JP6707905B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

Patent Document 1 describes that the linear velocity by the transport drive unit is determined based on at least one of the type, size, and fixing of the paper.

Patent Document 2 describes that the lateral width of a sheet to be conveyed (the direction orthogonal to the sheet conveying direction) is defined, and that the rotational conveying speed of a 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-A-2005-345531 JP, 2004-117397, A

When a conveying force is applied to the paper at a plurality of points in the conveying path and the conveying speeds are different between the upstream side and the downstream side so that tension or slack is imparted to the recording sheet to stabilize the conveying speed, If the length in the conveyance direction exceeds a certain amount, the balance of tension or slack applied to the paper may be lost, and the conveyance speed may become unstable.

SUMMARY OF THE INVENTION In consideration 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 invention, a classifying unit that classifies a recording medium having a predetermined basis weight or more according to the length in the transport direction, and a transfer that transfers the image developed on the image carrier to the recording medium. Section and a fixing section that fixes the transferred image on the downstream side of the transfer section, and a conveying unit that applies a conveying force to the recording medium at at least two positions, and the recording medium that is conveyed by the conveying unit is the classification unit. When the length in the transport direction is classified into a reference length by, the setting unit that sets the transport speed by the transport unit so that the transport speed at the fixing unit is faster than the transport speed at the transfer unit. When the recording medium conveyed by the conveying means is classified into the recording medium whose length in the conveying direction is longer than the reference length by the classifying means, the magnitude relation of the conveying speed set by the setting means is maintained. At the same time, the correction unit corrects the transfer speeds of the transfer unit and the fixing unit so as to slow the conveyance speed, and the type classification unit that classifies the recording medium according to the basis weight of the sheet. When carrying plain paper having a smaller basis weight than the recording medium, the carrying speed of the fixing unit is set to a carrying speed slower than the carrying speed of the transfer unit .

According to a second aspect of the present invention, in the first aspect of the invention, the correction unit corrects the average value of the conveyance speeds of the recording medium in the transfer section to be a desired conveyance speed. ..

According to a third aspect of the invention, a classifying unit that classifies the recording medium having a predetermined basis weight or more according to the length in the transport direction, and a transfer that transfers the image developed on the image carrier to the recording medium. Section and a fixing section that fixes the transferred image on the downstream side of the transfer section, and a conveying unit that applies a conveying force to the recording medium at at least two positions, and the recording medium that is conveyed by the conveying unit is the classification unit. When the length in the transport direction is classified into a reference length by, the setting unit that sets the transport speed by the transport unit so that the transport speed at the fixing unit is faster than the transport speed at the transfer unit. A detection unit that detects a load of a drive source of a conveyance unit that applies a conveyance force at the transfer unit; and a recording medium that is conveyed by the conveyance unit, the length in the conveyance direction of the classification unit is longer than a reference length. When the recording medium is classified as a long recording medium, a correction unit that corrects the conveyance speed at the transfer unit and the fixing unit to be slowed while maintaining the magnitude relation of the conveyance speed set by the setting unit, and the recording unit. After detecting a predetermined load fluctuation by the detection means during the transportation of the medium, a control means for controlling the respective transportation speeds so that the transportation speeds at the transfer portion and the fixing portion match. Have

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

According to the first aspect of the invention, it is possible to suppress the transport speed fluctuation regardless of the length of the recording medium in the transport direction.

Regardless of the type of record medium, it is possible to suppress the conveyance speed variations.

According to the second aspect of the invention, the average value of the transport speed of the recording medium at the reference position can be set as the desired transport speed.

According to the third aspect of the present invention, it is possible to suppress the transport speed fluctuation regardless of the length of the recording medium in the transport direction.

According to the invention described in claim 4 , it is possible to avoid the reverse phenomenon of the speed difference.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. FIG. 3 is an enlarged view of an image forming unit of the image forming apparatus according to the first embodiment and a sheet conveying unit around the image forming unit. FIG. 3 is a block diagram showing a control system of the image forming apparatus according to the first embodiment. 6 is a flowchart showing a transport speed/exposure cycle setting control routine according to the first embodiment. 6A and 6B are charts 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. 9A and 9B are charts showing a transfer speed transition in a thick paper mode according to Modification 1, where (A) shows a small size (A4 horizontal thick paper), and (B) shows a large size (A3 vertical thick paper). FIG. 9 is an enlarged view of an image forming unit of an image forming apparatus according to a second embodiment and a sheet conveying unit around the image forming unit. It is a flowchart which shows the electric current monitoring control routine which concerns on 2nd Embodiment. 9A and 9B are charts 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. 9 is a schematic configuration diagram of an image forming apparatus (full-color image forming apparatus) according to Modification Example 2. FIG.

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

The image forming apparatus 10 includes 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 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 section 14 and the sheet conveying section 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 photoconductor drum 22, along the rotation direction of the photoconductor drum 22 (clockwise direction indicated by arrow A in FIG. 2), the charger 24, the exposure unit 26, the developing unit 28, the transfer roll 30, the cleaner 32 and an erase lamp 34 are arranged in this order. Hereinafter, the charger 24, the exposure unit 26, the developing device 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 hereinafter, the exposure unit 26 may be referred to as the LPH 26.

The surface of the photoconductor drum 22 is uniformly charged by the charger 24, and then the light beam is irradiated by the LPH 26 to form a latent image on the photoconductor drum 22. The LPH 26 has its light emission controlled by the LPH drive unit 36 and emits a light beam based on image data.

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

The toner image on the photoconductor drum 22 is transferred by a transfer roll 30 onto a sheet 38 as a recording medium. Hereinafter, the area to which the toner image is transferred may be referred to as “transfer section TR”.

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

On the other hand, the paper 38 on which the toner image has been transferred at the transfer portion 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 to the outside of the apparatus.

It should be noted that, instead of being directly transferred from the photosensitive drum 12 to the paper, the primary transfer is performed to an intermediate transfer member (formed by a belt or a drum), and then the secondary transfer is performed to the paper (corresponding to transfer at the transfer portion TR). ).

In the case of a color image, a plurality of image forming units (for example, four units for each color of CMYK) are arranged, the toner images of the respective colors are superposed and transferred (primary transfer) on the intermediate transfer belt, and then the paper 38 is transferred at the transfer portion TR. Then, the image is transferred (secondary transfer) to and fixed.

(Details of paper 38 transportation system)
As shown in FIG. 1, the image forming apparatus 10 is equipped with a plurality of stages of supply devices 82 that supply the paper 38 to the image forming unit 14. Each of the supply devices 82 can be pulled out to the front side (the left side surface in FIG. 1) of the image forming apparatus 10, and the paper 38 is loaded (replenished) with the supply device 82 pulled out from the image forming apparatus 10.

The supply device 82 has different storage containers 84 that store paper such as plain paper and thick paper 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 order from the top according to the user's selection.

The supply device 82 has a conveyance roll 86 that takes out the uppermost sheet 38 stored in the storage container 84 and conveys the taken out sheet 38 toward the image forming unit 14.

As shown in FIG. 1 and FIG. 2, the image forming apparatus 10 is provided with a sheet conveying unit 16 used to convey the sheet 38. The paper transport unit 16 has a main transport path 88, a reverse transport path 90, and a sub transport path 91.

The main transport path 88 is used to transport the paper 38 supplied from any one of the supply devices 82 to the image forming unit 14 and discharge the paper 38 on which an image is formed to the outside of the image forming device 10.

Along the main transport path 88, the transport roll 86, the registration roll 92, the transfer roll 30, and the fixing device 40 (the pressure roller 40A and the heating roller 40B) are arranged in this order from the upstream side in the direction in which the paper 38 is transported. , Discharge rolls 94 are arranged.

The registration roll 92 is temporarily stopped, for example, with the leading end of the paper 38 conveyed from the supply device 82 side being sandwiched, and the paper 38 is adjusted so as to coincide with the timing when the toner image is transferred to the transfer portion TR. To the transfer roll 30.

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

The reverse conveyance path 90 is a conveyance path used for reversing the sheet 38 having the toner image fixed on one surface thereof and supplying the sheet 38 toward the image forming unit 14 again.

For example, a pair of reversal conveyance rolls 96 are appropriately arranged along the reversal conveyance path 90. In the reverse conveyance path 90, the sheet 38 is fed from the trailing edge side by the backward rotation of the sheet ejection roller 94 with the trailing edge of the sheet 38 sandwiched by the ejection rollers 94. The reversing conveyance rolls 96, 96 convey the reversal conveyance rolls 96 to a position upstream of the registration roll 92.

The sub transport path 91 is a transport path for feeding the paper 38 different from the paper 38 stored in the supply device 82 to the image forming unit 14. The sheet 38 is supplied to the sub transport path 91 from the left side surface of the image forming apparatus 10 in FIG. 1 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 relating to image formation or the like is given by a user's operation, and at the same time, the user is notified of information such as image formation.

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

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

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

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

A temperature sensor 62, a humidity sensor 64, and the like are connected to the main controller 20, and the ambient temperature and humidity in the housing 12 of the image forming apparatus 10 may be detected based on the temperature sensor 62 and the humidity sensor 64. .. Further, the main control 20 functions as, for example, a first classifying unit, a second classifying unit, a setting unit, and a correcting unit.

(Control of conveyance speed 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 of the first embodiment, as shown in FIG. 2, when the sheet 38 is conveyed by the main conveying path 88, the conveying force is applied at the following three conveying force applying points.

(Conveyance Force Application Point 1) The paper 38 is sandwiched by the registration rolls 92, and a conveyance force having a linear velocity vr depending on the rotation speed of the registration rolls 92 is applied.

(Conveyance Force Application Point 2) The paper 38 is sandwiched between the photoconductor drum 22 and the transfer roll 30 at the transfer portion TR, and a conveyance force having a linear velocity vb depending on the rotational speeds of the photoconductor drum 22 and the transfer roll 30 is provided. To be done. The transfer roll 30 is a driven roller.

(Conveyance Force Applying Point 3) The sheet 38 is sandwiched between the pressure roller 40A and the heating roller 40B of the fixing device 40, and the conveyance force of the linear velocity vf depending on the rotation speeds of the pressure roller 40A and the heating roller 40 is imparted. To be done.

Here, comparing plain paper and thick paper as the types of the paper 38, the plain paper has a carrying force applying point 2 (photosensitive drum 22 and transfer roll 30) and a carrying force applying point 3 (fixing device 40). In the meantime, unevenness in sheet conveyance may occur due to tensile force or twisting, 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 as to sag (form a loop) between the conveyance force application points 1 to 3 (vr>vb). >vf).

On the other hand, in the case of thick paper, when a bending (loop) of the sheet is formed between the conveying force applying points 1 to 3, the conveying force applying point 2 (photosensitive drum 22 and transfer roll 30 ) And the feeding force applying point 3 (fixing device 40), a force to return to a straight line is exerted, which may be rather unstable.

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 between the conveying force applying point 1 (registration roll 92) and the conveying force applying point 2 (photoreceptor drum 22 and transfer roll 30), the downstream side may be slow as in plain paper (vr>vb).

Table 1 shows the relative relationship of the transport speeds (linear velocities) at the transport force application points 1 to 3 using specific numerical values.

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。

Note that the numerical values in Table 1 are merely examples showing relative differences, and the transport speeds (linear velocities) at the respective transport imparting points 1 to 3 in the first embodiment are limited to these numerical values. Further, in the first embodiment, the drive sources for the conveying force applying point 1 and the conveying force applying point 3 (as an example, the motor M1 which is an example of the conveying means shown in FIG. 2) are common, and respectively. The target transport speeds vf and vr are set by the transmissions Gf and Gr. On the other hand, the drive source of the conveying force applying point 2 (as an example, the motor M2 which is an example of the conveying means shown in FIG. 2) is independent, and the target conveying speed vb is set by the transmission Gb.

Therefore, in Table 1, the speed change ratios of the carrying force applying point 1 and the carrying force applying point 3 are the same, but if the driving sources are independent of each other, in particular, the carrying force applying point 1 and the carrying force applying point It is not necessary that the speed change ratios at point 3 be the same.

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

On the other hand, the paper 38 has various sizes in addition to the paper quality (paper type) of plain paper and thick paper.

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

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

Note that the average magnification (longitudinal magnification) in the paper conveyance direction means that the image is actually formed 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 the length (measured 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 becomes long and the margin becomes narrow.

Therefore, the length in the carrying direction of the A3 size (vertical direction) is twice as large as that of the A4 size (horizontal direction). In (), the margin deviates from the allowable range, and as a result, the margin at the rear end of the sheet 38 in the transport direction becomes narrower than in the A4 size (sideways).

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

(Adjustment 1) The conveyance speeds vb and vf set at the conveyance force application point 2 and the conveyance force application point 3 on the A3 vertical size sheet 38 are set to the conveyance force application point 2 and the conveyance force application point 3 on the A4 horizontal size sheet 38. It is made slower than the transport 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 small.

The relative speeds (vb<vf, vr>vb) of the carrying force applying points 1 to 3 in the carrying control in the thick paper mode are maintained.

Adjustment 1 is the timing of the tension force generation (conveyance with tension) between the conveyance force application point 2 and the conveyance force application point 3 on the A3 portrait size thick paper 38, and the A4 landscape size thick paper 38. Compared to, it has the function of delaying.

Adjustment 2 has a function of adjusting the average longitudinal magnification in the transport direction to approach the average magnification (process speed) in the plain paper mode.

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

Table 2 shows the conveyance speed ratio of each portion when the conveyance speed at the conveyance force application point 2 (that is, the transfer portion TR) of plain paper is 100%. Note that this transport speed ratio is an example, and is not limited to the 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 horizontal size 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 sheet 38 is 99.7%, the transport force application point 3 is 100.3%, and the speed difference is 0.6 point. ..

According to Table 2, the conveyance force application point 2 of the A4 horizontal size paper 38 is 99.8% in the thick paper mode conveyance control, whereas the conveyance force application point 2 of the A3 vertical size paper 38 is This is 99.7%, and the transport speed is 0.1 point slower.

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

Further, the speed difference between the conveying force applying point 2 and the conveying force applying point 3 is 0.8 point for the A4 horizontal size paper 38, whereas it is 0.6 point for the A3 vertical size 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, the LPH drive unit 36 drives the LPH according to the gradation data to emit the exposure light, and the photosensitive drum 22 scans and exposes 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). Then, the toner image formed on the photoconductor drum 22 is transferred onto the paper 38 by the transfer roll 30.

The toner image of each color on the paper 38 is fixed by the fixing device 40, and the paper 38 after fixing is discharged to the outside of the apparatus (single-sided printing process), or the rear end of the paper 38 is pinched by the discharge roller 94. In this state, the sheet 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 photoconductor drum 22 after the transfer process of the toner image is completed. It is uniformly charged in the next image forming process.

The paper 38 (the paper 38 whose image has been formed on the front surface) sent to the reverse conveyance path 90 is the paper that is rotated by the discharge roller 94 in the reverse direction while the rear end of the paper 38 is sandwiched by the discharge rollers 94. 38 is fed from the rear end side, and the fed sheet 38 is conveyed to the position upstream of the registration roll 92 by the reversing conveyance rolls 96, 96 with its front and back reversed.

As a result, the image formation on the back side is performed in the same manner as the image forming step, the image is fixed by the fixing device 40, and the sheet 38 after fixing is discharged to the outside of the apparatus.

Next, the transport speed setting control routine for controlling the transport 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 set in each unit of the MCU 18, but it may be executed by the MCU 18.

In step 100, the type of the paper 38 selected for image formation by the input operation using the user interface 42 is, for example, 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 basis weight is proportional to the degree of stiffness of the paper, it is set as the requirement for the determination criterion of the paper type. However, the degree of stiffness of the paper is equal to the basis weight. Discrimination criteria that correlates with may be applied. In other words, in the first embodiment, “basis weight” is applied as a general term for the paper type determination standard.

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

In the next step 104, the transport speeds vr, vb and vf for plain paper read out 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 completion of setting the transport speeds vr, vb, and vf is notified to the MCU 18, and this routine ends.

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

(Choose thick paper)
When it is determined that the paper is thick paper in step 100, the process proceeds to step 120, and the transport speeds vr, vb, and vf at the transport force application points 1 to 3 based on the thick paper are read. In the case of thick paper, the relationship between the transport speeds is vr>vb, 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 having a relation of “small size” and “large size” is set to a small size, and the A3 vertical thick paper 38 is set to a large size. .. The relationship between the sizes “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 may be “small size” and the A4 horizontal size may be “large size”.

When 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 set. 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 transport speed difference Δv (|vb-vf|) between the transport force application point 2 and the transport force application point 3 is made smaller with respect to the speed Δv in the small size (Adjustment 2 ), and proceeds to step 128.

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

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

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

In the MCU 18, the above-mentioned image forming process is executed based on the set transport speeds vr, vb, vf for thick paper.

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

In the case of plain paper, as shown in Table 1, the linear velocity becomes slower toward the downstream side, and the paper 38 is conveyed so as to sag (form a loop) between the conveyance force applying points 1 to 3. (Vr>vb>vf).

As a result, the occurrence of unevenness in sheet conveyance due to a tensile force or a twist is suppressed between the conveying force applying point 2 and the conveying force applying point 3.

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

As a result, the paper 38 is conveyed without being bent, and therefore the force of the paper 38 to return to a straight line between the conveyance force application point 2 and the conveyance force application point 3 is exerted due to the stiffness of the paper 38. Is suppressed.

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

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 to be slower than the transport speed of the A4 horizontal size paper 38 (Adjustment 1).

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

Table 2 shows specific examples of Adjustment 1 and Adjustment 2, and FIG. 5 shows the transfer speed transition of the sheet 38 based on the transfer speed control in Table 2.

"Thick paper mode, A4 landscape size"
FIG. 5A shows a transfer speed transition when the A4 horizontal size thick paper 38 is conveyed 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 shift (smear) due to the impact at the time when the trailing end of the sheet 38 in the transport direction passes the registration roll 92 (separation from the transport force application point 1) is suppressed. It

As a reference, when the A4 horizontal size thick paper 38 is conveyed in the plain paper mode, when the rear end portion of the paper 38 in the conveyance direction passes the registration roll 92 (separation from the conveyance force application point 1), it suddenly increases. Speed fluctuations may occur and image shift (smear) may occur.

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

However, in the case of the A4 horizontal size 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 portion of the paper 38 exceeds the allowable range and decreases. Not available (maintaining proper condition).

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

In the latter half of the conveyance, the length of the A3 vertical size thick paper 38 that is conveyed depending on the conveyance speed vf of the conveyance force application point 3 is longer than that of the A4 horizontal size thick paper 38. , The error with respect to the appropriate average magnification (see the alternate long and short dash line L in FIG. 5A) is accumulated, and the margin at the rear end of the paper 38 is reduced.

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

In addition, since the conveyance speed of the sheet 38 is slowed at the conveyance force application point 2, it takes a longer time for the leading end of the sheet 38 to reach the conveyance force application point 3 as compared with FIG. 5A. Therefore, the time depending on the transport speed of the transport force application point 3 is delayed by that amount.

As a result, as compared with the comparative example of FIG. 5A (see the thin solid line B), the error with respect to the appropriate average magnification (see the alternate long and short dash line L of FIG. 5B) is reduced, and the margin of the trailing edge of the paper 38 is reduced. Does not decrease.

(Modification 1)
In the first embodiment, in the thick paper mode, the carrying speeds of the carrying force applying points 1 to 3 are adjusted according to the size of the paper 38, but in this case, the carrying speed is always before and after the adjustment. The speed was constant. The conveyance speed of the conveyance force application point 1 (registration roll 92) changes as a result because the same motor M1 as that of the conveyance force application point 3 is used.

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. The conveying speeds of the conveying force applying point 2 and the conveying force applying point 3 may be changed.

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

The slack of the sheet 38 is eliminated between the conveying force applying point 2 and the conveying force applying point 3, and the sheet 38 is separated from the conveying force applying point 1 and depends on the conveying speed of the conveying force applying point 3. At the time, the transport speed vf at the transport force applying point 3 (speed ratio 100.6% 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 to initial process speed 99.8%) 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 rear end of the sheet 38 has been conveyed.

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

Next, FIG. 6B is a transport speed transition chart when transporting 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 horizontal size thick paper 38 in FIG. 6A, but the adjustment 1 and the adjustment 2 are executed with respect to FIG. 6A.

The slack of the sheet 38 is eliminated between the conveying force applying point 2 and the conveying force applying point 3, and the sheet 38 is separated from the conveying force applying point 1 and depends on the conveying speed of the conveying force applying point 3. At a certain time, the conveyance speed vf at the conveyance force application point 3 (speed ratio 100.3% to the initial process speed) is decreased. Further, at the same time, the transport speed vb of the transport force application point 2 (speed ratio 99.7% to the initial process speed) is increased. These conveyance velocities vf and vb are matched at the process speed (vf=vb=process speed) when the rear end of the sheet 38 has been conveyed.

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

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

The feature of the second embodiment is that a change in the load when the sheet 38 is conveyed is detected, and based on the change in the load, the conveying force applying point, particularly the conveying speed vb of the conveying force applying point 2, and the conveying force. The point is that feedback control is performed on the transport speed balance with the transport speed vf at the applying point 3.

That is, in the modified example of the first embodiment, the slack of the sheet 38 between the conveying force applying point 2 and the conveying force applying point 3 is eliminated, and the sheet 38 depends on the conveying speed of the conveying force applying point 3. By predicting the timing, the transport speed vf at the transport force application point 3 is decreased, and the transport speed vb at the transport force application point 2 is increased at the same time, whereby the rear end of the sheet 38 is completely transported. At the time, the process speeds are matched (vf=vb=process speed).

On the other hand, in the second embodiment, the slack of the sheet 38 between the conveying force imparting point 2 and the conveying force imparting point 3 is eliminated, and the sheet 38 depends on the conveying speed of the conveying force imparting point 3. It was made sure to detect when.

(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 photoconductor drum 22, along the rotation direction of the photoconductor drum 22 (clockwise direction shown by arrow A in FIG. 7), the charger 24, the exposure unit 26, the developing unit 28, the transfer roll 30, the cleaner. 32 and an erase lamp 34 are arranged in this order. Hereinafter, the charger 24, the exposure unit 26, the developing device 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 hereinafter, the exposure unit 26 may be referred to as the LPH 26.

The surface of the photoconductor drum 22 is uniformly charged by the charger 24, and then the light beam is irradiated by the LPH 26 to form a latent image on the photoconductor drum 22. The LPH 26 has its light emission controlled by the LPH drive unit 36 and emits a light beam based on image data.

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

The toner image on the photoconductor drum 22 is transferred by a transfer roll 30 onto a sheet 38 as a recording medium. Hereinafter, the area to which the toner image is transferred may be referred to as “transfer section TR”.

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

On the other hand, the paper 38 on which the toner image has been transferred at the transfer portion 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 to the outside of the apparatus.

It should be noted that, instead of being directly transferred from the photosensitive drum 12 to the paper, the primary transfer is performed to an intermediate transfer member (formed by a belt or a drum), and then the secondary transfer is performed to the paper (corresponding to transfer at the transfer portion TR). ).

Further, in the second embodiment, the drive sources for the conveying force applying 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) are common, and the transmissions are respectively provided. Target conveyance velocities vf and vr are set by Gf and Gr. On the other hand, the drive source of the conveying force applying point 2 (as an example, the motor M2 as an example of the conveying means shown in FIG. 7) is independent, and the 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, and the drive current of the motor M2 is detected and sent to the drive system control unit 46.

Here, from the state where the sheet 38 is conveyed with slack between the conveying force imparting point 2 and the conveying force imparting point 3, the sheet 38 is conveyed between the conveying force imparting point 2 and the conveying force imparting point 3. There is a point when the slack is removed and the product is transported.

At this time, the dependency of the carrying force between the carrying force applying point 2 and the carrying force applying point 3 changes. That is, when the slack of the sheet 38 between the conveying force applying point 2 and the conveying force applying point 3 is eliminated, the sheet 38 becomes more dependent on being pulled by the conveying force applying point 3.

Since the drive current of the motor M2 changes when this dependence changes, in the second embodiment, the current detection unit 68 detects and monitors the current, thereby depending on the conveyance speed at the conveyance force application point 3. Be sure to detect when it will happen.

The operation of the second embodiment will be described below.

In the second embodiment, first, as a premise, the transport speed/exposure cycle setting control routine shown in FIG. 4 in the first embodiment is executed. Then, 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 a negative determination is made, it is determined that the image forming process has ended, and this routine ends.

On the other hand, if an affirmative decision is made in step 150, it is decided that the image forming process is in progress and the paper 38 is being conveyed, and the routine moves to step 152.

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

In the next step 154, it is judged whether or not there is a change in the detected drive current value of the motor M2 (whether or not there is a fixed increase or decrease).

When a negative determination is made in step 154, it is determined that the sheet 38 is conveyed with slack between the conveying force applying point 2 and the conveying force applying point 3, and the current conveying state should be continued. , This routine ends.

Further, when the affirmative determination is made in step 154, it is determined that the slack of the sheet 38 is eliminated between the conveying force applying point 2 and the conveying force applying point 3, and the process proceeds to step 156 to perform the following conveying. Velocity processing is executed, and this routine ends.

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

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

Here, theoretically, the allowable error is to set the transport speed vf of the transport force application point 3 and the transport speed vb of the transport force application point 2 to the process speed (vf=vb=process speed). Since the reverse phenomenon (vf<vb) does not occur due to the speed control error, the transport speed vf has a plus allowable error Δvf and the transport speed vb has a negative allowable error Δvb. Δv and Δvb are preferably larger than the transport error, but they do not have to be the same. As a result, vf>vb is maintained even if there is a transport error.

FIG. 9A is a transfer speed transition chart when a small size (A4 horizontal size thick paper 38) is conveyed in the thick paper mode.

When the slack of the paper 38 is eliminated between the conveyance force application point 2 and the conveyance force application point 3 and the current detection unit 68 detects the time depending on the conveyance speed of the conveyance force application point 3, the conveyance force application point 3 The transport speed vf is decreased to the process speed or the process speed+Δvf. Further, at the same time, the transport speed vb at the transport force applying point 2 is increased by 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 transport speed transition chart when transporting 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 horizontal size thick paper 38 in FIG. 9A), but the adjustment 1 and the adjustment 2 are executed with respect to FIG. 9A as in the first embodiment. ..

When the slack of the sheet 38 between the conveying force applying point 2 and the conveying force applying point 3 is eliminated, and the current detection unit 68 detects a time depending on the conveying speed of the conveying force applying point 3, the conveying force applying point 3 The transport speed vf is decreased to the process speed or the process speed+Δvf. Further, at the same time, the conveyance speed vb at the conveyance force applying point 2 is increased by 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 becomes stable.

(Modification 2)
In the first embodiment (including the modification 1) and the second embodiment, the image forming apparatus 10 for forming the monochrome image shown in FIG. 1 is described as an example, but as shown in FIG. It is also applicable 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 Modification 2.

The image forming apparatus 210 is capable of forming an image (may be referred to as “printing”) in full color of a 4-tandem system, and yellow (Y), magenta (M), cyan (C) in order from the upstream side. , A first image forming unit 212Y, a second image forming unit 212M, a third image forming unit 212C, and a fourth image forming unit 212K of an electrophotographic system that output images of respective colors of black (K) are predetermined with each other. They are arranged at intervals.

Note that, in the following, the four first image forming units 212Y, the second image forming units 212M, the third image forming units 212C, and the fourth image forming units 212K have the same configuration, and thus, when collectively referred to, "image forming" Unit 212”. Further, when description is made without distinguishing each constituent member of the image forming unit 212, the end (“Y”, “M”, “C”, “K”) of the reference numeral of each constituent member shown in the drawings is omitted. There is a case.

The image forming unit 212 includes a drum-shaped photoconductor drum 214 having a photoconductor layer on its surface, a charging unit 216 that uniformly charges the photoconductor drum 214, and a photoconductor drum 214 that is uniformly charged. An exposure unit 218 that radiates image light to form an electrostatic latent image, 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. And 226.

Further, the image forming apparatus 210 includes an endless belt-shaped intermediate transfer belt 222 as an image holding member, which is stretched around a path that comes 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 conveyance mechanism 228 that conveys the recording paper P stored 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 rotationally driven, a tension roll 234 that adjusts tension, and a backup roll 236 that is a facing member. The primary transfer roll 224 is disposed inside the intermediate transfer belt 222.

In addition, at a position facing the backup roll 236 with the intermediate transfer belt 222 interposed therebetween, a second transfer member that transfers the toner image on the intermediate transfer belt 222 onto the recording sheet P conveyed by the recording sheet conveying mechanism 228 is provided. A next transfer roll 238 is provided. A region where the backup roll 236 and the secondary transfer roll 238 face each other is referred to as a secondary transfer portion T2.

In addition, at a position facing the drive roll 232 with the intermediate transfer belt 222 interposed therebetween, a toner image is transferred onto the recording paper P by the secondary transfer roll 238, and then toner remaining on the intermediate transfer belt 222 is removed. The removing 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 thereof, a paper discharge roll 258, and a paper discharge tray (not shown). (Illustration) and the like. The recording paper conveyance mechanism 228 conveys and drives the recording paper P stored in the paper tray 229 to a 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, and then, The secondary transfer position is conveyed to the fixing unit 230, and then the fixing unit 230 is conveyed to the discharge tray.

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

10 image forming apparatus 12 housing 14 image forming unit 16 paper transport unit 18 MCU
20 Main Controller 22 Photosensitive Drum 24 Charging Device 26 Exposure Unit 28 Developing Device 30 Transfer Roll TR Transfer Unit 32 Cleaner 34 Erase Lamp 36 LPH Drive Unit 38 Paper 40A Pressure Roller 40B Heating Roller 40 Fixer 42 User Interface 44 Image Forming Processing Control unit 46 Drive system control unit 48 Charge control unit 50 Exposure control unit 52 Transfer control unit 54 Fixing control unit 56 Electrification control unit 58 Cleaner control unit 60 Development control unit 62 Temperature sensor 64 Humidity sensor 82 Supply device 84 Storage container 86 Conveying roll 88 main transport path 90 reverse transport path 91 secondary transport path 92 registration roll 94 discharge roll 96 reverse transport roll 98 supply opening/closing section 99 transport roll

Claims (4)

Classifying means for classifying recording media having a predetermined basis weight or more according to the length in the transport direction,
Conveying means for imparting a conveying force to the recording medium at least at two positions: a transfer part for transferring the image developed on the image carrier to the recording medium, and a fixing part for fixing the image transferred on the downstream side of the transfer part. When,
When the recording medium conveyed by the conveying means is classified by the sorting means into the length in the conveying direction as a reference length, the conveying speed in the fixing section is made higher than the conveying speed in the transfer section. Setting means for setting the carrying speed by the carrying means,
When the recording medium conveyed by the conveying unit is classified by the classifying unit into a recording medium whose length in the conveying direction is longer than the reference length, while maintaining the magnitude relation of the conveying speed set by the setting unit. A correction unit that corrects the transfer speed at the transfer unit and the fixing unit so as to slow it down ,
A type classification means for classifying the recording medium into types by basis weight of paper,
The setting unit sets the carrying speed of the fixing unit to a carrying speed slower than the carrying speed of the transfer unit when carrying the plain paper having a smaller basis weight than the recording medium.
Image forming apparatus. The correction means is
The image forming apparatus according to claim 1 , wherein the average value of the transport speed of the recording medium at the transfer unit is corrected to be a desired transport speed. Classifying means for classifying recording media having a predetermined basis weight or more according to the length in the transport direction,
Conveying means for imparting a conveying force to the recording medium at least at two positions: a transfer part for transferring the image developed on the image carrier to the recording medium, and a fixing part for fixing the image transferred on the downstream side of the transfer part. When,
When the recording medium conveyed by the conveying means is classified by the sorting means into the length in the conveying direction as a reference length, the conveying speed in the fixing section is made higher than the conveying speed in the transfer section. Setting means for setting the conveying speed by the conveying means,
A detection unit that detects the load of the drive source of the transfer unit that applies a transfer force at the transfer unit;
When the recording medium conveyed by the conveying unit is classified by the classifying unit into a recording medium whose length in the conveying direction is longer than the reference length, while maintaining the magnitude relation of the conveying speed set by the setting unit. A correction unit that corrects the transfer speed at the transfer unit and the fixing unit so as to slow it down,
After detecting a predetermined load fluctuation by the detection means during the conveyance of the recording medium, a control means for controlling the respective conveyance speeds so that the conveyance speeds of the transfer portion and the fixing portion match each other. ,
An image forming apparatus having. The control unit controls the conveyance speed of the transfer unit and the fixing unit to a process speed that 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 3 , wherein the conveyance speed of the fixing unit is controlled with a positive tolerance with respect to the process speed.

Images