JP2016180981A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a change in conveyance speed irrespective of the length in a direction of conveyance of recording sheets.SOLUTION: At a conveyance force applying point 2, the conveyance speed of large size sheet 38 is set slower than the conveyance speed of small size sheet 38 (adjustment 1), and a difference in conveyance speed between the conveyance force applying point 2 and a conveyance force applying point 3 is set small (adjustment 2). The large size sheet takes long time for the leading end of the sheet to reach the conveyance force applying point 3 compared with the small size sheet, which delays a time point for the large size sheet to depend on the conveyance speed at the conveyance force applying point 3. As a result, an error to a proper average magnification is reduced, and a reduction in margin at the rear end part of the sheet 38 is avoided.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus.

  Japanese Patent Application Laid-Open No. H10-228561 describes that the linear velocity by the conveyance driving unit is determined based on at least one of the type, size, and fixing of the paper.

  Japanese Patent Application Laid-Open No. 2004-228688 defines that the width of a conveyance sheet (the direction orthogonal to the sheet conveyance direction) is defined, and that the rotational conveyance speed of the transfer body is determined according to the density of an image to be developed. ing.

  Patent Document 3 describes that the rotation speed of the paper transport motor is changed according to the size or thickness of the paper to be passed.

JP 2002-287444 A JP 2005-345531 A Japanese Patent Laid-Open No. 2004-117397

  When the conveyance speed is applied to the paper at a plurality of locations in the conveyance path, and the conveyance speed applied on the upstream side and the downstream side is different, thereby applying tension or slack to the recording paper to stabilize the conveyance speed. If the length in the transport direction exceeds a certain amount, the balance of tension or slack applied to the paper may be lost, and the transport speed may become unstable.

  In view of the above facts, an object of the present invention is to obtain an image forming apparatus capable of suppressing fluctuations in the conveyance speed regardless of the length of the recording medium in the conveyance direction.

  According to a first aspect of the present invention, there is provided a classifying unit that classifies a recording medium having a predetermined grammage or more according to a length in a conveying direction, and a transfer that transfers an image developed on the image carrier to the recording medium. And a fixing unit that fixes an image transferred downstream of the transfer unit, a conveying unit that applies a conveying force to the recording medium at at least two positions, and a recording medium that is conveyed by the conveying unit includes the classification unit Setting means for setting the conveyance speed by the conveyance means so that the conveyance speed at the fixing unit is faster than the conveyance speed at the transfer unit when the length in the conveyance direction is classified as a reference length. When the recording medium conveyed by the conveying means is classified into a recording medium whose length in the conveying direction is longer than a reference length by the classification means, the magnitude relationship of the conveying speed set by the setting means is maintained. However, conveyance at the transfer unit and the fixing unit It has a correction means for correcting time the to slow respectively, the.

  The invention described in claim 2 further includes a type classification unit that classifies the recording medium according to type based on a basis weight of the paper in the invention according to the first aspect, and the setting unit is more than the recording medium. When transporting plain paper having a small basis weight, the transport speed of the fixing unit is set to a transport speed slower than the transport speed of the transfer unit.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the correction unit is configured such that an average value of the conveyance speed of the recording medium at the transfer unit is a desired conveyance speed. Correct as follows.

  According to a fourth aspect of the present invention, there is provided a classifying unit that classifies a recording medium having a predetermined basis weight or more according to a length in a conveying direction, and a transfer that transfers an image developed on the image carrier to the recording medium. And a fixing unit that fixes an image transferred downstream of the transfer unit, a conveying unit that applies a conveying force to the recording medium at at least two positions, and a recording medium that is conveyed by the conveying unit includes the classification unit Setting means for setting the conveyance speed by the conveyance means so that the conveyance speed at the fixing unit is faster than the conveyance speed at the transfer unit when the length in the conveyance direction is classified as a reference length. And a detection unit that detects a load of a driving source of the conveyance unit that applies conveyance force in the transfer unit, and a recording medium that is conveyed by the conveyance unit has a length in the conveyance direction that is longer than a reference length by the classification unit. If it is classified as a long recording medium, A correction unit that corrects the transfer unit and the fixing unit so as to slow down the conveyance speed while maintaining the magnitude relationship between the conveyance speeds set in (2) and the detection unit during the conveyance of the recording medium. And a control means for controlling the respective transport speeds so that the transport speeds at the transfer section and the fixing section coincide with each other.

  According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the control unit sets the transfer speed of the transfer unit and the fixing unit to a process speed that is a reference for a preset image forming process. The transfer section conveyance speed is controlled with a negative tolerance with respect to the process speed, and the fixing section conveyance speed has a plus tolerance with respect to the process speed. Control.

  According to the first aspect of the present invention, fluctuations in the conveyance speed can be suppressed regardless of the length of the recording medium in the conveyance direction.

  According to the second aspect of the present invention, the conveyance speed fluctuation can be suppressed regardless of the type of the recording medium.

  According to the third aspect of the present invention, the average value of the conveyance speed of the recording medium at the reference position can be set to a desired conveyance speed.

  According to the fourth aspect of the present invention, the conveyance speed fluctuation can be suppressed regardless of the length of the recording medium in the conveyance direction.

  According to the invention described in claim 5, the reverse phenomenon of the speed difference can be avoided.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. 2 is an enlarged view of an image forming unit and a peripheral paper transport unit of the image forming apparatus according to the first embodiment. FIG. 2 is a block diagram showing a control system of the image forming apparatus according to the first embodiment. FIG. It is a flowchart which shows the conveyance speed and exposure period setting control routine which concern on 1st Embodiment. 6 is a chart showing a transfer speed transition in the thick paper mode according to the first embodiment, where (A) is a small size (A4 horizontal thick paper) and (B) is a large size (A3 vertical thick paper). Indicates. 10 is a chart showing a conveyance speed transition in a thick paper mode according to Modification 1, wherein (A) shows a small size (A4 horizontal thick paper) and (B) shows a large size (A3 vertical thick paper). FIG. 6 is an enlarged view of an image forming unit and a surrounding paper transport unit of an image forming apparatus according to a second embodiment. It is a flowchart which shows the electric current monitoring control routine which concerns on 2nd Embodiment. 10 is a chart showing a transfer speed transition in the thick paper mode according to the second embodiment, where (A) is a small size (A4 horizontal thick paper) and (B) is a large size (A3 vertical thick paper). Indicates. It is a schematic block diagram of the image forming apparatus (full-color image forming apparatus) which concerns on the modification 2.

(First embodiment)
FIG. 1 schematically shows an image forming apparatus 10 according to the first embodiment.

  In the image forming apparatus 10, an image forming unit 14, a sheet conveying unit 16 that conveys a sheet 38 that is an example of a recording medium, and an MCU 18 that controls the image forming unit 14 are provided in a housing 12. The MCU 18 is connected to a main controller 20 that controls the entire image forming apparatus 10.

(Image forming unit 14)
FIG. 2 shows a schematic diagram of the image forming unit 14 and the sheet conveying unit 16.

  The image forming unit 14 includes a photosensitive drum 22 that rotates at a constant speed in the direction of arrow A in FIG.

  Around the photosensitive drum 22, along the rotation direction of the photosensitive drum 22 (clockwise direction indicated by an arrow A in FIG. 2), the charger 24, the exposure unit 26, the developing unit 28, the transfer roll 30, and the cleaner 32 and an erase lamp 34 are arranged in this order. Hereinafter, the charger 24, the exposure unit 26, the developing unit 28, the transfer roll 30, the cleaner 32, and the erase lamp 34 may be collectively referred to as an image forming unit. An LED printer head (LPH) is applied to the exposure unit 26, and in the following, the exposure unit 26 may be referred to as an LPH 26.

  The surface of the photosensitive drum 22 is uniformly charged by the charger 24 and then irradiated with a light beam by the LPH 26 to form a latent image on the photosensitive drum 22. The LPH 26 is controlled to emit light by the LPH driving unit 36 and emits a light beam based on image data.

  To the latent image formed on the photosensitive drum 22 by the light beam, toner is supplied by the developing unit 28, and a toner image is formed on the photosensitive drum 22.

  The toner image on the photosensitive drum 22 is transferred to a sheet 38 as a recording medium by a transfer roll 30. Hereinafter, the region where the toner image is transferred may be referred to as “transfer portion TR”.

  The toner remaining on the photosensitive drum 22 after the transfer at the transfer portion TR is removed by the cleaner 32, neutralized by the erase lamp 34, and then charged again by the charger 24, and the same image forming process is performed. It is possible to repeat.

  On the other hand, the paper 38 on which the toner image is transferred by the transfer unit TR is conveyed to a fixing device 40 including a pressure roller 40A and a heating roller 40B, and subjected to a fixing process. As a result, the toner image is fixed and a desired image is formed on the paper 38. The paper 38 on which the image is formed is discharged out of the apparatus.

  The photosensitive drum 12 is not directly transferred onto the paper, but is primarily transferred onto an intermediate transfer member (formed by a belt or a drum), and then secondary transferred onto the paper (corresponding to the transfer at the transfer unit TR). ).

  In the case of a color image, a plurality of image forming units (for example, four for each color of CMYK) are arranged, and a toner image of each color is superimposed on the intermediate transfer belt and transferred (primary transfer), and then the paper 38 is transferred by the transfer unit TR. (Secondary transfer) and fixing processing.

(Details of transport system of paper 38)
As shown in FIG. 1, the image forming apparatus 10 is equipped with a multi-stage supply device 82 that supplies the paper 38 to the image forming unit 14. Each of the supply devices 82 can be pulled out to the front side (left side in FIG. 1) of the image forming apparatus 10, and the paper 38 is loaded (supplemented) in a state where the supply device 82 is pulled out from the image forming apparatus 10.

  The supply device 82 includes different storage containers 84 that store paper such as plain paper and cardboard for each type. As the type of the paper 38, for example, A3 plain paper, A3 thick paper, A4 plain paper, and A4 thick paper are loaded in accordance with the user's selection in order from the top.

  The supply device 82 has a transport roll 86 that takes out the uppermost paper 38 stored in the storage container 84 and transports the taken-out paper 38 toward the image forming unit 14.

  As shown in FIGS. 1 and 2, the image forming apparatus 10 is formed with a paper transport unit 16 used for transporting the paper 38. The paper transport unit 16 includes a main transport path 88, a reverse transport path 90, and a sub transport path 91.

  The main conveyance path 88 is used for conveying the paper 38 supplied from any of the supply devices 82 to the image forming unit 14 and discharging the paper 38 on which an image has been formed to the outside of the image forming apparatus 10.

  Along the main conveyance path 88, in order from the upstream side in the direction in which the paper 38 is conveyed, a conveyance roll 86, a registration roll 92, a transfer roll 30, and a fixing device 40 (pressure roller 40A and heating roller 40B). A discharge roll 94 is disposed.

  For example, the registration roll 92 is temporarily stopped in a state where the leading end of the sheet 38 conveyed from the supply device 82 side is sandwiched, and the sheet 38 is matched with the timing at which the toner image is transferred to the transfer unit TR. To the transfer roll 30.

  The discharge roll 94 discharges the paper 38 on which the toner of each color is fixed by the fixing device 40 to the outside of the image forming apparatus 10.

  The reverse conveyance path 90 is a conveyance path that is used for supplying the paper 38 having the toner image fixed on one side thereof to the image forming unit 14 again while reversing.

  For example, a pair of reverse transfer rolls 96 are appropriately arranged along the reverse transfer path 90. In the reverse conveyance path 90, the paper 38 is supplied from the rear end side by the reverse rotation of the discharge roller 94 with the discharge roller 94 sandwiching the rear end of the paper 38, and the supplied paper 38 is supplied to the reverse conveyance path 90. The paper is conveyed to a position upstream of the registration roll 92 by the reverse conveyance rolls 96 and 96.

  The sub-transport path 91 is a transport path for supplying the image forming unit 14 with a sheet 38 different from the sheet 38 stored in the supply device 82. The paper 38 is supplied to the sub-transport path 91 from the left side of FIG. 1 of the image forming apparatus 10 with the supply opening / closing section 98 opened. A transport roll 99 is provided in the sub transport path 91. The transport roll 99 transports the paper 38 supplied to the sub transport path 91 toward the image forming unit 14.

(Engine control system)
FIG. 3 is a block diagram of a control system of the image forming apparatus.

  A user interface 42 is connected to the main controller 20, and an instruction regarding image formation or the like is given by a user's operation, and information on image formation or the like is notified to the user.

  The main controller 20 is connected to a network line with an external host computer (not shown) so that image data is input via the network line.

  When the image data is input, the main controller 20 analyzes, for example, the print instruction information included in the image data and the image data, and converts them into a format suitable for the image forming unit 14 (for example, bitmap data). The converted image data is sent to the image formation processing control unit 44 that functions as a part of the MCU 18.

  In the image formation processing control unit 44, based on the input image data, together with the image formation processing control unit 44, a drive system control unit 46, a charge control unit 48, and an exposure control as an example of a conveyance control device that functions as the MCU 18. Each of the image forming unit 50, the transfer control unit 52, the fixing control unit 54, the charge removal control unit 56, the cleaner control unit 58, and the development control unit 60 is synchronously controlled to execute image formation. In the first embodiment, the functions executed by the MCU 18 are classified and described as blocks, and the hardware configuration of the MCU 18 is not limited.

  The LPH driving unit 36 is controlled by the exposure control unit 50.

  The main controller 20 is connected to a temperature sensor 62, a humidity sensor 64, and the like, and may detect the environmental temperature / humidity in the housing 12 of the image forming apparatus 10 based on the temperature sensor 62 and the humidity sensor 64. . The main control 20 functions as a first classification unit, a second classification unit, a setting unit, and a correction unit, for example.

(Conveying speed control of paper 38)
The drive system control unit 46 shown in FIG. 3 controls the conveyance speed of the paper 38 in the paper conveyance unit 16.

  In the image forming apparatus 10 according to the first embodiment, as shown in FIG. 2, when the paper 38 is conveyed by the main conveyance path 88, conveyance force is applied at the following three conveyance force application points.

  (Conveying force application point 1) The paper 38 is sandwiched between the registration rolls 92, and is applied with a conveying force having a linear velocity vr depending on the rotation speed of the registration rolls 92.

  (Conveying force application point 2) The sheet 38 is sandwiched between the photosensitive drum 22 and the transfer roll 30 in the transfer unit TR, and is provided with a conveying force having a linear velocity vb depending on the rotational speeds of the photosensitive drum 22 and the transfer roll 30. Is done. The transfer roll 30 is a driven roller.

  (Conveying force application point 3) The sheet 38 is sandwiched between the pressure roller 40A and the heating roller 40B of the fixing device 40, and is imparted with a conveying force having a linear velocity vf depending on the rotation speed of the pressure roller 40A and the heating roller 40. Is done.

  Here, when the plain paper and the thick paper are compared as the types of paper 38, the plain paper has a conveyance force application point 2 (photosensitive drum 22 and transfer roll 30) and a conveyance force application point 3 (fixing device 40). In some cases, paper conveyance unevenness due to tensile force or twisting may occur, resulting in paper damage (paper wrinkles).

  Therefore, in the case of plain paper, the linear velocity is decreased toward the downstream side, and the paper 38 is conveyed so that the paper 38 sags (a loop is formed) between the respective conveyance force application points 1 to 3 (vr> vb). > Vf).

  On the other hand, in the case of thick paper, when a sheet deflection (loop) is formed between the conveyance force application points 1 to 3, the conveyance force application point 2 (the photosensitive drum 22 and the transfer roll 30) due to the stiffness of the paper 38. ) And the conveying force application point 3 (fixing device 40), there is a case where a force to return to a straight line is applied, which is not stable.

  Therefore, in the case of thick paper, the linear velocity is increased toward the downstream side, and the paper 38 is conveyed so as to be pulled between the respective conveyance force application points 2 and 3 (vb <vf). It should be noted that the downstream side may be slower between the conveyance force application point 1 (registration roll 92) and the conveyance force application point 2 (photosensitive drum 22 and transfer roll 30) as in the case of plain paper (vr> vb).

  In Table 1, the relative relationship of the conveyance speed (linear velocity) in the conveyance force provision points 1-3 is shown using a specific numerical value.

なお、表１の数値は、相対的な差を示すだけの一例であり、第１の実施の形態の各搬送付与点１〜３における搬送速度（線速度）は、当該数値に限定されるものではない
また、第１の実施の形態では、搬送力付与点１と搬送力付与点３の駆動源（一例として、図２に示す、搬送手段の一例であるモータＭ１）は共通であり、それぞれ変速機Ｇｆ、Ｇｒによって目的の搬送速度ｖｆ、ｖｒを設定している。一方、搬送力付与点２の駆動源（一例として、図２に示す、搬送手段の一例であるモータＭ２）は独立しており、変速機Ｇｂによって目的の搬送速度ｖｂを設定している。

In addition, the numerical value of Table 1 is an example which only shows a relative difference, and the conveyance speed (linear velocity) in each conveyance provision points 1-3 of 1st Embodiment is limited to the said numerical value. In addition, in the first embodiment, the driving sources for the conveying force application point 1 and the conveying force applying point 3 (for example, the motor M1 as an example of the conveying means shown in FIG. 2) are common, The target transport speeds vf and vr are set by the transmissions Gf and Gr. On the other hand, the driving source of the conveying force application point 2 (for example, the motor M2 as an example of the conveying means shown in FIG. 2) is independent, and the target conveying speed vb is set by the transmission Gb.

  For this reason, in Table 1, the speed change ratios of the conveyance force application point 1 and the conveyance force application point 3 are the same, but if the drive sources are independent from each other, the conveyance force application point 1 and the conveyance force application are particularly provided. It is not necessary for the speed change ratios of point 3 to be the same.

(Conveyance speed control based on paper length in thick paper mode)
In the above, by adjusting the conveyance speeds of the three conveyance force application points 1 to 3 in the type of the paper 38 (plain paper and thick paper), conveyance suitable for each paper quality (paper type) is executed.

  On the other hand, the paper 38 has various sizes apart from paper quality (paper type) such as plain paper and thick paper.

  In the transport speed control shown in Table 1 above, when transporting the downstream side faster than the upstream side (vb <vf) as in the thick paper mode, the transport is initially performed at the target transport speed (transport force application point 2). The

  However, the degree of dependence on the downstream conveyance speed (conveying force application point 3) gradually increases (acceleration), and the average magnification (vertical magnification) in the paper conveyance direction tends to increase. In particular, the acceleration that depends on the conveyance force application point 3 becomes significant after the trailing edge of the paper 38 leaves the registration roll 92 at the conveyance force application point 1.

  The average magnification (vertical magnification) in the paper conveyance direction is the actual image formation with respect to the length (target value) from the main scanning line position at the start of image formation to the main scanning line position at the end of image formation. It is the ratio of length (actual value).

  For example, when the vertical magnification is high, the length from the main scanning line position at the start of image formation to the main scanning line position at the end of image formation is increased, and the margin is reduced.

  Therefore, the A3 size (vertical orientation) is twice as long in the transport direction as the A4 size (horizontal orientation), and the average vertical magnification, which was acceptable in the A4 size (horizontal orientation), is A3 size (vertical orientation). ) Deviates from the permissible range, and as a result, the margin at the trailing edge of the paper 38 in the transport direction becomes narrower than the A4 size (landscape).

  Therefore, in the first embodiment, the following adjustment is performed according to the paper size in the transport control in the thick paper mode.

  (Adjustment 1) The conveyance speeds vb and vf set for the conveyance force application point 2 and the conveyance force application point 3 in the A3 vertical size paper 38 are set to the conveyance force application point 2 and the conveyance force application point 3 in the A4 horizontal size paper 38, respectively. It is slower than the conveyance speeds vb and vf set to.

  (Adjustment 2) The conveyance speed difference Δv (= | vb−vf |) between the conveyance force application point 2 and the conveyance force application point 3 is set to be small.

  Note that the relative speeds (vb <vf, vr> vb) of the conveyance force application point 1 to the conveyance force application point 3 are maintained in the conveyance control in the thick paper mode.

  In the adjustment 1, the tension generation (conveyance of tension) between the conveyance force application point 2 and the conveyance force application point 3 in the A3 vertical size thick paper 38 is set to the A4 horizontal size thick paper 38. Compared to, it has a function to delay.

  The adjustment 2 has a function of adjusting the average vertical magnification in the transport direction so as to approach the average magnification (process speed) in the plain paper mode.

  By the adjustment 1 and the adjustment 2, the conveyance speed fluctuation is suppressed regardless of the length of the paper 38 in the conveyance direction.

  Table 2 shows the conveyance speed ratio of each portion when the conveyance speed of the plain paper conveyance force application point 2 (that is, the transfer portion TR) is 100%. In addition, this conveyance speed ratio is an example and is not limited to the said numerical value.

この表２によれば、厚紙モードの搬送制御において、Ａ４横サイズの用紙３８の搬送力付与点２は９９．８％、搬送力付与点３は１００．６％で、速度差が０．８ポイントとなっている。

According to Table 2, in the transport control in the thick paper mode, the transport force application point 2 of the A4 landscape paper 38 is 99.8%, the transport force application point 3 is 100.6%, and the speed difference is 0.8. It is a point.

  On the other hand, in the transport control in the thick paper mode, the transport force application point 2 of the A3 vertical size paper 38 is 99.7%, the transport force application point 3 is 100.3%, and the speed difference is 0.6 points. .

  According to Table 2, in the transport control in the thick paper mode, the transport force application point 2 for the A4 landscape paper 38 is 99.8%, whereas the transport force application point 2 for the A3 portrait paper 38 is It is 99.7%, and the conveyance speed is 0.1 points slower.

  Further, in the transport control in the thick paper mode, the transport force application point 3 of the A4 landscape paper 38 is 100.6%, whereas the transport force application point 2 of the A3 portrait paper 38 is 100.3%. Yes, the transport speed is 0.3 points slower.

  Further, the speed difference between the conveyance force application point 2 and the conveyance force application point 3 is 0.8 points for the A4 landscape paper 38, and 0.6 points for the A3 portrait paper 38. The speed difference Δv is small.

  The operation of the first embodiment will be described below.

  First, the procedure of the image forming process will be described.

  Image data received from the outside by the main controller 20 is converted into, for example, gradation data, and is output to the image forming unit 14 via the MCU 18 (exposure control unit 50). In the image forming unit 14, LPH is driven by the LPH driving unit 36 in accordance with the gradation data to emit exposure light, and the photosensitive drum 22 is scanned and exposed to form a latent image (electrostatic latent image).

  The electrostatic latent image formed on the photosensitive drum 22 is visualized as a toner image by the developing device 28 (development). The toner image formed on the photosensitive drum 22 is transferred to the paper 38 by the transfer roll 30.

  The toner images of the respective colors on the paper 38 are fixed by the fixing device 40, and the paper 38 after fixing is discharged out of the apparatus (single-sided printing process), or the discharge roller 94 sandwiches the rear end portion of the paper 38. In this state, it is sent to the reverse conveyance path 90 (double-sided printing process).

  Residual toner, paper dust, and the like are removed from the surface of the photosensitive drum 22 after the toner image transfer process is completed. It is uniformly charged during the next image forming process.

  The paper 38 (the paper 38 on which image formation on the front surface has been completed) sent to the reverse conveyance path 90 is carried out by rotating the discharge roller 94 in the reverse direction with the discharge roller 94 sandwiching the rear end portion of the paper 38. 38 is supplied from the rear end side, and the supplied paper 38 is conveyed by the reverse conveying rolls 96, 96 to a position upstream of the registration roll 92 with the front and back sides reversed.

  As a result, image formation on the back surface is executed in the same manner as in the image forming process described above, fixed by the fixing device 40, and the paper 38 after fixing is discharged out of the apparatus.

  Next, a conveyance speed setting control routine for controlling the conveyance speed according to the type and size of the paper 38 will be described with reference to the flowchart of FIG. In the first embodiment, the setting of the conveyance speed at the time of image formation is executed by the main controller 20 and is set in each part of the MCU 18, but may be executed by the MCU 18.

In step 100, for example, the type of the paper 38 selected for image formation by the input operation using the user interface 42 is plain paper (small basis weight, for example, about 60 to 80 g / m ² ) or thick paper ( It is determined whether the basis weight is large (for example, about 100 g / m ² or more).

  In the first embodiment, since the grammage is proportional to the degree of stiffness of the paper, it is a requirement for the criteria for judging the paper type, but the degree of stiffness of the paper is equivalent to the basis weight. A criterion that is correlated with the above may be applied. In other words, in the first embodiment, “basis weight” is applied as a general term for the paper type determination criterion.

(Plain paper selection)
When it is determined that the paper is plain paper in step 100, the process proceeds to step 102, and the transport speeds vr, vb, vf at the respective transport force application points 1 to 3 based on the plain paper are read. In the case of plain paper, the relationship between the conveyance speeds is vr>vb> vf (see Table 1).

  In the next step 104, the plain paper transport speeds vr, vb, vf read in step 102 are set in the drive system control unit 46 of the MCU 18, and the process proceeds to step 118.

  In step 118, the end of setting of the conveyance speeds vr, vb, and vf is notified to the MCU 18, and this routine ends.

  In the MCU 18, the above-described image forming process is executed based on the set plain paper transport speeds vr, vb, and vf.

(Cardboard selection)
When it is determined that the paper is thick in Step 100, the process proceeds to Step 120, and the conveyance speeds vr, vb, and vf at the respective conveyance force application points 1 to 3 based on the thick paper are read. In the case of thick paper, the relationship between the conveyance speeds is vr> vb and vb <vf (see Table 1).

  In the next step 122, the size of the conveyed paper 38 is determined. In the first embodiment, the A4 horizontal thick paper 38, which has a relationship of “small size” and “large size”, is set to the small size, and the A3 vertical thick paper 38 is set to the large size. . Note that the relationship between “small size” and “large size” is relative and does not limit the absolute size. For example, between the A5 horizontal size and the A4 horizontal size, the A5 size horizontal can be “small size” and the A4 horizontal size can be “large size”.

  If it is determined in step 122 that the size is large (here, A3 vertical thick paper 38), the process proceeds to step 124, and the speed vb of the small size (here, A4 horizontal thick paper 38) is reached. On the other hand, the conveyance speed vb at the conveyance force application point 2 is decreased (Adjustment 1).

  Next, the routine proceeds to step 126, where the conveyance speed difference Δv (| vb−vf |) between the conveyance force application point 2 and the conveyance force application point 3 is reduced with respect to the small size speed Δv (Adjustment 2). ), The process proceeds to step 128.

  If the result of determination in step 122 is a small size (here, A4 wide thick paper 38), the process proceeds to step 128 without adjusting the conveyance speed.

  In step 128, the cardboard transport speeds vr, vb, and vf read in step 120 and adjusted in steps 124 and 126 as necessary are set in the drive system control unit 46 of the MCU 18, and the process proceeds to step 118. Transition.

  In step 118, the end of setting of the conveyance speeds vr, vb, and vf is notified to the MCU 18, and this routine ends.

  In the MCU 18, the above-described image forming processing is executed based on the set thick paper transport speeds vr, vb, and vf.

(Conveying speed control by paper type)
According to the first embodiment, the conveyance force is applied from three places to the paper 38 passing through the image forming unit 14 (conveyance force application points 1 to 3).

  In the case of plain paper, as shown in Table 1, the linear velocity is decreased toward the downstream side so that the paper 38 sags (forms a loop) between the respective conveying force application points 1 to 3. (Vr> vb> vf).

  As a result, the occurrence of uneven paper conveyance due to tensile force or twisting between the conveyance force application point 2 and the conveyance force application point 3 is suppressed.

  On the other hand, in the case of thick paper, as shown in Tables 1 and 2, the linear velocity is increased toward the downstream side so that the paper 38 is pulled between the respective conveyance force application points 2 and 3. (Vb <vf). It should be noted that the downstream side may be slower between the conveyance force application point 1 (registration roll 92) and the conveyance force application point 2 (photosensitive drum 22 and transfer roll 30) as in the case of plain paper (vr> vb).

  As a result, the paper 38 is transported without being bent, and therefore, a force for returning to the straight line between the transport force application point 2 and the transport force application point 3 works depending on the stiffness of the paper 38. Is suppressed.

(Conveying speed control based on paper length "Thick paper")
In the first embodiment, adjustment is made according to the paper size in the transport control in the thick paper mode.

  That is, at the transport speed vb set at the transport force application point 2, the transport speed of the A3 vertical size paper 38 is set slower than the transport speed of the A4 horizontal size paper 38 (Adjustment 1).

  Further, the conveyance speed difference Δv (= | vb−vf |) between the conveyance force application point 2 and the conveyance force application point 3 is set small (Adjustment 2).

  Specific examples of the adjustment 1 and the adjustment 2 are shown in Table 2, and the transition of the conveyance speed of the paper 38 based on the conveyance speed control in Table 2 is shown in FIG.

"Thick paper mode, A4 landscape size"
FIG. 5A shows the transition of the transport speed when the A4 landscape-sized thick paper 38 is transported in the thick paper mode (see the thick solid line A in FIG. 5A). First, the thick paper mode is set. By doing so (vb <vf), the occurrence of image displacement (smear) due to the impact at the time when the trailing end of the sheet 38 in the conveyance direction passes through the registration roll 92 (detachment from the conveyance force application point 1) is suppressed. The

  As a reference, when the A4-sized thick paper 38 is transported in the plain paper mode, when the rear end portion in the transport direction of the paper 38 passes through the registration roll 92 (separates from the transport force application point 1), the abrupt Speed fluctuations may occur and image shift (smear) may occur.

  Further, when the leading end of the sheet 38 in the conveyance direction reaches the conveyance force application point 3, there is a slack in the sheet 38 between the conveyance force application point 2 and the conveyance force application point 3. However, due to the relationship of vb <vf, this slack disappears, and the conveyance speed of the paper 38 gradually increases from the time when the tension (tensile force) is applied.

  However, in the case of A4 wide-sized thick paper 38, the conveyance of the paper 36 is completed before the average magnification is deteriorated, so that the margin at the rear end of the paper 38 exceeds the allowable range and decreases. No (maintain proper state).

  Here, FIG. 5A shows a transfer speed transition when a thick sheet 38 of A3 vertical size is transferred as a comparative example (see a thin solid line B).

  The A3 vertical size thick paper 38 is transported in the latter half of the transport depending on the transport speed vf at the transport force application point 3 as compared to the A4 horizontal size thick paper 38. The error with respect to the appropriate average magnification (see the one-dot chain line L in FIG. 5A) is accumulated, and the margin at the rear end of the paper 38 is reduced.

"Thick paper mode, A3 vertical size"
FIG. 5B shows the transfer speed transition when the A3 vertical size thick paper 38 is transported in the thick paper mode (see the thick solid line C in FIG. 5B). First, the thick paper mode is set. By doing so (vb <vf), the occurrence of image displacement (smear) due to the impact at the time when the trailing end of the sheet 38 in the conveyance direction passes through the registration roll 92 (detachment from the conveyance force application point 1) is suppressed. The

  Further, since the conveyance speed of the paper 38 is slowed at the conveyance force application point 2, it takes a longer time for the leading end of the paper 38 to reach the conveyance force application point 3 as compared with FIG. Accordingly, the time depending on the transport speed of the transport force application point 3 is delayed.

  As a result, compared to the comparative example of FIG. 5A (refer to the thin solid line B), an error with respect to the appropriate average magnification (refer to the alternate long and short dash line L in FIG. There is no such thing as less.

(Modification 1)
In the first embodiment, in the thick paper mode, the transport speed of the transport force application points 1 to 3 is adjusted according to the size of the paper 38. In this case, however, the transport speed is always transported before and after the adjustment. The speed was constant. In addition, since the same motor M1 as the conveyance force provision point 3 is used, the conveyance speed of the conveyance force provision point 1 (registration roll 92) changes as a result.

  In the modification, as shown in FIGS. 6A and 6B, the section magnification (the magnification in the unit sub-scanning direction, for example, the width for each line) may be constant. You may make it change the conveyance speed of the conveyance force provision point 2 and the conveyance force provision point 3. FIG.

  More specifically, FIG. 6A is a transport speed transition chart when transporting a small size (A4 landscape size thick paper 38) in the thick paper mode.

  The sagging of the paper 38 between the conveyance force application point 2 and the conveyance force application point 3 is eliminated, and further, the sheet 38 is separated from the conveyance force application point 1 and depends on the conveyance speed of the conveyance force application point 3. At the timing, the conveyance speed vf at the conveyance force application point 3 (speed ratio 100.6% with respect to the initial process speed) is decreased. Further, at the same time, the conveyance speed vb at the conveyance force application point 2 (speed ratio 99.8% with respect to the initial process speed) is increased. These conveyance speeds vf and vb are made to coincide with each other at the process speed (vf = vb = process speed) when the trailing edge of the paper 38 has been conveyed.

  As a result, the A4 horizontal size thick paper 38 is conveyed at the process speed, and the section magnification is stabilized.

  Next, FIG. 6B is a conveyance speed transition chart when conveying a large size (A3 vertical size thick paper 38) in the thick paper mode. The control pattern is the same as that of the A4-sized thick paper 38 in FIG. 6A, but Adjustment 1 and Adjustment 2 are executed with respect to FIG. 6A.

  The sagging of the paper 38 between the conveyance force application point 2 and the conveyance force application point 3 is eliminated, and further, the sheet 38 is separated from the conveyance force application point 1 and depends on the conveyance speed of the conveyance force application point 3. At the timing, the conveyance speed vf at the conveyance force application point 3 (speed ratio 100.3% relative to the initial process speed) is decreased. Further, at the same time, the conveyance speed vb at the conveyance force application point 2 (speed ratio 99.7% with respect to the initial process speed) is increased. These conveyance speeds vf and vb are made to coincide with each other at the process speed (vf = vb = process speed) when the trailing edge of the paper 38 has been conveyed.

  As a result, the A3 vertical size thick paper 38 is conveyed at the process speed, and the section magnification is stabilized.

(Second Embodiment)
The second embodiment will be described below. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description of the configuration is omitted.

  A feature of the second embodiment is that a change in load during the conveyance of the paper 38 is detected, and based on the change in the load, the conveyance force application point, particularly the conveyance speed vb at the conveyance force application point 2 and the conveyance force. This is in the point of feedback control of the conveyance speed balance with the conveyance speed vf of the grant point 3.

  In other words, in the modification of the first embodiment, the slack between the conveyance force application point 2 and the conveyance force application point 3 is eliminated in the paper 38 and the paper 38 depends on the conveyance speed of the conveyance force application point 3. The trailing edge of the paper 38 is finished being conveyed by predicting the time when the conveyance speed vf at the conveyance force application point 3 is decreased and the conveyance speed vb at the conveyance force application point 2 is increased at the same time. At the time, the process speed is matched (vf = vb = process speed).

  On the other hand, in the second embodiment, the slack between the conveyance force application point 2 and the conveyance force application point 3 is eliminated in the sheet 38 and the paper 38 depends on the conveyance speed of the conveyance force application point 3. The time to become surely detected.

(Image forming unit 14)
FIG. 7 shows a schematic diagram of the image forming unit 14 and the sheet conveying unit 16 according to the second embodiment.

  The image forming unit 14 includes a photosensitive drum 22 that rotates at a constant speed in the direction of arrow A in FIG.

  Around the photosensitive drum 22, along the rotation direction of the photosensitive drum 22 (clockwise direction indicated by arrow A in FIG. 7), the charger 24, the exposure unit 26, the developing device 28, the transfer roll 30, and the cleaner 32 and an erase lamp 34 are arranged in this order. Hereinafter, the charger 24, the exposure unit 26, the developing unit 28, the transfer roll 30, the cleaner 32, and the erase lamp 34 may be collectively referred to as an image forming unit. An LED printer head (LPH) is applied to the exposure unit 26, and in the following, the exposure unit 26 may be referred to as an LPH 26.

  The surface of the photosensitive drum 22 is uniformly charged by the charger 24 and then irradiated with a light beam by the LPH 26 to form a latent image on the photosensitive drum 22. The LPH 26 is controlled to emit light by the LPH driving unit 36 and emits a light beam based on image data.

  To the latent image formed on the photosensitive drum 22 by the light beam, toner is supplied by the developing unit 28, and a toner image is formed on the photosensitive drum 22.

  The toner image on the photosensitive drum 22 is transferred to a sheet 38 as a recording medium by a transfer roll 30. Hereinafter, the region where the toner image is transferred may be referred to as “transfer portion TR”.

  The toner remaining on the photosensitive drum 22 after the transfer at the transfer portion TR is removed by the cleaner 32, neutralized by the erase lamp 34, and then charged again by the charger 24, and the same image forming process is performed. It is possible to repeat.

  On the other hand, the paper 38 on which the toner image is transferred by the transfer unit TR is conveyed to a fixing device 40 including a pressure roller 40A and a heating roller 40B, and subjected to a fixing process. As a result, the toner image is fixed and a desired image is formed on the paper 38. The paper 38 on which the image is formed is discharged out of the apparatus.

  The photosensitive drum 12 is not directly transferred onto the paper, but is primarily transferred onto an intermediate transfer member (formed by a belt or a drum), and then secondary transferred onto the paper (corresponding to the transfer at the transfer unit TR). ).

  Further, in the second embodiment, the driving source for the conveying force application point 1 and the conveying force applying point 3 (for example, the motor M1 as an example of the conveying means shown in FIG. 7) is common, and each transmission is a transmission. The target transport speeds vf and vr are set by Gf and Gr. On the other hand, the driving source of the conveying force application point 2 (as an example, a motor M2 as an example of conveying means shown in FIG. 7) is independent, and a target conveying speed vb is set by the transmission Gb.

  Here, the motor M1 and the motor M2 are driven by receiving electric power from the power supply unit 66 based on a signal from the drive system control unit 46.

  The power supply unit 66 is provided with a current detection unit 68 so that the drive current of the motor M2 is detected and sent to the drive system control unit 46.

  Here, from the state where the paper 38 is conveyed with a slack between the conveyance force application point 2 and the conveyance force application point 3, the paper 38 is between the conveyance force application point 2 and the conveyance force application point 3. There is a point in time when the slack is eliminated and the sheet is conveyed.

  At this time, the dependency of the conveyance force between the conveyance force application point 2 and the conveyance force application point 3 changes. In other words, when the slack between the conveyance force application point 2 and the conveyance force application point 3 is eliminated, the paper 38 becomes more dependent on being pulled by the conveyance force application point 3.

  Since the driving current of the motor M2 changes when the dependence changes, in the second embodiment, the current is detected and monitored by the current detection unit 68, and thus depends on the conveyance speed of the conveyance force application point 3. Reliable detection of when to start.

  The operation of the second embodiment will be described below.

  In the second embodiment, first, as a premise, the conveyance speed and exposure cycle setting control routine shown in FIG. 4 in the first embodiment is executed. Thereafter, the current monitoring control routine shown in FIG. 8 is started.

  As shown in FIG. 8, in step 150, it is determined whether or not the motor M1 and the motor M2 are being driven. If the determination is negative, it is determined that the image forming process has ended, and this routine ends.

  If an affirmative determination is made in step 150, it is determined that the image forming process is in progress and the paper 38 is being conveyed, and the routine proceeds to step 152.

  In step 152, the current detection unit 68 detects the drive current value of the motor M2.

  In the next step 154, it is determined whether or not the detected drive current value of the motor M2 has changed (whether there has been a certain amount of increase or decrease).

  If a negative determination is made in step 154, it is determined that the paper 38 is being conveyed with a slack between the conveyance force application point 2 and the conveyance force application point 3, and the current conveyance state is to be continued. This routine ends.

  If the determination in step 154 is affirmative, it is determined that the paper 38 has just been freed from slack between the conveyance force application point 2 and the conveyance force application point 3, and the process proceeds to step 156 and the following conveyance is performed. Speed processing is executed and this routine ends.

  (Conveyance speed process 1) The conveyance speed vf at the conveyance force application point 3 is set to a process speed having a plus tolerance.

  (Conveyance speed process 2) The conveyance speed vb at the conveyance force application point 2 is set to a process speed having a minus tolerance.

  Here, the allowable error may theoretically be set such that the conveyance speed vf at the conveyance force application point 3 and the conveyance speed vb at the conveyance force application point 2 are set to the process speed (vf = vb = process speed). Since the reverse rotation phenomenon (vf <vb) does not occur due to the speed control error, the transport speed vf has a positive allowable error Δvf, and the transport speed vb has a negative allowable error Δvb. Although Δv and Δvb are preferably larger than the transport error, they need not be the same. Thereby, even if there is a conveyance error, vf> vb is maintained.

  FIG. 9A is a transport speed transition chart when transporting a small size (A4 landscape size thick paper 38) in the thick paper mode.

  When the slack of the paper 38 between the conveyance force application point 2 and the conveyance force application point 3 is eliminated and the current detection unit 68 detects a time depending on the conveyance speed of the conveyance force application point 3, the conveyance force application point 3 The conveyance speed vf is lowered to the process speed or the process speed + Δvf. Further, at the same time, the transport speed vb at the transport force application point 2 is increased to the process speed or the process speed Δvb.

  As a result, the A4 horizontal size thick paper 38 is conveyed at the process speed (including the allowable error range), and the section magnification is stabilized.

  Next, FIG. 9B is a conveyance speed transition chart when conveying a large size (A3 vertical size thick paper 38) in the thick paper mode. The control pattern is the same as that of the A4 landscape size thick paper 38 in FIG. 9A), but adjustment 1 and adjustment 2 are performed on FIG. 9A as in the first embodiment. .

  When the slack of the paper 38 between the conveyance force application point 2 and the conveyance force application point 3 is eliminated and the current detection unit 68 detects a time depending on the conveyance speed of the conveyance force application point 3, the conveyance force application point 3 The conveyance speed vf is lowered to the process speed or the process speed + Δvf. Further, at the same time, the transport speed vb at the transport force application point 2 is increased to the process speed or the process speed −Δvb.

  As a result, the A3 vertical size thick paper 38 is conveyed at the process speed, and the section magnification is stabilized.

(Modification 2)
In the first embodiment (including modification 1) and the second embodiment, the image forming apparatus 10 that forms the black and white image shown in FIG. 1 has been described as an example. However, as shown in FIG. The present invention can also be applied to the image forming apparatus 210 that forms a full-color image.

  FIG. 10 is a schematic configuration diagram of an image forming apparatus 210 according to the second modification.

  This image forming apparatus 210 is capable of image formation (sometimes referred to as “printing”) in a quadruple tandem full color, and in order from the upstream side, yellow (Y), magenta (M), and cyan (C). The first image forming unit 212Y, the second image forming unit 212M, the third image forming unit 212C, and the fourth image forming unit 212K that output an image of each color of black (K) are predetermined with each other. Arranged at intervals.

  In the following, the four first image forming units 212Y, the second image forming unit 212M, the third image forming unit 212C, and the fourth image forming unit 212K have the same configuration. Unit 212 ”. Further, in the description without distinguishing each constituent member of the image forming unit 212, the end of the reference numerals (“Y”, “M”, “C”, “K”) of each constituent member described in the drawings is omitted. There is a case.

  The image forming unit 212 includes a drum-shaped photosensitive drum 214 having a photosensitive layer on the surface, a charging unit 216 that uniformly charges the photosensitive drum 214, and a uniformly charged photosensitive drum 214. An exposure unit 218 that forms an electrostatic latent image by irradiating image light, a developing unit 220 that transfers toner to the latent image to form a toner image, and a cleaning unit that removes toner remaining on the photosensitive drum 214 after transfer. 226.

  In addition, the image forming apparatus 210 includes an endless belt-like intermediate transfer belt 222 as an image holding member, which is stretched around a path in contact with each of the photosensitive drums 214 of the four image forming units 212. A primary transfer roll 224 that transfers the toner image formed on the photosensitive drum 214 to the intermediate transfer belt 222. A region where the photosensitive drum 214 and the primary transfer roll 224 face each other is referred to as a primary transfer portion T1.

  Further, the image forming apparatus 210 includes a recording paper transport mechanism 228 that transports the recording paper P accommodated in the paper tray 229, and a fixing unit 230 that fixes the toner image on the recording paper P.

  The intermediate transfer belt 222 is wound around a drive roll 232 that is driven to rotate, a tension roll 234 that adjusts the tension, and a backup roll 236 as an opposing member. The primary transfer roll 224 is disposed inside the intermediate transfer belt 222.

  Further, at a position facing the backup roll 236 across the intermediate transfer belt 222, the second transfer member serving as a transfer member for transferring the toner image on the intermediate transfer belt 222 onto the recording paper P conveyed by the recording paper conveyance mechanism 228 is provided. A next transfer roll 238 is provided. A region where the backup roll 236 and the secondary transfer roll 238 are opposed to each other is referred to as a secondary transfer portion T2.

  Further, a toner that removes the toner remaining on the intermediate transfer belt 222 after the toner image is transferred onto the recording paper P by the secondary transfer roll 238 at a position facing the drive roll 232 across the intermediate transfer belt 222. A removal unit 240 is provided.

  The recording paper transport mechanism 228 includes a pickup roll 242, transport rolls 244 and 246, paper guides 248, 250, 252, 254 and 256 that guide the transport movement path, a paper discharge roll 258, and a paper discharge tray (not shown). Etc.). The recording paper transport mechanism 228 transports and drives the recording paper P stored in the paper tray 229 to the secondary transfer position where the secondary transfer roll 238 and the backup roll 236 face each other with the intermediate transfer belt 22 interposed therebetween. The conveyance is driven from the secondary transfer position to the fixing unit 230, and then the conveyance is driven from the fixing unit 230 to the paper discharge tray.

  In the image forming apparatus 210, the point where the paper P is sandwiched by the transport roll 246 corresponds to the transport force application point 1, and the point where the paper P is sandwiched between the secondary transfer roll 238 and the intermediate transfer belt 222 is the transport force application point 2. The point corresponding to the sheet P sandwiched by the fixing unit 230 corresponds to the conveyance force applying point 3.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Case 14 Image forming part 16 Paper conveyance part 18 MCU
DESCRIPTION OF SYMBOLS 20 Main controller 22 Photosensitive drum 24 Charger 26 Exposure part 28 Developing device 30 Transfer roll TR Transfer part 32 Cleaner 34 Erase lamp 36 LPH drive part 38 Paper 40A Pressure roller 40B Heating roller 40 Fixing device 42 User interface 44 Image formation process Control unit 46 Drive system control unit 48 Charge control unit 50 Exposure control unit 52 Transfer control unit 54 Fixing control unit 56 Static control unit 58 Cleaner control unit 60 Development control unit 62 Temperature sensor 64 Humidity sensor 82 Supply device 84 Storage container 86 Transport roll DESCRIPTION OF SYMBOLS 88 Main conveyance path 90 Reverse conveyance path 91 Sub conveyance path 92 Registration roll 94 Discharge roll 96 Reverse conveyance roll 98 Supply opening-closing part 99 Conveyance roll

Claims (5)

A classifying means for classifying a recording medium having a predetermined grammage or more according to a length in a transport direction;
Conveying means for applying a conveying force to the recording medium at at least two positions: a transfer unit that transfers the image developed on the image carrier to the recording medium, and a fixing unit that fixes the image transferred downstream from the transfer unit. When,
When the recording medium transported by the transport unit is classified by the classification unit in the transport direction as a reference length, the transport speed at the fixing unit is made faster than the transport speed at the transfer unit. Setting means for setting the conveying speed by the conveying means,
When the recording medium transported by the transporting means is classified into a recording medium whose length in the transporting direction is longer than a reference length by the classifying means, maintaining the magnitude relationship of the transport speed set by the setting means Correction means for correcting the transfer speed at the transfer section and the fixing section so as to slow down each;
An image forming apparatus. Further comprising a type classification means for classifying the recording medium by type based on the basis weight of the paper;
The image forming apparatus according to claim 1, wherein the setting unit sets the conveyance speed of the fixing unit to a conveyance speed slower than the conveyance speed of the transfer unit when conveying plain paper having a basis weight smaller than that of the recording medium. . The correction means includes
The image forming apparatus according to claim 1, wherein the average value of the conveyance speed of the recording medium in the transfer unit is corrected to a desired conveyance speed. A classifying means for classifying a recording medium having a predetermined grammage or more according to a length in a transport direction;
Conveying means for applying a conveying force to the recording medium at at least two positions: a transfer unit that transfers the image developed on the image carrier to the recording medium, and a fixing unit that fixes the image transferred downstream from the transfer unit. When,
When the recording medium transported by the transport unit is classified by the classification unit in the transport direction as a reference length, the transport speed at the fixing unit is made faster than the transport speed at the transfer unit. Setting means for setting the conveying speed by the conveying means,
Detecting means for detecting a load of a driving source of a conveying means for applying a conveying force at the transfer section;
When the recording medium transported by the transporting means is classified into a recording medium whose length in the transporting direction is longer than a reference length by the classifying means, maintaining the magnitude relationship of the transport speed set by the setting means Correction means for correcting the transfer speed at the transfer section and the fixing section so as to slow down each;
Control means for controlling the respective transport speeds so that the transport speeds at the transfer section and the fixing section coincide with each other after detecting a predetermined load fluctuation by the detection means during transport of the recording medium. ,
An image forming apparatus. The control unit controls the transfer speed of the transfer unit and the fixing unit so as to be a process speed which is a reference of a preset image forming process;
The transfer speed of the transfer unit is controlled with a negative tolerance with respect to the process speed,
The image forming apparatus according to claim 4, wherein the conveyance speed of the fixing unit is controlled with a plus tolerance with respect to the process speed.

Images