Image forming apparatus

Abstract

To provide an image forming apparatus that, when paper jam occurs in or around a fixing unit, clearly identifies the position of remaining paper and easily performs paper jam processing.SOLUTION: An image forming apparatus comprises: a fixing unit in which a fixing nip is formed between a heating unit including a heating roller having a heating function and a pressure unit including a pressure roller not having a heating function; a conveyance sensor that detects a sheet at a predetermined first conveyance position on the upstream side of the fixing unit and at a predetermined second conveyance position on the downstream side of the fixing unit; a temperature sensor that detects the temperature of the pressure roller; and a determination unit that determines the conveyance state of the sheet on the basis of a detection result from the conveyance sensor and a detection result from the temperature sensor.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] In an image forming apparatus, winding jams may occur in the fixing unit depending on the physical properties of the paper. In order to determine whether a jam such as a winding jam has occurred in the fixing unit and its vicinity, for example, in the conventional image forming apparatus described in Patent Document 1, the following configuration is adopted.

[0003] On the upstream side of the fixing unit, a first sheet sensor for detecting the presence or absence of a sheet is provided at a predetermined first conveyance position on the upstream side of the fixing unit. On the downstream side of the fixing unit, a second sheet sensor for detecting the presence or absence of a sheet is provided at a predetermined second conveyance position on the downstream side of the fixing unit. A temperature sensor for detecting the temperature of the first fixing member is provided at a position facing the first fixing member having a heating function in the fixing unit. The control unit determines whether a jam has occurred near a predetermined first conveyance position, near a predetermined second conveyance position, or between these conveyance positions based on the detection results of the first sheet sensor and the second sheet sensor. The control unit determines whether a winding jam in which the sheet is wound around the first fixing member has occurred based on the detection result of the temperature sensor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, although there are various modes of jams that can occur generally in the fixing unit and its vicinity, the conventional image forming apparatus has a problem in that the number of distinguishable jam modes is small. For example, regarding winding jams, the conventional image forming apparatus can only distinguish the mode in which the sheet winds around the first fixing member having a heating function. Therefore, when a jam occurs between a predetermined first conveyance position and a predetermined second conveyance position, the position of the residual paper cannot be clearly specified, and there is a problem that jam processing requires time and effort.

[0006] Therefore, an object of the present invention is to provide an image forming apparatus that can clearly specify the position of residual paper and easily perform jam processing when a jam occurs in the fixing unit and its vicinity.

Means for Solving the Problems

[0007] One aspect of the image forming apparatus of the present invention is a fixing unit in which a fixing nip is formed between a heating unit including a heating roller having a heating function and a pressing unit including a pressing roller not having a heating function, a conveyance sensor that detects a sheet at a predetermined first conveyance position upstream of the fixing unit and a predetermined second conveyance position downstream of the fixing unit, a temperature sensor that detects the temperature of the pressing roller, and a determination unit that determines the conveyance state of the sheet based on the detection result of the conveyance sensor and the detection result of the temperature sensor.

Effects of the Invention

[0008] According to the present invention, when a jam occurs in the fixing unit and its vicinity, the position of the residual paper can be clearly specified and jam processing can be easily performed.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

BEST MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, the present embodiment will be described with reference to the drawings. In the specification and claims of the present application, the upstream side means the upstream side in the paper conveyance direction, and the downstream side means the downstream side in the conveyance direction.

[0011] Referring to FIG. 1, the overall configuration of the image forming apparatus 10 according to the present embodiment will be described. FIG. 1 is a schematic diagram showing the overall configuration of the image forming apparatus 10 according to the present embodiment.

[0012] As shown in FIG. 1, the image forming apparatus 10 is a so-called tandem type image forming apparatus, and forms a toner image on a sheet S as a recording medium. The image forming apparatus 10 includes an apparatus main body 12.

[0013] On the upper part of the apparatus main body 12, an image reading unit 14 for reading the image of the document is provided. The image reading unit 14 optically scans the document D placed on the contact glass or the document D conveyed onto the contact glass. The image reading unit 14 optically reads the scanned image of the document by a CCD (Charge Coupled Device) sensor 16 to generate image data. Also, in the upper part inside the apparatus main body 12, an image processing unit 18 for performing image processing such as shading correction and compression processing on the image data from the image reading unit 14 is provided.

[0014] Above the image reading unit 14 in the apparatus main body 12, a document conveying unit 20 called ADF (Auto Document Feeder) is provided. The document conveying unit 20 conveys the document D set in the document tray onto the contact glass of the image reading unit 14. Also, on the front side (front) of the upper part of the apparatus main body 12, an operation display unit 22 having functions as an operation unit and a display unit is provided. The operation display unit 22 is composed of, for example, a liquid crystal display (LCD: Liquid Crystal Display) with a touch screen. The operation display unit 22 has various operation keys such as numeric keys and a start key, and as an operation unit, it accepts various input operations by the user. The operation display unit 22, as a display unit, displays various operation screens, the state of the image, and the operation status of each function, etc.

[0015] In the upper part inside the apparatus main body 12, an image forming unit 24 for forming an image by an electrophotographic method is provided. The image forming unit 24 has four image forming units 26Y, 26M, 26C, and 26K for forming an image by each colored toner of Y (yellow) component, M (magenta) component, C (cyan) component, and K (black) component based on the image data. The four image forming units 26Y, 26M, 26C, and 26K are arranged along the vertical direction.

[0016] The image forming units 26Y, 26M, 26C, and 26K for the Y, M, C, and K components have the same configuration. For the sake of convenience of illustration and description, common components are denoted by the same reference numerals, and when distinguishing them from each other, Y, M, C, or K is added to the reference numerals. In FIG. 1, only the components of the image forming unit 26Y for the Y component are labeled with reference numerals, and the components of the other image forming units 26M, 26C, and 26K are omitted.

[0017] The image forming unit 26 includes a photosensitive drum 28, and a charging unit 30, an exposure unit (scanning optical device) 32, a developing unit 34, and a drum cleaning unit 36 arranged around the photosensitive drum 28.

[0018] The photosensitive drum 28 is a negatively charged organic photoreceptor (OPC) in which an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) are sequentially laminated on the peripheral surface of a conductive cylindrical body made of, for example, aluminum. The photosensitive drum 28 rotates at a constant peripheral speed by the drive of a rotation motor (not shown).

[0019] The charging unit 30 uniformly charges the outer peripheral surface of the photosensitive drum 28 to a negative polarity. The exposure unit 32 forms an electrostatic latent image on the outer peripheral surface of the photosensitive drum 28 by scanning while irradiating laser light as scanning light to expose the outer peripheral surface of the photosensitive drum 28. The laser light emitted from the exposure unit 32 has its light amount modulated according to the image data of each of the YMCK colors.

[0020] The developing unit 34 is, for example, a developing unit using the two-component developing method. The developing unit 34 visualizes the electrostatic latent image on the outer peripheral surface of the photosensitive drum 28 by adhering toner of each color component to the outer peripheral surface of the photosensitive drum 28, thereby forming a toner image. Further, the drum cleaning unit 36 cleans the transfer residual toner remaining on the outer peripheral surface of the photosensitive drum 28 after primary transfer. The drum cleaning unit 36 has a drum cleaning blade or the like that is in sliding contact with the outer peripheral surface of the photosensitive drum 28.

[0021] An intermediate transfer unit 38 for transferring the toner image onto the paper S is provided in the upper part inside the apparatus main body 12. The intermediate transfer unit 38 includes an endless intermediate transfer belt 40, a plurality of support rollers 42, a primary transfer roller 44, a secondary transfer roller 46, and a belt cleaning unit 48.

[0022] The intermediate transfer belt 40 extends in the vertical direction and is stretched over the plurality of support rollers 42. The intermediate transfer belt 40 circulates and runs by the rotation of the plurality of support rollers 42. At least one of the plurality of support rollers 42 is composed of a drive roller connected so as to be interlocked with a rotation motor (not shown), and the other support rollers 42 are composed of driven rollers (idle rollers).

[0023] The primary transfer roller 44 is disposed to face the photosensitive drum 28 of each color component on the inner peripheral surface side of the intermediate transfer belt 40. The primary transfer roller 44 cooperates with the photosensitive drum 28 to sandwich the intermediate transfer belt 40. A primary transfer nip CN for transferring the toner image from the photosensitive drum 28 to the intermediate transfer belt 40 is formed between the outer peripheral surface of the primary transfer roller 44 and the outer peripheral surface of the photosensitive drum 28.

[0024] The secondary transfer roller 46 is disposed opposite to a predetermined support roller 42 on the outer peripheral surface side of the intermediate transfer belt 40. The secondary transfer roller 46 cooperates with the predetermined support roller 42 to sandwich the intermediate transfer belt 40. A secondary transfer nip TN for transferring the toner image from the intermediate transfer belt 40 to the sheet S is formed between the outer peripheral surface of the secondary transfer roller 46 and the outer peripheral surface of the predetermined support roller 42.

[0025] When the intermediate transfer belt 40 passes through the primary transfer nip CN, the toner image on the photoreceptor drum 28 is sequentially superimposed and primarily transferred onto the intermediate transfer belt 40. Specifically, a primary transfer bias is applied to the primary transfer roller 44, and a charge of the opposite polarity to the toner is applied to the back surface side of the intermediate transfer belt 40 (the side in contact with the primary transfer roller 44), so that the toner image is electrostatically transferred onto the intermediate transfer belt 40.

[0026] Thereafter, when the sheet S passes through the secondary transfer nip TN, the toner image on the intermediate transfer belt 40 is secondarily transferred onto the sheet S. Specifically, a secondary transfer bias is applied to the secondary transfer roller 46, and a charge of the opposite polarity to the toner is applied to the back surface side of the sheet S (the side in contact with the secondary transfer roller 46), so that the toner image is electrostatically transferred onto the sheet S, and an image can be formed on the sheet S.

[0027] The belt cleaning unit 48 removes the residual transferred toner remaining on the surface of the intermediate transfer belt 40 after secondary transfer. The belt cleaning unit 48 has a cleaning blade that slidably contacts the surface of the intermediate transfer belt 40.

[0028] On the outlet side of the secondary transfer nip TN in the apparatus main body 12, a fixing unit 50 for fixing the toner image to the sheet S is provided. The fixing unit 50 has a fixing nip FN for conveying the sheet S while heating and pressurizing it. The specific configuration of the fixing unit 50 will be described later.

[0029] A paper feeding unit 52 for feeding the paper S is provided at the lower part of the apparatus main body 12. The paper feeding unit 52 has a plurality of paper feeding trays 54 for accommodating a plurality of sheets of paper S. Each paper feeding tray 54 accommodates a preset type of paper S according to basis weight, size, etc.

[0030] A paper discharging unit 56 for discharging the paper S with an image formed thereon to the outside of the apparatus main body 12 is provided on the downstream side of the fixing unit 50 in the apparatus main body 12. The paper discharging unit 56 has a pair of paper discharging rollers 58. By rotating the pair of paper discharging rollers 58, the paper S with an image formed thereon can be discharged to the outside of the apparatus main body 12.

[0031] A main conveyance path 60 is provided between the paper feeding unit 52 and the paper discharging unit 56 in the apparatus main body 12. The main conveyance path 60 is a path for conveying the paper S when forming a toner image on the surface of the paper S. The main conveyance path 60 is a path for conveying the paper S via a plurality of pairs of conveyance rollers including a pair of registration rollers 62, a secondary transfer nip TN, and a fixing nip FN. Also, an inversion conveyance path 64 for inverting the front and back of the paper S is provided near the paper feeding unit 52 in the apparatus main body 12. The inversion conveyance path 64 is a path for conveying the paper S when forming a toner image on the back surface of the paper S and is connected to the main conveyance path 60.

[0032] The sheets of paper S accommodated in the paper feeding tray 54 are sent out one by one from the top and conveyed toward the secondary transfer nip TN by the main conveyance path 60. At this time, the inclination of the paper S is corrected by the pair of registration rollers 62 and the paper S conveyance timing is adjusted. Then, at the secondary transfer nip TN, the toner image on the intermediate transfer belt 40 is collectively secondarily transferred onto one surface (front or back) of the paper S, and at the fixing nip FN, the toner image is fixed to the paper S. Thereafter, the paper S with the image formed thereon is discharged from the paper discharging unit 56 to the outside of the apparatus main body 12.

[0033] Next, with reference to FIG. 2, the fixing unit 50 of the image forming apparatus 10 according to the present embodiment and the surrounding configuration thereof will be described. FIG. 2 is a schematic diagram showing the fixing unit 50 of the image forming apparatus 10 according to the present embodiment and the surrounding configuration thereof.

[0034] As shown in FIG. 2, the fixing unit 50 has a heating unit 66 for heating the sheet S. The heating unit 66 includes a heating roller 68, a fixing roller 70, and an endless fixing belt 72.

[0035] The heating roller 68 has, for example, a hollow cylindrical core made of aluminum, iron, SUS (stainless steel material), etc., and a heating device 74 such as a halogen lamp provided inside the core. The heating roller 68 incorporating the heating device 74 has a heating function. Also, the fixing roller 70 is disposed at a position facing the heating roller 68. The fixing roller 70 has, for example, a hollow cylindrical core made of aluminum, iron, SUS, etc., and a surface layer provided on the outer peripheral surface of the core and made of, for example, silicone rubber or silicone sponge. The fixing roller 70 not incorporating the heating device 74 does not have a heating function.

[0036] The fixing belt 72 is stretched between the heating roller 68 and the fixing roller 70. The fixing belt 72 has, for example, a base material made of polyimide resin (PI), an elastic layer laminated on the surface of the base material and made of, for example, silicone rubber, and a surface layer laminated on the surface of the elastic layer and made of, for example, PFA (polytetrafluoroethylene).

[0037] The fixing unit 50 has a pressing unit 76 for pressing the sheet S. The pressing unit 76 includes a pressing roller 78 that is press - contacted with the fixing roller 70 with a predetermined fixing load via the fixing belt 72. The pressing roller 78 is provided at a position facing the fixing roller 70 on the outer side of the fixing belt 72. The pressing roller 78 has, for example, a hollow cylindrical core metal made of aluminum, iron, SUS, etc., an elastic layer provided on the outer peripheral surface of the core metal and made of, for example, silicone rubber, etc., and a surface layer provided on the surface of the elastic layer and made of, for example, a PFA tube, etc. The pressing roller 78 that does not incorporate the heating device 74 does not have a heating function. Also, a fixing nip FN is formed between the fixing roller 70 (heating unit 66) and the pressing roller 78 (pressing unit 76).

[0038] When the pressing roller 78 rotates by the drive of a motor (not shown), the fixing belt 72 is driven to rotate. When the fixing belt 72 rotates, the heating roller 68 and the fixing roller 70 are driven to rotate. Thereby, the sheet S can be conveyed while being heated and pressed in the fixing nip FN, and the unfixed toner image can be fixed on the sheet S.

[0039] The fixing unit 50 has a contact - separating member 80 for separating the sheet S from the pressing roller 78. The contact - separating member 80 can contact the outer peripheral surface of the pressing roller 78. By the contact - separating member 80 contacting the outer peripheral surface of the pressing roller 78, the sheet S can be separated from the pressing roller 78.

[0040] The fixing unit 50 has an air - separating member 82 for separating the sheet S from the fixing belt 72. The air - separating member 82 can blow air toward the fixing nip FN. By the air - separating member 82 blowing air toward the fixing nip FN, the sheet S can be separated from the fixing belt 72.

[0041] Upstream of the fixing unit 50 in the main conveyance path 60, a first conveyance sensor 84 is provided to detect the sheet S at a predetermined first conveyance position upstream of the fixing unit 50. The first conveyance sensor 84 detects that the leading edge of the sheet S has passed through the predetermined first conveyance position. Also, downstream of the fixing unit 50 in the main conveyance path 60, a second conveyance sensor 86 is provided to detect the sheet S at a predetermined second conveyance position downstream of the fixing unit 50. The second conveyance sensor 86 detects the presence or absence of the sheet S at the predetermined second conveyance position.

[0042] At a position facing the pressure roller 78, a first temperature sensor 88 is provided to detect the temperature at a predetermined rotational position (circumferential position) on the outlet side of the fixing nip FN in the pressure roller 78. The distance from the predetermined rotational position on the outlet side of the fixing nip FN in the pressure roller 78 to the fixing nip FN is shorter than the distance from the predetermined second conveyance position to the fixing nip FN. Also, at a position facing the heating roller 68, a second temperature sensor 90 is provided to detect the temperature of the heating roller 68 (fixing belt 72).

[0043] Referring to FIGS. 3 to 6, the control configuration of the image forming apparatus 10 according to the present embodiment will be described. FIG. 3 is a control block diagram of the image forming apparatus 10 according to the present embodiment. FIG. 4 is a diagram showing the relationship between the temperature and time at a predetermined rotational position of the pressure roller 78. FIG. 5 is a schematic diagram showing a state where a pressure-side winding jam has occurred. FIG. 6 is a schematic diagram showing a state where a heating-side winding jam has occurred.

[0044] As shown in FIG. 3, the image forming apparatus 10 includes a control unit 92 that controls an image reading unit 14, an image processing unit 18, an operation display unit 22, an image forming unit 24, an intermediate transfer unit 38, a fixing unit 50, and the like. The control unit 92 plays a role of controlling the entire image forming apparatus 10. The control unit 92 includes a CPU (Central Processing Unit) 94, a ROM (Read Only Memory) 96, a RAM (Random Access Memory) 98, a storage unit 100, and a communication unit 102.

[0045] The CPU 94 comprehensively controls the overall operation of the image forming apparatus 10. The CPU 94 reads out various control programs and setting data stored in the ROM 96, stores them in the RAM 98, and executes the programs to perform various arithmetic processes. The RAM 98 provides a working memory space for the CPU 94 and stores temporary data. Also, when performing various arithmetic processes, the CPU 94 refers to various data stored in the storage unit 100. The storage unit 100 is constituted by, for example, a non-volatile semiconductor memory or a hard disk drive.

[0046] The control unit 92 performs transmission and reception of various data with an external device (such as a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 102. The control unit 92, for example, receives image data transmitted from the external device and forms a toner image on the paper S based on this image data (input image data). The communication unit 102 is constituted by, for example, a communication control card such as a LAN card.

[0047] By executing various control programs, the control unit 92 (CPU 94) functions as the "judgment unit", "notification unit", "display control unit", and "adjustment unit" in the claims as follows. And the configuration of the main part of the control unit 92 is as follows.

[0048] The control unit 92 determines the conveyance state of the paper S based on the detection results of the first conveyance sensor 84, the detection results of the second conveyance sensor 86, and the detection results of the first temperature sensor 88. Specifically, the control unit 92 determines the conveyance state of the paper S as follows.

[0049] As shown in FIGS. 3 and 4, after the leading edge of the sheet S passes through a predetermined first conveyance position, the control unit 92 determines whether an arrival jam has occurred based on a change in the detection result of the first temperature sensor 88 after a predetermined arrival time T1 has elapsed. The predetermined arrival time T1 is the time for confirming that the leading edge of the sheet S has reached the fixing nip FN. Specifically, the predetermined arrival time T1 is the sum of the time when it is estimated that the leading edge of the sheet S has reached the fixing nip FN and the time until the portion of the leading edge of the sheet S in contact with the pressure roller 78 reaches a predetermined rotational position. An arrival jam is a jam before the leading edge of the sheet S reaches the fixing nip FN.

[0050] Specifically, after the predetermined arrival time T1 has elapsed, if the temperature at a predetermined rotational position of the pressure roller 78 rises as shown by line L1 in FIG. 4, the control unit 92 determines that an arrival jam has occurred. If the temperature at a predetermined rotational position of the pressure roller 78 drops after the predetermined arrival time T1 has elapsed, the control unit 92 determines that the sheet S has reached the fixing unit 50.

[0051] After the leading edge of the sheet S passes through a predetermined first conveyance position, after a predetermined leading edge passage time T2 has elapsed, under a predetermined first condition, the control unit 92 determines whether either a heating-side winding jam or a pressure-side winding jam has occurred based on a change in the detection result of the first temperature sensor 88. The predetermined leading edge passage time T2 is the time when it is estimated that the leading edge of the sheet S passes through a predetermined second conveyance position. The predetermined first condition is that no sheet is detected at the predetermined second conveyance position by the second conveyance sensor 86. A heating-side winding jam is a jam in which the sheet S winds around the heating unit 66 side (heating roller 68 side) as shown in FIG. 5. A pressure-side winding jam is a jam in which the sheet S winds around the pressure unit 76 side (pressure roller 78 side) as shown in FIG. 6.

[0052] Specifically, after a predetermined leading-edge passing time T2 has elapsed, under a predetermined first condition, when the temperature at a predetermined rotational position of the pressure roller 78 drops below the reference value as shown by line L2 in FIG. 4, the control unit 92 determines that a pressure-side winding jam has occurred. After a predetermined leading-edge passing time T2 has elapsed, under a predetermined first condition, when the temperature at a predetermined rotational position of the pressure roller 78 drops below the reference value as shown by line L3 in FIG. 4, the control unit 92 determines that a heating-side winding jam has occurred. The reference value is a value serving as a reference for determining the type of jam. Specifically, it is the temperature drop per unit time serving as a reference for determining whether either a heating-side winding jam or a pressure-side winding jam has occurred. Note that line L3 shown in FIG. 4 is substantially the same as the temperature change at a predetermined rotational position of the pressure roller 78 during normal operation.

[0053] After the leading edge of the sheet S has passed through a predetermined first conveyance position, after a predetermined leading-edge passing time T2 has elapsed and before a predetermined trailing-edge passing time T3 has elapsed, under a predetermined second condition, the control unit 92 determines whether either a heating-side winding jam or a pressure-side winding jam has occurred based on the change in the detection result of the temperature sensor. The predetermined trailing-edge passing time T3 is the time when the trailing edge of the sheet S is estimated to pass through a predetermined second conveyance position. The predetermined second condition is that after the presence of the sheet has been detected at the predetermined second conveyance position by the second conveyance sensor 86, the absence of the sheet is detected.

[0054] Specifically, after a predetermined leading-edge passing time T2 has elapsed and before a predetermined trailing-edge passing time T3 has elapsed, under a predetermined second condition, when the temperature at a predetermined rotational position of the pressure roller 78 drops below the reference value, the control unit 92 determines that a pressure-side winding jam has occurred. After a predetermined leading-edge passing time T2 has elapsed and before a predetermined trailing-edge passing time T3 has elapsed, under a predetermined second condition, when the temperature at a predetermined rotational position of the pressure roller 78 drops below the reference value, the control unit 92 determines that a heating-side winding jam has occurred.

[0055] As shown in FIGS. 3 and 4, after the leading edge of the sheet S passes through a predetermined first conveyance position, after a predetermined trailing edge passing time T3 has elapsed, under a predetermined third condition, it is determined that a residual jam has occurred. The predetermined third condition is that the presence of a sheet is detected at a predetermined second conveyance position by the second conveyance sensor 86. A residual jam refers to a jam in which the sheet S remains at the predetermined second conveyance position.

[0056] When the control unit 92 determines that any one of an arrival failure jam, a pressure side winding jam, a heating side winding jam, or a residual jam has occurred, based on the determination result, it notifies the position of the remaining paper by display on the operation display unit 22.

[0057] When the control unit 92 determines that a pressure side winding jam or a heating side winding jam has occurred, it notifies by display on the operation display unit 22 to change the fixing condition or the image condition. Here, the fixing condition is at least any one of the nip width of the fixing nip FN, the temperature of the heating roller 68, the conveyance speed of the sheet S in the fixing unit 50, or the amount of air blown out from the air separation member 82. The image condition is at least any one of the leading edge margin amount of the sheet S or the toner adhesion amount.

[0058] When the control unit 92 determines that a pressure side winding jam or a heating side winding jam has occurred, it causes the operation display unit 22 to display so that the fixing condition or the image condition corresponding to the determination result can be selected. Further, when the control unit 92 determines that a pressure side winding jam or a heating side winding jam has occurred, based on the fixing condition or the image condition selected according to the determination result, it adjusts the fixing unit 50.

[0059] Subsequently, with reference to FIGS. 7 and 8, the determination process of the conveyance state of the sheet S will be described. FIGS. 7 and 8 are flowcharts for explaining the determination process of the conveyance state of the sheet S.

[0060] As shown in FIG. 7, when the leading edge of the sheet S passes through a predetermined first conveyance position, the first conveyance sensor 84 turns ON (step S101 in FIG. 7). Then, after a predetermined arrival time T1 has elapsed (step S102 in FIG. 7), the control unit 92 determines whether the temperature at a predetermined rotational position of the pressure roller 78 rises based on the detection result of the first temperature sensor 88 (step S103 in FIG. 7). When the temperature at the predetermined rotational position of the pressure roller 78 rises (YES in step S103 in FIG. 7), the control unit 92 determines that an arrival jam has occurred (step S104 in FIG. 7).

[0061] When the temperature at the predetermined rotational position of the pressure roller 78 drops (NO in step S103 in FIG. 7), the control unit 92 determines that the sheet S has reached the fixing nip FN (step S105 in FIG. 7). Then, after a predetermined leading-edge passage time T2 has elapsed (step S106 in FIG. 7), the control unit 92 determines whether the presence of the sheet is detected at a predetermined second conveyance position by the second conveyance sensor 86 (step S107 in FIG. 7).

[0062] When the absence of the sheet is detected at the predetermined second conveyance position (NO in step S107 in FIG. 7), the control unit 92 determines whether the temperature at the predetermined rotational position of the pressure roller 78 drops more than the reference value (step S108 in FIG. 7). When the temperature at the predetermined rotational position of the pressure roller 78 drops more than the reference value (YES in step S108 in FIG. 7), the control unit 92 determines that a pressure-side winding jam has occurred (step S109 in FIG. 7). When the temperature at the predetermined rotational position of the pressure roller 78 drops less than the reference value (NO in step S108 in FIG. 7), the control unit 92 determines that a heating-side winding jam has occurred (step S110 in FIG. 7).

[0063] As shown in FIGS. 7 and 8, when the presence of a sheet is detected at a predetermined second conveyance position (YES in step S107 of FIG. 7), the control unit 92 determines that the leading edge of the sheet S has passed the predetermined second conveyance position (step S111 in FIG. 7). Then, the control unit 92 determines whether or not a predetermined trailing-edge passage time T3 has elapsed since the leading edge of the sheet S passed the predetermined first conveyance position (step S112 in FIG. 8). If the predetermined trailing-edge passage time T3 has not elapsed (NO in step S112 of FIG. 8), it is determined whether or not the presence of a sheet is detected at the predetermined second conveyance position by the second conveyance sensor 86 (step S113 in FIG. 8).

[0064] As shown in FIG. 8, when the presence of a sheet is detected at the predetermined second conveyance position (YES in step S113 of FIG. 8), the control unit 92 returns to the step S112 process. On the other hand, when the absence of a sheet is detected at the predetermined second conveyance position (NO in step S113 of FIG. 8), the control unit 92 determines whether or not the temperature at a predetermined rotational position of the pressure roller 78 has dropped significantly below the reference value (step S114 in FIG. 8). Then, when the temperature at the predetermined rotational position of the pressure roller 78 has dropped significantly below the reference value (YES in step S114 of FIG. 8), the control unit 92 determines that a pressure-side winding jam has occurred (step S115 in FIG. 8). When the temperature at the predetermined rotational position of the pressure roller 78 has dropped less than the reference value (NO in step S114 of FIG. 8), the control unit 92 determines that a heating-side winding jam has occurred (step S116 in FIG. 8).

[0065] When a predetermined rear-end passing time T3 has elapsed (in the case of YES in step S112 of FIG. 8), the control unit 92 determines whether or not a sheet is detected at a predetermined second conveyance position by the second conveyance sensor 86 (step S117 of FIG. 8). Then, when no sheet is detected at the predetermined second conveyance position (in the case of NO in step S117 of FIG. 8), the control unit 92 determines that the conveyance state of the sheet S is normal (step S118 of FIG. 8). When a sheet is detected at the predetermined second conveyance position (in the case of YES in step S117 of FIG. 8), the control unit 92 determines that a residual jam has occurred (step S119 in FIG. 7).

[0066] According to the configuration of the image forming apparatus 10 according to the present embodiment, as described above, the first conveyance sensor 84 detects that the leading end of the sheet S has passed through a predetermined first conveyance position upstream of the fixing unit 50. The second conveyance sensor 86 detects the presence or absence of a sheet at a predetermined second conveyance position downstream of the fixing unit 50. The first temperature sensor 88 detects the temperature at a predetermined rotational position on the outlet side of the fixing nip FN in the pressure roller 78 that does not have a heating function. Then, the control unit 92 determines the conveyance state of the sheet S based on the detection result of the first conveyance sensor 84, the detection result of the second conveyance sensor 86, and the detection result of the first temperature sensor 88. Therefore, the control unit 92 can determine whether or not any of an arrival jam, a heating-side winding jam, or a pressure-side winding jam has occurred between the predetermined first conveyance position and the predetermined second conveyance position. Thus, according to the present embodiment, when a jam occurs between the predetermined first conveyance position and the predetermined second conveyance position, the position of the remaining paper can be clearly specified and the jam processing can be easily performed.

[0067] Further, according to the configuration of the image forming apparatus 10 according to the present embodiment, as described above, the distance from a predetermined rotational position on the exit side of the fixing nip FN in the pressure roller 78 to the fixing nip FN is shorter than the distance from a predetermined second conveyance position to the fixing nip FN. Therefore, according to the present embodiment, the control unit 92 can quickly determine whether any of an arrival jam, a heating-side winding jam, or a pressure-side winding jam has occurred between the predetermined first conveyance position and the predetermined second conveyance position.

[0068] Further, according to the configuration of the image forming apparatus 10 according to the present embodiment, as described above, after a predetermined arrival time T1 has elapsed, the control unit 92 determines whether an arrival jam has occurred based on a change in the detection result of the first temperature sensor 88. Therefore, according to the present embodiment, the control unit 92 can accurately determine whether an arrival jam has occurred between the predetermined first conveyance position and the predetermined second conveyance position.

[0069] Further, after a predetermined leading-edge passage time T2 has elapsed, the control unit 92 determines whether either a heating-side winding jam or a pressure-side winding jam has occurred based on a change in the detection result of the first temperature sensor 88 under a predetermined first condition. Therefore, according to the present embodiment, the control unit 92 can accurately determine whether either a heating-side winding jam or a pressure-side winding jam has occurred between the predetermined first conveyance position and the predetermined second conveyance position.

[0070] Also, according to the configuration of the image forming apparatus 10 according to the present embodiment, as described above, when the temperature at a predetermined rotational position of the pressure roller 78 rises after a predetermined arrival time T1 has elapsed, the control unit 92 determines that an arrival jam has occurred. After a predetermined leading edge passing time T2 has elapsed, when the temperature at a predetermined rotational position of the pressure roller 78 drops below a reference value under a predetermined first condition, the control unit 92 determines that a pressure side winding jam has occurred. After a predetermined leading edge passing time T2 has elapsed, when the temperature at a predetermined rotational position of the pressure roller 78 drops below a reference value under a predetermined first condition, the control unit 92 determines that a heating side winding jam has occurred. Therefore, according to the present embodiment, the control unit 92 can more accurately determine whether any of an arrival jam, a heating side winding jam, or a pressure side winding jam has occurred between a predetermined first conveyance position and a predetermined second conveyance position.

[0071] According to the configuration of the image forming apparatus 10 according to the present embodiment, the control unit 92 determines whether either a heating side winding jam or a pressure side winding jam has occurred based on a change in the detection result of the temperature sensor under a predetermined second condition at a predetermined time. The predetermined time is after a predetermined leading edge passing time T2 has elapsed and before a predetermined trailing edge passing time T3 has elapsed. Therefore, according to the present embodiment, the control unit 92 can accurately determine whether a jam has occurred in which the sheet S is wound around the heating roller 68 side or the pressure roller 78 side from the middle of the sheet.

[0072] As described above, when the temperature at a predetermined rotational position of the pressure roller 78 drops below the reference value under a predetermined second condition at a predetermined time, the control unit 92 determines that a pressure-side winding jam has occurred from the middle of the sheet S. When the temperature at a predetermined rotational position of the pressure roller 78 drops below the reference value under a predetermined second condition at a predetermined time, the control unit 92 determines that a heating-side winding jam has occurred. Therefore, according to the present embodiment, the control unit 92 can more accurately determine whether a jam has occurred that winds around the heating roller 68 side or the pressure roller 78 side from the middle of the sheet S.

[0073] According to the configuration of the image forming apparatus 10 according to the present embodiment, as described above, after a predetermined trailing-edge passage time T3 has elapsed, the control unit 92 determines that a residual jam has occurred under a predetermined third condition. Therefore, according to the present embodiment, even when a jam occurs downstream of the predetermined second conveyance position, the position of the remaining paper can be clearly specified.

[0074] According to the configuration of the image forming apparatus 10 according to the present embodiment, as described above, when the control unit 92 determines that any jam such as an arrival failure jam or a pressure-side winding jam has occurred, it notifies the position of the remaining paper based on the determination result. Therefore, according to the present embodiment, jam processing can be performed more easily.

[0075] According to the configuration of the image forming apparatus 10 according to the present embodiment, as described above, when the control unit 92 determines that a pressure-side winding jam or a heating-side winding jam has occurred, it notifies to change the fixing condition or the image condition. Therefore, according to the present embodiment, recurrence of the pressure-side winding jam or the heating-side winding jam can be suppressed.

[0076] According to the configuration of the image forming apparatus 10 according to the present embodiment, when the control unit 92 determines that a jam has occurred on the pressure side winding or the heating side winding, the control unit 92 causes the operation display unit 22 to display so that fixing conditions or image conditions corresponding to the determination result can be selected. Therefore, according to the present embodiment, it is possible to suppress the recurrence of a jam on the pressure side winding or the heating side winding.

[0077] According to the configuration of the image forming apparatus 10 according to the present embodiment, when the control unit 92 determines that a jam has occurred on the pressure side winding or the heating side winding, the control unit 92 adjusts the fixing unit 50 based on the fixing conditions or image conditions selected according to the determination result. Therefore, according to the present embodiment, it is possible to further suppress the recurrence of a jam on the pressure side winding or the heating side winding.

[0078] As described above, the present embodiment has been specifically described, but the present invention is not limited to the specific embodiments described above. Various modifications and changes can be made to the specific examples described in the above embodiments within the scope of the gist of the present invention described in the claims.

Industrial Applicability

[0079] The present invention is useful as an image forming apparatus that can clearly identify the position of the remaining paper and easily perform jam processing when a jam occurs between a predetermined first conveyance position and a predetermined second conveyance position.

Explanation of Signs

[0080] 10 Image forming apparatus 12 Apparatus main body 14 Image reading unit 16 CCD sensor 18 Image processing unit 20 Original document conveyance unit 22 Operation display unit 24 Image forming unit 26 Image forming unit 26C Image forming unit 26K Image forming unit 26M Image Forming Unit 26Y Image Forming Unit 28 Photoconductor Drum 30 Charging Unit 32 Exposure Unit 34 Developing Unit 36 Drum Cleaning Unit 38 Intermediate Transfer Unit 40 Intermediate Transfer Belt 42 Support Roller 44 Primary Transfer Roller 46 Secondary Transfer Roller 48 Belt Cleaning Unit 50 Fixing Unit 52 Paper Feeding Unit 54 Paper Feeding Tray 56 Paper Discharging Unit 58 Paper Discharging Roller Pair 60 Main Conveyor Path 62 Registration Roller Pair 64 Reversal Conveyor Path 66 Heating Unit 68 Heating Roller 70 Fixing Roller 72 Fixing Belt 74 Heating Device 76 Pressing Unit 78 Pressing Roller 80 Contact Separation Member 82 Air Separation Member 84 First Conveyor Sensor (Conveyor Sensor) 86 Second Conveyor Sensor (Conveyor Sensor) 88 First Temperature Sensor 90 Second Temperature Sensor 92 Control Unit (Judgment Unit, Notification Unit, Display Control Unit, Adjustment Unit) 94 CPU 96 ROM 98 RAM 100 Memory Unit 102 Communication Unit CN Primary Transfer Nip TN Secondary Transfer Nip FN Fixing Nip D Document S Paper

Claims

1. A fixing unit in which a fixing nip is formed between a heating unit including a heating roller having a heating function and a pressing unit including a pressing roller not having a heating function, a conveyance sensor that detects a sheet at a predetermined first conveyance position upstream of the fixing unit and at a predetermined second conveyance position downstream of the fixing unit, a temperature sensor that detects the temperature of the pressing roller, and a determination unit that determines the conveyance state of the sheet based on the detection result of the conveyance sensor and the detection result of the temperature sensor. An image forming apparatus.

2. The temperature sensor detects the temperature at a predetermined rotational position on the outlet side of the fixing nip in the pressing roller, and the distance from the predetermined rotational position to the fixing nip is shorter than the distance from the predetermined second conveyance position to the fixing nip. The image forming apparatus according to claim 1.

3. The determination unit determines whether or not an arrival jam before the sheet arrives at the fixing nip has occurred based on a change in the detection result of the temperature sensor after a predetermined arrival time has elapsed to confirm that the leading edge of the sheet has reached the fixing nip after the leading edge of the sheet has passed the predetermined first conveyance position. The image forming apparatus according to claim 1.

4. The determination unit determines that an arrival jam has occurred when the temperature of the pressing roller rises after the predetermined arrival time has elapsed. The image forming apparatus according to claim 3.

5. Based on a change in the detection result of the temperature sensor, on the condition that no sheet is detected at the predetermined second conveyance position after a predetermined leading-edge passage time has elapsed, which is estimated to be the time when the leading edge of the sheet passes the predetermined second conveyance position after the leading edge of the sheet has passed the predetermined first conveyance position, it is determined whether any of a heating-side winding jam in which the sheet is wound around the heating unit side or a pressing-side winding jam in which the sheet is wound around the pressing unit side has occurred. The image forming apparatus according to claim 1.

6. The determination unit determines that a pressing-side winding jam has occurred when the temperature of the pressing roller drops significantly below a reference value for determining the type of jam, and determines that a heating-side winding jam has occurred when the temperature of the pressing roller drops slightly below the reference value, on the condition that no sheet is detected at the predetermined second conveyance position after the predetermined leading-edge passage time has elapsed. The image forming apparatus according to claim 5. Claim 7 The determination unit after the leading edge of the sheet has passed the predetermined first conveyance position, after a predetermined leading edge passage time has elapsed, which is estimated to be when the leading edge of the sheet passes the predetermined second conveyance position, and before a predetermined trailing edge passage time has elapsed, which is estimated to be when the trailing edge of the sheet passes the predetermined second conveyance position, and after it has been once detected that there is a sheet at the predetermined second conveyance position and then it is detected that there is no sheet, based on the change in the detection result of the temperature sensor, determines whether either a heating-side wrapped jam or a pressure-side wrapped jam has occurred The image forming apparatus according to claim 1 Claim 8 The determination unit after the predetermined leading edge passage time has elapsed and before the predetermined trailing edge passage time has elapsed, and after it has been once detected that there is a sheet at the predetermined second conveyance position and then it is detected that there is no sheet, when the temperature of the pressure roller drops below a reference value for determining the type of jam, determines that a pressure-side wrapped jam has occurred, and when the temperature of the pressure roller drops below the reference value, determines that a heating-side wrapped jam has occurred The image forming apparatus according to claim 7 Claim 9 The determination unit after the leading edge of the sheet has passed the predetermined first conveyance position, and after a predetermined trailing edge passage time has elapsed, which is estimated to be when the trailing edge of the sheet passes the predetermined second conveyance position, and when it is detected that there is a sheet at the predetermined second conveyance position, determines that a residual jam has occurred in which the sheet remains at the predetermined second conveyance position The image forming apparatus according to claim 1 Claim 10 The determination unit determines that any one of a non-arrival jam in which the sheet does not reach the fixing nip, a heating-side wrapped jam in which the sheet wraps around the heating unit side, a pressure-side wrapped jam in which the sheet wraps around the pressure unit side, or a residual jam in which the sheet remains at the predetermined second conveyance position has occurred When it is determined that any one of a non-arrival jam, a pressure-side wrapped jam, a heating-side wrapped jam, or a residual jam has occurred, further includes a notification unit that notifies the position of the remaining paper based on the determination result The image forming apparatus according to claim 1 Claim 11 When it is determined that a pressure-side wrapped jam or a heating-side wrapped jam has occurred, the notification unit notifies to change the fixing conditions or the image conditions The image forming apparatus according to claim 10 Claim 12 The fixing conditions are at least any one of the nip width of the fixing nip, the temperature of the heating roller, the conveyance speed of the paper in the fixing unit, or the amount of air blown from the air separation member of the fixing unit. The image forming apparatus according to claim 11.

13. The image conditions are at least any one of the leading-edge margin amount of the paper or the toner adhesion amount. The image forming apparatus according to claim 11.

14. The determination unit determines that any one of a non-arrival jam where the paper does not reach the fixing nip, a heating-side winding jam where the paper winds around the heating unit side, a pressing-side winding jam where the paper winds around the pressing unit side, or a residual jam where the paper remains at the predetermined second conveyance position has occurred. When it is determined that a pressing-side winding jam or a heating-side winding jam has occurred, the display control unit further provided is configured to cause the display unit to display so that the fixing conditions or the image conditions corresponding to the determination result can be selected. The image forming apparatus according to claim 1.

15. When it is determined that a pressing-side winding jam or a heating-side winding jam has occurred, the apparatus further includes an adjustment unit that adjusts the fixing unit based on the fixing conditions or the image conditions selected according to the determination result. The image forming apparatus according to claim 14.

Images