JP2010072489A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that reduces looping of a recording medium without providing a loop detecting means. <P>SOLUTION: A printer 10 has: a conveying device 24; a fixing device 48; a paper detection sensor 23 that detects entry of recording paper P into a nip N of the fixing device 48; and a control unit 54 that increases the speed of the heat roll 48A, based on a predetermined speed increase for the heat roll 48A when the paper detection sensor 23 detects the entry of the recording paper P into the nip N. When the recording paper P enters the nip N of the fixing device 48, and the paper detection sensor 23 detects this, the control unit 54 increases the speed of the heat roll 48A based on the predetermined speed increase. The leading end of the recording paper P is pulled thereby. This reduces looping of the recording paper P without providing a loop detecting means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  Conventionally, a latent image on the surface of a photoreceptor is made visible with a developer such as toner to form a developer image, and the developer image is transferred by a transfer unit to a recording medium that has been conveyed by a conveyance unit such as a conveyance belt. In addition, there is an image forming apparatus in which fixing is performed on a recording medium by fixing means such as a roll pair provided with a heat source.

  In such an image forming apparatus, a so-called loop in which the recording medium bends in front of the fixing unit may occur due to the difference between the recording medium conveying speed by the conveying unit and the recording medium conveying rate by the fixing unit.

  Here, there is an image forming apparatus provided with a loop detection unit for the purpose of reducing the loop of the recording medium (see, for example, Patent Documents 1 and 2).

In each of the image forming apparatuses disclosed in Patent Documents 1 and 2, a loop detection unit that detects a loop of the recording medium is provided between the conveyance unit that conveys the recording medium after the developer transfer and the fixing unit.
JP-A-10-097154 JP 2003-345150 A

  An object of the present invention is to obtain an image forming apparatus capable of reducing a loop of a recording medium without providing a loop detection unit.

  An image forming apparatus according to a first aspect of the present invention is disposed opposite to a transfer unit provided inside an apparatus main body for transferring an image, and a conveyance unit that conveys a recording medium, and a conveyance direction of the recording medium relative to the conveyance unit A fixing rotator that is provided on the downstream side and rotates to fix the image to the recording medium; an entry detection unit that detects an entry of the recording medium between the fixing rotator; and the entry detection unit; And a speed controller that increases the speed of the fixing rotator based on a predetermined amount of increase in the speed of the fixing rotator when detecting the entry of the recording medium between the rotators.

  In the image forming apparatus according to a second aspect of the present invention, the speed increase amount of the fixing rotator includes the type of the recording medium, the temperature inside the apparatus main body, the relative humidity inside the apparatus main body, and the amount of the apparatus main body. Of the absolute humidity inside, it is determined according to at least one condition, and a condition detecting means for detecting the at least one condition is provided, and the fixing rotating body according to the condition detected by the condition detecting means The amount of speed increase is determined.

  In the image forming apparatus according to a third aspect of the present invention, the speed of the fixing rotator is increased in a plurality of stages.

  In the image forming apparatus according to a fourth aspect of the present invention, the approach detection unit is provided upstream of the fixing rotator in the conveyance direction of the recording medium, and detects the leading edge of the recording medium.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the fifth aspect of the present invention, the entry detection unit is provided downstream of the fixing rotator in the recording medium conveyance direction, and detects discharge of the recording medium from the apparatus main body. It is a sensor.

  According to the first aspect of the present invention, the loop of the recording medium can be reduced without providing a loop detecting means.

  The invention of claim 2 can cope with a change in loop formation of the recording medium due to at least one condition of the type of the recording medium, the temperature inside the apparatus main body, the relative humidity, and the absolute humidity.

  According to the third aspect of the present invention, the load acting on the recording medium can be reduced as compared with the case where this configuration is not provided.

  According to the fourth aspect of the present invention, a delay in the speed change timing of the fixing rotator can be suppressed as compared with the case where the present configuration is not provided.

  In the invention of claim 5, it is not necessary to newly provide a detection sensor.

  A first embodiment of an image forming apparatus of the present invention will be described with reference to the drawings.

  FIG. 1 shows a printer 10 as an image forming apparatus of the present invention. In the printer 10, image forming units 12Y, 12M, 12C, and 12K that perform full color image formation using four color toners (yellow (Y), magenta (M), cyan (C), and black (K)) are arranged in the vertical direction. Has been. Each of the image forming units 12Y, 12M, 12C, and 12K has the same configuration except for the accommodated toner.

  Note that when distinguishing each color of yellow, magenta, cyan, and black, Y, M, C, and K are added after the code. However, if there is no need to distinguish each color, Y, M, C, and K are omitted. The toners Y, M, C, and K are not particularly limited by the manufacturing method, and various toners can be used.

  As shown in FIG. 1, a paper feed cassette 14 in which recording paper P is stored is provided at the bottom of the printer 10. In the vicinity of the paper feed cassette 14, a pickup roll 16 that feeds the recording paper P at a predetermined timing is provided. A paper transport path 22 including a transport roll 18 and a resist roll 20 is provided on the downstream side of the pickup roll 16 in the transport direction of the recording paper P. Here, the recording paper P sent out from the paper feed cassette 14 by the pickup roll 16 is sent to the paper transport path 22 through the transport roll 18 and the registration roll 20, and transports the recording paper P to each image forming unit 12. It is transported to the transport device 24.

  The image forming unit 12 is arranged in the order of the aforementioned Y, M, C, and K colors from the upstream side of the paper conveyance path 22 (the lower side of the printer 10). On the left side of the image forming unit 12 in the drawing, an exposure device 26 that irradiates scanning light (exposure light) to the photosensitive member 36 provided in the image forming unit 12 is disposed.

  In the exposure device 26, a semiconductor laser (not shown), a polygon mirror 30, an imaging lens 32, and a mirror 34 are disposed in a housing 28. Light from the semiconductor laser is deflected and scanned by the polygon mirror 30 to form an image. Each photoconductor 36 is irradiated through a lens 32 and a mirror 34. As a result, an electrostatic latent image corresponding to the image information is formed on the photoreceptor 36. A control unit 54 that controls the operation of each unit of the printer 10 is provided in the vicinity of the exposure device 26 (left side in the drawing).

  On the other hand, on the right side of the printer 10 in the drawing (position facing the photoconductor 36), the above-described transport device 24 is disposed. The transport device 24 is wound around a pair of tension rolls 38 (lower side) and a tension roll 40 (upper side) provided up and down along the side wall 10 </ b> A of the printer 10, and the tension rolls 38 and 40. The conveyor belt 42 is configured.

  The tension roll 40 is rotated by a motor (not shown) so that the conveyor belt 42 moves. Further, a suction roll 44 is disposed in the vicinity of the tension roll 38 so that a voltage is applied to the suction roll 44 so that the recording paper P is electrostatically attracted to the conveyance belt 42. It has become.

  At a position close to the suction roll 44, an environmental sensor unit 31 that measures the temperature and relative humidity or absolute humidity inside the printer 10 is provided. The environment sensor unit 31 is connected to the control unit 54, and the temperature and relative humidity or absolute humidity measured by the environment sensor unit 31 is converted into data by the control unit 54.

  A transfer roll 46 is disposed at a position facing the photoconductor 36 of each color on the back surface of the transport belt 42. By the transfer roll 46, the toner image on the photoreceptor 36 is transferred onto the recording paper P conveyed by the conveyance belt 42. The recording paper P to which the toner image has been transferred is fixed by the action of heat and pressure by a fixing device 48 comprising a pair of rolls provided above the stretching roll 40. Then, the recording paper P on which the toner image is fixed is discharged to the discharge tray 52 by the transport roll 49 and the discharge roll 50.

  On the other hand, a paper reversing path 25 is provided between the stretching roll 40 of the transport device 24 and the fixing device 48 so that the recording paper P enters and is transported by the movement of a switching lever (not shown). The paper reversing path 25 includes a plurality of guide plates 27 arranged in a curved shape or a straight shape, and a transport roll 29 that is disposed between the guide plates 27 and rotates to transport the recording paper P.

  Here, the recording paper P on which the image on the front surface (one side) has been fixed is transported into the printer 10 again by the reverse rotation of the discharge roll 50 and the roll of the fixing device 48, and enters the paper reversing path 25. . Then, the recording paper P transported in the paper reversing path 25 is transported again by the transport device 24. At this time, the back surface where no image is formed faces the side facing each photoconductor 36, and the reversal of the recording paper P is completed.

  Next, the configuration of the image forming unit 12 will be described.

  As shown in FIG. 2, the image forming unit 12 contains a photosensitive unit 56 (upper part) having a photosensitive member 36, toner of each color, and an electrostatic latent image formed on the photosensitive member 36. And a developing device 58 (lower part) for developing each color toner. An optical path 59 through which the exposure light L passes is formed between the photoconductor unit 56 and the developing device 58 so that the exposure light L is irradiated onto the surface of the photoconductor 36 through the optical path 59. It has become.

  The photoconductor unit 56 includes a photoconductor 36 that is rotatably provided, a charging roll 60 that is provided around the photoconductor 36 and charges the surface of the photoconductor 36 with a predetermined potential difference, and a cleaning that cleans the surface of the photoconductor 36. A blade 62, an erase lamp 64 for removing the charge on the surface of the photosensitive member 36, and a sub-toner supply unit 66 provided at a position away from the cleaning blade 62 are integrally configured.

  The sub-toner supply unit 66 is provided with an agitating and conveying member 68 having a mylar film for agitating and conveying the toner. Further, a support protrusion 70 projects from the side wall of the sub toner supply unit 66, and the image forming unit 12 is mounted on the printer 10 by inserting the support protrusion 70 into a receiving portion (not shown) in the printer 10. It is like that.

  On the other hand, in the developing device 58, a developing unit 72 that visualizes the electrostatic latent image on the photoreceptor 36 with toner and a main toner supply unit 74 that supplies the toner T to the developing unit 72 are integrated in the horizontal direction. It becomes the composition. The developing device 58 uses a two-component developing system in which the toner T is triboelectrically developed by stirring and mixing with a carrier.

  The developing unit 72 has a housing 76 as a main body. The housing 76 is provided on the lower side of the photoconductor 36 and has an opening 78 that opens toward the photoconductor 36. A developer accommodating chamber 80 is formed in the housing 76. The developer storage chamber 80 stores therein a developer G composed of toner T and carrier. Note that the carrier is accommodated only in the developer accommodating chamber 80.

  Further, a developing roll 82 is disposed in the housing 76 so as to be partially exposed from the opening 78. The developing roll 82 includes a non-magnetic cylindrical developing sleeve (not shown) that is rotatably provided in the direction of the arrow, and a magnet roll that is fixed so as not to rotate inside the developing sleeve and is provided with a plurality of magnetic poles alternately. (Not shown). A gear (not shown) is fixed to the end portion of the developing sleeve, and the rotational force from the motor is transmitted to the gear so that the developing sleeve rotates via the gear.

  Here, the developing roll 82 adsorbs the carrier contained in the developer G by magnetic force, forms a magnetic brush of the developer G on the surface, and develops the toner T adsorbed on the carrier to the photosensitive member 36. Transport to (developer supply position). Then, the electrostatic latent image formed on the photosensitive member 36 by the exposure light L is visualized by a magnetic brush of the developer G made of carrier and toner formed on the surface of the developing roll 82. It has become.

  A cylindrical layer thickness regulating member 84 is disposed on the upstream side of the developing area in the developing roll 82 and spaced apart from the developing roll 82 by a predetermined distance and along the axial direction of the developing roll 82. The layer thickness regulating member 84 is made of a non-magnetic material such as aluminum and regulates the layer thickness of the developer G supplied onto the developing roll 82.

  On the other hand, below the developing roll 82, a first auger 86 and a second auger 88 are rotatably supported along the axial direction of the developing roll 82. Here, gears (not shown) are fixed to the end portions of the first auger 86 and the second auger 88, respectively, and a rotational force from a motor (not shown) is transmitted to the gears. Each of the second augers 88 rotates. By this rotation, the developer G accommodated in the developer accommodating chamber 80 is conveyed to the developing roll 82 while being stirred.

  Between the 1st auger 86 and the 2nd auger 88, the 1st partition wall 90 is standingly arranged, The 1st stirring path 92 by which the 1st auger 86 was arrange | positioned by this 1st partition wall 90, Divided into a second stirring path 94 provided with a second auger 88. Further, communication ports (not shown) are formed at both ends in the longitudinal direction of the first partition wall 90, and the first stirring path 92 and the second stirring path 94 are communicated with each other through the communication ports. .

  A main toner supply unit 74 adjacent to the developing unit 72 is provided with a toner storage chamber 102 in which the supply toner T is stored. A first agitator 104 and a second agitator 106 are rotatably provided in the toner storage chamber 102 along the axial direction of the developing roll 82.

  The first agitator 104 includes a first rotating shaft 104A and a first transport film 104B made of mylar, and is rotatably supported on the peripheral wall of the main toner supply unit 74. The second agitator 106 includes a first rotating shaft 106 </ b> A and a second transport film 106 </ b> B made of Mylar, and is rotatably supported on the peripheral wall of the main toner supply unit 74. The first transport film 104B and the second transport film 106B are cut obliquely in the toner transport direction.

  A gear (not shown) is fixed to the ends of the first rotating shaft 104A and the second rotating shaft 106A. Here, when the rotational force from a motor (not shown) is transmitted to the gear and the first transport film 104B and the second transport film 106B rotate, the toner T in the toner storage chamber 102 is transported while being stirred. Yes.

  On the other hand, a second partition wall 108, a curved wall 110, and a third partition wall 112 are provided between the toner storage chamber 102 and the developer storage chamber 80. From the lower part of the second partition wall 108, the curved wall 110 extends toward the toner storage chamber 102, and the third partition wall 112 extends toward the developer storage chamber 80, whereby a tunnel-shaped toner conveyance path is formed at the bottom of the housing 76. 114 is formed.

  The toner conveyance path 114 is provided in parallel with the toner feeding direction of the first agitator 104. In the toner conveyance path 114, a conveyance auger 116 that stirs and conveys toner along the longitudinal direction is rotatably provided. Here, an opening (not shown) is formed in the toner conveyance path 114, and the toner T accommodated in the toner accommodating chamber 102 passes through the toner accommodating chamber 102 while being stirred by the first agitator 104. It is conveyed in the axial direction and is fed into the toner conveyance path 114 from the opening.

  On the other hand, an opening (not shown) is formed in the vicinity of the other end in the longitudinal direction of the third partition wall 112 so as to communicate the toner conveyance path 114 and the developer storage chamber 80. Thus, the toner T in the toner conveyance path 114 is conveyed while being agitated by the conveyance auger 116 and is sent from the toner supply port 120 to the developer storage chamber 80.

  FIG. 3 is a schematic diagram around the paper conveyance path 22 of the printer 10. The conveying belt 42 of the conveying device 24 moves in the direction of the arrow at the peripheral speed VT by the rotation of the stretching roll 40. Further, on the upstream side of the conveying device 24 in the conveying direction of the recording paper P, it is composed of a pair of rolls and is driven by a motor (not shown) to send the recording paper P to the conveying belt 42 and transfer images onto the recording paper P. A resist roll 20 that matches the timing is provided.

  A paper detection sensor 23 that detects the leading edge of the recording paper P is provided between the transport roll 18 and the registration roll 20. The paper detection sensor 23 is a photo sensor, and includes a light emitting unit 23A that emits the light BM and a light receiving unit 23B that receives the light BM. The traveling direction of the light BM is a direction that intersects the conveyance direction of the recording paper P.

  Here, when there is no recording paper P between the light emitting unit 23A and the light receiving unit 23B, the light receiving unit 23B receives the light BM, and the amount of received light is large. On the other hand, when the recording sheet P enters between the light emitting unit 23A and the light receiving unit 23B, the light BM is blocked by the recording sheet P, so that the amount of light received by the light receiving unit 23B decreases. The timing at which the leading edge of the recording paper P passes through the paper detection sensor 23 is detected by the change in the amount of received light.

  On the other hand, the fixing device 48 is in contact with the heat roll 48A provided with a heater (heat source) and the outer peripheral surface of the heat roll 48, and is biased toward the heat roll 48A by a biasing means such as a spring (not shown). And a pressure roll 48B for forming N. The heat roll 48A is disposed on the image forming surface side of the recording paper P, and is rotated at a peripheral speed VH by a rotational drive of a motor (not shown) whose rotation is controlled by the control unit 54 (see FIG. 1). It has become. The peripheral speed VH is variable by the control unit 54. The pressure roll 48B rotates following the rotation of the heat roll 48A.

  Here, the distance from the sheet detection sensor 23 to the entrance of the nip portion N of the fixing device 48 is L1. Further, the recording paper P has a length in the transport direction that is close to the distance from the registration roll 20 to the fixing device 48. Therefore, if the recording paper P that has passed through the paper detection sensor 23 is conveyed to the entrance of the nip portion N at the peripheral speed (conveyance speed) VT of the conveyance belt 42, the leading edge of the recording paper P is the paper detection sensor 23. The time t from passing through to reaching the nip portion N is t = L1 / VT. By using this time t, the entry timing of the recording paper P to the nip portion N by the paper detection sensor 23 can be detected.

  Here, when the recording paper P enters the nip portion N of the fixing device 48, the peripheral speed VH of the heat roll 48 </ b> A is controlled by the control unit 54 in the range lower than the peripheral speed VT of the transport belt 42. Is increased from

Further, as shown in FIG. 4A, for example, the increased peripheral speed V of the heat roll 48A includes the types of recording paper (basis weight [g / cm ³ ]) A to C and the temperature T1 inside the printer 10. ~ T3, a combination of the relative humidity H1 to H3 inside the printer 10 and the absolute humidity SH1 to SH3 inside the printer 10 is provided with a data table set in advance from V1 to V29, and this data table is stored in the control unit 54. By storing it, the speed is increased in accordance with each condition.

  The increased peripheral speeds V1 to V29 are relative to the absolute speed value with the speed 0 when the heat roll 48A (see FIG. 3) is stopped, or when the heat roll 48A rotates at the initial speed V0. The speed increase value (ΔV) may be set. As described above, 0 <V1, V2,..., V29 <VT are set for the peripheral speed VT of the conveyor belt.

  Here, as the absolute humidity SH increases, the electrostatic force is weakened, and the adsorption force of the recording paper P to the transport belt 42 is reduced. Therefore, as shown in FIG. The increased peripheral speed of 48A also needs to be lowered. Note that the recording paper P with a large basis weight is graph A, and the recording paper P with a small basis weight is graph B, and the increased peripheral speed of the heat roll 48A required for the absolute humidity SHa is the recording paper A. Va and recording paper B are set to Vb (Vb <Va). This is because the recording paper A having a large basis weight has a longer apparent moving distance (radius) at the time of conveyance, and therefore needs to be conveyed faster than the recording paper B having a short apparent moving distance. Thus, the increased peripheral speed of the heat roll 48A is changed according to the type of the recording paper P.

  As shown in FIG. 5A, in this embodiment, when the peripheral speed (VH) of the heat roll 48A (see FIG. 3) is increased, it is gradually increased in a plurality of stages. As an example, when the increased peripheral speed (absolute value) of the heat roll 48A is V16 in FIG. 4A, the difference (V16−V0) from the initial peripheral speed V0 of the heat roll 48A is divided into six equal parts, From time t1 to time t2 (Δt1), ΔV = (V16−V0) / 6 is increased. It is assumed that the value of ΔV and the number of steps (6) are set in the increased peripheral speed column (V1 to V27) of the data table (FIG. 4A).

  The increase in the peripheral speed of the heat roll 48A starts a little after time t1, but this is because the recording paper P enters the nip portion N between the heat roll 48A and the pressure roll 48B. This indicates that the peripheral speed of the heat roll 48A is increased. The time t2 is the time when the trailing edge of the recording paper P passes through the nip portion N.

  Similarly, when the second and subsequent recording sheets P enter the nip portion N, they are increased by ΔV = (VT−V0) / 6 from time t3 to time t4 (Δt2 = Δt1). Here, the value of ΔV is about 0.1% of the initial speed V0, and the final increase in peripheral speed is 0.6% to 1.0%.

  In the present embodiment, the increased peripheral speed is divided and gradually increased. However, the present invention is not limited to this. For example, as shown in FIG. Also good. In addition, it is not necessary for the increased peripheral speed ΔV to be the same amount in a plurality of increasing steps, and it may be increased at the beginning and increased at the latter half.

  Next, the operation of the first embodiment of the present invention will be described.

  First, image formation of the printer 10 will be described. As shown in FIG. 1, image formation is started by pressing a start button on an operation panel (not shown) on the printer 10 or by transmitting from a computer. The control unit 54 selects the type of the recording paper P on which image formation is performed, and the environment sensor unit 31 measures either the temperature or the humidity in the printer 10 or the absolute humidity, as shown in FIG. The increased peripheral speed of the heat roll 48A is determined based on the data table of a). Here, it is assumed that the increased peripheral speed is V16.

  Subsequently, the control unit 54 controls the operation of each part of the printer 10, and the recording paper P is sent out from the paper feed cassette 14 by the pickup roll 16. The sent recording paper P is sent to the paper transport path 22 via the transport roll 18 and the registration roll 20 and transported to the transport device 24. Here, the paper detection sensor 23 detects the passage of the leading edge of the recording paper P, and the timing at which the recording paper P enters the nip portion N of the fixing device 48 is measured.

  Subsequently, in each image forming unit 12, the photosensitive member 36 is charged by the charging roll 60, and exposure light L is irradiated from the exposure device 26 to the photosensitive member 36 based on various data for forming an image. Thereby, an electrostatic latent image is formed on the photoconductor 36. The electrostatic latent image is made visible (developed) by the toner T on the developing roll 82 and becomes a toner image. The toner image on the photoreceptor 36 is sequentially transferred by the transfer electric field of the transfer roll 46 onto the recording paper P that has been transported by the transport belt 42, and the toner of each color is superimposed.

  Subsequently, as shown in FIGS. 6A and 6B, the recording paper P onto which the toner image has been transferred enters the nip portion N of the fixing device 48. At this time, the heat roll 48A rotates at a speed VH = V0 (initial speed).

  Here, by the control unit 54 (see FIG. 1), the speed VH of the heat roll 48A is V0 to V0 + ΔV, V0 + 2 × ΔV,..., V0 + 5 × ΔV, VT, where ΔV = (V16−V0) / 6. So that it is gradually increased. As a result, the leading edge of the recording paper P whose leading edge has entered the nip portion N of the fixing device 48 is being pulled in the conveying direction while being conveyed by the conveying belt 42, and the recording paper P is transferred to the transfer roll 46K. It is stretched between the position of N and the nip portion N. In this way, the occurrence of the loop RP (deflection) of the recording paper P before the nip portion N is suppressed, and the loop RP is reduced.

  Subsequently, the toner image on the recording paper P that has entered the nip portion N is fixed by the action of heat and pressure of the heat roll 48A and the pressure roll 48B. The recording paper P that has been fixed is discharged to the discharge tray 52 by the discharge roll 50. In the case of duplex printing, reverse printing is performed by reversing the paper reversing path 25. In this way, image formation is performed.

  Next, a second embodiment of the image forming apparatus of the present invention will be described with reference to the drawings. Note that components that are basically the same as those in the first embodiment described above are given the same reference numerals as those in the first embodiment, and descriptions thereof are omitted.

  FIG. 7 shows a schematic diagram around the paper conveyance path 22 of the printer 130. The printer 130 has a configuration in which a paper discharge sensor 140 is provided in front of (on the upstream side of) the discharge roll instead of the paper detection sensor 23 of the printer 10 described above, and other members are basically the same. .

  The paper discharge sensor 140 is a photo sensor, and includes a light emitting unit 140A that emits the light BM and a light receiving unit 140B that receives the light BM. Here, when there is no recording paper P between the light emitting unit 140A and the light receiving unit 140B, the light receiving unit 140B receives the light BM, and the amount of received light is large. On the other hand, when the recording paper P enters between the light emitting unit 140A and the light receiving unit 140B, the light BM is blocked by the recording paper P, so that the amount of light received by the light receiving unit 140B decreases. The timing at which the leading or trailing edge of the recording paper P passes through the paper discharge sensor 140 is detected based on the change in the amount of received light.

  Further, in the paper discharge sensor 140, when the light reception amount at the light receiving unit 140B is small, the detection signal falls (ON) corresponds to the passage of the leading edge of the recording paper P, and the rise (OFF) This corresponds to the passage of the trailing edge of the recording paper P.

  Next, the operation of the second embodiment of the present invention will be described.

  Image formation is started when the start button of an operation panel (not shown) is pressed by the printer 130 or transmitted from a computer. Here, in the control unit 54, the type of the recording paper P on which image formation is performed is selected, and further, either the temperature or humidity in the printer 10 or the absolute humidity is measured by the environment sensor unit 31, and FIG. Based on the data table of (a), the increased peripheral speed of the heat roll 48A is determined.

  Subsequently, the control unit 54 controls the operation of each part of the printer 130, and the recording paper P is sent out from the paper feed cassette 14 by the pickup roll 16. The sent recording paper P is sent to the paper transport path 22 via the transport roll 18 and the registration roll 20 and transported to the transport device 24.

  Subsequently, in each image forming unit 12, the photosensitive member 36 is charged by the charging roll 60, and exposure light L is irradiated from the exposure device 26 to the photosensitive member 36 based on various data for forming an image. Thereby, an electrostatic latent image is formed on the photoconductor 36. The electrostatic latent image is made visible (developed) by the toner T on the developing roll 82 to become a toner image. The toner image on the photosensitive member 36 is sequentially transferred onto the recording paper P conveyed by the conveying belt 42 by the transfer electric field of the transfer roll 46, and the toner of each color is superimposed.

  Subsequently, the recording paper P onto which the toner image has been transferred enters the nip portion N of the fixing device 48. At this time, the heat roll 48A rotates at a speed VH = V0 (initial speed).

  Subsequently, as shown in FIGS. 8A and 8B, when the leading edge of the recording paper P that has passed through the nip portion N of the fixing device 48 passes through the paper discharge sensor 140, the control unit 54 (see FIG. 1). ), The speed VH of the heat roll 48A is gradually increased from V0 to V0 + ΔV, V0 + 2 × ΔV,..., V0 + 5 × ΔV, VT. Note that ΔV = (VT−V0) / 6.

  As a result, the recording paper P whose leading edge has entered the nip portion N is pulled toward the conveyance direction while being conveyed by the conveyance belt 42, and the recording paper P is moved from the position of the transfer roll 46K to the nip portion N. It is stretched between. In this way, the occurrence of the loop RP (deflection) of the recording paper P before the nip portion N is suppressed, and the loop RP is reduced.

  The toner image on the recording paper P that has entered the nip portion N is fixed by the action of heat and pressure of the heat roll 48A and the pressure roll 48B. The recording paper P that has been fixed is discharged to the discharge tray 52 by the discharge roll 50. Here, the recording paper P is discharged to the discharge tray 52 after a predetermined time has elapsed since the paper discharge sensor 140 detected the passage of the trailing edge of the recording paper P.

  In addition, this invention is not limited to said embodiment.

  The environmental sensor unit 31 may be provided at another part of the printer 10 such as the downstream side of the transport device 24. Further, the speed increase of the heat roll 48A is not limited to six stages, and may be set in a plurality of stages including two or more stages.

  Further, the elapsed time of each increase stage when the peripheral speed is increased in a plurality of stages may not be the same, for example, it may be set to a short time at the beginning and gradually increased to a long time. Further, the increase speed data table is not only set for at least one condition of paper type, temperature, relative humidity, and absolute humidity, but includes, for example, the transfer voltage of the transfer roll 46, the temperature of the heat roll 48A, and the like. It is good also as conditions.

1 is an overall view of an image forming apparatus according to a first embodiment of the present invention. 1 is a cross-sectional view of an image forming unit according to a first embodiment of the present invention. It is a schematic diagram of the paper conveyance path | route which concerns on 1st Embodiment of this invention. (A) It is a data table of the increase speed in each setting condition of the heat roll which concerns on 1st Embodiment of this invention. (B) It is a graph which shows the change with respect to absolute humidity of the heat roll peripheral speed which concerns on 1st Embodiment of this invention. (A) It is a graph which shows the speed increase with respect to the time of the circumferential speed of the heat roll which concerns on 1st Embodiment of this invention. (B) It is a graph which shows the speed increase with respect to the time of the circumferential speed in the other Example of the heat roll which concerns on 1st Embodiment of this invention. FIGS. 3A and 3B are schematic diagrams illustrating a recording sheet conveyance state in the conveyance device and the fixing device according to the first embodiment of the present disclosure. FIGS. It is a schematic diagram of the paper conveyance path | route which concerns on 2nd Embodiment of this invention. (A), (b) is a schematic diagram showing a conveyance state of a recording sheet in a fixing device according to a second embodiment of the present invention.

Explanation of symbols

10 Printer (image forming device)
23 Paper detection sensor (entrance detection means)
24 Conveying device (conveying means)
31 Environmental sensor (condition detection means)
46 Transfer roll (transfer means)
48A heat roll (fixing rotating body)
48B pressure roll (fixing rotator)
54 Control unit (speed control unit, (condition detection means))
130 Printer (image forming apparatus)
140 Paper discharge sensor (discharge detection sensor)
P Recording paper (recording medium)

Claims (5)

A transfer means provided inside the apparatus main body and opposed to a transfer means for transferring an image, and for transferring a recording medium;
A fixing rotator which is provided on the downstream side in the conveyance direction of the recording medium with respect to the conveyance unit and rotates to fix the image on the recording medium;
An entry detecting means for detecting the entry of the recording medium between the fixing rotators;
Speed control for increasing the speed of the fixing rotator based on a predetermined amount of increase in the speed of the fixing rotator when the entry detecting means detects the entry of the recording medium between the fixing rotators. And
An image forming apparatus. The speed increase amount of the fixing rotator depends on at least one condition among the type of recording medium, the temperature inside the apparatus main body, the relative humidity inside the apparatus main body, and the absolute humidity inside the apparatus main body. Are determined,
A condition detecting means for detecting the at least one condition is provided;
The image forming apparatus according to claim 1, wherein the speed increase amount of the fixing rotator is determined in accordance with a condition detected by the condition detection unit.   The image forming apparatus according to claim 1, wherein the speed of the fixing rotator is increased in a plurality of stages.   4. The image forming apparatus according to claim 1, wherein the entry detection unit is provided upstream of the fixing rotator in a conveyance direction of the recording medium and detects a leading end of the recording medium.   4. The discharge detection sensor according to claim 1, wherein the entry detection unit is a discharge detection sensor that is provided downstream of the fixing rotating body in a conveyance direction of the recording medium and detects discharge of the recording medium from the apparatus main body. 2. The image forming apparatus according to item 1.

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