JP2009075608A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an image from being trasnsferred on the outside of a paper sheet, that is, on a carrying belt even when the paper sheet being shorter than that required originally for printing is inserted only by one paper edge detecting sensor and only by one detecting circuit in a tandem-type image forming device. <P>SOLUTION: The image forming device includes: a plurality of photosensitive drums (K3 to C3); a paper edge detecting section 3 to detect a front edge and a rear edge of a paper sheet 12; an exposure starting time calculating means 5 for each of the plurality of photosensitive drums (K3 to C3); an exposure inhibiting time calculating means 6 to inhibit printing, when paper having a length being smaller than a predetermined length of the paper sheet is inserted, on a portion being shorter than preset paper; and a control section 9 to control the entire image forming device. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a tandem image forming apparatus.

  In a conventional tandem type image forming apparatus, a system in which a plurality of image forming units are arranged in the sheet conveying direction is generally used. In such a conventional method, the leading edge of the paper is detected for each image forming unit. The recording timing of each photosensitive drum is generated from the relationship between the detection time, the mounting position of each image forming unit, and the conveyance speed of the sheet, and the recording is started in order and the image is transferred onto the sheet.

By the way, the conventional techniques as described above have the following problems to be solved.
It is necessary to provide a sheet edge detection sensor and a detection circuit for each image forming unit. In addition, when a paper having a length shorter than that originally required for printing is inserted, an image may be transferred to the outside of the paper, that is, onto a conveying means such as a conveying belt or a conveying roller. become. As a result, not only the conveying means such as the conveying belt and the conveying roller are soiled but also the toner is wasted.

The present invention adopts the following configuration in order to solve the above points.
<Configuration 1>
A plurality of image forming units each including a photoconductor and an exposure unit and spaced apart from each other by a predetermined distance in the paper transport direction of the paper transport path; The leading edge detection signal is output by detecting the leading edge of the sheet that is arranged on the upstream side and conveyed on the sheet conveying path, and the abnormal trailing edge detection signal is output by detecting the trailing edge of the sheet that is shorter than a predetermined sheet length. When the leading edge detection signal is input from the sheet edge detection unit and the sheet edge detection unit, the sheet conveyance speed and the distance between the sheet edge detection unit and the image forming unit in the sheet conveyance path The exposure start time calculating means for calculating the exposure start time for each of the plurality of image forming units, and when the abnormal rear end detection signal is input from the sheet end detecting unit, the sheet conveying speed, Above the paper edge detector in the paper transport path An exposure prohibition time calculating unit that calculates an exposure prohibition time for each of the plurality of image forming units from each distance to the image forming unit, the sheet end detection unit, the exposure start time calculating unit, and the exposure prohibition time calculating And controlling the means to expose and transfer a desired image for each of the plurality of image forming units, and if a sheet shorter than a predetermined sheet length is received, the plurality of image forming units lack a predetermined sheet length. An image forming apparatus comprising: a control unit that prohibits exposure of the part.

<Configuration 2>
A plurality of image forming units each including a photoconductor and an exposure unit and spaced apart from each other by a predetermined distance in the paper transport direction of the paper transport path; The leading edge detection signal is output by detecting the leading edge of the sheet that is arranged on the upstream side and conveyed on the sheet conveying path, and the abnormal trailing edge detection signal is output by detecting the trailing edge of the sheet that is shorter than a predetermined sheet length. When the leading edge detection signal is input from the sheet edge detecting section and the sheet edge detecting section, the speed at which the sheet is conveyed, the sheet edge detecting section of the sheet conveying path, and the image forming section, respectively. Image data supply start time calculating means for calculating the image data supply start time for each of the plurality of image forming units from the distance, and when the abnormal rear end detection signal is input from the paper end detection unit, Transport speed and the paper edge The supply start time of the white data supplied to each of the plurality of image forming units from the respective distances between the output unit and the image forming unit, the sheet conveyance speed, the sheet end detecting unit, and the image forming unit White data supply time calculating means for calculating a supply end time of white data calculated from each distance between them and a predetermined paper length; the paper edge detecting section; the image data supply start time calculating means; The white data supply time calculation means is controlled to expose and transfer a desired image for each of the plurality of image forming units, and when a sheet shorter than a predetermined sheet length is received, And a controller that exposes and transfers white data to a portion lacking from a predetermined sheet length.

<Configuration 3>
The image forming apparatus according to Configuration 1 or 2, further comprising: a sub-scanning clock generation unit that enables fine line feeding that is smaller than a line feeding interval of an image transferred from an external device, wherein the control unit includes the sub-scanning An image forming apparatus that performs all of the above control based on a clock generation means.

<Configuration 4>
In the image forming apparatus according to any one of the first to third aspects, the distance between the sheet edge detection unit and the image forming unit disposed at the uppermost stream in the transport direction is from an exposure position on the image forming unit. An image forming apparatus characterized in that a relationship of l <L is established, where l is a peripheral distance to a transfer position and L is a horizontal distance from the transfer position to the sheet edge detection unit.

<Configuration 5>
A plurality of image forming units each including a photoconductor and an exposure unit and spaced apart from each other by a predetermined distance in the paper transport direction of the paper transport path; A sheet end detection unit that detects a leading end of a sheet that is disposed on the upstream side and that is transported through the sheet transport path and outputs a leading end detection signal; Calculated from the conveyance speed and the distances between the sheet edge detection unit and the plurality of image forming units on the sheet conveyance path, from when the leading edge detection signal is received to when exposure can be started. Page data transfer start means for starting transfer of page data after the lapse of delay time, and page data transfer time for each of the plurality of image forming units are individually counted, and the page data transfer is started after the count number corresponding to the sheet length is completed. Page data transfer time measuring means for stopping data transfer, paper length count number setting means for setting a count number corresponding to the paper length in the page data transfer time measuring means, the paper edge detecting section, and the page data transfer When the start unit, the page data transfer time measuring unit, and the sheet length count number setting unit are controlled to expose and transfer a desired image for each of the plurality of image forming units, and when a predetermined sheet is received, the sheet When the page data transfer start unit starts to transfer the page data to the plurality of image forming units sequentially from the upstream side by controlling the length count number setting unit, the page data transfer time measuring unit has the predetermined sheet length An image forming apparatus comprising: a control unit that sequentially sets the number of counts according to the order.

<Configuration 6>
In the image forming apparatus according to Configuration 5, the page data transfer start unit is calculated from the sheet conveyance speed and the distances between the sheet edge detecting unit and the plurality of image forming units on the sheet conveyance path. An image forming apparatus comprising: a delay time storage unit that calculates and stores in advance each delay time from when the leading edge detection signal is received to when exposure can be started.

<Configuration 7>
6. The image forming apparatus according to claim 5, wherein the sheet length count number setting unit includes a sheet length count number storage unit that stores a count number corresponding to the sheet length in advance.

<Configuration 8>
A plurality of image forming units each including a photoconductor and an exposure unit and spaced apart from each other by a predetermined distance in the paper transport direction of the paper transport path; A sheet end detection unit that detects a leading end of a sheet that is disposed on the upstream side and that is transported through the sheet transport path and outputs a leading end detection signal; Calculated from the conveyance speed and the distances between the sheet edge detection unit and the plurality of image forming units on the sheet conveyance path, from when the leading edge detection signal is received to when exposure can be started. Page data transfer start means for starting transfer of page data after the lapse of delay time, and page data transfer time for each of the plurality of image forming units are individually counted, and the page data transfer is started after the count number corresponding to the sheet length is completed. Page data transfer time measuring means for stopping data transfer, sheet length count number setting means for setting a count number corresponding to the paper length in the page data transfer time measuring means, and page data transfer time measuring means for the page data Count number resetting means for resetting the remaining count number while counting the transfer time individually, the paper edge detection unit, the page data transfer start means, the page data transfer time measurement means, and the paper length count number setting means And a count number resetting means to control the exposure and transfer of a desired image for each of the plurality of image forming sections, and the page data transfer time measuring means individually detects the end of the page data transfer time during counting. When the signal is received, the count number resetting means is controlled and arranged in order from upstream to downstream in the transport direction. An image forming apparatus comprising a controller for resetting the remaining count of the page data transfer time measuring means corresponding to the plurality of image forming portions to be.

  By providing the plurality of image forming units, the sheet end detecting unit, the exposure start time calculating unit, the exposure prohibiting time calculating unit, and the control unit, one sheet end detecting sensor and 1 A tandem-type image forming apparatus can be realized by using only one detection circuit.

Hereinafter, embodiments of the present invention will be described using specific examples.
<Configuration of Specific Example 1>
FIG. 1 is a configuration diagram of the first specific example.
As shown in FIG. 1, the image forming apparatus according to the first specific example includes a conveyance belt 1, a conveyance roller 2, a paper edge detection unit 3, an equipment performance storage unit 4, an exposure start time calculation unit 5, and an exposure prohibition time calculation unit. 6, paper feed roller 7, fixing unit 8, control unit 9, clock oscillator 10, sub-scanning clock generation unit 11, LED control units K 1, Y 1, M 1, C 1, exposure units K 2, Y 2, M2, C2, photosensitive drums K3, Y3, M3, C3, and transfer units K4, Y4, M4, C4.

The transport belt 1 is a transport path for transporting the paper 12 at a predetermined transport speed, and photosensitive drums K3, Y3, M3, and C3, transfer devices K4, Y4, M4, and C4, which will be described later, along the transport belt 1 and the like. Is a portion arranged at a predetermined interval.
The conveyance roller 2 is a portion that drives the conveyance belt 1 at a predetermined conveyance speed.

  The paper edge detection unit 3 is arranged upstream of the plurality of photosensitive drums K3, Y3, M3, and C3 in the conveyance direction of the conveyance belt 1, and detects the leading end of the paper 12 conveyed on the conveyance belt 1. The leading edge detection signal is output, and the trailing edge of the sheet shorter than a predetermined sheet length is detected based on the control of the control unit 9 to output an abnormal trailing edge detection signal.

  The device performance storage unit 4 is a portion in which the device performance of the image forming apparatus is stored in advance. For example, the resolution of the apparatus, the conveyance speed of the conveyance belt 1, the plurality of photosensitive drums K3, Y3, M3, and C3 arranged along the conveyance belt 1, the distance between them, and the distance between the sheet edge detection unit 3 , The photosensitive drums K3, Y3, M3, and C3 diameters, the sheet length of the (predetermined) sheets that are scheduled to be used, and other data necessary for controlling the image forming apparatus.

  When the exposure start time calculating means 5 receives the leading edge detection signal from the paper edge detecting section 3, the exposure start time calculating means 5 performs the conveyance speed of the paper 12, the paper edge detecting section 3 on the conveying belt 1, the photosensitive drum K3, This is a part for calculating the exposure start time for each of the plurality of photosensitive drums from the distances to Y3, M3, and C3.

  This means is performed based on the control of the control unit 9, which will be described later, using the data stored in the device performance storage unit 4. By this means, the transfer positions of the images on the paper 12 by the plurality of photosensitive drums K3, Y3, M3, and C3 are accurately controlled. As a result, for example, in the case of a color image, color bleeding does not occur.

  The exposure prohibition time calculation means 6 receives the abnormal trailing edge detection signal from the paper edge detection unit 3, the conveyance speed of the paper 12, the paper edge detection unit 3 on the conveyance belt 1, and the photosensitive drum. This is a part for calculating the exposure inhibition time for each of the plurality of photosensitive drums from the distances to K3, Y3, M3, and C3.

  This means is performed based on the control of the control unit 9, which will be described later, using the data stored in the device performance storage unit 4. By providing this means, when a paper having a length shorter than the predetermined paper length is inserted, an image is not transferred to the outside of the paper (a portion lacking from the predetermined paper length), that is, onto the transport belt 1. .

The paper feed roller 7 is a roller that is disposed on the uppermost stream of the transport belt 1 and supplies the paper 12 to the transport belt 1.
The fixing device 8 is a portion that is arranged on the most downstream side of the conveying belt 1 and fixes a desired image transferred onto the paper 12 to the paper 12. Here, a plurality of images transferred onto the sheet by a plurality of photosensitive drums K3, Y3, M3, and C3 and a plurality of transfer devices K4, Y4, M4, and C4 are fixed together.

  The control unit 9 controls the sheet end detection unit 3, the exposure start time calculation unit 5, and the exposure prohibition time calculation unit 6 to control a desired image for each of the plurality of photosensitive drums K3, Y3, M3, and C3. Is a portion for prohibiting exposure to a portion lacking from the predetermined paper length for each of the plurality of photosensitive drums when a paper shorter than the predetermined paper length is received. That is, it is a CPU that controls all parts in the apparatus. The exposure start time calculation unit 5 and the exposure prohibition time calculation unit 6 may be configured as a control program for operating the CPU. It goes without saying that these means may be configured as separate circuits. A counter for storing the results calculated by these means as the count number of the sub-scanning clock described later is provided internally.

The clock oscillator 10 is a part that generates a clock signal that serves as a reference for the operation of the control unit 9.
The sub-scanning clock generation means 11 is a part that generates a sub-scanning clock that enables line feed finer than the line feed interval of an image transferred from an external device. This means is required to accurately match a plurality of images transferred onto a sheet by a plurality of photosensitive drums K3, Y3, M3, C3 and a plurality of transfer units K4, Y4, M4, C4, etc. . That is, it is a part that generates a clock signal required to enable mechanical line feed at a finer interval than the resolution stored in the device performance storage unit 4.

  The LED control means K1, Y1, M1, and C1 output the timing of transferring image data for one line, the timing of exposing an image on the photosensitive drum, and the like according to the instructions of the control unit, and the exposure devices K2, Y2, and M2 , C2 is a part for controlling. The LED control means K1 is a part that controls a black image. The LED control means Y1 is a part that controls a yellow image. The LED control means M1 is a part that controls a magenta image. The LED control means C1 is a part that controls a cyan image.

  The exposure devices K2, Y2, M2, and C2 are portions for selectively exposing a desired image on the photosensitive drum and creating an electrostatic latent image based on the control of the LED control means K1, Y1, M1, and C1. It is. Usually an LED array is used. The exposure device K2 is a portion that exposes a black image. The exposure device Y2 is a portion that exposes a yellow image. The exposure device M2 is a portion that exposes a magenta image. The exposure device C2 is a portion that exposes a cyan image.

  The surfaces of the photosensitive drums K3, Y3, M3, and C3 are uniformly charged by a charger (not shown), and a desired image is selectively exposed to the charged surface by the above-described exposure device to create an electrostatic latent image. It is a part to be done. This electrostatic latent image is developed by a developing device (not shown) and transferred onto the paper 12 by transfer devices K4, Y4, M4, and C4.

  The photosensitive drum K3 is a portion where an electrostatic latent image of a black image is created. The photosensitive drum Y3 is a portion where an electrostatic latent image of a yellow image is created. The photosensitive drum M3 is a portion where an electrostatic latent image of a magenta image is created. The photosensitive drum C3 is a portion where an electrostatic latent image of a cyan image is created.

  The photosensitive drums K3, Y3, M3, and C3 are disposed apart from each other by a predetermined distance in the paper conveyance direction on the conveyance belt 1. Arranged in the order of K, Y, M, and C from the upstream in the transport direction. The photosensitive drum K3 operates integrally with the LED control means K1 and the exposure device K2. Similarly, the photosensitive drum Y3 operates integrally with the LED control unit Y1 and the exposure unit Y2, the photosensitive drum M3 operates integrally with the LED control unit M1 and the exposure unit M2, and the photosensitive drum C3 includes The LED control means C1 and the exposure device C2 operate integrally.

  The transfer units K4, Y4, M4, and C4 are portions that transfer the toner adhering to the electrostatic latent image on the photosensitive drum onto the paper 12. The transfer unit K4 is a part that transfers toner from the photosensitive drum K3 onto the paper 12. The transfer unit Y4 is a part that transfers toner from the photosensitive drum Y3 onto the paper 12. The transfer unit M4 is a part that transfers toner from the photosensitive drum M3 onto the paper 12. The transfer unit C4 is a part that transfers the toner onto the paper 12 from the photosensitive drum C3.

<Operation of Specific Example 1>
First, the operation of the exposure start time calculation means 5 will be mainly described.
FIG. 2 is a time chart (part 1) of the first specific example.
The sensor signal, HSYNC-K, HSYNC-Y, HSYNC-M, HSYNC-C, and time are shown in order from the top of the vertical axis, and the elapsed time is shown on the horizontal axis.
Furthermore, taking HSYNC-C as an example, a part thereof is enlarged, and the vertical axis represents LSYNC, HSYNC, STROBE, and DATA, and the horizontal axis represents time. The operation of Example 1 (mainly the operation of the exposure start time calculating means) will be described with reference to FIG. 1 according to times T0 to T9 in FIG.

(Time T0)
The paper end detection unit 3 that has detected that the front end of the paper 12 inserted from the paper feed roller 7 has reached the paper end detection unit 3 sends a front end detection signal to the control unit 9. Under the control of the control unit 9, the exposure start time calculating unit 5 conveys the sheet 12 and the distance between the sheet end detection unit 3 on the conveyance belt 1 and the photosensitive drums K3, Y3, M3, and C3. To calculate an exposure start time and an exposure end time for each of the plurality of photosensitive drums.

  At this time, the exposure start time T1 of the photosensitive drum K3 is determined based on the distance between the sheet end detection unit 3 on the conveyor belt 1 and the photosensitive drum K3, and the transfer position (transfer position) from the recording position of the photosensitive drum K3 (position of the exposure device K2) The value t1 obtained by dividing the difference from the circumferential distance up to (positioning position of the device K4) by the transport speed is added to the time T0. The exposure end time T6 is obtained by adding the conveyance time t5 of a predetermined sheet length to the exposure start time T1.

  The exposure start time T2 of the photosensitive drum Y3 is obtained by adding a value t2 obtained by dividing the distance between the photosensitive drum K3 and the photosensitive drum Y3 on the conveying belt 1 by the conveying speed to the time T1. The exposure start time T3 of the photosensitive drum M3 is obtained by adding a value t3 obtained by dividing the distance between the photosensitive drum Y3 and the photosensitive drum M3 on the transport belt 1 by the transport speed to the time T2. Similarly, the exposure start time T4 of the photosensitive drum C3 is obtained by adding a value t4 obtained by dividing the distance between the photosensitive drum M3 and the photosensitive drum C3 on the conveying belt 1 by the conveying speed to the time T3.

  In addition, the exposure stop times T7, T8, T9 of the photosensitive drums Y3, M3, C3 are added to the exposure start times T2, T3, T4 by the transport time t5 of a predetermined sheet length as in the case of the photosensitive drum K3. Is required. The above calculation results are respectively set in the counters provided in the control unit 9 as the count number of the sub-scanning clock.

(Time T1)
The control unit 9 sends a transfer timing signal HSYNC-K to the LED control unit K1 based on the calculation result of the exposure start time calculation unit 5. The LED control means K1 controls the exposure device K2 to start creating an electrostatic latent image of a black image on the charged surface of the photosensitive drum K3.

(Time T2)
The control unit 9 sends a transfer timing signal HSYNC-Y to the LED control unit Y1 based on the calculation result of the exposure start time calculation unit 5. The LED control unit Y1 controls the exposure unit Y2 to start creating an electrostatic latent image of a yellow image on the charged surface of the photosensitive drum Y3.

(Time T3)
The control unit 9 sends a transfer timing signal HSYNC-M to the LED control unit M1 based on the calculation result of the exposure start time calculation unit 5. The LED control means M1 controls the exposure device M2 to start creating an electrostatic latent image of a magenta image on the charged surface of the photosensitive drum M3.

(Time T4)
The control unit 9 sends a transfer timing signal HSYNC-C to the LED control unit C1 based on the calculation result of the exposure start time calculation unit 5. The LED control means C1 controls the exposure device C2 to start producing an electrostatic latent image of a cyan image on the charged surface of the photosensitive drum C3.

(Time T5)
The rear end of the paper 12 inserted from the paper supply roller 7 passes through the paper end detection unit 3. Here, since the predetermined sheet passes through the sheet edge detection unit 3 at the scheduled time, the abnormal trailing edge detection signal is not output.

(Time T6)
The control unit 9 stops sending the transfer timing signal HSYNC-K to the LED control unit K1 based on the calculation result of the exposure prohibition time calculation unit 6. The LED control means K1 controls the exposure device K2 to stop producing an electrostatic latent image of a black image on the charging surface of the photosensitive drum K3.

(Time T7)
The controller 9 stops sending the transfer timing signal HSYNC-Y to the LED control unit Y1 based on the calculation result of the exposure prohibition time calculation unit 6. The LED control means Y1 controls the exposure device Y2 to stop producing an electrostatic latent image of a yellow image on the charging surface of the photosensitive drum Y3.

(Time T8)
The control unit 9 stops sending the transfer timing signal HSYNC-M to the LED control unit M1 based on the calculation result of the exposure start time calculation unit 5. The LED control means M1 controls the exposure device M2 to stop creating an electrostatic latent image of a magenta image on the charging surface of the photosensitive drum M3.

(Time T9)
The control unit 9 stops sending the transfer timing signal HSYNC-C to the LED control unit C1 based on the calculation result of the exposure start time calculation unit 5. The LED control means C1 controls the exposure device C2 to stop producing an electrostatic latent image of a cyan image on the charged surface of the photosensitive drum C3.

  Next, taking HSYNC-C as an example, the relationship between LSYNC (sub-scanning clock signal), HSYNC (transfer timing signal), and DATA (data) will be described.

  From the figure, the repetition cycle of LSYNC (sub-scanning clock signal) is controlled to 1/3 of the repetition cycle of HSYNC (transfer timing signal) as an example. By doing so, it becomes possible to keep the positional deviation of the image drawn on the paper 12 by the plurality of photosensitive drums within 1/3 of the line feed interval by HSYNC (transfer timing signal).

  Also, as shown in the figure, in synchronization with HSYNC (transfer timing signal), one line of DATA (data) is sent to the exposure device, and STROBE (strobe signal) is applied to the exposure device with a slight delay, and then on the photosensitive drum. An electrostatic latent image is created. Above, the description of the operation when a predetermined sheet is used is finished, and then the operation when a sheet shorter than a predetermined sheet length is used will be described.

FIG. 3 is a time chart (part 2) of the first specific example.
In order from the top of the vertical axis, the sensor signal, HSYNC-K, OVPR-K, HSYNC-Y, OVPR-Y, HSYNC-M, OVPR-M, HSYNC-C, OVPR-C, and time are shown, and the horizontal axis Represents the passage of time.
Furthermore, taking HSYNC-C as an example, a part thereof is enlarged, LSYNC, HSYNC, STROBE, OVPR are shown on the vertical axis, and the passage of time is shown on the horizontal axis. The operation of the first specific example (mainly the operation of the exposure inhibition time calculating means) will be described with reference to FIG. 1 according to the times T0 to Q8 in FIG.

(Time T0 to Time T4)
Since it is completely the same as the time T0 to the time T4 of the operation of the exposure start time calculation means 5, the description is omitted.

(Time Q0)
It is assumed that the paper passes the paper edge detection unit 3 at time Q0, which is a time (t5-t0) earlier than a predetermined time, at time Q0 after time t0 from when the leading edge detection signal is output. At this time, the sheet end detection unit 3 sends an abnormal rear end detection signal to the control unit 9. Under the control of the control unit 9, the exposure prohibition time calculating means 6 is configured to convey the sheet 12 and each distance between the sheet end detection unit 3 on the conveyance belt 1 and the photosensitive drums K3, Y3, M3, and C3. To calculate the exposure prohibition time for each of the plurality of photosensitive drums and the time for canceling the exposure prohibition.

  The exposure prohibition time Q1 of the photosensitive drum K3 is the distance from the sheet end detection unit 3 on the conveyor belt 1 to the photosensitive drum K3, and the transfer position (transfer unit K4) from the recording position of the photosensitive drum K3 (position of the exposure unit K2). The value t1 obtained by dividing the difference from the circumferential distance up to (positioning position) by the conveyance speed is added to the time Q0. The time Q5 at which the exposure prohibition is released is obtained by adding the time (t5-t0) to the exposure prohibition time Q1.

  The exposure inhibition time Q2 of the photosensitive drum Y3 is obtained by adding a value t2 obtained by dividing the distance between the photosensitive drum K3 and the photosensitive drum Y3 on the conveyance belt 1 by the conveyance speed to the time Q1. The exposure start time Q3 of the photosensitive drum M3 is obtained by adding a value t3 obtained by dividing the distance between the photosensitive drum Y3 and the photosensitive drum M3 on the transport belt 1 by the transport speed to the time Q2. Similarly, the exposure start time Q4 of the photosensitive drum C3 is obtained by adding a value t4 obtained by dividing the distance between the photosensitive drum M3 and the photosensitive drum C3 on the transport belt 1 by the transport speed to the time Q3.

  Further, the times Q6, Q7, and Q8 for releasing the exposure inhibition of the photosensitive drums Y3, M3, and C3 are obtained by adding the time (t5-t0) to the exposure inhibition time in the same manner as in the case of the photosensitive drum K3. The above calculation results are respectively set in the counters provided in the control unit 9 as the count number of the sub-scanning clock.

(Time Q1)
The control unit 9 sends an exposure prohibition signal OVPR-K to the LED control unit K1 based on the calculation result of the exposure prohibition time calculation unit 6. The LED control means K1 controls the exposure device K2 to stop the exposure to the photosensitive drum K3.

(Time Q2)
The control unit 9 sends an exposure prohibition signal OVPR-Y to the LED control unit Y1 based on the calculation result of the exposure prohibition time calculation unit 6. The LED control unit Y1 controls the exposure device Y2 to stop the exposure to the photosensitive drum Y3.

(Time Q3)
The control unit 9 sends an exposure prohibition signal OVPR-M to the LED control unit M1 based on the calculation result of the exposure prohibition time calculation unit 6. The LED control means M1 controls the exposure device M2 to stop the exposure to the photosensitive drum M3.

(Time Q4)
The control unit 9 sends an exposure prohibition signal OVPR-C to the LED control unit C1 based on the calculation result of the exposure prohibition time calculation unit 6. The LED control means C1 controls the exposure device C2 to stop the exposure to the photosensitive drum C3.

(Time Q5)
The control unit 9 stops sending the exposure prohibition signal OVPR-K to the LED control unit K1 based on the calculation result of the exposure prohibition time calculation unit 6.

(Time Q6)
The control unit 9 stops sending the exposure inhibition signal OVPR-Y to the LED control unit Y1 based on the calculation result of the exposure inhibition time calculation unit 6.

(Time Q7)
The controller 9 stops sending the exposure prohibition signal OVPR-M to the LED control means M1 based on the calculation result of the exposure prohibition time calculation means 6.

(Time Q8)
The control unit 9 stops sending the exposure prohibition signal OVPR-C to the LED control unit C1 based on the calculation result of the exposure prohibition time calculation unit 6.

  Next, taking HSYNC-C as an example, the relationship between LSYNC (sub-scanning clock signal), HSYNC (transfer timing signal), STROBE (strobe signal), and OVPR (exposure inhibition signal) will be described.

From the figure, the repetition cycle of LSYNC (sub-scanning clock signal) is controlled to 1/3 of the repetition cycle of HSYNC (transfer timing signal) as an example. By doing so, it becomes possible to keep the positional deviation of the image drawn on the paper 12 by the plurality of photosensitive drums within 1/3 of the line feed interval by HSYNC (transfer timing signal). Further, as shown in the figure, when OVPR (exposure inhibition signal) is output, STROBE (strobe signal) is stopped and no electrostatic latent image is created on the photosensitive drum.
In the above description, the conveyance belt is used as the conveyance unit. However, a conveyance roller including a plurality of roller pairs may be used.

<Effect of specific example 1>
As described above, the plurality of photosensitive drums, the sheet end detection unit, the exposure start time calculation unit, the exposure prohibition time calculation unit, and the control unit are included, so that one sheet of paper is provided. A tandem image forming apparatus can be realized only by the end detection sensor and one detection circuit. Further, even when a paper having a length shorter than that originally required for printing is inserted, an image is transferred to the outside of the paper, that is, on the conveying belt, and the conveying belt is soiled or toner is wasted. It has the effect that it is no longer consumed.

<Configuration of Specific Example 2>
FIG. 4 is a configuration diagram of the second specific example.
As shown in FIG. 4, the image forming apparatus according to the second specific example includes the transport belt 1, the transport roller 2, the paper end detection unit 3, the device performance storage unit 4, the paper feed roller 7, the fixing device 8, and the clock oscillator. 10, sub-scanning clock generation means 11, image data supply start time calculation means 21, white data supply time calculation means 22, control unit 23, LED control means K1, Y1, M1, C1, and exposure device K2. , Y2, M2, and C2, photosensitive drums K3, Y3, M3, and C3, and transfer units K4, Y4, M4, and C4.

Only differences from the first specific example will be described.
The image data supply start time calculation means 21 receives the leading edge detection signal from the paper edge detection unit 3, the speed at which the paper 12 is conveyed, the paper edge detection unit 3 on the conveyance belt 1, and the above. This is a part for calculating the image data supply start time and the image data supply end time for each of the plurality of photosensitive drums from the respective distances to the photosensitive drums K3, Y3, M3, and C3.

  When the white data supply time calculation means 22 receives the abnormal trailing edge detection signal from the paper edge detection unit 3, the white data supply time calculation means 22 performs the conveyance speed of the paper 12, the paper edge detection unit 3 on the conveyance belt 1, and the photosensitive element. From the respective distances to the drums, the supply start time of white data to be supplied to each of the plurality of photosensitive drums, the conveyance speed of the sheet, the sheet end detection unit 3 on the conveyance belt 1, and the photosensitive drum K3. , Y3, M3, and C3, and a white data supply end time calculated from a predetermined paper length.

  The control unit 23 controls the paper end detection unit 3, the image data supply start time calculation unit 21, and the white data supply time calculation unit 22 to expose and transfer a desired image for each of the plurality of photosensitive drums. In addition, when a paper shorter than a predetermined paper length is received, white data is exposed and transferred to a portion lacking from the predetermined paper length for each of the plurality of photosensitive drums.

  That is, it is a CPU that controls all parts in the apparatus. The image data supply start time calculating unit 21 and the white data supply time calculating unit 22 may be configured as a control program for operating the CPU. It goes without saying that these means may be configured as separate circuits. A counter for storing the results calculated by these means as the count number of the sub-scanning clock described later is provided internally. Since the other components are all the same as those in the first specific example, description thereof is omitted.

  In the second specific example, an image data supply start time calculating unit 21 is arranged in place of the exposure start time calculating unit 5 in the first specific example, and white data supply is performed in place of the exposure inhibition time calculating unit 6 (FIG. 1) in the first specific example. A time calculation means 22 is arranged. That is, in the first specific example, when a paper shorter than the predetermined paper length is inserted, exposure to the surface of the photosensitive drum corresponding to a portion lacking the predetermined paper length is prohibited. In this specific example, the white data is exposed and transferred to a portion where the paper is missing from the predetermined paper length. The operation will be described below.

<Operation of Specific Example 2>
FIG. 5 is a time chart of the second specific example.
In order from the top of the vertical axis, the sensor signal, HSYNC-K, DATA-K, HSYNC-Y, DATA-Y, HSYNC-M, DATA-M, HSYNC-C, DATA-C, and time are represented on the horizontal axis. Represents the passage of time. The operation of the specific example 2 will be described with reference to FIG. 4 according to the times R0 to P8 in FIG.

(Time R0)
The paper edge detection unit 3 that has detected that the leading edge of the paper 12 inserted from the paper feed roller 7 has reached the paper edge detection unit 3 sends a front edge detection signal to the control unit 23. The image data supply start time calculating unit 21 controls the conveyance speed of the paper 12 and the paper edge detection unit 3 on the conveyance belt 1 and the photosensitive drums K3, Y3, M3, and C3 based on the control of the control unit 23. The image data supply start time and the image data supply end time for each of the plurality of photosensitive drums are calculated from the distance.

  At this time, the image data supply start time R1 to the photosensitive drum K3 is transferred from the distance between the sheet end detection unit 3 on the conveying belt 1 and the photosensitive drum K3, and the recording position of the photosensitive drum K3 (positioning position of the exposure device K2). A value t1 obtained by dividing the difference from the circumferential distance to the position (arrangement position of the transfer device K4) by the conveyance speed is obtained by adding to the time R0. The image data supply end time is obtained by adding the conveyance time t5 of a predetermined sheet length to the image data supply start time R1.

  The image data supply start time R2 to the photosensitive drum Y3 is obtained by adding a value t2 obtained by dividing the distance between the photosensitive drum K3 and the photosensitive drum Y3 on the conveying belt 1 by the conveying speed to the time R1. The image data supply start time R3 to the photosensitive drum M3 is obtained by adding a value t3 obtained by dividing the distance between the photosensitive drum Y3 and the photosensitive drum M3 on the conveying belt 1 by the conveying speed to the time R2. Similarly, the image data supply start time R4 to the photosensitive drum C3 is obtained by adding a value t4 obtained by dividing the distance between the photosensitive drum M3 and the photosensitive drum C3 on the conveying belt 1 by the conveying speed to the time R3.

  Further, the image data supply end time of the photosensitive drums Y3, M3, and C3 is added to the image data supply start times R2, R3, and R4 by adding the conveyance time t5 of a predetermined sheet length in the same manner as in the case of the photosensitive drum K3. Desired. The above calculation results are respectively set in the counters provided in the control unit 23 as the count number of the sub scanning clock.

(Time R1)
The control unit 23 sends image data (black signal) to the LED control unit K1 together with the transfer timing signal HSYNC-K based on the calculation result of the image data supply start time calculation unit 21. The LED control means K1 controls the exposure device K2 to start creating an electrostatic latent image of a black image on the charged surface of the photosensitive drum K3.

(Time R2)
Based on the calculation result of the image data supply start time calculation unit 21, the control unit 23 sends image data (yellow signal) to the LED control unit Y1 together with the transfer timing signal HSYNC-Y. The LED control unit Y1 controls the exposure unit Y2 to start creating an electrostatic latent image of a yellow image on the charged surface of the photosensitive drum Y3.

(Time R3)
The control unit 23 sends image data (magenta signal) together with the transfer timing signal HSYNC-M to the LED control unit M1 based on the calculation result of the image data supply start time calculation unit 21. The LED control means M1 controls the exposure device M2 to start creating an electrostatic latent image of a magenta image on the charged surface of the photosensitive drum M3.

(Time R4)
The control unit 23 sends image data (cyan signal) to the LED control unit C1 together with the transfer timing signal HSYNC-C based on the calculation result of the image data supply start time calculation unit 21. The LED control means C1 controls the exposure device C2 to start producing an electrostatic latent image of a cyan image on the charged surface of the photosensitive drum C3.

(Time P0)
Assume that the sheet passes through the sheet edge detection unit 3 at a time P0 that is a time (t5-t0) earlier than a predetermined time at a time P0 that is a time t0 after the time R0 when the leading edge detection signal is output. At this time, the sheet end detection unit 3 sends an abnormal rear end detection signal to the control unit 23. Based on the control of the control unit 23, the white data supply time calculation unit 22 determines the conveyance speed of the paper 12 and the distance between the paper edge detection unit 3 on the conveyance belt 1 and the photosensitive drums K3, Y3, M3, and C3. The white data supply start time and the white data supply end time for each of the plurality of photosensitive drums are calculated from the predetermined sheet length.

  The white data supply start time P1 of the photosensitive drum K3 is determined based on the distance between the sheet end detection unit 3 on the conveyor belt 1 and the photosensitive drum K3, and the transfer position (transfer position) from the recording position of the photosensitive drum K3 (position of the exposure device K2). The value t1 obtained by dividing the difference from the circumferential distance up to (positioning position of the device K4) by the conveyance speed is added to the time P0. The white data supply end time P5 is obtained by adding the time (t5-t0) to the white data supply start time P1.

  The white data supply start time P2 of the photosensitive drum Y3 is obtained by adding a value t2 obtained by dividing the distance between the photosensitive drum K3 and the photosensitive drum Y3 on the conveying belt 1 by the conveying speed to the time P1. The white data supply start time P3 of the photosensitive drum Y3 of the photosensitive drum M3 is obtained by adding a value t3 obtained by dividing the distance between the photosensitive drum Y3 and the photosensitive drum M3 on the transport belt 1 by the transport speed to the time P2. It is done. Similarly, the white data supply start time P4 of the photosensitive drum C3 is obtained by adding a value t4 obtained by dividing the distance between the photosensitive drum M3 and the photosensitive drum C3 on the conveying belt 1 by the conveying speed to the time P3.

  Further, at the times P6, P7, and P8 when the supply of the white data to the photosensitive drums Y3, M3, and C3 is completed, the time (t5-t0) is added to the exposure prohibition time in the same manner as in the photosensitive drum K3. Desired. The above calculation results are respectively set in the counters provided in the control unit 23 as the count number of the sub scanning clock.

(Time P1)
The control unit 23 sends white data to the LED control unit K1 instead of image data based on the calculation result of the white data supply time calculation unit 22. The LED control means K1 controls the exposure device K2 to expose white data on the photosensitive drum K3.

(Time P2)
The control unit 23 sends the white data to the LED control unit Y1 instead of the image data based on the calculation result of the white data supply time calculation unit 22. The LED control means Y1 controls the exposure device Y2 to expose white data on the photosensitive drum Y3.

(Time P3)
The control unit 23 sends white data to the LED control unit M1 instead of the image data based on the calculation result of the white data supply time calculation unit 22. The LED control means M1 controls the exposure device M2 to expose white data on the photosensitive drum M3.

(Time P4)
Based on the calculation result of the white data supply time calculation unit 22, the control unit 23 sends the white data to the LED control unit C1 instead of the image data. The LED control means C1 controls the exposure device C2 to expose white data on the photosensitive drum C3.

(Time P5)
The control unit 23 ends sending the white data to the LED control unit K1 based on the calculation result of the white data supply time calculation unit 22.

(Time P6)
The control unit 23 ends sending the white data to the LED control unit Y1 based on the calculation result of the white data supply time calculation unit 22.

(Time P7)
The control unit 23 ends sending the white data to the LED control unit M1 based on the calculation result of the white data supply time calculation unit 22.

(Time P8)
The control unit 23 ends sending the white data to the LED control unit C1 based on the calculation result of the white data supply time calculation unit 22.

<Effect of specific example 2>
As described above, in the second specific example, instead of the exposure start time calculating unit 5 (FIG. 1) of the first specific example, the image data supply start time calculating unit 21 is replaced with the exposure inhibition time calculating unit 6 (FIG. 1) of the first specific example. ), White data supply time calculation means 22 is arranged. In this manner, when a paper shorter than the predetermined paper length is inserted, white data is exposed on the surface of the photosensitive drum corresponding to a portion lacking the predetermined paper length. As a result, there is no printing outside the paper, and the conveyance belt is not smudged and wasteful toner consumption is eliminated.

<Configuration of Specific Example 3>
FIG. 6 is a configuration diagram of the third specific example.
As shown in FIG. 6, the image forming apparatus of the third specific example includes the conveyance belt 1, the conveyance roller 2, the paper end detection unit 3, the device performance storage unit 4, the paper feed roller 7, the fixing device 8, and the clock oscillator. 10, sub-scanning clock generation means 11, page data transfer start means 31, page data transfer time measurement means 32, count stop means 33, control section 34, delay time storage section 35, and LED control means K1. Y1, M1, C1, exposure devices K2, Y2, M2, C2, photosensitive drums K3, Y3, M3, C3, and transfer devices K4, Y4, M4, C4.

Only differences from the first specific example will be described.
In the specific example 1 and the specific example 2, the details of the invention have been described from the viewpoint of starting and stopping the exposure. However, in the following and subsequent specific examples, the description will be made from the viewpoint of starting and stopping transfer of page data (image data). Since the exposure is started and stopped when the transfer of page data (image data) is started and stopped, both concepts are in an integrated relationship.

  The page data transfer start means 31 is calculated from the conveyance speed of the sheet 12 and the distances between the sheet end detection unit 3 on the conveyance belt 1 and the plurality of photosensitive drums (K3, Y3, M3, C3). This is a part for starting the transfer of page data (image data) after the lapse of each delay time from when the leading edge detection signal is received to when exposure can be started.

  The page data transfer time measuring means 32 individually counts the page data transfer time for each of the plurality of photosensitive drums (K3, Y3, M3, C3), and after the count number determined based on the predetermined sheet length is completed. This is the part that stops the transfer of page data. Usually, a counter built in the postscript controller 34 plays this role.

  The count stop means 33 is a part that stops counting all the plurality of photosensitive drums after the transfer of page data to all of the plurality of photosensitive drums (K3, Y3, M3, C3) is started.

  The control unit 34 controls the sheet end detection unit 3 (similar to the first specific example), the page data transfer start unit 31, the page data transfer time measurement unit 32, and the count stop unit 33 to control the plurality of the plurality of the plurality of page data transfer start unit 31, When a desired image is exposed and transferred for each photosensitive drum and a sheet longer than a predetermined sheet length is received, the count stop unit 33 is controlled to stop the count and detect the end from the sheet end detection unit 3. This is a part that accepts a signal and restarts the above-described count, thereby enabling transfer of page data to a sheet exceeding a predetermined count number.

  That is, it is a CPU that controls all parts in the apparatus. The page data transfer start unit 31, the page data transfer time measurement unit 32, and the count stop unit 33 may be configured as a control program for operating the CPU. It goes without saying that these means may be configured as separate circuits. A counter for storing the results calculated by these means as the count number of the sub-scanning clock described later is provided internally.

The delay time storage unit 35 is calculated from the conveyance speed of the sheet 12 and the distances between the sheet end detection unit 3 on the conveyance belt 1 and the plurality of photosensitive drums (K3, Y3, M3, C3). This is a part for calculating and storing in advance the individual delay time from when the detection signal is received to when exposure can be started.
Since other components are the same as those in the first specific example, description thereof is omitted.

<Operation of Specific Example 3>
FIG. 7 is a time chart of the third specific example.
The sensor signal, SKcont (exposure time of the exposure device K), PLcont-k (paper length count), FSYNC-k (page transfer signal), PLcont-y (paper length count), FSYNC- in order from the top of the vertical axis. y (page transfer signal), PLcont-m (paper length count), FSYNC-m (page transfer signal), PLcont-c (paper length count), FSYNC-c (page transfer signal), time, and horizontal axis Represents the passage of time.
The operation of the specific example 3 will be described with reference to FIG. 6 according to the times S0 to S10 in FIG.

(Time S0)
The paper edge detection unit 3 that has detected that the leading edge of the paper 12 inserted from the paper feed roller 7 has reached the paper edge detection unit 3 sends a front edge detection signal to the control unit 34 (the sensor signal is set to high). . The portion of the page data transfer start unit 31 corresponding to the photosensitive drum K3 reads the delay time t1 of the photosensitive drum K3 from the delay time storage unit 35 and starts counting SKcont (delay time of the exposure unit K).

(Time S1)
Based on the control of the control unit 34, the page data transfer start means 31 sets FSYNC-k (page transfer signal) to high when the delay time t1 of the photosensitive drum K3 elapses, and page data (image data) corresponding to the photosensitive drum K3. Start transferring. The LED control means K1 controls the exposure device K2 to start creating an electrostatic latent image of a black image on the charged surface of the photosensitive drum K3.

  At the same time, the page data transfer time measuring means 32 starts counting the page data transfer time based on the control of the control unit 34 (PLcont-k (paper length count)). At this time, the page data transfer time measuring means 32 is set with a count number corresponding to a predetermined paper length.

(Time S2)
When the controller 34 monitors PLcont-k (paper length count) and detects that t2 time has elapsed since time S1, the controller 34 controls the page data transfer start means 31 to set FSYNC-y (page transfer signal) to high. Then, transfer of page data (image data) corresponding to the photosensitive drum Y3 is started. The LED control unit Y1 controls the exposure unit Y2 to start creating an electrostatic latent image of a yellow image on the charged surface of the photosensitive drum Y3. Here, t2 is a delay time of the photosensitive drum Y3 with respect to the photosensitive drum K3, and is stored in advance in the delay time storage unit 35.

  At the same time, the page data transfer time measuring unit 32 starts counting the page data transfer time based on the control of the control unit 34 (PLcont-y (paper length count)). At this time, the page data transfer time measuring means 32 is set with a count number corresponding to a predetermined paper length.

(Time S3)
When the controller 34 monitors PLcont-y (paper length count) and detects that t3 time has elapsed from time S2, the controller 34 controls the page data transfer start means to set FSYNC-m (page transfer signal) to high. Transfer of page data (image data) corresponding to the photosensitive drum M3 is started. The LED control means M1 controls the exposure device M2 to start creating an electrostatic latent image of a magenta image on the charged surface of the photosensitive drum M3. Here, t3 is a delay time of the photosensitive drum M3 with respect to the photosensitive drum Y3, and is stored in the delay time storage unit 35 in advance.

  At the same time, the page data transfer time measuring unit 32 starts counting the page data transfer time based on the control of the control unit 34 (PLcont-m (paper length count)). At this time, the page data transfer time measuring means 32 is set with a count number corresponding to a predetermined paper length.

(Time S4)
When the controller 34 monitors PLcont-m (paper length count) and detects that t4 hours have elapsed since time S3, the controller 34 controls the page data transfer start means 31 to set FSYNC-c (page transfer signal) to high. Then, transfer of page data (image data) corresponding to the photosensitive drum C3 is started. The LED control means C1 controls the exposure device C2 to start producing an electrostatic latent image of a cyan image on the charged surface of the photosensitive drum C3. Here, t4 is a delay time of the photosensitive drum C3 with respect to the photosensitive drum C3, and is stored in the delay time storage unit 35 in advance.

  At the same time, the page data transfer time measuring unit 32 starts counting the page data transfer time based on the control of the control unit 34 (PLcont-c (paper length count)). At this time, the page data transfer time measuring means 32 is set with a count number corresponding to a predetermined paper length.

(Time S5)
The control unit 34 is supposed to detect the trailing edge of the sheet 12 and send a trailing edge detection signal to the control unit 34 (the sensor signal is set to low) at the sheet length scheduled in advance. Since it has not been sent yet, it is determined that the currently flowing paper 12 is longer than the paper length scheduled in advance. Therefore, the count stop means 33 is controlled to stop the counts of PLcont-k (paper length count), PLcont-y (paper length count), PLcont-m (paper length count), and PLcont-c (paper length count) simultaneously. .

(Time S6)
The rear end of the paper 12 inserted from the paper supply roller 7 and longer than the predetermined paper length passes through the paper end detection unit 3. The sheet edge detection unit 3 sends a trailing edge detection signal to the control unit 34 (the sensor signal is set to low). The control unit 34 deactivates the count stop means 33 and counts PLcont-k (paper length count), PLcont-y (paper length count), PLcont-m (paper length count), and PLcont-c (paper length count). At the same time.

(Time S7)
The controller 34 controls the page data transfer time measuring unit 32 to stop the transfer of page data (PLC-k (page transfer signal) is set to low) because PLcont-k (paper length count) has finished counting. ). At the same time, the control unit 34 controls the LED control unit K1 and the exposure device K2 to stop creating an electrostatic latent image of a black image on the charging surface of the photosensitive drum K3.

  The following points should be noted here. The paper length of the paper 12 that is longer than the predetermined paper length corresponds to the sensor signal length t5 + t6. Here, t5 is a portion corresponding to a predetermined paper length, and t6 is a portion corresponding to an extra long paper length. On the other hand, during this time t6, PLcont-k (paper length count) stops counting. Accordingly, the time from time S6 to time S7 coincides with the delay time t1 of the photosensitive drum K3.

(Time S8)
The controller 34 controls the page data transfer time measurement unit 32 to stop the transfer of page data (PLC-y (page transfer signal) is set to low) because PLcont-y (paper length count) has finished counting. ). At the same time, the control unit 34 controls the LED control unit Y1 and the exposure device Y2 to stop creating an electrostatic latent image of a yellow image on the charging surface of the photosensitive drum Y3.

(Time S9)
The controller 34 controls the page data transfer time measuring unit 32 to stop the transfer of page data (PLC-m (page transfer signal) is set to low) because PLcont-m (paper length count) has finished counting. ). At the same time, the control unit 34 controls the LED control unit M1 and the exposure device M2 to stop creating an electrostatic latent image of a magenta image on the charging surface of the photosensitive drum M3.

(Time S10)
The controller 34 controls the page data transfer time measuring unit 32 to stop the transfer of page data (PLC-c (page transfer signal) is set to low) because PLcont-c (paper length count) has finished counting. ). At the same time, the control unit 34 controls the LED control unit C1 and the exposure device C2 to stop creating an electrostatic latent image of a cyan image on the charged surface of the photosensitive drum C3.
In the above description, the conveyance belt is used as the conveyance unit. However, a conveyance roller including a plurality of roller pairs may be used.

<Effect of specific example 3>
As described above, a sheet that is scheduled in advance by temporarily stopping counting during printing, including a page data transfer start unit, a page data transfer time measurement unit, a count stop unit, and a delay time storage unit. Printing on paper longer than the length can be performed without any obstacles.

<Configuration of Specific Example 4>
FIG. 8 is a configuration diagram of the fourth specific example.
As shown in FIG. 8, the image forming apparatus of Example 4 includes the conveyance belt 1, the conveyance roller 2, the paper end detection unit 3, the device performance storage unit 4, the paper feed roller 7, the fixing device 8, and the clock oscillator. 10, sub-scanning clock generation means 11, page data transfer start means 31, page data transfer time measurement means 32, delay time storage section 35, paper length count number setting means 41, paper length count number storage section 42, a control unit 43, LED control means K1, Y1, M1, C1, exposure devices K2, Y2, M2, C2, photosensitive drums K3, Y3, M3, C3, transfer devices K4, Y4, M4, C4.

Only differences from the third specific example will be described.
The paper length count number setting means 41 is a part for setting a count number corresponding to the paper length in the page data transfer time measuring means 32 (similar to the third specific example).
The sheet length count number storage unit 42 is a part that stores in advance a count number corresponding to the sheet length of a sheet to be inserted.

  When the control unit 43 receives a predetermined sheet, the control unit 43 controls the sheet length count number setting unit 41 so that the page data transfer start unit 31 (similar to the third specific example) has the plurality of photosensitive drums (K3, Y3, M3). , C3), when the page data transfer is started in order from the upstream side, the count number corresponding to the predetermined sheet length is sequentially set in the page data transfer time measuring means 32 (similar to the third specific example). It is.

That is, it is a CPU that controls all parts in the apparatus. The sheet length count number setting means 41, the page data transfer start means 31, the photosensitive drum (K3, Y3, M3, C3), and the page data transfer time measurement means 32 may be configured as a control program for operating this CPU. . It goes without saying that these means may be configured as separate circuits. A counter for storing the results calculated by these means as the count number of the sub-scanning clock described later is provided internally.
Since other components are the same as those in the first specific example or the third specific example, the description is omitted.

<Operation of Specific Example 4>
FIG. 9 is a time chart of the fourth specific example.
In order from the top of the vertical axis, the sensor signal, SKcont (exposure time of the exposure unit K), PLcont-k (paper length count), FSYNC-k (page transfer signal), PL-y (paper length), PLcont-y (Paper length count), FSYNC-y (page transfer signal), PLcont-m (paper length count), FSYNC-m (page transfer signal), PLcont-c (paper length count), FSYNC-c (page transfer signal) , Time, and the horizontal axis represents the passage of time.
The operation of the specific example 4 will be described with reference to FIG. 8 according to the times U0 to U5 in FIG.

(Time U0)
The paper edge detection unit 3 that has detected that the leading edge of the paper 12 inserted from the paper feed roller 7 has reached the paper edge detection unit 3 sends a front edge detection signal to the control unit 43 (the sensor signal is set to high). . The portion of the page data transfer start unit 31 corresponding to the photosensitive drum K3 reads the delay time t1 of the photosensitive drum K3 from the delay time storage unit 35 and starts counting SKcont (delay time of the exposure unit K).

(Time U1)
Based on the control of the control unit 43, the page data transfer start means 31 sets FSYNC-k (page transfer signal) to high when the delay time t1 of the photosensitive drum K3 elapses, and page data (image data) corresponding to the photosensitive drum K3. Start transferring. The LED control means K1 controls the exposure device K2 to start creating an electrostatic latent image of a black image on the charged surface of the photosensitive drum K3.

  At this time, the control unit 43 controls the sheet length count number setting unit 41 to set the sheet length count number corresponding to the sheet length of the currently flowing sheet 12 in the page data transfer time measuring unit 32. The sheet length count number is stored in advance in the sheet length count number storage unit 42. At the same time, the page data transfer time measuring unit 32 starts counting the page data transfer time based on the control of the control unit 34 (PLcont-k (paper length count)).

(Time U2)
The control unit 43 monitors PLcont-k (paper length count), detects that t2 hours have elapsed from time U1, sets FSYNC-y (page transfer signal) to high, and sets page data corresponding to the photosensitive drum Y3 ( Image data transfer starts. The LED control unit Y1 controls the exposure unit Y2 to start creating an electrostatic latent image of a yellow image on the charged surface of the photosensitive drum Y3. Here, t2 is a delay time of the photosensitive drum Y3 with respect to the photosensitive drum K3, and is stored in advance in the delay time storage unit 35.

  At this time, the control unit 43 controls the sheet length count number setting unit 41 to set the sheet length count number corresponding to the sheet length of the currently flowing sheet 12 in the page data transfer time measuring unit 32. The sheet length count number is stored in advance in the sheet length count number storage unit 42. At the same time, the page data transfer time measuring unit 32 starts counting the page data transfer time based on the control of the control unit 43 (PLcont-y (paper length count)).

(Time U3)
The control unit 43 monitors PLcont-y (paper length count), detects that t3 time has elapsed from time U2, sets FSYNC-m (page transfer signal) to high, and sets page data corresponding to the photosensitive drum M3 ( Image data transfer starts. The LED control means M1 controls the exposure device M2 to start creating an electrostatic latent image of a magenta image on the charged surface of the photosensitive drum M3. Here, t3 is a delay time of the photosensitive drum M3 with respect to the photosensitive drum Y3, and is stored in the delay time storage unit 35 in advance.

  At this time, the control unit 43 controls the sheet length count number setting unit 41 to set the sheet length count number corresponding to the sheet length of the currently flowing sheet 12 in the page data transfer time measuring unit 32. The sheet length count number is stored in advance in the sheet length count number storage unit 42. At the same time, the page data transfer time measuring unit 32 starts counting the page data transfer time based on the control of the control unit 43 (PLcont-m (paper length count)).

(Time U4)
The control unit 43 monitors PLcont-m (paper length count), detects that t4 hours have elapsed from time U3, sets FSYNC-c (page transfer signal) to high, and sets page data corresponding to the photosensitive drum C3 ( Image data transfer starts. The LED control means C1 controls the exposure device C2 to start producing an electrostatic latent image of a cyan image on the charged surface of the photosensitive drum C3. Here, t4 is a delay time of the photosensitive drum C3 with respect to the photosensitive drum C3, and is stored in the delay time storage unit 35 in advance.

At this time, the control unit 43 controls the paper length count number setting means 41 to set the paper length count number corresponding to the paper length of the currently flowing paper 12 to PLcont-c (paper length count). The sheet length count number is stored in advance in the sheet length count number storage unit 42. At the same time, the page data transfer time measuring unit 32 starts counting the page data transfer time based on the control of the control unit 43 (PLcont-c (paper length count)).
Thereafter, in the same manner, the process advances to time U5.

<Effect of specific example 4>
As described above, the configuration of the specific example 3 further includes a sheet length count number setting unit and a sheet length count number storage unit, and starts transferring page data to a plurality of photosensitive drums in order from the upstream side. At that time, by sequentially setting the number of counts corresponding to the predetermined sheet length in the page data transfer time measuring means, it is possible to continuously print sheets of different lengths.

<Configuration of Specific Example 5>
FIG. 10 is a configuration diagram of the fifth specific example.
As shown in FIG. 10, the image forming apparatus of Example 5 includes the conveyance belt 1, the conveyance roller 2, the paper end detection unit 3, the device performance storage unit 4, the paper feed roller 7, the fixing device 8, and the clock oscillator. 10, sub-scanning clock generation means 11, page data transfer start means 31, page data transfer time measurement means 32, delay time storage section 35, paper length count number setting means 41, paper length count number storage section 42, count number resetting means 51, control section 52, LED control means K1, Y1, M1, C1, exposure devices K2, Y2, M2, C2, photosensitive drums K3, Y3, M3, C3, And transfer devices K4, Y4, M4, and C4.

Only differences from the fourth specific example will be described.
The count number resetting means 51 is a part for resetting the remaining count number while the page data transfer time measuring means 32 is counting the page data transfer time individually.

The control unit 52 controls the sheet end detection unit 3, the page data transfer start unit 31, the page data transfer time measurement unit 32, the sheet length count number setting unit 41, and the count number resetting unit 51 to control the plurality of photosensitive elements. When a desired image is exposed and transferred for each drum, and the end detection signal is received while the page data transfer time measuring means 32 is counting the page data transfer time individually, the count number resetting means 51 is controlled. The remaining count number of the page data transfer time measuring means 32 corresponding to a plurality of photosensitive drums arranged in order from the upstream to the downstream in the transport direction is reset.
The other components are the same as those in the first specific example, the third specific example, or the fourth specific example, and the description thereof is omitted.

<Operation of Specific Example 5>
FIG. 11 is a time chart of the fifth specific example.
The sensor signal, SKcont (exposure time of the exposure device K), PLcont-k (paper length count), FSYNC-k (page transfer signal), PLcont-y (paper length count), FSYNC- in order from the top of the vertical axis. y (page transfer signal), PLcont-m (paper length count), FSYNC-m (page transfer signal), PLcont-c (paper length count), FSYNC-c (page transfer signal), time, and horizontal axis Represents the passage of time. The operation of the specific example 5 will be described with reference to FIG. 11 according to the times V0 to V9 in FIG.

(Time V0)
The paper edge detection unit 3 that has detected that the leading edge of the paper 12 inserted from the paper feed roller 7 has reached the paper edge detection unit 3 sends a front edge detection signal to the control unit 52 (the sensor signal is set to high). . The portion of the page data transfer start unit 31 corresponding to the photosensitive drum K3 reads the delay time t1 of the photosensitive drum K3 from the delay time storage unit 35 and starts counting SKcont (delay time of the exposure unit K).

(Time V1)
Based on the control of the control unit 52, the page data transfer start means 31 sets FSYNC-k (page transfer signal) to high when the delay time t1 of the photosensitive drum K3 elapses, and page data (image data) corresponding to the photosensitive drum K3. Start transferring. The LED control means K1 controls the exposure device K2 to start creating an electrostatic latent image of a black image on the charged surface of the photosensitive drum K3.

  At this time, the control unit 52 controls the sheet length count number setting unit 41 to set the sheet length count number corresponding to the sheet length of the currently flowing sheet 12 in the page data transfer time measuring unit 32. The sheet length count number is stored in advance in the sheet length count number storage unit 42. At the same time, the page data transfer time measuring means 32 starts counting the page data transfer time based on the control of the control unit 34 (PLcont-k (paper length count)).

(Time V2)
The control unit 52 monitors PLcont-k (paper length count), detects that t2 hours have elapsed from time U1, sets FSYNC-y (page transfer signal) to high, and sets the page data corresponding to the photosensitive drum Y3 ( Image data transfer starts. The LED control unit Y1 controls the exposure unit Y2 to start creating an electrostatic latent image of a yellow image on the charged surface of the photosensitive drum Y3. Here, t2 is a delay time of the photosensitive drum Y3 with respect to the photosensitive drum K3, and is stored in advance in the delay time storage unit 35.

  At this time, the control unit 52 controls the sheet length count number setting unit 41 to set the sheet length count number corresponding to the sheet length of the currently flowing sheet 12 in the page data transfer time measuring unit 32. The sheet length count number is stored in advance in the sheet length count number storage unit 42. At the same time, the page data transfer time measuring unit 32 starts counting the page data transfer time based on the control of the control unit 43 (PLcont-y (paper length count)).

(Time V3)
The control unit 52 monitors PLcont-y (paper length count), detects that t3 time has elapsed from time U2, sets FSYNC-m (page transfer signal) to high, and sets the page data corresponding to the photosensitive drum M3 ( Image data transfer starts. The LED control means M1 controls the exposure device M2 to start creating an electrostatic latent image of a cyan image on the charged surface of the photosensitive drum M3. Here, t3 is a delay time of the photosensitive drum M3 with respect to the photosensitive drum Y3, and is stored in the delay time storage unit 35 in advance.

  At this time, the control unit 52 controls the sheet length count number setting unit 41 to set the sheet length count number corresponding to the sheet length of the currently flowing sheet 12 in the page data transfer time measuring unit 32. The sheet length count number is stored in advance in the sheet length count number storage unit 42. At the same time, the page data transfer time measuring unit 32 starts counting the page data transfer time based on the control of the control unit 43 (PLcont-m (paper length count)).

(Time V4)
The control unit 52 monitors PLcont-m (paper length count), detects that t4 hours have elapsed from time U3, sets FSYNC-c (page transfer signal) to high, and sets the page data corresponding to the photosensitive drum C3 ( Image data transfer starts. The LED control means C1 controls the exposure device C2 to start producing an electrostatic latent image of a cyan image on the charged surface of the photosensitive drum C3. Here, t4 is a delay time of the photosensitive drum C3 with respect to the photosensitive drum C3, and is stored in the delay time storage unit 35 in advance.

  At this time, the control unit 52 controls the sheet length count number setting unit 41 to set the sheet length count number corresponding to the sheet length of the currently flowing sheet 12 in the page data transfer time measuring unit 32. The sheet length count number is stored in advance in the sheet length count number storage unit 42. At the same time, the page data transfer time measuring unit 32 starts counting the page data transfer time based on the control of the control unit 43 (PLcont-c (paper length count)).

(Time V5)
The control unit 52 accepts the trailing edge detection signal from the sheet edge detection unit 3 (the sensor signal becomes low) even though the sheet edge detection unit 3 has no wrinkle to detect the trailing edge of the sheet 12 at the predetermined sheet length. . At this time, the control unit 52 determines that the currently flowing paper 12 is shorter than the paper length scheduled in advance. Therefore, the count number resetting means 51 is controlled to read the delay time t1 of the photosensitive drum K3 from the delay time storage unit 35 and reset the count of the page data transfer time measuring means 32 with the count number corresponding to the time t1.

(Time V6)
When the count of PLcont-k (paper length count) is completed, the control unit 52 controls the count number resetting unit 51 to read the delay time t2 from the photosensitive drum K3 to the photosensitive drum Y3 from the delay time storage unit 35. The count of the page data transfer time measuring means 32 is reset with a count corresponding to the time t2.

  The controller 52 controls the page data transfer time measuring unit 32 to stop the transfer of page data (PLC-k (page transfer signal) is set to low) because PLcont-k (paper length count) has finished counting. ). At the same time, the control unit 52 controls the LED control unit K1 and the exposure device K2 to stop creating an electrostatic latent image of a black image on the charging surface of the photosensitive drum K3.

(Time V7)
When the count of PLcont-y (paper length count) is completed, the control unit 52 controls the count number resetting unit 51 to read the delay time t3 from the photosensitive drum Y3 to the photosensitive drum M3 from the delay time storage unit 35. The count of the page data transfer time measuring means 32 is reset with a count corresponding to the time t3.

  The controller 52 controls the page data transfer time measuring means 32 to stop the transfer of page data (PLC-y (page transfer signal) is low) because PLcont-y (paper length count) has finished counting. ). At the same time, the control unit 52 controls the LED control unit Y1 and the exposure device Y2 to stop creating an electrostatic latent image of a yellow image on the charging surface of the photosensitive drum Y3.

(Time V8)
When the count of PLcont-m (paper length count) is completed, the control unit 52 controls the count number resetting unit 51 to read the delay time t4 from the photosensitive drum M3 to the photosensitive drum C3 from the delay time storage unit 35. The count of PLcont-c (paper length count) is reset with the count corresponding to time t4.

  The controller 52 stops the page data transfer by controlling the page data transfer time measuring means 32 because the PLcont-m (paper length count) has finished counting (FSYNC-m (page transfer signal) is set to low). ). At the same time, the control unit 52 controls the LED control unit M1 and the exposure device M2 to stop creating an electrostatic latent image of a magenta image on the charging surface of the photosensitive drum M3.

(Time V9)
The count of PLcont-c (paper length count) ends. The controller 52 controls the page data transfer time measuring unit 32 to stop the transfer of page data (PLC-c (page transfer signal) is low) because PLcont-c (paper length count) has finished counting. ). At the same time, the control unit 52 controls the LED control unit C1 and the exposure unit C2 to stop creating an electrostatic latent image of a cyan image on the charged surface of the photosensitive drum C3.
This completes printing.

  In the above description of the operation, the control unit 52 controls the count number resetting unit 51 to sequentially reset the sheet length count value sequentially from the upstream. However, this specific example is not limited to this example. For example, at time V5, the count of PLcont-k (paper length count) is reset to the count number corresponding to time t1, and at the same time, the count of PLcont-y (paper length count) is set to the count number corresponding to time t1 + t2. The count of PLcont-m (paper length count) may be reset to a count number corresponding to time t1 + t2 + t3, and the count of PLcont-c (paper length count) may be reset to a count number corresponding to time t1 + t2 + t3 + t4.

<Effect of Specific Example 5>
As described above, when the page data transfer time measuring means receives the end detection signal while the page data transfer time is individually counting, the control section controls the count number resetting means to control the upstream of the transport direction. Even if a paper shorter than planned is inserted by resetting the remaining count number of the page data transfer time measuring means corresponding to a plurality of photosensitive drums arranged in order from the downstream toward the downstream Will be able to.

FIG. 3 is a configuration diagram of a specific example 1; It is a time chart (the 1) of specific example 1. It is a time chart (the 2) of the specific example 1. It is a block diagram of the specific example 2. 10 is a time chart of a specific example 2; It is a block diagram of the specific example 3. 10 is a time chart of a specific example 3; It is a block diagram of the specific example 4. 10 is a time chart of Example 4. FIG. 10 is a configuration diagram of specific example 5. 10 is a time chart of Example 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Conveyance belt 2 Conveyance roller 3 Paper edge detection part 4 Equipment performance memory | storage part 5 Exposure start time calculation means 6 Exposure prohibition time calculation means 7 Paper feed roller 8 Fixing device 9 Control part 10 Clock oscillator 11 Sub-scanning clock generation means K1-C1 LED control means K2 to C2 Exposure unit K3 to C3 Photosensitive drum K4 to C4 Transfer unit

Claims (8)

A plurality of image forming units each including a photosensitive member and an exposure unit, each being spaced apart by a predetermined distance in the paper transport direction of the paper transport path;
The leading edge detection signal is output by detecting the leading edge of the sheet that is disposed upstream of the plurality of image forming units in the conveying direction and is conveyed along the sheet conveying path, and is configured to detect a sheet that is shorter than a predetermined sheet length. A paper edge detector that detects the trailing edge and outputs an abnormal trailing edge detection signal;
When the leading edge detection signal is input from the sheet edge detection unit, the plurality of images are determined from the sheet conveyance speed and the distances between the sheet edge detection unit and the image forming unit on the sheet conveyance path. Exposure start time calculating means for calculating an exposure start time for each forming unit;
When the abnormal trailing edge detection signal is input from the sheet edge detection unit, the plurality of sheets are determined based on the sheet conveyance speed and the distances between the sheet edge detection unit and the image forming unit on the sheet conveyance path. Exposure prohibition time calculating means for calculating an exposure prohibition time for each image forming unit of
The paper edge detection unit, the exposure start time calculation unit, and the exposure prohibition time calculation unit are controlled so that a desired image is exposed and transferred for each of the plurality of image forming units, and a paper shorter than a predetermined paper length is used. An image forming apparatus comprising: a control unit that, when received, prohibits exposure of a portion lacking from a predetermined sheet length for each of the plurality of image forming units. A plurality of image forming units each including a photosensitive member and an exposure unit, each being spaced apart by a predetermined distance in the paper transport direction of the paper transport path;
The leading edge detection signal is output by detecting the leading edge of the sheet that is disposed upstream of the plurality of image forming units in the conveying direction and is conveyed along the sheet conveying path, and is configured to detect a sheet that is shorter than a predetermined sheet length. A paper edge detector that detects the trailing edge and outputs an abnormal trailing edge detection signal;
When the leading edge detection signal is input from the paper edge detection unit, the plurality of papers are determined based on the speed at which the paper is conveyed and the distances between the paper edge detection unit and the image forming unit on the paper conveyance path. Image data supply start time calculating means for calculating an image data supply start time for each image forming unit;
When the abnormal trailing edge detection signal is input from the sheet edge detection unit, each of the plurality of image forming units is determined from the conveyance speed of the sheet and the distance between the sheet edge detection unit and the image forming unit. White data supply start time calculated from the supply start time of the white data supplied to the paper, the conveyance speed of the paper, the distance between the paper edge detection unit and the image forming unit, and a predetermined paper length White data supply time calculation means for calculating
The paper edge detection unit, the image data supply start time calculation unit, and the white data supply time calculation unit are controlled so that a desired image is exposed and transferred for each of the plurality of image forming units, and a predetermined paper length is set. And a controller that exposes and transfers white data to a portion lacking from a predetermined sheet length for each of the plurality of image forming units when a shorter sheet is received. The image forming apparatus according to claim 1, wherein:
Sub-scanning clock generation means that enables line feed finer than the line feed interval of images transferred from an external device,
The controller is
An image forming apparatus that performs all of the control based on the sub-scanning clock generation unit. The image forming apparatus according to any one of claims 1 to 3,
The distance between the paper edge detection unit and the image forming unit disposed at the uppermost stream in the transport direction is:
The relationship of l <L is established, where l is the circumferential distance from the exposure position to the transfer position on the image forming unit and L is the horizontal distance from the transfer position to the sheet edge detection unit. Image forming apparatus. A plurality of image forming units each including a photosensitive member and an exposure unit, each being spaced apart by a predetermined distance in the paper transport direction of the paper transport path;
A leading edge detection signal is output by detecting a leading edge of a sheet that is disposed upstream of the plurality of image forming units in the conveying direction and is conveyed along the sheet conveying path, and a trailing edge is detected by detecting the trailing edge of the sheet. A paper edge detector for outputting a detection signal;
From receiving the leading edge detection signal calculated from the sheet conveyance speed and the distances between the sheet edge detection unit and the plurality of image forming units on the sheet conveyance path until the exposure can be started. Page data transfer start means for starting transfer of page data after each delay time has elapsed;
Page data transfer time measuring means for individually counting the page data transfer time for each of the plurality of image forming units and stopping the transfer of page data after the count number corresponding to the paper length is terminated;
A paper length count number setting means for setting a count number corresponding to the paper length in a page data transfer time measuring means;
The sheet end detection unit, the page data transfer start unit, the page data transfer time measurement unit, and the sheet length count number setting unit are controlled to expose and transfer a desired image for each of the plurality of image forming units. When a predetermined sheet is received, the sheet length count number setting unit is controlled, and when the page data transfer start unit starts transferring page data to the plurality of image forming units in order from the upstream side, the page data An image forming apparatus comprising: a control unit that sequentially sets a count number corresponding to the predetermined sheet length in the transfer time measuring unit. The image forming apparatus according to claim 5.
The page data transfer start means
From receiving the leading edge detection signal calculated from the sheet conveyance speed and the distances between the sheet edge detection unit and the plurality of image forming units on the sheet conveyance path until the exposure can be started. An image forming apparatus comprising a delay time storage unit for calculating and storing individual delay times in advance. The image forming apparatus according to claim 5.
The sheet length count number setting means includes:
An image forming apparatus comprising a sheet length count number storage unit that stores a count number corresponding to a sheet length in advance. A plurality of image forming units each including a photosensitive member and an exposure unit, each being spaced apart by a predetermined distance in the paper transport direction of the paper transport path;
A leading edge detection signal is output by detecting a leading edge of a sheet that is disposed upstream of the plurality of image forming units in the conveying direction and is conveyed along the sheet conveying path, and a trailing edge is detected by detecting the trailing edge of the sheet. A paper edge detector for outputting a detection signal;
From receiving the leading edge detection signal calculated from the sheet conveyance speed and the distances between the sheet edge detection unit and the plurality of image forming units on the sheet conveyance path until the exposure can be started. Page data transfer start means for starting transfer of page data after each delay time has elapsed;
Page data transfer time measuring means for individually counting the page data transfer time for each of the plurality of image forming units and stopping the transfer of page data after the count number corresponding to the paper length is terminated;
A paper length count number setting means for setting a count number corresponding to the paper length in a page data transfer time measuring means;
Count number resetting means for resetting the remaining count number while the page data transfer time measuring means counts the page data transfer time individually;
The sheet end detection unit, the page data transfer start unit, the page data transfer time measurement unit, the sheet length count number setting unit, and the count number resetting unit are controlled so as to be set for each of the plurality of image forming units. When the image is exposed and transferred, and the page data transfer time measuring means receives the end detection signal in the middle of counting the page data transfer time individually, the count number resetting means is controlled to control the count direction resetting means from upstream to downstream in the transport direction. And a controller that resets the remaining count number of the page data transfer time measuring unit corresponding to the plurality of image forming units arranged sequentially toward the image forming unit.

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