JP2011141463A - Image forming apparatus and medium conveying method - Google Patents

Abstract

【Task】
The slack formed between the transfer unit and the fixing unit is not parabolic, and even if the paper is prone to swell or wavy, the difference in the paper conveyance speed between the transfer unit and the fixing unit can be reduced. Provided are an image forming apparatus and a medium transport method capable of preventing deterioration in print quality caused by a difference in paper transport speed between a transfer unit and a fixing unit by reliably detecting.
[Solution]
A transport unit that transports the medium on which the developer image has been transferred by the image forming unit, and a fixing unit that is disposed downstream of the transport unit in the medium transport direction, fixes the image on the transported medium, and transports the medium; An image forming apparatus comprising: a detection unit that detects a change in the conveyance speed of the medium in the fixing unit; and a control unit that changes a driving speed of the driving unit of the conveyance unit or the fixing unit based on a detection result of the detection unit; And a medium conveying method according to this.
[Selection] Figure 1

Description

  The present invention relates to medium feeding in an image forming apparatus.

  In general, an electrostatic latent image formed on a photosensitive drum as an image carrier is developed with toner as a developer to form a developer image, and the developer image is transferred to a sheet as a medium. In an image forming apparatus that includes a transfer unit and a fixing unit that fixes the developer image transferred onto the sheet by applying heat and pressure, the sheet conveyance speed between the transfer unit and the fixing unit In order to prevent a decrease in print quality caused by the difference in speed, a sheet slack is formed between the transfer unit and the fixing unit, and the sheet conveyance speed of either the transfer unit or the fixing unit is detected by detecting the slack. There is something to adjust (see, for example, Patent Document 1).

JP 2005-338252 A

  However, for example, in the image forming apparatus described in Patent Document 1, when the slack of the paper is formed between the transfer unit and the fixing unit, the paper transport speed in the fixing unit is slower than the paper transport speed in the transfer unit. Is set. In such an image forming apparatus, when the slack of the paper is formed between the transfer unit and the fixing unit, it is difficult to detect the slack, and for example, the formed slack is not a parabolic shape, and undulations are generated. If it occurs or becomes wavy, there is a difference between the actual amount of slack in the paper and the amount of slack that is detected, so a reliable detection result cannot be obtained, and the paper between the transfer portion and the fixing portion There has been a problem that the print quality is deteriorated due to the difference in transport speed.

  The present invention has been made in view of such circumstances, and the problem of the present invention is that the slack formed between the transfer portion and the fixing portion is not a parabolic shape, and undulation easily occurs or becomes wavy. An image forming apparatus and a medium transport method capable of preventing a decrease in print quality by reliably detecting a speed difference of a paper transport speed between a transfer unit and a fixing unit even for easy paper. Is to provide.

  In order to solve the above problems, an image forming apparatus according to the present invention includes a transport unit that transports a medium on which a developer image has been transferred by an image forming unit, and a transport unit that is disposed downstream of the transport unit in the medium transport direction. A fixing unit for fixing the image on the medium and detecting the change in the conveyance speed of the medium in the fixing unit, and driving the conveyance unit or the fixing unit based on the detection result of the detection unit. And a control unit that changes the drive speed of the unit.

  The medium conveying method according to the present invention includes a conveying step for conveying the medium on which the developer image has been transferred by the image forming unit, and a medium disposed on the downstream side in the medium conveying direction from the image forming unit. The fixing process for fixing the image and the medium, the detection process for detecting a change in the conveyance speed of the medium in the fixing process, and the driving speed of the conveyance process or the fixing process are changed based on the detection result in the detection process. And a control step.

  According to the present invention, since it is possible to reliably detect the speed difference of the sheet conveyance speed between the transfer unit and the fixing unit, an image forming apparatus and a medium capable of preventing a decrease in print quality due to the speed difference A conveyance method can be provided.

FIG. 2 is a schematic diagram of a printer. FIG. 4 is a perspective view illustrating the arrangement of both a transfer unit and a fixing unit. It is a perspective view of a fixing unit. FIG. 6 is a perspective view illustrating a state where an outer cover of the fixing unit is removed. FIG. 3 is an exploded perspective view illustrating component arrangement of a fixing unit. FIG. 3 is an exploded perspective view illustrating component arrangement of a fixing unit. 2 is a block diagram illustrating a functional configuration of a printer. FIG. FIG. 6 is an image diagram for explaining a state where a sheet P is slackened between both a transfer unit and a fixing unit. FIG. 6 is an image diagram for explaining a state in which a sheet P is stretched between both a transfer unit and a fixing unit. FIG. 6 is an image diagram for explaining a state in which the sheet P is most loosened between the transfer unit and the fixing unit when the driving speed of the fixing unit is changed. 2 is a block diagram illustrating a functional configuration of a printer. FIG. FIG. 6 is a diagram for explaining a variation in paper conveyance speed.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably.

[First embodiment]
In the description of the first embodiment, a tandem color printer 100 will be described with reference to FIGS. 1 to 6 as an image forming apparatus. FIG. 1 is an apparatus schematic diagram of the printer 100. FIG. 2 is a perspective view for explaining the arrangement of both the transfer unit 10 which is a transfer unit according to the present embodiment, which is also a transport unit, and a fixing unit 30 as a fixing unit. FIG. 3 is a perspective view of the fixing unit 30, and FIG. 4 is a perspective view illustrating a state in which the outer cover of the fixing unit 30 shown in FIG. 3 is removed. 5 and 6 are exploded perspective views for explaining the component arrangement of the fixing unit 30. FIG.

  The printer 100 includes a paper storage unit 20 having a paper cassette 22 that is detachably attached to the lower part of the printer 100, a paper feed roller 23 that feeds the paper P in the direction of the arrow x, and a paper P that is fed by the paper feed roller 23. The image forming unit 26C as image forming means for forming a toner image corresponding to each toner color (C: cyan, M: magenta, Y: yellow, BK: black). , 26M, 26Y, and 26BK, and a conveyance belt 12 as a conveyance unit that conveys the sheet P by electrostatic adsorption, and abuts against a photosensitive drum included in each image forming unit described later via the conveyance belt 12. The transfer rollers 27C, 27M, 27Y, and 27BK are arranged so as to transfer the toner images formed on the respective photosensitive drums to the paper P. The transfer unit 10 provided, LED (Light Emitting Diode) heads 28C, 28M, 28Y, and 28BK as exposure apparatuses for forming an electrostatic latent image on the surface of each photosensitive drum, and the paper P on which the toner image is transferred The fixing unit 30 as a fixing unit that fixes the toner image by applying heat and pressure, the discharge roller 31 that discharges the paper P that has passed through the fixing unit 30 to the outside of the printer 100, and the discharge roller 31. A paper stacker 32 on which the paper P is placed.

  The paper cassette 22 stores the paper P in a stacked state, and is detachably attached to the lower part of the printer 100. A paper feed roller 23 that separates and feeds the paper P one by one is disposed above the paper cassette 22.

  The registration roller 24 is rotated by a driving force transmitted from a driving source (not shown), corrects the skew of the paper P conveyed by the paper feed roller 23, and conveys the paper P toward the transfer unit 10.

  A transport belt 12 as a transport unit constituting the transfer unit 10 is an endless belt member that electrostatically attracts and transports the paper P. The conveying belt 12 is stretched between the driving roller Ra and the driven roller Rb, and a transfer unit driving source as a driving unit in the conveying unit rotates a driving gear (not shown) disposed at the end of the driving roller Ra. Drive by driving. The transfer rollers 27C, 27M, 27Y, and 27BK are disposed so as to come into contact with the photosensitive drums included in the respective image forming units via the transport belt 12, and are bias voltages applied from a transfer roller power source (not shown). Thus, the toner image formed on the photosensitive drum is transferred to the paper P. In addition to this, the transfer unit 10 is formed so as to be in contact with the conveyance belt 12 and is disposed below the cleaning roller for cleaning the residual toner adhering to the surface of the conveyance belt 12 and the driven roller Rb. A waste toner box portion 11 for collecting residual toner cleaned by the cleaning blade.

  The image forming units 26C, 26M, 26Y, and 26BK form toner images corresponding to cyan, magenta, yellow, and black toner colors based on the input image information. Here, the cyan image forming unit 26C will be described as an example. The image forming unit 26C includes a photosensitive drum 91 as an image carrier and a charging roller 92 for uniformly and uniformly charging the surface of the photosensitive drum 91. And an electrostatic latent image formed on the surface of the photoconductive drum 91 by the LED head 28C by developing cyan toner to form a toner image and a toner supply roller 96. And a cleaning unit 94 that removes unnecessary toner remaining on the surface of the photosensitive drum 91. Note that the image forming units 26C, 26M, 26Y, and 26BK are detachably mounted from the printer 100 along the transport belt 12, and the configuration differs only in the accommodated toner color.

  The LED heads 28C, 28M, 28Y, and 28BK are arranged so that the LED elements are arranged in the axial direction, and the irradiation light emitted from the LED elements is positioned on the surface of the photosensitive drum, By irradiating light based on the input image information, an electrostatic latent image is formed on the photosensitive drum.

  As shown in FIG. 1, FIG. 5, or FIG. 6, the fixing unit 30 includes a heating roller 30a, a pressure roller 30b, a halogen lamp 40 as a heat source, a fixed wire 41, a heating roller gear 50, and a fixing unit. A unit drive gear 51, a slit disk 52, and a photocoupler sensor 53 as a detection unit are provided. For example, the heating roller 30a covers a heat resistant elastic layer such as silicone rubber on a hollow cylindrical cored bar made of aluminum or the like, and covers a PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) tube thereon. It is formed by that. A halogen lamp 40 as a heat source is disposed in the cored bar. The pressure roller 30b has substantially the same configuration as the heating roller 30a, and is arranged to press the heating roller 30a. As the paper P on which the toner image is transferred passes through the nip formed by the heating roller 30a and the pressure roller 30b, heat and pressure are applied, and the toner image is fixed on the paper P. Further, the slit disk 52 is disposed at the shaft end of the heating roller 30a, and is fixed to the heating roller 30a by the fixed wire 41 without play. The slit disk 52 has a plurality of slits 52a formed on the surface. The photocoupler sensor 53 that detects the slit 52a is held by the fixing unit frame 42 at a position where the slit 52a can be detected by the sensor light.

  The discharge roller 31 is rotated by a driving force transmitted from a driving source (not shown), and discharges the paper P on which the toner image is fixed in the fixing unit 30 to the outside of the printer 100.

  The paper stacker 32 is formed using the outer casing of the printer 100 and stacks the paper P discharged by the discharge roller 31.

  Next, the functional configuration of the printer 100 will be described with reference to FIG. The printing control unit 700 as a control unit determines the rotation speed of the heating roller 30 a from the detection signal at a predetermined time output from the photocoupler sensor 53 that is the slit disk count detection unit 53, and the transfer unit 10 and the fixing unit 30. It is determined whether or not the sheet P between the two units is stretched or slack.

  The fixing unit drive control unit 71 controls the driving of the fixing unit drive motor 72 that is a DC motor based on an instruction from the print control unit 700. The fixing unit driving motor 72 is connected to the heating roller gear 50, and the rotation of the heating roller 30 a is controlled by driving the fixing unit driving motor 72.

  The operation of the printer 100 having such a configuration will be described with reference to FIGS. 8, 9, and 10. FIG. FIG. 8 is an image diagram for explaining a state in which the paper P is loose between the transfer unit 10 and the fixing unit 30. FIG. 9 is an image diagram illustrating a state in which the paper P is stretched between both the transfer unit 10 and the fixing unit 30. FIG. 10 is an image diagram illustrating a state where the driving speed of the fixing unit 30 is changed and the sheet P is most loose between both the transfer unit 10 and the fixing unit 30.

  As shown in FIG. 8, the sheet conveyance speed of the transfer unit 10 is VH1, the driving speed of the fixing unit 30 is D2, the rotation speed of the heating roller 30a is R2, and the sheet conveyance speed of the fixing unit 30 is VT2. Further, it is assumed that the sheet conveyance speed VT2 of the fixing unit 30 is set slightly faster than the sheet conveyance speed VH1 of the transfer unit 10, and VT2> VH1.

  Further, when the transfer unit 10, that is, the force that the conveyance roller 12 attracts and holds the paper P by electrostatic force is the paper conveyance force FH, and the force that the fixing unit 30 conveys the paper P is the paper conveyance force FT, the transfer unit It is assumed that the sheet conveyance force FT of the fixing unit 30 is set to be smaller than the sheet conveyance force FH of 10, and has a relationship of FH> FT.

  In this state, as the paper P is conveyed, the slack state shown in FIG. 8 changes to the tension state shown in FIG. In the state where the paper P shown in FIG. 8 is not loose and stretched, the heating roller 30a rotates at the rotational speed R2, and transports the paper P at the paper transport speed VT2. On the other hand, in the state in which the slack of the paper P shown in FIG. 9 is eliminated, the driving current of the fixing unit driving motor 72 which is a DC motor is constant, so that the paper transport load increases and the paper transport speed becomes slow. As a result, the heating roller 30a rotates at the rotational speed R1, and the paper P is transported at the paper transport speed VT1.

  As described above, the slit disk 52 is fixed to the shaft end portion of the heating roller 30a, and the slit disk 52 rotates with the rotation of the heating roller 30a. The photocoupler sensor 53 that is the slit disk count detection unit 53 detects the slit 52 a formed in the slit disk 52 and outputs the detection result to the print control unit 700. Then, the printing control unit 700 determines the rotation speed of the heating roller 30a from the detection signal of the photocoupler sensor 53 output from the slit disk count detection unit 53 for a predetermined time, and both units of the transfer unit 10 and the fixing unit 30 are detected. It is determined whether the sheet P placed between them is stretched or slack.

  Here, if it is determined that the paper P placed between the transfer unit 10 and the fixing unit 30 is in a tension state, the print control unit 700 causes the fixing unit drive control unit 71 to be slightly faster than the normal drive speed. Is instructed to change to a slower driving speed D0. Receiving the instruction, the fixing unit driving control unit 71 controls the driving speed of the fixing unit driving motor 72 to be D0. When a predetermined time elapses, the print control unit 700 instructs the fixing unit drive control unit 71 to set the driving speed of the fixing unit driving motor 72 to the normal speed D2. Receiving the instruction, the fixing unit driving control unit 71 controls the driving speed of the fixing unit driving motor 72 to be D2.

  Here, the rotation speed of the heating roller 30a at the fixing unit driving speed D0 shown in FIG. 10 is R0, and the sheet conveyance speed of the fixing unit 30 is VT0. Since this is a transport speed slower than the paper transport speed VH1 of the transfer unit 10, the tension of the paper P between the two units is gradually eliminated, and then slack is formed.

  Then, when the predetermined time elapses and the driving speed D0 of the fixing unit 30 returns to the driving speed D2, which is a normal driving speed, the slack of the paper P between the two units becomes the largest as shown in FIG. At this time, since the fixing unit 30 is driven at the driving speed D2, the heating roller 30a rotates at the rotational speed R2, and the paper P is transported at the paper transport speed VT2, and gradually enters a state as shown in FIG.

  Next, the operation described so far will be described with specific numerical values.

  For example, it is assumed that the roller diameter of the heating roller 30a is 40 mm, and the count number of the slits 52a per rotation of the heating roller 30a is set to 1440 Plus. Then, the sheet conveyance speed VH1 of the transfer unit 10 is set to 150.00 mm / sec, the fixing unit 30 is driven at the driving speed D2, there is no tension of the sheet P between the two units, and the rotation speed of the heating roller 30a is R2. In this case, the conveyance speed VT2 of the fixing unit 30 is 150.75 mm / sec, and the sheet conveyance speed VT2 of the fixing unit 30 with respect to the sheet conveyance speed VH1 of the transfer unit 10 is set to be larger by 0.5%. Originally, it is desirable that the sheet conveyance speed VT2 of the fixing unit 30 with respect to the sheet conveyance speed VH1 of the transfer unit 10 is set as small as possible, and ideally, 0.05% or less. In consideration of the variation in the sheet conveyance speed in the mass-produced products of both the unit 10 and the fixing unit 30, the value is set as large as 0.5% here.

  In a state where the paper P is not loose and stretched as shown in FIG. 8, the heating roller 30a rotates at the rotational speed R2, and the paper P is transported at the paper transport speed VT2 (150.75 mm / sec). At this time, the heating roller 30a rotates 1.200 per second, and the slit disk count detection unit 53 outputs a signal of 1727 Plus (863 Plus in 500 msec) to the print control unit 700.

  In the state where the slack of the paper P as shown in FIG. 9 is eliminated, the heating roller 30a rotates at the rotational speed R1, and the paper P is transported at the paper transport speed VT1 (150.00 mm / sec). At this time, the heating roller 30a rotates 1.194 per second, and the slit disk count detection unit 53 outputs a signal of 1718 Plus (859 Plus in 500 msec) to the print control unit 700.

  Whether the print control unit 700 is in a state where the sheet P spanned between both the transfer unit 10 and the fixing unit 30 is stretched based on the count value of the detection signal at a predetermined time input from the slit disk count detection unit 53. Determine if you are in a loose state. Specifically, for example, when the threshold value per 500 msec is set to 860 Plus, the print control unit 700 determines that the state of FIG. 8 in which the detection signal of 863 Plus is output per 500 msec is a state where the paper P is slack. Then, it can be determined that the state of FIG. 9 in which the detection signal of 859 Plus is output per 500 msec is the state where the paper P is stretched.

  Note that when the printing control unit 700 determines that the paper P placed between the transfer unit 10 and the fixing unit 30 is in a tension state, the paper conveyance of the fixing unit 30 when the driving speed of the fixing unit 30 is driven at D0. The speed VT0 is 149.25 mm / sec. Here, since the sheet conveyance speed VH1 of the transfer unit 10 is 150.00 mm / sec, the sheet conveyance speed VT0 of the fixing unit 30 is set to be 0.5% smaller than the sheet conveyance speed VH1 of the transfer unit 10. The Rukoto. Originally, the sheet conveyance speed VT0 of the fixing unit 30 with respect to the sheet conveyance speed VH1 of the transfer unit 10 is desirably set as small as possible in order to perform stable sheet conveyance, and ideally 0.05% or less. However, in consideration of variations in the sheet conveyance speed in the mass-produced products of both the transfer unit 10 and the fixing unit 30, the value is set as small as 0.5% here.

  In the above description, in the present embodiment, the count number of the slits 52a per rotation of the heating roller 30a has been described as 1440 Plus. However, for example, a sensor with higher resolution or a pitch of slit holes of the slit disk is used. It is easy to increase the count number of the slits 52 per rotation of the heating roller 30a by making the width of the heating roller 30a fine. In this case, the difference in the sheet conveyance speed between the two units can be reduced with a smaller rotation angle of the heating roller 30a. It is possible to detect and determine whether the sheet P between the two units is stretched or loose.

  In the description of the present embodiment, the transfer unit and the fixing unit have been described. However, the present invention is not limited to a unit disposed on the upstream side in the sheet conveyance direction and a unit disposed on the downstream side, such as a registration roller. Of course, it can be applied to the transfer unit. In the description of the present embodiment, the mode of adjusting the speed by changing the paper transport speed of the fixing unit with respect to the paper transport speed of the transfer unit has been described. However, the present invention is not limited to this, and the paper transport speed of the transfer unit is not limited thereto. It does not matter as a form of changing. In this case, the paper transport speed of the transfer unit is set faster than the paper transport speed of the fixing unit.

  As described above, according to the first embodiment, the speed difference of the sheet conveyance speed between the transfer unit and the fixing unit is changed depending on the tension state of the sheet between the transfer unit and the fixing unit. By detecting and adjusting the paper transport speed of the fixing unit, the slack formed between the transfer unit and the fixing unit is not a parabolic shape, and the paper tends to be swelled or wavy, for example, folded into a mountain valley. Even if it is folded fanfold paper or paper rolled up in a roll, it is possible to reliably detect the difference in paper transport speed between the transfer unit and the fixing unit without time loss. It is possible to prevent a decrease in print quality caused by a difference in paper conveyance speed between the unit and the fixing unit.

  Further, according to the first embodiment, it is not necessary to form a paper slack between the transfer unit and the fixing unit and detect the paper slack, and the ON / OFF switching point of the slack detection with respect to the paper transport surface. Since there is no need to make adjustments or adjustments in anticipation of fluctuations in the ON / OFF switching point of slack detection in anticipation of a decrease in sensor sensitivity due to temperature rise, the adjustment process during device manufacture can be reduced. Furthermore, according to the first embodiment, it is not necessary to secure a space for forming the slack of the paper, or an installation space for a mechanical lever, a rotating body, or a sensor for detecting the slack of the paper. Can be realized.

[Second Embodiment]
Since the configuration of the printer or the printing process according to the second embodiment is substantially the same as that of the first embodiment, the same portions are denoted by the same reference numerals and description thereof is omitted.

  FIG. 11 is a diagram illustrating the functional configuration of the printer according to the second embodiment. In the second embodiment, in addition to the configuration of the slit disk count unit 53, the fixing unit drive control unit 71, the fixing unit drive motor 72, and the print control unit 700 according to the first embodiment, a transfer unit drive control unit. 81 and a transfer unit drive motor 82.

  The transfer unit drive control unit 81 controls the drive of the transfer unit drive motor 82 based on an instruction from the print control unit 700. The transfer unit drive motor 82 is connected to the drive roller Ra of the transfer unit 10, and the rotation of the drive roller Ra is controlled by driving the transfer unit drive motor 82.

  In the description of the first embodiment, it is desirable that the sheet conveyance speed VT2 of the fixing unit 30 with respect to the sheet conveyance speed VH1 of the transfer unit 10 is large, but the speed difference is set as small as possible. Although 0.05% or less is desirable, in consideration of variations in the sheet conveyance speed in the mass-produced products of both the transfer unit 10 and the fixing unit 30, the value is set as large as 0.5% here. However, the variation in the sheet conveyance speed will be described in more detail with reference to FIG.

  The variation in the sheet conveyance speed in the mass-produced products of both the transfer unit 10 and the fixing unit 30 is about 0.1% in the transfer unit 10 as a result obtained from experience or experiments so far. In unit 30, it is about 0.3%. The main causes of variations in the sheet conveyance speed in the transfer unit 10 include variations in the belt thickness of the conveyance belt 12 and the roller diameter of the driving roller Ra. In addition, the main causes of variations in the sheet conveyance speed in the fixing unit 30 include variations in the roller diameter and hardness of the pressure roller 30a, nip load, and the like. Generally, the fixing unit is larger than the transfer unit 10 side. It is said that the variation in the paper conveyance speed on the 30th side is large.

  Regarding the above description, specific numerical values will be described in the same manner as in the first embodiment.

  For example, as shown in FIG. 8, in a state where the paper P is not loose and stretched, the heating roller 30a rotates at the rotational speed R2, and the paper P is transported at the paper transport speed VT2 (150.75 mm / sec). At this time, the heating roller 30a rotates 1.200 per second, and the slit disk count detection unit 53 outputs a detection signal of 1727 Plus (863 Plus in 500 msec) to the print control unit 700, but the fixing unit Considering a variation of ± 0.3% of 30, in the fixing unit 30 having a high paper conveyance speed, a signal of 865 Plus is output at 500 msec when the variation is + 0.3%. On the other hand, in the fixing unit 30 having a low paper conveyance speed, an 861 Plus signal is output in 500 msec when the variation is −0.3%.

  Further, as shown in FIG. 9, in the state where the slack of the paper P is eliminated and the tension is increased, the heating roller 30a rotates at the rotational speed R1, and the paper P is transported at the paper transport speed VT1 (150.00 mm / sec). At this time, the heating roller 30a rotates 1.194 per second, and the slit disk count detection unit 53 outputs a signal of 1718 Plus (859 Plus in 500 msec) to the print control unit 700, but the transfer unit 10 When the variation of ± 0.1% is taken into consideration, the transfer unit 10 having a high paper conveyance speed outputs a signal of 860 Plus at 500 msec when the variation is + 0.1%. On the other hand, in the transfer unit 10 having a low paper conveyance speed, a 858 Plus signal is output at 500 msec when the variation is −0.1%.

  Next, the operation of the printer having such a configuration will be described. First, the print control unit 700 instructs the fixing unit drive control unit 71 to drive at a driving speed D0 that is slower than the normal driving speed D2. Here, the sheet conveyance speed of the fixing unit 30 is VT0, which is lower than the sheet conveyance speed VH1 of the transfer unit 10. Therefore, the paper P forms a slack between the transfer unit 10 and the fixing unit 30. When a predetermined time elapses, the slack of the paper P between the two units becomes the largest as shown in FIG.

  Next, the print control unit 700 instructs the driving speed D2 to the fixing unit drive control unit 71. Then, the heating roller 30a rotates at the rotational speed R2, and the paper P is transported at the paper transport speed VT2. The print control unit 700 determines the sheet conveyance speed in the fixing unit 30 from the number of output signals from the slit disk count detection unit 53 during a predetermined time when the sheet is conveyed at the sheet conveyance speed VT2.

  Specifically, for example, when the count number per 500 msec is 861 Plus, the print control unit 700 determines that the fixing unit 30 has a low paper conveyance speed, and when the count number per 500 msec is 865 Plus, printing is performed. The control unit 700 determines that the fixing unit 30 has a high sheet conveyance speed.

  Similarly, the print control unit 700 determines the sheet conveyance speed in the transfer unit 10 from the count number of the output signal from the slit disk count detection unit 53 during a predetermined time when the sheet is conveyed at the sheet conveyance speed VT1.

  Specifically, for example, when the count number per 500 msec is 858 Plus, the print control unit 700 determines that the transfer unit 10 has a low paper conveyance speed, and when the count number per 500 msec is 859 Plus, printing is performed. The control unit 700 determines that the transfer unit 10 has a medium conveyance speed, and if the count per 500 msec is 860 Plus, the print control unit 700 determines that the transfer unit 10 has a high sheet conveyance speed. To do.

  Here, for example, in the case of a combination of the fixing unit 30 (861 Plus) having a low paper conveyance speed and the transfer unit 10 (860 Plus) having a high paper conveyance speed, the difference in paper conveyance speed between the two units is about 0. Since it is as small as 1%, the sheet conveyance does not become unstable when the sheet conveyance speed changes.

  In contrast, in the case of the combination of the fixing unit 30 (865 Plus) having a high paper conveyance speed and the transfer unit 10 (858 Plus) having a low paper conveyance speed, the speed of the paper conveyance speed between the two units is about 0. Since it is as large as .9%, the sheet conveyance becomes unstable when a change occurs in the sheet conveyance speed. Therefore, for example, when the print quality is deteriorated or the perforation strength is weak in the paper P having the perforation, the paper P may be torn when it is in a stretched state. In order to prevent such paper conveyance from becoming unstable, when it is determined that the paper conveyance speed of the fixing unit 30 is high (865 Plus), the print control unit 700 reduces the paper conveyance speed of the fixing unit 30 to approximately An instruction is given to the fixing unit drive control unit 71 so that it is delayed by 0.6%, that is, the count number in a predetermined time is 861 Plus.

  As described above, according to the second embodiment, in addition to the effects of the first embodiment, when the paper transport speed of the attached fixing unit is fast, the paper transport speed of the fixing unit is controlled to be slow. Thus, the difference in paper conveyance speed between the transfer unit and the fixing unit can be reduced, and stable paper conveyance can be achieved even when a change occurs in the paper conveyance speed.

  In the description of the second embodiment, the control of the sheet conveyance speed of the fixing unit has been described. However, the present invention is not limited to this, and the transfer unit and the fixing unit are controlled by controlling the sheet conveyance speed of the transfer unit. It is of course possible to reduce the difference in sheet conveyance speed between the two.

  In the description of the embodiments of the present invention, the printer is described as an example of the image forming apparatus. However, the present invention is not limited to this, and can be applied to an image forming apparatus such as a copying machine or a facsimile.

DESCRIPTION OF SYMBOLS 10 Transfer unit 11 Waste toner box part 12 Conveyor belt 20 Paper storage part 22 Paper cassette 23 Paper feed roller 24 Registration roller 26C, 26M, 26Y, 26BK Image forming unit 27C, 27M, 27Y, 27BK Transfer roller 28C, 28M, 28Y, 28BK LED head 30 Fixing unit 30a Heating roller 30b Pressure roller 31 Discharge roller 32 Paper stacker 40 Halogen lamp 41 Fixed wiring 42 Fixing unit frame 50 Heating roller gear 51 Fixing unit drive gear 52 Slit disk 52a Slit 53 Photocoupler sensor, Slit disk Count detection unit 71 Fixing unit drive control unit 72 Fixing unit drive motor 81 Transfer unit drive control unit 82 Transfer unit drive motor 10 The printer 700 print controller

Claims (10)

A transport unit for transporting the medium on which the developer image is transferred by the image forming unit;
A fixing unit that is disposed downstream of the transport unit in the medium transport direction, fixes the image on the transported medium, and transports the medium;
A detection unit for detecting a change in the conveyance speed of the medium in the fixing unit;
An image forming apparatus comprising: a control unit that changes a driving speed of the driving unit of the conveyance unit or the fixing unit based on a detection result of the detection unit. The controller is
The drive speed of the drive unit of the fixing unit is changed from a drive speed higher than a drive speed of the drive unit of the transport unit to a slow drive speed based on a detection result of the detection unit. Image forming apparatus. 2. The image formation according to claim 1, wherein the conveyance speed of the medium in the fixing unit is a conveyance speed faster than a medium conveyance speed of the conveyance unit arranged upstream in a medium conveyance direction in a default state. apparatus. In the default state, when the detection unit detects that the conveyance speed of the medium in the fixing unit becomes a low conveyance speed due to occurrence of tension of the medium, the control unit The image forming apparatus according to claim 3, wherein the conveyance speed of the medium is controlled to a conveyance speed that is slower than the medium conveyance speed of the conveyance unit disposed upstream in the medium conveyance direction. The image forming apparatus according to claim 1, wherein the driving unit of the fixing unit includes a DC motor. A transport step for transporting the medium having the developer image transferred thereon by the image forming means;
A fixing step that is arranged downstream of the image forming unit in the medium conveying direction and fixes the image on the conveyed medium, and conveys the medium;
A detection step of detecting a change in the conveyance speed of the medium in the fixing step;
A medium transporting method comprising: a control step of changing a driving speed of the transporting step or the fixing step based on a detection result in the detecting step. The control step includes
The medium conveying method according to claim 6, wherein the driving speed in the fixing process is changed from a driving speed higher than a driving speed in the conveying process to a slower driving speed based on a detection result in the detecting process. The medium conveyance method according to claim 6, wherein the conveyance speed of the medium in the fixing step is a conveyance speed faster than the medium conveyance speed in the conveyance step in a default state. In the default state, when it is detected in the detection step that the medium conveyance speed in the fixing step is a low conveyance speed due to the occurrence of tension of the medium, the control step includes the step in the fixing step. The medium conveyance method according to claim 6, wherein the medium conveyance speed is controlled to be a conveyance speed slower than the medium conveyance speed in the conveyance step. The medium conveying method according to claim 6, wherein the driving unit that is driven in the fixing step includes a DC motor.