JP4000755B2 - Image forming apparatus and paper conveying apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to control related to conveyance of recording paper in an image forming apparatus. More specifically, the present invention relates to control of moving speed of an image forming body and recording paper conveyance speed when changing image magnification, and fine adjustment of paper conveyance speed. The present invention relates to control of conveyance of recording paper related to adjustment and setting of the size of recording paper.
[0002]
[Prior art]
(1) A means for changing the moving speed of the image forming body is widely used as a means for changing the magnification of the image formed on the recording paper, in particular, the magnification in the conveyance direction of the recording paper (hereinafter referred to as the vertical magnification). It has been. That is, for scanning exposure performed at a constant speed in the main scanning direction (direction perpendicular to the moving direction of the image forming body) and the sub-scanning direction (moving direction of the image forming body) by a laser diode or a light emitting diode array, The vertical magnification is changed by changing the moving speed of the formed body.
[0003]
In order to transfer the image formed on the image forming body onto the recording paper, the recording paper needs to be transported at the same speed as the image forming body at the transfer position. Along with the movement speed of the body, the conveyance speed of the recording paper is changed.
[0004]
(2) In an image forming apparatus that transfers an image from an image forming body to recording paper after forming an image on the image forming body, the recording paper transport speed at the transfer position is set to the moving speed of the image forming body. It is necessary to match. For this purpose, fine adjustment of the conveyance speed of the paper feeding means for feeding the recording paper to the transfer position is performed. A stepping motor is usually used as a driving means for driving the paper feeding means for feeding the recording paper to the transfer position. By adjusting the frequency of the driving clock for driving the stepping motor, the conveyance speed of the paper feeding means can be adjusted. Fine adjustments have been made.
[0005]
(3) In an image forming apparatus that forms an image by an electrophotographic method, the recording paper is selected in the automatic paper feeding mode and the recording paper is fed in the manual paper feeding mode with respect to the selection of the recording paper size. There is something to do. In the image forming apparatus in the automatic sheet feeding mode, the control unit selects a recording sheet from the size of the read document and the set magnification, feeds the sheet, and forms an image. In the image forming apparatus in the manual sheet feeding mode, the control unit selects and feeds a recording sheet according to the size set by the operator in the sheet feeding unit or the like, and forms an image.
[0006]
[Problems to be solved by the invention]
(1) When changing the vertical magnification, the conventional image forming apparatus sets the change timing while avoiding the exposure and the transfer.
[0007]
For this reason, if the vertical magnification is changed during the continuous image forming process, the image interval at the time of the change is extended, and the reduction in the image forming efficiency is unavoidable. There is.
[0008]
(2) In order to reliably convey the recording paper at the transfer position, an image forming apparatus provided with a pre-transfer conveyance roller between the registration roller and the transfer position has been proposed and put into practical use. In such a paper feed system of the image forming apparatus, the registration roller and the pre-transfer paper feed roller are driven by a common driving unit. However, the registration roller temporarily stops after the trailing edge of the recording paper has passed, and forms a recording paper loop by temporarily stopping the leading edge of the succeeding recording paper. Then, the conveyance of the recording paper that follows after the loop formation is started.
[0009]
In order to increase the image forming efficiency, the interval between the trailing edge of the preceding recording sheet and the leading edge of the succeeding recording sheet, i.e., the sheet interval, is narrowed. If the resist roller to be stopped and the pre-transfer sheet feeding unit are driven by a common driving unit, the conveyance of the recording paper at the transfer position becomes unstable, and transfer deviation or transfer omission may occur, resulting in a decrease in image quality.
[0010]
(3) In a transport apparatus that is required to operate while accurately maintaining a synchronous relationship with other operation units, such as a paper feed unit that transports a recording sheet to a transfer position, the transport speed is fine. Adjustment is required. However, it is not sufficient to adjust the frequency of the drive clock as in the prior art, and in order to perform fine adjustment by the conventional technique, high-cost means such as increasing the frequency of the basic clock has to be taken.
[0011]
Further, as a paper feeding means for transporting the recording paper to the transfer position, there is one using a pre-transfer paper feed roller between the registration roller and the transfer position in addition to the registration roller. Conventionally, in such a sheet feeding unit, the registration roller and the pre-transfer sheet feeding roller are integrated to adjust the recording sheet conveyance speed. However, the recording sheet of the pre-transfer sheet feeding roller closer to the transfer position is used. Adjustment of the conveyance speed was not sufficient.
[0012]
(4) In setting the recording paper size, the operator does not always set the correct recording paper size. For example, there may be a case where the A4 size is actually set even though the B5 size is set in the paper feed cassette. In such a case, the control means performs image formation control and jam control based on the B5 size set by the operator, so the jam monitoring conditions are set based on the B5 size. Therefore, a situation occurs in which the recording paper does not pass through the jam monitoring sensor within the time set for the B5 size, and the control means determines the jam.
[0013]
As described above, the conventional image forming apparatus has a disadvantage that the apparatus is stopped due to an erroneous jam determination caused by an erroneous operation.
[0014]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems in conveying recording paper in a conventional image forming apparatus.
[0015]
[Means for Solving the Problems]
The object of the present invention is achieved by the following invention.
[0016]
1. An image forming body, an exposure means for performing scanning exposure of an image on the moving image forming body, a developing means for developing an electrostatic latent image formed by the exposure means, and an image formed on the image forming body are recorded. A transfer means for transferring to the paper, and a paper feed means for transporting the recording paper to a transfer position where transfer by the transfer means is performed, and the moving speed of the image forming body and the transport speed of the paper feed means are changed. In the image forming apparatus in which the magnification of the image is changed by
An image forming apparatus, wherein the longitudinal magnification is changed by changing the moving speed of the image forming body and the conveying speed of the recording paper while the recording paper passes through the transfer position.
2. The image forming apparatus includes a fixing unit that fixes an image to the recording paper that has passed the transfer position, and a recording paper guide unit that allows a loop of the recording paper to be formed between the transfer position and the fixing unit. 2. The image forming apparatus as described in 1 above.
3. 3. The image forming apparatus according to 1 or 2 above, wherein the change of the magnification is performed when exposure by the exposure unit is not performed.
4). After forming an image on the surface of the recording paper, reverse the front and back of the recording paper, transport the recording paper to the transfer position again, and form an image on the back surface. Before the transfer of the front image formed prior to the back image formed by the magnification change is completed, the magnification change for the back image formation when the back image formation is performed differently from the magnification in the image formation 4. The image forming apparatus according to any one of 1 to 3, wherein the image forming apparatus is performed.
5). An image forming body, an exposure means for exposing the moving image forming body, a developing means for developing an electrostatic latent image formed by the exposing means, and an image formed on the image forming body is transferred to a recording paper In an image forming apparatus, the image forming apparatus includes: a transfer unit that transfers the recording paper to a transfer position where an image is transferred by the transfer unit;
A stepping motor for driving the paper feeding means, a clock generating means, a frequency dividing means for dividing the basic clock from the clock generating means, and a drive for driving the stepping motor based on a speed command clock from the frequency dividing means A drive circuit for generating a clock, and an adjusting means for changing the rotational speed of the stepping motor by changing the duty ratio of the speed command clock, and the rough rotational speed of the stepping motor is adjusted by frequency control. An image forming apparatus, wherein the fine adjustment of the rotational speed is performed by controlling the duty ratio.
6). A pre-transfer paper feeding means is provided between the paper feeding means and the transfer position, and a stepping motor for driving the pre-transfer paper feeding means is provided, and the adjustment means is the stepping motor for driving the paper feeding means. 6. The image forming apparatus according to 5, wherein a rotation speed of the stepping motor that drives the motor and the pre-transfer sheet feeding unit is adjusted.
7). 7. The image forming apparatus according to any one of claims 1 to 6, wherein the sheet feeding unit includes a registration roller that conveys a recording sheet to the transfer position in synchronization with image formation on the image forming body. .
8). In a paper conveying apparatus having a conveying means for conveying paper and a stepping motor for driving the conveying means,
A clock generator, a frequency divider for dividing the basic clock from the clock generator, a drive circuit for generating a drive clock for driving the stepping motor based on a speed command clock from the frequency divider, and the speed Adjusting means for changing the rotational speed of the stepping motor by changing the duty ratio of the command clock, and roughly adjusting the rotational speed of the stepping motor by frequency control, and finely adjusting the rotational speed. A paper conveying device characterized by being controlled by a ratio.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
(1) Embodiment 1
FIG. 1 shows an image forming apparatus according to an embodiment of the present invention.
[0034]
Around the photosensitive member 1 as an image forming member, there are a charging device 2 as a charging unit, an exposure device 3 as an exposure unit, a developing device 4 as a developing unit, a transfer separating device 5 as a transfer unit, and a cleaning unit. A cleaning device 8 is arranged. A paper feed cassette 10 for storing the recording paper P is disposed at the lower part of the apparatus, and a paper feeding unit 11, a registration sensor S, and a resist as a paper feeding means are provided in a conveyance path for the recording paper carried out of the paper feeding cassette 10. A roller 12, a transfer separating device 5, a conveying belt 6 as recording paper guiding means, and a fixing device 7 as fixing means are arranged.
[0035]
At the time of image formation, the photosensitive member 1 rotates as indicated by an arrow, and according to the rotation of the photosensitive member 1, charging by the charging device 2, image exposure by the exposure device 3 and development by the developing device are performed, and an image is formed on the photosensitive member 1. It is formed. The formed image is transferred to the recording paper P by the transfer / separation device 5 and then fixed to the recording paper P by the fixing device 7. The photoreceptor 1 that has passed the transfer position T to which the image is transferred by the transfer separation device 5 is cleaned by the cleaning device 8 to remove residual toner.
[0036]
In the double-sided image formation, the recording paper P on which the image is formed on the front surface passes through the fixing device 7 and then is sent to the back surface transport unit 13. The recording paper P is turned upside down in the transport unit 13 for the back surface, and then supplied again to the registration roller 12 and transported to the transfer position T by the registration roller 12. After the image is transferred to the back surface of the recording paper P at the transfer position T, the transferred image is fixed on the recording paper P by the fixing device 7.
[0037]
As the exposure device 3, a scanning exposure device composed of a laser diode and a scanning optical system or a scanning exposure device composed of a light emitting diode array is used, and image exposure is performed by scanning the photosensitive member 1 in the main scanning direction and the sub scanning direction. Further, as the developing device 4, a developing device that performs reversal development in which toner is attached to an exposed portion on the photoreceptor 1 with a developing bias having the same polarity as the electrostatic latent image on the photoreceptor 1 is used.
[0038]
The transport belt 6 supports and transports the recording paper P to be transported, but is not a transport means having a restraining function for transporting the recording paper P with the transport belt 6 interposed therebetween. Further, the distance from the transfer position T to the nipping portion of the recording paper P in the fixing device 7 is longer than the maximum size of the recording paper P. Therefore, as will be described later, even when the conveyance speed of the recording paper P at the transfer position T and the conveyance speed of the recording paper P in the fixing device 7 are different, the difference in speed between the two is absorbed at the conveyance belt 6. Even when the magnification is changed, the recording paper P is smoothly transported and no transfer deviation or the like occurs.
[0039]
Changing the magnification, that is, changing the magnification of the image in the moving direction of the photosensitive member 1 and the conveying direction of the recording paper P changes the rotational speed of the photosensitive member 1 and corresponds to the change in the rotational speed. It is executed by changing the rotation speed of the. That is, while the exposure means performs exposure in the main scanning and sub-scanning directions at a constant speed, the vertical magnification is changed by changing the rotation speed of the photoconductor 1 and is synchronized with the change in the rotation speed of the photoconductor 1. Thus, by changing the rotation speed of the registration roller 12, the image is transferred onto the recording paper P without causing any deviation from the photoreceptor 1.
[0040]
The motor 21 for driving the photosensitive member 1 and the motor 22 for driving the registration roller 12 are controlled and rotated by the control means 20 so that the moving speed of the peripheral surface of the photosensitive member 1 coincides with the conveyance speed of the recording paper P. To do.
[0041]
In the embodiment of the present invention, the vertical magnification of the image is changed as described above by changing the moving speed of the photosensitive member 1 and the conveying speed of the recording paper P while the recording paper P passes the transfer position T. It is configured to be able to. By such setting of the magnification change timing, it is possible to prevent a decrease in image formation efficiency when the magnification is changed.
[0042]
The prevention of a decrease in image formation efficiency at the time of changing the magnification will be described with reference to FIG.
[0043]
FIG. 2 is a diagram showing image intervals in a continuous image forming process, FIG. 2 (a) shows the timing of image formation when the magnification is changed in a conventional image forming apparatus, and FIG. 2 (b) shows the embodiment of the present invention. The timing of image formation in the case of changing the magnification in the form is shown.
[0044]
In FIG. 2, the horizontal axis is time, and the vertical axis is the distance of the image forming process. For example, the first surface image H1 is exposed at the exposure position Ex to form an electrostatic latent image, developed at De to form an image, moved to the transfer position T, and transferred to the transfer position T. Transferred to the recording paper P at T.
[0045]
In the image forming apparatus shown in FIG. 1, a non-stack type back surface transport unit 13 is provided, and the recording paper P on which an image is formed on the front surface is accumulated in the back surface transport unit 13 in the double-sided image forming process. Without being supplied to the registration roller 12.
[0046]
In double-sided image formation using such a non-stack type back surface transport unit 13, the number of recording sheets that can exist in the transport path from the transfer position T to the registration roller 12 through the back surface transport unit 13. Front surface image formation and back surface image formation are repeatedly performed in units of P. In the example of FIG. 2, the front surface image formation and the back surface image formation are repeated every three sheets as in the case of the front surface images H1, H2, and H3 and the back surface images R1, R2, and R3.
[0047]
By the way, in the rear surface image formation, a reduced image is formed on the photoreceptor 1 than in the front surface image formation, that is, in a reduced image than in the front surface image formation. The reason is the countermeasure against the following phenomenon. In the surface image forming process, the recording paper P shrinks slightly (several percent) by heat treatment by the fixing device 7. For this reason, the front image formed on the recording paper P is also reduced, and if the reduced image corresponding to this reduction is not formed in the rear image formation, a difference in image magnification occurs between the front image and the rear image. It is not preferable.
[0048]
In the prior art, such a change in magnification at the time of backside image formation is performed as shown in FIG.
[0049]
That is, the exposure of the surface images H1, H2, and H3 on the three recording papers P by the exposure device 3 is performed at the exposure position Ex and moved to the transfer position T. The recording paper P on which the image is transferred at the transfer position T is sent to the back surface transport unit 13, while the back surface of the recording paper P on which the image is formed on the front surface in the previous front surface image forming process from the back surface image transport unit 13. In order to form an image, exposure of the back images R1, R2, and R3 is performed at the exposure position Ex. At that time, as described above, the image formation is performed by changing the rotation speed of the photosensitive member 1 and the rotation speed of the registration roller 12 and the pre-transfer paper feed roller 12a so as to change the magnification of the back surface image. The time of this change is set to a time after the time TR at which the transfer of the surface image H3 to the recording paper P is completed. For this reason, a period L is inserted between the front surface image formation and the back surface image formation, and the image interval D1 becomes longer as indicated by D2. Since such a wide image formation interval D2 is set every time switching from the front surface image formation to the back surface image formation and from the back surface image formation to the front surface image formation, the image formation efficiency is lowered.
[0050]
Such a decrease in image formation efficiency at the time of changing the magnification occurs not only in the double-sided image forming process but also at the time of changing the magnification by an operator's setting operation. For example, in a continuous image forming process in which originals of various sizes are read and an image is formed on a recording paper P of a fixed size, the image interval is changed in the same manner as described above when the magnification is changed corresponding to the difference in the original size. This extends the image forming efficiency.
[0051]
The timing at the time of double-sided image formation in the embodiment of the present invention is shown in FIG.
[0052]
In the present embodiment, the magnification of the image for forming the back image R1 is changed from the front surface image formation at a time point before the time point TR at which the image transfer of the image H3 to the recording paper P is completed. That is, while the surface image H3 is at the transfer position T, the rotation speed of the photosensitive member 1 and the conveyance speed of the recording paper P are changed. When the magnification is changed, the synchronization relationship between the photosensitive member 1 and the recording paper P is maintained, so that the image is not disturbed. In such an image forming process, as shown in the figure, image formation is continuously performed at an image interval D1 without an extra period L interposed between the front surface image H3 and the back surface image R1. As a result, a decrease in image formation efficiency in double-sided image formation is prevented.
[0053]
Such an effect of preventing a decrease in image formation efficiency is exhibited not only when the double-sided image is formed, but also when changing other vertical magnifications.
[0054]
Regarding the change in the moving speed of the photosensitive member 1 accompanying the magnification change in the embodiment of the present invention, this is the image exposure period, that is, the period of passing through the exposure positions Ex of H1 to H3 and R1 to R3 in FIG. The change of the conveyance speed of the recording paper P is preferably performed by changing the rotation speed of the registration roller 12 when the registration sensor S detects the leading edge of the recording paper P. . Further, it is preferable that the fixing device 7 always transports the recording paper P at a constant transport speed. Therefore, when the rotational speeds of the photosensitive member 1 and the registration roller 12 are changed as described above, the difference between the traveling speed of the recording paper P at the transfer position T and the traveling speed of the recording paper P in the fixing device 7 is the transfer position. For example, a loop of the recording paper P is provided on the transport belt 6 as a guide means without providing a restraining means for sandwiching and transporting the recording paper P so as to be absorbed between T and the fixing device 7. It is desirable to adopt a configuration that allows it to be formed. Further, it is desirable that the distance between the transfer position T and the nipping position of the fixing device 7 by the heating / pressure roller is longer than the maximum size of the recording paper P.
[0055]
(2) Embodiment 2
FIG. 3 shows an image forming apparatus according to Embodiment 2 of the present invention.
[0056]
Around a photosensitive member 31 as an image forming member, a charging device 32 as a charging unit, an exposure device 33 as an exposure unit, a developing device 34 as a developing unit, a transfer separation device 35 as a transfer unit, and a cleaning unit A cleaning device 38 is arranged. A registration roller 41 as a paper feed unit, a pre-transfer paper feed roller 42 as a pre-transfer paper feed unit, a transfer separation device 35 as a transfer unit, and a fixing device 37 as a fixing unit are arranged in the conveyance path of the recording paper P. Is done.
[0057]
At the time of image formation, the photoconductor 31 rotates as shown by an arrow, and according to the rotation of the photoconductor 31, charging by the charging device 32, image exposure by the exposure device 33 and development by the developing device 34 are performed. Is formed. The formed image is transferred to the recording paper P by the transfer / separation device 35 and then fixed to the recording paper P by the fixing device 37. The photoreceptor 31 that has passed the transfer position T to which the image is transferred by the transfer separation device 35 is cleaned by the cleaning device 38, and the residual toner is removed.
[0058]
As the exposure device 33, a scanning exposure device including a laser diode and a scanning optical system or a scanning exposure device including a light emitting diode array is used, and image exposure is performed by scanning the photosensitive member 1 in the main scanning direction and the sub scanning direction. Further, as the developing device 34, a developing device that performs reversal development in which toner is attached to an exposed portion on the photoconductor 31 with a developing bias having the same polarity as the electrostatic latent image on the photoconductor 31 is used.
[0059]
In the present embodiment, a pre-transfer paper feed roller 42 is provided between the registration roller 41 and the transfer position T. The leading edge of the recording paper P conveyed by the registration roller 41 is correctly regulated by the pre-transfer paper feed roller 42, so that the transfer is performed stably, and transfer blur and transfer omission are prevented. The pre-transfer paper feed roller 42 is driven by a motor 51 different from the drive motor 50 of the registration roller 41. The motors 50 and 51 are stepping motors. The motor 51 has a clock generating circuit 52 as clock generating means for generating a basic clock, a frequency divider 53 as frequency dividing means for dividing the basic clock to generate a speed command clock, and a drive clock based on the speed command clock. It is driven by a drive means having a drive circuit 54 to be generated.
[0060]
The registration roller 41 temporarily stops when the leading edge of the recording paper P reaches and forms a loop of the recording paper P. This control of the registration roller 41 is performed based on a recording paper leading edge detection signal from a sensor (not shown) provided in the vicinity of the registration roller 41. In such recording paper conveyance control, the pre-transfer paper feed roller 42 is driven independently of the registration roller 41, and therefore the conveyance of the recording paper P is continued without stopping when the registration roller 41 is temporarily stopped. . Such conveyance control of the pre-transfer paper feed roller 42 stabilizes the conveyance of the recording paper P at the transfer position T, and prevents transfer deviation and transfer omission.
[0061]
The motors 50 and 51 are controlled by a control unit 56 as an adjustment unit configured by a microcomputer.
[0062]
That is, the control unit 56 starts driving the motors 50 and 51 so that the top of the image formed on the photoconductor 31 and the top of the recording paper P coincide with each other at the transfer position T. Then, the recording paper P is conveyed by the pre-transfer paper feed roller 42.
[0063]
The control means 56 also adjusts the rotational speed of the motor 51 by the method described below. This adjustment is performed in order to make the conveyance speed of the pre-transfer paper feed roller 42 coincide with the movement speed of the photoconductor 31.
[0064]
In the following, this control, that is, the adjustment of the rotation speed of the motor 51 in the present embodiment will be described with reference to FIG.
[0065]
4A shows the speed adjustment of the conventional stepping motor, and FIG. 4B shows the speed adjustment of the motor 51 in the present embodiment. In FIG. 4, TM indicates the period of the speed command clock, PL indicates the pulse width of the speed command clock, and BL indicates the pulse width of the speed command clock. In FIG. 4 and the following description, the period, the pulse width, and the inter-pulse width are represented by a frequency Hz that is the reciprocal number thereof.
[0066]
Conventional speed adjustment is performed by adjusting the period of the speed command clock divided by the frequency divider 53 as shown in FIG. It is assumed that the minimum change value of the period in this drive system is 100 Hz. When the speed command clock has a duty ratio of 50:50 and the speed command clock having a frequency TM of 1000 Hz is changed in units of the minimum change value, as shown in FIGS. The pulse width PL and the pulse width BL of the pulse can be adjusted to 2000 Hz, 2100 Hz, and 2200 Hz.
[0067]
By such adjustment, the cycle TM of the speed command clock to be formed is 1000 Hz, 1050 Hz, 1100 Hz, and 50 Hz is adjusted with the minimum change value.
[0068]
In contrast to the speed control described above, in this embodiment, as shown in FIGS. 4B, 4B, 4C, the duty ratio is set to further reduce the minimum change value of the cycle TM of the speed command clock. Is changed from 50:50 to 60:40, and each pulse is changed with a minimum change value.
[0069]
While the pulse width PL of the pulse constituting the speed command clock is changed as 2000 Hz, 2000 Hz, 2100 Hz, the pulse width BL is changed as 2000 Hz, 2100 Hz, 2100 Hz. In this change, the duty ratio changes as 50:50, 60:40, and 50:50. Then, the cycle TM of the speed command clock changes with 25 Hz as a minimum change value, such as 1000 Hz, 1025 H, and 1050 Hz. Therefore, the adjustment of the rotation speed of the stepping motor 51 can be reduced from 5% to 2.5%. As a result, finer adjustment of the pre-transfer paper feed roller 42 becomes possible, and high image quality can be achieved.
[0070]
In the present embodiment, the rotation speed of the pre-transfer sheet feed roller 42 is adjusted by a conventional control method as shown in FIG. 4A in the rough adjustment stage, and in the stage where fine adjustment is performed. The adjustment by the control method shown in FIG. With this adjustment method, it is possible to perform speed adjustment with high accuracy at low cost.
[0071]
Note that even in an image forming apparatus in which the pre-transfer sheet feeding roller 42 is not provided, that is, in an image forming apparatus in which the sheet feeding unit is configured only by registration rollers, the control method according to FIG. This adjustment makes it possible to finely adjust the recording sheet conveyance speed of the sheet feeding means.
[0072]
Further, the adjustment of the rotation speed of the paper feeding unit shown in FIG. 4B can be used for a paper transporting device other than the paper feeding unit that transports the recording paper to a transfer position such as a document transporting device.
[0073]
(3) Embodiment 3
FIG. 5 shows an image forming apparatus according to Embodiment 3 of the present invention.
[0074]
Around a photosensitive member 61 as an image forming member, a charging device 62 as a charging unit, an exposure device 63 as an exposure unit, a developing device 64 as a developing unit, a transfer separating device 65 as a transfer unit, and a cleaning unit. A cleaning device 68 is arranged. Paper cassettes 70a, 70b, and 70c that store recording paper P are disposed at the lower portion of the apparatus. The recording paper P that is stored in the paper cassettes 70a, 70b, and 70c is fed by a feed roller 73 and then separated. The sheet is separated into one sheet by the conveying roller 74 and the separating roller 75, conveyed, and conveyed to the registration roller 71 through the sheet feeding path 76. In the conveyance path of the recording paper P, a registration roller 71, a pre-transfer paper feed roller 72, a transfer separation device 65, and a fixing device 67 are arranged.
[0075]
Reference numeral 77 denotes a sensor serving as a size sensor that detects the passage of the recording paper discharged from the recording paper carrying sections of the paper feeding cassettes 70a, 70b, and 70c and carried out of these paper feeding cassettes. Whether or not P is carried out in accordance with a paper feed command, the timing of carrying out the recording paper P from the paper feed cassettes 70a, 70b and 70c, the length of the recording paper P, and the like are detected. Reference numeral 80 denotes a control means for controlling the hull of the image forming apparatus, and 81a, 81b and 81c are size setting sections provided in the paper feed cassettes 0a, 70b and 70c, respectively. Each of these size setting units is constituted by, for example, a dial, the size of the recording paper stored according to the angle of the dial is set, and the set size information is taken into the control means 80. Based on the recording paper detection signal of the sensor 77, the control means 80 detects jamming in the recording paper carry-out portions of the paper feed cassettes 70a, 70b, 70c. A display / setting unit 82 is provided with an image formation start button, a number setting button, and a display panel for performing various displays.
[0076]
At the time of image formation, the photoconductor 61 rotates as indicated by an arrow, and according to the rotation of the photoconductor 61, charging by the charging device 62, image exposure by the exposure device 63 and development by the developing device 64 are performed. Is formed. The formed image is transferred to the recording paper P by the transfer / separation device 65 and then fixed to the recording paper P by the fixing device 67. The photoreceptor 61 that has passed the transfer position T to which the image is transferred by the transfer separation device 65 is cleaned by the cleaning device 68, and the residual toner is removed.
[0077]
In the double-sided image formation, the recording paper P on which the image is formed on the front surface passes through the fixing device 67 and then is sent to the back surface transport unit 63. After the recording paper P is turned upside down in the transport unit 69 for the back surface, the recording paper P is supplied again to the registration roller 71 and is transported to the transfer position T by the registration roller 71. After the image is transferred to the back surface of the recording paper P at the transfer position T, the transferred image is fixed on the recording paper P by the fixing device 67.
[0078]
As the exposure device 63, a scanning exposure device comprising a laser diode and a scanning optical system or a scanning exposure device comprising a light emitting diode array is used, and image exposure is performed by scanning the photosensitive member 61 in the main scanning direction and the sub scanning direction. Further, as the developing device 64, a developing device that performs reversal development in which toner is attached to an exposed portion on the photosensitive member 61 by a developing bias having the same polarity as the electrostatic latent image on the photosensitive member 61 is used.
[0079]
In the present embodiment, the control means 80 selects the paper feed cassette 70a, 70b or 70c according to the size information set in the size setting section 81a, 81b or 81c, paper feed is performed, and image formation is performed. .
[0080]
Then, the control unit 80 controls the conveyance of the recording paper and the control of image formation in the image forming apparatus according to the size information set by the size setting unit 81a, 81b or 81c.
[0081]
Although not shown, in an image forming apparatus provided with a post-processing device that performs sorter, stapler, inter-sheet, reverse paper discharge, bookbinding, etc., the control means 80 performs recording paper P in post-processing according to the size information. And control in the conveyance of cover sheets, partition sheets and the like.
[0082]
By the way, in the size setting in the size setting units 81a, 81b, and 81c, the setting is not always performed correctly by the operator, and an incorrect size may be set. When such an incorrect setting is made, the control means 80 often judges that a jam has occurred and stops the apparatus.
[0083]
That is, the determination of the recording paper jam is made based on the detection of the recording paper P by the recording paper sensor including the sensor 77 provided in the recording paper conveyance path. For example, the sensor 77 corresponds to the paper size. When the recording paper P does not pass within the set time when the set size paper passes, the control unit 80 determines that a jam has occurred and stops the image forming apparatus. Let
[0084]
If the operator mistakenly operates and sets a size smaller than the size of the recording paper that is actually conveyed, the sensor 77 detects a passage time longer than the time specified by the operator setting. . In such a case, the control unit 80 determines that a jam has occurred even though a jam has not occurred. As a result, a jam is displayed on the display / setting unit 82, and the control unit 80 stops the entire apparatus.
[0085]
In this embodiment, in this case, that is, the length of the recording paper P corresponding to the recording paper size set by the operator (length in the transport direction) and the length of the recording paper P detected by the sensor 77. When the length (the length in the transport direction) does not match, the control unit 80 adopts the length of the recording paper P detected by the sensor 77, executes the transport of the recording paper P, and executes the image formation. . This control eliminates problems such as inconvenience in operation, wasteful consumption of the recording paper P, and reduction in image forming efficiency due to the image forming apparatus being unnecessarily stopped.
[0086]
FIG. 6 is a flowchart of control by the control means 80 in the present embodiment.
[0087]
The control means 80 performs control as described below.
In F2, paper is fed from the paper feed cassette 70a, 70b or 70c. Next, in F3, the size information set in the size setting unit 81a, 81b or 81c is read, and the size detection for reading the output of the sensor 77 is performed.
[0088]
When the detected size of the recording paper P matches the size set by the operator (Y in F4), it has become clear that the operator has not made a wrong setting, and normal image formation is performed. In other words, the conveyance control of the recording paper P and the image formation in F5 are performed, and the process ends.
[0089]
If the detected size of the recording paper P does not match the size set by the operator (N in F4), it is checked whether the length of the recording paper P detected by the sensor 77 is equal to or less than the maximum size. (F7). When the length is larger than the maximum size, it is determined that a jam has occurred, the jam is displayed, and the apparatus is stopped (F10). When the detected length is less than or equal to the maximum size, the conveyance control of the recording paper P according to the size of the recording paper P detected by the sensor 77 and the detected size of the recording paper P are used. After the image formation is performed (F8), a display for prompting the operator to correct the size setting is performed, the apparatus is stopped (F9), and the process is terminated.
[0090]
Since the selection of the recording paper size different from the operator setting and the image formation on the selected recording paper P are not normal image formation, the image forming apparatus is stopped after the image formation is completed. It is desirable to restore it to its original state. In the present embodiment, in F9, a display prompting the operator to set the size is performed, and a flag is set in F9 (f = 1). With this process, when carrying and image formation in F8, a size setting warning is displayed. When the size is not reset at the start of the next image formation, that is, when f = 1 in the determination of F1, a display prompting the size setting is displayed (F11), and the recording paper is conveyed. And the image formation is completed without starting. As a result of the resetting, when the set recording paper size matches the detected recording paper size (N of F1), the recording paper P is transported and images are formed in F2 and F5. In F6, the flag is reset (f = 0).
[0091]
【The invention's effect】
According to the first aspect of the present invention, when the magnification in the moving direction of the image forming body is changed during the continuous image forming process, the image interval is not greatly increased by the change. The reduction is prevented, and continuous image formation can be performed with high image formation efficiency.
[0092]
According to the second aspect of the present invention, the difference between the recording paper conveyance speed at the transfer position and the recording paper conveyance speed at the fixing means is absorbed by the recording paper guiding means between them, so that the recording paper accompanying the change in magnification The problem of inconsistency in conveyance is solved.
[0093]
According to the third aspect of the present invention, even if the magnification is changed during the continuous image forming process, a good image is formed without causing inconveniences such as image distortion.
[0094]
According to the invention of claim 4, a double-sided image having no size difference between the front image and the back image due to fixing is formed with high image forming efficiency.
[0098]
Claim 5, 6 or 7 With this invention, the conveyance speed of the paper feeding means for conveying the recording paper in synchronization with the image formation on the image forming body can be finely adjusted by a simple method, so that the conveyance of the recording paper at the transfer position is stable. It is possible to form a high-quality image.
[0099]
Claim 8 According to the present invention, a paper transport device that feeds recording paper to the transfer position of the image forming apparatus, and a paper transport device that can finely adjust the transport speed of the paper feed means that transports the document to the reading position of the document reading device. Is realized.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an entire image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating image intervals in a continuous image forming process.
FIG. 3 is a diagram illustrating an entire image forming apparatus according to a second embodiment of the present invention.
FIG. 4 is a diagram for explaining speed control of a stepping motor.
FIG. 5 is a diagram illustrating an entire image forming apparatus according to a third embodiment of the present invention.
FIG. 6 is a flowchart of control in Embodiment 3 of the present invention.
[Explanation of symbols]
1, 31, 61 Photoconductor
2, 32, 62 Charging device
3, 33, 63 Exposure apparatus
4, 34, 64 Development device
5, 35, 65 Transfer separation device
7, 37, 67 Fixing device
21, 22, 50, 51 Motor
12, 41, 71 Registration roller
42, 72 Pre-transfer feed roller
20, 56, 80 Control means
P Recording paper
T Transcription position

Claims (8)

An image forming body, an exposure means for performing scanning exposure of an image on the moving image forming body, a developing means for developing an electrostatic latent image formed by the exposure means, and an image formed on the image forming body are recorded. A transfer means for transferring to the paper, and a paper feed means for transporting the recording paper to a transfer position where transfer by the transfer means is performed, and the moving speed of the image forming body and the transport speed of the paper feed means are changed. In the image forming apparatus in which the magnification of the image is changed by
An image forming apparatus, wherein the longitudinal magnification is changed by changing the moving speed of the image forming body and the conveying speed of the recording paper while the recording paper passes through the transfer position.   The image forming apparatus has fixing means for fixing an image to the recording paper that has passed the transfer position, and recording paper guide means for allowing a recording paper loop to be formed between the transfer position and the fixing means. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the change of the magnification is performed when exposure by the exposure unit is not performed.   After forming an image on the surface of the recording paper, reverse the front and back of the recording paper, transport the recording paper to the transfer position again, and form an image on the back surface. Before the transfer of the front image formed prior to the back image formed by the magnification change is completed, the magnification change for the back image formation when the back image formation is performed differently from the magnification in the image formation The image forming apparatus according to claim 1, wherein the image forming apparatus is performed. An image forming body, an exposure means for exposing the moving image forming body, a developing means for developing an electrostatic latent image formed by the exposing means, and an image formed on the image forming body is transferred to a recording paper In an image forming apparatus, the image forming apparatus includes: a transfer unit that transfers the recording paper to a transfer position where an image is transferred by the transfer unit;
A stepping motor for driving the paper feeding means, a clock generating means, a frequency dividing means for dividing the basic clock from the clock generating means, and a drive for driving the stepping motor based on a speed command clock from the frequency dividing means A drive circuit for generating a clock, and an adjusting means for changing the rotational speed of the stepping motor by changing the duty ratio of the speed command clock, and the rough rotational speed of the stepping motor is adjusted by frequency control. An image forming apparatus, wherein the fine adjustment of the rotational speed is performed by controlling the duty ratio.   A pre-transfer paper feeding means is provided between the paper feeding means and the transfer position, and a stepping motor for driving the pre-transfer paper feeding means is provided, and the adjustment means is the stepping motor for driving the paper feeding means. The image forming apparatus according to claim 5, wherein a rotation speed of the stepping motor that drives the motor and the pre-transfer sheet feeding unit is adjusted.   The image forming apparatus according to claim 1, wherein the sheet feeding unit includes a registration roller that conveys a recording sheet to the transfer position in synchronization with image formation on the image forming body. apparatus. In a paper conveying apparatus having a conveying means for conveying paper and a stepping motor for driving the conveying means,
A clock generator, a frequency divider for dividing the basic clock from the clock generator, a drive circuit for generating a drive clock for driving the stepping motor based on a speed command clock from the frequency divider, and the speed Adjusting means for changing the rotational speed of the stepping motor by changing the duty ratio of the command clock, and roughly adjusting the rotational speed of the stepping motor by frequency control, and finely adjusting the rotational speed. A paper conveying device characterized by being controlled by a ratio.

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