JP5473392B2 - Image forming apparatus - Google Patents

Description

The present invention is related to an image forming apparatus for forming a developer image on the sheet.

  Conventionally, some image forming apparatuses such as copying machines and printers form images by an electrophotographic method. In such an electrophotographic image forming apparatus, a developer image formed by developing an electrostatic latent image formed on an image carrier with a developer is transferred to a sheet, and the transferred developer image is fixed. The sheet is fixed by heating and pressing with an apparatus. Here, such an electrophotographic image forming apparatus is used in various fields, and accordingly, a demand for higher image quality is increasing. Further, when used in a POD (print on demand) field where an output image is a product as a product, many attempts have been made to prevent output of a defective image.

  As one of them, an inspection device for inspecting the quality of an image (developer image) formed on a sheet is used. Previously, in the printing industry and the like, inspection (inspection) of printed matter was generally performed by human eyes, but when a person checks all of the printed matter that has been output in this way, the cost and time required for it are checked. Is very large.

  Therefore, an inspection device is used to automate these operations. As an inspection method for this inspection apparatus, for example, a method of accurately inspecting using original image data has been proposed (see Patent Document 1). In this inspection method, the inspection is performed by comparing the data stored in the scanner frame memory with the data stored in the printer frame memory one dot at a time. There is also an inspection method for inspecting the quality of an image by comparing original image data and a value obtained by reading an actual output image with a sensor in order to guarantee a product more reliably. When a defect image is found by such an inspection method, the sample to be inspected is excluded (see Patent Document 2). The contents of inspections vary widely, such as gloss unevenness, color variation and unevenness, color misregistration, image position, and information error.

JP-A-8-228250 JP 2004-20650 A

  By the way, in the case of a conventional electrophotographic image forming apparatus, after a developer image formed on an image carrier is transferred onto a sheet, the toner image is fixed on the sheet by heating and pressing with a fixing device. I try to let them. Here, as the fixing device, there is a heating roller type in which a sheet is sandwiched and heated by a heating roller maintained at a predetermined temperature and a pressure roller pressed against the heating roller. However, in such a heating roller type fixing device, if the heating roller is rotated for a long time, the pressure roller pressed against the heating roller becomes too warm and the amount of heat applied to the sheet increases. In this case, not only is the sheet wavy, but also when a halftone or solid black image is printed, gloss unevenness occurs, resulting in a defective image.

  Therefore, conventionally, in an inspection apparatus provided in an image forming apparatus for detecting uneven glossiness, unevenness in glossiness of an output image is detected by irradiating a sheet with light and detecting reflected light. However, when detecting such gloss unevenness, the gloss unevenness differs greatly depending on how the light enters when viewing an image, so when detecting gloss unevenness with a sensor using a fixed optical system, Sensitivity may be insufficient. Further, when the inspection apparatus performs detection in-line with the image forming apparatus main body, it may be difficult to capture regular reflection light due to the behavior of the sheet to be detected. In such a case, the gloss unevenness, that is, the accuracy of glossiness detection is lowered, so that the occurrence of gloss unevenness cannot be detected with high accuracy. Furthermore, when an inspection device is provided, there is a problem of cost and space. Therefore, an inspection device having a simple structure as much as possible is desired.

  Therefore, the present invention has been made in view of such a current situation, and an object thereof is to provide an image forming apparatus capable of detecting glossiness with high accuracy.

In the present invention, a developer image formed by developing an electrostatic latent image formed on an image carrier with a developer is transferred to a sheet, and the transferred developer image is heated and pressed by a fixing device. In an image forming apparatus for fixing on a sheet, at least one of a glossiness detecting unit for detecting the glossiness of the developer image fixed on the sheet, and the color, density and position of the developer image fixed on the sheet A measurement unit for measuring the crystallization of the wax contained in the developer, the temperature of the sheet being cooled when the gloss detecting unit is cooled when passing through the fixing nip of the fixing device The glossiness of the developer image is disposed at a position where the temperature can be detected before the temperature reaches, and the measurement unit is arranged so that the color, density, and position of the developer image when the sheet temperature is equal to or lower than the crystallization temperature of the wax. Can measure at least one of It is characterized in that arranged in the location.

  In the present invention, the glossiness detection unit can detect glossiness with high accuracy.

1 is a schematic diagram showing an overall configuration of a color laser printer that is an example of an image forming apparatus according to a first embodiment of the present invention. 2 is a diagram illustrating a configuration of a glossiness measuring device provided in the color laser printer. FIG. (A) is a figure which shows transition of time and glossiness immediately after fixing, (b) is a figure which shows transition of time and sheet temperature. FIG. 3 is a control block diagram of a controller that controls an image forming operation and the like of the color laser printer. The flowchart explaining the flow of the inspection control by the said controller. The figure which shows the example of the glossiness characteristic by an image data and a certain sheet | seat. (A) is a predicted gloss profile, (b) is a measured gloss profile, (c) is a difference between the predicted gloss profile and the measured gloss profile, and (d) is a diagram showing a change amount of the difference. The figure which shows the temperature characteristic of the hardness of resin. FIG. 5 is a schematic diagram illustrating an overall configuration of a color laser printer that is an example of an image forming apparatus according to a second embodiment of the present invention. The figure which shows the relationship between time and sheet | seat temperature.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

  FIG. 1 is a schematic diagram showing an overall configuration of a color laser printer which is an example of an image forming apparatus according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a color laser printer, and 1A denotes a color laser printer main body (hereinafter referred to as a printer main body). The printer main body 1A includes an image forming unit 1B that forms an image on a sheet, a feeding unit 1C that feeds the sheet, and a sheet conveying unit that conveys the sheet fed from the feeding unit 1C to the image forming unit 1B. 1D and a fixing device 40 for fixing an image formed on the sheet are provided.

  The image forming unit 1B includes an image forming station including a photosensitive drum 11 (11a to 11d) that is an image carrier that carries toner images that are developer images of four colors of yellow, magenta, cyan, and black, respectively. ing. The photosensitive drum 11 is rotated clockwise by a rotating means (not shown). Each image forming station includes a charger 21 (21a to 21d) that is arranged around the photosensitive drum in the rotation direction and uniformly charges the surface of the photosensitive drum. In addition, a scanner unit 12 (12a to 12d) that irradiates a laser beam based on image information to form an electrostatic latent image on the photosensitive drum is provided. Furthermore, a developing device 31 (31a to 31d) that visualizes a toner image by attaching toner, which is a developer of yellow, cyan, magenta, and black, to the electrostatic latent image is provided.

  Further, inside the transfer conveyance belt 32 which is an endless sheet conveyance member for conveying a sheet to be described later, transfer rollers 22 (22a to 22d) sandwiching the transfer conveyance belt 32 together with the four photosensitive drums 11 are respectively provided. It is attached. These transfer rollers 22 are connected to a transfer bias power source (not shown), and positive charges are applied to the sheet from the transfer roller 22 via the transfer conveyance belt 32. By thus applying the transfer bias, the negative color toner images on the photosensitive drum are sequentially transferred to the sheet in contact with the photosensitive drum 11 to form a multicolor image.

  The feeding unit 1C stores a plurality of sheets S, and feed cassettes 3a and 3b loaded on the bottom of the printer main body, pickup rollers 13a and 13b that send out the sheets S stored in the sheet feeding cassettes 3a and 3b, and the like. It is composed of When forming an image, the sheet S is separated and fed one by one by the pickup rollers 13a and 13b from the sheet feeding cassettes 3a and 3b, and then the sheet S is conveyed to the sheet conveying unit 1D at a predetermined timing. Is done. The sheet conveyance unit 1D includes a transfer conveyance belt 32 as a sheet carrier that is stretched over a driving roller 32a and a driven roller 32b and is disposed to face all the photosensitive drums 11. The transfer conveyance belt 32 electrostatically attracts the sheet to the outer peripheral surface facing the photosensitive drum 11 and circulates counterclockwise by the driving roller 32 a so that the sheet contacts the photosensitive drum 11. Then, the sheet is conveyed to the transfer position by the transfer conveyance belt 32 by being electrostatically attracted to the transfer conveyance belt 32 that circulates in this way, and the toner image on the photosensitive drum 11 is transferred.

  The fixing device 40 applies heat and pressure to the image transferred onto the sheet to fix the toner image. The fixing device 40 is in contact with the heating roller 41 as a heating member and the heating roller 41 to heat and press the sheet. A pressure roller 42 that is a pressure contact member that sandwiches and conveys the sheet is provided. The heating roller 41 is rotationally driven by a driving means (not shown) and is made of an aluminum alloy and is hollow, and inside, the light distribution intensity is higher at the center portion than at the end portion. A halogen heater 43 is provided. A temperature detecting element 44 is attached to the heating roller 41, and means for controlling the energization to the halogen heater 43 according to the detected temperature to keep the surface at a predetermined temperature, the heating roller 41 and the pressure roller 42. Means for controlling contact rotation are provided. The pressure roller 42 is pressed against the heating roller 41 by urging both ends of the shaft toward the heating roller 41, and is rotated by the heating roller 41. In addition, in order to form a fixing nip that gives a sufficient amount of heat to heat and fix the toner when the sheet is nipped and conveyed on the core of the pressure roller 42, silicone rubber, fluorine rubber, or the like is used. An elastic layer is formed. Reference numeral 2 denotes a controller for controlling the image forming operation and the like of the color laser printer 1.

  Next, an image forming operation of the color laser printer 1 configured as described above will be described. First, the photosensitive drum 11 of each image forming station is driven to rotate clockwise, and the scanner unit 12 is sequentially driven. By this driving, the charger 21 applies a uniform charge to the peripheral surface of the photoconductive drum 11, and the scanner unit 12 exposes the peripheral surface of the photoconductive drum 11 in accordance with an image signal to perform photoconductor drum 11 exposure. An electrostatic latent image is formed on the peripheral surface. Further, the latent image is developed by the developing unit 31 to form toner images of four colors of yellow, magenta, cyan and black on the surface of the photosensitive drum. In parallel with the toner image forming operation, the sheet S accommodated in the paper feed cassettes 3a and 3b is picked up by the pickup rollers 13a and 13b. Thereafter, the sheet S is conveyed by a pair of registration rollers (not shown) whose rotation is stopped by the conveyance rollers 23a and 23b, and skew feeding is corrected by the pair of registration rollers.

  Next, at the timing when the leading edge of the toner image on the most upstream photosensitive drum 11a (on the image carrier) is rotationally conveyed to the contact point (transfer position) with the transfer conveyance belt 32, the contact point is The registration roller pair starts to rotate so that the printing start positions of the sheets S coincide. Then, the registration roller pair rotates to be placed on the transfer conveyance belt 32 and conveyed to the transfer portion where the photosensitive drum 11 and the transfer conveyance belt 32 are in pressure contact with each other. Next, the toner image of each color on the photosensitive drum 11 is applied to the sheet conveyed to the transfer unit in this manner by the action of the transfer roller 22 that is disposed in each transfer unit and is applied with a voltage having a polarity opposite to that of the toner. The images are sequentially superimposed and transferred on the sheet. Then, the sheet S on which the full color toner image is formed by the multiple transfer of the four color toner images in this manner is separated from the transfer conveyance belt 32 and carried into the fixing device 40. Thereafter, in the fixing device 40, the toner image is fixed on the sheet S by being heated and pressed by the heating roller 41 and the pressure roller 42, and the sheet S on which the toner image is fixed is transferred to the discharge roller pair. 60 is discharged to the sheet discharge tray 6a.

  By the way, as shown in FIG. 1, a glossiness detecting device 50 which is a glossiness detecting unit for measuring glossiness is provided between the paper discharge roller pair 60 and the fixing device 40, and a toner image is formed. An inspection device 50A for inspecting the quality of the sheet is provided. That is, in this embodiment, the quality of the sheet is inspected by detecting the glossiness of the toner image formed on the sheet.

  This glossiness measuring device 50 performs measurement by a method defined in JISZ8741 and enters a light beam having a specified opening angle with respect to the output image surface and reflects it in the specular reflection direction. Glossiness is measured by measuring the luminous flux with a specified opening angle with a light receiver. In the present embodiment, as shown in FIG. 2, the glossiness measuring apparatus 50 irradiates a light beam L from the light source 51 toward the sheet S and makes it incident on the sheet S through the lens 52a at an angle θ. Thereafter, the light beam L reflected in the specular reflection direction is directed to the light receiver 53 through the lens 52b, and the glossiness is detected by the amount of the light beam L input to the light receiver 53. Note that the glossiness detection devices 50 are arranged in a line in the width direction orthogonal to the sheet conveyance direction, so that when the sheet S passes, the glossiness of the entire surface of the sheet S can be measured.

  Then, after the toner image is fixed by the fixing device 40, the sheet whose glossiness is measured by the glossiness detecting device 50 is below the sheet discharge tray 6a as shown in FIG. It is discharged to the provided escape tray 6b. That is, when it is determined as NG by the inspection operation by the glossiness detection device 50 of the inspection device 50A, the sheet S is discharged to the escape tray 6b.

  Conventionally, a factor that affects the gloss of an image is the amount of heat applied to the sheet during fixing. For example, when fixing a toner image, if a small amount of heat is applied by a fixing device, the toner is not completely melted, and in this case, the toner image has unevenness on the surface of the toner image. The light is irregularly reflected, resulting in a dull image. When a sufficient amount of heat is applied, the toner image surface melts and becomes smooth, and light is not irregularly reflected, so that a glossy image can be obtained. As described above, the glossiness of the image surface increases as the amount of heat increases, and the glossiness disappears when the amount of heat decreases. Therefore, if the sheet has a partial difference in heat amount, uneven glossiness occurs.

  Further, as a factor affecting the gloss of the image, there is a magnitude of a temperature drop of the sheet after fixing. That is, the glossiness of the image after fixing decreases as the sheet temperature decreases. Here, the toner is composed of pigment (also referred to as a color material), resin, wax, and the like. For example, when a sufficient amount of heat is applied to the toner on the sheet, the wax contained in the toner melts and covers the surface of the toner pigment and the like, and the surface becomes smoother. Shows high gloss. However, after that, when the sheet is cooled and the toner image is cooled accordingly, the melted wax is solidified. In this solidification process, the wax covers the toner pigment. It cannot be maintained completely, and as a result, some unevenness is generated on the surface.

  FIG. 3 (a) is a diagram showing the transition of time and glossiness immediately after fixing when a sufficient amount of heat is applied to the sheet and when it is not, and (b) of FIG. It is a figure which shows transition of time and the temperature of a sheet | seat when it is not so when heat amount is given enough. In FIG. 3, “A” indicates the state of the sheet when a sufficient amount of heat is applied, and “B” indicates the state of the sheet when a sufficient amount of heat is not applied. As shown in FIG. 3 (a), the sheet with a sufficient amount of heat shows a high gloss immediately after fixing as compared to a sheet with no sufficient amount of heat, but the glossiness increases with time. The width of the decrease is larger than that of a sheet that is not given sufficient heat. This is because, as shown in FIG. 3 (b), the temperature change width of the sheet in the case where the sufficient amount of heat is given is larger than that of the sheet in the case where the sufficient amount of heat is not given. .

  From FIG. 3, it can be seen that the degree of gloss is the largest immediately after fixing, and then the degree becomes weaker. Therefore, if the glossiness is detected before the wax is solidified, the glossiness can be detected with higher sensitivity than after the wax is solidified, and accordingly, uneven glossiness can be detected. That is, in order to detect uneven glossiness with high sensitivity, the glossiness detecting device 50 may be installed at a position where the sheet is at or above the temperature at which the wax solidifies. For this purpose, since the crystallization temperature of a general wax has a range of 70 ° C. to 110 ° C., the gloss detecting device 50 takes into account the actually used wax and fixing temperature, sheet conveyance speed, in-machine temperature, and the like. Need to be placed.

  Here, the color laser printer 1 uses a wax having a crystallization temperature of 70 ° C. as the wax, a fixing temperature of 160 ° C., a sheet conveyance speed of 200 mm / s, and an in-machine temperature of 50 ° C. In the present embodiment, the glossiness detecting device 50 is installed at a position 200 mm from the rear end of the fixing nip, which is a pressure contact portion between the heating roller 41 and the pressure roller 42. By installing the glossiness detection device 50 at such a position, it is possible to detect the glossiness when the sheet temperature is around 100 ° C., and to detect gloss unevenness with high sensitivity.

The following expression is an expression showing the distance S from the rear end of the fixing nip to the measurement position for measuring the glossiness of the image fixed on the sheet under general conditions. By disposing the glossiness detecting device 50 at a position satisfying such a relationship, the glossiness can be detected in a state where the sheet temperature is equal to or higher than the wax crystallization temperature.
S <4V (Tf-Tg) / 3 (Tf-Te)

  In the above equation, Tf is the fixing temperature, Te is the ambient temperature, Tg is the wax crystallization temperature contained in the developer, and V is the sheet conveyance speed.

  FIG. 4 is a control block diagram of the controller 2 that controls the image forming operation and the like of the color laser printer 1. The color laser printer 1 is controlled by a controller 2, and input image data is processed by the controller 2 and output. As illustrated in FIG. 4, the controller includes an image processing unit 60 including a color processing unit 61, an LUT 62, and a halftone processing unit 63. In addition, the image processing unit 60 includes a CPU 64 and a RAM 65, an image processing unit 60 and an engine control unit 66 connected to the CPU 64, and a laser driver 67 connected to the engine control unit 66.

  Next, inspection control by the controller 2 having such a configuration will be described with reference to a flowchart shown in FIG. First, when image data is input to the image processing unit 60, the image processing unit 60 performs image processing such as color processing on the image data so that an excellent color reproduction is obtained (S100). Thereafter, a predicted value of the glossiness of the output image is calculated from the image data and the sheet characteristics (S101). After the predicted value is calculated, the image data is subjected to tone correction by the LUT 62, then passes through the halftone processing unit 62, and is sent to the laser driver 67 by the engine control unit 66. The predicted value is stored in the RAM.

  Next, the controller 2 performs image formation (S102), and thereafter performs glossiness detection by the glossiness measuring device 50 (S103), and the engine control unit 66 compares the predicted glossiness value with the detected value. This is performed (S104). FIG. 6 is a diagram illustrating an example of image data and glossiness characteristics of a certain sheet. Here, since the detected value does not indicate the absolute value of the glossiness, the comparison is performed as a profile in a certain range as shown in FIG. In this case, the change amount of the difference between the predicted gloss profile shown in FIG. 7A and the actually measured gloss profile shown in FIG. 7B shown in FIG. A threshold is set so that inspection is performed. The sheet information and the inspection threshold can be arbitrarily set. Next, it is determined whether or not the change amount of the difference shown in (d) of FIG. 7 is less than the threshold value (S105). If it is less than the threshold value (Y in S105), it is determined that there is no gloss unevenness, and the discharge tray Paper is discharged to 6a (S106), and N described later is set to 0 (S107).

  On the other hand, if the change amount of the difference exceeds the threshold value (N in S105), it is determined that there is gloss unevenness, and the sheet determined as NG by inspection is discharged to the escape tray 6b (S110). Here, the number of times the sheet is discharged to the escape tray 6b in this way is sequentially counted by a counter (not shown). That is, when the sheet is discharged to the escape tray 6b, the count N of the counter is set to N + 1 (S111). Next, it is determined whether the count N of this counter exceeds 3 (S112). That is, it is determined whether NG determination has occurred an arbitrary number of times, or four times in the present embodiment. If the count N does not exceed 3 (N in S112), a recovery operation is performed by the engine control unit (S113). As a result, image formation is performed again using the image data output to the sheet discharged to the escape tray 6b.

  On the other hand, when the NG determination occurs four times, that is, when the count N exceeds 3 (Y in S112), the engine control unit In response to the instruction, image formation is interrupted. Thereafter, fixing temperature control for reducing the temperature of the heating roller 41 is performed (S114). Specifically, the energization to the heater is stopped and the fixing device is rotated. Then, by such fixing temperature control, the temperature of the heating roller 41 is lowered by the lower set temperature, and when this is detected by the temperature detection element 44, the heater is turned on again and the rotation of the fixing device is stopped. Thereafter, a Ready signal is transmitted when the Ready temperature is reached. When the Ready signal is transmitted in this way, the controller 2 resumes energization of the heater, sets the count N of the counter to 0 (S115), and performs a recovery operation by the engine control unit (S113).

  In this way, space can be saved by disposing the glossiness detection device 50 at a position where the glossiness of the toner image can be detected when the sheet temperature is equal to or higher than the temperature at which the surface of the toner image is uneven. At the same time, it is possible to detect glossiness with high accuracy. In addition, the fixing temperature of the fixing device can be automatically adjusted.

  In the above description, the temperature for determining the detection position of the glossiness detecting device 50 is set based on the crystallization temperature of the wax. However, the present invention is not limited to this, and the temperature of the resin contained in the developer is not limited. You may set based on softening point temperature.

  FIG. 8 is a diagram showing the relationship between the temperature and hardness of the resin contained in the developer. Generally used resins have a softening point in the vicinity of 90 ° C. to 100 ° C., and soften at higher temperatures. As in the case of the wax described above, the resin maintains a high degree of smoothness in a soft state at a high temperature. However, the resin hardens when the temperature is lower than the softening point, and unevenness tends to appear on the image surface. In the embodiment, the softening point is 90 ° C., and the glossiness detection device is placed at a position 150 mm from the center of the fixing nip, so that the glossiness can be detected when the sheet temperature is around 110 ° C. High sensitivity detection has become possible.

Also in this case, under general conditions, the distance S from the rear end of the fixing nip to the measurement position for measuring the glossiness of the image fixed on the sheet is expressed by the following equation. Further, by arranging the glossiness detecting device 50 at a position satisfying such a relationship, the glossiness can be detected in a state where the sheet temperature is equal to or higher than the softening point temperature of the resin.
S <4V (Tf-Tm) / 3 (Tf-Te)

  In the above equation, Tf is the fixing temperature, Te is the ambient temperature, Tm is the softening point temperature of the resin contained in the developer, and V is the sheet conveyance speed.

  By the way, in the description so far, the installation position of the glossiness detection device 50 that detects the gloss unevenness of the inspection device 50A has been described, but the inspection device 50A is a measurement that measures the color, density, and position of the output image. Some have parts. As an image forming apparatus, there is an image forming apparatus provided with an inspection apparatus 50A including both a glossiness detection apparatus 50 and a measurement unit.

  Next, a second embodiment of the present invention in which the image forming apparatus is provided with the inspection device 50A including both the glossiness detection device 50 and the measurement unit will be described. FIG. 9 is a schematic diagram showing an overall configuration of a color laser printer which is an example of the image forming apparatus according to the present embodiment. In FIG. 9, the same reference numerals as those in FIG. 1 described above indicate the same or corresponding parts. In FIG. 9, 8 is an image sensor which is provided in the inspection apparatus 50A and is a measurement unit that measures at least one of the color, density, and position of an output image (developer image). The sensor 8 is a linear CIS parallel to the glossiness sensor. Here, as described above, the glossiness measuring device 50 is installed at a position where the sheet is equal to or higher than the temperature at which the wax solidifies. However, the color, density, and position of the output image (developer image) measured by the image sensor 8 are influenced by temperature, unlike the gloss unevenness detected by the gloss measurement device 50.

  That is, it is known that the color and density of the output image change with the temperature of the sheet, and it is preferable that the color and temperature match the absolute target. It is better after the temperature has settled down. Moreover, the temperature which does not expand / contract even if it sees a position is good. In addition, about the defect by the nonuniformity of temperature, the glossiness measuring apparatus 50 can detect as mentioned above. For this reason, in the present embodiment, the image sensor 8 is not more than the crystallization temperature of the wax, which is not affected by temperature, so that at least one of the color, density, and position of the developer image can be accurately measured. It is installed in the position that becomes. That is, the image sensor 8 is disposed at a position where the image sensor 8 can be measured when the sheet temperature becomes equal to or lower than the crystallization temperature of the wax. Specifically, the measurement position by the image sensor 8 is set to a position separated from the rear end of the fixing nip by the distance from the rear end of the fixing nip to the gloss detection position of the gloss detecting device 50.

  In the present embodiment, as shown in FIG. 9, a cooling fan 7 is disposed as a sheet cooling device in the conveyance path between the glossiness detection device 50 and the image sensor 8. By arranging the cooling fan 7 in this manner, the sheet to which the glossiness detecting device 50 is added at a high temperature is rapidly cooled as shown in FIG. 10, which shows the relationship between time and sheet temperature. . Thereby, the detection by the image sensor 8 can be performed when the temperature becomes lower than the crystallization temperature of the wax.

  As described above, since the measurement by the image sensor 8 can be performed without waiting for a decrease in the sheet temperature by using the cooling device 7, at least one of the color, density, and position of the developer image is accurately measured. It is possible to reduce the size and the measurement time. Heretofore, the temperature for determining the position of the image sensor 8 has been set based on the crystallization temperature of the wax. However, the present invention is not limited to this, and development is performed as in the first embodiment described above. You may set based on the softening point temperature of resin contained in an agent. That is, the detection by the image sensor 8 can be performed when the temperature becomes lower than the softening point temperature of the resin. In the above description, the inspection apparatus 50A according to the present invention is provided in a color laser printer which is an example of an image forming apparatus. However, various types of electrophotographic copying machines, printers, and monocolor type image forming are described. Needless to say, it can also be applied to devices. Needless to say, the inspection apparatus 50A according to the present invention can be applied to various types of inspections, automatic correction, and recovery operations.

DESCRIPTION OF SYMBOLS 1 ... Color laser printer, 1A ... Color laser printer main body, 1B ... Image formation part, 1C ... Feeding part, 2 ... Controller, 8 ... Image sensor, 40 ... Fixing device, 41 ... Heating roller, 42 ... Pressure roller, 50 ... Glossiness detection device, 50A ... Inspection device, S ... Sheet

Claims (8)

The developer image formed by developing the electrostatic latent image formed on the image carrier with a developer is transferred to a sheet, and the transferred developer image is heated and pressed by a fixing device to be fixed on the sheet. In the image forming apparatus,
A glossiness detecting unit for detecting the glossiness of the developer image fixed on the sheet ;
A measurement unit that measures at least one of the color, density, and position of the developer image fixed on the sheet ,
When the heated sheet is cooled when passing through the fixing nip of the fixing device and the temperature of the sheet reaches the crystallization temperature of the wax contained in the developer, Arranged in a position where the glossiness can be detected , and the measuring unit is arranged in a position where at least one of the color, density and position of the developer image can be measured when the temperature of the sheet is equal to or lower than the crystallization temperature of the wax. An image forming apparatus. The fixing device includes a heating member, and a pressure contact member that presses the heating member to form the fixing nip,
The distance S from the rear end of the fixing nip to the position where the glossiness of the developer image is detected, the fixing temperature is Tf, the ambient temperature is Te, and the wax crystallization temperature contained in the developer Is Tg and the sheet conveyance speed is V.
S <4V (Tf−Tg) / 3 (Tf−Te)
The image forming apparatus according to claim 1, wherein: Claim 2, wherein said measurement positions by the measuring unit, from said rear end of the fixing nip the above distance to the position of detecting the glossiness of the toner image, is set to away from the fixing nip the rear end position The image forming apparatus described. Between the measuring unit and the glossiness detecting unit, an image forming apparatus according to claim 2 or 3, characterized in placing a cooling device for cooling the sheet. The developer image formed by developing the electrostatic latent image formed on the image carrier with a developer is transferred to a sheet, and the transferred developer image is heated and pressed by a fixing device to be fixed on the sheet. In the image forming apparatus,
A glossiness detecting unit for detecting the glossiness of the developer image fixed on the sheet ;
A measurement unit that measures at least one of the color, density, and position of the developer image fixed on the sheet ,
When the heated sheet is cooled when passing through the fixing nip of the fixing device and the temperature of the sheet reaches the softening point temperature of the resin contained in the developer, Arranged at a position where glossiness can be detected , and the measurement unit is arranged at a position where at least one of the color, density and position of the developer image can be measured when the temperature of the sheet falls below the softening point temperature of the resin. An image forming apparatus. The fixing device includes a heating member, and a pressure contact member that presses the heating member to form the fixing nip,
A distance S from the rear end of the fixing nip to a position where the glossiness of the developer image is detected by the glossiness detection unit, a fixing temperature Tf, an ambient temperature Te, and a softening point of the resin contained in the developer When the temperature is Tm and the sheet conveyance speed is V,
S <4V (Tf-Tm) / 3 (Tf-Te )
The image forming apparatus according to claim 5, characterized in that a. Claim 6, characterized in that said measurement positions by the measuring unit, from said rear end of the fixing nip the above distance to the position of detecting the glossiness of the toner image, is set to away from the fixing nip the rear end position The image forming apparatus described. The image forming apparatus according to claim 6 or 7, characterized in placing a cooling apparatus for cooling the sheet between the measuring unit and the gloss detector.

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