JP2010134190A - Image detection device and multicolor image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image detection device capable of easily and accurately detecting speed variation of a moving medium in an image forming apparatus, and to provide a multicolor image forming apparatus having the image detection device and achieving high image quality. <P>SOLUTION: The image detection device 100 is configured such that th light emitted from a light source 51 is radiated to the moving medium 53 on which an image pattern is formed, and reflected light from the moving medium is imaged on a one-dimensional or two-dimensional area sensor 56 through an imaging lens 54. The image detection device 100 includes an image signal acquisition means for acquiring one-dimensional or two-dimensional image signals different temporally as the moving medium moves, and performs cross-correlation operation between the acquired image signals different temporally and obtains shift of a position where a correlation peak in the cross-correlation operation is found, thereby detecting the moving speed of the moving medium, and also detecting shift of an image pattern formed on the moving medium from the acquired image signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention detects the speed of a moving medium such as an intermediate transfer belt or a recording medium conveyed by a conveying belt, and detects an image pattern positional deviation or image density formed on the moving medium. The present invention relates to a detection apparatus, a copier equipped with the image detection apparatus, a printer, a facsimile machine, a plotter, and a multicolor image forming apparatus such as a multi-function machine equipped with at least one of them.

In order to meet the demand for higher speed in recent color image forming apparatuses, a so-called tandem system in which four photoconductors (image carriers) corresponding to toners of four colors (black, cyan, magenta, yellow) are arranged in parallel. Is becoming mainstream.
In the tandem method, each color toner image developed on each photoconductor needs to be finally superimposed on a recording medium such as paper (standard paper, postcard, cardboard, continuous paper, OHP sheet, etc.). As a superimposing method, a direct transfer method that directly superimposes on a recording medium, and an intermediate transfer belt method that superimposes each color toner image on an intermediate transfer belt using an intermediate transfer belt, and transfers the images onto a recording medium all at once. There are two methods.
If the transfer belt for feeding a recording medium such as paper is not driven in the direct transfer method and the intermediate transfer belt is driven with high accuracy in the intermediate transfer belt method, color misregistration occurs.
In order to drive the intermediate transfer belt with high accuracy, for example, as described in Patent Document 1, a mark is directly formed on the belt, and the speed fluctuation of the belt is detected by reading the mark. A method for realizing high-precision driving by feeding back to the above is known.
Patent Document 2 discloses an embodiment in which high-precision paper conveyance is performed by detecting laser speckle from an observation object with a two-dimensional image sensor and performing drive control.

On the other hand, an image formed by such an image forming apparatus is a “toner image”. As is well known, in order to obtain a good image, the amount of toner used for developing an electrostatic latent image Must be appropriate. The amount of toner supplied to the developing unit where the electrostatic latent image is developed is referred to as “toner density”. When the toner density is too low, a sufficient amount of toner is not supplied to the electrostatic latent image, and the resulting toner image is an image with insufficient image density.
When the toner density is too high, the image density distribution of the toner image is biased toward the “high density side”, and the toner image is difficult to see. Thus, in order to form an appropriate toner image, the toner density must be in an appropriate range.

In order to control the toner density within an appropriate range, conventionally, a method of forming a toner pattern for detecting toner density and irradiating it with detection light to detect a change in reflected light has been widely used.
An optical device that irradiates a toner pattern with detection light and receives reflected light is called a “reflective optical sensor”. Various reflective optical sensors have been proposed for a long time (for example, Patent Documents 3 to 6).
These conventionally known reflection-type optical sensors are composed of 1 to 3 light emitting units (LEDs) and 1 to 2 light receiving units (photodiodes or phototransistors) for receiving reflected light. .

JP 2008-65743 A JP 2003-266828 A JP-A 64-35466 JP 2004-21164 A JP 2002-72612 A Japanese Patent No. 4154272

However, in the prior art described in Patent Document 1, it is very time-consuming to directly form a mark on the intermediate transfer belt, so that the mass productivity is poor, which causes a large cost increase. Further, in Patent Document 1, there is no disclosure of a method for detecting image density at the same time as detecting belt speed fluctuation.
In Patent Document 2, there is no disclosure of a method for detecting the image density at the same time as detecting the belt speed fluctuation.
In Patent Documents 3 to 6, there is no disclosure of a method for detecting the image density and simultaneously detecting the belt speed fluctuation.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image detection apparatus that can easily and accurately detect a speed variation of a moving medium in an image forming apparatus.
Here, the moving medium refers to a moving member that carries an image among moving members such as an intermediate transfer belt, a conveyance belt, or a recording medium such as paper. Although the transport belt is not a moving member that directly carries an image, the speed fluctuation of a recording medium such as paper can be grasped by detecting the speed of the transport belt that transports the paper.
Further, according to the present invention, it is possible to obtain a high-quality multicolor image with reduced color misregistration by correcting the speed fluctuation of the moving member using the speed fluctuation result of the moving member detected by the image detection device. Further, the image position shift and / or image density of each color image pattern formed on the moving member is also detected by using the image detecting device, and in addition to correction by speed detection of the moving member, in the formed actual image An object of the present invention is to provide a multicolor image forming apparatus capable of correcting the positional deviation of each color image and / or detecting and correcting the gradation of the formed image.

  To achieve the above object, according to the first aspect of the present invention, the moving medium on which an image pattern is formed is irradiated with light emitted from a light source that emits coherent light, and the reflected light from the moving medium is imaged. An image signal acquisition unit configured to form an image on a one-dimensional or two-dimensional light receiving unit via a lens, and acquiring a one-dimensional or two-dimensional image signal that is temporally different with the movement of the moving medium; The cross-correlation calculation between temporally different image signals acquired by the image signal acquisition means is performed, and the moving speed of the moving medium is detected by obtaining the shift of the position where the correlation peak of the cross-correlation calculation occurs. A positional deviation of an image pattern formed on the moving medium is detected from a signal.

According to a second aspect of the present invention, in the image detecting device according to the first aspect, the image density of the image pattern formed on the moving medium is further detected from the image signal acquired by the image signal acquiring means. To do.
According to a third aspect of the present invention, in the image detection device according to the second aspect, the positional deviation and the image density of the image pattern formed on the moving medium are detected using a correlation peak value in the cross-correlation calculation. It is characterized by.
According to a fourth aspect of the present invention, in the image detecting apparatus according to the second aspect, the positional deviation and the image density of the image pattern formed on the moving medium are one-dimensionally obtained at each time obtained by the image signal obtaining means or Detection is performed using a smoothed image signal obtained by smoothing a two-dimensional image signal.

  According to a fifth aspect of the present invention, there are provided a plurality of image carriers, an optical scanning device that optically scans the plurality of image carriers with a beam spot to form an electrostatic latent image, and the optical scanning device. A developing unit that visualizes the electrostatic latent image formed on the image carrier in each color; an intermediate transfer belt movably provided facing the plurality of image carriers; and first and second Each of the color toner images visualized on the plurality of image carriers is transferred to the intermediate transfer belt by the first transfer unit, and the intermediate transfer belt is provided on the intermediate transfer belt. The color toner images are superimposed on each other, the superimposed color toner images are transferred to a sheet-like recording medium by the second transfer unit, and the color toner images transferred to the recording medium are fixed by the fixing unit. Multicolor image form to form multicolor or color image In the apparatus, the image detection device according to any one of claims 1 to 4 is provided to detect a speed of the intermediate transfer belt, a positional deviation of each color toner image on the intermediate transfer belt, or an image density. It is characterized by.

  According to a sixth aspect of the present invention, there are provided a plurality of image carriers, an optical scanning device that optically scans the plurality of image carriers with a beam spot to form an electrostatic latent image, and the optical scanning device. A developing unit that visualizes the electrostatic latent image formed on the image carrier in each color; a conveyance belt that conveys a sheet-like recording medium that is movably provided facing the plurality of image carriers; Each of the color toner images visualized on the plurality of image carriers is directly transferred to the recording medium conveyed by the conveying belt by the transferring means, 2. A multicolor image forming apparatus that superimposes color toner images on a recording medium and fixes the color toner images superimposed on the recording medium by the fixing unit to form a multicolor or color image. Image inspection as described in any one of -4 The device is provided, and detects the positional deviation amount or the image density of each color toner image on the recording medium conveyed the speed of the conveyor belt or the conveyor belt.

According to a seventh aspect of the present invention, in the multicolor image forming apparatus according to the fifth or sixth aspect, a writing start position correcting means for correcting a writing start position by the optical scanning device, or a feed speed of the intermediate transfer belt Belt speed correcting means for correcting the belt speed, or belt speed correcting means for correcting the feeding speed of the conveying belt is provided.
According to an eighth aspect of the invention, in the multicolor image forming apparatus according to the fifth or sixth aspect, means for correcting the image density is provided.

According to the present invention, it is possible to detect the speed fluctuation, image position shift, and image density of a moving medium with high accuracy, and to improve image quality.
Specifically, according to the first aspect of the present invention, the speed fluctuation of the moving member (intermediate transfer belt, transport belt, or recording medium such as paper) in the image forming apparatus can be detected easily and with high accuracy. In addition, it is possible to provide an image detection apparatus capable of detecting an image position shift of each color image pattern formed on the moving member using the image detection apparatus.
According to the second aspect of the present invention, it is possible to detect the image density of each color image pattern formed on the moving member.
According to the third aspect of the present invention, the moving speed of the moving member can be detected without a mark without forming a specific scale pattern on the moving member, and the toner image forming position deviation on the moving member can be detected. And an image density distribution can be detected, and an image detection apparatus having three detection functions can be provided by one detection apparatus.

According to the fourth aspect of the present invention, the toner image formation position shift on the moving member and the detection of the image density distribution can be detected even with a finer toner image pattern. Even fine objects can be detected.
According to the fifth aspect of the present invention, it is possible to detect the speed fluctuation of the intermediate transfer belt, the formation position shift of the toner image pattern on the intermediate transfer belt, and the image density.
According to the sixth aspect of the present invention, it is possible to detect the speed fluctuation of the conveying belt that conveys a medium such as paper, the misalignment of the toner image pattern formed on the paper medium on the conveying belt, and the image density. it can.
According to the seventh aspect of the present invention, in addition to correcting the speed fluctuation of the moving member using the speed fluctuation detection result of the moving member detected by the mounted image detection device, each color image in the formed actual image Thus, it is possible to obtain a high-quality multicolor image in which the color misregistration is greatly reduced by detecting and correcting the misregistration.
According to the eighth aspect of the invention, in addition to detecting the speed fluctuation of the moving member and the toner image positional deviation with the mounted image detection device, the image density of the formed toner image is detected, and the detection result By correcting the image density of the toner image using, a high-quality multicolor image in which the gradation of the multicolor image is appropriately corrected can be obtained.

Embodiments of the present invention will be described below with reference to the drawings.
Based on FIGS. 1-3, while showing the basic structural example of the multi-color image forming apparatus which concerns on this embodiment, and an optical scanning apparatus, the outline | summary is demonstrated.
FIG. 1 shows a basic configuration example of a multicolor image forming apparatus according to the present invention. Reference numerals 1Y, 1M, 1C, and 1K in the figure are image carriers arranged side by side along the intermediate transfer belt 105, and the image carriers are drum-shaped photosensitive members. Each of the photoconductors 1Y, 1M, 1C, and 1K is rotated in the direction of the arrow in the figure, and around the chargers 2Y, 2M, 2C, and 2K as charging means (in the figure, a contact type using a charging roller is shown) However, a charging brush, a non-contact type corona charger, etc. can also be used), developing devices 4Y, 4M, 4C, 4K for each color as developing means, primary transfer means (transfer charger, transfer roller) 6Y, 6M, 6C, 6K, photoconductor cleaning means 5Y, 5M, 5C, 5K, etc. are provided. In the figure, reference numeral 30 denotes a fixing unit, 40 denotes a secondary transfer unit, and 41 denotes a conveying unit.

  The photoconductors 1Y, 1M, 1C, and 1K are uniformly charged by the chargers 2Y, 2M, 2C, and 2K, and then light beams that are intensity-modulated in accordance with image information by the optical scanning device 20 that is a latent image forming unit. (For example, a laser beam) is exposed to form an electrostatic latent image. The basic configuration of the optical scanning device 20 that performs this exposure process will be described later.

The electrostatic latent images formed on the photosensitive drums 1Y, 1M, 1C, and 1K are yellow (Y) developing device 114Y, magenta (M) developing device 114M, cyan (C) developing device 114C, and black (K) developing. The image is developed by the device 114K and is visualized as toner images of each color of yellow (Y), magenta (M), cyan (C), and black (K).
The multicolor image forming apparatus shown in FIG. 1 is an intermediate transfer belt type multicolor image forming apparatus, and the toner images on the photoreceptors 1Y, 1M, 1C, and 1K visualized in the above-described development process are as follows. Primary transfer is performed by sequentially superimposing on the intermediate transfer belt 105. Then, the toner images of the respective colors superimposed on the intermediate transfer belt 105 are fed from a paper feeding unit (not shown), and are recorded on paper or the like that is conveyed to the position of the secondary transfer unit 40 via a conveyance unit (not shown). Secondary transfer is performed collectively on the medium. Then, the recording medium on which the toner image is transferred is conveyed to the fixing unit 30 by a conveying unit 41 such as a conveying belt, and the toner image is fixed on the recording medium by the fixing unit 30 to obtain a multicolor image or a full color image. . Then, the fixed recording medium is discharged to a discharge unit (not shown), a post-processing device, or the like.
Further, the photoreceptors 1Y, 1M, 1C, and 1K after the toner image transfer are cleaned by cleaning members (blades, brushes, and the like) of the cleaning units 5Y, 5M, 5C, and 5K to remove residual toner. Further, the intermediate transfer belt 105 after the toner image transfer is also cleaned by a belt cleaning unit (not shown) to remove residual toner.

  In the multicolor image forming apparatus shown in FIG. 1, a single color mode for forming an image of any one of yellow (Y), magenta (M), cyan (C), and black (K), yellow (Y), A two-color mode in which images of two colors of magenta (M), cyan (C), and black (K) are overlaid, yellow (Y), magenta (M), cyan (C), and black (K). There is a three-color mode in which images of any three colors are superimposed and a full-color mode in which a four-color superimposed image is formed as described above, and these modes are specified and executed by an operation unit (not shown). Single-color, multicolor, and full-color image formation is possible.

Further, the multicolor image forming apparatus having the configuration shown in FIG. 1 uses the intermediate transfer belt 105 to perform primary transfer from each of the photoreceptors 1Y, 1M, 1C, and 1K to the intermediate transfer belt 105 to form an overlapping image of each color. The intermediate transfer type multicolor image forming apparatus is configured to perform secondary transfer collectively from the intermediate transfer belt 105 to a recording medium such as paper, but the multicolor image forming apparatus configured as shown in FIG. As a multi-color image forming apparatus of a type in which a conveyance belt 106 that carries and conveys a recording medium such as paper is used instead of the intermediate transfer belt and is directly transferred from each photosensitive drum 1Y, 1M, 1C, 1K to a recording medium such as paper. Also good.
In this direct transfer type multi-color image forming apparatus, as shown in FIG. 2, the approach path of the recording medium such as paper is different from that in FIG. 1, and the recording medium is transferred to each of the photosensitive drums 1Y, 1M by the conveyor belt 106. , 1C, 1K.

In the multicolor image forming apparatus shown in FIG. 2 as well, each of the photoconductors 1Y, 1M, 1C, and 1K is uniformly charged by the chargers 2Y, 2M, 2C, and 2K, and then the light that is a latent image forming unit. A light beam (for example, laser light) whose intensity is modulated according to image information is exposed by the scanning device 20 to form an electrostatic latent image. The electrostatic latent images formed on the photosensitive drums 1Y, 1M, 1C, and 1K are yellow (Y) developing device 114Y, magenta (M) developing device 114M, cyan (C) developing device 114C, and black (K) developing. The image is developed by the device 114K and is visualized as toner images of each color of yellow (Y), magenta (M), cyan (C), and black (K). Then, a recording medium such as paper is fed from a paper feeding unit (not shown) at the same timing as the developing process, and is conveyed to the conveyance belt 106 through a conveyance unit (not shown) and is carried on the conveyance belt 106. The recording medium carried on the conveying belt 106 is conveyed toward the photosensitive drums 1Y, 1M, 1C, and 1K, and the toner on the photosensitive members 1Y, 1M, 1C, and 1K that has been visualized in the above development process. The images are sequentially transferred onto the recording medium by transfer means 6Y, 6M, 6C, and 6K. Then, the four-color superimposed toner image transferred onto the recording medium is conveyed to the fixing unit 30, and the fixing unit 30 fixes the toner image on the recording medium, thereby obtaining a multicolor or full-color image. Then, the fixed recording medium is discharged to a discharge unit (not shown), a post-processing device, or the like.
Further, the photoreceptors 1Y, 1M, 1C, and 1K after the toner image transfer are cleaned by cleaning members (blades, brushes, and the like) of the cleaning units 5Y, 5M, 5C, and 5K to remove residual toner.

The optical scanning device 20 will be described. FIG. 3 is a schematic configuration diagram showing an example of an optical scanning device developed in each of the multicolor image forming apparatuses.
3, four photosensitive drums 301, 302, 303, and 304 (corresponding to the photosensitive members 1Y, 1M, 1C, and 1K in FIG. 1 or 2) are transferred to a transfer belt 400 (the intermediate transfer belt 105 in FIG. 1 or In the image forming apparatus that forms a color image by sequentially transferring toner images of different colors, the optical scanning devices are integrally configured. A single light deflector (for example, a polygon mirror) 1050 scans all light beams. The polygon mirror 1050 has six surfaces and a two-stage structure.

  More specifically, the optical scanning device 20 includes a light source unit 1001, a single polygon mirror 1050 that deflects and scans a light beam from the light source unit 1001, and a scanning beam scanned by the polygon mirror 1050 as a photosensitive member. A scanning lens 1061 that forms an image on the surface to be scanned of the drum 302 is included, and here, scanning is performed for two stations in a direction facing the polygon mirror 1050. In FIG. 3, for simplification of explanation, three light source units for scanning the other photosensitive drums 301, 303, and 304 and the optical system after the scanning lens are omitted, and only one station is illustrated. ing.

  The light source unit 1001 includes a light source (for example, a semiconductor laser (LD), an LD array, etc.), a coupling lens, and an aperture. A light beam emitted from a light source (not shown) of the light source unit 1001 is converted into a substantially parallel light, a substantially divergent light beam, or a substantially convergent light beam by a coupling lens (not shown), and then cut into a desired light beam width by an aperture (not shown). A linear image forming lens (for example, a cylindrical lens) 1041 condenses once in the sub-scanning direction in the vicinity of the polygon mirror 1050, and a beam spot is formed on the image plane (scanned surface) 2001 by the scanning optical system including the scanning lenses L1: 1061. Form. As described above, the normal optical scanning apparatus employs a surface tilt correction optical system that once collects light in the sub-scanning direction in the vicinity of the polygon mirror in order to reduce deterioration of optical characteristics due to surface tilt between the mirrors of the polygon mirror 1050. ing. The scanning lens is made of resin, and the diffraction grating may be formed on one or a plurality of optical surfaces. Normally, folding mirrors 1111 and 1121 are inserted between the light deflection means and the image plane, and the optical path is folded. Further, although the scanning optical system has been shown as an example constituted by a single scanning lens, two or more scanning lenses may be used.

  Here, a writing start position correcting unit (for example, a liquid crystal deflecting element) for correcting a writing start position by the optical scanning device is preferably provided between the coupling lens of the light source unit 1001 and the cylindrical lens 1041.

In the multicolor image forming apparatus configured as shown in FIGS. 1 and 2, color shift occurs unless the intermediate transfer belt 105 is driven with high accuracy in the case of the intermediate transfer method and the conveyance belt 106 is driven with high accuracy in the case of the direct transfer method. Resulting in.
In order to drive the belt with high accuracy, a method of making all the components with high accuracy is conceivable, but there are many components and it is difficult to realize from the viewpoint of cost.
Therefore, it is preferable to provide a detecting means for detecting the speed fluctuation of the belt and feed back the detection result to the belt drive motor. For this purpose, a speed detecting means for detecting the speed fluctuation of the belt is required.
Conventionally, in order to detect the speed fluctuation of the belt, a mark is directly formed on the belt (Patent Document 1). However, it is difficult to directly process the belt, and it takes time to process, so mass productivity is poor. This was a major cost increase factor.

Therefore, in the present invention, the speed fluctuation of a moving member (moving medium) such as a belt is easily detected without directly processing the belt, and the positional deviation and image density of the toner image pattern formed on the belt are simultaneously detected. A novel image detection apparatus capable of detection is provided.
FIG. 4 shows a basic configuration example of the image detection apparatus of the present invention. The image detection apparatus 100 has a function of detecting the formation position deviation of the toner image pattern formed on the moving member and the image density in parallel with the detection of the moving speed of the moving member. Although not shown in FIG. 4, the image detection apparatus 100 includes an image signal acquisition unit and the like which will be described later.
Regarding speed detection, the speed and speed fluctuations of a moving member 53 (endless belt-like member such as an intermediate transfer belt or a conveyance belt, or drum-like member, or a recording medium such as paper) 53 are detected. As a laser light source 51 that emits a certain laser beam, a collimator lens 52 that makes the laser beam emitted from the laser light source substantially parallel, and a light receiving means (for example, a light receiving element array) that can acquire a one-dimensional or two-dimensional image , An imaging lens (hereinafter also simply referred to as “lens”) 54 and an aperture stop 55 provided between the moving member 53 and the area sensor 56.

A laser beam emitted from the laser light source 51 and made into a substantially parallel beam by the collimator lens 52 is irradiated obliquely onto the moving member 53, and a one-dimensional or two-dimensional area from a direction perpendicular to the moving plane of the moving member 53. An image is picked up by the sensor 56. The moving member 53 is a member having light diffusibility on the surface or inside thereof. When irradiated with laser light, diffuse reflected light having a distribution indicated by reference numeral 57 is reflected. When a part of such diffuse reflected light is taken into the lens 54 and imaged on the area sensor 56, a random image pattern called a speckle pattern by the diffused laser light is obtained.
This speckle pattern is a pattern corresponding to a fine random uneven shape on the surface or inside of the moving member 53, and is formed by random interference of laser light.

When the moving member 53 moves, the speckle pattern also moves. As a feature of the speckle pattern, the speckle pattern is not lost even if the imaging position is moved back and forth in the optical axis direction of the lens. Therefore, the speckle pattern corresponding to the uneven shape on the surface or inside of the moving member 53 is very stable. An image pattern can be obtained. Therefore, a lens between the area sensor 56 and the moving member 53 is usually not necessary. However, when the moving member 53 is tilted with respect to the moving plane due to some disturbance, the speckle pattern changes on the area sensor 56, and a detection error occurs when detecting a speed change described later. Will occur.
Therefore, in order to avoid the above problem, the imaging lens 54 is disposed between the area sensor 56 and the moving member 53, and the moving member 53 and the area sensor 56 are set so as to have an imaging conjugate relationship. Is desirable. Thereby, even if the moving member 53 is inclined with respect to the moving plane, the change in the speckle pattern on the area sensor 56 can be reduced, and the speed detection error can be suppressed small.

The imaging lens 54 is preferably set so that the moving member 53 and the area sensor 56 have an imaging conjugate relationship. However, the moving lens 53 is not necessarily limited to this, and even if the imaging lens 54 is shifted from the imaging conjugate relationship, the moving member There is an effect of reducing the change amount of the speckle pattern due to the inclination of 53.
Therefore, if the inclination generated in the moving member 53 is not so large, even if it is shifted from the conjugate relationship, it can be suppressed to a practically sufficient speed detection error.
Further, it is desirable that the imaging lens 54 be used at an imaging magnification for reducing and imaging the moving member 53 on the area sensor 56. By doing so, the wide range on the moving member 53 can be reduced on the area sensor 56, and the area sensor 56 can be reduced in size. Further, by using the reduction optical system, the moving speed of the speckle pattern on the area sensor 56 can be reduced even when the moving speed of the moving member 53 is high. If the moving speed on the area sensor is low, the time interval for acquiring the speckle pattern can be lengthened, and as a result, the time for the calculation process can be increased and the high-speed movement of the moving member 53 can be dealt with. . In addition, the processing speed of the electronic circuit can be reduced, and low power consumption and low cost can be realized.
In this embodiment, the collimating lens 52 illuminates the moving member 53 by making the laser light substantially parallel light. However, the moving member 53 is not limited to this, and the moving member is made by converting the laser light into focused light or divergent light depending on the arrangement of the collimating lens. 53 may be illuminated.

The aperture stop 55 in FIG. 4 greatly affects the size of the minimum diameter of the speckle pattern on the area sensor 56. At the time of detection in the speckle pattern, it is desirable that the minimum diameter of the speckle pattern on the area sensor is an appropriate size with respect to the size of one pixel of the area sensor. The minimum diameter of the speckle pattern on the area sensor is directly proportional to the light source wavelength and inversely proportional to the angle at which the pupil of the imaging lens is viewed.
The pupil diameter of the imaging lens is optimized by the aperture stop, and the minimum diameter of the speckle pattern is optimized with the size of one pixel of the area sensor 56.

In order to detect the speed of the moving member 53 from the one-dimensional or two-dimensional image acquired by the area sensor 56, a cross-correlation function between two speckle images acquired at a time interval τ is calculated and the cross-correlation is calculated. The amount of deviation Δ of the speckle pattern at the time interval τ is obtained from the position where the peak occurs.
From the above time interval τ and the peak position deviation amount Δ, the moving speed v of the moving member 53 is
v = KΔ / τ
As required. Here, K is a proportional constant, which is determined from the optical arrangement such as the position of the laser light source and the lens, and this K needs to be obtained in advance.

The calculation of the cross-correlation function between the two speckle images is performed by the following equation. Here, let two speckle images be f1 and f2. Further, Fourier transform is F [], inverse Fourier transform is F ^-1 [], symbol * indicates cross-correlation calculation, and ^* indicates phase conjugation.
f1 * f2 ^* = F− ¹ [F [f1] · F [f2] ^* ]
f1 * f2 ^* is image data after the cross-correlation calculation, and is two-dimensional if f1 and f2 are two-dimensional images, and one-dimensional data if f1 and f2 are one-dimensional images. In the image data of f1 * f2 ^* , the position of the steepest peak (correlation peak) intensity represents the amount of displacement between the two speckle images. Therefore, the amount of movement between the two speckle images can be calculated by searching for the steepest peak.
Since the above-described cross-correlation calculation method can use fast Fourier transform, the amount of positional deviation Δ between speckle patterns can be detected with a relatively small amount of calculation and with high accuracy. Therefore, since the positional deviation amount Δ and the time difference τ between the two speckle images are known, the moving speed v of the moving member 53 can be calculated.
4 shows a case where the moving direction of the moving member 53 is the 58 direction in the figure, that is, the direction perpendicular to the paper surface. The present invention is not limited to this, and can be similarly applied to a case where the moving member moves in any direction within the plane.

FIG. 8 shows an example of the shape of a toner pattern for detecting a deviation in the formation position of the toner image pattern formed on the moving member. Four color toner pattern groups are formed on a moving member that moves in the x direction.
In the drawing, the x direction and the y direction correspond to the y direction in the main scanning method of the image forming apparatus and the x direction in the sub scanning direction.
The four-color toner patterns are cyan (c), magenta (M), yellow (Y), and black (B) toner patterns, respectively.
The toner pattern A group in FIG. 8 is a rectangular pattern whose long sides are formed in parallel to the y-axis, and is a pattern group for detecting a toner formation position shift in the sub-scanning direction. The toner pattern B group is a rectangular pattern whose long sides are formed in the direction of 45 ° with respect to the y-axis, and is a pattern group for detecting a toner formation position shift in the main scanning direction.
In order to detect a toner formation position shift in the sub-scanning and main-scanning directions using the above-described A group and B group, the following is performed. The center of each color rectangular toner pattern from the edge positions on both sides of the long side is defined as the toner formation position.

In FIG. 8, the deviation in the formation position of each color toner pattern in the sub-scanning direction is obtained by measuring the time to the formation position of each color toner with reference to the leading cyan toner formation position. The time t1 for the magenta toner, the time t2 for the yellow toner, and the time t3 for the black toner are the formation positions for the cyan toner.
If each time is equal, there is no color shift, but if it is not equal, it is a formation position shift.
On the other hand, the formation position shift in the main scanning direction is detected by the time difference between the same colors of the A group and the B group. That is, time t4 for cyan toner, time t5 for magenta toner, time t6 for yellow toner, and time t7 for black toner. If t4 to t7 are the same, there is no displacement in the formation position in the main scanning direction for each color, but if this is not equal, it can be detected that there is a displacement in the main scanning direction for each color.
By the above method, the formation position shift of the toner pattern formed on the moving member can be detected.

In the image detection apparatus of FIG. 4, the image pattern positional deviation of the toner image pattern formed on the above moving medium can also be detected. 5 and 6 show an example of image pattern positional deviation detection.
FIG. 5 shows a state in which the toner pattern formed on the belt-like substrate is incident on the laser beam of the image detection apparatus shown in FIG. FIG. A cross-correlation operation is performed on the captured speckle image, and the value of the correlation peak is extracted.
The cross-correlation calculation and the correlation peak value are sequentially extracted while moving the belt-like substrate in the direction of the arrow in FIG.
FIG. 6 shows an example of actual measurement values in which the horizontal axis represents the belt base movement amount and the vertical axis represents the correlation peak value. The zero point on the horizontal axis indicates when the laser light illumination beam of the image detection apparatus is on the toner pattern. The value of the correlation peak is equivalent to the integral value of the imaging pattern on the area sensor and represents the light intensity of the image captured by the area sensor.

When the laser light illumination beam of the image detection device is on the toner pattern, there is diffuse light from the toner pattern, the correlation peak value is high, and when the laser light illumination beam hits the toner edge due to the movement of the belt substrate, The correlation peak value decreases, and when the laser light illumination beam is on a belt substrate without a toner pattern, the correlation peak value is low because most of the reflected light is regular reflection light and the diffuse reflection light component is eliminated. Therefore, the graph of FIG. 6 represents the diffuse reflectance distribution near the toner pattern edge.
As described above, an appropriate threshold value is set for the correlation peak value in the graph of FIG. 6, and the edge position of the toner pattern can be detected from the amount of movement across the threshold value.

FIG. 7 shows another embodiment. In addition to the above, an object of the present embodiment is to provide an image detection device that also detects the image density of a toner pattern on a moving member.
In FIG. 7A, a toner gradation pattern is formed on a belt substrate which is a moving member. 4 is incident on the belt substrate, and the laser beam illuminates the toner gradation pattern as the belt substrate moves in the x direction. Go. FIG. 7B shows a schematic diagram when the correlation peak value is plotted with respect to the x direction of the belt substrate when the laser light illumination beam traces the toner gradation pattern.
In FIG. 7B, the correlation peak value is plotted as being proportional to the reflectance of the toner pattern with gradation. Since the absolute value of the reflectance of the belt substrate without the toner pattern is known, the absolute value on the vertical axis in FIG. 7B can be specified as the reflectance R. From the reflectance R, the image density D of the toner pattern can be calculated by the definition formula D = −logR. FIG. 7C is a schematic diagram when the reflectance distribution of FIG. 7B is converted into an image density distribution by a definition formula. From FIG. 7C, the image density of the toner pattern on the moving member can also be detected from the correlation calculation of the speckle image.

FIG. 12 shows a flowchart of the processing for detecting the moving speed of the moving member and detecting the positional deviation and the image density of the toner image pattern formed on the moving member, as shown in the above embodiment.
The speckle pattern image of the moving member detected by the area sensor as the image sensor passes through a video processing circuit, and a plurality of pieces of image information with different detection times are stored in the frame memory. The speckle patterns at different times are read from this frame memory, the cross-correlation calculation is executed in the correlation calculation processing unit, one detects the positional shift of the cross-correlation peak, and then calculates the moving speed of the moving member It becomes the flow to do.
The video processing circuit and the frame memory constitute image signal acquisition means in this embodiment.
The other is the flow of detecting the cross-correlation peak value and then calculating the toner image pattern position deviation and the image density. With one image detection device, the moving speed of the moving member and the toner image pattern formation position deviation, and It is possible to know the image density.

Next, in the image detection apparatus shown in FIG. 4, an embodiment for detecting the toner pattern formation position deviation and the image density by another method will be described. In the image detection apparatus of FIG. 4, the moving member 53 is imaged on the area sensor 56 by the imaging lens 54.
Therefore, when a toner pattern is formed on the moving member, the pattern is imaged on the area sensor by the imaging lens. FIG. 9A shows a toner pattern image formed on the area sensor 54. A speckle pattern area in which a speckle pattern is generated in an area corresponding to the laser illumination area on the moving member is imaged on an area sensor in which pixels are arranged in a square shape, and the speckle pattern area is formed on the moving member in the area. There is a formed toner pattern image.
Of the output signals of the area sensor, the image signal of the A pixel row is shown in FIG. The waveform has a speckle pattern on the intensity distribution of the toner pattern. FIG. 9C shows the result of smoothing this signal.

Since the speckle pattern is distributed over a certain spatial frequency, the intensity distribution of the toner pattern can be generated by passing through a low-pass filter. By this method, an image of the toner pattern formed on the moving member can be detected from the speckle pattern on the area sensor. From the toner pattern image obtained by the smoothing process, the center position of the toner pattern can be specified from the front and rear edges thereof, and the formation position of the toner pattern can be specified. Thereby, the positional deviation of the toner image for detecting the positional deviation of the toner pattern shown in FIG. 8 can be detected from the speckle pattern.
In FIG. 9, the toner pattern image is extracted based on the image signal of one row of the A pixels. However, the present invention is not limited to this, and the toner pattern image is extracted by adding the image signals of a plurality of rows in the column direction. May be.

FIG. 11 shows detection of image density. In FIG. 11A, a toner gradation pattern is formed on a belt substrate which is a moving member. The laser light illumination beam of the image detection apparatus of FIG. 4 is incident on the belt substrate, and the laser light illumination beam traces the toner gradation pattern as the belt substrate moves in the x direction.
FIG. 11B shows an addition signal of one line or a plurality of lines on the area sensor when the laser light illumination beam traces the toner gradation pattern.
In the figure, the waveform has a speckle pattern on the intensity distribution of the toner pattern. Smoothing processing is performed on this signal. Since the speckle pattern is distributed over a certain spatial frequency, the intensity distribution of the toner pattern can be generated by passing through a low-pass filter.
By this method, it is possible to detect the intensity distribution of the toner gradation pattern formed on the moving member from the speckle pattern on the area sensor. FIG. 11C shows a schematic diagram of a waveform obtained by density conversion from the intensity distribution of the toner gradation pattern detected by the smoothing process. From FIG. 11C, the gradation image density of the toner pattern on the moving member can also be detected from the smoothing process of the speckle image signal.

FIG. 13 shows a flowchart of the processing for detecting the moving speed of the moving member and detecting the positional deviation and the image density of the toner image pattern formed on the moving member, as shown in the above embodiment.
The speckle pattern image of the moving member detected by the area sensor as the image sensor passes through a video processing circuit, and a plurality of pieces of image information with different detection times are stored in the frame memory. One is to read speckle pattern signals at different times from this frame memory, the cross-correlation calculation is executed in the correlation calculation processing section, detect the position shift of the cross-correlation peak, and then calculate the moving speed of the moving member It becomes the flow to do.
The video processing circuit and the frame memory constitute image signal acquisition means in this embodiment.
The other is extracting a video signal of one or more lines of a toner image pattern at a specific time from the frame memory, smoothing the video signal, and calculating the positional deviation and image density of the toner image pattern. It becomes a flow. From both of these flows, it is possible to know the moving speed of the moving member, the formation position deviation of the toner image pattern, and the image density with a single image detection apparatus.

  An embodiment in which the above-described image detection apparatus is applied to the intermediate transfer type multicolor image forming apparatus of FIG. 1 will be described. The image detection device 100 is disposed downstream of the final photoconductor 1K position of the intermediate transfer belt 105, and always detects the feed speed of the intermediate transfer belt itself. In parallel with this, it is possible to detect a toner mark pattern as shown in FIG. 8 among the toner image patterns transferred from the respective photoreceptors to the intermediate transfer belt, thereby detecting a deviation in the formation position of the toner image pattern. Further, the toner gradation pattern as shown in FIG. 7A can be detected to detect the image density of the toner image pattern. As described above, one image detection device can detect three of the speed fluctuation of the intermediate transfer belt, the toner image pattern formation position shift, and the image density.

An embodiment in which the above-described image detection apparatus is applied to the direct transfer type multicolor image forming apparatus of FIG. 2 will be described. The image detection apparatus 100 is disposed downstream of the position of the final photoreceptor 1K of the conveyance belt 106 that conveys a recording medium such as paper, and always detects the feed speed of the conveyance belt itself. In parallel with this, a toner image pattern transferred to a recording medium such as paper conveyed on the conveying belt is also detected.
A toner mark pattern as shown in FIG. 8 can be detected from the toner image patterns transferred from the respective photoreceptors to the paper transported on the transport belt, thereby detecting the misalignment of the toner image pattern. Further, the toner gradation pattern as shown in FIG. 7A can be detected to detect the image density of the toner image pattern. As described above, one image detecting device can detect three of the speed fluctuation of the conveying belt, the toner image pattern forming position shift, and the image density.

In a multicolor image forming apparatus, by controlling the multicolor image forming apparatus in accordance with the detection signal of the mounted image detecting apparatus, it is possible to form a good color image with good gradation and no color shift. .
Specifically, when applied to the multi-color image forming apparatus of FIG. 1, the belt feed is fed back to the motor drive of the intermediate transfer belt feeding means based on the speed fluctuation of the intermediate transfer belt detected by the image detecting apparatus 100. Control the speed constant.
When applied to the other multicolor image forming apparatus of FIG. 2, the belt feed speed is made constant by feeding back to the motor drive of the transport belt feeding means based on the speed fluctuation of the transport belt detected by the image detection apparatus 100. Control.
Based on the toner image pattern formation position deviation result detected by the image detection device 100, the multi-color image forming apparatus in FIGS. The line selection is changed to reduce the toner image position shift in the sub-scanning direction.
For correcting the deviation below the sub-scanning line interval, there is a method of correcting the writing beam by slightly deflecting it in the sub-scanning direction using a variable light deflection element formed of liquid crystal or the like in the scanning optical system.

The positional deviation in the main scanning direction of the toner image pattern detected by the image detection apparatus 100 is corrected by shifting the main scanning writing position of each main scanning.
In the above multicolor image forming apparatus, both the writing start position correcting means for correcting the writing start position by the optical scanning device, or the belt speed correcting means for correcting the feed speed of the intermediate transfer belt or the conveying belt. However, at least one of them may be provided.
Furthermore, the image density value of the toner gradation pattern detected by the image detection device is fed back to the developing bias of the toner developer so that each color has an image density having an appropriate gradation, or the photosensitive member charging voltage Or the exposure amount is adjusted by adjusting the laser writing power to control each color to have an image density having an appropriate gradation.

  As described above, the image detection apparatus according to the present invention has been described as an example in which the image detection apparatus according to the present invention is applied to a multicolor image forming apparatus using an electrophotographic process, but the image detection apparatus according to the present invention is not limited thereto. The present invention can be similarly applied to detection of movement speed fluctuation of a recording sheet of a multicolor image forming apparatus by an inkjet process or the like, positional deviation of each color ink image pattern on the recording sheet, and detection of image density.

1 is a schematic configuration diagram of an intermediate transfer type multicolor image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram of a direct transfer multicolor image forming apparatus. It is a perspective view which shows the structure of the optical scanning in a multicolor image forming apparatus. It is a figure which shows the structure and function of an image detection apparatus. FIG. 6 is a plan view showing a toner pattern detection state by the image detection device. 6 is a graph showing a relationship between a correlation peak and a movement amount of a toner pattern. 4A and 4B are diagrams illustrating detection of image density of a toner pattern, where FIG. 5A is a plan view illustrating a toner gradation pattern, FIG. 5B is a plot of correlation peak values when the toner gradation pattern is traced, and FIG. It is the schematic diagram which converted this reflectance distribution into image density distribution. FIG. 6 is an explanatory diagram for detecting a formation position shift of a toner image pattern formed on a moving medium. FIG. 4 is a diagram illustrating smoothing processing of an image signal, where (a) is a diagram illustrating an image of a toner pattern formed on an area sensor, and (b) is an image signal of an A pixel row among output signals of the area sensor. The figure which shows an output waveform, (c) is a figure which shows the output waveform of the signal which smoothed the signal of (b). It is a figure which shows the image of the inclined toner pattern imaged on the area sensor. FIG. 5 is a diagram illustrating detection of image density of a toner pattern by smoothing processing, where (a) is a plan view illustrating a toner gradation pattern, (b) is an output diagram when the toner gradation pattern is traced, and (c) is (b). FIG. 6 is a schematic diagram in which the intensity distribution of the toner gradation pattern obtained in step 1 is converted into an image density distribution. 5 is a flowchart for detecting speed detection of a moving medium, positional deviation of a toner image pattern, and image density. 10 is a flowchart for detecting a positional shift and an image density of a toner image pattern by moving medium speed detection and smoothing processing.

Explanation of symbols

20 optical scanning device 51 laser light source as light source 53 moving member as moving medium 54 imaging lens 56 area sensor as light receiving means

Claims (8)

Light emitted from a light source that emits coherent light is irradiated onto a moving medium on which an image pattern is formed, and reflected light from the moving medium is imaged on a one-dimensional or two-dimensional light receiving means via an imaging lens. Comprising image signal acquisition means for acquiring a one-dimensional or two-dimensional image signal that is temporally different with the movement of the moving medium,
The cross-correlation calculation between temporally different image signals acquired by the image signal acquisition means is performed, and the moving speed of the moving medium is detected and obtained by obtaining the shift of the position where the correlation peak of the cross-correlation calculation occurs. An image detection apparatus for detecting a positional deviation of an image pattern formed on the moving medium from an image signal. The image detection apparatus according to claim 1,
An image detection apparatus for detecting an image density of an image pattern formed on the moving medium from an image signal acquired by the image signal acquisition means. The image detection apparatus according to claim 2,
An image detection apparatus for detecting a positional shift and an image density of an image pattern formed on the moving medium using a correlation peak value in the cross-correlation calculation. The image detection apparatus according to claim 2,
Detecting a positional shift and an image density of an image pattern formed on the moving medium by using a smoothed image signal obtained by smoothing a one-dimensional or two-dimensional image signal of each time acquired by the image signal acquisition unit. An image detection apparatus characterized by the above. A plurality of image carriers, an optical scanning device that optically scans the plurality of image carriers with a beam spot to form an electrostatic latent image, and the optical scanning device formed on the plurality of image carriers. A developing unit that visualizes the electrostatic latent image in each color; an intermediate transfer belt that is movably provided facing the plurality of image carriers; first and second transfer units; and a fixing unit. Each of the color toner images visualized on the plurality of image carriers is transferred to the intermediate transfer belt by the first transfer unit, and the color toner images are superimposed on the intermediate transfer belt, The superimposed color toner images are transferred to a sheet-like recording medium by the second transfer unit, and the color toner images transferred to the recording medium are fixed by the fixing unit to form a multicolor or color image. In a multicolor image forming apparatus,
5. The image detection device according to claim 1, wherein the image detection device detects a speed of the intermediate transfer belt, a positional deviation of each color toner image on the intermediate transfer belt, or an image density. Multicolor image forming apparatus. A plurality of image carriers, an optical scanning device that optically scans the plurality of image carriers with a beam spot to form an electrostatic latent image, and the optical scanning device formed on the plurality of image carriers. A developing unit that visualizes the electrostatic latent image in each color, a conveyance belt that conveys a sheet-like recording medium that is movably provided facing the plurality of image carriers, a transfer unit, and a fixing unit; Each color toner image visualized on the plurality of image carriers is directly transferred to the recording medium conveyed by the conveying belt by the transfer means, and the respective color toner images are formed on the recording medium. In a multicolor image forming apparatus that forms a multicolor or color image by superimposing and fixing each color toner image superimposed on the recording medium by the fixing unit,
5. The image detection device according to claim 1 is provided, and detects the speed of the conveyance belt, the amount of misregistration of each color toner image on the recording medium conveyed by the conveyance belt, or the image density. A multicolor image forming apparatus. The multicolor image forming apparatus according to claim 5 or 6,
Write start position correcting means for correcting the writing start position by the optical scanning device, belt speed correcting means for correcting the feed speed of the intermediate transfer belt, or belt speed correcting means for correcting the feed speed of the transport belt. A multicolor image forming apparatus characterized by being provided. The multicolor image forming apparatus according to claim 5 or 6,
A multicolor image forming apparatus comprising means for correcting image density.

Images