JP2004066811A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of efficiently changing a resolution. <P>SOLUTION: In the case where changing of the resolution is requested when a second sheet of paper is checked (3), the conveyance of the second sheet of paper is not performed and the changing of the resolution is not carried out at the timing (3) because the first sheet of paper is being conveyed and the writing of the image is being performed at the timing (3). The checking of the resolution is carried out at the timing (4) by being triggered by passing of the first sheet of paper (precedent paper) through a paper discharge sensor. When the changing of the resolution is requested, a conveyance speed is changed by changing a rotational speed of a main motor and the sheet of paper is fed by turning on a feed clutch, and then the resolution is changed. At that time, a resolution change flag is set and the changing of the resolution is not changed at the timing (5). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
[Industrial applications]
The present invention relates to an image forming apparatus capable of setting a plurality of resolutions.
[0002]
[Prior art]
Some digital image forming apparatuses are capable of printing at a plurality of resolutions as disclosed in, for example, JP-A-1-138524 and JP-A-2-238963. That is, Japanese Patent Application Laid-Open No. 1-138524 has a plurality of laser optical devices corresponding to images having different image densities, and the number of rotations and the pixel frequency of the rotary polygon mirror corresponding to the laser optical device having the selected image density are different. An invention characterized by driving an optical writing device is disclosed. Japanese Unexamined Patent Publication (Kokai) No. 2-289663 discloses an input means for inputting resolution instruction information, and controls the frequency of a clock signal according to the input resolution and instruction information. And a second control unit for controlling the number of scanning lines of the beam on the recording medium in accordance with the resolution instruction information input by the input unit, wherein the resolution is switched in page units. Is disclosed. The latter discloses that the number of scanning lines of the beam is controlled by controlling the rotation speed of the polygon mirror and controlling the transport speed of the storage medium.
[0003]
In the prior art configured in this way, since most of the scanning is performed using a polygon mirror, in other words, using a polygon mirror, if the resolution selection range is widened, the rotation range of the polygon mirror is widened, and the rotation of the polygon mirror is increased. May become unstable, or may become a non-rotatable area depending on the resolution. Therefore, in order to increase the resolution by suppressing the number of rotations of the polygon mirror as in the latter case, a method of changing the paper conveyance speed is used.
[0004]
That is, the resolution, the main scanning speed, and the paper transport speed are:
Resolution ∝ Main scanning speed / paper transport speed Main scanning speed ∝ Since the relationship is such as polygon mirror rotation speed, when continuous printing is considered, if the resolution differs between the previous paper and the subsequent paper In this method, if the change in resolution can be dealt with only by changing the rotation of the polygon mirror, paper conveyance should be started in advance, and the rotation of the polygon motor should be changed before printing starts.
[0005]
Here, a specific description will be given with reference to FIGS. 7 and 8. FIG. 7 is a schematic configuration diagram illustrating a printer 701 as an image forming apparatus and a sheet conveyance path of a sheet feeding unit 702. The printer 701 includes a process unit that performs a series of image formation of charging, exposure, development, transfer, cleaning, and charge removal. A photosensitive belt 703 disposed, a toner of (-) charge is attached to the electrostatic latent image on the photosensitive belt, a developing unit 704 that visualizes the toner to execute the developing process, and adheres to paper. A fixing unit 705 that heats and pressurizes the formed toner with a fixing roller and fuses the toner onto a sheet is provided. Paper feed trays 706, 707, and 708 as a paper feed unit 702 are provided in three stages below the printer 701, and feed rollers 709, 710 for feeding out paper are respectively provided in the paper feed trays 706, 707, and 708. , 711 are provided, and the sheet is sent out to the process section 703 side via the conveyance path 712. A registration sensor 713 and a registration roller 714 are provided on the upstream side of the process unit 703 in the sheet conveyance direction, and a fixing unit 705 and a sheet ejection sensor 715 are provided on the downstream side of the process unit 704 in the sheet conveyance direction. On the side, a paper discharge tray 716 is provided.
[0006]
In the printer 701 configured as described above, the sheet that has started feeding is sent to the process unit 703 at a timing by the registration roller 714 after passing through the registration sensor 713, and is visualized by the developing unit 704. The image is transferred, and the sheet is discharged to the sheet discharge tray 716 after the sheet discharge is confirmed via the fixing unit 705 and the sheet discharge sensor 715.
[0007]
The drive timing at this time is shown in the timing chart of FIG. As can be seen from this figure, first, the main motor 8 (see FIG. 1 described later; the same applies hereinafter) is first turned on, and then the feed clutch 9 for transmitting the driving force from the main motor 8 to the feed rollers 709, 710, 711. Is turned on to start conveying the paper. When the sheet reaches the registration sensor 713, the feed clutch 9 is turned off so that the next sheet is not fed. In parallel with this, before turning on the image writing signal FG, a change in resolution indicated by ↓ is checked, and then image writing is performed. Then, the registration clutch 10 is turned on at the timing when the leading edge of the image matches the leading edge of the sheet. When the trailing edge of the sheet cuts off the registration sensor 713, the registration clutch 10 is turned off. The same operation is performed for the second sheet, and when the discharge of the second sheet is completed, the main motor 8 is turned off.
[0008]
As can be seen from this timing chart, conventionally, the change in resolution is checked before the image writing signal is output.
[0009]
[Problems to be solved by the invention]
When the resolution is changed, for example, as shown in the timing chart of FIG. 8, the main motor MM starts rotating, the feed clutch FDC for rotating the feed roller is turned on, and the paper is fed to one of the paper feed trays 706 to 708. , The leading edge of the sheet is detected by a registration sensor (RGS) 713, and the resolution is checked at the position of the registration roller 714 while waiting for an image. This is the same for the second sheet. During this time, as can be seen from the timing chart, the main motor MM is rotating, and if the resolution only needs to be changed by changing the rotation speed of the polygon mirror, the change can be followed.
[0010]
However, if the resolution cannot be changed only by changing the rotation speed of the polygon mirror and the paper conveyance speed also needs to be changed, the second check should be made only immediately before the second image write signal. Since the main motor of the conveyance system continues to rotate and one of the feed rollers 709 to 711 is rotated by the feed clutch FDC to convey the sheet to the registration sensor position, it is not possible to cope with a change in the conveyance speed. . Therefore, in order to cope with the change of the transport speed from this state, after discharging the main sheet, the rotation speed of the main motor MM is changed to the rotation speed according to the resolution set next, and the transport of the sheet is started from the beginning. Must be done and take extra time.
[0011]
The present invention has been made in view of such problems of the related art, and an object of the present invention is to provide an image forming apparatus capable of efficiently changing a resolution.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a first means includes an image forming apparatus which has a plurality of paper transport speeds and a plurality of writing resolutions, and changes the transport speed and / or the resolution according to the set resolution to form an image. In the forming apparatus, it is determined whether there is a second sheet that is being conveyed prior to the first sheet to be printed, and when the second sheet is being conveyed and an image is being written, If there is a resolution change request accompanied by a change in the transport speed for the first paper, the transport of the first paper is not started, and the resolution of the first paper is checked at a predetermined timing thereafter. When there is a request to change the resolution accompanied by a change in the transport speed of the first sheet, a control means for changing the transport speed of the first sheet to change the resolution is provided.
[0013]
A second means is the first means, wherein the control means prohibits further change of the resolution after changing the resolution of the first sheet and before writing an image on the first sheet. It is characterized by.
[0014]
The third means is the first or second means, wherein the subsequent predetermined timing is a timing after the discharge of the second paper and the timing at which the first paper is not conveyed. Features.
[0015]
In a fourth aspect, in the first to third means, when the control means cannot transport the first sheet at a specific transport speed, setting of a resolution for transporting at the transport speed is prohibited. It is characterized by the following.
[0016]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
Since the printer itself is the same as that described with reference to FIG. 7, the same components are denoted by the same reference characters, and redundant description will be omitted.
[0018]
FIG. 1 is a block diagram schematically illustrating a control circuit for changing the resolution of the printer according to the embodiment. In FIG. 1, a CPU 1 is connected to a ROM 2 in which a control program is stored, and a RAM 3 which stores data and functions as a work area of the CPU 1. The write gate array 4 and the serial communication unit 5 are connected to each other via a bus, and the write gate array 4 and the serial communication unit 5 are connected to the printer controller 6, respectively. Further, the CPU 1 is connected to a main motor 8, a feed clutch 9, a registration clutch 10, a registration sensor 713, and other input / output 11 via an I / O port 7.
[0019]
Here, the drive timing of the printer according to the embodiment will be described with reference to the timing chart of FIG. As can be seen from this timing chart, in this embodiment, the resolution check indicated by ↓ is performed twice for one sheet of paper. In the figure, the first sheet is (1) and (2), and the second sheet is (3) and (4). Note that the timing chart itself is the same as that in FIG. 8, and a description thereof will be omitted.
[0020]
As can be seen from this timing chart, the main motor 8 starts rotating and the check is performed twice before the image writing signal is turned on. However, when the first sheet (1) without the preceding paper is checked, the feed clutch 9 is also turned off. Since it is not turned on, you can change the resolution. Therefore, if there is a resolution change request, the resolution is changed. Then, the fact that the change of resolution has not been finished in the check of (2) is stored.
[0021]
On the other hand, if it is the second and subsequent sheets, that is, if there is a preceding sheet, at the time of the check (3) before the second sheet is fed (the feed clutch 9 is turned off), the registration clutch 10 is turned on to convey the sheet, and Since the write signal FG is ON and an image is being written, the resolution cannot be changed. Then, the writing of the image is completed, and the resolution is changed by checking (4) that the second sheet is not conveyed by the registration roller 714. The timing itself in this timing chart is the same as that in FIG. 8 because the transport speed is not changed when the resolution is changed.
[0022]
FIG. 3 is a timing chart when the transport speed is changed when the resolution is changed. In this example, the check on the first sheet is the same as in FIG. 2, but if there is a resolution change request at the time of the check (3) on the second sheet, at the timing of (3) Since the first sheet is being conveyed and an image is being written, the resolution is not changed at this timing without starting the conveyance of the second sheet. When the first sheet (previous sheet) has passed the sheet ejection sensor 205, the resolution is checked at the timing of (4). If there is a request to change the resolution, the rotation speed of the main motor 8 is reduced. Then, the feed speed is changed, the feed clutch 9 is turned on to feed the paper, and the resolution is changed. At this time, by setting the resolution changed flag, the resolution is not changed at the timing (5).
[0023]
The processing procedure at the above timing will be described with reference to the flowcharts of FIGS. 4 shows a processing procedure of a resolution check before paper transport before transport, FIG. 5 shows a processing procedure of a resolution check before image writing, and FIG. 6 shows a processing procedure of a resolution check at the time of discharging the preceding paper.
[0024]
In the process of FIG. 4, first, it is determined whether or not there is a preceding sheet (step 401). This determination is a check of whether the sheet is the first sheet or a subsequent sheet. In this check, if there is no preceding paper, in other words, if it is the first sheet, the resolution can be changed irrespective of the preceding sheet, so the resolution is changed (step 404), and the above (5) A resolution changed flag is set so that the resolution is not changed at the timing (step 405), and this processing ends. On the other hand, when it is determined in step 401 that there is a preceding sheet, it is determined whether or not an image is being written at the time of the determination (step 402). . If the writing is not being performed, the resolution can be changed, so it is checked whether a change in the transport speed is requested (step 403). If the change is requested, a resolution change request flag is set (step 406). , And terminates this processing. On the other hand, if a change in the transport speed is not requested in step 403, the resolution is changed without changing the transport speed (step 404), and a resolution change request flag is set (step 405), and this process ends.
[0025]
In the resolution check before writing the image, first, it is determined whether or not the resolution changed flag is set (step 501). If it is set, the resolution changed flag is cleared (step 502). Then, it is determined whether or not the resolution change request flag is set (step 503). In this determination, if the resolution change request flag is set, the resolution is changed (step 504), and if not, the process is terminated as it is.
[0026]
In the resolution check at the time of discharging the preceding sheet, first, it is determined whether or not a resolution change request flag is set (step 601). If it is set, the resolution is changed (step 602), and the resolution change request flag is set. Clear (step 603), and this process ends. If the resolution request flag has not been set in step 601, the process ends.
[0027]
When the resolution is changed by changing the transport speed, the paper may not be able to be transported at the transport speed corresponding to the resolution change due to a failure or the like. In such a case, it becomes impossible to write at a resolution that must be conveyed at the conveyance speed to be changed, and the printer goes down. Therefore, when an instruction to be written at that resolution is input, the instruction is not accepted from the beginning. , It is possible to prevent the printer from going down. In order to do this, it is sufficient to store only the error when the transport speed is high or the error when the transport speed is low, thereby disabling only the resolution corresponding to the speed at which the error occurred.
[0028]
To do this, for example,
Resolution Conveyance speed DPI_A Fast DPI_B Slow DPI_C Slow DPI_D If the error occurs at a fast speed, printing with DPI_A and DPI_D is not performed after that, but printing with DPI_B and DPI_C is not performed. Just do it. This can prevent the machine from going down.
[0029]
Note that the CPU 1 executes these processing procedures and the setting of the transport speed in accordance with a program written in the ROM 2.
[0030]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an image forming apparatus capable of efficiently changing the resolution.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a main part of a control unit of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a timing chart of an embodiment in which the resolution is changed without changing the paper conveyance speed.
FIG. 3 is a timing chart of an embodiment in which the resolution is changed by changing the paper conveyance speed.
FIG. 4 is a flowchart illustrating a processing procedure in an embodiment in which a resolution check is performed before a sheet is conveyed.
FIG. 5 is a flowchart illustrating a processing procedure in an embodiment in which a resolution check is performed before writing an image.
FIG. 6 is a flowchart illustrating a processing procedure in an embodiment in which a resolution check is performed when a preceding sheet is discharged.
FIG. 7 is a schematic configuration diagram of a transport system of the printer.
FIG. 8 is a timing chart when performing a resolution check according to a conventional example.
[Explanation of symbols]
1 CPU
2 ROM
3 RAM
4 Write G / A
5 Serial communication unit 6 Printer controller 7 I / O port 8 Main motor 9 Feed clutch 10 Registration clutch 713 Registration sensor

Claims (4)

An image forming apparatus that has a plurality of paper transport speeds and a plurality of writing resolutions, and forms an image by changing the transport speed and / or the resolution according to the set resolution,
It is determined whether there is a second sheet that is being conveyed prior to the first sheet to be printed, and when the second sheet is being conveyed and an image is being written, the first sheet is conveyed. If there is a request to change the resolution accompanied by a change in the transport speed for the paper, the transport of the first paper is not started, and the resolution of the first paper is checked at a predetermined timing thereafter, and the first paper is checked. An image forming apparatus comprising: a control unit configured to change a resolution by changing a transport speed of the first sheet when a resolution change request accompanied by a change in a transport speed for the sheet is received. 2. The image forming apparatus according to claim 1, wherein the control unit prohibits a further change in resolution after changing the resolution of the first sheet and before writing an image on the first sheet. 3. apparatus. 3. The image forming apparatus according to claim 1, wherein the predetermined timing is a timing after the second sheet is discharged and the first sheet is not conveyed. 4. 4. The control unit according to claim 1, wherein when the first sheet cannot be transported at a specific transport speed, a setting of a resolution for transporting at the transport speed is prohibited. 5. The image forming apparatus according to claim 1.

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