Image forming apparatus

Abstract

An image forming apparatus includes a photosensitive drum, a developing roller, a fixing unit including a fixing film, a pressure roller, and a heating member forming a fixing nip between itself and the pressure roller, and a driving source transmitting a driving force to the developing roller and the pressure roller. Determining whether the recording material is a normal-size sheet or a small-size sheet, in the case of the normal-size sheet, executing a first mode of executing a post-rotation operation after the recording material passes through the fixing nip, and in the case of the small-size sheet, executing a second mode of executing a post-rotation operation after the recording material passes through the fixing nip; in the second mode, a post-rotation operation and a process of putting into an image forming job stop state are performed, the driving source is stopped, then the driving source is driven, and then the driving source is stopped.

Description

Technical Field

[0001] The present invention relates to an imaging device. Background Art

[0002] Image forming apparatuses such as copying machines, printers, and facsimile apparatuses are known, which form images on recording materials using an electrophotographic system or an electrostatic recording system. In an image forming operation in such image forming apparatuses, an electrostatic latent image is formed on an image bearing member, and a developing apparatus supplies toner to the electrostatic latent image and forms a toner image. There are cases in which such a developing apparatus is configured to be detachable from and attachable to an apparatus main unit of an image forming apparatus alone as an independent unit or as a part of a process cartridge.

[0003] The developing device generally has: a developer container that contains toner; and a developing roller that is disposed in an opening portion of the developing container and that conveys the toner to the outside of the developing container by rotating while carrying the toner. The developing device also has a supply roller that supplies the toner to the developing roller, and a developing blade that controls the amount of toner carried by the developing roller.

[0004] The imaging device also has a fixing device that fixes the toner image transferred to the recording material. The fixing device is usually provided with a cylindrical or columnar pressure roller, a fixing film, and a heating device having a heating surface, and is configured so that the fixing film is supported to slide on the heating surface. Heating and fixing are performed at the fixing nip between the fixing film and the pressure roller. In this film-type fixing device, since the fixing film has a low heat capacity, when heat is supplied from the heating device, the temperature of the fixing nip rises in a short time. Therefore, the time for supplying power to the heating device is set to be approximately the same as the time when the recording material carrying the unfixed image enters the fixing nip. This is how to save energy consumption of the heating device, etc. and prevent excessive temperature rise in the imaging device.

[0005] In addition, in such a fixing device, after the recording material as the fixing object passes through the fixing nip, the back rotation of the pressure roller can be performed to reduce the temperature at the end portion of the pressure roller, etc. The back rotation time of the pressure roller in the fixing device is usually set to meet the normal sheet size (for example, a letter (LTR) size or A4 size recording material). At the same time, there is a case where the imaging device performs printing on a small-sized sheet (for example, a recording material with a width smaller than a normal-sized sheet, such as an envelope, a postcard, etc.). Now, when the back rotation is performed on the small-sized sheet under a time setting similar to that of the normal-sized sheet, there is a case where a problem occurs in temperature management. That is, when the area of ​​the sheet passing area of ​​the fixing nip where the small-sized sheet passes is defined as a "first area" and the area excluding the first area from the entire sheet passing area is defined as a "second area", the second area does not contact the recording material, and therefore the heat is not taken away from it by the recording material. Therefore, the back rotation does not sufficiently reduce the temperature in the second area, and the temperature therein is higher than that in the first area.

[0006] Therefore, when a fixing process is performed on a normal-size sheet in a state where there is a temperature difference between the middle portion and the end portion of the fixing nip after the fixing process is performed on the small-size sheet, the next fixing process will be performed before the surface temperature distribution of the pressure roller returns to the prescribed state. As a result, excessive heat is supplied particularly in the second area of ​​the fixing nip, which may cause a defective image. An example of a defective image is a high-temperature offset in which unfixed toner is transferred from the surface of the normal-size sheet to the peripheral surface of the fixing film.

[0007] Therefore, Japanese Patent Application Laid-Open No. 11-073055 discloses a configuration in which the post-rotation time is extended in the case of a small-sized sheet compared with the case of a normal-sized sheet to perform temperature suppression of a high-temperature portion. Summary of the invention

[0008] In recent years, in order to reduce the size of monochrome image forming apparatus in particular, a structure has been adopted which has a driving source shared between a fixing device and a developing roller and does not have a developing roller drive disengagement mechanism. For such an image forming apparatus, the unnecessary rotation of the developing roller will continue until the driving of the fixing device ends. In such a configuration, as described in Japanese Patent Application Publication No. 11-073055, when a control of a prolonged post-rotation for suppressing the temperature of the fixing device is performed for the case of a small-sized sheet passing through, the number of rotations of the developing roller will be further increased compared to a normal-sized sheet. The increase in the number of rotations of the developing roller results in repeated friction of the toner in the developing device by the supply roller and the developing blade. Such friction may cause deterioration of the toner due to the freeing or embedding (embedding) of the external additive added to the toner relative to the resin particles as the toner base. The premature deterioration of the toner may lead to a situation in which the toner cannot perform the desired function due to reasons such as the deterioration of the charge amount of the toner and the failure to obtain the desired charge amount. This may cause image defects such as so-called fogging in which the toner adheres to the white background portion of the recording material.

[0009] The present invention has been proposed in view of the above problems. An object of the present invention is to suppress image defects caused by toner deterioration in an image forming apparatus having a structure in which a driving source is shared between a fixing apparatus and a developing roller, and the connection between the developing roller and the driving source is not disconnected, and the image forming apparatus is also capable of forming images on normal-sized sheets and small-sized sheets.

[0010] The present invention provides an imaging device, comprising:

[0011] a photosensitive drum on which an electrostatic latent image is formed on a surface of the photosensitive drum according to image information;

[0012] a developing roller configured to supply toner to the photosensitive drum to develop the electrostatic latent image and form a toner image;

[0013] a transfer unit for transferring the toner image onto a recording material;

[0014] a fixing unit for performing heat fixing of the toner image on the recording material, the fixing unit comprising a pressure roller and a heating member, the heating member forming a fixing nip portion between the heating member and the pressure roller;

[0015] a driving source for transmitting a driving force to the developing roller and the pressing roller; and

[0016] control unit, wherein

[0017] The control unit is configured as:

[0018] determining whether the recording material is a normal-size sheet whose width in the cross direction is at least a predetermined distance or a small-size sheet whose width is smaller than the predetermined distance,

[0019] In a case where the recording material is a normal size sheet, a first mode is performed in which a post-rotation operation is performed in which the driving source is driven for a predetermined amount of time after the recording material passes through the fixing nip, and

[0020] In the case where the recording material is a small-size sheet, a second mode is executed, in which a post-rotation operation is performed after the recording material passes through the fixing clamping portion, and in an imaging job stop state where an imaging operation is not performed, a first stop of stopping the driving source, a first drive of driving the driving source after the first stop, and a second stop of stopping the driving source after the first drive are executed.

[0021] According to the present invention, image defects due to colorant deterioration can be suppressed in an imaging device having the following configuration, in which a driving source is shared between a fixing device and a developing roller, and the connection between the developing roller and the driving source is not disconnected, and the imaging device is capable of forming images on normal-sized sheets and small-sized sheets.

[0022] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of the overall configuration of an imaging device according to the present invention;

[0024] Figure 2 is a block diagram showing a control system of an imaging device according to the present invention;

[0025] Figure 3A and Figure 3B is a schematic diagram of a fixing device according to the present invention;

[0026] Figure 4 is a schematic diagram showing a sheet passing sequence according to a conventional example;

[0027] Figure 5 is a schematic diagram showing a sheet passing sequence according to the first embodiment;

[0028] Fig. 6A and Figure 6B is a schematic diagram showing a driving operation according to the first embodiment;

[0029] Figure 7 is a diagram showing image evaluation results of the first embodiment;

[0030] Figure 8is a diagram showing image evaluation results and time measurement results according to the second embodiment; and

[0031] 9A to 9C is a diagram showing an example of a notification device according to the present invention. DETAILED DESCRIPTION

[0032] The imaging device according to the present invention will be described in more detail below with reference to the accompanying drawings. It should be noted that the size, material, shape, relative position, etc. of the components described in the following embodiments should be appropriately changed according to the configuration of the device to which the present invention is applied and various types of conditions, and it is not intended to limit the scope of the present invention to the embodiments described below. Technologies known in the relevant field or widely known technologies can be applied to configurations and processes that are not specifically shown or described. In addition, repeated descriptions can be omitted.

[0033] First embodiment

[0034] Overall configuration of imaging equipment

[0035] First, a schematic configuration of an imaging apparatus according to a first embodiment will be described. Figure 1 1 is a schematic cross-sectional view of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 according to the present embodiment is a monochrome laser printer capable of forming a black monochrome image on a sheet-like recording material P by an electrophotographic system. The process cartridge 9 is configured as a device main unit M that can be detachably attached to the image forming apparatus 100. It should be noted that the device main unit M is a configuration portion of the image forming apparatus 100, in which the process cartridge 9 is excluded.

[0036] It should be noted that the image forming apparatus to which the present invention is applicable is not limited thereto. The present invention can also be applied to a color laser printer that has a plurality of process cartridges 9 in a detachably attachable manner and transfers a plurality of color toner images onto a recording material P using an intermediate transfer member such as an intermediate transfer belt or the like so as to form a full-color image, for example. Furthermore, although the image forming apparatus 100 has a configuration in which the process cartridge 9 can be detachably attached in the present embodiment, the present invention can also be applied to an image forming apparatus in which a process unit having the same components as the process cartridge 9 is provided in the apparatus main unit.

[0037] The processing box 9 has a photosensitive drum 1, which is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) and serves as an image bearing member. In addition, the processing box 9 has a charging roller 2 and a developing device 8 provided around the photosensitive drum 1, the charging roller is a roller-type charging member used as a charging device, and the developing device serves as a developing device. The processing box 9 also has a brush member 12 provided around the photosensitive drum 1 and serves as a paper dust recovery member, and an electrostatic elimination device 11 used as an electrostatic elimination device. The processing box 9 also has a memory 15 used as a non-volatile storage device. In addition, the processing box 9 has a toner amount sensor 20 used as a developer amount sensing device. The charging roller 2, the developing roller 4 used as a developer bearing member provided to the developing device 8, and the brush member 12 are provided to contact the surface (peripheral surface) of the photosensitive drum 1. The processing box 9 is configured to be easily attached to and detached from the device main unit M in an integral manner by providing an attachment device (omitted from the illustration) (such as an attachment guide and a positioning member) provided to the device main unit M and the processing box 9.

[0038] The image forming apparatus 100 also has a transfer roller 13 (which is a roller transfer member) serving as a transfer device, an exposure device 10 serving as an exposure device, and a fixing device 14 serving as a fixing device. The transfer roller 13 is provided in contact with the surface of the photosensitive drum 1 .

[0039] Furthermore, the image forming apparatus 100 has a control unit 200 for controlling the entire image forming apparatus 100, an operation panel 60 serving as an operation unit, and the like. Figure 2 As shown. The operation panel 60 is configured to have a display unit for displaying information for an operator such as a user, a service person, etc. under the control of the control unit 200, an input unit for inputting information to the control unit 200 according to an operation performed by the operator, etc. The control unit 200 includes a CPU 201 that performs calculations according to a program and serves as a control circuit for controlling various components, a ROM 203 that stores programs, etc., a RAM 205 for loading programs, etc., and an I / O 207 for performing communication with an external device, etc. The ROM 203 and the RAM 205 are recording devices, for which existing memories, etc. can be used.

[0040] Imaging Operation

[0041] Next, the image forming operation of the image forming apparatus 100 according to the present embodiment will be described. The driving force from the drive motor 90 serving as a driving source constituting the driving means provided to the apparatus main unit M is transmitted to the photosensitive drum 1, which moves along the direction of the image forming apparatus 100 at a predetermined process speed. Figure 1 The direction of the arrow R1 in ( Figure 1It should be noted that the process speed here corresponds to the peripheral speed (surface travel speed) of the photosensitive drum 1. The process speed in this embodiment is 140 mm / sec.

[0042] The charging roller 2 contacts the surface of the photosensitive drum 1 with a predetermined contact pressure, thereby forming a charging portion. A predetermined charging voltage (charging bias) is applied to the charging roller 2, which is a DC voltage from a charging voltage applying circuit, which serves as a charging voltage applying device provided to the device main unit M. Therefore, the charging roller 2 performs a charging process in which the surface of the photosensitive drum 1 is uniformly subjected to a charging process to a predetermined potential of a predetermined polarity (negative polarity in this embodiment). In this embodiment, a charging voltage of -1400 V is applied to the charging roller 2 so that the surface potential (pre-exposure potential VD) of the photosensitive drum 1 will be -800 V. It should be noted that although a DC voltage is used as a charging voltage in this embodiment, this is not restrictive, and an oscillating voltage in which a DC voltage and an AC voltage are superimposed may be used as a charging voltage. The power supply 95 of the image forming device 100 is a high-voltage power supply for supplying voltage when performing various operations including an image forming operation, and serves as various types of voltage applying devices.

[0043] By irradiating a laser beam based on image information, the exposure device 10 scans and exposes the surface of the photosensitive drum 1 that has uniformly undergone a charging process, thereby forming an electrostatic latent image on the photosensitive drum 1. In the present embodiment, the exposure device 10 is composed of a scanner unit. Image information input to the imaging device 100 from an external device such as a personal computer or the like (omitted from the illustration) connected to the imaging device 100 is converted into a time-series electrical digital image signal by a video controller (omitted from the illustration) provided in the imaging device 100. The exposure device 10 is controlled by the control unit 200 to emit a laser beam that has been modulated according to the time-series electrical digital image signal, and scan and expose the surface of the photosensitive drum 1. Therefore, an electrostatic latent image corresponding to the image information is formed on the photosensitive drum 1. In the present embodiment, the exposure device 10 is used with an intensity of 0.45 µJ / cm 2 The surface of the photosensitive drum 1 is irradiated with the laser beam, so that the post-exposure potential VL of the surface of the photosensitive drum 1 becomes -100 V.

[0044] The electrostatic latent image formed on the photosensitive drum 1 is then developed (visualized) by the toner 3 used as a developer supplied from the developing device 8. Thus, a toner image (developer image) is formed on the photosensitive drum 1. The developing device 8 has a developing roller 4 used as a developer carrying member. The developing roller 4 forms a developing portion by contacting the surface of the photosensitive drum 1 with a predetermined contact pressure. A toner layer of the toner 3 charged to a predetermined polarity (negative polarity in this embodiment) is formed on the developing roller 4. A predetermined developing voltage (developing bias) is applied to the developing roller 4, which is a DC voltage from a developing charging voltage applying circuit, which serves as a developing charging voltage applying device supplied to the device main unit M. Therefore, the toner 3 adheres to the electrostatic latent image on the photosensitive drum 1 in the developing portion. The toner image is thus formed on the photosensitive drum 1. In this embodiment, a developing voltage of -400 V is applied to the developing roller 4. In this embodiment, the toner 3 charged to the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to the exposed portion (image portion) on the photosensitive drum 1, where the absolute value of the potential has been lowered by exposure after uniformly undergoing the charging process (reversal development system). In this embodiment, the normal charging polarity of the toner 3 (the main charging polarity of the toner 3 at the time of development) is negative polarity.

[0045] The transfer roller 13 forms a transfer portion by contacting the photosensitive drum 1 with a predetermined contact pressure. The toner image formed on the photosensitive drum 1 is transferred to the recording material P, which is conveyed by being sandwiched between the photosensitive drum 1 and the transfer roller 13 at the transfer portion. At the time of transfer, a predetermined transfer voltage (transfer bias) as a DC voltage is applied to the transfer roller 13 from a transfer voltage applying circuit serving as a transfer voltage applying means. In this embodiment, a transfer voltage of +1500 V is applied to the transfer roller 13.

[0046] A recording material (transfer material, recording medium, sheet) P is supplied to the transfer unit from a sheet feeding unit 30. The sheet feeding unit 30 is composed of a cassette 31 serving as a recording material accommodation unit, a sheet feeding roller 32 serving as a sheet feeding member, and the like. The recording material P accommodated in the cassette 31 is separated one sheet at a time by the sheet feeding roller 32 and is sent out from the cassette 31. The recording material P is conveyed to the transfer portion by a conveying roller (registration roller) 50 serving as a conveying member so that the timing matches the timing of the toner image on the photosensitive drum 1.

[0047] The recording material P on which the toner image is transferred is conveyed to a fixing device 14 serving as fixing means. The fixing device 14 applies heat and pressure to the recording material P, thereby fixing (melting, fixing) the toner image on the recording material P. The recording material P on which the toner image has been fixed is discharged (output) to a tray 40 serving as a discharge portion provided outside the apparatus main unit M.

[0048] At the same time, the toner 3 (transfer residual toner) remaining on the photosensitive drum 1 that was not transferred to the recording material P during the transfer process is removed from the photosensitive drum 1 as described below. After the transfer process, the surface of the photosensitive drum 1 is subjected to static elimination by the static elimination device (static elimination lamp) 11 so that its surface potential is 0 V, and then enters the charging part. The toner 3 charged to the positive polarity and the toner 3 charged to the negative polarity but without sufficient charge coexist in the transfer residual toner remaining on the photosensitive drum 1. This transfer residual toner is charged to the negative polarity by discharging in the charging part. As the photosensitive drum 1 rotates, the transfer residual toner charged to the negative polarity in the charging part reaches the developing part. Now, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1 that reaches the developing part. Due to the potential difference between the pre-exposure potential VD on the photosensitive drum 1 and the development voltage at the development portion, the transfer residual toner of the non-exposed portion (non-image portion) on the photosensitive drum 1 is relocated from the photosensitive drum 1 to the development roller 4, and is recovered to the development chamber 8b of the development device 8. It should be noted that the toner 3 recovered to the development chamber 8b is used again for image formation. At the same time, the transfer residual toner of the exposed portion (image portion) on the photosensitive drum 1 is not relocated from the photosensitive drum 1 to the development roller 4 at the development portion, and constitutes a toner image together with the toner 3 that has been relocated from the development roller 4 to the photosensitive drum 1. Then, this toner 3 is transferred to the recording material P at the transfer portion, and is thus removed from the photosensitive drum 1.

[0049] The process cartridge 9 is also provided with a brush member 12. The brush member 12 is a paper dust recovery member for removing paper dust fibers generated from the recording material P and having adhered to the photosensitive drum 1 from the recording material P during the transfer process. The brush member 12 is provided to contact the photosensitive drum 1 on the downstream side of the transfer portion in the rotation direction of the photosensitive drum 1, and also to contact the photosensitive drum on the upstream side of the charging portion. As the photosensitive drum 1 rotates, the brush member 12 picks up the paper dust fibers on the photosensitive drum 1 by rubbing the surface of the photosensitive drum 1, thereby removing the paper dust fibers from the photosensitive drum 1.

[0050] In this embodiment, a single drive motor 90 is used as a drive source to reduce the size of the image forming apparatus. The photosensitive drum 1, the developing roller 4, and the fixing device 14 are all connected by a gear train, and are driven by the drive motor 90 to be operated. This is a configuration in which there is no mechanism for separating the developing roller 4 from the drive motor 90. Not requiring a space for such separation also reduces the size of the image forming apparatus.

[0051] Detailed configuration of the developing equipment

[0052] Next, the detailed configuration of the developing device 8 in the image forming apparatus 100 according to the present embodiment will be described.

[0053] Development equipment

[0054] In the present embodiment, the developing device 8 is a single-component contact developing device using a non-magnetic single-component developer (toner 3) as a developer. The developing device 8 has a developer container 80 (frame body), which is composed of a developing chamber 8b used as a developing member accommodating chamber and a toner accommodating chamber 8a used as a developer accommodating chamber. The developing chamber 8b and the toner accommodating chamber 8a are connected via an opening portion. The developing chamber 8b is provided with a developing roller 4 used as a developer carrying member (developing member), a supply roller 5 used as a supply member for supplying the toner 3 to the developing roller 4, and a developing scraper 6 used as a control member, which is used to control the amount of the toner 3 on the developing roller 4 while applying a charge of a predetermined polarity to the toner 3 on the developing roller 4.

[0055] The developing roller 4 is rotatably disposed at the opening portion of the developing chamber 8b (developer container 80), and conveys the toner 3 from the inside of the developing chamber 8b (developer container 80) to the outside by rotating while carrying the toner 3. The toner 3 used as a developer is contained in the toner containing chamber 8a. In addition, a stirring member 7 for conveying the toner 3 from the toner containing chamber 8a to the developing chamber 8b while stirring the toner 3 in the toner containing chamber 8a is disposed in the toner containing chamber 8a.

[0056] It should be noted that although the developing device 8 adopts a contact developing system in which the image bearing member and the developer bearing member are arranged in contact in the present embodiment, this is not restrictive. The developing device 8 may adopt a two-component developing system using a two-component developer, and may adopt a non-contact developing system in which the image bearing member and the developer bearing member are arranged facing each other with a predetermined gap therebetween.

[0057] In this embodiment, the developing roller 4 is made by coating a silicone rubber base layer and a polyurethane rubber surface layer on the outer periphery of a metal core having a diameter of 6 mm in sequence, so that the outer diameter is 15 mm. In addition, in this embodiment, the resistance value of the developing roller 4 is 1×10 4 Up to 1×1012 Ω.

[0058] Furthermore, in the present embodiment, the supply roller 5 is an elastic sponge roller having conductivity, which is made by forming a foam material layer on the outer periphery of a metal core having a diameter of 6 mm. Furthermore, in the present embodiment, the resistance value of the supply roller 5 is 1 × 10 4 Up to 1×10 8 Ω, and the hardness is 200 gf. It should be noted that the hardness of the supply roller 5 is a load value measured in a case where a flat plate having a longitudinal length of 50 mm intrudes 1 mm from the surface of the supply roller 5.

[0059] In the present embodiment, the developing scraper 6 is a stainless steel flat plate having a thickness of 0.1 mm, which has a predetermined length in the longitudinal direction and in the transverse direction substantially orthogonal to the longitudinal direction, and is arranged along the rotation axis direction of the developing roller 4. The developing scraper 6 is arranged so that its free end in the transverse direction faces the upstream side in the rotation direction of the developing roller 4, and its side surface close to the free end contacts the developing roller 4 along the longitudinal direction. In the present embodiment, a product obtained by cutting the distal end (free end) of the stainless steel plate from one side of the surface in contact with the developing roller 4 is used for the developing scraper 6. The distal end portion of the developing scraper 6 is bent in the cutting direction by cutting, and the bending amount of the distal end of the developing scraper 6 equal to the radius of curvature R is 0.02 mm.

[0060] The movement of the toner 3 in the developing device 8 when driven will be described. The driving force is transmitted to the developing device 8 from the driving motor 90 serving as a driving source, which constitutes a driving device provided to the device main unit M. Therefore, the developing roller 4, the supply roller 5, and the stirring member 7 are each moved along the same direction. Figure 1 The photosensitive drum 1 rotates in the direction of arrow R2 (clockwise), arrow R3 (clockwise) and arrow R4 (counterclockwise). It should be noted that the driving source of the photosensitive drum 1 and the rotating members of the developing device 8 (developing roller 4, supply roller 5 and stirring member 7) can be shared.

[0061] As the stirring member 7 in the toner accommodating chamber 8a rotates, the toner 3 in the toner accommodating chamber 8a is stirred and also conveyed toward the supply roller 5 in the developing chamber 8b. By the rotation of the supply roller 5, the toner 3 held by the foamed material layer of the supply roller 5 is supplied to the contact portion with the developing roller 4. The toner 3 reaching the contact portion is then rubbed by the contact portion of the surface of the developing roller 4 and the surface of the supply roller 5, which move in directions opposite to each other, and a portion of the toner adheres to the surface of the developing roller 4.

[0062] As the developing roller 4 rotates, the toner 3 adhering to the surface of the developing roller 4 is supplied to the contact portion in contact with the developing blade 6. The developing blade 6 limits the amount of the toner 3 adhering to the surface of the developing roller 4 to form a uniform thin layer, and also performs friction charging of the toner 3. As the developing roller 4 rotates, the toner 3 formed into a thin layer is supplied to the contact portion in contact with the photosensitive drum 1, and is used to develop the electrostatic latent image formed on the photosensitive drum 1. The toner 3 remaining on the surface of the developing roller 4 that is not used for development is conveyed to the contact portion in contact with the supply roller 5, and is removed from the surface of the developing roller 4 by the supply roller 5. The removed toner 3 is supplied to the inside of the toner accommodating chamber 8a, and is stirred and mixed with the toner 3 inside the toner accommodating chamber 8a.

[0063] Detailed configuration of the fixing device

[0064] Will refer to Figure 3A Cross-sectional view and Figure 3B 14 is described in a side view in FIG. The fixing device 14 according to the present embodiment is configured so that the heating heater 113 is held by a heater holder 130, and the fixing film 112 is provided on its periphery as a heating member in the form of an endless belt. The heater holder 130 is preferably made of a heat insulating material so that the heat of the heating heater 113 is not easily taken away. In the present embodiment, a liquid crystal polymer (LCP) as a heat-resistant resin is used. For reasons of strength, the heater holder 130 is supported from the side opposite to the heating heater 113 by a support member 120 made of metal. The support member 120 is squeezed from its two end portions in the longitudinal direction by a pressure spring omitted from the illustration.

[0065] like Figure 3A As shown, the heating heater 113 contacts the inner surface of the fixing film 112 to form an inner surface clamping portion and heats the fixing film 112 from the inside. The pressure roller 110 faces the heating heater 113, wherein the fixing film 112 is interposed between them, thereby forming a fixing clamping portion. The pressure roller 110 receives the force of the pressure spring through bearings (omitted in the figure) provided at both end portions of its metal core 117, and is driven by receiving the driving force at the drive gear 131 provided on the end portion of the metal core 117 from the driving source. When the pressure roller 110 is driven, the fixing film 112 is driven to rotate at the fixing clamping portion under the power from the pressure roller 110.

[0066] The fixing flanges 150 are provided at both end portions of the fixing film 112 for limiting deviation. Figure 3B As shown, the fixing film 112 is prevented from being deflected rightward or leftward in the longitudinal direction. The fixing flange 150 is provided and fixed by being fitted to the support 120. The rotation of the fixing film 112 is supported from the inner face thereof by the fixing flanges 150 located at both end portions thereof.

[0067] In an undeformed state, the fixing film 112 according to the present embodiment has an outer diameter of 20 mm when in a cylindrical state, and has a multilayer structure in the thickness direction. The composition of the layered structure of the fixing film 112 is a base layer 126 for maintaining film strength and a release layer 128 for reducing dirt adhering to its surface. For the material of the base layer 126, it is preferred to use a metal such as stainless steel or nickel or the like, or a heat-resistant resin such as polyimide or the like, because heat resistance is required due to the heat from the heating heater 113, and strength is required due to sliding on the heating heater 113. Compared with resin, metal has strength, so it can be formed thin, and the thermal conductivity is also high, and therefore the heat from the heating heater 113 is easily conducted to the surface of the fixing film 112. On the contrary, the advantage of resin is that, due to its small specific gravity, the heat capacity is small, and it heats faster. In addition, the molding of the resin can be performed inexpensively because the film can be molded by coating molding. In the present embodiment, polyimide resin is used as the material of the base layer 126 for the fixing film 112, and a carbon-based filler is added to improve thermal conductivity and strength. The thinner the base layer 126 is, the faster the heat of the heating heater 113 reaches the surface of the fixing film 112, but the strength becomes poor, and therefore the thickness is preferably about 15 μm to 100 μm. In the present embodiment, the thickness is 60 μm.

[0068] The conductive primer layer 127 is made of polyimide resin or fluorine resin to which carbon or the like has been added to reduce resistance. By grounding the exposed portion of the conductive layer, the potential of the fixing film 112 is stabilized when the sheet passes.

[0069] The material for the release layer 128 is preferably a fluororesin, such as a perfluoroalkoxyalkane (PFA) resin, a polytetrafluoroethylene (PTFE) resin, a tetrafluoroethylene-hexafluoropropylene (FEP) resin or the like. In the present embodiment, PFA having excellent release properties and heat resistance in a fluororesin is used, in which a conductive material is dispersed to achieve a medium level of resistance. The release layer 128 can be formed by covering it with a tube, or can be obtained by coating its surface with a coating material. In the present embodiment, the release layer 128 is molded by coating molding with excellent thin molding capability. The thinner the release layer 128 is, the easier it is for the heat of the heating heater 113 to be transferred to the surface of the fixing film 112, but if it is too thin, the durability will deteriorate, and therefore 5 µm to 30 µm is preferred, and is set to 10 µm in the present embodiment.

[0070] The pressure roller 110 according to the present embodiment has an outer diameter of 14 mm, in which silicone rubber is provided with a thickness of 2.5 mm on a portion of a metal core 117 made of iron having an outer diameter of 9 mm, thereby forming an elastic layer 116 .

[0071] Heat-resistant silicone rubber and fluororubber are used for the elastic layer 116, and silicone rubber is used in this embodiment. An article with an outer diameter of about 10 to 50 mm is used for the pressure roller 110. The smaller the outer diameter, the more the heat capacity can be suppressed, but if it is too small, the width of the fixing nip becomes narrow, so a suitable outer diameter is required. In this embodiment, the outer diameter is set to 14 mm. Appropriate thickness is also required for the thickness of the elastic layer 116, because if it is too thin, heat will be attracted to the core made of metal. In this embodiment, the thickness of the elastic layer 116 is set to 2.5 mm.

[0072] A release layer 118 made of a perfluoroalkoxyalkane (PFA) resin is formed on the elastic layer 116 as a release layer of the toner 3. The release layer 118 can be formed by covering with a tube in the same manner as the release layer 128 for the fixing film 112, or can be obtained by coating its surface with a coating material, but for excellent durability, a 20 μm thick tube is used in this embodiment. In addition to PFA, a fluororesin such as PTFE, FEP or the like can be used, or a fluororubber, silicone rubber or the like with good release properties can be used as a material for the release layer 118. The lower the surface hardness of the pressure roller 110, the wider the fixing nip that can be obtained under low pressure, but if it is too low, the durability will deteriorate. In this embodiment, this is set to 40° (600g weight) on the Asker-C hardness scale. The pressure roller 110 rotates at a surface travel speed of 140 mm / second under the action of a driving source.

[0073] The heating heater 113 of this embodiment is a general-purpose heater used in a film heating type heating device, and uses an article in which a resistance heating element is arranged in series on a ceramic substrate. The heating heater 113 used is made by coating a 10 μm high silver / palladium (Ag / Pd) resistance heating element on the surface of a 6 mm wide and 1 mm thick alumina substrate by screen printing, and the resistance heating element is then covered with 50 μm thick glass as a heating element protective layer.

[0074] like Figure 3A and Figure 3BAs shown, a temperature sensing element 115 for sensing the temperature of the ceramic substrate is provided on the back of the heating heater 113. According to the signal from the temperature sensing element 115, the temperature of the heating heater 113 is adjusted by appropriately controlling the current to be applied to the resistance heating element. When the temperature is high, the power consumption is large, so it is necessary to set the temperature to an appropriate level. In this embodiment, the control temperature of ordinary paper is set to 180°C. In addition, a temperature fuse (omitted in the figure) is a safety element for interrupting the circuit and ensuring safety in the case where the heating heater 113 exhibits an abnormally high temperature, and the temperature fuse can be provided on the back of the heating heater 113. The heating heater 113 is connected to the power supply via the temperature fuse. When the temperature fuse is subjected to an abnormally high temperature, the temperature fuse is melted, and the power supply from the power supply to the heating heater 113 is interrupted. It should be noted that the construction of the fixing device 14 is not limited thereto. For example, the fixing device 14 can be composed of a heating roller having a halogen heater therein. As long as the driving source to be used to drive the fixing device 14 and the developing device 8 is common, this embodiment is applicable.

[0075] Features of this embodiment: Sheet material passes through control

[0076] The sheet passing control which is a feature of the present embodiment will be described. When the recording material P enters the fixing nip N1, the toner image is heated and fixed to the recording material P at the fixing nip N1. Thereafter, after the trailing end of the recording material P leaves the fixing nip N1, the motor stops. In the present embodiment, the time from when the trailing end of the recording material P leaves the fixing nip N1 until the motor stops is the time for the post-rotation operation. In the present embodiment, the post-rotation operation is performed while the recording material P is conveyed from the fixing nip N1 to the tray 40. That is, during the post-rotation operation, the motor is driven for more than a predetermined amount of time.

[0077] In the present embodiment, a recording material P whose width is a predetermined value or more (here, 200 mm or more) will be referred to as a "normal size sheet". In addition, a recording material P whose width is smaller than that of a normal size sheet (i.e., whose width is smaller than a predetermined value, here, less than 200 mm) will be referred to as a "small size sheet". When a small size sheet is used, heat is taken away by the sheet in the area of ​​the sheet passing area of ​​the clamping portion through which the small size sheet passes (hereinafter referred to as the "first area"). On the contrary, heat is not taken away by the sheet in the area of ​​the normal sheet area other than the area through which the small size sheet passes (hereinafter referred to as the "second area"). Therefore, at a time point after fixing, the temperature value of the second area is higher than that in the first area. When a toner image is fixed to a normal size sheet in a state in which such a temperature difference occurs between the first area and the second area, a high temperature offset may occur, which is a phenomenon in which an unfixed image carried by a normal size sheet is supplied with excessive heat in the second area outside the sheet passing area and is transferred from the surface of the normal size sheet to the outer peripheral surface of the fixing film.

[0078] Traditional example process

[0079] As a conventional example, there is a method of extending the drive after the post-rotation after the small-sized sheet passes to eliminate the temperature difference between the first area and the second area. Figure 4 The operation flow of a conventional example is described. In step S100, printing is started. In step S101, the control unit 200 determines whether the recording material P in which the sheet passage has been performed is a small-size sheet based on the sensing result of the sheet width sensor 500. In the case where it is determined that this is not a small-size sheet (No in S101), the above-mentioned post-rotation is performed in step S102, and printing is ended in step S103. On the contrary, in the case where it is determined that this is a small-size sheet (Yes in S101), post-rotation is performed in step S200, motor driving is performed for a predetermined amount of time in S201, and printing is ended in step S103. In the case of a small-size sheet, the motor driving in S201 is preferably performed only for a period of time until the temperature difference between the first area and the second area is eliminated. In the example here, the motor driving time is set to 10 seconds.

[0080] However, in a configuration in which the drive source of the fixing device 14 and the developing device 8 is shared, the transmission of the driving force cannot be stopped between the developing roller 4 and the driving source, and when an operation flow such as the conventional example described above is followed, the following problem occurs. That is, even when the motor drive is extended after the post-rotation due to a small-sized sheet (a period of S201), the developing roller 4 continues to rotate, and thus the toner 3 is repeatedly rubbed at the photosensitive drum 1 and the developing blade 6, causing the toner 3 to further deteriorate. Now, in the rotation of the developing roller 4 for image formation, although the toner 3 is rubbed at the photosensitive drum 1 and the developing blade 6, even so, the toner has been used and consumed in the image formation before the toner 3 is further deteriorated. On the contrary, when the developing roller 4 rotates without consuming the toner 3, as in the extended post-rotation due to a small-sized sheet, the deterioration of the toner 3 is aggravated.

[0081] The process of this embodiment

[0082] Therefore, in the present embodiment, in order to suppress the temperature in the second area after the post-rotation, an image forming job stop time is provided as a time to stop the execution of an operation involving the drive of at least the developing device 8 (for example, an operation for rotating the developing roller 4 so as to develop an electrostatic latent image in a printing job). During the image forming job stop time, the image forming device 100 is in an image forming job stop state in which a job involving driving the developing roller 4 cannot be executed. It should be noted that even during the image forming job stop time, not all jobs related to imaging are necessarily unexecutable, but only the job portion requiring the operation of the driving source is unexecutable. Therefore, image processing (for example, loading processing of image data) performed in the background is executable. In addition, even during the image forming job stop time, a job for a print instruction or the like from a user can be accepted and saved in an execution queue, and the job can be executed after the image forming operation involving driving the developing roller 4 becomes available. However, an arrangement may be made in which, during the image forming job stop time, a notification is issued in response to a job such as a print instruction or the like from a user indicating that the job cannot be accepted. In addition, the developing roller 4 is not available for driving during the entire period of the image forming job stop time, and the developing roller 4 can also be driven at the moment when the motor is driven again from the stop state, for example, which will be described later. However, this re-driving is temporarily performed and is not sufficient in time to perform image forming. In the present embodiment, an operation is performed in which, during the image forming job stop time, driving is performed from a state in which the motor is stopped and then returns to the stop state. Reference will be made to Figure 5 Describe the operation flow of this embodiment. Figure 4 The same processing as in the conventional example, and the description will be simplified.

[0083] Printing is started in step S100, and in step S101, it is determined whether the recording material P is a small size sheet. In the case where it is determined that it is not a small size sheet, post-rotation is performed in step S102 in the same manner as the conventional example, and printing is ended in step S103.

[0084] On the contrary, in the case where it is determined in step S101 that this is a small-size sheet, post-rotation is performed in step S200, and the motor is stopped in step S210 (first stop). Next, in step S211, the motor is driven (first drive), and thereafter in step S212, the motor is stopped again (second stop). Subsequently, in step S103, printing ends. That is, stopping the motor also stops the rotation of the developing roller 4 in the developing device 8, so the deterioration of the toner 3 can be suppressed.

[0085] However, stopping the motor may have adverse effects. That is, when the motor is kept Fig. 6A In the stopped state shown in FIG. 1 , the area of ​​the dotted line A including the fixing nip N1 is not in contact with the outside air and is not easily cooled. Therefore, in this process, after stopping the motor, a temporary driving operation (S211) is performed, and then the motor is stopped again (S212). Therefore, the area of ​​the dotted line A moves by rotating in the direction of the arrow R5, so that the heat of the fixing nip N1 can be moved to the outside of the nip, as shown in FIG. Figure 6B Furthermore, the surface of the pressure roller that has been cooled by the outside air also reaches the fixing nip N1 on the fixing film 112 side of the fixing nip N1 , so cooling can be performed efficiently.

[0086] Here, the motor stop time in step S210 is set to 1 second. Regarding the drive time in S211, it is necessary to move the position of the area constituting the fixing clamping portion N1 while suppressing the rotation. Therefore, the drive time in which the distance moved by the area of ​​the dotted line A is less than the range of the outer diameters of the pressure roller and the fixing film is ideal. In this embodiment, the drive time is set to 150ms (a drive distance of about 20 mm). The total time of steps S210, S211 and S212 is set to 12 seconds.

[0087] In the present embodiment, the judgment of whether it is a small-sized sheet is performed by the sheet width sensor 500 provided near the conveying roller 50. For the sheet width sensor 500, a sensing member having two marks in the width direction intersecting (usually orthogonal) with the conveying direction of the recording material P and also having a sensing unit, wherein the light from the light emitting unit is blocked, for example, in a state where the marks are raised, and the light is transmitted in a state where the marks are dropped. In such a sheet width sensor 500, when a sheet having a sheet width wider than the distance between the marks is conveyed, the marks hit by the sheet fall down, and at the same time, the transmitted light is sensed. Therefore, it can be determined whether the sheet width is greater than or equal to a predetermined distance, or less than a predetermined distance. The sheet width sensor 500 according to the present embodiment has sheet width sensor marks, each of which is provided at a position 100 mm away from the center of the sheet in the longitudinal direction, so that when a recording material P having a width of 200 mm or more is conveyed, the sheet width sensor marks fall down, and it is sensed that the sheet is not a small-sized sheet. When none of the sensors senses or only one of the sensors senses, the sheet is judged to be a small-sized sheet. It should be noted that the sheet width sensor is not necessarily a system using a flag. In addition, it is possible to judge whether it is a small-sized sheet based on the print setting of the image forming device. It is sufficient to compare the width of the recording material with a predetermined distance, and if the width of the recording material is the predetermined distance or more, it can be determined to be a normal-sized sheet, and if the width of the recording material is less than the predetermined distance, it can be determined to be a small-sized sheet.

[0088] Now, during the period from the motor stop in step S210 until the end of printing in S103, the motor for rotating the fixing device 14 and the developing roller 4 is stopped, and thus the image forming apparatus 100 is in a state in which a print job cannot be performed. Therefore, for example, even if the user executes a print instruction from the host PC, the image forming operation will not start. Therefore, the control unit 200 according to the present embodiment puts the image forming apparatus into such an image forming job stop state after the post-rotation.

[0089] Furthermore, in the imaging job stop state, not only is the motor stopped for a long time, but even if the user executes a print instruction from the host PC, no response is received from the imaging device 100. Therefore, the user can be notified that the imaging device 100 is operating during the imaging job stop time. Therefore, even if the motor is in a stop state, the user can recognize that the imaging device 100 is operating. It is sufficient for the content of the notification to the user to be content indicating that the imaging device 100 is operating, and may be, for example, a message displayed on the operation panel 60. Furthermore, sometimes a notification device, such as a light emitting diode (LED) or the like, is provided on the imaging device 100. For example, 9A to 9CThe manner in which indicators 400 ( 400 a to 400 c ) for notifying the user of the remaining toner amount are provided on the housing of the device is shown. Fig.9A shows a low residual (low), Fig. 9B shows a medium residual amount (Medium), and Fig. 9C The full remaining amount (full) is shown. In this case, the user can be notified of the job stop state by the indicator 400 (400a to 400c) flashing.

[0090] Effects of the Invention

[0091] The sheet passing durability test was performed, and the presence or absence of a blurred image as an image defect was evaluated. The passing of two sheets was repeated, and the sheet passing of 5000 sheets was performed. For the sheet passing, Canon Office 70 (gram weight 70 g, A4 size) and PB paper (gram weight 64 g, A5 size) were used. As a comparative example, the sheet passing was performed with a normal-sized Canon Office 70, the sheet passing of PB paper was performed under the conditions of the conventional example, and the sheet passing of PB paper was performed under the conditions of the present embodiment.

[0092] The images on the passed sheets were evaluated, and the cases where a blurred image occurred were marked with a cross, and the cases where a blurred image did not occur were marked with a circle. Figure 7 shown.

[0093] For the comparative example, no defective image occurred for up to 5,000 sheets of printing. In contrast, in the conventional example, blurred image defects occurred starting from 3,500 sheets of printing. This is due to an increase in the number of development revolutions caused by the extended post-rotation running from the passage of a small-sized sheet, which resulted in an increase in the number of frictions of the toner 3, resulting in deterioration of the toner 3. For the present embodiment, even when a small-sized sheet is passed, there is no extended rotation of the post-rotation, so that no blurred image defects occurred after 5,000 sheets of printing in the same manner as in the conventional example.

[0094] Although the drive time after the rear rotation in the conventional example and the imaging job stop time in the present embodiment are described as fixed values, the temperature difference between the first area and the second area varies depending on the number of sheets passing continuously, so the drive time in the conventional example and the imaging job stop time in the present embodiment are ideally set according to the number of sheets passing.

[0095] As described above, in a structure in which the driving source of the fixing device 14 and the developing roller 4 is shared and a developing roller drive disengagement mechanism is not provided, in order to reduce the size of the imaging device, a time period in which the next job cannot be accepted is set to suppress the temperature of the second area after the rear rotation after the sheet of small-sized sheet passes through, and during this time period, the drive is started from the stopped state of the motor and then returns to the stopped state, thereby suppressing the occurrence of blurred images and suppressing the reduction in production.

[0096] Furthermore, in the present embodiment, the driving of the fixing device 14 is also stopped, so this suppresses the peeling of the release layer 128 due to the wear occurring due to the rotation of the fixing film 112. Therefore, the effect of extending the service life of the fixing device 14 can be expected.

[0097] Second embodiment

[0098] Next, the second embodiment will be described. The configuration and operation of the imaging device 100 are the same as those in the first embodiment.

[0099] Features of this embodiment

[0100] In this embodiment, the following reduction in the image forming job stop time is performed while suppressing image defects. Here, the image forming apparatus 100 is capable of performing Figure 4 The sheets shown are passed through the sequence and Figure 5 The sheet shown goes through both sequences and a method of switching between the two sequences. Figure 4 The driving time in step S201 in is 10 seconds, which is the same as in the first embodiment, and Figure 5 The time for S210, S211 and S212 is 12 seconds.

[0101] In the following, Figure 4 The mode shown is called the "first mode", and Figure 5 The mode shown is called the "second mode". Figure 4 In the first mode shown, the motor driving time after the post-rotation is extended, so it is easy to suppress the temperature rise of the fixing nip N1. Therefore, this is a mode that prioritizes production, in which the next print job can be quickly executed. On the contrary, in Figure 5 In the second mode shown, the motor is stopped after the post-rotation, so this is a durability priority mode in which the friction of the toner 3 by the rotation of the developing roller 4 can be suppressed.

[0102] The switching method of the mode will be described. Here, the first mode is set in the initial setting. Then each time a sheet is passed (each time an imaging operation is performed), the control unit 200 according to the present embodiment records the sensing result of the sheet width sensor 500 (whether it is a sensing result of a small-size sheet or a normal-size sheet) in the ROM 203 used as a recording device. In addition, each time a sheet is passed, the control unit 200 uses the CPU 201 to calculate the ratio of the normal-size sheet and the small-size sheet. When the ratio of the small-size sheet in the cumulative number of prints of the recording material so far becomes not less than a predetermined value (here at least 40%), the control unit 200 then switches from the next job to the second mode. On the contrary, when the ratio of the small-size sheet is lower than 40%, the control unit 200 switches to the first mode.

[0103] It should be noted that although the predetermined ratio value for switching the mode is described as 40% here, this is not restrictive. In addition, once the mode switching is performed, in order to prevent the mode switching from being frequently performed, the determination of the switching may be stopped thereafter until the predetermined number of sheets of the recording material P has passed. In addition, the calculation of the ratio for mode switching may be reset at a predetermined timing (for example, when the device has been restarted, when sheet passing has not been performed for a predetermined period of time, when maintenance such as cartridge replacement has been performed, etc.).

[0104] Effects of the Invention

[0105] The sheet passing durability test was conducted in the same manner as in the first embodiment, by repeating two sheet passing for 5000 sheets, and evaluating the blurred image, and measuring the drive extension time and the imaging job stop time after the post rotation. Two types of Canon Office 70 (gram weight 70 g, A4 size) and PB paper (gram weight 64 g, A5 size) were used as sheets, and the sheet passing was conducted at various sheet passing ratios.

[0106] This was conducted under the conditions of the present embodiment, the conventional example, and the first embodiment as the second comparative example. For the image evaluation, the case where a blurred image occurred during the sheet passing 5000 sheets of printing was marked with a cross, and the case where a blurred image did not occur was marked with a circle. The imaging job stop time was measured, and the total time was calculated. The results are shown in FIG. Figure 8 shown.

[0107] With the conventional example, the image forming job stop time is short, but when the sheet passing ratio of the A5 sheet becomes 40% or higher, the number of developing rotations increases, and a blurred image occurs. With the second comparative example, the operation is stopped during the image forming job stop time, so a blurred image does not occur, but when the sheet passing ratio of the A5 sheet is 20%, the image forming job stop time is longer than that of the conventional example. In contrast, with the present embodiment, a blurred image does not occur, and the image forming job stop time is also suppressed to a minimum.

[0108] This is because the image forming apparatus has two modes of the conventional example and the first example, and the mode is automatically switched according to the sheet passing ratio of the normal size sheet and the small size sheet. In addition, although the present embodiment has the conventional example and the first embodiment mode, instead of the first embodiment, a mode of stopping the motor in S201 after the rear rotation in S200 may be included, such as 9A to 9C Here S201 is the imaging operation stop time, and 15 seconds is required to avoid thermal offset.

[0109] Furthermore, although the image forming apparatus performs automatic switching in the present embodiment, an arrangement may be made in which a notification of switching of two modes is issued to the user, and the user performs switching on the operation panel 60 .

[0110] As described above, in a configuration in which the driving source of the fixing device 14 and the developing roller 4 is shared and a developing roller drive disengagement mechanism is not provided, in order to reduce the size of the imaging device, two modes are provided for use after a small-size sheet passes through, and by switching the mode according to a switching notification, the occurrence of blurred images can be suppressed while suppressing a reduction in yield.

[0111] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An imaging device, comprising: a photosensitive drum on which an electrostatic latent image is formed on a surface according to image information; a developing roller configured to supply toner to the photosensitive drum to develop the electrostatic latent image and form a toner image; a transfer unit for transferring the toner image onto a recording material; a fixing unit for performing heat fixing of the toner image onto the recording material, the fixing unit comprising a pressure roller and a heating member, the fixing unit forming a fixing nip portion between the heating member and the pressure roller; a driving source for transmitting a driving force to the developing roller and the pressing roller; and control unit, wherein The control unit is configured to: determining whether the recording material is a normal-size sheet whose width in the cross direction is at least a predetermined distance or a small-size sheet whose width is smaller than the predetermined distance, In a case where the recording material is the normal size sheet, a first mode is performed in which a post-rotation operation is performed in which the drive source is driven for a predetermined amount of time after the recording material passes through the fixing nip, and In the case where the recording material is the small-size sheet, a second mode is executed, in which the post-rotation operation is performed after the recording material passes through the fixing clamping portion, and also in an imaging job stop state where an imaging operation is not performed, a first stop of stopping the driving source, a first drive of driving the driving source after the first stop, and a second stop of stopping the driving source after the first drive are executed.

2. The imaging device according to claim 1, wherein In the first driving, when the post-rotation operation of the pressure roller is finished, the region in contact with the fixing nip moves to a position not in contact with the fixing nip.

3. The imaging device according to claim 2, wherein: In the first driving, when the post-rotation operation of the pressure roller is finished, the movement distance of the region in contact with the fixing nip is a distance smaller than the outer diameter of the pressure roller.

4. The imaging device according to claim 1, wherein During the image forming job stop state, the control unit notifies a user that the image forming apparatus is currently operating.

5. The imaging device according to any one of claims 1 to 4, wherein The control unit records in a recording unit a determination result of whether the recording material is the normal-size sheet or the small-size sheet, calculates a ratio of the number of small-size sheets to the cumulative number of sheets of the recording material based on the determination result obtained regarding a predetermined number of sheets of the recording material, and switches the operation mode of the imaging device to the second mode when the ratio is at least a predetermined value.

6. The imaging device according to any one of claims 1 to 4, wherein In which of the first mode and the second mode the imaging device operates is determined based on a user operation.

Images