JP2014119727A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of using small detection images for controlling image forming conditions related to density.SOLUTION: An image forming apparatus includes: image forming means for forming detection images having one or more lines extending in a direction different from a direction of movement of the surface of an image carrier on the surface of the image carrier; detection means for detecting the detection images formed by the image forming means and outputting output signals; and control means for controlling image forming conditions related to the density of the images to be formed on the basis of peak values of the output signals output from the detection means. The detection means includes: light emitting means for irradiating the image carrier with light; light receiving means for receiving the light emitted from the light emitting means and reflected on the image carrier, and outputting detection signals according to the amount of received light; and output means for outputting, as output signals, signals according to a difference between the values of the detection signals corresponding to the amount of received light including regular reflection light components from different positions on the surface of the image carrier.

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer, and more particularly to a technique for adjusting image forming conditions in the image forming apparatus.

  An electrophotographic image forming apparatus forms an image by developing an electrostatic latent image formed on a photosensitive member with laser light with toner and transferring the developed toner image directly or indirectly to a recording material. . Particularly in a color image forming apparatus, it is important to accurately adjust the density of each toner image in order to form an image by superimposing the toner images of the respective colors to be used. However, even if the image forming conditions are kept constant, the characteristics of each member related to image formation change due to environmental factors such as temperature and humidity, and the density fluctuates due to these changes. Furthermore, the characteristics of each member related to image formation change due to secular change, which also leads to density fluctuations.

  For this reason, the image forming apparatus executes density correction for adjusting the maximum density and the gradation of density. Specifically, a detection image for density detection is formed on an image carrier such as a photoconductor, an intermediate transfer body, or a recording material, and the density of the detection image is detected by a sensor and fed back to image forming conditions. Note that the image forming conditions to be adjusted include the charging potential of the photoconductor, the amount of light applied to the photoconductor, the development bias, the amount of toner supplied for development, and the like. Such a correction operation is called calibration.

  Here, Patent Document 1 discloses an optical sensor for reading a detected image. The optical sensor disclosed in Patent Document 1 includes an LED and a phototransistor that receives regular reflection light and diffuse reflection light when a detection image is illuminated by the LED. When the density is detected using the optical sensor described in Patent Document 1, a detection image drawn with toner in an area of about 10 mm × 10 mm is read. Here, it is desirable that the detection image used for density correction is as small as possible. This is because if the detected image is small, the amount of toner consumed is reduced and the calibration time is shortened. For this reason, Patent Document 2 discloses a configuration in which a small detection image is used by using a CCD sensor.

JP-A-3-134678 Japanese Patent Laid-Open No. 7-20670

  However, the CCD is expensive, and if the CCD is used, the detected image can be made small, but the cost of the image forming apparatus becomes high.

  The present invention provides an image forming apparatus that can use a small detection image for controlling image forming conditions relating to density using a sensor having a simple configuration.

  According to one aspect of the present invention, image forming means for forming a detection image having one or more lines in a direction different from the moving direction of the surface of the image carrier on the surface of the image carrier, and the image carrier Detection means for detecting the formed detection image and outputting an output signal; and control means for controlling an image forming condition relating to the density of the image to be formed based on a peak value of the output signal of the detection means. The detection means includes a light emitting means for irradiating the image carrier with light, and a light receiving means for receiving the light emitted from the light emitting means and reflected by the image carrier and outputting a detection signal corresponding to the amount of received light. And an output means for outputting, as the output signal, a signal corresponding to a difference in value of the detection signal corresponding to the amount of received light including specularly reflected light components from different positions on the surface of the image carrier. It is characterized by being.

  A detection image including one or more lines is formed on the image carrier, and an output signal corresponding to a difference in detection signal values corresponding to received light amounts including specularly reflected light components from different positions on the surface of the image carrier. Control image forming conditions. With this configuration, it is possible to control the image forming conditions with a detection image smaller than the conventional one using a sensor with a simple configuration.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. 1 is a schematic diagram of an optical sensor according to an embodiment. FIG. 1 is a schematic circuit diagram of an optical sensor according to an embodiment. FIG. The figure which shows the pattern image by one Embodiment. The figure which shows the output signal of the optical sensor at the time of detecting the pattern image whose line width is equal to the target by one Embodiment. The figure which shows the output signal of the optical sensor at the time of detecting the pattern image whose line width is thinner than the target by one Embodiment. The figure which shows the output signal of the optical sensor at the time of detecting the pattern image whose line width is thicker than the target by one Embodiment. The figure which shows the relationship between the deviation | shift amount from the target value of the line width of a pattern image, and the peak value of the output signal of an optical sensor. The figure explaining the relationship between the line width of a pattern image, and development bias. The figure which shows the relationship between the developing bias, the line width of a pattern image, and maximum density, respectively. The flowchart of the initial maximum density calibration by one Embodiment. The figure which shows schematically the pattern image used by the initial maximum density calibration by one Embodiment. The figure which shows the relationship between the developing bias detected by the initial maximum density calibration by one Embodiment, and the peak value of the output signal of an optical sensor. The flowchart of the maximum density calibration during printing by one Embodiment. The figure which shows schematically the pattern image used by the maximum density calibration during printing by one Embodiment. The figure which shows the relationship between the developing bias detected by the maximum density calibration during printing by one Embodiment, and the peak value of the output signal of an optical sensor. The flowchart of the maximum density setting change process by one Embodiment. The figure which shows the conversion table used by the maximum density setting change process by one Embodiment. The schematic block diagram of the optical sensor by one Embodiment. 1 is a schematic circuit diagram of an optical sensor according to an embodiment. FIG. The figure which shows the pattern image by one Embodiment. The figure which shows the output signal of the optical sensor at the time of detecting the pattern image whose line width is equal to the target by one Embodiment. The figure which shows the output signal of the optical sensor at the time of detecting the pattern image whose line width is thinner than the target by one Embodiment. The figure which shows the output signal of the optical sensor at the time of detecting the pattern image whose line width is thicker than the target by one Embodiment. The figure which shows the relationship between the deviation | shift amount from the target value of the line width of a pattern image, and the peak value of the output signal of an optical sensor. Explanatory drawing of the process with respect to the output signal of the optical sensor by one Embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

<First embodiment>
First, the image forming unit and the control unit 25 of the image forming apparatus 101 according to the present embodiment will be described with reference to FIG. The Y, M, C, and Bk at the end of the reference numerals in FIG. 1 indicate that the colors of the developer (toner) targeted by the corresponding members are yellow, magenta, cyan, and black, respectively. In the following description, when it is not necessary to distinguish between colors, reference numerals without Y, M, C, and Bk at the end are used. The photosensitive member 1, which is an image carrier that is rotationally driven in the direction of the arrow in the figure, is uniformly charged by the charging unit 2, and the exposure unit 7 irradiates the photosensitive member 1 with a laser beam to emit an electrostatic latent image. Form. The developing unit 3 supplies toner that is a developer to the electrostatic latent image by a developing bias, and converts the electrostatic latent image into a toner image that is a visible image. The primary transfer roller 6 transfers the toner image on the photoreceptor 1 to the intermediate transfer belt 8 by the primary transfer bias. The intermediate transfer belt 8 is rotationally driven in the direction of the arrow 81. Each photoconductor 1 transfers the toner image on the intermediate transfer belt 8 so as to form a color image. The cleaning blade 4 removes the toner that is not transferred to the intermediate transfer belt 8 and remains on the photoreceptor 1.

  The conveyance rollers 14, 15 and 16 convey the recording material in the paper feed cassette 13 to the secondary transfer roller 11 along the conveyance path 9. The secondary transfer roller 11 transfers the toner image on the intermediate transfer belt 8 to the recording material by a secondary transfer bias. The toner that is not transferred to the recording material and remains on the intermediate transfer belt 8 is removed by the cleaning blade 21 and collected in a waste toner collecting container 22. The recording material onto which the toner image has been transferred is heated and pressurized in the fixing unit 17 to fix the toner image, and is discharged out of the apparatus by the transport roller 20. The control unit 25 includes a CPU 26, and performs sequence control of various drive sources (not shown) of the image forming apparatus 101, various controls using sensors, and the like. An optical sensor 27 is provided at a position facing the intermediate transfer belt 8.

  Hereinafter, details of the optical sensor 27 of the present embodiment will be described with reference to FIG. 2A is a perspective view of the optical sensor 27, and FIG. 2B is a view seen from the X direction of FIG. 2A. The optical sensor 27 according to the present embodiment includes a light emitting element 272, a light receiving unit 270 including a plurality of light receiving elements 273p, 273n, 274p, and 274n, a control circuit 275, and a light shielding wall 276. ,have. The light emitting element 272 includes, for example, an LED chip without a reflector, and irradiates the intermediate transfer belt 8 with a divergent light beam of a point light source without constricting the light beam with a lens or the like. The light receiving elements of the light receiving unit 270 are arranged in an array along the moving direction 81 of the intermediate transfer belt 8. Each light receiving element is, for example, a photodiode that outputs a current corresponding to the amount of light received. In this embodiment, each light receiving element receives the reflected light from the intermediate transfer belt without passing through a condensing lens or other optical member for condensing or condensing light, and converts it into a current. To do. In the following description, the light receiving element 273n and the light receiving element 274n are also referred to as a light receiving part An, and the light receiving elements 273p and 274p are also referred to as a light receiving part Ap. That is, the light receiving unit 270 is configured such that the light receiving unit Ap (first light receiving unit) and the light receiving unit An (second light receiving unit) are alternately arranged. As described above, in this embodiment, one light receiving portion Ap corresponds to one light receiving element 273p, 274p, and one light receiving portion An corresponds to one light receiving element 273n, 274n. The part Ap and one light receiving part An may include three or more light receiving elements. That is, in the present embodiment, the light receiving portions Ap and the light receiving portions An, each of which is composed of two or more light receiving elements, can be alternately arranged.

  As shown in FIG. 2A, in this embodiment, the widths of the light receiving portions Ap and An in the arrangement direction are equal Wsns, the pitches of the light receiving portions Ap and the light receiving portions An are equal, and the value Psns is It is twice the width of Ap and the light receiving part An. In the present embodiment, the pitch of the light receiving portions Ap means a distance between corresponding positions of the adjacent light receiving portions Ap, for example, a distance between the centers, and does not mean a distance between the adjacent light receiving portions Ap. Similarly, in the present embodiment, the pitch of the light receiving portions An means the distance between the corresponding positions of the adjacent light receiving portions An, and does not mean the distance between the adjacent light receiving portions An. In the present embodiment, the light receiving areas of the light receiving portions Ap and the light receiving portions An are assumed to be equal. Furthermore, the width in the arrangement direction of the light receiving surfaces of each light receiving part Ap and each light receiving part An is substantially equal to the width Wsns of the light receiving part Ap and the light receiving part An.

  The control circuit 275 is electrically connected to the light emitting element 272 and the light receiving unit 270, and has a signal processing circuit described later. The light shielding wall 276 is provided to prevent the light emitted from the light emitting element 272 from entering the light receiving unit 270 without passing through the intermediate transfer belt 8. Note that the surface of the intermediate transfer belt 8 is often subjected to a glossy coating process, and the light emitted from the light emitting element 272 is mainly regularly reflected on the surface of the intermediate transfer belt 8. On the other hand, in the toner portion of the image formed on the intermediate transfer belt 8, the light emitted from the light emitting element 272 is absorbed or diffusely reflected. For example, when the light source is a red LED, the irradiation light is absorbed by cyan and black toners and diffusely reflected by yellow and magenta toners. For example, when the light source is an infrared LED, the irradiation light is absorbed by the black toner and diffusely reflected by the yellow, magenta, and cyan toners. In FIGS. 2A and 2B, the light irradiated by the light emitting element 272 and regularly reflected on the surface of the intermediate transfer belt 8 is indicated by arrows. In FIG. 2B, the reflected light is weakened in the region where the light receiving portion 270 is formed as the irradiated light is absorbed or diffusely reflected by the toner, that is, a shadow is formed by the toner. Is denoted by reference numeral 279.

  Hereinafter, the relationship between the pattern image 40 that is a density detection image shown in FIG. 2A and the light projected on the light receiving unit 270 will be described. In the present embodiment, the pattern image 40 is a striped toner image in which two lines having the same length in the direction orthogonal to the moving direction 81 of the surface of the intermediate transfer belt 8 are formed along the moving direction 81. Note that the number of lines to be formed is an example, and any number of two or more can be used. Moreover, although this embodiment demonstrates a line as a continuous line, the broken line or dotted line which consists of fine spots may be sufficient. Hereinafter, a portion between lines of the pattern image 40 is referred to as a space. As shown in FIG. 2A, the line width in the movement direction 81 of the pattern image 40 of the present embodiment is Wt40, the space width is Wb40, and the pitch between the lines is Pt40. The line width of the pattern image 40 is, for example, several dots level (600 dpi resolution, 1 dot is 42.3 μm). In this embodiment, the pitch between lines means a distance between corresponding positions of two adjacent lines, for example, a distance between centers, and does not mean a width of a space.

  Since the light emitting element 272 is a type of LED that emits a divergent light beam of a point light source, an image of the pattern image 40 formed on the intermediate transfer belt 8 is projected onto the light receiving unit 270 at a predetermined magnification. In this embodiment, since the intermediate transfer belt 8 and the substrate 271 are arranged in parallel, the incident light from the light emitting element 272 to the intermediate transfer belt 8 and the regular reflection light are equiangular. Further, the light emitting element 272 and the light receiving portion 270 are configured such that the surface height on the substrate 271 is the same. That is, the optical path lengths of incident light (outward path) and regular reflection light (return path) are equal. Therefore, the striped pattern image 40 formed on the intermediate transfer belt 8 is projected onto the light receiving unit 270 as an image having a double size. That is, the line width Wt40, the space width Wb40, and the pitch Pt40 between the lines of the pattern image 40 of the intermediate transfer belt 8 are all twice as large when projected onto the light receiving unit 270. Further, the length in the X direction in FIG. 2A of the shadow by the line of the pattern image 40 is longer than the length in the X direction of the light receiving part Ap and the light receiving part An. In the present embodiment, the length in the X direction of the light receiving part Ap and the light receiving part An is about 0.2 mm. Therefore, if the length of the line of the pattern image 40 in the X direction in FIG. 2A is equal to or longer than the length obtained by adding image formation variation to about 0.1 mm, the shadow of the pattern image 40 is reflected by the light receiving portion Ap and the light receiving portion. Cover the part An. The shadow of the pattern image 40 may not cover and hide the light receiving part Ap and the light receiving part An.

  Next, the control circuit 275 will be described with reference to FIG. The control circuit 275 is connected to the light receiving unit 270 on the substrate 271. Further, inside the control circuit 275, the light receiving elements 273p and 274p constituting the light receiving part Ap are connected, and the light receiving elements 273n and 274n constituting the light receiving part An are connected. The light receiving part Ap is connected to the IV conversion amplifier 281, and the light receiving part An is connected to the IV conversion amplifier 284. When the light receiving unit 270 receives light, the current Iap corresponding to the total light receiving amount of the light receiving unit Ap and the current Ian corresponding to the total light receiving amount of the light receiving unit An are converted into voltages by the IV conversion amplifier, respectively. .

A reference voltage Vref1 generated by dividing the voltage Vcc by the resistors 287 and 288 is input to the non-inverting input terminals of the IV conversion amplifiers 281 and 284 by the voltage follower 289. Therefore, the IV conversion amplifiers 281 and 284 output a voltage S1 and a voltage S2 represented by the following equations, respectively.
S1 = Vref1− (R ₂₈₂ × Iap)
S2 = Vref1- ( _R285 * Ian)
Here, R ₂₈₂ is the resistance value of the resistor 282, and R ₂₈₅ is the resistance value of the resistor 285. Capacitors 283 and 286 are provided for phase compensation and noise removal.

  The reference voltage Vref <b> 2 is input from the voltage follower 298 to the non-inverting input terminal of the differential amplifier 290. The reference voltage Vref2 is generated by dividing the voltage Vcc by the resistors 296 and 297. The differential amplifier 290 performs differential amplification of the reference voltage Vref2 and S1 and S2, and outputs a sensor signal Vsns = Vref2 + S2-S1 which is an output signal of the optical sensor 27 to the terminal 295. Therefore, when the total amount of light received by the light receiving portion Ap is equal to the total amount of light received by the light receiving portion An, the sensor signal becomes the reference voltage Vref2. On the other hand, if the total light receiving amount of the light receiving part Ap is larger than the total light receiving amount of the light receiving part An, the sensor signal becomes larger than the reference voltage Vref2. On the other hand, when the total light receiving amount of the light receiving part Ap is smaller than the total light receiving amount of the light receiving part An, the sensor signal becomes smaller than the reference voltage Vref2. That is, the optical sensor 27 outputs a signal having an amplitude corresponding to a value obtained by subtracting the total light receiving amount of the light receiving unit An from the total light receiving amount of the light receiving unit Ap.

  Next, a lighting circuit of the light emitting element 272 will be described. The control circuit 275 is provided with an operational amplifier 299 and an accompanying circuit for driving the light emitting element 272 at a constant current. The operational amplifier 299 drives the light emitting element 272 by driving the transistor 302 to light it. The current flowing through the light emitting element 272 when the light is on is detected by the resistor 301 and monitored by the inverting input terminal of the operational amplifier 299. On the other hand, a voltage input terminal Trgt for setting the drive current of the light emitting element 272 by the CPU 26 is connected to the non-inverting input terminal of the operational amplifier 299. That is, the operational amplifier 299 drives the light emitting element 272 at a constant current so as to have a value set from the terminal Trgt.

  Hereinafter, detection of the pattern image 40 including a plurality of lines using the optical sensor 27 described above will be described. In the following description, the widths of lines and spaces are widths in the moving direction of the surface of the intermediate transfer belt 8 when a pattern image is formed on the intermediate transfer belt 8. The width of the light receiving part is the width in the arrangement direction of the light receiving part Ap and the light receiving part An. In addition, the arrangement direction of the light receiving part Ap and the light receiving part An is equal to the direction in which the shadow by the line of the pattern image moves. In the following description, it is assumed that the width Wsns of the light receiving portions An and Ap is 254 μm.

  FIG. 4 shows three types of pattern images with different line widths. Each pattern image is composed of two lines. Note that a width Lw indicated by a dotted line in FIG. 4 is a formation target line width and space width. Here, the target line width Lw is half the width Wsns (= 127 μm) of the light receiving elements 273 and 274, and the target line pitch (2Lw) is half of the pitch Psns of the light receiving elements 273 and 274. is there. That is, the line width of the pattern image when the width in the moving direction of the bright and dark bright parts and dark parts by the pattern image is equal to the width Wsns of the light receiving elements 273 and 274 at the place where the light receiving part 270 is disposed. The target line width.

  The line pitches of the pattern images 41, 42 and 43 in FIG. 4 are all 2Lw which is the target line pitch, but the line widths are different. Specifically, the line width of the pattern image 41 is equal to the target line width Lw. However, the line width of the pattern image 42 is 101.6 μm, which is 0.8 times the target line width Lw, and the line width of the pattern image 43 is 152.4 μm, which is 1.2 times the target line width Lw.

  FIG. 5 shows an output signal of the optical sensor 27 when the pattern image 41 of FIG. 4 is detected. Note that, below the output signal, a positional relationship between a shadow caused by a line of the pattern image 41 that is moved by the movement of the pattern image 41 and the light receiving unit 270 is shown. The output signal is normalized so that the maximum value is 1 when the value is the reference voltage Vref2, that is, when the total light reception amount of the light receiving portion Ap is equal to the total light reception amount of the light receiving portion An. Yes.

  State (a) is a state in which the shadow of the line does not cover any of the light receiving parts Ap and An. In this case, the total amount of light received by the light receiver Ap is equal to the total amount of light received by the light receiver An, and thus the output of the optical sensor 27 is zero. The state (b) is a state where the shadow of the line covers one light receiving part An. At this time, the total amount of light received by the light receiving portion Ap is twice the total amount of light received by the light receiving portion An, and the output of the optical sensor 27 is 0.5. State (c) is a state in which the shadow of the line covers one light receiving part Ap, contrary to state (b). At this time, the total amount of light received by the light receiving portion An is twice the total amount of light received by the light receiving portion Ap, and the output of the optical sensor 27 is −0.5. The state (d) is a state in which the shadow of the line covers all the light receiving parts An. At this time, the total amount of light received by the light receiving unit An is almost 0, and the output of the optical sensor 27 is 1.0. The state (e) is a state in which the shadow of the line covers all the light receiving parts Ap, contrary to the state (d). At this time, the total amount of light received by the light receiving portion Ap is substantially 0, and the output of the optical sensor 27 is −1.0. Thereafter, when the pattern image 41 moves and the shadow of the line changes to the states (f), (g), and (h), the output of the optical sensor 27 changes to 0.5, −0.5, and 0. To do.

FIG. 6 shows the output signal of the optical sensor 27 when the pattern image 42 of FIG. 4 is detected by the same notation method as in FIG. Note that the maximum value of the output waveform is standardized so that the maximum value when the pattern image 41 is detected is 1. As shown in FIG. 6, since the line width of the pattern image 42 is 0.8 times the target line width, the shadow is smaller than the width of the light receiving portions Ap and An, and the shadow by the line is the light receiving portion Ap or the light receiving portion. It does not cover the whole of An. Therefore, the decrease in the amount of received light due to being covered with a shadow is smaller than when the pattern image 41 shown in FIG. 5 is detected. Therefore, even in the states (d) and (e) in which the difference between the total light reception amount of the light receiving portion Ap and the total light reception amount of the light receiving portion An is maximum, the difference is the difference between the states (d) and (e) in FIG. It becomes smaller than when. Specifically, the peak value of the output signal of the optical sensor 27 when the pattern image 42 is detected is 0.8 times the peak value of the output signal of the optical sensor 27 when the pattern image 41 is detected. Here, the ratio of the line widths of the pattern image 41 and the pattern image 42 is
127 μm: 101.6 μm = 1: 0.8
It is. That is, the peak value of the output signal of the optical sensor 27 decreases in proportion to the line width becoming smaller than the target.

  FIG. 7 shows the output signal of the optical sensor 27 when the pattern image 43 of FIG. 4 is detected, using the same notation method as in FIG. As shown in FIG. 7, since the line width of the pattern image 43 is 1.2 times the target line width, the shadow is larger than the width of the light receiving part Ap or the light receiving part An. Therefore, even in the states (d) and (e) in which the difference between the total light reception amount of the light receiving portion Ap and the total light reception amount of the light receiving portion An is maximum, the difference is the difference between the states (d) and (e) in FIG. It becomes smaller than when. In the state (d), the shadow by the line covers not only the light receiving part An but also the light receiving part Ap. In the state (e), the shadow by the line is not only the light receiving part Ap but the light receiving part An. Because it covers. Specifically, the peak value of the output signal of the optical sensor 27 when the pattern image 43 is detected is 0.9 times the peak value of the output signal of the optical sensor 27 when the pattern image 41 is detected. In FIG. 7, the timings of the states (d) and (e) where the sensor output is maximized are slightly different from the timings of the states (d) and (e) in FIG.

  As described above, when light from the light emitting element 272 irradiates the pattern image 40 formed at a predetermined line pitch and the light and darkness pass through the light receiving unit 270 by the movement of the intermediate transfer belt 8, the optical sensor 27 is A signal that oscillates around the reference voltage Vref2 is output. The peak value of this signal varies depending on the line width of the pattern image 40. Specifically, the peak value of the output signal of the optical sensor 27 is maximum when the width of the shadow generated at the position of the light receiving unit 270 by the line is the same as the width of the light receiving unit Ap and the light receiving unit An. Become. Even if the line width is smaller or larger than that, the peak value of the output signal of the optical sensor 27 becomes smaller. FIG. 8 shows the relationship between the amount of deviation from the target line width and the peak value of the output signal of the optical sensor 27. The peak value of the output signal of the optical sensor 27 does not depend on the moving speed (rotational speed) of the intermediate transfer belt 8.

Subsequently, formation of the pattern image 40 will be described. FIG. 9 shows a potential distribution in the line width direction when an electrostatic latent image of one line in the main scanning direction is formed on the photoconductor 1. Note that the vertical axis of the graph shown in FIG. 9 represents a negative potential. The amount of laser light has an intensity distribution that attenuates from the center toward the outside. For this reason, when an electrostatic latent image is formed on the charged photosensitive member 1 with laser light, the potential of the photosensitive member 1 at the edge portion is changed from the charged potential Vd to the potential Vl after exposure as shown in the graph of FIG. Will gradually change. When such an electrostatic latent image is developed with the development bias Vdc1, the development contrast Vcnt1 is
Vcnt1 = | Vdc1-Vl |
It becomes. Since the toner is developed so as to satisfy the electrostatic latent image corresponding to the development contrast, when development is performed with the development bias Vdc1, a toner image having a line width Wt1 is formed as shown by a toner image 71 in FIG.

Similarly, when development is performed with a development bias Vdc2 that is negative and higher than the development bias Vdc1, the development contrast Vcnt2 is Vcnt2 = | Vdc2-Vl |
It becomes. Therefore, when development is performed with the development bias Vdc2, a toner image having a line width Wt2 indicated by the toner image 72 in FIG. 9 is formed.

  Therefore, when the development contrast is increased, the line width is increased and the development density is increased. FIG. 10A shows the measurement result of the change in line width when the development bias is changed, and FIG. 10B shows the measurement result of the change in maximum density when the development bias is changed. is there. As shown in FIGS. 10A and 10B, the line width and the maximum density are proportional to the developing bias. FIG. 10C shows the relationship between the line width and the maximum density derived from the measurement results of FIGS. 10A and 10B. As shown in FIG. 10C, the line width and the maximum density are in a substantially direct relationship. Therefore, the maximum density can be controlled by controlling the line width.

  Hereinafter, the maximum density calibration in the present embodiment will be described. In the present embodiment, two calibrations, initial maximum density calibration performed in an initial state such as when the power is turned on, and maximum density calibration during printing performed to cope with a change in the maximum density little by little during printing. Execute. Note that the maximum density changes during printing because the temperature of the photoconductor 1 changes due to continuous printing, and the resistance value of the photoconductor 1 changes, thereby changing the amount of charge leakage of the photoconductor 1. It is considered that one reason is that the latent image potential changes.

<Initial maximum concentration calibration>
The initial maximum density calibration according to the present embodiment will be described with reference to the flowchart of FIG. When the power of the image forming apparatus 101 is turned on in S1, the control unit 25 performs a failure check of the image forming apparatus 101 in S2. Subsequently, in S <b> 3, the control unit 25 forms pattern images 43 to 46 for initial maximum density calibration shown in FIG. 12 on the intermediate transfer belt 8. The pattern images 43 to 46 are formed of yellow, magenta, cyan, and black toners, respectively, but are the same except for the colors. In FIG. 12, the optical sensor 27 is provided on each side in the direction orthogonal to the traveling direction 81 of the intermediate transfer belt 8, and the pattern images 43 and 44 are on one side, and the pattern images 45 and 46 are on the other side. Provided. However, this is exemplary and any number of optical sensors 27 can be used. FIG. 12 representatively shows details of the pattern image 43 formed with yellow toner, but the same applies to pattern images of other colors. Here, the pattern image 43 includes a plurality of pattern images 40 including two lines shown in FIG. However, the developing bias when forming each pattern image 40 is gradually changed. In the present embodiment, one pattern image 43 includes 20 pattern images 40, the first pattern image 40 is formed with a developing bias of −280V, and thereafter the developing bias is changed in order of −5V to −375V. It is formed with.

  In S <b> 4, the control unit 25 detects the formed pattern images 43 to 46 with the optical sensor 27. Here, with respect to each pattern image 40 included in the pattern image 43, if the relationship between the development bias when the pattern image 40 is formed and the peak value of the output of the optical sensor 27 when the pattern image is detected is plotted, FIG. A graph represented by 13 Y is obtained. Similarly, graphs indicated by M, C, and Bk in FIG. 13 are obtained from the pattern images 44 to 46, respectively. These data are preserve | saved at the memory | storage part which is not shown in figure, and the control part 25 determines the pattern image 40 corresponding to the maximum value of 20 peak values about each color from the graph of FIG. 13 in S5. In S6, the development bias when the determined pattern image 40 is formed is set as the development bias used for the color. Thereafter, the control unit 25 executes other calibration such as density gradation calibration and color misregistration calibration in S7, and then shifts to a standby state in S8. In S5 and S6, the actually formed pattern image 40 is detected by the optical sensor 27, the peak value of the output signal is measured, and the development bias when the pattern image 40 having the maximum peak value is formed is determined. I was judging. However, the measurement result of the peak value of the output signal is interpolated to obtain the relationship between the development bias and the peak value of the output signal of the optical sensor 27, thereby determining the development bias that maximizes the peak value of the output signal. The form to do may be sufficient.

<Maximum density calibration during printing>
Next, the maximum density calibration during printing will be described with reference to the flowchart of FIG. In a general image forming apparatus, when printing is performed continuously, the conveyance interval between recording materials to be printed is set to about 70 mm, for example. Therefore, the intermediate transfer belt 8 includes an area between the images to be transferred to the recording material, which is not transferred to the recording material, corresponding to the conveyance interval between the recording materials. Hereinafter, such an area of the intermediate transfer belt 8 corresponding to the interval between the recording materials is referred to as a non-transfer area. In this embodiment, calibration is executed during printing using this non-transfer area.

  By starting the maximum density calibration during printing, the control unit 25 forms pattern images 53 to 56 for maximum density calibration during printing shown in FIG. 15 in the non-transfer area of the intermediate transfer belt 8 in S10. In FIG. 15, the shaded area is an area where an image to be transferred to the recording material is formed during the secondary transfer, and the area between the shaded areas is a non-transfer area. The pattern images 53 to 56 are formed of yellow, magenta, cyan, and black toners, respectively, but are the same except for the colors. The number of optical sensors 27 to be used is also arbitrary. FIG. 15 representatively shows details of the pattern image 53 formed with yellow toner, but the same applies to other colors. Here, the pattern image 53 includes a plurality of pattern images 40 including the two lines shown in FIG. However, the developing bias when forming each pattern image 40 is gradually changed. Specifically, the development bias to be used is a current set value and a value obtained by increasing or decreasing the current set value by a predetermined value. In the present embodiment, the pattern image 40-1 to the pattern image 40-5 are changed from the current setting value + 10V, the current setting value +5, the current setting value, the current setting value -5V, and the current setting value -10V, respectively. It is formed with. The number of pattern images 40 included in each color pattern image is not limited to five, and any number can be used.

  The controller 25 detects the formed pattern images 53 to 56 with the optical sensor 27 in S11. Here, for each pattern image 40 included in the pattern image 53, when the relationship between the development bias when the pattern image 40 is formed and the peak value of the output signal of the optical sensor 27 when the pattern image is detected is plotted, A graph indicated by Y in FIG. 16 is obtained. Similarly, graphs indicated by M, C, and Bk in FIG. 16 are obtained from the pattern images 54 to 56, respectively. In S12, the control unit 25 determines the pattern image 40 corresponding to the maximum value of the five peak values for each color from the graph of FIG. Subsequently, in S13, the control unit 25 determines whether or not the printing is finished. If the printing is not finished, the developing bias when the pattern image 40 determined in S12 is formed for each color in S14. Is set as the developing bias to be actually used. On the other hand, when printing ends, the process ends as it is. As in the initial maximum density calibration shown in FIG. 11, the development bias value set in S14 is not determined from the development bias value actually used for forming the pattern image 40, but the measurement result is interpolated. It is also possible to adopt a form to be obtained.

  In an image forming apparatus that does not perform maximum density calibration during printing, the temperature and humidity of the photoconductor and the like may change during continuous printing, and the image density may gradually change due to the influence. In the present embodiment, by performing the maximum density calibration during printing, it is possible to feed back the maximum density that changes every moment and suppress the fluctuation of the maximum density.

  As described above, the peak value of the amplitude of the optical sensor 27 is maximized when the line width of the pattern image is a specific value determined by the width of the light receiving surface of the light receiving element, the positional relationship with the light emitting element, and the like. Is used to control the density with a pattern image having a line width smaller than 1 mm. Specifically, density control is performed by forming a plurality of pattern images with different development biases and determining the development bias at which the peak value of the output signal of the optical sensor 27 is the maximum value that is the target value. This minute size pattern image allows the maximum density calibration to be performed at low cost and with high accuracy without using a CCD.

  Further, since the size of the pattern image is small, the amount of toner used in calibration is reduced, and therefore the amount of collected toner used in calibration can be reduced. Furthermore, since the maximum density calibration can be executed even during continuous printing, the density difference during printing can be reduced without pausing printing during continuous printing. .

  In the present embodiment, the optical sensor 27 is a reflective sensor that receives reflected light from the pattern image 40 formed on the intermediate transfer belt 8. However, the present invention is not limited to a reflection type sensor, and can be realized with a transmission type sensor. In the above-described embodiment, the value of the developing bias is controlled and set as the image forming condition relating to the density. However, other image forming conditions for changing the development contrast, for example, the charging potential of the charging unit 2 or the exposure intensity by the exposure unit 7 may be controlled.

  In the embodiment described above, the pattern image 40 includes two lines. However, it may include three or more lines. For example, when the pattern image 40 including three lines is read by the optical sensor 27, the peak value is output from the optical sensor 27 twice. By calculating the average of these plural peak values, it is possible to reduce variations in reading by the optical sensor 27. Moreover, the pattern image containing one line may be sufficient. In this case, a signal having an amplitude corresponding to the line width is output twice. Furthermore, in the embodiment described above, the optical sensor 27 has two light receiving portions Ap and two light receiving portions An. However, the number of the light receiving parts Ap and the light receiving parts An can be three or more, respectively. By increasing the number of the light receiving portions Ap and the light receiving portions An, the total area of the light receiving portions Ap and the total area of the light receiving portions An are increased, and the amount of light received by the optical sensor 27 can be increased.

  Furthermore, the present embodiment can be configured with one light receiving portion Ap and one light receiving portion An by performing control that uses only data before and after the timing at which a peak is obtained for the output signal information of the optical sensor 27. It becomes.

  In the embodiment described above, the light receiving areas of the light receiving unit An and the light receiving unit Ap are equal to the width of the light receiving surface in the arrangement direction, and the length in the direction orthogonal to the shadow arrangement direction of the pattern image is the light receiving unit An and The length of the light receiving portion An is longer than that in the direction. These conditions equalize the amount of light received when not affected by the pattern image of each light receiving portion An and each light receiving portion Ap, and each light receiving portion An and each light receiving portion Ap are affected by the pattern image. This was to make the amount of decrease in the amount of received light equal. However, it is obvious to those skilled in the art that even if not all of the above conditions are satisfied, the amount of received light when not affected by the pattern image can be made equal and the amount of decrease in the amount of received light by the pattern image can be made the same. The present invention is not limited to the above conditions.

  Further, in the above-described embodiment, the line of the pattern image 40 has been described by using an example in which the line is formed in a direction orthogonal to the moving direction of the intermediate transfer belt 8. However, the line is drawn obliquely with respect to the orthogonal direction. It may be a line. That is, the pattern image 40 may be an image in which the toner amount (developer amount) regularly changes when the intermediate transfer belt 8 moves, and includes a line in a direction different from the moving direction of the pattern image 40. be able to.

<Second embodiment>
In the first embodiment, the maximum density is controlled by controlling the shadow width of the line of the pattern image 40 to be the same as the width of the light receiving portion Ap and the light receiving portion An. For example, if the width of the light receiving portion Ap and the light receiving portion An is 254 μm, the line width is adjusted to 127 μm, which is to adjust the maximum density to 1.32 from FIG. there were. In the present embodiment, the target line width of the pattern image 40 is not a fixed value determined by the widths of the light receiving part Ap and the light receiving part An, but a variable value. In this embodiment, the user selects “standard”, “+1” to “+5”, and “−1” to “−5” from 11 levels as the maximum density setting value for each color. Shall. Then, the relationship between the maximum density setting value and the target line width as shown in FIG. 18 is obtained in advance and stored in the storage unit. The target line width when the maximum density setting value is “standard” is the reference line width, and the relationship between the deviation from the reference line width and the peak value of the output signal of the optical sensor as shown in FIG. Are obtained in advance and stored in the storage unit. Further, the initial set value of the maximum density is “standard”, and the image forming apparatus 101 has already executed the initial maximum density calibration shown in FIG. 11, and thus the data shown in FIG. 13 is stored in the storage unit. Shall. The data shown in FIG. 13 may be stored in advance in the storage unit. Hereinafter, the maximum density control process according to the present embodiment will be described with reference to FIG.

  In S20, the control unit 25 detects a change command of the maximum density setting value by a user operation. In the following description, it is assumed that the user selects the maximum density setting value +2 for all colors. In S21, the control unit 25 acquires the target line width from the conversion table of FIG. For example, for the maximum density setting value “+2”, a target line width of 137 μm is obtained.

In S22, the control unit 25 calculates the difference between the target line width of 137 μm and the reference line width (= 127 μm). In this example, 137 μm−127 μm = + 10 μm is calculated. Subsequently, in S23, the peak value of the sensor output corresponding to the deviation obtained in S22 is determined using the relationship between the deviation from the reference line width and the peak value of the sensor output as shown in FIG. To the target value. In this example, since the deviation amount of the target line width from the reference line width is +10 μm, the ratio of the output peak value of the sensor to the maximum value of the target value is 0.96 from FIG. Subsequently, in S24, the control unit 25 determines the development bias from the target value of the peak of the output signal of the sensor 27, using the result obtained by the initial maximum density calibration shown in FIG. Specifically, from the graph of FIG. 13, the maximum value of the peak of the yellow (Y) output signal is 2.00V. Therefore, the target value of the peak value of the output signal of the sensor 27 is 1.92 (V) obtained by multiplying 2.00 V by 0.96. Since the maximum density setting value is “+2”, which is darker than the standard, a peak value of 1.90 V closest to 1.92 V on the right side of the maximum value in the graph of FIG. 13 is selected, and the developing bias applied at that time − 305V can be derived. In this way, the developing bias to be used is determined to be “−305 V” from the maximum density setting value “+2”. As described above, in this embodiment, it is possible to control the density to a desired maximum density using the result of the initial maximum density calibration. In this embodiment as well, the development bias can be determined by interpolating the measurement results of the development bias and the peak value of the output signal.

  In the first embodiment, the target line width used for the maximum density control is determined by the widths of the light receiving portions An and Ap of the optical sensor 27. In the present embodiment, maximum density control is possible regardless of the widths of the light receiving portions An and Ap.

<Third embodiment>
In the first embodiment, the number of the light receiving parts Ap and the light receiving parts An is equal. In the present embodiment, the number of light receiving portions An is one, the number of light receiving portions Ap is two, and a pattern image with one line is used. Hereinafter, the present embodiment will be described focusing on differences from the first embodiment. In the present embodiment, the configuration of the image forming apparatus 101 is the same as that of the first embodiment, and a description thereof will be omitted.

  FIG. 19A is a perspective view of the optical sensor 77 according to the present embodiment, and FIG. 19B is a view seen from the X direction of FIG. 19A. As shown in FIG. 19A, the pattern image 90 of this embodiment is an image including one line having a width Wt90. The optical sensor 77 is obtained by replacing the light receiving unit 270 of the optical sensor 27 in the first embodiment with a light receiving unit 770, and the other configuration is the same as that of the optical sensor 27, and thus the description thereof is omitted. The light receiving unit 770 includes light receiving elements 773p, 775n, and 774p arranged in an array along the moving direction 81 of the intermediate transfer belt 8. The light receiving element 775n constitutes the light receiving part An, and the light receiving elements 773p and 774p constitute the light receiving part Ap, respectively. As described above, the light receiving unit 770 is configured by alternately arranging the light receiving units Ap and the light receiving units An.

  As shown in FIG. 19A, in the present embodiment, the width of the light receiving portion Ap is Wsnsp, and the width Wsnsn of the light receiving portion An is twice the width Wsnsp of the light receiving portion Ap. In the present embodiment, it is assumed that the width Wsnsp of the light receiving part Ap is 127 μm and the width Wsnsn of the light receiving part An is 254 μm. Further, the light receiving area of each light receiving portion Ap is half of the light receiving area of the light receiving portion An, that is, the total light receiving area of the two light receiving portions Ap is equal to the total light receiving area of the light receiving portion An. As in the first embodiment, the width of the light receiving surface of the light receiving portion Ap in the arrangement direction is substantially equal to the width Wsnsp of the light receiving portion Ap, and the width of the light receiving surface of the light receiving portion An in the arrangement direction is equal to that of the light receiving portion An. It is assumed that it is substantially equal to the width Wsnsn. Furthermore, the line width Wt90 of the pattern image 90 is equal to the width Wsnsp of the light receiving part Ap, that is, half the width Wsnsn of the light receiving part An. Therefore, as shown in FIG. 19B, the shadow by the line of the pattern image 90 becomes equal to the width Wsnsn of the light receiving portion An at the position of the light receiving portion 770. In addition, the length of the X direction of FIG. 19A of the shadow by the line of the pattern image 90 shall be longer than the length of the light reception part Ap and the light reception part An of the said direction similarly to 1st embodiment. Note that the arrows in FIGS. 19A and 19B indicate the light irradiated by the light emitting element 272 and regularly reflected on the surface of the intermediate transfer belt 8.

  FIG. 20 illustrates a connection configuration of the control circuit 275, the light receiving unit 770, and the light emitting element 272. 2 is the same as that of the first embodiment except that the light receiving elements 273p and 274p are replaced with light receiving elements 773p and 774p, and the light receiving elements 273n and 274n are replaced with light receiving elements 775n. Therefore, as in the first embodiment, the optical sensor 77 outputs a signal having an amplitude corresponding to a value obtained by subtracting the total light reception amount of the light receiving portion An from the total light reception amount of the light receiving portion Ap.

  Hereinafter, detection of the pattern image 90 including one line by the optical sensor 77 will be described. FIG. 21 shows pattern images having different line widths. Note that a width Lw indicated by a dotted line in FIG. 21 is a formation target line width. Here, the target line width Lw is a half width (= 127 μm) of the width Wsnsn of the light receiving portion An. That is, the target line width Lw is a value that forms a shadow having a width equal to the width Wsnsn of the light receiving portion An at the position of the light receiving portion 770. Here, the line width of the pattern image 91 in FIG. 21 is the target line width Lw, but the line width of the pattern image 92 is 101.6 μm, which is smaller than the target line width Lw, and the line width of the pattern image 93 is the target line width. It is 152.4 μm larger than Lw.

  FIG. 22 shows an output signal of the optical sensor 77 when the pattern image 91 of FIG. 21 is detected. Note that, below the output signal, the positional relationship between the shadow caused by the line that is moved by the movement of the pattern image 91 and the light receiving unit 770 is shown. The output signal is normalized so that the maximum value is 1 when the value is the reference voltage Vref2, that is, when the total light reception amount of the light receiving portion Ap is equal to the total light reception amount of the light receiving portion An. Yes.

  State (a) is a state in which the shadow of the line does not cover any of the light receiving parts Ap and An. In this case, the total amount of light received by the light receiver Ap is equal to the total amount of light received by the light receiver An, and therefore the output of the optical sensor 77 is zero. State (b) is a state in which the shadow of the line covers one of the light receiving parts Ap. At this time, the total amount of light received by the light receiving portion An is twice the total amount of light received by the light receiving portion Ap, and the output of the optical sensor 77 is −0.5. State (c) is a state in which the shadow of the line covers one of the light receiving portions Ap and half of the light receiving portion An, and the total light receiving amount of the light receiving portion Ap is equal to the total light receiving amount of the light receiving portion An. The output of the optical sensor 77 is zero. The state (d) is a state in which the shadow of the line covers the entire light receiving unit An. At this time, the total amount of light received by the light receiving unit An is almost 0, and the output of the optical sensor 77 is +1.0 at the maximum. In the state (e), as in the state (c), the shadow of the line covers one of the light receiving parts Ap and half of the light receiving part An, and the output of the optical sensor 77 is zero. Similarly to the state (b), the state (f) is a state in which the shadow of the line covers one of the light receiving parts Ap, and the output of the optical sensor 77 is −0.5. Similarly to the state (a), the state (g) is a state in which the shadow of the line does not cover any light receiving part, and the output of the optical sensor 77 is zero.

FIG. 23 shows an output signal of the optical sensor 27 when the pattern image 92 of FIG. 21 is detected. The notation of FIG. 23 is the same as FIG. Note that the peak value of the output signal is normalized so that the peak value becomes 1 when the pattern image 91 in FIG. 22 is detected. As shown in FIG. 23, since the line width of the pattern image 92 is 0.8 times the target line width, the shadow does not cover the entire light receiving portion An. Accordingly, as shown in the state (d), even when the entire shadow of the line covers the light receiving part An, the light receiving part An receives the regular reflection light. Therefore, the maximum value of the difference between the total light receiving amount of the light receiving part Ap and the total light receiving amount of the light receiving part An is smaller than the state (d) in FIG. Specifically, the peak value of the output signal of the optical sensor 77 when the pattern image 92 is detected is 0.8. The ratio of the line width between the pattern image 91 and the pattern image 92 is
127 μm: 101.6 μm = 1: 0.8
It is. That is, when the line width becomes smaller than the target width, the peak value of the output signal of the optical sensor 77 becomes smaller in proportion thereto.

FIG. 24 shows an output signal of the optical sensor 77 when the pattern image 93 of FIG. 21 is detected. Note that the notation in FIG. 24 is the same as that in FIG. As shown in FIG. 24, since the line width of the pattern image 93 is 1.2 times the target width, there is no state in which the shadow covers only the light receiving portion An, and the shadow of the light receiving portion An After covering the whole, a part of one of the light receiving parts Ap is covered. Therefore, as shown in the state (d), when the shadow by the line covers the entire light receiving portion An, the light receiving portion Ap is also partially covered by the shadow, and accordingly, the total amount of light received by the light receiving portion Ap and the light receiving portion An. The difference from the total amount of received light is smaller than the state (d) in FIG. Specifically, the peak value of the output signal of the optical sensor 77 when the pattern image 93 is detected is 0.8. The ratio of the line widths of the pattern image 91 and the pattern image 93 is
127 μm: 152.4 μm = 1: 1.2
It is. The deviation amount of the line width of the pattern image 93 from the line width of the pattern image 91 is 25.4 μm, and the deviation amount ratio is 0.2 (= 25.4 ÷ 127).

  On the other hand, based on the peak value when the pattern image 91 is detected, the amount of deviation from the reference value of the peak value when the pattern image 93 is detected is 0.2 (= 1-0.8). Thus, when the line width is larger than the target value, the amount of deviation of the peak value of the output signal of the optical sensor 77 from the reference value coincides with the amount of deviation of the line width from the target value.

  As described above, in this embodiment, when the shadow of the line is the same as the width of the light receiving portion An, the peak value of the output signal of the optical sensor 77 is maximized, and even if the line width is smaller than that, it is large. However, the peak value of the output signal of the optical sensor 77 becomes small. FIG. 25 shows the relationship between the deviation amount from the target line width and the peak value of the output signal of the optical sensor 77. The peak value of the output signal of the optical sensor 77 does not depend on the moving speed (rotational speed) of the intermediate transfer belt 8. In this way, the density correction calibration described in the first embodiment and the second embodiment can be executed using the characteristics shown in FIG. In this embodiment, since a pattern image with one line is used, a detection image smaller than those in the first embodiment and the second embodiment can be obtained.

  In the present embodiment, the light receiving part 770 of the optical sensor 77 has two light receiving parts Ap and one light receiving part An. However, it is assumed that (n + 1) light receiving portions Ap and n light receiving portions An are alternately arranged, where n is a natural number, such as alternately arranging three light receiving portions Ap and two light receiving portions An. be able to. At this time, the sum of the light receiving areas of the two light receiving parts Ap arranged at both ends of the light receiving part 770 is made equal to the light receiving areas of the other light receiving parts Ap and An of the light receiving part 770. The widths in the array direction of the light receiving surfaces of the light receiving units other than both ends of the light receiving unit 770 are the same, and are double the width in the array direction of the light receiving surfaces of the two light receiving units Ap arranged at both ends of the light receiving unit 770. In addition, although the number of the light receiving parts Ap is increased by one more than the number of the light receiving parts An and the light receiving parts Ap are arranged at both ends of the light receiving part 770, the light receiving part Ap and the light receiving part An are replaced with each other. You can also

<Other embodiments>
In the above-described embodiment, the differential processing of the signal indicating the temporal change in the amount of light received by each of the light receiving part Ap and the light receiving part An is performed. The light receiving part Ap and the light receiving part An are arranged along the moving direction of the intermediate transfer belt 8. Therefore, the temporal changes in the amounts of light received by the light receiving part Ap and the light receiving part An are shifted from each other by a time determined by the distance between the light receiving part Ap and the light receiving part An and the moving speed of the intermediate transfer belt 8. Accordingly, the differential processing of the signals indicating the temporal changes in the received light amounts of the light receiving unit Ap and the light receiving unit An is performed by, for example, bifurcating the signal corresponding to the received light amount output by one light receiving unit, It can also be realized by performing differential processing while shifting by a predetermined time. The time shifted at this time is determined by the distance between the light receiving portion Ap and the light receiving portion An and the moving speed of the intermediate transfer belt 8. That is, in each of the above embodiments, a differential process is performed between the total amount of light received by one or more light receivers Ap and the total amount of light received by one or more light receivers An. This is equivalent to performing differential processing of a signal indicating the amount of received light with a sum of one or more first time positions and a sum of one or more second time positions. For example, when a pattern image of a plurality of lines is moved, the amount of light received by the light receiving unit vibrates at a period corresponding to the plurality of lines. Therefore, for example, the first time positions are set so that the periods are in phase with each other, and the second time positions are also set so that the periods are in phase with each other. On the other hand, the first time position and the second time position are set so as to be in opposite phases, for example, so that the phases of this period are different.

  Moreover, in the said embodiment, the relationship between the width | variety of the arrangement direction of the light-receiving surface of the light-receiving part Ap and the light-receiving part An, and the width | variety of a line was demonstrated. Here, the light receiving portions Ap and An receive the reflected light from a certain region at the same time on the light receiving surface, which is equivalent to obtaining the average value of the reflected light received simultaneously. Therefore, increasing the width of the light receiving surface in the arrangement direction is equivalent to, for example, obtaining a moving average with respect to a signal indicating a temporal change in the amount of light received output from the light receiving part Ap and the light receiving part An. Here, in the form of performing differential processing at different time positions of signals output from one light receiving unit, a memory is required to branch and shift the signals. Therefore, by using this memory, two sections of the first section and the second section are set in the signal output from one light receiving unit, the moving average value of the first section, and the second section The differential processing of the moving average value can be easily performed. Thereby, the section according to the width of the line can be set easily. At this time, the time interval between the first section and the second section corresponds to the distance between the light receiving section Ap and the light receiving section An in the above embodiment, and the section lengths of the first section and the second section are as follows: This corresponds to the width of the light receiving surface in the arrangement direction.

  FIG. 26 is a configuration diagram for performing the above-described processing on a signal output from one light receiving unit. In the present embodiment in which differential processing of signals output from one light receiving unit is performed at different times, for example, the optical sensor 27 simply outputs a light detection signal corresponding to the amount of light received by the light receiving unit to the engine control unit 25. To do. Note that the sampling unit 31, the moving average processing units 32 and 33, and the differential processing unit 34 in FIG. 26 are provided in the engine control unit 25, for example. However, the sampling unit 31, the moving average processing units 32 and 33, and the differential processing unit 34 may be provided in the control circuit 275, for example. The light detection signals are sampled by the sampling unit 31 and output to the moving average processing units 32 and 33, respectively. The moving average processing units 32 and 33 obtain a moving average value of a section having a predetermined length, and output the obtained moving average values to the differential processing unit 34, respectively. As described above, the period between the section corresponding to the moving average value output by the moving average processing unit 32 and the section corresponding to the moving average value output by the moving average processing unit 33 at the same time is, for example, The phase of the light detection signal is set to be different. The differential processing unit 34 performs differential processing of the moving average value from the moving average processing units 32 and 33. With this configuration, the differential processing unit 34 outputs, for example, an output signal similar to the output signal of the differential amplifier 290 of FIG.

  In other words, it can be said that the above embodiment takes the difference in the amount of reflected light including the regular reflected light components from different positions on the surface of the intermediate transfer belt 8 before and after the pattern image. For example, this is apparent from the fact that the regular reflection light received by the light receiving part Ap and the light receiving part An at the same time is reflected at different positions on the surface of the intermediate transfer belt 8 before and after the pattern image. Also, in the form of performing differential processing at different time positions of signals output by one light receiving unit, the difference in the amount of reflected light including specularly reflected light components from different positions on the surface of the pattern image and the surrounding intermediate transfer belt 8 is also obtained. It is what you take. For example, it is assumed that differential processing is performed between a first time position of the light detection signal and a second time position after the first time position. In addition, the position on the pattern image that is the reflection position of the regular reflection light to the light receiving unit in the first time is defined as the first position, and the reflection position of the regular reflection light to the light reception unit in the second time is the second position. Position. In this case, the distance between the first position and the second position is equal to a value obtained by multiplying the moving speed of the surface of the intermediate transfer belt 8 by the difference between the first time and the second time. Therefore, performing the differential processing between the first time position and the second time position means that the total amount of received light when the light receiving unit receives specularly reflected light from the first position and the light receiving unit is second. This is because it corresponds to performing differential processing with the total amount of light received when the regular reflection light is received from the position.

  As described above, when the light emitting element irradiates the intermediate transfer belt 8 with the divergent light beam, a certain wide range of the intermediate transfer belt 8 is illuminated by the light emitting element. Therefore, the diffusely reflected light by the line of the pattern image received by the light receiving element becomes substantially constant while the pattern image passes through this irradiation region. Therefore, the diffuse reflection light can be removed or suppressed and only the specular reflection light component can be extracted by the difference in the light reception amounts of the plurality of light receiving elements or the difference in the light reception amounts at different time positions of one light receiving element. With this configuration, it is possible to control the density while suppressing the influence of diffuse reflected light.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (15)

Image forming means for forming a detection image having one or more lines in a direction different from the moving direction of the surface of the image carrier on the surface of the image carrier;
Detection means for detecting the detection image formed on the image carrier and outputting an output signal;
Control means for controlling image forming conditions relating to the density of the image to be formed based on the peak value of the output signal of the detecting means;
With
The detection means includes
A light emitting means for irradiating the image carrier with light;
A light receiving means for receiving the light emitted from the light emitting means and reflected by the image carrier and outputting a detection signal corresponding to the amount of received light;
An output means for outputting, as the output signal, a signal corresponding to a difference in value of the detection signal corresponding to the amount of received light including specularly reflected light components from different positions on the surface of the image carrier;
An image forming apparatus comprising:   The control means forms a plurality of the detected images on the image carrier using different values of the image forming conditions, and forms the image so that a peak value of an output signal of the detecting means becomes a target value. The image forming apparatus according to claim 1, wherein conditions are controlled.   The image forming apparatus according to claim 2, wherein the target value is a maximum value of a peak value of an output signal that is output when the detection unit detects each of the plurality of detection images.   The image forming apparatus according to claim 2, wherein the target value is indicated by a ratio with respect to a maximum value of a peak value of an output signal output when the detection unit detects each of the plurality of detection images. . The light receiving means includes one or more first light receiving units and one or more second light receiving units arranged alternately,
The output means outputs, as the output signal, a signal corresponding to a difference between a total light reception amount of the one or more first light receiving units and a total light reception amount of the one or more second light receiving units. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 5, wherein a light receiving area of each of the first light receiving parts is equal to a light receiving area of each of the second light receiving parts.   The width of the light receiving surface of each of the first light receiving portions in the arrangement direction, which is the direction in which the first light receiving portions and the second light receiving portions are alternately arranged, and the light receiving of each of the second light receiving portions. The image forming apparatus according to claim 5, wherein the widths of the surfaces in the arrangement direction are equal. The detected image includes a plurality of lines in a direction orthogonal to the moving direction along the moving direction of the surface of the image carrier,
The light receiving means includes a plurality of the first light receiving portions and a plurality of the second light receiving portions,
The light / dark pitch formed at the position of the light receiving means by the light emitting means irradiating the detection image is equal to the pitch of the first light receiving section and the pitch of the second light receiving section, respectively. The image forming apparatus according to any one of claims 5 to 7. Both ends of the light receiving means are the first light receiving portions,
The light receiving areas of the light receiving parts excluding the first light receiving parts arranged at both ends of the light receiving means are equal, and are equal to the sum of the light receiving areas of the two first light receiving parts arranged at both ends. The image forming apparatus according to claim 5. Both ends of the light receiving means are the first light receiving portions,
Arrangement direction which is a direction in which the first light receiving portions and the second light receiving portions are alternately arranged on the light receiving surfaces of the light receiving portions excluding the first light receiving portions arranged at both ends of the light receiving means. 6. The image forming apparatus according to claim 5, wherein the widths of the light receiving surfaces of the first light receiving portions arranged at both ends are equal to a width of the light receiving surfaces of the first light receiving portions in the arrangement direction.   The image forming apparatus according to claim 5, wherein each of the first light receiving unit and the second light receiving unit includes one or more light receiving elements.   The output means outputs a signal according to a difference between a first time position of the detection signal and a second time position separated from the first time position by a predetermined period as the output signal. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The output means uses, as the output signal, a signal corresponding to a difference between an average value of the first section of the detection signal and an average value of a second section that is separated from the first section by a predetermined period. The image forming apparatus according to claim 1, wherein the image forming apparatus outputs the image. The detected image includes a plurality of lines in a direction orthogonal to the moving direction along the moving direction of the surface of the image carrier,
The image forming apparatus according to claim 12, wherein the predetermined period is a period different from a period of vibration caused by the plurality of lines generated in the detection signal. The image forming unit includes a photosensitive member, a charging unit that charges the photosensitive member, an exposure unit that exposes the photosensitive member to form an electrostatic latent image, and a developing bias to apply the electrostatic latent image. And developing means for developing with a developer,
The image forming condition is a development contrast that is a difference between the development bias and a potential at a position exposed by the exposure unit of the photoreceptor.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

Images