JP2001296785A - Image-formation timing control method and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new image-formation timing control method for preventing the adverse effect of the slip amount of a corresponding page from affecting the transport of the recording paper of a next page. SOLUTION: In this image-formation timing control method for an image forming device where the paper transport path is shorter than the image forming path, and skew correction and the adjustment of the position of an image on the recording paper are performed by a resist roller; an image-formation operation for the next page in which writing operation is set as a top is started roughly in timing by setting timing to detect the leading edge of the recording paper transported from a paper supply part to the resist roller part at the time of consecutive printing by a sensor (for example, paper supply sensor) arranged in a paper supply transport path as reference. That is, in the printing of the second and succeeding sheets of paper, the image-formation operation in which the writing is set as the top is started after a fixed time (t) elapses by setting the point of time when the leading edge of the recording paper of the previous page is detected by the paper supply sensor as the starting point of time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming timing control method in an image forming apparatus involving paper conveyance, and to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter, or a printing apparatus. The present invention relates to a forming apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine and a printer which involves paper conveyance, there are two methods of adjusting an image position on a recording sheet, a registration roller method and a registration sensor method. As an example of the prior art based on these methods, Japanese Patent Application Laid-Open No. 8-106186 discloses that a registration roller that adjusts the writing position of a sheet and corrects skew, and that is positioned upstream of the registration roller. In an image forming apparatus having a grip roller that absorbs a load of a paper feeding unit so as to maintain the conveyance accuracy of the sheet by the registration roller, and a registration sensor that detects that the leading end of the sheet has reached the registration roller, A sheet conveyance device for an image forming apparatus, wherein a time for stopping the driving of the grip roller and slackening the sheet from the detection of the front end of the sheet by the registration sensor is changed for each predetermined number of sheets passed. Japanese Patent Application Laid-Open No. Hei 10-291563 discloses that “a first paper feed unit having a first paper feed roller, A detection sensor for detecting passage of a predetermined position, and at least one or more second supply units disposed at a position where a distance from the detection sensor is longer than a distance between the detection sensor and the first sheet supply unit. A paper section, a second paper supply roller provided in the second paper supply section, and a paper sheet fed from the second paper supply section located between the second paper supply section and the detection sensor. And a driving unit that drives the second paper feed roller based on a detection result of the rear end detection sensor during continuous paper feeding from the second paper feeding unit. And a sheet feeding device characterized in that detection of a sheet by a detection sensor triggers writing of an electrostatic latent image by a laser writing unit.
Is disclosed. The above prior art is an invention based on a registration roller system, and the prior art is an invention based on a registration sensor system.

[0003]

In the registration roller system, skew (skew) is corrected by once stopping the recording paper by abutting the recording paper against the registration roller, and then adjusting the image forming timing of the image forming unit. By rotating the registration roller and re-conveying, the image position on the recording paper can be adjusted. In this method, the image writing timing in the image forming unit is not particularly defined, and an image written at an arbitrary timing is
The recording paper is conveyed by adjusting the position of the recording paper in the registration roller section. Normally, in the registration roller method, an image forming operation, a paper feeding operation, and a registration paper feeding operation starting with writing are written in a series of sequences, and the time relationship between them is fixed by the sequence.
On the other hand, in the registration sensor system, the image forming operation starting from writing is started by an input from the registration sensor as a trigger, so that the paper feeding operation and the image forming operation do not always have a fixed time relationship. This is because, when the recording paper conveyed by the paper feeding operation is slipped, the start of the image forming operation is delayed by that much.
Therefore, in the registration sensor method, the image forming operation and the paper feeding operation are not written in a series of sequences, but are usually written separately.

[0004] The image position adjustment methods of the resist roller method and the registration sensor method can be summarized as follows. The former is a method of transporting a recording paper in accordance with a created toner image, and the latter is a method of transporting a toner image in accordance with a transported recording paper. How to create, can be said. The registration roller method has a drawback in that the time relationship between the sheet feeding operation, the resist sheet feeding operation, and the image forming operation is determined, and therefore, there is little margin for a time delay due to slippage during paper conveyance. Of course, there is a time to stop in the state of hitting the registration roller, so there is no problem if the time delay is long enough to absorb it, but if it is delayed more, the image position on the recording paper shifts forward and if it is severe, The image may protrude from the leading edge of the recording paper. Most of the slip mentioned here occurs at the time of sheet pickup. The slip distance tends to increase as the sheet feeding speed increases. In the resist sensor method,
Since the image writing is started based on the leading edge of the recording paper, the recording paper slip distance until reaching the registration sensor is automatically canceled. However, since there is no skew correction mechanism, when the recording paper is skewed, the image is transferred in an inclined state with respect to the recording paper,
In the first place, this registration sensor method has a drawback that it cannot be established unless the paper transport path is longer than the image forming path.
In addition, if the detection of the leading edge of the paper by the registration sensor is not processed by the first-priority interrupt, the image position on the recording paper is shifted every time.

Here, in the image forming apparatus to which the present invention is applied, since it is assumed that "the paper transport path is shorter than the image forming path", the registration sensor method cannot be adopted. Therefore, the registration roller system must be used, but as described above, the registration roller system is somewhat disadvantageous with respect to slip of the recording paper. This is because the image forming operation is started prior to the sheet feeding operation (because the paper transport path is shorter than the image forming path), so the time from the start of sheet feeding to the registration unit is limited to a certain time. Because it can be done. In addition, this point is disadvantageous because the slip amount increases as the conveying linear velocity increases. Normally, the image forming sequence start timing is set at a constant interval converted from the recording paper length and the paper interval. If the recording paper slips in this case,
When the slip amount is large, the recording paper of the next page may not have passed through the paper feeding unit by the timing of feeding the recording paper of the next page, and the paper may be continuously fed. Although the probability of occurrence of this continuous feed varies depending on the set values of the paper conveyance linear speed and the paper interval, it is ideal to configure and control the paper so that it can be conveyed at high speed between short papers.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and provides a novel image forming timing control method for preventing the adverse effect of the slip amount of a next page on the conveyance of a recording sheet. And an image forming apparatus equipped with the control method. More specifically, by using the recording paper leading edge detection signal after the completion of the pickup operation in which the recording paper slip is most likely to occur as a trigger for the image forming / feeding operation of the next page, the occurrence of the continuous feeding due to the occurrence of the slip is generated. An object of the present invention is to provide an image forming apparatus which eliminates the possibility and enables high-speed conveyance between short sheets.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, a paper transport path is shorter than an image forming path, and skew correction and image position adjustment on recording paper are performed by registration rollers. In the image forming timing control method in the apparatus, during continuous printing, the leading end of the recording paper conveyed from the paper supply unit to the registration roller unit is roughly determined based on the timing detected by a sensor arranged in the paper supply conveyance path. The image forming operation of the next page is started with the writing operation at the beginning.

According to a second aspect of the present invention, there is provided an image forming section for performing an image forming operation, a paper feeding section for storing recording paper, and means for feeding and conveying the recording paper of the paper feeding section to the image forming section. An image forming apparatus in which a paper transport path is shorter than an image forming path, and a skew correction and an image position adjustment on a recording sheet are performed by a registration roller, wherein a sheet feeding operation is performed at a fixed timing in an image forming operation sequence. The image forming timing control method described in Item 1 is mounted.

According to a third aspect of the present invention, there is provided an image forming unit for performing an image forming operation, a paper feeding unit for storing recording paper, and means for feeding and conveying the recording paper of the paper feeding unit to the image forming unit. In the image forming apparatus in which the paper transport path is shorter than the image forming path, and the skew correction and the image position adjustment on the recording paper are performed by the registration rollers, the sensor disposed in the paper transport path detects the trailing edge of the previous recording paper. In this method, the sheet feeding operation is performed so that the distance between sheets becomes constant based on the time point, and the image forming timing control method according to claim 1 is mounted.

According to a fourth aspect of the present invention, in the image forming timing control method according to the first aspect, a paper feed sensor installed immediately after the pickup unit is used as the sensor for detecting the leading end of the recording paper, and the control is performed. By using a timer function in the unit, the image forming operation start timing of the next page starting from the write operation is roughly adjusted.

According to a fifth aspect of the present invention, in the image forming timing control method according to the first aspect, a jam detection sensor disposed in a paper feed path is used as a sensor for detecting the leading edge of the recording sheet, and the jam is detected. By installing the detection sensor at an appropriate position at the writing start timing of the next page,
It is characterized in that the image forming operation start timing of the next page starting from the write operation is roughly adjusted.

According to a sixth aspect of the present invention, there is provided an image forming section for performing an image forming operation, a paper feeding section for storing recording paper, and means for feeding and conveying the recording paper of the paper feeding section to the image forming section. An image forming apparatus in which a paper conveying path is shorter than an image forming path, and skew correction and image position adjustment on recording paper are performed by a registration roller, wherein the image forming timing control method according to claim 4 or 5 is mounted. I have. According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, since the number of paper supply units is multi-stage and various, and the recording paper size is also various, the length of the paper transport path and the image forming operation for the next page are performed. If the start timing is not uniform and a problem occurs in one of the control methods of claims 4 and 5, it is necessary to use the image formation timing control method of claims 4 and 5 together. Features.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction, operation and operation of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. In this image forming apparatus, an image forming unit 10 includes four image forming units 10a, 10b, 10c, and 10d, and different color images are formed on the respective photoconductors 11 of the four image forming units 10a, 10b, 10c, and 10d. After forming an image (for example, a single-color image of each color of cyan, magenta, yellow, and black), the image is superimposed on the same position of one intermediate transfer belt 15 and primary-transferred, and then superimposed on the intermediate transfer belt 15 This is a color image forming apparatus in which images are secondarily transferred collectively to recording paper fed and conveyed from a paper feeding unit 30 and fixed to obtain a multi-color image or a full-color image.

In FIG. 1, four image forming units 10
a, 10b, 10c, and 10d are similarly configured,
Each photoconductor 11 is provided as an image carrier, and each photoconductor 11 is rotated in a direction indicated by an arrow in FIG. Each photoconductor 11
A charging unit 12 for uniformly charging the photoconductor 11, a writing unit for forming an electrostatic latent image by exposing each charged photoconductor 11 to a laser beam or the like controlled in accordance with image data 13, a developing unit 14 for developing and visualizing the electrostatic latent image on the photoconductor with toner, a primary transfer roller 16 for transferring the toner image on the photoconductor to the intermediate transfer belt 15,
Static elimination lamp 1 for neutralizing the photoreceptor surface after transfer of the toner image
7. A cleaning unit 18 for removing residual toner on the surface of the photoconductor is provided. Further, an intermediate transfer belt 1 for superimposing a single color image of each color on each photoconductor 11
5 so that the primary transfer roller 1
6 is suspended. The intermediate transfer belt 15 includes a plurality of rollers 19, 20, 21, 22, 23, 2 including drive rollers and driven rollers in addition to the primary transfer roller 16.
4 and rotated in the direction of the arrow in the figure. Also,
Contact position between the intermediate transfer belt 15 and the recording paper (secondary transfer section)
, A secondary transfer roller 25 is provided so as to face the intermediate transfer belt 15, and a belt cleaning unit 26 is provided at a position of the roller 20 opposite to the secondary transfer portion. Further, a fixing unit 27 is provided downstream of the secondary transfer section in the recording paper conveyance direction.

Further, below the image forming section 10, there is provided a sheet feeding section 30 having three sheet feeding cassettes 31, 32, 33, and tray bottom plates 31a, 31a of the respective sheet feeding cassettes 31, 32, 33 are provided. Recording papers (not shown) of various sizes are placed on 32a and 33a, respectively. In the paper supply unit 30, recording paper is supplied from any one of the three paper supply cassettes 31, 32, and 33 by paper supply means in accordance with the image forming operation of the image forming unit 10. In the example shown in the figure, the sheet cassettes 31 and 3 are used as sheet feeding units.
Pickup rollers 34 corresponding to 2, 33, respectively.
A paper feed roller 35 and a reverse roller 36 are provided, and a paper feed sensor 37 is provided near each paper feed roller 35.
-1, 37-2 and 37-3 are provided. Further, jam detection sensors 38-1, 38-2, and 38-3 and conveyance rollers 39- are provided in the conveyance path 41 of the fed recording paper.
1, 39-2, 39-3 are provided, and in the vicinity of the secondary transfer roller 25 in the transport path 41, the timing on the image on the intermediate transfer belt 15 comes to the position of the secondary transfer roller 25. A registration roller 43 is provided to feed the recording paper toward a contact portion (secondary transfer portion) between the intermediate transfer belt 15 and the secondary transfer roller 25. In addition, a pre-registration sensor 42 is provided on the conveyance path before the registration roller 43.

In the image forming apparatus having the configuration shown in FIG. 1, when an image forming operation is started, each of the image forming units 10a, 10b,
First, the surfaces of the photoconductors 10c and 10d are uniformly charged by the charging charger 12, and then the surfaces are exposed by the writing unit 13 in accordance with the image data.
An electrostatic latent image is formed. The formed electrostatic latent image is developed by supplying toner of each color (for example, cyan, magenta, yellow, and black) in the developing unit 14 to form a toner image. The toner images of the respective colors formed on the respective photoconductors 11 are sequentially superimposed and transferred onto the intermediate transfer belt 15 by the pressure and electric field by the respective primary transfer rollers 16 to form a color image on the intermediate transfer belt 15. The intermediate transfer belt 15 carrying the full-color image on its surface further comes into contact with the secondary transfer roller 25 at any one of the three paper feed cassettes 31, 32, and 33 of the paper feed unit 30 in the lower part of FIG. The sheet comes in contact with the recording sheet fed from one of the sheet feeding cassettes and conveyed through the conveyance path 41, and is transferred onto the recording sheet by the pressure and electric field applied by the secondary transfer roller 25. The recording paper to which the full-color toner image has been transferred passes through the fixing unit 27, where the image is fixed, and is discharged to a discharge unit outside the apparatus. Further, the intermediate transfer belt 15 carrying the secondary transfer residual toner image on its surface is rotated as it is, and its surface is cleaned by a belt cleaning unit 26 installed at the left end in the figure to prepare for transfer of the next image. On the other hand, each photoconductor 11 after the primary transfer process is provided with a discharging lamp 17.
The surface of the toner is discharged, and the cleaning unit 18 removes all residual toner. This is one cycle of image formation.

In FIG. 1, the static elimination lamp 17 is installed in front of the cleaning unit 18; however, the order may be reversed, and one static elimination lamp may be arranged before and after the cleaning unit 18. In some cases, it is installed. In addition, the paper feed unit 30 includes each paper feed cassette 3
1, 32, and 33, a pickup roller 34, a paper feed roller 35, a reverse roller 36, a paper feed sensor 37-
1-37-3, which are commonly referred to as FRR
Although the paper feeding method is used, it is only drawn as a representative example of the paper feeding means, and is not particularly limited to this paper feeding method. Also,
Although not shown in FIG. 1, the image forming apparatus is provided with a control unit for controlling an image forming operation, a sheet feeding / conveying operation, and the like. The control unit includes a central processing unit including a microcomputer. It is composed of a processing unit (CPU), memories such as ROM and RAM, clocks, various timers, counters, input / output circuits, various control circuits, etc., and receives signals from various sensors such as a paper feed sensor, a jam detection sensor, and a pre-registration sensor. Based on the detection information, various controls such as a sheet feeding / transporting operation and image forming timing control described below are performed.

Although the configuration example of the image forming apparatus has been described above, according to the first aspect of the present invention, the paper transport path is shorter than the image forming path, and the skew correction and the image position adjustment on the recording paper are performed by the registration rollers. This is an image forming timing control method in the apparatus, and detects the timing at which the leading edge of the recording paper conveyed from the paper supply unit 30 to the registration roller unit 43 is detected by various sensors arranged in the paper supply conveyance path 41 during continuous printing. It is characterized in that the image forming operation of the next page, starting from the writing operation, is started roughly in synchronization with the reference. Here, the above-mentioned "paper transport path" means a distance from the leading position of the recording paper in the paper feed cassette to the contact position between the intermediate transfer belt 15 and the secondary transfer roller 25. Similarly, the “image forming pass” is the first color (the image forming unit 1 at the left end in FIG. 1).
0a) is the distance from the exposure position on the photoconductor 11 (the lower side of the photoconductor) to the contact position between the intermediate transfer belt 15 and the secondary transfer roller 25. The relationship between the lengths is
This is important when selecting an image position adjustment method on recording paper. Generally, in an image forming apparatus, there are two methods for adjusting an image position on a recording sheet. One is a method of conveying a recording sheet in accordance with a formed toner image (registration roller method), and the other is a method of conveying a recording sheet. This is a method (registration sensor method) in which a toner image is formed in conformity with the recording paper that has been received. In the former case, the secondary transfer position (FIG. 1)
The positional relationship between the toner image and the recording paper is adjusted by controlling the registration roller 43 installed immediately before (the contact position between the intermediate transfer belt 15 and the secondary transfer roller 25). In this method, it is essential that the distance from the registration roller 43 to the secondary transfer position is shorter than the image forming path. However, if the registration roller 43 is installed so as to satisfy this condition, the distance between the paper conveyance path and the image forming path can be reduced. The length relationship is not important. However, in the latter case, it is an essential condition that the paper transport path is longer because image formation is started in accordance with the transported recording paper.

In the present invention, as described above, it is assumed that "the paper transport path is shorter than the image forming path", so that the registration roller method is inevitably adopted. The three paper cassettes 31, 32,
33, the paper cassette 31 and the paper cassette 3
It can be seen from FIG. 2 that the paper transport path for No. 2 is shorter than the image forming path. However, regarding the paper feed cassette 33, the paper transport path may be longer. Accordingly, the present invention relates to an image forming apparatus equipped with a paper cassette having a distance relationship such as a paper cassette 31 or a paper cassette 32.
An image forming apparatus including a paper cassette 32 and a paper feeding path shorter than the image forming path and performing skew correction and image position adjustment on the recording paper by the registration rollers 43 will be described.

In the image forming timing control method according to the first aspect of the present invention, it is preferable that the timing at which the leading end of the recording paper conveyed from the paper supply unit to the registration roller unit is detected by a sensor arranged in the paper supply conveyance path is used. The sensor is typically a paper feed sensor 37- shown in FIG.
1, 37-2. These paper feed sensors 37-1, 37-
Numeral 2 is always installed at the exit of the paper feed cassette in order to check whether the recording paper has been normally picked up from the paper feed cassette. This type of sensor input is recognized and processed in a periodic interrupt, and precise timing cannot be obtained in a strict sense.However, if it is only a rough timing to start an imaging sequence, there is no problem. No. Therefore, when the sheet feed sensor detects the leading edge of the recording sheet, the timer starts counting the time using a timer function in a control unit (not shown), and counts up to a count value corresponding to a desired timing. Just start it. Since this count value depends on the length of the paper feed path and the length of the recording paper, it naturally differs for each paper feed cassette and recording paper size. FIG. 2 shows an example of the sequence control operation when this series of sequence control is applied to a sheet cassette meeting the conditions of the present invention.
(A) and (b) show the timing charts.

Although the timing charts shown in FIGS. 2A and 2B show only a part of the components in the image forming apparatus, what is necessary for explaining the timing control of the image position adjustment on the recording paper is described here. Only the parts described.
In FIG. 2, in the first printing, after starting an image forming operation starting with writing at an arbitrary timing, a paper feeding operation is performed roughly in synchronization with the image, and the recording paper is transferred to a registration roller. The sheet is conveyed, and the resist sheet feeding operation is performed at exactly the right timing. In the printing of the second and subsequent sheets, the time when the leading end of the recording paper of the previous page is detected by the paper feed sensor is set as the starting point of time, and an image forming operation starting with writing is started after a fixed time. Note that this fixed time is indicated as t in FIG. The advantage of using the recording paper of the previous page as a reference is that the influence of the distance that the recording paper of the previous page has slipped during pickup is not exerted on the next page and thereafter.

After the writing operation is started after a predetermined time t,
With this timing as the starting point of time, the resist feeding operation is performed after time R. The paper feeding operation is performed at an arbitrary timing in time for registration paper feeding after time R. FIG.
(A) and (b) show the timing chart of the sheet cassette and the sheet cassette, and the time from the start of the writing operation to the start of the sheet feeding operation (in FIG. Is denoted by K), the paper feed cassette is shorter. This is because the paper cassette has a longer paper transport path,
This is because sheet feeding must be performed at an earlier timing for the writing operation. On the other hand, the time R has the same length. This is because the time R is based on the length of the image forming path and not on the length of the paper transport path. Conversely, the time t is shorter in the sheet cassette. This is because it is necessary to shorten the time from the start of sheet feeding to the start of the next image formation because the sheet feeding cassette is slower in sheet feeding timing than image forming timing. Considering that the operation interval of the pickup roller is constant irrespective of the paper feed cassette as long as the sheet interval is constant, it can be easily understood that the time length of t + K is constant. If the length of the time t in the figure exceeds the distance between the dotted lines (t + K in the figure), the condition that the paper transport path is shorter than the image forming path, which is a premise of the present invention, is not satisfied. Situation shall not be considered. Conversely, when the image forming pass is extremely longer than the paper transport pass, the time when the recording paper of the previous page is detected, not the time when the previous page of recording paper is detected by the paper feed sensor, is set as the starting point of time. Situations that must occur can occur. Actually, it seems that there is not so much, but the concept of the timing in that case is based on the concept shown in FIG. In other words, the image forming operation is started at an arbitrary timing up to the second page using the detection of the leading edge of the recording paper as the timing reference for the image formation after the third page.

According to the second aspect of the present invention, in the image forming apparatus, the paper transport path is shorter than the image forming path and the skew correction and the image position adjustment on the recording paper are performed by the registration rollers. In this method, the sheet feeding operation is performed at a fixed timing in the sequence, and the image forming timing control method according to claim 1 is mounted. FIG. 3 shows a timing chart in this case.
This timing chart is based on the timing of the "sheet feed cassette" in FIG.

In [Case 1] of FIG. 3A, a timing chart when the recording paper is conveyed without slipping is shown. The paper feeding operation (the operation of the pickup roller in the figure) is performed after a time K from the start of the image forming sequence.
It is stipulated that the recording is performed later, and the picked-up recording paper is detected by the paper feed sensor after a predetermined time a. The image forming operation start timing of the next page is set to be performed after time t, with the detected time as the start point of time. The registration sheet feeding is performed after a time R from the start of the image forming operation, and the image position on the recording paper is determined by the time R. Note that if the recording paper is not present in the registration unit after the time R from the start of the image forming operation (that is, the recording paper slips greatly during pickup), or if the recording paper slips after the registration paper is fed, the image position on the recording paper will be shifted. However, there is no workaround for these (although the former has the option to be stopped as a jam error).

FIG. 3 (b) [Case 2] shows a timing chart when the recording paper slips during pickup. When no slip occurs, it takes only a time from the pickup to the detection of the paper feed sensor (see [Case 1] in FIG. 3A), but when a slip occurs as in [Case 2], it is longer. It can be seen that time b is required. Depending on the time b, the image position on the paper corresponding to the slip may be shifted.
However, since the image forming start timing of the next page is performed with reference to the leading edge of the slipped recording paper, the image formation is temporally shifted by the slip distance. For this reason, the paper feeding operation fixed in the image forming operation sequence is also shifted backward, and the paper is fed at a fixed interval (L in the timing chart of [Case 2]) for the slipped recording paper. Will start.

For comparison, FIG. 3C shows [Case 2].
-1] is a timing chart when the image forming start timing is set to a fixed interval. In this case, the start of the image forming operation is performed after a predetermined time i from the start of the image forming operation of the previous page. In this case, if the recording paper slips, the image forming operation of the next page starts without considering the slip amount, so that the recording paper interval with the next page is narrowed (interval L becomes short), and there is a slip distance. If it becomes larger than a certain value, there is no space between sheets, resulting in continuous feeding jam. Therefore, the advantage of mounting the image forming timing control method according to claim 1 on an image forming apparatus that performs a sheet feeding operation at a fixed timing in the image forming operation sequence (claim 2) is that slippage occurs during pickup. When the error occurs, the continuous printing operation can be continued while avoiding continuous feeding of the next page.

According to a third aspect of the present invention, in the image forming apparatus in which the paper transport path is shorter than the image forming path and the skew correction and the image position adjustment on the recording paper are performed by the registration rollers, the trailing edge of the previous recording paper is adjusted. A paper feed operation for performing a paper feed operation such that a distance between sheets becomes constant based on a time point detected by a sensor disposed in a paper feed path.
The image forming timing control method described in (1) is mounted. FIG. 4 shows a timing chart in this case.
Note that this timing chart is also based on the timing of the "sheet feed cassette" in FIG. 2, as in FIG.

FIG. 4A shows a case 1 in which the recording sheet is conveyed without slippage. The paper feeding operation (the operation of the pickup roller in the drawing) is defined to be performed after a time K from the detection of the trailing edge of the recording paper of the previous page. Detected by paper feed sensor. That is, the sheet feeding operation is repeated while keeping the sheet interval at K + a (the unit is time). The timing of starting the image forming operation on the next page is exactly the same as that described in the preceding paragraph.

FIG. 4B shows a timing chart when the recording paper slips during pickup. Normally, it takes only a time a from the start of the pickup to the detection of the paper feed sensor, but it can be seen that a longer time b is required due to the occurrence of the slip. Depending on the time b, the image position on the paper corresponding to the slip may be shifted. However, since the image forming operation start timing of the next page is performed with reference to the leading end of the slipped recording paper, image formation is temporally shifted by the slip distance. Also, the start of the feeding operation of the next page is performed on the basis of the trailing end of the slipped recording paper, and therefore, similarly, the paper is shifted backward in time by the slip amount. Therefore, both the start of image formation and the start of sheet feeding are shifted backward, so that the image formation of the next page is not affected by the slip.

For comparison, FIG. 4C shows [Case 2].
-1] is a timing chart when the image forming start timing is set to a fixed interval. In this case, the start of the image forming operation is performed after a predetermined time i from the start of the image forming operation of the previous page. In this case, if the recording paper slips, the paper feeding operation of the next page shifts backward according to the slipped recording paper, but the image forming operation starts at a predetermined timing. Therefore, the amount of slip once cannot be eliminated during continuous printing, and in the timing chart of [Case 2-1], the recording paper does not reach the registration section at the registration sheet feeding timing of the next page. It can be seen that the paper corresponding to the slip has not reached the resist part in the same manner. Therefore, the advantage of mounting the image forming timing control method of claim 1 on an image forming apparatus that performs a sheet feeding operation so that the distance between sheets is constant (claim 3) is that slip occurs. In this case, the slip amount is eliminated within one page of printing, and the continuous printing operation can be continued.

According to a fourth aspect of the present invention, in the image forming timing control method according to the first aspect, a paper feed sensor installed immediately after the pickup unit is used as a sensor for detecting the leading end of the recording paper. In addition, by using the timer function in the control unit together, the start timing of the image forming operation starting from the writing operation on the next page is roughly adjusted. The image forming apparatus equipped with this image forming timing control method (Claim 6) performs the same timing control as that described in the second and third embodiments. Specifically, the sensor from which the writing is started is the paper feed sensor 37-1 when feeding paper from the paper feed cassette 31 shown in FIG. These paper feed sensors are sensors that are always installed to detect a pickup failure, and are used together for starting writing. Usually, the control unit of the image forming apparatus has several types of timer functions, and one of them may be used to count time. 2 to 4 using this timer.
After counting the time t shown in (1), the image forming operation including the writing operation may be started.

According to a fifth aspect of the present invention, in the image forming timing control method according to the first aspect, a jam detection sensor disposed in a paper feed conveyance path is used as a sensor for detecting the leading edge of the recording paper, and By installing this jam detection sensor at an appropriate position for the writing start timing of the next page, the image forming operation start timing of the next page starting with the writing operation is roughly adjusted. In the image forming apparatus equipped with this image forming timing control method (Claim 6), the function of the paper feed sensor described in the second and third embodiments is replaced by a jam detection sensor (reference numeral 38 in FIG. 1). −
1, 38-2, 38-3) to perform timing control. Unlike the paper feed sensors, these jam detection sensors 38-1, 38-2, and 38-3 do not have one for each paper feed cassette. However, the longer the paper transport path, the more
Since the probability of occurrence of jam on the route increases, it becomes necessary to install a sensor for detecting the jam. Therefore, in the image forming apparatus shown in FIG. 1, three jam detection sensors 38-1, 38-2, and 38-3 are installed (not limited to three). It is the content of the control method according to claim 5 that it is set at a position corresponding to the page writing start timing.

The “position corresponding to the writing start timing of the next page” is obtained by subtracting “recording paper length + inter-paper distance” from the distance of “exposure position of photosensitive member of first color−secondary transfer position”. The distance −α is a position that is traced back from the secondary transfer position. Here, α is a value that allows the recording paper conveyance to be temporarily stopped at the registration roller unit and a margin for the rough writing start timing. In the case of a system in which the distance obtained by subtracting the former from the latter is negative, the proper installation position of the jam detection sensor is downstream of the secondary transfer roller 25. Since this proper position varies depending on the paper transport path length, the image forming path length, the recording paper length, the distance between the papers, and the like, it is unconditionally determined where the proper position is in the recording paper transport path of the image forming apparatus of FIG. I can't say. The meaning of the image forming timing control method according to the fifth aspect is that, after including the registration unit stop time, the jam detection sensor is roughly arranged at a proper position for starting the writing of the next page, and the time counting by the timer is performed. That is, the writing start timing is measured without performing the operation. FIG. 5 shows a timing chart in this case.

In the timing chart of FIG. 5, the writing start timing of the next page is between the start of sheet feeding and the arrival of the recording sheet at the registration portion (between AB). A realistic range to apply. The condition may be purely downstream of the registration roller 43, at the secondary transfer position, in front of the fixing unit 27, or anywhere. Usually, the jam detection sensor is installed before reaching the registration unit and downstream of the fixing unit. And it is hardly installed between the registration roller and the fixing unit. Although it is not impossible to install it, considering the stance of diverting the installed jam detection sensor,
The range between the sheet feeding section and the resist section is a substantial application range. Thus, only when the timing to start writing the next page arrives between A and B in FIG. 5, the jam detection sensor is disposed at an appropriate position between the sheet cassette and the registration unit to detect the detection signal. Can be used as a trigger to start writing the next page. By using this method, writing of the next page can be started without using the timer function of the control unit.
It is not necessary to increase the load on the control unit. However, since the substantive conditions are narrow, the stance of using the control method according to claim 5 is good only when the conditions are naturally satisfied, rather than forcibly satisfying the conditions.

In the image forming apparatus according to the present invention, the number of paper feed units is multi-stage and various, and the size of recording paper is also various. If the control method according to any one of claims 4 and 5 causes a problem, the image forming timing control method according to claims 4 and 5 is used in combination. . Here, the image forming apparatus according to claim 7 is, for example, the image forming apparatus shown in FIG. This is because the sheet feeding path of the sheet feeding cassette 33 is longer than that of the image forming path, and therefore is outside the scope of the first aspect. Even when the sheet cassette 33 is removed, the sheet cassettes are mounted in two types, the sheet cassette 31 and the sheet cassette 32. If the sheet cassette size is A3 length, the size is smaller than that. Can be loaded into the paper feed cassette 31 or the paper feed cassette 32, and various types of recording paper can be employed. For example, when A4 landscape recording paper (half the length of the paper feed cassette in the drawing) is loaded in the paper feed cassette 31 or the paper feed cassette 32, the jam detection sensor 38-1 depends on the paper distance. It is located at a position suitable for the image forming timing control method according to claim 5 (for the image forming path length, "secondary transfer position-jam detection sensor (3)
8-1) + A4 horizontal recording paper length + paper distance (approximately 1/4 of A4 width) "is almost equal.) Therefore, in this case, the image forming timing control method described in claim 5 can be employed. However, when the recording paper size is A3 portrait, the recording paper length is doubled, so that it is appropriate as the image formation start timing trigger. The position of the jam detection sensor is further downstream of the paper transport path, and may be the position of the registration roller 43 or the secondary transfer roller 25. Then, it becomes impossible to substantially install the sensor at that position, and the image forming timing control method according to claim 5 cannot be adopted. This condition is determined by a plurality of factors such as the position of the paper feed tray (paper transport path length), the length of the image forming path, the length of the recording paper, the distance between papers, and the like. Even if a short manual feed tray is installed, it is not always determined whether the method of claim 5 can be adopted.

As described above, the case where the image forming timing control method according to the fifth aspect can be adopted is limited. However, when the method can be adopted, the timer function of the control unit need not be used, so that the method is actively used. You should adopt it. However, when a paper feed cassette or a recording paper size that cannot adopt the control method of claim 5 is selected, it is preferable to adopt the control method of claim 4 and to use both of them. It is.

[0037]

As described above, in the image forming timing control method according to the first aspect, the leading edge of the recording paper conveyed after the pickup in the paper feeding unit is detected and the writing operation of the next page is started. , It is possible to avoid occurrence of a failure in feeding the next page (mainly continuous feeding) due to the influence of the recording paper of the page slipping during pickup. Normally, the image forming operation sequence starting with the start of the writing operation is repeated at a constant interval in consideration of the recording sheet length and the sheet interval. The paper feeding operation and the registration paper feeding operation are repeated in accordance with the image position formed repeatedly in such a manner. However, if the recording paper conveyance of the previous page slips and is delayed more than the sheet interval, the previous page is fed. The recording paper conveyance of the next page starts even though the paper has not completely exited from the paper tray, and a jam occurs as a continuous feed.
Therefore, the recording paper is detected after the pick-up operation in which the slip is most likely to occur, and the image forming operation of the next page is started from the timing, so that the paper feeding operation and the registration paper feeding operation of the next page are performed by the slip distance. By delaying it, it is possible to prevent the recording paper slip of the page from adversely affecting the sheet feeding and conveyance operation of the next page.

The image forming apparatus according to the second aspect is a system in which the sheet feeding operation is performed at a fixed timing in the image forming operation sequence. When performing the sheet feeding operation in this system, the image forming sequence operation is constant. In the case where the operation is performed at intervals, as described in the operation and effect of the first aspect, if the previous page slips during pickup and is delayed, the next page is transported continuously. there is a possibility. The fact that the imaging sequence is a constant interval means
In this case, the paper feed operation at a fixed timing is also performed at a constant interval, and the influence of the slip amount on the previous page cannot be canceled. Therefore, in the image forming apparatus according to the second aspect, by adopting the image forming timing control method according to the first aspect, the image forming start timing of the next page is delayed by the slip amount of the previous page to feed the next page. It is possible to avoid adversely affecting the transport operation.

According to a third aspect of the present invention, in the image forming apparatus, the rear end of the previous recording sheet is fed such that the distance between the sheets becomes constant with reference to a point in time when a sensor arranged in the sheet feeding path detects the rear end. The sheet feeding operation of this method is a method of controlling the distance between successively fed sheets to be constant. In this case, if the previous recording paper slips, the next recording paper will be fed with a delay of the slip amount, so if the imaging operation is performed at a constant interval, the image forming operation sequence The feeding operation sequence is gradually delayed. This is a direction in which the margin of the recording paper stop time in the registration roller section is reduced, and if the slip amount of the previous recording paper is large, an error occurs that the recording paper does not reach the registration roller section by the registration sheet feeding timing. I will. Therefore, in the image forming apparatus according to the third aspect, it is necessary to feed back the slip amount of the recording paper to the image forming operation start timing, and the image forming apparatus employs the image forming timing control method according to the first aspect. And By doing so, the slip amount at the time of picking up the previous page can be fed back to the next page, so that the adverse effect of the slip of the previous recording sheet on the next page can be avoided.

In the present invention, it is assumed that the leading edge of the conveyed recording paper is detected by a sensor as the time starting point of the image forming operation starting from the writing operation of the next page. Therefore, in the image forming timing control method according to the fourth aspect and the image forming apparatus using the control method (claim 6), a paper feed sensor installed immediately after the pickup unit is used as the sensor, and the control unit controls the image forming apparatus. By using the above timer function, the write start timing can be roughly adjusted without installing a special sensor. Since it is only necessary to roughly adjust the timing (to start writing with a margin more than just), it is not necessary to use the priority interrupt for detecting the recording paper by this sensor, and it is sufficient to monitor by a periodic interrupt. Therefore, there is no burden on the control unit.

As described above, in the present invention, the time starting point of the image forming operation starting from the writing operation of the next page is
It is assumed that the leading edge of the conveyed recording paper is detected by a sensor. Therefore, an image forming timing control method according to claim 5 and an image forming apparatus using the control method (claim 6) use a jam detection sensor disposed in a paper feed conveyance path as the sensor, and use this sensor. Is placed in a place suitable for the writing start timing of the next page,
The writing start timing can be roughly adjusted without requiring a special sensor or a timer function of the control unit. still,
Since it is only necessary to roughly adjust the timing (start writing with a margin more than just), there is no need to use priority interrupt for recording paper detection by this sensor.
Since it is only necessary to monitor by periodic interruption, there is no burden on the control unit.

In the image forming apparatus according to the present invention, since the number of paper feeding units is multi-stage and various, and the recording paper size is also various, the paper feeding path length and the start timing of the next page image forming operation are uniform. In the case where any one of the control methods according to the fourth and fifth aspects causes a problem, the image forming timing control method according to the fourth and fifth aspects is used in combination.
In an image forming apparatus having a multi-stage and various types of paper feed trays, the length of the paper feed path differs depending on the position of the paper feed tray. Also, even when paper is fed from the same paper feed tray, if the recording paper size is different, the writing start timing of the next page will be different. Therefore, the method using the jam detection sensor as in the control method according to claim 5 may be adopted, and sometimes it is not. In the method using the sheet feed sensor as in the control method according to the fourth aspect, a timer function built in the control unit is used, so that the control unit is slightly burdened. On the other hand, in the jam detection sensor use method, since the sensor is installed at a location convenient for the writing start timing of the next page, it is not necessary to use the timer function of the control unit. Therefore, the method of using the jam detection sensor according to claim 5 is more advantageous in terms of the load on the control unit, but the method using the paper conveyance path length, the image forming path length, the recording paper length, the distance between papers, etc. In some cases, the jam detection sensor cannot be installed at a convenient location. In such a case, it is preferable to use the paper feed sensor in accordance with the fourth aspect.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a timing chart showing an example of a sequence control operation of the image forming apparatus according to the present invention.

FIG. 3 is a timing chart showing another example of the sequence control operation of the image forming apparatus according to the present invention.

FIG. 4 is a timing chart showing still another example of the sequence control operation of the image forming apparatus according to the present invention.

FIG. 5 is a timing chart showing still another example of the sequence control operation of the image forming apparatus according to the present invention.

[Explanation of symbols]

 10: Image forming unit 10a, 10b, 10c, 10d: Image forming unit 11: Photoconductor 12: Charger 13: Writing unit 14: Developing unit 15: Intermediate transfer belt 16: Primary transfer roller 17: Static elimination lamp 18: Cleaning Unit 25: Secondary transfer roller 26: Belt cleaning unit 27: Fixing unit 30: Paper feed unit 31, 32, 33: Paper feed cassette 31a, 32a, 33a: Tray bottom plate 34: Pickup roller 35: Paper feed roller 36: Reverse Rollers 37-1, 37-2, 37-3: paper feed sensors 38-1, 38-2, 38-3: jam detection sensors 39-1, 39-2, 39-3: transport rollers 41: transport path 42 : Pre-registration sensor 43: Registration roller

Claims (7)

[Claims] An image forming timing control method for an image forming apparatus in which a paper conveying path is shorter than an image forming path and skew correction and image position adjustment on recording paper are performed by a registration roller. An image forming operation starting from the writing operation of the next page, roughly adjusting the timing based on the timing at which the leading edge of the recording paper conveyed to the paper feeding section is detected by a sensor arranged in the paper feeding conveyance path. Starting the image formation. 2. An image forming section for performing an image forming operation, a paper feeding section for storing recording paper, and a paper feeding section for feeding recording paper from the paper feeding section to the image forming section.
In an image forming apparatus that includes a conveying unit, a paper conveying path is shorter than an image forming path, and skew correction and image position adjustment on recording paper are performed by a registration roller, a method of performing a sheet feeding operation at a fixed timing in an image forming operation sequence. An image forming apparatus comprising the image forming timing control method according to claim 1. 3. An image forming section for performing an image forming operation, a paper feeding section for storing recording paper, and a paper feeding section for feeding recording paper from the paper feeding section to the image forming section.
In an image forming apparatus comprising a conveying means, a paper conveying path shorter than the image forming path, and skew correction and image position adjustment on the recording paper by a registration roller, the rear end of the previous recording paper is arranged in a paper feeding conveying path. 2. An image forming apparatus according to claim 1, wherein a sheet feeding operation is performed so that a distance between sheets becomes constant based on a time point detected by the sensor. . 4. The image forming timing control method according to claim 1, wherein a sheet feed sensor installed immediately after the pickup section is used as a sensor for detecting the leading end of the recording sheet, and a timer function in the control section is used together. An image forming timing control method for roughly adjusting the image forming operation start timing of the next page starting with the writing operation. 5. The image forming timing control method according to claim 1, wherein a sensor for detecting the leading edge of the recording paper is a jam detection sensor arranged in a paper feed conveyance path, and this jam detection sensor is used for the next page. An image forming timing control method characterized by roughly adjusting an image forming operation start timing of a next page, starting from a write operation, by being set at an appropriate position for the write start timing. 6. An image forming section for performing an image forming operation, a paper feeding section for storing recording paper, and a paper feeding section for feeding the recording paper of the paper feeding section to the image forming section.
6. An image forming apparatus comprising: a conveying unit, wherein a paper conveying path is shorter than an image forming path, and skew correction and image position adjustment on recording paper are performed by a registration roller, wherein the image forming timing control method according to claim 4 or 5 is mounted. An image forming apparatus comprising: 7. The image forming apparatus according to claim 6, wherein the number of paper feeding units is multi-stage and various, and the recording paper size is also various. Instead, when a failure occurs in any one of the control methods according to the fourth and fifth aspects, the image forming timing control method according to the fourth and fifth aspects is used in combination. apparatus.