JP2010145605A - Image forming device and detection auxiliary device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect the density of a fixed image and stably provide a target image quality, by suppressing conveyance flopping itself of a recording medium without requiring a means for detecting the conveyance flopping of the recording medium after fixing. <P>SOLUTION: This image forming device includes a density sensor 54 for detecting the density of an image formed on a surface of paper YS conveyed along a conveyance passage, a light shielding guide 81 that is arranged near the density sensor and suppresses displacement of the paper YS in the direction perpendicular to the paper surface, and a controlling means for correcting an image forming condition based on the density of the image detected by the density sensor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a recording medium by an electrophotographic method or the like, and a detection assisting device for a density sensor that detects the density of the formed image.

  Conventionally, copiers, printers, facsimiles, and multi-function machines that form images by electrophotographic methods, electrostatic recording methods, ionography, or magnetic recording methods (herein, these are referred to as “electrophotographic methods”). Alternatively, an image forming apparatus such as a multi-function device called MFP (Multi Function Peripherals) is used.

  In general, in an image forming apparatus, the image quality fluctuates due to environmental changes, changes over time due to use, and the like. Feedback control (image stabilization control) is performed so that an image with an appropriate image quality is always formed against such fluctuations. In the image stabilization control, a test patch image is formed, and the density of the image is detected by a density sensor. Based on the obtained detection signal, it is determined whether or not the image is within the target image quality range. If the image is not within the target image quality range, various image forming conditions are corrected or adjusted.

  Image density detection for image stabilization control is performed by developing a toner image on a photosensitive drum, a toner image formed on an intermediate transfer belt, a toner image on unfixed paper after secondary transfer, Alternatively, it is performed on an image (fixed image) fixed on the recording medium. When detecting the density of an image with respect to a fixed image, there is a demerit that the recording medium is consumed for testing as compared with the case with other images. There is a merit that it is possible to detect the density of an image including fluctuations in the image, and it is possible to stabilize the image with higher accuracy.

  By the way, when detecting the density of the fixed image formed on the recording medium on the conveyance path downstream from the fixing step, the detection surface (medium surface) of the recording medium that is the detection target is fluttered, that is, the recording medium Variations in the direction perpendicular to the transport direction may be a problem and may not be detected accurately.

  For example, when a general optical reflection type sensor is used as the density sensor, if the detection distance between the density sensor and the detection surface varies, the amount of reflected component received from the detection surface changes greatly, and accurate Cannot detect. If the detection cannot be performed accurately, the image forming conditions cannot be corrected or adjusted accurately, and the target image quality cannot be obtained.

Conventionally, in addition to the color sensor that detects the density of the fixed image, a sensor that detects the floating amount and the inclination of the recording medium is provided, and the output of the color sensor according to the output of the sensor that detects the state of the recording medium. A technique for correcting image data after correcting the above has been proposed (Patent Document 1).
JP2008-89697

  However, in the invention described in Patent Document 1, it is necessary to provide a plurality of sensors for detecting various states. In order to correct the image forming conditions based on the information detected by the multiple sensors, it is necessary to perform complicated calculation processing, and error propagation occurs due to each detection error in the calculation process, and the error range is increased. There is a high possibility that In addition, there is a time loss between the detection of various states and the completion of the correction of the image forming conditions. During that time, image formation conforming to the target image quality is not performed, and new image forming operations can be stopped. Must be considered. In such a case, it is a major disadvantage in terms of productivity.

  In view of the above-described problems, the present invention accurately detects the density of a fixed image by suppressing the conveyance flutter of the recording medium itself without using the means for detecting the conveyance flutter of the recording medium after fixing. The purpose is to stably obtain the desired image quality.

  An image forming apparatus according to the present invention is a density that detects the density of an image formed on a medium surface of a recording medium conveyed along a conveying path in an image forming apparatus that forms an image on the medium surface of the recording medium. An image is formed on the basis of the density of the image detected by the sensor, the flutter suppressing means which is disposed in the vicinity of the density sensor and suppresses the recording medium from fluctuating in a direction perpendicular to the medium surface. Control means for correcting the conditions.

  Preferably, the density sensor includes a light projecting unit that irradiates light on the medium surface and a light receiving unit that receives light reflected from the medium surface by irradiation of the light projecting unit, and suppresses the fluttering. The means has a light-shielding portion having a shape surrounding at least a part of the outer periphery of the density sensor so as to block external light from entering the light-receiving portion.

  The flutter suppression means is provided at the container-shaped light-shielding portion having an opening portion that accommodates the concentration sensor therein and opens to a light projecting / receiving surface side of the concentration sensor, and an end portion of the opening portion, A first guide portion that guides the recording medium along the conveyance path.

  The first guide portion may have an inclined surface that is inclined at an acute angle with respect to the conveyance direction of the recording medium. Alternatively, the first guide portion may include a flexible brush-like member provided so that the tip portion is in contact with the medium surface.

  The flutter suppressing means suppresses flutter that is likely to occur when the recording medium is conveyed. Since such fluttering suppression means is arranged in the vicinity of the density sensor, detection by the density sensor is performed accurately.

  According to the present invention, it is possible to accurately detect the density of a fixed image and stably obtain a target image quality by suppressing the conveyance flutter of the recording medium after fixing itself.

[Overall Description of Image Forming Apparatus]
FIG. 1 is a diagram showing a schematic internal configuration of an image forming apparatus 1 according to an embodiment of the present invention, FIG. 2 is an enlarged view showing an image forming unit 20 that is a part of the image forming apparatus 1, and FIG. 2 is a block diagram illustrating a main control system of the image forming apparatus 1. FIG.

  As shown in FIG. 1, the image forming apparatus 1 is an electrophotographic full-color copying machine incorporating a tandem type print engine. Such an image forming apparatus 1 may be referred to as a multi function peripheral or MFP (Multi Function Peripherals).

  1, the image forming apparatus 1 includes an image reading unit 10, an image forming unit 20, a paper supply unit 60, a control unit 100, and the like.

  Referring also to FIG. 2, the image reading unit 10 reads an image of a document placed on a document glass table by moving the scanner. That is, an original is irradiated with an exposure lamp installed in a scanner, and an image of the reflected light is read by a CCD image sensor corresponding to the three primary colors of red (R), green (G), and blue (B). As a result, R, G, and B image data corresponding to the document image are obtained.

  The image data obtained by the image reading unit 10 is subjected to various processes in the control unit 100, and further, image data of reproduction colors of yellow (Y), magenta (M), cyan (C), and black (K). Is converted to The converted image data is stored for each reproduction color in an image memory provided in the control unit 100. In synchronization with the transport state of the paper YS supplied from the paper supply unit 60, image data is read from the image memory for each scanning line and output as a drive signal for a laser diode that exposes the photosensitive drum.

  Note that paper, a plastic sheet, and other recording media can be used as the paper YS. That is, the paper can be restated as a recording paper, a recording material, a recording medium, a transfer medium, or the like.

  The image forming unit 20 forms an image on a sheet by electrophotography, and includes an imaging unit U, an intermediate transfer unit 40, a fixing unit 50, and the like.

  As the imaging unit U, imaging units UY, UM, UC, UK of four colors Y, M, C, and K are provided, and are arranged along the intermediate transfer belt 41 in this order. In each imaging unit U, the photosensitive drum 21, the charging charger 22, the exposure unit 23 that exposes the surface of the photosensitive drum 21 to form an electrostatic latent image, and the electrostatic latent image is developed with toner of each color. A developing unit 24 for forming an image, a transfer charger 25 for transferring the toner image to the intermediate transfer belt 41 (primary transfer), a transfer roller (not shown), and a cleaner 26 for cleaning the surface of the photosensitive drum 21 are provided.

  The toner images (toner images) of the respective colors formed by these imaging units U are superimposed on the same position on the traveling intermediate transfer belt 41, transferred, and combined.

  The intermediate transfer unit 40 is provided with a plurality of rollers 42, 43, and 44 that support the intermediate transfer belt 41 so that it can run. A transfer roller 45 is provided at a position facing the roller 44. The transfer roller 45 is provided so as to be able to come into contact with and separate from the intermediate transfer belt 41, and forms a transfer nip portion by being pressed against the intermediate transfer belt 41. Further, a bias voltage for transfer is applied to the transfer roller 45.

  The sheet YS is fed to the transfer nip portion in synchronization with the travel of the intermediate transfer belt 41, and the toner image formed on the intermediate transfer belt 41 is transferred onto the sheet YS at the transfer nip portion. Next transfer). The toner remaining on the intermediate transfer belt 41 after the secondary transfer is removed by the cleaner 46.

  The fixing unit 50 is provided with a fixing roller 51, a heating roller 52, a paper conveyance guide 53, and the like. The sheet YS on which the toner image is formed by the secondary transfer is guided by the sheet transport guide 53 and transported on the transport path HR, and is fixed by passing between the fixing roller 51 and the heating roller 52. The fixed sheet YS is transported on the transport path HR and discharged onto the tray 65.

  A density sensor (IDC sensor) 54 for detecting the density of the image formed on the paper YS is provided on the transport path HR. An optical reflective sensor is used as the density sensor 54. The density sensor 54 detects the density of a test patch image (test pattern) formed on the paper YS for image stabilization control (IDC). For example, the density of four colors (toner density and toner adhesion amount) is detected for each of Y, M, C, and K. In the vicinity of the density sensor 54, a flutter suppressing device 80 for suppressing flutter of the paper YS is provided.

  Various sizes of paper YS are stored in the paper supply unit 60, and are sent out to the transport path HR at a predetermined timing by a paper feed transport unit including rollers 61 to 63 and the like. An intermediate roller and a registration roller (not shown) are provided in the middle of the conveyance path HR, and the sheet YS is conveyed to the secondary transfer position by these.

  In FIG. 3, the control unit 100 includes a storage unit including a CPU, a semiconductor memory, a magnetic storage device, and the like, a control circuit, a communication unit including various interfaces, and the like. Image processing is performed on image data read by the image reading unit 10 or image data output from a personal computer (not shown), and the operation of each unit of the image forming apparatus 1 is controlled.

  As shown in FIG. 3, the image forming apparatus 1 includes a charging grid high-voltage power source 71 that applies a charging bias voltage Vg to the charging charger 22, and a developing bias high-voltage power source 72 that applies a developing bias voltage Vdc to the developing roller of the developing unit 24. , And a secondary transfer high voltage power source 73 for applying a bias voltage to the transfer roller 45 is provided. In addition to the concentration sensor 54 described above, a temperature / humidity sensor 55, a PH temperature sensor 56, and the like are provided.

  The control unit 100 controls the charging grid high-voltage power supply 71, the developing bias high-voltage power supply 72, and the secondary transfer high-voltage power supply 73 so as to output appropriate voltages or currents, respectively. In addition, a drive signal is output to the laser diode of the exposure unit 23. This drive signal is modulated by various methods in order to adjust the emission intensity of the laser diode.

  The control unit 100 receives an input signal from the operation unit 11 by the user and outputs various signals to the operation unit 11. The operation unit 11 is provided with a switching unit including push buttons for switching the operation of the image forming apparatus 1, a display panel or a touch panel for displaying images and messages, and the like.

In addition, the control unit 100 inputs the detection signal S1 from the concentration sensor 54 described above, and other detection signals from the temperature / humidity sensor 55 and the PH temperature sensor 56, and uses them for various controls.
(Image stabilization control)
In the image forming apparatus 1, the image quality fluctuates due to environmental changes, changes over time due to use, and the like. Image stabilization control (image stabilization processing) is performed so that an image with appropriate image quality is always formed against such fluctuations. In the image stabilization control in the present embodiment, a test patch image is formed on the paper YS, and the density of the image is detected (measured) by the density sensor 54. Based on the detection signal detected by the density sensor 54, it is determined whether or not the image is within a target image quality range. If the image is not within the target image quality range, each image forming condition is corrected or adjusted based on the detection signal.

  In image stabilization control, for example, when the image forming apparatus 1 is turned on, when returning from the energy saving mode, the temperature change or humidity change in the apparatus after the previous image stabilization process has exceeded each threshold value. Or when the total number of printed sheets exceeds a threshold value.

  FIG. 4 is a diagram showing an example of the structure of the density sensor 54.

  In FIG. 4, a light projecting element 541 and light receiving elements 542 and 543 are provided in a case 544. The light projecting element 541 is, for example, an LED lamp, and the light receiving elements 542, 543 are, for example, photodiodes. Light SK is emitted from the light projecting element 541 to the patch image, and regular reflected light is received by the light receiving element 543 and irregularly reflected light is received by the light receiving element 542 out of the reflected light HK by irradiation. The density sensor 54 outputs a detection signal S1 corresponding to the amount of received light and transmits it to the control unit 100.

  The case 544 is formed in a substantially truncated cone shape from a synthetic resin material. In the case 544, the opening KB where the light SK is irradiated and the reflected light HK is incident is substantially circular. A transparent window is provided in the opening KB. Except for the opening KB of the case 544, it has light shielding properties.

  The control unit 100 corrects or sets various image forming conditions based on the detection signal S1 received from the density sensor 54. The image forming conditions here are diverse, such as a charge amount, an exposure amount, a developing bias voltage, a transfer voltage, a transfer current, a fixing temperature, and a fixing speed.

  As described above, the information detected by the density sensor 54 is fed back to various image forming conditions and correction is performed, so that an image having an appropriate image quality is always obtained without being affected by changes in the environment or changes over time due to use. Can be formed.

When the density sensor 54 detects a patch image, if the paper YS is in a fluttered state, the density of the patch image cannot be detected accurately. Therefore, a means for suppressing the paper YS flutter is taken. Yes.
[Embodiment 1 of Flutter Suppression Device]
5 is an enlarged cross-sectional view of the flutter suppression device 80 shown in FIG. 2, FIG. 6 is a view of the flutter suppression device 80 viewed from the direction of arrow A in FIG. 5, and FIG. FIG. 8 is an enlarged cross-sectional view showing the shape of a guide portion 812 provided in the light shielding guide 81. FIG.

  In FIG. 7, for the sake of convenience, a state in which the light shielding portion 811 is placed on the upper side and the guide portion 812 is placed on the lower side is shown.

  The flutter suppression device 80 is disposed in the vicinity of the density sensor 54, and suppresses the paper YS from fluctuating in a direction perpendicular to the paper surface.

  As shown in FIG. 5, the flutter suppression device 80 includes a light shielding guide 81 and an auxiliary guide 82.

  First, the configuration of the light shielding guide 81 will be described.

  The light shielding guide 81 has a light shielding portion 811 and a guide portion 812, which are integrally formed of synthetic resin. Moreover, you may assemble and comprise a some component. The synthetic resin used for the light-shielding guide 81 is preferably one having a light-shielding property, and one having a certain degree of heat resistance is preferable because it is disposed in the vicinity of the fixing roller 51. Therefore, when a transparent synthetic resin is used as the material of the light shielding guide 81, the light shielding property may be imparted by applying black or an appropriate color paint or applying an appropriate coating. The light shielding guide 81 can also be formed by sheet metal processing using a steel plate or the like.

  In FIG. 7, the light-shielding portion 811 is a rectangular parallelepiped container having an opening KK on the bottom surface. That is, the light-shielding portion 811 has an upper surface portion 811a and side surface portions 811c to 811f. The upper surface portion 811a and the opening KK have a square shape with a size corresponding to one patch image TP. The height H1 of the side surface portions 811c to 811f is a dimension that accommodates the density sensor 54 and allows for the detection distance.

  The guide unit 812 is provided at the end of the opening KK and guides the paper YS along the transport path HR. That is, the guide part 812 has the guide surface 813 provided in the edge of the side part 811c, and the guide surface 814 provided in the edge of the side part 811e.

  The height H2 of the guide surfaces 813 and 814 in the vertical direction in the drawing is about several millimeters to several centimeters. In this embodiment, the guide surfaces 813 and 814 are provided only at the two end edges of the light shielding portion 811, but may be provided on the entire circumference including the four end edges.

  As shown in FIG. 8A, the guide surface 813 is planar and is inclined with an angle α with respect to the side surface portion 811c. The angle α is, for example, about 30 to 60 degrees. The guide surface 814 is also inclined at the same angle α with respect to the side surface portion 811e. However, the angle α and the inclination direction of the guide surfaces 813 and 814 are not necessarily the same.

  A sliding layer 815 is formed on the outer wall surface of the guide surface 813 by applying a coating agent having good slidability. A similar sliding layer 815 is also formed on the inner wall surface of the guide surface 814. Note that the light shielding guide 81 itself may be formed of a synthetic resin having good slidability, and the sliding layer 815 may be omitted.

  In the above example, the guide surface 813 is a flat surface, but may have a shape other than this. The same applies to the guide surface 814.

  For example, the guide surface 813B shown in FIG. 8B is inclined so that the angle inclined with respect to the side surface portion 811c is not constant as shown in FIG. ing. That is, the guide surface 813B is smoothly curved in an arc shape toward the inner side of the light shielding guide 81.

  A guide surface 813C shown in FIG. 8C has a shape extending to the outer wall surface of the side surface portion 811c while curving in an arc shape outside the side surface portion 811c. That is, it projects so as to draw an arc outside the light shielding guide 81. For example, the cross section is a shape close to the handle of the cup.

  In FIG. 8D, a brush 816 is attached to an end portion of the side surface portion 811c with an adhesive or a screw. The brush 816 is obtained by planting a large number of linear hair materials 818 having elasticity on a base material 817. The brush 816 is attached to two edge portions of the side surface portions 811c and 811e, which is usually sufficient, but may be attached to the entire circumference including the edge portions of the side surface portions 811d and 811f.

  Further, as shown in FIGS. 8A to 8D, an antireflection layer 819 is formed on the entire inner wall surface of the light shielding guide 81 by applying a low reflective coating agent. The antireflection layer 819 prevents reflected light or external light due to irradiation of the light projecting element 541 from being reflected inside the light shielding guide 81 and unexpectedly entering the light receiving elements 542 and 543.

  Returning to FIG. 5, the substrate 55 is attached to the inner wall surface side of the upper surface portion 811 a of the light shielding guide 81 by fitting or using screws or the like. The density sensor 54 described above is mounted on the substrate 55, and thus the density sensor 54 is attached to the light shielding guide 81 via the substrate 55.

  The density sensor 54 is disposed such that the light projecting / receiving surfaces of the light projecting element 541 and the light receiving elements 542, 543, that is, the opening KB faces the opening KK of the light shielding guide 81. The substrate 55 may be provided at an appropriate location outside the light shielding guide 81. In this case, for example, the concentration sensor 54 connected to the external substrate 55 with a lead wire or the like is attached to the inner wall surface of the upper surface portion 811a.

  Since the light shielding guide 81 is formed of a synthetic resin having a light shielding property as described above, the light shielding guide 81 surrounds the outer periphery excluding the opening KB of the density sensor 54, so that the light receiving elements 542 and 543 are provided. It is possible to prevent external light from being incident unexpectedly. Here, the external light includes light entering the image forming apparatus 1 from outside the apparatus and light emitted inside the image forming apparatus 1 for purposes other than detection by the density sensor 54. Since the position where the density sensor 54 is provided is close to the location where the paper YS is discharged outside the apparatus, it can be said that the density sensor 54 is particularly susceptible to external light from outside the apparatus.

  The density sensor 54 and the light shielding guide 81 constitute a fixed image detection unit TY.

  Next, the auxiliary guide 82 will be described.

  As shown in FIG. 5, the auxiliary guide 82 has a flat surface portion 821 and inclined surface portions 822 on both sides thereof. The auxiliary guide 82 is manufactured by bending and inclining a metal plate such as a steel plate or a stainless steel plate at both ends thereof. Further, it can be formed using a synthetic resin or the like.

  The inclined surface portion 822 is inclined with an angle β with respect to the flat surface portion 821. The angle β is about 30 to 45 degrees although it depends on the type of the paper YS.

  As shown in FIG. 6, it is desirable that the width W of the auxiliary guide 82 is slightly wider than the lateral width of the paper YS. The length L1 of the flat surface portion 821 is a size corresponding to several patch images TP, and the length L2 of the inclined surface portion 822 is about 1 to several centimeters.

  Next, the arrangement relationship between the light shielding guide 81 and the auxiliary guide 82 will be described.

  In FIG. 5, the light shielding guide 81 and the auxiliary guide 82 are provided at positions facing each other in the detection range of the density sensor 54, and are attached to the main body frame of the image forming apparatus 1 with screws or the like. The end surfaces of the guide surfaces 813 and 814 of the light shielding guide 81, that is, the opening KK, and the flat portion 821 of the auxiliary guide 82 are close to each other with the paper YS interposed therebetween. The gap G in the adjacent portion is set to a large size with a margin as compared with the maximum thickness of the paper YS to be used. In this state, the guide surfaces 813 and 814 are in a state where the guide surfaces 813 and 814 are swung along the traveling direction of the transport path HR of the paper YS. Further, the upstream inclined surface portion 822 is in an open state so as to smoothly convey the paper YS onto the flat surface portion 821.

  When the brush 816 shown in FIG. 8D is used instead of the guide portion 812, the gap G is set to almost zero. That is, when the paper YS passes through the gap G, the front end portion of the bristle material 818 is in contact with the paper YS. However, contact is not made when the sheet YS before fixing is passed.

  By disposing the light shielding guide 81 and the auxiliary guide 82 as described above, even when the paper YS is conveyed in a fluttered state during the image stabilization control, the leading end portions of the guide surfaces 813 and 814 As a result, the floating and inclination of the paper YS within the detection range of the density sensor 54 can be suppressed.

  When the brush 816 shown in FIG. 8D is used, the tip of the brush 816 is in contact with the paper YS and presses the paper YS, so that the effect of suppressing the lifting and tilting of the paper YS is further enhanced. Further, the sheet YS can smoothly enter or be discharged into the gap G by the inclination and slidability of the guide surfaces 813 and 814.

  In addition, the paper YS may curl as it passes between the fixing roller 51 and the heating roller 52. Even in this case, the paper YS within the detection range of the density sensor 54 is prevented from being lifted. The sheet YS can smoothly enter or be discharged into the gap G.

  Accordingly, the sheet YS within the detection range of the density sensor 54 is within a predetermined detection position, and the density sensor 54 can accurately detect the density of the patch image TP.

Further, since the light shielding guide 81 has a light shielding property and an antireflection layer 819 is formed on the inner wall surface thereof, the density sensor 54 receives externally reflected light and irregularly reflected light caused by the fluttering of the paper YS. The density sensor 54 can detect the density of the patch image TP more accurately.
[Embodiment 2 of Flutter Control Device]
Generally, the fixing device is heated and pressure-bonded while the recording medium is sandwiched between a pair of rollers, which may cause the recording medium to curl. In order to remove the curl generated in the fixing process, a device (referred to as a decurler) that corrects and removes curl using a roller pair is provided on the discharge side of the fixing device (see FIG. JP-A-5-221574).

  FIG. 9 is a cross-sectional view illustrating an example in which a decurler 90 is provided downstream of the fixing unit 50 in the conveyance direction of the paper YS. FIG. 9 shows an example in which the decurler 90 is used as a flutter suppressing device.

  As shown in FIG. 9, the decurler 90 includes a hard roller 901 and a soft roller 902 having an outer diameter larger than that of the roller 901 and having elasticity. In this embodiment, the decurler is composed of a pair of rollers, but may be composed of three or more rollers.

  The density sensor 54 described in the first embodiment is provided downstream of the decurler 90. Further, the auxiliary guide 82 described in the first embodiment is provided at a position facing the density sensor 54. The rollers 901 and 902 are arranged such that the direction in which the paper YS is sent out from the decurler 90 is along the flat portion 821 of the auxiliary guide 82.

  The decurler 90 presses the paper YS by the roller 901 and the roller 902 so as to bend in a direction opposite to the curl of the curl to remove the curl of the paper YS generated in the fixing process. The pressed sheet YS is sent out along the flat portion 821 of the auxiliary guide 82.

  As a result, even when the paper YS is conveyed to the decurler 90 in a state of fluttering during image stabilization control, the paper YS is fixed to the pressure contact surfaces of the rollers 901 and 902, and the plane of the auxiliary guide 82 Since it is sent out along the part 821, the floating and inclination of the paper YS can be suppressed in the detection range of the density sensor 54.

  In other words, by arranging the density sensor 54 on the conveyance path immediately after the decurler 90, the decurler 90 not only functions as a means for removing the curl of the paper YS generated in the fixing process, but also the density sensor 54 is used for the patch image. It also functions as a flutter suppressing device that suppresses fluttering of the paper YS during detection.

  Accordingly, the sheet YS within the detection range of the density sensor 54 is within the predetermined detection position, and the density sensor 54 can accurately detect the density of the patch image.

  Further, as in the case of the first embodiment, by further providing the light shielding guide 81 so as to surround the density sensor 54, the effect of suppressing the fluttering is further enhanced, and the adverse effect of external light and irregular reflection light on the density sensor 54 is increased. The density sensor 54 can detect the density of the patch image more accurately.

The decurler 90 may be provided in a finisher device that finishes the fixed sheet YS. In that case, the density sensor 54 and the like are provided in the same finisher device.
[Explanation by Flowchart of Image Stabilization Control]
FIG. 10 is a flowchart showing an outline of an example of image stabilization control based on patch image density detection.

  As shown in FIG. 10, when the image stabilization control is started with the power-on or the like as a trigger, first, a test patch image is formed on the paper YS (# 11). The density of the patch image is detected by the density sensor 54 (# 12), and based on the detected density value, an optimal image forming condition for obtaining the target image quality is calculated (# 13). Then, the calculated image forming conditions are set in the storage unit of the control unit 100 (# 14).

  As described in the first and second embodiments, by providing the flutter suppression device 80 or the decurler 90, the flutter of the paper YS within the detection range of the density sensor 54 can be suppressed. In addition, since the flutter suppressing device 80 includes the light shielding guide 81 as shown in the first embodiment, it is possible to prevent adverse effects of external light and irregularly reflected light on the density sensor 54 at the same time.

  As described above, according to the present embodiment, the density sensor 54 accurately detects the density of the fixed image, the control unit 100 can calculate appropriate image forming conditions, and the image forming apparatus 1 stabilizes the target image quality. Can be supplied.

  In the embodiment described above, the light shielding guide 81 corresponds to the detection assisting device of the present invention. The light shielding guide 81, or the set of the light shielding guide 81 and the auxiliary guide 82, or the decurler 90, or the set of the decurler 90, the light shielding guide 81, and the auxiliary guide 82, corresponds to the flutter suppressing means of the present invention. The guide portion 812 corresponds to the first guide portion of the present invention, and the auxiliary guide 82 corresponds to the second guide portion of the present invention.

  In the above-described embodiment, the density sensor 54, the light shielding unit 811, the guide unit 812, the light shielding guide 81, the auxiliary guide 82, the flutter suppressing device 80, the decurler 90, the control unit 100, or each part or the whole of the image forming apparatus 1. The configuration, structure, shape, size, number, arrangement, circuit, and the like of the above can be appropriately changed in accordance with the gist of the present invention.

1 is a diagram illustrating a schematic internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged view showing an image forming unit that is a part of the image forming apparatus. FIG. 3 is a block diagram illustrating a main control system of the image forming apparatus. It is a figure which shows the example of the structure of a density sensor. It is sectional drawing which expands and shows a fluttering suppression apparatus. It is the figure which looked at the flutter suppression device from the direction of arrow A in FIG. It is a perspective view which shows the external appearance of the light-shielding guide which comprises a fluttering suppression apparatus. It is sectional drawing which expands and shows the shape of the guide part provided in a light-shielding guide. It is sectional drawing which shows the example which used decurler as a flutter suppression device. It is a flowchart which shows the outline of the example of image stabilization control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 54 Density sensor 80 Flutter suppression device (flutter suppression means)
81 Shading guide (detection assist device)
82 Auxiliary guide (second guide)
90 decurler (fuzziness suppression means)
100 Control unit (control means)
541 Light Emitting Element (Light Emitting Section)
542 Light-receiving element (light-receiving part)
543 Light-receiving element (light-receiving part)
811 Light shielding portion 812 Guide portion (first guide portion)
819 Anti-reflective layer YS paper (recording medium)

Claims (10)

In an image forming apparatus for forming an image on a medium surface of a recording medium,
A density sensor for detecting the density of an image formed on the medium surface of the recording medium conveyed along the conveyance path;
Flutter suppressing means that is disposed in the vicinity of the density sensor and suppresses the recording medium from fluctuating in a direction perpendicular to the medium surface;
Control means for correcting image forming conditions based on the density of the image detected by the density sensor;
An image forming apparatus comprising: The concentration sensor is
A light projecting unit for irradiating the medium surface with light;
A light receiving unit that receives reflected light from the medium surface by irradiation of the light projecting unit;
Have
The flutter suppression means has a light shielding portion having a shape surrounding at least a part of the outer periphery of the density sensor so as to block the incidence of external light to the light receiving portion.
The image forming apparatus according to claim 1. The flutter suppression means is:
The container-shaped light-shielding portion that has an opening portion that accommodates the concentration sensor therein and opens to a light projecting / receiving surface side of the concentration sensor;
A first guide portion provided at an end of the opening and guiding the recording medium along the conveyance path;
The image forming apparatus according to claim 2. The first guide portion has an inclined surface that is inclined at an acute angle with respect to the conveyance direction of the recording medium.
The image forming apparatus according to claim 3. The first guide portion includes a flexible brush-like member provided so that a tip portion is in contact with the medium surface.
The image forming apparatus according to claim 3. The light-shielding portion has an antireflection layer formed on the inner surface thereof.
The image forming apparatus according to claim 2. The flutter suppression means further includes a second guide portion that is provided at a position facing the first guide portion with the recording medium interposed therebetween and guides the recording medium along the conveyance path.
The image forming apparatus according to claim 2. The flutter suppression means is a decurler that removes curl of the recording medium, and is disposed upstream of the detection position of the density sensor in the conveyance direction of the recording medium.
The image forming apparatus according to claim 1. The flutter suppression means further includes a light-shielding portion that surrounds at least a part of the outer periphery of the density sensor so as to block external light from entering the density sensor.
The image forming apparatus according to claim 8. A detection assisting device disposed in the vicinity of a density sensor for detecting the density of an image formed on a recording medium conveyed along a conveyance path,
A container-shaped light-shielding portion that has an opening that accommodates the concentration sensor therein and opens on a light projecting / receiving surface side of the concentration sensor so as to block the incidence of external light to the concentration sensor;
A guide portion provided at an end of the opening and guiding the recording medium along the conveyance path;
A detection assisting device comprising:

Images