JP2008122513A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of carrying out suitable fixing temperature control by uniformly heating a fixing roller by easing in a non-paper passing part (or easing lowering of temperature in a paper passing part) even when small size sheet material is continuously passed. <P>SOLUTION: The image forming apparatus includes a plurality of paper supplying cassettes with a sheet material restricting means restricting sheet material to a transporting reference position in a direction orthogonal to transporting direction of the sheet and a control means, wherein the control means alternately selects one paper supplying cassette and another in a pair of paper supplying cassettes and carry out supplying of the sheet material every time one piece or a plurality of pieces of the sheet material is transported when the pair of paper supplying cassettes (8a, 8b) with different sheet transporting reference positions restricted by the sheet restricting means from each other exists in a plurality of the paper supplying cassettes when the sheet material is continuously transported. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to mitigation of non-sheet passing portion temperature rise (or sheet passing portion temperature drop) in the fixing device.

Conventionally, in the electrophotographic method which is an example of the image forming method, as a fixing method of the toner image visualized on the sheet material, there is the following method that can realize power saving and time reduction from power-on to image output. Are known.
A heater unit comprising a heater and a heat-resistant film that moves while being in pressure contact with the heater, and a pressurizing member that causes the recording material to adhere to the heater unit are applied to the recording material through the film. A method for fixing a toner image is known (Patent Documents 1 and 2).

However, when the fixing device having the above-described configuration is used, it is common to use several kinds of sheet materials having different sizes. For example, in an image forming apparatus capable of vertical feeding with a maximum size of A3 (sheet passing width 297 mm), the width of A4 (sheet passing width 211 mm), B5 (sheet passing width 182 mm), envelope (sheet passing width 105 mm), business card (sheet passing width 55 mm), etc. Narrow sheet material is continuously fed. Then, a non-sheet passing portion is generated in the fixing unit of the fixing device, and the amount of heat is not absorbed by the sheet material in the non-sheet passing portion. "Paper rise" occurs. As a result, the following problems a, b, and c occur.
a The fixing roller becomes hot at the non-sheet passing portion, which causes deterioration of the rubber material of the pressure roller, and the thermal expansion of the pressure roller at the sheet passing portion and the non-sheet passing portion becomes non-uniform. The sheet material is wrinkled or skewed due to the difference in outer shape.
b Since the non-sheet passing portion is higher than the set temperature of the fixing roller after the small-size sheet material is passed, if a larger-size recording material is passed after passing the small-size sheet material, At the non-sheet passing portion, the toner is overmelted and hot offset occurs.
c These are problems when the temperature detection element is set to the sheet passing area. However, when the temperature detection element is set to the non-sheet passing part, the sheet passing part becomes lower than the set temperature. Therefore, fixing failure or cold offset occurs.

  As a measure to prevent the non-sheet passing portion temperature rise, a method for preventing the local temperature rise of the fixing roller by increasing the interval of the recording material sheet passing than the normal continuous sheet passing has been proposed. In this method, it takes a very long time to print a small size paper, and the printing speed is slowed down.

According to the film heating and fixing method as described above, since the heat capacity of the fixing roller and the fixing film is small, the problem of the temperature rise in the non-sheet passing portion is very noticeable, and the temperature difference between the sheet passing portion and the non-sheet passing portion. May reach 200 ° C.
In order to solve such a problem of the temperature increase in the non-sheet passing portion, a fixing unit is used by changing the sheet feeding position of the sheet material with respect to the image forming apparatus for each sheet using a small size sheet material dedicated sheet cassette. A method for changing the sheet material passing area in the paper has been proposed (Patent Document 3).

  In the conventional image forming apparatus, a mechanical sensing lever type sensor is mainly used for detecting the leading edge of the sheet material. FIG. 13 shows the mechanical sensing lever type. Reference numeral 25 denotes a lever, and 26 denotes a photocoupler. The lever 25 is arranged so as to block the paper path, and when one of the levers is pushed to the leading edge of the paper passing through the paper path, a signal is generated by blocking the light beam of the photocoupler 26 arranged on the other side of the lever. It has a configuration.

However, this mechanical sensing lever type sensor causes an unstable state (chattering) with the detection signal level being high and low due to the vibration of the lever at the timing of signal change. Therefore, in order to detect the leading edge of the sheet material, it is necessary to widen the sheet material conveyance interval in consideration of chattering of the sensor. As a result, the printing speed of the image forming apparatus is lowered, and the convenience for the user is impaired.
Therefore, in order to solve the above-mentioned problems in recent high-speed image forming apparatuses, the front end of the sheet material is detected using a non-contact type optical sensor instead of a mechanical sensing lever type.
JP-A-63-313182 Japanese Patent Laid-Open No. 02-157878 Japanese Patent Application Laid-Open No. 07-013450

  However, the conventional example shown in Patent Document 3 requires a moving mechanism for moving the sheet material for each sheet feeding, resulting in an increase in the cost of the apparatus. Further, in order to print a small size sheet material, it is necessary to use a dedicated paper feed cassette, and there is a problem that the convenience of the user is impaired.

Next, in the case of an image forming apparatus using a non-contact type optical sensor, there are the following problems.
Cost is high compared to mechanical sensing lever type sensors.
The optical sensor is contaminated with toner and paper dust in the apparatus.
Since the leading end of a transparent resin sheet (hereinafter referred to as OHP sheet) cannot be detected, a dedicated OHP sheet having an opaque shading mark on the end of the OHP sheet must be used.

The present invention has been made under such circumstances, and even when a small-size sheet material is passed, the non-sheet passing portion temperature rise (or the sheet passing portion temperature drop) is alleviated, and the fixing roller It is an object of the present invention to provide an image forming apparatus that can uniformly heat the toner and perform appropriate fixing temperature control.
It is another object of the present invention to provide an image forming apparatus that can solve the problems caused by chattering of a sensor even if a mechanical sensing lever type sensor is used and can increase the printing speed at a low cost.

  In order to solve the above-described problems, in the present invention, an image forming apparatus is configured as described in (1) below.

(1) A plurality of sheet feeding cassettes having sheet material regulating means for regulating a sheet material to a conveyance reference position in a direction orthogonal to the conveyance direction, and a sheet material fed from the sheet feeding cassette on a photosensitive member Transfer means for transferring the formed toner image; a fixing device for fixing the toner image transferred to the sheet material by the transfer means to the sheet material by heat and pressure; and control means for controlling an image forming process; An image forming apparatus comprising:
The control unit includes a pair of sheet feeding cassettes having different sheet conveyance reference positions regulated by the sheet material regulating unit among the plurality of sheet feeding cassettes when the sheet material is continuously conveyed. In some cases, the sheet material is supplied by alternately selecting one of the pair of paper feed cassettes and the other paper feed cassette each time one or a plurality of the sheet materials are conveyed.

  According to the present invention, even when a small-size sheet material is passed, it is possible to change the sheet material passage area of the fixing device without impairing the convenience for the user, and as a result, the length of the fixing device is changed. The temperature distribution in the direction can be made uniform, and the non-sheet passing portion temperature rise (or the sheet passing portion temperature drop) can be mitigated.

  According to the invention of claim 5, it is possible to detect the leading edge of the sheet material by using a different sensor for each sheet feeding. As a result, even if the sheet material reaches the sensor position before the chattering of the sensor converges, the leading edge can be reliably detected, and as a result, the printing speed of the image forming apparatus can be improved.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to an embodiment of an image forming apparatus.

First, an “image forming apparatus” that is Embodiment 1 will be described with reference to FIGS.
FIG. 2 shows a schematic configuration of the image forming apparatus.
The image forming apparatus includes a paper feed cassette 8 a and a paper feed cassette 8 b, a cartridge 20, a scanner unit 4, and a fixing device 6.

The paper feed cassettes 8a and 8b pick up the paper 17 by the paper feed pads 3a and 3b, and feed the paper 17 in the direction of the arrow L1 by driving the paper feed roller pairs 3c and 3d.
In the cartridge 20, as shown in the figure, a photosensitive drum 1 that is an electrophotographic photosensitive member, a charging roller 2 that is a charging device, and a developing roller 7 are integrated by a frame body, and can be exchanged with respect to the apparatus main body 18. Yes.

  In addition, a transfer roller 9 serving as a transfer charging device is disposed in the apparatus main body 18 located below the photosensitive drum 1 in the cartridge 20. Further, the fixing roller 13 for fixing the toner 5 transferred to the recording paper on the paper discharge side to the transfer roller 9, the recording paper is pressed against the fixing roller 13, and the pressure roller 14 for assisting the fixing and the paper 17 are attached to the apparatus main body 18. A paper discharge roller 16 that constitutes a part of a discharge device that discharges outside is disposed.

  Further, a scanner unit 4 is disposed above the cartridge 20 to irradiate the photosensitive drum 1 charged by the charging roller 2 with laser light and form an electrostatic latent image on the photosensitive surface.

The image forming process of this image forming apparatus will be described below.
The photosensitive drum 1 rotates in one direction around its axis. The surface of the photosensitive drum 1 is uniformly charged by a primary bias that is supplied to the charging roller 2 and superimposed with an AC component and a DC component. An electrostatic latent image is formed by the laser light emitted from the scanner unit 4. The developing roller 7 receives the replenishment of the toner, and attaches the toner to the electrostatic latent image on the photosensitive drum 1 and visualizes it with a developing bias.
Thereafter, the image of the photosensitive drum 1 visualized by the toner is transferred onto the paper 17 by the transfer roller 9. The toner image transferred onto the paper 17 is fixed by the heat generated by the fixing roller 13 and the pressure applied by the pressure roller 14 to form a recorded image.
Thereafter, the paper 17 is discharged out of the image forming apparatus 18 by the paper discharge roller 16, and thereafter the above-described steps are repeated.

  In this embodiment, the sheet material transport reference position is different between the paper feed cassette 8a and the paper feed cassette 8b. When small-size paper is continuously fed, the paper feed cassette 8a and the paper feed cassette 8a are fed each time the paper 17 is transported. Paper feeding is performed by alternately switching the paper cassettes 8b. By performing this control, it is possible to change the paper passage area of the fixing device 6 every time the paper is transported, thereby preventing the temperature rise of the non-sheet passing portion.

  This will be described in detail. First, FIG. 3 shows details of the paper feed cassette. By restricting the position of the edge of the sheet by the sheet regulating plate 21, the sheet is conveyed in a state biased in a direction orthogonal to the conveying direction. The paper 17 is stacked on the left side (left end reference) facing the paper transport direction on the paper feed cassette 8a, and is stacked on the right side (right end reference) facing the paper transport direction on the paper feed cassette 8b.

  When the user selects the small-size paper alternate paper feed mode, the first paper 17a is fed from the paper feed cassette 8a. At this time, as shown in FIG. 1, the paper 17 a passes through the right side of the photosensitive drum 1 and the fixing roller 13. Subsequently, by feeding the second sheet 17b from the sheet feeding cassette 8b, the sheet 17 can be passed through the left side of the photosensitive drum 1 and the fixing roller 13 this time. By switching between the paper feed cassette 8a and the paper feed cassette 8b each time the paper 17 is fed in this way, it is possible to prevent the paper feeding area of the fixing device 6 from being biased, and the non-paper feeding portion rises. Can solve the temperature problem.

  The sheet material presence / absence detection control in this embodiment will be described in detail below. As shown in FIG. 1, two mechanical detection lever type sheet material detection sensors are arranged on the same line perpendicular to the sheet conveyance direction, and the outputs of the sensors S1 and S2 are input to a microcomputer (not shown). It is processed. In this embodiment, for the paper 17a fed from the paper feed cassette 8a, the sensor S1 is used as a top sensor for detecting the leading edge of the sheet material, and the sensor S2 is a width sensor for detecting the width of the sheet material. It is used as. On the other hand, for the paper 17b fed from the paper feed cassette 8b, the sensor S1 is used as a width sensor and the sensor S2 is used as a top sensor. In this way, by switching between the sensor used as the top sensor and the sensor used as the width sensor according to the paper feed cassette, there is no need to prepare a sensor for each conveyance reference position, and image formation The cost of the main body can be reduced.

  Next, image writing position control in this embodiment will be described in detail below. FIG. 12 is a diagram showing the configuration of the scanner unit used in this embodiment. 401 is a polygon mirror, and 402 is a polygon scanner motor that rotationally drives the polygon mirror 401. Reference numeral 406 denotes a semiconductor laser disposed in the laser circuit, and laser light emitted from the semiconductor laser 406 is irradiated toward the rotating polygon mirror 401. The polygon mirror 401 is rotated in the direction of the arrow, and the laser light emitted from the semiconductor laser 406 is reflected as a change beam that continuously changes its angle on its reflection surface as the polygon mirror 401 rotates. The reflected light is corrected for distortion by the lens 405 and scans the photosensitive drum in the main scanning direction.

  Further, a BD (Beam Detect) sensor 403 is disposed outside the scanning direction in order to generate a scanning start position reference signal in the main runner direction. Laser light is guided to the BD sensor 403 by using a mirror 404. That is, the laser beam reflected by each reflecting surface of the polygon mirror 401 is detected by the BD sensor 403 prior to scanning each line. The detected BD signal is used as a scanning start reference signal in the main scanning direction, and synchronization with the writing start position of each line in the main scanning direction is taken with reference to this signal.

  In this embodiment, the time from the detection of the BD signal to the start of writing in the main scanning direction must be switched for each paper feed cassette. FIG. 4 shows the BD signal and the timing of laser emission to the photosensitive drum in the main scanning direction. Writing in the main scanning direction to the first sheet 17a fed from the sheet feeding cassette 8a starts after t1 after detecting the falling edge of the BD signal. After the printing on the first sheet 17a is completed up to the nth line, it waits for the second sheet 17b to be conveyed to a predetermined position. Thereafter, writing in the main scanning direction of the second sheet fed from the sheet feeding cassette 8b starts after t2 after the falling edge of the BD signal is detected. Similarly, after the printing on the second sheet 17b up to the nth line is completed, the writing in the main scanning direction is again performed on the third sheet 17 fed from the sheet feeding cassette 8a again after t1 with respect to the BD signal. Start. Thereafter, by switching between t1 and t2 according to the paper feed cassette, it is possible to provide a normal print result to the user even if the paper transport reference position is different for each paper feed cassette.

FIG. 5 shows a flowchart for explaining the control of this embodiment. First, after a print signal is received in step 501, return processing from the standby state is performed in step 502. Thereafter, in step 503, it is determined whether the print command designates a small size paper. If the small size paper is designated, it is determined in step 504 whether or not the user desires to feed paper alternately using the paper feed cassette 8a and the paper feed cassette 8b. If the user desires the alternate paper feeding mode, the first paper 17a is first fed from the paper feeding cassette 8a in step 505. At this time, in order to align the laser writing position with respect to the photosensitive drum in step 506, t1 is set as a time from the BD signal to writing in a microcomputer (not shown). Thereafter, in step 507, it is determined whether the sensor S1 has detected the leading edge of the paper. If the sensor S1 cannot detect the leading edge of the paper after a predetermined time, it is determined in step 520 that a paper feed error has occurred, and a warning is given to the user (step 521). After shifting to the standby state (step 523).
After detecting the leading edge of the paper 17a in step 507, it is determined in step 508 whether or not the width of the paper 17a is within a specified range using the detection output of the sensor S2. If the width of the paper 17a is within the specified range, it is determined that the paper is a small size paper, and image forming processing is started in step 510 in synchronization with the output of the sensor S1. If it is determined in step 508 that the width of the paper 17a is greater than or equal to the specified value, the small size alternate paper feed mode is exited, and image formation processing for the normal size (step 519) is performed.

After image formation is completed in step 510, it is determined in step 511 whether the print job is completed. If the print job has been completed, the process proceeds to the standby state in step 523. If the print job is not completed, the second sheet 17b is fed from the sheet cassette 8b in step 512. At that time, in step 513, the time from the BD signal to writing is changed to t2 corresponding to the paper feed cassette. Thereafter, in step 514, it is determined whether the sensor S2 has detected the leading edge of the paper 17b. If the sensor S2 cannot detect the leading edge of the paper 17b after a predetermined time, it is determined in step 520 that there is a paper feed error, a warning (step 521) is given to the user, and the process proceeds to a standby state (step 523).
After detecting the leading edge of the paper 17b in step 514, it is determined in step 515 whether the width of the paper 17 is within a specified range using the output of the sensor S1. If the width of the paper 17b is within the specified range, it is determined that the paper is a small size paper, and an image forming process is started in step 517 in synchronization with the output of the sensor S2. If it is determined in step 515 that the width of the paper 17b is equal to or larger than the specified width, the small size alternate paper feed mode is exited, and the normal size image forming process (step 519) is performed.

After image formation is completed in step 517, it is determined in step 518 whether the print job is completed. If the print job has been completed, the process proceeds to the standby state in step 523. If the print job has not ended, the process returns to step 505 to feed the third sheet 17 from the sheet cassette.
If it is determined in step 503 that the print is not a small size print, an image forming process for a normal size is performed in step 519. After the print job is completed, the process shifts to a standby state in step 523. If it is determined in step 504 that the user does not perform the process of alternately feeding small-size paper from the paper feed cassette 8a and the paper feed cassette 8b, the small-size paper is fed from one paper feed cassette in step 522. The image forming process is performed. After the small size paper print job is completed in step 522, the image forming apparatus main body is shifted to a standby state in step 523.

As described above, according to this embodiment, when small-size paper is continuously printed, the sheet material conveyance reference position of each paper feed cassette is set to be different. When continuously printing small-size sheet materials, paper feed cassettes with different sheet material conveyance reference positions are selected and fed each time the sheet materials such as the first and second sheets are conveyed. By performing the above-described paper feeding method, it becomes possible to change the sheet material passing area of the fixing device, and as a result, the temperature distribution in the longitudinal direction of the fixing device can be made uniform, and the temperature rise of the non-sheet passing portion Can solve the problem.
Further, the time from receiving the main scanning direction synchronization position detection signal to writing the image on the photosensitive drum is appropriately changed according to the sheet material conveyance reference position set in the sheet feeding cassette. Thereby, even in an image forming apparatus having a plurality of sheet feeding cassettes having different sheet material conveyance reference positions, it is possible to provide a normal print to the user.
Furthermore, by switching the sensor used as the top sensor and the sensor used as the paper width sensor according to the paper transport reference position, it is not necessary to prepare a top sensor and a paper width sensor according to the transport reference position. Cost reduction of the forming apparatus main body can be realized.

  An “image forming apparatus” that is Embodiment 2 will be described. In this embodiment, a sheet conveyance reference position detection device that detects a sheet conveyance reference position in a paper feed cassette and a stacked sheet width detection device that detects the width of stacked sheets are provided. Note that the main configuration of the image forming apparatus according to the present embodiment is the same as that of the first embodiment, and thus detailed description thereof is omitted.

  FIG. 6 is a diagram showing a paper feed cassette used in this embodiment. Sensors S <b> 3 to S <b> 6 are sheet material presence / absence detection sensors that detect the presence / absence of the paper 17. A circuit diagram of the sheet material presence / absence detection sensor is shown in FIG. In the circuit of FIG. 7, when paper 17 is detected, the output becomes High when the mechanical flag interrupts the photo interrupter. As shown in FIG. 6, for example, if the state of the sensor S3 is High, it is possible to detect that the paper 17 is set by being moved to the right in the transport direction by a microcomputer (not shown). Further, in the state of FIG. 6, since the outputs of the sensors S3 and S4 are High, it can be detected that a small size paper is set.

  In this embodiment, the paper transport reference position and width of the paper 17 loaded in the paper feed cassettes 8a and 8b are detected by the above-described configuration. Assume that when continuously printing small-size paper, it is detected that the paper transport reference positions set in the paper feed cassette 8a and the paper feed cassette 8b are different and the width of the paper 17 is the same. In this case, each time the paper 17 such as the first sheet and the second sheet is transported, the user automatically switches to the sheet feeding cassette 8a and the sheet feeding cassette 8b to perform the sheet feeding, so that the user can control the image forming apparatus. It becomes possible to save the trouble of setting.

  In this configuration, since the paper width can be automatically detected, it is possible to automatically change the time from the BD signal to the image writing on the photosensitive drum in accordance with the paper width. FIG. 8 illustrates that the laser writing time on the photosensitive drum varies depending on the sheet width. As shown in FIG. 8, since the region where the paper 17 passes through the photosensitive drum 1 varies depending on the paper width, it is necessary to change the time from the detection of the BD signal to the image writing on the photosensitive drum 1 to t3 or t4. Arise.

FIG. 9 is a flowchart showing the control of this embodiment. First, after receiving a print signal in step 901, a return process from the standby state is performed in step 902. Thereafter, in step 903, it is determined whether or not the print command specifies a small size paper. If the small-size paper is designated, in step 904, the paper transport reference position and paper width set in the paper feed cassette 8a are detected. In step 905, the paper conveyance reference position and the paper width set in the paper feed cassette 8b are detected. Next, based on the information, it is determined in step 906 whether or not the small-size paper alternate paper feeding mode for alternately feeding paper from the paper feeding cassette 8a and the paper feeding cassette 8b can be executed. If the paper cassette 8a and the paper cassette 8b have the same paper width and different paper transport reference positions, the mode automatically shifts to the small-size paper alternate paper feed mode. In step 907, image writing times t1 and t3 corresponding to the widths of the sheets stacked in each paper cassette are calculated. In step 908, the first sheet 17a is first fed from the paper cassette 8a. At this time, in order to align the laser writing position on the photosensitive drum in step 908, t1 is set in a microcomputer (not shown) as the time from the detection of the BD signal to the writing. Thereafter, in step 910, it is determined whether the sensor S1 has detected the leading edge of the paper 17a. If the sensor cannot detect the leading edge of the paper 17a after a predetermined time, it is determined in step 922 that a paper feed error has occurred, the user is warned (step 923), and the process proceeds to a standby state (step 926).
After detecting the leading edge of the paper 17a in step 910, in step 911, the sensor S2 determines whether or not the width of the paper 17a is within a specified range. If the width of the paper 17a is within the specified range, it is determined that the paper is a small size paper, and in step 913, image forming processing is started in synchronization with the output of the sensor S1. If it is determined in step 912 that the width of the paper 17a is equal to or larger than the specified width, the small size alternate paper feed mode is exited, and the normal size image forming process (step 925) is performed.
After image formation is completed in step 913, it is determined in step 914 whether the print job is completed. If the print job has been completed, the process proceeds to a standby state in step 926. If the print job has not ended, the second sheet 17b is fed from the sheet cassette 8b in step 915. At that time, in step 916, the time from the detection of the BD signal to the writing is changed to t3 corresponding to the paper feed cassette 8b. Thereafter, in step 917, it is determined whether the sensor S2 has detected the leading edge of the paper 17b. If the sensor S2 cannot detect the leading edge of the paper 17b after a predetermined time, it is determined in step 922 that a paper feed error has occurred, and a warning (step 923) is given to the user, followed by a transition to a standby state (step 926).
After detecting the leading edge of the paper 17b in step 917, in step 918, the sensor S1 determines whether or not the width of the paper 17b is within a specified range. If the width of the paper 17b is within the specified range, it is determined that the paper is a small size paper, and image forming processing is started in step 920 in synchronization with the output of the sensor S2. If it is determined in step 919 that the width of the paper 17b is greater than or equal to the specified value, the small size alternate paper feed mode is exited, and the normal size image forming process (step 925) is performed.
After image formation is completed in step 920, it is determined in step 921 whether the print job is completed. If the print job has been completed, the process proceeds to a standby state in step 926. If the print job has not ended, the process returns to step 908 to feed the third sheet 17 from the sheet cassette.
If it is determined in step 903 that the print is not a small size print, an image formation process for a normal size is performed in step 925. After the print job is completed, the process shifts to a standby state in step 926. If it is determined in step 906 that the small-size paper alternate paper feed mode cannot be executed, in step 924, an image forming process for feeding small-size paper from one paper feed cassette is performed. After the small-size paper print job is completed in step 924, the image forming apparatus main body is shifted to a standby state in step 926.

  As described above, according to the present embodiment, the apparatus for detecting the sheet conveyance reference position and the apparatus for detecting the width of the stacked sheet material are provided in the sheet feeding cassette. This makes it possible to determine whether or not paper can be alternately fed from paper feed cassettes with different paper transport reference positions when small-size paper is continuously printed. As a result, it is not necessary for the user to make a setting for performing the small-size paper alternate paper feeding mode in the image forming apparatus, and usability is improved.

  “An image forming apparatus according to a third embodiment will be described. This embodiment is an example in which control is performed to narrow the sheet conveyance interval when sheets are alternately fed from sheet cassettes having different conveyance reference positions. The main part configuration of the image forming apparatus according to the present embodiment is the same as that of the first embodiment, and thus detailed description thereof is omitted.

In this embodiment, when the conveyance reference positions of a plurality of paper feed cassettes are different from each other, control for narrowing the sheet material conveyance interval is performed. FIG. 1 shows an example of sheet material conveyance in this embodiment and the position of the sensor. The paper 17 is loaded on the left side (left end reference) in the paper feeding cassette 8a and loaded on the right side (right side reference) in the paper feeding cassette 8b. The image forming apparatus feeds the first sheet 17a from the sheet feeding cassette 8a. At this time, as shown in FIG. 10, the leading edge of the sheet material is detected by the sensor S1. Subsequently, by feeding the second sheet 17b from the sheet cassette 8b, the leading edge of the sheet 17b can now be detected by the sensor S2. Thus, by switching between the paper feed cassette 8a and the paper feed cassette 8b each time paper is fed, it is possible to divide the sensor for detecting the leading edge of the paper for each paper. FIG. 10 is a timing chart of the sensors S1 and S2 when printing is performed continuously. When the leading edge of the first sheet 17a reaches the sensor, the output of the sensor S1 changes to High while chattering. However, since the first sheet 17a is not detected by the sensor S2, the output of the sensor S2 does not change. Next, when the first sheet 17a passes the sensor S1, the output of the sensor S1 changes to Low while chattering. Thereafter, the second sheet 17b reaches the sensor. Even if the leading edge of the second sheet reaches the sensor position when the chattering of the sensor S1 has not converged, the leading edge of the second sheet is detected by the sensor S2, so that the leading edge can be reliably detected. Become.
As described above, by alternately feeding paper from the paper feed cassette 8a and the paper feed cassette 8b set so that the paper conveyance reference position is different, the leading edge of the sheet material can be detected by a separate sensor for each paper passing. Become. Therefore, even if the next sheet material reaches the sensor in a state where chattering occurs, the leading edge of the sheet material can be reliably detected.

  FIG. 11 is a flowchart showing the control of this embodiment. First, after receiving a print signal in step 1101, a return process from the standby state is performed in step 1102. Thereafter, in step 1103, it is determined whether or not the user desires an alternate sheet feeding mode in which sheets are alternately fed from the sheet feeding cassette 8a and the sheet feeding cassette 8b. If the user desires the alternate sheet feeding mode, 10 mm is set in the microcomputer (not shown) as the 1104 sheet material conveyance interval in the step, and then in step 1105, the first sheet 17a from the sheet feeding cassette 8a is first set. Paper feed. At that time, in order to adjust the laser writing position on the photosensitive drum in step 1106, t1 is set in a microcomputer (not shown) as the time from the detection of the BD signal to the writing. Thereafter, in step 1107, it is determined whether the sensor S1 has detected the leading edge of the paper 17a. If the sensor S1 cannot detect the leading edge of the paper after a predetermined time, it is determined that there is a paper feed error in step 1114, a warning (step 1115) is given to the user, and the process proceeds to a standby state (step 1119). If the sensor can detect the leading edge of the paper in step 1107, image forming processing is started in step 1108 in synchronization with the output of the sensor S1. After image formation is completed in step 1108, it is determined in step 1109 whether the print job is completed. If the print job has been completed, the process shifts to a standby state in step 1119.

If the print job is not completed, the second sheet 17b is fed from the sheet cassette 8b in step 1110. At this time, in step 1111, the time from the detection of the BD signal to writing is changed to t5 corresponding to the paper width and the paper feed cassette. Thereafter, in step 1112, it is determined whether the sensor S2 has detected the leading edge of the paper. If the sensor S2 cannot detect the leading edge of the paper after a predetermined time, it is determined in step 1114 that a paper feed error has occurred, the user is warned (step 1115), and the process proceeds to a standby state (step 1119). If the sensor S2 can detect the leading edge of the paper in step 1112, the image forming process is started in synchronization with the output of the sensor S2 in step 1113.
After image formation is completed in step 1113, it is determined in step 1116 whether the print job is completed. If the print job has been completed, the process shifts to a standby state in step 1119. If the print job is not completed, the process returns to step 1105 to feed the third sheet material from the paper feed cassette 8a.

  If it is determined in step 1103 that the user does not wish to perform processing for alternately feeding sheets from the sheet feeding cassette 8a and the sheet feeding cassette 8b, in step 1117, 20 mm is set as a sheet conveyance interval in a microcomputer (not shown). To do. In step 1118, image forming processing for feeding paper from one paper feeding cassette is performed. Thereafter, in step 1119, the main body of the image forming apparatus is shifted to a standby state.

  As described above, according to the present embodiment, a sheet feeding cassette having a different sheet material conveyance reference position is switched for each sheet conveyance and used to feed the image forming apparatus. The front end of the sheet material can be detected using the sensor. As a result, even if the sheet material reaches the sensor position before the chattering of the sensor converges, the leading edge can be reliably detected, and as a result, the printing speed of the image forming apparatus can be improved.

(Modification of Example)
In each embodiment, each time a sheet material is conveyed, the sheet material is supplied by alternately selecting one of the pair of paper feed cassettes and the other paper feed cassette. However, the present invention is not limited to this, and each time a plurality of sheet materials, such as two or three, are conveyed, the sheet material may be supplied by alternately selecting one and the other of the pair of paper feed cassettes. Similar effects can be obtained.

FIG. 6 is a diagram illustrating a paper feeding method according to the first embodiment. Sectional drawing which shows schematic structure of the image forming apparatus which is Example 1. FIG. Explanatory drawing of the paper feed cassette in Embodiment 1 Timing chart showing relationship between BD signal and image signal in Embodiment 1 Flowchart showing processing in the first embodiment. Explanatory drawing of the paper feed cassette in Example 2 Circuit diagram of sensor in Example 2 Explanatory drawing of the write-out timing in Example 2. Flowchart showing processing in the second embodiment. Explanatory drawing of the output of the sensor in Example 3 The flowchart which shows the process of Example 3. Explanatory drawing of the scanner unit in the embodiment The figure which shows the structure of the sensor in a prior art example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 6 Fixing device 8a, 8b Paper feed cassette 9 Transfer roller 21 Paper control board

Claims (7)

A plurality of sheet feeding cassettes having sheet material regulating means for regulating the sheet material to a conveyance reference position in a direction orthogonal to the conveyance direction, and a sheet material fed from the sheet feeding cassette are formed on the photosensitive member. A transfer unit that transfers a toner image; a fixing unit that fixes the toner image transferred to the sheet material by the transfer unit to the sheet material by heat and pressure; and a control unit that controls an image forming process. An image forming apparatus,
The control unit includes a pair of sheet feeding cassettes having different sheet conveyance reference positions regulated by the sheet material regulating unit among the plurality of sheet feeding cassettes when the sheet material is continuously conveyed. When the sheet material is conveyed one sheet or a plurality of sheets, one of the pair of sheet cassettes and the other sheet cassette are alternately selected to supply the sheet material. Forming equipment. The image forming apparatus according to claim 1,
Laser scanning means for scanning the photosensitive member with laser light to form an electrostatic latent image;
Synchronization signal generating means for generating a main scanning direction synchronization signal for determining a writing position in the main scanning direction on the photosensitive member based on scanning of laser light by the laser scanning means;
With
The control means determines a specified time from receipt of the main scanning direction synchronization signal generated by the synchronization signal generation means to the start of writing in the main scanning direction according to the sheet conveyance reference position set in the paper feed cassette. An image forming apparatus characterized in that it is set to a predetermined value. The image forming apparatus according to claim 1, wherein
A sheet conveyance reference position detecting unit for detecting a sheet conveyance reference position set in the sheet cassette;
According to a detection result by the sheet conveyance reference position detection unit, the control unit includes a pair of sheet feed cassettes having different sheet conveyance reference positions regulated by the sheet material regulation unit among the plurality of sheet feed cassettes. If the sheet material is continuously conveyed when determined, each time one or more sheet materials are conveyed, one and the other of the pair of sheet cassettes are alternately selected and the sheet material is selected. An image forming apparatus that supplies a sheet material. The image forming apparatus according to any one of claims 1 to 3,
A stacking sheet width detecting means for detecting the width of the sheet material stacked on the sheet feeding cassette;
When the control unit determines that the widths of the sheet materials stacked on the pair of paper feed cassettes are equal based on the detection result of the stacked sheet width detection unit, the control unit conveys a single sheet or a plurality of sheets. An image forming apparatus, wherein the sheet material is supplied by alternately selecting one of the pair of paper feed cassettes and the other paper feed cassette. The image forming apparatus according to claim 1,
A sheet material detection means arranged in the sheet material conveyance path to detect the leading edge of the sheet material or the width of the sheet material,
The control means uses the sheet material detection means by switching the sheet material detection means to a sheet material leading edge detection means or a sheet material width detection means in accordance with a sheet conveyance reference position set in the paper feed cassette. Image forming apparatus. The image forming apparatus according to claim 1,
The user selects whether to supply the sheet material by alternately selecting one of the pair of paper feed cassettes and the other paper feed cassette each time one or more of the sheet materials are conveyed. An image forming apparatus comprising a selection unit that enables the image forming apparatus. The image forming apparatus according to claim 1,
When the control means supplies the sheet material by alternately selecting one of the pair of paper feed cassettes and the other paper feed cassette each time one or a plurality of the sheet materials are conveyed, An image forming apparatus characterized in that a sheet interval during sheet feeding is shortened compared to a case where sheet materials are continuously fed by the same sheet feeding cassette.

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