JP2010072210A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain color reproducibility on a fixed image in an excellent state by controlling a fixing condition by using surface diffused light, thereby attaining a desired color reproduction. <P>SOLUTION: An image forming apparatus has an image forming part 100 which forms a toner image and transfers it to recording material, and a fixing device 30 which fixes the toner image transferred to the recording material by the image forming part 100, and includes a fixed image characteristic acquisition part 150 which obtains the surface diffused light from a surface of the toner image on the recording material, which has been fixed by the fixing device 30, and a fixing controller 110 which controls the fixing condition of the fixing device 30 based on the acquired surface diffused light. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a color copying machine, a color printer, and a color facsimile apparatus using an electrophotographic system.

  In recent years, color image forming apparatuses such as color printers and color copiers are required to improve the output image quality. In an electrophotographic image forming apparatus configured as a printer, a copier, a facsimile, or a complex machine thereof, an electrostatic latent image is written by irradiating light onto a photosensitive drum charged by a charging device. By supplying toner to the photosensitive drum by a developing device, the electrostatic latent image is developed as a toner image (forming a toner image), and the toner image is directly on a predetermined recording material such as recording paper or in the middle An image forming process is performed in which the image is indirectly transferred via an intermediate recording material such as a transfer belt and finally heated and fixed by a heating roller or the like provided in the fixing device.

  In such an image forming apparatus, due to a change in the environment in which the apparatus is placed and deterioration of the photosensitive drum and developer over time, the amount of toner adhered and the fixability of the toner image vary, and the image is formed on the recording paper. The color reproducibility typified by density and glossiness fluctuates. Therefore, a method of monitoring the image density and glossiness and feeding back the results and controlling the density and glossiness is widely used so that the desired density and glossiness can be obtained even if fluctuations occur in each part of the apparatus. Yes. The following techniques are disclosed as conventional examples related to these.

  The density of the control patch image to be output before and after fixing is measured, and the glossiness of the image after fixing is measured, and the density control value (image forming condition) is determined from the density measurement result. An apparatus that controls gloss control values (fixing conditions) based on the measurement result of glossiness is disclosed (for example, see Patent Document 1). It is also described that this apparatus transports again using a duplex printing mechanism.

  Similarly, there is disclosed an apparatus for determining the density and glossiness by measuring the density of the control patch before and after fixing the toner image, and controlling the image forming conditions and the fixing conditions based on them (for example, Patent Document 2). In particular, this cited document 2 is provided with a gloss processing device that further performs a fixing process after the normal fixing device to increase the glossiness.

  Here, the image forming conditions include, for example, the setting value of the developing bias potential, the setting value of the charging potential of the image carrier, the exposure intensity for the image carrier (exposure intensity for electrostatic latent image writing and static elimination) 1 of the setting value of the ratio of the peripheral speed of the rotating image carrier and the peripheral speed of the developing roller rotating in opposition thereto (so-called peripheral speed ratio) or There are a plurality of them, which mainly relate to the control of the toner adhesion amount. The fixing conditions include, for example, one including one or more of a fixing temperature, a nip pressure, and a recording material conveyance speed, and mainly relates to fixing property control.

JP 2006-171104 A JP 2006-267165 A

  However, as described above, the conventional technique for controlling the fixing conditions using the glossiness and density as target values has a problem that desired color reproduction cannot be performed for the reasons described below.

  First, it will be described that the color reproducibility depends not only on the toner adhesion amount but also on the fixing property. When the image is irradiated with light in a normal colorimetry system and the reflected light is measured, the measured reflected light includes surface diffused light reflected from the image surface and reflected light from the toner layer. It is out. When this surface diffused light increases, the light reflected without touching the color material inside the toner layer increases, and the reproducible color space becomes smaller (the color becomes dull). As an example, FIG. 14 is a graph showing the relationship between surface diffused light and saturation. FIG. 14 shows how the saturation decreases as the surface diffused light increases. Thus, it can be seen that the color reproducibility depends on the surface diffused light. Since the surface diffused light depends on the surface state of the image, that is, the fixability, it can be seen that the color reproducibility depends on the fixability.

  Here, the principle of measurement of surface diffused light will be described with reference to FIG. FIG. 15A shows how the reflectance of a toner image is measured by a measurement system of 0/45 ° (0 ° incidence, 45 ° light reception), which is a normal color measurement system. At this time, the reflected light 201 to be measured includes reflected light (surface diffused light) 201a from the surface and reflected light (internally reflected light) 201b from the inside of the toner layer. On the other hand, FIG. 15B shows a state in which a transparent film having a mirror surface is optically adhered to the surface of the toner image of the above (A) and is measured by the same optical system as in the above (A). Is. Here, the A layer and the B layer are in optical contact refers to a state in which there is no air layer between them and the interface between them is optically continuous. At this time, the reflected light 202a on the surface in (B) is specularly reflected because the surface is in a mirror state as described above, and is reflected in the 0 ° direction. Further, as described above, the toner layer 212 and the transparent film 213 are in optical contact, and no air layer or the like exists between them. Further, it is preferable that the refractive indexes are equal to prevent reflected light from being generated at the interface between the toner layer 212 and the transparent film 213. Therefore, at this time, the reflected light 202 received is only the internally reflected light 202b. Since the internally reflected light 201b and 202b are equal, by subtracting 202 from the measured value 201, the internally reflected light is canceled and the surface diffused light 201a can be obtained. The surface diffused light thus obtained can be directly incorporated into the color evaluation because the color colorimetry system and the measurement system are equal as described above.

  As described above, it is desirable that the fixing conditions of the fixing device can be controlled so that the desired color reproduction can be maintained when the fixing property changes due to deterioration of the device over time or the like. However, as described above, the conventional technique of measuring glossiness and density and controlling the fixing conditions cannot achieve desired color reproduction.

  First, since the glossiness differs in color and measurement system, the color cannot be directly evaluated from the glossiness. FIG. 16 shows an optical system for measuring glossiness and color. FIG. 16A shows a glossiness measurement system, and FIG. 16B shows a color measurement system. As shown in FIG. 16A, the gloss level measures specularly reflected light, while the color measures diffused light as shown in FIG. 16B. Accordingly, the glossiness is not directly related to the color and cannot be used for the evaluation of the color (note that FIG. 16B shows a 0/45 ° system (0 ° incidence, 45 ° light reception). The measurement system also includes 0 / d (measurement using an integrating sphere), etc. In any case, the color measurement system measures diffused light).

  Further, the glossiness has no one-to-one correlation because the measurement system is different from the surface diffused light using the same measurement system as the color. FIG. 17 is a graph showing the relationship between glossiness and surface diffused light. As described above, the gloss level is for measuring specular reflection light, and is related to the unevenness of the surface, but as shown in FIG. 17, the surface diffused light is not uniquely determined for a certain gloss level, and has a certain width. Have. Therefore, the surface diffused light cannot be controlled from the gloss level. As described above, the target color can be reproduced by controlling the surface diffused light. However, as described above, the surface diffused light cannot be controlled from the gloss level. Can not.

Next, in the case where the density is used for controlling the fixing condition, the density is calculated from only the average value of the spectral reflectance or the value of the absorption band. Therefore, the L ^* a ^* b ^* color space representing the color from the density. The value of cannot be determined uniquely. In other words, even if the density is controlled to a desired value, the L ^* a ^* b ^* value of the reproduced color may be deviated and cannot be controlled to the target color. Even if the spectral reflectance (spectral density) is measured and used for control, the spectral reflectance is a value including both internally reflected light and surface diffused light, that is, fluctuation of toner adhesion amount and fixing. It includes both sex changes. Therefore, when the density changes, it cannot be determined whether the toner adhesion amount changes or the fixing property changes, and it is impossible to control the fixing property properly.

  The present invention has been made in view of the above. By controlling the fixing conditions using surface diffused light, the desired color reproduction can be achieved and the color reproduction in the image after fixing can be performed in a good state. The purpose is to obtain.

  In order to solve the above-described problems and achieve the object, the invention according to claim 1 is an image forming unit that forms a toner image and transfers it to a recording material, and a toner that is transferred to the recording material by the image forming unit. An image forming apparatus comprising: a fixing unit that fixes an image; and a surface diffused light acquiring unit that acquires surface diffused light from a toner image surface on the recording material fixed by the fixing unit; And a fixing control means for controlling the fixing conditions of the fixing means based on the surface diffused light.

  According to a second aspect of the present invention, in the first aspect, the surface diffused light obtaining unit includes a measuring unit that measures the reflection characteristic 1 of the toner image fixed by the fixing unit, and the surface of the toner image is a mirror surface. A specular reflection characteristic acquisition unit that acquires a reflection characteristic 2 measured under the same optical conditions as the reflection characteristic 1 in a state; and a calculation unit that calculates surface diffused light using the reflection characteristic 1 and the reflection characteristic 2; It is characterized by providing.

  According to a third aspect of the present invention, in the second aspect, the reflection characteristic 1 and the reflection characteristic 2 are reflectances, and the calculation unit is configured to reflect the reflection characteristic 1 and the specular reflection characteristic obtained by the measurement unit. The difference between the reflection characteristics 2 obtained by the acquisition means is taken and the surface diffused light is calculated.

  According to a fourth aspect of the present invention, in the second aspect, the reflection characteristic 1 and the reflection characteristic 2 are density values, and the calculation means converts each density value into a reflectance, and then calculates a difference between the two. The surface diffused light is calculated by taking

  According to a fifth aspect of the present invention, in the second aspect, the optical condition of the measuring means is the same optical condition as that for evaluating the color.

  According to a sixth aspect of the present invention, in the second aspect, the specular reflection characteristic acquisition unit includes a storage unit that holds the reflection characteristic 2 of the specular state measured in advance.

  An image forming apparatus according to the present invention acquires surface diffused light from the surface of a toner image on a recording material fixed by a fixing unit, and controls fixing conditions of the fixing unit based on the acquired surface diffused light. Thus, it is possible to achieve desired color reproduction and to obtain an image after fixing with good color reproduction.

  Exemplary embodiments of an image forming apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings. In addition, the following embodiment is an example and is not limited to this.

(First embodiment)
≪Example using spectral reflectance≫
In this embodiment, an example in which spectral reflectance is used for reflection characteristics 1 and 2 used for calculation of surface diffused light will be described.

  FIG. 1 is a block diagram showing a main system configuration of the color image forming apparatus according to the first embodiment. In FIG. 1, reference numeral 100 denotes an image having a sheet feeding unit 101, a writing optical system 24, an image forming unit 103 for forming a toner image on a photosensitive drum by a process step according to an electrophotographic process, and transferring the toner image to a recording material. A forming unit, 110 is a fixing control unit having a driver 111 for energizing the heater so as to reach a predetermined fixing temperature, a storage unit 112 for storing fixing conditions, etc., and 120 controls the entire image forming apparatus. Main control unit, 130 is an image processing unit that executes various image processing, 140 is an operation display unit that has a function of displaying various input settings, device statuses, and the like, and 150 stores data described later. A memory 151, a post-fixing image characteristic acquisition unit having a calculation unit 152 for calculating surface diffused light, and a reference numeral 30 includes a fixing roller 31, a pressure roller 32, and the like. A fixing device, reference numeral 41 will be described later spectrocolorimeter, reference numeral 33 is a heater, reference numeral 35a, b is a thermistor for detecting the fixing temperature.

  FIG. 2 is an explanatory diagram showing the overall configuration of the color image forming apparatus according to the first embodiment, and shows the configuration of the image forming unit in FIG. 1 in detail. As shown in the figure, this apparatus is a tandem color image forming apparatus that employs an intermediate transfer member 27 that is an example of an electrophotographic color image forming apparatus. In addition to this embodiment, other configurations such as a revolver type color image forming apparatus may be used.

  This color image forming apparatus includes a paper feeding unit 21, photoconductors (22Y, 22M, 22C, 22K) for each station arranged in parallel for development colors, injection charging means (23Y, 23M, 23C, 23K) as primary charging means, A toner cartridge (25Y, 25M, 25C, 25K), a developing unit (26Y, 26M, 26C, 26K), an intermediate transfer member 27, a transfer roller 28, a cleaning unit 29, a fixing device 30, a spectral colorimeter 41, and the like are provided.

  Next, the operation of the color image forming apparatus shown in FIGS. This operation is comprehensively controlled by the main control unit 120. The image forming unit 100 forms an electrostatic latent image by irradiating the charged photosensitive drum with exposure light by the writing optical system 24 based on the exposure time converted by the image processing unit 130. Is developed to form a single color toner image, the single color toner images are superimposed to form a multicolor toner image, the multicolor toner image is transferred to the recording material 11, and the multicolor toner image on the recording material 11 is transferred. Is fixed by the action of heat and pressure.

  In FIG. 2, photosensitive drums 22Y, 22M, 22C, and 22K are configured by applying an organic photoconductive layer to the outer periphery of an aluminum cylinder, and rotate by receiving a driving force of a driving motor (not shown). Rotates the photoconductive drums 22Y, 22M, 22C, and 22K in the counterclockwise direction according to the image forming operation.

  As primary charging means, four chargers 23Y, 23M, 23C, and 23K for charging the photosensitive drums of yellow (Y), magenta (M), cyan (C), and black (K) are provided for each station. In configuration, each charger is provided with a sleeve 23YS, 23MS, 23CS, 23KS.

  Exposure light to the photosensitive drums 22Y, 22M, 22C, and 22K is sent from the writing optical systems 24Y, 24M, 24C, and 24K, and selectively exposes the surfaces of the photosensitive drums 22Y, 22M, 22C, and 22K. The electrostatic latent image is formed.

  As developing means, in order to visualize the electrostatic latent image, four developing units 26Y, 26M for developing yellow (Y), magenta (M), cyan (C), and black (K) for each station, Each developing device is provided with sleeves 26YS, 26MS, 26CS, and 26KS. Each developing device is detachably attached.

  The intermediate transfer member 27 is in contact with the photosensitive drums 22Y, 22M, 22C, and 22K, and rotates in the clockwise direction when forming a color image, and rotates with the rotation of the photosensitive drums 22Y, 22M, 22C, and 22K. A single color toner image is transferred. Thereafter, a transfer roller 28 (to be described later) comes into contact with the intermediate transfer member 27 to sandwich and convey the recording material 11, and the multicolor toner image on the intermediate transfer member 27 is transferred to the recording material 11.

  The transfer roller 28 contacts the recording material 11 at a position 28a while transferring a multicolor toner image onto the recording material 11, and is separated to a position 28b after the printing process.

  Next, the fixing device 30 in the color image forming apparatus will be described. The fixing device 30 melts and fixes the transferred multi-color toner image while conveying the recording material 11. As shown in FIGS. 1 and 2, the fixing device 30 includes a fixing roller 31 that heats the recording material 11 and the recording material 11. A pressure roller 32 for press-contacting the fixing roller 31 and thermistors (thermometers) 35a and 35b are arranged on the surfaces of these rollers in a state where they are in contact with each other with a slight pressure. The fixing roller 31 and the pressure roller 32 are formed in a hollow shape, and heaters 33 and 34 are incorporated therein, respectively. That is, the recording material 11 holding the multicolor toner image is conveyed by the fixing roller and the pressure roller, and heat and pressure are applied to fix the toner on the surface. Further, the fixing temperature at that time is successively monitored by the thermistor 35. Although two thermistors are illustrated, a plurality of thermistors may be arranged for reasons such as device configuration and accuracy improvement, and this temperature value is fed back to the fixing control unit 110.

  The recording material 11 after the toner image has been fixed is discharged to a discharge tray (not shown) by a discharge roller (not shown), and the image forming operation is completed. The cleaning unit 29 cleans the toner remaining on the intermediate transfer member 27. Waste toner after the four color toner images formed on the intermediate transfer member 27 are transferred to the recording material 11 is removed from the cleaner container. Stored in

  Next, an outline of the control operation of the fixing conditions in the image forming apparatus of this embodiment will be described with reference to FIG. The image forming apparatus according to this embodiment includes an image processing unit 130 including an image forming condition, a fixing condition, a memory for storing patch images, an IC 1 for performing image processing, and a fixing control unit 110 for controlling fixing. It is out. As described above, the toner image is transferred to and fixed on the recording material. In this case, a patch image (see FIG. 4) is formed on the recording material, transferred and fixed, and the reflection characteristics of the patch image after fixing. Is measured by the spectrocolorimeter 41, and the measured value is input to the post-fixing image characteristic acquisition unit 150 to calculate surface diffused light. Subsequently, the fixing control unit 110 determines fixing conditions according to information from the post-fixing image characteristic acquisition unit 150.

  The post-fixing image characteristic acquisition unit 150 inputs the measurement value from the spectrocolorimeter 41 that measures the spectral reflectance 1 for the image fixed on the recording material, and stores the specular state of the memory 151 that is measured in advance. The surface diffused light is calculated from the spectral reflectances 1 and 2 by the calculation unit 112 with reference to the spectral reflectance 2 of FIG.

  The spectrocolorimeter 41 is disposed toward the image forming surface of the recording material 11 downstream of the fixing device 30 in the recording material conveyance path, and has a spectral reflectance of 1 with respect to the image after fixing formed on the recording material 11. Is detected. By disposing the spectrocolorimeter 41 inside the color image forming apparatus, it is possible to automatically detect the fixed image before discharging it to the paper discharge unit.

  FIG. 3 shows an example of the configuration of the spectrocolorimeter 41. The spectrocolorimeter 41 processes a light source 51 such as a halogen lamp, a lens 52 for shaping a collimator lens, a spectroscopic element 54 such as a slit 53, a concave diffraction grating, a light receiving element 55 such as a C-MOS sensor, and light reception data. It is comprised by IC etc. which are not illustrated.

  The light source 51 and the lens 52 are arranged on a straight line perpendicular to the surface of the recording material 11 and irradiate the recording material 11 perpendicularly. The slit 53 and the spectroscopic element 54 are arranged in a direction of 45 ° with respect to the direction perpendicular to the recording material surface. Of the reflected light from the measurement object, the light reflected in the 45 ° direction passes through the slit 53 and then is split. The light is dispersed by the element 54 and received by the light receiving element 55. In this embodiment, 0/45 ° is used, but an integrating sphere such as 0 / d (SCE) may be used as described above.

  As described above, the spectral reflectance 1 is measured by the spectrocolorimeter 41 with respect to the toner image fixed on the recording material 11 and sent to the calculation unit 152. On the other hand, the spectroscopic reflectance 2 and the like stored in advance are read from the memory 151 and sent to the calculation unit 152 in the same manner. The calculation unit 152 calculates the surface diffused light by taking the difference between the transmitted spectral reflectances 1 and 2. Then, the calculation result is sent to the fixing control unit 110. The fixing control unit 110 controls fixing conditions based on the sent data.

  Next, a series of control operations under the fixing conditions described above will be described with reference to the flowchart shown in FIG. In this operation, a patch image is formed on a recording material, and the fixing condition is controlled using the image after fixing. The operation is controlled by the main control unit 120 and the fixing control unit 110. First, an outline of this flowchart will be described. The patch image is transferred onto a predetermined recording material (step S1) and fixed (step S2). Subsequently, the reflection characteristic 1 is measured for the fixed patch image (step S3), the reflection characteristic in the mirror state is read from the memory 151 (step S4), and the surface diffused light is calculated (step S5). Subsequently, it is determined whether or not the calculated surface diffused light is not more than an upper limit value (step S6). Here, when it is determined that the surface diffused light is equal to or less than the upper limit value, a series of the present processing ends. On the other hand, if it is determined that the surface diffused light is not less than the upper limit value, it is further determined whether there is room for control of the fixing conditions (step S7). If there is room for control of the fixing conditions, the fixing conditions are controlled. (Step S8), the process returns to Step S1, and the above operation is repeatedly executed.

  As described above, the operation for controlling the fixing condition based on the acquired surface diffused light is started upon receiving a request for controlling the fixing condition from the user, or the fixing condition control is automatically performed when a predetermined number of sheets are printed. You may start. Further, the fixing condition control may be started at the time of fixing adjustment at the time of shipment from the factory, at the time of maintenance and inspection by a service person (particularly when the fixing device and the roller are replaced), and the like. Further, the control (setting) of the fixing condition may be performed by an instruction from the operation display unit 140 or a special operation by a service person having a specific technique.

  In step S <b> 1, control patch data is sent from the storage unit 112 to the image processing unit 130, a patch is formed on the recording material 11, and the toner is heated and fixed by the fixing device 30. Here, the fixing conditions used for heat fixing are the latest fixing conditions stored in the storage unit 112. Further, it is assumed that the recording material 11 used for patch image output is a predetermined recording material described later.

  FIG. 4 is an example of a patch image that is heat-fixed on the recording material 11. In FIG. 4, patches each having a C, M, Y, and K monochrome area ratio of 100% are arranged in a line in the conveyance direction of the recording material. The reason why only a patch with an area ratio of 100% is used is that a patch with an area ratio of 100% is most suitable for confirming a change in fixability. Of course, instead of a single color, a patch having a secondary color area ratio of 100% such as R, G, and B may be used. The reason why the fixing members 30 are arranged in a line in the recording material conveyance direction is that the fixing device 30 has a fixing unevenness in a direction (main scanning direction) perpendicular to the recording material conveyance direction.

  Steps S3 to S6 for acquiring the surface diffused light in FIG. 7 will be further described. In step S <b> 3, the spectral reflectance 1 is measured by the spectrocolorimeter 41 for each color patch heat-fixed on the recording material 11. In step S4, data such as the spectral reflectance 2 in the mirror surface state is read from the memory 151. In step S5, the surface diffused light is calculated by calculating the difference between the spectral reflectances 1 and 2 in the calculation unit 152. In step S <b> 6, the surface diffused light calculated by the calculation unit 152 is compared with the upper limit value (allowable range) of the surface diffused light held in the memory 151.

  FIG. 5 shows an example of a data table read from the memory 151 in step S4 of FIG. The data table of FIG. 5 includes the recording material used at the time of measurement, the spectral reflectance of the specular state of each color of C, M, Y, and K and the upper limit value of the surface diffused light of each color. Here, the recording material on which the patch image is formed needs to be the same as the recording material used for the measurement of the data stored in the memory 151. If this data table is held only for a single recording material, the recording material may not be stored, but for the purpose of announcing the recording material for fixing condition control to the user, the data table is used here. Added. In addition, when there is only data on a single recording material, it is not preferable because the user is forced to use (hold) the recording material only for the purpose of controlling fixing conditions. Therefore, the data table of FIG. 5 may be stored for a plurality of recording materials so that the user can select the recording material used for fixing condition control. In that case, a data table corresponding to the recording material selected by the user may be read from the memory 151.

  In step S5 in FIG. 7, surface diffused light is calculated using the spectral reflectance 1 measured in step S3 and the specular reflectance 2 read from the memory 151 in step S4. The principle is as described with reference to FIG. 15. Specifically, surface diffused light is obtained by subtracting the spectral reflectance 2 from the spectral reflectance 1. However, although the calculated surface diffused light is spectral data at this time, a single value is more convenient in consideration of comparison with the upper limit value. Therefore, for example, a method of taking the value of the surface diffused light at the wavelength having the smallest spectral reflectance or a method of taking the average value of the surface diffused light in the absorption band can be considered. In any case, it is desirable to use the absorption band because the surface diffusion light has higher sensitivity in the absorption band. Of course, the calculation method of the surface diffused light used here (the process of obtaining a single value from the spectroscopic data) needs to use the same method as that used when the upper limit value of the surface diffused light stored in the memory 151 is calculated. . The above operation is performed for each color of the patch image.

  In step S6 in FIG. 7, the surface diffused light calculated in step S5 is compared with the upper limit value of the surface diffused light read from the memory 151 in step S4 for each color. And when surface diffused light exceeds an upper limit, it progresses to Steps S7-S8. Steps S5 and S6 are executed by the calculation unit 152. When the process proceeds to steps S7 to S8, data is sent from the calculation unit 152 to the fixing control unit 110, and the fixing control unit 110 performs step S7. ~ S8 are executed. As data transmitted at this time, a value of surface diffused light, a difference value from an upper limit value, or the like can be considered.

  In steps S7 and S8 in FIG. 7, the fixing conditions are controlled based on the data sent from the calculation unit 152. In step S7, it is determined whether there is room for control in the fixing conditions (usually, it is determined that there is room in the first cycle). If it is determined that there is room, fixing conditions are controlled in step S8. Then, the fixing condition is updated, and based on the updated fixing condition, the process returns to step S1 to output the patch image again.

  Here, the fixing control unit 110 that executes steps S7 and S8 includes a storage unit 112 that stores data necessary for controlling the fixing conditions.

  Hereinafter, specific examples of the fixing condition control in steps S7 and S8 will be described. The control of the fixing conditions referred to here is aimed at reducing the surface diffused light. Here, examples of the fixing condition to be controlled include a fixing temperature and a recording material conveyance speed. Here, the conveyance speed is constant, and the fixing temperature, which is the surface temperature of the fixing roller 31 and the pressure roller 32 detected by the thermistors 35a and 35b, is the control target. FIG. 6 shows how the surface diffused light changes with respect to the fixing temperature. As shown in FIG. 6, the surface diffused light has a downwardly convex curve with respect to the fixing temperature. In the region where the fixing temperature is low, the toner is not sufficiently melted and many irregularities remain on the surface, so that the surface diffused light becomes large. As the fixing temperature is raised, the toner is sufficiently melted, surface irregularities are reduced, and surface diffused light is reduced. However, when the temperature is raised above a certain level, this time, hot offset begins to occur, peeling occurs on the toner surface, and unevenness is generated, resulting in an increase in surface diffused light. Therefore, in order to reduce the surface diffused light, the fixing temperature may be controlled so as to approach the minimum point of the curve in FIG.

  Here, the intention of determining the room for fixing condition control in step S7 in FIG. 7 will be described. Even if the surface diffused light is increased as much as possible by the control method described later (the minimum value in FIG. 6 has been reached) due to a change in fixing property due to deterioration of the components constituting the fixing device with the passage of time or the like. However, there may be a case where the value exceeds the upper limit value stored in the memory 151 described above. Step S7 considers such a case. Even if the surface diffused light exceeds the upper limit value in step S6, if it is determined in step S7 that the surface diffused light has reached the minimum value, the fixing condition is controlled. End.

  As described above, the control of the fixing condition referred to here is to control the fixing parameter (fixing temperature) so as to approach the minimum point in FIG. Here, since the fixing roller or the like deteriorates with time, even if the fixing temperature is the same, the magnitude of the surface diffused light is not always the same. Also, the fixing temperature cannot always be measured in the same way, and the measured value varies from time to time. Accordingly, the curves in FIG. 6 are only relative and fluctuate from time to time. That is, controlling the fixing temperature means bringing the temperature close to the temperature corresponding to the minimum point in FIG. Therefore, it is meaningless to store the temperature of the minimum point in FIG. 6 in advance and control the fixing temperature using the temperature as a target value, and from the size of the surface diffused light to the minimum point of the curve in FIG. The current position needs to be determined and controlled.

  Hereinafter, an example of the fixing temperature control method will be described. First, considering that the rough characteristics of the curve in FIG. 6 (sensitivity to changes in fixing temperature, etc.) do not change, a predetermined temperature ΔT to be changed during fixing temperature control is stored in advance in the storage unit 112 of the fixing control unit 110. deep. Then, a patch image is output under the latest fixing conditions (fixing temperature) once stored in the storage unit 112, and the surface diffused light is measured. At this time, the measured surface diffused light value is stored in the storage unit 112 of the fixing control unit 110. If the calculation unit 152 determines that fixing condition control is necessary, the fixing temperature is changed by ΔT, a patch image is output again, and the surface diffused light is measured. Then, the fixing control unit 110 compares the measured surface diffused light value with the immediately preceding surface diffused light value stored in the storage unit 112. If the surface diffused light is reduced, it can be seen that the minimum point in FIG. 6 has been approached, so that the fixing temperature can be controlled in that direction. On the other hand, when the surface diffused light increases, it can be seen that the fixing temperature is away from the minimum point in FIG. 6. In this case, the fixing temperature may be controlled in the opposite direction. In this way, the relative position at the present time with respect to the minimum point in FIG. 6, that is, the direction in which the fixing temperature is controlled is obtained, and the above cycle may be repeated until the surface diffused light becomes sufficiently small. Here, when it is determined that the surface diffused light has reached the minimum point in FIG. 6 as described above, even if the surface diffused light still exceeds the upper limit value, the surface diffused light cannot be reduced any further, so that the fixing condition is determined there. The control operation ends.

  The predetermined temperature ΔT needs not be too large and not too small. That is, when the fixing temperature is changed once by ΔT and the minimum point is skipped, ΔT is too large. Conversely, if ΔT is too small, the patch image must be output many times before reaching the minimum point. Therefore, ΔT may be manually input sequentially, but it is desirable to measure the optimal ΔT in advance and store it in the storage unit 112 of the fixing control unit 110. Further, it is desirable that ΔT is large when it is far from the minimum point and is small when it is close to the minimum point. Therefore, in the case of automatic control, it is desirable to store the optimum control method for ΔT in the storage unit 112 of the fixing control unit 110 in advance.

  Heretofore, an example of the control method has been described with the fixing temperature as the control target. In the above method, ΔT or the like may be manually input and controlled as described above, and a software program having the above functions may be stored in the storage unit 112 of the fixing control unit 110 or the like. It may be controlled automatically.

  Further, when the surface diffused light always exceeds the upper limit value of the surface diffused light held in the storage unit 112 of the fixing control unit 110 due to deterioration with time of the fixing device (fixing roller, pressure roller, etc.) In the above-described method, every time the fixing condition correction control is executed, the result that the upper limit value is exceeded in step S7 of FIG. 7 is obtained. In this case, even if the surface diffused light has not increased since the previous correction of the fixing conditions (even if it is already at the minimum point in FIG. 6), until it is determined in step S8 that the minimum point has been reached, A patch image must be output at least several times, which is not preferable. Therefore, once the minimum value of the surface diffused light exceeds the upper limit value of the surface diffused light held in the storage unit 112 of the fixing control unit 110, the surface diffusion held in the storage unit 112 of the fixing control unit 110. A method of updating the upper limit value of light to the current value is also conceivable. Then, after the next time, the updated latest data table (upper limit value of surface diffused light) may be used. By doing so, it is possible to suppress the useless output of the patch image and to perform the fixing condition control more efficiently.

(Second Embodiment)
≪Example using concentration≫
In the first embodiment described above, the spectral reflectance is used for the reflection characteristics 1 and 2 used for calculating the surface diffused light. In this case, a spectrocolorimeter was required for measuring the spectral reflectance. However, there may be a desire to make the device simpler. Therefore, in the second embodiment, an example in which the image density after fixing is used instead of the spectral reflectance will be described.

  FIG. 8 is a block diagram showing a main system configuration of the color image forming apparatus according to the second embodiment. FIG. 9 is an explanatory diagram showing the overall configuration of the color image forming apparatus according to the second embodiment. The configuration of the color image forming apparatus shown in FIGS. 8 and 9 includes a densitometer 42 instead of the spectrocolorimeter 41 shown in the first embodiment. The other configurations are the same as those shown in FIGS. 1 and 2, and are therefore denoted by the same reference numerals, and redundant description is omitted here.

  FIG. 10 shows an example of the configuration of the densitometer 42. The densitometer 42 includes a light source 61 such as a gas-filled filament lamp, a light receiving element 62 such as a photodiode, and an IC (not shown) that processes received light data. The light source 61 in FIG. 10 is installed perpendicular to the recording material 11 and irradiates the recording material 11 perpendicularly. The light receiving element 62 is installed in a 45 ° direction with respect to the vertical direction of the recording material 11, and detects reflected light from the recording material 11.

  In the flow of controlling the fixing conditions in the second embodiment, the reflection characteristic measured in step S3 in FIG. 7 is density 1 instead of the spectral reflectance 1, and the other operations are the same as those shown in FIG. It is the same. In the fixing condition control, the patch image after fixing is measured by the densitometer 42 and the density value is sent to the calculation unit 152. An example of the data table stored in the memory 151 is as shown in FIG. When the density is used, the data stored in the memory 151 can be reduced. As shown in FIG. 11, the specular reflection characteristic data for each color need only be the density 2 in the specular state.

  The calculation unit 152 calculates the surface diffused light using the density 1 for each color measured by the densitometer 42 and the density 2 of the mirror surface state stored in the memory 151. At this time, the calculation unit 152 converts the density into the reflectance according to the formula D = −log (R) [D is the density, and R represents the reflectance], and then calculates the difference value between the two to obtain the surface diffused light. obtain. The subsequent processing in the fixing control unit 110 and the like is the same as in the first embodiment.

  The first embodiment and the second embodiment have been described above. Here, instead of the patch image of FIG. 4 used in both embodiments, a method using the patch image shown in FIG. 12 is also conceivable. In the patch image shown in FIG. 12, patches of C, M, Y, and K with an area ratio of 100% are arranged in a line in the recording material conveyance direction, and the patches of each color are perpendicular to the recording material conveyance direction. It is also juxtaposed in the direction (main scanning direction). Patches of the same color are juxtaposed in a direction orthogonal to the recording material conveyance direction, a spectrocolorimeter 41 or a densitometer 42 is arranged for each patch, the reflection characteristics are measured, and surface diffused light is obtained, thereby conveying the recording material It is possible to detect whether or not fixing unevenness occurs in the direction perpendicular to the direction. When fixing unevenness occurs, the fixing conditions can be controlled so as to reduce the fixing unevenness. In this case, the detected non-uniformity of fixing is the fluctuation of the surface diffused light in the direction orthogonal to the recording material conveyance direction (main scanning direction). For example, a method of controlling the fixing conditions so that the total sum of the surface diffused light at the surface is minimized. Further, in this case, by arranging a plurality of thermistors for detecting the fixing temperature in the roller axial direction, it is possible to detect the fixing temperature more finely and to perform the fixing control more satisfactorily.

  In this embodiment, the fixing device 30 in which the fixing roller 31 and the pressure roller 32 are opposed to each other is described as an example of the configuration of the fixing device. However, the configuration of the fixing device is not limited to this. A configuration example of another fixing device is shown in FIG. In this fixing device, an endless belt 8 is used as a fixing member. The endless belt 8 is stretched around at least two support rollers 9 and 10, and the pressure roller 2 is endless with a constant pressing force by a pressing means (not shown). Pressed against the belt 8. The support roller 9 is heated by the heater 3 disposed therein to heat the endless belt 8, and the auxiliary heating roller 11 is brought into contact with the surface of the pressure roller 2. The auxiliary heating roller 11 is heated by the heater 4 disposed therein to heat the pressure roller 2. In FIG. 13, reference numeral 6 denotes a toner image after transfer, and reference numeral 7 denotes a recording material.

  Therefore, according to the embodiments described above, the following effects are listed. First, surface diffused light from the surface of the toner image with respect to the patch image on the recording material fixed by the fixing device 30 is acquired, and the reflection characteristic 1 of the acquired surface diffused light and the specular state stored in advance are obtained. By controlling the fixing conditions of the fixing device 30 using the reflection characteristic 2, it is possible to achieve desired color reproduction and obtain an image after fixing with good color reproduction. Second, in the above description, the reflection characteristics 1 and 2 are spectral reflectances, and the difference between the two is obtained to enable acquisition of surface diffused light. Thirdly, in the above, the reflection characteristics 1 and 2 are used as the density, and the difference is taken after the density is converted into the reflectance, thereby obtaining the surface diffused light, and the spectral reflectance can be obtained by using the density. The apparatus can be simplified more than the case where it is used.

  Fourth, in the above, the obtained surface diffused light is directly linked to the color evaluation by using the same optical condition as the color evaluation for the optical conditions for measuring the reflection characteristics 1 and 2. Is possible. Fifth, in the above, by storing the reflection characteristic 2 in the specular state measured in advance in the apparatus, it is possible to omit the mirroring means of the patch image and the measurement means of the reflection characteristic 2, and the apparatus Simplification and correction processing time can be reduced.

  As described above, the image forming apparatus according to the present invention is useful for electrophotographic color copiers, color printers, color facsimile apparatuses, and the like. Suitable for devices and systems that control

1 is a block diagram showing a main system configuration of a color image forming apparatus according to a first embodiment. It is explanatory drawing which shows the whole structure of the color image forming apparatus concerning this 1st Embodiment. It is explanatory drawing which shows the structure of the spectral colorimeter concerning this 1st Embodiment. It is explanatory drawing which shows the example of the patch image 1 concerning this 1st Embodiment. It is a chart which shows the example of the data table 1 used for fixing control as the reflection characteristic 2 of this 1st Embodiment. It is a graph which shows the relationship between the fixing temperature concerning the fixing control of this 1st Embodiment, and surface diffused light. 3 is a flowchart illustrating an operation procedure of fixing control according to the first embodiment. It is a block diagram which shows the main system structures of the color image forming apparatus concerning this 2nd Embodiment. It is explanatory drawing which shows the whole structure of the color image forming apparatus concerning this 2nd Embodiment. It is explanatory drawing which shows the structure of the densitometer concerning this 2nd Embodiment. It is a chart which shows the example of the data table 2 used for fixing control as the density | concentration characteristic 2 of this 2nd Embodiment. It is explanatory drawing which shows the example of the patch image 2 concerning this Embodiment. FIG. 10 is an explanatory diagram illustrating a configuration example of another fixing device. It is a graph which shows the relationship between surface diffused light and saturation. It is explanatory drawing which shows the measurement principle of the surface diffused light with respect to an image. It is explanatory drawing which shows the glossiness and color measurement optical system of an image. It is a graph which shows the relationship between the glossiness of an image, and surface diffused light.

Explanation of symbols

DESCRIPTION OF SYMBOLS 30 Fixing device 31 Fixing roller 32 Pressure roller 33, 34 Heater 35a, b Thermistor 41 Spectrocolorimeter 42 Densitometer 100 Image forming part 110 Fixing control part 111 Driver 112 Storage part 120 Main control part 130 Image processing part 140 Operation display Unit 150 image characteristic acquisition unit after fixing 151 memory 152 calculation unit

Claims (6)

An image forming apparatus comprising: an image forming unit that forms a toner image and transfers the toner image to a recording material; and a fixing unit that fixes the toner image transferred to the recording material by the image forming unit.
Surface diffused light acquisition means for acquiring surface diffused light from the surface of the toner image on the recording material fixed by the fixing means;
Fixing control means for controlling fixing conditions of the fixing means based on the acquired surface diffused light;
An image forming apparatus comprising: The surface diffused light acquisition means includes
Measuring means for measuring the reflection characteristic 1 of the toner image fixed by the fixing means;
Specular reflection characteristic acquisition means for acquiring a reflection characteristic 2 measured under the same optical conditions as the reflection characteristic 1 when the surface of the toner image is in a mirror state;
Calculating means for calculating surface diffused light using the reflection characteristic 1 and the reflection characteristic 2;
The image forming apparatus according to claim 1, further comprising:   The reflection characteristic 1 and the reflection characteristic 2 are reflectances, and the calculation means takes a difference between the reflection characteristic 1 obtained by the measurement means and the reflection characteristic 2 obtained by the specular reflection characteristic acquisition means, and The image forming apparatus according to claim 2, wherein surface diffused light is calculated.   The reflection characteristic 1 and the reflection characteristic 2 are density values, and the calculation means calculates the surface diffused light by taking the difference between the two after converting each density value into a reflectance. The image forming apparatus according to claim 2.   The image forming apparatus according to claim 2, wherein the optical condition of the measuring unit is the same optical condition as that for evaluating the color.   The image forming apparatus according to claim 2, wherein the specular reflection characteristic acquisition unit includes a storage unit that holds a reflection characteristic 2 of a specular state measured in advance.

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