed to a conveyance path in the printer main body by a conveyance roller (not shown). The transfer paper 105 conveyed in this way is stopped when it hits the registration roller 107.

  When the transfer paper 105 not set in the paper feed cassette (not shown) is used, the transfer paper 105 set on the manual feed tray (not shown) is fed by a paper feed roller (not shown) and separated into one sheet by a separation roller (not shown). Thereafter, the sheet is conveyed through a manual sheet feeding path (not shown). Then, it stops when it hits the registration roller 107.

  The registration roller 107 starts to rotate in accordance with the timing at which the composite toner image formed on the intermediate transfer belt 105 as described above is conveyed to the secondary transfer unit facing the secondary transfer roller 108. Here, in general, the registration roller 107 is often used while being grounded, but a bias may be applied to remove the paper dust of the transfer paper 105.

  The transfer paper 105 sent out by the registration roller 107 is sent between the intermediate transfer belt 105 and the secondary transfer roller 108, and the composite toner image on the intermediate transfer belt 105 is transferred onto the transfer paper 105 by the secondary transfer roller 108. Secondary transfer is performed.

  Thereafter, the transfer paper 105 is conveyed to the fixing device 111 while being attracted to the secondary transfer roller 108, and heat and pressure are applied by the fixing device 111 to perform a toner image fixing process. The transfer sheet 105 that has passed through the fixing device 111 is discharged and stacked on a discharge tray (not shown) by a discharge roller (not shown).

  When image formation is also performed on the back surface of the surface on which the toner image is fixed, the transfer direction of the transfer paper 105 that has passed through the fixing device 111 is switched by a switching claw (not shown) and sent to a paper reversing device (not shown). The transfer paper 105 is reversed there and guided to the secondary transfer roller 108 again.

  Next, image process control performed by the CPU 402 according to the present embodiment based on a computer program will be described with reference to FIG. FIG. 6 is a schematic diagram showing a flowchart showing a flow of execution in the image process control.

  The image process control determines whether it is necessary when the power switch of the main body is turned on or when printing is started, and is executed if necessary (steps S501, S502, S503). Immediately after the power is turned on, the heating time of the fixing heater and the preparation time of the print controller are necessary, and the image processing control should be performed because it may be left until then or the usage environment may change. There is.

  Further, during the printing operation, there is a possibility that toner supply and consumption, and changes in the characteristics of the photosensitive member of the photosensitive drum 101 and the intermediate transfer belt 105 may occur, and image process control may be performed. Immediately after the power is turned on, image process control is executed when the photoreceptor stop time is 6 hours or more, the temperature in the machine has changed by 10 ° C or more, or the relative humidity in the machine has changed by 50% or more. To do.

  Among the above, the stop time of the photosensitive member is obtained as follows. When the photosensitive member stops, time information is acquired from the real-time clock held by the print controller 410 shown in FIG. 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 changes are obtained by acquiring temperature information and relative humidity information from the in-machine temperature / humidity sensor 414 when the photoconductor is stopped, and similarly acquiring temperature information and relative humidity information from the temperature / humidity sensor 414 at power-on. The temperature change amount and the relative humidity change amount are obtained from the difference.

  During printing, a test pattern is created when the number of printed sheets reaches a predetermined interval. The interval 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 set as a threshold value.

  Next, when it is determined that image process control is necessary, a test pattern is formed (step S504 in FIG. 6). FIG. 7 shows a state where the test pattern is formed on the transfer belt. Reference numeral 201 in FIG. 7 indicates a test pattern (P pattern) for detecting the toner adhesion amount. Reference numeral 202 in FIG. 7 denotes a test pattern (TM pattern) for detecting the image position. The P pattern and the TM pattern are formed on the near side and the far side in the axial direction, and the near side P pattern is denoted by 201F, the far side P pattern is denoted by 201R, the near side TM pattern is denoted by 202F, and the far side TM pattern is denoted by 202R.

  Image process control includes potential potential control, toner density target value correction control, and alignment correction control, and the test pattern formation conditions differ depending on which control is performed. First, conditions for forming a test pattern for controlling potential potential will be described.

  The test pattern 201 is used for potential potential control. Of the test patterns 201, only 201F is formed, but if necessary, only 201R may be formed, and both 201F and 201R may be formed. 201F and 201R are formed to have a size of 10 mm in the axial direction (main scanning) and 15 mm in the traveling direction of the intermediate transfer belt 105 (sub scanning).

  The size in the main scanning direction includes the irradiation range (spot diameter) of the P / TM sensor 109 on the intermediate transfer belt 105, the conditions under which the test pattern is stably formed in the process (a region where no edge effect or the like occurs), and the main size. It is determined from the maximum scanning position deviation amount.

  The size in the sub-scanning direction needs to be the same as that in the main scanning. However, when the sampling frequency or gradation pattern of the A / D conversion circuit is formed with the developing bias variable, the rise time of the high-voltage generator 416 is increased. Etc. need to be considered. The exposure value is the same as that for printing, and is 0.47 mW in this embodiment.

  The development bias is switched to about 50 msec immediately before the test pattern exposure unit comes on the photosensitive member 101 and the developing sleeve 305. This switching timing is set in consideration of the response of the high voltage generation circuit. Five types of test patterns are formed, and the value of the developing bias is switched from the first to −100V, −150V, −200V, −250V, and −300V.

  The charging bias is set so as to always maintain a potential of 200 V with respect to the developing bias. In this case, the charging bias is set to -300 V, -350 V, -400 V, -450 V, and -500 V. In this case, the test pattern for controlling the potential potential is formed by changing the developing bias and cannot be executed simultaneously with the printing operation. Therefore, the test pattern is formed at the timing of the non-image forming area 710 during printing shown in FIG. However, when the exposure energy is made variable in order to obtain a gradation (development γ) by the development potential of the test pattern, the test pattern may be formed simultaneously with printing. Toner density target value correction control is also performed using the same test pattern as this potential potential control.

  Next, test pattern formation conditions for alignment correction control will be described. In the alignment correction control, the front side TM pattern 202F and the back side TM pattern 202R are used. The near-side TM pattern 202F and the back-side TM pattern 202R are formed by inclining 45 ° of the same size as 10 mm in the main scanning direction and 1 mm in the sub-scanning direction.

  The size in the sub-scanning direction is determined by the irradiation range (spot diameter) of the P / TM sensor 109 on the intermediate transfer belt 105. Each color is formed in the order of K, M, C, and Y. The exposure value is the same as that for printing (0.47 mW in this embodiment), but a dedicated exposure pattern may be used. The development bias and the charging bias are the same as those for printing. However, if the toner adhesion amount of the test pattern portion is a condition that the surface of the intermediate transfer belt 105 is covered, if it is not simultaneous with printing, it can be set individually. Good. Details of the positional deviation correction control will be described later.

  Next, a test pattern detection method and calculation method for potential potential control will be described. Before the first formed test pattern passes through the P / TM sensor 109, the light emission amount adjustment (Vsg adjustment) of the light emitting element 603 is performed for the P / TM sensor 109F (front side) and the P / TM sensor 109R (back side). I do. The Vsg adjustment may be completed before the test pattern passes through the P / TM sensor 109.

  The Vsg adjustment will be described. When Vsg adjustment starts, turn on the LED. As the current PWM value at this time, the previous adjustment value (IF) stored in the RAM 403 is used. Next, the output data of the regular reflection output element 603 is read. The sampling time interval at this time is 2 msec, and 10 points are sampled to obtain the average value so as not to be affected by the uneven reflection of the intermediate transfer belt 105. This average value is referred to as Vsg_REG.

  If Vsg_REG is within 4.0V ± 0.5V, IF is not updated and the previous value is maintained. If Vsg_REG is not within 4.0V ± 0.5V, adjustment operation is performed. An IF that makes Vsg_REG closest to 4.0 V is detected using a two-part search method as the adjustment operation.

  If the IF is found, the IF data on the RAM 403 is updated. If the IF is not found, an adjustment abnormality is detected, the abnormality is notified to the print controller 410, and the abnormality is displayed on the printer driver or the operation unit of the main body. Further, when Vsg_REG is detected using the final IF, the output voltage of the diffuse reflection light receiving element 604 is also detected at the same time. This value is called Vsg_DIF.

  Next, Vsg_REG and Vsg_DIF are stored in the RAM 403. When the infrared LED 602 for the P / TM sensor is continuously turned on, the test pattern reaches the light irradiation portion position of the intermediate transfer belt 105 of the P / TM sensor 109. The output is sampled every 2 msec at the timing when the test pattern reaches the P / TM sensor 109 and converted into digital data by the A / D conversion circuit 401.

  The digitally converted data is returned to analog output data by a conversion formula preset in the ROM 405. In the CPU 402, since the size of the sub-scan of the test pattern is 15 mm and the linear velocity is 200 mm / sec, the sampling is (15/200 × 1000) / 2≈38 data.

  In order to remove noise, 10 pieces of sampled data are removed from a large value and 10 pieces from a small value, an average value of the remaining data is obtained, and the first test pattern regular reflection output data (Vsp [1 ] _REG). Similarly, the output data of the diffusion light receiving element is also obtained as Vsp [1] _DIF. The same applies to the second and subsequent test patterns (Vsp [2-5] _REG, Vsp [2-5] _DIF).

Next, a method for converting (Vsp [n]) data into toner adhesion amount data will be described. FIG. 9A shows the relationship between the color toner adhesion amount and the output voltage of the regular reflection light receiving element 603. FIG. 9B shows the relationship between the color toner adhesion amount and the output voltage of the diffuse reflection light receiving element 604.
FIG. 9C shows the relationship between the black toner adhesion amount and the output voltage of the regular reflection light receiving element 603. Since the black toner does not have a diffuse reflection component, the diffuse reflection light receiving element 604 is not used for detecting the black toner.

In the present embodiment, a case where only the regular reflection light receiving element 603 is used for conversion of the color toner adhesion amount will be described. The following sensitivity correction coefficient (K2) of the regular reflection light receiving element 603 is obtained from the relationship of the data Vsp [1-5] _REG and Vsp [1-5] _DIF obtained first. K2 is obtained from the following equation (1).
K2 = MIN (Vsp [n] _REG / Vsp [n] _DIF) Expression (1)

Next, an expression (2) for obtaining a value (K [n]) obtained by removing the toner diffuse reflection component from the output voltage of the regular reflection light receiving element 603. This value represents a regular reflection light component from the intermediate transfer belt 105 in the test pattern portion.
K [n] = (Vsp [n] _REG−Vsp [n] _DIF × K2) / (Vsg [n] _REG−Vsg [n] _DIF × K2) (2)

Next, the diffuse reflection component from the intermediate transfer belt 105 is removed from the output voltage of the diffuse reflection light receiving element 604 and separated only into the diffuse reflection component from the color toner. This separation method is obtained by the following equation (3).
Vsp [n] _DIF_dush = Vsp [n] _DIF−Vsg [n] _DIF × K [n] — Expression (3)

Next, gain adjustment is performed to correct variations in the toner output of the diffuse reflection light receiving element 604. This gain adjustment is performed by obtaining a gain adjustment coefficient K5. Equation (4) shows how to obtain K5.
K5 = 1.63 / (α × 0.15 ^ 2 + β × 0.15 × γ) (4)
In equation (4), α, β, and γ are square terms obtained by quadratic approximation when the test axis is K [n] on the X axis and Vsp [n] _DIF_dush of each test pattern is on the Y axis. Coefficient, coefficient of the first power term, and y-intercept. The approximate straight line is obtained by the method of least squares. In addition, the constant in the equation (4) is a value obtained in advance by experiments or the like.

Next, normalization calculation is performed. An equation for obtaining the normalized value (R [n]) is shown in Equation (5).
R [n] [YCMK] = K5 × Vsp [n] _DIF_dush (5)
At this point, sensor attachment and individual variation of the detection system and reflection characteristic change of the intermediate transfer belt 105 are almost canceled and determined uniquely. Next, the toner adhesion amount is calculated from the LUT, R [n], and [YCMK] shown in FIG. Find MA [n].

Next, how to determine the black toner adhesion amount will be described. In the case of black toner, it is determined only by the regular reflection light reflectance from the intermediate transfer belt 105 and the light absorption characteristics of the toner, so the relationship of the following equation (6) may be obtained.
R [n] [Bk] = Vsp_REG / Vsg_REG Formula (6)
When R [n] [Bk] is obtained, the LUT and R [n] shown in FIG. 10 are shown in a table showing the relationship between R [n] [Bk] obtained in advance through experiments or the like and the toner adhesion amount in the same manner as for color toners. , [Bk], the toner adhesion amount MA [n] [Bk] is obtained for black Bk.

  When the adhesion amount MA [n] is obtained, the relationship between the developing bias Vb [n] of the test pattern and the adhesion amount MA [n] is linearly approximated. The linear approximation is obtained by the least square method. Next, the optimum developing bias Vb is obtained from the target value (MA_REF) of the adhesion amount obtained in advance and the approximate linear equation, and stored in the RAM. The charging bias Vc is determined by the relationship of Vc = Vb + 200 (V) and is similarly stored in the RAM.

  The determined Vc and Vb are used in the next printing operation. The toner density target value correction control is performed using the slope data of an approximate linear equation. Since the inclination of the approximate linear equation is an alternative characteristic of development γ (the inclination when the Y-axis is the toner adhesion amount on the photoconductor and the X-axis is the development potential), toner supply control is performed with respect to the approximate linear inclination target value. Control the target value.

Hereinafter, with respect to the positional deviation correction control, an embodiment will be described with reference to Japanese Patent Laid-Open No. 2002-207338.
FIG. 11 shows the contents of “color matching” (CPA). When proceeding to this “color matching” (CPA), the CPU 402 first performs “test pattern formation and measurement” (PFM) on the intermediate transfer belt 105 on the rear r side (axial direction) as shown in FIG. A test pattern of start marks Msr, Msf and 8 sets (front 1st set to front 8th set) is formed on each of the back side and the front f side (front side in the axial direction), and the P / TM sensor 109F, The mark is detected by 109R (steps S505 and S506 in FIG. 6), and the mark detection signals Sdr and Sdf are converted into digital data, that is, mark detection data Ddr and Ddf by the A / D conversion circuit 401 and read.
In the flowchart of FIG. 6, the process condition is determined (step S508) through the calculation process in step S507. Details of the calculation process in step S507 are as described below.

  The position (distribution) of the center point of each mark on the intermediate transfer belt 105 is calculated. Further, an average pattern of the rear side 8 sets (an average value group of mark positions) and a similar average pattern of the front side 8 sets are calculated. The contents of this “test pattern formation and measurement” (PFM) will be described later.

  When the average pattern is calculated, the image forming deviation amount by each of the Bk, Y, C, and M image forming units is calculated based on the average pattern (DAC), and adjustment for eliminating the deviation based on the calculated deviation amount is performed. (DAD).

  FIG. 13 shows a flowchart of “test pattern formation and measurement” (PFM). When proceeding to this, as shown in FIG. 12, the CPU 402 simultaneously, for example, the width of the mark in the Y direction on each of the rear r side and front f side surfaces of the intermediate transfer belt 105 driven at a constant speed of 200 mm / sec. Formation of start marks Msr and Msf and 8 sets of test patterns having w of 1 mm, length A in the X direction of, for example, 10 mm, pitch d of, for example, 6 mm, and interval c between the sets of, for example, 9 mm is started. The timer Tw1 with a time limit value Tw1 for starting the timing immediately before Msf arrives immediately below the P / TM sensors 109F and 109R is started (step 1) and waits for the timing.

  That is, it waits for the timer Tw1 to time out (step 2). When the timer Tw1 expires, the timer Tw2 whose time limit is Tw2 is used to determine when the last of the eight test patterns on the rear and front ends through the P / TM sensors 109F and 109R. Is started (step 3).

  When there is no Bk, Y, C or M mark in the field of view of the P / TM sensors 109F and 109R, the detection signals Sdr and Sdf of the P / TM sensors 109F and 109R are at a high level H (about 4V), and there is a mark. The detection signal Sdr is at a low level L (about 1 V), and the detection signal Sdr varies as shown in FIG. 14 due to the constant speed movement of the intermediate transfer belt 105. A part of the fluctuation is enlarged and shown in FIG.

  In FIG. 15A, the descending area where the level of the mark detection signal is reduced corresponds to the leading edge area of the mark, and the rising area where the mark is rising corresponds to the trailing edge area of the mark. A region having a mark width w is between the rising region and the rising region.

  In step 4 of FIG. 13, in the process where the start marks Msr and Msf arrive in the field of view of the P / TM sensors 109F and 109R and the detection signals Sdr and Sdf change from H to L, the window comparator 39r or 39f of FIG. The detection signal Sdr or Sdf waits until the detection signal Swr = L or Swf = L indicating that the detection signal Sdr or Sdf is 2 to 3V. That is, it is monitored whether at least one edge region of the start marks Msr and Msf has arrived in the visual field of the P / TM sensors 109F and 109R.

  When it arrives, the timer Tsp whose time limit value is Tsp (for example, 50 μsec) is started, and when it times out, the “timer Tsp interrupt” (TIP) shown in FIG. 17 is executed and the timer interrupt is permitted (step of FIG. 13). 5). Then, the sampling number value Nos of the sampling number register Nos is initialized to 0, and writing to the r memory (rear side mark read data storage area) and the f memory (front side mark read data storage area) allocated to the FIFO memory in the CPU 402 is performed. Addresses Noar and Noaf are initialized to start addresses (step 6 in FIG. 13). Then, it waits for the timer Tw2 to time out. That is, it waits for all the eight sets of test patterns to pass through the field of view of the P / TM sensors 109F and 109R (step 7 in FIG. 13).

  Here, with reference to FIG. 17, the contents of the “interrupt of timer Tsp” (step TIP in FIG. 17) will be described. It should be noted that this process is executed every time the timer Tsp whose time limit value is Tsp expires. At the beginning of this process, the CPU 402 restarts the timer Tsp (step 11 in FIG. 17) and instructs the A / D conversion circuit 401 to perform A / D conversion (step 12 in FIG. 17). That is, the instruction signals Scr and Scf are temporarily set to the A / D conversion instruction level L. Then, the sampling number value Nos in the sampling number register Nos, which is the number of instructions, is incremented by 1 (step 13 in FIG. 17).

  As a result, the elapsed time since Nos × Tsp detected the leading edge of the start mark Msr or Msf (= the belt movement direction y along the surface of the intermediate transfer belt 105 based on the start mark Msr or Msf). This represents the current detected position on the intermediate transfer belt 105 by the P / TM sensors 109F and 109R.

  Then, it is checked whether the detection signal Swr of the window comparator 39R (see FIG. 16) is L (P / TM sensor 20R is detecting the edge portion of the mark and 2V ≦ Sdr ≦ 3V) (step of FIG. 17). 14) If so, the sampling number value Nos of the sampling number register Nos and the A / D conversion data Ddr (value of the mark detection signal Sdr of the P / TM sensor 109R) are written as write data to the address Noar of the r memory. Write (step 15 in FIG. 17).

  Then, the write address Noar of f memory is incremented by 1 (step 16 in FIG. 17). When the detection signal Swr of the window comparators 39R and 39f is H (Sdr <2V or 3V <Sdr), data is not written into the r memory. This is for reducing the amount of data written to the memory and simplifying subsequent data processing.

  Next, similarly, it is checked whether the detection signal Swf of the window comparator 39f is L (P / TM sensor 109f is detecting the edge portion of the mark and 2V ≦ Sdf ≦ 3V) (step 17 in FIG. 17). If so, the sampling number value Nos of the sampling number register Nos and the A / D conversion data Ddf (the value of the mark detection signal Sdf of the P / TM sensor 109f) are written as write data to the address Noaf of the f memory. (Step 18 in FIG. 17). Then, the write address Noaf of the f memory is incremented by 1 (step 19 in FIG. 17).

  Since such interrupt processing is repeatedly executed at the Tsp cycle, when the mark detection signals Sdr and Sdf of the P / TM sensors 109F and 109R change to high and low as shown in FIG. In the r memory and the f memory allocated to the FIFO memory, only the digital data Ddr and Ddf of the detection signals Sdr and Sdf within the range of 2V to 3V shown in FIG. Stored.

  Since the sampling number value Nos of the sampling number register Nos is incremented by 1 in the Tsp cycle, and the intermediate transfer belt 105 moves at a constant speed, the number value Nos is based on the detected start mark as the intermediate transfer belt 105. It shows the y position along the top surface.

  In addition, as shown in FIG. 15B, the center position “a” of the descending area where the level of the mark detection signal is lowered and the center position “b” of the ascending area that is rising next are within the range of 2V to 3V. Is the center position of one mark Akr in the y direction, and similarly, the center position c of the descending area where the level of the mark detection signal that appears next to the mark Akr decreases, and the next rising position. The middle point Ayrp of the center position d of the rising area is the center position of the other mark Ayr in the y direction. These mark center positions Akrp, Ayrp,... Are calculated by calculation CPA (FIG. 13, FIG. 18) of the mark center point position described later.

  Reference is again made to FIG. After the last mark of the last 8th set in the test pattern passes the P / TM sensors 109F and 109R, the timer Tw2 times out. Then, the CPU 402 prohibits interruption of the timer Tsp (steps 7 and 8 in FIG. 13).

  As a result, the A / D conversion of the detection signals Sdr and Sdf in the Tsp cycle shown in FIG. 17 stops. The CPU 402 calculates the center position of the mark based on the detection data Ddr and Ddf in the R memory and f memory of the FIFO memory therein (step CPA in FIG. 13), and sets 8 sets for each of the rear R and the front f. In this pattern, the appropriateness of the distribution of the detected mark center point positions is verified, the inappropriate detection pattern (set) is deleted (step SPC in FIG. 13), and the average pattern of the proper detection patterns is obtained ( Step MPA in FIG. 13).

  FIG. 13 and FIG. 18 show the contents of “calculation of mark center point position” (CPA). Here, “calculation of mark center point position of rear r” (CPAr) and “calculation of mark center point position of front f” (CPAf) are executed.

  In “calculation of mark center point position of rear r” (CPAr), the CPU 402 first initializes the read address RNoar of the r memory allocated to the FIFO memory in the first, and the data of the center point number register Noc is set to the first edge. Is initialized to 1 (step 21 in FIG. 18).

  Then, the data Ct in the one-edge region sample number register Ct is initialized to 1, and the data Cd and Cu in the descending number register Cd and the ascending number register Cu are initialized to 0 (step 22 in FIG. 18). Then, the read address RNoar is written into the edge area data group start address register Sad (step 23 in FIG. 18). The above is preparation processing for data processing of the first edge region.

  Next, the CPU 402 sends data (y position Nos: N · RNoar, detection level Ddr: D · RNoar) from the r memory address RNoar, and data (y position Nos: N · (RNoar + 1) from the next address RNoar + 1. ), Detection level Ddr: D · (RNoar + 1)), and first, whether the y position difference between the two data is E (for example, E = w / 2 = for example, a value corresponding to 1/2 mm) or less (on the same edge region). A check is made (step 24 in FIG. 18), and if so, it is checked whether the mark detection data Ddr has a downward trend or an upward trend (step 25 in FIG. 18). Cd is incremented by 1 (step 27 in FIG. 18), and if there is an upward trend, the data Cu in the rise count register Cu is incremented by 1 That (step 26 in FIG. 18).

  Then, the data Ct in the one-edge sample number register Ct is incremented by one (28). Then, it is checked whether the r memory read address RNoar is the end address of the r memory (step 29 in FIG. 18). If it is not the end address, the memory read address RNoar is incremented by 1 (step 30 in FIG. 18). The above-described processing (steps 24 to 30 in FIG. 18) is repeated.

  When the y position (Nos) of the read data is changed to that of the next edge area, the position difference between the position data of the front and rear memory addresses checked in step 24 of FIG. 18 is larger than E, and the CPU 402 From step 24, the process proceeds to step 31 in FIG. Here, all the sampling data of one mark edge (leading edge or trailing edge) area have been checked for downward and upward tendency.

  Therefore, it is checked whether the sample number data Ct in the one-edge sample number register Ct at this time is an equivalent value in one edge region (in the range of 2V to 3V). That is, it is checked whether F ≦ Ct ≦ G (step 31 in FIG. 19). F is a lower limit (setting of the number of times of writing the sample value Ddr to the r memory while the detection signal Sdr is 2 V or more and 3 V or less when the leading edge or the trailing edge of the mark formed normally is detected. Value) and G are upper limit values (set values).

  If Ct is F ≦ Ct ≦ G, the correctness / incorrectness of the data of one mark edge that has been normally read and stored is completed, and the result is “appropriate”. It is checked whether the obtained detection data group has a downward tendency or an upward tendency as a whole of the edge region (2 V or more and 3 V or less) (steps 32 and 34 in FIG. 19).

  In this embodiment, when the data Cd in the descending number register Cd is 70% or more of the sum Cd + Cu of the data Cu in the descending number register Cu and the data Cu in the ascending number register Cu, the memory edge No. When the information Down indicating the descending is written to the address addressed to Noc (step 33 in FIG. 19) and the data Cu in the ascending number register Cu is 70% or more of Cd + Cu, the memory edge No. Information Up indicating an increase is written in the address addressed to Noc (step 35 in FIG. 19). Further, the average value of the y position data of the edge region, that is, the center point position of the edge region (a, b, c, d,... Write to the address addressed to Noc (step 36 in FIG. 19).

  Next, the edge No. It is checked whether Nos has become 130 or more, that is, calculation of the center positions of the leading edge region and trailing edge region of all of the start mark Msr and the eight sets of mark patterns has been completed (step 37 in FIG. 19). . If this has been completed, or if all of the stored data has been read from the r memory, the mark center point position is calculated based on the edge center point position data (y position calculated in step 36). (Step 39 in FIG. 19).

  That is, the memory edge No. The address data (falling / rising data & edge center point position data) is read, and the position difference between the center point position of the preceding falling edge area and the center point position of the immediately following rising edge area is the width of the mark in the y direction. Check if it is within the range corresponding to w, and if it is off, delete these data.

  If it is within the range, the average value of these data is set as the center point position of one mark. Write to memory. If mark formation, mark detection, and detection data processing are all appropriate, with respect to rear r, start mark Msr and 8 sets of marks (1 set 8 marks × 8 sets = 64 marks), a total of 65 mark center points Position data is obtained and stored in memory.

  Next, the CPU 402 executes “calculation of the mark center point position of the front f” (step CPAf in FIG. 19), and performs the data processing of the “calculation of mark center point position of the rear r” CPAr (see FIG. 18). Are similarly performed on the measurement data in the f memory. With respect to the front f, if mark formation, measurement, and measurement data processing are all appropriate, start mark Msf and 8 sets of marks (64 marks), a total of 65 mark center point position data are obtained and stored in memory. Is done.

  Refer to FIG. 13 again. When the mark center point position is calculated as described above (step CPA in FIG. 13), the CPU 402 performs the following “validation of each set pattern” (step SPC in FIG. 13) and the mark center point position written in the memory. It is verified whether the data group is the center point distribution corresponding to the mark distribution shown in FIG. Here, the data deviating from the mark distribution equivalent to that shown in FIG. 17 is deleted in units of sets, and only the data set corresponding to the mark distribution shown in FIG. leave. If all are appropriate, 8 sets of data remain on the rear r side and 8 sets of data remain on the front f side.

  Next, the CPU 402 changes the center point position data of the first mark in each set after the second set to the first center point position of the first set in the rear r-side data set. The center point position data of the second to eighth marks are also changed by the changed difference value. That is, the center point position data group of each set after the second set is changed to a value shifted in the y direction so that the top of each set is aligned with the top of the first set. Similarly, the center point position data in each set after the second set on the front f side is also changed.

Next, the CPU 402 calculates average values Mar to Mhr (FIG. 20) of the center point position data of each mark in all sets on the rear r side in “calculation of average pattern” (step MPA in FIG. 13). Then, average values Maf to Mhf (FIG. 20) of the center point position data of each mark of all sets on the front f side are calculated. These average values are distributed as shown in FIG. 20, virtual average position marks MAkr (representative of Bk rear orthogonal mark), MAyr (representative of Y rear orthogonal mark), MAcr (rear orthogonal mark of C). Representative), MAmr (representative of M rear orthogonal mark), MBkr (representative of Bk rear oblique mark), MByr (representative of Y rear oblique mark), MBcr (representative of C rear oblique mark), And MBmr (representative of M rear oblique mark), MAkf (representative of front orthogonal mark of Bk), MAyf (representative of front orthogonal mark of Y), MAcf (representative of front orthogonal mark of C), MAmf (Representative of M front orthogonal mark), MBkf (representative of Bk front oblique mark), MByf (representative of Y front oblique mark), MBcf (representative of C front flow mark) Representative DOO diagonal mark), and indicates the center point position of MBmr (representative of front diagonal mark of M).
The above is the content of “test pattern formation and measurement” (PFM) shown in FIG.

  Reference is again made to FIG. Please also refer to FIG. 21 showing the distribution of the test pattern formed in one circumference of the intermediate transfer belt 105 together with the mark formation position shift corresponding to the rotation angle of the photosensitive drum. In the displacement amount calculation (DAC) shown in FIG. 11, the CPU 402 calculates the image formation displacement amount as follows. The calculation (Acy) of the image forming deviation amount of Y is specifically shown below.

  Sub-scanning deviation amount dyy: deviation amount dyy = (Mbr−Mar) − of the difference (Mbr−Mar) in the center point position between the Bk orthogonal mark MAkr and the Y orthogonal mark MAyr on the rear r side with respect to the reference value d (FIG. 17) d.

Main scanning deviation amount dxy: deviation amount dxyr = (Mfr−Mbr) −4d with respect to the reference value 4d (FIG. 17) of the difference (Mfr−Mbr) of the center point position between the orthogonal mark MAyr on the rear r side and the oblique mark MByr
And the deviation dxyf = (Mff−Mbf) −4d of the difference (Mff−Mbf) between the center point positions of the orthogonal mark MAyf and the oblique mark MByf on the front f side with respect to the reference value 4d (FIG. 17).
The average value of dxy = (dxyr + dxyf) / 2 = (Mfr−Mbr + Mff−Mbf−8d) / 2.

Skew dSqy: difference dSqy = (Mbf−Mbr) between the center points of the orthogonal mark MAyr on the rear R side and the orthogonal mark MAyf on the front f side.

Main scanning line length shift amount dLxy: Skew dSqy = (Mff−Mfr) is subtracted from the difference (Mff−Mfr) between the center point positions of the rear r side oblique mark MByr and the front f side oblique mark MByf. Value dLxy = (Mff−Mfr) −dSqy
= (Mff-Mfr)-(Mbf-Mbr).

  The other C and M image forming deviation amounts are calculated in the same manner as the calculation related to Y (Acc, Acm). Although Bk is substantially the same, in this embodiment, since color matching in the sub-scanning direction y is based on Bk, the positional deviation amount dyk in the sub-scanning direction is not calculated for Bk (Ack). .

  In the shift adjustment (DAD) shown in FIG. 11, the CPU 402 adjusts the image forming shift amount of each color as follows. The Y shift amount adjustment (Ady) is specifically shown below.

  Adjustment of sub-scanning deviation amount dy: The start timing of image exposure (latent image formation) for forming a Y toner image is set by shifting the calculated deviation amount dyy from the reference timing (y direction).

  Adjustment of main scanning deviation amount dxy: The image data at the head of the line to the exposure laser modulator of the exposure device 109 for the line synchronization signal representing the head of the line in image exposure (latent image formation) for Y toner image formation. The sending timing (x direction) is set to be shifted from the reference timing by the calculated shift amount dxy.

  Adjustment of the skew dSqy: The rear r side of the axially extending mirror that reflects the laser beam modulated by the Y image data facing the photosensitive drum 101 and projects it onto the photosensitive drum 101 of the exposure device 109 is supported by a fulcrum. The front f side is supported by a block slidable in the y direction. The skew dSqy can be adjusted by moving this block back and forth in the y direction with a y drive mechanism mainly composed of a pulse motor and a screw. In “adjustment of skew dSqy”, the pulse motor of this y driving mechanism is driven to drive the block from the reference y position by an amount corresponding to the calculated skew dSqy.

  Adjustment of main scanning line length shift amount dLxy: The frequency of the pixel synchronization clock for allocating image data in units of pixels on the line is set to reference frequency × Ls / (Ls + dLxy). Ls is the reference line length.

  The other adjustments of C and M image formation shift amounts are adjusted in the same manner as the adjustment for Y (Adc, Adm). Although Bk is generally the same, in this embodiment, since color matching in the sub-scanning direction y is based on Bk, the positional deviation amount dyk in the sub-scanning direction is not adjusted for Bk (Adk). . Until the next “color matching”, a color image is formed under the adjusted conditions.

[2] Example in which the influence of the detection surface distance and angle variation with respect to the sensor is reduced.
In a density detector that obtains density information of a test pattern by irradiating light from a light emitting element to a test pattern formed on the image carrier and the image carrier and detecting the reflected light by two light receiving elements In this case, the concentration detection apparatus includes one light emitting unit 51 (corresponding to the light emitting element 602 in FIGS. 4, 25, and 27) and the first light receiving unit in a case not shown in FIGS. 28 to 31. 62 (corresponding to the regular reflection light receiving element 603 in FIGS. 4, 25, and 27) and the second light receiving unit 63 (corresponding to the diffuse reflection light receiving element 604 in FIGS. 4, 25, and 27). .

  28 and 29, the first light receiving unit 62 is disposed at a position for receiving specular reflection light in relation to the light emitting unit 51 and the image carrier 105, and the second light receiving unit 63 is a position for receiving diffused light. And a surface including the optical axis of the light emitted from the light emitting unit 51 and the specularly reflected light from the surface of the image carrier 105 (more specifically, the light emitted from the light emitting unit 51 and the image carrier) The light is emitted so that the virtual plane including the optical axis of the regular reflected light from the surface 105 intersects with the traveling direction of the image carrier 105 indicated by the arrow 64 (the direction of a virtual straight line formed at a location where the virtual plane intersects the image carrier surface). 51 and the first light receiving unit 62 are disposed, and the second light receiving unit 63 is not on a surface including the optical axis of the light emitted from the light emitting unit 51 and the regular reflection light from the surface of the image carrier 105. Are arranged as follows.

The reason why the problem can be improved with this configuration will be described.
FIG. 30 shows a schematic diagram of a regular reflection detector. This conforms to the arrangement of the sensors in FIGS. Reference numeral 41 denotes a light emitting section, reference numeral 42 denotes a light receiving section, reference numeral R denotes a light beam diameter when viewed from the front, reference numeral 44 denotes a cross section of a spot diameter on the surface of the image carrier 105, and reference numeral X denotes a front view. The spot diameter, symbol Y indicates the spot diameter when viewed from the side, and symbol θ1 indicates the irradiation angle. The emission beam diameter is a perfect circle. In this case, the spot diameter X viewed from the front can be expressed as the following <Formula 1>.
X = R / COS (90−θ1) (Formula 1)
According to this <Formula 1>
For example, if θ = 60 degrees and R = 1.0 mm, X≈1.15 mm.

  Accordingly, the spot of light that irradiates the image carrier surface when it is regularly reflected on the surface of the image carrier 105 is incident on the surface of the image carrier at an angle, and thus has an elliptical shape. A virtual plane including the optical axis of the regular reflection light from the 105 plane and a direction of a virtual straight line formed at a location intersecting with the plane of the image carrier 105 (the linear direction showing the image carrier 105 in FIG. 30) is parallel to the direction. The spot diameter is longer.

  FIG. 31 and FIG. 32 schematically show the above phenomenon. In FIG. 31, a hollow ellipse 51 represents an irradiation range on the image carrier surface, and a crescent moon shaped portion 52 in the major axis direction of the ellipse indicated by cross hatching represents an enlargement amount of the irradiation area when the angle of the image carrier surface is changed. That is, the spot diameter Y does not change, the spot diameter X increases to X ′, and the amount of irradiation area expansion associated with the increase is the crescent moon shaped portion 52.

On the other hand, FIG. 32 shows a comparative example. In FIG. 29, it is assumed that the traveling direction of the image carrier 105 is an arrow 640 orthogonal to the arrow 64, and light emitted from the light emitting unit 51. And the direction of the imaginary straight line formed at the location where the virtual plane including the optical axis of the regular reflected light from the surface of the image carrier 105 intersects the image carrier surface) is perpendicular to the traveling direction of the image carrier 105 indicated by the arrow 640. In the case where the light emitting unit 51 and the first light receiving unit 62 are arranged as described above, the displacement of the spot that irradiates the image carrier surface when the image carrier 105 fluctuates in a virtual plane including the traveling direction thereof is shown. .
In this case, the spot of light that irradiates the image carrier surface when specularly reflected by the surface of the image carrier 105 is incident on the surface of the image carrier at an angle, and thus has an elliptical shape. The virtual plane including the optical axis of the regular reflected light from the surface of the image carrier 105 becomes an ellipse having a long axis in the direction of a virtual straight line formed at a location that intersects the surface of the image carrier 105 as in FIG. Although there is an ellipse shift direction by 90 degrees. For this reason, in FIG. 32, the open ellipse 51 is the irradiation range on the image carrier surface, but the irradiation area when the angle of the image carrier surface of the crescent-shaped portion 520 in the minor axis direction of the ellipse indicated by cross-hatching is changed. Represents the amount of enlargement. That is, the spot diameter X does not fluctuate, the spot diameter Y increases to Y ′, and the amount of irradiation area expansion associated with the increase is the crescent moon shape portion 520.

  In the comparison between FIG. 31 and FIG. 32, the area of the irradiated light on the image carrier (test pattern) is smaller in the case of FIG. 31 where the major axis of the ellipse increases, and increases in the minor axis of the ellipse. It is clear that the case of FIG. 32 is larger. Therefore, the light emitting unit 51 and the first light receiving unit 62 are arranged so that the plane including the optical axis of the light emitted from the light emitting unit and the regular reflection light from the surface of the image carrier is parallel to the traveling direction of the image carrier. As a result, the change in the output of the light receiving unit becomes smaller with respect to the angle variation of the image carrier 105.

  22 to 24, the direction in which the surface of the image carrier 105 fluctuates includes the traveling direction of the image carrier 105 indicated by the arrow 64 and is a virtual plane perpendicular to the surface of the image carrier 105. There is a tendency to swing within. Therefore, when the light receiving / emitting part is arranged in parallel to the virtual plane on which the image carrier whose angle changes with the image carrier changes, the area where the reflected light is out of the light receiving range in the light receiving part is smaller.

  As shown in FIG. 33, if the image carrier 105 includes the traveling direction indicated by the arrow 64 and changes with a shake angle of an angle α in a virtual plane perpendicular to the surface of the image carrier 105, the light receiving unit If 42 is a diffused light receiving part and this is on a surface including the optical axes of the light emitting part 41 and the specularly reflected light, the specularly reflected light may enter the diffused light receiving part. Therefore, as described in FIGS. 28 and 29, the first light receiving unit 62 is disposed at a position for receiving regular reflection, the second light receiving unit 63 is disposed at a position for receiving diffused light, and the light emitting unit. The light emitting unit 41 and the first light receiving unit 62 are arranged so that the surface including the optical axis of the light emitted from the light beam 41 and the regular reflection light from the surface of the image carrier is parallel to the traveling direction of the image carrier 105. In addition, the second light receiving unit 63 is arranged so as not to be on the surface including the optical axis of the light emitting unit 41 and the regular reflection light, so that it is possible to detect the density with a small variation with respect to the angle variation of the image carrier. Become.

Example 2.
An image forming apparatus to which the present invention is applied is based on an electrophotographic system. The image forming condition control device controls the development potential. In an electrophotographic image forming apparatus, the method of controlling the image density using the result of the density detection apparatus is generally used. However, if an error occurs in the result of the density detection apparatus, the image density change or the two-component developer is controlled. In this case, the toner density may change, and background stains and toner scattering may occur.

  In this regard, an image forming apparatus using an electrophotographic system, which controls the development potential as an image forming condition control apparatus, can accurately detect the density even if the image forming conditions change due to environment or aging deterioration. The image density can be kept constant.

Example 3
The image forming apparatus to which the present invention is applied is a tandem type color electrophotographic apparatus. The image carrier is a transfer belt. In the tandem type color image forming apparatus, since there are a plurality of photoconductors, a plurality of sensors are required for density detection on the photoconductor. In addition, when the density is detected with the transfer body, the density after transfer is measured, so that there is an advantage that a density closer to the image can be detected. However, in general, the transfer belt is not as rigid as the photoconductor, so that the running is unstable. In the density detection unit, the unstable running appears as an angle change with respect to the sensor, resulting in a density detection error. In this regard, if the image forming apparatus is a tandem color electrophotographic apparatus and the image carrier is a transfer belt, an inexpensive and stable image can be formed by accurately detecting the density of multiple colors with a small number of sensors. can do.

Example 4
In this example, in FIG. 29, the irradiation range of the light emitting unit 51 is a range in a direction parallel to the traveling direction indicated by the arrow 64 of the image carrier 105, and a direction perpendicular to the traveling direction indicated by the arrow 64 of the image carrier. When the range is b, a ≧ b. This is particularly effective for the problem of detection variation of the regular reflection light receiving unit, and accurate density detection can be performed. A wider light receiving range of the light receiving unit in the direction of fluctuation of the irradiation area accompanying the change in the angle of the image carrier is advantageous because the change in output is smaller. Therefore, as shown in FIG. 29, the beam diameter of the light emitting unit 51 is set so that the irradiation range of the light emitting unit 51 is a range in the direction parallel to the traveling direction of the image carrier indicated by the arrow 64, and the traveling of the image carrier. When the range between the direction and the vertical direction is b, if a ≧ b, both sensitivity enhancement and robustness against the angle change of the image carrier can be achieved.

Example 5.
In this example, in FIG. 29, the light receiving range of the first light receiving unit 62 is indicated by the arrow 64 of the image carrier 105, where a ′ is a range in the direction parallel to the traveling direction of the image carrier 105 indicated by the arrow 64. When the range between the traveling direction and the vertical direction is b ′, a ′ ≧ b ′. This is particularly effective for the problem of detection variation of the regular reflection light receiving unit, and more accurate density detection can be performed.

Example 6
In this example, both the irradiation range of the light emitting unit in Example 4 and the light receiving range of the light receiving unit in Example 5 are used. In particular, it is effective for the problem of variation in detection of the regular reflection light receiving part, and since both the light receiving range of the light emitting part and the light receiving part of the light emitting part are used, more accurate density detection can be performed. By reducing the influence of the variation of the image carrier on the irradiation range of the light emitting unit and the light receiving range of the light receiving unit, the sensitivity can be improved and the robustness against the angle change of the image carrier can be further achieved by the combination.

Example 7.
In FIG. 28, when the distance between the second light receiving unit 63 and the light emitting unit 51 is L1, and the distance between the first light receiving unit 62 and the second light receiving unit 63 is L2, L1 <L2. More accurate density detection can be performed. The distance of the diffuse reflection light receiving unit and the light - emitting unit L1, and a distance between the specular reflection light receiving portion and the diffuse reflection light receiving portion and the L2, the diffuse reflection light receiving portion is the closer to the specular reflection light receiving portion, of the image bearing member When the angle of the reflection surface changes, the possibility that regular reflection light enters the diffused light receiving unit increases. Therefore, if L1 <L2, the detection accuracy of the diffused light receiving unit is improved.

Example 8
In this example, a lens is used for at least one of the light emitting unit 51 or the first light receiving unit 62. This improves detection accuracy and enables more accurate concentration detection.
When a lens is used, the beam diameter of the light emitted from the LED can be accurately controlled by the lens unit. Therefore, the irradiation ranges a and b of the light emitting part can be controlled more accurately by the lens, so that both sensitivity enhancement and robustness against the angle change of the image carrier can be achieved.

Example 8
It uses position detection together. In addition to solving the problem with respect to the density detection exemplified, the same problem can be solved in the positional deviation detection. Therefore, the position detection accuracy can be improved at low cost by using the position detection together.

It is the schematic of the image forming apparatus which shows an image formation process part. It is a front view of an image forming unit. FIG. 2 is a perspective view during a test pattern creation operation in the image forming apparatus of FIG. 1. It is a block diagram of a P / TM sensor. 1 is an overall schematic diagram of an image forming process control system. 3 is a flowchart of image forming process control. FIG. 2 is a top view of an intermediate transfer belt during a test pattern creation operation in the image forming apparatus of FIG. 1. FIG. 2 is a top view of an intermediate transfer belt during a test pattern creation operation in the image forming apparatus of FIG. 1. FIG. 5A is a characteristic diagram when the amount of color toner adhesion of a test pattern on an intermediate transfer belt is detected by a regular reflection light receiving element, and FIG. FIG. 6C is a characteristic diagram when the black toner adhesion amount of the test pattern on the intermediate transfer belt is detected by the regular reflection light receiving element. FIG. 6 is a diagram illustrating a table used when converting normalized values into toner adhesion amounts. It is a flowchart which shows the outline | summary of "color matching" CPA. FIG. 3 is a plan view schematically showing an intermediate transfer belt and each color mark formed on the surface thereof. It is a flowchart which concerns on formation and measurement of a test pattern. FIG. 6 is a diagram showing side-by-side time charts showing a distribution of color marks formed on an intermediate transfer belt and a change in mark detection signal level of an optical sensor. (A) is a time chart showing an enlarged part of the time chart of the detection signal shown in FIG. 14, and (b) is the A / D conversion data of the detection signal shown in (a) whose CPU is CPU. It is the time chart which extracted and showed only the range written in the FIFO memory inside. It is the block diagram which showed the structure of a part of main body control part. It is a flowchart which shows the content of the interruption process permitted at step 5 in FIG. 14 is a flowchart showing a part of the content of “calculation of mark center point position” CPA shown in FIG. 13; It is a flowchart which shows the remainder of the content of "calculation of mark center point position" CPA shown in FIG. It is a top view which shows the average value data calculated by "calculation of an average pattern" MPA shown in FIG. 13, and the virtual mark which becomes a center point position. 6 is a graph showing the distribution of test patterns formed on the circumference of the intermediate transfer belt, along with mark formation position deviation corresponding to the rotation angle of the photosensitive drum. It is a figure explaining the example of a change of an image carrier. It is a figure explaining the example of a change of an image carrier. It is a figure explaining the example of a change of an image carrier. It is a block diagram of a sensor. It is the figure which represented the incident amount change of the light to the regular reflection light receiving element of the light irradiated from the light emitting element by transition of time. It is a block diagram of a sensor. (A) is a front view explaining the arrangement of the sensor, (b) is a side view explaining the arrangement of the sensor, and (c) is a plan view explaining the arrangement of the sensor. It is a perspective view explaining arrangement of a sensor. It is a figure explaining the relationship between the state of an image carrier and an irradiation spot. It is a figure explaining the change part by the irradiation spot displacement direction which consists of ellipses. It is a figure explaining the change part by the irradiation spot displacement direction which consists of ellipses. It is a figure explaining the relationship between the state of an image carrier and an irradiation spot.

Explanation of symbols

41, 51 Light emitting part 42 Light receiving part 44 Spot cross section 51 Ellipse (outlined)
62 1st light-receiving part (regular reflection light-receiving element)
63 2nd light-receiving part (diffuse reflection light-receiving element)
64 Arrows 101Y, 101C, 101M, 101K Photosensitive drum (first image carrier)
102Y, 102C, 102M, 102K Developing device 105 (constituting the first transfer device) Intermediate transfer belts 106Y, 106C, 106M, 106K (constituting the first transfer device) Primary transfer device 108 Secondary transfer roller (constituting the first transfer device) Second transfer device)
200 Exposure apparatus 201 Test pattern (P pattern)
201F Front P Pattern 201R Back P Pattern 202F Front TM Pattern 202R Back TM Pattern 202 Test Pattern (TM Pattern 301 Charging Device

Claims (7)

A density detector for acquiring density information of a test pattern by irradiating light from a light emitting element to a test pattern formed on the image carrier and the image carrier and detecting reflected light by two light receiving elements; In an image forming apparatus having an image forming condition control device that controls image forming conditions based on information obtained from a density detecting device,
The concentration detection apparatus includes one light emitting unit and two light receiving units, the first light receiving unit is disposed at a position for receiving regular reflection, and the second light receiving unit is disposed at a position for receiving diffused light, In addition, the light emitting part and the first light receiving part are arranged so that the surface including the optical axis of the light irradiated from the light emitting part and the regular reflection light from the surface of the image carrier is parallel to the traveling direction of the image carrier. And the second light receiving part is not on the surface including the optical axis of the light emitting part and the regular reflection light,
Irradiation range of the light-emitting portion, the traveling direction and in the direction parallel to the range of the image carrier is a, when the traveling direction and in the vertical direction range of the image bearing member and is b, Ri a ≧ b der, and
When the distance between the second light receiving unit and the light emitting unit is L1, and the distance between the first light receiving unit and the second light receiving unit in the direction perpendicular to the traveling direction of the image carrier is L2, An image forming apparatus, wherein L1 <L2 .   2. The image forming apparatus according to claim 1, wherein the image forming apparatus is an electrophotographic system, and the image forming condition control device controls a developing potential.   2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a tandem color electrophotographic apparatus, and the image carrier is a transfer belt.   2. The image forming apparatus according to claim 1, wherein the light receiving range of the first light receiving unit is a 'in a range parallel to the traveling direction of the image carrier and b is a range perpendicular to the traveling direction of the image carrier. An image forming apparatus, wherein “a” ≧ b ′. 2. The image forming apparatus according to claim 1, wherein when the irradiation range of the light emitting portion is a, the range in the direction parallel to the traveling direction of the image carrier is b, and the range in the direction perpendicular to the traveling direction of the image carrier is b. ≧ b, and
When the light receiving range of the first light receiving portion is a ′ in the range parallel to the traveling direction of the image carrier and b ′ in the direction perpendicular to the traveling direction of the image carrier, a ′ ≧ b ′. An image forming apparatus. The image forming apparatus according to claim 1,
An image forming apparatus using a lens for at least one of the light emitting unit or the first light receiving unit . The image forming apparatus according to claim 1 is a color image forming apparatus that obtains a color image by superimposing a plurality of colors, and includes a density detecting device. The density detecting device according to claim 1, an image forming apparatus according to claim Rukoto be combined to detect the positional deviation of the plurality of colors.

Images