JP4349304B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus provided with a fixing device used for image formation, such as a copying machine, a printer, and a fax machine. For example, a toner image is formed on one or both sides of transfer paper by an electrophotographic method, and the fixing device uses the fixing device. The present invention relates to an image forming apparatus for fixing a toner image.

  As a fixing device used in an electrophotographic image forming apparatus such as a copying machine, a printer, or a fax machine, a fixing roller having an elastic layer and maintained at a predetermined temperature, and the elastic layer is pressed against the fixing roller. A heat roller fixing method is often used in which a transfer sheet on which an unfixed toner image is formed is nipped and conveyed while being heated by a pressure roller.

  Further, there is a fixing belt type fixing device in which an endless belt member (fixing belt) is used as a fixing member of the fixing device, and the fixing belt is supported and stretched by a plurality of roller members.

  However, when the toner image is heated and fixed by these fixing devices, the transfer paper is heated, and the moisture contained in the transfer paper is evaporated by heat, so that the transfer paper is fixed after fixing. Shrink. If the shrinkage amount of the transfer paper is large, the user's request may not be satisfied if the image size requires accuracy.

  Further, due to deviations in the feeding device and changes over time, the feeding timing to the transfer unit may deviate from the design value, and the image position with respect to the transfer paper may deviate.

  In the case of double-sided copying in which images are formed on both sides of the transfer paper, the toner image is transferred to one side of the transfer paper, fixed by passing through a fixing device, and then transferred to the other side of the transfer paper. It passes through the fixing device again and is fixed.

  In addition, in the case of multiple copying in which two images are combined on one side of a transfer paper, a toner image is transferred to one side of the transfer paper, passed through a fixing device and fixed, and then the toner image is transferred to the same side of the transfer paper. Is transferred and fixed again by passing through a fixing device.

  In these two-sided copying and multiple copying, the transfer paper is thermally contracted during the second transfer of the toner image, so the image size may differ between the first image and the second image. There was a problem that the position would change.

  In order to avoid such a difference in image size, a method of measuring the dimensions of the transfer paper before and after heat-fixing, calculating the expansion / contraction ratio of the transfer paper based on this, and controlling the optical system is disclosed in, for example, Patent Document 1. Is disclosed.

  In the image forming apparatus disclosed in Patent Document 2, when a plurality of double-sided copies are repeated, the expansion / contraction rate is determined based on the difference in transfer paper size before and after fixing the front surface detected only by the sensor for the first copy. For the second and subsequent images, the expansion / contraction rate is used to correct the image size.

  The image forming apparatus disclosed in Patent Literature 3 detects the measurement pattern formed at a predetermined position on the surface of the transfer paper, and detects the back surface of the transfer paper based on the detection result of the misalignment detection means that detects the registration error and the tilt of the transfer paper. The image forming position with respect to is corrected.

  The color image forming apparatus disclosed in Patent Document 4 includes a first transfer sheet measuring unit that measures the length of the transfer sheet before or during transfer of the image to the transfer sheet surface, and a back surface of the transfer sheet. A second transfer paper measuring unit that measures the length of the transfer paper before transferring the image. From the measurement results of the first transfer paper measuring unit and the second transfer paper measuring unit, This controls the position and length of the image to be transferred.

The image forming apparatus having the double-sided copying mode disclosed in Patent Document 5 measures the vertical and horizontal dimensions of the transfer paper before and after the transfer paper is fixed by the fixing device, and fixes the transfer paper. The expansion / contraction ratio is calculated by the apparatus, and a toner image having a magnification corresponding to the expansion / contraction ratio is formed on the photoconductor. When copying on both sides, the first transfer sheet is used for the calculation of the expansion / contraction ratio. For the transfer paper, the toner image transferred to the first surface is formed on the photoconductor by normal image formation, and the toner image transferred to the second surface of the same transfer paper is formed on the first transfer paper. A toner image having a magnification corresponding to the calculated expansion / contraction ratio is formed on the photosensitive member.
JP-A-4-288560 Japanese Patent Laid-Open No. 10-149057 Japanese Patent Laid-Open No. 10-319674 JP-A-10-319675 JP 2002-258680 A

  Conventionally, as shown in Patent Documents 1 to 5, a measurement pattern is formed at the time of initial fixing in order to correct variations in transfer paper conveyance and image position and magnification deviation due to shrinkage of the transfer paper due to fixing. In other words, the position of the front and rear edges of the transfer paper is detected to correct the image position and magnification. When the pattern for measurement is formed, an extra transfer sheet is required, and the position deviation of the image relative to the position of the transfer sheet cannot be corrected by detecting the leading and trailing edges of the transfer sheet.

  The present invention aims to solve the above-described problems, and is achieved by the following configuration.

An image forming apparatus comprising a fixing device for fixing an unfixed image formed on a transfer paper onto the transfer paper, the image forming means for forming the unfixed image based on image data, and the fixing paper on the transfer paper after fixing image pattern detection sensor for detecting the image pattern, and having a case, images pattern the sensed by the image pattern detection sensor for the image formed on the basis of the previous image data to perform a series of image forming And at least one of the magnification and the position of the unfixed image formed on the transfer paper is determined based on the image data so as to match the output corresponding to each, and when image formation of the subsequent image data is performed an image forming apparatus characterized by correcting for image formation by said image forming means based on the determination is made.

Other features of the image forming apparatus of the present invention are listed below.
(1) Correction is performed using input image data, image pattern detection data after fixing, and leading and trailing edge position detection data of transfer paper.
(2) The detection of the image pattern and the transfer paper front / rear edge sensor is attached to a position where the paper discharge rollers and the like are opposed to each other to ensure high detection accuracy.
(3) A calculation corresponding to the sensor sensitivity distribution is performed on the input image data, and the magnification and the position correction amount are set so that the difference between the two data is minimized. That is, the magnification and the position correction amount are determined so that the integral value over the entire length of the difference between the two data becomes small.
(4) If the positional deviation amount is equal to or less than the predetermined amount, the output is continued as it is. If the positional deviation amount exceeds the predetermined amount, correction is applied and the first sheet is output again. While the second and subsequent sheets are corrected based on the measurement result at the previous output, the output is continued if the deviation is equal to or less than a predetermined amount.
(5) For the position in the width direction of the sensor, a pattern for detecting the position in the axial direction is output during machine installation or maintenance, the position in the axial direction is measured, and the result is stored as position data for use.
(6) In the image pattern detection, the sensor is moved to a position suitable for the expansion / contraction rate detection according to the image data. If there is no image pattern at the position corresponding to the sensor, the previous correction data is used.

Alternatively, a plurality of sensors are arranged in a direction perpendicular to the transfer paper conveyance direction, and image pattern detection is performed using any of the plurality of sensors according to image data.
(7) The image forming means can form an image on both sides of the transfer paper, or can perform multiple copying, and performs correction for image formation so that the position or size of each image matches.
(8) Correction by the image forming means is performed by changing the image forming conditions or expanding / contracting and moving the original image data.

  As described above, according to the image forming apparatus provided with the fixing device of the present invention, since the image data itself after fixing is used, no extra transfer paper is required for contraction of the transfer paper due to fixing. Therefore, useless output (consumption of transfer paper and toner) can be minimized, and output with high image position accuracy and image magnification accuracy with respect to the transfer paper can be obtained.

  Embodiments of the present invention will be described below. The description in this column does not limit the technical scope of the claims or the meaning of terms. In addition, the following assertive description in the embodiment of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.

[Image forming apparatus]
FIG. 1 is a configuration diagram of an image forming apparatus including a fixing device according to the present invention.

  The image forming apparatus A is called a tandem color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, a belt-like intermediate transfer member 6, a sheet feeding device 20, and a fixing device described later. 30.

  On the upper part of the image forming apparatus A, an image reading apparatus B is installed. The document placed on the document table is scanned and exposed by the optical system of the document image scanning exposure apparatus of the image reading apparatus B, and read by the line image sensor. The analog signal photoelectrically converted by the line image sensor is subjected to analog processing, A / D conversion, shading correction, image compression processing and the like in the data processing unit 11, and then input to the exposure means 3Y, 3M, 3C, 3K. The

  The image forming unit 10Y that forms a yellow (Y) image includes a charging unit 2Y, an exposure unit 3Y, a developing device 4Y, and a cleaning unit 5Y disposed around a photosensitive drum 1Y as an image carrier. The image forming unit 10M that forms a magenta (M) color image includes a photosensitive drum 1M as an image carrier, a charging unit 2M, an exposure unit 3M, a developing device 4M, and a cleaning unit 5M. An image forming unit 10C for forming a cyan (C) color image includes a photosensitive drum 1C as an image carrier, a charging unit 2C, an exposure unit 3C, a developing device 4C, and a cleaning unit 5C. The image forming unit 10K that forms a black (K) image includes a photosensitive drum 1K as an image carrier, a charging unit 2K, an exposure unit 3K, a developing device 4K, and a cleaning unit 5K. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit.

  4Y, 4M, 4C, and 4K are developing devices that contain a two-component developer composed of a small particle size toner of yellow (Y), magenta (M), cyan (C), and black (K) and a carrier.

  The intermediate transfer body 6 is wound around a plurality of rollers and is rotatably supported.

  The images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred (primary transfer) and synthesized by the primary transfer units 7Y, 7M, 7C, and 7K on the rotating intermediate transfer body 6. A color image is formed.

  The transfer paper S accommodated in the transfer paper storage unit (paper feed cassette) 21 of the paper supply device 20 is fed by a paper feed means (first paper feed unit) 22 and fed by paper feed rollers 23, 24, 25, 26, a registration roller (second paper feed unit) 27, etc., and then conveyed to a secondary transfer means (transfer roller) 9, and a color image is transferred onto the transfer paper S (secondary transfer).

  It should be noted that the three-stage transfer paper storage units 21 arranged in the vertical direction in the lower part of the image forming apparatus A have substantially the same configuration, and thus are given the same reference numerals. Further, the three-stage sheet feeding means 22 has almost the same configuration, and therefore is given the same reference numeral. The transfer paper storage unit 21 and the paper supply means 22 are collectively referred to as a paper supply device 20.

  The transfer sheet S to which the color image has been transferred is sandwiched by the fixing device 30, and the color toner image (or toner image) on the transfer sheet S is fixed by applying heat and pressure to transfer the transfer sheet S. The sheet is fixed on the upper side, sandwiched between the sheet discharge rollers 28 and placed on a sheet discharge tray 29 outside the apparatus.

  On the other hand, after the color image is transferred onto the transfer sheet S by the secondary transfer unit 9, the residual toner is removed by the cleaning unit 8 from the intermediate transfer body 6 from which the transfer sheet S is separated by curvature.

  When reversely discharging the transfer sheet S that has been subjected to the fixing process, the transfer sheet S passes through the conveyance path on the right side of the branch plate 28A arranged between the fixing device 30 and the sheet discharge roller 28, and the lower conveyance path. After being transported to r1, it is transported in the reverse direction, passes through the transport path r2 on the left side of the branch plate 28A, and is discharged out of the apparatus by the paper discharge roller 28.

  When copying on both sides of the transfer sheet S, after fixing the image formed on the first surface of the transfer sheet S, the transfer sheet S is introduced into the transport path r1 and further into the transport path r3, and then transported in reverse. After being transported to the transport path r4, it is detoured upward and transported by the paper feed roller 26. The transfer paper S is formed on both sides by the image forming means 10Y, 10M, 10C, and 10K. Images of the respective colors are formed on both sides, heated and fixed by the fixing device 30, and discharged to the outside by the paper discharge roller 28.

  In the description of the image forming apparatus A, the color image formation has been described. However, the present invention includes a case of forming a monochrome image.

[Fixing device]
FIG. 2 is a cross-sectional view of the fixing device 30 according to the present invention.

  The fixing device 30 according to the present invention includes a heating unit including a support pressure roller 32, a support heating roller 33, a heating source 34, a pad 35, and a guide member 36 disposed inside the fixing belt 31. It is composed of an external pressure roller 37 disposed on the outside.

  The fixing belt 31 is composed of an endless belt member, and surrounds and stretches the outer circumferences of the support pressure roller 32, the support heating roller 33, the pad 35, and the guide member 36.

  The support pressure roller 32 faces the external pressure roller 37 and supports the fixing belt 31 on one of the inner peripheral surfaces of the fixing belt 31. The support heating roller 33 includes a heat source 34 and supports the fixing belt 31 on one of the inner peripheral surfaces of the fixing belt 31.

  The external pressure roller 37 has a built-in heating source 38 and presses the support pressure roller 32 and the pad 35 while sandwiching the fixing belt 31 and the transfer sheet S.

  As the heating sources 34 and 38, a radiation heating source such as a halogen lamp, a carbon heater, or a xenon lamp can be applied. However, if an appropriate roller core metal is selectively printed, heating by electromagnetic induction or the like is also possible. In addition, it is possible to incorporate a plurality of heaters in each roller as necessary, such as those having different heat distribution.

  A fixing nip portion Na is formed between the support pressure roller 32 and the external pressure roller 37 with the fixing belt 31 heated by the support heating roller 33 interposed therebetween. An auxiliary nip portion Nb that wraps around the external pressure roller 37 is formed between the fixing belt 31 and the external pressure roller 37 on the upstream side of the fixing nip portion Na in the recording transfer paper conveyance direction.

  The fixing device 30 fixes the single color toner image or the multicolor toner image on the transfer paper S by heating and pressurizing through the auxiliary nip portion Nb and the fixing nip portion Na. Further, a pad 35 provided opposite to the external pressure roller 37 and a guide member 36 for stretching the fixing belt 31 are provided inside the fixing belt 31.

  The fixing belt 31 uses a nickel electroformed belt having an inner diameter of 60 to 150 mm and a thickness of 20 to 80 μm as a base, or a heat resistant resin belt such as polyimide having a thickness of 50 to 200 μm as a base. The outer peripheral surface) is coated with silicone rubber having a thickness of 100 to 500 μm as a rubber layer, and the surface of the rubber layer as a release layer is 30 to 50 μm thick PFA (perfluoroalkoxy) or PTFE (polytetrafluoroethylene). ) Use a coating or a PFA tube or a PFA coating layer.

  The support pressure roller 32 uses, for example, a steel material such as STKM (carbon steel pipe for mechanical structure), and has a cylindrical metal pipe 32a having a thickness of 2 to 5 mm and a thickness of 0.5 on the outer peripheral surface of the metal pipe 32a. A ˜5 mm silicone rubber layer 32b is provided, and a PFA tube 32c having a thickness of 30 to 70 μm is formed outside the silicone rubber layer 32b. Further, a silicone sponge or the like can be applied instead of the silicone rubber layer 32b.

  The external pressure roller 37 uses, for example, a steel material such as STKM or an aluminum alloy material, a cylindrical metal pipe 37a having a thickness of 2 to 5 mm, and a silicone rubber layer having a thickness of 1 to 3 mm on the outer peripheral surface of the metal pipe 37a. 37b and a soft roller having an outer diameter of 40 to 80 mm, further comprising a release layer 37c using a PFA tube having a thickness of 20 to 50 μm on the outside of the silicone rubber layer 37b.

  Further, a heating source 38 as a heating element for heating the external pressure roller 37 is provided inside the external pressure roller 37. The surface temperature of the external pressure roller 37 is detected by the temperature sensor TS2 and maintained at a predetermined temperature.

  The support heating roller 33 has an outer diameter of 40 mm having a pipe 33a having a thickness of 1 to 2 mm made of an aluminum alloy material as a base and a coating layer 33b made of PFA having a thickness of 10 to 30 μm on the outer peripheral surface of the pipe 33a. It is configured as a roller member of ˜80 mm.

  Further, a heater 34 as a heating element for heating the support heating roller 33 is provided inside the support heating roller 33. The surface temperature of the support heating roller 33 is detected by the temperature sensor TS1 and maintained at a predetermined temperature.

  The supporting pressure roller 32 is rotationally driven by a driving unit (not shown), and the fixing belt 31 is supported and conveyed by the rotation of the supporting pressure roller 32 to be driven and rotated. Alternatively, the external pressure roller 37 may be rotationally driven by a driving unit, the fixing belt 31 may be conveyed by the external pressure roller 37, and the fixing belt 31 may be driven to rotate. Further, driving may be input to both the support pressure roller 32 and the external pressure roller 37.

  The auxiliary nip portion Nb formed between the fixing belt 31 and the external pressure roller 37 and the pad 35 and the fixing nip portion Na formed between the support pressure roller 32 and the external pressure roller 37 enter. A single-color toner image or a multi-color toner image on the transfer paper S entering the fixing region through the guide plate 30S is heated under pressure and fixed on the transfer paper S.

  The auxiliary nip portion Nb is effective in securing a large heating time with a small diameter of the supporting pressure roller 32 by making use of the flexibility of the fixing belt 31.

[Write control of image forming apparatus]
3A is a front view of the paper discharge unit of the fixing device 30, and FIG. 3B is a side view. 4A is an image pattern formed on the transfer paper S, and FIG. 4B is a diagram illustrating an output example of an image pattern detection sensor corresponding to the image pattern of FIG. In addition, the white arrow in Fig.4 (a) shows the advancing direction of an image. FIG. 5 shows the overall control flow when adjusting the front / back magnification and position (timing).

  The transfer sheet S fixed by the fixing device 30 is sent out to the image forming conveyance path to the outside or the back surface by the discharge roller pair 39. As shown in FIG. 5, after fixing, the sensor PS provided opposite to the nip position of the paper discharge roller pair 39 composed of the upper roller 39A and the lower roller 39B passes the front and rear ends of the transfer paper S and transfers. An output change corresponding to the image pattern p actually formed on the paper S is obtained as a voltage.

  The axial position of the sensor PS, that is, the position perpendicular to the transfer paper running direction, is determined by outputting a pattern for detecting the position of the sensor PS during machine installation or maintenance, storing the detection result, and comparing it. .

  FIG. 4C shows an example of a pattern for grasping the sensor position.

  When the lines P1, P2 and P3 are formed and the lines P1, P2 and P3 are detected by the sensor, the position of the sensor with respect to the writing position = image forming position can be confirmed by the time interval ratio t1 / t2. .

  Even if the speed of each part of the image forming apparatus is not as designed, as long as it is constant, t1 / t2 is constant at the axial position of each sensor. Therefore, by measuring t1 / t2, the positional relationship between the sensor position and the unfixed image can be uniquely determined. If t1 / t2 = 1, it is the center of this line pattern, and if t1 / t2> 1, the sensor is located on the left side of the center in the traveling direction. These correspond to t1 'and t2' in the figure. Such a means for grasping the relationship between the sensor position and the image writing position is particularly effective when the sensor is moved as will be described later.

  When obtaining the expected output by calculating the sensitivity distribution of this sensor with the image data, when the image is a color image, the sensitivity to the color is also matched with the sensitivity distribution in the sensor's measurement field of view. To calculate.

  4 (d) and 4 (e) are output characteristic diagrams of the sensor.

  As shown in FIG. 4 (d), if there is a red and blue pattern and the sensor has uniform sensitivity over all wavelengths, the same output is obtained. However, sensors generally have different sensitivities depending on the wavelength. For example, a sensor having a high sensitivity to blue has a higher output with respect to light from a blue pattern, and thus the output is as shown in FIG. For this reason, it is preferable to perform correction based on color sensitivity during the predicted output calculation. That is, when the sensitivity to blue is high as in the example, when the sensor expected output distribution is calculated from the image data, the blue pattern is assumed to be output high and the red pattern is output low. For other colors, it is desirable to divide and correct the colors as finely as possible. However, the toner used for image formation is generally yellow, magenta, cyan, and black, and image data is finally output for each color. Therefore, output correction for the color of the sensor may be performed for each color.

  In the writing data processing unit 11 of the image forming apparatus A, the image data corresponding to the sensor position is multiplied by the sensitivity distribution of the sensor PS, and the expected image pattern detection output and the leading and trailing edges of the transfer paper S are predicted. An output is generated and compared with the actually obtained detection output in the virtual space configured on the control unit memory, and the correction magnification and the write start timing correction amount are determined (comparison between the detection pattern of FIG. 5 and the expected output). ).

  For simplicity, a case where a simple image pattern as shown in FIG. 4A is output will be described. When the image pattern of FIG. 4A is detected, a rectangular output corresponding to the density is ideally obtained. However, in reality, when an inexpensive element such as a photosensor is used for the sensor PS, the spatial sensitivity distribution is obtained. Depending on, a distorted output is obtained. The spatial sensitivity distribution of the sensor PS is schematically shown in FIG. A curve indicated by a solid line in FIG. 4B is an output of the sensor PS to be obtained when the image of FIG. 4A is output.

  When the photosensitive member speed / writing speed / intermediate transfer member speed / paper speed, each timing, etc. are as designed, the output of the detected sensor PS is equal to the solid line in FIG. Due to various manufacturing errors, the speed of each part differs from the design speed, and deviates from this solid line. As an example, the deviation when the timing of the intermediate transfer member is slightly slow while the timing and other speeds coincide with the design values with sufficient accuracy is shown by a broken line. Even if an image as designed is formed on the photosensitive member, if the speed of the intermediate transfer member is low, the image transferred onto the intermediate transfer member becomes an image reduced in the feeding direction. The paper feed speed from the paper feeder is designed to be slightly faster than the intermediate transfer member, and the paper feed speed from the transfer unit is designed to be slightly faster than the fixing unit. Therefore, the reduced image on the intermediate transfer member is formed on the paper as it is. On the other hand, for example, when the paper feeding speed of the paper feeding device is slow with respect to the intermediate transfer member, the image is stretched at the transfer portion.

  Various algorithms can be used to correct the writing magnification and the writing timing. In this embodiment, first, the detection output is moved within a predetermined amount with respect to the expected output, and the movement amount is selected so that the difference is minimized. Next, starting from the center of the image area, the image is expanded or contracted within a predetermined amount, and the magnification is selected so that the difference is minimized. By repeating this, the movement amount and the magnification correction amount with respect to the reference position of the transfer paper S are determined.

  That is, in the present embodiment, the image position and the magnification are selected so that the solid line and the broken line in FIG. 4B match in the virtual space configured on the control unit memory. For example, as shown in FIG. 6, the algorithm for matching the solid line and the broken line normalizes the detected broken line data and the solid line data generated from the image data and the sensor sensitivity distribution (so that the integral value over the entire length becomes equal). After multiplying by a constant, the origin of the time axis (corresponding to the traveling direction position) of the measured data is shifted and the time axis magnification is changed so that the integral value over the entire length of both data differences becomes the smallest. . This change is made by shifting a predetermined interval from the expected position to find a position where the integral value of both data differences is minimized, and after shifting by that amount, the magnification is changed at a predetermined interval to minimize the integral value. Find the magnification. The position at which the integral value is minimized is found by shifting the data multiplied by the magnification by an amount smaller than the previously shifted interval. Further, after shifting by that amount, the magnification is shifted by an interval smaller than the magnification interval shifted last time to find a position where the integral value is minimized.

  In this embodiment, the magnification is adjusted after the position (timing) is adjusted, but can be appropriately changed depending on the image forming apparatus to be applied. In particular, it is desirable to perform the adjustment from the magnification and timing that are more likely to deviate more greatly in the default state (in terms of integration of the difference), that is, from the larger reduction amount of the difference integration when the initial adjustment is performed.

  The range (predetermined value A) for shifting the origin (p0, t0) and the magnification change, the step size (pe, te) to be shifted, and the number of repetitions are the required performance, paper feed timing variation, and the amount of paper expansion and contraction. Decide on it. For example, if there is a possibility that the paper feeding timing varies by ± 10 mm in position, the paper is moved to ± 12 mm in increments of 2 mm. After correcting the magnification in the range of ± 5% in 1% increments, in the range of ± 4mm in 0.5mm increments, the position where the integrated value of both data differences is minimized is searched, and the range of ± 2% is further reduced to 0.00. The magnification is corrected in increments of 2%, and position correction and magnification correction with a smaller increment are performed a predetermined number of times. The number of repetitions may be repeated as many times as necessary until the integral value over the entire length of both data differences becomes smaller than a predetermined value.

  In FIG. 6, the repetition routine for determining the magnification and determining the timing is predicted with the magnification and timing shifted by −2, −1, 0, 1, 2 times, with pe and te as the unit, with p0 and t0 as the center. The output is deformed and moved to integrate the difference with the detected output. Each system is tried to determine how many times the calculation is shifted around the first p0, t0 or pe, te, p0, t0, and an appropriate value is selected. The predetermined value A determines how much positional deviation and magnification deviation are allowed, and is set for each machine. Also, it may be changed according to the user's request or operated by the user.

In the example, the position correction and the magnification correction were repeated three cycles, and this information was used for the next image formation, so that the front / back registration difference including the magnification / position shift in the A3 size could be kept within 0.5 mm. .
The transfer paper after fixing tends to curl particularly at the leading and trailing edges due to the fixing nip shape and temperature difference. As described above, the detection accuracy can be greatly improved by detecting the pattern of the image actually formed and fixed on the transfer paper.

  Based on the above control, when the next print is the back side, the image formation writing start timing and the magnification are selected so that the front and back image positions coincide on the front and back sides of the transfer paper S, and the back side is output.

  If the next print is the next leaf, the image formation / writing start timing and the magnification are set so that the image has the position and size as instructed by the image data with respect to the detected leading and trailing edge timing of the transfer sheet S.

  For example, when the image is too close to the leading edge of the transfer paper, the timing control delays the start of writing or speeds up the transfer paper. The alignment is the same in both cases, but it is easy to change the writing start without affecting the paper feeding control.

  In the configuration of back side copying (or multiple copying) in which there are a plurality of moving transfer sheets S in the path from fixing to the next transfer / fixing, the correction amount of the front side is set to the back side image formation of the corresponding print. However, since these correction amounts rarely change greatly during continuous printing, there is no problem even if the data of the first print is used for subsequent printing. Of course, when the temperature of the fixing device changes greatly during the continuous fixing operation, it is desirable to perform correction corresponding to each print. However, when the type of the transfer sheet S changes during the continuous operation, correction is performed every time the change is made.

  The writing magnification may be changed by changing the image forming writing clock and the speed of the image forming process, changing the speed of the scanning optical system, or changing the writing clock. Changing the writing clock changes the magnification in the scanning direction, changing the speed of the image forming process changes the magnification in the sub-scanning direction, and changing the speed of the scanning optical system simultaneously changes the magnification in both the scanning direction and the sub-scanning direction. When changing the image process speed or scanning optical system speed, it takes time to stabilize after each speed change, so the next print is taken off when the paper interval is short = productivity decreases, etc. Is necessary. Depending on the type of image data, image quality may be disadvantageous, but the original image data may be simply expanded and contracted as indicated by the dotted line in FIG. Since it is not necessary to switch the speed of the mechanical part such as the speed of the image forming process and the speed of the scanning optical system, the productivity is not reduced even if the interval between the sheets is short.

  The image data is supplied from the outside, and the installed sensor PS is not always located at a position corresponding to the image pattern p.

  When the writing data processing unit 11 of the image forming apparatus A detects an image pattern p suitable for detecting the position and expansion / contraction of the output image and moves the position of the sensor PS, higher detection becomes possible. Various suitable detection algorithms for the image pattern p are possible. In the present embodiment, the transfer paper is fed in increments of 2 mm within the movable range of the sensor PS in the virtual space configured on the control unit memory. The image density distribution is calculated by multiplying the image pattern along the line parallel to the direction by the sensitivity distribution of the sensor PS, and the peak having an output of 50% or more of the output corresponding to the image having the maximum image density is the transfer paper. Positions existing with an interval of 80% or more of the length of S in the feeding direction are extracted as appropriate. As will be described later, the sensor PS is moved to the extracted position by a known moving mechanism using a screw or a wire.

  If there is no peak with a maximum image density of 50% or more, or the distance is insufficient, each threshold position is lowered and selected. If the peak value is too small or the interval is too narrow (for example, the peak value is 30% or less and the interval is 60% or less), the correction cannot be made accurately, and there is a risk that the image position and the magnification may be changed. Stop the correction operation.

  In addition, when the absolute value of the correction movement amount or the correction magnification is too large (for example, when the correction movement amount exceeds ± 5 mm and the correction magnification ± 2%), whether a feeding abnormality has occurred, the correction algorithm, the sensor sensitivity of the sensor PS, etc. When this occurs, it is determined that the compatibility with the image pattern p is poor, and the correction operation is similarly stopped, and output is performed under the initial setting condition or the previous output condition. The limit values of these magnifications and movement amounts are determined based on the actual variation (experimental values) during production. This prevents excessive correction.

  The pair of paper discharge rollers 39 is composed of a combination of a rubber upper roller 39A and a resin lower roller 39B, and the sensor PS is disposed on the rubber upper roller 39A side in contact with the image surface side immediately after fixing. .

  The sensor PS detects the amount of light reflected from the transfer paper S or the lower roller 39B, and outputs a voltage corresponding to this. The lower roller 39B facing the sensor PS is colored black or dark in order to detect the leading and trailing edges of the transfer sheet S with high sensitivity with respect to a general white transfer sheet S. Although the detection accuracy decreases for high-density colored paper, most of the paper is white, which has a great merit for the user.

  The upper roller 39A is not disposed at the detection position of the sensor PS, and is installed so as to detect the position of the transfer paper S and the image pattern p at a position where the transfer paper S is in contact with the lower roller 39B. is there. By placing the sensor at such a position, the distance between the sensor and the paper is stabilized, and image density detection and paper edge detection can be performed stably and with high accuracy.

  The range in which the sensor PS can move is desirably the entire image width, but even if it is a part of the range, the probability that an appropriate image pattern p can be obtained increases, or the detection accuracy increases. The sensor support member is fitted to a screw provided in parallel with the roller and can move between the upper rollers 39A. The sensor PS moves to a position where a more appropriate image pattern p selected by the image pattern detection position setting algorithm can be detected. Various selection algorithms can be applied to select the position. In this embodiment, the height of the peak detected at each position (percentage with respect to the maximum image density) and the distance between the peaks (percentage with respect to the paper size in the running direction). The position with the largest product was selected. The sensor position is controlled by detecting the screw rotation speed (not the rotation speed) with an encoder or the like.

  Instead of moving the sensor PS, a plurality of sensors PS may be installed, and the sensor PS at the most suitable position may be used for image and transfer sheet detection based on the expected output for each position. Which sensor is selected is the same as in the case of performing the sensor movement. Also in this case, when it is determined that any image corresponding to the position of any sensor PS is inappropriate for detection for correction of magnification or position (according to the algorithm), the correction operation is stopped.

  If the positional deviation amount and magnification deviation amount of the first output in the series of image formation output commands are less than the allowable amount (for example, positional deviation amount ± 1 mm, magnification deviation amount ± 0.3%, etc.), the output is output as it is. If the positional deviation amount or magnification deviation correction amount exceeds a predetermined allowable amount by fixing the first sheet, the correction is applied and the first sheet is output again. When the first sheet is re-output, the user is notified through the display of the image forming apparatus operation unit or the like, thereby preventing duplicate pages from being mixed.

  While the second and subsequent sheets are corrected based on the measurement result at the previous output, the output is continued if the deviation is equal to or less than a predetermined amount. As described above, in the case of continuous output using the same paper, the first measurement correction condition may be applied to the subsequent main output. If the user can set the criterion for determining whether or not to perform this re-output (the above-mentioned predetermined amount), it is possible to operate according to the user's request, such as whether to prioritize quality or not waste. become.

  The configuration of the present invention is particularly effective in a high-speed image forming apparatus and a color image forming apparatus that are often used in the POD (publish, on-demand) market where the accuracy requirement level for images is high.

  Prior to the image forming operation, the image magnification and position are determined based on the previous print (front surface print at the time of backside fixing) information, and the linear velocity is changed accordingly, and an unfixed image is formed on the transfer paper S. Is done. The transfer sheet S holding the toner image conveyed to the fixing area by a paper feed guide or the like and the fixing belt 31 are sandwiched between the external pressure rollers 37 and heated and pressed to fix the toner image on the transfer sheet S.

  According to the above embodiment, useless output (consumption of transfer paper) can be minimized, and output with high image position accuracy and image magnification accuracy with respect to the transfer paper can be obtained.

  Further, it is possible to obtain an image with higher magnification accuracy by correcting the characteristics of the sensor.

  In addition, it is possible to prevent an excessive correction or unnecessary correction from being applied to the image position and magnification due to disturbance.

  Further, it is possible to prevent the deviation of the first one image position and magnification of a series of image outputs from increasing.

  In addition, it is possible to prevent a deviation amount of the first one image position in a series of image output from increasing due to a paper delay that is likely to occur when the type of transfer paper is changed.

  Further, it is possible to prevent unnecessary transfer paper having a defective image output from being mixed.

  Further, it is possible to prevent the image position and the magnification detection accuracy from being lowered due to instability of the position in the thickness direction of the transfer paper.

  In addition, high detection accuracy of the leading edge and trailing edge of the transfer paper can be obtained with respect to the commonly used white transfer paper.

  Further, by selecting an appropriate detection position, high image position and magnification accuracy can be obtained.

  In addition, an appropriate detection position can be selected without a sensor moving mechanism.

  In the present embodiment, the belt fixing type fixing device has been described as an example, but it goes without saying that the fixing device is also effective with a roller fixing device.

1 is a configuration diagram of an image forming apparatus including a fixing device according to the present invention. 1 is a cross-sectional view of a fixing device according to the present invention. FIG. 4 is a front view and a side view of a paper discharge unit of the fixing device. FIG. 4 is a diagram illustrating an image pattern formed on a transfer sheet and an output example of an image pattern detection sensor corresponding to the image pattern. The figure which shows the whole flow at the time of front and back magnification and position alignment. The figure which shows a detailed algorithm flow.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Data processing part 30 Fixing device 31 Fixing belt 32 Support pressure roller 33 Support heating roller 34,38 Heat source 37 External pressure roller 39 Paper discharge roller pair 39A Upper roller 39B Lower roller A Image forming apparatus Na Fixing nip part Nb Auxiliary Nip part PS sensor S Transfer paper p Image pattern

Claims (18)

An image forming apparatus comprising a fixing device for fixing an unfixed image formed on a transfer paper on the transfer paper,
An image forming means for forming the unfixed image based on image data, and an image pattern detection sensor for detecting an image pattern on the transfer paper after fixing,
When the series of image formation, based on the image pattern detection images pattern is detected by the sensor and the image data for the image that is formed on the basis of the previous image data, so to match the output corresponding to each In addition, when at least one of the magnification and the position of the unfixed image to be formed on the transfer paper is determined and image formation of the subsequent image data is performed, correction for image formation by the image forming unit is performed based on the determination. An image forming apparatus that is performed.   The image forming apparatus according to claim 1, wherein the image forming unit is capable of forming an image a plurality of times on the same transfer sheet. 3. The image according to claim 1, wherein the image forming unit can form an image on both sides of the transfer paper, and the correction is performed so that the front and back image positions coincide on the front and back of the transfer paper. Forming equipment.   The image forming apparatus according to claim 1, wherein the image forming apparatus is capable of multiple copying. Furthermore, the leading edge or trailing edge of the transfer paper can be detected,
The image forming apparatus according to claim 1, wherein the magnification or the position is determined in accordance with the detected timing of the leading edge or the trailing edge of the transfer paper.   The image forming apparatus according to claim 1, wherein the magnification or the position is determined so that an integrated value based on the detected image pattern and the image data is small. .   The image forming apparatus according to claim 6, wherein the magnification or the position is determined so that an integral value over the entire length of a data difference between the detected image pattern and the image data is small.   The image forming apparatus according to claim 1, wherein the correction is performed by changing an image forming condition.   The image forming apparatus according to claim 1, wherein the correction is performed by expanding or contracting or moving the original image data. The image data is corrected based on an input sensitivity distribution of the image pattern detection sensor, and the magnification or the position is determined using the corrected image data. The image forming apparatus described in the item.   The image forming apparatus according to claim 10, wherein the image data is multiplied by a sensitivity characteristic with respect to a wavelength of the image pattern detection sensor, and then correction is performed based on an input sensitivity distribution of the image pattern detection sensor.   The image forming apparatus according to claim 1, wherein the correction is stopped when the magnification or the displacement amount of the position is a predetermined value or more.   The image forming apparatus according to claim 1, wherein when the magnification or the displacement amount of the position is equal to or greater than a predetermined value, correction is performed and the image is output again.   14. The image forming apparatus according to claim 13, further comprising means for notifying a user that the re-output has been performed.   15. The image pattern detection sensor according to claim 1, wherein the image pattern detection sensor is provided to face one of a pair of paper discharge rollers provided downstream of the fixing device in a transfer paper conveyance direction. The image forming apparatus described.   16. The image pattern detection sensor according to claim 1, wherein the image pattern detection sensor is movable in a direction perpendicular to a transfer sheet conveyance direction by the fixing device based on the image data. Image forming apparatus.   A plurality of the image pattern detection sensors are installed in a direction perpendicular to the transfer paper conveyance direction by the fixing device, and an image pattern is detected using any of the plurality of image pattern detection sensors based on the image data. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 1, wherein the fixing device fixes an unfixed image formed on the transfer paper on the transfer paper by applying pressure or heating.

Images