Image formation device

Abstract

To suppress generation of image defect due to dew condensation occurring from water generated through a fixing step.SOLUTION: An image formation device 100 comprises: an environmental temperature sensor 301 detecting a temperature of an environment where the image formation device is installed; a fixing device 30 heating and pressing a toner image formed on a recording material P for fixation; a fixing temperature sensor 39 detecting a temperature of the fixing device 30; and a control part 200 controlling the fixing device 30 based on the detection result of the fixing temperature sensor 39. After heating operation of the fixing device 30 is complete, the control part 200 compares a first temperature estimated based on the detection result of the environmental temperature sensor 301 to a second temperature estimated based on the detection result of the fixing temperature sensor 39, and performs dew condensation removal operation of removing dew condensation in the image formation device 100 when the second temperature is lower than the first temperature.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as an electrophotographic printer or an electrophotographic copying machine that forms an image on a recording material.

Background Art

[0002] In an image forming apparatus, after transferring the toner image formed on the photosensitive drum onto the recording material, the toner image is fixed to the recording material by a fixing device, which is an example of an image heating device. In these image forming apparatuses, when condensation occurs inside the apparatus, there is a risk of deterioration in image quality such as a change in image density. Therefore, for example, in Patent Document 1, a configuration is disclosed in which a temperature and humidity detection element that detects the temperature and humidity of the installation environment of the image forming apparatus and a temperature detection element that detects the temperature inside the apparatus are used to predict the occurrence of condensation inside the apparatus and reduce the deterioration of image quality.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a configuration that detects the temperature inside and outside the image forming apparatus and detects the occurrence of condensation inside the apparatus from the difference, if outside air flows into the image forming apparatus from the fixing discharge portion, condensation may occur inside the apparatus and there is a risk of deterioration in image quality. Examples of cases where outside air flows into the apparatus include wind from air conditioning equipment. Wind from a so-called blower such as a fan or circulator installed for indoor air circulation, a ceiling-mounted ceiling fan, or an air conditioner hits the discharge port of the image forming apparatus, and outside air may flow into the apparatus from the discharge port.

[0005] In an image forming apparatus that fixes a recording material on which a toner image is formed by heating and pressing, moisture absorbed by the recording material during the fixing process is released from the recording material. Since the atmosphere near the fixing device has a high temperature due to the heat generated from the fixing device and a high saturated water vapor pressure, most of the moisture generated from the recording material is absorbed into the atmosphere. There are cases where air containing a large amount of these moisture is pushed by the outside air flowing in from the exhaust port and enters the apparatus without being exhausted outside the apparatus. When relatively high-temperature air containing a large amount of moisture near the fixing device cools down inside the apparatus and reaches a temperature below the dew point, condensation may occur inside the apparatus. The condensation inside the apparatus generated as described above is caused by the moisture generated when the recording material undergoes the fixing process, and thus occurs regardless of the presence or absence of a temperature difference between the inside and outside of the apparatus. That is, unlike condensation caused by a temperature difference between the inside and outside of the apparatus, it is difficult to predict the occurrence of condensation from the temperatures inside and outside the apparatus. In particular, when dew condensation occurs on the surface of the photosensitive drum, the electrical resistance of the surface of the photosensitive drum becomes low due to the condensed moisture, so that an excessive current is supplied during charging, causing the potential of the photosensitive drum to become higher (the absolute value is larger) than normal. As a result, an image defect (hereinafter referred to as "low density") may occur in which an electrostatic latent image cannot be normally formed by exposure with a laser and the image density decreases. Furthermore, when the dew condensation progresses, it may cause an image defect (hereinafter referred to as "fogging") in which the toner on the developing roller is transferred to the photosensitive drum due to the condensed moisture.

[0006] The present invention has been made under such circumstances, and an object thereof is to suppress the occurrence of image defects caused by condensation resulting from moisture generated through the fixing process.

Means for Solving the Problems

[0007] In order to solve the above-described problems, the present invention comprises the following configuration.

[0008] (1) An image forming apparatus that forms an image on a recording material, comprising: a first detection means for detecting the temperature of the environment in which the image forming apparatus is installed; a fixing device for fixing a toner image formed on the recording material by heating and pressurizing; a second detection means for detecting the temperature of the fixing device; and a control means for controlling the fixing device based on the detection result of the second detection means. After the heating operation of the fixing device is completed, the control means compares a first temperature estimated based on the detection result of the first detection means with a second temperature based on the detection result of the second detection means. When the second temperature is lower than the first temperature, the image forming apparatus executes a dew condensation removing operation for removing dew condensation in the image forming apparatus.

Advantages of the Invention

[0009] According to the present invention, it is possible to suppress the occurrence of image defects caused by dew condensation generated by moisture generated through the fixing process.

Brief Description of the Drawings

[0010]

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Best Mode for Carrying Out the Invention

[0011] Hereinafter, with reference to the drawings, preferred embodiments of the present invention will be illustratively described in detail. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless otherwise specifically stated, the scope of the present invention is not intended to be limited only to those.

Example

[0012] <Image forming apparatus> FIG. 1 is a schematic diagram showing an example of a color image forming apparatus, and the configuration and operation of the image forming apparatus 100 of Example 1 will be described with reference to FIG. 1. Note that the image forming apparatus 100 of Example 1 is a so-called tandem type printer provided with image forming stations a to d. The first image forming station a forms images of each color of yellow (Y), the second image forming station b forms magenta (M), the third image forming station c forms cyan (C), and the fourth image forming station d forms black (K). The configurations of the respective image forming stations are the same except for the color of the toner they contain. Hereinafter, the description will be made using the first image forming station a. Further, hereinafter, when no particular distinction is required, a to d in Y, M, C, and K will be omitted from the description.

[0013] The first image forming station a includes a photosensitive drum 1a, a charging roller 2a as a charging means, an exposure unit 3a, and a developing unit a. The photosensitive drum 1a is an image carrier that is rotationally driven by a photosensitive drum driving unit 110 (see FIG. 2) at a peripheral speed (process speed) of 150 mm / sec in the direction of the arrow and carries a toner image. The photosensitive drum 1a is provided with a photosensitive layer and a surface layer on an aluminum base tube having a diameter of φ20 mm, and a thin film layer having a thickness of 20 μm formed of polyarylate is used for the surface layer.

[0014] When the control unit 200 (see FIG. 2), which is a control means such as a controller, receives an image signal, an image forming operation is started, and the photosensitive drum 1a is rotationally driven. During the rotation of the photosensitive drum 1a, it is uniformly charged to a predetermined potential with a predetermined polarity (the normal polarity is the negative polarity in Example 1) by the charging roller 2a, and is exposed according to the image signal by the exposure unit 3a, which is an exposure means having a light source. As a result, an electrostatic latent image corresponding to the yellow color component image of the target color image is formed on the photosensitive drum 1a. Next, the electrostatic latent image is developed by a developing device 4a (yellow developing device) at the developing position and visualized as a yellow toner image on the photosensitive drum 1a.

[0015] The charging roller 2a, which is a charging member, is in contact with the charging portion on the surface of the photosensitive drum 1a with a predetermined pressure contact force and is driven to rotate passively with respect to the photosensitive drum 1a due to friction with the surface of the photosensitive drum 1a. Also, a predetermined DC voltage is applied from a charging voltage power supply 120 (see FIG. 2) to the rotation axis of the charging roller 2a according to the image forming operation. In Example 1, the charging roller 2a uses a roller provided with an elastic layer made of a conductive elastic body having a thickness of 1.5 mm and a volume resistivity of about 1×10 6 Ω·cm on a metal shaft with a diameter of φ5.5 mm. Then, according to the image forming operation, the control unit 200 applies a DC voltage of -1050 V as a charging voltage to the rotation axis of the charging roller 2a to charge the surface of the photosensitive drum 1a to -500 V, which is a predetermined potential. The surface potential of the photosensitive drum 1a was measured with a surface potentiometer Model 344 manufactured by Trek. The surface potential of the photosensitive drum 1a at this time, -500 V, is the surface potential of the photosensitive drum 1 during non-image formation and is the dark part potential (Vd) at which toner image development is not performed.

[0016] The exposure unit 3a includes a laser driver, a laser diode (light source), a rotating polygon mirror, an optical lens system, etc. As shown in FIG. 2, the exposure unit 3 receives, via the interface 201 from the controller 202, the time-series electrical digital pixel signals of the image information that has been subjected to image processing. In the first embodiment, the exposure amount (light amount) is adjusted so that the image formation potential Vl of the photosensitive drum 1a of the electrostatic latent image portion after being exposed by the exposure unit 3a becomes -100V. The image formation potential is also referred to as the bright portion potential.

[0017] The developing unit 4a includes a developing roller 41a as a developing means (developing member) (developer carrier) and toner as a one-component developer. The developing unit 4a is a developing means that performs a developing action on the photosensitive drum 1a in order to develop an electrostatic latent image into a toner image, and is a developer accommodating portion that accommodates the developer. The developing unit 4a and the main body of the image forming apparatus 100 are provided with a developing contact / separation mechanism 40 that controls the contact / separation (developing separation) state between the developing roller 41a and the photosensitive drum 1a as shown in FIG. 2. The control unit 200 causes the developing roller 41a and the photosensitive drum 1a to contact and separate according to the image forming operation and the like. When the developing roller 41a is in contact with the photosensitive drum 1a, the developing roller 41a contacts the photosensitive drum 1a with a pressing force of 1.96 N. The width of the developing nip portion, which is the contact portion between the developing roller 41a and the photosensitive drum 1a, is 2 mm in the rotational direction of the photosensitive drum 1a and 220 mm in the longitudinal direction (rotation axis direction) of the photosensitive drum 1a. And the developing roller 41a is rotationally driven by the developing roller driving unit 130 so that the surface movement direction of the developing roller 41a in the opposing portion (contact portion) with the photosensitive drum 1a is in the same direction as the surface movement direction of the photosensitive drum 1a at a peripheral speed higher than the peripheral speed of the photosensitive drum 1a.

[0018] The pre-exposure unit 5a as a charge removing means exposes the surface of the photosensitive drum 1a before the surface of the photosensitive drum 1a is charged by the charging roller 2a, thereby removing the charge from the surface of the photosensitive drum 1a. By removing the charge from the surface of the photosensitive drum 1a, it has the role of equalizing the surface potential formed on the photosensitive drum 1a and the role of controlling the discharge amount due to the discharge occurring in the charged portion.

[0019] Also, during the contact between the developing roller 41a and the photosensitive drum 1a during the image forming operation, the control unit 200 controls to apply a DC voltage of -300V as the developing voltage Vdc from the developing voltage power supply 140 to the shaft of the developing roller 41a. During image formation, due to the electrostatic force generated by the potential difference between the developing voltage Vdc = -300V and the image forming potential Vl = -100V of the photosensitive drum 1a, the toner carried on the developing roller 41a is developed on the image forming potential Vl portion of the photosensitive drum 1a.

[0020] Here, in the following description, regarding the potential and the applied voltage, when the absolute value is larger on the negative electrode side (for example, -1000V compared to -500V), it is referred to as a high potential, and when the absolute value is smaller on the negative electrode side (for example, -300V compared to -500V), it is referred to as a low potential. This is for considering the toner with negative chargeability in Example 1 as a reference. Also, the voltage in Example 1 is expressed as the potential difference from the ground potential (0V). Therefore, the developing voltage Vdc = -300V is interpreted as having a potential difference of -300V due to the developing voltage applied to the shaft of the developing roller 41a with respect to the ground potential. This is the same for the charging voltage, transfer voltage, etc.

[0021] The voltage output by each power supply is appropriately adjusted based on the values of the environmental temperature sensor 301 and the environmental humidity sensor 302 as the first detection means. The image forming apparatus 100 includes a cooling fan 303 for cooling heat generated by the power supply, the motor, and the rotation drive of the members. The cooling fan 303 sucks in outside air and blows it to each heat generating part to suppress the temperature rise. The cooling fan 303 corresponds to a cooling member that sucks in outside air and cools the fixing device 30. The environmental temperature sensor 301 is preferably installed in a place where the temperature rise caused by various power supplies and the fixing device 30 in the image forming apparatus 100 has little influence. In the first embodiment, the environmental temperature sensor 301 is disposed at the suction port of the cooling fan 303 that sucks in outside air (see FIG. 6). The cooling fan 303 starts driving when the power is turned on and continues driving during the operation of the image forming apparatus 100. The cooling fan 303 stops when the image forming operation ends and the image forming apparatus 100 shifts to the sleep state. In the first embodiment, the time from the end of the image forming operation until the image forming apparatus 100 shifts to the sleep state is 5 seconds. Note that the sleep state is a state in which the image forming apparatus 100 suppresses power consumption to achieve power saving. For example, in the sleep state, the power supply to the fixing device 30 and the rotation drive of each rotating member are stopped, and a minimum function such as the control unit 200 necessary to receive the next image forming command and return to the print state is operating.

[0022] Next, the control unit 200 will be described. FIG. 2 is a control block diagram showing a schematic control mode of the main part of the image forming apparatus 100 in the first embodiment. The controller 202 exchanges various electrical information with the host device, and controls the image forming operation of the image forming apparatus 100 through the interface 201 in the control unit 200 according to a predetermined control program and reference table. The control unit 200 includes a CPU 155 that performs various arithmetic processes, and a memory 154 such as a ROM and a RAM which are storage elements. The sensor detection results, counter count results, arithmetic results, etc. are stored in the RAM, and the control program, data tables obtained in advance by experiments, etc. are stored in the ROM. Each control target, sensor, counter, etc. in the image forming apparatus 100 is connected to the control unit 200. The control unit 200 controls the transmission and reception of various electrical information signals, the driving timing of each part, etc., and performs control of a predetermined image forming sequence. For example, the control unit 200 controls the voltages applied by the charging voltage power supply 120, the developing voltage power supply 140, the exposure units 3, the primary transfer voltage power supply 160, and the secondary transfer voltage power supply 150, as well as the exposure amount. In addition, control of the photosensitive drum driving unit 110, the developing roller driving unit 130, the developing contact / separation mechanism 40, and the fixing driving unit 400 is also performed. Then, the image forming apparatus 100 forms an image on the recording material P (on the recording material) based on the electrical image signal input from the host device to the controller 202. Examples of the host device include an image reader, a personal computer, a facsimile machine, a smartphone, etc.

[0023] The toner in the first embodiment is a non-magnetic toner having a negative charge property manufactured by the suspension polymerization method, with a volume average particle diameter of 7.0 μm, and is charged negatively when carried on the developing roller 41a. The volume average particle diameter of the toner was measured with a laser diffraction particle size distribution analyzer LS-230 manufactured by Beckman Coulter, Inc.

[0024] As an intermediate transfer member, the intermediate transfer belt 10 in FIG. 1 is stretched by a plurality of stretching members 11, 12, and 13. The stretching member 13 is rotationally driven at a peripheral speed of 103% with respect to the photosensitive drum 1a in a direction of moving in the circumferential direction at a contact portion in contact with the photosensitive drum 1a by a motor (not shown). The stretching members 11 and 12 are rotationally driven following the rotation of the intermediate transfer belt 10. A DC voltage of 250 V is applied from a primary transfer voltage power source 160 to the primary transfer roller 14a as a primary transfer member during primary transfer in the image forming operation. In Example 1, a configuration is adopted in which a DC voltage is also applied from the primary transfer voltage power source 160 to the stretching member 13. A configuration may also be adopted in which a DC voltage is applied from the primary transfer voltage power source 160 to the stretching members 11 and 12. The yellow toner image formed on the photosensitive drum 1a is electrostatically transferred onto the intermediate transfer belt 10 in the process of passing through the primary transfer portion which is the contact portion of the primary transfer roller 14a via the photosensitive drum 1a and the intermediate transfer belt 10. In Example 1, a difference in peripheral speed is provided between the photosensitive drum 1a and the intermediate transfer belt 10. Thereby, the toner moves on the photosensitive drum 1a in the primary transfer portion, and the primary transfer efficiency is improved by reducing the adhesion force. Here, the developer remaining on the photosensitive drum 1a without being transferred to the intermediate transfer belt 10 is configured to be recovered by the developing roller 41a.

[0025] The primary transfer roller 14a is a cylindrical metal roller with a diameter of φ6mm, and the material used is nickel-plated steel. The primary transfer roller 14a is arranged at a position offset by 8mm downstream in the moving direction of the intermediate transfer belt 10 with respect to the center position of the photosensitive drum 1a, and the intermediate transfer belt 10 is configured to wrap around the photosensitive drum 1a. Among the plurality of photosensitive drums 1 and the plurality of primary transfer rollers 14, they are arranged such that the distances from the axis centers of the respective photosensitive drums 1 to the axis centers of the respective primary transfer rollers 14 are equal. The offset amount may be changed for each image forming station. The primary transfer roller 14a is arranged at a position lifted by 1mm with respect to the horizontal plane formed by the photosensitive drum 1a and the intermediate transfer belt 10 so as to ensure the winding amount of the intermediate transfer belt 10 around the photosensitive drum 1a. And the primary transfer roller 14a presses the intermediate transfer belt 10 with a force of about 1.96N. The primary transfer roller 14a rotates passively as the intermediate transfer belt 10 rotates. Also, the primary transfer roller 14b arranged at the second image forming station b, the primary transfer roller 14c arranged at the third image forming station c, and the primary transfer roller 14d arranged at the fourth image forming station d have the same configuration as the primary transfer roller 14a.

[0026] Hereinafter, similarly, a second-color magenta toner image, a third-color cyan toner image, and a fourth-color black toner image are formed by the second, third, and fourth image forming stations b, c, and d, and are sequentially transferred and stacked on the intermediate transfer belt 10. Then, a composite color image corresponding to the target color image is obtained on the intermediate transfer belt 10.

[0027] The four-color toner images on the intermediate transfer belt 10 are collectively transferred onto the surface of the recording material P fed by the paper feed roller 51 as the paper feed means during the secondary transfer process through the secondary transfer nip formed by the secondary transfer roller 15 as the intermediate transfer belt 10 and the secondary transfer member. The secondary transfer roller 15 is in contact with the intermediate transfer belt 10 with a pressure of 50 N to form the secondary transfer nip. The secondary transfer roller 15 rotates passively with respect to the intermediate transfer belt 10, and when the toner on the intermediate transfer belt 10 is secondarily transferred onto the recording material P such as paper, a voltage of 1500 V is applied from the secondary transfer voltage power supply 150.

[0028] Thereafter, the recording material P carrying the four-color toner images is introduced into the fixing device 30. By being heated and pressurized by the fixing device 30, the four-color toner is melted and mixed and fixed to the recording material P. Details of the configuration and operation of the fixing device 30 will be described later. The toner remaining on the intermediate transfer belt 10 after the secondary transfer is cleaned and removed by the cleaning device 17. The cleaning device 17 has a cleaning blade or the like that contacts the outer peripheral surface of the intermediate transfer belt 10 to scrape off the toner remaining on the intermediate transfer belt 10 and collect it into the cleaning device 17. The cleaning device 17 is arranged to collect the toner adhering to the intermediate transfer belt 10 on the downstream side in the rotation direction of the intermediate transfer belt 10 from the secondary transfer portion of the intermediate transfer belt 10. Through the above operations, a full-color printed image is formed.

[0029] (Configuration of the intermediate transfer belt) The intermediate transfer belt 10 has a circumference of 700 mm and a thickness of 92 μm, and is formed by a base layer (first layer) and a surface layer (second layer). For the base layer, an endless polyvinylidene fluoride (PVdF) mixed with an ionic conductive agent such as a polyvalent metal salt or a quaternary ammonium salt as a conductive agent is used. For the surface layer, an acrylic resin mixed with a metal oxide or the like as a conductive agent is used. Defining the thickness of the base layer as t1 and the thickness of the surface layer as t2, t1 = 87 μm and t2 = 2 μm.

[0030] (Fixing device) Next, the configuration of the fixing device 30 in Example 1 will be described with reference to FIG. 3. Here, the longitudinal direction is the direction of the rotation axis of the pressure roller 33 that is substantially orthogonal to the conveyance direction of the recording material P described later. Also, the length of the recording material P in the direction (longitudinal direction) substantially orthogonal to the conveyance direction is referred to as the width. FIG. 3 is a schematic cross-sectional view of the fixing device 30. Also, FIG. 4(a) is a schematic cross-sectional view of the heater. Further, FIG. 4(a) is a cross-sectional view at the center in the longitudinal direction of the heating element 34b, which coincides with the center in the longitudinal direction of the recording material P conveyed in the fixing device 30.

[0031] The recording material P holding the unfixed toner image T from the right side of FIG. 3 is heated while being conveyed from right to left in the drawing at the fixing nip portion N, whereby the toner image T is fixed to the recording material P. The fixing device 30 in Example 1 includes a cylindrical film 31, a nip forming member 32 that holds the film 31, a pressure roller 33 that forms the fixing nip portion N together with the film 31, and a heater 34 for heating the recording material P.

[0032] The film 31, which is the first rotating body, is a fixing film as a heating rotating body. In Example 1, for example, polyimide is used as the base layer 31a. The inner diameter of the base layer 31a is 18 mm. An elastic layer 31b made of silicone rubber and a release layer 31c made of PFA are used on the base layer 31a. The thicknesses of the elastic layer 31b and the release layer 31c are 190 μm and 15 μm, respectively. In order to reduce the frictional force generated between the nip forming member 32 and the heater 34 and the film 31 due to the rotation of the film 31, grease is applied to the inner surface of the film 31.

[0033] The nip forming member 32 guides the film 31 from the inside and serves to form a fixing nip portion N between the film 31 and the pressure roller 33. The nip forming member 32 is a member having rigidity, heat resistance, and heat insulation properties and is formed of a liquid crystal polymer or the like. The film 31 is externally fitted to the nip forming member 32. The pressure roller 33, which is the second rotating body, is a roller as a pressure rotating body. The pressure roller 33 includes a core metal 33a, an elastic layer 33b, and a release layer 33c. The outer diameter of the pressure roller 33 is 20 mm, the thickness of the elastic layer 33b is 3.5 mm, and the thickness of the release layer 33c is 40 μm. The pressure roller 33 is rotatably held at both ends and is rotationally driven by a fixing drive unit 400 (see FIG. 2). Further, due to the rotation of the pressure roller 33, the film 31 rotates passively. The heater 34, which is a heating member, is held by the nip forming member 32 and is in contact with the inner surface of the film 31. The substrate 34a, the heating element 34b, the protective glass layer 34e, and the fixing temperature sensor 39 will be described later.

[0034] The heater 34 will be described in detail with reference to FIGS. 4(a) and 4(b). The heater 34 includes a substrate 34a, a heating element 34b, a conductor 34c, two contacts 34d1 and 34d2, and a protective glass layer 34e. The conductor 34c and the heating element 34b are electrically connected between the two contacts 34d1 and the contact 34d2, and the heating element 34b generates heat by applying an alternating voltage through a bidirectional thyristor (hereinafter referred to as a triac) (not shown).

[0035] The substrate 34a is made of alumina (Al2O3), which is a ceramic. As ceramic substrates, alumina (Al2O3), aluminum nitride (AlN), zirconia (ZrO2), silicon carbide (SiC), etc. are widely known. Among them, alumina (Al2O3) is inexpensive and easily available industrially. Also, a metal excellent in terms of strength may be used for the substrate 34a. As a metal substrate, stainless steel (SUS) is excellent in terms of both price and strength and is preferably used. In the case of using either a ceramic substrate or a metal substrate as the substrate 34a, if it has conductivity, an insulating layer may be provided for use. A protective glass layer 34e is formed to ensure insulation between the heating element 34b and the film 31. The length of the heating element 34b in the longitudinal direction is L = 222 mm. The electrical resistance between the two contacts 34d1 and 34d2 is 13 Ω.

[0036] The fixing temperature sensor 39 as the second temperature detection element is a thermistor. The configuration of the thermistor will be described with reference to FIG. 4(a). The fixing temperature sensor 39, which is the second detection means, is composed of a thermistor element 39a, a holder 39b, a ceramic paper 39c, and an insulating resin sheet 39d. The ceramic paper 39c serves to inhibit heat conduction between the holder 39b and the thermistor element 39a. The insulating resin sheet 39d serves to physically and electrically protect the thermistor element 39a. The thermistor element 39a is a temperature detection means whose output value changes according to the temperature of the heater 34, and is connected to the CPU 155 by a Jument wire (not shown) and wiring. The thermistor element 39a detects the temperature of the heater 34 and outputs the detection result to the CPU 155.

[0037] The fixing temperature sensor 39 is located on the surface of the substrate 34a opposite to the protective glass layer 34e, and is installed at the center in the longitudinal direction of the heating element 34b and is in contact with the substrate 34a. The CPU 155 controls the temperature in the fixing process based on the detection result of the fixing temperature sensor 39. The above is the description of the configuration of the fixing temperature sensor 39.

[0038] (Operation of the fixing device) The operation of the fixing device 30 will be described. When the control unit 200 receives an image signal, the image forming operation is started and the operation of the fixing device 30 is also started. When the image signal is received, the fixing drive unit 400 starts rotating to rotate the pressure roller 33 (forward rotation operation). Along with the rotation of the pressure roller 33, power is supplied to the heating element 34b of the heater 34, and the power supplied to the heating element 34b is adjusted so that the detected temperature (notification temperature) of the thermistor element 39a becomes a desired value. When the fixing device 30 is sufficiently heated in the forward rotation, the recording material P is conveyed to the fixing nip portion N to perform a fixing operation. The forward rotation operation can be said to be an operation until the temperature of the heating element 34b reaches the control temperature and the unfixed toner on the recording material P can be fixed. After the recording material P passes through the fixing nip portion N, the power supply to the heater 34 is terminated and the fixing drive unit 400 is stopped (reverse rotation).

[0039] Here, the control temperature of the fixing temperature sensor 39 during the fixing operation is determined in advance according to the type of the recording material P to be printed and the temperature of the environment where the image forming apparatus 100 is installed. The temperature and humidity information of the installation environment of the image forming apparatus 100 is obtained from the detection results of the temperature sensor 301 and the humidity sensor 302 connected to the image forming apparatus 100, respectively.

[0040] <Features of Example 1> The feature of Example 1 is that the control unit 200 determines whether the image forming apparatus 100 is installed in an environment where condensation is likely to occur based on the detected temperature of the fixing temperature sensor 39. When the image forming apparatus 100 is installed in an environment where condensation is likely to occur, the control unit 200 performs an operation to suppress the occurrence of image defects due to condensation. This will be described in detail below.

[0041] As described above, when the printing operation is executed in an environment where outside air is blown onto the image forming apparatus 100, condensation may occur inside the apparatus due to the inflow of outside air. Examples of cases where outside air flows into the apparatus include the wind generated by air conditioning equipment. The wind from so-called air blowers such as a fan or a circulator installed for indoor air circulation, a ceiling-mounted ceiling fan, or an air conditioner hits the discharge port 60 (see FIG. 1) of the image forming apparatus 100, and outside air may flow into the apparatus from the discharge port 60.

[0042] In the image forming apparatus 100 including the fixing device 30 that fixes the recording material P on which the toner image T is formed by heating and pressing, the moisture that the recording material P has absorbed is released from the recording material P during the fixing process. The atmosphere near the fixing member has a high temperature due to the heat generated from the fixing member and a high saturated water vapor pressure, so most of the moisture generated from the recording material P is absorbed into the atmosphere. There is a case where the air containing a large amount of these moisture enters the apparatus being pushed by the outside air flowing in from the discharge port 60 without being exhausted outside the apparatus. When the relatively high-temperature air containing a large amount of moisture near the fixing device 30 cools down inside the apparatus and reaches a temperature below the dew point, condensation may occur inside the apparatus.

[0043] Particularly, when condensation occurs on the surface of the photosensitive drum 1, the electrical resistance of the surface of the photosensitive drum 1 decreases due to the condensed moisture. In such a state, an excessive current is supplied to the photosensitive drum 1 in the charging process during charging, causing the potential of the photosensitive drum 1 to become higher than normal. As a result, an image defect (hereinafter referred to as "low density") in which an electrostatic latent image cannot be normally formed by laser exposure and the image density decreases may occur. Furthermore, when the condensation on the photosensitive drum 1 progresses, it may cause an image defect (hereinafter referred to as "fogging") in which the toner on the developing roller 41 is transferred to the photosensitive drum 1 due to the condensed moisture.

[0044] The detection operation of the outside air inflow environment in Example 1 for detecting the inflow of outside air will be described below. In Example 1, the control unit 200 determines whether the image forming apparatus 100 is installed in an environment where outside air flows in from the discharge port 60 based on the detected temperature of the fixing temperature sensor 39 in the fixing device 30 and the threshold temperature based on the detected temperature (notification temperature) of the environment temperature sensor 301.

[0045] (Dew condensation environment detection operation) The dew condensation environment detection operation in Example 1 will be described with reference to FIGS. 5 to 7. FIG. 5 is a flowchart when performing the dew condensation environment detection operation in Example 1. FIG. 6 is a diagram showing the state in which the image forming apparatus 100 is set. FIG. 7 is a diagram for explaining the dew condensation environment detection operation in Example 1. When the power of the image forming apparatus 100 is turned on, the control unit 200 starts the processing after step (hereinafter referred to as S) 501. In S501, the control unit 200 starts the initial processing for setting the image forming apparatus 100 to the ready state. In S502, the control unit 200 determines whether an abnormality has occurred during the initial processing. If the control unit 200 determines that there is no abnormality in S502, the processing proceeds to S503, and if it determines that there is an abnormality, the processing proceeds to S507.

[0046] In S503, the control unit 200 executes a dew condensation environment detection operation for detecting the installation environment of the image forming apparatus 100. In the dew condensation environment detection operation, the control unit 200 performs temperature control so that the detected temperature of the fixing temperature sensor 39 becomes a predetermined temperature, for example, 150° C. (control temperature, target temperature) in synchronization with the start of the rotational drive of the fixing drive unit 400. In Example 1, the control unit 200 performs an operation of ending the power supply to the heater 34 after rotation with heating for 10 seconds and continuing the rotational drive of the pressure roller 33 for 20 seconds. The control unit 200 performs temperature detection by the fixing temperature sensor 39 20 seconds after ending the power supply to the heater 34, stores the detected temperature of the fixing temperature sensor 39 in the memory 154 (RAM), and ends the rotation of the pressure roller 33.

[0047] In S504, based on the information obtained in the dew condensation environment detection operation executed in S503, the control unit 200 determines whether the environment where the image forming apparatus 100 is installed is a dew condensation environment. The dew condensation environment is an environment in which dew condensation likely to occur due to moisture generated through the fixing process is likely to occur.

[0048] Here, the control unit 200 compares the detected temperature of the fixing temperature sensor 39 measured in the dew condensation environment detection operation with the temperature (dew condensation environment threshold temperature) recorded in advance in the memory 154. When the detected temperature of the fixing temperature sensor 39 measured in the dew condensation environment detection operation is lower than the dew condensation environment threshold temperature, the control unit 200 determines that the fixing member is cooled by the outside air flowing in from the discharge port 60. That is, the control unit 200 determines that the image forming apparatus 100 is in a dew condensation environment.

[0049] In the configuration of the first embodiment, the fixing temperature sensor 39 for controlling the fixing temperature is disposed on the back surface of the heater 34. When the outside air flowing in from the discharge port 60 hits, the film 31 and the pressure roller 33 are directly cooled. When the fixing temperature sensor 39 is present at a position thermally distant from the fixing members to be cooled as in the first embodiment, after the heating is completed, the pressure roller 33 is driven so that the portions of the film 31 and the pressure roller 33 cooled by the outside air enter the fixing nip portion N. Thereby, the detection sensitivity by the fixing temperature sensor 39 can be enhanced. The dew condensation environment threshold temperature is determined from a table stored in advance in the memory 154 based on the installation environment of the image forming apparatus 100 detected by the environment temperature sensor 301.

[0050] In S504, when the control unit 200 determines that it is in an installation environment where outside air flows in from the discharge port 60, that is, in a dew condensation environment, the process proceeds to S506. In S506, since there is a risk of image defects due to dew condensation in the image forming apparatus 100, an operation for reducing this (dew condensation reduction operation (dew condensation removal operation)) is executed, and the process proceeds to S505.

[0051] In the first embodiment, as an operation for reducing condensation inside the image forming apparatus 100, the control of the cooling fan 303 is changed. Specifically, the air volume of the cooling fan 303 is increased and the cooling fan 303 is continuously driven even after the printing operation ends. The cooling fan 303 is driven for a predetermined time, for example, 5 minutes, after the image forming operation ends. When outside air is flowing into the image forming apparatus 100 from the discharge port 60, increasing the air volume of the cooling fan 303 can increase the pressure inside the image forming apparatus 100, thereby reducing the amount of outside air that enters the image forming apparatus 100. Furthermore, the outside air inhaled by the cooling fan 303 can dry the condensation inside the image forming apparatus 100.

[0052] If the control unit 200 determines in S504 that it is not a condensation environment, the process proceeds to S505, and in S505, it is set as print ready and the process ends. In S507, the control unit 200 stops the operation of the image forming apparatus 100 and ends the process.

[0053] (Regarding the condensation environment threshold temperature) When the image forming apparatus 100 is installed in an environment with a predetermined room temperature (e.g., 15°C), the control unit 200 controls the heater 34 for a first period (e.g., 10 seconds) so that the temperature becomes the control temperature. Thereafter, the control unit 200 stops the power supply to the heater 34 and rotates the pressure roller 33 for a second period (e.g., 20 seconds). In the first embodiment, at a plurality of room temperatures, when the above-described operation is performed, a predicted temperature profile of the fixing member, that is, a predicted temperature drop curve of the fixing member is obtained in advance. The temperature drop curve may be obtained by experiment or by simulation. Then, at the timing (t13 described later) when the temperature is detected by the fixing temperature sensor 39, the temperature predicted by the temperature drop curve is set as the dew condensation environment threshold temperature, and the room temperature and the dew condensation environment threshold temperature are associated and stored in the memory 154 as a table. The control unit 200 refers to the table stored in the memory 154 and acquires the dew condensation environment threshold temperature based on the detected temperature by the environment temperature sensor 301. For example, the control unit 200 acquires, from the table in the memory 154, a dew condensation environment threshold temperature associated with a room temperature of 15°C, for example, 73°C, based on the room temperature of 15°C which is the detection result of the environment temperature sensor 301. Note that a calculation formula for obtaining the dew condensation environment threshold temperature from the room temperature may be stored in the memory 154.

[0054] As described above, after the heating operation of the fixing device 30 is completed, the control unit 200 compares a first temperature (dew condensation environment threshold temperature) estimated based on the detection result of the environment temperature sensor 301 with a second temperature based on the detection result of the fixing temperature sensor 39. When the second temperature is lower than the first temperature, the control unit 200 executes a dew condensation removing operation for removing dew condensation in the image forming apparatus 100. The fixing temperature sensor may detect the temperature of any one of the heater 34, the film 31, and the pressure roller 33. The fixing temperature sensor 39 in the first embodiment detects the temperature of the heater 34. In the first embodiment, the control unit 200 rotationally drives the pressure roller 33 at the timing of detecting the second temperature when performing the above-described comparison.

[0055] <Operation of First Embodiment> The effects of Example 1 will be described using a comparative example. As a comparative example, an image forming apparatus was used that did not predict the installation environment due to outside air inflow using the fixing temperature sensor 39 of the fixing device 30, which is a feature of Example 1. The configurations and various setting values of the other image forming apparatuses are the same as those of Example 1. The verification of the effects was carried out at an ambient environmental temperature and humidity of 15°C and 80%.

[0056] FIG. 6 is a diagram for explaining the environment in which the image forming apparatuses of Example 1 and the comparative example were installed in this verification. A blower 312 is installed on the ceiling 310 above the image forming apparatus 100. The blower 312 generates wind 314. Assuming an installation environment in which the wind 314 from the blower 312 blows onto the image forming apparatus 100, the blower 312 was installed above the image forming apparatus 100 in the vertical direction, and printing was performed while blowing air. The wind speed of the wind 314 measured directly above the image forming apparatus 100 was 2.0 mm / s. The wind speed was measured with a testo 435 multi-environment measuring instrument manufactured by Testo.

[0057] The detection results of the dew condensation environment detection operation of Example 1 will be described with reference to FIG. 7. The dew condensation detection results will also be described together with the results when there is no air blowing. FIG. 7 shows time (seconds) on the horizontal axis and temperature (°C) on the vertical axis. t11 is the timing when the rotation of the pressure roller 33 starts and the power supply to the heater 34 starts. The heater 34 is controlled to a control temperature (150°C). t12 is the timing when the power supply to the heater 34 ends. The first time from timing t11 to timing t12 is 10 seconds. t13 is the timing when the rotation of the pressure roller 33 stops and the value detected by the fixing temperature sensor 39 is recorded in the memory 154. The second time from timing t12 to timing t13 is 20 seconds. Also, the two-dot chain line indicates the dew condensation environment threshold temperature (73°C) used in the determination of S504 in FIG. 5. Note that the value 73°C of the dew condensation environment threshold temperature is the value at timing t13 of the above-described temperature drop curve when the environmental temperature is 15°C.

[0058] The solid line L1 in Fig. 7 is the profile of the detected temperature of the fixing temperature sensor 39 in the dew condensation environment detection operation when there is air blowing from the blower 312 installed above the image forming apparatus 100. The dotted line L2 in Fig. 7 is the profile of the detected temperature of the fixing temperature sensor 39 in the dew condensation environment detection operation performed in a state where there is no air blowing from the upper blower 312.

[0059] When comparing the solid line L1 and the dotted line L2, there is almost no difference in the detected temperature of the fixing temperature sensor 39 until the timing t12 until the power supply to the heater 34 is terminated. On the other hand, when the power supply to the heater 34 stops at the timing t12, the detected temperatures of the fixing temperature sensors 39 of both deviate, and the detected temperature of the fixing temperature sensor 39 becomes lower compared to the case where there is air blowing and the case where there is no air blowing. In the solid line L1, the detected temperature of the fixing temperature sensor 39 at the timing t13 when 20 seconds have elapsed since the timing t12 when the power supply to the heater 34 was stopped was 67°C.

[0060] Here, in the first embodiment, the fixing temperature sensor 39 is disposed behind the heater 34 and is within the fixing nip portion N. In order to detect the temperature change in which outside air flows in from the discharge port 60 into the image forming apparatus 100 and the flowing outside air cools the fixing member, the control unit 200 also rotates the pressure roller 33 by the fixing drive unit 400 after the timing t12. Thereby, the surface of the fixing member cooled by the outside air is conveyed into the fixing nip portion N.

[0061] The dew condensation environment threshold temperature based on the detected temperature of the environment temperature sensor 301 in a 15°C environment is 73°C, and the detected temperature of 67°C by the fixing temperature sensor 39 at the timing t13 is lower than the dew condensation environment threshold temperature of 73°C. It can be seen that although the fixing member is cooled by the air flowing in from the discharge port 60, the fact that the cooling of the fixing member has been detected by the fixing temperature sensor 39 in contact with the back surface of the heater 34.

[0062] 7 is expected to be in an installation environment where condensation may occur inside the image forming apparatus 100 due to water vapor generated in the fixing process caused by wind flowing in from the exhaust port 60. Therefore, the image forming apparatus 100 of the first embodiment executes the condensation reduction operation of S506 in FIG. 5 in order to reduce the occurrence of image defects due to condensation inside the apparatus.

[0063] <Effects of Example 1> Next, the condensation reduction effect by executing the condensation reduction operation in response to the condensation environment detection result of Example 1 will be described with reference to Fig. 8. Fig. 8 shows the result of confirming the occurrence level of image defects (low density) caused by condensation occurring in the image forming apparatus 100 when a total of 30 sheets were printed by continuously printing 10 sheets with an intermittent time of 60 seconds using Example 1 and the comparative example.

[0064] The recording material P used for printing is Vitality paper manufactured by Xerox with a basis weight of 75 g / m 2 The recording material P used in the verification was left in an environment with a temperature and humidity of 15°C and 80% for 72 hours to fully absorb moisture. The moisture content of the recording material P used for printing was around 9%. The moisture content of the recording material P was measured using a Moistrex MX8000 manufactured by NDC Technologies. The printed image was a horizontal strip of halftone with an image density of 50% for Y, M, C, and K. In Figure 8, "◯" indicates that no unacceptable decrease in density of the halftone image occurred, and "×" indicates that an unacceptable decrease in density of the halftone occurred.

[0065] In the configuration of Example 1 in which the control of the cooling fan 303 was changed as the condensation reduction operation, no image defects (low density) occurred in any of the 30 sheets printed due to condensation in the image forming apparatus 100. On the other hand, in the comparative example in which the condensation reduction operation was not performed, a decrease in density occurred in halftones from the 18th sheet onwards.

[0066] (Reason for low density in the comparative example) Here, the mechanism by which the halftone density decreased in the comparative example will be described. FIG. 9(a) shows the surface potential Vd of the photosensitive drum 1 after charging during the printing operation of Example 1 (hereinafter referred to as the charged drum potential Vd), and the surface potential Vht of the exposed portion of the photosensitive drum 1 of the halftone with an image density of 50% (hereinafter referred to as the halftone portion potential Vht). The black circles in the figure indicate the charged drum potential Vd, and the open circles indicate the halftone portion potential Vht. Also, FIG. 9(b) shows the charged drum surface potential Vd and the halftone portion potential Vht with an image density of 50% during the printing operation of the comparative example. The horizontal axis of each graph represents the number of printed sheets (sheets). The vertical axis (potential (V)) is taken upward in the direction of increasing absolute value. In the following description, it will be described as rising or large with respect to the absolute value.

[0067] First, FIG. 9(a) will be described. The charged drum potential Vd for the first sheet of printing is -500 V as set above, and the halftone portion potential Vht is about -200 V on average. When 10 consecutive prints are performed, both the charged drum potential Vd and the halftone portion potential Vht increase slightly. This is because the moisture generated in the fixing process during 10 consecutive prints entered the image forming apparatus 100 due to the outside air flowing in from the discharge port 60, and moisture due to slight dew condensation adhered to the surface of the photosensitive drum 1, resulting in a decrease in electrical resistance.

[0068] As a result, since the potential difference between the developing roller potential Vdc and the halftone portion potential Vht becomes small, the halftone density slightly decreased in the latter half of the printing. However, with the configuration of Example 1, a halftone density decrease at an unacceptable level did not occur. Also, the dew condensation dried during the 60 - second interval, and in the 10 consecutive prints (sheets 11 - 20) after the 60 - second interval, the same potential change as in the first 10 consecutive prints occurred. The same is true for the next 10 consecutive prints (sheets 21 - 30).

[0069] Next, the potential change in the comparative example will be described with reference to FIG. 9(b). After charging the first sheet of the print, the drum potential Vd is -500V as set above, and the halftone potential Vht averages around -200V. When 10 consecutive prints are made, both the charged drum potential Vd and the halftone potential Vht increased significantly compared to the configuration of Example 1. This is due to the following reasons. Compared to the configuration of Example 1 in which the control of the cooling fan 303, which is an intake fan as a dew condensation reduction operation, is performed based on the result of the dew condensation environment detection operation, in the comparative example, since the air pressure inside the image forming apparatus 100 is low, more outside air flows in from the discharge port 60, resulting in a larger amount of dew condensation. Furthermore, in the configuration of the comparative example, even in 10 consecutive prints after a 60-second intermittent time, the potential did not return to the initial potential and further increased with the number of sheets. Specifically, both the charged drum potential Vd and the halftone potential Vht increased more at the 20th sheet than at the 10th sheet, and further increased more at the 30th sheet than at the 20th sheet. For this reason, density thinning occurred at a faster stage in the prints after the intermittent period.

[0070] As described above, in Example 1, the control unit 200 compares the detected temperature of the fixing temperature sensor 39 in the fixing device 30 with the dew condensation environment threshold temperature determined in advance based on the detected temperature of the environment temperature sensor 301. When the detected temperature of the fixing temperature sensor 39 is lower than the dew condensation environment threshold temperature, the control unit 200 determines that the image forming apparatus 100 is installed in an environment where outside air flows in from the discharge port 60. When it is determined that the image forming apparatus 100 is installed in an environment where outside air flows in, there is a possibility of dew condensation occurring inside the image forming apparatus 100 due to the water vapor generated by the recording material in the fixing process. In such a case, the control unit 200 executes a dew condensation reduction operation for suppressing image defects caused by dew condensation occurring inside the image forming apparatus 100.

[0071] In Example 1, as a dew condensation reduction operation, the control of the cooling fan 303 installed in the image forming apparatus 100 is changed. Specifically, the control unit 200 increases the intake amount of the cooling fan 303 and / or extends the driving time of the cooling fan 303. Thereby, by increasing the pressure inside the image forming apparatus 100, the inflow of outside air from the discharge port 60 is suppressed, and by promoting the drying of the dew condensation generated inside the image forming apparatus 100, the occurrence of image defects caused by dew condensation inside the apparatus can be reduced.

[0072] Also, in Example 1, the control of the cooling fan 303 is changed as an example of the dew condensation reduction operation when it is determined that the apparatus is installed in a dew condensation environment. The dew condensation reduction operation is not limited to this. For example, a configuration may be provided in which the time for reducing the moisture inside the image forming apparatus 100 is provided by extending the pre-rotation or post-rotation. Alternatively, instead of reducing the dew condensation itself, for example, the latent image setting (charging voltage, exposure light amount, developing voltage, etc.) during image formation may be adjusted, and the image formation may be performed under conditions where the reduction in image density is less likely to occur. For example, the charging voltage may be controlled so as to lower the drum potential Vd after charging compared to the case where the dew condensation reduction operation is not performed.

[0073] In this way, the control unit 200 executes a dew condensation removal operation by operating the cooling fan 303. The dew condensation removal operation may include an operation of extending the time until the fixing device 30 becomes in a state where fixing processing is possible (pre-rotation operation), and an operation of extending the time until shifting to the sleep state (post-rotation operation). Further, the dew condensation removal operation may include an operation of controlling the charging voltage applied to the charging roller, an operation of controlling the light amount of the light source of the exposure unit 3, and an operation of controlling the developing voltage applied to the developing roller 41.

[0074] As described above, according to Example 1, the occurrence of image defects caused by dew condensation generated by the moisture generated through the fixing process can be suppressed.

Example

[0075] In Example 2, the installation configuration of the fixing temperature sensor 59, which is different from that in Example 1, will be described. The configuration of the image forming apparatus used in Example 2 is the same as that in Example 1, and the same members are denoted by the same reference numerals, and the description thereof will be omitted.

[0076] [Fixing device] The configuration of the fixing device 50 in Example 2 will be described with reference to FIG. 10. FIG. 10 is a schematic cross-sectional view of the fixing device 50. The fixing device 50 in Example 2 includes a cylindrical film 31, a nip forming member 32 that holds the film 31, a pressure roller 33 that forms a fixing nip portion N together with the film 31, and a heater 34 for heating the recording material P. The film 31, the nip forming member 32, the pressure roller 33, and the heater 34 are the same as those in Example 1. A fixing temperature sensor 59 as a second detection means is disposed in contact with the inner surface of the film 31 on the heater 34 side.

[0077] The fixing temperature sensor 59 is a thermistor. The configuration of the thermistor will be described with reference to FIG. 11. The fixing temperature sensor 59 as the second detection means includes a thermistor element 59a, a holder 59b, a leaf spring 59c that also serves as a conductor wire, and an insulating resin sheet 59d. The leaf spring 59c is a conductor wire for measuring the voltage at both ends of the thermistor element 59a and serves to press the thermistor element 59a against the inner surface of the film 31. The insulating resin sheet 59d serves to physically and electrically protect the thermistor element 59a. The thermistor element 59a is a temperature detection means whose output value changes according to the temperature of the heater 34, and is connected to the CPU 155 by the leaf spring 59c and wiring. The thermistor element 59a detects the temperature of the inner surface of the film 31 and outputs the detection result to the CPU 155.

[0078] The fixing temperature sensor 59 is disposed on the nip forming member 32 and is arranged in contact with the inner surface of the film 31 at a position on the downstream side in the rotational direction of the film 31 in the fixing nip portion N. The fixing temperature sensor 59 is arranged along the forward direction in the rotational direction of the film 31. The position where the fixing temperature sensor 59 is inscribed in the film 31 is approximately at the center in the longitudinal direction of the film 31. The CPU 155 controls the temperature of the fixing process based on the detection result of the fixing temperature sensor 59. The above is the description of the configuration of the fixing temperature sensor 59 having the thermistor 59a.

[0079] [Operation of the fixing device 50] In the second embodiment, the control unit 200 performs fixing temperature control based on the temperature of the back surface of the film 31 detected by the fixing temperature sensor 59 inscribed in the film 31. The dew condensation environment detection operation of the second embodiment will be described with reference to FIG. 12. Note that FIG. 12 is the same graph as FIG. 7. t21 is the timing at which the rotation of the pressure roller 33 is started. t22 is the timing at which the rotation of the pressure roller 33 is stopped. The first hour from the timing t21 to the timing t22 is 10 seconds. t23 is the timing at which the value detected by the fixing temperature sensor 59 is recorded. The second hour from the timing t22 to the timing t23 is 20 seconds. The two-dot chain line indicates the dew condensation environment threshold temperature.

[0080] When the control unit 200 receives an image signal, the image forming operation is started and the operation of the fixing device 50 is also started. The control unit 200 starts the rotation of the fixing drive unit 400 and rotates the pressure roller 33 (forward rotation operation). The control unit 200 supplies power to the heating element 34b of the heater 34 as the pressure roller 33 rotates, and adjusts the power supplied to the heating element 34b so that the detected temperature of the fixing temperature sensor 59 becomes a desired value. When the fixing device 50 is sufficiently heated in the forward rotation, the recording material P is conveyed to the fixing nip portion N and the fixing operation is performed. After the recording material P passes through the fixing nip portion N, the control unit 200 ends the power supply to the heater 34 and stops the fixing drive unit 400 at the timing t22.

[0081] Here, the control temperature of the fixing temperature sensor 59 during the fixing operation is determined in advance according to the type of the recording material P to be printed and the temperature of the environment where the image forming apparatus 100 is installed. The temperature and humidity information of the installation environment of the image forming apparatus is obtained from the detection results of the temperature sensor 301 and the humidity sensor 302 connected to the image forming apparatus 100, respectively.

[0082] <Features of Example 2> In the configuration of Example 2, different from the dew condensation environment detection operation in Example 1, in the dew condensation environment detection operation, the rotation of the pressure roller 33 is stopped together with the end of the power supply to the heater 34 at timing t22. Hereinafter, the detection operation of the outside air inflow environment of Example 2 for detecting the inflow of the outside air will be described.

[0083] The control unit 200 of Example 2 determines whether the image forming apparatus 100 is installed in an environment where outside air flows in from the discharge port 60 based on the detected temperature of the fixing temperature sensor 59 that contacts the inner surface of the film 31 and the dew condensation environment threshold temperature based on the detected temperature of the environment temperature sensor 301. In Example 2, the fixing temperature sensor 59 detects the temperature of the film 31. The fixing temperature sensor 59 is disposed on the downstream side in the rotation direction of the film 31.

[0084] In the initial process for setting the image forming apparatus 100 to the ready state, the control unit 200 executes a dew condensation environment detection operation for detecting the installation environment of the image forming apparatus 100. The control unit 200 executes temperature adjustment control so that the detected temperature of the fixing temperature sensor 59 becomes 130°C (control temperature) in synchronization with the start of the rotational drive of the fixing drive unit 400. In Example 2, after rotation with heating for 10 seconds, the power supply to the heater 34 is terminated, and the rotational drive of the pressure roller 33 is stopped (timing t22). The control unit 200 stores the detected temperature of the fixing temperature sensor 59 in the memory 154 (RAM) at timing t23 after 20 seconds have elapsed from timing t22 when the fixing drive unit 400 stops.

[0085] The control unit 200 compares the temperature of the fixing temperature sensor 59 measured in the dew condensation environment detection operation with the dew condensation environment threshold temperature based on the temperature drop curve previously recorded in the memory 154. When the detected temperature of the fixing temperature sensor 59 measured in the dew condensation environment detection operation is lower than the dew condensation environment threshold temperature, the control unit 200 determines that the film 31 has been cooled by the inflow of outside air from the discharge port 60. That is, the control unit 200 determines that the image forming apparatus 100 is installed in a dew condensation environment.

[0086] In the configuration of the first embodiment, the fixing temperature sensor 39 was disposed behind the heater 34 and was inside the fixing nip portion N. In the first embodiment, in order for outside air to flow into the image forming apparatus 100 from the discharge port 60 and cool the fixing member to detect a temperature change, the fixing driving unit 400 was rotationally driven to perform an operation of conveying the surface of the fixing member cooled by the outside air into the fixing nip portion N.

[0087] In the configuration of the second embodiment, the fixing temperature sensor 59 directly measures the temperature of the film 31 which is the fixing member. Therefore, even without rotationally driving the fixing driving unit 400, a temperature change of the fixing member due to the inflow of outside air can be detected. In the second embodiment, since the fixing temperature sensor 59 is disposed on the downstream side in the rotational direction of the film 31, it is closer to the discharge port 60. Since it is cooled by the more directly flowing outside air, the inflow of outside air can be detected.

[0088] In the second embodiment, a configuration in which the fixing temperature sensor 59 for controlling the temperature of the fixing member is brought into contact with the inner surface of the film 31 has been described. However, the temperature measurement position of the film 31 is not limited to this. For example, the same applies to a configuration in which the temperature of the surface of the film 31 is measured. Further, the temperature sensor for performing the dew condensation environment detection operation is not limited to the film 31, and may be a configuration in which the temperature of the pressure roller 33 facing the film 31 is measured. On the other hand, as described in the second embodiment, measuring the temperature drop of the fixing member using the temperature change of a member with a small heat capacity such as the film 31 can perform detection with higher accuracy because it is more easily cooled by the outside air.

[0089] In addition, in the second embodiment, the configuration in which the dew condensation environment detection operation is performed using the fixing temperature sensor 59 that controls the temperature of the fixing member has been described as an example. However, the dew condensation environment detection operation may be performed using a temperature sensor that measures the temperature of the fixing member separately from the temperature sensor that controls the temperature.

[0090] As described above, according to the second embodiment, it is possible to suppress the occurrence of image defects caused by dew condensation generated by moisture generated through the fixing process.

[0091] <Other Embodiments> In the first and second embodiments, the dew condensation environment detection operation is performed during the heating and rotation operation of the fixing device that does not involve a conveyance operation different from the fixing process for the recording material P. However, the present invention is not limited to this. For example, the temperature of the fixing member may be measured during the heat dissipation process after the fixing process for the recording material P is completed, and the dew condensation environment detection operation may be performed.

[0092] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. Further, it can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

[0093] The disclosure of the present embodiment includes the following configurations. (Configuration 1) An image forming apparatus that forms an image on a recording material, a first detection unit that detects the temperature of the environment in which the image forming apparatus is installed, a fixing device that fixes a toner image formed on the recording material by heating and pressurizing, a second detection unit that detects the temperature of the fixing device, a control unit that controls the fixing device based on the detection result of the second detection unit, and After the heating operation of the fixing device is completed, the control means compares a first temperature estimated based on the detection result of the first detection means with a second temperature based on the detection result of the second detection means, and when the second temperature is lower than the first temperature, executes a dew removal operation for removing dew condensation in the image forming apparatus. The image forming apparatus is characterized by this. (Configuration 2) The fixing device includes a heating member, a first rotating body that contacts the heating member and is heated by the heating member, and a second rotating body that forms a nip portion together with the first rotating body. The image forming apparatus according to Configuration 1, wherein the second detection means detects the temperature of any one of the heating member, the first rotating body, and the second rotating body. (Configuration 3) The image forming apparatus according to Configuration 2, wherein the control means rotationally drives the second rotating body until the second temperature is detected when performing the comparison after the heating operation of the fixing device is completed. (Configuration 4) The image forming apparatus according to Configuration 3, wherein the second detection means detects the temperature of the heating member. (Configuration 5) The fixing device includes a heating member, a first rotating body that contacts the heating member and is heated by the heating member, and a second rotating body that forms a nip portion together with the first rotating body. The image forming apparatus according to Configuration 1, wherein the second detection means detects the temperature of the first rotating body. (Configuration 6) The image forming apparatus according to Configuration 5, wherein the second detection means is disposed on the downstream side in the rotation direction of the first rotating body. (Configuration 7) It includes a cooling member that sucks outside air and cools the fixing device. The image forming apparatus according to any one of Configurations 1 to 6, wherein the control means executes the dew removal operation by operating the cooling member.

Explanation of Signs

[0094] 30 Fixing device 39 Fixing temperature sensor 200 Control unit 301 Ambient temperature sensor

Claims

1. An image forming apparatus that forms an image on a recording material, comprising: first detection means for detecting the temperature of the environment in which the image forming apparatus is installed; a fixing device that fixes a toner image formed on the recording material by heating and pressing; second detection means for detecting the temperature of the fixing device; control means for controlling the fixing device based on the detection result of the second detection means; The control means compares a first temperature estimated based on the detection result of the first detection means with a second temperature based on the detection result of the second detection means after the heating operation of the fixing device is completed, and when the second temperature is lower than the first temperature, executes a dew removal operation for removing dew in the image forming apparatus. An image forming apparatus characterized by that.

2. The fixing device has a heating member, a first rotating body that contacts the heating member and is heated by the heating member, and a second rotating body that forms a nip portion together with the first rotating body. The second detection means detects the temperature of any one of the heating member, the first rotating body, and the second rotating body. The image forming apparatus according to claim 1.

3. The control means rotationally drives the second rotating body until the second temperature at the time of performing the comparison after the heating operation of the fixing device is completed is detected. The image forming apparatus according to claim 2.

4. The second detection means detects the temperature of the heating member. The image forming apparatus according to claim 3.

5. The fixing device has a heating member, a first rotating body that contacts the heating member and is heated by the heating member, and a second rotating body that forms a nip portion together with the first rotating body. The second detection means detects the temperature of the first rotating body. The image forming apparatus according to claim 1.

6. The second detection means is disposed on the downstream side in the rotation direction of the first rotating body. The image forming apparatus according to claim 5.

7. A cooling member that sucks outside air and cools the fixing device is provided. The control means executes the dew removal operation by operating the cooling member. The image forming apparatus according to any one of claims 1 to 6. ​

Images