JP2015105174A - Image forming apparatus - Google Patents

Abstract

A printing start position on a sheet is made constant.
An image forming apparatus includes a transfer unit that transfers a toner image formed on a photosensitive drum to a sheet, a conveyance path that conveys the sheet to the transfer unit, and a conveyance path. And a control for controlling the conveyance speed of the sheet 11 in the conveyance path 15 so that the sheet 11 reaches the registration roller pair 13 at a predetermined timing. Department.
[Selection] Figure 1

Description

  The present invention relates to an electrophotographic image forming apparatus.

  In general, in order to adjust the printing start timing of the registration roller pair, a sheet supplied to the registration roller pair is detected by a registration sensor. It is known to use a transmissive sensor as a resist sensor. The transmission type sensor has an actuator that is switched by contacting a sheet supplied to the registration roller pair.

  However, in recent years, since the printing speed has been increased, the operation of the actuator cannot catch up with the sheet conveyed at high speed, and it is difficult to reliably detect the sheet by the transmission type sensor.

  Therefore, it is known to use a reflective sensor as a resist sensor instead of a transmissive sensor. That is, by directly detecting the leading edge of the sheet by the reflection type sensor, the timing of starting printing by the registration roller pair is adjusted.

JP 2003-40487 A

  However, when a reflective sensor is used as a resist sensor, there is a problem that the sheet cannot be detected depending on the type of the sheet. In particular, this problem is remarkable in a sheet that transmits light, such as an OHP sheet.

  The present invention has been made in view of such a point, and an object thereof is to make the printing start position on the sheet constant.

  An image forming apparatus according to the present invention is provided in a transfer unit that transfers a toner image formed on a photosensitive drum to a sheet, a conveyance path for conveying the sheet to the transfer unit, and the conveyance path. A registration roller pair that supplies the sheet to the transfer unit; and a control unit that controls a conveyance speed of the sheet in the conveyance path so that the sheet reaches the registration roller pair at a predetermined timing. .

  According to the present invention, the printing start position on the sheet can be made constant.

FIG. 1 is a side view schematically showing a main part of the image forming apparatus according to the present embodiment. FIG. 2 is a block diagram illustrating a main part of the image forming apparatus. FIG. 3 is a flowchart showing a control flow by the control unit. FIG. 4 is a flowchart showing a control flow by the control unit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiment.

  FIG. 1 schematically shows a main part of an image forming apparatus 1 in the present embodiment. The image forming apparatus 1 is, for example, a laser printer. As shown in FIG. 1, the image forming apparatus 1 includes a photosensitive drum 10 as an image carrier constituting an image forming unit, and a transfer unit that transfers a toner image formed on the photosensitive drum 10 to a sheet 11. The transfer roller 12 and a resist roller pair 13 that supplies the sheet 11 to the transfer roller 12 are provided.

  The image forming apparatus 1 further includes a paper feed cassette (not shown) in which sheets 11 such as paper before printing and OHP sheets are accommodated. The sheet 11 is, for example, an OHP sheet. The sheets 11 are separated and sent out one by one from the paper feed cassette. A conveyance path 15 for conveying the sheet 11 to the transfer roller 12 is formed between the paper feed cassette and the transfer roller 12.

  The registration roller pair 13 is provided in the conveyance path 15, and supplies the sheet 11 sent from the sheet feeding cassette via the conveyance path 15 to the transfer roller 12 at a predetermined timing after temporarily waiting.

  The outer peripheral surface of the photosensitive drum 10 is scanned by laser light emitted from an optical scanning unit (not shown). As a result, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 10. The electrostatic latent image formed on the photosensitive drum 10 is developed with toner supplied from a developing unit (not shown). As a result, a toner image is formed on the outer peripheral surface of the photosensitive drum 10.

  The transfer roller 12 extends in parallel with the photosensitive drum 10 and abuts against the photosensitive drum 10 to form a nip portion 17 between the transfer roller 12 and the photosensitive drum 10. The sheet 11 sent out from the registration roller pair 13 is supplied to the nip portion 17 through the conveyance path 15. Then, when the sheet 11 passes through the nip portion 17, the toner image formed on the photosensitive drum 10 is transferred to the sheet 11.

  The sheet 11 to which the toner image has been transferred is then conveyed to a fixing unit (not shown), and the toner image is fixed to the sheet 11 by being heated and pressed in the fixing unit. As described above, the image forming apparatus 1 performs a printing process by forming an image on the sheet 11.

  The conveyance path 15 is provided with a plurality of sensors for detecting the sheet 11. As shown in FIG. 1, the conveyance path 15 is provided with a paper feed sensor 19 as a first sensor, a registration sensor 20 as a second sensor, and a JAM sensor 21 as a third sensor.

  The resist sensor 20 is configured by a reflective sensor that emits light and receives light reflected by the sheet 11. The registration sensor 20 is disposed in the vicinity of the registration roller pair 13 (immediately upstream in the conveyance direction of the sheet 11 with respect to the registration roller pair 13), emits light, and receives reflected light from the leading end of the sheet 11. The sheet 11 supplied to the registration roller pair 13 is detected.

  The paper feed sensor 19 and the JAM sensor 21 are constituted by transmissive sensors. The paper feed sensor 19 is disposed between the registration sensor 20 and the paper feed cassette. The paper feed sensor 19 detects whether or not the sheet 11 has been normally fed.

  On the other hand, the JAM sensor 21 is disposed between the registration roller pair 13 and the transfer roller 12. That is, the registration sensor 20 is disposed between the JAM sensor 21 and the paper feed sensor 19.

  The JAM sensor 21 detects a conveyance failure of the sheet 11 in the conveyance path 15. For example, when the sheet 11 is jammed in the conveyance path 15, the sheet 11 is continuously detected by the JAM sensor 21. At such time, a conveyance failure of the sheet 11 in the conveyance path 15 is detected.

  The image forming apparatus 1 detects the sheet 11 that has reached the registration roller pair 13 by the registration sensor 20 when the sheet 11 is a sheet that does not easily transmit light, while the sheet 11 is an OHP sheet that easily transmits light. In this case, the timing at which the sheet 11 reaches the registration roller pair 13 is predicted using the paper feed sensor 19 and the JAM sensor 21 without using the registration sensor 20.

  FIG. 2 is a block diagram illustrating a main part of the image forming apparatus 1. As shown in FIG. 2, the image forming apparatus 1 includes a control unit 25 that controls the conveyance speed of the sheet 11 in the conveyance path 15 so that the sheet 11 reaches the registration roller pair 13 at a predetermined timing. Further, the image forming apparatus 1 includes a transport mechanism 26 for transporting the sheet 11 through the transport path 15. The transport mechanism 26 has, for example, a plurality of rollers (not shown), a drive motor (not shown), and the like.

  The control unit 25 is configured to set the conveyance speed of the sheet 11 to a predetermined set speed based on detection results by the paper feed sensor 19 and the JAM sensor 21. Further, the control unit 25 is configured to maintain the conveyance speed at the set speed when the conveyance speed of the sheet 11 varies.

  Next, the control flow by the control part 25 is demonstrated with reference to FIG.3 and FIG.4. Here, FIG. 3 and FIG. 4 are flowcharts showing a control flow by the control unit 25.

  If the sheet 11 is an OHP sheet, for example, in step S1, the user registers in the image forming apparatus 1 that the sheet 11 to be printed is an OHP sheet. Subsequently, in step S <b> 2, the control unit 25 measures the conveyance speed of the sheet 11 based on the detection results by the paper feed sensor 19 and the JAM sensor 21 in image formation.

  Next, in step S3, the control unit 25 determines whether or not the conveyance speed measured in step S2 is higher than a predetermined reference speed. The reference speed is a speed determined in advance so that the sheet 11 reaches the registration roller pair 13 at an appropriate timing. When the sheet 11 reaches the registration roller pair 13 at an appropriate timing, the sheet 11 can reach the transfer roller 12 from the registration roller pair 13 at an appropriate transfer timing.

  If the conveyance speed is equal to or lower than the reference speed and NO is determined in step S3, the process proceeds to step S4, where the conveyance speed is set as the set speed, and printing processing for the next page and thereafter is performed based on the set speed.

  On the other hand, when the conveyance speed is higher than the reference speed and YES is determined in step S3, the control unit 25 proceeds to step S5 to control the conveyance mechanism 26 so that the conveyance speed of the sheet 11 is measured. And the calculated value calculated so as to eliminate the difference between the reference speed and the reference speed. Thereafter, in step S6, it is determined whether or not the conveyance speed detected by the paper feed sensor 19 and the JAM sensor 21 is equal to or lower than the reference speed. As a result, when it is determined that the conveyance speed is greater than the reference speed and NO, only the calculated value is calculated so that the difference between the conveyance speed and the reference speed obtained by returning to step S5 and further measuring the conveyance speed is eliminated. Reduce.

  If it is determined in step S6 that the conveyance speed is equal to or lower than the reference speed and YES, the process proceeds to step S4. In step S4, the conveyance speed set in steps S5 and S6 is set as the set speed, and printing processing for the next page and thereafter is performed based on the set speed.

  Next, in step S <b> 7, the control unit 25 measures the conveyance speed of the sheet 11 by the paper feed sensor 19 and the JAM sensor 21 in the subsequent print processing. Next, in step S <b> 8, the control unit 25 determines whether or not the conveyance speed of the sheet 11 has varied. As a result, if there is no variation in the conveyance speed, the flow proceeds to step S9 and the printing process is performed while measuring the conveyance speed of the sheet 11 based on the detection results of the paper feed sensor 19 and the JAM sensor 21.

  On the other hand, if the transport speed varies, YES is determined in step S8 and the process proceeds to step S10. In step S <b> 10, the control unit 25 controls the transport mechanism 26 to change the transport speed. Thereafter, in step S11, it is determined whether or not the conveyance speed of the sheet 11 is constant. As a result, when it is determined that the transport speed is not constant and NO, the process returns to step S10 and the transport speed is further changed. Then, when the conveyance speed is constant and it is determined YES, the process proceeds to step S9. In step S <b> 9, the printing process is performed while measuring the conveyance speed of the sheet 11 based on the detection results of the paper feed sensor 19 and the JAM sensor 21.

  Therefore, the image forming apparatus 1 according to the present embodiment includes the control unit 25 that sets the conveyance speed of the sheet 11 to a predetermined setting speed based on the detection results of the paper feed sensor 19 and the JAM sensor 21. Even if the sheet 11 is an OHP sheet or the like that is easy to transmit light and difficult to detect by the reflective resist sensor 20, the printing start position on the sheet 11 can be made constant by the control unit 25. On the other hand, when the sheet 11 is a paper that does not easily transmit light, the registration sensor 20 can detect the sheet 11, so that the print start position can be kept constant.

  Further, since the control unit 25 is configured to maintain the conveyance speed at the set speed when the conveyance speed of the sheet 11 varies, even when the conveyance speed changes with time, The printing position can be maintained appropriately.

  In this embodiment, a laser printer has been described as an example of an image forming apparatus. However, the image forming apparatus according to the present invention is not limited to this, and may be other image forming apparatuses such as a copying machine or a multifunction peripheral. Also good.

  As described above, the present invention is useful for an electrophotographic image forming apparatus.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Photosensitive drum 11 Sheet 12 Transfer roller 13 Registration roller pair 15 Conveyance path 19 Paper feed sensor 20 Registration sensor 21 JAM sensor 25 Control part 26 Conveyance mechanism

Claims (3)

A transfer portion for transferring a toner image formed on the photosensitive drum to a sheet;
A conveyance path for conveying the sheet to the transfer unit;
A pair of registration rollers provided in the conveyance path and supplying the sheet to the transfer unit;
An image forming apparatus comprising: a control unit that controls a conveyance speed of the sheet in the conveyance path so that the sheet reaches the registration roller pair at a predetermined timing. The image forming apparatus according to claim 1.
The conveyance path is provided with a plurality of transmission sensors for detecting the sheet,
The image forming apparatus, wherein the control unit sets the sheet conveyance speed to a predetermined setting speed based on detection results of the plurality of transmission sensors. The image forming apparatus according to claim 2.
The control unit is an image forming apparatus that maintains the conveyance speed at the set speed when a variation occurs in the conveyance speed of the sheet.

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