JP2006145679A - Image forming apparatus and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect the density of a density detection pattern, even when the sensitivity of an optical sensor detecting the density detection pattern is reduced due to soiling or the like, and the output value varies. <P>SOLUTION: A solid pattern of maximum toner density is formed on a carrying belt, and the maximum density pattern is irradiated with light emitted from a light emitting element, and the diffused/reflected light is detected by a diffused/reflected light receiving element, and the detected light quantity is compared with a light quantity detected and stored in a memory at a reference time (before a printing operation), and when the detected light quantity is different from the light quantity at the reference time, the correction value of the light quantity of the light emitting element is calculated so as to obtain the diffused/reflected light quantity equal to the light quantity at the reference time. Next, an area with toner density O on the carrying belt is irradiated with the corrected light quantity, and the specular-reflected light quantity is detected by a specular-reflected light receiving element, and the detected light quantity is compared with the light quantity detected at the reference time (stored in the memory), and a specular-reflected light correction gain Gf is calculated so that the detected light quantity becomes equal to the light quantity detected at the reference time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus such as a color printer and a color copying machine, a control method therefor, a control program, and a recording medium.

  In an electrophotographic color image forming apparatus, images of different colors are sequentially transferred onto an intermediate transfer belt and collectively transferred onto a print paper, or images of different colors are sequentially applied onto a print paper held on a conveyance belt. Various methods for transferring the image have been proposed.

  In general, in an electrophotographic image forming apparatus, the characteristics change due to the usage environment, the developing device, the number of printed photosensitive drums, the sensitivity variation during manufacturing of the photosensitive drum, the variation in frictional charging characteristics during developer (toner) manufacturing, etc. Therefore, the density characteristics of the printed image vary. Efforts to stabilize these changes and fluctuation characteristics are made every day, but it is not enough. In particular, in a color image forming apparatus, color reproduction is performed by superposing four toners of yellow, magenta, cyan, and black. Therefore, if the density of the developer of four colors, that is, the toner image is not accurately adjusted, it is good. Can not get a good color balance.

  Therefore, many color image forming apparatuses are equipped with an image density adjusting mechanism that automatically adjusts image forming conditions such as a charging potential, an exposure amount, and a developing bias. First, a toner image is formed on an image carrier or transfer material carrier under predetermined image forming conditions, and the density of the toner image is detected by an optical sensor comprising a light emitting element and a light receiving element. Then, the image forming conditions are adjusted according to the detected density of the toner image.

  FIG. 1C is a diagram illustrating the optical sensor. Reference numeral 501 denotes a pattern to be detected, 502 a light emitting element made of LED, 503 a diffuse reflection light receiving element made of a phototransistor, and 504 a regular reflection light receiving element made of a phototransistor. The light emitting element 502 is installed at an angle of 30 degrees with respect to the direction perpendicular to the surface of the transport belt, and irradiates the pattern on the transport belt with infrared light. The regular reflection light receiving element 504 is installed at a symmetrical position with respect to the light emitting element 502 and detects regular reflection light from the pattern. The diffuse reflection light receiving element 503 is installed at an angle of 60 degrees with respect to the direction perpendicular to the surface of the conveyance belt, and detects diffuse reflection light from the pattern.

  FIG. 1E is a diagram showing output characteristics when a pattern made of toner is formed on the conveyance belt, and reflected light from the pattern is detected by the regular reflection light receiving element 504 and the diffuse reflection light receiving element 503. G711 is an output value detected by the regular reflection light receiving element, G712 is an output value detected by the diffuse reflection light receiving element 503, and G713 is an output value of the regular reflection light receiving element 504 and an output value of the diffuse reflection light receiving element 503. The difference value is shown. In FIG. 1E, the vertical axis indicates sensor output values of the specular reflection light component and the diffuse reflection light component, and the horizontal axis indicates a density value obtained by subtracting the paper density from the optical density after the pattern is transferred and fixed on the paper. is there.

  In FIG. 1E, the detection output value G712 of the diffuse reflection light receiving element 503 increases as the toner density increases. The detected output value G711 of the specular reflection light component is mixed with the irregular reflection light component in the detection output G711 of the specular reflection light component as the toner density increases. Therefore, it is preferable to use the difference between the regular reflection component and the diffuse reflection component when detecting the toner density of the pattern using the toner. The toner concentration is determined from the detection output of the regular reflection light receiving element and the detection output of the diffuse reflection light receiving element 503. The calculation is generally performed (see Patent Document 1). When performing this calculation, it is necessary that the ratio between the specular reflection light characteristic and the diffuse reflection light characteristic is always constant with respect to the toner density, and sensitivity adjustment is performed so that each ratio is constant before the sensor operation. .

  However, as the image forming apparatus of this configuration repeatedly performs the printing operation, the conveyance belt is damaged due to various factors such as a speed difference between the image forming medium and the conveyance belt, and the glossiness of the belt is reduced by the optical sensor. The detected sensitivity is reduced. Further, the sensitivity of the optical sensor is reduced due to a cause such as paper dust on the paper adhering to the optical sensor becoming dirty. As described above, when the characteristics of the optical sensor are deteriorated due to the above-described causes, the adjustment accuracy of the image forming conditions is lowered.

Therefore, in order to improve the adjustment accuracy of the image forming conditions, a method for preventing a decrease in the detection accuracy of the optical sensor has been considered. For example, in the detection output of the regular reflection light receiving element when the surface of the conveyor belt is exposed (toner density 0), the detection output before the printing operation (initial state) and the detection output after the printing operation (after durability) There is one that maintains the initial detection output characteristics by calculating a correction gain from the output and correcting the detection output values of the regular reflection light receiving element and the diffuse reflection light receiving element (see Patent Document 1).
JP 2000-39746 A

  However, the above correction method has the following drawbacks. That is, the sensitivity of the optical sensor is caused by the reason that the gloss of the image carrier or transfer material carrier described above is decreased with the printing operation (after endurance), or the optical sensor is soiled due to paper dust or the like adhering to the paper. Is reduced, the specular reflection light reception characteristic (output) and diffuse reflection light reception characteristic (output) of the optical sensor do not necessarily decrease at the same rate, and may decrease at different rates.

  FIG. 1E shows a pattern formed by toner on the conveyance belt when the sensitivity of the optical sensor is lowered due to a decrease in gloss of the image carrier or transfer material carrier after the printing operation (durability), contamination of the sensor, etc. It is the figure which showed the output characteristic when the reflected light by a pattern is detected by the regular reflection light receiving element 504 and the diffuse reflection light receiving element 503. G731 indicates the output characteristics of the regular reflection light receiving element, and G732 indicates the output characteristics of the diffuse reflection light receiving element 503. In FIG. 1E, a pattern made of toner is formed on the conveyance belt before the printing operation (initial state), and reflected light from the pattern is detected by the regular reflection light receiving element 504 and the diffuse reflection light receiving element 503. The output characteristics are also shown.

  In FIG. 1E, the vertical axis indicates sensor output values of the specular reflection light component and the diffuse reflection light component, and the horizontal axis indicates a density value obtained by subtracting the paper density from the optical density after the pattern is transferred and fixed on the paper. is there. The density of the toner pattern formed at the maximum density formed on the conveyance belt does not change in the printing operation, and the output characteristics shown in G731 and G732 are caused by the reduction in belt gloss and the sensitivity of the optical sensor described in the background art. Become.

  At this time, as in the technique disclosed in Japanese Patent Laid-Open No. 2000-39746, the gain correction value of both light receiving elements due to the detection output fluctuation of one of the light receiving elements (in this case, the regular reflection light receiving element). , Since the output value of the regular reflection light characteristic is large on the low toner density side (low density side), a reference is set on the low density side, and a correction gain for the standard is calculated. For this reason, there is no reference on the high toner density side (high density side), and the correction gain on the low density side is used on the high density side as an estimated value on the high density side. G733 in FIG. 1E indicates a difference value between the output of the regular reflection light receiving element corrected with the correction gain described above and the output of the diffuse reflection light receiving element 503 corrected with the correction gain.

  For this reason, in the technique disclosed in Japanese Patent Laid-Open No. 2000-39746, the detection accuracy on the high density side decreases as indicated by G733 in FIG. 1E, so that the adjustment accuracy of the image forming conditions is necessarily improved. I could not say.

  The present invention has been made starting from solving the above-described problems of the prior art, and the object thereof is, for example, a reduction in gloss of an image carrier or a transfer material carrier that forms a density detection pattern, or Provided is an image forming apparatus that can accurately detect the density of a density detection pattern even when the output value of the optical sensor fluctuates due to a decrease in sensitivity due to contamination of the optical sensor that detects the density detection pattern, and a control method therefor It is to be.

  In order to achieve the above object, an image forming apparatus according to an embodiment of the present invention has the following arrangement. That is, an image forming apparatus for controlling image forming conditions by detecting the density of a reference toner image for density measurement formed on an image carrier using an optical detection means, and the optical detection at a reference time Means for irradiating light to the reference toner image, diffusely reflected by the reference toner image, and storing a reference diffuse reflection light quantity detected by the diffuse reflection light receiving element of the optical detection means; When the amount of diffuse reflection detected when light is applied to the reference toner image from the optical detection means does not match the reference diffuse reflection amount, the diffuse reflection amount detected by the diffuse reflection light receiving element is stored in the memory. Control means for controlling the optical detection means so as to coincide with the reference diffuse reflection light quantity stored in the means.

  Here, for example, the control means corrects the light quantity of the light emitting element of the optical detection means so that the detected diffuse reflection light quantity matches the reference diffuse reflection light quantity stored in the storage means. Is preferred.

  Here, for example, the control means outputs the output of the diffuse reflection light receiving element of the optical detection means so that the detected diffuse reflection light quantity matches the reference diffuse reflection light quantity stored in the storage means. It is preferable to correct.

  Here, for example, it is preferable that the reference toner image includes a maximum density toner image, and the storage unit stores the amount of light diffusely reflected by the maximum density toner image at the reference time.

  Here, for example, it is preferable that the storage means stores the reference diffuse reflection light amount for each color.

  Here, for example, the reference toner image for density measurement is preferably a color misregistration detection pattern for detecting color misregistration.

  Here, for example, it has a transfer material carrying and conveying body that conveys and conveys a transfer material facing the image carrying body, and the optical detection means is the reference toner image formed on the image carrying body, or Preferably, the reference toner image formed on the image carrier and subsequently transferred onto the transfer material carrier is detected.

  Here, for example, at the time of the reference, the storage means emits light from the light emitting element of the optical detection means, a part having a toner density of 0 on the image carrier where the reference toner image is not formed, or the Irradiate a portion with a toner density of 0 on the transfer material carrying and conveying body to which a reference toner image is not transferred, and regularly reflect at the portion, and a toner density of 0 detected by a regular reflection light receiving element of the optical detection means It is preferable to further store the reference regular reflection light amount at.

  Here, for example, when the corrected light quantity is applied to the part on the image carrier or the transfer material carrier, the control unit is regularly reflected from the part and receives the regular reflected light. When the light amount detected by the element does not coincide with the reference regular reflection light amount, it is preferable to further correct the output value of the regular reflection light receiving element so as to coincide with the reference regular reflection light amount.

  Here, for example, the control means receives the specularly reflected light when the part on the image carrier or the part on the transfer material carrier is irradiated with light from the optical detector at the predetermined time. When the amount of light detected by the element does not coincide with the reference regular reflection light amount, it is preferable to further correct the output value of the regular reflection light receiving element so as to coincide with the reference regular reflection light amount.

  In order to achieve the above object, a control method of an image forming apparatus according to an embodiment of the present invention has the following configuration. That is, a control method of an image forming apparatus for controlling image forming conditions by detecting the density of a reference toner image for density measurement formed on an image carrier using an optical detection unit, The apparatus irradiates the reference toner image with light from the optical detection means at the time of reference, diffuses and reflects the reference toner image, and generates a reference diffuse reflection light amount detected by the diffuse reflection light receiving element of the optical detection means. Storage means for storing, and when the diffuse reflected light amount detected when the reference toner image is irradiated with light from the optical detection unit at a predetermined time does not match the reference diffuse reflected light amount, the diffuse reflected light reception A control step of controlling the optical detection unit so that the diffuse reflection amount detected by the element matches the reference diffuse reflection amount stored in the storage unit; And wherein the door.

  In order to achieve the above object, a control program for controlling an image forming apparatus according to an embodiment of the present invention has the following configuration. That is, a control program for controlling an image forming apparatus that controls image forming conditions by detecting the density of a reference toner image for density measurement formed on an image carrier using an optical detection means, The image forming apparatus irradiates the reference toner image with light from the optical detection unit at a reference time, is diffusely reflected by the reference toner image, and is detected by a diffuse reflection light receiving element of the optical detection unit. A storage unit that stores a light amount; and the diffuse reflection light amount detected when the reference toner image is irradiated with light from the optical detection unit at a predetermined time does not coincide with the reference diffuse reflection light amount. The optical detection means is controlled so that the diffuse reflection light amount detected by the light receiving element coincides with the reference diffuse reflection light amount stored in the storage means. It characterized by having a program code process.

  According to the present invention, for example, when the gloss of the image carrier or transfer material carrier that forms the density detection pattern decreases, or when the optical sensor that detects the density detection pattern decreases in sensitivity due to dirt or the like. Thus, even when the output value of the optical sensor varies, the optical sensor can be adjusted with high accuracy. Therefore, it is possible to provide an image forming apparatus that can easily and accurately detect the density of the density detection pattern, and has excellent color reproduction stability at low cost, and a control method thereof.

  Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

<First Embodiment>
[Overview of this embodiment]
In the present embodiment, even when the output of the optical sensor fluctuates due to paper dust or the like adhering to the paper and soiling of the optical sensor, or when the gloss of the transport belt (or image carrier) decreases, According to the first method, the ratio between the specular reflection light characteristic and the diffuse reflection light characteristic can be controlled to be substantially constant at all times. Therefore, since the density pattern for density measurement can be accurately measured, an image forming apparatus having excellent color reproduction stability and a control method thereof can be provided.

  That is, in the first method, first, at a predetermined time (after the printing operation: after durability), a maximum density pattern (solid pattern with the maximum toner density) is formed on the conveyance belt (or on the image carrier). Light is emitted from the light emitting element to the maximum density pattern, diffuse diffused light is detected by the light receiving element, and the detected light quantity is detected at the reference time (before printing operation: initial) and stored in the memory. If the detected light amount is different from the light amount at the reference time, a correction value for the light amount of the light emitting element is calculated so that a diffuse reflection light amount that matches the light amount at the reference time is obtained.

  Next, the light amount of the light emitting element that can obtain the diffuse reflection light amount at the reference time is irradiated to the toner density 0 region (or the toner density 0 region on the image carrier) on the conveying belt, and the reflected regular reflection light amount is reflected. Detected by the regular reflection light receiving element, and compares the detected light amount with the light amount (stored in the memory) detected at the reference time (before printing operation: initial). The regular reflection correction gain Gf is calculated so as to match. As a result, even when the output of the optical sensor fluctuates due to a decrease in gloss of the conveyor belt or sensor contamination, the specular reflection characteristics and diffuse reflection are obtained using the corrected light amount of the light emitting element and the specular reflection correction gain Gf. It is possible to control so that the ratio of optical characteristics is always substantially constant.

  Therefore, a density pattern for density measurement (such as FIGS. 2 and 3) is formed on the conveyor belt, and the corrected emission light quantity is irradiated to the density measurement density pattern to diffusely reflect the diffuse reflected light quantity and the regular reflected light quantity. By detecting the element and the regular reflection light receiving element and correcting the detected regular reflection light amount with the correction gain Gf of the regular reflection light, the difference between the diffuse reflection light amount and the proper optical sensor output-toner density is obtained. The following relational expression can be obtained. Therefore, even when the output of the optical sensor fluctuates due to contamination of the optical sensor or a decrease in gloss of the conveyance belt, the image forming conditions can be appropriately adjusted, and color reproduction can be performed stably. . Hereinafter, the content described above will be specifically described.

[Overall Configuration of Image Forming Apparatus: FIG. 1B]
FIG. 1B shows an overall configuration of a color image forming apparatus showing an example of the first embodiment of the present invention. This image forming apparatus is a color image forming apparatus provided with image forming means for four colors, that is, yellow Y, magenta M, cyan C, and black K. In the figure, reference numeral 101 denotes a photosensitive drum for forming an electrostatic latent image. (A, b, c, and d correspond to Black, Cyan, Magenta, and Yellow, respectively) 102 is a laser scanner that exposes the photosensitive drum 101 based on image data to form an electrostatic latent image, and 103 is a print An endless conveyance belt that also serves as a transfer belt, which sequentially conveys paper to each color image forming unit, 104 is a driving roller that is connected to a driving means configured by a motor and a gear (not shown) to drive the conveyance belt 103, Reference numeral 105 denotes a driven roller that rotates with the movement of the conveyance belt 103 and applies a constant tension to the conveyance belt 103. Reference numeral 107 denotes an optical sensor provided at the center of the conveyance belt 103 in the main scanning direction for detecting a pattern formed on the conveyance belt 103.

  In these color image forming apparatuses, density control is performed in order to accurately match the density of each color and obtain an image having a desired color. Specifically, the density control includes Dmax control for optimizing image forming conditions so that desired development characteristics of each color can be obtained, and a look-up table so that input image data and halftone image density have good linearity. And Dhalf control for changing.

[Optical sensor: FIG. 1C]
Details of the optical sensor 107 are shown in FIG. 1C. FIG. 1C is a diagram illustrating an optical sensor. Reference numeral 501 denotes a pattern to be detected, 502 a light emitting element made of LED, 503 a diffuse reflection light receiving element made of a phototransistor, and 504 a regular reflection light receiving element made of a phototransistor. The light emitting element 502 is installed at an angle of 30 degrees with respect to the direction perpendicular to the surface of the transport belt, and irradiates the pattern on the transport belt with infrared light. The regular reflection light receiving element 504 is installed at a symmetrical position with respect to the light emitting element 502 and detects regular reflection light from the pattern. The diffuse reflection light receiving element 503 is installed at an angle of 60 degrees with respect to the direction perpendicular to the surface of the conveyor belt, and detects diffuse reflection light from the pattern.

[Control Configuration of Image Forming Apparatus: FIG. 1D]
FIG. 1D shows a control configuration of the image forming apparatus. In the figure, 211 is a CPU, 212 is a drive control unit having a conveyor belt, a drive roller, a drive unit, and the like, 213 is a detection unit having an optical sensor, an optical sensor control unit, and the like, and 214 is various types of sensors. A ROM having a control program, various data, a lookup table, and the like, 215 is a RAM, and 216 is an image forming unit having a photosensitive drum, a laser scanner, a density control unit, and the like. Based on a control program stored in the ROM 214, the CPU 211 performs processing shown in FIGS. 5 and 7 to be described later while controlling each unit using the RAM 215 as a work area.

[Density detection pattern (Dmax control): FIG. 2]
FIG. 2 is a schematic diagram illustrating an example of a density detection pattern for Dmax control. In FIG. 2, reference numeral 103 denotes an endless conveyance belt that also serves as a transfer belt, and sequentially conveys print paper to the image forming units for each color, and 107 detects a density detection pattern formed on the conveyance belt 103. , An optical sensor provided in the center of the conveyance belt 103 in the main scanning direction.

  Reference numerals 4101Y, 4102Y, 4103Y, and 4104Y are patch images of yellow toners having the same image pattern and different densities by changing the developing bias. Similarly, 4101M, 4102M, 4103M, 4104M, 4101C, 4102C, 4103C, 4104C, 4101K, 4102K, 4103K, and 4104K have the same image pattern and magenta, cyan, and black with different density by changing the development bias. This is a patch image. An arrow indicates the moving direction of the conveyor belt 103.

[Density detection pattern (Dmax control): FIG. 3]
FIG. 3 is a schematic diagram illustrating an example of a density detection pattern for Dhalf control. In FIG. 3, reference numeral 103 denotes an endless conveyance belt that also serves as a transfer belt, and sequentially conveys print paper to the image forming units for each color, and 107 detects a density detection pattern formed on the conveyance belt 103. , An optical sensor provided in the center of the conveyance belt 103 in the main scanning direction.

  Reference numerals 4201Y, 4202Y, 4203Y, and 4204Y are patch images of yellow toner that have the same developing bias and have different densities by changing the input image signal. 4201M, 4202M, 4203M, 4204M, 4201C, 4202C, 4203C, 4204C, 4201K, 4202K, 4203K, and 4204K are similarly developed biases are the same, and magenta, cyan, This is a black patch image. An arrow indicates the moving direction of the conveyor belt 103.

  First, during Dmax control, an image is formed while switching the developing bias with the same image data (density detection pattern) at a predetermined density. Then, the specular reflection light detection output and the diffuse reflection light detection output are detected by the optical sensor 107, and a development bias value appropriate for desired development characteristics is obtained.

  Next, Dhalf control cancels the γ characteristic in order to prevent a natural image from being formed due to a shift in output density with respect to the input image signal due to the non-linear input characteristic (γ characteristic) peculiar to electrophotography. Image processing that keeps the input characteristics linear is performed. At the time of Dhalf control, the developing bias is fixed to a value optimized after Dmax control, and an image is formed with a plurality of image data. Then, the specular reflection detection output and the diffuse reflection detection output are detected by the optical sensor 107, and the image data input to the image forming apparatus that can obtain a desired halftone density is converted by the controller of the image forming apparatus. The Dhalf control is performed after the image forming conditions are determined by the Dmax control.

[Relationship between optical sensor output and toner density (achromatic color): FIG. 4A]
FIG. 4A shows that a pattern of achromatic black toner is formed on the transport belt, and the pattern is irradiated with infrared light from the light emitting element 502, and the reflected light from the pattern is received by the specular reflected light receiving element 504 and the diffuse reflected light. 6 is a diagram showing output characteristics when detected by an element 503. FIG. G721 is an output characteristic of the regular reflection light receiving element 504, G722 is an output characteristic of the diffuse reflection light receiving element 503, and G723 is a difference value between the detection output of the regular reflection light receiving element 504 and the detection output of the diffuse reflection light receiving element 503. Indicates. In FIG. 4A, the vertical axis indicates the sensor output values of the specular reflection light component and the diffuse reflection light component, and the horizontal axis indicates the density value obtained by subtracting the paper density from the optical density after the pattern is transferred and fixed on the paper. is there.

  In FIG. 4A, the vertical axis indicates the sensor output values of the specular reflection light component and the diffuse reflection light component, and the horizontal axis indicates the density value obtained by subtracting the paper density from the optical density after the pattern is transferred and fixed on the paper. is there. In this embodiment, the surface color of the conveyor belt is black, and almost no diffuse reflection occurs on the new belt. When there is no pattern on the surface of the transport belt and the surface is exposed (toner concentration 0), the surface of the transport belt has gloss, and the regular reflection light receiving element 504 detects light as shown in FIG. 4A. To do. On the other hand, when a black toner pattern is formed on the conveyor belt, the regular reflection output gradually decreases as the toner density of the pattern increases (G721). This is because the regular reflection light from the belt surface is reduced by the toner covering the surface of the conveyance belt. On the other hand, the detection output of the diffuse reflection light receiving element 503 is a low value as shown in FIG. 4A, and the output value of the sensor does not change with a certain toner density (G722).

[Optical sensor output-toner density relationship (chromatic color): FIG. 4B]
On the other hand, FIG. 4B shows output characteristics when a pattern with a chromatic color toner is detected and reflected light from the pattern is detected by the regular reflection light receiving element 504 and the diffuse reflection light receiving element 503. G711, G712, and G713 shown indicate the same characteristics as G711, G712, and G713 described in FIG. 1E. FIG. 6 is a diagram illustrating output characteristics when a pattern made of toner is formed on a conveyance belt (or an image carrier) and reflected light from the pattern is detected by a regular reflection light receiving element 504 and a diffuse reflection light receiving element 503. G711 is an output value detected by the regular reflection light receiving element, G712 is an output value detected by the diffuse reflection light receiving element 503, and G713 is an output value of the regular reflection light receiving element 504 and an output value of the diffuse reflection light receiving element 503. The difference value is shown. In FIG. 1E, the vertical axis indicates the sensor output values of the specular reflection light component and the diffuse reflection light component, and the horizontal axis indicates the density value obtained by subtracting the paper density from the optical density after the pattern is transferred and fixed on the paper. is there.

[Density control method: FIG. 5]
FIG. 5 is a flowchart for explaining the density control method in the image forming apparatus described above. This processing is executed while the CPU controls each unit based on the control program.

  In step S1000, when the power is turned on, the process proceeds to step S10001, and the execution of the density control is awaited. In step S10001, if execution of the density control is requested, the process proceeds to step S10011, and the light quantity control sequence process is executed. Then, control proceeds to step S10002. Details of the light quantity control sequence processing in step S10001 will be described later with reference to FIG.

  Next, in step S10002, the light emitting element 502 including the LED of the optical sensor 107 emits light with the light amount Pd subjected to the light amount control sequence process (the corrected light amount Pd used in step S13007 in FIG. 7 (Pd + Pr before correction)). To control.

  In step S1003, after the light emitting element 502 emits light, control is performed so that a density detection pattern including Y, M, C, and K is formed on the conveyance belt.

  In step S1004, control is performed so that the optical sensor 107 shown in FIG. 1C detects the density detection pattern. Next, in step S1005, control is performed to perform density control calculation based on the detection result. That is, regarding the density pattern detection for each toner, the detection output values of the specular reflection light receiving element 504 and the diffuse reflection light receiving element 503 are used from the output characteristics shown in FIGS. 4A and 4B, and then the specular reflection light reception is performed. The detection output of the element 504 is corrected using the regular reflection light correction gain, and then controlled so as to obtain a difference value from the detection output of the diffuse reflection light receiving element 503. Next, using this difference value, control is performed so as to calculate an appropriate development bias value as an image forming condition.

[Maximum density pattern (solid pattern): FIG. 6]
FIG. 6 is a schematic diagram showing an example of the maximum density pattern (solid pattern) used in the light amount control sequence process in step S1000011 in FIG. In FIG. 6, reference numeral 103 denotes an endless conveyance belt that also serves as a transfer belt, and sequentially conveys print paper to the image forming units for each color, and 107 detects a density detection pattern formed on the conveyance belt 103. , An optical sensor provided in the center of the conveyance belt 103 in the main scanning direction. Reference numeral 1701Y denotes a patch image of the maximum density yellow toner. Similarly, 1701M and 1701C are patch images of magenta toner and black toner having the maximum densities.

[Light intensity control sequence processing: FIG. 7]
FIG. 7 is a flowchart for explaining the details of the light amount control sequence corresponding to step S1000011 in FIG.

  When the light quantity control sequence is requested in step S1000011 in FIG. 5, the process proceeds to step S13002 in FIG. 7, and control is performed so that the light emitting element 502 including the LED of the optical sensor emits light with a predetermined light quantity Pd.

  In step S13003, control is performed so as to form a maximum density pattern (solid pattern) including Y, M, and C shown in FIG. 6 on the conveyance belt.

  In step S13004, the optical sensor shown in FIG. 1C detects the diffuse reflected light amounts Ly, Lm, and Lc of the maximum density pattern (solid pattern) of Y, M, and C. When there are a plurality of Y, M, and C patterns in the maximum density pattern (solid pattern), the average value of the diffuse reflected light amount detected for each color is used as the diffuse reflected light amount for each color. The reason why the K diffused reflected light quantity is not detected is that, as described above, the output value of the detection output of the diffuse reflected light receiving element 503 hardly changes depending on the toner density, and the density detection is difficult.

  In step S13005, control is performed so as to calculate the maximum value Ld of Ly, Lm, and Lc. Here, Ld = max (Ly, Lm, Lc) (Formula 101).

  Next, proceeding to step S13006, a light emission quantity correction value Pr is calculated such that the calculated maximum value Ld of the diffuse reflected light quantity of Y, M, and C becomes the desired light quantity Ltgt. Details of the calculation will be described later with reference to FIG. Here, Pr = f (Ld) (Formula 102).

  In step S13007, the light emission amount Pd of the light emitting element 502 is corrected with the light emission amount correction value Pr. That is, correction is performed according to Pd ← Pd + Pr (Formula 103).

  In step S130071, the light emitting element 502 including the LED of the optical sensor emits light with the corrected light emission amount Pd.

  Next, the process proceeds to step S130072, and when the light emitting element 502 emits light with the corrected light emission amount Pd, the regular reflection light amount Lf that is regularly reflected on the surface of the conveyance belt (the toner density 0 portion) is detected.

Next, proceeding to step S130073, the regular reflection light correction gain Gf is calculated by the following equation. Gf = Lf ₀ / Lf (Formula 104)
Here, Lf ₀ is a detected output value before the printing operation (initial), and is stored in advance in a storage unit such as the ROM 214.

[Relationship between diffuse reflection light quantity Ld, emission light quantity correction value, and Pr: FIG. 8]
FIG. 8 is a diagram for explaining the relationship among the diffuse reflected light amount Ld, the emitted light amount correction value, and Pr. A light emission quantity correction value Pr is calculated such that the diffusely reflected light quantity Ld calculated in step S13005 in FIG. 7 becomes a desired light quantity Ltgt. That is, in FIG. 8, when Ld> Ltgt, it is determined that the diffuse reflected light amount is larger (larger) than the desired light amount, and Pr (= f (Ld)) <0, and the emitted light amount of the light emitting element 502 Decrease. On the other hand, in the case of Ld <Ltgt, it is determined that the diffuse reflected light amount is smaller (smaller) than the desired light amount, and Pr (= f (Ld))> 0, and the emitted light amount of the light emitting element 502 is increased.

[Summary of processing when sensitivity of optical sensor decreases: Fig. 1]
FIG. 1 is a diagram showing output characteristics when a pattern made of toner is formed on a conveyor belt and light reflected by the pattern is detected by a regular reflection light receiving element 504 and a diffuse reflection light receiving element 503 in this embodiment. G711 is the output characteristic of the regular reflection light receiving element before the printing operation (that is, at the reference time), G712 is the output characteristic of the diffuse reflection light receiving element 503 at the reference time, and G713 is the output characteristic of the regular reflection light receiving element 504 at the reference time. A difference value between the detection output and the detection output of the diffuse reflection light receiving element 503 is shown. On the other hand, G7111 is a diffuse reflection light receiving element after a printing operation (after endurance) (that is, at a predetermined time: when the sensitivity of the optical sensor is lowered due to a decrease in gloss of the image carrier or transfer material carrier, contamination of the sensor, etc.). An output characteristic, G7131, indicates a difference value between the detection output of the regular reflection light receiving element 504 and the detection output of the diffuse reflection light receiving element 503 at a predetermined time. The horizontal axis in FIG. 1 is a density value obtained by subtracting the paper density from the optical density after the formed toner pattern is transferred and fixed on the paper.

  As shown in FIG. 1, before the printing operation (during reference time), the image forming condition is set using the difference value G713 between the detection output of the regular reflection light receiving element 504 and the detection output of the diffuse reflection light receiving element 503 obtained. It can be set with high accuracy. However, as shown in FIG. 1, after the printing operation (at a predetermined time), the difference value G7131 between the detection output of the regular reflection light receiving element 504 and the detection output of the diffuse reflection light receiving element 503 obtained is the value before the printing operation (reference). Therefore, if the difference value G7131 is used, the image forming conditions cannot be set with high accuracy.

  Therefore, in the present embodiment, after the printing operation (endurance), for example, from the detection pattern when the sensitivity of the optical sensor is lowered due to the gloss reduction of the image carrier or the transfer material carrier shown in FIG. Even when the output characteristic G7111 of the regular reflection light receiving element and the output characteristic G7121 of the diffuse reflection light receiving element 503 are obtained, the diffuse reflection light receiving element 503 detects by performing the light amount control sequence described in FIG. The light amount of the light emitting element 502 can be controlled (corrected) so that the light amount of the diffusely reflected light is a predetermined light amount. Further, the corrected amount of light is applied to the surface of the conveyor belt (the toner density is 0 area), the reflected regular reflection light amount is detected by the regular reflection light receiving element, and the detected light amount is a reference time (before printing operation: initial) ), The regular reflection correction gain Gf can be calculated from the detected light quantity (stored in the memory).

  As described above, in the image forming apparatus of the present embodiment, the light amount of the light emitting element 502 is controlled from the diffuse reflected light amount of the maximum density pattern (solid pattern), and the specular reflected light detection output is output from the regular reflected light amount on the surface of the conveyor belt. Since the correction gain can be calculated and corrected, for example, even when a fluctuation factor occurs in the output of the optical sensor such as the glossiness of the conveyor belt or the contamination of the sensor, the specular reflection characteristics and the diffuse reflection characteristics The ratio can be made almost constant at all times. Therefore, it is possible to provide a color image forming apparatus with improved density control detection accuracy, lower cost, and excellent color reproduction stability.

  Note that the light emitting element light amount Pd and the regular reflection correction gain Gf calculated in steps S13007 and SS130073 in FIG. 7 can be reflected in the light amount of the light emitting element 502 formed of the LED of the optical sensor 107 in the next density control. .

  In the above description, the optical sensor has been described using an example in which the toner image transferred onto the conveyance belt (transfer material carrier) is detected and the gloss reduction of the transfer material carrier is detected. However, the optical sensor is an image carrier. The toner image formed on the (photosensitive drum) may be detected and the gloss reduction on the image carrier (photosensitive drum) may be detected.

<Second Embodiment>
Hereinafter, the second embodiment will be described. However, the image forming apparatus according to the second embodiment described below is similar to the image forming apparatus according to the first embodiment. Therefore, the description is omitted and only different points will be described.

[Overview of this embodiment]
In the present embodiment, even when the output of the optical sensor fluctuates due to paper dust or the like adhering to the paper and soiling of the optical sensor, or when the gloss of the transport belt (or image carrier) decreases, According to the second method shown in (2), it is possible to control the ratio of the regular reflection light characteristic and the diffuse reflection light characteristic to be substantially constant. Therefore, since the density pattern for density measurement can be accurately measured, an image forming apparatus having excellent color reproduction stability and a control method thereof can be provided.

That is, in the second method, first, at a predetermined time (after the printing operation: after the endurance), light from the light emitting element is applied to a portion of the conveying belt surface (or image carrier) where there is no density pattern (a portion where the toner density is 0). The regular reflection light Lf that is irradiated and reflected is detected by the regular reflection light receiving element, and the detected regular reflection light amount Lf is the amount of light detected at the reference time (before printing operation: initial) (stored in the memory). Compared with Lf ₀ , the correction gain Gf of regular reflection light is calculated. Next, a maximum density pattern (solid pattern with the maximum toner density) is formed on the conveyor belt, light is emitted from the light emitting element to this maximum density pattern, and the diffuse reflected light amount is detected and detected. The correction light amount Gd of diffuse reflection light is calculated by comparing the light amount thus obtained with the diffuse reflection light amount (stored in the memory) at the reference time (before the printing operation: initial stage).

  As a result, even when the output of the optical sensor fluctuates due to a decrease in gloss of the conveying belt or dirt on the sensor, the specular reflected light characteristics are corrected by using the correction gains Gd and Gf of the specular reflection light and diffuse reflection light. And the ratio of diffuse reflected light characteristics can be controlled to be substantially constant.

  Therefore, next, a density pattern for density measurement (FIGS. 2 and 3, etc.) is formed on the conveying belt (or image carrier), and the density pattern for density measurement is irradiated from the light emitting element to obtain the density pattern. The amount of diffusely reflected light and the amount of specularly reflected light that are reflected are detected by a diffuse reflection or regular reflection light receiving element, respectively. By correcting with Gd and Gf and taking the difference between the corrected regular reflection light quantity and the diffuse reflection light quantity, an appropriate optical sensor output-toner density relational expression can be obtained. For this reason, even when the output of the optical sensor fluctuates due to dirt on the sensor or the glossiness of the conveying belt, the image forming conditions can be appropriately adjusted, and color reproduction can be performed stably. Hereinafter, the content described above will be specifically described.

[Density control method: FIG. 9]
FIG. 9 is a flowchart for explaining a density control method in the image forming apparatus according to the present embodiment. This processing is executed while the CPU controls each unit based on the control program.

  The processing in steps S10000 to S10001 is similar to the processing in steps S10000 to S10001 in the first embodiment described with reference to FIG.

  Next, when density control is required in step S140011, control is performed to execute a gain calculation sequence. Details of processing of the gain calculation sequence will be described later with reference to FIG.

  Next, after executing the gain calculation sequence processing, the processing from step S10002 to step S10004 is the same as that of step S10002 to step S10004 in FIG. 5 in the first embodiment.

  Next, in step S140041, the density detection pattern (FIGS. 2 and 3) formed in step S10003 is detected by the optical sensor 107 shown in FIG. 1C in step S1000, and the regular reflection light receiving element having the pattern for each toner is detected. With respect to the detection outputs of 504 and the diffuse reflection light receiving element 503, the regular reflection correction gain Gf obtained in step S140011 is used for the regular reflection light reception output, and the diffuse reflection correction gain obtained in step S140011 is used for the diffuse reflection light reception output. Each Gd is controlled to perform a correction operation by performing integration or the like.

  Next, in step S14005, control is performed so as to obtain corrected output values of the detection outputs of the regular reflection light receiving element 504 and the diffuse reflection light receiving element 503 obtained by the correction calculation in step S140041. Next, using this difference value, control is performed so as to calculate an appropriate development bias value as an image forming condition.

[Gain calculation sequence processing: FIG. 10]
FIG. 10 is a flowchart illustrating details of the gain calculation sequence corresponding to step S140011 in FIG.

  When the gain calculation sequence is requested in step S140011 in FIG. 9, the process proceeds to step S15000 in FIG. 10n, and control is performed so that the light emitting element 502 including the LED of the optical sensor emits light with a predetermined light amount Pd. In step S 15001, the regular reflected light amount Lf on the surface of the conveyance belt (the toner density 0 portion) is detected.

Next, proceeding to step S15002, the regular reflected light correction gain Gf is calculated by the following equation. Gf = Lf ₀ / Lf (Formula 201) Here, Lf ₀ is a detected output value before the printing operation (initial), and is stored in advance in the ROM 214 (FIG. 1D) or the like.

  In step S15003, a maximum density pattern (solid pattern) composed of Y, M, and C is formed on the conveyance belt. In step S15004, after the maximum density pattern (solid pattern) is formed, the diffuse reflected light amounts Ly, Lm, and Lc of the maximum density pattern (solid pattern) of Y, M, and C are obtained by the optical sensor shown in FIG. 1C. To detect. When there are a plurality of Y, M, and C patterns in the maximum density pattern (solid pattern), the average value of the diffuse reflected light amount detected for each color is used as the diffuse reflected light amount for each color. The reason why the amount of K diffuse reflected light is not detected is that, as described above, the output value of the detection output of the diffuse reflected light receiving element 503 hardly changes depending on the toner density.

Next, proceeding to step S 15006, the diffuse reflected light correction gain Gd is calculated from the diffuse reflected light amounts of Y, M, and C by the following formula. Gd = Ld ₀ / Ld (Formula 202) Here, Ld ₀ is a detected output value before the printing operation (initial), and is stored in advance in the ROM 214 (FIG. 1D) or the like.

[Summary of processing when sensitivity of optical sensor decreases: Fig. 1]
As shown in FIG. 1, before the printing operation (reference time), the image forming condition is determined using the difference value G713 between the detection output of the regular reflection light receiving element 504 and the detection output of the diffuse reflection light receiving element 503 obtained. It can be set with high accuracy. However, as shown in FIG. 1, after the printing operation (at a predetermined time), the difference value G7131 between the detection output of the regular reflection light receiving element 504 and the detection output of the diffuse reflection light receiving element 503 obtained is the value before the printing operation (reference). Therefore, if the difference value G7131 is used, the image forming conditions cannot be set with high accuracy.

  Therefore, in the present embodiment, after the printing operation (endurance), for example, from the detection pattern when the sensitivity of the optical sensor is lowered due to the gloss reduction of the image carrier or the transfer material carrier shown in FIG. Even when the output characteristic G7111 of the regular reflection light receiving element and the output characteristic G7121 of the diffuse reflection light receiving element 503 are obtained, the processing of the gain calculation sequence described in FIG. The correction gain Gd of the diffuse reflection light detection output is calculated from the diffuse reflection light amount of the solid pattern), and the correction gain Gf of the regular reflection light detection output is calculated from the regular reflection light amount of the surface of the conveying belt (the area of toner density 0). be able to.

  Therefore, by correcting each of these using the correction gains Gd and Gf, in the image forming apparatus of the present embodiment, for example, as described in the first embodiment, the gloss of the conveyor belt is reduced, the sensor Even when a fluctuation factor occurs with respect to the output of the optical sensor, such as dirt, the ratio of the specular reflection light characteristic to the diffuse reflection light characteristic can always be made substantially constant. Therefore, it is possible to provide a color image forming apparatus with improved density control detection accuracy, lower cost, and excellent color reproduction stability. Therefore, it is possible to provide a color image forming apparatus with improved density control detection accuracy, lower cost, and excellent color reproduction stability.

  In addition, the regular reflection light correction gain Gf and the diffuse reflection light correction gain Gd calculated in steps S15002 and S15006 in FIG. 10 can be reflected in the detection result in the next density control.

<Third Embodiment>
Hereinafter, the third embodiment will be described. Since the image forming apparatus according to the third embodiment described below is similar to the image forming apparatus according to the first or second embodiment, description of common points will be given. Will be omitted, and only different points will be described.
[Overview of this embodiment]
In the first embodiment described above, the maximum density pattern (solid pattern) is formed as the light amount control sequence and the diffuse reflected light is detected during the density control execution. In the present embodiment, the color shift correction control performs color control. The light quantity control of the light emitting element is performed from the diffuse reflected light quantity of the deviation detection pattern. For this reason, in the image forming apparatus of the present embodiment, the process of the first method (the light amount control of the light emitting element) described in the first embodiment can be performed during the process of color misregistration correction control. The processing time can be shortened compared to the embodiment. Hereinafter, the content described above will be specifically described.

[Example of color misregistration: FIG. 11]
Uneven movement of multiple photosensitive drums and conveyor belts due to machine accuracy for each color in multiple image forming units, and relationship between the movement amount of the photosensitive drum outer peripheral surface and the conveyance belt at the transfer position of each image forming unit And the like occur in different colors for each color and do not match when the images are superimposed, resulting in a color shift (positional shift). In particular, in an apparatus having a plurality of image forming units having a laser scanner and a photosensitive drum, there is an error in the distance between the laser scanner and the photosensitive drum in each image forming unit. A difference occurs in the scanning width of the laser on the drum, and color misregistration occurs.

  An example of color misregistration is shown in FIG. 201 indicates an original image position, and 202 indicates an image position when color misregistration occurs. Also, (a), (b), and (c) are cases where there is a color shift in the scanning direction, but for the sake of explanation, two lines are drawn apart in the transport direction. (A) shows an inclination shift of the scanning line, which occurs when there is an inclination between the optical unit and the photosensitive drum. For example, the position is corrected in the direction of the arrow by adjusting the position of the optical unit or the photosensitive drum or the position of the lens. (B) shows color misregistration due to variations in scanning line width, and is caused by a difference in distance between the optical unit and the photosensitive drum. It tends to occur when the optical unit is a laser scanner. For example, the image frequency is finely adjusted (if the scanning width is long, the frequency is increased) and the length of the scanning line is changed to correct in the arrow direction. (C) shows the writing position error in the scanning direction. For example, if the optical unit is a laser scanner, it is corrected in the direction of the arrow by adjusting the writing start timing from the beam detection position. (D) shows the writing position error in the paper transport direction. For example, the correction is made in the direction of the arrow by adjusting the writing start timing of each color from the detection of the leading edge of the paper. In order to correct the color misregistration, a color misregistration detection pattern is formed for each color on the conveyor belt 103, detected by an optical sensor provided on the conveyor belt, and the color misregistration is detected and corrected. Perform correction control.

[Color misregistration detection pattern: FIG. 12]
FIG. 12 is a schematic diagram illustrating an example of a color misregistration detection pattern. Reference numeral 103 denotes an endless conveyance belt that also serves as a transfer belt, and sequentially conveys print paper to the image forming units for each color. Reference numeral 107 denotes a conveyance belt that detects a color misregistration detection pattern formed on the conveyance belt 103. Reference numeral 103 denotes an optical sensor provided in the main scanning direction. Here, reference numerals 309 to 3020 denote patterns for detecting the amount of color misregistration in the paper conveyance direction and the scanning direction, the pattern for detecting color misregistration 309 to 3012 is pattern 1, and the pattern for detecting color misregistration 3013 to 3016 is pattern 2. , 3017 to 3020 are color misregistration detection patterns. A, c, e, and g represent K as a reference color, and b, d, and f represent Y, M, and C as detected colors, respectively. An arrow indicates the moving direction of the conveyor belt 103. According to the detection timing of each pattern, the amount of color misregistration for each color is calculated, corrected to a desired writing start timing, and color misregistration is reduced.

[Density control method: FIG. 13]
FIG. 13 is a flowchart for explaining the density control method in the image forming apparatus described above. This processing is executed while the CPU controls each unit based on the control program.

  Steps S10000 to S10005 in FIG. 13 are the same as steps S10000, S10001, and S10002 to S10005 in FIG. 5 of the first embodiment, and therefore, the description thereof is duplicated, so the individual description is omitted. . Although the light amount control sequence (step SS1000011) is executed in the first embodiment, it is not executed in this embodiment, and is executed in the color misregistration correction control process described in FIG.

[Color misregistration correction control method: FIG. 14]
FIG. 15 is a flowchart for explaining the density control method in the image forming apparatus described above. This processing is executed while the CPU controls each unit based on the control program.

  When the power is turned on, the process proceeds to step S8001 to enter a state of waiting for execution of color misregistration correction control, and when execution of color misregistration correction control is requested, the process proceeds to step S8002 and light emission composed of LEDs of the optical sensor 107 with a predetermined light amount Pd. The element 502 is controlled to emit light.

  In step S8003, control is performed so that a color misregistration detection pattern including Y, M, C, and K is formed on the conveyance belt. Next, the process proceeds to step S8004. After the color misregistration detection pattern is formed, if the timing of the color misregistration detection pattern is detected from the regular reflection light of the color misregistration detection pattern by the optical sensor 107 shown in FIG. 1C, the process proceeds to step S8005. Control is performed so as to detect the diffuse reflected light amounts Ly, Lm, and Lc of Y, M, and C. When there are a plurality of Y, M, and C patterns in the detection pattern, control is performed so that the average value of the diffuse reflected light amount detected for each color is used as the diffuse reflected light amount for each color.

  In step S8006, control is performed so as to calculate the maximum value Ld of Ly, Lm, and Lc. Here, Ld = max (Ly, Lm, Lc) (Formula 301).

  In step S8007, the color misregistration amount δep of each color is calculated from the color misregistration detection pattern detected in step S8004, and the optimum writing start timing is determined for each color. Next, proceeding to step S8008, a correction value Pr is calculated so that the maximum value Ld of the diffuse reflected light amount of the color color calculated at step S8006 becomes a desired light amount. Here, Pr = f (Ld) (Formula 302). Note that the details of the calculation are the same as those described in the first embodiment, and thus description thereof is omitted here.

  Next, proceeding to step S8009, after calculating the correction value Pr, the Pr light amount Pd of the light emitting element 502 is corrected. Here, Pd ← Pd + Pr (Formula 303).

  In step S8010, after the light emission amount Pd is corrected, the light emitting element 502 including the LED of the optical sensor emits light with the corrected light amount Pd. In step S8011, after the light emitting element 502 emits light, the regular reflected light amount Lf on the surface of the conveyor belt (toner density 0) is detected.

Next, proceeding to step S8012, the regular reflection light correction gain Gf is calculated. Gf = Lf ₀ / Lf (Formula 104)
Here, Lf ₀ is a detected output value before the printing operation (initial), and is stored in advance in a storage unit such as the ROM 214.

  As described above, in the color misregistration correction control, the light amount of the light emitting element 502 is controlled from the diffuse reflection light amount of the color misregistration detection pattern, and the correction gain of the regular reflection light detection output is calculated from the regular reflection light amount on the surface of the conveyor belt. Can be corrected. Therefore, in the present embodiment, since the light amount control sequence described in the first embodiment can be performed in the color misregistration correction control, for example, while reducing the downtime due to the light amount control sequence, Even when fluctuation factors occur with respect to the output of the optical sensor, such as gloss reduction and sensor contamination, the ratio of the specular reflection light characteristic and the diffuse reflection light characteristic can always be made substantially constant. Therefore, it is possible to provide a color image forming apparatus with improved density control detection accuracy, lower cost, and excellent color reproduction stability.

  Note that the light emitting element light amount Pd calculated in step S8009 in FIG. 8 can be reflected in the light amount of the light emitting element 502 including the LED of the optical sensor 107 in the next density control.

  The concept of the color misregistration correction control described above can also be applied to the second embodiment, and the gain calculation sequence execution processing time of the second embodiment can be reduced by applying the idea. Can do.

  Furthermore, although the present invention has been described with an example in which one optical sensor is provided, the number of optical sensors is not limited to this. In addition, the structure of the optical sensor has been described with reference to FIG. 1C, but the structure is not limited thereto as long as the structure includes the light emitting element 502, the regular reflection light receiving element 504, and the diffuse reflection light receiving element 503. For example, a pair of optical sensors are provided at both ends of the conveyance belt in the main scanning direction, a specular reflection light receiving element is detected by one optical sensor, and a diffuse reflection light receiving element is detected by the other optical sensor. Also good. Furthermore, a structure as shown in FIG. 15 may be used.

[Another example of optical sensor: FIG. 15]
FIG. 15 is a diagram for explaining an example of the structure of the optical sensor of the present invention. Reference numeral 501 denotes a pattern to be detected, 502a and 502b are light emitting elements made of LEDs, and 505 is a reflected light receiving element made of a phototransistor. In this configuration, the reflected light receiving element 505 detects regular reflected light by emitting only the light emitting element 502a. The reflected light receiving element 505 detects diffuse reflected light by emitting only the light emitting element 502b. By alternately causing the light emitting elements 502a and 502b to emit light in chronological order in each detection pattern, it is possible to detect the regular reflected light amount and the diffuse reflected light amount. Further, the arrangement angle is not limited to 30 degrees and 60 degrees.

  The light amount correction value of the light emitting element 502 is calculated based on the maximum value of the chromatic diffuse reflected light amount, but other operations may be used as long as the light emission amount output after the correction is not saturated. In the third embodiment, the color misregistration detection pattern is detected from specular reflection light, but may be detected from diffuse reflection light.

[Other Embodiments]
An object of the present invention is to supply a recording medium (or storage medium) that records software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and the computer of the system or apparatus (or CPU or MPU). Needless to say, this can also be achieved by reading and executing the program code stored in the recording medium. In this case, the program code itself read from the recording medium realizes the functions of the above-described embodiment, and the recording medium on which the program code is recorded constitutes the present invention.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  Furthermore, after the program code read from the recording medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is based on the instruction of the program code. It goes without saying that the CPU or the like provided in the expansion card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

  Also, program data for realizing the functions of the above-described embodiment is downloaded from the CD-ROM set in the own device or an external supply source such as the Internet to the memory of the own device, and A form in which the function is realized is also included in the present invention.

  When the present invention is applied to the recording medium, it is preferable that program code corresponding to the flowchart described above is stored in the recording medium.

It is a figure explaining the relationship between an optical sensor output and a toner density | concentration when an initial stage and sensor sensitivity fall. 1 is a diagram illustrating an example of an overall configuration of an image forming apparatus according to an exemplary embodiment. It is a figure explaining an example of the optical sensor of this embodiment. It is a figure explaining an example of the control structure of the image forming apparatus of this embodiment. It is a figure explaining the process when the sensor sensitivity in a prior art example falls. It is a figure explaining an example of the density | concentration detection pattern of Dmax control. It is a figure explaining an example of the density detection pattern of Dhalf control. It is a figure explaining the optical sensor output characteristic at the time of achromatic toner detection at the time of initial stage. It is a figure explaining the optical sensor output characteristic at the time of chromatic color toner detection at the time of initial stage. It is a flowchart explaining the density | concentration control method of 1st Embodiment. It is a figure explaining an example of the maximum density pattern (solid pattern) of 1st, 2nd embodiment. It is a flowchart explaining the detail of the process of the light quantity control sequence of 1st Embodiment. It is a figure explaining the relationship between a diffuse reflected light light quantity and the light emission light quantity correction value. It is a flowchart explaining the density | concentration control method of 1st Embodiment. It is a flowchart explaining the detail of the process of the gain correction sequence of 2nd Embodiment. It is a figure explaining the color shift of 3rd Embodiment. It is a figure explaining an example of the color shift detection pattern of 3rd Embodiment. It is a flowchart explaining an example of the density | concentration control method of 3rd Embodiment. 10 is a flowchart illustrating a color misregistration correction control method according to a third embodiment. It is a figure explaining an example of another optical sensor of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Photosensitive drum 102 ... Laser scanner 103 ... Conveyance belt 104 ... Belt drive roller 105 ... Belt driven roller 107 ... Optical sensor 502 ... Light emitting element 503 ... Diffuse reflected light receiving element 504 ... Regular reflection Light receiving element

Claims (12)

An image forming apparatus for controlling image forming conditions by detecting the density of a reference toner image for density measurement formed on an image carrier using an optical detection means,
A memory for storing a reference diffuse reflection light quantity that is irradiated from the optical detection means at the time of reference to the reference toner image, diffusely reflected by the reference toner image, and detected by the diffuse reflection light receiving element of the optical detection means. Means,
The diffuse reflected light amount detected by the diffuse reflected light receiving element when the diffuse reflected light amount detected when the reference toner image is irradiated with light from the optical detection means at a predetermined time does not match the reference diffuse reflected light amount. Control means for controlling the optical detection means so as to match the reference diffuse reflection light amount stored in the storage means,
An image forming apparatus comprising:   The control means corrects the light quantity of the light emitting element of the optical detection means so that the detected diffuse reflection light quantity matches the reference diffuse reflection light quantity stored in the storage means. The image forming apparatus according to claim 1.   The control means corrects the output of the diffuse reflection light receiving element of the optical detection means so that the detected diffuse reflection light quantity matches the reference diffuse reflection light quantity stored in the storage means. The image forming apparatus according to claim 1, wherein:   2. The reference toner image includes a toner image having a maximum density, and the storage unit stores an amount of light diffusely reflected by the toner image having the maximum density at the reference time. The image forming apparatus according to claim 3.   The image forming apparatus according to claim 1, wherein the storage unit stores the reference diffuse reflection light amount for each color.   The image forming apparatus according to claim 1, wherein the reference toner image for density measurement is a color misregistration detection pattern for detecting color misregistration.   A transfer material carrying / conveying body that conveys and conveys a transfer material facing the image carrying body, wherein the optical detection means is the reference toner image formed on the image carrying body or the image carrying The image forming apparatus according to claim 1, wherein the reference toner image formed on the body and subsequently transferred onto the transfer material carrying and conveying body is detected.   The storage means emits light from the light emitting element of the optical detection means at the reference time so that a portion of the image carrier on which the reference toner image is not formed, or the reference toner image is not formed. Irradiates a portion of the transfer material-carrying carrier that has not been transferred with a toner density of 0, is regularly reflected at the portion, and is regularly reflected by the specular reflection light receiving element of the optical detection means. The image forming apparatus according to claim 7, further storing a light amount.   The control means is regularly reflected from the portion when the corrected amount of light is irradiated on the image carrier or the transfer material carrier and is detected by the specular light receiving element. 9. The image formation according to claim 8, further comprising: correcting the output value of the regular reflection light receiving element so as to coincide with the reference regular reflection light amount when the light amount to be matched does not coincide with the reference regular reflection light amount. apparatus.   The control means is detected by the specular reflection light receiving element when the optical detection means irradiates the part on the image carrier or the part on the transfer material carrying carrier at the predetermined time. 9. The image formation according to claim 8, further comprising: correcting the output value of the regular reflection light receiving element so as to coincide with the reference regular reflection light amount when the light amount to be matched does not coincide with the reference regular reflection light amount. apparatus. An image forming apparatus control method for controlling image forming conditions by detecting the density of a reference toner image for density measurement formed on an image carrier using an optical detection means, wherein the image forming apparatus includes: The reference toner image is irradiated with light from the optical detection means at the time of reference, diffused and reflected by the reference toner image, and the reference diffuse reflection light quantity detected by the diffuse reflection light receiving element of the optical detection means is stored. Having storage means;
The diffuse reflected light amount detected by the diffuse reflected light receiving element when the diffuse reflected light amount detected when the reference toner image is irradiated with light from the optical detection means at a predetermined time does not match the reference diffuse reflected light amount. And a control step of controlling the optical detection means so as to coincide with the reference diffuse reflection light quantity stored in the storage means. A control program for controlling an image forming apparatus for controlling image forming conditions by detecting the density of a reference toner image for density measurement formed on an image carrier using an optical detection means, the image forming apparatus comprising: The apparatus irradiates the reference toner image with light from the optical detection means at the time of reference, diffuses and reflects the reference toner image, and generates a reference diffuse reflection light amount detected by the diffuse reflection light receiving element of the optical detection means. Storing means for storing;
The diffuse reflected light amount detected by the diffuse reflected light receiving element when the diffuse reflected light amount detected when the reference toner image is irradiated with light from the optical detection means at a predetermined time does not match the reference diffuse reflected light amount. A control program for controlling an image forming apparatus, comprising: a program code of a control process for controlling the optical detection unit so that the optical detection unit coincides with the reference diffuse reflection light quantity stored in the storage unit.

Images