JP2007065297A - Image forming apparatus and image density measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and an image density measuring method thereof, which measure a density of an image formed on a sheet with a high precision and are capable of achieving such density adjustment that the density measurement value is reflected on a density of an image to be formed by an image forming part. <P>SOLUTION: A controller C for controlling the entire image forming apparatus in accordance with the quantity of light received by a density sensor 9 calculates and acquires density measurement values of a plurality of reference images (patch images) on a sheet conveyed into, for example, a both-face conveyance path 67. The controller C compares the acquired density measurement values of these patch images with a density target value and feeds back comparison results to an image density for image formation in the image forming part to adjust a density of an image to be formed on a sheet sent into the image forming part. Since a sheet conveyance speed V2 is kept low, for example, at 150 mm/sec until a sheet trailing end passes the density sensor 9, density measurement of high precision is possible though patch images as reference images are narrow. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine. In addition, image density measurement that obtains high-precision density measurement values by sampling a reference density image formed on a sheet (recording medium) being conveyed in order to reflect the density adjustment of an image formed by the image forming unit. It is about.

  In recent years, colorization has progressed in image forming apparatuses that form images using an electrophotographic system, and higher image quality and higher stability of images have been further demanded. Therefore, many techniques have been proposed for always maintaining the density of an image formed by the image forming unit in an appropriate state.

  For example, after forming a reference image having a predetermined density, the density of the reference image is measured, the obtained density measurement value is compared with the density target value, a conversion table is created, and the created conversion table There has been proposed a technique for controlling the density of an image by converting the density characteristics of the image data using.

  As an example, a density sensor is placed in the conveyance path that conveys the sheet after image transfer or image fixing, and the density is detected and measured from the reference image formed on the sheet being conveyed, and the detection result A technique has been proposed in which the density measurement value obtained in the above step is fed back to the density of an image formed by an image forming unit (see, for example, Patent Document 1).

JP 2000-1332013 A

  By the way, as disclosed in the above publication, when an optical density sensor is used as the density detection means, the sensitivity is easily influenced by the vertical fluctuation of the sheet being measured, which is the object to be measured. There is a problem that the value changes greatly. For example, if the leading end of the sheet reaches a curved conveyance path during the density measurement and collides, the sheet fluctuates in the vertical direction with respect to the density sensor due to the impact force, so high-precision density measurement cannot be expected. Such a problem becomes more prominent as the conveyance speed of the sheet being conveyed increases. Although high-speed conveyance of a sheet is a technique necessary for improving productivity, on the other hand, such high-speed conveyance of a sheet is also an adverse effect when highly accurate density measurement is performed.

  On the other hand, with the goal of highly accurate density measurement, the reference image is sampled several times from the image formed on the sheet being conveyed, and the averaged density value is fed back as the target value. It can also be reflected. However, in that case, it takes a considerable time to sample the reference image density several times from the sheet being conveyed. Moreover, it is necessary to increase the size of the reference image to be detected in proportion to the increase in the sheet conveyance speed. That is, the number of reference images on one sheet is reduced, and high-precision measurement cannot be expected. If the number of sheets is increased in order to increase the number of samplings, the number of reference images increases and the measurement accuracy increases, but this is not practical because it increases the running cost.

  Therefore, an object of the present invention is to detect and measure the density of an image formed on a sheet with high accuracy, and to reflect the density measurement value on the image density formed in the image forming unit, so that the stable and An object of the present invention is to provide an image forming apparatus and an image density measuring method capable of adjusting the density with high accuracy.

  In order to achieve the above object, an image forming apparatus according to the present invention includes an image forming unit that forms an image on a sheet, and a reference image is formed in the image forming unit and is passing through a sheet conveyance path. Density detecting means for detecting the density of the reference image with respect to the sheet, control means for controlling to adjust the density of the image formed in the image forming unit to a detection value from the density detecting means, The sheet conveyance speed V2 at the time of density detection by the density detection unit in the density measurement mode for measuring the density of the reference image by the density detection unit is the same as that of the sheet on the sheet conveyance path in the image forming mode at normal operation. And a conveyance control means for controlling the conveyance speed to be lower than the conveyance speed V1.

  The representative image density measurement method of the present invention detects the density of the reference image on the sheet when the sheet passing through the sheet conveyance path reaches the detection portion of the density detection means, and based on the detected value. An image density measuring method for adjusting an image density of an image formed by the image forming unit, wherein the sheet conveyance speed V2 passing through the density detecting means in the density measuring mode is set to a value during normal operation. Control is performed so as to be lower than the sheet conveyance speed V1 when the sheet is passed through the sheet conveyance path in the image forming mode, and the density of the reference image on the sheet is detected at the position of the detection unit of the sheet conveyance path. It is characterized by.

  According to the image forming apparatus and the image density measurement method of the present invention, the density adjustment is performed by reflecting the density measurement value obtained with high accuracy in the density of the formed image in the image forming unit. Can meet the demands of

  Hereinafter, preferred embodiments of an image forming apparatus and an image density measuring method of the present invention will be described in detail with reference to the drawings.

(Configuration and operation of image forming apparatus main body)
As shown in FIG. 1, a photosensitive drum 1 serving as an image carrier is provided, and a pre-exposure lamp, a corona electric resistance and a potential sensor (not shown), and a laser exposure optical system 2 are provided around the photosensitive drum 1. The intermediate transfer member 3, the cleaning unit 4, and the rotary developing member 5. In the laser exposure optical system 2, the image signal from the reader unit is converted into an optical signal by the laser output unit, and the laser beam converted into the optical signal is reflected by the polygon mirror, and passes through the lens and each reflecting mirror to the photosensitive drum 1. Projected onto the surface. The rotary developing body 5 has four color developing devices: a black developing device 5K, a yellow developing device 5Y, a magenta developing device 5M, and a cyan developing device 5C. The rotary developer 5 rotates around a cylindrical rotation shaft provided at the center of the rotary developer in the counterclockwise direction indicated by the arrow a in FIG. It is possible to move it to a development position opposite to.

  At the time of image formation, the photosensitive drum 1 is rotated, and the photosensitive drum 1 after being neutralized by the pre-exposure lamp is uniformly charged by a charger, irradiated with the first color light image E, and a latent image is formed on the photosensitive drum. Form. Next, the latent image on the photosensitive drum 1 is developed by a developing device, and a toner image using a resin and a pigment as a base is formed on the photosensitive drum 1. Thereafter, the toner image formed on the photosensitive drum 1 is primarily transferred to the intermediate transfer member 3. When the development of the first color is completed, the rotary developer 5 is rotated by 90 ° in the direction of arrow a in the figure, the developer of the second color is moved to the development position facing the photosensitive drum 1, the primary transfer is completed, and the cleaning device The photosensitive drum 1 cleaned by 4 repeats the latent image, development, and primary transfer with the second, third, fourth, and fourth colors as well as the first color, and sequentially superimposes the toner images of the respective colors on the intermediate transfer body 3. Here, the toner in the developing device is replenished as needed from the toner storage portion at a desired timing so as to keep the toner ratio (or toner amount) in the developing device constant. Further, the sheets are conveyed one by one from the storage units 61, 62, 63, 64 by the respective sheet feeding means 71, 72, 73, 74, and the skew is corrected by the registration rollers 75 at a desired timing. It is conveyed to the secondary transfer unit 76. The sheet on which the toner image has been transferred by the secondary transfer unit 76 passes through the conveyance unit 77, fixes the toner image by the fixing device 8, and is discharged toward the discharge tray 65 or the sheet post-processing apparatus.

  On the other hand, when a double-sided image is formed on a sheet or when a sheet is reversely discharged by forming a single-sided image, the following operations are performed. At the time of double-sided image formation, the sheet is once guided to the reverse conveyance path 66 by driving the conveyance path switching guide immediately after the sheet passes through the fixing device 8. Then, with the reverse roller 78A rotating in the reverse direction, the sheet is fed back to the double-sided conveyance path 67 with the trailing edge of the sheet at the top as the leading edge, retreating in the direction opposite to the fed direction. Thereafter, the sheet passes through the double-sided conveyance path 67 and is conveyed to the registration roller 75, and the image is transferred to the other side again through the above-described image forming process, and then discharged. At the time of reverse discharge, the sheet is guided to the reverse conveyance path 66 by driving the conveyance path switching guide immediately after the sheet passes through the fixing device 8. Then, with the reverse roller 78A rotated in the reverse direction, the sheet trailing edge is fed to the front, the sheet is retracted in the direction opposite to the fed direction, and is discharged toward the discharge tray 65 or the sheet post-processing device. .

(Image density measurement method)
The density of the image formed on the sheet being conveyed is measured, the measured density value is compared with the density target value, and corrected, and fed back to the image formation in the image forming unit. For the concentration measurement, a concentration sensor 9 as concentration detecting means shown in FIGS. 1 and 3 is used. In FIG. 1, when the density sensor 9 is installed in the double-sided conveyance path 67, or in FIG. 3, when the density sensor 9 is arranged in the reverse conveyance path 66, highly accurate density measurement is performed. Hereinafter, in order to perform highly accurate density measurement, the sheet conveyance speeds V1 and V2 are controlled for each of the image forming mode and the density measurement mode].

(1-a) Sheet conveyance speed control in the image forming mode in the double-sided conveyance path In the image forming mode in which an image is formed on the sheet during normal operation, the sheets being conveyed from the storage units 61 to 64 to the image forming unit The conveyance speed V1 is higher than the conveyance speed (for example, 250 mm / sec) during image formation in the image forming unit. This conveyance speed is set to a high speed of 500 mm / sec, for example. The reason is that the first copy time of the sheet when fed from the storage units 61 to 64 is advanced, and the sheet is conveyed by being picked up by the pickup rollers 71 to 74 at a high speed of 500 mm / sec. The conveyed sheet is temporarily stopped by the registration roller 75, the skew is corrected, and is conveyed again at a desired timing. Here, the toner is decelerated to a conveyance speed of 250 mm / sec and sent to the secondary transfer unit 76 after being decelerated. After the secondary transfer, the fixing device 8 fixes the toner image. As soon as the sheet passes through the fixing device 8, the path switching guide is actuated to once guide the sheet to the reverse conveyance path 66.

  By the way, it is desired to improve the productivity by securing the number of sheets circulating in the main body of the image forming apparatus and to widen the jam margin by widening the interval between the preceding and succeeding sheets. In order to achieve this, after the trailing edge of the sheet passes through the nip portion of the fixing device 8 in the reverse conveyance path 66, the sheet conveyance speed V1 is increased to, for example, 600 mm / sec. The reverse roller 78A is reversely rotated at a rotation speed synchronized with the increased sheet conveyance speed V1, and the sheet is conveyed in the opposite direction with the trailing edge of the sheet being fed at the top and retreating in the direction opposite to the fed-in direction. Send to pass 67. The sheet conveyance speed in the duplex conveyance path 67 is 600 mm / sec. The sheet that has passed through the double-sided conveyance path 67 is conveyed to the registration roller 75 and is conveyed again at the sheet conveyance speed (250 mm / sec) at the time of image formation in the image forming process. The image is transferred to the other side of the sheet at the image forming unit, and is discharged when the double-sided image formation is completed. Note that the conveyance speed of these sheets is controlled by a conveyance control device (conveyance control means) CC.

(1-b) Sheet conveyance speed control in the density measurement mode in the double-sided conveyance path In order to read and measure the density of the image on the sheet passing through the double-sided conveyance path 67, as shown in FIGS. The density sensor 9 is installed at a suitable part of the double-sided conveyance path 67. In that case, highly accurate density measurement can be realized by controlling the sheet conveyance speed V2 when the sheet passes in front of the density sensor 9 as follows.

  If the sheet conveyance speed in the density measurement mode is set to, for example, 600 mm / sec in the same manner as the sheet conveyance speed V1 in the image forming mode, the influence on the detection accuracy of the density sensor 9 can be considered. Therefore, the sheet conveyance speed V2 is controlled to decelerate to a suitable constant speed, and the density is detected from the image on the sheet and measured.

  Therefore, as soon as the sheet passes through the fixing device 8, the conveyance path switching guide is driven to temporarily guide the sheet to the reverse conveyance path 66. Therefore, when the trailing edge of the sheet passes through the nip of the fixing device 8, the sheet conveyance speed V2 is increased to, for example, 600 mm / sec, which is equivalent to the sheet conveyance speed V1 during normal operation. The reverse roller 78A is rotated in reverse in synchronization with the increased sheet conveying speed V2, and the sheet is retreated in the direction opposite to the fed direction with the trailing edge of the sheet as the leading end, and the duplex conveying path 67 To send. The sheet conveyance speed V2 when the sheet is fed into the duplex conveyance path 67 is controlled to a low speed such as 150 mm / sec in consideration of sheet flapping and the required number of sheets for image density adjustment. In this way, the sheet sent to the double-sided conveyance path 67 is conveyed at low speed for the purpose of measuring the image density, and the density is detected from the reference image formed on the sheet when passing through the density sensor 9 and measured. To do.

  As shown in FIG. 2, the reference light is irradiated from the irradiation means 91 provided in the density sensor 9 to a plurality of standard images (patch images) on the sheet carried into the double-sided conveyance path 67, and the reference light The reflected light from the light is received by the light receiving means 92, and a signal corresponding to the received light quantity is output. A control device (control means) C that controls the entire image forming apparatus calculates and acquires each density measurement value of the patch image based on the detection signal output from the density sensor 9. The control device C creates a reference table for comparing the obtained density measurement values of the patch images with the target density value determined as a target, and stores the reference table in a storage unit including a memory. That is, when an image is formed in the image forming unit, the density characteristic of the image data is fed back by converting the density characteristic data read from the reference table, and sent to the image forming unit in the image forming mode during normal operation. The density of the image formed on the coming sheet is adjusted.

  The sheet conveyance speed V2 is as low as 150 mm / sec until the density of the patch image is measured by the density sensor 9 on the sheet being conveyed on the duplex conveyance path 67 and the trailing edge of the sheet passes through the density sensor 9. Maintained. The low speed of 150 mm / sec is a speed further reduced than the sheet conveyance speed when the sheet is fed into the double-sided conveyance path 67 and enters. However, during the image forming mode during normal operation, it is necessary to correct the skew in the double-sided conveyance path 67 or to set the timing between the sheets while a plurality of sheets are circulating in the image forming apparatus main body. There are several stop points for this purpose, but the stop at that stop point is not performed in the concentration measurement mode. The reason is to suppress fluttering of the sheet due to the effect of acceleration / deceleration at the stop or to minimize the image width having the reference density. Thereafter, the sheet is conveyed to the registration roller 75, accelerated to a speed of, for example, 250 mm / sec without image formation on the back surface, transferred at the conveyance speed, and discharged via the fixing device 8.

(2-a) Sheet Conveyance Speed Control in the Image Forming Mode in the Reverse Conveyance Pass FIG. 3 shows a structure in which the density sensor 9 is arranged facing the reverse conveyance path 66. Other configurations are the same as those in FIG. Also at the time of reverse discharge, the sheet is fed out by the pickup rollers 71, 72, 73, 74 at the same feeding speed as the sheet conveying speed V1 at the time of normal operation image formation as in the case of double-sided image formation. After the toner image is fixed by the fixing device 8, the path switching guide is actuated as soon as the sheet passes therethrough, and the sheet is once guided to the reverse conveyance path 66. When the rear end of the sheet passes through the nip portion of the fixing device 8 as in the case of both sides, the sheet conveyance speed is increased to, for example, 600 mm / sec. In this speed state, the reversing roller 78B is rotated in the reverse direction, and the sheet is discharged while being retracted in the direction opposite to the feeding direction with the trailing edge of the sheet as the leading edge.

(2-b) Sheet Conveyance Speed Control in Density Measurement Mode in Reverse Conveyance Pass When the sheet conveyance speed V1 is a high speed of 600 mm / sec, as described above, conveyance in which the sheet is curved during density measurement is also performed in this density measurement mode. The sheet sways and fluctuates with respect to the density sensor 9 due to an impact when entering the path. As a result, high-precision concentration measurement cannot be performed. For this reason, the conveyance speed V1 of the sheet conveyed through the reverse conveyance path 66 is set to a low speed such as 150 mm / sec in the density measurement mode.

  The density is measured by the density sensor 9 using a plurality of images on the sheet sent to the reverse conveyance path 66 as reference images (patch images). The control device C calculates and acquires each density measurement value of the patch image based on the detection signal output from the density sensor 9. The control device C further creates a reference table for comparing the obtained density measurement values of the patch images with the density target value determined as a target, and stores the reference table in a storage unit including a memory. That is, when an image is formed in the image forming unit, the density characteristics of the image data are fed back by converting density density data read from the reference table, and the image formed on the sheet sent to the image forming unit is fed back. Adjust the density.

  The trailing edge of the sheet passing through the reverse conveyance path 66 passes through the position opposite the density sensor 9 and is conveyed at a constant speed, that is, at a low speed of 150 mm / sec until the density measurement is completed. During normal operation image formation, there is a brake sequence that slows down the sheet transport speed to improve stackability after reverse discharge, and conversely, it is kicked out at an increased speed to eliminate the back edge of the sheet from the outer discharge roller. There is a sequence, but here it is transported at a constant speed until the concentration measurement is completed. This is to eliminate the effect of fluttering of the sheet due to the effect of acceleration / deceleration and to minimize the reference density image width. The sheet for which the image density measurement has been completed is discharged toward the discharge tray 65 or the sheet post-processing apparatus.

  As the deceleration point, the reverse roller 78A is described when the density sensor 9 is disposed in the double-sided conveyance path 67, and the reverse roller 78B is described when the density sensor 9 is disposed in the reverse conveyance path 66. What is necessary is just to finish deceleration before reaching the opposing position of the sensor 9. Further, although the system has been described in which the speed is increased after the sheet trailing edge has passed through the nip of the fixing device 8 as in the normal operation, the speed is not increased unlike the control in the normal operation, and the constant speed is maintained as it is. Thus, the sheet may be conveyed to a position opposite to the density sensor 9 or may be further decelerated from here.

  Therefore, in the present embodiment, the sheet conveyance speed V2 such as 150 mm / sec when measuring the image density is significantly reduced than the high sheet conveyance speed V1 such as 600 mm / sec during normal operation image formation. Limit to a maximum of a quarter. Therefore, even if the width of the image having the reference density is narrow by a quarter, the density can be measured with high accuracy, and the required number of sheets can also be suppressed to a quarter. In other words, since a highly accurate density measurement can be performed with only one sheet with the minimum density width, the running cost can be reduced accordingly.

  In addition, according to the present embodiment, when the image density of the sheet after fixing is detected and reflected in the image density adjustment in the image forming unit by feedback of the detection result, desired reading is performed with a narrow reference density image. Reserve time to minimize the number of sheets required. As a result, the burden on the user and the cost can be minimized, and the density is measured in a state where the influence of the vertical movement of the sheet, which should be called the problem of the scanning sensor, is small, and stable density adjustment is realized.

  The present invention is not limited to the above embodiment, and other embodiments, application examples, modified examples, and combinations thereof are possible as long as they do not depart from the gist of the present invention.

  For example, in the above-described embodiment, white light such as an LED, a halogen lamp, or a xenon lamp, red light, blue light, green light, or the like can be used as the reference light emitted from the density sensor 9 to the standard image. In addition, a CCD, a photodiode, a photomultiplier, a CMOS sensor, or the like can be employed as a photoelectric conversion element provided in the light receiving unit.

  Further, although specific numerical values are shown and described as the sheet conveyance speeds V1 and V2, the numerical values of the speeds are illustrated for the sake of easy understanding for comparison, and the present invention is limited to these numerical values. is not.

FIG. 4 is a diagram illustrating an image forming apparatus that performs density measurement by performing density measurement with a density sensor disposed in a double-sided conveyance path according to an embodiment. The sensor block diagram which shows the aspect which collects and measures a density | concentration from the some reference image (patch image) on a sheet | seat by a density sensor. FIG. 3 is a diagram illustrating an image forming apparatus that performs image density adjustment during image formation by performing density measurement with a density sensor installed in a reverse conveyance path as an embodiment.

Explanation of symbols

9 Concentration sensor 66 Reverse conveyance path 67 Double-sided conveyance path 91 Irradiation means 92 Light receiving means C Control device CC Conveyance control device

Claims (8)

In an image forming apparatus having an image forming unit that forms an image on a sheet,
Density detecting means for detecting the density of the reference image with respect to a sheet that has been formed through the image forming section and is passing through a sheet conveyance path;
Control means for controlling to adjust the density of the image formed by the image forming unit to the detection value from the density detection means;
The sheet conveyance speed V2 at the time of density detection by the density detection means in the density measurement mode for measuring the density of the reference image by the density detection means is the sheet on the sheet conveyance path in the image forming mode at normal operation. Transport control means for controlling the speed to be lower than the transport speed V1 of
An image forming apparatus comprising: The sheet conveyance path in which the density detection unit is disposed reverses the sheet on which the image is formed on the one side by the image forming unit and conveys the sheet again to the image forming unit in order to form images on both sides of the sheet. The image forming apparatus according to claim 1, wherein the image forming apparatus is a double-sided conveyance path. The image forming apparatus according to claim 1, wherein the sheet conveyance path in which the density detection unit is arranged is a reversal conveyance path for reversing the front and back of the sheet. The conveyance control unit forms an image at the same speed as that in the image formation mode when the reference image is formed in the image forming unit in the density measurement mode, and the low speed before the sheet reaches the image density detection unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is decelerated to a predetermined speed. 5. The control unit according to any one of claims 1 to 4, wherein the control unit obtains a density measurement value based on an amount of received light reflected from the sheet passing through the sheet conveyance path. 2. The image forming apparatus according to item 1. When the sheet passing through the sheet conveyance path reaches the detection part of the density detection means, the density of the reference image on the sheet is detected, and the image density of the density of the image formed by the image forming unit based on the detected value An image density measurement method for performing adjustment,
Control is performed such that the conveyance speed V2 of the sheet passing through the density detection unit in the density measurement mode is lower than the conveyance speed V1 of the sheet passing through the sheet conveyance path in the image forming mode during normal operation. An image density measuring method comprising: detecting a density of a reference image on a sheet at a position of a detection unit of the sheet conveyance path. The image density measuring method according to claim 6, wherein the sheet conveyance speed V <b> 2 being detected is maintained constant at a detection portion of the sheet conveyance path. 8. The image according to claim 6, wherein the sheet conveyance speed V <b> 2 is a speed that is decelerated from an entry speed immediately before the sheet enters the sheet conveyance path and reaches a detection site. Concentration measurement method.

Images