IMAGE FORMING APPARATUS

Abstract

An image forming apparatus includes a paper cassette feeding a recording material, an image forming unit forming an image on a photosensitive member, a primary transfer roller transferring the image onto an intermediate transfer belt, a secondary transfer roller transferring the image onto the recording material, and a sensor detecting the size of the recording material. The timing of starting feeding the recording material is earlier than the timing of starting forming the image. When image formation on the recording material is started, until the sensor detects the size of the recording material, a plurality of images are formed on the intermediate transfer belt at a first interval according to a predetermined recording material size, and after the sensor detects the size of the recording material, a plurality of images are formed on the intermediate transfer belt at a second interval according to the detected recording material size.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an overall example structure of a color laser printer as an example of an image forming apparatus to which the present invention is applicable.

FIG. 2 is a block diagram of parts of the color laser printer of FIG. 1.

FIG. 3 is a timing chart for use in explaining a conventional method of improving throughput in the FIG. 1 printer.

FIG. 4 is a timing chart for use in explaining the printing operation in the FIG. 1 printer in the case where the sheet size is unknown.

FIG. 5 is a timing chart illustrating the printing operation in a first embodiment.

FIG. 6 is a flowchart illustrating the printing operation in the first embodiment.

FIG. 7 is a timing chart illustrating the printing operation in a second embodiment.

FIG. 8 is a flowchart illustrating the printing operation in the second embodiment.

FIG. 9 is a first flowchart illustrating the printing operation in a third embodiment.

FIG. 10 is a second flowchart illustrating the printing operation in the third embodiment.

DESCRIPTION OF THE EMBODIMENTS

Various embodiments, features and aspects of the present invention will now herein be described with reference to the drawings.

First Exemplary Embodiment

Since the structure and operation of a color laser printer as an image forming apparatus are similar to those of FIG. 1, the detailed description will be omitted. It will be assumed in the present embodiment that the distance from the image formation starting position of the first image forming unit to the secondary transfer position is larger than the distance from the paper feeding position to the secondary transfer position. Here will be described how to perform the image forming operation without degrading performance in this case even if the size of recording material (hereinafter referred to as “sheet”) is unknown.

Since the system configuration of the image forming apparatus is the same as that of FIG. 2, the detailed description will be omitted. The first image forming unit refers to the yellow image forming unit. The image formation starting position refers to the position where the development is started on the photosensitive drum. In this embodiment, until the engine control unit 202 detects the length of recording material, the engine control unit 202 outputs /TOP signals at such an interval that printing can be performed on the maximum size sheets that can be set in the paper feeding unit. After detecting the length of sheet, the engine control unit 202 outputs /TOP signals at an interval according to the detected length of sheet so that an optimum throughput can be achieved.

Here will be described an example case where the maximum size sheets that can be set in the paper feeding unit are legal size (sheet size in the conveying direction: 355.6 mm), and sheets actually set in the paper feeding unit are letter size (sheet size in the conveying direction: 279.4 mm).

FIG. 5 is a timing chart of the printing operation utilized in the first embodiment. Since the sheet size is unknown (undetermined), the engine control unit 202 outputs the /TOP signal of the first sheet and then outputs /TOP signals (511, 521, 531) for the subsequent sheets based on the premise that the sheets are legal size. The time interval between the /TOP signals is Tmax based on the maximum size (legal size). That is to say, Tmax=(legal size)+margin. The margin is a value that is appropriately set in accordance with the paper feeding interval.

A predetermined time after outputting the /TOP signal of the first sheet, the engine control unit 202 starts the paper feeding operation (512) for the first sheet. Based on the time point (513) when the supplied first sheet reaches the registration roller 3, the engine control unit 202 conveys the leading edge of the first sheet to a desired position and temporarily stops the conveyance of the sheet (514). In synchronization with the toner image for the first sheet formed on the intermediate transfer member, the engine control unit 202 resumes the conveyance of the sheet (515) and transfers the toner image onto the sheet. At this time, the engine control unit 202 measures the time from when the leading edge of the first sheet reaches the sensor 19 (513) to when the trailing edge of the sheet leaves the sensor 19 (516), and based on the result, calculates the actual size of the first sheet, the size detection operation being completed at time 517.

In the present example, a /TOP signal for the second sheet is output (521) before the detection of the length of the first sheet is completed. The engine control unit 202 uses Tmax as the interval between the /TOP signals for the first and second sheets. This operation is based on the premise that the maximum size (legal size) sheets are set in the paper feeding unit. The interval Tmax has a predetermined value and is set independently of the size detection operation. The size detection operation in this example is completed before the /TOP signal for the third sheet is output but, in this embodiment, the interval Tmax is used once again as the interval between the /TOP signals for the second and third sheets. In this embodiment the engine control unit switches to using an interval T based on the detected length of sheet (sheet size) starting with the interval between the /TOP signals (541) for the third and fourth sheets.

In the case of FIG. 5 of this embodiment, since the detection of the length of the first sheet is completed after the /TOP signal of the second sheet, the outputting interval Tmax between the /TOP signals of the second and third sheets is determined based on the legal size. After the /TOP signal of the third sheet is output, since the detection of the length of the first sheet is already completed (517), the outputting interval T between the /TOP signals of the third and subsequent sheets is set based on the detected length of the sheet (letter size). Reference numeral 522 denotes the start of feeding of the second recording material. Reference numeral 523 denotes the time point when the second recording material reaches the registration roller. Reference numeral 526 denotes the time point when the second recording material passes the sensor 19. Reference numerals 524 and 525 denote the timing of driving the registration roller for the second recording material. Reference numeral 532 denotes the start of feeding of the third recording material. Reference numeral 533 denotes the time point when the third recording material reaches the registration roller. Reference numeral 536 denotes the time point when the third recording material passes the sensor 19. Reference numerals 534 and 535 denote the timing of driving the registration roller for the third recording material.

FIG. 6 is a flowchart illustrating the operational timing in this embodiment. The engine control unit 202 outputs the /TOP signal of the first sheet and sets the timing of outputting the /TOP signal of the second sheet based on the maximum size (legal size) (601 and 602). Next, it is determined whether printing continues (603). If not, the process ends. If printing continues, the process proceeds to 604.

At the timing of outputting the /TOP signal of the second sheet, the engine control unit 202 outputs the /TOP signal of the second sheet (604 and 605). After outputting the /TOP signal of the second sheet, the engine control unit 202 checks if the detection of the length of the first sheet is completed (606).

If the detection of the length of the first sheet is completed, the timing of outputting the /TOP signal of the next sheet is set based on the detected length of sheet (letter size) (607). If the detection of the length of the first sheet is not completed, as with the second sheet, the timing of outputting the /TOP signal of the third sheet is set based on the maximum size (legal size).

Hereafter, the timing of outputting the /TOP signal of the next sheet is determined depending on whether or not the detection of the length of the first sheet is completed.

As described above, until the engine control unit 202 detects the length of sheet, the engine control unit 202 outputs /TOP signals at such an interval that printing can be performed on the maximum size (legal size in this embodiment) sheets that can be set in the paper feeding unit.

That is to say, since /TOP signals are output based on the maximum size before the detection of the length of sheet is completed, the interval between the first and second sheets is smaller compared to the conventional method in which /TOP signals are output after the detection of the length of sheet is completed.

In the conventional method, after the image of the first sheet is formed on the intermediate transfer member until the detection of the length of the first sheet is completed, image formation of the second sheet is not performed. In contrast, in the method of this embodiment, the image of the second sheet can be formed without waiting for the completion of detecting the length of the first sheet. The interval between /TOP signals #1 and #2 in FIG. 5 of this embodiment is smaller than the interval between /TOP signals #1 and #2 in FIG. 4 of the conventional method. Therefore, compared to the conventional method, degradation in throughput is smaller.

After the detection of the length of sheet, printing operation is performed in accordance with the detected length of sheet so that an optimum throughput can be achieved. Thus, printing operation can be performed with minimum degradation in performance.

Second Exemplary Embodiment

In the first embodiment, although the size detection operation was completed before the /TOP signal for the third sheet was output, the timing of outputting the /TOP signal for the third sheet was still determined based on the maximum size (legal size).

In a second embodiment, when the detection of the length of the first sheet is completed before output of the /TOP signal for a given sheet (e.g. the third sheet), the timing of outputting the /TOP signal for that sheet is changed in accordance with the detected length of sheet.

Since the structure and operation of a color laser printer as an image forming apparatus are similar to those of FIG. 1, the detailed description will be omitted. Since the system configuration of the image forming apparatus is the same as that of FIG. 2, the detailed description will be omitted. The first image forming unit refers to the yellow image forming unit. The image formation starting position refers to the position where the development is started on the photosensitive drum.

In this embodiment, the maximum size sheets that can be set in the paper feeding unit are legal size (sheet size in the conveying direction: 355.6 mm), and sheets actually set in the paper feeding unit are letter size (sheet size in the conveying direction: 279.4 mm).

FIG. 7 is a timing chart of the printing operation in this embodiment. The engine control unit 202 outputs the /TOP signal of the first sheet (711) and sets the outputting interval Tmax of /TOP signals for the subsequent sheets based on the premise that the sheets are legal size. A predetermined time after outputting the /TOP signal of the first sheet, the engine control unit 202 starts the paper feeding operation (712). Based on the time point (713) when the supplied sheet reaches the registration roller 3, the engine control unit 202 conveys the leading edge of the sheet to a desired position and temporarily stops the conveyance of the sheet (714). In synchronization with the toner image formed on the intermediate transfer member, the engine control unit 202 resumes the conveyance of the sheet (715) and transfers the toner image onto the sheet. At this time, the engine control unit 202 measures the time from when the leading edge of the first sheet reaches the sensor 19 (713) to when the trailing edge of the sheet leaves the sensor 19 (716), and based on the measured time, calculates the actual size of the first sheet, the size detection operation being completed at time 717.

The engine control unit 202 monitors the detection of the length of the first sheet during the printing operation. When the detection is completed, the engine control unit 202 calculates the outputting interval T of the /TOP signal for the next sheet based on the elapsed time T1 from the outputting of the last /TOP signal and the detected length of sheet.

Specifically, the engine control unit 202 calculates the /TOP signal outputting interval T from the detected length of sheet. If the time T has elapsed since the outputting of the last /TOP signal, the engine control unit 202 outputs the /TOP signal of the next sheet at that time point.

Until the detection of the length of the first sheet is completed, the engine control unit 202 outputs /TOP signals at the predetermined interval Tmax set based on the maximum size (legal size) of sheets that can be set in the paper feeding unit.

In the case of FIG. 7 of this embodiment, the detection of the length of the first sheet is completed after the outputting of the /TOP signal of the second sheet. Therefore, when the detection of the length of the first sheet is completed, the engine control unit 202 calculates the timing of outputting the /TOP signal of the third sheet and outputs the /TOP signal of the third sheet (717 and 731).

In FIG. 7, the outputting interval T of /TOP signals is calculated by counting the time T1 from the last /TOP signal 721 to the time point 717 when the detection of the length of sheet is completed and adding a predetermined time in accordance with the detected length of sheet (letter size in this embodiment). That is to say, T is calculated from the following formula:

T=T1+α

where T1 is the elapsed time from the last /TOP signal to the completion of the detecting the length of sheet, and α is the predetermined time. This time α can be appropriately set for each sheet size. It will be appreciated that T1 is being used as a measure of the detected size in this case (instead of the difference between times 713 and 716 at which the leading and trailing edges of the first sheet are detected. This is possible because the time period from the time 721 when the /TOP signal for the second sheet is output to the time 713 is substantially fixed and the delay in completing the size detection (717) after detecting the trailing edge (716) is also fixed and/or negligible.

The interval Tmax between the /TOP signals for the first and second sheets is calculated based on the maximum size (legal size) of sheets that can be set in the paper feeding unit. Reference numeral 722 denotes the start of feeding of the second recording material. Reference numeral 723 denotes the time point when the second recording material reaches the registration roller. Reference numeral 726 denotes the time point when the second recording material passes the sensor 19. Reference numerals 724 and 725 denote the timing of driving the registration roller for the second recording material. Reference numeral 732 denotes the start of feeding of the third recording material. Reference numeral 733 denotes the time point when the third recording material reaches the registration roller. Reference numeral 736 denotes the time point when the third recording material passes the sensor 19. Reference numerals 734 and 735 denote the timing of driving the registration roller for the third recording material.

FIG. 8 is a flowchart illustrating the operational of this embodiment. The engine control unit 202 outputs the /TOP signal of the first sheet and sets the timing of outputting the /TOP signal of the next sheet based on the maximum size (legal size) (801 and 802). Then it is determined whether printing continues at 803. If not, the process ends. If printing does continue, then the process proceeds to 804.

The engine control unit 202 monitors the detection of the length of the first sheet during the printing operation. When the detection is completed, the engine control unit 202 calculates the timing of outputting the /TOP signal of the next sheet based on the elapsed time from the outputting of the last /TOP signal and the detected length of sheet (804 and 805).

Next, it is determined whether the timing of outputting /TOP signal of next sheet is available at 806. If not, the process returns to 804. If yes, the process proceeds to 807 where if the detection of the length of the first sheet is completed, the engine control unit 202 outputs the /TOP signal for the next sheet at the outputting interval of /TOP signals calculated on the above condition (807).

Next, it is determined whether detection of the actual length of the first sheet is completed (808). Once the detection of the length of sheet is completed, the engine control unit 202 determines the timing of outputting the /TOP signal of the next sheet based on the detected length of sheet (809). If the detection of the length of sheet is not completed, the timing of outputting the /TOP signal of the next sheet is determined based on the maximum size (legal size) (802).

As described above, until the engine control unit 202 detects the length of sheet, the engine control unit 202 outputs /TOP signals at such an interval that printing can be performed on the maximum size (legal size in this embodiment) sheets that can be set in the paper feeding unit. When the detection of the length of the first sheet is completed, the engine control unit 202 calculates the timing of outputting the /TOP signal of the next sheet. Therefore, even if the sheet size is unknown, printing operation can be performed without degrading performance.

In this embodiment, since the interval of /TOP signal can be changed earlier compared to the first embodiment, the throughput can be further improved.

Third Exemplary Embodiment

In the first and second embodiments, until the detection of the length of the first sheet is completed, the interval of /TOP signal is determined based on the maximum size (legal size) of sheets that can be set in the paper feeding unit.

In this embodiment, until the detection of the length of sheet is completed, the outputting interval of /TOP signal is determined not based on the maximum size (legal size) but based on a sheet size specified by the controller 201.

Since the timing chart is the same as that of the first embodiment, the description will be omitted. In this embodiment, the interval between /TOP signals is set to a value Tcont specified by the controller, instead of the value Tmax.

Here will be described how to set the outputting interval of /TOP signals based on a sheet size specified by the controller 201 until the detection of the length of sheet is completed.

Here will be described a first case where, when a /TOP signal is output, the timing of outputting the next /TOP signal is set (as in the first embodiment) and a second case where, when the detection of the length of the first sheet is completed, the timing of outputting /TOP signal is calculated (as in the second embodiment).

FIG. 9 is a flowchart in the case where, when a /TOP signal is output, the timing of outputting the next /TOP signal is set. The engine control unit 202 outputs the /TOP signal of the first sheet and sets the timing of outputting the /TOP signal of the second sheet based on a sheet size specified by the controller 201 (901 and 902). Next, it is determined whether printing continues (903). If not, the process ends. If printing does continue, the process proceeds to 904.

At the timing of outputting the /TOP signal of the second sheet, the engine control unit 202 outputs the /TOP signal of the second sheet (904 and 905). After outputting the /TOP signal of the second sheet, the engine control unit 202 checks if the detection of the length of the first sheet is completed (906). If the detection of the length of the first sheet is completed, the timing of outputting the /TOP signal of the next sheet is set based on the detected length of sheet (907). If the detection of the length of the first sheet is not completed, as with the second sheet, the timing of outputting the /TOP signal of the third sheet is set based on the sheet size specified by the controller 201. Hereafter, the timing of outputting the /TOP signal of the next sheet is determined depending on whether or not the detection of the length of the first sheet is completed.

FIG. 10 is a flowchart in the case where, when the detection of the length of the first sheet is completed, the timing of outputting /TOP signal is recalculated.

The engine control unit 202 outputs the /TOP signal of the first sheet and sets the timing of outputting the /TOP signal of the next sheet based on a sheet size specified by the controller 201 (1001 and 1002). Next, it is determined whether printing continues (1003). If not, the process ends. If printing does continue, the process proceeds to 1004. The engine control unit 202 monitors the detection of the length of the first sheet during the printing. When the detection is completed, the engine control unit 202 calculates the timing of outputting the /TOP signal for the next sheet based on the elapsed time from the outputting of the last /TOP signal and the detected length of sheet (1004 and 1005).

Next, it is determined whether the timing of outputting /TOP signal of next sheet is available at 1006. If not, the process returns to 1004. If yes, the process proceeds to 1007 where if the detection of the length of the first sheet is completed, the engine control unit 202 outputs the /TOP signal for the next sheet at the calculated timing (1007).

Next, it is determined whether detection of the actual length of the first sheet is completed (1008). Once the detection of the length of sheet is completed, the engine control unit 202 determines the timing of outputting the /TOP signal of the next sheet based on the detected length of sheet (1009). If the detection of the length of sheet is not completed, the timing of outputting the /TOP signal of the next sheet is determined based on the sheet size specified by the controller 201 (1002).

The controller can specify a particular sheet size or a free size. When a free size is specified, an outputting interval of /TOP signal is set so that printing can be surely performed on sheets having a size less than or equal to a certain sheet size.

For example, when the controller specifies “free size 1,”/TOP signals are output based on the legal size. When the controller specifies “free size 2,”/TOP signals are output based on the letter size.

In recent years, a paper cassette capable of accommodating free size sheets has been provided as a paper feeding unit that allows a user to freely set the sheet size. In that case, the controller specifies the maximum sheet size that the free size paper cassette supports as a free size so that printing operation can be performed without degrading performance.

As described above, until the engine control unit 202 completes the detection of the length of sheet, the engine control unit 202 outputs /TOP signals at such an interval that printing can be performed on sheets having the size specified by the controller 201. After the detection of the length of the first sheet is completed, the timing of outputting /TOP signal is set based on the detected sheet length. This makes it possible to perform printing operation without degrading performance even if the sheet size is unknown.

Various changes may be made in each of the above-described first, second, and third embodiments without departing from the spirit of the present invention. Such changes are also included in the scope of the present invention.

The present invention is not limited to the above-described embodiments but includes modifications of the same technical idea.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions.

This application claims the benefit of Japanese Application No. 2006-286471 filed Oct. 20, 2006, which is hereby incorporated by reference herein in its entirety.

Claims

1. An image forming apparatus comprising: a paper feeding unit configured to feed a recording material;an image forming unit configured to form an image on an image bearing member;a primary transfer unit configured to transfer the image formed on the image bearing member onto an intermediate transfer member;a secondary transfer unit configured to transfer the image transferred onto the intermediate transfer member onto the recording material fed from the paper feeding unit;a size detecting unit configured to detect the size of the recording material; anda setting unit configured to set the interval of image formation,wherein the timing of starting feeding the recording material from the paper feeding unit is later than the timing of starting forming the image with the image forming unit, andwherein the setting unit sets the interval of image formation so that when image formation on the recording material is started, until the size detecting unit detects the size of the recording material, a plurality of images are formed on the intermediate transfer member at a first interval according to a predetermined recording material size, and after the size detecting unit detects the size of the recording material, a plurality of images are formed on the intermediate transfer member at a second interval according to the detected recording material size.

2. The image forming apparatus according to claim 1, wherein the distance from the position where feeding of the recording material is started from the paper feeding unit to the position where an image is transferred onto the recording material by the secondary transfer unit is smaller than the distance from the position where image formation on the image bearing member is started by the image forming unit to the position where an image is transferred onto the recording material by the secondary transfer unit.

3. The image forming apparatus according to claim 1, wherein the second interval is smaller than the first interval.

4. The image forming apparatus according to claim 1, wherein the predetermined recording material size is the length in the conveying direction of a recording material and the maximum length of the recording material supplied to the paper feeding unit.

5. The image forming apparatus according to claim 1, wherein after the size detecting unit detects the size of the recording material, the setting unit calculates the second interval in accordance with the detected recording material size.

6. An image forming apparatus comprising: a paper feeding unit configured to feed a recording material;an image forming unit configured to form an image on an image bearing member;a primary transfer unit configured to transfer the image formed on the image bearing member onto an intermediate transfer member;a secondary transfer unit configured to transfer the image transferred onto the intermediate transfer member onto the recording material fed from the paper feeding unit;a size detecting unit configured to detect the size of the recording material;a setting unit configured to set the interval of image formation; anda specifying unit configured to specify a recording material size,wherein the timing of starting feeding the recording material from the paper feeding unit is later than the timing of starting forming the image with the image forming unit, andwherein the setting unit sets the interval of image formation so that when image formation on the recording material is started, until the size detecting unit detects the size of the recording material, until the size detecting unit detects the size of the recording material, a plurality of images are formed on the intermediate transfer member at a first interval according to the recording material size specified by the specifying unit, and after the size detecting unit detects the size of the recording material, a plurality of images are formed on the intermediate transfer member at a second interval according to the detected recording material size.

7. The image forming apparatus according to claim 6, wherein the distance from the position where feeding of the recording material is started from the paper feeding unit to the position where an image is transferred onto the recording material by the secondary transfer unit is smaller than the distance from the position where image formation on the image bearing member is started by the image forming unit to the position where an image is transferred onto the recording material by the secondary transfer unit.

8. The image forming apparatus according to claim 6, wherein the paper feeding unit is capable of supplying a free-size recording material.

9. The image forming apparatus according to claim 6, wherein the recording material size specified by the specifying unit is the length in the conveying direction of a recording material and the maximum length of the recording material supplied to the paper feeding unit.

10. The image forming apparatus according to claim 6, wherein after the size detecting unit detects the size of the recording material, the setting unit calculates the second interval in accordance with the detected recording material size.

11. The image forming apparatus according to claim 6, wherein the specifying unit is capable of specifying a plurality of recording material sizes.