JP2005241933A - Test pattern density detecting device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a test pattern density detecting device keeping the accuracy of an irradiation angle high even when a diaphragm on a light emitting side is small and keeping the reading accuracy of a test pattern high even when irradiation area is fluctuated due to manufacture variance in an optical system density detecting device. <P>SOLUTION: The test pattern density detecting device has a light emitting element 1 radiating light to the test pattern formed on a developer carrier, a light receiving element 2 detecting the light reflected by the developer carrier or the test pattern, and a diaphragm 45 restricting emitted light quantity at a position more proximate to the test pattern than the light emitting surface of the light emitting element 1. The diaphragm 45 is formed by fitting a plurality of bodies 40 and 55 on a plane 56 proximate to the test pattern. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the present invention, light from a light emitting element is applied to a test pattern (test developer image) formed on a developer carrier, and the reflected light is incident on a light receiving element. The present invention relates to a test pattern density detecting device that detects the density of the test pattern based on an output, and an image forming apparatus including the test pattern density detecting device.

  Currently, printers as image output terminals are rapidly spreading due to advances in computer network technology. Further, in recent years, with the progress of colorization of output images, there are increasing demands for improving the stability of image quality of color printers and making the color image quality uniform between color printers. In particular, with regard to color reproducibility, a high degree of stability is required that does not depend on changes in the installation environment, changes over time, or machine differences (differences in imaging conditions such as charging voltage and development voltage due to manufacturing variations of high-voltage power supplies). Yes.

  However, since the image reproducibility of an electrophotographic image forming apparatus fluctuates due to a change in the environmental conditions in which the apparatus is placed and deterioration with time of the photosensitive member / developer, the above-mentioned high demands are left as it is. Can't meet.

  Therefore, it is common to use an image density detection device that performs feedback control to keep the image density optimal. This feedback control is performed as follows. A test developer image (hereinafter referred to as a test pattern) is formed on a circulating moving body (developer carrier) such as a photoconductor, an intermediate transfer body, or a transfer conveyance belt, and the density of the test pattern is measured. To do. And the surrounding environment (temperature, humidity), deterioration with time (photoreceptor wear, transferer wear, contamination, toner deterioration), solids variation (charging voltage, development voltage, etc., manufacturing variations of high voltage power supply between devices, etc. The control factor of the patch density is controlled so that the test pattern approaches the target density in consideration of the variation between devices affecting the image density. There has also been proposed a method in which the test pattern is formed on a recording medium and the test pattern density on the recording medium is measured.

  For example, Japanese Patent Laid-Open No. 01-169467 (hereinafter referred to as Patent Document 1) discloses a method of obtaining a desired image density by measuring the density of a test pattern and controlling exposure conditions and development bias conditions. As the test pattern, an unfixed developer image after the developing process or an image on the recording paper after the fixing process is used. The reason why such a test pattern is used is that an image in the same state as the image finally obtained by the user is monitored, so that the image quality including density fluctuation in the transfer process and the fixing process can be evaluated. There are other methods for measuring the density of the test pattern. For example, as disclosed in Japanese Patent Application Laid-Open No. 09-089769 (hereinafter referred to as Patent Document 2), many sensors for optical measurement are used. There are also things. Even when an optical sensor is used, when the object to be measured is various toners having different colors, the reflection characteristics of each color toner (yellow, magenta, cyan, black, etc.) are different. There are few cases where the output represents the toner amount as it is, and some correction is generally performed on the output of the sensor. As described above, the sensor output is corrected by calculation in order to accurately detect even a measurement object having different reflection characteristics. For example, as disclosed in Japanese Patent Laid-Open No. 03-209281 (hereinafter referred to as Patent Document 3), both regular reflection light from a toner image carrier on which a toner image is formed and irregular reflection light irregularly reflected from the toner image are measured. There are known methods for calculating net specularly reflected light. Further, in order to improve the measurement accuracy of such an optical sensor, a configuration in which an optical stop is provided on the light emitting side and the light receiving side as disclosed in Japanese Patent Laid-Open No. 03-045972 (hereinafter referred to as Patent Document 4). Has also been proposed. Furthermore, in order to alleviate the influence of the disturbance factor of the sensor, a configuration strong against the disturbance factor of the sensor as disclosed in Japanese Patent No. 2584136 (hereinafter referred to as Patent Literature 5) is also disclosed.

Japanese Patent Laid-Open No. 01-169467 JP 09-089769 A Japanese Patent Laid-Open No. 03-209281 JP 03-059472 A Japanese Patent No. 2584136 Japanese Patent Laid-Open No. 11-142329

  However, in the image forming apparatus that forms the test pattern as described above in order to keep the image density optimal, the developer, which is a resource of the user, is consumed for the test of the image forming apparatus itself, unlike the original purpose. In addition, it is required to reduce the amount of use as much as possible. For this reason, it is preferable to make the test pattern as small as possible. Further, in order to accurately detect a density even with a small test pattern, a sensor (density detecting device) having a high spatial resolution is required. In order to increase the spatial resolution of the sensor, it is effective to reduce the irradiation area on the light emitting side as disclosed in Japanese Patent Application Laid-Open No. 11-142329 (hereinafter referred to as Patent Document 6). However, if the aperture on the light emission side for reducing the irradiation area is made small, there are cases where the variation in irradiation angle becomes large due to a manufacturing problem. Further, the variation in the spatial resolution due to the variation in the irradiation area is one of the causes of the decrease in the test pattern reading accuracy.

  An object of the present invention is to provide a test pattern density detecting device that has high accuracy of an irradiation angle even when the aperture on the light emitting side is small and has high test pattern reading accuracy even if the irradiation area varies due to manufacturing variations. That is. Another object of the present invention is to provide an image forming apparatus with high color reproducibility.

  In order to achieve the above object, a typical configuration of the present invention includes a pattern forming unit that forms a test pattern on a developer carrier, a light emitting unit that irradiates light to the test pattern, and the developer carrier or A light-receiving unit that detects light reflected by the test pattern; and a diaphragm that restricts the amount of light emitted from the light-emitting unit at a position closer to the test pattern than the light-emitting surface of the light-emitting unit. A plurality of bodies are fitted together in a plane close to the surface.

  According to the present invention, even when the aperture diameter on the light emission side is small, it is possible to suppress variations in the irradiation angle on the light emission side and to prevent the measurement accuracy of the test pattern density detection apparatus from being lowered. Further, even if the irradiation area varies due to manufacturing variations, it is possible to prevent a decrease in the reading accuracy of the test pattern. Furthermore, it is possible to provide a test pattern density detection device that suppresses a decrease in spatial resolution even when the irradiation area varies.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
A test pattern density detector according to a first embodiment of the present invention and an image forming apparatus including the density detector will be described. In the following description, first, a schematic configuration of the image forming apparatus will be described, and then a test pattern density detecting apparatus as an image density detecting apparatus in the image forming apparatus will be described.

{Image forming device}
First, a schematic configuration of the image forming apparatus according to the present embodiment will be described. FIG. 8 is a schematic sectional view showing an example of the image forming apparatus. As shown in FIG. 8, this multi-color image forming apparatus uses an electrophotographic system in the image forming unit, forms a latent image on the photosensitive member by optical writing, and converts this latent image into a toner image (development). Then, the developed toner image is transferred and fixed on a recording material such as paper. To reproduce a normal color image on a recording material, the subtractive three primary colors Y (yellow) toner, M (magenta) toner, and C (cyan) toner, and printing of characters and black portions of images (image formation) A full color is expressed by superimposing a total of four toners of K (black) toner used in (1). A recording material cassette 123 is detachably attached to the lower part of the apparatus main body. After a controller (not shown) receives a print command from the host computer, the recording material P in the recording material cassette 123 is taken out one by one by rotating the feeding roller 121 at a predetermined timing. The fed recording material P is conveyed to the registration roller pair 122 and stops when the leading edge of the recording material is sandwiched between the registration roller pair 122. When image formation preparation is completed and image formation is started, the recording material P is fed to the image forming unit by the registration roller pair 122 at a predetermined timing. The registration roller pair 122 has a function of adjusting the feeding timing of the recording material P and adjusting the position of the recording material front end so that the front end of the recording material is perpendicular to the conveyance direction (skew correction function).

  The image forming apparatus according to the present embodiment includes four image forming stations as image forming units as shown in FIG. In FIG. 8, only the yellow image forming station, which is the first image forming station, is provided with a symbol, but magenta (second image forming station), cyan (with the same configuration as yellow on the downstream side in the recording material conveyance direction) The four image forming stations Y, M, C, and K of the third image forming station) and black (fourth image forming station) are arranged in the above order. The toner image forming method for each color is not particularly limited, and is performed by a known developing method such as two-component development or nonmagnetic one-component development. In this embodiment, an image forming apparatus using a non-magnetic one-component contact developing method will be described as an example.

  The surface of the photosensitive drum 101Y is charged by a charging roller 102Y that receives power from a high voltage power supply (not shown), and an electrostatic latent image is formed on the surface of the photosensitive drum upon receiving the exposure light beam 114Y from the exposure unit 103. The developing roller 105Y of the developing unit 108Y contacts the electrostatic latent image, and the toner 107Y as a developer is developed at a location corresponding to the electrostatic latent image to obtain a toner image. A supply / peeling roller 106Y for supplying or stripping toner to the surface of the developing roller is in contact with the developing roller 105Y with a difference in peripheral speed, and also plays a role of charging the toner on the developing roller. The toner on the developing roller 105Y is rubbed while the layer thickness is regulated by the toner layer thickness regulating blade 113Y, and the toner suitable for development is supplied to the photosensitive drum by being frictionally charged by the rubbing.

  The toner image formed on the photosensitive drum 101Y is transferred to the recording material P by the transfer unit 119Y. An electrostatic adsorption conveyance belt 120 (hereinafter referred to as ETB) is interposed between the photosensitive drum 101Y and the transfer roller 119Y, and the ETB 120 is rotated by the driving roller 130 to adsorb the recording material P to each color image. The recording material is conveyed to the forming station. The tension roller 124 is rotated in accordance with the movement of the ETB 120 while applying pressure in the direction in which the ETB 120 is stretched so that the ETB 120 does not loosen. By transferring the recording material by the ETB 120, the transfer position accuracy is improved and the image deviation between the respective colors is reduced. In order to collect and clean the transfer residual toner remaining without being transferred onto the photosensitive drum, the cleaning unit 110Y is brought into contact with the photosensitive drum 101Y, and the collected toner is stored in the waste toner container 111Y.

  The recording material P to which the toner image has been transferred is separated from the photosensitive drum 101Y, and then conveyed to the next image forming station. Then, magenta, cyan, and black toner images provided by the same image forming method as yellow are sequentially transferred onto the yellow toner image. The recording material onto which the toner images of each color have been transferred is conveyed to a fixing nip portion constituted by a portion where the pressure roller 126 and the heating device 125 are opposed to each other. The toner image is heated and pressed at the fixing nip portion, and the toner melts and comes into close contact with the recording material to form a permanent image. The recording material P on which the color image has been fixed is conveyed to the outside of the image forming apparatus by the discharge roller 127 and is stacked on the upper part of the apparatus so that the user can take it as the final output recording material P.

{Test pattern density detector}
By the way, as the problem of the electrophotographic image forming apparatus, the image density varies depending on the temperature and humidity conditions in which the image forming apparatus is used and the degree of use of each color image forming station. In order to correct this variation, the image density is measured, and the image forming factor is controlled so as to obtain desired characteristics. In order to measure the image density, a test pattern image of each color is formed on the ETB 120 as a developer carrier, and this is read by a density detection sensor 131 as an image density detection means (test pattern density detection device). FIG. 1 is a cross-sectional view for explaining the operation of the density detection sensor 131. A light-emitting element 1 such as an LED and a light-receiving element 2 such as a photodiode are attached to the housing 4. The housing 4 is provided with a tunnel-shaped optical path 9 that regulates and guides the light emitted from the light-emitting element 1, and functions as a diaphragm for limiting the irradiation area to the measurement object. As will be described in detail later, in the concentration detection device according to the present embodiment, the housing 4 includes a plurality of housings, and the plurality of housings are fitted so that a fitting line appears in a plane close to the test pattern. Is formed. In FIG. 1, reference numerals 11 and 12 denote the optical axes of the light emitting element 1 and the light receiving element 2, respectively.

  Similarly, the housing 4 is provided with a tunnel-like optical path 14 for restricting and guiding the light entering the light receiving element 2, and serves as a diaphragm for limiting the incident area of light from the measurement object. The irradiation area on the light emitting side and the sensitive area on the light receiving side on the surface of the measurement object are adjusted to have desired characteristics depending on the distance from each element to the measurement object and the diameter of the stop. The housing 4 also serves as a holding member for the light emitting element 1, the light receiving element 2 and the like as well as the function of restricting the irradiation area on the light emitting side and the sensitive area on the light receiving side as described above. The housing 4 serves to cover the light receiving element 2 so that light does not enter the light receiving element 2 directly from the light emitting element 1 or due to disturbance light, and a material having a very low transmittance with respect to the central emission wavelength of the light emitting element 1 is used. Light irradiated by the light emitting element 1 is incident on the measurement object at an angle θ and is reflected by the measurement object. The light receiving element 2 faces the measurement object at an angle ψ, and detects the reflected light from the measurement object. In order to efficiently measure regular reflection light, it is preferable that the emission angle θ on the light emission side and the incident angle ψ on the light reception side are equal.

  Here, the detection principle of the density patch (test pattern) in the density detection sensor which is this optical sensor will be described. The light beam emitted from the light emitting element 1 is reflected with a reflectance determined according to the refractive index specific to the material and the surface state of the ETB as the developer carrier represented by B in the figure, which is the base of the measurement object, It is detected by the light receiving element 2. When the test pattern T is formed on the developer carrying member B, the base of the portion where the toner is present is hidden, and the amount of reflected light is reduced. Accordingly, the amount of reflected light decreases as the toner amount of the density patch increases, and the density of the density patch is obtained based on this decreased amount. Actually, the amount of reflected light also fluctuates due to the surface state of the base fluctuating depending on the degree of use of the developer carrier (ETB) that is the measurement target surface. After normalization with the amount of reflected light at the time, it is converted into density information. By performing such normalization, sufficient detection accuracy can be ensured even if there is some variation in the light amount of the light emitting element, variation in the size of the irradiation spot, sensitivity variation in the light receiving element, sensor contamination, and the like.

  FIG. 9A is a block diagram for explaining the image density detection operation in the image forming apparatus, and FIG. 9B is a flowchart (sequence diagram) for density detection. When density detection is started (S301), the CPU 202 in the printer engine 201 sets density factors such as a charging voltage 203, a development voltage 204, and an exposure light amount to specific values (S302), and starts printing a test pattern (S303). ). The test pattern is generated by the PC 206 in the case of the host-based printer 205, and is formed by the exposure device 208 through the exposure control device 207 at a predetermined timing controlled by the engine CPU 202. The test pattern may be generated by the controller 209. The formed test pattern is measured by the density detector 210 (S304), and the measurement result is processed by the engine CPU 202. In the measurement, the received light amount signal of the density detection device 210 is A / D converted and then processed by the CPU 202 to calculate a value corresponding to the density (S305). Based on the result, each concentration factor is determined (S306). In some cases, the above-described concentration detection is repeated with a newly set concentration factor to optimize each concentration factor. The setting results of these density factors are stored in the memory 211 in the printer engine 201 and are used for normal image formation or the next density detection. In this way, by feeding back the density detection result to process formation conditions such as high-pressure conditions and laser power, the maximum density of each color is adjusted to the desired value, and by setting the appropriate development settings, unnecessary toner adheres to the white background. This prevents the occurrence of defects called “fogging”. In addition, by performing the above-described density control, the color balance of each color is kept constant, and at the same time, it is significant to prevent scattering of overlaid characters and fixing failure due to excessive toner loading.

  The test pattern (density patch) uses toner, which is a user's resource, for automatic adjustment of the image forming apparatus. The amount of toner that can be used by the user without printing on the recording material is reduced. Therefore, the amount used is preferably as small as possible. For this reason, it is preferable to make the test pattern as small as possible. Also, even if the test pattern is small, it is necessary to increase the spatial resolution of the sensor in order for the sensor to respond and read sufficiently.

  Patent Document 6 described above discloses a technique for reducing the irradiation spot diameter by reducing the aperture on the light emission side and improving the spatial resolution of the sensor. The diaphragm on the light emission side is often circular, and a mold technique is used when mass-producing sensors in large quantities. In this case, the housing that holds the light emitting element and the light receiving element and is integrally provided with the diaphragm is often molded using a mold. The mold used to reduce the aperture diameter on the light emission side is also reduced, which may reduce the angular accuracy of the irradiated light.

  FIG. 11 is a perspective view showing a mold for molding a narrow-diameter diaphragm. Although only the light emitting side is shown, regardless of the light emitting side or the light receiving side, when a plurality of optical paths are formed, a plurality of similar structures (molds) may be prepared. Reference numeral 15 in FIG. 11A denotes a cylindrical slide mold (hereinafter referred to as a cylindrical mold) in which the vicinity of the tip for forming the light path on the light emission side is movable in the direction of the arrow in the figure. The end of the cylindrical mold 15 is cut obliquely, and comes into contact with the other mold 16 to determine the angle of the cylindrical mold 15 with respect to the mold 16, and the above-described emission angle (see the emission angle θ in FIG. 1). Can be obtained. The mold 16 is a mold that forms a surface of the housing that faces the object to be measured. When molding the housing, which is a molded product, the cylindrical mold 15 is slid before the resin is poured, and is fixed at a position where it abuts the mold 16. Thereafter, the resin is poured, and when the resin is hardened, the cylindrical mold 15 is slid out in a direction away from the mold 16 and the molded product (housing) is taken out of the mold 16. In this molded product, an optical path on the light emission side is formed at the position where the cylindrical mold 15 was present. Therefore, if the cylindrical mold 15 and the mold 16 do not adhere to each other, the resin flows into the gap and the light path on the light emitting side is blocked. FIG. 11B is a side view for explaining a state in which the cylindrical mold 15 and the mold 16 are brought into close contact with each other. The cylindrical mold 15 is slid in the direction of the arrow 17 and comes into contact with the mold 16, but is not always at the same contact position. The tip may be bent and deviate from the position 19. In particular, in order to obtain a narrow diaphragm having a diameter of 1 mm or less, it is necessary to make the cylindrical mold 15 thin, and the cylindrical mold 15 is easily bent. When the positional deviation due to the bending occurs, there may be a molded product in which the angle of the optical path varies. Further, the tip of the cylindrical mold 15 is easily deformed because of its low strength, and the pressure applied to the tip is increased, so that the tip is easily worn. If the tip of the cylindrical mold 15 is worn, burrs are generated in the molded product, which is not preferable.

  FIG. 12 is a diagram for explaining detection errors when the incident angle on the irradiation side (the emission angle θ on the light emission side) fluctuates. The test pattern T on the base B of the measurement object is made by depositing toner and has a height of about several μm to 500 μm. The test pattern uses not only a so-called solid image with a printing rate of 100% but also a halftone image. The halftone test pattern is vulnerable to various disturbances such as uneven driving speed and uneven toner charge, so it is rare to use a pattern with a uniform toner height. It is preferable to use an area gradation test pattern that can be regarded as a key. As described above, in the area gradation test pattern in which the non-printing portion and the printing portion are distributed, the amount of toner in the test pattern is different between the case where the incidence and reflection are indicated by the arrow 20 and the case where the incidence and reflection are shallower than that. Even if they are the same, the amount of reflection from the base B varies depending on the height of the test pattern. For this reason, if the irradiation angle varies, the amount of reflected light varies, which causes an error in the detection result. This error is a phenomenon peculiar to the angle fluctuation of the optical axis on the light emitting side.

  FIG. 13 is a diagram illustrating fluctuations in the output of the sensor when the irradiation angle varies. The horizontal axis represents the toner amount per unit area of the test pattern, and the vertical axis represents the sensor output normalized by the base output. When the angle of the optical axis is ideal, the characteristic of the sensor is as shown by a curve 22. When the emission angle θ (see incident angle θ in FIG. 1) increases due to the above-described problem, the characteristic of the sensor is as shown by a curve 23. become. That is, when the diaphragm on the light emission side is formed by the above-described cylindrical mold and the irradiation angle varies depending on the housing, it is erroneously detected that the amount of toner is larger than the actual amount in the high density test pattern in the housing where the irradiation angle is changed.

  Therefore, as shown in FIGS. 1 and 8, the concentration detection sensor 131 as the concentration detection apparatus according to the present embodiment is a light emitting element that emits light to a test pattern formed on the developer carrier B (ETB 120 in FIG. 8). (Light emitting means) 1, light receiving element (light receiving means) 2 for detecting light reflected by the developer carrier B or the test pattern, and the light emission at a position closer to the test pattern than the light emitting surface of the light emitting element 1 And an optical path 9 that functions as a diaphragm for limiting the amount of light emitted from the element 1, and the diaphragm 9 is formed by fitting a plurality of bodies in a plane close to the test pattern. In this embodiment, the image forming stations Y, M, C, and K shown in FIG. 8 are used as pattern forming means for forming a test pattern on the developer carrier B. This will be described more specifically with reference to FIG.

  FIG. 2A shows a perspective view of the sensor as the concentration detection apparatus according to the present embodiment as viewed from the front side. The concentration detection sensor 131 according to the present embodiment includes a plurality of housings 40 and 55 that are fitted on the surface 56 including the exit hole 45 and the entrance hole 46 that are close to the test pattern, and the exit side, A stop on each incident side (optical paths 9 and 14 shown in FIG. 1) is formed. FIG. 2B shows a perspective view of the housing 40 side when the housing 55 is removed. One housing 40 is provided with a U-shaped groove portion that forms an emission hole 45 (optical path 9 shown in FIG. 1) on the light emission side. Similarly, a U-shaped groove portion that forms an incident hole 46 (light path 14 shown in FIG. 1) on the light receiving side is also provided. The light emitting element 1 and the light receiving element 2 are attached to and held in the housing 40. The other housing 55 has the shape of a mirror image of the housing 40. By using the housing 55 as a lid of the housing 40, the U-shaped groove portions of the housings 40 and 55 are vertically aligned so that both the light emitting side and the light receiving side have a cylindrical optical path. 45, 46 are formed.

  As described above, in this embodiment, the optical paths 45 and 46 are formed into U-shaped groove portions that are divided into upper and lower parts, so that the housing 40 and the housing 55 are respectively cylindrical slide types (the conventional cylindrical mold 15 shown in FIG. 11). ), And can be molded with a vertical split. As described above, according to the present embodiment, the diaphragms (optical paths 45 and 46) are formed by fitting the two housings 40 and 55 within the surface 56 close to the test pattern. It is no longer necessary to move a weak slide type (cylindrical mold), the angle variation of the optical axis due to the use of the slide type can be reduced, and detection errors in high density test patterns due to housing manufacturing tolerances can be reduced. Can be reduced. Therefore, according to this embodiment, even if the aperture diameter on the light emission side is small, variations in the irradiation angle can be suppressed and the measurement accuracy of the sensor can be prevented from decreasing. Further, by providing the image forming apparatus with the density detection sensor, an image forming apparatus with high color reproducibility can be provided.

[Second Embodiment]
A second embodiment of the present invention will be described. FIG. 3 is a perspective view for explaining a test pattern density detecting apparatus according to the second embodiment of the present invention. Similar to the first embodiment described above, the sensor 131 as the concentration detection device according to the present embodiment has a configuration in which the upper and lower housings 40 and 55, which are a plurality of bodies, are fitted to each other. There are two upper and lower divided surfaces so as to divide the hole 46 vertically, and a dividing line (fitting line) 33 formed by the divided surface is visible on the front surface of the sensor facing the ETB 120 (the surface where the test pattern is close). The ETB 120 is moved at a speed of 94 mm / s in the direction of the arrow 39 by the driving means. Test patterns 35, 36, and 37 having a size of 10 mm in the width direction and 6 mm in the height direction are formed on the ETB 120 by image forming means (the image forming station shown in FIG. 1). It is attached to the surface facing 131, and crosses the irradiation position of the sensor 131 as the ETB 120 moves. An arrow 34 schematically represents the ray trajectory of the irradiation light and reflected light of the sensor 131. The front surface of the sensor 131 is arranged in parallel with the ETB 120, the distance from the sensor 131 surface to the ETB 120 is about 6 mm, the emission angle θ on the light emission side is 30 °, and the aperture diameter is about 1 mm. The incident angle ψ on the light receiving side was 30 °, and the aperture diameter was about 2 mm. As the light emitting element, an LED having a diameter of about 3 mm and a center emission wavelength of 900 nm was used. As the light receiving element, a phototransistor having a diameter of about 3 mm and a peak sensitivity wavelength of 800 nm was used. When the irradiation area on the ETB 120 was measured with a camera having sensitivity in the infrared area, the diameter (irradiation spot diameter) was approximately 3 mm. The distance from the chip surface (light emitting surface) of the light emitting element to the ETB surface was about 12 mm.

  In the second embodiment, the dividing line 33 of the sensor 131 is arranged so as to be substantially perpendicular to the moving direction of the test pattern (the direction of the arrow 39). With this arrangement, the test pattern can be measured with high accuracy even if the upper and lower housings 40 and 55 constituting the optical paths 45 and 46 of the sensor 131 are misfit.

  FIG. 5 shows the irradiation spot shape on the ETB by the sensor. The direction of the arrow in the figure is the moving direction of the test pattern. As shown in FIG. 5A, when the upper and lower housings are fitted with no gap when viewed from the front of the sensor, the irradiation spot shape on the ETB is substantially circular (exit angle) as shown in FIG. When θ is large, it is close to an ellipse). However, there may be a gap in the fitting of the upper and lower housings due to part tolerances and assembly errors of the upper and lower housings. When a gap is generated in the upper and lower housings, a gap is generated in the sensor dividing line as viewed from the front of the sensor as shown in FIG. Since light is emitted also from this gap, a Saturn-like irradiation spot shape is formed on the ETB as shown in FIG. By the way, the height of the spatial resolution of the sensor is determined by the size of the irradiation spot. The smaller the irradiation spot, the higher the spatial resolution of the sensor. Considering that the test pattern crosses the irradiation spot, the amount of received light starts to change when the edge of the test pattern enters the irradiation spot, and the output continues to change until the edge has crossed the irradiation spot. For this reason, the smaller the irradiation spot, the smaller the moving distance of the test pattern until the change is saturated, and the higher the response of the sensor, that is, the spatial resolution. In the present embodiment, as shown in FIGS. 5C and 5D, the direction in which the space is partially increased due to the formation of a gap in the housing, that is, the growth direction of the Saturn spot-shaped ring is substantially the moving direction of the test pattern. By setting the vertical direction, an increase in irradiation length in the moving direction of the test pattern is suppressed. Although the sensor output change profile changes by suppressing the increase in irradiation length in the test pattern movement direction, it is possible to secure a sufficient area where the sensor output is saturated during test pattern measurement. There is an effect that the accuracy can be maintained.

  As described above, in this embodiment, as shown in FIG. 3, the fitting lines 33 of the two housings 40 and 55 in the plane close to the test pattern of the diaphragm (optical path 45) indicate the moving direction of the test pattern ( Since it is provided substantially perpendicular to the direction of the arrow 39), it is possible to prevent a decrease in the reading accuracy of the test pattern even if the irradiation area varies due to manufacturing variations. The effect of the present embodiment will be further clarified by comparison with the following comparative example.

  FIG. 4 is a perspective view for explaining a comparative example for clarifying the effect of the present invention. Components having the same functions as those already described are given the same reference numerals and description thereof is omitted. In the comparative example shown in FIG. 4, the sensor 131 is configured in the same manner as in the above-described embodiment. The ETB 120 is moved by the driving means in the direction of the arrow 39 at a speed of 94 mm / s. The front surface of the sensor 131 is arranged in parallel with the ETB 120, the distance from the sensor 131 surface to the ETB 120 is about 6 mm, the emission angle θ on the light emission side is 30 °, and the aperture diameter is about 1 mm. The incident angle ψ on the light receiving side was 30 °, and the aperture diameter was about 2 mm. As the light emitting element, an LED having a diameter of about 3 mm and a center emission wavelength of 900 nm was used. As the light receiving element, a phototransistor having a diameter of about 3 mm and a peak sensitivity wavelength of 800 nm was used. When the irradiation area on the ETB 120 was measured with a camera having sensitivity in the infrared area, the diameter (irradiation spot diameter) was approximately 3 mm. The distance from the chip surface (light emitting surface) of the light emitting element to the ETB surface was about 12 mm.

  In this comparative example, the dividing line 33 of the sensor 131 is arranged substantially parallel to the moving direction of the test pattern (the direction of the arrow 39). FIGS. 5E and 5F show the irradiation spot shapes on the ETB in the case where a gap is generated in the divided portions of the housings 40 and 55 of the sensor 131.

  Also in the comparative examples shown in FIGS. 5 (e) and 5 (f), the irradiation spot shape becomes Saturn due to the irradiation light leaking from the gap between the divided portions, and the growth direction of the portion corresponding to the ring of Saturn is the same direction as the test pattern moving direction. become. As a result, the edge of the test pattern first enters the ring portion on one side of the irradiation spot shape shown in FIG. 5 (f), and the distance until the amount of received light begins to change and passes through the opposite side of the ring becomes longer. The time until the output becomes stable increases, and the detection accuracy is lowered as compared with the embodiment described above.

  FIG. 6 shows the transition of the sensor output when the M (magenta) test pattern is measured. The sensor output is obtained by performing amplification after converting the photocurrent generated by the light incident on the light receiving element into current and voltage, and changes in proportion to the amount of received light. The light entering the light receiving element is the sum of specularly reflected light reflected by the ETB and diffusely reflected light diffusely reflected by the test pattern. When there is no test pattern, the sensor output becomes a large value because the reflected light amount of the ground is large. When the edge of the test pattern enters the irradiation spot, the irregular reflection of the test pattern starts to increase, and when the test pattern further advances, the regular reflection light rapidly decreases. When the test pattern reaches the rear end of the irradiation spot, the decrease in specular reflection light is saturated, but the irregular reflection light continues to rise until the edge of the test pattern passes through the irradiation spot. When the trailing edge of the test pattern passes, the sensor output changes in the reverse process. As described above, the timing of the change is different between the regular reflection light and the irregular reflection light, and the spatial resolution of the sensor is regulated mainly by the influence of the irregular reflection light having a slow change rate.

  In the comparative example, when there is a gap in the fitting part (divided part), the irradiation spot becomes larger in the direction of movement of the test pattern, so the increase in the diffuse reflection light from the test pattern starts quickly, and the test pattern enters the entire area within the irradiation spot. Since it takes time, it can be seen that the time during which the output is stable is short. In the case where the sensor output is sampled at a point marked with Δ and the average value is calculated as a value for image density control, in the comparative example, as in the example (when the dividing line is substantially perpendicular to the test pattern moving direction) Since the output is not saturated at this point, measurement is performed even at a point in the middle of saturation, and an error from the original value occurs. That is, the spatial resolution of the sensor is low, and it is not preferable because the test pattern length needs to be increased in order to prevent this.

  On the other hand, in the case of the embodiment, the absolute value of the sensor output changes because the irradiation area becomes large. However, since the irradiation spot length in the test pattern moving direction does not change greatly, the spatial resolution of the sensor is maintained. Further, even if the absolute value changes, it changes almost linearly in the portion where the output such as the ETB which is the base or the inside of the test pattern is saturated. As described above, since the sensor output is normalized by the reflected light from the ETB which is the base, the change in the absolute value does not affect the density calculation result. Sampling at the points marked with ○ in the figure at the same timing as in the comparative example to obtain the average value of the sensor output is almost the same as when there is no gap because the measurement is almost in the saturation region. Can be maintained.

  In addition, the sensor according to the second embodiment is configured to obtain the same effect as when there is no gap in the divided portion even when a gap is generated in the divided portion of the sensor. Even if the fitting line (partition line) is substantially parallel to the moving direction of the test pattern, it goes without saying that the same effect as in the above-described embodiment can be obtained if there is no gap in the sensor part.

[Third Embodiment]
A third embodiment of the present invention will be described. FIG. 7 is a perspective view for explaining a test pattern density detecting apparatus according to the third embodiment of the present invention. As shown in FIG. 7, the sensor 131 as the concentration detection device according to the present embodiment has a configuration formed by fitting two upper and lower housings 54 having a plurality of emission holes 52 on the light emitting side, and similarly receives light. The side entrance hole 51 is formed by fitting a plurality of upper and lower housings 53, and a housing fitting line 33 of each optical path is provided on the front surface of the sensor (surface close to the test pattern) facing the ETB 120. I can see it. The ETB 120 is moved by the driving means in the direction of the arrow 39 at a speed of 94 mm / s. The front surface of the sensor 131 is arranged in parallel with the ETB 120, the distance from the sensor 131 surface to the ETB 120 is about 6 mm, the emission angle θ on the light emission side is 30 °, and the aperture diameter is about 1 mm. The incident angle ψ on the light receiving side was 30 °, and the aperture diameter was about 2 mm. As the light emitting element, an LED having a diameter of about 3 mm and a center emission wavelength of 900 nm was used. As the light receiving element, a phototransistor having a diameter of about 3 mm and a peak sensitivity wavelength of 800 nm was used. When the irradiation area on the ETB 120 was measured with a camera having sensitivity in the infrared area, the diameter (irradiation spot diameter) was approximately 3 mm. The distance from the chip surface (light emitting surface) of the light emitting element to the ETB surface was about 12 mm.

  In the sensor 131 according to the present embodiment, the exit hole 52 and the entrance hole 51 of the sensor are arranged side by side in the test pattern movement direction (arrow 39 direction), but a diaphragm (emission hole 52) provided in the light emitting element on the light emitting side. The dividing line 33 of the housing 54 that forms a line is arranged in a direction substantially perpendicular to the moving direction of the test pattern. With this configuration, sufficient measurement accuracy can be maintained even when the exit hole 52 and the entrance hole 51 of the sensor 131 are aligned in the moving direction of the test pattern.

  In the present embodiment, since the incident holes 51 are not arranged on the dividing line 33 of the upper and lower housings 54 that form the emission holes 52, it is necessary to separately prepare a housing 53 that forms the incident holes 51. The response characteristics of the sensor are mainly influenced by the shape of the irradiation spot on the light emitting side, and are not greatly affected by the shape on the incident side. For this reason, the housing on the incident side may be an integrally molded product using a normal slide mold (the conventional cylindrical mold 15 shown in FIG. 11). Even if a housing with a dividing surface is used as the incident side housing, the direction is not particularly limited, but when the incident hole 51 is in the dividing surface, the dividing line is provided substantially perpendicular to the moving direction of the test pattern. The configuration is more preferable. The decrease in sensor spatial resolution when a gap is formed at the fitting portion of the housing is caused by the relationship between the direction of the gap on the output side and the moving direction of the patch, and is less affected by the gap on the light receiving side. For this reason, the light on the emission side is obtained by adopting the configuration of this embodiment (that is, separating the light emitting side housing and the light receiving side housing so that the gap that may occur in the light emitting side housing is made substantially perpendicular to the patch moving direction). Even if there is a deviation between the two housings that form the optical path on the emission side, regardless of the direction of the surface formed by the axis and the optical axis of the specularly reflected light beam (that is, regardless of the direction in which the light receiving side is arranged) As with the configuration, it is possible to prevent a reduction in the spatial resolution of the sensor. In addition, since the degree of freedom of arrangement on the light receiving side increases, the degree of freedom in device design increases.

[Other Embodiments]
In the above-described embodiment, the case where an LED having a diameter of 3 mm is used as the light-emitting element is illustrated. However, the present invention is not limited to this. For example, the smaller one is preferable if a necessary light amount can be obtained. Further, the light emitting element is not limited to an LED having a hemispherical tip having a lens property and directivity, and a chip-shaped LED may be used. In the case of a chip-like LED as the light emitting element, the effect of the present invention is further obtained because the portion of the Saturn-like spot-shaped ring formed when there is little directivity and there is a gap in the housing becomes large. However, in the case of a chip-shaped LED, since there is no directivity, the amount of light that can pass through the aperture is small, and the amount of light that can be received by the light receiving element is small relative to the amount of light emitted. From the viewpoint of light receiving efficiency, it is preferable to use the LED as a light emitting element using a light-emitting LED.

  FIG. 10 is a cross-sectional view illustrating dimensions that affect the optical characteristics of the housing. When an LED having directivity is used as a light emitting element, the diameter D1 of the LED may be considered as the size of the light emitting surface. When the semiconductor chip contained is considered as the position of the light emitting source, from the chip position to the developer carrier. When the distance to the B surface is L1, the distance of the diaphragm surface farthest from the developer carrier B is L2, the diaphragm diameter is D2, and the irradiation spot diameter on the developer carrier B is D3, D3≈ (L2 / L1 × D1 + D2) / (1−L2 / L1). In order to reduce the size of the test pattern and reduce toner consumption, the irradiation spot diameter D3 is preferably 10 mm or less, and more preferably 5 mm or less. The relationship between the distances L1 and L2 is a relationship satisfying 0 <L2 / L1 <1, and it is preferable to reduce the irradiation spot diameter D3 within this range. In order to increase the amount of light, a LED having a large chip area and a large aperture D1 is generally advantageous. However, the irradiation spot diameter D3 is also increased, and the spatial resolution is inferior. For this purpose, the light emitting element diameter D1 is preferably small, and as a result of the examination, the light emitting element diameter D1 is also preferably 10 mm or less, and more preferably 5 mm or less. The ratio L2 / L1 of the distances L1 and L2 is preferably set to 0.8 or less because the aperture effect is suddenly reduced as the distance L1 approaches 1, and the irradiation spot diameter D3 increases. Further, if the ratio L2 / L1 is made small, the sensor surface relatively approaches the ETB surface (distance L2 becomes short) when the LED position, that is, the distance L1, is not changed, which is not preferable. If the position of the sensor surface, that is, the distance L2 is not changed, the LED is relatively away from the ETB surface (distance L1 becomes longer), and the amount of light decreases, which is not preferable. From these, the distance ratio L2 / L1 is preferably 0.1 or more, and if the aperture effect is too great, the variation in the irradiation spot shape becomes too large when there is a gap in the housing, so it is 0.2 or more. It is more preferable. With this configuration, even if there is a variation in irradiation area due to manufacturing variations, sufficient spatial resolution can be ensured and a decrease in test pattern reading accuracy can be prevented.

  In the embodiment described above, the case where the background of the measurement object of the sensor is an ETB is exemplified. However, the background is not limited to the ETB, and a test pattern is carried during density control, such as an intermediate transfer member, a photosensitive member, and a recording material. Any medium can be used. In the above-described embodiment, the case where the measurement target is a substantially flat surface is exemplified. However, for example, when the measurement target is a cylindrical photosensitive drum or a bent portion of a stretched transfer belt, the present invention is more preferably used. be able to. When measuring a curved surface, specularly reflected light incident on the light receiving element is scattered on the curved surface, making it difficult to enter the light receiving side, and the diffusely reflected light that was originally scattered light is relatively increased compared to the amount of specularly reflected light. To do. For this reason, normalization is performed with the amount of specularly reflected light from the ground with a relatively small output, so that the influence of irregularly reflected light on the correction result increases, and it becomes necessary to perform measurement in a stable region where the change of irregularly reflected light is saturated. When a curved surface is a measurement target in the configuration of the second and third embodiments described above, sufficient spatial resolution is ensured because the change in reflected light is saturated and measurement can be performed in a stable region even when the influence of the amount of irregularly reflected light is large. In addition, it is possible to prevent a decrease in the reading accuracy of the test pattern, and the effect of the present invention becomes remarkable and can be used more suitably.

  In the above-described embodiment, the test pattern density detection apparatus is exemplified for one sensor having one light emitting element and one sensor having a light receiving element. However, the diaphragm of at least one light emitting element only needs to have the configuration of the present invention. Needless to say, the number of light emitting elements, the number of light receiving elements, and the number of apertures may be arbitrary. In the case where a plurality of light emitting elements are included, it is more preferable that all the light emitting elements have the structure of the present invention.

  Further, in the above-described embodiment, the case where the fitted dividing line of the housing is substantially perpendicular to the test pattern moving direction is exemplified, but the Saturn spot-shaped ring portion when the housing has a gap is the central circular portion. Any range that does not protrude in the moving direction may be used. Therefore, it is particularly preferable that the angle of the dividing line with respect to the test pattern moving direction is exactly 90 °, but it may be in the range of 60 ° to 120 °, and more preferably in the range of 70 ° to 110 °.

  In the embodiment described above, an image forming apparatus capable of forming a multicolor image having a plurality of image forming stations having different colors is illustrated as the image forming apparatus. However, it is possible to form a monochrome image having a single color image forming section. The present invention is effective even for a simple image forming apparatus. Further, the printer is exemplified as the image forming apparatus. However, the present invention is not limited to this. For example, other image forming apparatuses such as a copying machine and a facsimile machine, or a multifunction machine combining these functions, etc. An image that uses another image forming apparatus or an intermediate transfer member, sequentially transfers the toner images of the respective colors onto the intermediate transfer member, and transfers the toner images carried on the intermediate transfer member onto a recording material in a batch. A similar effect can be obtained by applying the present invention to the image forming apparatus.

It is sectional drawing of the sensor used for the density | concentration detection apparatus of 1st Embodiment of this invention. It is a perspective view of the sensor used for the density | concentration detection apparatus of 1st Embodiment of this invention. It is a perspective view explaining the density | concentration detection apparatus of 2nd Embodiment of this invention. It is a perspective view explaining the density | concentration detection apparatus of the comparative example of this invention. It is a schematic diagram explaining 2nd Embodiment and a comparative example of this invention. It is a figure explaining the characteristic of 2nd Embodiment of this invention and a comparative example. It is a perspective view explaining the density | concentration detection apparatus of 3rd Embodiment of this invention. 1 is a cross-sectional view illustrating an image forming apparatus of the present invention. 1 is a block diagram and a sequence diagram illustrating an image forming apparatus of the present invention. It is a figure explaining the sensor used for the density | concentration detection apparatus of this invention. It is a perspective view explaining the sensor used for the conventional density | concentration detection apparatus. It is a figure explaining the sensor used for the conventional density | concentration detection apparatus. It is a figure explaining the characteristic of the sensor used for the conventional density | concentration detection apparatus.

Explanation of symbols

T, 35, 36, 37 ... Test pattern B, 120 ... Electrostatic adsorption transport belt (developer carrier)
1 ... Light emitting element (light emitting means)
2. Light receiving element (light receiving means)
9, 14 ... Optical path (aperture)
11, 12 ... Optical axis 33 ... Dividing line (fitting line)
40, 55 ... housing 45, 46 ... optical path (aperture)
51, 52 ... Optical path (aperture)
53, 54 ... housing 56 ... surface close to the test pattern

Claims (5)

A light emitting means for irradiating the test pattern formed on the developer carrier with light;
A light receiving means for detecting light reflected by the developer carrier or the test pattern;
A diaphragm for limiting the amount of light emitted from the light emitting means at a position closer to the test pattern than the light emitting surface of the light emitting means,
2. The test pattern density detecting apparatus according to claim 1, wherein the diaphragm is formed by fitting a plurality of bodies in a plane close to the test pattern. The test pattern density detection apparatus according to claim 1, wherein a plurality of fitting lines in a plane close to the test pattern of the diaphragm are provided substantially perpendicular to a moving direction of the test pattern. The distance in the light emitting optical axis direction from the light emitting position of the light emitting means to the developer carrying member is L1, and the distance in the light emitting optical axis direction from the surface close to the test pattern of the diaphragm to the developer carrying member is L2. 3. The test pattern density detection apparatus according to claim 1, wherein 0.1 <L2 / L1 <0.8. The test pattern according to claim 1, wherein the light emitting unit irradiates a bent portion of the developer carrying member, and the light receiving unit detects reflected light from the bent portion. Concentration detector. 5. An image forming apparatus for forming an image with a developer on a recording material in accordance with an image signal, comprising the test pattern density detecting device according to claim 1. .

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