Image forming device

Abstract

To provide an image forming apparatus that can prevent deterioration of color samples.SOLUTION: An image forming apparatus of an intermediate transfer system comprising an optical reading sensor 50 on a sheet conveyance path including a fixing device, includes a sheet reading mode for conveying a sheet on the conveyance path while adjusting a temperature of the fixing device to a temperature lower than that in an image forming operation and reading an image on the sheet with the optical reading sensor 50, and in the reading mode, performs at least one of separating image carriers and an intermediate transfer body from each other at primary transfer units and stopping application of a secondary transfer bias at a secondary transfer unit.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Conventionally, when calibrating a color measurement unit using a color sample, the fixing unit is controlled under conditions different from those during image formation to transport the color sample, allowing the used color sample to be reused (Patent Document 1). Summary of the Invention [Problem to be solved by the invention]

[0003] However, there is a problem in that the color sample becomes dirty when passing through the image forming unit. [Means for solving the problem]

[0004] In order to solve the above-mentioned problems, the present invention provides a sheet conveying path including a fixing device. on the downstream side of the fixing device in the sheet conveying direction. In an intermediate transfer type image forming apparatus equipped with an optical reading sensor, a sheet reading mode is provided in which a temperature of the fixing device is set to a lower temperature than that during an image forming operation, a sheet is conveyed through the conveying path, and an image on the sheet is read by the optical reading sensor, and in the sheet reading mode, a separation between an image carrier and an intermediate transfer body in a primary transfer portion and application of a secondary transfer bias in a secondary transfer portion are stopped. both The present invention is characterized in that: Effect of the Invention

[0005] According to the present invention, deterioration of the color sample can be suppressed. [Brief description of the drawings]

[0006] [Figure 1] FIG. [Diagram 2] FIG. 2 is a schematic diagram showing a schematic configuration of a reading device. [Diagram 3] FIG. 2 is a block diagram showing an example of the configuration of a control unit of the printer. [Figure 4] FIG. 4 is an explanatory diagram of a state of the mechanism section in a sheet reading mode. [Diagram 5] 11 is a flowchart of control in a sheet reading mode. [Figure 6] 4 is a flow chart showing a procedure for determining and storing a correction amount. [Figure 7] 13 is a procedural flow of a modified example. [Figure 8] 4 is a flow chart of a procedure according to another modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] An embodiment in which the present invention is applied to a printer, which is a color-compatible electrophotographic image forming apparatus, will be described with reference to the drawings. First, an outline of a printer 300 of this embodiment will be described. FIG. 1 is an overall configuration diagram of the printer 300. The printer 300 has an operation / display unit 200 on top of a device main body 100. The device main body 100 of the printer 300 has an image forming section as a tandem type image forming means having four process units 1Y, C, M, and Bk.

[0008] The four process units 1Y, C, M, and Bk have the same configuration, except that they contain toners of different colors: yellow (Y), cyan (C), magenta (M), and black (Bk). Each process unit 1 forms an image by electrophotography, and includes a photoconductor 2, a charging device 3, a developing device 4, and a cleaning blade 5. Other methods, such as an inkjet method, can be used instead of the electrophotographic method.

[0009] The transfer device 7 provided below each process unit 1 has an intermediate transfer belt 10 as an intermediate transfer body. The intermediate transfer belt 10 is stretched around a first tension roller 21, a second tension roller 22, and a third tension roller 23, and is pressed against the inner periphery by a tension roller 24.

[0010] Four primary transfer rollers 11 are disposed at positions facing the four photoconductors 2 via the intermediate transfer belt 10. Each primary transfer roller 11 is connected to a power source. A secondary transfer roller 12 serving as a secondary transfer means is provided at a position facing a third tension roller 23 that tensions the intermediate transfer belt 10. This secondary transfer roller 12 forms a secondary transfer nip at a position where it comes into contact with the intermediate transfer belt 10. The secondary transfer roller 12 is connected to a power source so that a secondary transfer bias can be supplied. The secondary transfer means is not limited to a roller, and may be a belt.

[0011] A plurality of paper feed cassettes 13 that store paper P such as paper sheets and overhead projectors as sheet-like recording materials are disposed at the bottom of the device main body 100. Paper feed cassettes 13 are provided with paper feed rollers 14 that feed out the stored paper P. A paper output tray 20 is provided on the outer surface of device main body 100 on the left side of the drawing.

[0012] The device main body 100 includes a transport path 25 for transporting the paper P from the paper feed cassette 13 through the secondary transfer nip to the paper discharge tray 20. In this transport path 25, a registration roller pair 15 is provided upstream in the paper transport direction from the position of the secondary transfer roller 12. In addition, a fixing device 8, a cooling device 9, a reading device 50 such as an image reading device, and a discharge roller pair 16 are sequentially arranged downstream in the paper transport direction from the position of the secondary transfer roller 12.

[0013] The fixing device 8 includes, for example, a fixing roller 17 as a fixing member having an internal heater, and a pressure roller 18 as a pressure member that presses the fixing roller 17. A fixing nip is formed at a location where the fixing roller 17 and the pressure roller 18 come into contact with each other.

[0014] In addition, a switching claw 26, which will be described later, is provided between the reading device 50 and the pair of discharge rollers 16. When double-sided printing, in which images are formed on both sides of the paper P, is selected in the print mode as the image formation mode, the switching claw 26 rotates to guide the paper P from the conveying path 25 to a reversing path 27 provided between the fixing device 8, the cooling device 9, etc., and the paper feed cassette 13. The paper P guided to the reversing path 27 switches back within the reversing path 27 to be reversed, and enters the conveying path 25 upstream of the pair of registration rollers 15 to form an image on the back side.

[0015] The cooling device 9 has an endless front belt 97a and an endless back belt 97b. A front cooling plate 91a is disposed on the inner periphery of the extended surface of the front belt 97a that holds the paper P, and a back cooling plate 91b is disposed on the inner periphery of the extended surface of the back belt 97b that holds the paper P.

[0016] The cooling device 9 also has a pump 92, a tank 93, a radiator 94, a cooling fan 95, piping 96, etc. Cooling liquid can circulate between the cooling plates 91a, 91b, the radiator 94, the tank 93, and the pump 92. Arrow A indicates the flow of liquid in the circulation path of the cooling liquid. The cooling fan 95 and the radiator 94 are disposed in the duct 28. The duct 28 has an intake port 28a provided below and an exhaust port 28b provided above.

[0017] The basic operation of the printer 300 is as follows. A case where single-sided printing is selected as the printing mode will be described. When image data is received from an external device such as a personal computer and an image forming operation is started, a laser beam is irradiated from the exposure device 6 onto each charged photoconductor 2 based on image information obtained by processing the image data from the external device by an image processing unit, and an electrostatic latent image is formed on the surface of each photoconductor 2. The image information exposed to each photoconductor 2 is monochromatic image information obtained by decomposing a desired full-color image into color information of yellow, cyan, magenta, and black. The electrostatic latent image formed on the photoconductor 2 is made into a toner image by each developing device 4. The toner images are transferred to the intermediate transfer belt 10 in a superimposed manner in sequence. The toner images carried on the intermediate transfer belt 10 are secondarily transferred collectively onto the paper P conveyed out of the paper feed cassette 13.

[0018] The paper P onto which the toner image has been secondarily transferred is transported to a fixing device 8, where the paper P is pressurized and heated by a fixing roller 17 and a pressure roller 18, so that the toner image is fixed onto the paper P. Then, the paper P is cooled by a cooling device 9, and then discharged onto a paper discharge tray 20 by a pair of discharge rollers 16.

[0019] 2 is a schematic diagram showing a schematic configuration of the reading device 50. The reading device 50 has a first image reading unit 60A, a second image reading unit 60B, a first reading conveying roller pair 55 consisting of a first driving conveying roller 55a and a first driven conveying roller 55b, and a second reading conveying roller pair 56 consisting of a second driving conveying roller 56a and a second driven conveying roller 56b.

[0020] Each image reading unit 60A, 60B is composed of a reading device 51, an illumination unit 52, and a background member 54, and reads an image on the paper P during transport. The second image reading unit 60B is disposed downstream in the paper transport direction from the first image reading unit 60A. The first image reading unit 60A is disposed at one end in the width direction, and the second image reading unit 60B is disposed at the other end in the width direction. By disposing the first image reading unit 60A and the second image reading unit 60B at different positions in the width direction, and performing image processing to join (combine) the read images read by each image reading unit (reading device), an output image formed on the paper is obtained (read).

[0021] The reading device 51 of each of the image reading sections 60A and 60B is composed of an image sensor 51a, a lens 51b, mirrors 51c, 51d, and 51e, and reads an image on the paper P illuminated by an illumination unit 52.

[0022] The background member 54 of each image reading unit 60A, 60B includes a black large diameter roller 54a with a black outer circumferential surface, a black small diameter roller 54b with a black outer circumferential surface, a white large diameter roller 54c with a white outer circumferential surface, and a white small diameter roller 54d with a white outer circumferential surface. These four rollers 54a, 54b, 54c, 54d are rotatably supported by a rotating support 54e, and by rotating the rotating support 54e, any of the rollers 54a, 54b, 54c, 54d can be positioned at the image reading position. The background member 54 positions any of the corresponding rollers 54a, 54b, 54c, 54d at the image reading position according to the information of the paper P (information for identifying the thickness and color of the paper, etc.) and the operation mode of the image forming system (difference in conveying speed, etc.).

[0023] In this embodiment, the tone reproduction curve is corrected using a composite read image obtained by combining a first read image read by the first image reading unit 60A and a second read image read by the second image reading unit 60B. The tone reproduction curve is a tone reproduction condition, which is one of the image formation conditions. The tone reproduction curve is corrected based on a full-color output image on paper of the composite read image and a master image, which is the original data of this output image, to suppress variation in color output on the paper surface. This correction of the tone reproduction curve corresponds to a correction of the image formation conditions performed by the second image correction control unit, which forms a predetermined image on a sheet by the image forming unit, reads the formed image by the optical reading sensor, and performs the correction based on the reading result.

[0024] Fig. 3 is a block diagram showing an example of the configuration of the control unit 110 of the printer 300 shown in Fig. 2. The printer 300 and the PC 500 are connected via a LAN 510. The PC 500 transmits print data to the printer 300, the print data including an image to be printed.

[0025] The printer 300 executes printing based on print data transmitted from the PC 500 and performs calibration. The printer 300 includes an engine 400 and a DFE (digital front end) 300 that controls the engine 400.

[0026] The DFE 300 includes a print control unit 310 and a calibration control unit 320. The print control unit 310 includes an I / F 311, a rasterizer 312, a correction curve generator 313, a corrector 314, and a correction curve memory unit 315. The calibration control unit 320 includes an I / F 321, a density conversion information memory unit 322, and a density converter 323. The engine 400 includes an exposure device 6, a sensor control unit 420, an image sensor 51a, a color converter 440, an I / F 450, and a correction amount memory unit 460.

[0027] A specific example of the operation of correcting the tone reproduction polarity is as follows. The engine 400 performs engine adjustment to set the maximum density in order to achieve an optimal state. Next, the image forming unit including the exposure device 6 of the engine 400 forms (prints) a predetermined density correction pattern 550 on paper. An example of the density correction pattern 550 is a pattern in which patches of multiple colors (for example, patches of each color of CMYK) are arranged.

[0028] Next, the image sensor 51a of the engine 400 reads the density correction pattern 550 (color of each patch) formed on the paper under the control of the sensor control unit 420, and generates first color information in the RGB color space (RGB data that is the read value of the image sensor 51a). The color conversion unit 440 converts the first color information into second color information. The second color information is, for example, color information in the RGBY color space (RGBY data 411).

[0029] In the calibration control unit 320, the density conversion unit 323 converts the second color information into density information (calculates density information from the second color information) using density conversion information for the type of paper on which the density correction pattern is formed, stored in the density conversion information storage unit 322. The RGBY data 411, which is the second color information, is converted into CMYK data, which is density information. The correction curve generation unit 313 of the print control unit 310 generates correction curve information for the tone reproduction curve based on the density information converted by the second density conversion unit 324, and stores it in the correction curve storage unit 315.

[0030] Next, a description will be given of measures against the change over time in the output characteristics of the image sensor 51a, which is an optical reading sensor and is a characteristic part of this embodiment. In the technology of Patent Document 1, an adjustment chart (color matching chart) attached to the main body is detected by a color sensor (optical reading sensor) at the shipping destination, and an output correction table of the color sensor is created and stored in a non-volatile storage device, and is used for density gradation characteristic control using the color sensor to be executed thereafter. However, if the optical reading sensor causes a change in characteristics over time, it is necessary to correct the output correction table. At this time, when the adjustment chart attached to the main body is read by an optical reading sensor provided in the sheet conveying path including the fixing device, the adjustment chart shrinks or changes in color due to the reduction in heat and humidity due to the heat of the fixing device. As a result, the color of the adjustment chart itself changes and deteriorates, and it becomes impossible to correct the ideal output correction table.

[0031] In this embodiment, in order to allow repeated use of the adjustment chart, which is a color sample attached to the main body, without deterioration, a sheet reading mode is provided in which the fixing device is kept at a temperature lower than that during image formation, a sheet is conveyed through a conveying path, and an optical reading sensor reads the image on the sheet. FIG. 4 is an explanatory diagram of the state of the mechanism in the sheet reading mode. In this embodiment, at least one of the following is performed: separating the photoconductor 2, which is an image carrier at the primary transfer section, from the intermediate transfer belt 10, which is an intermediate transfer section, and stopping the application of the secondary transfer bias at the secondary transfer section. Preferably, separating the photoconductor 2, which is an image carrier at the primary transfer section, from the intermediate transfer belt 10, which is an intermediate transfer section, is performed. More preferably, both are performed. The sandwiched state of the intermediate transfer belt 10 between the photoconductor 2 and the primary transfer roller 11 is released by the separation. The separation can be performed by any of the following: moving the primary transfer roller 11 in the separating direction; moving the photoconductor 2 in the separating direction; moving both the primary transfer roller 11 and the photoconductor 2 in the separating direction.

[0032] In this embodiment, at least one of the following is performed: separating the photoconductor 2, which is the image carrier at the primary transfer section, from the intermediate transfer belt 10, which is the intermediate transfer section, and stopping the application of the secondary transfer bias at the secondary transfer section, thereby suppressing deterioration (such as dirt) of the adjustment chart.

[0033] It is preferable that the secondary transfer roller 12 eliminates the secondary transfer nip as shown by the arrow Y12, and leaves a gap between the intermediate transfer belt 10 and the secondary transfer roller 12 so that a sheet can pass through. It is also preferable that the pressure roller 18 of the fixing device 8 separates from the fixing roller 17 as shown by the arrow Y18, and the cooling device 9 separates from the front belt 97a from the back belt 97b as shown by the arrow Y9, and both leave a gap so that a sheet can pass through. Then, the heater of the fixing device 8 is turned off, and the fixing device 8 is brought into a state in which fixing is not possible in terms of temperature, that is, a lower temperature than during image formation, and preferably a low enough temperature state not to deteriorate the adjustment chart. Hereinafter, this state of the fixing device is referred to as a non-operating state.

[0034] FIG. 5 is a flow chart of the control of the sheet reading mode. First, at least one of the following, preferably both, is performed: the supply of the secondary transfer bias to the secondary transfer roller 12 is stopped, and the intermediate transfer belt 10 is released from the sandwiched state between the primary transfer roller 11 and the photoconductor 2 (STEP 1). More preferably, as described with reference to FIG. 4, the member contacting the adjustment chart is retracted from the sheet conveying path. However, if it is desired to apply a conveying force to the adjustment chart in the secondary transfer section, the intermediate transfer belt 10 and the secondary transfer roller 12 may be kept in the same sandwiched state as during image formation, or may be changed to a weaker sandwiched state than during image formation within a range where a conveying force can be applied. In this way, even when a conveying force is applied to the adjustment chart between the intermediate transfer belt 10 and the secondary transfer roller 12, deterioration (such as dirt) of the adjustment chart can be suppressed. Then, the fixing temperature is lowered below the temperature during image formation, or heating is turned off (STEP 2). Next, the adjustment chart is fed and conveyed (STEP 3). Then, the adjustment chart is read by the reading device 50 (STEP 4). After reading, the adjustment chart is discharged onto the discharge tray 20 (STEP 5).

[0035] In order to ensure the accuracy of the correction of the output correction table by reading the adjustment chart in this sheet reading mode, a correction amount is calculated from the result of reading the image on the sheet in the sheet reading mode, and the fixing device is put into an operating state, the sheet is transported along the transport path, and the same image on the sheet is read by the optical reading sensor, and this correction amount is stored in the storage means. The correction amount can also be calculated, for example, as follows: the adjustment chart is read in the sheet reading mode at the time of factory shipment, and then the fixing device is put into an operating state (a state in which normal fixing during image formation operation is possible), the adjustment chart is transported along the transport path, and read by the optical reading sensor, and the correction amount is calculated from the results of both readings.

[0036] FIG. 6(a) shows a flow of the procedure from obtaining the correction amount to storing it. For example, it is executed at the time of shipment from the factory. The first mode is the sheet reading mode, and the second mode is the reading mode with the fixing device in the operating state. The first chart represents the first adjustment chart, and the second chart represents the second adjustment chart (the printed patches are the same image). The first correction amount represents a correction amount for obtaining the result when the fixing device is in the operating state, the sheet is transported through the transport path, and the image on the sheet is read by the optical reading sensor, from the result of reading the image on the sheet in the sheet reading mode. The second correction amount represents an output correction table. For example, the memory unit 460 of the engine 400 can be used as the storage means for the first correction amount. A storage unit provided on the control unit 110 side can be used as the storage means for the second correction amount.

[0037] In FIG. 6(a), the first chart is read in the first mode (STEP 1), the first chart is read in the second mode (STEP 2), and a first correction amount is calculated from the difference between the two read results (STEP 3). This difference in results represents the degree of influence of the temperature difference, which occurs when the fixing device 8 is in operation and the surrounding temperature rises and is relatively low when the fixing device 8 is not in operation, and changes the characteristics of the image sensor 51a and the like. Taking this degree of influence into consideration, a correction amount is calculated from the result of reading the image on the sheet in the first mode to obtain the result when the image on the sheet is read in the second mode. The calculated first correction amount is stored in the memory unit (STEP 4). Along with the calculation of this first correction amount, the output characteristics of the sensor are also calculated, and a sensor output table is created and stored in the memory unit.

[0038] Then, the second chart is read in the first mode (STEP 5), a second correction amount is calculated (STEP 6), and the second correction amount is stored in the storage unit (STEP 7). This second correction amount is a correction curve stored in the correction curve storage unit of the print control unit 310, and is the first calibration of the printer, and the second chart is used instead of reading the image formed in the calibration process described above. The correction curve is calculated with reference to the first correction amount (STEP 6). This calculation is executed by the correction curve generation unit 313 of the print control unit 310, and is performed with reference to the density conversion information according to the type of paper in the density conversion information storage unit 322 as described above, together with the first correction information. This step corresponds to a step in which the first image correction control unit reads the adjustment chart (second chart) in the sheet reading mode (first mode), and corrects the image formation conditions (correction curve) based on the reading result and the correction amount (first correction amount) stored in the storage unit. Then, the second chart is packed into the main unit (STEP 8) and shipped.

[0039] Fig. 6(b) shows the correction process of the sensor output table using the second chart included in Fig. 6(a) and taking into consideration the change over time of the output characteristics of the image sensor 51a at the customer's site. The second chart is read in the first mode (STEP 1), and the output characteristics (sensor output table) are corrected (STEP 2) taking into account the first correction amount.

[0040] FIG. 7 is a flow chart of the procedure of the modified example of FIG. 6. The difference between this modified example and the example of FIG. 6 is that, whereas in the example of FIG. 6, the second chart is enclosed in STEP 8 of FIG. 6(a), in this modified example, the second chart is not enclosed, and instead, as shown in FIG. 7(b), for example, a patch identical to the adjustment chart is formed on paper by image formation at the customer's site (STEP 1) and stored (STEP 2). Then, in the calibration of FIG. 7(c), this stored adjustment chart is used. The other points are the same as in the example of FIG. 6. The formation of a patch identical to the adjustment chart on paper by image formation at the customer's site is performed when the printer is brand new immediately after delivery to the customer. For this purpose, the original data of the adjustment chart is stored in the memory of the printer, and is used for output in STEP 1 of FIG. 7(b).

[0041] Figure 8 is a flow chart of the procedure of another modified example. The procedure in Figure 8 differs from the procedures in Figures 6 and 7 in that the initial calibration (STEPs 5 to 7 in (a)) that is performed at the time of shipment from the factory in Figures 6 and 7 is performed, for example, at the customer's site (STEPs 1 to 3 in Figure 8 (b)). For this reason, the second chart is included in the package before shipment. This initial calibration is performed when the printer is brand new, immediately after delivery to the customer.

[0042] 6 and 7, the reading and calculation of the first correction amount in the first and second modes for obtaining the first correction amount at the time of shipment from the factory are performed for, for example, one of multiple printers shipped at the same time, and for the other printers, the first correction amount obtained for one printer is stored as is in storage unit 460, thereby eliminating the need to determine the first correction amount for the other printers. Of course, since there may be variations between printers, it is preferable in terms of accuracy to perform this for each printer, but if accuracy allows, it is possible to save time and effort.

[0043] In the above description, the first correction amount is stored in the storage unit 460 as is, but instead, even if the output of the image sensor 51a is used without correction by the first correction amount, the parameters (image forming conditions) can be corrected to produce the same results as when the first correction amount is used. For example, in the case of gradation curve correction, the correction is applied to the correction curve. Corrections may also be applied to other parameters. In addition, in the case of a model in which the image sensor output characteristics change between single-sided printing and double-sided printing, the correction amounts for correcting the image sensor output characteristics after single-sided fixing and the image sensor output characteristics after double-sided maintenance fixing may be calculated and stored. [Explanation of symbols]

[0044] 1: Process unit 2: Photoreceptor 3: Charging device 4: Developing device 5: Cleaning blade 6: Exposure equipment 7: Transfer device 8: Fixing device 9: Cooling device 10: Intermediate transfer belt 11: Primary transfer roller 12: Secondary transfer roller 13: Paper feed cassette 14: Paper feed roller 15: Registration roller pair 16: Discharge roller pair 17: Fuser roller 18: Pressure roller 20: Paper output tray 21: First tension roller 22: Second tension roller 23: Third tension roller 24: Tension roller 25: Transport path 26: Switching claw 27: Reverse Path 28: Duct 28a: Air intake 28b: Exhaust port 50: Reading device 51: Reading device 51a: Image sensor 51b: Lens 51c: Mirror 51d: Mirror 51e: Mirror 52: Lighting unit 54: Background material 54a: Black large diameter roller 54b: Black small diameter roller 54c: White large diameter roller 54d: White small diameter roller 54e: Rotating support 55: First reading conveying roller pair 55a: First driving conveying roller 55b: First driven conveying roller 56: second reading conveying roller pair 56a: second driving conveying roller 56b: second driven conveying roller 60A: First image reading unit 60B: Second image reading unit 91a: Front cooling plate 91b: Back cooling plate 92: Pump 93: Tank 94: Radiator 95: Cooling fan 96: Piping 97a: Outer belt 97b: Back belt 100: Device body 110: Control unit 200:Display section 300: Printer 310: Print control unit 311: Interface 312: Rasterization section 313: Correction curve generator 314: Correction section 315: Correction curve memory section 320: Calibration control section 321: Interface 322: Density conversion information storage unit 323: Density conversion section 324: Second density conversion unit 400: Engine 411: RGBY data 420: Sensor control unit 440: Color conversion section 450: Interface 460: Correction amount storage section 500: PC 510: LAN 550: Density correction pattern P:Paper [Prior art documents] [Patent documents]

[0045] [Patent Document 1] JP 2017-072698 A

Claims

1. 1. An image forming apparatus of an intermediate transfer type, comprising: an optical reading sensor disposed downstream of a fixing device in a sheet transport path including the fixing device, the optical reading sensor being disposed downstream of the fixing device in a sheet transport direction; a sheet reading mode in which a temperature of the fixing device is set to a lower temperature than that during an image forming operation, a sheet is conveyed through the conveying path, and an image on the sheet is read by the optical reading sensor; In the sheet reading mode, the image forming apparatus performs both of the steps of separating the image carrier from the intermediate transfer body in the primary transfer portion and stopping application of the secondary transfer bias in the secondary transfer portion.

2. In the image forming apparatus according to claim 1, An image forming apparatus characterized by being provided with a memory means for storing a correction amount to obtain the result when the image on the sheet is read by the optical reading sensor after the fixing device is set to the temperature state during image formation operation, the sheet is transported along the transport path, and the image on the sheet is read by the optical reading sensor, based on the result of reading the image on the sheet in the sheet reading mode.

3. 3. The image forming apparatus according to claim 2, an adjustment chart is read in the sheet reading mode, and an output characteristic correction control means is provided for correcting the output characteristics of the optical reading sensor based on the reading result and the correction amount stored in the memory means.

4. 4. The image forming apparatus according to claim 2, an image forming apparatus including a first image correction control means for reading an adjustment chart in the sheet reading mode and correcting image formation conditions based on the reading result and the correction amount stored in the memory means.

5. 5. The image forming apparatus according to claim 1, an optical sensor for detecting a position of the image forming apparatus and a second image correction control means for correcting image forming conditions based on the reading result;

6. 6. The image forming apparatus according to claim 4, The image forming apparatus according to claim 1, wherein the image forming conditions are tone reproduction conditions.

7. 7. The image forming apparatus according to claim 1, In the sheet reading mode, the image forming apparatus is characterized in that a sheet on a sheet placement unit for forming an image is fed into the transport path.

8. 8. The image forming apparatus according to claim 1, The image forming apparatus is characterized in that the fixing device has a fixing member that holds a sheet, and in the sheet reading mode, the fixing member is separated.

Images