JP2017207671A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To bring the difference between the position of the leading end of an image in a sub scanning direction and the ideal position within an allowable range with a simpler method.SOLUTION: A measuring part 44 measures a difference in time between a first reference signal and a second reference signal. A conveyance control part 41 controls a sheet conveyance speed and a sheet feed timing according to the measured difference in time so that the difference between the timing at which a toner image carried on an image carrier reaches a transfer part and the timing at which a sheet reaches the transfer part falls within an allowable range.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus using an electrophotographic process.

  Image forming apparatuses such as laser beam printers form an electrostatic latent image on a photoreceptor using a laser beam. More specifically, the scanning optical device rotates the polygon mirror and scans the photosensitive drum with a laser beam, whereby an electrostatic latent image is formed on the photosensitive drum. The direction in which the polygon mirror is rotated and scanned is called the main scanning direction. Further, by rotating the photosensitive drum, scanning in a direction orthogonal to the main scanning direction is realized. A direction orthogonal to the main scanning direction is referred to as a sub-scanning direction.

  When the image forming apparatus is ready for image formation, the image forming apparatus outputs a TOP signal for starting sheet feeding from the sheet feeding cassette. On the other hand, a BD signal, which is a synchronization signal for main scanning, is output in conjunction with the scanning cycle of the polygon mirror. When the image forming apparatus receives the BD signal after receiving the TOP signal, it actually starts scanning the photosensitive drum. Here, since the TOP signal and the BD signal are generated by using independent events as triggers, the TOP signal and the BD signal are not synchronized. That is, the period from when the TOP signal is received until the BD signal is received varies from sheet to sheet, and the timing at which scanning of the photosensitive drum is actually started varies from sheet to sheet. Therefore, the timing at which the sheet arrives at the transfer position and the timing at which the toner image arrives vary, and the image forming position varies from sheet to sheet. According to Patent Document 1, a laser beam used for recording of the first line among a plurality of laser beams according to a time difference between an image recording start signal (TOP signal) and a main scanning synchronization signal (BD signal). It has been proposed to choose. This reduces the variation in the image forming position for each sheet.

JP-A-8-142424

  However, in the invention of Patent Document 1, since lines assigned to a plurality of laser beams change each time, complicated assignment control of video signals will be required. Therefore, an object of the present invention is to keep the difference between the leading edge position and the ideal position of an image in the sub-scanning direction within an allowable range by a simpler method.

According to the present invention,
First generation means for generating a first reference signal that serves as an image writing reference in the sub-scanning direction parallel to the sheet conveying direction;
A second generation means for generating a second reference signal that serves as an image writing reference in the main scanning direction orthogonal to the sub-scanning direction;
Measuring means for measuring a time difference between the first reference signal and the second reference signal;
In response to the first reference signal, a sheet feeding unit that feeds the sheets stacked on the stacking unit;
Conveying means for conveying a sheet fed by the paper feeding means;
An image having an image carrier, a light source, and a scanning unit that scans the surface of the image carrier in the main scanning direction with light output from the light source, and forms a toner image on the surface of the image carrier. Forming means;
Transfer means for transferring the toner image formed on the image carrier onto the sheet conveyed by the conveyance means, timing at which the toner image carried on the image carrier arrives at the transfer means, and the sheet The sheet conveying speed by the conveying unit or the sheet feeding timing by the sheet feeding unit is controlled according to the time difference measured by the measuring unit so that the difference from the timing to arrive at the transfer unit is within an allowable range. And an image forming apparatus including the control unit.

  According to the present invention, the difference between the leading edge position of the image and the ideal position in the sub-scanning direction can be kept within an allowable range by a simpler method.

Schematic sectional view of the image forming apparatus Diagram explaining exposure tool Diagram explaining the control system Timing chart for paper feed control The figure explaining the image formation position in a subscanning direction Timing chart for paper feed control Timing chart for paper feed control Timing chart for paper feed control Flow chart showing paper feed control Flow chart showing paper feed control Timing chart for paper feed control

<Example 1>
[Outline of image forming apparatus]
FIG. 1 shows an outline of the configuration of the image forming apparatus 100. The image forming apparatus 100 may be realized as a printing apparatus, a printer, a copier, a multifunction machine, a facsimile, or the like. The pickup roller 12 feeds the sheets P stacked on the lifting plate 11 of the paper feeding unit 10 one by one to the conveyance path. The lifting plate 11 is an example of a stacking unit for sheets P. The registration roller 13 is a conveyance roller that sandwiches and conveys the sheet P fed from the sheet feeding unit 10 and sends it to the image forming unit 1. The registration sensor 14 is a sheet sensor that detects the sheet P. The sheet P may be called a recording material, a recording medium, paper, a transfer material, or transfer paper. The image forming unit 1 forms a toner image by developing an electrostatic latent image formed by a photosensitive drum 2 that is an image carrier, a charger 3 that uniformly charges the photosensitive drum 2, and an exposure unit 4. A developing unit 5 is provided. The exposure unit 4 may be called by another name such as a scanning optical device. The transfer device 6 includes a transfer roller and a transfer member that transfer the toner image carried on the photosensitive drum 2 to the sheet P. The nip portion formed by the contact between the photosensitive drum 2 and the transfer roller of the transfer device 6 may be referred to as a transfer portion. The toner image carried on the photosensitive drum 2 may be primarily transferred to the intermediate transfer member, and the toner image may be secondarily transferred from the intermediate transfer member to the sheet P. In this case, the transfer portion is a nip portion formed by the intermediate transfer member and the secondary transfer roller. The fixing device 15 fixes the toner image to the sheet P by applying heat and pressure to the toner image and the sheet P. The discharge roller 16 discharges the sheet P to the discharge tray 17.

[Exposure tool]
FIG. 2 shows a schematic configuration of the exposure unit 4. The laser unit 21 is a light source that outputs light in accordance with a laser drive signal output from the engine controller 20. The laser drive signal is modulated in accordance with a video signal generated by analyzing input image information. A motor drive signal output from the engine controller 20 is output to the motor drive circuit 25. The motor drive circuit 25 drives the scanner motor 24 according to the motor drive signal. The scanner motor 24 drives the polygon mirror 23 so that the rotational speed of a rotary polygon mirror (hereinafter referred to as a polygon mirror 23), which is an example of a deflector, becomes a target speed. The laser beam L output from the laser unit 21 passes through an optical system such as a collimator lens, is deflected by the reflection surface of the polygon mirror 23, and scans the surface of the photosensitive drum 2. An optical system such as an fθ lens or a reflection mirror may be provided between the polygon mirror 23 and the photosensitive drum 2. Scanning by the polygon mirror 23 is called main scanning. Note that the laser beam L not only scans the photosensitive drum 2 in one scanning cycle, but also enters the detection unit 22. The detection unit 22 outputs a BD signal to the engine controller 20 that is at a low level during the period when the laser beam L is incident and is at a high level during the period when the laser beam L is not incident. BD is an abbreviation for beam detect. The BD signal functions as a horizontal synchronization signal that serves as a reference for the writing position of the laser beam L in the main scanning direction. The detection unit 22 includes a light receiving element (photoelectric conversion element) such as a photodiode.

[Control system]
FIG. 3 shows a control system for controlling the image forming apparatus 100. Each function provided in the engine controller 20 and the printer controller 30 may be realized by a CPU executing a control program, or may be realized by hardware such as an ASIC or FPGA. ASIC is an abbreviation for application specific integrated circuit. FPGA is an abbreviation for field programmable gate array.

  The engine controller 20 mainly controls the image forming unit 1 and controls the feeding and conveyance of the sheet P. For example, when a TOP signal serving as a reference for starting image formation is output from the TOP signal unit 42, the transport control unit 41 starts driving the motor 31 and switches on the clutch 32. As a result, the driving force of the motor 31 is transmitted to the pickup roller 12 via the clutch 32, the pickup roller 12 rotates, and the sheet P is fed. The driving force of the motor 31 is transmitted to the registration roller 13, and the registration roller 13 conveys the sheet P. The conveyance control unit 41 adjusts (increases / decelerates) the conveyance speed of the sheet P by the registration rollers 13 by controlling the rotation speed of the motor 31. The conveyance control unit 41 increases the conveyance speed if the time from the start of feeding the sheet P to the timing when the registration sensor 14 detects the leading edge of the sheet P is longer than the specified time. On the other hand, the conveyance control unit 41 decelerates the conveyance speed if the time from the start of feeding the sheet P to the timing at which the registration sensor 14 detects the leading edge of the sheet P is shorter than the specified time. As a result, the sheet P arrives at the transfer unit 6 when a certain time has elapsed since the start of feeding. When receiving the image forming command from the printer controller 30, the TOP signal unit 42 raises the fixing temperature of the fixing device 15 to the target temperature or accelerates the rotational speed of the scanner motor 24 to the target speed. The TOP signal unit 42 generates a TOP signal and outputs it to the printer controller 30 when the image forming apparatus 100 is ready for image formation. The measuring unit 44 measures a time difference Δ from the falling timing of the TOP signal to the falling timing of the BD signal immediately after that. The determination unit 45 is optional and determines whether the time difference Δ is less than a threshold value. The correction unit 46 is also an option, and corrects the time difference Δ using a threshold value. The correction of the time difference Δ will be described in detail in the second embodiment. The exposure control unit 43 generates a laser drive signal according to the video signal (Video) supplied from the printer controller 30 and supplies the laser drive signal to the laser unit 21. The exposure control unit 43 also generates a motor drive signal for driving the scanner motor 24 and supplies it to the motor drive circuit 25.

  The printer controller 30 analyzes job data received from the host computer 40 to generate a video signal, and supplies the video signal to the engine controller 20. The counter 33 is reset to 0 when the TOP signal is input, and counts the number of BD signals input from the engine controller 20. The comparison unit 34 compares the count value of the counter 33 with a predetermined value, and causes the supply unit 35 to start outputting a video signal when the count value matches the predetermined value. For example, the supply unit 35 starts outputting the video signal in synchronization with the falling edge of the BD signal.

[Timing chart]
First, the technology that is the basis of this embodiment will be described. FIG. 4A shows a case where the timing at which the paper feeding unit 10 starts feeding and the BD signal are not synchronized. That is, the timing for starting paper feeding is synchronized with the TOP signal. The timing at which the paper feeding unit 10 starts feeding paper may be referred to as a paper feeding timing. FIG. 4B shows a case where the paper feed timing and the BD signal are synchronized. Therefore, the paper feed timing is not synchronized with the TOP signal. As shown in FIG. 4A, the TOP signal unit 42 of the engine controller 20 outputs a TOP signal at time t1, and starts feeding and transporting the sheet P. The conveyance control unit 41 of the engine controller 20 accelerates or decelerates the conveyance speed of the sheet P by the registration roller 13 so that the sheet P reaches the transfer unit 6 when a predetermined time T has elapsed from the time t1. The predetermined time T is the conveyance time of the sheet P determined by the conveyance distance from the paper supply unit 10 to the transfer device 6 and the rotational speed of the photosensitive drum 2. The rotational speed of the photosensitive drum 2 is sometimes called a process speed. If the time required to reach the registration sensor 14 is later than the specified time, the registration roller 13 temporarily increases the conveyance speed of the sheet P in order to reduce this delay. For example, the sheet P is temporarily transported at a second transport speed that is faster than the process speed (first transport speed). As a result, every sheet P reaches the transfer portion in a predetermined time T.

  On the other hand, when the TOP signal is input, the counter 33 of the printer controller 30 starts counting the number of BD signals. The counter 33 increments the count value by one each time the falling edge of the BD signal is detected. The comparison unit 34 compares the count value of the counter 33 with a predetermined value, and when the count value matches the predetermined value, causes the supply unit 35 to start outputting a video signal. Here, the output of the video signal is started at time t3 when the count value matches the predetermined value and is the falling timing of the BD signal. As a result, the video signal is synchronized with the BD signal. If the falling edge of the TOP signal, which is the reference for the paper feed timing, deviates from the falling edge of the BD signal, which is the reference for the image writing timing, the leading edge position of the image on the sheet P deviates from the ideal position. . As shown in FIG. 4A, the time difference Δ between the falling edge of the TOP signal and the falling edge of the BD signal is t2−t1. Accordingly, the sheet P reaches the transfer portion at time t4, whereas the toner image reaches the transfer portion at time t5 delayed by Δ. The time difference between time t4 and time t5 is also Δ. As shown in FIG. 5A, the leading edge position of the image on the sheet P in the sub-scanning direction is shifted from the ideal position by a distance corresponding to the time difference Δ. The maximum value of the time difference Δ is one scanning period (the period of the BD signal). When a multi-beam light source that forms four lines in one main scan is employed, the amount of deviation in the sub-scanning direction is a maximum of four lines.

  On the other hand, as illustrated in FIG. 4B, the conveyance control unit 41 may synchronize the sheet P feeding timing with the BD signal by detecting the BD signal as an interrupt signal at time t2. By determining the paper feed timing in synchronization with the BD signal, paper feed and image formation are synchronized. As a result, as shown in FIG. 4B, the sheet P and the toner image reach the transfer portion at time t5. As a result, as shown in FIG. 5B, the leading end position of the image on the sheet P matches the ideal position.

  By the way, an image may be continuously formed on a plurality of sheets P (continuous printing). The TOP signal is output for each sheet P, but how to set the interval between the TOP signal for the preceding sheet P and the TOP signal for the succeeding sheet P becomes a problem. In the case where the paper feed timing is synchronized with the BD signal as shown in FIG. 4B, the BD signal may deviate from the TOP signal. That is, the paper feed timing is delayed from the falling edge of the TOP signal. Therefore, the interval between the TOP signals must be determined so as to ensure a sufficient space between the sheets even if the paper feed timing is delayed from the TOP signal. As a result, the interval between the TOP signals becomes longer than necessary. The sheet interval is the interval from the trailing edge of the preceding sheet P to the leading edge of the succeeding sheet P. The gap between the sheets is necessary for the sheet sensor to detect the sheet P. Note that the interval between the TOP signals may be determined by the TOP signal unit 42, but may be determined by a determination unit independent of the TOP signal unit 42.

  FIG. 6 is a timing chart showing continuous printing on three sheets P. In this example, the interval between the TOP signals is set to a constant value so as to cope with the case where the time difference Δ is the maximum value (worst case). For example, the interval from the timing t1 ′ for outputting the TOP signal for the Nth sheet P to the timing t1 ″ for outputting the TOP signal for the (N + 1) th sheet P is set to this constant value Dw (here, (N = 2) This constant value Dw is determined so as to secure a sheet space necessary for printing on the (N + 1) th sheet P even if the timing t2 ′ at which the BD signal is interrupted is delayed. That is, the interval between the TOP signals (t1 ′ to t1 ″) is a constant value Dw determined in preparation for the maximum interval between the fall of the TOP signal and the fall of the BD signal. Thus, since the interval between the TOP signals is a constant value Dw assuming the worst case, a wasteful waiting time will occur depending on the actual interval between the fall of the TOP signal and the fall of the BD signal. . This means that the image formation on the (N + 1) th sheet P is started after a lapse of more time than necessary, even though the preparation for image formation on the (N + 1) th sheet P is ready. .

  FIG. 7 is a timing chart regarding image formation according to the first exemplary embodiment. Here, the paper feed timing and the BD signal are not synchronized, and the paper feed timing and the TOP signal are synchronized. At time t1, the TOP signal unit 42 outputs a TOP signal. The conveyance control unit 41 drives the motor 31 in synchronization with the TOP signal, and starts feeding and conveying the sheet P. The supply unit 35 of the printer controller 30 outputs a video signal in synchronization with the BD signal at time t3 when the number of BD signals detected after the TOP signal is output reaches a predetermined value. The measuring unit 44 of the engine controller 20 measures a time difference Δ from the falling edge of the TOP signal (time t1) to the falling edge of the BD signal (time t2). The conveyance control unit 41 determines the target time T ′ by adding the time difference Δ to the predetermined time T described above. The conveyance control unit 41 controls the rotation speed of the motor 31 so that the sheet P arrives at the transfer unit at time t5 when the elapsed time from the fall of the TOP signal (time t1) reaches the target time T ′. That is, the conveyance speed of the sheet P is adjusted. The normal sheet P conveyance speed matches the rotational speed (circumferential speed) of the photosensitive drum 2. In this embodiment, since it is necessary to delay the arrival of the sheet P by the time difference Δ, the conveying speed of the sheet P is increased so as to return to the original speed (the rotational speed of the photosensitive drum 2) after being temporarily reduced. The As described above, the conveyance control unit 41 measures the time difference Δ between the TOP signal serving as the reference for the paper feed timing and the BD signal serving as the reference for the image writing timing, and adjusts the conveyance speed of the sheet P according to the time difference Δ. To do. As a result, the leading end position of the image matches the ideal position.

  FIG. 8 is a timing chart showing continuous printing. The time t1 ″ for outputting the TOP signal for the (N + 1) th sheet P is adjusted according to the time difference Δ from the time t1 ′ for outputting the TOP signal for the Nth sheet P to the time t2 ′ for detecting the BD signal. That is, the interval (t1 ′ to t1 ″) between the TOP signals is the sum of the constant value Db and the time difference Δ for the best case where the time difference Δ is zero. The constant value Db for the best case is a time corresponding to the sum of the length in the transport direction of the Nth sheet P and the interval between the trailing edge of the Nth sheet P and the leading edge of the (N + 1) th sheet P. is there. Note that the sheet interval is set to the minimum interval between sheets where the sheet sensor such as the registration sensor 14 can detect the trailing edge of the Nth sheet P and the leading edge of the (N + 1) th sheet P. This is because a jam or the like cannot be found if the sheet sensor cannot detect the interval between sheets. In this way, by adjusting the interval between the TOP signals in accordance with the time difference Δ, it is possible to secure an interval between sheets where continuous printing can be performed and to shorten the processing time from the start to the end of continuous printing. It becomes. 8, compared with FIG. 6, the output timing (time t1 ″) of the TOP signal of the (N + 1) th sheet P is earlier by one cycle of the BD signal. That is, in the case shown in FIG. Compared with FIG. 6, the printing completion timing of the (N + 1) th sheet P is earlier.

[flowchart]
A flowchart of processing for adjusting the position of the leading edge of the image executed by the engine controller 20 will be described with reference to FIG. In step S <b> 101, the engine controller 20 determines whether the image forming apparatus 100 has completed preparation for image formation. As described above, when the engine controller 20 receives a print start command from the printer controller 30, the engine controller 20 activates the fixing device 15, the exposure device 4, and the like. The conveyance control unit 41 activates the motor 31 and adjusts the rotational speeds of the registration roller 13, the photosensitive drum 2, the pressure roller of the fixing device 15, and the discharge roller 16 to a predetermined process speed. The exposure controller 43 increases the rotational speed of the scanner motor 24 to the target speed. The engine controller 20 supplies power to the heater of the fixing device 15 so that the fixing temperature of the fixing device 15 becomes a target temperature. When preparation for image formation is completed, the engine controller 20 proceeds to S102.

  In S102, the engine controller 20 (TOP signal unit 42) outputs a TOP signal as the first reference signal. In S103, the engine controller 20 (measurement unit 44) starts measuring the time difference Δ with reference to the falling edge of the TOP signal. In S104, the engine controller 20 (conveyance control unit 41) switches the clutch 32 on the basis of the falling edge of the TOP signal, rotates the pickup roller 12, and starts feeding the sheet P.

  In S105, the engine controller 20 (measurement unit 44) determines whether the falling edge of the BD signal that is the second reference signal is detected. If the falling edge of the BD signal is detected, the engine controller 20 proceeds to S106. In S106, the engine controller 20 (measurement unit 44) stops measuring the time difference Δ and determines the time difference Δ. S107 is an optional process required when images are successively formed on a plurality of sheets P. In S107, the engine controller 20 (TOP signal unit 42) determines the output timing of the next first reference signal (the TOP signal for the (N + 1) th sheet P) according to the time difference Δ. In step S108, the engine controller 20 (conveyance control unit 41) controls the conveyance speed of the sheet P (rotation speed of the motor 31) according to the time difference Δ, and determines the timing at which the sheet P arrives at the transfer unit as a toner image (developer image). Is coincident with the timing of arrival at the transfer portion.

  According to this embodiment, the conveyance speed of the sheet P is controlled according to the time difference Δ between the TOP signal and the BD signal. As a result, the timing at which the toner image carried on the photosensitive drum 2 arrives at the transfer portion coincides with the timing at which the sheet P arrives at the transfer portion. Further, according to the present embodiment, in the continuous printing, the output timing of the TOP signal for the (N + 1) th sheet P is determined according to the time difference Δ measured for the Nth sheet P. This makes it possible to advance the time for completing the image formation on the (N + 1) th sheet P. In other words, since paper feeding is executed in synchronization with the TOP signal, image formation is completed earlier by one scanning cycle at the maximum than in the case where paper feeding is executed in synchronization with the BD signal.

  In this embodiment, the conveyance speed of the sheet P is controlled according to the time difference Δt, but the sheet feeding timing may be changed. For example, the conveyance control unit 41 and the sheet feeding unit 10 may be configured to start feeding the sheet P a predetermined time after receiving the TOP signal. That is, the paper feed timing is a timing that is a predetermined time after the output timing of the TOP signal. The conveyance control unit 41 controls the sheet feeding timing of the sheet P in the sheet feeding unit 10 by adjusting the predetermined time according to the time difference Δt. In this manner, the conveyance control unit 41 supplies the toner image so that the difference between the timing at which the toner image carried on the image carrier arrives at the transfer device 6 and the timing at which the sheet P arrives at the transfer device 6 falls within an allowable range. The paper timing may be controlled.

<Example 2>
In the first embodiment, the image leading edge position of the sheet P is adjusted to the ideal position according to the time difference Δ between the TOP signal and the BD signal. In the second embodiment, the TOP signal and the BD signal are not synchronized as in the first embodiment, and the error between the image front end position and the ideal position is suppressed within an allowable range according to the time difference Δ. In the second embodiment, description of parts common to the first embodiment is omitted.

[flowchart]
The flowchart of the process which adjusts the front-end | tip position of the image which the engine controller 20 performs using FIG. 10 is demonstrated. Compared to FIG. 9, in FIG. 10, a step is added between S106 and S107 for correcting the adjustment amount of the conveyance speed and the interval between the TOP signals depending on whether or not the time difference Δ is less than the threshold value. .

  In S201, the engine controller 20 (determination unit 45) determines whether or not the time difference Δ is less than the threshold value Δth. The threshold value Δth is determined according to, for example, an allowable amount of error between the image front end position and the ideal position. For example, when a multi-beam light source that performs main scanning of four lines in one scan is employed, a shift amount corresponding to two lines, that is, half of the period of the BD signal is set as the threshold value Δth. If the time difference Δ is less than the threshold value Δth, the error is within the allowable range, and the engine controller 20 proceeds to S202. In S202, the engine controller 20 (correction unit 46) corrects the time difference Δ to zero. The corrected time difference Δ may be expressed as a time difference Δ ′. If the time difference Δ is not less than the threshold value Δth, the error is not within the allowable range, so the engine controller 20 proceeds to S203. In S203, the engine controller 20 (correction unit 46) corrects the time difference Δ using the threshold value Δth. For example, the engine controller 20 may subtract the threshold value Δth from the time difference Δ to determine the corrected time difference Δ ′. Thereby, the corrected time difference Δ ′ is used in S107 and S108.

[Timing chart for continuous printing]
FIG. 11 is a timing chart showing continuous printing. With respect to FIG. 11, differences from FIG. 8 will be described. As described above, the paper feed timing is not synchronized with the BD signal, but is synchronized with the TOP signal. The engine controller 20 outputs a TOP signal for the Nth sheet P at time t1, and starts feeding the Nth sheet P. The video signal is output in synchronization with the BD signal at time t3. The engine controller 20 measures a time difference Δ between the TOP signal (time t1) and the BD signal (time t2). The engine controller 20 obtains a time t4 when the sheet P arrives at the transfer portion according to the corrected time difference Δ ′. In this example, the time T ′ from time t1 to time t2 is determined by adding the time difference Δ ′ to the predetermined time T described above. The engine controller 20 adjusts the conveyance speed of the sheet P so that the sheet P arrives at the transfer portion at time t4. Here, the corrected time difference Δ ′ is small compared to the measured time difference Δ. The timing at which the sheet P arrives at the transfer portion is delayed according to the time difference. When the arrival of the sheet P is delayed based on the time difference Δ ′ that is smaller than the time difference Δ, the time t4 arrives before the time t5. That is, the sheet P arrives at the transfer portion before the image. As described above, the timing at which the sheet P arrives at the transfer portion in the second embodiment is advanced compared to the timing in the first embodiment. That is, the timing at which image formation on the sheet P is completed is also advanced. As described above, in the second embodiment, it is possible to complete image formation early instead of allowing an error in the image forming position.

  Furthermore, the time t1 ′, which is the output timing of the TOP signal for the Nth sheet P in the continuous image formation, is determined as the time when the time that is the sum of the constant value Db and the time difference Δ ′ has elapsed from the time t1. . The constant value Db is an interval between the TOP signals in the best case where the falling edge of the TOP signal coincides with the falling edge of the BD signal. Similarly, time t1 ″, which is the timing for outputting the (N + 1) th TOP signal, is a time difference Δ between time t1 ′, which is the timing for outputting the Nth TOP signal, and time t2 ′, which is the timing for detecting the BD signal. The time difference Δ is corrected to the time difference Δ ′ using the threshold value Δth. Thus, the interval between the TOP signals (t1 ′ to t1 ″) is the time difference Δ ′ to the constant value Db of the best case. It is determined by adding. As a result, image formation can be completed quickly instead of allowing an error in the image formation position. The constant value may be obtained by dividing the sum of the length of the preceding sheet P in the conveyance direction and the minimum sheet interval by the process speed.

<Summary>
As described with reference to FIG. 3, the TOP signal unit 42 is a first generation unit that generates a first reference signal (for example, a TOP signal) that serves as an image writing reference in the sub-scanning direction parallel to the conveyance direction of the sheet P. It is an example. The detection unit 22 is an example of a second generation unit that generates a second reference signal (BD signal) serving as an image writing reference in the main scanning direction orthogonal to the sub-scanning direction. The measurement unit 44 is an example of a measurement unit that measures a time difference between the first reference signal and the second reference signal. The pickup roller 12 is an example of a sheet feeding unit that feeds the sheets P stacked on the stacking unit according to the first reference signal. The registration roller 13 is an example of a transport unit that transports the sheet P fed by the paper feed unit. The image forming unit 1 is an example of an image forming unit that forms a toner image on the surface of the image carrier. The photosensitive drum 2 is an example of an image carrier. The laser unit 21 is an example of a light source. The polygon mirror 23 is an example of a scanning unit that scans the surface of the image carrier in the main scanning direction with the light output from the light source. The transfer device 6 is an example of a transfer unit that transfers the toner image formed on the image carrier onto the sheet P that has been transported by the transport unit. The conveyance control unit 41 conveys the sheet P so that the difference between the timing at which the toner image carried on the image carrier arrives at the transfer unit 6 and the timing at which the sheet P arrives at the transfer unit 6 falls within an allowable range. It is an example of the control means which controls. In particular, the conveyance control unit 41 controls the conveyance speed of the sheet P by the registration roller 13 according to the time difference Δ measured by the measurement unit 44. This makes it possible to keep the difference between the leading edge position of the image in the sub-scanning direction and the ideal position within an allowable range by a simpler technique than before.

  As shown in FIG. 6, the TOP signal unit 42 is N + 1 sheets when a predetermined value Dw has elapsed from the timing (t1 ′) when the first reference signal is generated for the Nth sheet P (t1 ″). The first reference signal may be generated for the eye sheet P. Dw is a time corresponding to the length in the transport direction of the Nth sheet P and the (N + 1) th sheet from the rear end of the Nth sheet P. This is the sum of the time corresponding to the interval between the sheets up to the leading edge of the sheet P and the maximum deviation time of the first reference signal and the second reference signal The conveyance control unit 41 measures the measurement unit for the (N + 1) th sheet P. 44 may be configured to control the conveyance speed of the (N + 1) th sheet P by the registration roller 13 in accordance with the time difference (t2 ″ −t1 ″) measured in Step 44. Accordingly, even in continuous printing, the leading edge of the image may be configured. The difference between the position and the ideal position It is possible to fit the Contents range. Maximum deviation time is the time corresponding to one cycle of the second reference signal (BD signal).

  As shown in FIG. 8, the TOP signal unit 42 receives the (N + 1) th sheet when a predetermined time has elapsed (t1 ″) from the timing (t1 ′) when the first reference signal is generated for the Nth sheet P. The first reference signal may be generated for the sheet P. The predetermined time is a sum of the constant value Db and the time difference measured for the Nth sheet P. The constant value Db is N sheets. The time corresponding to the length of the eye sheet P in the conveying direction and the time corresponding to the interval between the trailing edge of the Nth sheet P and the leading edge of the (N + 1) th sheet P. That is, a constant value Db. Is the best case interval at which the time difference Δ is 0. The conveyance control unit 41 determines the registration roller 13 according to the time difference Δ (= t2 ″ −t1 ″) measured by the measurement unit 44 for the (N + 1) th sheet P. N + 1 sheet P by Thus, it is possible to advance the image formation completion time while keeping the error of the leading end position of the image within an allowable range.

  As described in the second embodiment, the determination unit 45 functions as a determination unit that determines whether the time difference Δ measured by the measurement unit 44 is less than a predetermined threshold value ΔTh. If the time difference is less than the threshold, the conveyance control unit 41 does not need to adjust the sheet conveyance speed according to the time difference. This is realized by setting the time difference Δ to 0. Further, the conveyance control unit 41 may be configured to adjust the sheet conveyance speed according to the time difference unless the time difference is less than the threshold value. As described above, the technical idea described in the second embodiment may be applied to the first embodiment.

  As described with reference to FIG. 11, the TOP signal unit 42 receives the (N + 1) th sheet when a predetermined time has elapsed (t1 ″) from the timing (t1 ′) when the first reference signal is generated for the Nth sheet P. The first reference signal may be generated for the sheet P. The predetermined time is a sum of a value (time difference Δ ′) obtained by correcting the time difference Δ measured for the Nth sheet P with a predetermined threshold Δth and a constant value Db. The conveyance control unit 41 adjusts the time difference (t2 ″ −t1 ″) measured by the measurement unit 44 for the (N + 1) th sheet P with the threshold value, and adjusts the N + 1th sheet by the registration roller 13. By controlling the conveyance speed, it is possible to advance the image formation completion time while keeping the error of the leading end position of the image within an allowable range.If the time difference is less than the threshold value, the conveyance control unit 41 reduces the time difference. zero Modified, the unless the time difference Δ is less than the time difference threshold, may be used correction unit 46 for correcting using a threshold .DELTA.th.

  Note that the measurement unit 44 may be configured to measure a time difference from the fall of the first reference signal to the fall of the second reference signal that arrives immediately after the fall of the first reference signal. The measuring unit 44 may be configured to measure a time difference from the rising edge of the first reference signal to the rising edge of the second reference signal that comes immediately after the rising edge of the first reference signal. The TOP signal unit 42 may be configured to generate a first reference signal for the first sheet when the image forming unit 1 is ready for image formation. The detection unit 22 may include a light receiving unit that generates the second reference signal by receiving the light deflected by the polygon mirror 23. The transfer unit such as the transfer device 6 is configured to primarily transfer the toner image formed on the image carrier to the intermediate transfer member, and secondarily transfer the toner image primarily transferred to the intermediate transfer member to the sheet. Also good. The laser unit 21 may be a multi-beam light source that outputs a plurality of lights in parallel in one main scan.

  In the above embodiment, the leading edge position of the image is adjusted by delaying the arrival timing of the sheet P at the transfer portion according to the time difference Δ. However, the leading edge position of the image may be adjusted by advancing the arrival timing of the image according to the time difference Δ. For example, if the time difference Δ is equal to or greater than the threshold value Δth, the engine controller 20 advances the output start timing of the video signal with respect to the printer controller 30 by one scanning cycle (one BD cycle). This can be realized by subtracting 1 from the predetermined value used in the comparison unit 34 and adjusting the predetermined value. Thereby, it is possible to reduce the error of the image forming position within an error corresponding to half of the BD period. In this case, the counter 33 functions as a counting unit that counts the number of second reference signals based on the first reference signal. The supply unit 35 functions as a supply unit that starts supplying an image signal (video signal) to the laser unit 21 when the count value of the counter 33 reaches a predetermined value. The engine controller 20 may include an adjustment unit that adjusts the predetermined value according to the time difference measured by the measurement unit 44 so that the timing difference falls within an allowable range. The timing difference is a difference between the timing at which the toner image carried on the image carrier arrives at the transfer device 6 and the timing at which the sheet arrives at the transfer device 6.

  P: Sheet recording material, 100: Image forming apparatus, 42: TOP signal section, 22: Detection section, 44: Measuring section, 12: Feed roller, 13: Registration roller, 1: Image forming section, 6: Transfer device 20 Engine controller

Claims (14)

First generation means for generating a first reference signal that serves as an image writing reference in the sub-scanning direction parallel to the sheet conveying direction;
A second generation means for generating a second reference signal that serves as an image writing reference in the main scanning direction orthogonal to the sub-scanning direction;
Measuring means for measuring a time difference between the first reference signal and the second reference signal;
In response to the first reference signal, a sheet feeding unit that feeds the sheets stacked on the stacking unit;
Conveying means for conveying a sheet fed by the paper feeding means;
An image having an image carrier, a light source, and a scanning unit that scans the surface of the image carrier in the main scanning direction with light output from the light source, and forms a toner image on the surface of the image carrier. Forming means;
Transfer means for transferring the toner image formed on the image carrier onto the sheet conveyed by the conveyance means, timing at which the toner image carried on the image carrier arrives at the transfer means, and the sheet The sheet conveying speed by the conveying unit or the sheet feeding timing by the sheet feeding unit is controlled according to the time difference measured by the measuring unit so that the difference from the timing to arrive at the transfer unit is within an allowable range. And an image forming apparatus. The first generation means includes a time corresponding to a length in the conveyance direction of the Nth sheet, and a time corresponding to a gap between the trailing edge of the Nth sheet and the leading edge of the (N + 1) th sheet, When the first reference signal has been generated for the Nth sheet (t1 ′) by the sum of the maximum deviation time of the first reference signal and the second reference signal (t1 ″) In addition, the first reference signal is generated for the (N + 1) th sheet,
The control unit is configured to control a conveyance speed of the N + 1th sheet by the conveyance unit according to a time difference (t2 ″ −t1 ″) measured by the measurement unit with respect to the N + 1th sheet. The image forming apparatus according to claim 1, wherein:   The image forming apparatus according to claim 2, wherein the maximum deviation time is a time corresponding to a period of the second reference signal. The first generation means includes a time corresponding to a length in the conveyance direction of the Nth sheet, and a time corresponding to a gap between the trailing edge of the Nth sheet and the leading edge of the (N + 1) th sheet, When N + 1 has elapsed from the timing (t1 ′) when the first reference signal was generated for the Nth sheet by the sum of the time difference measured for the Nth sheet, the N + 1 Configured to generate the first reference signal for a first sheet,
The control unit is configured to control a conveyance speed of the N + 1th sheet by the conveyance unit according to a time difference (t2 ″ −t1 ″) measured by the measurement unit with respect to the N + 1th sheet. The image forming apparatus according to claim 1, wherein: A determination unit for determining whether the time difference measured by the measurement unit is less than a predetermined threshold;
If the time difference is less than the threshold, the control unit does not adjust the sheet conveyance speed according to the time difference, and if the time difference is not less than the threshold, the sheet conveyance speed according to the time difference. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to perform the adjustment. The first generation means includes a time corresponding to a length in the conveyance direction of the Nth sheet, and a time corresponding to a gap between the trailing edge of the Nth sheet and the leading edge of the (N + 1) th sheet, When the time (t1 ′) when the first reference signal is generated for the Nth sheet is equal to the sum of the time difference measured for the Nth sheet and a value obtained by correcting the time difference with a predetermined threshold. (T1 ″) is configured to generate the first reference signal for the (N + 1) th sheet,
The control means controls the conveyance speed of the (N + 1) th sheet by the conveyance means according to a value obtained by correcting the time difference (t2 ″ −t1 ″) measured by the measurement means for the (N + 1) th sheet with the threshold value. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to control the image forming apparatus. A determination unit for determining whether the time difference measured by the measurement unit is less than the threshold;
The control means is configured to correct the time difference to zero if the time difference is less than the threshold, and to correct the time difference using the threshold if the time difference is not less than the threshold. The image forming apparatus according to claim 6. The sheet feeding means is configured to start sheet feeding after a predetermined time after receiving the first reference signal,
The control means uses the measurement means so that a difference between a timing at which the toner image carried on the image carrier arrives at the transfer means and a timing at which the sheet arrives at the transfer means falls within an allowable range. The image forming apparatus according to claim 1, wherein the predetermined time is adjusted according to the measured time difference.   The measurement means is configured to measure a time difference from a fall of the first reference signal to a fall of the second reference signal that arrives immediately after the fall of the first reference signal. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   10. The first generation unit is configured to generate the first reference signal for the first sheet when the image forming unit is ready for image formation. The image forming apparatus according to claim 1.   11. The second generation means includes light receiving means for generating the second reference signal by receiving light deflected by the scanning means. The image forming apparatus described in 1.   The transfer unit is configured to primarily transfer a toner image formed on the image carrier to an intermediate transfer member, and secondarily transfer the toner image primarily transferred to the intermediate transfer member to a sheet. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 1, wherein the light source is a multi-beam light source that outputs a plurality of lights in parallel in one main scanning. First generation means for generating a first reference signal that serves as an image writing reference in the sub-scanning direction;
Second generation means for generating a second reference signal that is a reference for writing an image in the main scanning direction;
Measuring means for measuring a time difference between the first reference signal and the second reference signal;
In response to the first reference signal, a sheet feeding unit that feeds the sheets stacked on the stacking unit;
Conveying means for conveying a sheet fed by the paper feeding means;
An image carrier, a light source, and a scanning unit that scans the image carrier in the main scanning direction with light output from the light source, and an image forming unit that forms a toner image on the image carrier;
Transfer means for transferring the toner image formed on the image carrier onto the sheet conveyed by the conveyance means; and counting means for counting the number of the second reference signals based on the first reference signal;
Supply means for starting supply of an image signal to the light source when the count value of the counting means reaches a predetermined value;
The time difference measured by the measurement unit is set so that the difference between the timing at which the toner image carried on the image carrier arrives at the transfer unit and the timing at which the sheet arrives at the transfer unit falls within an allowable range. And an image forming apparatus having control means for controlling the predetermined value in response.

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