JP2007079605A - Alignment pattern detection sensor, image forming apparatus, color shift detection method, and color shift correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely detect color shift by a simple and low-cost configuration. <P>SOLUTION: Each patch is constituted of a plurality of lines formed by putting line images Bk in black being a reference color and line images C in a color other than the reference color, for example, cyan, one over the other, and an alignment pattern Pm is constituted by continuously forming patches of which the relative positional relations between line images in two colors are shifted from one another by an arbitrary amount. An alignment pattern detection sensor 40 includes a light emitting diode (LED) 40A and a photo diode (PD) 40B, these elements are disposed along the scanning direction of the alignment pattern Pm, and the photo diode 40B is disposed so as to receive only diffused reflection light of reflected light from the alignment pattern Pm. The spot 40A-1 of the light emitting diode 40A and the spot 40B-1 of the photo diode 40B are formed like squares. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms a color image, such as a copying machine, a printer, a facsimile machine, a plotter, and an ink jet recording apparatus, an alignment pattern detection sensor as an alignment pattern detection unit used in the image forming apparatus, and color misregistration. The present invention relates to a detection method and a color misregistration correction method.

Up to now, each color toner image is formed using one photosensitive drum and a revolver type developing device, and each toner image is transferred onto an intermediate transfer member, and then transferred onto a transfer sheet as a sheet-like recording medium. A color image forming apparatus of a transfer type has been mainstream.
On the other hand, due to the recent trend toward higher speed and higher functionality of color image output devices, a plurality of image forming units including a photosensitive member (image carrier) and a developing device corresponding to the photosensitive member are opposed to the transfer belt. A so-called quadruple tandem color image forming apparatus, which is arranged side by side at such positions and sequentially transfers toner images on an image carrier onto transfer paper or a transfer belt, has come to dominate.

In such a type of color image forming apparatus, the toner image formed on the image carrier of each color can be transferred simultaneously, so that there is an advantage that the printing speed can be increased. Compared to a drum intermediate transfer type color image forming apparatus, this method is disadvantageous for color misregistration between colors.
A number of correction methods have been proposed for the technical problem of color misregistration. For example, in Patent Document 1, a line image of each color is formed on a transfer belt, the passage of the line image is detected by a detection sensor, and the deviation amount from the ideal passage timing of the line image of each color is measured. A technique for grasping and correcting the positional deviation amount of each color is disclosed.

Since such a method is a method for detecting the edge of the pattern passing through the detection sensor, the detection accuracy is determined by the sampling frequency. That is, if the resolution is 600 dpi and the correction unit is 42.3 μm (= 25.4 / 600 × 1000), detection is at least ± 1/2 (= 21.7 μm) or less of the correction unit. If the linear velocity of the line image on the transfer belt is 125 mm / sec, it can be detected by the following equation: [Sampling frequency] = [Line velocity] / [25.4 / Resolution dpi / 2] The minimum required sampling frequency is calculated to be 6 kHz or more. In this case (= 6 kHz), the detection accuracy (= detection error) is 21.7 μm.
If this numerical value is directly fed back to the misregistration correction, there may be no problem with this level of sampling frequency. However, if this detection result (= x μm) needs to be used for other calculations, for example, When such detection is performed at both the left and right ends of the sheet conveyance direction, and skew correction is performed based on the detection results at both ends, or magnification error correction is performed, higher detection accuracy is required. For example, when 2 μm is required as the detection accuracy, the sampling frequency needs to be very high such as 60 kHz.

As described above, since the necessary sampling frequency is proportional to the linear velocity and the resolution, the processing block after the data sampling needs to have a high processing speed that can cope with the high-speed sampling. However, there is a problem that the speed increases almost in proportion to the speeding up of the apparatus.
As a detection means for improving the detection accuracy of the edge of the pattern, a method of detecting with a CCD sensor having high accuracy and high resolution has been proposed, but even when such a detection means is used, Problems such as complicated equipment and increased costs could not be avoided.

In order to deal with such a problem, for example, Patent Document 2 discloses a relative positional relationship between a toner image pattern formed by superimposing a second color toner image on a first color toner image and a two color pattern. An average density of the toner image pattern formed at a timing shifted by a predetermined amount is detected by an optical sensor, and a positional shift amount and a positional shift direction between the first color and the second color are determined from the signal output. A technique for correcting is disclosed.
In this technique, the amount of misregistration is not detected by the edge detection of the pattern image (line image), but by detecting the average optical sensor output signal of the entire pattern. Detection is possible at a sampling frequency of about 500 Hz or less (every 2 msec), that is, about 1/100 lower than that described in Patent Document 1.

Therefore, even when the positional deviation detection method described in Patent Document 2 is used, if the detection accuracy of the same level as the technique described in Patent Document 1 is obtained, the hardware can be configured more inexpensively for positional deviation amount detection. Significant cost reduction is possible.
Examples of methods similar to the positional deviation detection method described in Patent Document 2 include those described in Patent Document 4, Patent Document 5, Patent Document 6, Patent Document 7, Patent Document 8, and the like.
Here, when it is considered to perform misregistration correction based on the output signal from the optical sensor of the superposed pattern of the two-color toner images disclosed in Patent Document 1, the maximum correction amount that must be corrected is If it is ± 10 dots, if 21 patterns in which the relative positional relationship between the two colors is shifted by 1 dot are formed, the amount of misalignment correction and its direction can be determined by reading the extreme values.
However, if so many patterns are created, it is not desirable because not only the wasteful toner consumption increases, but also the time required for the automatic misalignment adjustment becomes longer.
To deal with this problem, for example, Patent Document 4 discloses a method for detecting a positional deviation amount with higher accuracy by calculating the intersection of two straight lines when the vertical axis is the reflection optical density with respect to the print position parameter on the horizontal axis. It is shown.

Japanese Patent Publication No.7-19084 Japanese Patent No. 3254244 Japanese Patent Laid-Open No. 6-1002 Japanese Patent Laid-Open No. 10-329381 JP 2000-81745 A JP 2001-209223 A JP 2002-40746 A JP 2002-229280 A JP 2001-312115 A JP 2002-62707 A Japanese Patent Laid-Open No. 5-100556 JP 2002-148890 A JP 2002-6580 A JP 2000-35704 A

According to the method disclosed in Patent Document 4, even when the maximum correction amount is ± 10 dots, it is not necessary to form 21 patterns, and a pattern that is appropriately shifted by several dots, for example, 2 dots, is used. It is only necessary to form 11 patterns, and if the pattern is shifted by 5 dots, it is sufficient to form 5 patterns. Therefore, while greatly reducing the number of patterns and greatly reducing the time required for misalignment adjustment, More accurate displacement correction can be realized.
Since misalignment adjustment is an operation that is not related to normal printing operations, the longer the processing time, the longer it takes to complete the first print.If productivity is considered, such adjustment time should be short. Shorter is better.
However, when the amount of positional deviation is obtained by calculating the intersection of two straight line approximation formulas, the output characteristic of the sensor output signal of each patch linearly increasing or decreasing with respect to a predetermined arbitrary shift amount, that is, two straight lines the coefficient of determination R ² each approximate expression must first linear is obtained near as possible.

  Thus, for example, a color image forming apparatus of a quadruple tandem direct transfer system (a system in which the transfer paper is electrostatically adsorbed on the transfer belt 18 and images of each color are sequentially transferred and superimposed on the transfer paper) as shown in FIG. 35, as shown in FIG. 35, the minimum number of each color line of the patch configured by superimposing the two colors of the reference color black (Bk) and another color (for example, cyan (c)). One patch is formed by superimposing one line, and the relative positional relationship between the two colors is shifted by an arbitrary amount to continuously form 13 pieces (P1 to P13) for detecting displacement in the main scanning direction. The detection pattern (positioning pattern) Pk is read by a conventional optical sensor (positioning pattern detection sensor) as shown in FIG. 36, and each patch is output for an arbitrary shift amount of a line other than the reference color. Experiments were carried out to plot the voltage.

In FIG. 35, each patch is arranged along the scanning direction of the optical sensor, that is, the moving direction of the transfer belt, and colors other than the reference color in a direction orthogonal to the main scanning direction in order to detect a color shift in the main scanning direction. Is shifted by an arbitrary amount.
36, the optical sensor includes an LED (light emitting diode) 700, a regular reflection light receiving element 701, and a diffused light (hereinafter also referred to as diffuse reflected light) light receiving element 702. These elements are mounted on a support substrate 703. It is supported. These elements are actually arranged in a substantially vertical plane with respect to the movement plane of the alignment pattern, but in FIG. 36 (a), they are displayed in a plane by being tilted by 90 ° for easy understanding. 36B, reference numeral 700a indicates the spot shape of the LED 700, 701a indicates the spot shape of the regular reflection light receiving element 701, and 702a indicates the spot shape of the diffused light receiving element 702.

As a result of the experiment, as shown in FIG. 37, R ² = 0.9275 in the approximate line obtained by the minus plot point with respect to the extreme value, while R ^{2 in the} approximate line obtained by the plus plot point with respect to the extreme value. = 0.9555 was obtained, and an output characteristic that was hardly called a straight line was obtained.
Further, as a result of calculating the intersection point from these two approximate lines, a result of positional deviation amount = 34.74 μm (= 0.82 dots) was obtained. Experimental conditions such as detection patterns and detection sensors are as follows.

[Detection pattern] (= detailed parameters of the pattern shown in FIG. 35)
Bk line width: 24 dots (= 1.016 mm)
Color line width: 24 dots (= 1.016 mm)
Arbitrary shift amount: 4 dots (= 25.4 / 600 × 1000 × 4 = 169.3 μm)
Total number of patches: 13 patches (P1 and P13 are not completely overlapped, P7 is both completely overlapped)
[Detection sensor] (= Detailed specification of sensor shown in FIG. 36)
Light-emitting side Device: GaAs infrared light-emitting diode (peak emission wavelength: λp = 950 nm), top view type Spot diameter: 1.0 mm
Light-receiving side Element: Si phototransistor (peak spectral sensitivity: λp = 800 nm), top view type Spot diameter: specular light receiving side: 1.0 mm
Diffuse reflected light receiving side: 3.0 mm
[Detection distance]: 5 mm (distance from the top of the sensor to the detection target surface (patch))
[Line speed]
245mm / sec
[Sampling frequency]
500 Sampling / sec

  Therefore, the present invention provides an alignment pattern detection sensor as an alignment pattern detection unit capable of detecting color misregistration with high accuracy with a simple and low-cost configuration, an image forming apparatus using the same, a color misregistration detection method, and color misregistration. The main purpose is to provide a correction method.

  In order to achieve the above object, according to the first aspect of the present invention, the alignment pattern formed by superimposing the reference color image and the color image other than the reference color is irradiated with light from the light emitting portion, and In the alignment pattern detection sensor for detecting the reflected light from the alignment pattern by the light receiving unit, the light receiving unit is configured to detect diffuse reflection light or a diffuse reflection component of the reflected light, and the light emitting unit and the light receiving unit Are arranged along the scanning direction of the alignment pattern, and at least the spot shape of the light receiving unit has a constant area increment with respect to a shift amount of a color other than the reference color with respect to the reference color at a different position of the alignment pattern. It has a configuration that is set to a shape that becomes.

  According to a second aspect of the present invention, a plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color are used as one patch, and the relative positions of the two color line images are determined. In an alignment pattern detection sensor that detects light reflected from the alignment pattern by irradiating light from the light-emitting portion to an alignment pattern formed by continuously forming patches with the relationship shifted by an arbitrary amount, The light receiving unit is configured to detect diffuse reflection light or a diffuse reflection component of the reflected light, the light emitting unit and the light receiving unit are arranged along a scanning direction of the alignment pattern, and at least a spot of the light receiving unit The shape is such that the area increment with respect to the shift amount of the line image of the color other than the reference color with respect to the black line image of the reference color at a different position of the alignment pattern is constant. It adopts a configuration that is set to.

  According to a third aspect of the present invention, in the alignment pattern detection sensor according to the first or second aspect of the present invention, the spot shape of the light receiving portion is a quadrangle.

  According to a fourth aspect of the present invention, in the alignment pattern detection sensor according to any one of the first to third aspects, a central axis of directivity characteristics of the light emitting unit and the light receiving unit is a scanning direction of the alignment pattern. It has a configuration that is consistent with.

  According to a fifth aspect of the present invention, in the alignment pattern detection sensor according to any one of the first to fourth aspects, the light emitting unit is configured by a light emitting diode, and the light receiving unit is configured by a photodiode or a phototransistor. It has the configuration of being configured.

  According to a sixth aspect of the present invention, in the alignment pattern detection sensor according to the fifth aspect, the light receiving section is a light receiving element with a wide directivity angle.

  In the seventh aspect of the invention, the alignment pattern detection sensor according to the fifth aspect of the invention employs a configuration in which one or both of the light emitting part and the light receiving part are elements having a half-value angle of 30 ° or more. .

  According to an eighth aspect of the present invention, in the alignment pattern detection sensor according to the fifth aspect, either one or both of the light emitting part and the light receiving part is a side view type element.

  According to the ninth aspect of the present invention, in the alignment pattern detection sensor according to the fifth aspect, either one or both of the light emitting part and the light receiving part is a chip type element.

  In the invention according to claim 10, in the alignment pattern detection sensor according to claim 9, a configuration is adopted in which a collimating lens is provided between the chip type element and the alignment pattern to be detected. .

  According to the invention of claim 11, by having a plurality of image carriers, and sequentially transferring the toner images formed on the respective image carriers on the transfer member, the images are collectively transferred to a sheet-like recording medium. An image forming apparatus for obtaining a color image, an alignment pattern formed by superimposing a reference color image and an image of a color other than the reference color, an alignment pattern detection means for detecting the alignment pattern, A misregistration amount correcting means for judging a misregistration amount and a direction by judging the misregistration amount and direction between the reference color image and the non-reference color image based on an output signal from the alignment pattern detecting means. In the image forming apparatus having the above configuration, the alignment pattern detection unit is the alignment pattern detection sensor according to any one of claims 1 to 9.

  The invention according to claim 12 includes a plurality of image carriers, and the toner images formed on the image carriers are sequentially transferred onto the transfer member, and then transferred onto a sheet-like recording medium at a time. An image forming apparatus for obtaining a color image, wherein a plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color are used as one patch, Based on an alignment pattern formed by continuously forming patches whose relative positional relationship is shifted by an arbitrary amount, an alignment pattern detection means for detecting the alignment pattern, and an output signal from the alignment pattern detection means An image forming apparatus having a misregistration amount correcting unit that determines a misregistration amount and a direction of the misregistration amount between the black line image of the reference color and a line image of a color other than the reference color and corrects the misregistration amount. Place The combined pattern detecting means is a alignment pattern detection sensor according to any one of claims 1 to 9, it adopts a configuration that.

  In the invention described in claim 13, a plurality of image carriers are provided, and toner images formed on the respective image carriers are sequentially transferred onto a sheet-like recording medium carried on the transfer member, thereby transferring the color. An image forming apparatus for obtaining an image, comprising: an alignment pattern formed by superimposing a reference color image and an image of a color other than the reference color; an alignment pattern detection unit that detects the alignment pattern; Misregistration amount correction means for judging the misregistration amount and the direction by judging the misregistration amount and direction between the reference color image and the non-reference color image based on the output signal from the alignment pattern detection means; In the image forming apparatus according to the present invention, the alignment pattern detection unit is an alignment pattern detection sensor according to any one of claims 1 to 9.

  According to the fourteenth aspect of the present invention, the toner image formed on each image carrier having a plurality of image carriers is sequentially transferred onto the sheet-like recording medium carried on the transfer member, thereby transferring the color. An image forming apparatus for obtaining an image, wherein a plurality of lines formed by superimposing a black line image which is a reference color and a line image of a color other than the reference color are used as one patch, and the relative of two line images Based on an alignment pattern formed by continuously forming patches whose target positional relationship is shifted by an arbitrary amount, an alignment pattern detection means for detecting the alignment pattern, and an output signal from the alignment pattern detection means In the image forming apparatus having a misregistration amount correcting means for judging a misregistration amount and a direction by judging a misregistration amount and a direction between the black line image of the reference color and a line image of a color other than the reference color. Together Was pattern detecting means is a alignment pattern detection sensor according to any one of claims 1 to 9, it adopts a configuration that.

  According to a fifteenth aspect of the present invention, in the image forming apparatus according to the twelfth or fourteenth aspect, the image forming order of the black line image as the reference color is a final color of the color superposition on the transfer body. Adopted.

According to a sixteenth aspect of the present invention, in the image forming apparatus according to any one of the eleventh to fourteenth aspects, the lightness (L ^* ) of the transfer body forming the alignment pattern is 40 or less, preferably The configuration is 20 or less.

  According to a seventeenth aspect of the present invention, in the image forming apparatus according to the twelfth or fourteenth aspect, from the alignment pattern detecting means for an arbitrary shift amount of the line image other than the reference color with respect to the reference color line image of the alignment pattern. When the output signal has one or more extreme values and the horizontal axis is an arbitrary shift amount, the positional deviation correction means calculates the intersection of two straight lines formed on both sides of the extreme value. Is used to determine the amount of misregistration and direction of a color other than the reference color with respect to the reference color, and the intersection point is not calculated using data points in the extreme value or in the vicinity of the extreme value. .

  According to the eighteenth aspect of the present invention, the image forming apparatus according to the seventeenth aspect has a two-component developing type developing device.

  The image forming apparatus according to claim 19 is an image forming apparatus that obtains a color image by an ink jet method, the registration pattern formed by superimposing an image of a reference color and an image of a color other than the reference color, and the alignment An alignment pattern detection means for detecting a pattern, and based on an output signal from the alignment pattern detection means, a positional deviation amount between the image of the reference color and an image of a color other than the reference color and its direction are determined and An image forming apparatus having a misregistration amount correction means for correcting misregistration amount, wherein the alignment pattern detection means is the alignment pattern detection sensor according to any one of claims 1 to 9. The composition is taken.

  The invention according to claim 20 is an image forming apparatus for obtaining a color image by an ink jet method, wherein a plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color are provided. An alignment pattern formed by continuously forming patches in which the relative positional relationship between the two color line images is shifted by an arbitrary amount as one patch, an alignment pattern detecting means for detecting the alignment pattern, Based on the output signal from the alignment pattern detection means, a positional deviation for correcting the positional deviation amount by judging the positional deviation amount and the direction between the black line image of the reference color and the line image of the color other than the reference color. In the image forming apparatus having an amount correction unit, the alignment pattern detection unit is the alignment pattern detection sensor according to any one of claims 1 to 9. Adopts a configuration say.

  In the invention described in Item 21, the alignment pattern formed by superimposing the image of the reference color and the image of the color other than the reference color is detected by the alignment pattern detection means, and the output from the alignment pattern detection means In a color misregistration detection method for determining a misregistration amount and a direction between the reference color image and a color image other than the reference color based on a signal, the alignment pattern detection sensor detects diffuse reflection light or a diffuse reflection component. The light-emitting part and the light-receiving part of the alignment pattern detection means are arranged along the scanning direction of the alignment pattern, and at least the spot shape of the light-receiving part is arranged at a different position of the alignment pattern. The shape is such that the area increment with respect to the shift amount of the color other than the reference color with respect to the reference color is constant.

  According to a twenty-second aspect of the present invention, in the color shift detection method according to the twenty-first aspect, the correlation between the brightness of the detected object on which the alignment pattern is formed and the diffuse reflected light is experimentally grasped and obtained. An appropriate value is determined from the data, and based on this, the brightness of the detected object is set.

  According to a twenty-third aspect of the present invention, in the color misregistration detection method according to the twenty-second aspect, the reference color of the alignment pattern and the output characteristics related to the brightness of the detected object are made substantially equal.

  According to a twenty-fourth aspect of the present invention, based on an output signal from the alignment pattern detection means for an arbitrary shift amount of the line image other than the reference color with respect to the reference color line image of the alignment pattern, the output signal is output by the positional deviation amount correction means. In the color misregistration correction method for correcting the misregistration by calculating the misregistration amount and direction of the color other than the reference color with respect to the reference color by calculating the intersection of two straight lines formed on both sides with respect to the extreme value of For the calculation of the intersection of two straight lines, the data point at or near the extreme value was not used for the calculation.

  According to a twenty-fifth aspect of the present invention, based on an output signal from the alignment pattern detection means for an arbitrary shift amount of the line image other than the reference color with respect to the reference color line image of the alignment pattern, the output signal is output by the positional deviation amount correction means. In the color misregistration correction method for correcting the misregistration by calculating the misregistration amount and direction of the color other than the reference color with respect to the reference color by calculating the intersection of two straight lines formed on both sides with respect to the extreme value of The light emitting part and the light receiving part of the alignment pattern detection means are arranged so as to correct the nonlinearity of the two straight lines.

  According to the first aspect of the present invention, the alignment pattern formed by superimposing the image of the reference color and the image of the color other than the reference color is irradiated with light from the light emitting portion and reflected from the alignment pattern. In the alignment pattern detection sensor for detecting light by the light receiving unit, the light receiving unit is configured to detect diffuse reflection light or a diffuse reflection component of the reflected light, and the light emitting unit and the light receiving unit are configured to detect the alignment pattern. Arranged along the scanning direction, at least the spot shape of the light receiving unit is set to a shape in which the area increment with respect to the shift amount of the color other than the reference color with respect to the reference color at a different position of the alignment pattern is constant. Because of this configuration, it is possible to eliminate the non-linear factors of the two straight lines with respect to the shift amount of the color other than the reference color with respect to the reference color, and the high without using an expensive sensor It can be aligned pattern detection degrees.

  According to the second aspect of the present invention, a plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color are used as one patch, and the relative relationship between the two color line images is determined. Alignment pattern detection sensor that detects light reflected from the alignment pattern by irradiating light from the light-emitting part to an alignment pattern that is formed by continuously forming patches with arbitrary positional shifts by an arbitrary amount The light receiving unit is configured to detect diffuse reflection light or a diffuse reflection component of the reflected light, the light emitting unit and the light receiving unit are disposed along a scanning direction of the alignment pattern, and at least the light receiving unit In the spot shape, the area increment with respect to the shift amount of the line image of the color other than the reference color with respect to the black line image of the reference color at a different position of the alignment pattern is constant. Since the configuration is set to the shape, it is possible to eliminate the non-linear factor of the two straight lines in the shift amount of the line image of the color other than the reference color with respect to the black line image of the reference color, and the high without using an expensive sensor. Accurate alignment pattern detection can be performed.

  According to a third aspect of the present invention, in the alignment pattern detection sensor according to the first or second aspect, since the spot shape of the light receiving portion is a quadrangle, a shift amount of a color other than the reference color with respect to the reference color Since the area increment with respect to is reliably constant, highly accurate alignment pattern detection can be performed.

  According to a fourth aspect of the present invention, in the alignment pattern detection sensor according to any one of the first to third aspects, a central axis of directivity characteristics of the light emitting unit and the light receiving unit is the alignment pattern. Since the configuration coincides with the scanning direction, the linearity of the two straight lines can be further enhanced, and the accuracy of the alignment pattern detection can be further enhanced.

  According to a fifth aspect of the present invention, in the alignment pattern detection sensor according to any one of the first to fourth aspects, the light emitting unit is configured by a light emitting diode, and the light receiving unit is a photodiode or a photo. Since it is composed of transistors, non-linear factors caused by the characteristics of a single element can be reduced, and the linearity of two straight lines can be further improved.

  According to the sixth aspect of the present invention, in the alignment pattern detection sensor according to the fifth aspect, since the light receiving unit is a light receiving element having a wide directivity angle, nonlinear factors caused by characteristics of the single element are obtained. The linearity of two straight lines can be further improved.

  According to the seventh aspect of the invention, in the alignment pattern detection sensor according to the fifth aspect, since the half-value angle of either one or both of the light emitting part and the light receiving part is an element of 30 ° or more, Non-linear factors caused by the characteristics of a single element can be reduced, and the linearity of two straight lines can be further improved.

  According to the invention described in claim 8, in the alignment pattern detection sensor according to claim 5, since either one or both of the light emitting part and the light receiving part is a side view type element, Non-linear factors caused by the characteristics possessed can be reduced, and the linearity of the two straight lines can be further improved.

  According to the ninth aspect of the present invention, in the alignment pattern detection sensor according to the fifth aspect, since either one or both of the light emitting portion and the light receiving portion is a chip-type element, the single element has Non-linear factors caused by the characteristics can be reduced, and the linearity of the two straight lines can be further improved.

  According to the invention described in claim 10, in the alignment pattern detection sensor according to claim 9, since the collimating lens is provided between the chip type element and the alignment pattern to be detected, Non-linear factors caused by the characteristics of a single element can be reduced, and the linearity of two straight lines can be further improved.

According to the eleventh aspect of the present invention, the image forming apparatus includes a plurality of image carriers, and the toner images formed on the image carriers are sequentially transferred onto the transfer member, and then transferred to a sheet-like recording medium. An image forming apparatus for obtaining a color image by using a registration pattern formed by superimposing a reference color image and a color image other than the reference color, and a registration pattern detection unit for detecting the registration pattern And a misregistration amount for correcting the misregistration amount by judging the misregistration amount and direction between the reference color image and the non-reference color image based on an output signal from the alignment pattern detecting means. In the image forming apparatus having the correction unit, the alignment pattern detection unit is the alignment pattern detection sensor according to any one of claims 1 to 9. (1) Conventional edge detection Compared to the formula, it becomes possible to accurately detect at low sampling frequency of about 1/100.
(2) As a result of (1), it is not necessary to increase the speed of the processing circuit section after sampling, so that the cost of the electric hardware configuration can be greatly reduced.
(3) Since the linearity of the two straight lines with respect to an arbitrary shift amount of the color line is greatly improved, the number of patches constituting the alignment pattern can be greatly reduced.
(4) As a result of (3), since the processing time required for the adjustment not related to the normal printing can be greatly shortened like the positional deviation adjustment, the productivity can be greatly improved.
Moreover, since the detection performance is a detection method using diffused light that does not depend on the wear deterioration of a transfer body (positioning pattern carrier) such as a transfer belt, detection accuracy equivalent to the edge detection method using regular reflection light can be obtained. In addition, it can greatly contribute to the extension of the life of the alignment pattern carrier such as a belt, that is, the reduction of the running cost.

  According to the twelfth aspect of the present invention, the image forming apparatus includes a plurality of image carriers, and the toner images formed on the image carriers are sequentially transferred onto the transfer member, and then transferred onto a sheet-like recording medium. An image forming apparatus for obtaining a color image by using a plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color as one patch. An alignment pattern formed by continuously forming patches in which the relative positional relationship of images is shifted by an arbitrary amount, an alignment pattern detection means for detecting the alignment pattern, and an output signal from the alignment pattern detection means In the image forming apparatus having a misregistration amount correcting means for judging the misregistration amount and the direction of the misregistration amount between the black line image of the reference color and the line image of the color other than the reference color based on ,Up Since the alignment pattern detection means is the alignment pattern detection sensor according to any one of claims 1 to 9, the same effect as that of the invention according to claim 11 can be obtained. .

  According to the thirteenth aspect of the present invention, a plurality of image carriers are provided, and the toner images formed on the respective image carriers are sequentially superimposed and transferred onto a sheet-like recording medium carried on the transfer member. An image forming apparatus that obtains a color image by using an alignment pattern formed by superimposing a reference color image and a color image other than the reference color, and an alignment pattern detection unit that detects the alignment pattern; Then, based on an output signal from the alignment pattern detection means, a positional deviation amount correction for judging the positional deviation amount and the direction between the reference color image and the color image other than the reference color and correcting the positional deviation amount. In the image forming apparatus having the above-described configuration, since the alignment pattern detection unit is the alignment pattern detection sensor according to any one of claims 1 to 9, the invention according to claim 11 is provided. Same as It is possible to obtain an effect.

  According to the fourteenth aspect of the present invention, a plurality of image carriers are provided, and the toner images formed on the image carriers are sequentially transferred onto the sheet-like recording medium carried on the transfer member. An image forming apparatus for obtaining a color image by using a plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color as one patch, and a two-color line image An alignment pattern formed by continuously forming patches whose relative positional relationship is shifted by an arbitrary amount, an alignment pattern detection means for detecting the alignment pattern, and an output signal from the alignment pattern detection means In an image forming apparatus having a misregistration amount correcting means for judging a misregistration amount and a direction of a misregistration amount between a black line image of the reference color and a line image of a color other than the reference color based on the direction, and a direction thereof. Above The combined pattern detecting means, since a configuration is a alignment pattern detection sensor according to any one of claims 1 to 9, it is possible to obtain the same effect as described in claim 11.

  According to a fifteenth aspect of the present invention, in the image forming apparatus according to the twelfth or fourteenth aspect, the image forming order of the black line image as the reference color is a final color of the color superposition on the transfer body. As a result, a high S / N ratio can be obtained and the detection accuracy can be improved.

According to a sixteenth aspect of the present invention, in the image forming apparatus according to any one of the eleventh to fourteenth aspects, the lightness (L ^* ) of the transfer body forming the alignment pattern is 40 or less, Since the configuration is preferably 20 or less, a high SN ratio can be obtained and detection accuracy can be improved.

  According to a seventeenth aspect of the present invention, in the image forming apparatus according to the twelfth or fourteenth aspect, the alignment pattern detection means for an arbitrary shift amount of a line image other than a reference color with respect to a reference color line image of the alignment pattern. When the output signal from the output signal has one or more extreme values and an arbitrary shift amount is on the horizontal axis, the positional deviation correction means calculates the intersection of two straight lines formed on both sides of the extreme value. By determining the amount of misregistration and the direction of the color other than the reference color relative to the reference color, the calculation of the intersection point does not use data points in the extreme value or near the extreme value for the calculation. Regardless of the formation state of the alignment pattern, the linearity of the approximate straight line can be further improved, so that the positional deviation detection accuracy can be improved.

  According to the eighteenth aspect of the present invention, since the image forming apparatus according to the seventeenth aspect includes the two-component developing type developing device, line thickening or thinning is liable to occur in forming the alignment pattern. Therefore, in particular, it is possible to exert an effect of improving the positional deviation detection accuracy by further improving the linearity of the approximate straight line.

  According to the nineteenth aspect of the present invention, there is provided an image forming apparatus for obtaining a color image by an ink jet method, wherein a registration pattern formed by superimposing a reference color image and a color image other than the reference color, Alignment pattern detection means for detecting the alignment pattern, and based on an output signal from the alignment pattern detection means, a positional deviation amount and a direction between the reference color image and the color image other than the reference color are determined. An image forming apparatus having a misregistration amount correcting means for correcting the misregistration amount, wherein the alignment pattern detection means is the alignment pattern detection sensor according to any one of claims 1 to 9. Since it was set as the structure, the effect similar to the invention of Claim 11 can be acquired.

  According to the invention of claim 20, there is provided an image forming apparatus for obtaining a color image by an ink jet method, wherein a plurality of lines are formed by superimposing a black line image as a reference color and a line image of a color other than the reference color. An alignment pattern formed by continuously forming patches in which a line is a single patch and the relative positional relationship between two line images is shifted by an arbitrary amount; and an alignment pattern detecting means for detecting the alignment pattern; Then, based on the output signal from the alignment pattern detection means, the amount of misregistration between the black line image of the reference color and the line image of the color other than the reference color and its direction are determined to correct the misregistration amount. 10. The image forming apparatus having a misregistration amount correction unit, wherein the alignment pattern detection unit is the alignment pattern detection sensor according to claim 1. Since a configuration, it is possible to obtain the same effect as described in claim 11.

  According to the twenty-first aspect of the present invention, the alignment pattern formed by superimposing the reference color image and the color image other than the reference color is detected by the alignment pattern detection means, and the alignment pattern detection means In the color misregistration detection method for judging the misregistration amount and direction between the reference color image and the color image other than the reference color based on the output signal, the alignment pattern detection sensor detects the diffuse reflection light or the diffuse reflection. The component is detected, the light emitting portion and the light receiving portion of the alignment pattern detecting means are arranged along the scanning direction of the alignment pattern, and at least the spot shape of the light receiving portion is at a different position of the alignment pattern. Since the area increment with respect to the shift amount of the color other than the reference color with respect to the reference color is constant, the color other than the reference color with respect to the reference color Shift can be eliminated nonlinear factor 2 straight relative amount, it is possible to perform the alignment pattern detection precision without using an expensive sensor.

  According to a twenty-second aspect of the present invention, in the color misregistration detection method according to the twenty-first aspect, the correlation between the brightness of the detected object on which the alignment pattern is formed and the diffuse reflected light is experimentally grasped and obtained. Since an appropriate value is determined from the obtained data and the brightness of the detected object is set based on the determined value, a high SN ratio can be obtained and detection accuracy can be improved.

  According to the invention described in claim 23, in the color misregistration detection method according to claim 22, since the output characteristic related to the reference color of the alignment pattern and the lightness of the detected object are made substantially equal, An SN ratio can be obtained and detection accuracy can be improved.

  According to the twenty-fourth aspect of the present invention, based on an output signal from the alignment pattern detection means for an arbitrary shift amount of the line image other than the reference color with respect to the reference color line image of the alignment pattern, the positional deviation amount correction means performs the above-described operation. In a color misregistration correction method for correcting a misregistration by calculating the misregistration amount and direction of a color other than the reference color with respect to the reference color by calculating the intersection of two straight lines formed on both sides with respect to the extreme value of the output signal. Since the calculation of the intersection of the two straight lines does not use the extreme value or the data point in the vicinity of the extreme value for the calculation, the linearity of the approximate straight line can be further improved regardless of the formation state of the alignment pattern. The positional deviation detection accuracy can be improved.

  According to a twenty-fifth aspect of the present invention, based on an output signal from the alignment pattern detection means for an arbitrary shift amount of the line image other than the reference color with respect to the reference color line image of the alignment pattern, the positional deviation amount correction means performs the above-described operation. In a color misregistration correction method for correcting a misregistration by calculating the misregistration amount and direction of a color other than the reference color with respect to the reference color by calculating the intersection of two straight lines formed on both sides with respect to the extreme value of the output signal. Since the light emitting portion and the light receiving portion of the alignment pattern detecting means are arranged so as to correct the nonlinearity of the two straight lines, the positional deviation detection accuracy can be improved.

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
First, a schematic configuration of a four-tandem direct transfer color printer as an image forming apparatus according to the present embodiment will be described with reference to FIG.
The color printer has three paper feed trays, one manual feed tray 36, two paper feed cassettes 34 (first paper feed tray), and 34 (second paper feed tray). Transfer sheets (not shown) as the sheet-like recording medium are separated one by one in order from the uppermost one by the paper feeding roller 37 and conveyed toward the registration roller pair 23. The transfer sheets fed from the first sheet feed tray 34 or the second sheet feed tray 34 are separated one by one from the uppermost one by the sheet feed roller 35 and are transferred to the registration roller pair 23 via the transport roller pair 39. It is conveyed toward.
The fed transfer paper is temporarily stopped by the pair of registration rollers 23, the skew is corrected, and then the leading edge of the image formed on the photosensitive drum 14Y positioned at the uppermost stream described later and the transfer paper in the transport direction. At a timing coincident with the predetermined position, the sheet is conveyed toward the transfer belt 18 by the rotation operation of the registration roller pair 23 by ON control of a registration clutch (not shown).
When the transfer paper passes through a paper suction nip composed of the transfer belt 18 and a paper suction roller 41 in contact with the transfer belt 18, the transfer paper is attracted to the transfer belt 18 by an electrostatic force by a bias applied to the paper suction roller 41. It is conveyed at a process linear velocity of 125 mm / sec.

The transfer paper adsorbed by the transfer belt 18 has toner transferred to the transfer brushes 21B, 21C, 21M, and 21Y disposed at positions facing the photosensitive drums 14B, 14C, 14M, and 14Y of the respective colors with the transfer belt 18 interposed therebetween. By applying a transfer bias (plus) opposite to the charging polarity (minus), the toner images of the respective colors formed on the photoconductor drums 14B, 14C, 14M, and 14Y are converted into yellow (Y) and magenta (M ), Cyan (C), and black (Bk).
The transfer paper that has undergone the transfer process of each color is separated from the transfer belt 18 by the downstream drive roller 19 and is conveyed to the fixing device 24. By passing through a fixing nip constituted by the fixing belt 25 and the pressure roller 26 in the fixing device 24, the toner image is transferred onto the transfer paper by heat and pressure. In the single-sided printing mode, the fixed transfer paper is discharged to an FD (face-down) tray 30 formed on the upper surface of the apparatus main body.
When the double-sided printing mode is selected in advance, the transfer paper that has exited the fixing device 24 is sent to a reversing unit (not shown), and the front and back sides are reversed by the unit, and then the double-sided transport unit positioned below the transfer unit. It is conveyed to 33. The transfer paper is fed again from the double-sided conveyance unit 33 and conveyed to the registration roller pair 23 through the conveyance roller pair 39. Thereafter, it passes through the fixing device 24 through the same operation as in the single-sided printing mode, and is discharged to the FD tray 30.

Next, the configuration and image forming operation in the image forming unit of the color printer will be described in detail.
Since the image forming unit has the same configuration and operation for each color, the configuration and operation for forming a yellow image will be described as a representative, and the other components are denoted by reference numerals corresponding to the respective colors and description thereof is omitted.
An image forming unit 12Y having a charging roller 42Y and a cleaning unit 43Y, a developing unit 13Y, an optical writing unit 16, and the like are provided around the photosensitive drum 14Y positioned on the most upstream side in the transfer paper conveyance direction.
At the time of image formation, the photosensitive drum 14Y is driven to rotate clockwise by a main motor (not shown), is neutralized by an AC bias (DC component is zero) applied to the charging roller 42Y, and the surface potential is a reference of approximately −50v. It becomes a potential.
Next, the photosensitive drum 14Y is uniformly charged to a potential substantially equal to the DC component by applying a DC bias with an AC bias superimposed on the charging roller 42Y, and the surface potential thereof is approximately −500 v to −700 v (target charging). The potential is determined by the process control unit).
Digital image information sent from a controller unit (not shown) as a print image is converted into a binarized LD light emission signal for each color, and a cylinder lens, a polygon motor, an fθ lens, first to third mirrors, and a WTL. Exposure light 16Y is irradiated onto the photosensitive drum 14Y by an optical writing unit 16 having a lens or the like.
The drum surface potential of the irradiated portion becomes approximately −50 v, and an electrostatic latent image corresponding to image information is formed at a writing density (= resolution) of 600 dpi.

The electrostatic latent image corresponding to the yellow image information on the photosensitive drum 14Y is visualized by the developing unit 13Y. By applying DC (-300 to -500 v) with an AC bias superimposed on the developing sleeve 44Y of the developing unit 13Y, toner (Q / M: -20 to -30 μC / g) is developed to form a toner image. The development unit 13Y is a so-called two-component development type developer containing a mixed developer of carrier and toner.
The formed toner images on the photosensitive drums 14B, 14C, 14M, and 14Y of the respective colors are transferred onto the transfer paper adsorbed on the transfer belt 18 by the transfer bias.

In the color printer according to the present embodiment, a color misregistration adjustment operation is performed prior to the above-described image forming operation. In the color misregistration adjustment operation, an alignment pattern described later is formed on the transfer belt 18, and this alignment pattern is read (detected) by an alignment pattern detection sensor 40 as an alignment pattern detection unit.
The alignment pattern detection sensor 40 is disposed on the lower surface side of the transfer belt 18 facing the photosensitive drum 14B.

As shown in FIG. 2, the alignment pattern Pm for detecting the misregistration in the main scanning direction overlaps a black line image Bk as a reference color and a color other than the reference color, for example, a cyan line image C. A plurality of lines formed in this manner are used as one patch, and patches in which the relative positional relationship between the two color line images is shifted by an arbitrary amount (an arbitrary shift amount) are continuously formed. It is not intended to limit the reference color to black (the same applies to other embodiments below).
Here, the “arbitrary shift amount” includes that the shift amount between P1 and P2 is 50 μm, and the shift amount of P2 to P3 may not always be constant, such as 20 μm.
In the present embodiment, the alignment pattern Pm has a configuration in which one patch has a black line of the same width superimposed on a 12-dot width (= 0.008 mm) color line other than the reference color. The overall configuration of such patches is made up of 13 patches in which the color line C is shifted by 2 dots from the Bk line.
Here, the meaning of “continuously forming patches” means that the patches are arranged along the scanning direction (advancing direction of the transfer belt 18), and the arrangement is, for example, P1, P11, P2, and P10. Even if the order is different, it means that it is included continuously. Moreover, even if the interval between P1 and P2 and the interval between P2 and P3 are different, they are included continuously.

As shown in FIG. 3B, the alignment pattern detection sensor 40 in the present embodiment includes a light emitting diode (LED) 40A as a light emitting unit and a photodiode (PD) 40B as a light receiving unit. The element is supported by a support substrate 45. The light receiving unit may be formed of a phototransistor instead of the photodiode 40B.
The light emitting diode 40A and the photodiode 40B are arranged along the scanning direction of the alignment pattern Pm, and the photodiode 40B is arranged so as to receive only the diffuse reflected light of the reflected light from the alignment pattern Pm.
As shown in FIG. 3A, the spot shape 40A-1 of the light emitting diode 40A and the spot shape 40B-1 of the photodiode 40B are both formed in a square shape. The spot shapes of the light emitting diode 40 </ b> A and the photodiode 40 </ b> B are determined by the shape of the slit formed on the upper surface of the support substrate 45.
As shown in FIG. 4, the alignment pattern Pm is formed at three positions on both sides and the center of the transfer belt 18, and the alignment pattern detection sensor 40 is also supported by a support substrate (not shown) corresponding to this position. (40a, 40b, 40c) are provided. Of these alignment pattern detection sensors 40a, 40b, and 40c, the displacement amount of the alignment pattern Pm for detecting the displacement in the main scanning direction shown in FIG. By detecting this, main scanning deviation and magnification error are corrected.
Further, by detecting the shift amount of the alignment pattern Ps for detecting the positional shift in the sub-scanning direction shown in FIG. Correct the skew.

Next, the reason for the point where the light receiving part of the alignment pattern detection sensor 40 is arranged so as to receive only diffuse reflected light, at least the point where the spot shape of the light receiving part is a square shape, that is, the present invention is conceived. Explain the background and basis for the realization.
As shown in FIG. 37, in the positional deviation detection by the conventional optical sensor, output characteristics that are hardly called a straight line were obtained.
However, as a result of measuring the actual shift amount of the alignment pattern created on the transfer belt 18 with a digital microscope equipped with a 2 million pixel CCD, the two lines completely overlap as shown in FIG. The deviation amount at P7 is almost zero. This means that an error has occurred in the light emission, light reception, and output processes of the conventional optical sensor, although there is almost no displacement in the actual alignment pattern.
As shown in FIG. 10, ^R 2 = 0.9988 in approximate line obtained by plotting points on the negative side with respect to the extreme value, and so ^R 2 = 0.9996 in approximate line obtained by plotting points on the positive side with respect to the extreme value In addition, a result that is as close as possible to the straight line (R ² = 1) is obtained, and as a result of calculating the intersection point from these two straight lines, the displacement amount is 4.13 μm, which is a value that is almost close to the actual value (= 0). .

Here, there are the following two reasons for the difference between the output voltage plot of the sensor shown in FIG. 37 and the deviation plot by the microscope observation shown in FIG.
(1) In the microscopic observation result shown in FIG. 10, the difference value of the deviation amount between adjacent patches is substantially constant (= linear), whereas the output voltage value shown in FIG. The output voltage difference (= change amount) decreases as the distance from the extreme value increases.
(2) In the microscopic observation result shown in FIG. 10, the amount of shift between the mirror images (for example, P4 and P10) is almost equal, whereas the output voltage shown in FIG. There is a difference in the output voltages of P4 and P10).
Therefore, if measures are taken against the causes of these two points, it can be estimated that the amount of positional deviation can be calculated with high accuracy from the intersection calculation result obtained from the two straight lines obtained from the plot of the actual sensor signal output. .

First, in order to consider the result of (1), FIG. 11 shows a relationship between a conventional sensor light receiving surface shape and a pattern.
Since the diffused light output voltage of the sensor is considered to have a certain correlation with the increase in the color line area in the light receiving surface, the area increment with respect to the difference value (4 dots in this case) of the deviation amount between adjacent patches. If is constant, it should be linear.
However, as is clear from FIG. 11, the circular light-receiving surface allows the “area change amount (region P2-1 in P2) with respect to the shift of the color line 4dot of P1 to P2” and “colors of P2 to P3”. It can be understood that the latter is larger in the “area change amount with respect to the shift of the line 4 dots (region P3-1 in P3)”. This is not limited to the case where the light receiving surface is circular, but the same applies to an elliptical shape.
Therefore, it can be understood that the shape of the light receiving surface may be, for example, a quadrangle in order to make the area increment relative to the shift amount constant.

In order to verify that the result as in (1) occurs due to the circular shape of the light receiving surface, “the diffused light output of the optical sensor is 1 with respect to the area of the color line image in the light receiving surface. Assuming that there is a “linear relationship”, the area of the color line image in the optical sensor light receiving surface of each patch of the two-color superposition pattern is calculated, and this area value is used as the output value of each patch. Simulation calculations were performed.
In addition, a calculation for obtaining a detection error of the misregistration amount is also performed by calculating the intersection of two straight lines obtained when this area value is plotted against “shift amount of the color line image with respect to the reference color (black) on the horizontal axis”. It was.

[a formula]
As shown in FIG. 12, the rectangular area S of one section located at a distance a from the center of the light receiving surface is S = 2 × [a × tan (acos (a / 1.5))] × (25. 4/600) as a function of the distance a from the center of the light receiving surface.
[Calculation condition]
(1) Sensor light receiving diameter: (diameter = 3.0 mm)
(2) Line width (Bk, Color): 24 dots (= 1.016 mm)
* Here, 600 dpi, that is, 1 dot = 42.3 μm.

FIG. 13 shows the calculation result by simulation. The result shown in FIG. 13 is almost the same as the result of the output voltage shown in FIG. 37, and the shape of the light receiving surface is disclosed in Japanese Patent No. 3254244, Japanese Patent Laid-Open No. 11-291477, and the like. If the color line of the patch formed by superimposing two color lines is superposed by one superposition of the minimum number of lines, the shift amount of the color line It was confirmed that linearity was not obtained in the output characteristics of the sensor, that is, non-linearity.
Accordingly, an alignment pattern formed by continuously forming patches in which a plurality of line images formed by superimposing two color line images is one patch, and the relative positional relationship between the two color line images is shifted by an arbitrary amount. If the light receiving surface of the optical sensor for detecting the circular shape is circular, the output characteristics with respect to an arbitrary shift amount will be nonlinear, and high-accuracy misalignment detection will not be possible, so the area increment with respect to the shift amount is constant. The conclusion is that it must be set to a shape such as a square or a rectangle.

Next, let us examine the cause of the result of (2).
As a cause of the difference in output between patches having a mirror image relationship with respect to the extreme value described in (2), it is conceivable that the areas of the color toner portions are different from each other as in (1).
Therefore, the same simulation calculation as described above was performed when the center of the black line was shifted by 2 dots with respect to the center of the light receiving surface. The result is shown in FIG.
As shown in FIG. 14, it was found that the output voltages of the mirror images of the patches are not equal because the center of the Bk line as the reference color is shifted from the center of the light receiving surface. From this, when the experiment shown in FIG. 37 was performed, the intention was that the center of the Bk line was almost aligned with the center of the light receiving surface, but this was actually caused by a slight shift. I think that the.
The results shown in FIG. 37 are for the case where the number of lines is the minimum configuration number, and in order to eliminate such an error factor, it is considered that the light receiving width should be sufficiently wider than the line width. It is.

Considering that there are other factors that cause a difference in the output voltage of the patch having such a mirror image relationship, the optical sensor shown in FIG. The LED and the light receiving element are composed of phototransistors, and these elements have directivity characteristics as characteristics of the element alone.
15 shows a directivity characteristic diagram of the LED shown in FIG. 36, and FIG. 16 shows a directivity characteristic diagram of the phototransistor shown in FIG. Since the single element has directivity characteristics as shown in FIGS. 15 and 16, as shown in FIG. 17, the central axis of the directivity characteristics of the light emitting element and the light receiving element is shifted with respect to the pattern scanning direction. (Conventional sensor arrangement) will obviously have an output distribution within the light receiving area, so the output voltage of the patch having a mirror image relationship as described in (2) may differ. .

Accordingly, an alignment pattern formed by continuously forming patches in which a plurality of line images formed by superimposing two color line images is one patch, and the relative positional relationship between the two color line images is shifted by an arbitrary amount. In the optical sensor for detecting the light, the central axis of the directivity of the light receiving element and the light emitting element needs to coincide with the pattern scanning direction. That is, it is necessary to arrange the light receiving element and the light emitting element along the pattern scanning direction.
Based on the knowledge based on this experiment, in the present embodiment, as shown in FIG. 5, the central axes of the directivity characteristics of the light emitting diode 40A and the photodiode 40B are aligned with respect to the pattern scanning direction.

Further, in order to make the light intensity distribution and the light receiving sensitivity distribution in the light receiving surface as uniform as possible, a light receiving element having a wide directivity angle is selected. 6 shows a directional characteristic diagram of the light emitting diode 40A, and FIG. 7 shows a directional characteristic diagram of the photodiode 40B. Compared to the conventional optical sensor shown in FIG. 36, the half-value angle of the light emitting diode 40A is widened to 35 °, and the half-value angle of the photodiode 40B is widened to 45 °. It has changed.
The conventional optical sensor shown in FIG. 36 simply requires high output to the sensor element, and both the light emitting element and the light receiving element adopt elements called radial type, top view type, or bullet type. is doing.
On the other hand, in the present embodiment, as described above, in order to eliminate the light emission distribution and the light reception sensitivity distribution in the light receiving surface as much as possible, that is, to make the distribution uniform, the wide directivity angle and the variation in directivity characteristics in the manufacturing method of the element A so-called side view type element having a small size is selected.

In this embodiment, a polyimide belt having a lightness L ^* (JISZ8729) = 1.7 is used as the transfer belt 18 on which the alignment pattern Pm is formed. The reason for the above-described configuration including this will be described in further detail below.
(Registration pattern configuration)
FIG. 18 is a graph in which the specular reflection light output voltages of the belt background portion, Bk solid patch portion, and C (cyan) patch portion of the conventional sensor shown in FIG. 36 are plotted against the LED current on the horizontal axis.
Here, for example, looking at the output voltage of each patch portion when the LED current setting (= 37 mA) at which the output voltage of the transfer belt background portion is 4.0 V, the results shown in Table 1 are obtained.

Here, considering that the alignment pattern of FIG. 18 is read with specular reflection light output, the area ratio of P1 and P13 is black line × 50% + color line × 50%, and the area ratio of P7 is Since it is black line × 50% + color line × 50%, the sensor output of each patch portion is approximately as follows.
(When "Bk line group" is formed on "Color line group")
Output voltage of P1 and P13 = 0.12 (Bk solid) × 0.5 + 1.91 (C solid) × 0.5 = 1.015v
P7 output voltage = 0.12 (Bk solid) × 0.5 + 4.0 (belt portion) × 0.5 = 2.06v
(When “Bk line group” is formed under “Color line group”)
Output voltage of P1 and P13 = 0.12 (Bk solid) × 0.5 + 1.91 (C solid) × 0.5 = 1.015v
Output voltage of P7 = 1.91 (C solid) × 0.5 + 4.0 (belt portion) × 0.5 = 2.955v

When the output voltage of each patch is plotted against “arbitrary shift amount of the color line on the horizontal axis”, the result shown in FIG. 19 is obtained. The following can be understood from FIG.
(When detecting with specular reflection light)
(A) The output voltage becomes maximum at the patch (P7) in which the two color lines are completely overlapped, and the output voltage is almost determined by the output from the belt background portion.
(B) When the “black line group” is above the “color line group”, the output difference between the minimum values (P1, P13) and the maximum value (P7) is smaller than when the “black line group” is below. Become.
As described above, since the output of the maximum value (P7) in the case of performing detection with specular reflection light is determined by the output from the belt background portion (glare gloss),
(C) When the glossiness decreases due to wear over time or partial scratches, the output of the portion decreases. In other words, since the belt cannot be detected due to deterioration of the belt due to wear over time, this determines the belt life.

  That is, as in P2 to P12 shown in FIG. 2, the specular reflection light output voltage of the patch part where the belt surface is partially exposed is a surface shape represented by belt glossiness, surface roughness Rz, or the like. As a result of being easily affected by characteristic noise, for example, if there is a scratch in the background portion of the P6 patch, the output differs from this in the mirror image P8, and as a result, the intersection position obtained by calculation is shifted. Will occur.

On the other hand, when detection is performed using diffuse reflected light, the amount of misalignment can be detected almost without being affected by the roughness of the surface of the transfer belt 18.
FIG. 20 is a graph in which the diffuse reflected light output voltages of the belt background portion, Bk solid portion, and C (cyan) solid portion of the conventional sensor shown in FIG. 36 are plotted against the LED current on the horizontal axis.
As shown in FIG. 22, the specular reflection light output has a high correlation with the glossiness of the detected object (transfer belt 18 on which the alignment pattern is formed), whereas the diffused light output is detected as shown in FIG. Since the correlation with the lightness L ^{* of the} object is high and there is no correlation with the glossiness, the transfer belt 18 of L ^* = 1.7 mounted on the color printer in this embodiment has almost the same output characteristics as black toner. Have. As is clear from FIG. 23, linearity is obtained up to lightness L ^* of about 40, and linearity is extremely high up to lightness L ^* of 20.
Here, when considering the following two cases in the same manner as described above, the output voltage of each part is as shown in Table 2.

(When "Bk line group" is formed on "Color line group")
Output voltage of P1 and P13 = 0.16 (Bk solid) × 0.5 + 3.42 (C solid) × 0.5 = 1.79v
Output voltage of P7 = 0.16 (Bk solid) × 0.5 + 0.07 (belt portion) × 0.5 = 0.115v
(When “Bk line group” is formed under “Color line group”)
Output voltage of P1 and P13 = 0.16 (Bk solid) × 0.5 + 3.42 (C solid) × 0.5 = 1.79v
Output voltage of P7 = 3.42 (C solid) × 0.5 + 0.07 (belt portion) × 0.5 = 1.745v

When the output voltage of each patch is plotted against “arbitrary shift amount of the color line on the horizontal axis”, the result shown in FIG. 21 is obtained. The following can be understood from FIG.
(When detecting by diffuse reflection)
(A) The output voltage becomes minimum at a patch (P7) in which two color lines are completely overlapped, and the output voltage is determined by the output voltage of the “color line group”.
(B) When the “black line group” is above the “color line group”, the output difference between the maximum values (P1, P13) and the minimum value (P7) can be made larger than when the “black line group” is below. .
Thus, since the output of the maximum value (P7) in the case of performing detection by diffuse reflection light is determined by the output (brightness) from the “color line group”,
(C) It is not affected at all by wear over time or partial scratches.
In other words, since the detection performance does not depend on the belt deterioration, the life of the transfer belt can be extended.

As described above, a patch in which a plurality of lines formed by superimposing a black line image that is a reference color and a line image other than the reference color are used as one patch, and the relative positional relationship between the two color line images is shifted by an arbitrary amount. When detecting the alignment pattern formed continuously by the optical sensor for detecting this alignment pattern, the transfer belt wears or changes with time such as partial scratches. In order to perform detection without any influence of factors,
(1) It is desirable to detect by diffused light output,
(2) It is desirable that the image forming order of the black line image as the reference color is the final color of color superimposition on the transfer body,
(3) It can be said that the lightness (L ^* ) of the transfer body forming the alignment pattern is 40 or less, preferably 20 or less.

The results shown in FIG. 20 indicate that the output light value of the specular reflection light when the LED current If is fixed at 20 mA for the transfer belts having 42 kinds of glossiness and lightness is 60 ° gloss on the surface of the transfer belt on the horizontal axis. It is plotted against degrees. Moreover, the glossiness measured value shown in this figure is a value measured under the condition of a measurement angle of 60 ° using a gloss meter PG-1 manufactured by Nippon Denshoku.
The results shown in FIG. 23 are plotted with respect to the lightness L ^* of the transfer belt surface on the horizontal axis when the LED current is fixed at 20 mA for the same 42 types of belts shown in FIG. It is a thing. In addition, the brightness measurement value shown to this figure is the value measured on condition of the light source D50 and the viewing angle of 2 degrees using X-Rite938 made from X-Rite.

Next, a method for calculating the positional deviation amount from the output voltage value of each patch unit will be described.
First, in the state where there is no positional deviation, since the output becomes the minimum value in the patch (P7) that is completely overlapped, two approximations that can be made on the plus side and minus side in the X-axis direction with respect to this minimum value. The amount of deviation can be calculated by obtaining a straight line by, for example, the least square method and obtaining the value of the X axis that is the intersection.
That is, the shift amount x = (db) / (ac) can be calculated from two simultaneous equations of y = ax + b and y = cx + d.
Next, considering the case where color misregistration occurs, the output value of each patch changes according to the color misregistration amount. Therefore, if the intersection of two line segments obtained from each output value is obtained, the same applies. Therefore, the amount of color misregistration can be calculated.

Here, examination is made as to which data point is used when obtaining each of the two approximate lines. First, the experimental results are shown in FIG.
The graph of FIG. 24 is a superposition pattern of the Bk line and the color line (C line) as shown in FIG. 2, and each patch has a line width of 1000 μm and the color line is shifted by 100 μm from the Bk line. An individual alignment pattern is formed on the transfer belt 18, and the line width ratio between C (cyan) and Bk of each patch is measured with a digital microscope equipped with a 2 million pixel CCD. It is plotted against "arbitrary shift amount of color line", but the rate of change of the line width ratio to "arbitrary shift amount of color line on the horizontal axis" has decreased near the maximum value. I understand.
FIG. 25 shows the relationship between the amount of shift on the horizontal axis and the sensor output voltage on the vertical axis when the sensor detects a patch in which the line width of each color is 500 μm and the color line is shifted by 10 μm from the Bk line. It is a graph. From this figure, it can be seen that the linearity deteriorates in the vicinity of the maximum value and in the vicinity of the minimum value.

This was investigated because the output was saturated when the actual output voltage was in the vicinity of the maximum value, but as shown in FIGS. 24 and 25, the actual patch is almost the same. It was confirmed that it was saturated like this.
Therefore, it can be said that the saturation phenomenon of the output in the vicinity of the maximum value and the minimum value is not a problem on the sensor side but a problem on the image forming apparatus side where the pattern is formed.
It was confirmed by observation with a digital microscope that the reason for this result was that both the Bk and C lines had become thicker than the target line width (= 1000 μm). The cause of such a phenomenon includes the influence of toner density and the like, but it has been confirmed that the phenomenon becomes remarkable particularly when a two-component developing device in which a line edge effect easily occurs.

In this result, as shown in FIG. 26, since both the Bk line and the C line were thickened, such output saturation appeared only on the maximum value side. As shown in FIG. 26, when line weighting occurs, even if the C line is shifted from the state of the patch A shown in FIG. 26A to the state of the patch B shown in FIG. There is no change in the C line in the meantime, and the output is the same and cannot be detected.
Based on this experimental rule, if the Bk toner density is very high, only the Bk line is thickened, and the color toner density is very low. It can be estimated that the same output saturation phenomenon occurs near the minimum value.
That is, as shown in FIG. 27, even if the C line is shifted from the state of the patch A shown in FIG. 27A to the state of the patch B shown in FIG. 27B, the shift of the C line is within the range of the Bk line. The output is the same and cannot be detected.

Therefore, it is desirable to exclude the maximum value and the minimum value or data in the vicinity of the data point used for obtaining the approximate straight line in order to eliminate the influence of the inherent characteristic of the image forming apparatus as much as possible. Specifically, for example, only the data of (maximum value + minimum value) / 2 ± (maximum value-minimum value) × 0.4 is used for the calculation from the maximum value and the minimum value of the outputs of the plurality of patches. .
In order to show a clear effect of the alignment pattern detection sensor 40 in this embodiment on the conventional sensor, comparison data with the case where the alignment pattern Pk shown in FIG. 35 is detected by the conventional sensor shown in FIG. As shown in FIG.
With the structure described above the alignment pattern detection sensor 40, in order to determine the coefficient R ² of the approximate straight line representing the two lines of the linear approaches 1 as possible, thereby enabling highly accurate position deviation amount detected by I understand.

Note here, in order to compare the coefficient of determination of an approximate expression under the same conditions, the approximate expression is the X axis direction negative side of the data all points to the extreme values of the two straight lines, the R ² using the positive side of the data all points However, if the extreme value data is not used for the intersection calculation due to the reason mentioned above (thickness or thinning of the line), the straight line on the left side of the minimum value is R ² = 0.9996 becomes 0.9989, The straight line on the right side becomes 0.9967 when R ² = 0.9901.
Thus, it was found that almost the same linearity (= coefficient of determination R ² is substantially equal) and two straight lines obtained 2 million observation by a digital microscope of the pixel CCD mounting results shown in FIG. 10 is obtained.

As described above, the linearity is improved by improving the alignment pattern detection sensor side, and the linearity is further improved by excluding extreme value data from the data points used for the intersection calculation. The number of data points (that is, the number of patterns) used for calculating the formula can be reduced to a minimum of two points for each straight line (the total number of patches is up to four).
Therefore, it is possible to greatly reduce the processing time of the misregistration adjustment operation that is not related to the normal printing operation, that is, does not contribute to productivity.
In addition, even when such a sensor is used, it is possible to detect the amount of misalignment with high accuracy. Therefore, sufficient amount of misregistration can be detected by sampling at a low sampling frequency of about 1/100 of the conventional edge detection method. Is possible.

The positional deviation correction based on the alignment pattern detection sensor 40 and the method described above is performed by the positional deviation amount correction means. The positional deviation amount correcting means 46 will be described with reference to FIG.
The light emitting diode 40A, which is the light emitting part of the alignment pattern detection sensors 40a, 40b, 40c, is controlled in light emission quantity by the light emission quantity control part 47, and the photodiode 40B on the output side is an amplifier 48, a filter 49, an A / D converter. 50, connected to the I / O port 54 via the FIFO memory 51.
Detection signals obtained from the alignment pattern detection sensors 40a, 40b, and 40c are amplified by an amplifier (AMP) 48, pass through a filter 49, and converted from analog data to digital data by an A / D converter 50. .
Sampling of data is controlled by the sampling control unit 52, and the sampled data is stored in the FIFO memory 51. The sampling control unit 52 and the write control board 53 are connected to the I / O port 54.

The I / O port 54, the CPU 55, the ROM 56, and the RAM 57 are connected by a data bus 58 and an address bus 59.
The ROM 56 stores various programs including a program for calculating the positional deviation amount of the alignment pattern Pm. The program for calculating the positional deviation amount of the alignment pattern Pm includes conditions such as excluding extreme value data from the data points used for the intersection calculation described above.
The address bus 59 designates a ROM address, a RAM address, and various input / output devices.
The CPU 55 monitors the detection signals from the alignment pattern detection sensors 40a, 40b, and 40c at a predetermined timing, and reliably ensures that the light emitting diode 40A of the alignment pattern detection sensors 40a, 40b, and 40c is deteriorated. The light emission amount of the light emitting diode 40A is controlled by the light emission amount control unit 47 so that the alignment pattern Pm can be detected so that the output level of the light reception signal from the photodiode 40B is always constant.

Further, the CPU 55 is based on the correction amount obtained from the detection result of the alignment pattern (including the alignment pattern for the purpose of detecting the displacement in the sub-scanning direction to be described later), based on the change of the main and sub-registration and the magnification error. In order to change the image frequency, the setting is made to the writing control board 53.
The write control board 53 is provided with a device capable of setting the output frequency very finely, for example, a clock generator using a VCO (Voltage Controlled Oscillator) for each color including the reference color. This output is used as an image clock. The CPU 55 also controls a stepping motor (not shown) for skew adjustment in the optical writing unit 16 based on the correction amount obtained from the detection result of the alignment pattern.
The above-described elements other than the alignment pattern detection sensors 40a, 40b, and 40c constitute a positional deviation amount correction means 46. The misregistration amount correction means 46 can also serve as the main controller of the color printer.

The positional deviation adjustment operation by the positional deviation amount correction means 46 includes (1) when the power is turned on, (2) when the temperature change of the optical system is a predetermined value (for example, 5 deg) or more, and (3) a certain number of prints or more. Executed when a job matches one of the conditions at the end of the job.
In the present embodiment, a general-purpose side view type element is selected from the viewpoint of configuring the alignment pattern detection sensor 40 as a single unit as inexpensively as possible. However, the light emission distribution or the light sensitivity distribution in the light receiving surface is as uniform as possible. For example, a wide area chip type flat lens element is selected, and a collimating lens having a collimating function is provided on the entire surface of the chip type element on the alignment pattern Pm side. High linearity can be obtained (second embodiment).
In the first embodiment, the alignment pattern for detecting color misregistration in the main scanning direction has been described. However, when color misregistration in the sub-scanning direction (the same direction as the moving direction of the transfer belt 18) is detected. 28, the alignment pattern Ps as shown in FIG. 28 is formed on the transfer belt 18 in the same manner as the case shown in FIG.
Similar to the alignment pattern Pm, the alignment pattern Ps includes a plurality of lines formed by superimposing a black line image Bk as a reference color and a color other than the reference color, for example, a cyan line image C, as one patch. The patch is formed by continuously forming patches in which the relative positional relationship between the two color line images is shifted by an arbitrary amount.

The present invention is also effective for the shape of the light receiving surface of the sensor and the arrangement of the sensor in the pattern scanning direction so as to decompose light into P wave and S wave components by using a beam splitter (third). Embodiment).
One example will be described with reference to FIG. The alignment pattern detection sensor 60 as the alignment pattern detection means in this embodiment includes a light emitting diode (hereinafter referred to as LED) 61 as one light emitting unit and a photodiode (hereinafter referred to as PD) as three light receiving units. 62, 63, 64 and two polarization beam splitters (hereinafter referred to as PBS) 65, 66.

The polarization state of the projection 67 emitted from the LED 61 is random, but the PBS 65 causes a light component (S wave light) to vibrate in a direction perpendicular to the incident surface and a light component to vibrate in a direction parallel to the incident surface. (P wave light). The S wave light 68 is reflected by the PBS 65 and enters the PD 62, and the P wave light 69 is transmitted through the PBS 65 and projected onto the alignment pattern of the transfer belt 18.
The P wave light 69 reflected from the alignment pattern has a random polarization state due to irregular reflection, and is separated into P wave light 70 and S wave light 71 by the PBS 66. The P wave light 70 passes through the PBS 66 and enters the PD 63, and the S wave light 71 is reflected by the PBS 66 and enters the PD 64.
In the present embodiment, the PDs 62, 63, and 64 serving as light receiving units receive diffuse reflection components instead of diffuse reflection light.

In each of the above embodiments, an example of application in a four-tandem direct transfer type color image forming apparatus has been shown. However, as shown in FIG. 30, after transferring to an intermediate transfer body in a four-tandem tandem configuration, batch transfer to a transfer sheet The same can be applied to the color image forming apparatus of the method (fourth embodiment).
In the present embodiment, the alignment patterns Pm and Ps described above are formed on the intermediate transfer belt 2 as an intermediate transfer member, and this is detected by the alignment pattern detection sensor 40 disposed in the vicinity of the support roller 2B. The positional deviation correction means is the same as in the first embodiment.

The outline of the configuration and operation of a tandem type color copying machine as an image forming apparatus according to this embodiment will be described below. The color copying machine 1 has an image forming unit 1A located at the center of the apparatus main body, a paper feeding unit 1B located below the image forming unit 1A, and an image reading unit 1C located above the image forming unit 1A. is doing.
An intermediate transfer belt 2 as a transfer body having a transfer surface extending in the horizontal direction is disposed in the image forming unit 1A, and an image of a color complementary to the color separation color is disposed on the upper surface of the intermediate transfer belt 2. The structure for forming is provided. That is, the photoreceptors 3Y, 3M, 3C, and 3B as image carriers capable of carrying an image of toners of complementary colors (yellow, magenta, cyan, and black) are juxtaposed along the transfer surface of the intermediate transfer belt 2. Has been.

Each of the photoconductors 3Y, 3M, 3C, and 3B is composed of a drum that can rotate in the same counterclockwise direction, and around the charging device 4 is a charging unit that performs image forming processing in the rotation process. An optical writing device 5 as an exposure unit for forming an electrostatic latent image having a potential _VL based on image information on each of the photoconductors 3Y, 3M, 3C, and 3B, and an electrostatic latent image on each photoconductor 3 A developing device 6 as a developing means for developing the toner with toner having the same polarity as that of the electrostatic latent image, a transfer bias roller 7 as a primary transfer means, an applied voltage member 15, and a cleaning device 8 are disposed. The alphabet added to each symbol corresponds to the color of the toner as in the photosensitive member 3. Each developing device 6 accommodates each color toner.
The intermediate transfer belt 2 is configured to be wound around a plurality of rollers 2A to 2C and move in the same direction at a position facing the photoreceptors 3Y, 3M, 3C, and 3B. A roller 2C, which is different from the rollers 2A and 2B that support the transfer surface, faces the secondary transfer device 9 with the intermediate transfer belt 2 interposed therebetween. In FIG. 30, reference numeral 10 denotes a cleaning device for the intermediate transfer belt 2.

The surface of the photoreceptor 3Y is uniformly charged by the charging device 4Y, and an electrostatic latent image is formed in the form of the photoreceptor 3Y based on image information from the image reading unit 1C. The electrostatic latent image is visualized as a toner image by a developing device 6Y containing yellow toner, and the toner image is applied to the transfer bias roller 7Y on the intermediate transfer belt 2 as a first transfer step. It is attracted by the electric field generated by the voltage and transferred.
The applied voltage member 15Y is provided on the upstream side of the transfer bias roller 7Y in the rotation direction of the photoreceptor 3Y. The applied voltage member 15Y applies a voltage to the intermediate transfer belt 2 that has the same polarity as the charging polarity of the photosensitive member 3Y and has an absolute value that is greater than the solid _VL. The toner is prevented from being transferred to the transfer belt 2, thereby preventing disturbance due to dust when the toner is transferred from the photoreceptor 3 </ b> Y to the intermediate transfer belt 2.

The other photoconductors 3M, 3C, and 3B also form similar images only with different toner colors, and the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 2 and superimposed.
The toner remaining on the photosensitive member 3 after the transfer is removed by the cleaning device 8, and the potential of the photosensitive member 3 is initialized by a neutralizing lamp (not shown) after the transfer to prepare for the next image forming process.
The secondary transfer device 9 includes a transfer belt 9 </ b> C that is wound around the charging drive roller 9 </ b> A and the driven roller 9 </ b> B and moves in the same direction as the intermediate transfer belt 2. By charging the transfer belt 9C with the charging drive roller 9A, it is possible to transfer a multicolor image superimposed on the intermediate transfer belt 2 or a single color image carried on a sheet 28 as a transfer material.

The paper 28 is fed from the paper feed unit 1B to the secondary transfer position. The paper feed unit 1B has a plurality of paper feed cassettes 1B1 in which papers 28 are stacked and housed, and a paper feed roller 1B2 that separates and feeds the papers 28 contained in the paper feed cassette 1B1 one by one in order from the top. A pair of conveying rollers 1B3, a pair of registration rollers 1B4 positioned upstream of the secondary transfer position, and the like.
The paper 28 fed from the paper feed cassette 1B1 is temporarily stopped by the registration roller pair 1B4, and after correcting the oblique displacement and the like, the front end of the toner image on the intermediate transfer belt 2 and a predetermined position at the front end in the transport direction are set. Are sent to the secondary transfer position by the registration roller pair 1B4. A manual feed tray 29 is provided on the right side of the apparatus main body so that it can be turned up and down, and the paper 28 accommodated in the manual feed tray 29 joins the paper feed path from the paper feed cassette 1B1 fed by the paper feed roller 31. The paper is sent toward the registration roller pair 1B4 by the conveying path.

In the optical writing device 5, writing light is controlled by image information from the image reading unit 1C or image information output from a computer (not shown), and writing is performed on the photoconductors 3Y, 3M, 3C, and 3B according to the image information. Light is emitted to form an electrostatic latent image at a writing density (= resolution) of 600 dpi.
The image reading unit 1C includes an automatic document feeder 1C1, a scanner 1C2 having a contact glass 80 as a document table, and the like. The automatic document feeder 1C1 has a configuration capable of reversing the document fed on the contact glass 80, and can perform scanning on each surface of the document.
The visible image processing is performed by the electrostatic latent image two-component (carrier and toner) developing device 6 formed on the photoconductor 3 formed by the optical writing device 5 and is primarily transferred to the intermediate transfer belt 2. When the toner images for each color are superimposed and transferred onto the intermediate transfer belt 2, they are secondarily transferred onto the paper 28 by the secondary transfer device 9. The second-transferred paper 28 is sent to the fixing device 11 where the unfixed image is fixed by heat and pressure. Residual toner on the intermediate transfer belt 2 after the secondary transfer is removed by the cleaning device 10.

  The paper 28 that has passed through the fixing device 11 is selectively guided to the conveyance path toward the paper discharge tray 27 and the reverse conveyance path RP by the conveyance path switching claw 12 provided on the downstream side of the fixing apparatus 11. When the paper is conveyed toward the paper discharge tray 27, it is discharged onto the paper discharge tray 27 by the paper discharge roller pair 32 and stacked. When guided to the reversal conveyance path RP, it is reversed by the reversing device 38 and sent again toward the registration roller pair 1B4.

With the above configuration, in the color copying machine 1, an electrostatic charge is applied to the uniformly charged photoconductor 3 by exposing and scanning a document placed on the contact glass 80 or by image information from a computer. A latent image is formed, and the electrostatic latent image is subjected to visible image processing by the developing device 6, and then the toner image is primarily transferred to the intermediate transfer belt 2.
In the case of a single image, the toner image transferred to the intermediate transfer belt 2 is transferred as it is to the paper 28 fed out from the paper supply unit 1B. In the case of a multi-color image, the images are superimposed by repeating primary transfer, and then secondary transferred onto the paper 28 at once.
After the secondary transfer, the paper 28 is fixed with an unfixed image by the fixing device 11 and then discharged to the paper discharge tray 27 or reversed and sent again toward the registration roller pair 1B4 for double-sided image formation.

Further, each color toner image is formed using one photosensitive drum and a revolver type developing device, and each toner image is transferred onto an intermediate transfer member, and then transferred onto a transfer sheet as a sheet-like recording medium. The same can be applied to the color image forming apparatus of the type (fifth embodiment). An example is shown in FIG.
In the present embodiment, the above-described alignment patterns Pm and Ps are formed on an intermediate transfer belt 426 as an intermediate transfer body, and this is detected by an alignment pattern detection sensor 40 disposed in the vicinity of the driving roller 444. The positional deviation correction means is the same as in the first embodiment.

The outline of the configuration of a color copying machine as an image forming apparatus in the present embodiment will be described below.
In a color copying machine, a writing optical unit 400 serving as an exposure unit converts color image data from the color scanner 200 into an optical signal and performs optical writing corresponding to a document image, on a photosensitive drum 402 serving as an image carrier. An electrostatic latent image is formed on the surface.
The writing optical unit 400 includes a laser diode 404, a polygon mirror 406, a rotation motor 408 thereof, an f / θ lens 410, a reflection mirror 412, and the like.
The photosensitive drum 402 is rotated in the counterclockwise direction as indicated by an arrow, and the photosensitive drum cleaning unit 414, the charge eliminating lamp 416, the potential sensor 420, and the rotary developing device 422 are selected around the photosensitive drum 402. A developing device, a development density pattern detector 424, an intermediate transfer belt 426 as an intermediate transfer member, and the like are arranged.

The rotary developing device 422 includes a black developing unit 428, a cyan developing unit 430, a magenta developing unit 432, a yellow developing unit 434, and a rotation driving unit (not shown) that rotates each developing unit. Each developing device has the same configuration as the developing device 4 shown in the above embodiment. The conditions and specifications of the magnetic carrier are the same.
In the standby state, the rotary developing device 422 is set at the black development position. When the copying operation is started, the color scanner 200 starts reading the black image data at a predetermined timing. Based on the above, optical writing with a laser beam and formation of an electrostatic latent image (black latent image) are started.

In order to develop from the leading edge of the black latent image, before the leading edge of the latent image reaches the developing position of the black developing device 428, the developing sleeve is started to rotate and the black latent image is developed with black toner. A negative polarity toner is formed on the photosensitive drum 402.
Thereafter, the development operation of the black latent image area is continued, but when the trailing edge of the latent image passes the black development position, the rotary development is quickly performed from the development position for black to the development position for the next color. The device 422 rotates. This operation is completed at least before the leading edge of the latent image by the next image data arrives.
When the image forming cycle is started, first, the photosensitive drum 402 is rotated counterclockwise as indicated by an arrow, and the intermediate transfer belt 426 is rotated clockwise by a drive motor (not shown). As the intermediate transfer belt 426 rotates, black toner image formation, cyan toner image formation, magenta toner image formation, and yellow toner image formation are performed. Finally, black (Bk), cyan (C), and magenta (M) are formed. , Yellow (Y) in this order (primary transfer) on the intermediate transfer belt 426 to form a toner image.

The intermediate transfer belt 426 includes a primary transfer electrode roller 450 that faces the photosensitive drum 402, a drive roller 444, a secondary transfer counter roller 446 that faces the secondary transfer roller 454, and a cleaning unit that cleans the surface of the intermediate transfer belt 426. It is stretched between the supporting members of the cleaning facing roller 448A facing the surface 452, and is driven and controlled by a driving motor (not shown).
The black, cyan, magenta, and yellow toner images sequentially formed on the photosensitive drum 402 are accurately and sequentially aligned on the intermediate transfer belt 426, thereby forming a four-color superimposed belt transfer image. This belt transfer image is collectively transferred onto a sheet by a secondary transfer counter roller 446.

Each of the recording paper cassettes 458, 460, and 462 in the paper supply bank 456 contains various sizes of paper different from the size of the paper stored in the cassette 464 in the apparatus body. The designated paper is fed and conveyed in the direction of the registration roller pair 470 by the paper feed roller 466 from the size paper storage cassette. In FIG. 31, reference numeral 468 denotes a manual paper feed tray for OHP paper, thick paper, and the like.
At the time when image formation is started, the paper is fed from the paper feed port of one of the above cassettes and waits at the nip portion of the registration roller pair 470. Then, when the leading edge of the toner image on the intermediate transfer belt 426 approaches the secondary transfer counter roller 446, the registration roller pair 470 is driven so that the leading edge of the sheet exactly coincides with the leading edge of the image. Is done.

In this manner, the sheet is overlapped with the intermediate transfer belt 426 and passes under the secondary transfer counter roller 446 to which a voltage having the same polarity as the toner is applied. At this time, the toner image is transferred to the paper. Subsequently, the sheet is neutralized, peeled off from the intermediate transfer belt 426, and moved to the sheet conveying belt 472.
The sheet onto which the four-color superimposed toner images have been collectively transferred from the intermediate transfer belt 426 is conveyed to the belt fixing type fixing device 470 by the paper conveying belt 472, and the toner image is fixed by the fixing device 470 by heat and pressure. The sheet that has been fixed is discharged out of the apparatus by the discharge roller pair 480 and stacked on a tray (not shown). Thereby, a full color copy is obtained.

The above-described alignment pattern detection sensor according to the present invention is an image forming apparatus that detects and corrects a misregistration amount by detecting an alignment pattern configured by forming a plurality of two-color superposed patches. Since any of them can be applied, it can also be applied as a positional deviation detection sensor of an ink jet apparatus (sixth embodiment).
One example will be described with reference to FIGS.

First, a schematic configuration and printing function of an ink jet recording apparatus 500 as an image forming apparatus will be described with reference to FIG. An ink jet recording apparatus 500 includes a printing mechanism that includes a carriage movable in the main scanning direction, a recording head including an ink jet head mounted on the carriage, an ink cartridge that supplies ink to the recording head, and the like inside the apparatus main body 501. Part 502 and the like.
A paper feed cassette 504 capable of stacking and accommodating sheets 503 as sheet-like recording media is provided at a lower portion of the apparatus main body 501, and the paper feed cassette 504 is located from the front side (left side in the drawing) to the apparatus main body 501. And detachable.
A manual feed tray 505 is openably and closably provided on the front surface of the apparatus main body 501. After a sheet 503 fed from the paper feed cassette 504 or the manual feed tray 505 is conveyed and a predetermined image is recorded by the print mechanism unit 502. The paper is discharged onto a paper discharge tray 506 provided on the rear side of the apparatus main body 501. An upper cover 507 is provided on the upper surface of the apparatus main body 501 so as to be freely opened and closed.

In the printing mechanism 502, a carriage 510 is slidably held in a main scanning direction (perpendicular to the paper surface) by a main guide rod 508 and a sub guide rod 509 supported between left and right side plates (not shown). A recording head 511 including an ink jet head having nozzles for ejecting ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk) is provided on the lower surface side. Each ink cartridge 512 for supplying ink of each color to the recording head 511 is replaceably provided on the upper side of the carriage 510.
The recording head 511 may be a recording head in which a plurality of heads that discharge ink droplets of each color are arranged in the main scanning direction, or a head that has a nozzle that discharges ink droplets of each color.

Below the recording head 511, the sheet 503 is electrostatically adsorbed and conveyed between the conveying roller 513 and the driven roller 514 in order to convey the sheet 503 in the sub-scanning direction with respect to the printing position by the recording head 511. A conveyor belt 515 is wound around. The conveyor belt 515 is tensioned by an intermediate roller 516.
A bias roller 517 for charging the conveyor belt 515 is disposed at a position facing the conveyor roller 513 across the conveyor belt 515. A pressing roller 518 that presses the sheet 503 against the conveying belt 515 is disposed near the plane starting point of the conveying belt 515. Here, the plane starting point portion of the conveyance belt 515 is the upstream side in the sheet conveyance direction of the portion of the conveyance belt 515 on the recording head 511 side parallel to the recording head 511, specifically, the conveyance belt 5151 from the conveyance roller 513. It means the part that leaves.

The paper sheets 503 stored in the paper feed cassette 504 are separated one by one from the uppermost one by a paper feed roller 519 and a friction pad 520, and directed toward the nip portion between the bias roller 517 and the conveyance belt 515 by a curved guide member 521. Are transported.
An alignment pattern detection sensor 40 that detects an alignment pattern Pm formed on the sheet 503 is provided on the upstream side of the conveyance belt 515 in the sheet conveyance direction. The positional deviation correction means is the same as in the first embodiment.
FIG. 33 is an enlarged view of the periphery of the conveyor belt 515, but a plate-like pressing member 522 may be provided instead of the pressing roller 518 shown in FIG.
As shown in FIG. 34, for example, the alignment pattern Pk shown in FIG. 35 is formed on a sheet 503 as a transfer body on which the alignment pattern is formed, and this is detected by the alignment pattern detection sensor 40 to cause color misregistration. Correct.

1 is a schematic front view of a color printer as an image forming apparatus according to a first embodiment of the present invention. FIG. 5 is a schematic plan view of an alignment pattern for detecting misalignment in the main scanning direction. It is a schematic plan view showing the arrangement relationship of the alignment pattern detection sensor with respect to the scanning direction of the alignment pattern. FIG. 6 is a schematic plan view showing a positional relationship between an alignment pattern formation position on the transfer belt and an alignment pattern detection sensor. It is an outline top view showing the state where the central axis of the directivity of each element of the alignment pattern detection sensor was aligned with the scanning direction of the alignment pattern. It is a figure which shows the directional characteristic of the light emission part of a position alignment pattern detection sensor. It is a figure which shows the directional characteristic of the light-receiving part of a position alignment pattern detection sensor. It is a graph which shows the improvement effect of the linearity with respect to the conventional optical sensor. It is a block diagram which shows a positional deviation amount correction | amendment means. It is a graph which shows the actual value of the color line width of each patch by microscope observation. It is a figure which shows the nonlinearity of the area increment which arises when the light-receiving surface shape in the conventional optical sensor is circular. It is a figure which calculates | requires the area of the rectangle in a circular light-receiving surface. It is a graph which shows the simulation result of the area of a color line part with respect to the shift amount of a color line. It is a graph which shows the simulation result when the center of a Bk line has shifted | deviated with respect to the center of a light-receiving surface. It is a figure which shows the directional characteristic of the light emitting element in the conventional optical sensor. It is a figure which shows the directional characteristic of the light receiving element in the conventional optical sensor. It is a general | schematic top view which shows the directional characteristic of each element of the conventional optical sensor with respect to the scanning direction of an alignment pattern. It is a graph which shows the relationship between LED light emission current and the regular reflection light output in the conventional optical sensor. It is a graph which shows the position shift pattern output at the time of detecting by regular reflection light in the conventional optical sensor. It is a graph which shows the relationship between the LED light emission current in a conventional optical sensor, and a diffuse reflected light output. It is a graph which shows the position shift pattern output at the time of detecting by diffused reflected light in the conventional optical sensor. It is a graph which shows the relationship between the glossiness of a transfer belt surface, and a sensor output. It is a graph which shows the relationship between the brightness of a transfer belt surface, and diffused light output. It is a graph which shows the measurement result of the deviation | shift amount of the alignment pattern on a transfer belt. It is a graph which shows the measurement result by the sensor of the deviation | shift amount of the alignment pattern on a transfer belt. It is a figure which shows the state in which the Bk line and the C line have produced line weight. It is a figure which shows the state in which the line fat has arisen only in the Bk line. FIG. 6 is a schematic plan view of an alignment pattern for detecting misalignment in the sub-scanning direction. It is a figure which shows the structure of the alignment pattern detection sensor in 3rd Embodiment. It is a general | schematic front view of the color copying machine as an image forming apparatus in 4th Embodiment. FIG. 10 is a schematic front view of a color copying machine as an image forming apparatus according to a fifth embodiment. It is a general | schematic front view of the inkjet recording device as an image forming apparatus in 6th Embodiment. FIG. 33 is an enlarged view around the conveyor belt in FIG. 32. FIG. 3 is a schematic plan view showing the positional relationship between the alignment pattern formation and the alignment pattern detection sensor in the inkjet recording apparatus. It is a general | schematic top view of the alignment pattern comprised by the superimposition of the line of two colors. It is a general | schematic top view which shows arrangement | positioning of each element of the conventional optical sensor with respect to the scanning direction of an alignment pattern. It is a graph which shows the output voltage of a position shift pattern at the time of using the conventional optical sensor, and an intersection calculation result.

Explanation of symbols

Pm, Ps Alignment pattern 40, 60 Alignment pattern detection sensor 40A as alignment pattern detection means 40A Light emitting diode 40B as light emitting part 46 Photodiode as light receiving part 46 Misalignment correction means Bk Black line image

Claims (1)

Based on the output signal from the alignment pattern detection means for an arbitrary shift amount of the line image other than the reference color with respect to the reference color line image of the alignment pattern, it is formed on both sides with respect to the extreme value of the output signal by the positional deviation amount correction means. In the color misregistration correction method for correcting the misregistration by calculating the misregistration amount and the direction of the color other than the reference color with respect to the reference color by calculating the intersection of the two straight lines,
A color misregistration correction method, wherein the data point at or near the extreme value is not used for calculation of the intersection of the two straight lines.

Images