JP2016206351A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce downtime accompanying toner density adjustment.SOLUTION: A printer control part 40 detects, with an optical sensor 60, the intensity of light reflected on an empty surface generated between a preceding toner image and a subsequent toner image (between sheets) on the surface of an intermediate transfer belt 51. The printer control part 40 integrates the intensities of the light reflected on the plurality of empty surfaces to create a profile indicating the intensity of light reflected on the surface over one cycle of the intermediate transfer belt 51.SELECTED DRAWING: Figure 1

Description

  The present invention relates to density adjustment control of an image formed by an image forming apparatus.

  The electrophotographic image forming apparatus measures toner patches and adjusts image forming conditions such as developing bias (toner density adjustment) in order to maintain the tone characteristics and color reproducibility of toner images at desired characteristics. The intensity of the reflected light from the toner patch depends on the state of the surface of the image carrier (sometimes called a base). For this reason, according to Patent Document 1, the intensity of reflected light from the background of one rotation of the image carrier is measured in advance, and the sensor output value corresponding to the measurement result of the toner patch is applied to the background area where the toner patch is formed. It has been proposed to subtract the corresponding sensor output value.

JP 2005-345740 A

  The image forming apparatus described in Patent Document 1 is excellent in that the detection accuracy of the intensity of reflected light from the toner patch can be improved. However, the image forming apparatus must rotate the image carrier at least once around each timing of toner density adjustment, and acquire a profile of the intensity of reflected light from the base (hereinafter referred to as the base profile). It was. In order to acquire the base profile, the image forming apparatus must stop image formation. Therefore, a time during which the user cannot use the image forming apparatus (so-called down time) occurs. Accordingly, an object of the present invention is to reduce downtime associated with toner density adjustment.

  In order to solve the above problem, an image forming apparatus according to the present invention is based on an image carrier that is rotationally driven, a correction unit that corrects image data based on gradation correction conditions, and the corrected image data. Image forming means for forming an image on the image carrier, transfer means for transferring the image formed on the image carrier by the image forming means to a recording material, and light toward the image carrier. An output unit that outputs a signal according to the intensity of the reflected light received by the light receiving unit, and an image forming unit that outputs the image. A first signal from the output unit corresponding to the position determined by the determination unit while the image forming unit is forming a plurality of images; 1 of the image carrier Generating means for generating correction data for a minute, and causing the image forming means to form a measurement image on the image carrier, and a second signal corresponding to the intensity of reflected light from the measurement image by the output means; And updating means for updating the gradation correction condition based on the correction data generated by the generating means.

  According to the present invention, it is possible to reduce downtime associated with toner density adjustment.

The figure which shows the structure of an image forming apparatus The figure explaining HP mark and an optical sensor Block diagram of printer controller Diagram showing an example of a toner patch The figure which shows an example of the intensity | strength of the reflected light about a base | substrate or a toner patch Diagram showing when to obtain the base profile Diagram showing when to obtain the base profile Diagram showing when to obtain the base profile The figure which shows an example of the function of CPU Flow chart showing toner density adjustment executed during image formation Flow chart showing background profile creation processing

[Entire configuration of image forming apparatus]
FIG. 1 is a schematic sectional view of the image forming apparatus 100. The image forming apparatus 100 is a copier capable of forming a multicolor image on a sheet (recording paper, OHT sheet, cloth, resin, etc.) using an electrophotographic method, and includes a printer unit 10 and a reader unit 20. doing.

  The printer unit 10 serves as first, second, and third images for forming yellow (Y), magenta (M), cyan (C), and black (K) images as image forming units that form toner images. And a fourth image forming unit (station). The configuration of each image forming unit is the same except for the color of the toner to be used. The printer control unit 40 controls the four image forming units based on the image signal output from the reader unit 20.

  The image forming unit is provided with a photosensitive drum 1 which is a cylindrical photosensitive member as an image carrier. The photosensitive drum 1 rotates in the direction of arrow R1. The surface of the photosensitive drum 1 is charged to a uniform potential by a charging roller 2 as a charging unit. The laser beam scanner 3 as an exposure unit irradiates the surface of the photosensitive drum 1 with a light beam while controlling the amount of light by the printer control unit 40 to form an electrostatic latent image. A developing device 4 as a developing unit is supplied with a predetermined developing voltage from a high voltage driver (not shown), and attaches toner to the electrostatic latent image to develop the toner image (visible image). The developing device 4 of this embodiment contains a two-component developer having non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as developers. The developing device 4 has a developing sleeve 44 as a developer carrying member disposed to face the photosensitive drum 1. Then, by supplying toner from the developer carried on the developing sleeve 44 to the photosensitive drum 1, the electrostatic latent image on the photosensitive drum 1 is developed into a toner image. The toner image is primarily transferred to the intermediate transfer belt 51 by the primary transfer roller 6. The intermediate transfer belt 51 is an endless belt and functions as an image carrier and an intermediate transfer member. The intermediate transfer belt 51 rotates in the direction indicated by the arrow R2. Toner remaining without primary transfer is removed from the surface of the photosensitive drum 1 by a cleaning device 7 as a cleaning means. The toner image formed on the intermediate transfer belt 51 is secondarily transferred to the sheet by a secondary transfer roller pair (roller 71 and roller 72). The toner image secondarily transferred to the sheet is fixed on the sheet by the fixing device 73. Note that the sheet may be referred to as a recording medium, a recording material, a sheet, a transfer paper, a transfer material, or a transfer medium.

  The reader unit 20 is a so-called image scanner. A light source 23 irradiates illumination light to the document 21 placed on the document table 22. Reflected light from the document 21 forms an image on the CCD sensor 25 via an optical system 24 such as a lens. The CCD sensor 25 is an image sensor that outputs an image signal corresponding to reflected light from the document 21. In particular, the intensity of the reflected light from the toner image indicates the reflection density (luminance value) of the toner image. A reading unit composed of the light source 23, the optical system 24, and the CCD sensor 25 moves in the direction of the arrow A (sub-scanning direction) shown in FIG. The image processing unit 26 converts the analog image signal from the CCD sensor 25 into a digital image signal and generates image data. Image data is a set of reflection densities (luminance values). The image processing unit 26 converts image data composed of RGB luminance values into image data composed of YMCK density values and outputs the image data to the printer control unit 40.

<Detection of intermediate transfer belt surface position>
An HP mark 53 is provided on the inner peripheral side of the intermediate transfer belt 51. The HP sensor 52 is a sensor that detects the home position (HP) of the intermediate transfer belt 51. The HP sensor 52 outputs a detection signal every time it detects the HP mark 53 that is a position detection member. The position detection member is, for example, a member that can be detected optically or magnetically.

  As shown in FIG. 2A, the HP mark 53 is affixed to the inner peripheral surface of the intermediate transfer belt 51 so as to pass through the detection region 54 of the HP sensor 52. When the HP mark 53 is an optical member, the HP sensor 52 is an optical sensor. The HP sensor 52 can detect the HP mark 53 from the difference between the reflectance of the inner peripheral surface of the intermediate transfer belt 51 and the reflectance of the HP mark 53.

  The optical sensor 60 is a light detection unit that detects reflected light from the surface (which may be called an outer peripheral surface, an image forming surface or a base) of the intermediate transfer belt 51 and reflected light from a toner image formed on the surface. is there. The light receiving surface of the optical sensor 60 is disposed to face the surface of the intermediate transfer belt 51.

<Detection of reflected light intensity>
FIG. 2B shows the moment when the toner image 104 formed on the surface of the intermediate transfer belt 51 passes through the detection area of the optical sensor 60. The LED driving unit 106 is a circuit that drives the LED 107 that is a light emitting unit. The light receiving circuit 109 is a circuit that amplifies a detection signal output from the photodiode 108 that is a light receiving unit, converts the detection signal into a digital value, and calculates data indicating the intensity of reflected light based on the converted detection signal. is there. The light receiving circuit 109 may further calculate and output the toner density of the toner image from this data. These arithmetic functions provided in the light receiving circuit 109 may be implemented in a CPU of the printer control unit 40 described later. However, in the following, it is assumed that the light receiving circuit 109 outputs data on the intensity of reflected light. As described above, the optical sensor 60 may output an analog detection signal indicating the intensity of the reflected light, or may output a digital detection signal (data). The analog detection signal is converted into digital data by an analog-digital conversion circuit provided outside the optical sensor 60 and input to the CPU. The analog-digital conversion circuit may be built in the CPU. In any case, the optical sensor 60 outputs a first signal corresponding to the intensity of the reflected light and a second signal corresponding to the intensity of the reflected light from the measurement image from the ground on which no image is formed.

  The angle formed by the optical axis of the LED 107 and the normal line of the intermediate transfer belt 51 is, for example, 45 degrees. That is, the light irradiation angle is inclined 45 degrees with respect to the normal line. The photodiode 108 is installed at a symmetrical position with respect to the LED 107 around the normal line of the intermediate transfer belt 51. The photodiode 108 receives the reflected light from the surface of the intermediate transfer belt 51 or the toner image 104, and outputs a detection signal corresponding to the intensity of the reflected light to the light receiving circuit 109.

  The intermediate transfer belt 51 is made of a resin film such as polyimide, for example. The reflectance of the surface of the intermediate transfer belt 51 is higher than the reflectance of the toner image 104. The optical sensor 60 detects this difference in reflectance, and calculates the intensity (toner density) of reflected light from the toner image 104.

<Functions of printer control unit>
FIG. 3 is a block diagram of the printer control unit 40 according to the present embodiment. The CPU 201 is a central arithmetic processing unit in the printer control unit 40. The profile memory 202 functions as a first storage unit that stores the intensity of the reflected light from the surface of the intermediate transfer belt 51 and the position of the surface where the intensity of the reflected light is acquired in association with each other. The intensity of the reflected light is acquired by the optical sensor 60. The position of the surface where the intensity of the reflected light is acquired is detected by the HP sensor 52. The patch memory 203 stores the intensity of the reflected light detected by the optical sensor 60 for the toner image formed on the surface of the intermediate transfer belt 51 and the position of the surface where the intensity of the reflected light is acquired in association with each other. It functions as a second storage means. The timer 204 measures an elapsed time from the timing when the HP mark 53 is detected. This elapsed time indicates the position of each surface on the intermediate transfer belt 51 based on the position where the HP mark 53 is provided. The intermediate transfer belt 51 is controlled to have a predetermined rotation speed. Therefore, the elapsed time measured by the timer 204 indicates the amount of rotational movement of the intermediate transfer belt 51 with reference to the position where the HP mark 53 is provided. The CPU 201 calculates the toner density based on the output results of the HP sensor 52 and the optical sensor 60, and controls the image forming conditions (tone correction conditions) of the printer unit 10 so as to maintain the desired toner density. A plurality of timers 204 may be provided to measure various timings and elapsed times. The timing and elapsed time described below are measured by one of the plurality of timers 204. The timer 204 may be a counter or a real time clock.

<Toner patch (measurement image)>
FIG. 4 shows an example of a toner patch formed on the surface of the intermediate transfer belt 51. The toner patch has a square shape of 25 mm in length and width. For each of Y, M, C, and K, toner patches are formed with eight gradation levels. That is, a total of 32 toner patches are formed on the intermediate transfer belt 51 along the rotational direction. Here, the toner patch is disposed so as to pass through the detection region 61 of the optical sensor 60 indicated by a broken line. The density gradation for each toner patch is set as follows.

Y1, M1, C1, K1 = 12.5%
Y2, M2, C2, K2 = 25%
Y3, M3, C3, K3 = 37.5%
Y4, M4, C4, K4 = 50%
Y5, M5, C5, K5 = 62.5%
Y6, M6, C6, K6 = 75%
Y7, M7, C7, K7 = 87.5%
Y8, M8, C8, K8 = 100%
<Correction of reflected light intensity>
FIG. 5A shows a detection signal output from the photodiode 108 when the optical sensor 60 measures the intermediate transfer belt 51 on which no toner image is formed. FIG. 5B shows a detection signal output from the photodiode 108 when the toner patches M <b> 1 to M <b> 4 formed on the intermediate transfer belt 51 pass through the detection region 61. The horizontal axis indicates the rotational movement amount x of the intermediate transfer belt 51 with the origin at the timing when the HP mark 53 is detected. The rotational movement amount x may be indicated by a distance or may be indicated by time. Here, the rotational movement amount x is described as a parameter having a unit of distance. The area of the intermediate transfer belt 51 shown in FIG. 5A and the area of the intermediate transfer belt 51 shown in FIG. 5B are the same area.

  As shown in FIG. 5A, the detection signal corresponding to the intermediate transfer belt 51 on which the toner image is not formed is uneven. This is because the surface of the intermediate transfer belt 51 has minute irregularities. Further, the surface of the intermediate transfer belt 51 is changed by sliding between the intermediate transfer belt 51 and the photosensitive drum 1, sliding between the intermediate transfer belt 51 and the roller 72, and sliding with a cleaning member that cleans the intermediate transfer belt 51. It is also known to do. As shown in FIG. 5B, unevenness due to the surface state of the intermediate transfer belt 51 also occurs in the detection signals corresponding to the toner patches M1 to M4. The unevenness on the surface of the intermediate transfer belt 51 has caused the measurement accuracy of the toner patch by the optical sensor 60 to be lowered. Therefore, if the influence of unevenness of the detection signal corresponding to the intermediate transfer belt 51 on which no toner image is formed can be reduced, the measurement accuracy is increased.

  Based on the output of the HP sensor 52, the CPU 201 specifies an area (hereinafter referred to as a surface area) where each toner patch is formed in the circumferential direction (rotational direction) of the intermediate transfer belt 51. Specifically, when the HP sensor 52 detects the HP mark 53, the CPU 201 measures the elapsed time T by the timer 204 and calculates the circumferential movement amount x of the intermediate transfer belt 51. The elapsed time T may be used as it is as the rotational movement amount x. The rotational movement amount x is obtained by multiplying the elapsed time T by the peripheral speed v of the intermediate transfer belt 51. In the present embodiment, it is assumed that the peripheral length xb of the intermediate transfer belt 51 is 895 mm and the peripheral speed V is 246 mm / s. For this reason, if the elapsed time T is 2 seconds, the rotational movement amount x is 492 mm. The CPU 201 calculates the rotational movement amount x1 of the front end of the toner patch and the rotational movement amount x2 of the rear end, and specifies the surface area X of the toner patch. Thus, the surface region X may be used as data indicating the range of the surface on which the toner patch is formed. The surface region Xi may be defined as a surface region from the surface position xj to the surface position xk, for example.

  The CPU 201 acquires a background profile corresponding to the calculated surface area X with reference to the profile memory 202. As shown in FIG. 5A, the profile memory 202 stores a background profile for one rotation of the intermediate transfer belt 51 measured in advance. That is, the background profile is data in which a position on the intermediate transfer belt 51 is associated with a detection signal when the optical sensor 60 measures the position.

  The CPU 201 calculates the difference between the detection signal Ai corresponding to the toner patch and the detection signal Bi corresponding to the position where the toner patch is formed. Then, the CPU 201 determines the detection signal Ai ′ in which the influence of the unevenness on the surface of the intermediate transfer belt 51 is reduced. Note that i indicates the surface region Xi. FIG. 5C shows a detection signal in which the influence of the unevenness on the surface of the intermediate transfer belt 51 is reduced. As can be seen by comparing FIG. 5B and FIG. 5C, the nonuniformity of the detection signal due to the surface state of the intermediate transfer belt 51 is reduced.

  The method for correcting the detection signal of the optical sensor 60 is not limited to this method. This is because the feature of the present embodiment is the method of creating a base profile. For example, the CPU 201 may create a normalized background profile in advance and correct the detection signal corresponding to the toner patch. More specifically, the CPU 201 normalizes the background profile acquired in advance, and calculates the correction magnification according to the area (the rotational movement amount x from the HP mark 53) where the toner patch is formed from the normalized background profile. . The CPU 201 multiplies the detection signal corresponding to the toner patch by a correction magnification corresponding to the surface area where the toner patch is formed. As a result, unevenness of the detection signal due to the surface state of the intermediate transfer belt 51 is reduced.

<Toner density adjustment (correction of image forming conditions)>
The CPU 201 performs toner density adjustment based on the detection signal Ai ′. The toner density adjustment method is not limited to the method described here. This is because the feature of the present embodiment is the method of creating a base profile. The CPU 201 maintains the toner density at a desired density by adjusting the developing bias applied to the developing device 4. Further, the CPU 201 may be configured to generate a lookup table that corrects the gradation characteristics of the toner image formed by the printer unit 10 to ideal gradation characteristics. The look-up table is a conversion table showing the correspondence between the value of the input image signal and the signal value for forming an image with the target density. That is, the look-up table holds tone correction conditions. The CPU 201 converts the image signal transferred from the external PC based on the lookup table, and converts the image signal output from the reader unit 20 based on the lookup table. The printer unit 10 forms a toner image based on the converted signal value. For example, the CPU 201 may update the lookup table based on the detection signal Ai ′ corresponding to the toner patch. In this embodiment, correcting the lookup table in this way is also a method for correcting the image forming condition.

  For example, the CPU 201 executes the toner density adjustment after the number of pages of the image formed by the printer unit 10 has reached the threshold after the previous toner density adjustment. The CPU 201 includes a counter that is reset when the intermediate transfer belt 51 is replaced (when the image forming apparatus 100 is powered on). The CPU 201 starts toner density adjustment when the number of formed toner images counted by the counter exceeds a threshold value. When the toner density adjustment is executed, the CPU 201 resets the counter. In addition to the number of toner images formed, the toner density adjustment may be executed after a predetermined time has elapsed since the image forming apparatus 100 was turned on. Alternatively, the toner density adjustment may be performed after the elapsed time from the time when the printer unit 10 performed the toner density adjustment last time exceeds a predetermined time. That is, the CPU 201 executes toner density adjustment based on information correlated with the deterioration of the surface state of the intermediate transfer belt 51. Note that the CPU 201 may perform the toner density adjustment when the user is instructed to perform the toner density adjustment through the operation unit.

<Preparation method of ground profile>
FIG. 6A shows the acquisition timing of the background profile of the conventional example. In the conventional example, the intermediate transfer belt 51 is idled immediately before the toner density adjustment is executed, and the background profile is acquired. The idling means that the intermediate transfer belt 51 is rotated in a state where no toner image is formed on the surface of the intermediate transfer belt 51. During this idle rotation, image formation is interrupted. In particular, when a job for continuously forming a large number of toner images (continuous printing) is executed, downtime occurs.

  During continuous printing, an area (inter-paper or non-image forming area) where a toner image is not formed occurs between the preceding toner image and the subsequent toner image on the intermediate transfer belt. Therefore, downtime can be reduced if a background profile that covers the entire circumference of the intermediate transfer belt 51 can be created by using the gap between sheets.

  FIG. 6B shows the base profile acquisition timing in this embodiment. In the present embodiment, the CPU 201 acquires the intensity of reflected light from the background between a plurality of sheets, and creates a background profile over the entire circumference of the intermediate transfer belt 51. That is, the CPU 201 detects the intensity of the reflected light on the surface over the circumference of the intermediate transfer belt 51 by the optical sensor 60, and creates a base profile from the detection signals of the optical sensor 60 corresponding to a plurality of sheets. That is, it is possible to create a background profile by integrating the detection signals of the optical sensors 60 corresponding to a plurality of sheets.

FIG. 7 is a diagram showing the acquisition timing of the base profile during the rotation of the intermediate transfer belt 51 in the present embodiment. The CPU 201 identifies surface areas Xa, Xb, and Xc between the sheets with respect to the intermediate transfer belt 51. As described above, the surface regions Xa, Xb, and Xc can be specified based on the elapsed time by the timer 204. According to FIG. 7, the surface region Xa corresponds to the period from time ta0 to ta1. The surface region Xb corresponds to a period from time tb0 to tb1. The surface region Xc corresponds to a period from time tc0 to tc1. The CPU 201 stores the detection signals of the surface areas Xa, Xb, and Xc in the profile memory 202 in association with the surface areas Xa, Xb, and Xc. The surface regions Xa, Xb, and Xc are further divided into a plurality of surface regions. When one circumference of the intermediate transfer belt 51 is divided into ₁₀₂₄ surface regions, surface regions X _{1 to} X ₁₀₂₄ exist. Further, 1024 detection signals corresponding to the intensity of the reflected light for one turn of the intermediate transfer belt 51 in a state where no toner is formed are also acquired.

  The circumferential length xb of the intermediate transfer belt 51 is designed to be a length suitable for acquiring a base profile for one round of the intermediate transfer belt 51 between sheets. If the space between the sheets is limited to the same surface area for each turn, the background profile for one turn of the intermediate transfer belt 51 cannot be acquired. For this reason, the circumferential length xb is designed so that a different surface area is provided between the sheets each time the intermediate transfer belt 51 is rotated once.

  FIG. 8 shows the update timing of the base profile when a standard size sheet (for example, A4 sheet) is continuously fed in the horizontal feed. As an example, it is assumed that the circumferential length xb is 895 mm, the length L in the A4 paper conveyance method is 210 mm, and the length Ps between the sheets is 55 mm. As shown in FIG. 8, when 27 A4 size toner images are formed, a background profile for one rotation of the intermediate transfer belt 51 is acquired.

  In this way, the CPU 201 updates the background profile for one turn of the intermediate transfer belt 51 every time 27 pages of A4 size images are formed in continuous printing. For this reason, it is not necessary to rotate the intermediate transfer belt 51 immediately before the toner density adjustment to acquire the background profile. As a result, when toner density adjustment is performed, a toner patch can be formed on the intermediate transfer belt 51 without idling the intermediate transfer belt 51, so that downtime during toner density adjustment is reduced.

<Function and Flowchart of CPU 201>
The function of the CPU 201 will be described with reference to FIGS. 9, 10, and 11. The function of the CPU 201 may be realized by executing a control program, or may be realized by a logic circuit such as an ASIC. Further, a part may be realized by software, and the other part may be realized by hardware. FIG. 9 shows the functions of the CPU 201. When the CPU 201 is instructed to copy a document through the operation unit or receives a print job from an external device, the CPU 201 starts control of the printer unit 10 according to the flowchart shown in FIG.

  In step S <b> 701, the CPU 201 (determination unit 84) determines whether the number of toner images formed by the measurement unit 83 is equal to or less than a threshold value. If the number of formations is less than or equal to the threshold, the CPU 201 proceeds to S702 to create a background profile, and if it exceeds the threshold, proceeds to S704 to execute toner density adjustment.

  In step S <b> 702, the CPU 201 (creating unit 80) creates a background profile and stores the background profile in the profile memory 202. At this time, the CPU 201 acquires a detection signal output from the optical sensor 60 every time the interval between sheets passes through the detection region 61 while forming a toner image on the printer unit 10. The CPU 201 updates the data corresponding to the paper between the background profiles stored in the profile memory 202 every time a detection signal corresponding to the paper is acquired. In step S703, the CPU 201 (measurement unit 83) counts up the number of formed toner images. Thereafter, the CPU 201 proceeds to step S708, and determines whether the continuous print job is completed. When the job is completed, the CPU 201 transitions to the standby mode. If the job has not been completed, the CPU 201 returns to S701.

  In step S <b> 704, the CPU 201 controls the printer unit 10 to interrupt image formation in order to start toner density adjustment. In step S <b> 705, the CPU 201 (the density adjustment unit 82 and the light amount correction unit 81) executes toner density adjustment. The density adjustment unit 82 calculates the rotational movement amount x from the HP mark 53 in order to specify the position of the intermediate transfer belt 51 on which the toner patch is formed. The density adjustment unit 82 controls the printer unit 10 to form a toner patch on the intermediate transfer belt 51 and acquires the detection signal output from the optical sensor 60. The density adjustment unit 82 stores the detection signal output from the optical sensor 60 in the patch memory 203. The light amount correction unit 81 corrects the detection signal stored in the patch memory 203 for each position on the surface of the intermediate transfer belt 51 using the background profile stored in the profile memory 202. The density adjustment unit 82 converts the detection signal corrected by the light amount correction unit 81 into the density of the toner patch formed on the intermediate transfer belt 51 based on the density conversion table. Then, the density adjusting unit 82 updates the image forming conditions so that the density of the toner patch becomes the target density. As described above, the density adjusting unit 82 updates the development bias and the lookup table, which are image forming conditions, based on the density of the toner patch. For example, when the density of the toner patch is higher than the target density, the developing bias is lowered. The toner density adjustment is executed for each of YMCK.

  In step S <b> 706, the CPU 201 (measurement unit 83) clears (resets) the number of toner image formations (count value) to zero. In step S707, the CPU 201 controls the printer unit 10 to resume image formation. Thereafter, the CPU 201 proceeds to S708.

  The background profile creation processing will be described with reference to FIG. In step S <b> 801, the CPU 201 (creating unit 80) determines whether the detection area 61 of the optical sensor 60 is between sheets. For example, the CPU 201 determines that the detection area 61 of the optical sensor 60 is between sheets when image formation is completed for one image or when a predetermined time has elapsed from the timing when the laser beam scanner 3 is turned off. The latent image formed by the laser beam scanner 3 is developed and transferred as a toner image to the intermediate transfer belt 51, and the time until the trailing edge of the toner image passes through the detection region 61 is a fixed value. Therefore, the CPU 201 can determine whether or not the detection area 61 is between sheets based on the elapsed time from the timing when the laser beam scanner 3 is turned off. If the detection area 61 of the optical sensor 60 is between sheets, the process proceeds to S802. As described above, the CPU 201 also functions as a paper gap determination unit.

  In step S <b> 802, the CPU 201 (creating unit 80) calculates the rotational movement amount x from the HP mark 53 and specifies the surface position of the intermediate transfer belt 51. In step S803, the CPU 201 (sensor control unit 85) turns on the LED 107 of the optical sensor 60. For example, the sensor control unit 85 transmits a detection instruction to the optical sensor 60. The detection instruction may simply be energization (power-on) of the optical sensor 60. The optical sensor 60 turns on the LED 107 in accordance with the detection instruction, acquires the intensity of the reflected light from the intermediate transfer belt 51, and outputs the detection signal output from the optical sensor 60 to the creation unit 80. The HP sensor 52 outputs position information (rotational movement amount x) based on the HP mark 53 to the CPU 201.

  In step S <b> 804, the CPU 201 (creating unit 80) uses the optical sensor 60 to detect a detection signal corresponding to the gap between sheets. In step S <b> 805, the CPU 201 (creating unit 80) associates the surface position (surface region) acquired using the HP mark 53 with the detection signal acquired by the optical sensor 60, and stores the background profile stored in the profile memory 202. The detection signal corresponding to the surface position is updated.

  In step S806, the CPU 201 (creating unit 80) determines whether the detection area 61 of the optical sensor 60 is between sheets. The length between the sheets is a fixed value, and the peripheral speed of the intermediate transfer belt 51 is also constant. The creation unit 80 can determine whether or not the detection area 61 of the optical sensor 60 is still between papers based on the elapsed time from the timing when the leading edge of the paper enters the detection area 61. If it is between sheets, the CPU 201 returns to S802 and updates the base profile for the next surface position. On the other hand, when the paper interval is completed, the process proceeds to S807. In step S807, the CPU 201 (sensor control unit 85) turns off the LED 107 and proceeds to step S703.

<Summary>
As described above, the printer unit 10 functions as an image forming unit that forms a toner image or a toner patch for density adjustment on an image carrier that is rotationally driven, such as the endless intermediate transfer belt 51. The optical sensor 60 functions as a light detection unit that detects the intensity of reflected light from the surface of the intermediate transfer belt 51 and the intensity of reflected light from the toner patch. That is, the optical sensor 60 includes an irradiation unit that irradiates light toward the image carrier and a light receiving unit that receives reflected light, and outputs a signal corresponding to the intensity of the reflected light received by the light receiving unit. Functions as a means. The HP sensor 52 functions as a position detection unit that detects the position of the HP mark 53 provided on the intermediate transfer belt 51 and detects the position of each surface of the intermediate transfer belt 51 using the position of the HP mark 53 as a reference. That is, the HP sensor 52 functions as a determining unit that determines a position where an image is not formed by the image forming unit. The creating unit 80 controls the optical sensor 60 so as to detect the intensity of reflected light from the space between the preceding toner image and the succeeding toner image on the surface of the intermediate transfer belt 51 (empty surface). Further, the creating unit 80 creates a profile over the entire circumference of the intermediate transfer belt 51 by integrating detection signals corresponding to a plurality of sheets detected by the optical sensor 60 and stores the profile in the profile memory 202. The profile memory 202 stores the profile created by the creation unit 80. The profile associates the intensity of the reflected light detected on the surface of the intermediate transfer belt 51 by the optical sensor 60 with the position of the surface from which the intensity of the reflected light detected by the HP sensor 52 is acquired. . That is, the profile is a correction for one rotation of the image carrier generated by acquiring the first signal of the optical sensor 60 corresponding to the position where no image is formed while a plurality of images are formed. It is an example of data. In this way, the creation unit 80 acquires the first signal of the output unit corresponding to the position determined by the determination unit while the image forming unit is forming a plurality of images, and outputs one round of the image carrier. It functions as a generating means for generating correction data. The patch memory 203 includes a detection signal corresponding to the toner patch formed on the surface of the intermediate transfer belt 51 by the optical sensor 60 and the position of the surface of the intermediate transfer belt 51 on which the toner patch detected by the HP sensor 52 is formed. Are stored in association with each other. The detection signal corresponding to the toner patch is an example of a second signal corresponding to the intensity of reflected light from the measurement image. The light quantity correction unit 81 corrects the detection signal output from the optical sensor 60 when the optical sensor 60 measures the intermediate transfer belt 51 in a state where the toner patch is formed based on the background profile. Then, the density adjusting unit 82 determines the density of the toner patch from the corrected detection signal, and updates the image forming condition (tone correction condition) so that the density of the toner patch becomes the target density. The CPU 201 creates a background profile by integrating detection signals corresponding to a region (inter-paper) where toner between two toner images is not formed on the intermediate transfer belt 51. Therefore, the interruption time of image formation is reduced, and the downtime associated with toner density adjustment is reduced. The light amount correction unit 81 and the density adjustment unit 82 cause the image forming unit to form a measurement image on the image carrier, and the output unit generates a second signal corresponding to the intensity of reflected light from the measurement image. It is an example of the update means which updates a gradation correction condition based on the correction data produced | generated by the means.

  In particular, the creation unit 80 creates a background profile by integrating detection signals corresponding to a plurality of sheets while the printer unit 10 continuously forms a plurality of toner images. Accordingly, it is not necessary to idle the intermediate transfer belt 51 for one rotation or more before executing the toner density adjustment, so that the downtime until the toner density adjustment is completed can be reduced.

  When the creation unit 80 acquires a plurality of detection signals in duplicate for the same position among a plurality of sheets, the creation unit 80 creates a base profile with a newer detection signal for the position. As a result, the background profile can be maintained in the latest state, and the measurement accuracy of the toner density by the optical sensor 60 is improved.

  When the creation unit 80 acquires detection signals for the same position among the detection signals corresponding to a plurality of papers, the background profile is obtained with an average value of the previous detection signal and the current detection signal for the position. May be created. A plurality of detection signals may be acquired in duplicate for the same position in a short time. In this case, the creation unit 80 may be able to reduce the influence of noise by averaging the previous detection signal and the current detection signal regarding the same position. The average value may be a weighted average value. For example, the correction coefficient multiplied by the current detection signal is set to a value larger than the correction coefficient multiplied by the previous detection signal.

  The CPU 201 may manage each position on the surface of the intermediate transfer belt 51 as a distance from the position of the HP mark 53. Further, the CPU 201 may manage each position on the surface as the rotational movement amount x of the intermediate transfer belt 51 with the position of the HP mark 53 as a reference. Further, the CPU 201 may manage each position on the surface as an elapsed time from the timing when the HP sensor 52 detects the HP mark 53.

  The circumferential length xb of the intermediate transfer belt 51 is the length of the recording medium to which the toner image formed on the intermediate transfer belt 51 is transferred, and the length L in the conveyance direction of the recording medium, and the surface of the intermediate transfer belt 51 This is different from an integral multiple of the sum S of the inter-paper length Ps in the moving direction (S = L + Ps). If the circumference xb is an integral multiple of the sum S, the gap between the sheets generated during continuous printing will be at the same surface position. If the circumference xb is the sum S plus the length Ps between sheets, a profile can be created efficiently. When such a relationship is established, the position between the sheets is shifted by the length Ps every time the intermediate transfer belt 51 is rotated once.

  The length L of the recording medium is a fixed-size recording medium, and may be the length of a fixed-size recording medium that is most frequently used among a plurality of different fixed-size recording media. For example, the length of an A4 size recording medium is used as a reference. Further, it may be based on whether the recording medium is laterally fed or vertically fed (A4 / A4R). Note that the lateral feed means that the short side of the long side and the short side of the recording medium is parallel to the conveyance direction of the recording medium.

  The CPU 201 may further include a measuring unit 83 that measures the number of toner images formed, and a determination unit 84 that determines whether the number of toner images formed by the measuring unit 83 exceeds a predetermined threshold. The density adjusting unit 82 adjusts the density of the toner image formed on the intermediate transfer belt 51 using the intensity of the reflected light corrected by the light amount correcting unit 81 when the number of toner images formed exceeds a predetermined threshold. The surface state of the intermediate transfer belt 51 correlates with the number of toner images formed. Therefore, the conditions that require density adjustment are generally predictable, and the threshold value can be easily determined by simulation or experiment.

  The intermediate transfer belt 51 may be an endless belt, and the HP mark 53 may be provided on the inner peripheral surface of the endless belt. This eliminates the need to place the HP mark 53 on the image forming surface of the intermediate transfer belt 51. There is little space for arranging the HP mark 53 on the outer peripheral surface (image forming surface) of the intermediate transfer belt 51, and the degree of freedom of arrangement is small. Further, the HP mark 53 is contaminated with toner, and the detection accuracy of the HP sensor 52 can be lowered. Therefore, providing the HP mark 53 on the inner peripheral surface will increase the degree of freedom in arrangement and improve detection accuracy. The HP mark 53 may be a position detection member that is detected optically or magnetically.

  DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 40 ... Printer control part, 51 ... Intermediate transfer belt, 52 ... HP sensor, 53 ... HP mark, 60 ... Optical sensor

Claims (13)

A rotationally driven image carrier;
Correction means for correcting image data based on gradation correction conditions;
Image forming means for forming an image on the image carrier based on the corrected image data;
Transfer means for transferring the image formed on the image carrier by the image forming means to a recording material;
An output unit that irradiates light toward the image carrier and a light receiving unit that receives reflected light, and outputs a signal corresponding to the intensity of the reflected light received by the light receiving unit;
Determining means for determining a position where the image is not formed by the image forming means;
While the image forming unit forms a plurality of images, the first signal of the output unit corresponding to the position determined by the determining unit is acquired, and correction data for one round of the image carrier is obtained. Generating means for generating
The image forming unit forms a measurement image on the image carrier, the output unit generates a second signal corresponding to the intensity of reflected light from the measurement image, and the correction data generated by the generation unit. And an update unit that updates the gradation correction condition based on the image forming apparatus.   The generating unit uses the plurality of empty surfaces on the image carrier on which the image is not formed while the image forming unit is continuously forming a plurality of toner images, and uses the plurality of empty surfaces. The image forming apparatus according to claim 1, wherein correction data is generated.   When the generation unit obtains a plurality of the first signals by duplicating the same position among the plurality of empty surfaces, the generation unit obtains the correction data by using the first signal newly acquired for the position. The image forming apparatus according to claim 2, wherein the image forming apparatus generates the image forming apparatus.   When the generating unit obtains a plurality of the first signals at the same position among the plurality of empty surfaces, the correction data is obtained with an average value based on the plurality of first signals for the position. The image forming apparatus according to claim 2, wherein the image forming apparatus is formed. The determination unit includes a position detection unit that detects a position of a position detection member provided on the image carrier and detects a position of each surface of the image carrier based on the position of the position detection member;
5. The image forming apparatus according to claim 1, wherein each position on the surface is managed as a distance from the position of the position detection member. The determination unit includes a position detection unit that detects a position of a position detection member provided on the image carrier and detects a position of each surface of the image carrier based on the position of the position detection member;
5. The image forming apparatus according to claim 1, wherein each position of the surface is managed as a rotational movement amount of the image carrier with reference to a position of the position detection member. The determination unit includes a position detection unit that detects a position of a position detection member provided on the image carrier and detects a position of each surface of the image carrier based on the position of the position detection member;
5. The image forming apparatus according to claim 1, wherein each position on the surface is managed as an elapsed time from a timing at which the position detection member is detected. The image carrier is an endless belt,
The image forming apparatus according to claim 5, wherein the position detection member is provided on an inner peripheral surface of the endless belt.   The image forming apparatus according to claim 5, wherein the position detection member is a member that is detected optically or magnetically.   The circumferential length of the image carrier is the length of the recording material to which the toner image formed on the image carrier is transferred, the length in the transport direction of the recording material, and the moving direction of the surface of the image carrier 10. The image forming apparatus according to claim 1, wherein the image forming apparatus is different from an integral multiple of a sum of a length of an empty surface on which the image is not formed.   The length of the recording material is a recording material of a fixed size, and is a length of a recording material of a fixed size that is most frequently used among a plurality of recording materials of a different fixed size. The image forming apparatus described in 1. A measuring means for measuring the number of formed images;
Determination means for determining whether the number of images formed by the measurement means exceeds a predetermined threshold, and
The image forming apparatus according to claim 1, wherein the update unit updates the gradation correction condition when the number of formed images exceeds the predetermined threshold. An endless image carrier;
Image forming means for forming a toner image or a toner patch for density adjustment on the image carrier;
Light detecting means for detecting the intensity of reflected light from the surface of the image carrier and the intensity of reflected light from the toner patch;
Position detection means for detecting the position of a position detection member provided on the image carrier and detecting the position of each surface of the image carrier with reference to the position of the position detection member;
The light detection means is controlled so as to detect the intensity of reflected light of a free surface generated between the preceding toner image and the subsequent toner image on the surface of the image carrier, and is detected by the light detection means. Creating means for creating a profile indicating the intensity of the reflected light of the surface over the circumference of the image carrier by integrating the intensity of the reflected light of a plurality of empty surfaces;
As the profile created by the creating means, the intensity of the reflected light detected on the surface of the image carrier by the light detecting means and the intensity of the reflected light detected by the position detecting means are obtained. First storage means for storing the position in association with each other;
Correspondence between the intensity of the reflected light detected for the toner image formed on the surface of the image carrier by the light detecting means and the position of the surface where the intensity of the reflected light detected by the position detecting means is acquired. Second storage means for storing additionally,
The influence of the surface by correcting the intensity of the reflected light stored in the first storage means for each position on the surface of the image carrier using the intensity of the reflected light stored in the second storage means. Correction means for reducing
An image forming apparatus comprising: an adjusting unit that adjusts a density of a toner image formed on the image carrier using the intensity of the reflected light corrected by the correcting unit.