Image forming device

Abstract

To provide a technique that can prevent the occurrence of an image defect due to excessive fixing and faulty fixing.SOLUTION: An image forming apparatus comprises: an image carrier that carries a developer image; a transfer member that forms a transfer nip part with the image carrier and transfers the developer image from the image carrier to a recording material at the transfer nip part; a fixing unit that has a heater and fixes the developer image to the recording material by using heat of the heater; a temperature detection unit that detects a temperature of the fixing unit; and a control unit that controls power supplied to the heater so that the temperature detected by the temperature detection unit becomes a predetermined control target temperature. The image forming apparatus has an acquisition unit that acquires a temperature of the image carrier or the transfer member. The control target temperature is changed based on the temperature acquired by the acquisition unit.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] In recent years, there has been an increasing demand for double-sided printing functions in image forming devices, such as printers (e.g., laser printers, LED printers), and electrophotographic copiers (e.g., digital copiers), printers, and other devices. For example, Patent Document 1 discloses a technology that improves productivity during double-sided printing by alternately printing the front and back sides of both sides. However, during double-sided printing, the heated recording material passes through a heating device once, and then circulates within the image forming device, which can cause temperature rise within the device. To address this issue, Patent Document 2, for example, introduces a technology that suppresses image defects caused by temperature rise within the device by gradually changing the set temperature of the heating device at predetermined intervals for each specified number of sheets. Furthermore, Patent Document 3 proposes a device that changes the set temperature of the heating device depending on the warm-up state when multiple sheets are being printed, regardless of whether single-sided or double-sided printing is being performed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-030476 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-287566 [Patent Document 3] Patent No. 3125569 Summary of the Invention [Problem to be solved by the invention]

[0004] When the set temperature of the heating device is gradually changed by a predetermined temperature for each specified number of sheets, as in Patent Document 2, the following problems can occur. For example, consider the case where a double-sided printing job of several hundred sheets is intermittently processed. When an image forming apparatus is started, double-sided printing of several hundred sheets is completed, and then another double-sided printing job is performed immediately after that, the image forming apparatus is cooled down in the early stages of the first double-sided printing (e.g., sheets 1 to 10) during the first double-sided printing. Therefore, during the first double-sided printing, the target temperature of the heating device must be set higher to fuse the toner on the recording material. If the same target temperature setting as for the first double-sided printing is used for the second double-sided printing, the image forming apparatus will be warm, which may result in excessive heat being applied to the recording material and toner, resulting in image defects (hot offset). Hot offset refers to an image defect in which toner on the recording material adheres to the fixing film due to excessive heating (hereinafter referred to as over-fixing), and adheres to the recording material after one revolution of the fixing film.

[0005] On the other hand, if the temperature setting is maintained from the previous time paper was printed, the temperature setting may drop during double-sided printing, and then a long pause may occur, causing the image forming device to cool down before double-sided printing can be performed again. In this case, poor fixing (cold offset) may occur due to insufficient heat. Here, cold offset refers to a condition in which part of the toner image does not adhere to the recording material due to poor fixing ability, resulting in loss.

[0006] Furthermore, if the temperature control during double-sided printing as in Patent Document 2 and the control that sets the temperature according to the state of warmth of the heating device (hereinafter referred to as the warm-up state) as in Patent Document 3 are used independently to set the temperature, the temperature may be lowered more than necessary, which may also result in poor fixing.

[0007] In addition, as in Patent Document 2, when the set temperature of the heating device is changed stepwise by a predetermined temperature for each predetermined number of sheets, the target temperature when the first double-sided print job is processed is changed twice. When a job is taken over when processing the first double-sided print job, the following problem occurs: If the heated image carrier is removed from the printer between the first and second double-sided print jobs and replaced with an image carrier that has cooled to room temperature, cold offset occurs due to insufficient heat.

[0008] An example of a case where an image carrier needs to be replaced is when the image carrier reaches the end of its life and needs to be replaced with a new image carrier.

[0009] Furthermore, when the set temperature of the heating device is changed stepwise by a predetermined temperature for each predetermined number of sheets, as in Patent Document 2, there is a possibility that the previous warm-up state cannot be correctly determined when the power is turned on or when the printer returns from sleep mode. In such cases, the set temperature of the heating device may deviate from the optimum temperature, resulting in hot offset or cold offset.

[0010] The present invention aims to provide a technology that can suppress the occurrence of image defects due to over-fixing or poor fixing, even when the warm-up state of the image forming device or heating device changes due to differences in double-sided printing or printing pause intervals. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, an image forming apparatus according to the present invention comprises: an image carrier that carries a developer image; a transfer member that forms a transfer nip between itself and the image carrier and transfers the developer image from the image carrier to a recording material at the transfer nip; a fixing unit having a heater and fixing the developer image onto the recording material by using heat from the heater; a temperature detection unit that detects the temperature of the fixing unit; a control unit that controls the power supplied to the heater so that the temperature detected by the temperature detection unit becomes a predetermined control target temperature; In an image forming apparatus comprising: an acquisition unit that acquires the temperature of the image carrier or the transfer member, The control target temperature isThe higher the temperature acquired by the acquisition unit, the lower the temperature. It is characterized by being changed. In order to solve the above-mentioned problems, an image forming apparatus according to the present invention comprises: an image carrier that carries a developer image; a transfer member that forms a transfer nip between itself and the image carrier and transfers the developer image from the image carrier to a recording material at the transfer nip; a fixing unit having a heater and fixing the developer image onto the recording material by using heat from the heater; a temperature detection unit that detects the temperature of the fixing unit; a control unit that controls the power supplied to the heater so that the temperature detected by the temperature detection unit becomes a predetermined control target temperature; In an image forming apparatus comprising: an acquisition unit that acquires the temperature of the image carrier or the transfer member, The control target temperature is changed based on a first temperature change amount based on the temperature acquired by the acquisition unit, a second temperature change amount based on a time for which power is supplied to the heater, and a predetermined coefficient. 、 The first temperature change amount is set to an amount that increases as the temperature acquired by the acquisition unit increases, and the second temperature change amount is set to an amount that increases as the time for which power is supplied to the heater increases, and the control target temperature is changed to a temperature obtained by subtracting the first temperature change amount multiplied by the predetermined coefficient and the second temperature change amount multiplied by the predetermined coefficient from a reference target temperature. It is characterized by the following. In order to solve the above-mentioned problems, an image forming apparatus according to the present invention comprises: an image carrier that carries a developer image; a transfer member that forms a transfer nip between itself and the image carrier and transfers the developer image from the image carrier to a recording material at the transfer nip; a fixing unit having a heater and fixing the developer image onto the recording material by using heat from the heater; a temperature detection unit that detects the temperature of the fixing unit; a control unit that controls the power supplied to the heater so that the temperature detected by the temperature detection unit becomes a predetermined control target temperature; In an image forming apparatus comprising: an acquisition unit that acquires the temperature of the image carrier or the transfer member, The control target temperature is changed based on a larger amount of change between a first temperature change amount based on the temperature acquired by the acquisition unit and a second temperature change amount based on a time for which power is supplied to the heater. 、 The first temperature change amount is set to an amount that increases as the temperature acquired by the acquisition unit increases, and the second temperature change amount is set to an amount that increases as the time for which power is supplied to the heater increases, and the control target temperature is changed from a reference target temperature to a temperature obtained by subtracting the larger of the first temperature change amount and the second temperature change amount. It is characterized by 。 [Effects of the Invention]

[0014] As described above, according to the present invention, even if the warm-up state of the image forming device or heating device changes due to differences in double-sided printing or printing pause intervals, the occurrence of image defects due to over-fixing or poor fixing can be suppressed. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view showing the schematic configuration of an image forming apparatus according to a first embodiment. [Figure 2] Cross-sectional view showing the schematic configuration of a heating device [Figure 3] Schematic diagram of the heater configuration used in the heating device [Figure 4] Flowchart showing a method for setting a target fixing temperature [Figure 5] Relationship between image carrier temperature and target fixing temperature adjustment amount D [Figure 6] Schematic diagram of image patterns used in the comparison experiment [Figure 7] Results of comparative experiments using the control of Example 1 [Figure 8] Table showing the order and intervals of paper feed in the comparison experiment (2 sheets waiting double-sided) [Figure 9] Results of a comparative experiment using the control of Comparative Example 1 (fixing target temperature constant control) [Figure 10] Results of a comparative experiment using the control of Comparative Example 2 (number control A) [Figure 11] Results of a comparative experiment using the control of Comparative Example 3 (number control B) [Figure 12] Temperature transition of intermediate transfer belt when double-sided / single-sided / main unit is stopped [Figure 13] Flowchart for determining variable E for calculating intermediate transfer belt predicted value [Figure 14] FIG. 10 is a cross-sectional view showing the schematic configuration of an image forming apparatus according to a second embodiment. [Figure 15] Flowchart showing a method for setting a fixing target temperature in the third embodiment [Figure 16] Relationship between the temperature of the intermediate transfer belt and the target fixing temperature adjustment amount D1 [Figure 17] Relationship between heating device rotation time and target fixing temperature adjustment amount D2 [Figure 18] Results of comparative experiments using the control of Example 3 [Figure 19] Results of comparative experiment using control of Comparative Example 4 [Figure 20] Results of comparative experiment using control of Comparative Example 5 [Figure 21] Flowchart showing a method for setting a fixing target temperature in the fourth embodiment [Figure 22] Results of comparative experiments using the control of Example 4 [Figure 23] FIG. 10 is a diagram showing the relationship between the double-sided paper feed time and the fixing target temperature adjustment amount D1 in the fifth embodiment. [Figure 24] Results of comparative experiments using the control of Example 5 [Figure 25] Control block diagram in the first embodiment [Figure 26] 6 is a cross-sectional view of an image forming apparatus according to a sixth embodiment of the present invention; [Figure 27] Flowchart showing a method for setting a target temperature in Example 6 [Figure 28] Experimental results using the control of Example 6 [Figure 29] Experimental results using the control of Comparative Example 6 [Figure 30] Experimental results using the control of Comparative Example 7 [Figure 31] Experimental results using the control of Comparative Example 8 [Figure 32] 10 is a cross-sectional view of an image forming apparatus according to a seventh embodiment of the present invention; [Figure 33] A diagram showing the temperature transition of the photosensitive body (photosensitive drum) [Figure 34] Flowchart showing a method for setting a target temperature in the seventh embodiment [Figure 35] Relationship diagram between the temperature of the intermediate transfer body and the target temperature adjustment amount D [Figure 36] Experimental results using the control of Example 7 [Figure 37] Experimental results using the control of Example 7 [Figure 38] Experimental results using the control of Example 7 [Figure 39] FIG. 10 is a diagram showing the resistance-temperature characteristics of the intermediate transfer belt of Example 8. [Figure 40] Flowchart showing a method for setting a target temperature in the eighth embodiment DETAILED DESCRIPTION OF THE INVENTION

[0016] The following describes in detail exemplary embodiments of the present invention with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiments may be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions. In other words, the scope of the present invention is not limited to the following embodiments.

[0017] Example 1 <Explanation of image forming device> 1 is a cross-sectional view showing the schematic configuration of an image forming apparatus according to this embodiment. Image forming apparatuses to which the present invention can be applied include electronic devices such as laser printers, LED printers, and digital copiers. Examples of such an image forming apparatus include a photographic printer and a copier. In this embodiment, the present invention will be described as being applied to a color laser printer. The image forming apparatus according to this embodiment forms a multi-color toner image by superimposing toner images (developer images) of multiple colors, and then transfers and fixes the multi-color toner image onto a recording material, thereby forming a color image on the recording material.

[0018] The image forming unit of the image forming apparatus according to this embodiment forms an electrostatic latent image for each of the different monochromatic toner images constituting the multicolor toner image by illuminating the image with exposure light based on the exposure time converted by the image processing unit, and develops the electrostatic latent image to form a monochromatic toner image. The image forming unit then superimposes the monochromatic toner images of different colors onto one another to form a multicolor toner image, which is then transferred to a recording material. The fixing unit of the image forming apparatus fixes the multicolor toner image on the recording material.

[0019] The image forming unit in this embodiment has four image forming stations (hereinafter, "stations") that form multiple monochromatic toner images of different colors. Each station includes a photosensitive drum 22 as a first image carrier, an injection charger 23 as a primary charging unit, a scanner unit 24 as an exposure unit, a toner cartridge 25 as a toner container, a developing unit 26, and a primary transfer roller 27. In this embodiment, toners of four colors—yellow (Y), magenta (M), cyan (C), and black (K)—are used to form a monochromatic toner image of each color. Each station has the same configuration except for the toner color. In FIG. 1, the reference numerals of the components of each station are denoted with suffixes Y, M, C, and K to distinguish the corresponding colors of each station. However, in the following description, the suffixes may be omitted if there is no particular need to distinguish between the colors.

[0020] The above stations are arranged inline with respect to intermediate transfer belt 28. Also, as a configuration for supplying and conveying recording material 11 such as copy paper, a paper feed tray 12, paper feed roller 13, pair of registration rollers 14, registration sensor 15, secondary transfer roller 29, paper discharge roller 61, etc. are arranged. Also, a heating device (image heating device) 40 is arranged as a fixing unit. The operation of these is controlled by control unit 108.

[0021] The photosensitive drum 22 is constructed by coating the outer periphery of an aluminum cylinder with an organic photoconductive layer, and is rotated by the driving force of a drive motor (not shown). The drive motor rotates the photosensitive drum 22 clockwise in response to image formation operations. The outer diameter of the photosensitive drum 22 is 24 mm. Four injection chargers 23Y, 23M, 23C, and 23K are provided as primary charging means for each station to charge the yellow (Y), magenta (M), cyan (C), and black (K) photosensitive drums. Each injection charger 23Y, 23M, 23C, and 23K is provided with a sleeve 23YS, 23MS, 23CS, or 23KS.

[0022] Exposure light is sent from a scanner unit 24 to the photosensitive drum 22, selectively exposing the surface of the photosensitive drum 22 to light, thereby forming an electrostatic latent image. To visualize the electrostatic latent image, four developing units 26Y, 26M, 26C, and 26K are provided, each developing yellow (Y), magenta (M), cyan (C), and black (K) colors. Each developing unit 26Y, 26M, 26C, and 26K is provided with a sleeve 26YS, 26MS, 26CS, or 26KS. A power supply (not shown) applies a development voltage between the sleeve 26YS, 26MS, 26CS, or 26KS and the corresponding photosensitive drum 22Y, 22M, 22C, or 22K. During image formation, the photosensitive drum 22 rotates clockwise, and the developing unit 26 develops a toner image of each color onto the electrostatic latent image formed on the photosensitive drum 22.

[0023] The intermediate transfer belt 28, which is a second image carrier and an intermediate transfer member, is the first transfer member. The primary transfer roller 27 contacts the photosensitive drum 22 with a pressing force, forming a primary transfer portion, which is a first transfer nip portion. A primary transfer voltage is applied between the primary transfer roller 27 and the corresponding photosensitive drum 22 from a power source (not shown). The intermediate transfer belt 28 is an endless, circular belt with an inner peripheral length of 790 mm. It is made primarily of polyimide and has a thickness of 65 μm. During image formation, the intermediate transfer belt 28 and primary transfer roller 27 rotate relative to the photosensitive drum 22, and perform a primary transfer of the toner image on the photosensitive drum 22 (on the first image carrier) onto the intermediate transfer belt 28.

[0024] The recording material 11 stored in the paper feed tray 12 is transported by the paper feed roller 13 and reaches the pair of registration rollers 14, where it is detected by the registration sensor 15. During image formation, the recording material 11 is transported in accordance with the timing detected by the registration sensor 15 and the timing at which the multicolor toner image on the intermediate transfer belt 28 reaches the secondary transfer roller 29. Here, the recording material 11 reaches the secondary transfer roller 29 from the pair of registration rollers 14.

[0025] The intermediate transfer belt 28 is tensioned by support rollers 33 (33a, 33b, 33c). The portion of the intermediate transfer belt 28 tensioned by the support roller 33a comes into contact with the secondary transfer roller 29, which is the opposing member (second transfer member), forming a second transfer nip. In the secondary transfer process, the recording material 11 is sandwiched and conveyed through this secondary transfer nip, and the multicolor toner image on the intermediate transfer belt 28 (on the second image carrier) is transferred to the recording material 11. The support roller 33a is made of an iron pipe (Φ18, thickness 1.5 mm). The secondary transfer roller 29 has a cross-sectional configuration in which a core (Φ8) is mounted on an elastic layer made of NBR hydrin rubber with a thickness of 4 mm, and the surface length (axial direction) of the elastic layer is 220 mm. The secondary transfer roller 29 contacts the intermediate transfer belt 28 by a contact mechanism (not shown), with a contact pressure of 30 N. Here, the contact width between the secondary transfer roller 29 and the intermediate transfer belt 28 when the recording material 11 is not being conveyed is 2.0 mm, and the contact width between the intermediate transfer belt 28 and the recording material 11 when the recording material 11 is being conveyed is 5.0 mm. A secondary transfer voltage is applied between the secondary transfer roller 29 and the intermediate transfer belt 28 from a power source (not shown).

[0026] Here, the belt thermistor 30 is a transfer unit temperature detection means for detecting the temperature of the intermediate transfer belt 28. The control unit 108 has an acquisition unit that acquires the temperature of the image carrier or transfer member, and the belt thermistor 30 is an example of a temperature detection member used when the acquisition unit acquires the temperature of the intermediate transfer belt 18 as an image carrier. The specific configuration of the temperature detection member is not limited to the configuration described here. The transport guide 32 is a guide member for transporting the recording material 11 from the secondary transfer unit to the heating device 40.

[0027] The heating device 40, which serves as a fixing process, heats, melts, and fixes the toner image on the recording material 11 by sandwiching and transporting it, and the recording material 11 that has been fixed by the heating device 40 reaches the double-sided flapper 31. The image forming apparatus according to this embodiment has a double-sided printing mechanism that can perform a single-sided printing operation as a single-sided image formation operation and a double-sided printing operation as a double-sided image formation operation. The double-sided flapper 31 is a movable guide member that switches the transport direction of the recording material 11 depending on the printing operation. The double-sided flapper 31 can switch between position a and position b by the operation of an electromagnetic solenoid (not shown) by the control unit 108.

[0028] When the recording material 11 is a recording material on which an image is formed only on one side (first recording material), the double-sided flapper 31 is set to position a. When the double-sided flapper 31 is set to position a, the recording material 11 is discharged by a discharge roller 61 onto a discharge tray 62 outside the image forming apparatus, and the image forming operation is completed. When the recording material 11 is a recording material on which an image is formed on both sides (second recording material), the double-sided flapper 31 is set to position b. When the double-sided flapper 31 is set to position b, the recording material 11 is printed for the first time with a developer image transferred only on one side in automatic double-sided printing. After heat fixing, the recording material 11 is conveyed to the switchback roller 63 to reverse its conveying direction. The switchback roller 63 rotates forward (clockwise in FIG. 1) until the trailing edge of the recording material 11 passes the double-sided flapper 31, and then rotates reverse (counterclockwise in FIG. 1) after passing through. Simultaneously with the reverse rotation of the switchback roller 63, the double-sided flapper 31 switches to position a, and the recording material 11 is conveyed toward the double-sided rollers 64 and 65 in the double-sided conveyance path. From the double-sided rollers 64 and 65, the recording material 11 is conveyed to the double-sided refeed roller 66 and reaches the pair of registration rollers 14 again. Here, the other unprinted side of the recording material similarly undergoes the aforementioned secondary transfer process and fixing process (second heat fixing), whereby an image is formed. The double-sided flapper 31 is then set to position a, and the recording material is discharged onto the discharge tray 62, completing the image forming operation. In the following description, the first printed side in double-sided printing will be referred to as the first side, and the side reversed by the switchback and printed a second time will be referred to as the second side.

[0029] <Explanation of the heating device configuration> The heating device 40 will be described using FIG. 2(a). The heating device 40 includes a cylindrical fixing film 41 serving as a fixing member and a heater 42 serving as a heating member disposed within the interior space of the fixing film 41 and in contact with the inner surface. The heater 42 is held by a holding member 43, which also functions as a guide for guiding the rotation of the fixing film 41. The stay 44 is made of a highly rigid metal and applies pressure from a pressure spring (not shown) to the holding member 43 in the direction of a pressure roller 45 serving as a pressure member to form a fixing nip N in which toner on the recording material 11 is heated and fixed. The recording material 11 is sandwiched in the fixing nip N formed between the outer circumferential surface of the pressure roller 45 and the outer circumferential surface of the fixing film 41, and the toner image is fixed thereon using the heat of the heater 42. The heater 42, holding member 43, and stay 44 constitute a heater unit 46. Note that other members, such as a heat transfer member, may be interposed between the fixing film 41 and the heater 42.

[0030] Here, the total pressure of the pressure springs was 250 N, and the width of the fixing nip N in the recording material conveyance direction was set to 9.0 mm. A drive gear (not shown) is attached to the end of the pressure roller 45, and the pressure roller 45 receives power from a motor (not shown) and rotates clockwise. As the pressure roller 45 rotates, the fixing film 41 is rotated counterclockwise, and the recording material 11 carrying the toner image is heated and fixed while being sandwiched and conveyed in the direction of the arrow in the nip N.

[0031] The fixing film 41 had an outer diameter of 24 mm and a 60 μm-thick polyimide resin base layer, a 300 μm-thick elastic layer made of heat-conducting rubber, and a 20 μm-thick release layer made of PFA tubing. The pressure roller 45 had an outer diameter of 25 mm and a 17 mm-thick iron core, a 4 mm-thick elastic layer made of silicone rubber, and a 40 μm-thick release layer made of PFA tubing. The fixing thermistor Th was a temperature detector for non-contact detection of the surface temperature of the fixing film 41 and was installed in the center of the fixing film 41 in a direction perpendicular to the recording material conveyance direction. The fixing thermistor Th is an example of a temperature detector for detecting the temperature of the fixing section, and the specific configuration of the temperature detector is not limited to the configuration described here. During normal use, power supply to the heater 42 begins when the pressure roller 45 starts rotating, and the temperature of the heater 42 rises, causing the inner surface temperature of the fixing film 41 to also rise.

[0032] The control unit 108 controls the heater 42 as a fixing target temperature control unit that controls the target temperature during the fixing process and as a power control unit. That is, a target value (fixing target temperature) of the temperature detected by the fixing thermistor Th is determined as the control target temperature so that the surface temperature of the fixing film 41 becomes a predetermined temperature, and the input power is controlled so that the temperature detected by the fixing thermistor Th becomes the target value.

[0033] The structure of the heater 42 will be described using the schematic diagrams of FIGS. 3(a) and (b). FIG. 3(a) is a cross-sectional view of the heater 42. The heater 42 has a substrate (base material) 401 made of a 0.6 mm thick aluminum nitride ceramic substrate arranged so that the long side (longitudinal direction) is perpendicular to the conveyance direction of the recording material 11. The substrate 401 has a longitudinal width of 260 mm and a transverse width (paper feed direction) of 9 mm. The front side of the heater 42, which contacts the fixing film 41, has a sliding glass layer 404 with a thickness of 15 μm. The sliding glass layer 404 contacts the fixing film 41 via fluorine grease (not shown), providing excellent sliding properties. The rear side of the heater 42 has a resistance heating layer 402 with a thickness of 10 μm and a protective glass 403 with a thickness of 50 μm. Resistance heating layer 402 is formed by applying a conductive paste containing a silver-palladium (Ag / Pd) alloy onto aluminum nitride substrate 401 by screen printing and then firing it.

[0034] FIG. 3(b) is a schematic diagram showing the planar configuration of the heater as viewed from the rear side. The resistive heating layer 402, which is a resistive heating element that generates heat when current is applied, is formed in a strip shape along the longitudinal direction of the substrate 401. A protective glass 403 (dotted line) covers the resistive heating layer 402 and the conductor portion 406 to ensure insulation. The resistive heating layer 402 of the heater 42 generates heat when current is applied from an external power source between the electrode portions 405a and 405b. The heating area A in the longitudinal direction heated by the resistive heating layer 402 is 220 mm. In this example, the power supply voltage of the external power source is 120 V, and the resistance of the heater 42 is set to 10 Ω. To measure the fusing power consumption described below, a Yokogawa Meters & Instruments WT310 power meter is connected via a cable (not shown) that supplies power to the electrode portions 405a and 405b.

[0035] During single-sided printing, the heating device performs a single-sided fixing operation to heat a first recording material on which an image is formed only on one side, and during double-sided printing, it performs a double-sided fixing operation to heat a second recording material on which an image is formed on both sides. In the double-sided fixing operation, the recording material to be double-sided printed is heated a first time with a developer image transferred to only one side, and then heated a second time with a developer image transferred to the other side. Note that when double-sided printing is performed continuously on multiple recording materials, a continuous double-sided fixing operation can be performed in which the second heating of the preceding recording material is performed after the first heating of the subsequent recording material.

[0036] FIG. 25 is a block diagram that schematically shows the control configuration of the image forming apparatus according to this embodiment. [Control block configuration] 25 is a control block diagram of this embodiment. Video controller 120 receives and processes image information and print instructions transmitted from external device 501, such as a host computer. When video controller 120 receives image information and print instructions transmitted from external device 501, it creates information necessary for the image forming apparatus to perform a print operation, such as paper size information and number of prints, and transmits this information to control unit 108. Based on this information, control unit 108 operates temperature adjustment control unit 505, toner image control unit 503, etc., to perform printing.

[0037] In response to instructions from the video controller 120, the image forming control unit 502 controls preparatory operation 1 in response to a preparatory operation instruction issued before an image forming operation is instructed, preparatory operation 2 in response to a print mode issued after an image forming operation is instructed, and the image forming operation. In the preparatory operation, the heating device 40 and the scanner unit 24 are started to be driven. In preparatory operation 2, preparatory operations necessary for the image forming operation that were not executed in preparatory operation 1 are executed. Specifically, in preparatory operation 2, the photosensitive drum 22, primary transfer roller 27, developing means 26, intermediate transfer belt 28, and secondary transfer roller 29 are started to be driven. The print mode refers to image forming conditions in accordance with the type of recording material, and includes the conveying speed, transfer conditions, target temperature for fixing, etc.

[0038] The toner image control unit 503 controls the driving of various components of the image forming unit and the fixing unit to form a toner image in accordance with an image formation instruction from the image formation control unit 502. These include the laser 241 of the scanner unit 24, the scanner motor 242, the drum motor 222, the transfer bias of the primary transfer roller 27, the developing motor 232, the intermediate transfer motor 282, and the transfer bias of the secondary transfer roller 29. The temperature adjustment control unit 505 determines the target temperature of the heater 42, which is controlled by the heating element control unit 507, based on preparatory operation instructions and image formation instructions from the image formation control unit 502. The heating element control unit 507 includes a power supply circuit for supplying power from an external AC power source to the heater 42 and controls the power supplied to the heater 42 in accordance with instructions from the temperature adjustment control unit 505. The transfer unit temperature acquisition unit 506 acquires the temperature of the intermediate transfer belt 28 using the belt thermistor 30, or acquires the predicted temperature of the intermediate transfer belt 28 predicted by the transfer unit temperature prediction unit 508 based on information such as the operating status of the image forming apparatus. The memory unit 509 stores various information required for control, particularly various information related to the temperature adjustment control of the heating device 40, which will be described later.

[0039] <How to set the target fixing temperature> Next, a method for setting the target fixing temperature, which is a feature of this embodiment, will be described. Fig. 4 is a flowchart of this embodiment. When a print job (501) is started, first, a reference fixing temperature Ta is determined as a reference target temperature (502). In this embodiment, the fixing temperature Ta is a parameter determined from the paper basis weight. The user inputs the paper basis weight of the recording material 11 to be used into an operation panel (not shown), and the control unit 108 sets the reference fixing temperature Ta according to the paper basis weight based on Table 1. Table 1. Relationship between paper basis weight and reference fixing temperature Ta TIFF0007753036000001.tif30153

[0040] In this embodiment, the reference fixing temperature is determined based on the paper basis weight, but the reference fixing temperature may also be determined according to, for example, the size and smoothness of the paper, or the amount of toner applied to each print image.

[0041] Next, the temperature of the intermediate transfer belt 28 is measured by the belt thermistor 30 (503), and a fixing target temperature adjustment amount D corresponding to the temperature of the intermediate transfer belt 28 is calculated (504). The fixing target temperature adjustment amount D is a parameter set in advance according to the temperature of the intermediate transfer belt 28, as shown in FIG. 5(a), and the fixing target temperature adjustment amount D increases as the temperature of the intermediate transfer belt 28 increases. Finally, the fixing target temperature Ttgt is calculated and determined using equation (1) (505). Ttgt=Ta-D (1)

[0042] Steps 502 to 505 are repeated until the last recording material 11 is printed, and the print job is completed (506).

[0043] Here, in order to confirm the effect of controlling the target fixing temperature of the heating device based on the temperature of the intermediate transfer belt 28 in this embodiment, the following comparative experiment was conducted and compared with the prior art. The conditions of the comparative experiment were: recording material conveyance speed: 300 mm / sec, printing speed (throughput): 60 ppm, recording material: Red Label manufactured by Canon Oce, paper basis weight: 80 g / m 2 The paper is A4 size. From Table 1, the fixing reference temperature Ta for Red Label is 180°C.

[0044] Figure 6 is a schematic diagram showing the image patterns for the comparison experiment. In addition to a low-print halftone image (Bk: 5%), a high-print image (Y: 100%, M: 100%) of pattern B was printed. The images were created using Adobe Photoshop CS4 in YMCK color mode.

[0045] Furthermore, it is desirable to conduct comparative experiments in an environment where temperature and humidity are controlled using air conditioning or other means. In this example, the comparative experiments were conducted in an environment with a temperature of 23°C and a relative humidity of 50%. After cooling the image forming apparatus down to 23°C, intermittent printing was performed on 20 sheets, with a 10-second pause between each single-sided print. This single-sided intermittent printing was conducted to warm up the heating device, including the pressure roller and internal components of the fixing film, which have a large thermal capacity, as well as the atmosphere within the heating device. While the heating device was warming up, the comparative experiments were conducted under conditions where other internal components, such as the intermediate transfer belt and photosensitive drum, were kept as cool as possible. This eliminated the effects of fluctuations in the heating device's warm-up state during the comparative experiments, allowing for a clear understanding of the effects of temperature rises in internal components, such as the intermediate transfer belt and photosensitive drum, and the corresponding effects of this example.

[0046] FIG. 7(a) shows the results of a double-sided continuous paper feed test using the control of this embodiment, showing the target fixing temperature and the temperature transition of the intermediate transfer belt 28 when 500 sheets were continuously fed on both sides (1000 images on both sides). FIG. 8 is a table illustrating the paper feed order and paper feed intervals during double-sided continuous printing in this experiment. The test was performed using a paper feed method in which two A4 recording materials were placed in a waiting state in the conveyance path of the image forming apparatus main body, and the front and back sides of both sheets were printed alternately (alternate front and back paper feed with two sheets waiting on both sides). The interval between the recording materials in the recording material conveyance direction during alternate paper feed was 12 mm.

[0047] As shown in Figure 7(a), the temperature of the intermediate transfer belt 28 rises simultaneously with the start of double-sided continuous paper feed, and the target fixing temperature drops as the temperature of the intermediate transfer belt 28 rises. Specifically, before and after double-sided continuous printing, the temperature of the intermediate transfer belt 28 rises from room temperature (23°C) to 43°C, while the target fixing temperature drops from 180°C to 170°C. This is because, as mentioned above, the target fixing temperature adjustment amount D is set large depending on the warm-up state of the intermediate transfer belt 28. This allows the target fixing temperature to be lowered by the amount of the temperature rise of the intermediate transfer belt 28, thereby maintaining good fixing performance without over-fixing or poor fixing. The temperature rise of the intermediate transfer belt during double-sided printing is primarily due to the effect of the recording material 11, which has been warmed up by the heating device, passing through the secondary transfer process again for image formation on the second side. Other possible causes include heat radiation from the heating device and frictional heat from rotating parts such as the developing unit and primary and secondary transfer units. Table 2. Temperature of recording material inside image forming equipment TIFF0007753036000002.tif50153

[0048] Table 2 shows the temperature of the recording material 11 in the paper-passing image forming apparatus at the time of passing 490 sheets in a double-sided continuous paper-passing test using the control of this embodiment. The temperature of the recording material rises from room temperature 23°C to 30°C immediately after passing through the secondary transfer process in the first-side image formation (B), and is heated to 100°C by the heating device 40 immediately after passing through the fixing nip N (C). It further drops to 78°C near the switchback roller 63 (D) and 55°C near the double-sided roller 65 (E), and the temperature of the recording material 11 reaches the secondary transfer step. Furthermore, the temperature of the recording material is 50°C immediately after passing through the secondary transfer step in the second-side image formation (B), is heated to 110°C by the heating device 40 immediately after passing through the fixing nip N (C), and reaches 85°C near the paper discharge roller 61 (F), and is discharged onto the paper discharge tray 62. For the purpose of the experiment, thermocouples were placed in the recording material transport path to measure the recording material temperatures during the image formation operation.

[0049] As can be seen from Table 2, the recording material 11 is approximately 50°C when it passes through the secondary transfer process again for image formation on the second side. This warmed recording material 11 is the main cause of the gradual rise in temperature of the intermediate transfer belt 28 from room temperature (23°C). Furthermore, by warming the first-side recording material 11 through the secondary transfer process, the intermediate transfer belt 28, whose temperature has risen, can reduce the amount of heat applied to the recording material 11 by the heating device 40, thereby lowering the target fixing temperature. On the other hand, if the target fixing temperature is not lowered, the recording material 11 will be further heated, further worsening the internal temperature rise, including the temperature rise of the intermediate transfer belt 28. The internal temperature rise, including the temperature rise of the intermediate transfer belt, during double-sided printing is more likely to worsen as the recording material transport speed and printing speed (throughput) of the image forming apparatus main body increase, because more recording material 11 circulates within the apparatus. Furthermore, as the image forming apparatus main body becomes smaller, the thermal capacity of components such as the intermediate transfer belt 28 decreases, making it easier for the temperature to rise within the apparatus, thereby worsening the internal temperature rise.

[0050] Figure 7(b) shows the results of a double-sided intermittent paper feed test using the control of this embodiment. Specifically, the graph shows the temperature trends of the fixing target temperature and the intermediate transfer belt 28 in four sets of double-sided printing with two-sheet standby, each run consisting of 160 sheets (320 images on the first and second sides combined), with breaks in between. The break times were 10 seconds between the first and second sets, 10 seconds between the second and third sets, and 15 minutes between the third and fourth sets. Before starting the fourth set, five sheets were printed intermittently, with a 10-second break between each single-sided print, to warm up the heating device 40 again. The temperature of the intermediate transfer belt 28 rose intermittently between the first and fourth sets, reaching 40°C by the end of the fourth set. During this time, the fixing target temperature dropped from an initial 180°C to 171°C. In the experiments using the control of this embodiment, no fixing problems occurred in either the double-sided continuous paper feed test or the double-sided intermittent paper feed test.

[0051] FIG. 9(a) shows the temperature transitions of the fixing target temperature and the intermediate transfer belt 28 when a double-sided continuous paper feed test was conducted using the control of Comparative Example 1. Here, the fixing target temperature control was performed, with the fixing target temperature kept constant from the start of paper feed. As shown in FIG. 9(a), when the fixing target temperature was kept constant, the intermediate transfer belt 28 rose to 48°C, a temperature rise greater than in this example. This is because, when the fixing target temperature was kept constant, the recording material 11 on the first side of both sides was subjected to excessive heat (an over-fixed state) when the intermediate transfer belt 28 rose in temperature, and as this recording material 11 circulated within the device, the temperature of the intermediate transfer belt 28 also rose excessively.

[0052] FIG. 9(b) shows the temperature transitions of the fixing target temperature and the intermediate transfer belt 28 when a double-sided intermittent paper feed test was conducted using the control of Comparative Example 1 (constant fixing target temperature). The temperature of the intermediate transfer belt 28 rose intermittently between the first and fourth sets, reaching 45°C by the end of the fourth set. In the experiment of Comparative Example 1 using constant fixing target temperature control, no fixing defects occurred in either the double-sided continuous paper feed test or the double-sided intermittent paper feed test. However, image defects (hot offset) due to over-fixing occurred in the latter half of the double-sided continuous paper feed test and the double-sided intermittent paper feed test. To address hot offset in the latter half of the double-sided continuous paper feed test when using constant fixing target temperature control, one method is to uniformly lower the fixing target temperature. However, this could result in fixing defects in the initial stages of continuous paper feed (1st to 10th sheets).

[0053] 10A shows the temperature transition of the fixing target temperature and the intermediate transfer belt 28 when a double-sided continuous paper feed test was conducted using the control of Comparative Example 2. Here, the fixing target temperature is set to the reference temperature at the start of paper feed. This section describes the fixing target temperature control (number of sheets control A) in which the target temperature is gradually lowered by 1°C for every 50 double-sided sheets (100 images on the first and second sides combined). The maximum temperature reduction is 15°C. With this fixing target temperature control (number of sheets control A), if paper feed is stopped, the temperature reduction due to the number of sheets control is reset when the next paper feed begins, and the temperature is returned to the initial value (180°C in this case). As shown in Figure 10(a), when the fixing target temperature is controlled by the number of sheets, it is possible to gradually lower the fixing target temperature from 180°C to 170°C in the double-sided continuous paper feed test. As a result, the temperature of the intermediate transfer belt 28 after the test was 45°C, which is higher than in this embodiment, but is lower than that of the constant fixing target temperature control.

[0054] FIG. 10(b) shows the temperature transitions of the fixing target temperature and the intermediate transfer belt 28 during a double-sided intermittent paper feed test using the control of Comparative Example 2 (sheet count control A). The temperature of the intermediate transfer belt 28 rose intermittently between the first and fourth sets, reaching 42°C at the end of the fourth set. This is because the fixing target temperature control resets the temperature drop due to the sheet count control at the end of each set, so the fixing target temperature only dropped from 180°C to 177°C during the double-sided intermittent paper feed test. As a result, when the image forming apparatus and intermediate transfer belt 28 were warming up, such as during the fourth set, the recording material 11 was over-fixed. Furthermore, image defects (hot offset) occurred at this time. To prevent hot offset during the latter half of double-sided intermittent paper feed using sheet count control, one method would be to lower the fixing target temperature from the beginning. However, this could result in poor fixing during the initial stages of continuous paper feed (sheets 1 through 10).

[0055] FIG. 11(a) shows the temperature transitions of the fixing target temperature and the intermediate transfer belt 28 when a double-sided continuous paper feed test was conducted using the control of Comparative Example 3. Here, we will explain fixing target temperature control (sheet count control B), in which the fixing target temperature is gradually lowered by 1°C for every 50 double-sided sheets (100 images total on the first and second sides) based on the starting point of paper feed. The maximum temperature reduction is 15°C. As shown in FIG. 11(a), in the double-sided continuous paper feed test, it was possible to gradually lower the fixing target temperature from 180°C to 170°C, as in Comparative Example 2. As a result, the temperature of the intermediate transfer belt 28 after the test was 45°C, which is higher than in this embodiment, but is lower than that of constant fixing target temperature control.

[0056] FIG. 11(b) shows the temperature transitions of the fixing target temperature and the intermediate transfer belt 28 during a double-sided intermittent paper feed test using the control of Comparative Example 3 (sheet count control B). The temperature of the intermediate transfer belt 28 rose intermittently between the first set and the fourth set, reaching 40°C by the end of the fourth set. With this fixing target temperature control (sheet count control B), cold offset due to poor fixing occurred early in the fourth set (sheets 1 to 10). This is because the fixing target temperature was lowered to 171°C at the end of the third set, and the temperature of the intermediate transfer belt 28 dropped from 44°C to 33°C during the long pause (15 minutes) between the third and fourth sets, and the fourth set was fed at the same fixing target temperature (171°C) as at the end of the third set. Table 3 is a list summarizing the results of the comparative experiment. Table 3: Results of the comparative experiment TIFF0007753036000003.tif75153

[0057] Table 3 compares the progress of the fixing target temperature, the temperature of the intermediate transfer belt 28 after it has been heated in the comparative experiment, whether or not image defects occurred, and the average fixing power consumption for the last five sheets in the comparative experiment. The progress of the fixing target temperature, the temperature of the intermediate transfer belt 28 after it has been heated in the comparative experiment, and the results of whether or not image defects occurred are as described above. In this embodiment, the fixing target temperature is set in accordance with the temperature rise of the intermediate transfer belt, so excessive heat (electricity) is not applied to the recording material 11, and therefore fixing power consumption is kept low.

[0058] As described above, by setting the target fixing temperature according to the intermediate transfer belt in this embodiment, it is possible to appropriately set the target fixing temperature even under conditions such as continuous double-sided paper feed, which can cause internal temperature increases. As a result, it is possible to apply an appropriate amount of heat to the recording material 11 during the fixing process, thereby suppressing image defects such as over-fixing and fixing failure, suppressing temperature increases in the intermediate transfer belt, and reducing fixing power consumption. Regarding changing the target fixing temperature based on the temperature of the intermediate transfer belt, this embodiment has been described as a method of changing the temperature only for double-sided printing, but this is not limited to double-sided printing. Because the minimum amount of heat required to fix the recording material changes even in single-sided printing depending on the temperature of the intermediate transfer belt, the target fixing temperature may also be changed based on the temperature of the intermediate transfer belt in single-sided printing.

[0059] In this embodiment, the heating device 40 is configured with a fixing thermistor Th as a temperature detector positioned to measure the surface temperature of the fixing film 41 in a non-contact manner. However, other configurations are also possible. For example, as shown in FIG. 2(b), the fixing thermistor Th may be positioned behind the heater 42 and control the temperature of the fixing film 41 to match the target fixing temperature. The configuration of the heating device 40 is not limited to that shown in FIG. 2(a) and may be, for example, as shown in FIG. 2(c). That is, the heating device 40 includes a fixing roller 71 as a fixing member, a pressure film 72 as a pressure member, a halogen heater 73 as a heating member, a holding member 74 that applies pressure from the inner surface of the pressure film 72 toward the fixing roller 71 using a pressure mechanism (not shown), and a stay 75. The target temperature of the fixing roller 71 is controlled by the fixing thermistor Th. The heating device may be configured as desired based on factors such as the cost and size of the image forming apparatus.

[0060] In this embodiment, the temperature of the intermediate transfer belt 28 is actually measured using the belt thermistor 30, but instead of providing a temperature detection means for directly obtaining the temperature of the intermediate transfer belt 28, the temperature of the intermediate transfer belt 28 may be predicted and obtained from information such as the operating status of the image forming apparatus. For example, the temperature rise during printing and the temperature drop during standby may be grasped in detail in advance, and the predicted temperature of the intermediate transfer belt 28 may be obtained in combination with the operating status of the image forming apparatus (transfer section temperature prediction means). 12(a) to 12(c) show the temperature of the intermediate transfer belt measured in advance in the following three states. FIG. 12(a) shows the temperature rise of the intermediate transfer belt during double-sided continuous printing, where the intermediate transfer belt rises from room temperature (RT) of 23°C to a saturation temperature (Tdx) of 50°C. FIG. 12(b) shows the temperature rise of the intermediate transfer belt during single-sided continuous printing, where the intermediate transfer belt rises from room temperature (RT) of 23°C to a saturation temperature (Tsx) of 30°C. FIG. 12(c) shows the temperature drop of the intermediate transfer belt when the main body is stopped, where the intermediate transfer belt drops from a raised temperature (50°C) to a saturation temperature (Twx) of 23°C (room temperature). At this time, the temperature of the intermediate transfer belt can be predicted using the following prediction formulas (2) and (3). Tb(t)=Tb(t-1)+ΔTb (2) ΔTb=[Tdx-Tb(t-1)]×Kd×Ed +[Tsx-Tb(t-1)]×Ks×Es +[Twx-Tb(t-1)]×Kw×Ew (3)

[0061] Here, Tb(t) represents the predicted intermediate transfer belt temperature at time t, where t is measured in one-second increments. From equation (2), Tb(t) is calculated by adding ΔTb to the predicted intermediate transfer belt temperature at time t-1, Tb(t-1). From equation (3), ΔTb can be expressed using the difference between Tb(t-1) and the saturation temperature during double-sided continuous printing (Tdx), the saturation temperature during single-sided continuous printing (Tdx), and the saturation temperature when the printer is stopped (Twx), as well as the constants K (Kd, Ks, Kw) and variables E (Ed, Es, Ew). Here, variable E varies depending on the operating status of the image forming apparatus. During double-sided printing, Ed = 1, Es = 0, Ew = 0; during single-sided printing, Ed = 0, Es = 1, Ew = 0; and during printer stoppage, Ed = 0, Es = 0, Ew = 1. That is, equation (3) is divided into terms for double-sided printing, single-sided printing, and when the printer is stopped, and which term is active is determined by variable E. Each term is expressed by the difference between the respective saturation temperatures (Tdx, Tsx, Twx) and Tb(t-1). For example, if double-sided printing continues for a long period of time, Tb(t-1) in equation (3) approaches Tdx, and ΔTb ≒ 0, so Tb(t) in equation (2) approaches the saturation temperature Tdx during double-sided printing. Similarly, if single-sided printing or when the printer is stopped continues for a long period of time, they will approach Tsx and Twx, respectively. Furthermore, the constants K (Kd, Ks, Kw) are used to adjust the estimated values ​​and actual measured values ​​for double-sided printing, single-sided printing, and when the printer is stopped so that they match.

[0062] The variables E (Ed, Es, Ew) in equation (3) are determined based on the operating status of the image forming apparatus itself, as shown in the flowchart of FIG. 13. When the power switch (not shown) of the image forming apparatus is turned on (601), the belt temperature prediction formula Tx(t) is set to the standby prediction formula Tw(t) (602). When a print job is received (603), it is determined whether the print job is double-sided printing (604), and if so, the belt temperature prediction formula Tx(t) is set to the standby prediction formula Td(t) (605). If it is single-sided printing, the belt temperature prediction formula Tx(t) is set to the standby prediction formula Ts(t) (606). The processes of 604 to 606 are repeated until the print job is completed (607). When the print job is completed, the processes of 602 to 607 are repeated until the power is turned off (608), and the flow ends when the power is turned off (609). By setting the variable E according to the operating state of the image forming apparatus body and by using equations (2) and (3), it is possible to predict the temperature of the intermediate transfer belt in detail.

[0063] When setting the target fixing temperature, a suitable configuration can be selected according to the required accuracy. In addition, in this embodiment, the target fixing temperature is set based on the temperature of the intermediate transfer belt as the image carrier, but the target fixing temperature may also be set based on the temperature of the secondary transfer roller as the opposing member to the image carrier. The most suitable method can be selected to appropriately set the target fixing temperature that can obtain good fixing performance.

[0064] Example 2 In the first embodiment, a method for setting a target fixing temperature based on the temperature of an intermediate transfer belt as an image carrier that contacts the recording material 11 in a color image forming apparatus using a secondary transfer method is described. In the second embodiment, a method for setting a target fixing temperature based on the temperature of a photosensitive drum as an image carrier that contacts the recording material 11 in a monochrome image forming apparatus using a direct transfer method in which an image is transferred directly from a photosensitive drum to the recording material 11 is described.

[0065] FIG. 14 is a cross-sectional view showing the schematic configuration of a monochrome image forming apparatus according to this embodiment. Details already described in the first embodiment will not be described here. The drum thermistor 33 is a transfer section temperature detector for detecting the temperature of the photosensitive drum 22. The photosensitive drum 22 is constructed by coating the outer periphery of a hollow aluminum cylinder (Φ30, thickness 1.0 mm) with an organic photoconductive layer (thickness 60 μm). The transfer roller 34 is an opposing member that contacts the photosensitive drum 22. It has a cross-sectional configuration in which a core (Φ6) is provided with a 4 mm-thick elastic layer made of NBR hydrin rubber, and the surface length (axial direction) of the elastic layer is 220 mm. The transfer roller 34 contacts the photosensitive drum 22 by a contact mechanism (not shown), with a contact pressure of 13 N. The contact width between the transfer roller 34 and the photosensitive drum 22 is 2.0 mm.

[0066] In this embodiment, the fixing target temperature adjustment amount D is a parameter preset in accordance with the temperature of the photosensitive drum 22, as shown in FIG. 5(b). The higher the temperature of the photosensitive drum 22, the larger the fixing target temperature adjustment amount D. In this embodiment, the fixing target temperature is also linked to the temperature of the photosensitive drum, which is the image carrier. This, for the same reasons as in the first embodiment, makes it possible to suppress photosensitive drum temperature rise, power consumption, and image defects such as over-fixing and poor fixing, compared to conventional control such as constant fixing target temperature control and sheet count control. In this embodiment, the photosensitive drum temperature is measured using the drum thermistor 33. However, for example, the photosensitive drum temperature may be predicted without a photosensitive drum temperature detection device by obtaining detailed information about temperature rise during printing and heat dissipation during standby, and combining this information with the operating status of the image forming apparatus. When setting the fixing target temperature, a suitable configuration may be selected based on the required accuracy.

[0067] In addition, in this embodiment, the fixing target temperature is set based on the temperature of the photosensitive drum as the image carrier, but the fixing target temperature may also be set based on the temperature of the transfer roller as the opposing member of the image carrier.The most appropriate method can be selected to properly set the fixing target temperature that can obtain good fixing performance.

[0068] Example 3 Next, a third embodiment of the present invention will be described. The basic configurations and operations of the image forming apparatus and heating device of the third embodiment are the same as those of the first embodiment. Therefore, elements having the same or equivalent functions and configurations as those of the first embodiment are given the same reference numerals, and detailed descriptions thereof will be omitted. In the first embodiment, the warm-up state of the heating device 40 was fixed in order to clearly grasp the influence of temperature rises of the intermediate transfer belt and the photosensitive drum. In the third embodiment, the warm-up state of the heating device 40 also changes, and the fixing target temperature is changed in response to the change.

[0069] In the third embodiment, the reference fixing temperatures Ta shown in Table 4 are used. Table 1 shows the reference fixing temperatures Ta in a warmed-up state after 20 sheets of intermittent printing, but Table 4 shows the reference fixing temperatures Ta when the heating device 40 is in a cooled state (room temperature state). Table 4. Relationship between paper basis weight and fixing reference temperature Ta (heating unit 40, room temperature) TIFF0007753036000004.tif31153

[0070] A method for setting the target fixing temperature will be described using the flowchart in FIG. 15. When a print job (701) is started, first, a reference fixing temperature Ta is determined (702). Next, the temperature of the intermediate transfer belt 28 is measured by the belt thermistor 30 (703), and a target fixing temperature adjustment amount D1 corresponding to the temperature of the intermediate transfer belt 28 is calculated (704). The target fixing temperature adjustment amount D1 is a parameter set in advance according to the temperature of the intermediate transfer belt 28 as shown in FIG. 16, and the higher the temperature of the intermediate transfer belt 28, the larger the target fixing temperature adjustment amount D1 becomes. Note that the adjustment of the target fixing temperature according to the temperature of the intermediate transfer belt 28 is a first temperature change means, and the target fixing temperature adjustment amount D1 is the first temperature change amount.

[0071] Next, the fixing target temperature adjustment amount D2 is calculated (705) according to the heating time of the heating device 40 (the time for which power is supplied to the heater 42). The fixing target temperature adjustment amount D2 will be described using FIGS. 17(a) to 17(c). The fixing target temperature adjustment amount D2 increases when the temperature of the components inside the heating device 40 rises (hereinafter referred to as "warming up"). The fixing target temperature is set lower. FIG. 17(a) shows the transition of the fixing target temperature adjustment amount D2 when heating is in progress and no recording material is present inside the heating device 40. Because heat from the heater 42 is transferred to components such as the pressure roller 45 and warming up progresses, the fixing target adjustment temperature D2 increases as the heating time of the heating device 40 increases. On the other hand, FIG. 17(b) shows the transition of the fixing target temperature adjustment amount D2 when a recording material passes through the heating device 40. Because the pressure roller 45 and other components are cooled by the recording material, the fixing target adjustment temperature D2 decreases. Furthermore, since the heating device 40 is cooled by heat radiation even when the heating device 40 is stopped (not heating), the fixing target adjustment temperature D2 becomes small as shown in Fig. 17(c). Note that the adjustment of the fixing target temperature according to the heating time of the heating device 40 is the second temperature change means, and the fixing target temperature adjustment amount D2 is the second temperature change amount. Note that in Example 3, the maximum value of the fixing target temperature adjustment amount D2 is set to 10°C.

[0072] Finally, the target fixing temperature Ttgt is calculated and determined using equation (4) (706). Ttgt=Ta-(αD1+βD2) (4) α and β are coefficients, and can be set arbitrarily depending on the paper feed conditions, etc. However, both α and β are between 0 and 1. For example, if the warm-up state of the heating device 40 is fixed as in the first embodiment, and the target fixing temperature Ttgt is determined only by temperature adjustment according to the intermediate transfer belt 28, then α=1 and β=0, which is the same as equation (1). Steps 702 to 706 are repeated until the last recording material 11 is printed, and the print job is completed (707).

[0073] To demonstrate the effect of Example 3, a comparative experiment was conducted under the same conditions as Example 1, except that the paper basis weight was 80 g / m 2According to Table 4, the reference fixing temperature Ta when using this recording material is 190°C. Furthermore, the experiment was conducted in a state where the image forming apparatus, including the heating device 40, was cooled to room temperature of 23°C. As comparative examples for Example 3, experiments were also conducted under the conditions of Comparative Example 4 and Comparative Example 5. Comparative Example 4 is an example in which the target fixing temperature Ttgt is adjusted only by the heating time of the heating device 40. Comparative Example 5 is an example in which the target fixing temperature Ttgt is adjusted by independently adjusting the temperature of the intermediate transfer belt 28 and adjusting the heating time of the heating device 40.

[0074] 18A shows the target fixing temperature Ttgt, the target fixing temperature adjustment amount D1, and the target fixing temperature adjustment amount D2 during the double-sided continuous paper feed test in Example 3. As the temperature of the belt 28 rises, the fixing target temperature adjustment amount D1 increases. The fixing target temperature adjustment amount D2 increases when the heating device 40 is started up, but during continuous paper feed, the time when no recording material is present in the heating device 40 (the time between sheets) is shorter than the time when recording material is present in the heating device 40, so the value decreases as the paper feed progresses. The coefficients used in the double-sided continuous paper feed test were α = 0.8 and β = 0.9. At the end of the continuous paper feed, the fixing target temperature Ttgt is lowered to 180°C. The reason the final fixing target temperature is higher than in Example 1 is that the heating device 40 in Example 3 has not yet warmed up.

[0075] Figure 18(b) shows the fixing target temperature Ttgt, the fixing target temperature adjustment amount D1, and the fixing target temperature adjustment amount D2 during the double-sided intermittent paper feed test in Example 3. In Example 3, double-sided printing with two-sheet standby was performed in three sets of 160 sheets each (320 images on the first and second sides combined) with a 10-second pause between sets. The target temperature adjustment amount D2 decreased during the continuous paper feed and during the pause between sets. However, with the continuous paper feed of 160 sheets, the target temperature adjustment amount D2 did not decrease significantly. Furthermore, because there was a heating period (pre-rotation and post-rotation) at the beginning and end of each set without the recording material present in the heating device 40, the value of the fixing target temperature adjustment amount D2 gradually increased with continued intermittent paper feed. The coefficients used in the double-sided intermittent paper feed test were α = 0.8 and β = 0.7. In the experiment using the control of Example 3, no image defects occurred in either the double-sided continuous paper feed test or the double-sided intermittent paper feed test. Furthermore, the coefficients α and β are not limited to the values ​​in Example 3, and may be changed depending on the operating conditions of the image forming operation, such as the printing mode, type of recording material, and the environment in which the image forming device is used (e.g., environmental information such as temperature and humidity), or may be changed during one print job.

[0076] FIG. 19(a) shows the fixing target temperature Ttgt and the fixing target temperature adjustment amount D2 when a double-sided continuous paper feed test was performed using the control of Comparative Example 4. In Comparative Example 4, the fixing target temperature Ttgt was changed only depending on the heating time of the heating device 40. In other words, the target temperature was not adjusted based on the temperature of the intermediate transfer belt 28. In FIG. 19(a), as the paper feed progressed, the fixing target temperature Ttgt became higher than the temperature shown in FIG. 18(a), reaching 188°C at the end of the paper feed (180°C in Example 3). As a result, hot offset occurred in the latter half of the paper feed. As described in Example 1, as double-sided continuous paper feed continued, the intermediate transfer belt 28 warmed up, and the temperature of the recording material before entering the heating device 40 increased. Therefore, image defects may occur if the fixing target temperature Ttgt is not lowered accordingly. FIG. 19(b) shows the fixing target temperature Ttgt and the fixing target temperature adjustment amount D2 when a double-sided intermittent paper feed test was performed using the control of Comparative Example 4. In FIG. 19(b), the target fixing temperature Ttgt was 181° C. at the beginning of the third set of intermittent paper feeding, which was higher than the temperature in FIG. 18(b), but no image defects occurred.

[0077] FIG. 20(a) shows the target fixing temperature Ttgt, the target fixing temperature adjustment amount D1, and the target fixing temperature adjustment amount D2 when a double-sided continuous paper feed test was conducted using the control of Comparative Example 5. In Comparative Example 5, the target fixing temperature Ttgt was changed by independently adjusting the target fixing temperature according to the intermediate transfer belt 28 and the heating time of the heating device 40. In other words, the sum of the target fixing temperature adjustment amount D1 and the target fixing temperature adjustment amount D2 was used, and the target fixing temperature Ttgt was calculated using equation (4) with coefficients α=1 and β=1. In FIG. 20(a), the target fixing temperature Ttgt at the end of paper feed was 178°C, and a slight cold offset occurred.

[0078] FIG. 20(b) shows the target fixing temperature Ttgt, target fixing temperature adjustment amount D1, and target fixing temperature adjustment amount D2 when a double-sided intermittent paper feed test was conducted using the control of Comparative Example 5. In FIG. 20(b), the initial target fixing temperature Ttgt for the third set of intermittent paper feed was 175°C, and cold offset occurred. As described above, when both the intermediate transfer belt 28 and the heating device 40 are warming up, the target fixing temperature may be lowered below a temperature at which fixation is possible, which may result in poor image quality. Therefore, it is better to change the target fixing temperature by multiplying it by an appropriate coefficient, as in Example 3. .

[0079] In this comparative experiment, cold offset occurred in Comparative Example 5, but depending on the configuration of the image forming apparatus and the paper passing conditions, image defects may not occur even with the control method of Comparative Example 5. Therefore, if image defects do not occur, the fixing target temperature Ttgt may be determined by the method of Comparative Example 5, and the values ​​of the coefficients α and β in equation (4) are not limited.

[0080] Table 5 is a summary of the results of the comparative experiments. It summarizes the results of the comparisons based on the number of sheets passed at which the effect of Example 3 was most pronounced. In the double-sided continuous paper feed test, the results at the end of the paper feed are shown, and in the double-sided intermittent paper feed test, the results at the beginning of the third set are shown. The average power consumption of the fixing unit is shown when five sheets are passed. Table 5. Results of the comparative experiment in Example 3 TIFF0007753036000005.tif62153

[0081] As a result of the comparative experiment, as mentioned above, only Example 3 did not produce defective images. Furthermore, in Example 3, the fixing power consumption was kept low because excessive heat (electric power) was not applied.

[0082] As described above, in the third embodiment, the fixing target temperature Ttgt is changed in accordance with both the fixing target temperature adjustment amount D1 corresponding to the temperature of the intermediate transfer belt 28 and the fixing target temperature adjustment amount D2 corresponding to the heating time of the heating device 40. This makes it possible to suppress image defects due to over-fixing or poor fixing and to reduce fixing power consumption. More specifically, in the third embodiment, the fixing target temperature adjustment amount D1 and the fixing target temperature adjustment amount D2 are each multiplied by a coefficient, and the sum is added. This changes the fixing target temperature Ttgt to achieve the above-described effects. In the third embodiment, the temperature of the intermediate transfer belt 28 is actually measured using the belt thermistor 30. However, as in the first embodiment, the temperature of the intermediate transfer belt 28 may be predicted and the fixing target temperature adjustment amount D1 may be determined in accordance with the predicted temperature. Alternatively, as in the second embodiment, the fixing target temperature adjustment amount D1 may be determined in accordance with the temperature of the photosensitive drum.

[0083] Example 4 Next, a fourth embodiment of the present invention will be described. The basic configurations and operations of the image forming apparatus and heating device of the fourth embodiment are the same as those of the first and third embodiments. Therefore, elements having the same or equivalent functions and configurations as those of the first and third embodiments are denoted by the same reference numerals, and detailed descriptions thereof will be omitted.

[0084] In the third embodiment, the fixing target temperature is determined by multiplying the fixing target temperature adjustment amount D1 and the fixing target temperature adjustment amount D2 by the coefficients α and β and adding them together. In the fourth embodiment, the fixing target temperature is determined by using only the fixing target temperature adjustment amount D1 or the fixing target temperature adjustment amount D2, whichever has the larger temperature change amount. The coefficients α and β can be changed depending on the paper feed conditions and the type of recording material. It is a power value, and it may be difficult to optimize for all conditions or the temperature control may become complicated. In Example 4, by using only the one with the larger temperature change amount between the fixing target temperature adjustment amount D1 and the fixing target temperature adjustment amount D2, image defects can be suppressed with simple temperature control.

[0085] Figure 21 is a flowchart for determining the fixing target temperature Ttgt in Example 4. When the printing job (801) starts, first, the fixing reference temperature Ta is determined (802). The fixing reference temperature Ta uses the values in Table 4 shown in Example 3. Next, the temperature of the intermediate transfer belt 28 by the belt thermistor 30 is measured (803), and the fixing target temperature adjustment amount D1 corresponding to the temperature of the intermediate transfer belt 28 is obtained (804). Subsequently, the fixing target temperature adjustment amount D2 corresponding to the heating time of the heating device 40 is obtained (805). The obtained fixing target temperature adjustment amount D1 and the fixing target temperature adjustment amount D2 are compared. When D1≧D2, the fixing target temperature Ttgt = Ta - D1 (806, 807). When D1 < D2, the fixing target temperature Ttgt = Ta - D2 (808). Steps 802 to 808 are repeated until the last recording material 11 is printed, and the printing job is terminated (809).

[0086] FIG. 22 shows the transitions of the fixing target temperature Ttgt, the fixing target temperature adjustment amount D1, and the fixing target temperature adjustment amount D2 when the fixing target temperature Ttgt was determined using the method of Example 4. The fixing target temperature adjustment amount D1 and the fixing target temperature adjustment amount D2 are plotted on the same graph to facilitate comparison of their magnitude relationships. The conditions for the comparative experiment were the same as those of Example 3. FIG. 22(a) shows the results of a double-sided continuous paper feed test. At the beginning of paper feed, the temperature of the intermediate transfer belt 28 is relatively low, and the fixing target temperature adjustment amount D1 is less than the fixing target temperature adjustment amount D2. Therefore, the fixing target temperature Ttgt = Ta - D2. As paper feed progresses, the temperature of the intermediate transfer belt 28 increases, but the heating device 40 gradually cools. Once the fixing target temperature adjustment amount D1 is greater than or equal to the fixing target temperature adjustment amount D2, the fixing target temperature Ttgt = Ta - D1. FIG. 22(b) shows the results of a double-sided intermittent paper feed test. At the beginning of each set of intermittent paper feed, the heating time is affected by the heating time when no recording material is present in the heating device 40, so the fixing target temperature adjustment amount D1<the fixing target temperature adjustment amount D2, and the fixing target temperature Ttgt=Ta-D2. As the paper feed for each set progresses, as in the double-sided continuous paper feed test, the fixing target temperature adjustment amount D1≧the fixing target temperature adjustment amount D2, and the fixing target temperature Ttgt=Ta-D1.

[0087] When the fixing target temperature Ttgt was set using the method of Example 4, no image defects occurred in either the double-sided continuous paper feed test or the double-sided intermittent paper feed test. In Comparative Example 4 of Example 3, the fixing target temperature Ttgt was changed only depending on the heating time of the heating device 40, so hot offset occurred when the temperature of the intermediate transfer belt 28 had a large effect. In Comparative Example 5, cold offset occurred when the fixing target temperature Ttgt was lowered too much. In Example 4, the fixing target temperature Ttgt was changed using either the temperature of the intermediate transfer belt 28 or the heating time of the heating device 40, whichever had the larger effect, thereby preventing over-fixing and image defects due to poor fixing.

[0088] The methods for determining the fixing target temperature Ttgt in the third and fourth embodiments may be used in combination. For example, when the fixing target temperature adjustment amount D1 and the fixing target temperature adjustment amount D2 are equal to or less than preset values, the fixing target temperature Ttgt is changed using the temperature of the intermediate transfer belt 28 or the heating time of the heating device 40, whichever has the greater influence, as in the fourth embodiment. On the other hand, when the fixing target temperature adjustment amount D1 and the fixing target temperature adjustment amount D2 both exceed preset values, the fixing target temperature Ttgt is changed using the formula (4) shown in the third embodiment. Such combined control may be used.

[0089] Example 5 Next, a fifth embodiment of the present invention will be described. The basic configuration and operation of the device are the same as those of Example 1. Therefore, elements having the same or equivalent functions and configurations as those of Example 1 are assigned the same reference numerals, and detailed description thereof will be omitted. In Examples 1 to 4, the temperature of the intermediate transfer belt or photosensitive drum is actually measured or predicted, and the target fixing temperature is changed according to the temperature. Example 5 is an example in which the target fixing temperature is changed according to the execution time of double-sided printing, even when the temperature of the intermediate transfer belt or photosensitive drum cannot be accurately determined. In other words, adjusting the target fixing temperature according to the execution time of double-sided printing (operation time of double-sided fixing operation) is the first temperature change means in Example 5, and the target fixing temperature adjustment amount D1x is the first temperature change amount in Example 5 and the third temperature change amount in the present invention.

[0090] Using FIG. 23, the fixing target temperature adjustment amount D1x (first temperature change amount in the fifth embodiment) according to the execution time of double-sided printing will be described. As shown in FIG. 23(a), the fixing target temperature adjustment amount D1x increases as double-sided printing is performed more frequently, and the fixing target temperature Ttgt is set lower. The reason for this is the same as when the intermediate transfer belt 28 increases in temperature as described in the first embodiment. That is, once the recording material 11 is warmed by the heating device 40, the temperatures of the components inside the image forming apparatus (e.g., the intermediate transfer belt 28) increase, and the temperature of the recording material 11 before entering the heating device 40 also increases. Note that the saturation temperature of the fixing target temperature adjustment amount D1x in the fifth embodiment is set to 15°C.

[0091] FIG. 23(b) shows the change in the target fixing temperature adjustment amount D1x during single-sided printing, in which an image is formed on only one side of the recording material 11. FIG. 23(c) shows the change in the target fixing temperature adjustment amount D1x when the image forming apparatus is stopped. Since double-sided printing is not performed in either case, the target fixing temperature adjustment amount D1x decreases over time. However, single-sided printing differs from stopped image forming apparatuses in that the target fixing temperature adjustment amount D1x does not decrease to 0°C. This is because, as shown in FIG. 12(b) in the first embodiment, components within the image forming apparatus are heated by radiant heat from the heating device 40 during single-sided printing. Strictly speaking, when the first side of the sheet is passed through during double-sided printing, components within the image forming apparatus may not be heated but may be cooled, just as they are during single-sided printing. However, since the effect of the temperature rise caused by the second-side paper passing is greater than the cooling caused by the first-side paper passing, the fixing target temperature adjustment amount D1x is assumed to monotonically increase with respect to the double-sided printing execution time, as shown in FIG. 23(a).

[0092] In the fifth embodiment, the fixing target temperature adjustment amount D1x described above is compared with the fixing target temperature adjustment amount D2 according to the heating time of the heating device 40 described in the third embodiment, and the larger value is used to change the fixing target temperature Ttgt. In other words, as in the fourth embodiment, when D1x≧D2, Ttgt=Ta−D1x, and D1x <D2のとき、Ttgt=Ta-D2である。

[0093] 24 shows the transitions of the fixing target temperature Ttgt, the fixing target temperature adjustment amount D1x, and the fixing target temperature adjustment amount D2 when the fixing target temperature Ttgt is determined by the method of Example 5. The experimental conditions are the same as those of Example 4. In both the double-sided continuous paper feed test (Fig. 24(a)) and the double-sided intermittent paper feed test (Fig. 24(b)), the transitions of the fixing target temperature Ttgt are not significantly different from those of Example 4 in Fig. 23, and no image defects occurred.

[0094] As described above, by changing the target fixing temperature according to the execution time of double-sided printing, it is possible to prevent image defects due to over-fixing and poor fixing, without measuring or predicting the temperature of the intermediate transfer belt 28. Alternatively, as in the third embodiment, the target fixing temperature adjustment amount D1x and the target fixing temperature adjustment amount D2 may each be multiplied by a coefficient, and the results may be added together to change the target fixing temperature Ttgt. In particular, when the image forming apparatus main body and the heating device 40 are warming up, adding the target fixing temperature adjustment amount D1x and the target fixing temperature adjustment amount D2 together can effectively prevent image defects.

[0095] Example 6 In Example 6, an example of setting a target fixing temperature in an image forming apparatus in a monochrome printer in which the photosensitive drum 22 serving as a photosensitive member is replaceable is shown. FIG. 26 is a cross-sectional view of a monochrome printer in which the photosensitive drum 22 is replaceable. In this example, the photosensitive drum 22, charger 23, developing unit 26, toner container 25, and cleaner 21 are unitized as a CRG (cartridge) 20, which is replaceable in the printer 1 body. When the CRG 20 is installed in the printer 1 body, a contact connector 35 in the printer 1 body electrically connects to a memory chip 36 disposed in the CRG 20, enabling communication. Reading the information in this memory chip 36 into the control unit 108 further improves image quality and maintenance of the CRG 20. The basic configuration and operation of the image forming apparatus and heating device other than the CRG 20 are the same as those in Example 2.

[0096] (How to set the target temperature) Next, a method for setting the target temperature during the fixing process will be described with reference to the flowchart of FIG.

[0097] First, the reference temperature Ta during the fixing process is determined (901). Next, whether the photosensitive drum 22 has been replaced, i.e., whether the CRG 20 has been replaced, is detected (902). The control unit 108 accesses the memory chip 36 attached to the CRG 20, reads information such as the serial number, and compares it with information stored in the control unit 108 to detect whether the CRG 20 has been replaced. If the information stored in the control unit 108 matches the information newly retrieved from the memory chip 36, i.e., if the CRG 20 newly installed in the printer 1 is the same as the CRG 20 before installation, the control unit 108 reads the duplex count Cd stored at the end of the previous job (903). On the other hand, if the newly installed CRG 20 is different from the CRG 20 before installation, i.e., if the CRG 20 has been replaced, the duplex count Cd is set to 0 (904). Here, the duplex count Cd is a value that is added each time a double-sided print is processed and is a warm-up index that indicates the temperature rise of the photosensitive drum 22. The double-sided count Cd is set within the range of 0 as the minimum value and 750 as the maximum value.

[0098] The time elapsed since the end of the previous job is measured (905), and a predetermined double-sided count subtraction amount Ce shown in Table 6 is determined (906) based on the elapsed time. The double-sided count subtraction amount Ce is a value for reflecting the temperature of the photosensitive drum 22, which decreases with the passage of time since the end of the previous job, in the double-sided count Cd. In this embodiment, the double-sided count Cd is set to zero after 120 minutes have passed since the previous job. [Table 6]

[0099] The double-sided count Cd at the start of the job is determined by subtracting the double-sided count subtraction amount Ce from the read double-sided count Cd at the end of the previous job (907).

[0100] Next, if the job is a single-sided print, 0 is added to the double-sided count Cd (908), and if it is a double-sided print, 1 is added to the double-sided count Cd (909). Then, the adjustment amount D of the target temperature shown in Table 7 is determined (910). [Table 7]

[0101] As shown in Table 7, the target temperature adjustment amount D is a parameter set in advance according to the double-sided count Cd, and the target temperature adjustment amount D increases as the number of double-sided prints processed increases. In this embodiment, the double-sided count subtraction amount Ce and the target temperature adjustment amount D for the number of double-sided prints are set discretely, but they may also be set continuously and are not limited to these settings. Finally, the target temperature Ttgt during fixing process is calculated and determined based on equation (5) (911). Ttgt=Ta-D (5)

[0102] Steps 908 to 911 are repeated until the last recording material 11 is printed, and when the print job is completed, the double-sided count Cd is recorded in the control unit 108 (912), and the process is terminated (913).

[0103] Next, we will explain the difference in effect between this embodiment, which sets the target temperature of the heating device (fixing device) 40 based on the detection of replacement of the CRG 20 and the double-sided count Cd, and a comparative example. The printer settings used in the experiment were a recording material conveyance speed of 300 mm / sec and a print speed (throughput) of 60 ppm. The recording material used was A4-sized Red Label paper manufactured by Canon / Oce, with a paper basis weight of 80 g / m. 2 The reference temperature Ta of RedLabel is 180°C. It is desirable to conduct the experiment in an environment where temperature and humidity conditions are controlled by air conditioning or other means, and the experiment was carried out in an environment with a temperature of 23°C and a relative humidity of 50%. The experiment was started when the temperature inside the printer 1 was 23°C, the same as the room temperature.

[0104] The printing conditions for this experiment were to print 500 double-sided sheets, then open and close the CRG access door (the door on the printer 1 for removing the CRG 20) once and print 10 double-sided sheets, then open the CRG access door again, replace the CRG 20 with a new one, and print another 10 double-sided sheets.

[0105] In Comparative Example 6, the CRG replacement detection information is not used, and neither the double-sided count information is used, and the reference temperature Ta of 180° C. is set as the target temperature and printing continues regardless of events such as CRG replacement.

[0106] In Comparative Example 7, the double-sided count is used to adjust the target temperature according to the temperature of the photosensitive drum 22, but information on CRG replacement detection is not used. Therefore, regardless of whether the CRG has been replaced or not, even if the CRG access door is opened or closed, the double-sided count is not reset, and the double-sided count from the previous job is continued to set the target temperature and print.

[0107] In Comparative Example 8, the target temperature is adjusted using double-sided counting, but CRG replacement detection is not performed. Each time the CRG access door is opened or closed, the CRG is considered to have been replaced, and double-sided counting is performed. Set Cd to 0 and print. [Table 8]

[0108] Table 8 shows the occurrence of image defects in double-sided printing in Example 6 and Comparative Examples 6 to 8. In the table, ◯ indicates that no image defects occurred, and × indicates that an image defect occurred.

[0109] Figure 28 shows the time progression of the target temperature Ttgt and photosensitive drum temperature in this example when the above-mentioned experiment was conducted. At the start of double-sided printing of 500 sheets, the double-sided count Cd was 0, and the target temperature adjustment amount D was also 0, so the target temperature Ttgt was 180°C, the reference temperature Ta. At this time, the temperature of the photosensitive drum 22 was 23°C, or room temperature. As double-sided printing progressed, the double-sided count Cd increased, and the target temperature adjustment amount D increased according to Table 7, causing the target temperature Ttgt to decrease. At the end of double-sided printing of 500 sheets, the double-sided count Cd was 500, and the target temperature adjustment amount was 8, so the target temperature Ttgt was 172°C. The photosensitive drum temperature at this time was 44°C.

[0110] In this example, after 500 sheets of double-sided printing, the CRG access door was opened and closed (but the CRG 20 was not replaced), and then 10 sheets of double-sided printing were performed. In this case, the control unit 108 determined based on the memory information of the CRG 20 that the CRG 20 had not been replaced, and therefore, as shown in Figure 5, when processing 10 sheets of double-sided printing, the final target temperature Ttgt of the previous job was continued to be set to 172°C. At this time, the temperature of the photosensitive drum 22 remained at 44°C. Next, the CRG access door was opened, and a new CRG 20 was replaced with one whose temperature was the same as room temperature. The CRG access door was then closed, and 10 sheets of double-sided printing were performed again. In this case, the control unit 108 determined based on the memory information that the CRG 20 had been replaced with a new one, set the double-sided count Cd to 0, and set the target temperature Ttgt to 180°C. In this example, the control unit 108 detected the replacement of the CRG 20 and set the target temperature Ttgt in accordance with the temperature rise of the photosensitive drum 22, so no image defects occurred during the series of double-sided printing operations.

[0111] FIG. 29 shows the time transition of the target temperature Tgt and the temperature of the photosensitive drum 22 in Comparative Example 6. In Comparative Example 6, regardless of the temperature of the photosensitive drum 22, the target temperature Ttgt is set to the reference temperature Ta of 180°C and all double-sided printing is performed. In the latter half of the double-sided printing of 500 sheets, the temperature of the photosensitive drum 22 reaches 52°C. Therefore, in the latter half of the double-sided printing of 500 sheets and in double-sided printing after the CRG access door is opened and closed, the temperature of the recording material 11 becomes high and hot offset continues to occur in the second-side printing. However, in the double-sided printing after the CRG 20 is replaced, In printing, since the photosensitive drum 22 is at room temperature, no image defects occur even when the fixing process is performed at the reference temperature Ta.

[0112] FIG. 30 shows the target temperature Tgt and the temperature of the photosensitive drum 22 over time in Comparative Example 7. In Comparative Example 7, the target temperature Ttgt is adjusted according to the temperature rise of the photosensitive drum 22 using the double-sided counter Cd, as in Example 1. Therefore, no image defects occurred in the 500 double-sided prints or the 10 double-sided prints after the CRG access door was opened and closed. The temperature change of the photosensitive drum 22 is also similar to that in Example 6. However, Comparative Example 7 does not have a mechanism for detecting the replacement of the CRG 20, so the double-sided counter Cd is not reset even when the CRG 20 is replaced. Therefore, the double-sided counter value for the 10 double-sided prints after the CRG 20 replacement starts from 510, and fixing is performed at the final target temperature Ttgt of 172°C of the previous job. Because the temperature of the replaced photosensitive drum 22 is the same as room temperature, the recording material 11 is not warmed by the photosensitive drum 22. As a result, fixing at the target temperature Ttgt of 172°C results in insufficient heat, resulting in cold offset.

[0113] Figure 31 shows the target temperature Tgt and the temperature of the photosensitive drum 22 over time in Comparative Example 8. In Comparative Example 8, as in Example 1, the target temperature Ttgt was adjusted using the double-sided count Cd in accordance with the temperature rise of the photosensitive drum 22, so no image defects occurred after 500 double-sided prints. However, after the CRG access door was opened and closed, it was determined that the CRG 20 had been replaced, and the double-sided count Cd was reset to 0. As a result, the target temperature Ttgt was returned to the reference temperature Ta of 180°C, even though the temperature of the photosensitive drum 22 actually remained high. This resulted in excessive heat being applied to the recording material 11 and the toner image, causing hot offset during the fixing process on the second side. After the CRG 20 was replaced with a new one, the double-sided count Cd started again from 0 after 10 double-sided prints were made, but because the photosensitive drum 22 was also at room temperature, no image defects occurred.

[0114] As explained above, the control unit 108 sets the target temperature lower as the number of double-sided prints increases. Furthermore, it sets the target temperature higher for the print immediately after the CRG 20 replacement is detected. For large-volume double-sided prints, adjusting the target temperature based on the temperature of the photosensitive drum 22 prevents excessive heat supply to the recording material 11 and toner image, thereby preventing hot offset. However, if the CRG replacement detection cannot accurately detect whether the CRG 20 has been replaced when the CRG access door is opened or closed, it becomes difficult to set an appropriate target temperature. It is extremely important to reflect the results of the CRG replacement detection in the target temperature in order to prevent fixing problems.

[0115] In this embodiment, the CRG 20 has been described as being configured as a unit including the photosensitive drum 22, charger 23, cleaner 21, developing means 26, and toner container 25. However, the CRG 20 may be configured to include at least the photosensitive drum 22. Furthermore, as the CRG replacement detection means, a method has been described in which a memory chip mounted on the CRG 20 is brought into contact with a contact connector on the main body of the printer 1 for communication. However, an RF tag (radio frequency tag) may be attached to the CRG 20 for contactless communication. Alternatively, a sticker bearing a serial number, such as a barcode or two-dimensional code, may be affixed to the CRG 20 and read by an optical sensor provided on the main body of the printer 1. These points also apply to the other embodiments described below.

[0116] Example 7 In the sixth embodiment, the setting of the target fixing temperature was explained in a monochrome printer of a direct transfer type in which a toner image is directly transferred from the photosensitive drum 22 to the recording material 11, in which the photosensitive drum 22 is replaceable. In the seventh embodiment, an example is shown in which the warm-up state of the printer is predicted according to the operating status of the printer in a color printer 100 using a secondary transfer type in which the intermediate transfer belt 28 is replaceable, and the target fixing temperature is set. The rollers (33a, 33b, 33c) and the primary transfer rollers (27Y, 27M, 27C, 27K) are unitized as an ITB unit 37 (intermediate transfer unit). This ITB unit 37 is replaceable via an ITB unit access door (not shown). In other words, this ITB unit 37 corresponds to a transfer member that forms a transfer nip portion between itself and the photosensitive drum 22, which is an image carrier.

[0117] 32 is a cross-sectional view of an electrophotographic color printer of Example 7. The printer 100 has a CRG (20Y, 20M, 20C, 20K) having a plurality of photosensitive drums (22Y, 22M, 22C, 22K) as a plurality of replaceable first image carriers, and an intermediate transfer belt (intermediate transfer member) 28 as a replaceable second image carrier.

[0118] The photosensitive drum 22Y, charger 23Y, developing means 26Y, and cleaner 21Y are unitized as a CRG (cartridge) 20Y, and the CRG 20Y is replaceable in the main body of the printer 100. The other colors are also unitized as CRG 20M, CRG 20C, and CRG 20K, and each is replaceable in the main body of the printer 100 via a CRG access door (not shown). Each of the CRGs 20Y, 20M, 20C, and 20K is equipped with a memory chip (not shown) similar to that in the first embodiment. Contact connectors (not shown) corresponding to the memory chips of the CRGs 20Y, 20M, 20C, and 20K are arranged in the main body of the printer 100, enabling communication.

[0119] As described above, the intermediate transfer belt 28, support rollers (33a, 33b, 33c), and primary transfer rollers (27Y, 27M, 27C, 27K) serving as first transfer members are unitized as the ITB unit 37. This ITB unit 37 is replaceable via an ITB unit access door (not shown). The ITB unit 37 also includes a memory chip 371 as storage means. A contact connector (not shown) corresponding to the memory chip 371 of the ITB unit 37 is disposed in the main body of the printer 100, enabling communication. The basic configurations and operations of the image forming device and heating device other than the ITB unit 37, CRGs 20Y, 20M, 20C, and 20K are the same as those in the first embodiment, and therefore will not be described here.

[0120] If the intermediate transfer belt 28 has a function for forming a toner patch for detecting image density and detecting it with an optical sensor, the surface shape of one revolution of the intermediate transfer belt 28 is digitized by the optical sensor. Replacement of the ITB unit 37 may be detected by comparing the result with the result of the previous measurement. Alternatively, whether the ITB unit 37 is new or not may be detected by a method that uses a fuse that is installed in the printer 100 when it is new and destroyed when it is driven for the first time, thereby emitting a signal that is different from normal when used for the first time. Regardless of the detection means described above, the method for detecting replacement is not limited as long as it can be detected that the ITB unit 37 has been replaced.

[0121] (How to set the target temperature) Next, a method for setting the target temperature in Example 7 will be described. In Example 6, a double-sided counter that counts the number of double-sided prints was used as a warm-up index for the photosensitive drum, which is the image carrier. While this can be controlled using a sheet counter in a monochrome printer, in a color printer using a secondary transfer method, the intermediate transfer belt 28, which directly contacts the recording material 11, is in contact with four photosensitive drums 22Y, 22M, 22C, and 22K in addition to the recording material 11. The increased number of factors that affect the temperature of the intermediate transfer belt 28 complicates the mechanism of the sheet counter. This can lead to a large discrepancy between the temperature of the intermediate transfer belt 28 and the sheet counter, potentially making it difficult to set the target temperature appropriately. Therefore, in a color printer using a secondary transfer method, it is necessary to accurately grasp the temperature rise during printing and the temperature fall during standby, and to predict the temperature of the intermediate transfer belt 28 in combination with the printer's operating status. Furthermore, when predicting the temperature of the replaceable intermediate transfer belt 28, the intermediate transfer belt 28 is connected to four replaceable photosensitive drums (22Y, 22M, 22C, 22K). Therefore, it is necessary to predict the temperature of the photosensitive drum (22Y, 22M, 22C, 22K) as well.

[0122] In Example 7, we will explain the case where the temperatures of the intermediate transfer belt 28 included in the replaceable ITB unit 37 and the photosensitive drums (22Y, 22M, 22C, 22K) included in the replaceable CRG (20Y, 20M, 20C, 20K) are predicted and the adjustment amount D of the target temperature is determined.

[0123] The temperature rise of the intermediate transfer belt 28 during double-sided continuous printing, the temperature rise during single-sided continuous printing, and the temperature drop of the intermediate transfer belt 28 when the machine is stopped are the same as those shown in Figures 12(a) to 12(c) in Example 1. These are the temperatures of the intermediate transfer belt 28 measured in advance in the three states.

[0124] 33 shows the temperature of one photosensitive drum (denoted by reference numeral 22) measured in advance in the following two states. FIG. 33(a) shows the self-temperature rise caused by friction with the cleaning blade (denoted by reference numeral 21) when the photosensitive drum 22 is driven, where the photosensitive drum 22 rises in temperature from room temperature (RT) of 23°C to a saturation temperature (Tex) of 50°C. FIG. 33(b) shows the temperature drop caused by heat dissipation into the atmosphere of the photosensitive drum 22 when the photosensitive drum is stopped, where the photosensitive drum 22 drops in temperature from a heated state (50°C) to a saturation temperature (Tfx) of 23°C (room temperature).

[0125] At this time, the temperature Ti of the intermediate transfer belt 28 and the temperature Tj of each photosensitive drum 22 can be predicted by the following prediction formulas (6), (7), (8), and (9). Ti(t)=Ti(t-1)+ΔTi +α[4Ti(t-1)-Ty(t-1)-Tm(t-1)-Tc(t-1)-Tk(t-1)] (6) Tj(t)=Tj(t-1)+ΔTj+β[Tj(t-1)-Ti(t-1)] (j=y, m, c, k) (7) ΔTi=[Tdx-Ti(t-1)]×Kd×Ed +[Tsx-Ti(t-1)]×Ks×Es +[Twx-Ti(t-1)]×Kw×Ew (8) ΔTj=[Tex-Tj(t-1)]×Ke×Ee +[Tfx-Tj(t-1)]×Kf×Ef (9)

[0126] The temperature of the intermediate transfer belt 28 can be expressed by the heat exchange with the recording material 11 and the atmosphere in the print mode (single-sided printing, double-sided printing) and in the stopped state, and the heat exchange with each photosensitive drum 22 due to the temperature difference.

[0127] The temperature of the photosensitive drum 22 can be expressed by heat generated by itself during operation (when operating or stopped), heat radiation to the atmosphere, and heat exchange due to the temperature difference with the intermediate transfer belt 22.

[0128] Here, Ti(t) is the predicted temperature of the intermediate transfer belt 28 at time t, where t is measured in units of one second. Tj(t)[j=y, MS, k] is the predicted temperature of the photosensitive drum 22j[j=y, MS, k] at time t. Ti(t-1) is the predicted temperature of the intermediate transfer belt 28 at time t-1. 4Ti(t-1)-Ty(t-1)-Tm(t-1)-Tc(t-1)-Tk(t-1) is the sum of the temperature differences between each photosensitive drum 22 and the intermediate transfer belt 28 at time t-1, and α is a constant. α is a constant determined by the difference in heat capacity between the intermediate transfer belt 28 and the photosensitive drum 22.

[0129] Tj(t-1) is the predicted value of the temperature of the photosensitive drum 22 at time t-1, Tj(t-1 )-Ti(t-1) is the temperature difference between the intermediate transfer belt 28 and the photosensitive drum 22 at time T-1, and β is a constant determined by the difference in heat capacity between the photosensitive drum 22 and the intermediate transfer belt 28.

[0130] ΔTi represents the heat exchange with the recording material and atmosphere in each print mode at time t. Therefore, ΔTi can be expressed using the difference between Ti(t-1) and the saturation temperature (Tdx) during double-sided continuous printing, the saturation temperature (Tsx) during single-sided continuous printing, and the saturation temperature (Twx) when the main unit is stopped, as well as constants K (Kd, Ks, Kw) and variables E (Ed, Es, Ew).

[0131] Here, variable E varies depending on the operating status of printer 100, with Ed=1, Es=0, Ew=0 during double-sided printing, Ed=0, Es=1, Ew=0 during single-sided printing, and Ed=0, Es=0, Ew=1 when the printer is stopped. That is, equation (8) is divided into terms for double-sided printing, single-sided printing, and when the printer is stopped, and which term is valid is determined by variable E. Furthermore, each term is expressed by the difference between the respective saturation temperatures (Tdx, Tsx, Twx) and Ti(t-1).

[0132] ΔTj represents the self-heating and heat dissipation to the atmosphere during operation (when operating, when stopped). Therefore, it can be expressed by the difference between the saturation temperature (Tex) during operation and the saturation temperature (Tfx) when the photosensitive drum 22 is stopped, and Tj(t-1), as well as constants (Ke, Kf) and variables E (Ee, Ef). Here, variable E varies depending on the operating conditions of the photosensitive drum, with Ee = 1 and Ef = 0 during operation and Ee = 0 and Ef = 1 during stoppage. That is, equation (9) is divided into terms for when the photosensitive drum 22 is operating and when the photosensitive drum 22 is stopped, and which term is valid is determined by variable E. Each term is expressed by the difference between the respective saturation temperatures (Tex, Tfx) and Ti(t-1).

[0133] For example, if double-sided printing continues for a long period of time, Ti(t-1) in equation (8) approaches Tdx, and ΔTi ≒ 0, so Ti(t) in equation (6) approaches the saturation temperature Tdx during double-sided printing. This also applies to single-sided printing and when the printer is stopped, as they approach Tsx and Twx, respectively, over a long period of time. Furthermore, the constants K (Kd, Ks, Kw) are constants used to adjust the estimated values ​​and actual measured values ​​for double-sided printing, single-sided printing, and when the printer is stopped so that they match.

[0134] In addition, the temperature of the intermediate belt 28 and the temperature of the photosensitive drum 22 influence each other, and each has a term that acts in the direction of reducing the temperature difference, so as the temperature difference increases, the influence of the term that reduces the temperature difference also increases.

[0135] A method for setting the target temperature Ttgt in the seventh embodiment will be described with reference to the flowchart in Fig. 34. When the power switch (not shown) of the printer 100 is turned on (1001), Ed = 0, Es = 0, Ew = 1, Ee = 0, and Ef = 1 are set in the temperature prediction formula (belt temperature prediction formula) Ti(t) of the intermediate transfer belt 28 and the drum temperature prediction formula Tj(t), respectively. Furthermore, the belt temperature prediction formula Ti(t) is set to the standby prediction formula Tw(t), and the drum temperature prediction formula Tj(t) is set to the standby prediction formula Tf (1002). Furthermore, the initial values ​​of the belt temperature prediction formula Ti(t) and the drum temperature prediction formula Tj(t) at power on are set to room temperature (RT).

[0136] Here, the room temperature is the detected temperature if a temperature sensor for detecting the room temperature is installed, and if no temperature sensor is installed, it may be a fixed value such as 23°C. Also, if the temperatures of the belt temperature prediction formula Ti(t) and the drum temperature prediction formula Tj(t) at the time of the previous power OFF can be stored and the elapsed time from when the power was turned OFF to when the power was turned ON can be measured, the temperature may be determined as follows: That is, the temperature of the power supply can be calculated from the elapsed time using the above formulas (6) to (9). The belt temperature and drum temperature when the device is ON may be calculated.

[0137] Next, ITB unit replacement is detected (1003), and if it has been replaced, room temperature (RT) is set to Ti(t) (1004). Next, CRG replacement is detected (1005), and room temperature (RT) is set to Tj(t) for the color for which replacement is detected (1006). When a print job is received (1007), it is determined whether the print job is double-sided printing (1008). If double-sided printing, Ed=1, Es=0, Ew=0, Ee=1, and Ef=0 are set, respectively, and the belt temperature prediction formula Ti(t) is set to the prediction formula for double-sided paper feeding Td(t), and the drum temperature prediction formula Tj(t) is set to the prediction formula for driving Te(t) (1009). In the case of single-sided printing, Ed=0, Es=1, Ew=0, Ee=1, and Ef=0 are set, and the belt temperature prediction formula Ti(t) is set to the prediction formula Ts(t) for single-sided paper feed, and the drum temperature prediction formula Tj(t) is set to the prediction formula Te(t) for driving (1010).

[0138] Next, a reference temperature Ta is determined (1011). The method for determining the reference temperature Ta is the same as in the sixth embodiment. A target temperature adjustment amount D is found (1012) according to the temperature of the intermediate transfer belt 28 calculated using the belt temperature prediction formula Ti(t). The target temperature adjustment amount D is a parameter set in advance according to the temperature of the intermediate transfer belt 28 as shown in FIG. 15, and has a relationship in which the higher the temperature of the intermediate transfer belt 28, the larger the target temperature adjustment amount D. Specifically, the target temperature adjustment amount D is set to increase by 1°C every time the temperature of the intermediate transfer belt 28 rises by 1°C from room temperature. Finally, the target temperature Ttgt is calculated and determined using formula (10) (1013). Ttgt=Ta-D (10)

[0139] The processing of steps 1008 to 1013 is repeated until the print job is completed (1014), and when the print job is completed, the processing of steps 1002 to 1014 is repeated until the power is turned off (1015), and when the power is turned off, the flow ends (1016).

[0140] By setting the variable E according to the operating state of the printer 100 and using equations (6), (7), (8) and (9), it is possible to predict in detail the temperature of the intermediate transfer belt 28 and the temperature of the photosensitive drum of each color, and to set an appropriate target temperature Tgt.

[0141] Here, the following experiment was conducted to confirm the effect of detecting replacement of the ITB unit 37, detecting replacement of the CRG, and controlling the target temperature of the heating device based on the temperature of the intermediate transfer belt 28 using the belt temperature prediction formula Ti(t) in this embodiment. The conditions of the experiment were a recording material conveying speed of 300 mm / sec and a print speed (throughput) of 60 ppm. The recording material used was A4 size Red Label paper manufactured by Canon / Oce, with a paper basis weight of 80 g / m. 2 The reference temperature Ta was set to 180°C.

[0142] It is also desirable to carry out the experiment in an environment where temperature and humidity conditions are controlled to a certain level using air conditioning or the like, and in this example, the experiment was carried out in an environment of temperature: 23°C and relative humidity: 50%.

[0143] The printing conditions were as follows: 500 double-sided prints were made, the ITB unit access door was opened and closed once, 10 double-sided prints were made, and then the ITB unit access door was opened again, the ITB unit was replaced with a new one, and another 10 double-sided prints were made.The experiment also started with the interior of the machine at room temperature of 23°C.

[0144] FIG. 36 shows the time transition of the temperature of the intermediate transfer belt 28 calculated from the target temperature Ttgt of this embodiment in this experiment, the belt temperature prediction formula Ti(t), and the temperature of each color drum calculated from the drum temperature prediction formula Tj(t). Since the temperature is 23°C, the target temperature adjustment amount D is also 0, so the target temperature Ttgt is the reference temperature Ta, 180°C. At this time, the temperature of the photosensitive drums for each color was also room temperature, 23°C. As double-sided printing progresses, the temperature of the intermediate transfer belt 28 rises, and the target temperature adjustment amount D increases and the target temperature Ttgt decreases according to the relationship in Figure 35. When double-sided printing has been completed for 500 sheets, the temperature of the intermediate transfer belt 28 has reached 37°C, and the target temperature adjustment amount D is 14, so the target temperature Ttgt is 166°C. Also, the temperature of the photosensitive drums for each color at this time was 35°C.

[0145] Next, the ITB unit access door was opened and closed, and 10 double-sided prints were made. At this time, the ITB unit replacement detection did not detect any replacement, so the belt temperature prediction formula Ti(t) remained at 37°C without being reset to room temperature. Therefore, the target temperature Ttgt remained at 166°C, corresponding to the temperature of the intermediate transfer belt 28. Also, the temperature of the photosensitive drum at this time remained at 35°C.

[0146] Next, the ITB unit access door was opened, the ITB unit was replaced with a new one at room temperature, the access door was closed, and 10 duplex prints were performed again. At this time, the ITB unit replacement detection before printing began detected the replacement, so the belt temperature prediction formula Ti(t) was reset to room temperature, 23°C. Because the temperature of the intermediate transfer belt 28 was 23°C at the start of printing, the target temperature adjustment amount D was set to 0, and the target temperature Ttgt was set to 180°C. After printing 10 duplex prints, the drum temperature prediction formula Tj(t) for each color photosensitive drum showed a drop to 34°C. This was because the intermediate transfer belt 28 had returned to room temperature, and heat from the photosensitive drum was absorbed by the intermediate transfer belt 28.

[0147] In this way, replacement of the intermediate transfer belt 28 that comes into direct contact with the recording material 11 is detected by ITB unit replacement detection, and the replacement is reflected in the belt temperature prediction formula Ti(t), thereby preventing cold offset.

[0148] The next experiment will explain how the target temperature Ttgt behaves when the CRG is replaced during double-sided printing. Figure 37 shows a case where, after 300 sheets of double-sided printing, the CRG 20K was replaced through the CRG access door, and then 200 more sheets of double-sided printing were performed. The graph shows the target temperature Ttgt and the temperature of the intermediate transfer belt 28 using the belt temperature prediction formula Ti(t), as well as the time progression of the temperature of each color drum using the drum temperature prediction formula Tj(t).

[0149] After 300 sheets of double-sided printing were completed, the temperature of the intermediate transfer belt 28 reached 33°C. Since the target temperature adjustment value D was 10, the target temperature Ttgt was 170°C. The temperature of the photosensitive drums for each color at this time was also 33°C. After this, the CRG20K was replaced with a new one, and double-sided printing of 200 sheets was started. As double-sided printing progressed, the temperature of the intermediate transfer belt 28 dropped to 31°C, then began to rise. By the time 200 sheets of double-sided printing was completed, the temperature of the intermediate transfer belt 28 had risen to 33°C. This was because the photosensitive drum 22K had been replaced with a new one, and the drum temperature prediction formula Tk(t) for the photosensitive drum 22K was reset to room temperature (23°C), increasing the temperature difference between the intermediate transfer belt 28 and the photosensitive drum 22K. This was because the heat of the intermediate transfer belt 28 was absorbed by the photosensitive drum 22K. As the temperature of the photosensitive drum 22K increases, the difference with the temperature of the intermediate transfer belt 28 decreases, and the temperature of the intermediate transfer belt 28 begins to rise. At this time, the target temperature Ttgt is also set by the target temperature adjustment amount D in response to the temperature change of the intermediate transfer belt 28, so that when 200 sheets are printed on both sides, the target temperature Ttgt gradually rises from 170°C to 172°C and then falls back to 170°C.

[0150] Figure 38 shows the case where after 300 double-sided prints, three CRGs, 20M, 20C, and 20K, were replaced through the CRG access door, and then 200 double-sided prints were made. The graph shows the target temperature Ttgt, the temperature of the intermediate transfer belt calculated by the belt temperature prediction formula Ti(t), and the time transition of the temperature of each color drum calculated by the drum temperature prediction formula Tj(t).

[0151] After 300 sheets of double-sided printing were completed, the temperature of the intermediate transfer belt 28 was 33°C, as before. Since the target temperature adjustment value D was 10, the target temperature Ttgt was 170°C. The temperature of each color photosensitive drum at this time was also 33°C. After this, the three CRGs (20M, 20C, and 20K) were replaced with new ones, and double-sided printing of 200 sheets was initiated. As double-sided printing progressed, the temperature of the intermediate transfer belt 28 decreased, and by the end of double-sided printing of 200 sheets, the temperature of the intermediate transfer belt 28 had dropped to 27°C. The temperature of the intermediate transfer belt 28 dropped significantly compared to when only the CRG 20K was replaced. This was because the heat from the intermediate transfer belt 28 was absorbed by the three photosensitive drums 22M, 22C, and 22K, which were at room temperature. The temperature of the photosensitive drum 22Y, which was not replaced, also dropped from 33°C to 28°C due to the decrease in the temperature of the intermediate transfer belt 28. At this time, the target temperature Ttgt is also set by an adjustment amount D in response to the temperature change of the intermediate transfer belt 28, so that the target temperature Ttgt is gradually increased from 170° C. to 176° C. for double-sided printing of 200 sheets.

[0152] As explained above, when the CRG is replaced with a new one, the temperature of the intermediate transfer belt 28 gradually decreases according to the number of replacements, and then begins to rise again when the temperature difference with the replaced photosensitive drum becomes smaller. The control unit 108 also adjusts the target temperature adjustment amount D according to the temperature change of the intermediate transfer belt 28 using this belt temperature prediction formula Ti(t), so that the target temperature Ttgt is gradually increased after the CRG is replaced.

[0153] In this way, replacement detection of the ITB unit 37 including the intermediate transfer belt 28 and replacement detection of the CRG including the photosensitive drum are performed, and the replacement detection results are reflected in the belt temperature prediction formula Ti(t) and the drum temperature prediction formula Tj(t). This makes it possible to calculate the complex temperature of the intermediate transfer belt 28 and set an appropriate target temperature, thereby preventing the occurrence of cold offset and hot offset.

[0154] Example 8 As in Example 7, when the temperature of the intermediate transfer belt 28 is predicted using the belt temperature prediction formula Ti(t), calculations stop when the printer is turned off or in sleep mode. For example, the ambient temperature may change significantly between powering off / sleeping and powering on / releasing from sleep mode. As a result, the predicted temperature based on the current room temperature may differ from the actual temperature of the intermediate transfer belt. Furthermore, when replacing the ITB unit 37, the predicted temperature of the replaced intermediate transfer belt is set to the temperature of the printer's installation environment. However, if the ITB unit 37 is stored in an environment with a temperature different from that of the printer's installation location, the predicted temperature may differ from the actual temperature of the intermediate transfer belt 28.

[0155] In the eighth embodiment, an example of a method for correcting the temperature difference immediately after power-on or when replacing an ITB unit, when a difference from the predicted temperature is likely to occur, is shown.

[0156] A constant current is applied to at least one of the primary transfer rollers (27Y, 27M, 27C, 27K) from a high-voltage circuit not shown when image formation is not taking place. Alternatively, a constant voltage (transfer bias) is applied by transfer voltage application means 109 shown in FIG. 32, and the voltage value at that time is detected by transfer voltage detection means 110, or the current value (transfer current value) is detected by transfer current detection means 111. These detected results are monitored, and the resistance value of the primary transfer unit, consisting of photosensitive drum 22, intermediate transfer belt 28, and primary transfer roller 27, is calculated by transfer calculation processing means 112, thereby measuring the resistance value. The result of this resistance measurement is used to determine the optimum voltage to be applied to the primary transfer roller during image formation.

[0157] Studies have shown that the resistance value measured at the primary transfer unit correlates with the temperature of the intermediate transfer belt 28. Figure 39 shows the relationship between the resistance value at the primary transfer unit and the temperature of the intermediate transfer belt 28, revealing a strong correlation between the resistance value and the temperature of the intermediate transfer belt 28. This is because the intermediate transfer belt 28 has a resistance-temperature characteristic in which the resistance decreases as the temperature increases. The resistance-temperature characteristic varies depending on the type and amount of conductive material that provides conductivity, as well as the dispersion state of the conductive material, and therefore differs depending on the configuration of the intermediate transfer belt. This resistance-temperature characteristic is measured in advance for a representative intermediate transfer belt and stored as a resistance-temperature conversion table in the control unit 108. By calculating the temperature of the intermediate transfer belt 28 from the resistance value, it is possible to correct the belt predicted temperature in the temperature prediction formula Ti(t).

[0158] A method for correcting the belt temperature prediction formula Ti(t) in the eighth embodiment will be described with reference to the flowchart in FIG. 40. When the power switch (not shown) of the printer 100 is turned on (1101), the resistance at the primary transfer unit is measured (1102). The measured resistance value is referenced to a resistance-temperature conversion table stored in the control unit 108 (1103), and the temperature of the intermediate transfer belt calculated from the resistance is set in the belt temperature prediction formula Ti(t) (1104). The contents of the belt temperature prediction formula Ti(t) are the same as those in the seventh embodiment, so a description thereof will be omitted. Next, ITB unit replacement is detected (1105), and if the ITB unit has been replaced, the resistance value at the primary transfer unit is measured (1102), and the temperature of the intermediate transfer belt calculated from the resistance value is set in the belt temperature prediction formula Ti(t) (1104). Also, if the device goes into sleep mode (1106), when the device returns from sleep mode, the resistance value at the primary transfer unit is measured (1102), and the temperature of the intermediate transfer belt calculated from the resistance value is set in the belt temperature prediction formula Ti(t) (1104). When a print job is received (1108), the fixing reference temperature Ta (1109) is determined. The temperature adjustment amount D is determined (1110) according to the belt temperature prediction formula Ti(t), which starts calculations using the temperature calculated from the resistance value as the starting point, and the fixing target temperature Ttgt is determined (1111). The processing of steps 1108 to 1111 is repeated until the print job is completed (1112). When the print job is completed, the processing of steps 1105 to 1112 is repeated until the power is turned off (1113), and the flow ends when the power is turned off (1114).

[0159] As explained above, when the power is turned on, when waking up from sleep mode, or when replacing the ITB unit, deviations between the actual temperature of the intermediate transfer belt 28 and the temperature predicted by the belt temperature prediction formula Ti(t) are likely to occur, and this temperature deviation can be eliminated by updating the belt temperature prediction formula Ti(t) to a temperature calculated from the resistance value of the primary transfer unit. By performing this update, deviations between the belt temperature prediction formula Ti(t) and the actual temperature of the intermediate transfer belt can be reduced, and an appropriate fixing target temperature Ttgt can be set, thereby preventing cold offset and hot offset.

[0160] In this embodiment, the resistance-temperature characteristics of a representative intermediate transfer belt 28 are stored as a resistance-temperature conversion table (resistance-temperature characteristic information) in the control unit 108, and the resistance value of the primary transfer unit is referenced. However, if the ITB unit 37 is provided with a memory chip 371, a resistance-temperature conversion table obtained by measuring the intermediate transfer belts 28 individually in the ITB unit may be written to the memory chip 371. In this case, more accurate updates are possible without being affected by individual variations.

[0161] Furthermore, the relationship between the resistance value of the primary transfer unit and the temperature of the intermediate transfer belt may deviate from the previously determined resistance-temperature characteristic relationship due to the influence of the humidity of the printer's installation environment and the durability of the photosensitive drum, intermediate transfer belt, and primary transfer roller that make up the primary transfer unit. In such cases, the amount of change due to durability and humidity in a representative intermediate transfer belt is measured in advance, and the respective influences are tabulated as coefficients and stored in the control unit 108. By adding the coefficients obtained from the table based on the actual durability of the printer and the humidity of the installation environment detected by the humidity sensor (humidity information) to the resistance value and referencing the resistance-temperature conversion table, more accurate temperature updating becomes possible.

[0162] Furthermore, if the printer is connected to a network, each time the resistance of the primary transfer section is measured, the resistance value, the temperature and humidity of the printer's installation environment, and the printer's operating status are saved on a server on the network. Data is saved from multiple printers connected to the network, and statistical processing is performed using averaging and regression equations. The analysis results can eliminate the effects of durability and humidity from the measured resistance value. Accurate temperature updates are possible by referencing a resistance-temperature conversion table using this processed resistance value.

[0163] In this embodiment, the predicted temperature of the intermediate transfer belt is updated based on resistance measurement at the primary transfer unit using examples of when the power is turned on, when waking up from sleep mode, and when the ITB unit is replaced, all of which are times when temperature deviations are likely to occur. However, since resistance measurement at the primary transfer unit is generally performed before image formation at the start of printing for each print job, the predicted temperature may also be updated for each print. The temperature may also be updated each time the cumulative number of printed sheets exceeds a certain number, each time a certain amount of time has passed, or when the deviation between the temperature calculated from the belt temperature prediction formula Ti(t) and the resistance measurement exceeds a certain temperature. It may also be updated when the CRG is replaced.

[0164] It is also possible to determine the target fixing temperature Ttgt using only the temperature of the intermediate transfer belt 28 calculated from the resistance value of the primary transfer section, without using the belt temperature prediction formula Ti(t). However, if resistance measurement is performed only once before image formation, such as during continuous double-sided printing of large volumes, the temperature may rise as the continuous double-sided printing progresses beyond the temperature measured at the beginning of printing, making hot offset more likely to occur. Furthermore, increasing the frequency of resistance measurements during continuous printing increases downtime and reduces productivity. Therefore, by using both the temperature of the intermediate transfer belt 28 calculated from the resistance value of the primary transfer section and the belt temperature prediction formula Ti(t), it is possible to achieve both appropriate target temperature setting and high productivity.

[0165] In this embodiment, the temperature is updated based on the resistance measurement results at the primary transfer unit of a color printer using a secondary transfer method, but correction may also be performed based on the resistance measurement results at the secondary transfer unit.Furthermore, when calculating the drum temperature using a prediction formula in a monochrome printer, the predicted drum temperature may also be corrected based on the resistance measurement results at the transfer unit. [Explanation of symbols]

[0166] 22...photosensitive drum, 28...intermediate transfer belt, 30...belt thermistor, 33...drum thermistor, 40...heating device

Claims

1. an image carrier that carries a developer image; a transfer member that forms a transfer nip between itself and the image carrier and transfers the developer image from the image carrier to a recording material at the transfer nip; a fixing unit having a heater and fixing the developer image onto the recording material by using heat from the heater; a temperature detection unit that detects the temperature of the fixing unit; a control unit that controls the power supplied to the heater so that the temperature detected by the temperature detection unit becomes a predetermined control target temperature; In an image forming apparatus comprising: an acquisition unit that acquires the temperature of the image carrier or the transfer member, The image forming apparatus is characterized in that the control target temperature is changed to a lower temperature as the temperature acquired by the acquisition unit increases.

2. 2. The image forming apparatus according to claim 1, wherein the control target temperature is changed to a temperature obtained by subtracting a temperature change amount based on the temperature acquired by the acquisition unit from the reference target temperature.

3. an image carrier that carries a developer image; a transfer member that forms a transfer nip between itself and the image carrier and transfers the developer image from the image carrier to a recording material at the transfer nip; a fixing unit having a heater and fixing the developer image onto the recording material by using heat from the heater; a temperature detection unit that detects the temperature of the fixing unit; a control unit that controls the power supplied to the heater so that the temperature detected by the temperature detection unit becomes a predetermined control target temperature; In an image forming apparatus comprising: an acquisition unit that acquires the temperature of the image carrier or the transfer member, the control target temperature is changed based on a first temperature change amount based on the temperature acquired by the acquisition unit, a second temperature change amount based on a time period for which power is supplied to the heater, and a predetermined coefficient; The first temperature change amount is set to an amount that increases as the temperature acquired by the acquisition unit increases, and the second temperature change amount is set to an amount that increases as the time for which power is supplied to the heater increases. and the control target temperature is changed to a temperature obtained by subtracting the first temperature change amount multiplied by the predetermined coefficient and the second temperature change amount multiplied by the predetermined coefficient from the reference target temperature.

4. 4. The image forming apparatus according to claim 3, wherein the predetermined coefficient is acquired based on at least one of a plurality of pieces of information including operating conditions of the image forming operation, the type of recording material, and environmental information of the apparatus.

5. an image carrier that carries a developer image; a transfer member that forms a transfer nip between itself and the image carrier and transfers the developer image from the image carrier to a recording material at the transfer nip; a fixing unit having a heater and fixing the developer image onto the recording material by using heat from the heater; a temperature detection unit that detects the temperature of the fixing unit; a control unit that controls the power supplied to the heater so that the temperature detected by the temperature detection unit becomes a predetermined control target temperature; In an image forming apparatus comprising: an acquisition unit that acquires the temperature of the image carrier or the transfer member, the control target temperature is changed based on a larger amount of change between a first temperature change amount based on the temperature acquired by the acquisition unit and a second temperature change amount based on a time period during which power is supplied to the heater; an image forming apparatus characterized in that the first temperature change amount increases as the temperature acquired by the acquisition unit increases, and the second temperature change amount increases as the time for which power is supplied to the heater increases, and the control target temperature is changed from a reference target temperature to a temperature obtained by subtracting the larger of the first temperature change amount and the second temperature change amount.

6. The second temperature change amount is When the recording material is not present in the fixing portion, the longer the supply time, the larger the difference. When the recording material is present in the fixing portion, the longer the supply time, the smaller the 6. The image forming apparatus according to claim 3, wherein the longer the time during which power is not supplied to the heater, the smaller the difference becomes.

7. 6. The image forming apparatus according to claim 1, wherein the acquisition unit has a temperature detection member that detects the temperature of the image carrier or the transfer member.

8. The image forming apparatus according to any one of claims 1 to 5, characterized in that the acquisition unit acquires a predicted temperature of the image carrier or the transfer member, which is predicted based on information including the operating status of the image forming apparatus.

9. The image forming apparatus described in any one of claims 1 to 8 is characterized in that, in a double-sided fixing operation in which the fixing section performs a first heating on a recording material on which an image is formed on both sides, with a developer image transferred only to one side, and then performs a second heating on the other side, with a developer image also transferred to the other side, when the double-sided fixing operation is performed continuously on multiple recording materials, the image forming apparatus is capable of performing a continuous double-sided fixing operation in which the second heating of a preceding recording material is performed after the first heating of a succeeding recording material.

10. 7. The image forming apparatus according to claim 2, wherein the reference target temperature is set based on the type of recording material.

11. The image carrier carries a developer image when the electrostatic latent image carried thereon is developed. The image forming apparatus according to any one of claims 1 to 10, characterized in that the toner image is either a photosensitive drum or an intermediate transfer body that carries a toner image by transferring the toner image from the photosensitive drum.

12. The image forming apparatus of any one of claims 1 to 11, characterized in that the fixing section has a cylindrical film, a heater provided in the internal space of the film, and a pressure roller in contact with the outer surface of the film, and a fixing nip section for sandwiching and transporting the recording material is formed by the heater and the pressure roller via the film.

Images