Image forming apparatus

Abstract

To suppress image defects due to deterioration of toner in an image forming apparatus which is configured in such a manner that a fixing device and a development roller have a common driving source and the development roller and the driving source cannot be disconnected and is capable of forming an image on a normal size paper and a small size paper.SOLUTION: An image forming apparatus comprises: a photoreceptor drum; a development roller; a fixing film; a pressure roller; fixing means having a heating member forming a fixing nip part between itself and the pressure roller; a driving source which transmits driving force to the development roller and the pressure roller; and a control part which determines whether a recording material is a normal size paper or a small size paper and if it is a normal size paper, executes a first mode which performs a rearward rotation operation after the recording material passes the fixing nip part, while if it is a small size paper, executes a second mode which performs the rearward rotation operation, puts the apparatus in an image forming job stop state, stops the driving source, then drives the driving source and then stops the driving source.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] There are known image forming apparatuses, such as copiers, printers, and facsimile machines, that form images on recording materials using electrophotography or electrostatic recording. In an image forming operation, such image forming apparatuses form an electrostatic latent image on an image carrier, and a developing device supplies toner to the electrostatic latent image to form a toner image. Such a developing device may be configured as an independent unit, or as a part of a process cartridge, so as to be detachable from the main body of the image forming apparatus.

[0003] The developing device typically has a developing container that contains toner, and a developing roller that is disposed at the opening of the developing container and carries the toner and rotates to transport the toner to the outside of the developing container. The developing device also has a supply roller that supplies toner to the developing roller, and a developing blade that regulates the amount of toner carried by the developing roller.

[0004] The image forming apparatus also has a fixing device for fixing the toner image transferred to the recording material. The fixing device typically includes a cylindrical or columnar rotatable pressure roller, a fixing film, and a heating means having a heat generating surface, and the fixing film is supported so as to be freely in sliding contact with the heat generating surface. Then, heat fixing is performed in the fixing nip between the fixing film and the pressure roller. In such a film-type fixing apparatus, since the fixing film has a low heat capacity, the fixing nip rises in temperature in a short time when heat is supplied from the heating means. Therefore, the timing of energizing the heating means is set to be almost simultaneous with the entry of the recording material carrying an unfixed image into the fixing nip. This has been intended to save energy consumption of the heating means and the like and to prevent excessive temperature rise inside the image forming apparatus.

[0005] In addition, in such a fixing device, the pressure roller may be post-rotated after the recording material to be fixed passes through the fixing nip portion in order to lower the temperature of the end of the pressure roller. The time for post-rotation of the pressure roller in the fixing device is often set to suit normal size paper (for example, LTR size or A4 size recording material). On the other hand, in the image forming device, printing may be performed on small size paper (for example, envelopes, postcards, and other recording materials that are narrower than normal size paper). Here, if post-rotation is performed for small size paper for the same set time as for normal size paper, a problem may occur in temperature management. That is, if the area where small size paper passes through the paper passing area of ​​the fixing nip portion is set as the "first area" and the area excluding the first area from the entire paper passing area is set as the "second area," the second area does not come into contact with the recording material and therefore does not lose heat to the recording material. Therefore, the temperature in the second area does not drop completely even by the post-rotation, and the temperature becomes higher than that in the first area.

[0006] In this way, if a fixing process is performed on a normal-sized sheet in a state where there is a temperature difference between the center and ends of the fixing nip after the fixing process on the small-sized sheet, the next fixing process will be performed before the surface temperature distribution of the pressure roller returns to a specified state. As a result, there is a risk that excessive heat will be supplied, especially in the second region of the fixing nip, resulting in image defects. For example, image defects include high-temperature offset, in which unfixed toner transfers from the surface of the normal-sized sheet to the outer peripheral surface of the fixing film.

[0007] Therefore, in Patent Document 1 (JP Patent Publication No. 11-073055), The structure disclosed herein suppresses the temperature of the high-temperature portion by extending the post-rotation time compared to the case of normal-size paper. There are. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 11-073055 Summary of the Invention [Problem to be solved by the invention]

[0009] In recent years, in order to reduce the size of monochrome image forming apparatuses in particular, a configuration has been adopted in which the drive source for the fixing device and the developing roller are shared and there is no developing roller drive release mechanism. In such an image forming apparatus, the developing roller rotates unnecessarily until the drive of the fixing device is terminated. In such a configuration, when small-sized paper is passed through, as described in Patent Document 1, if control is performed to extend the post-rotation period in order to suppress the temperature of the fixing device, the number of rotations of the developing roller increases further compared to normal-sized paper. When the number of rotations of the developing roller increases, the toner in the developing device is repeatedly rubbed by the supply roller and the developing blade. This rubbing can cause the external additives added to the toner to become detached or embedded (buried) in the resin particles that are the base of the toner, resulting in deterioration of the toner. When the toner deterioration progresses, the toner may no longer be able to perform the desired function due to factors such as a decrease in the charge amount of the toner and a failure to obtain the desired charge amount. This can cause image defects such as so-called fogging, in which the toner adheres to the white background of the recording material.

[0010] The present invention has been made in view of the above problems, and an object of the present invention is to suppress image defects caused by toner deterioration in an image forming apparatus that has a configuration in which a fixing device and a developing roller share a common drive source, the developing roller and the drive source are not disconnected, and that is capable of forming images on normal size paper and small size paper. [Means for solving the problem]

[0011] The present invention employs the following configuration. a photosensitive drum on whose surface an electrostatic latent image is formed in accordance with image information; a developing roller that supplies toner to the photosensitive drum to develop the electrostatic latent image and form a toner image; a transfer means for transferring the toner image onto a recording material; a fixing unit for heat-fixing the toner image onto the recording material, the fixing unit including a pressure roller and a heating member forming a fixing nip portion between the pressure roller and the heating member; a drive source that transmits a drive force to the developing roller and the pressure roller; A control unit; An image forming apparatus comprising: The control unit is determining whether the recording material is a normal size paper whose width in the cross direction is equal to or greater than a predetermined distance, or a small size paper whose width is less than the predetermined distance; executing a first mode in which, when the recording material is the normal size paper, a post-rotation operation is performed by driving the driving source for a predetermined time after the recording material has passed through the fixing nip portion; When the recording material is the small size paper, the post-rotation operation is performed after the recording material has passed through the fixing nip portion, and the image forming apparatus is placed in an image forming job stop state, and a second mode is executed in which a first stop is performed to stop the driving source, a first drive is performed to drive the driving source after the first stop, and a second stop is performed to stop the driving source after the first drive in the image forming job stop state. The image forming apparatus is characterized in that: Effect of the Invention

[0012] According to the present invention, in an image forming device in which a fixing device and a developing roller share a common driving source, the connection between the developing roller and the driving source is not released, and the image forming device is capable of forming images on normal size paper and small size paper, image defects caused by toner deterioration can be suppressed. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic diagram of an overall configuration of an image forming apparatus according to the present invention; [Diagram 2] FIG. 1 is a block diagram showing a control system of an image forming apparatus according to the present invention. [Diagram 3] Schematic diagram of a fixing device according to the present invention. [Figure 4]FIG. 1 is a schematic diagram showing a sheet passing sequence according to a conventional example. [Diagram 5] FIG. 1 is a schematic diagram showing a sheet passing sequence according to the first embodiment; [Figure 6] 5A to 5C are schematic diagrams showing a driving operation according to the first embodiment. [Figure 7] FIG. 1 shows image evaluation results in Example 1. [Figure 8] FIG. 13 shows image evaluation and time measurement results in Example 2. [Figure 9] FIG. 1 shows an example of a notification means according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following examples may be changed as appropriate depending on the configuration and various conditions of the apparatus to which the present invention is applied, and the scope of the present invention is not limited to the following examples. Well-known or publicly known techniques in the relevant technical field can be applied to configurations and processes that are not particularly shown or described. Also, duplicated explanations may be omitted.

[0015] [Example 1] <General Configuration of Image Forming Apparatus> First, a schematic configuration of the image forming apparatus of this embodiment will be described. Fig. 1 is a schematic cross-sectional view of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a monochrome laser printer capable of forming a black monochrome image on a sheet-shaped recording material P using an electrophotographic method. A process cartridge 9 is configured to be detachably attached to an apparatus main body M of the image forming apparatus 100. Here, the apparatus main body M is the constituent parts of the image forming apparatus 100 excluding the process cartridge 9.

[0016] Note that the image forming apparatus to which the present invention can be applied is not limited to this. For example, the present invention can also be applied to a color laser printer that has a plurality of detachable process cartridges 9 and transfers a plurality of color toner images onto a recording material P using an intermediate transfer body such as an intermediate transfer belt to form a full-color image. In addition, in this embodiment, the image forming apparatus 100 is configured so that the process cartridges 9 are detachable, but the present invention can also be applied to an image forming apparatus in which a process unit similar to the components of the process cartridges 9 is provided in the apparatus main body.

[0017] The process cartridge 9 has a photosensitive drum 1, which is a rotatable drum-type (cylindrical) photosensitive body (electrophotographic photosensitive body) serving as an image carrier. The process cartridge 9 also has a charging roller 2, which is a roller-type charging member serving as a charging means, and a developing device 8 serving as a developing means, around the photosensitive drum 1. The process cartridge 9 also has a brush member 12 serving as a paper dust collecting member and a static eliminator 11 serving as a static eliminator, around the photosensitive drum 1. The process cartridge 9 also has a memory 15 serving as a non-volatile storage means. The process cartridge 9 also has a toner amount sensor 20 serving as a developer amount detection means. The charging roller 2, the developing roller 4 serving as a developer carrier provided in the developing device 8, and the brush member 12 are arranged in contact with the surface (outer circumferential surface) of the photosensitive drum 1. The process cartridge 9 is mounted on the apparatus main body M and the mounting guide provided on the process cartridge 9. The device is configured so that it can be easily attached to and detached from the device main body M as a whole via attachment means (not shown) such as a screw or a positioning member.

[0018] The image forming apparatus 100 also includes a transfer roller 13, which is a roller-type transfer member serving as a transfer means, an exposure device 10 serving as an exposure means, and a fixing device 14 serving as a fixing means. The transfer roller 13 is disposed in contact with the surface of the photosensitive drum 1.

[0019] 2, the image forming apparatus 100 further includes a control unit 200 which controls the entire image forming apparatus 100, and an operation panel 60 as an operation unit. The operation panel 60 includes a display unit for displaying information to an operator such as a user or a service person under the control of the control unit 200, and an input unit for inputting information to the control unit 200 according to an operation by the operator. The control unit 200 includes a CPU 201 as a control circuit which performs calculations according to a program and controls each component, a ROM 203 which stores the program, a RAM 205 which is used for program deployment, an I / O 207 which communicates with an external device, and the like. The ROM 203 and the RAM 205 are recording means, and existing memories, etc. can be used.

[0020] <Image formation operation> Next, an image forming operation in the image forming apparatus 100 of this embodiment will be described. The photosensitive drum 1 is rotated in the direction of arrow R1 in the figure (counterclockwise in the figure) at a predetermined process speed by a driving force transmitted from a driving motor 90 serving as a driving source constituting a driving means provided in the apparatus main body M. Here, the process speed corresponds to the circumferential speed (surface moving speed) of the photosensitive drum 1. The process speed in this embodiment is 140 mm / sec.

[0021] The charging roller 2 contacts the surface of the photosensitive drum 1 with a predetermined contact pressure to form a charging portion. A predetermined charging voltage (charging bias) which is a DC voltage is applied to the charging roller 2 from a charging voltage application circuit as a charging voltage application means provided in the main body M of the apparatus. As a result, the charging roller 2 uniformly charges the surface of the photosensitive drum 1 to a predetermined potential of a predetermined polarity (negative polarity in this embodiment). In this embodiment, a charging voltage of -1400V is applied to the charging roller 2 so that the surface potential (potential VD before exposure) of the photosensitive drum 1 becomes -800V. In this embodiment, a DC voltage is used as the charging voltage, but this is not limited thereto, and an oscillating voltage in which a DC voltage and an AC voltage are superimposed may be used as the charging voltage. The power source 95 of the image forming apparatus 100 is a high-voltage power source for supplying voltage when performing each operation including the image forming operation, and functions as various voltage application means.

[0022] The uniformly charged surface of the photosensitive drum 1 is irradiated with a laser beam by the exposure device 10 based on image information, and is scanned and exposed, forming an electrostatic latent image (electrostatic image) on the photosensitive drum 1. In this embodiment, the exposure device 10 is configured as a scanner unit. Image information input to the image forming apparatus 100 from an external device (not shown) such as a personal computer connected to the image forming apparatus 100 is converted into a time-series electric digital image signal by a video controller (not shown) provided in the image forming apparatus 100. The exposure device 10 is controlled by the control unit 200 to emit a laser beam modulated in response to the time-series electric digital image signal, and scans and exposes the surface of the photosensitive drum 1. As a result, an electrostatic latent image corresponding to the image information is formed on the photosensitive drum 1. In this embodiment, the exposure device 10 is configured to emit a light amount of 0.45 μJ / cm so that the post-exposure potential VL of the surface of the photosensitive drum 1 is −100 V. 2 The surface of the photosensitive drum 1 is irradiated with laser light.

[0023] The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by supplying toner 3 as a developer by a developing device 8. As a result, a toner image (toner A toner image (a developer image) is formed on the photosensitive drum 1. The developing device 8 has a developing roller 4 as a developer carrier. The developing roller 4 contacts the surface of the photosensitive drum 1 with a predetermined contact pressure to form a developing section. A toner layer is formed on the developing roller 4 by the toner 3 charged to a predetermined polarity (negative polarity in this embodiment). A predetermined developing voltage (developing bias) which is a direct current voltage is applied to the developing roller 4 from a developing voltage application circuit as a developing voltage application means provided in the main body M of the device. As a result, the toner 3 adheres to the electrostatic latent image on the photosensitive drum 1 in the developing section. As a result, a toner image is formed on the photosensitive drum 1. In this embodiment, a developing voltage of -400V is applied to the developing roller 4. In this embodiment, the toner 3 charged to the same polarity (negative polarity in this embodiment) as the charging polarity of the photosensitive drum 1 adheres to the exposed section (image section) on the photosensitive drum 1, the absolute value of the potential of which has been reduced by being exposed after being uniformly charged (reverse development method). In this embodiment, the normal charging polarity of the toner 3, which is the main charging polarity of the toner 3 during development, is negative.

[0024] The transfer roller 13 comes into contact with the photosensitive drum 1 at a predetermined contact pressure to form a transfer section. The toner image formed on the photosensitive drum 1 is transferred in the transfer section onto a recording material P that is being conveyed while being sandwiched between the photosensitive drum 1 and the transfer roller 13. During transfer, a predetermined transfer voltage (transfer bias), which is a DC voltage, is applied to the transfer roller 13 from a transfer voltage application circuit as a transfer voltage application means. In this embodiment, a transfer voltage of +1500V is applied to the transfer roller 13.

[0025] A recording material (transfer material, recording medium, sheet) P is supplied from a feeding section 30 to the transfer section. The feeding section 30 is configured to have a cassette 31 as a recording material storage section, a feeding roller 32 as a feeding member, and the like. The recording material P stored in the cassette 31 is separated one by one by the feeding roller 32 and sent out from the cassette 31. This recording material P is transported to the transfer section by a transport roller (registration roller) 50 as a transport member so as to be synchronized with the toner image on the photosensitive drum 1.

[0026] The recording material P onto which the toner image has been transferred is conveyed to a fixing device 14 serving as a fixing means. The fixing device 14 applies heat and pressure to the recording material P to fix (melt and adhere) the toner image onto the recording material P. The recording material P onto which the toner image has been fixed is discharged (output) onto a tray 40 serving as a discharge unit provided outside the apparatus main body M.

[0027] On the other hand, the toner 3 (transfer residual toner) remaining on the photosensitive drum 1 without being transferred to the recording material P during the transfer process is removed from the photosensitive drum 1 as follows. The surface of the photosensitive drum 1 after the transfer process is discharged by a discharger (discharging lamp) 11 so that the surface potential becomes 0V, and then enters the charging section. The transfer residual toner remaining on the photosensitive drum 1 includes a mixture of toner 3 positively charged and toner 3 negatively charged but not sufficiently charged. These transfer residual toners are charged negatively by discharge in the charging section. The transfer residual toner negatively charged in the charging section reaches the developing section as the photosensitive drum 1 rotates. Here, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1 that has reached the developing section. The transfer residual toner adhering to the non-exposed portion (non-image portion) on the photosensitive drum 1 moves from the photosensitive drum 1 to the developing roller 4 in the developing section due to the potential difference between the pre-exposure potential VD on the photosensitive drum 1 and the developing voltage, and is collected in the developing chamber 8b of the developing device 8. The toner 3 collected in the developing chamber 8b is used again for image formation. On the other hand, the transfer residual toner adhering to the exposed portion (image portion) on the photosensitive drum 1 does not move from the photosensitive drum 1 to the developing roller 4 in the developing portion, but forms a toner image together with the toner 3 that has moved from the developing roller 4 to the photosensitive drum 1. Then, this toner 3 is transferred onto the recording material P in the transfer portion and removed from the photosensitive drum 1.

[0028] The process cartridge 9 is also provided with a brush member 12. is a paper dust recovery member for removing paper dust fibers generated from the recording material P that adhere to the photosensitive drum 1 from the recording material P during the transfer process. The brush member 12 is disposed so as to come into contact with the photosensitive drum 1 downstream of the transfer unit in the rotation direction of the photosensitive drum 1 and upstream of the charging unit. As the photosensitive drum 1 rotates, the brush member 12 rubs against the surface of the photosensitive drum 1, thereby picking up and removing the paper dust fibers on the photosensitive drum 1 from the photosensitive drum 1.

[0029] In this embodiment, in order to reduce the size of the image forming apparatus, only one drive motor 90 is used as a drive source. The photosensitive drum 1, the developing roller 4, and the fixing device 14 are all connected by a gear train, and are driven and operated by this drive motor 90. In addition, the developing roller 4 does not have a mechanism for separating it from the drive motor 90. This also eliminates the need to provide a space for separation, which contributes to the miniaturization of the image forming apparatus.

[0030] <Details of the developing device> Next, a detailed configuration of the developing device 8 in the image forming apparatus 100 of this embodiment will be described.

[0031] (Developing device) In this embodiment, the developing device 8 is a one-component contact developing device that uses a non-magnetic one-component developer (toner 3) as a developer. The developing device 8 has a developing container 80 (frame body) that is configured with a developing chamber 8b as a developing member housing chamber and a toner housing chamber 8a as a developer housing chamber. The developing chamber 8b and the toner housing chamber 8a communicate with each other through an opening. The developing chamber 8b is provided with a developing roller 4 as a developer carrier (developing member), a supply roller 5 as a supply member for supplying the toner 3 to the developing roller 4, and a developing blade 6 as a regulating member for regulating 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.

[0032] The developing roller 4 is rotatably disposed at the opening of the developing chamber 8b (developing container 80), and rotates while supporting the toner 3 to transport the toner 3 from the inside to the outside of the developing chamber 8b (developing container 80). The toner accommodating chamber 8a accommodates the toner 3 as a developer. The toner accommodating chamber 8a is also provided with an agitating member 7 for agitating the toner 3 in the toner accommodating chamber 8a and transporting the toner 3 from the toner accommodating chamber 8a to the developing chamber 8b.

[0033] In this embodiment, the developing device 8 uses a contact development method in which the image carrier and the developer carrier are arranged in contact with each other, but is not limited to this. The developing device 8 may use a two-component development method that uses a two-component developer, or a non-contact development method in which the image carrier and the developer carrier are arranged opposite each other with a predetermined gap between them.

[0034] In this embodiment, the developing roller 4 is configured by coating a base layer of silicone rubber and a surface layer of urethane rubber in this order on the outer periphery of a core metal having a diameter of 6 mm so that the outer diameter becomes 15 mm. Also, in this embodiment, the electrical resistance value of the developing roller 4 is 1×10 4 ~1×10 12 It is Omega.

[0035] In this embodiment, the supply roller 5 is a conductive elastic sponge roller that is configured by forming a foam layer on the outer periphery of a core metal having a diameter of 6 mm. In this embodiment, the electrical resistance of the supply roller 5 is 1×10 4 ~1×10 8 The hardness of the supply roller 5 is measured by applying a load of 1 mm to a flat plate having a longitudinal width of 50 mm on the surface of the supply roller 5.

[0036] In this embodiment, the developing blade 6 is disposed along the direction of the rotation axis of the developing roller 4. The developing blade 6 is a 0.1 mm thick SUS sheet metal made of metal, having a predetermined length in the longitudinal direction and in the transverse direction approximately perpendicular to the longitudinal direction. The developing blade 6 is disposed so that the free end in the transverse direction faces the upstream side in the rotation direction of the developing roller 4, and the side surface near the free end is in contact with the developing roller 4 along the longitudinal direction. In this embodiment, the developing blade 6 is one in which the tip (free end) of the SUS sheet metal is cut from the contact surface side with the developing roller 4. The tip portion of the developing blade 6 is bent in the cutting direction by the cutting process, and the amount of bending of the tip of the developing blade 6, which corresponds to the radius of curvature R, is 0.02 mm.

[0037] The movement of toner 3 in developing device 8 during operation will be described. A driving force is transmitted to developing device 8 from a driving motor 90 serving as a driving source constituting a driving means provided in apparatus main body M. This causes developing roller 4, supply roller 5, and stirring member 7 to rotate in the directions of arrows R2 (clockwise), R3 (clockwise), and R4 (counterclockwise) in the figure, respectively. Note that the photosensitive drum 1 and each rotating member of developing device 8 (developing roller 4, supply roller 5, stirring member 7) may share a driving source.

[0038] As the stirring member 7 in the toner storage chamber 8a rotates, the toner 3 in the toner storage chamber 8a is stirred and transported toward the supply roller 5 in the development chamber 8b. The toner 3 held in the foam layer of the supply roller 5 is sent to the contact portion with the development roller 4 by the rotation of the supply roller 5. The toner 3 that has reached this contact portion is rubbed by the surfaces of the development roller 4 and the supply roller 5, which move in opposite directions at this contact portion, and some of the toner adheres to the surface of the development roller 4.

[0039] The toner 3 adhering to the surface of the developing roller 4 is sent to the contact portion with the developing blade 6 as the developing roller 4 rotates. The developing blade 6 regulates the amount of toner 3 adhering to the surface of the developing roller 4 to form a uniform thin layer, and also frictionally charges the toner 3. The thin layer of toner 3 is sent to the contact portion with the photosensitive drum 1 as the developing roller 4 rotates, and is used to develop the electrostatic latent image formed on the photosensitive drum 1. The toner 3 that is not used for development and remains on the surface of the developing roller 4 is transported to the contact portion 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 sent into the toner storage chamber 8a, where it is stirred and mixed with the toner 3 in the toner storage chamber 8a.

[0040] <Detailed configuration of the fixing device> The fixing device 14 will be described with reference to the cross-sectional view of FIG. 3(a) and the side view of FIG. 3(b). The fixing device 14 of this embodiment is configured such that the heater 113 is held by a heater holder 130, and a fixing film 112, which is an endless belt and serves as a heating member, is provided around the heater holder 130. The heater holder 130 is preferably made of a heat insulating material so as not to easily take away heat from the heater 113, and in this embodiment, liquid crystal polymer (LCP), which is a heat-resistant resin, is used. The heater holder 130 is supported by an iron stay 120 on the side opposite the heater 113 to provide strength. The stay 120 is configured to be pressed by pressure springs (not shown) from both ends in the longitudinal direction.

[0041] 3A, the heater 113 comes into contact with the inner surface of the fixing film 112 to form an inner surface nip and heat the fixing film 112 from the inside. The pressure roller 110 forms a fixing nip facing the heater 113 so as to sandwich the fixing film 112. The pressure roller 110 receives the force of a pressure spring at bearings (not shown) provided at both ends of the core metal 117, and is driven by power received from a drive source by a drive gear 131 provided at the end of the core metal 117. When the pressure roller 110 is driven, the fixing film 112 receives power from the pressure roller 110 at the fixing nip and rotates.

[0042] In order to prevent the fixing film 112 from being biased to the left or right in the longitudinal direction, 2, fixing flanges 150 for preventing deviation are provided at both ends of the fixing film 112. The fixing flanges 150 are fitted into and fixedly installed in the stays 120. The rotation of the fixing film 112 is supported from the inner surfaces of both ends by the fixing flanges 150.

[0043] The fixing film 112 of this embodiment has an outer diameter of 20 mm in a cylindrical state without deformation, and has a multi-layer structure in the thickness direction. The fixing film 112 has a layer structure consisting of a base layer 126 for maintaining the strength of the film and a release layer 128 for reducing adhesion of dirt to the surface. The material of the base layer 126 needs to be heat-resistant to receive the heat of the heater 113, and also needs to be strong to slide against the heater 113, so it is recommended to use metals such as SUS (Stainless Used Steel) and nickel, or heat-resistant resins such as polyimide. Metals are stronger than resins, so they can be made thin, and also have high thermal conductivity, so they easily transfer heat from the heater 113 to the surface of the fixing film 112. On the other hand, resins have an advantage of being smaller in specific gravity than metals, so they have a smaller heat capacity and are easier to heat up. In addition, resins can be molded into thin films by coating molding, so they can be molded at low cost. In this embodiment, polyimide resin is used as the material of the base layer 126 of the fixing film 112, and carbon-based filler is added to improve thermal conductivity and strength. The thinner the base layer 126 is, the easier it is to transfer heat from the heater 113 to the surface of the fixing film 112, but the strength decreases, so the thickness of about 15 μm to 100 μm is preferable, and in this embodiment, it is set to 60 μm.

[0044] The conductive primer layer 127 is made of polyimide resin or fluororesin, and carbon or the like is added to reduce resistance. When paper is passed through, the exposed portion of the conductive layer is grounded to stabilize the potential of the fixing film 112.

[0045] The material of the release layer 128 is preferably a fluororesin such as perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), or tetrafluoroethylene-hexafluoropropylene resin (FEP). In this embodiment, PFA, which has excellent releasability and heat resistance among fluororesins, is used, and a conductive material is dispersed to give it a medium resistance. The release layer 128 may be a tube covered or a surface coated with paint. In this embodiment, the release layer 128 is molded by a coat that is excellent in thin-wall molding. The thinner the release layer 128, the easier it is to transfer heat from the heater 113 to the surface of the fixing film 112. However, if the release layer 128 is too thin, durability deteriorates, so the thickness is preferably about 5 μm to 30 μm, and in this embodiment, it is 10 μm.

[0046] The pressure roller 110 in this embodiment has an outer diameter of 14 mm, and silicone rubber is arranged to a thickness of 2.5 mm on an outer diameter 9 mm portion of an iron core metal 117 to form an elastic layer 116 .

[0047] The elastic layer 116 is made of heat-resistant silicone rubber or fluororubber, but silicone rubber is used in this embodiment. The pressure roller 110 has an outer diameter of about 10 to 50 mm. A smaller outer diameter reduces the heat capacity, but if it is too small, the width of the fixing nip becomes narrow, so an appropriate diameter is necessary. In this embodiment, the outer diameter is 14 mm. Regarding the thickness of the elastic layer 116, if it is too thin, heat will escape to the metal core, so an appropriate thickness is also necessary, and in this embodiment, the thickness of the elastic layer 116 is 2.5 mm.

[0048] On the elastic layer 116, a release layer 118 made of perfluoroalkoxy resin (PFA) is formed as a release layer for the toner 3. Like the release layer 128 of the fixing film 112, the release layer 118 may be covered with a tube or coated with paint, but in this embodiment, a tube with excellent durability is used and the thickness is 20 μm. In addition to PFA, the material of the release layer 118 may be fluororesins such as PTFE and FEP, or fluororubber or silicone rubber with good release properties. The lower the surface hardness of the pressure roller 110, the lighter the pressure required to obtain the fixing nip width, but if it is too low, durability deteriorates. In this embodiment, the Asker-C hardness is used. The pressure roller 110 was rotated by a drive source at a surface movement speed of 140 mm / sec.

[0049] The heater 113 in this embodiment is a typical heater used in a film heating type heating device, and is made by providing a resistance heating element in series on a ceramic substrate. The heater 113 is made by applying a 10 μm-high Ag / Pd (silver-palladium) resistance heating element by screen printing on the surface of an alumina substrate 6 mm wide and 1 mm thick, and then covering it with a 50 μm-thick layer of glass as a heating element protection layer.

[0050] As shown in FIG. 3(a) and FIG. 3(b), a temperature detection element 115 for detecting the temperature of the ceramic substrate is disposed on the rear side of the heater 113. The temperature of the heater 113 is adjusted by appropriately controlling the current flowing through the resistance heating element according to the signal of the temperature detection element 115. If the temperature is high, the power consumption increases, so it is necessary to set it appropriately. In this embodiment, the temperature control temperature for plain paper is set to 180° C. In addition, a temperature fuse (not shown) as a safety element may be disposed on the rear side of the heater 113 to cut off the circuit and ensure safety when the heater 113 generates abnormal heat. The heater 113 is connected to a power source via a temperature fuse. When the temperature of the temperature fuse becomes abnormally high, the temperature fuse is blown and the power supply from the power source to the heater 113 is cut off. Note that the configuration of the fixing device 14 is not limited to this. For example, it may be configured by a heat roller equipped with a halogen heater inside. This embodiment is applicable as long as the driving source used to drive the fixing device 14 and the developing device 8 is common.

[0051] <Feature of this embodiment: Paper passing control> The paper passing control, which is a feature of this embodiment, will now be described. When the recording material P enters the fixing nip N1, the toner image is heated and fixed to the recording material P in the fixing nip N1. Thereafter, the rear end of the recording material P leaves the fixing nip N1, and the motor stops. In this embodiment, the time from when the rear end of the recording material P leaves the fixing nip N1 until the motor stops is defined as the time of the post-rotation operation. In this embodiment, the post-rotation operation is performed until the recording material P is transported from the fixing nip N1 to the tray 40. That is, during the post-rotation operation, the motor is driven for a predetermined time.

[0052] In this embodiment, a recording material P whose width is equal to or greater than a predetermined value (here, 200 mm or greater) is referred to as a normal size paper. A recording material P whose width is smaller than that of a normal size paper (i.e., whose width is less than a predetermined value, here, less than 200 mm) is referred to as a small size paper. When a small size paper is used, heat is absorbed by the paper in the area (hereinafter referred to as the first area) of the paper passing area of ​​the fixing nip portion where the small size paper passes. On the other hand, heat is not absorbed by the paper in the area (hereinafter referred to as the second area) excluding the area where the small size paper passes from the paper passing area. Therefore, after fixing, the temperature value of the second area becomes higher than that of the first area. When a toner image is fixed to a normal size paper in such a state where a temperature difference occurs between the first area and the second area, a high temperature offset, which is a phenomenon in which an unfixed image carried on the normal size paper receives an excessive heat supply from the second area of ​​the paper passing area and transfers from the surface of the normal size paper to the outer peripheral surface of the fixing film, may occur.

[0053] (Conventional flow) In a conventional example, after a small-size sheet has passed, driving is extended after post-rotation to eliminate the temperature difference between the first and second regions. The operation flow of the conventional example is described with reference to FIG. 4. Printing begins in step S100. In step S101, the control unit 200 determines whether the passed recording material P is a small-size sheet based on the detection result of the paper width sensor 500. If it is determined that the sheet is not a small-size sheet (S101: No), the above-mentioned post-rotation is performed in step S102, and printing ends in step S103. On the other hand, if it is determined that the sheet is a small size (S101: Yes), In step S200, post-rotation is performed, in step S201 the motor is driven for a certain period of time, and in step S103 the printing ends. In the case of small size paper, it is desirable to drive the motor in step S201 only for the time until the temperature difference between the first and second areas disappears. In this example, the motor drive time is set to 10 seconds.

[0054] However, in a configuration in which the drive source of the fixing device 14 and the developing device 8 is common and the developing roller 4 cannot stop transmitting the drive force to the drive source, the following problem occurs when the operation flow of the conventional example described above is followed. That is, since the developing roller 4 rotates even while the motor drive is extended (period of S201) after the post-rotation due to the passage of small-sized paper, the toner 3 repeatedly rubs against the photosensitive drum 1 and the developing blade 6, and the deterioration of the toner 3 progresses. Here, if the developing roller 4 rotates for image formation, even if the toner 3 rubs against the photosensitive drum 1 and the developing blade 6, the toner 3 is used and consumed for image formation before the toner deterioration progresses. On the other hand, if the developing roller 4 rotates without consuming the toner 3, as in the case of the post-rotation extension due to the passage of small-sized paper, the deterioration of the toner 3 is accelerated.

[0055] (Flow of this embodiment) Therefore, in this embodiment, in order to suppress the temperature of the second region after the post-rotation, an image formation job stop time is provided as a time for stopping the execution of at least an operation involving the driving of the developing device 8 (for example, an operation of rotating the developing roller 4 to develop an electrostatic latent image in a print job). During the image formation job stop time, the image forming apparatus 100 is in an image formation job stop state in which a job involving the driving of the developing roller 4 cannot be performed. Note that even during the image formation job stop time, not all jobs related to image formation cannot be executed, but only parts of the job that require the operation of the driving source cannot be executed. Therefore, image processing performed in the background (for example, image data expansion processing) can be executed. Also, even during the image formation job stop time, it is possible to accept a job such as a print instruction from a user, store it in an execution queue, and execute it after an image formation operation involving the driving of the developing roller 4 becomes possible. However, during the image formation job stop time, it is possible to notify a job such as a print instruction from a user that the job cannot be accepted. Furthermore, it is not impossible to drive the developing roller 4 throughout the entire period of the image formation job stop time, and for example, as described later, at the timing when the motor is re-driven from a stopped state, the developing roller 4 can also be driven. However, such re-driving is performed temporarily, and the time is insufficient to execute image formation. In this embodiment, during this image formation job stop time, the motor is driven from a stopped state and returned to a stopped state. The operation flow of this embodiment will be explained with reference to Figure 5. The same reference numerals are used for the same processes as those in the conventional example in Figure 4, and the explanation will be simplified.

[0056] Printing begins in step S100, and a determination is made in step S101 as to whether the recording material P is small size paper. If it is determined that the recording material P is not small size paper, post-rotation is performed in step S102 as in the conventional example, and printing ends in step S103.

[0057] On the other hand, if the size is determined to be small in step S101, post-rotation is performed in step S200, and the motor is stopped in step S210 (first stop). Next, the motor is driven in step S211 (first drive), and then the motor is stopped again in step S212 (second stop). After that, printing ends in step S103. That is, by stopping the motor, the rotation of the developing roller 4 in the developing device 8 is also stopped, so deterioration of the toner 3 can be suppressed.

[0058] However, stopping the motor can have undesirable effects. That is, as shown in FIG. 6A, if the motor remains stopped, the area enclosed by the dashed line A, including the fixing nip N1, is not exposed to the outside air, and the temperature is difficult to decrease. Therefore, in this flow, after stopping the motor, a drive operation (S211) is performed once, and then the motor is started again. The pressure roller is stopped (S212). As a result, as shown in FIG. 6B, the area of ​​the broken line A rotates in the direction of the arrow R5, and the heat of the fixing nip N1 can be transferred to the outside of the nip. Also, on the fixing film 112 side of the fixing nip N1, the surface of the pressure roller whose temperature has been lowered by the outside air comes to the fixing nip N1, so the temperature can be efficiently lowered.

[0059] Here, the motor stop time in step S210 is set to 1 second. For the drive time in S211, it is necessary to shift the position of the area constituting the fixing nip portion N1 while suppressing the number of rotations. Therefore, it is desirable to set the drive time in a range in which the movement distance of the area of ​​the broken line A is smaller than the outer diameter of the pressure roller and the fixing film. In this embodiment, the drive time is set to 150 ms (drive distance: about 20 mm). The total time for steps S210, S211, and S212 is set to 12 seconds.

[0060] In this embodiment, the determination of whether the paper is a small size paper is performed by a paper width sensor 500 installed near the conveying roller 50. For example, the paper width sensor 500 can be a detection member having two flags in the width direction intersecting (typically perpendicular to) the conveying direction of the recording material P, and a detection section that blocks light from a light projecting section when the flags are standing and transmits light when the flags are down. In such a paper width sensor 500, when paper with a paper width wider than the distance between the flags is conveyed, the transmitted light is detected in conjunction with the flags hitting the paper falling down. This makes it possible to determine whether the paper width is equal to or greater than a predetermined distance or less than a predetermined distance. In the paper width sensor 500 of this embodiment, the paper width sensor flags are installed at positions of 100 mm from the center of the paper in the longitudinal direction, and when a recording material P with a width of 200 mm or more is conveyed, the paper width sensor flags fall down, and it is detected that the paper is not a small size paper. If both sensors are not detected, or if only one side is detected, it is determined that the paper is a small size paper. Note that the paper width sensor does not have to be a type that uses flags. Also, it may be possible to determine whether the paper is a small size paper or not based on the print settings of the image forming device. The width of the recording material may be compared with a predetermined distance, and if the distance is equal to or greater than the predetermined distance, the paper may be determined to be a normal size paper, and if the distance is less than the predetermined distance, the paper may be determined to be a small size paper.

[0061] Here, from when the motor is stopped in step S210 until printing is completed in S103, the motors used to rotate the fixing device 14 and the developing roller 4 are stopped, so the image forming apparatus 100 is in a state where it cannot execute a print job. Therefore, even if the user executes a print instruction from the host PC, for example, the image forming operation will not start. Therefore, the control unit 200 of this embodiment puts the image forming apparatus into such an image formation job stop state after the post-rotation operation.

[0062] In addition, in the image forming job stop state, the motor is stopped for a long time, and even if the user issues a print instruction from the host PC, no response is obtained from the image forming apparatus 100. Therefore, during the image forming job stop time, the user may be notified that the image forming apparatus 100 is operating. This allows the user to recognize that the image forming apparatus 100 is operating even when the motor is stopped. The content of the notification to the user may be a message displayed on the operation panel 60, for example, as long as it indicates that the image forming apparatus 100 is operating. In addition, the image forming apparatus 100 may be provided with a notification means such as an LED. For example, FIG. 9 shows a state in which indicators 400 (400a to 400c) for notifying the user of the remaining toner amount are provided on the housing of the apparatus. FIG. 9(a) shows low remaining amount (Low), FIG. 9(b) shows medium remaining amount (Mid), and FIG. 9(c) shows full remaining amount (Full). In this case, the indicators 400 (400a to 400c) may be blinked to notify the user that the job is stopped.

[0063] <Effects of the present invention> A paper feed test was conducted, and an evaluation was conducted to see if fogged images occurred as an image defect. The above was repeated and 5000 sheets were passed through. Canon Office70 (grammage 70g, A4 size) and PB-PAPER (grammage 64g, A5 size) were used for the paper passing. As a comparative example, Canon office70, which is a normal size, was used for the paper passing, and PB-PAPER was used under the conditions of the conventional example, and PBPAPER was used under the conditions of this embodiment.

[0064] The image on the paper was evaluated, and when a fogged image occurred, it was marked with "X", and when no fogged image occurred, it was marked with "O". The results are shown in FIG.

[0065] In the comparative example, no image defects occurred up to 5000 sheets. In contrast, in the conventional example, image defects such as fog occurred from 3500 sheets onwards. This is because the number of developing rotations increased due to the extension of the post-rotation that occurs when small size paper is passed, and the number of frictions of the toner 3 increased, causing the toner 3 to deteriorate. In this embodiment, the post-rotation is not extended even when small size paper is passed, so no image defects such as fog occurred after 5000 sheets were passed, as in the comparative example.

[0066] The drive time after post-rotation in the conventional example and the image formation job stop time in this embodiment are fixed values, but since the temperature difference between the first and second areas changes depending on the number of sheets of paper passed continuously, it is desirable to set the drive time in the conventional example and the image formation job stop time in this embodiment according to the number of sheets of paper passed.

[0067] In view of the above, in a configuration in which the drive source for the fixing device 14 and the developing roller 4 is common and there is no developing roller drive release mechanism due to the small size of the image forming device, in order to suppress the temperature of the second area after the post-rotation following the passage of small-sized paper, a period of time is set during which the next job cannot be accepted, and during that period the motor is driven from a stopped state and then returned to a stopped state, thereby suppressing the occurrence of fogged images while minimizing declines in productivity.

[0068] In addition, in this embodiment, the driving of the fixing device 14 is also stopped, which also serves to suppress scraping due to wear of the release layer 128 caused by the rotation of the fixing film 112. Therefore, the life extension effect of the fixing device 14 can be expected.

[0069] [Example 2] Next, a description will be given of a second embodiment. The configuration and operation of the image forming apparatus 100 are similar to those of the first embodiment.

[0070] <Features of this embodiment> In this embodiment, the stop time of the next image forming job is shortened while suppressing image defects. Here, the image forming apparatus 100 can execute both the paper passing sequence shown in Fig. 4 and the paper passing sequence shown in Fig. 5, and a method of switching between these two sequences will be described. The drive time of step S201 in Fig. 4 is 10 seconds as in the first embodiment, and the times of S210, S211, and S212 in Fig. 5 are 12 seconds.

[0071] Hereinafter, the mode shown in FIG. 4 will be referred to as the first mode, and the mode shown in FIG. 5 as the second mode. In the first mode shown in FIG. 4, the motor drive time after post-rotation is extended, making it easier to suppress temperature rise in the fixing nip N1. This is a mode that prioritizes productivity, allowing the next print job to be performed quickly. On the other hand, the second mode shown in FIG. 5 is a mode that prioritizes durability, stopping the motor after post-rotation and suppressing friction of the toner 3 caused by the rotation of the developing roller 4.

[0072] A method of switching between modes will now be described. Here, the first mode is set as the initial setting. Then, the control unit 200 of this embodiment records the result of detection by the paper width sensor 500 (determination result of whether the paper is small size or normal size paper) in the ROM 203 as a recording means every time a paper is passed (every time an image forming operation is performed). Also, every time a paper is passed, the control unit 200 The ratio of normal size paper to small size paper is calculated by the CPU 201. Then, when the ratio of small size paper to the total number of prints of recording materials up to now is equal to or greater than a predetermined value (here, 40% or more), the control unit 200 switches to the second mode from the next job. On the other hand, when the ratio of small size paper is less than 40%, the control unit 200 switches to the first mode.

[0073] Here, the predetermined value of the ratio at the time of mode switching is set to 40%, but is not limited to this. Also, in order to prevent mode switching from being performed frequently, once mode switching has been performed, switching judgment may be suspended until a predetermined number of sheets of recording material P have been passed through. Also, the ratio calculation for mode switching may be reset at a predetermined timing (for example, when the apparatus is restarted, when no paper has been passed for a certain period of time, when maintenance such as cartridge replacement is performed, etc.).

[0074] <Effects of the present invention> As in Example 1, two sheets were repeatedly passed through the printer for 5,000 sheets, and the printer was evaluated for fog images and measured the drive extension time and image formation job stop time after post-rotation. Two types of paper, Canon Office70 (basis weight 70g, A4 size) and PB-PAPER (basis weight 64g, A5 size), were used, and the paper was passed through at different paper passing ratios.

[0075] The conditions of Example 1 were used for this embodiment, the conventional example, and Comparative Example 2. The image evaluation was performed with a rating of × if fogged images occurred during the 5,000 sheets of paper passing, and ◯ if they did not occur. The image formation job stop time was measured, and the total time was calculated. The results are shown in FIG.

[0076] In the conventional example, the image formation job downtime was short, but when the A5 paper feed rate was 40% or more, the number of developer rotations increased and fogged images occurred. In comparative example 2, a stop operation was inserted during the image formation job downtime, so no fogged images occurred, but when the A5 paper feed rate was 20%, the image formation job downtime was longer than in the conventional example. In contrast, in this embodiment, no fogged images occurred and the image formation job downtime could be kept to a minimum.

[0077] This is because the image forming apparatus has two modes, the conventional example and the embodiment 1, and the mode is automatically switched depending on the paper passing ratio of normal size paper and small size paper. Also, in this embodiment, the conventional example and the embodiment 1 modes are provided, but instead of the embodiment 1, a mode in which the motor is stopped in S201 after the post-rotation in S200 may be provided as shown in Fig. 9. In this case, S201 becomes the image formation job stop time, and 15 seconds are required to prevent hot offset.

[0078] In this embodiment, the image forming apparatus automatically switches between the two modes. Alternatively, the user may be notified of the two modes and allowed to switch between them via the operation panel 60.

[0079] As described above, in a configuration in which the drive source for the fixing device 14 and the developing roller 4 is common and there is no developing roller drive release mechanism due to the small size of the image forming device, by having two modes after small-sized paper is passed and switching between modes in response to a switching notification, it is possible to suppress the occurrence of fog images while suppressing a decrease in productivity.

[0080] [Configuration 1] a photosensitive drum on whose surface an electrostatic latent image is formed in accordance with image information; a developing roller that supplies toner to the photosensitive drum to develop the electrostatic latent image and form a toner image; a transfer means for transferring the toner image onto a recording material; a fixing unit for heat-fixing the toner image onto the recording material, the fixing unit including a pressure roller and a heating member forming a fixing nip portion between the pressure roller and the heating member; a drive source that transmits a drive force to the developing roller and the pressure roller; A control unit; An image forming apparatus comprising: The control unit is determining whether the recording material is a normal size paper whose width in the cross direction is equal to or greater than a predetermined distance, or a small size paper whose width is less than the predetermined distance; executing a first mode in which, when the recording material is the normal size paper, a post-rotation operation is performed by driving the driving source for a predetermined time after the recording material has passed through the fixing nip portion; When the recording material is the small size paper, the post-rotation operation is performed after the recording material has passed through the fixing nip portion, and the image forming apparatus is placed in an image forming job stop state, and a second mode is executed in which a first stop is performed to stop the driving source, a first drive is performed to drive the driving source after the first stop, and a second stop is performed to stop the driving source after the first drive in the image forming job stop state. 1. An image forming apparatus comprising: [Configuration 2] In the first driving, a region of the pressure roller that is in contact with the fixing nip portion when the post-rotation operation is completed is moved to a position where it is not in contact with the fixing nip portion. 2. The image forming apparatus according to claim 1, [Configuration 3] In the first driving, a moving distance of a region of the pressure roller that is in contact with the fixing nip portion when the post-rotation operation is completed is a distance that is smaller than an outer diameter of the pressure roller. 3. The image forming apparatus according to claim 2, [Configuration 4] The control unit notifies a user that the image forming apparatus is in operation during the image forming job stop state. 4. The image forming apparatus according to claim 1, wherein the first and second electrodes are disposed on the first and second electrodes. [Configuration 5] The control unit records in a recording means a determination result as to whether the recording material is the normal size paper or the small size paper, calculates a ratio of the number of the small size paper sheets to the total number of the recording materials based on the determination result obtained for a predetermined number of the recording materials, and switches the operation mode of the image forming apparatus to the second mode when the ratio becomes equal to or greater than a predetermined value. 5. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. [Configuration 6] Whether the image forming apparatus operates in the first mode or the second mode is determined based on a user's operation. 5. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. [Explanation of symbols]

[0081] 1: photosensitive drum, 4: developing roller, 8: developing device, 13: transfer roller, 14: fixing device, 90: driving motor, 100: image forming device, 200: control unit

Claims

1. a photosensitive drum on whose surface an electrostatic latent image is formed in accordance with image information; a developing roller that supplies toner to the photosensitive drum to develop the electrostatic latent image and form a toner image; a transfer means for transferring the toner image onto a recording material; a fixing unit for heat-fixing the toner image onto the recording material, the fixing unit including a pressure roller and a heating member forming a fixing nip portion between the pressure roller and the heating member; a drive source that transmits a drive force to the developing roller and the pressure roller; A control unit; An image forming apparatus comprising: The control unit is determining whether the recording material is a normal size paper whose width in the cross direction is equal to or greater than a predetermined distance, or a small size paper whose width is less than the predetermined distance; executing a first mode in which, when the recording material is the normal size paper, a post-rotation operation is performed by driving the driving source for a predetermined time after the recording material has passed through the fixing nip portion; When the recording material is the small size paper, the post-rotation operation is performed after the recording material has passed through the fixing nip portion, and the image forming apparatus is placed in an image forming job stop state, and a second mode is executed in which a first stop is performed to stop the driving source, a first drive is performed to drive the driving source after the first stop, and a second stop is performed to stop the driving source after the first drive in the image forming job stop state.

1. An image forming apparatus comprising:

2. In the first driving, a region of the pressure roller that is in contact with the fixing nip portion when the post-rotation operation is completed is moved to a position where it is not in contact with the fixing nip portion.

2. The image forming apparatus according to claim 1,

3. In the first driving, a moving distance of a region of the pressure roller that is in contact with the fixing nip portion when the post-rotation operation is completed is a distance that is smaller than an outer diameter of the pressure roller.

3. The image forming apparatus according to claim 2,

4. The control unit notifies a user that the image forming apparatus is in operation during the image forming job stop state.

2. The image forming apparatus according to claim 1,

5. The control unit records in a recording means a determination result as to whether the recording material is the normal size paper or the small size paper, calculates a ratio of the number of the small size paper sheets to the total number of the recording materials based on the determination result obtained for a predetermined number of the recording materials, and switches the operation mode of the image forming apparatus to the second mode when the ratio becomes equal to or greater than a predetermined value.

5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a multi-color image forming apparatus.

6. Whether the image forming apparatus operates in the first mode or the second mode is determined based on a user's operation.

5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a multi-color image forming apparatus.

Images