Image forming apparatus and image forming method

Abstract

The present invention provides an image forming apparatus capable of stabilizing the temperature of the recording medium. [Solution] The image forming apparatus 1 includes a paper temperature sensor 93 that detects the paper temperature before fixing the toner image to the paper P, a preheating unit 80 that heats at least the surface of the paper P before forming the toner image on the paper P, and a control unit 101 that controls the heating by the preheating unit 80 during printing based on the paper temperature detected by the paper temperature sensor 93.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and an image forming method.

Background Art

[0002] When the paper is cold in a low-temperature environment, toner may be difficult to fuse to the paper, or the temperature of the fixing member may decrease, resulting in fixing under-offset (low-temperature fixing). As a countermeasure, the paper is heated before fixing to raise the paper temperature.

[0003] In Patent Document 1, it is proposed to heat the paper from both the front and back sides before printing, stop the paper conveyance when a predetermined paper temperature is reached, and warm the member temperature in the front stage of fixing with the warmed paper.

[0004] In Patent Document 2, it is proposed to perform preheating from the back side of the recording material on which toner has been placed by a preheating unit provided in the front stage of the fixing unit. Specifically, in the invention described in Patent Document 2, the paper temperature reaching the fixing unit is predicted, and when the predicted temperature is not a predetermined temperature, feedback is given to the heating control in the latter half of the preheating unit.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the invention described in Patent Document 1, if the paper temperature changes during printing, it is difficult to stabilize the temperature of the paper as it enters the fuser nip. Also, in the invention described in Patent Document 2, when handling cardboard or multilayer media such as roll paper, heating from only the back side is insufficient, and the paper temperature may not be stable.

[0007] The present invention aims to solve the aforementioned problems and provide an image forming apparatus and an image forming method that can stabilize the temperature of the recording medium. [Means for solving the problem]

[0008] In other words, the above-mentioned problems of the present invention are solved by the following configuration. (1) A temperature detection unit that detects the temperature of the recording medium before fixing the toner image onto the recording medium, A preheating unit that heats at least the surface of the recording medium before forming a toner image on the recording medium, A control unit controls heating by a preheating unit during printing based on the temperature of the recording medium detected by a temperature sensing unit, An image forming apparatus equipped with the following features.

[0009] (2) The preheating section heats the front and back surfaces of the recording medium, The control unit controls heating by the preheating unit for both the front and back surfaces of the recording medium. (1) The image forming apparatus described above.

[0010] (3) The temperature detection unit detects the temperature of the recording medium at multiple locations, The control unit controls the heating by the preheating unit based on the temperature of the recording medium detected at multiple locations by the temperature sensing unit. (1) The image forming apparatus described above.

[0011] (4) The temperature detection unit detects the temperature of the recording medium in the image forming unit that forms the toner image on the recording medium and the paper feeding unit that feeds the recording medium. (3) The image forming apparatus described above.

[0012] (5) The temperature detection unit detects the temperature of the recording medium on the front and back surfaces of the recording medium. The image forming apparatus according to (3).

[0013] (6) The temperature detection unit detects the temperature of the recording medium that passes through before printing and enters the fixing nip. When the temperature of the recording medium detected by the temperature detection unit is equal to or higher than a preset target temperature, the control unit starts printing. The image forming apparatus according to (1).

[0014] (7) The preheating unit has a housing separate from the main body of the image forming apparatus. The image forming apparatus according to (1).

[0015] (8) The preheating unit includes a front-side roller that is arranged to contact the front surface of the recording medium and heats the front surface of the recording medium, and a back-side roller that is arranged to contact the back surface of the recording medium at a position not facing the front-side roller and heats the back surface of the recording medium. The image forming apparatus according to (1) comprising the above.

[0016] (9) The preheating unit includes a front-side roller that is arranged to contact the front surface of the recording medium and heats the front surface of the recording medium, and a back-side roller that is arranged to contact the back surface of the recording medium at a position facing the front-side roller and heats the back surface of the recording medium. The image forming apparatus according to (1) comprising the above.

[0017] (10) When the determination result of fixing failure is input, the control unit controls the heating by the preheating unit based on the determination result of fixing failure in addition to the temperature of the recording medium. The image forming apparatus according to (1).

[0018] (11) A fixing failure detection unit that determines fixing failure from an image after fixing a toner image on the recording medium and outputs the determination result of fixing failure to the control unit. The image forming apparatus according to (10) comprising the above.

[0019] (12) The control unit receives the characteristic information of the recording medium and controls the heating by the preliminary heating unit based on the characteristic information of the recording medium in addition to the recording medium temperature. The image forming apparatus according to (1).

[0020] (13) The characteristic information of the recording medium includes at least one of the type of the recording medium or the basis weight of the recording medium. The image forming apparatus according to (12).

[0021] (14) A recording medium characteristic detection unit that detects the characteristic information of the recording medium and outputs it to the control unit The image forming apparatus according to (12), comprising the above.

[0022] (15) A detection step of detecting the recording medium temperature before fixing the toner image on the recording medium; A calculation step of calculating the temperature difference between the recording medium temperature and a preset target temperature as a correction amount; A heating step of heating at least the surface of the recording medium at a temperature based on the correction amount and the target temperature; A printing step of printing on the recording medium whose at least surface has been heated; An image forming method of sequentially executing the above.

Advantages of the Invention

[0023] According to the present invention, the recording medium temperature can be stabilized.

Brief Description of the Drawings

[0024] [Figure 1] It is a diagram schematically showing the overall configuration of the image forming apparatus according to the first embodiment. [Figure 2] It is a block diagram showing the configuration of the main part of the image forming apparatus according to the first embodiment. [Figure 3] In the first embodiment, it is a diagram schematically showing the configuration of the fixing unit. [Figure 4] In the first embodiment, it is a diagram schematically showing the first example of the configuration of the preliminary heating unit. [Figure 5] This figure schematically shows a second example of the configuration of the preheating section in the first embodiment. [Figure 6] In the first embodiment, this is a graph showing the change in paper temperature. [Figure 7] This is a flowchart illustrating the preheating control process in the first embodiment. [Figure 8] In the modified example, this is a graph showing the change in paper temperature. [Figure 9] This figure schematically shows the overall configuration of the image forming apparatus according to the second embodiment. [Figure 10] In the second embodiment, this is a graph showing the change in paper temperature. [Figure 11] This diagram schematically shows the overall configuration of the image forming apparatus according to the third embodiment. [Figure 12] This is a block diagram showing the configuration of the main part of the image forming apparatus according to the third embodiment. [Figure 13] This figure schematically shows the overall configuration of the image forming apparatus according to the fourth embodiment. [Figure 14] This is a block diagram showing the configuration of the main part of the image forming apparatus according to the fourth embodiment. [Modes for carrying out the invention]

[0025] The embodiments for carrying out the present invention will be described in detail below. The embodiments described below are merely examples for realizing the present invention and should be modified or changed as appropriate depending on the configuration of the apparatus to which the present invention is applied and various conditions. The present invention is not limited to the embodiments described below. Furthermore, in each figure, identical components are denoted by the same reference numerals, and their descriptions are omitted as appropriate.

[0026] (First Embodiment) [Configuration of the image forming apparatus] The configuration of the image forming apparatus 1 will be described with reference to Figures 1 and 2. Figure 1 is a schematic diagram showing the overall configuration of the image forming apparatus 1 according to the first embodiment. Figure 2 is a block diagram showing the configuration of the main parts of the image forming apparatus 1 according to the first embodiment.

[0027] Image forming apparatus 1 is a color image forming apparatus that uses an intermediate transfer method utilizing electrophotographic process technology. As shown in Figure 1, image forming apparatus 1 first transfers the toner images of each color, Y (yellow), M (magenta), C (cyan), and K (black), formed on the photoreceptor drum 413 to the intermediate transfer belt 421. After superimposing the four toner images on the intermediate transfer belt 421, image forming apparatus 1 forms a toner image by secondarily transferring it to paper P.

[0028] For example, in the image forming apparatus 1, a tandem system is employed in which photoreceptor drums 413 corresponding to the four YMCK colors are arranged in series in the direction of travel of the intermediate transfer belt 421, and the toner images of each color are sequentially transferred to the intermediate transfer belt 421 in a single procedure.

[0029] Paper P refers to the material (media) that is printed on. Examples of paper P include multilayer media such as printing paper, cardboard, and roll paper, as well as recording media such as OHP (Overhead Projector) sheets.

[0030] As shown in Figure 2, the image forming apparatus 1 comprises an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper transport unit 50, a fixing unit 60, a communication unit 71, a storage unit 72, a preheating unit 80, a front-side roller temperature sensor 91, a back-side roller temperature sensor 92, a paper temperature sensor 93, and a control unit 101.

[0031] The image reading unit 10 comprises an automatic document feeder (ADF) 11 and a document image scanning device 12, which is a scanner. The image reading unit 10 generates input image data based on the reading results from the document image scanning device 12. This input image data is then subjected to predetermined image processing by the image processing unit 30.

[0032] The automatic document feeder 11 transports documents placed in the document tray using a transport mechanism and sends them to the document image scanner 12. The automatic document feeder 11 can continuously scan images (including both sides) of multiple documents placed in the document tray at once. The automatic document feeder 11 is not limited to scanning single-sided images of multiple documents placed in the document tray, but may also continuously scan double-sided images at once.

[0033] The document image scanning device 12 optically scans a document transported from the automatic document feeder 11 onto the contact glass or a document placed on the contact glass. The document image scanning device 12 forms an image of the reflected light from the document onto the light-receiving surface of a CCD (Charge Coupled Device) sensor and reads the document image.

[0034] The operation display unit 20 consists of a touch panel liquid crystal display (LCD) and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, image status displays, and the operating status of each function in accordance with display control signals input from the control unit 101. The operation unit 22 is equipped with various operation keys such as a numeric keypad and a start key, and accepts various input operations from the user and outputs operation signals to the control unit 101.

[0035] The image processing unit 30 includes a circuit that performs digital image processing on the input image data according to the initial settings or user settings. For example, under the control of the control unit 101, the image processing unit 30 performs gradation correction based on gradation correction data. This gradation correction data is sometimes called a gradation correction table. In addition to gradation correction, the image processing unit 30 also performs various correction processes on the input image data, such as color correction and shading correction, as well as compression processing. The image forming unit 40 is controlled based on the input image data that has undergone these processes.

[0036] The image forming unit 40 comprises an image forming unit 41 and an intermediate transfer unit 42. The image forming unit 41 forms an image using colored toners of the Y, M, C, and K components based on the input image data.

[0037] The image forming units 41Y, 41M, 41C, and 41K for the Y, M, C, and K components have similar configurations. For the sake of illustration and explanation, common components are indicated by the same reference numeral, and when distinguishing them, Y, M, C, and K are added to the reference numerals. In Figure 1, only the components of the image forming unit 41Y for the Y component are given reference numerals, while the components of the other image forming units 41M, 41C, and 41K are omitted.

[0038] The image forming unit 41 includes an exposure device (not shown), a developing device (not shown), a photoreceptor drum 413, a charging device (not shown), and a drum cleaning device (not shown).

[0039] The photoreceptor drum 413 is a negatively charged organic photoreceptor in which an undercoat layer, a charge generation layer, and a charge transport layer are sequentially laminated on the circumferential surface of an aluminum conductive cylindrical aluminum tube. The charge generation layer consists of an organic semiconductor in which a charge generation material is dispersed in a resin binder, and generates a pair of positive and negative charges by exposure using an exposure apparatus. For example, the charge generation material is a phthalocyanine pigment, and the resin binder is polycarbonate. The charge transport layer consists of an electron-donating nitrogen-containing compound, which is a hole-transporting material, dispersed in a resin binder, and transports the positive charge generated in the charge generation layer to the surface of the charge transport layer.

[0040] The charging device uniformly charges the surface of the photoconductor drum 413 to a negative polarity. The exposure device, for example, consists of a semiconductor laser and irradiates the photoconductor drum 413 with laser light corresponding to the image of each color component. Positive charges are generated in the charge generation layer of the photoconductor drum 413 and transported to the surface of the charge transport layer, thereby neutralizing the negative charge on the surface of the photoconductor drum 413. Electrostatic latent images of each color component are formed on the surface of the photoconductor drum 413 due to the potential difference with the surroundings.

[0041] The developing device is a two-component developing device that forms a toner image by visualizing an electrostatic latent image by depositing toner of each color component onto the surface of the photoreceptor drum 413.

[0042] The drum cleaning device has a drum cleaning blade that slides against the surface of the photoreceptor drum 413, and removes any remaining toner after primary transfer from the surface of the photoreceptor drum 413.

[0043] The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller (not shown), a plurality of support rollers (not shown), a secondary transfer roller 424, and a belt cleaning device (not shown).

[0044] The intermediate transfer belt 421 is an endless belt and is stretched in a loop shape over a plurality of support rollers. At least one of the plurality of support rollers is a drive roller, and the others are driven rollers. For example, the drive roller is preferably a roller positioned downstream in the belt travel direction from the primary transfer roller for component K. This makes it easier to maintain a constant belt travel speed in the primary transfer section. As the drive roller rotates, the intermediate transfer belt 421 travels at a constant speed in the direction of arrow A.

[0045] The primary transfer rollers are positioned on the inner circumferential side of the intermediate transfer belt 421, facing the photoreceptor drums 413 for each color component. The primary transfer rollers are pressed against the photoreceptor drums 413 with the intermediate transfer belt 421 in between. This forms a primary transfer nip for transferring the toner image from the photoreceptor drums 413 to the intermediate transfer belt 421.

[0046] The secondary transfer roller 424 is positioned on the outer circumferential surface side of the intermediate transfer belt 421, opposite the backup roller 423B which is located downstream of the drive roller in the belt travel direction. The secondary transfer roller 424 is pressed against the backup roller (not shown) with the intermediate transfer belt 421 in between. This forms a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the paper P.

[0047] As the intermediate transfer belt 421 passes over the primary transfer nip, the toner image on the photoreceptor drum 413 is sequentially superimposed onto the intermediate transfer belt 421 and primary transferred. Specifically, by applying a primary transfer bias to the primary transfer roller and applying a charge with the opposite polarity to the toner to the back side of the intermediate transfer belt 421, that is, the side that contacts the primary transfer roller, the toner image is electrostatically transferred to the intermediate transfer belt 421.

[0048] Subsequently, as the paper P passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is transferred to the paper P. Specifically, a secondary transfer bias is applied to the secondary transfer roller 424, and a charge with the opposite polarity to the toner is applied to the back side of the paper P, that is, the side that contacts the secondary transfer roller 424, thereby electrostatically transferring the toner image to the paper P. The paper P on which the toner image has been transferred is then transported toward the fuser unit 60.

[0049] The belt cleaning device (not shown) has a belt cleaning blade that slides against the surface of the intermediate transfer belt 421 and removes residual transfer toner remaining on the surface of the intermediate transfer belt 421 after secondary transfer. Alternatively, instead of the secondary transfer roller 424, a configuration in which the secondary transfer belt is stretched in a loop between a plurality of support rollers including the secondary transfer roller (a so-called belt-type secondary transfer unit) may be adopted.

[0050] The paper transport unit 50 comprises a paper feeding unit 51, a paper discharge unit 52, and a transport path unit 53. The paper feeding unit 51 has a feed roller 51a that feeds out the rolled paper P downstream.

[0051] The paper feeding unit 51 feeds the paper P to the downstream transport path unit 53 via the preheating unit 80. The transport path unit 53 has transport rollers 53a that hold and transport the paper P, and transports the paper P to the image forming unit 40. The transport path unit 53 may also have a paper tensioning roller (not shown) that applies tension to the paper P, and a meandering adjustment roller (not shown) that adjusts the meandering of the paper P. In the image forming unit 40, the toner image on the intermediate transfer belt 421 is transferred collectively to one side of the paper P, and a fixing process is performed in the fixing unit 60. The paper discharge unit 52 has a winding roller 52a that winds the image-formed paper P into a roll.

[0052] The fuser unit 60 heats and pressurizes the paper P, which has been transported after the toner image has been secondarily transferred, using a fuser nip 65, thereby fixing the toner image to the paper P. The fuser unit 60 is arranged as a unit within the fuser unit, i.e., the housing.

[0053] The fixing unit 60 comprises an upper fixing unit 60A, a lower fixing unit 60B, and a heating source 60C. The upper fixing unit 60A has a fixing surface side member positioned on the fixing surface side of the paper P, that is, the surface side where the toner image is formed. The lower fixing unit 60B has a back side support member positioned on the back side of the paper P, that is, the side opposite the fixing surface. When the back side support member is pressed against the fixing surface side member, a fixing nip 65 is formed that grips and transports the paper P.

[0054] The communications unit 71 controls communications such as LAN (Local Area Network) and WAN (Wide Area Network).

[0055] The storage unit 72 stores various data necessary for controlling the image forming apparatus 1. For example, the storage unit 72 is composed of non-volatile memory such as flash memory or a hard disk drive.

[0056] The preheating unit 80 heats at least the surface of the paper P before forming a toner image on the paper P. The preheating unit 80 may be either a contact type or a non-contact type. Details of the preheating unit 80 will be described later.

[0057] The front-side roller temperature sensor 91, the back-side roller temperature sensor 92, and the paper temperature sensor 93 are temperature sensors positioned at various locations in the image forming apparatus 1. For example, the front-side roller temperature sensor 91, the back-side roller temperature sensor 92, and the paper temperature sensor 93 are general non-contact type temperature sensors. Details of the front-side roller temperature sensor 91, the back-side roller temperature sensor 92, and the paper temperature sensor 93 will be described later.

[0058] The control unit 101 comprises a CPU (Central Processing Unit) 102, a ROM (Read Only Memory) 103, and a RAM (Random Access Memory) 104. The CPU 102 reads a program corresponding to the processing content from the ROM 103, loads it into the RAM 104, and works in cooperation with the loaded program to centrally control the operation of each block of the image forming apparatus 1. At this time, various data stored in the storage unit 72 are referenced.

[0059] The control unit 101 transmits and receives various data to and from external devices connected to a communication network such as a LAN or WAN, such as a personal computer, via the communication unit 71. For example, the control unit 101 receives image data transmitted from an external device and forms a toner image on the paper P based on this image data.

[0060] The control unit 101 controls the drive current supplied to the drive motor (not shown) that rotates the photoreceptor drum 413, thereby rotating the photoreceptor drum 413 at a constant peripheral speed.

[0061] [Configuration of the fixing unit] Referring to Figure 3, the configuration of the fixing unit 60 will be described. Figure 3 is a schematic diagram showing the configuration of the fixing unit in the first embodiment. In this embodiment, the fixing method is described as a belt fixing method, but it is not limited to this.

[0062] As shown in Figure 3, the upper fixing section 60A comprises an endless fixing belt 61, which is a fixing surface side member, a heating roller 62, and an upper pressure roller 63. The fixing belt 61 is stretched between the heating roller 62 and the upper pressure roller 63 while maintaining a predetermined tension.

[0063] For example, the fixing belt 61 has a base made of PI (polyimide) with its outer surface covered with a heat-resistant silicone rubber as an elastic layer, and the surface layer is covered or coated with a tube of PFA (perfluoroalkoxy), which is a heat-resistant resin.

[0064] The fixing belt 61 comes into contact with the paper P on which the toner image has been formed, and heats and fixes the toner image to the paper P within a predetermined temperature range.

[0065] The heating roller 62 heats the fixing belt 61. For example, the heating roller 62 incorporates a heating source 60C, which is a halogen heater. The heating roller 62 is covered with a resin layer in which the outer surface of a cylindrical core made of aluminum is coated with PTFE (polytetrafluoroethylene).

[0066] The temperature of the heating source 60C is controlled by the control unit 101. The heating source 60C heats the heating roller 62, which in turn heats the fixing belt 61. This heats the toner formed on the paper P. For example, the control unit 101 controls the fixing temperature of the toner by controlling the heating source 60C based on an on / off pattern of half-wave units of the duty cycle.

[0067] For example, the upper pressure roller 63 is made of a solid core metal made of iron or other metal, covered with an elastic layer. For example, the material of the elastic layer can be heat-resistant silicone rubber. Alternatively, the elastic layer may be a resin layer in which heat-resistant silicone rubber is coated with PTFE.

[0068] The lower fixing section 60B has a lower pressure roller 64 that constitutes the back-side support member. The lower pressure roller 64 has an outer surface of a base material layer made of Al (aluminum) covered with an elastic layer. For example, the material of the elastic layer may be heat-resistant silicone rubber. Alternatively, the elastic layer may be constructed by covering the heat-resistant silicone rubber with a resin layer of PFA tubing as a surface release layer.

[0069] The lower pressure roller 64 may have a built-in heating source, such as a halogen heater. When this heating source generates heat, the lower pressure roller 64 is heated. This heats the toner formed on the paper P. For example, the control unit 101 controls the toner fixing temperature by controlling the heating source based on an on / off pattern in half-wave units of the duty cycle.

[0070] The lower pressure roller 64 is pressed against the upper pressure roller 63 with a predetermined fixing load via the fixing belt 61. In this way, a fixing nip 65 is formed between the upper pressure roller 63 and fixing belt 61 and the lower pressure roller 64, which grips and conveys the paper P.

[0071] The lower pressure roller 64 is connected to a motor and gears, and the driving force of the motor is transmitted to the lower pressure roller 64. The control unit 101 outputs a drive signal to the motor that drives the lower pressure roller 64 and controls the peripheral speed of the lower pressure roller 64.

[0072] The upper fixing unit 60A, the lower fixing unit 60B, and the heating source 60C heat and pressurize the paper P with the fixing nip 65 while transporting it, thereby fixing the unfixed toner image onto the paper P.

[0073] [Configuration of the preheating section] The configuration of the preheating unit 80 will be described below.

[0074] The preheating unit 80 prevents fixing under-offset, image unevenness, and image formation defects. As shown in Figure 1, the preheating unit 80 is positioned on the upstream side of the intermediate transfer unit 42 in the paper transport direction (hereinafter referred to as the "upstream side") and on the downstream side of the paper feeding unit 51 in the paper transport direction (hereinafter referred to as the "downstream side").

[0075] The preheating unit 80 has a separate housing 85 from the main body of the image forming apparatus 1. In other words, the preheating unit 80 is housed in a separate housing from the main body of the image forming apparatus 1, which consists of the image forming unit 40 and the fixing unit 60. For example, the housing 85 is a box-shaped housing made of the same material as the main body of the image forming apparatus 1. This allows the image forming apparatus 1 to suppress the temperature rise of the main body due to preheating and reduce toner adhesion. Furthermore, the image forming apparatus 1 can suppress heat dissipation in the preheating unit 80. Note that the preheating unit 80 may not have a housing 85 and may be housed in the same housing as the main body of the image forming apparatus 1.

[0076] Figure 4 is a schematic diagram showing a first example of the configuration of the preheating section in the first embodiment. As shown in Figure 4, the preheating section 80 includes a front-side roller 81 and a back-side roller 82. In the preheating section 80, the front-side roller 81 is located downstream of the back-side roller 82.

[0077] The surface-side roller 81 is positioned to contact the surface of the paper P and heat the surface of the paper P. The surface-side roller 81 incorporates a surface-side heating source 83 that heats the surface side of the paper P. For example, the surface-side heating source 83 is a halogen heater. The diameter of the surface-side roller 81 is larger than the diameter of the back-side roller 82. A surface-side roller temperature sensor 91 is positioned near the surface-side roller 81 to detect the temperature of the surface-side roller 81.

[0078] The back-side roller 82 is positioned so as to contact the back surface of the paper P at a position not facing the front-side roller 81, and heats the back surface of the paper P. The back-side roller 82 incorporates a back-side heating source 84 that heats the back surface of the paper P. For example, the back-side heating source 84 is a halogen heater. The back-side roller 82 is positioned so as not to face the front-side roller 81 with the paper P in between. A back-side roller temperature sensor 92 is positioned near the back-side roller 82 to detect the temperature of the back-side roller 82. This increases the contact area with the paper P, thereby improving heating efficiency. Furthermore, the behavior of the paper P is stabilized and paper wrinkles are reduced, so the paper temperature can be controlled with high precision. For example, if the paper P is a multilayer media, the preheating section 80 may be configured as shown in Figure 4. Note that the paper temperature corresponds to the "recording medium temperature" described in the claim.

[0079] Figure 5 is a schematic diagram showing a second example of the configuration of the preheating section in the first embodiment. As shown in Figure 5, the back-side roller 82 may be positioned opposite the front-side roller 81 and in contact with the back surface of the paper P, thereby heating the back surface of the paper P. That is, the front-side roller 81 and the back-side roller 82 are positioned opposite each other with the paper P in between. The diameter of the front-side roller 81 is equal to the diameter of the back-side roller 82. This stabilizes the behavior of the paper P and reduces paper wrinkling, so the paper temperature can be controlled with high precision. For example, if the paper P is a single sheet, the preheating section 80 may be configured as shown in Figure 5.

[0080] Although the preheating unit 80 is described as heating both the front and back surfaces of the paper P, the preheating unit 80 may heat only the front surface of the paper P. In this case, the preheating unit 80 does not need to be equipped with a back-side roller 82.

[0081] <Control of preheating> Refer to Figures 6 and 7 to explain the control of preheating. For example, when printing on paper P placed in a low-temperature environment, the paper temperature changes (decreases) during printing, making it difficult to stabilize the temperature of the paper P as it enters the fuser nip 65. Also, when handling thick paper or multilayer media, heating from only the back side is insufficient, and the paper temperature may not stabilize. As a result, fuser under-offset may occur. Therefore, the image forming apparatus 1 is designed to detect the temperature of the paper P before it enters the fuser nip 65, both before and during printing, and to control preheating.

[0082] The paper temperature sensor 93 is a temperature detection unit that detects the paper temperature before fixing the toner image to the paper P. For example, the paper temperature sensor 93 is located above the entrance of the fixing unit 60 and detects the surface temperature of the paper P just before it enters the fixing nip 65. The paper temperature sensor 93 outputs the detected paper temperature to the control unit 101.

[0083] The control unit 101 controls heating by the preheating unit 80 during printing based on the paper temperature detected by the paper temperature sensor 93. For example, the control unit 101 controls the front-side heating source 83 and the back-side heating source 84 so that the paper temperature input from the paper temperature sensor 93 maintains a preset target temperature. In this case, the control unit 101 can utilize general feedback control such as PID control. The target temperature can be arbitrarily set by the user using the operation display unit 20.

[0084] Figure 6 is a graph showing the change in paper temperature in the first embodiment. In Figure 6, the vertical axis represents the paper temperature before entering the fixing nip 65, and the horizontal axis represents the paper feeding distance. In Figure 6, the solid line represents the case when preheating is controlled by the image forming apparatus 1, the dashed line represents the case when preheating is controlled by the method described in Patent Document 1, and the double dashed line represents the case when no preheating is performed.

[0085] As shown by the dashed line in Figure 6, if preheating is not performed, the paper temperature drops significantly after printing begins. As shown by the dashed line, when preheating is controlled by the method described in Patent Document 1, the paper temperature drops gradually after printing begins. In contrast, as shown by the solid line, when preheating is controlled by the image forming apparatus 1, the paper temperature rises to the target temperature after printing begins and is maintained at the target temperature.

[0086] Figure 7 is a flowchart illustrating the preheating control process in the first embodiment. As shown in Figure 7, in step S1, the user submits a job, such as printing, to the image forming apparatus 1. That is, the user uses the operation display unit 20 to set the job to the control unit 101.

[0087] In step S2, the user uses the operation display unit 20 to set the process conditions in the control unit 101. For example, the process conditions include the target temperature and the characteristic information of the paper P, which will be described later.

[0088] In step S3, the control unit 101 commands the paper transport unit 50 to transport the paper P. In response to this command, the paper transport unit 50 starts transporting the paper P.

[0089] In step S4, the control unit 101 starts printing. In other words, the control unit 101 centrally controls the operation of each block of the image forming apparatus 1 in order to start the print job set in step S1.

[0090] In step S5, the paper temperature sensor 93 detects the paper temperature before it enters the fuser nip 65.

[0091] In step S6, the control unit 101 determines whether the paper to be printed P is the second page or later. If the paper to be printed P is not the second page or later (No in step S6), the control unit 101 proceeds to step S7. If the paper to be printed P is the second page or later (Yes in step S6), the control unit 101 proceeds to step S9.

[0092] In step S7 (detection step), the control unit 101 controls the heating by the preheating unit 80 so that the paper temperature detected by the paper temperature sensor 93 maintains the target temperature.

[0093] In step S8, the control unit 101 prints on paper P. In other words, the control unit 101 centrally controls the operation of each block of the image forming apparatus 1 so that the first page is printed.

[0094] In step S9 (calculation step), the control unit 101 calculates the temperature difference between the target temperature and the paper temperature.

[0095] In step S10, the control unit 101 adds the temperature difference calculated in step S9 to the target temperature as a correction amount. The target temperature to which the correction amount has been added may be referred to as the temperature with the correction amount added.

[0096] In step S11 (heating step), the control unit 101 controls the heating by the preheating unit 80 so that the paper temperature detected by the paper temperature sensor 93 maintains the corrected temperature. Then, the preheating unit 80 heats at least the surface of the paper P to a temperature based on the corrected temperature and the target temperature.

[0097] In step S12 (printing step), the control unit 101 prints on paper P. In other words, the control unit 101 centrally controls the operation of each block of the image forming apparatus 1 so that the second page and subsequent pages are printed.

[0098] In step S13, the control unit 101 determines whether the printed paper P is the last page. If the printed paper P is not the last page (No in step S13), the control unit 101 returns to the process in step S5. If the printed paper P is the last page (Yes in step S13), the control unit 101 terminates printing.

[0099] As described above, the image forming apparatus 1 according to the first embodiment detects the temperature of the paper P before it enters the fixing nip 65, whether before or during printing, and controls preheating so that the paper temperature remains constant. This allows the image forming apparatus 1 to stabilize the paper temperature even during printing. Furthermore, since the image forming apparatus 1 heats at least the surface of the paper P, it can stabilize the paper temperature even when handling cardboard or multilayer media.

[0100] Furthermore, the image forming apparatus 1 detects the paper temperature immediately before the fixing nip 65 and feeds it back to the control unit 101, thus achieving sufficient responsiveness. In contrast, the invention described in Patent Document 2 requires detecting and feeding back the paper temperature at a short distance, immediately before fixing the toner image and over the preheating stage, resulting in insufficient responsiveness. Consequently, in the invention described in Patent Document 2, if the paper temperature fluctuates before preheating, it is difficult to stabilize the paper temperature.

[0101] (Modification: Control of preheating) Refer to Figure 8 to explain a modified example of preheating control.

[0102] The paper temperature sensor 93 detects the temperature of the paper P before it is fed through the machine and enters the fuser nip 65. The control unit 101 may then start printing if the paper temperature detected by the paper temperature sensor 93 is equal to or above a preset target temperature.

[0103] Figure 8 is a graph showing the change in paper temperature in the modified example. In Figure 8, the dashed line represents the case where preheating is controlled using this modified method. Other aspects are the same as in Figure 6. As shown by the dashed line in Figure 8, when preheating is controlled using the modified method, printing starts only after the paper temperature reaches the target temperature, so the paper temperature is always maintained at the target temperature during printing.

[0104] (Second Embodiment) [Configuration of the image forming apparatus] Referring to Figure 9, the differences between the configuration of the image forming apparatus 1B according to the second embodiment and that of the first embodiment will be explained. Figure 9 is a schematic diagram showing the overall configuration of the image forming apparatus 1B according to the second embodiment.

[0105] The paper temperature sensors 93a to 93d detect the paper temperature at multiple locations. The control unit 101 then controls the heating by the preheating unit based on the paper temperature detected at multiple locations by the paper temperature sensors 93a to 93d.

[0106] The paper temperature sensor 93a is the same as the paper temperature sensor 93 in Figure 1. The paper temperature sensor 93b is positioned below the entrance of the fuser unit 60 and detects the temperature of the back surface of the paper P just before it enters the fuser nip 65. For example, the paper temperature sensor 93b is positioned opposite the paper temperature sensor 93a, with the paper P in between. In this case, the control unit 101 controls the heating by the preheating unit 80 for both the front and back surfaces of the paper P. That is, the control unit 101 controls the front-side heating source 83 based on the paper temperature of the front surface detected by the paper temperature sensor 93a, and controls the back-side heating source 84 based on the paper temperature of the back surface detected by the paper temperature sensor 93b. In this way, the image forming apparatus 1B can detect the temperature of both the front and back surfaces of the paper P, so it can appropriately control preheating even if the paper P has different materials on the front and back surfaces.

[0107] The paper temperature sensor 93c detects the paper temperature in the paper feeding unit 51, which feeds the paper P. For example, the paper temperature sensor 93c is located in the paper feeding unit 51 and detects the surface temperature of the paper P that is transported to the image forming unit 40. This allows the image forming apparatus 1B to detect the paper temperature early before preheating and feed the results back to the control unit 101, enabling it to reach the target temperature more quickly.

[0108] The paper temperature sensor 93d detects the temperature in the image forming unit 40, which forms a toner image on the paper P. For example, the paper temperature sensor 93d is positioned in front of the image forming unit 41 and detects the surface temperature of the paper P. This allows the image forming apparatus 1B to detect the paper temperature even before transferring the toner image and feed the results back to the control unit 101, thereby preventing toner melting due to overheating of the paper P.

[0109] Figure 10 is a graph showing the change in paper temperature in the second embodiment. In Figure 10, the dotted line represents the case where preheating is controlled by the image forming apparatus 1B. Other aspects are the same as in Figure 6. As shown in Figure 10, when a paper temperature sensor 93c is provided, the paper temperature can be detected early, so the paper temperature is kept constant in a short time after printing starts.

[0110] As described above, the image forming apparatus 1B according to the second embodiment can detect the paper temperature at multiple locations and feed it back to the control unit 101, thereby enabling more precise control of preheating.

[0111] (Third embodiment) [Configuration of the image forming apparatus] Referring to Figures 11 and 12, the differences in the configuration of the image forming apparatus 1C according to the third embodiment compared to the second embodiment will be explained. Figure 11 is a schematic diagram showing the overall configuration of the image forming apparatus 1C according to the third embodiment. Figure 12 is a block diagram showing the configuration of the main parts of the image forming apparatus 1C according to the third embodiment.

[0112] The control unit 101 receives the fixing failure determination result and controls heating by the preheating unit 80 based on the paper temperature and the fixing failure determination result. The fixing failure determination result is information indicating whether or not fixing failures such as fixing under-offset or gloss fluctuations have occurred. Note that gloss fluctuations indicate things like gloss being too strong or too weak. For example, a user visually determines the fixing failure and inputs the determination result to the control unit 101. Alternatively, the image forming apparatus 1C may be equipped with a fixing failure detection unit 110 that determines fixing failures.

[0113] For example, if an offset occurs, the control unit 101 raises the target temperature by a preset value. Also, if the gloss is too strong, the control unit 101 raises the target temperature by a preset value. On the other hand, if the gloss is too weak, the control unit 101 lowers the target temperature by a preset value.

[0114] The fixing failure detection unit 110 determines fixing failures from the image after the toner image has been fixed to the paper P, and outputs the fixing failure detection result to the control unit 101. The fixing failure detection unit 110 is located upstream of the paper discharge unit 52 and has a scanner that reads the image of the paper P transported from the fixing unit 60. The fixing failure detection unit 110 generates read image data based on the reading result of the paper P. The fixing failure detection unit 110 compares the read image data with the input image data of the image forming unit 40 and determines fixing failures. At this time, the fixing failure detection unit 110 can use general image processing, such as deep learning.

[0115] As described above, the image forming apparatus 1C according to the third embodiment can further stabilize the paper temperature by taking into account the result of determining fixing failure in the control of preheating.

[0116] (Fourth Embodiment) [Configuration of the image forming apparatus] Referring to Figures 13 and 14, the differences in the configuration of the image forming apparatus 1D according to the fourth embodiment compared to the second embodiment will be explained. Figure 13 is a schematic diagram showing the overall configuration of the image forming apparatus 1D according to the fourth embodiment. Figure 14 is a block diagram showing the configuration of the main parts of the image forming apparatus 1D according to the fourth embodiment.

[0117] The control unit 101 receives paper characteristic information and controls heating by the preheating unit 80 based on the paper temperature and the paper characteristic information of the paper P. The paper characteristic information of the paper P is information that represents the characteristics of the paper P and includes at least one of the type of paper P or the basis weight. For example, the user inputs the paper characteristic information of the paper P to the control unit 101. The image forming apparatus 1C may also be equipped with a paper characteristic detection unit 120 that detects the characteristics of the paper P.

[0118] Here, the heat transfer properties of the paper P can be determined from the type or basis weight of the paper P. Therefore, the control unit 101 changes the target temperature according to the type or basis weight of the paper P. If the basis weight of the paper P exceeds a predetermined threshold, the control unit 101 raises the target temperature by a preset value. On the other hand, if the basis weight of the paper P is below a predetermined threshold, the control unit 101 lowers the target temperature by a preset value.

[0119] The paper characteristic detection unit 120 detects characteristic information of the paper P and outputs it to the control unit 101. The paper characteristic detection unit 120 is located between the paper feeding unit 51 and the preheating unit 80 and detects characteristic information of the paper P transported from the paper feeding unit 51. For example, the paper characteristic detection unit 120 may be a sensor that measures the type and basis weight of the paper P.

[0120] As described above, the image forming apparatus 1D according to the fourth embodiment also takes into account the characteristic information of the paper P when controlling preheating, so the paper temperature can be further stabilized. [Explanation of Symbols]

[0121] 1,1B,1C,1D image forming device 101 Control Unit 80 Preheating section 81 Surface-side roller 82 Backside roller 93, 93a, 93b, 93c, 93d Paper temperature sensor (temperature detection unit) 110 Fixing failure detection unit 120 Paper characteristics detection unit

Claims

1. A temperature detection unit that detects the temperature of the recording medium before fixing the toner image onto the recording medium, A preheating unit that heats at least the surface of the recording medium before forming the toner image on the recording medium, A control unit controls heating by the preheating unit during printing based on the temperature of the recording medium detected by the temperature detection unit, An image forming apparatus equipped with the following features.

2. The preheating unit heats the front and back surfaces of the recording medium, The control unit controls heating by the preheating unit for the front and back surfaces of the recording medium, respectively. The image forming apparatus according to claim 1.

3. The temperature detection unit detects the temperature of the recording medium at multiple locations, The control unit controls the heating by the preheating unit based on the temperature of the recording medium detected at multiple locations by the temperature detection unit. The image forming apparatus according to claim 1.

4. The temperature detection unit detects the temperature of the recording medium in the image forming unit that forms the toner image on the recording medium and the paper feeding unit that feeds the recording medium. The image forming apparatus according to claim 3.

5. The temperature detection unit detects the temperature of the recording medium on the front and back surfaces of the recording medium. The image forming apparatus according to claim 3.

6. The temperature detection unit detects the temperature of the recording medium that is fed through the paper before printing and enters the fuser nip. The control unit starts printing when the temperature of the recording medium detected by the temperature detection unit is equal to or greater than a preset target temperature. The image forming apparatus according to claim 1.

7. The preheating unit has a housing separate from the main body of the image forming apparatus. The image forming apparatus according to claim 1.

8. The aforementioned preheating unit is A surface-side roller is positioned to contact the surface of the recording medium and heat the surface of the recording medium, A rear-side roller is positioned so as to contact the back surface of the recording medium at a position not facing the front-side roller, and heats the back surface of the recording medium. The image forming apparatus according to claim 1, comprising:

9. The aforementioned preheating unit is A surface-side roller is positioned to contact the surface of the recording medium and heat the surface of the recording medium, A rear-side roller is positioned opposite the front-side roller and in contact with the back surface of the recording medium, and heats the back surface of the recording medium. The image forming apparatus according to claim 1, comprising:

10. The control unit receives the result of determining a fixing failure and controls the heating by the preheating unit based on the fixing failure determination result in addition to the recording medium temperature. The image forming apparatus according to claim 1.

11. A fixing failure detection unit determines the fixing failure from the image after fixing the toner image onto the recording medium and outputs the fixing failure determination result to the control unit. The image forming apparatus according to claim 10, comprising:

12. The control unit receives characteristic information of the recording medium and controls heating by the preheating unit based on the recording medium temperature and characteristic information of the recording medium. The image forming apparatus according to claim 1.

13. The characteristic information of the recording medium includes at least one of the type of recording medium or the basis weight. The image forming apparatus according to claim 12.

14. A recording medium characteristic detection unit that detects characteristic information of the recording medium and outputs it to the control unit, The image forming apparatus according to claim 12, comprising:

15. A detection step to detect the temperature of the recording medium before fixing the toner image onto the recording medium, A calculation step in which the temperature difference between the recording medium temperature and a preset target temperature is calculated as a correction amount, A heating step of heating at least the surface of the recording medium at a temperature based on the correction amount and the target temperature, A printing step of printing on a recording medium whose surface has been heated, An image formation method that performs the following steps in order.

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