阅读说明：本技术 图像形成装置 (Image forming apparatus with a toner supply device ) 是由 猪浩一朗 于 2019-08-09 设计创作，主要内容包括：公开了图像形成装置。图像形成装置包括被配置成检测在中间转印带上形成的图像的光学传感器。光学传感器包括第一LED、第二LED、第一PD和第二PD。第一LED和第二LED照射中间转印带的光轴中心点。第一PD布置在从第二LED发射的光的镜面反射光的光轴和从第一LED发射的光的镜面反射光沿着其被接收的光轴形成角度Ψ的位置处。第二PD布置在从第二LED发射的光的镜面反射光的光轴和从第二LED发射的光的漫反射光沿着其被接收的光轴形成比角度Ψ大的角度Φ的位置处。(An image forming apparatus is disclosed. The image forming apparatus includes an optical sensor configured to detect an image formed on an intermediate transfer belt. The optical sensor includes a first LED, a second LED, a first PD and a second PD. The first LED and the second LED irradiate the center point of the optical axis of the intermediate transfer belt. The first PD is disposed at a position where an optical axis of the specular reflection light of the light emitted from the second LED and an optical axis along which the specular reflection light of the light emitted from the first LED is received form an angle Ψ. The second PD is disposed at a position where an optical axis of specular reflection light of light emitted from the second LED and diffuse reflection light of light emitted from the second LED form an angle Φ larger than the angle Ψ along an optical axis along which they are received.)

1. An image forming apparatus configured to form an image on a sheet, the image forming apparatus comprising:

a plurality of image forming members configured to form images of different colors;

an image bearing member on which a test image and pattern images of different colors are formed;

a sensor including a substrate on which a light emitting element, a first light receiving element, and a second light receiving element are formed; and

a control component configured to:

adjusting color misregistration based on a result of receiving diffuse reflected light from the pattern image by the first light receiving element; and

adjusting image densities of the plurality of image forming components based on a result of receiving the diffuse reflection light from the test image by the second light receiving element,

wherein:

a first angle formed between a first virtual line and a normal line perpendicular to a surface of the image bearing member is smaller than an incident angle of light from the light emitting element, wherein the first virtual line passes through an incident point of light from the light emitting element and the first light receiving element, and wherein the normal line passes through the incident point;

a second angle formed between a second virtual line and a normal line perpendicular to the surface of the image bearing member is smaller than an incident angle of light from the light emitting element, wherein the second virtual line passes through an incident point of light from the light emitting element and the second light receiving element, and wherein the normal line passes through the incident point; and is

The second angle is greater than the first angle.

2. The image forming apparatus according to claim 1, wherein:

forming a test image between image forming members for color among the plurality of image forming members; and is

The control section is configured to adjust image densities of the image forming sections for colors.

3. The image forming apparatus according to claim 1, wherein:

the sensor further comprises another light emitting element for a black test image different from the test image, the other light emitting element being formed on the substrate; and is

The control section is configured to adjust the image density of black based on a result of receiving the specular reflection light from the black test image.

4. The image forming apparatus according to claim 3, wherein the control means is configured to adjust the image density of black based on a result of receiving the specular reflection light from the black test image by the first light receiving element.

5. An image forming apparatus according to claim 3, wherein a third angle formed between a third virtual line passing through the incident point of the light from the another light emitting element and the first light receiving element and a normal line passing through the incident point of the light from the another light emitting element and perpendicular to the surface of the image bearing member is equal to the incident angle of the light from the another light emitting element.

6. The image forming apparatus according to claim 1, wherein:

the sensor further includes another light emitting element formed on the substrate; and is

The first light receiving element and the second light receiving element are formed between the light emitting element and the other light emitting element.

7. The image forming apparatus according to claim 1, wherein the first light receiving element is formed on a light emitting element side of a position where the normal line and the substrate intersect each other.

8. The image forming apparatus according to claim 1, wherein:

the substrate comprises a semiconductor substrate; and is

The light emitting element, the first light receiving element, and the second light receiving element include semiconductor elements formed on a semiconductor substrate.

9. The image forming apparatus according to claim 1, wherein the control means is configured to control the image forming conditions for adjusting the density of the images formed by the plurality of image forming means based on a result of receiving the diffuse reflection light from the test image by the second light receiving element.

10. The image forming apparatus according to claim 9, wherein:

the plurality of image forming components each include a photosensitive member, a light source configured to expose the photosensitive member to light to form an electrostatic latent image, and a developing roller configured to develop the electrostatic latent image formed on the photosensitive member; and is

The image forming conditions include light intensity of the light source.

11. An image forming apparatus configured to form an image on a sheet, the image forming apparatus comprising:

a plurality of image forming members configured to form images of different colors;

an image bearing member on which a pattern image and a test image are formed;

a sensor including a substrate on which a first light emitting element, a second light emitting element, a first light receiving element, and a second light receiving element are formed; and

a control component configured to:

adjusting an image density of black based on a result of receiving, by the first light receiving element, specular reflection light from the black test image during a period in which the first light emitting element emits light; and

adjusting color misregistration based on a result of receiving diffuse reflection light from pattern images of different colors by the first light receiving element during a period in which the second light emitting element emits light; and

the image density of the color is adjusted based on a result of receiving the diffuse reflection light from the color test image by the second light receiving element during a period in which the second light emitting element emits light,

wherein:

a first angle formed between a first virtual line and a normal line perpendicular to a surface of the image bearing member is smaller than an incident angle of light from the second light emitting element, wherein the first virtual line passes through an incident point of light from the second light emitting element and the first light receiving element, and wherein the normal line passes through an incident point of light from the second light emitting element;

a second angle formed between a second virtual line passing through an incident point of light from the second light emitting element and the second light receiving element and a normal line passing through an incident point of light from the second light emitting element and a normal line perpendicular to the surface of the image bearing member is smaller than an incident angle of light from the second light emitting element;

the second angle is greater than the first angle; and is

A third angle formed between a third virtual line passing through an incident point of light from the first light emitting element and the first light receiving element and a normal line perpendicular to the surface of the image bearing member passing through an incident point of light from the first light emitting element and the normal line is equal to an incident angle of light from the first light emitting element.

12. An image forming apparatus according to claim 11, wherein the third angle is equal to the first angle.

Technical Field

The present disclosure relates to an image forming apparatus configured to detect a detection image formed on an image bearing member.

Background

An electrophotographic image forming apparatus is configured to form images of yellow (Y), magenta (M), cyan (C), and black (K) on a sheet by an electrophotographic process of charging, exposure, development, and transfer. The density of an image formed on a sheet varies depending on the temperature and humidity of the image forming apparatus, the number of prints of the image forming apparatus, and the operating time of the image forming apparatus. To solve this problem, the image forming apparatus is configured to form a detection image on an image bearing member different from the sheet, detect the detection image by an optical sensor included in the image forming apparatus, and adjust an image forming condition for an image density based on a detection result.

The image forming apparatus is also configured to superimpose images of different colors to form an image of mixed colors. Therefore, when the image forming positions of the yellow image, the magenta image, the cyan image, and the black image are different, the color tone of the mixed-color image does not become a desired color tone. This is called "color misregistration". As with the density of the image described above, it is known that color misregistration also varies depending on the temperature and humidity of the image forming apparatus, the number of prints of the image forming apparatus, and the operating time of the image forming apparatus. To solve this problem, the image forming apparatus is configured to correct color misregistration before the color tone of a colored image (color image) is changed. For example, the image forming apparatus is configured to form detection images of different colors for detecting color misregistration on the image bearing member, detect the detection images by an optical sensor, and detect the amount of color misregistration based on the detection results. The image forming apparatus is configured to adjust image forming positions of respective colors based on the detected color misregistration amounts.

An optical sensor included in the image forming apparatus includes a light emitter and a light receiver configured to receive reflected light from a detection image on the image bearing member. The method of detecting a detection image by an optical sensor includes: a specular reflection light method of detecting specular reflection light from a detection image, and a diffuse reflection light method (diffuse reflection light method) of detecting diffuse reflection light from a detection image. For example, the image forming apparatus described in japanese patent application laid-open No.2013-031333 is configured to perform processing of detecting specular reflection light from a detection image and processing of detecting diffuse reflection light from the detection image by an optical sensor including two light emitting elements and two light receiving elements.

However, the optical sensor described in japanese patent application laid-open No.2013-031333 is assembled by soldering a bullet (bullet) light emitting element and a bullet light receiving element on a substrate, and thus it is difficult to reduce the size of the optical sensor. In addition, when a light receiving element for detecting color misregistration and a light receiving element for detecting image density are mounted on one sensor, the arrangement of these light receiving elements is limited, and therefore it is difficult for the optical sensor to receive reflected light from a detection image at an ideal angle. Therefore, in an image forming apparatus including an optical sensor including a bullet element for detecting color misregistration and a bullet element for detecting image density, there is a fear that the color misregistration amount and the image density cannot be detected with high accuracy.

Disclosure of Invention

An image forming apparatus configured to form an image on a sheet according to the present disclosure includes an image forming apparatus including: a plurality of image forming members configured to form images of different colors; an image bearing member on which a test image and pattern images of different colors are formed; a sensor including a substrate on which a light emitting element, a first light receiving element, and a second light receiving element are formed; and a control component configured to: adjusting color misregistration based on a result of receiving diffuse reflected light from the pattern image by the first light receiving element; and adjusting image densities of the plurality of image forming components based on a result of receiving the diffuse reflection light from the test image by the second light receiving element, wherein: a first angle formed between a first virtual line and a normal line perpendicular to a surface of the image bearing member is smaller than an incident angle of light from the light emitting element, wherein the first virtual line passes through an incident point of light from the light emitting element and the first light receiving element, and wherein the normal line passes through the incident point; a second angle formed between a second virtual line and a normal line perpendicular to the surface of the image bearing member is smaller than an incident angle of light from the light emitting element, wherein the second virtual line passes through an incident point of light from the light emitting element and the second light receiving element, and wherein the normal line passes through the incident point; and the second angle is greater than the first angle.

Other features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).

Drawings

Fig. 1 is a schematic cross-sectional view of an image forming apparatus according to at least one embodiment of the present disclosure.

Fig. 2 is a schematic diagram of a main part of the optical sensor.

Fig. 3A and 3B are explanatory views of a detection position shift due to vibration of the intermediate transfer belt.

Fig. 4 is an angle distribution characteristic diagram of the amount of light reflected by the intermediate transfer belt and the test image.

Fig. 5 is a schematic diagram of a main part of an optical sensor including a bullet element.

Fig. 6 is a control block diagram of the image forming apparatus.

Fig. 7 is an explanatory diagram of a first pattern image for detecting color misregistration.

Fig. 8 is a diagram for illustrating an example of an analog signal corresponding to a result of detecting a first pattern image for detecting color misregistration.

Fig. 9A and 9B are explanatory views of a second pattern image for detecting color misregistration.

Fig. 10 is a diagram for illustrating an example of an analog signal corresponding to a result of detecting a first pattern image for detecting color misregistration.

Fig. 11 is a diagram for illustrating an example of an analog signal corresponding to a result of detecting the second pattern image for detecting color misregistration.

Fig. 12A and 12B are explanatory diagrams of a test image for detecting image density.

Fig. 13 is a graph for illustrating an example of an analog signal corresponding to a result of detecting the first test image for detecting the image density.

Fig. 14 is a graph for illustrating an example of an analog signal corresponding to a result of detecting the second test image for detecting the image density.

Fig. 15 is a flowchart for illustrating the color-misregistration detection processing.

Fig. 16 is a flowchart for illustrating the image density detection processing.

Fig. 17 is a schematic diagram of a main part of the optical sensor.

Fig. 18 is a schematic diagram of a main portion of an optical sensor including a semiconductor substrate on which a light emitting element and a light receiving element are formed.

Detailed Description

At least one embodiment of the present disclosure will now be described in detail with reference to the accompanying drawings.

Integral arrangement

Fig. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to at least one embodiment. The image forming apparatus 100 includes photosensitive drums 1a to 1d, charging devices 2a to 2d, exposure devices 15a to 15d, developing devices 16a to 16d, an intermediate transfer belt 5, a belt supporting roller 3, a transfer roller 4, and a fixing device 17. In the following description, the photosensitive drums 1a to 1d, the charging devices 2a to 2d, the exposure devices 15a to 15d, and the developing devices 16a to 16d are referred to as "image forming units 10", and the "image forming units 10" are configured to form yellow (Y), cyan (C), magenta (M), and black (K) toner images. The letter "a" of the reference numeral suffix indicates a configuration for forming a yellow image. The letter "b" of the reference numeral suffix indicates a configuration for forming a cyan image. The letter "c" of the reference numeral suffix indicates a configuration for forming a magenta image. The letter "d" of the reference numeral suffix indicates a configuration for forming a black image.

The intermediate transfer belt 5 is stretched around a plurality of rollers including a driving roller and a belt supporting roller 3. The toner image formed by the image forming unit 10 is conveyed toward the intermediate transfer belt 5. The intermediate transfer belt 5 serves as an image bearing member configured to bear and convey a toner image. Further, the intermediate transfer belt 5 also serves as an intermediate transfer member to which the toner image is to be transferred. The transfer roller 4 is disposed on the side opposite to the belt supporting roller 3 with respect to the intermediate transfer belt 5. The nip N formed by the transfer roller 4 pressing the intermediate transfer belt 5 is referred to as a "transfer portion". The image on the intermediate transfer belt 5 is transferred onto the sheet at the nip N. The sheet is conveyed to the transfer portion by a conveying roller. The transfer roller 4 is configured to transfer the toner image formed on the transfer belt 5 onto a sheet at a transfer portion.

The photosensitive drums 1a, 1b, 1c, and 1d each rotate in the direction of arrow a. The photosensitive drums 1a, 1b, 1c, and 1d each have a photosensitive layer on its surface. The photosensitive drums 1a, 1b, 1c, and 1d function as photosensitive members. The charging devices 2a, 2b, 2c, and 2d are configured to charge the surfaces of the photosensitive drums 1a, 1b, 1c, and 1d, respectively. The exposure devices 15a, 15b, 15c, and 15d are configured to expose the charged surfaces of the photosensitive drums 1a, 1b, 1c, and 1d, respectively. The surfaces of the photosensitive drums 1a, 1b, 1c, and 1d are scanned with laser light emitted from the exposure devices 15a, 15b, 15c, and 15d, thereby forming electrostatic latent images on the surfaces of the photosensitive drums 1a, 1b, 1c, and 1d, respectively. The developing devices 16a, 16b, 16c, and 16d are configured to develop the electrostatic latent images with toner (developer) to form toner images of the respective colors on the photosensitive drums 1a, 1b, 1c, and 1d, respectively.

The driving roller of the intermediate transfer belt 5 is rotated to rotate the intermediate transfer belt 5 in the direction of arrow B. The toner images of the respective colors formed on the photosensitive drums 1a, 1b, 1c, and 1d are sequentially transferred in an overlapping manner onto an intermediate transfer belt 5 as an image bearing member. Thus, a full-color toner image 6 is formed on the intermediate transfer belt 5.

The intermediate transfer belt 5 is rotated to convey the toner image 6 to the transfer portion. The toner image 6 is transferred onto a sheet while passing through a transfer portion. The sheet on which the toner image 6 is transferred is conveyed to a fixing device 17 by a conveying belt 12. The fixing device 17 includes a heater 171. The heater 171 is configured to heat the toner image 6 to fix the toner image 6 onto the sheet. Then, the sheet is delivered to a tray (not illustrated) of the image forming apparatus 100. In this way, the image forming process of the image forming apparatus 100 ends.

On the downstream side of the photosensitive drum 1d in the conveying direction (direction B) of the intermediate transfer belt 5, an optical sensor 7 is arranged. The optical sensor 7 is configured to detect a pattern image for detecting color misregistration and a test image for detecting image density, which are formed on the intermediate transfer belt 5. The result of detecting the pattern image is used to determine the color misregistration amount used for color misregistration correction. The result of detecting the test image is used to determine a correction amount to be used for image density correction. Hereinafter, when the pattern image and the test image are not distinguished, the pattern image and the test image are referred to as a "detection image".

The transfer positions of the toner images of the respective colors transferred from the photosensitive drums 1a to 1d onto the intermediate transfer belt 5 may be shifted on the intermediate transfer belt 5. This is known to be caused by a temperature increase of the exposure apparatuses 15a to 15 d. The shift of the transfer position causes color misregistration, which changes the chromaticity and hue of the full-color image. To solve this problem, the image forming apparatus 100 is configured to detect a pattern image by the optical sensor 7 and correct color misregistration detected as a result of the detection.

Moreover, the image forming apparatus 100 may vary in the density of an image to be formed due to an increase in the use environment (temperature and humidity) and the number of prints. To solve this problem, the image forming apparatus 100 is configured to detect a test image by the optical sensor 7 and perform image density correction in which image forming conditions regarding image density are controlled based on the result of detecting the test image. In this case, the image forming conditions regarding the image density include, for example: the intensity of laser light emitted by the exposure devices 15a to 15d, a developing bias to be applied to the developing devices 16a to 16d, a charging bias to be applied to the charging devices 2a to 2d, or a transfer bias to be applied to the transfer roller 4. In order to correct the image density, the image forming apparatus 100 may control a plurality of image forming conditions or only a specific image forming condition.

Optical sensor

Fig. 2 is an explanatory diagram of the optical sensor 7. The optical sensor 7 includes two light emitting elements and two light receiving elements. The optical sensor 7 includes two Light Emitting Diodes (LEDs) (a first LED701 and a second LED702) as light emitting elements. The optical sensor 7 includes two Photodiodes (PDs) (a first PD711 and a second PD712) as light receiving elements. The first LED701, the second LED702, the first PD711, and the second PD712 are bonded to a predetermined surface (mounting surface) of the same substrate 201 by die bonding and wire bonding. The optical axes of the light emitted from the first LED701 and the second LED702 are perpendicular to a predetermined surface (mounting surface) of the substrate 201. In addition, the optical axes of the reflected lights received by the first PD711 and the second PD712 are also perpendicular to a predetermined surface (mounting surface) of the substrate 201.

Since all the components are mounted on a predetermined surface (mounting surface) of the substrate 201, a plurality of components can be mounted on the substrate 201 when the reflow step is performed once. Therefore, the manufacturing cost of the optical sensor 7 can be reduced as compared with the manufacturing cost of an optical sensor in which a plurality of elements are mounted on both sides of the substrate 201. For example, the substrate 201 is a Printed Circuit Board (PCB), but the present disclosure is not limited thereto. The first LED701, the second LED702, the first PD711, and the second PD712 are electrically connected to a power supply circuit (not shown) and a detection circuit (not shown), for example, via the substrate 201.

The first LED701 is configured to emit light to an object to be measured (the intermediate transfer belt 5 or a detection image on the intermediate transfer belt 5). The first PD711 is disposed at a position where it can receive specular reflection light from an object to be measured when the first LED701 emits light. An optical axis center point P (incident point) of fig. 2 indicates a position where light emitted from the first LED701 to the intermediate transfer belt 5 is reflected. In other words, the first LED701 and the first PD711 are arranged such that light emitted from the first LED701 is specularly reflected at the optical axis center point P (such that the incident angle and the reflection angle are equal to each other), and the reflected light is received by the first PD 711. The optical axis center point P is a detection position of the optical sensor 7.

The second LED702 is arranged at a position where the first PD711 or the second PD712 does not receive the specular reflection light of the light emitted to the intermediate transfer belt 5 in other words, the second LED702 is arranged such that the reflection light is not received by the first PD711 or the second PD712 even when the light emitted from the second LED702 is specularly reflected at the optical axis center point P of the intermediate transfer belt 5, the specular reflection light from the detection image is not received by the first PD711 or the second PD712 even when the light emitted from the second LED702 is specularly reflected by the detection image, the second LED702 is arranged at a position where the diffuse reflection light of the light emitted to the intermediate transfer belt 5 is received by the first PD711 and the second PD712, the first LED701 and the second LED702 are arranged to irradiate the optical axis center point P at the same position, the second LED702 is arranged at a position where a virtual line connecting the second LED702 and the optical axis center point P forms an angle α (an incident angle) with respect to a normal line of the intermediate transfer belt 5 at the optical axis P, for example, an angle α is 35 °.

The first PD711 is disposed at a position that receives 1) the specular reflection light of the light emitted from the first LED701 to the intermediate transfer belt 5 and 2) the diffuse reflection light of the light emitted from the second LED702 to the intermediate transfer belt 5, the second PD712 is disposed at a position that receives the diffuse reflection light of the light emitted from the second LED702 to the intermediate transfer belt 5, the second PD712 is not disposed at a position that receives the specular reflection light of the light emitted from the first LED701 to the intermediate transfer belt 5, the first PD711 and the second PD712 are not disposed at positions that receive the specular reflection light of the light irradiated from the second LED702 to the intermediate transfer belt 5, the first PD711 and the second PD712 are disposed at a position on the second LED702 side (light emitting element side) where a normal line at the optical axis center point P of the intermediate transfer belt 5 intersects with the substrate 201, the first PD711 is disposed at a position where a virtual line connecting the first PD711 and the optical axis center point P forms an angle θ with respect to a normal line at the optical axis P of the intermediate transfer belt 5, the second PD712 is an angle 6332.

The substrate 201 is mounted to the housing 203. The casing 203 has a light guiding path for guiding irradiation light so that light emitted from the first LED701 and the second LED702 efficiently irradiates the intermediate transfer belt 5. The housing 203 also has an optical guiding path for guiding the reflected light so that the first PD711 and the second PD712 effectively receive the reflected light from the intermediate transfer belt 5. On a light guiding path for guiding irradiation light and a light guiding path for guiding reflection light, a lens group 204 including lenses 204a to 204d is provided.

In other words, the light emitted from the first LED701 travels in the optical axis direction (single-dot broken line in fig. 2), and illuminates the intermediate transfer belt 5 through the light guiding path formed in the housing 203 and the lens 204 a. The specular reflection light from the intermediate transfer belt 5 or the detection image travels in the optical axis direction (single-dot broken line in fig. 2), and reaches the first PD711 through a light guiding path formed in the housing 203 and the lens 204 c. Light emitted from the second LED702 travels in the optical axis direction (single-dot broken line in fig. 2), and illuminates the intermediate transfer belt 5 through the light guiding path in the housing 203 and the lens 204 b.

The first PD711 is configured to receive diffuse reflection light of the second LED702 irradiating the intermediate transfer belt 5 through the light guiding path formed in the housing 203 and the lens 204 c. The specular reflection light from the first LED701 received by the first PD711 is used for color misregistration detection and image density detection. The diffusely reflected light from the second LED702 received by the first PD711 is used for color misregistration detection. In other words, the first PD711 is used for color misregistration detection by specular reflection, color misregistration detection by diffuse reflection, and density detection by specular reflection.

When receiving the specular reflection light of the first LED701 irradiating light of a pattern image for color misregistration detection, the first PD711 is used for color misregistration detection by specular reflection, the pattern image being formed on the intermediate transfer belt 5. When receiving the specular reflection light of the first LED701 irradiating the test image for image density detection, the first PD711 is used for density detection by specular reflection, the test image being formed on the intermediate transfer belt 5. When receiving the diffuse reflection light of the light with which the second LED702 irradiates the pattern image for color misregistration detection, the first PD711 is used for color misregistration detection by diffuse reflection, the pattern image being formed on the intermediate transfer belt 5.

In order to accurately detect the position of the pattern image for color misregistration detection, it is preferable that the first PD711 has a small acceptance angle θ with respect to the normal line of the intermediate transfer belt 5 at the optical axis center point P. The reason is described with reference to fig. 3A and 3B. Fig. 3A and 3B are explanatory views of the detection position shift due to the vibration of the intermediate transfer belt 5. In fig. 3A, a state in which the intermediate transfer belt 5 is not vibrated is illustrated. In fig. 3B, a state in which the intermediate transfer belt 5 vibrates is illustrated. When the intermediate transfer belt 5 is not vibrated, the distance between the optical sensor 7 and the intermediate transfer belt 5 has a predetermined value zref. When the intermediate transfer belt 5 vibrates, the distance between the optical sensor 7 and the intermediate transfer belt 5 is a distance zp, which is greater than a predetermined value zref. When the light receiving angle of the light receiver 71 of the optical sensor 7 is the angle θ with respect to the normal direction of the intermediate transfer belt 5, the optical axis center point P of the detection image is shifted by (zp-zref) × tan θ due to the vibration of the intermediate transfer belt 5. Therefore, in order to accurately detect the color misregistration amount, it is preferable that an angle (light receiving angle θ) with respect to a normal line of the intermediate transfer belt 5 at the optical axis center point P is small. In fig. 2, the first PD711 is arranged such that the light acceptance angle θ (which is an angle of a virtual line connected to the optical axis center point P with respect to a normal line of the intermediate transfer belt 5 at the optical axis center point P) is smaller.

The second PD712 is configured to receive diffuse reflection light of light emitted from the second LED702 to irradiate the optical axis center point P of the intermediate transfer belt 5 through a light guiding path formed in the housing 203 and the lens 204 d. The diffusely reflected light from the second LED702 received by the second PD712 is used for image density detection. It is preferable that the second PD712 receive the reflected light of the optical axis at an angle (to increase the angle Φ) away from the optical axis of the specular reflected light (optical axis of specular reflection) of the light emitted from the second LED702 to irradiate the intermediate transfer belt 5. In this case, the density of the test image for image density detection can be accurately detected. The reason is described with reference to fig. 4.

Fig. 4 is an angle distribution characteristic diagram of the amount of light reflected by the intermediate transfer belt 5 and the test image for image density detection. When the light emitter 70 emits light from a predetermined direction, the reflected light from the intermediate transfer belt 5 is stronger in the specular reflection direction (direction a) with respect to the irradiated light. The test image for image density detection exhibits reflection angle characteristics of substantially Lambertian (Lambertian) reflection, as shown by the broken line and single-dot broken line of fig. 4. Image density detection is performed by forming a test image in which images of different densities are combined on the intermediate transfer belt 5 and detecting the amount of light reflected by the test image by the optical sensor 7. The solid line indicates the reflection characteristic of the intermediate transfer belt 5. The dotted line indicates the reflection characteristic of the high density image. The single-dot broken line indicates the reflection characteristic of the low density image.

The amount of light reflected by the low-density image is substantially equal to the amount of light reflected by the intermediate transfer belt 5 in the direction B of fig. 4. In this case, it is difficult to detect a low-density image of the test image. This is because, in the angular characteristics of the reflected light from the intermediate transfer belt 5, there is reflected light even at a diffuse reflection angle near the specular reflection angle. Therefore, it is preferable that the optical sensor 7 receives the reflected light at an angle away from the specular reflected light (at a larger Φ with respect to the specular reflected light) as in the direction C of fig. 4. In fig. 2, the second PD712 is arranged such that the acceptance angle Φ is large.

Both the first PD711 and the second PD712 are configured to detect the diffusely reflected light of the irradiated light from the second LED702 on the intermediate transfer belt 5. Accordingly, the first PD711 and the second PD712 have a relationship of (the angle Φ formed by the second PD712) > (the angle Ψ formed by the first PD711) with respect to the specular reflection angle of the second LED702 (see FIG. 2). In other words, the angle Ψ is smaller than the angle Φ. An angle Ψ formed by the first PD711 is an angle of a virtual line connecting the first PD711 and the optical axis center point P with respect to the optical axis of the specular reflected light of the second LED702 (optical axis of specular reflection). The angle Φ formed by the second PD712 is an angle of a virtual line connecting the second PD712 and the optical axis center point P with respect to the optical axis of the specular reflected light of the second LED 702. The angle Φ is, for example, 53 °. The angle Ψ is, for example, 42 °.

The first LED701, the second LED702, the first PD711, and the second PD712 are mounted on the same substrate 201, and thus the elements can be mounted substantially parallel to the intermediate transfer belt 5. Therefore, the displacement of the optical axis from the optical axis center point P can be reduced as compared with the case where the element is formed by a bullet element having a pin. In addition, the first LED701, the second LED702, the first PD711, and the second PD712 are elements bonded to the substrate 201 by die bonding and wire bonding, and thus the element interval can be reduced. Therefore, the overall size of the optical sensor 7 can be reduced. For example, although typical components are about 3mm by about 2mm by about 1mm, bullet components have dimensions of about 5mm by about 10mm by about 5mm even without pins. Therefore, the component volume can be significantly reduced, and the size of the optical sensor 7 itself can be reduced.

Now, as a comparative example, an optical sensor including a bullet element is described. Fig. 5 is an explanatory diagram of an optical sensor including a bullet element. When the positional relationship between the light emitting elements 161 and 162 and the light receiving elements 163 and 164 is realized via a relationship (irradiation angle, reception angle) similar to the case where the elements are bonded to a substrate by die bonding and wire bonding, it is necessary to bring the light emitting element 161 and the light receiving element 163 closer to each other. When the light emitting element 161 and the light receiving element 163 have a positional relationship with respect to the intermediate transfer belt 5 similar to that of fig. 2, the light emitting element 161 and the light receiving element 163 are too close to each other. Therefore, the function of the light shielding wall of the housing 166 provided on the substrate 165 is hindered. Therefore, in order to prevent the light emitting elements 161 and 162 and the light receiving elements 163 and 164 from interfering with the light shielding wall, it is necessary to increase the interval between the elements as shown in fig. 3A, but in this case, the size of the optical sensor is increased.

As described above, in the optical sensor 7 of at least one embodiment, the light emitting element and the light receiving element are bonded to the substrate 201 by die bonding and wire bonding. By bonding the first LED701, the second LED702, the first PD711, and the second PD712 to the substrate 201 by die bonding and wire bonding, the distance between the elements can be reduced. Therefore, the optical sensor 7 can be reduced in size as compared with an optical sensor including a bullet element (fig. 5). Also, according to the optical sensor 7, the distance between the first LED701 and the first PD711 can be reduced, and thus specular reflection light of light emitted to the object to be measured can be detected at a sharper angle than that of an optical sensor including a bullet light emitting element and a bullet light receiving element. Therefore, even when the distance from the optical sensor 7 to the object to be measured is changed, the irradiation area on the object to be measured is hardly changed. When the intermediate transfer belt 5 rotates, the distance from the optical sensor 7 to the detection image tends to change. According to the optical sensor 7 of at least one embodiment, even when the distance from the optical sensor 7 to the detection image is changed, the irradiation area hardly changes, and thus the specular reflection light from the detection image can be detected with high accuracy. In addition, the optical sensor 7 may reduce the distance between the first LED701 and the first PD711, thus also increasing design flexibility. Therefore, according to the optical sensor 7, the first LED701, the second LED702, the first PD711, and the second PD712 can be arranged in a positional relationship suitable for detecting specular reflection light and diffuse reflection light from the object to be measured. In particular, in the optical sensor 7 sharing the light emitting element or the light receiving element, specular reflection light and diffuse reflection light from the detection image can be detected more accurately than in the optical sensor of the related art including the bullet element.

Controller

Turning now to a description of the image forming apparatus 100 of at least one embodiment, fig. 6 is an exemplary diagram of an example of a configuration of a controller configured to control the image forming apparatus 100. The controller 40 includes a Central Processing Unit (CPU)109, a Read Only Memory (ROM)111, and an image formation controller 101. The CPU109 includes an a/D converter 110. The image forming controller 101 includes an exposure device controller 112, a developing device controller 113, a photosensitive drum controller 114, and an intermediate transfer belt driver 115. The exposure apparatus controller 112 is configured to control the intensity of laser light emitted from light sources included in the exposure apparatuses 15a to 15 d. The developing device controller 113 is configured to control a motor for rotating the developing rollers included in the developing devices 16a to 16 d. The photosensitive drum controller 114 is configured to control motors for rotating the photosensitive drums 1a to 1 d. The intermediate transfer belt driver 115 is configured to control a motor for rotating the intermediate transfer belt 5. The CPU109 is configured to control the image forming apparatus 100 by executing a computer program stored in the ROM 111. In addition to the computer program, the ROM111 stores therein pattern image data (to be described later) for forming a pattern image for color misregistration detection, and test image data for forming a test image for image density detection. The controller 40 may be realized not only by executing a computer program but also by discrete components or a single-chip semiconductor product. The single-chip semiconductor product includes, for example, a Micro Processing Unit (MPU), an Application Specific Integrated Circuit (ASIC), or a system on a chip (SOC).

The CPU109 is configured to control the optical sensor 7 to cause the first LED701 and the second LED702 to emit light (to be lit) independently.

The optical sensor 7 is configured to receive reflected light from the intermediate transfer belt 5 or a detection image formed on the intermediate transfer belt 5 through the first PD711 and the second PD 712. The first PD711 and the second PD712 are configured to output an analog signal obtained by converting the received reflected light into a voltage as a detection result. The CPU109 is configured to take in analog signals output from the first PD711 and the second PD712 through the a/D converter 110. The CPU109 is configured to store a digital signal obtained by converting an analog signal by the a/D converter 110 in a memory (not shown).

The CPU109 is configured to control the exposure devices 15a to 15d, the developing devices 16a to 16d, and the photosensitive drums 1a to 1d through the image formation controller 101 to form detection images on the intermediate transfer belt 5. The CPU109 is configured to cause the first LED701 and the second LED702 of the optical sensor 7 to be lit. The first LED701 and the second LED702 are configured to irradiate the surface (front surface) of the intermediate transfer belt 5 on which a detection image is to be formed and the detection image formed on the intermediate transfer belt 5. The first PD711 and the second PD712 are configured to receive reflected light from the front surface of the intermediate transfer belt 5 and a detection image formed on the intermediate transfer belt 5 to output an analog signal corresponding to the reflected light. The CPU109 is configured to detect a color misregistration amount and an image density from analog signals output from the first PD711 and the second PD712 to perform color misregistration correction and image density correction.

Pattern image

Fig. 7 is an explanatory diagram of a first pattern image for color misregistration detection. The first pattern image includes a colored pattern of yellow as a reference color, and colored patterns of other colors (magenta, cyan, and black). The colored pattern is an image formed inclined at a predetermined angle (for example, 45 °) with respect to the conveying direction of the intermediate transfer belt 5. Two pattern images of the same color are formed. The pattern images of the same color are formed to be inclined in different directions with respect to the conveying direction of the intermediate transfer belt 5.

The first pattern image is used in a case where the first PD711 receives specular reflection light of light emitted from the first LED 701. In other words, when the amount of reflected light from the intermediate transfer belt 5 is a predetermined amount or more, the color misregistration amount is detected using the first pattern image. When the glossiness of the front surface of the intermediate transfer belt 5 is not reduced, the amount of specular reflection light from the front surface of the intermediate transfer belt 5 is larger than the amount of specular reflection light from the first pattern image. Therefore, the analog signal value corresponding to the result of receiving the reflected light from the area (the front surface of the intermediate transfer belt 5) where the first pattern image is not formed is higher than the analog signal value corresponding to the result of receiving the reflected light from the first pattern image.

Fig. 8 is a graph for illustrating an example of an analog signal in a case where reflected light from the first pattern image is detected by the first LED701 and the first PD 711. The analog signal value of the first PD711 obtained when the reflected light from the colored pattern is received is lower than the analog signal value of the first PD711 obtained when the reflected light from the front surface of the intermediate transfer belt 5 is received.

CPU109 is configured to convert the analog signal to a binary signal indicative of the first level or the second level based on the first threshold. The converted signal corresponds to the result of the comparison between the analog signal value (fig. 8) and the first threshold value. At this time, the CPU109 determines the first threshold value based on an analog signal value obtained when the specular reflection light from the front surface of the intermediate transfer belt 5 of the light emitted from the first LED701 is received by the first PD 711. Then, the CPU109 detects the color misregistration amount of the colored pattern of the first pattern image based on the above-described binary signal. Color misregistration correction is a known technique, and a detailed description thereof is omitted here.

Fig. 9A and 9B are explanatory diagrams of a second pattern image for color misregistration detection. The second pattern image includes a colored pattern of yellow as a reference color, and colored patterns of other colors (magenta, cyan, and black). However, it should be noted that the black colored pattern of the second pattern image is formed to be superimposed on the magenta colored pattern. When the diffuse reflected light of the light emitted from the second LED702 is received by the first PD711, the second pattern image is used. In other words, when the amount of reflected light from the intermediate transfer belt 5 is not a predetermined amount or more, the color misregistration amount is detected using the second pattern image. In other words, when the amount of reflected light from the intermediate transfer belt 5 is less than a predetermined amount, the color misregistration amount is detected using the second pattern image.

When the glossiness of the intermediate transfer belt 5 is reduced due to the abrasion of the intermediate transfer belt 5, the amount of specular reflection light from the front surface of the intermediate transfer belt 5 is reduced. Fig. 10 is a diagram for illustrating an example of an analog signal obtained when reflected light from the first pattern image formed on the intermediate transfer belt 5, which has a reduced amount of specular reflection light, is detected by the first LED701 and the first PD 711. When the amount of the specular reflection light from the intermediate transfer belt 5 decreases, as shown in fig. 10, the difference between the analog signal value obtained when the specular reflection light from the colored patterns of the respective colors is received and the analog signal value obtained when the specular reflection light from the intermediate transfer belt 5 is received decreases. Therefore, in some cases, the CPU109 cannot detect the color misregistration amount from the binary signal with high accuracy.

To solve this problem, a second pattern image is formed in a state where the amount of specular reflection light from the intermediate transfer belt 5 is reduced, and diffuse reflection light from the second pattern image is detected by the optical sensor 7. The optical sensor 7 receives the diffuse reflection light of the light emitted from the second LED702 through the first PD 711. Fig. 11 is a graph for illustrating an example of an analog signal obtained when reflected light from the second pattern image formed on the intermediate transfer belt 5, which has a reduced amount of specular reflection light, is detected by the second LED702 and the first PD 711.

As shown in fig. 9A, the second pattern image is different from the first pattern image. Specifically, a colored pattern of black is superimposed on a colored pattern of magenta. When a colored pattern of black is detected using diffuse reflected light, light emitted from the second LED702 is absorbed by the black toner. Therefore, the difference between the amount of diffuse reflected light from the black-only colored pattern and the amount of diffuse reflected light from the intermediate transfer belt 5 is very small. In each black colored pattern of the second pattern image, the pattern formed using the magenta toner is exposed from the gaps of the pattern formed at intervals using the black toner. This is called a "composite pattern". A cross-sectional view of the composite pattern is shown in fig. 9B. The result of detecting the second pattern image including the composite pattern is shown in fig. 11. The analog signal value corresponding to the diffuse reflected light from the composite pattern is a value corresponding to the diffuse reflected light from the area of the composite pattern formed using the magenta toner. The interval between the patterns of the black toner is predetermined, so the CPU109 can determine the color misregistration amount of the color pattern of black based on the relative position between the region of the composite pattern formed using magenta and the reference color pattern using yellow toner.

The CPU109 is configured to convert the analog signal (fig. 11) into a binary signal indicating the first level or the second level based on the second threshold. The converted signal corresponds to the result of the comparison between the analog signal value (fig. 11) and the second threshold value. At this time, the CPU109 determines the second threshold value based on the analog signal value obtained when the diffusely-reflected light from the front surface of the intermediate transfer belt 5 of the light emitted from the second LED702 is received by the first PD 711. Then, the CPU109 detects the color misregistration amount of the colored pattern of the second pattern image based on the above binary signal. Color misregistration correction using a composite pattern is a known technique, and a detailed description thereof is omitted here.

In the image forming apparatus 100 according to at least one embodiment, the color misregistration amount of an image is detected using the above-mentioned pattern images (the first pattern image and the second pattern image). The CPU109 detects the positions of the colored patterns of the respective colors to calculate the relative positions of the pattern images of the other colors with respect to the pattern image of the reference color (yellow). The CPU109 determines the color misregistration amount of each color based on the difference between the calculated relative position and the target relative position. The CPU109 controls the write timing by the exposure apparatuses 15a to 15d based on the determined color misregistration amount to perform color misregistration correction. Further, the CPU109 may correct the image data based on the detected color misregistration, thereby suppressing, for example, the amount of color misregistration of the image to be formed by the image forming unit 10. The reference color is not limited to yellow, and may be magenta or cyan.

As described with reference to fig. 2, the first PD711 is arranged so that the light receiving angle θ with respect to the normal direction of the intermediate transfer belt 5 is small. Therefore, the position of the first pattern image can be accurately detected while suppressing the influence of the vibration of the intermediate transfer belt 5 described with reference to fig. 3A and 3B.

Test image

Fig. 12A and 12B are explanatory diagrams of a test image used for image density detection. In fig. 12A, an example of a first test image for image density detection to be detected with specular reflection light is shown. In fig. 12B, an example of a second test image for image density detection to be detected with diffuse reflected light is shown.

When the specular reflection light of the light emitted from the first LED701 is received by the first PD711, the first test image is used. Specifically, the first test image is used to detect the image density of black. The black toner absorbs light, and thus the amount of diffusely reflected light from the black test image is very small. Therefore, when the density of an image formed of black toner is to be detected, the CPU109 detects specular reflection light from the black test image. The first test image is formed of a piecewise gradient pattern of four image densities: 70%, 50%, 30% and 10%. The image forming unit 10 forms a first test image based on the image signal value of the test image data. The image signal value of the test image data is predetermined.

The first test image formed on the intermediate transfer belt 5 is read by the optical sensor 7. The analog signal output from the first PD711 is converted into a digital signal by the a/D converter 110. The CPU109 controls the image forming conditions for the image density based on the difference between the digital signal value and the target value. For example, the CPU109 controls the intensity of laser light emitted from the exposure apparatus 15d through the image formation controller 101 to adjust the image density of black.

Fig. 13 is a graph for illustrating an example of analog signals obtained when the first LED701 and the first PD711 detect reflected light from the first test image. The amount of specular reflection light of the image of the density of 70% (the highest density of the first test image) is reduced because the toner adhesion amount is large in addition to the fact that the black toner absorbs light. Therefore, the analog signal value output by the optical sensor 7 (the first PD711) decreases. The amount of light absorbed by the black toner of the image having a density of 10% (the lowest density of the first test image) is reduced, and the toner adhesion amount is reduced, as compared with the case where the density is 70%, with the result that the amount of specular reflection light is increased. Therefore, the analog signal value output by the optical sensor 7 (the first PD711) increases.

When the diffuse reflected light of the light emitted from the second LED702 is received by the second PD712, the second test image is used. The second test image is used to detect image densities of colors (chromatic colors), such as yellow, magenta, and cyan, in particular. The image densities of yellow, magenta, and cyan are detected using diffuse reflected light. The second test image was formed from a segmented gradation pattern of four densities: 70%, 50%, 30% and 10%. In fig. 12B, a yellow test image is shown. A second test image of these colors of yellow, magenta and cyan is formed on the intermediate transfer belt 5.

The second test image formed on the intermediate transfer belt 5 is read by the optical sensor 7. The analog signal output from the second PD712 is converted into a digital signal by the a/D converter 110. The CPU109 controls the image forming condition of the image density based on the difference between the digital signal value and the target value. In this way, the CPU109 adjusts the image densities of yellow, magenta, and cyan.

Fig. 14 is a graph for illustrating an example of analog signals obtained when the second LED702 and the second PD712 detect reflected light from the second test image. Here, an analog signal for a second test image of yellow is shown. The amount of diffuse reflection light of the image with the density of 70% (the highest density of the second test image) increases because the toner adhesion amount is large in addition to the fact that the yellow toner reflects light. Therefore, the analog signal value output by the optical sensor 7 (second PD712) increases. The amount of light reflected by the yellow toner of the image having the density of 10% (the lowest density of the second test image) is reduced, and the amount of diffuse reflection light is reduced, as compared with the case where the density is 70%. Therefore, the analog signal value output by the optical sensor 7 (second PD712) decreases. The analog signals obtained for the second test images for magenta and cyan showed similar trends.

Color misregistration correction

FIG. 15 is a flow diagram that illustrates processing to detect an amount of color misregistration in at least one embodiment.

The CPU109 first detects the amount of light reflected on the front surface of the intermediate transfer belt 5 by the optical sensor 7 (step S1201). The CPU109 causes the first LED701 to emit light. At this time, no image is formed on the intermediate transfer belt 5, and thus the light from the first LED701 illuminates the front surface of the intermediate transfer belt 5. The first PD711 receives the specular reflection light from the front surface of the intermediate transfer belt 5 to output an analog signal corresponding to the amount of the specular reflection light. The CPU109 takes an analog signal from the first PD711 to detect the amount of light reflected by the front surface of the intermediate transfer belt 5.

The CPU109 determines whether the acquired amount of light reflected by the front surface of the intermediate transfer belt 5 is a predetermined amount or more (step S1202). Through this processing, the CPU109 determines whether the glossiness of the front surface of the intermediate transfer belt 5 is high.

When the amount of light reflected by the front surface of the intermediate transfer belt 5 is a predetermined amount or more (step S1202: YES), the CPU109 determines that the glossiness of the front surface of the intermediate transfer belt 5 is not decreased. In this case, the CPU109 detects the color misregistration amount using the first pattern image. In other words, the CPU109 conveys the pattern image data P1 to the image formation controller 101, and controls the image formation controller 101 to form the first pattern image on the intermediate transfer belt 5 (step S1203). The CPU109 causes the first LED701 to emit light, and reads the first pattern image formed on the intermediate transfer belt 5 by the first PD711 (step S1204). In step S1204, the CPU109 acquires an analog signal output from the first PD 711. The CPU109 calculates the color misregistration amount from the results of detecting the first pattern images of the respective colors of yellow, magenta, cyan, and black (step S1207).

When the amount of light reflected by the front surface of the intermediate transfer belt 5 is less than the predetermined amount (step S1202: no), the CPU109 determines that the glossiness of the front surface of the intermediate transfer belt 5 is reduced. In this case, the CPU109 detects the color misregistration amount using the second pattern image. In other words, the CPU109 conveys the pattern image data P2 to the image formation controller 101, and controls the image formation controller 101 to form the second pattern image on the intermediate transfer belt 5 (step S1205). The CPU109 causes the second LED702 to emit light, and reads the second pattern image formed on the intermediate transfer belt 5 through the first PD711 (step S1206). In step S1206, the CPU109 acquires an analog signal output from the first PD 711. Then, the CPU109 advances the process to step S1207. The CPU109 calculates the color misregistration amount based on the results of detecting the second pattern images of the respective colors of yellow, magenta, cyan, and black (step S1207). After the process of step S1207 is completed, the CPU109 ends the process of detecting the color misregistration amount.

The CPU109 stores the calculated color misregistration amount in a memory (not shown). When the image forming apparatus 100 is to form an image on a sheet, the CPU109 reads the color misregistration amount from the memory and corrects the image forming position of an image to be formed based on image data according to the color misregistration amount.

As described above, the CPU109 uses the pattern images (the first pattern image and the second pattern image) for color misregistration detection corresponding to the result of detecting the glossiness of the intermediate transfer belt 5 to obtain the color misregistration amount by the optimum combination of the light emitter and the light receiver. Therefore, the CPU109 can detect an accurate color misregistration amount to perform accurate color misregistration correction.

Image density correction

Fig. 16 is a flowchart for illustrating an image density detection process in at least one embodiment. In at least one embodiment, the case where image density detection of colors is performed after image density detection of black is described, but the order may be reversed.

The CPU109 transfers the test image data TK to the image formation controller 101, and controls the image formation controller 101 to form a test image (first test image) of black on the intermediate transfer belt 5 (step S1301). The CPU109 causes the first LED701 to emit light and acquires an analog signal from the first PD711 that receives the specular reflection light to read a test image in black (step S1302). The CPU109 converts the level of the analog signal corresponding to the read black test image into a digital signal value through the a/D converter 110. The CPU109 determines the image forming conditions for the image density based on the digital signal value (step S1303). In step S1303, the CPU109 determines the correction amount of the laser intensity of the exposure apparatus 15d as the image forming condition for the image density of black, and stores the correction amount in a memory (not shown). When a black image is to be formed, the CPU109 reads the correction amount from the memory and controls the density of the black image to be formed by the image forming unit 10 according to the correction amount.

After calculating the correction amount of the black image density, the CPU109 determines whether the image density detection process has been performed for all the colors of yellow, magenta, and cyan (step S1304).

When image density detection has not been performed for all colors (no in step S1304), the CPU109 first performs image density detection for yellow. In other words, the CPU109 conveys the test image data TY to the image formation controller 101, and controls the image formation controller 101 to form a test image of yellow (second test image) on the intermediate transfer belt 5 (step S1305). The CPU109 causes the second LED702 to emit light, and takes an analog signal from the second PD712 that receives the diffuse reflected light to read a test image in yellow (step S1306). The CPU109 converts the level of the analog signal corresponding to the read yellow test image into a digital signal value through the a/D converter 110. The CPU109 determines the image forming conditions for the image density based on the digital signal value (step S1307). In step S1307, the CPU109 determines the correction amount of the laser intensity of the exposure apparatus 15a as the image forming condition for the image density of yellow, and stores the correction amount in the memory (not shown). When a yellow image is to be formed, the CPU109 reads the correction amount from the memory and controls the density of the yellow image to be formed by the image forming unit 10 according to the correction amount.

The CPU109 repeatedly executes the processing of steps S1305 to S1307 until the image density detection processing of all colors ends. When the image density detection processing has been performed for all of the colors yellow, magenta, and cyan (step S1304: yes), the CPU109 ends the image density detection processing.

As described above, the CPU109 uses the test images (first test image, second test image) for image density detection corresponding to the color to be detected to obtain the image density by the optimum combination of the light emitter and the light receiver. Therefore, the CPU109 can detect an accurate image density correction amount to perform accurate image density correction.

As described above, the image forming apparatus 100 according to at least one embodiment includes the optical sensor 7, and the optical sensor 7 has a plurality of elements bonded on the same substrate 201 by die bonding and wire bonding. Therefore, the size and cost of the optical sensor 7 itself can be reduced. The image forming apparatus 100 uses the optical sensor 7 in both the specular reflection light method and the diffuse reflection light method. Further, the image forming apparatus 100 prepares a detection image used in the specular reflection method and a detection image used in the diffuse reflection method, respectively.

In the process of detecting the color misregistration amount, the image forming apparatus 100 can realize detection of a pattern image suitable for the state of the intermediate transfer belt 5 by combining the first LED701, the second LED702, and the first PD711 together in an optimum manner. The first PD711 configured to receive specular reflection light for detecting the color misregistration amount is arranged so that the light receiving angle θ is as small as possible with respect to the normal direction of the intermediate transfer belt 5. Therefore, even with respect to a change in the detection position due to vibration of the intermediate transfer belt 5, the color misregistration amount can be detected with high accuracy. Further, in the image density detection process, the image forming apparatus 100 can realize detection of a test image suitable for the color of the test image by combining the first LED701, the second LED702, the first PD711, and the second PD712 in an optimum manner. The second PD712 configured to receive the diffuse reflected light of the second LED702 for image density detection is arranged to form an angle as far as possible with respect to the specular reflected light of the second LED 702. Therefore, even for a test image having a low density, the image density can be detected with high accuracy.

In order to maximize the detection capability of the optical sensor 7, it is necessary to compensate the positional relationship between the elements with high accuracy. In the optical sensor 7, the first LED701, the second LED702, the first PD711, and the second PD712 are bonded to the substrate 201 by chip bonding and wire bonding, and thus the first LED701 and the first PD711 used in the specular reflection light method are accurately positioned. Meanwhile, positioning between other elements may be performed with a margin. Therefore, the assembling operation of the optical sensor 7 is easier than that of the related art.

In the process of detecting the color misregistration amount, the first LED701 or the second LED702 and the first PD711 are combined. In other words, in the process of detecting the color misregistration amount, the same element (the first PD711) is used on the light receiving side. Since the position of the light receiving element (first PD711) is fixed, the accuracy of detecting the color misregistration amount is increased as compared with a case where the first pattern image and the second pattern image are detected by different light receiving elements. In the image density detection process, the first LED701 and the first PD711 or the second LED702 and the second PD712 are combined.

Another configuration example of the optical sensor

In the optical sensor 7 described with reference to fig. 2, the first LED701, the second LED702, the first PD711, and the second PD712 are separate components. In this case, there is a fear that the mounting accuracy of each component may be lowered. Fig. 17 is an explanatory diagram of the optical sensor 7 in a case where the mounting accuracy of each component is lowered. When the mounting accuracy of each component is lowered, the optical sensor 7 cannot detect a detection image with the optical axis center point P as a detection position. Therefore, it is preferable to increase the mounting accuracy of the first LED701, the second LED702, the first PD711, and the second PD 712.

Fig. 18 is a schematic diagram of a main part of the optical sensor 14. The optical sensor 14 includes a first LED 721 and a second LED 722 as light emitting elements, and a first PD 731 and a second PD 732 as light receiving elements. The first LED 721, the second LED 722, the first PD 731, and the second PD 732 are formed as semiconductor elements on the same semiconductor substrate 141. In the semiconductor substrate 141, a surface on which the first LED 721, the second LED 722, the first PD 731, and the second PD 732 are formed is referred to as a "processed surface". The optical axis of the irradiation light from the first LED 721 and the second LED 722 is orthogonal to the processed surface of the semiconductor substrate 141. In addition, the optical axis of the reflected light received by the first PD 731 and the second PD 732 is also orthogonal to the processed surface of the semiconductor substrate 141. The semiconductor substrate 141 is fixed on the substrate 201 with an adhesive (e.g., epoxy resin).

The substrate 201 is mounted on the housing 203. The casing 203 has a light guiding path for guiding irradiation light so that light emitted from the first LED 721 and the second LED 722 efficiently irradiates the intermediate transfer belt 5. The housing 203 also has an optical guiding path for guiding the reflected light so that the first PD 731 and the second PD 732 efficiently receive the reflected light from the intermediate transfer belt 5. On a light guiding path for guiding the irradiation light and a light guiding path for guiding the reflection light, a lens group 214 including lenses 214a to 214d is provided.

In other words, the light emitted from the first LED 721 travels in the optical axis direction (single-dot broken line in fig. 18), and illuminates the intermediate transfer belt 5 through the optical guiding path formed in the housing 203 and the lens 214 a. The specular reflection light from the intermediate transfer belt 5 or the detection image travels in the optical axis direction (single-dot dashed line in fig. 18), and reaches the first PD 711.

Light emitted from the second LED 722 travels in the optical axis direction (single-dot broken line in fig. 18), and illuminates the intermediate transfer belt 5 through the light guiding path in the housing 203 and the lens 214 b. The first PD 731 is configured to receive diffuse reflection light of which the intermediate transfer belt 5 is irradiated by the second LED 722. The second PD 732 is configured to receive diffuse reflected light of light emitted from the second LED 722 to irradiate the intermediate transfer belt 5.

The arrangement of the first PD 731 and the second PD 732 is similar to that of the first PD711 and the second PD712 of fig. 2. Thus, the optical sensor 14 can provide effects similar to those of the optical sensor 7 shown in fig. 2. In the optical sensor 14 mentioned above, the elements are formed on the semiconductor substrate 141, and therefore the positional accuracy of each element can be ensured at a high level. In other words, the optical sensor 14 can easily focus the optical axis of each element on the optical axis center point P. Therefore, the detection accuracy of the detected image is further increased than that obtained by the optical sensor 7 directly bonded to the substrate.

Also, in the optical sensor 14 according to at least one embodiment, the light emitter and the light receiver are formed on the semiconductor substrate 141, and thus the distance between elements can be reduced. Therefore, the optical sensor 14 can be reduced in size as compared with an optical sensor including a bullet element (fig. 5). Also, according to the optical sensor 14, the distance between the first LED 721 and the first PD 731 can be reduced, and thus specular reflection light of light emitted to the object to be measured can be detected at a sharper angle than that of an optical sensor including a bullet light emitting element and a bullet light receiving element. Therefore, even when the distance from the optical sensor 14 to the object to be measured is changed, the irradiation area on the object to be measured is hardly changed. When the intermediate transfer belt 5 rotates, the distance from the optical sensor 14 to the detection image tends to vary. According to the optical sensor 14 of at least one embodiment, even when the distance from the optical sensor 14 to the detection image is changed, the irradiation area is hardly changed, and thus the specular reflection light from the detection image can be detected with high accuracy. In addition, the optical sensor 14 may reduce the distance between the first LED 721 and the first PD 731, thus also increasing design flexibility. Therefore, according to the optical sensor 14, the first LED 721, the second LED 722, the first PD 731, and the second PD 732 may be arranged in a positional relationship suitable for detecting specular reflection light and diffuse reflection light from the object to be measured. In particular, in the optical sensor 14 sharing the light emitting element or the light receiving element, the specular reflection light and the diffuse reflection light from the detection image can be detected more accurately than in the optical sensor of the related art including the bullet element.

With the optical sensors 7, 14 in at least one of the embodiments described above, reflected light from a detection image can be detected with high accuracy.

The configuration in which the light emitters and the light receivers of the optical sensors 7, 14 have been described above as being arranged in the order that the first LEDs 701, 721, the first PDs 711, 731, the second PDs 712, 732 and the second LEDs 702, 722. the arrangement of the light emitters and the light receivers is not limited thereto for the optical sensors, it is only necessary that the light receivers are arranged such that the angles Φ and Ψ are at predetermined angles with respect to the direction of specular reflection light of the object to be measured of light emitted by the light emitters and, moreover, it is only necessary that the light receivers are arranged such that the angles α and β are at respective predetermined angles with respect to the normal of the intermediate transfer belt 5 at the irradiation position (optical axis center point P). for example, the first LEDs, the first PDs, the second LEDs and the second PDs may be arranged in the order.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims priority to japanese patent application No.2018-152596, filed on 14/8/2018, which is incorporated herein by reference in its entirety.