JPH0971349A - Sheet conveying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the conveying condition of many sizes of sheets by less sheet sensors by arranging a pair of sheet sensors at prescribed positions, converting the sheet conveying timing into those values corresponding to the size of sheets, and comparing the values obtained after conversion with reference values so as to detect the time lag and the lag of the movement aslant. SOLUTION: Sheets fed from sheet feed cassettes 9a and 9b by sheet feed rolls 7a and 7b, respectively, are stopped temporarily at a register gate 11, and started to move simultaneously when the gate is opened. After passing the register call 12, they pass through two sheet sensors 13 and 14 which are arranged near both ends of the minimum feedable size of sheets in the direction at the right angle to the conveying direction, and arrive at a transfer equipment 5 for the transfer of toner images. Also a time from the opening of the gate to the passing of sheets through the sheet sensors 13 and 14 is measured, these values are converted into those values at the central part or both end parts of the sheets, and the time lag caused by the delay or advancement of the sheets and the sheet feed aslant are judged. If any abnormality occurs, an abnormality display lamp will light up and the printing will be stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying device used in an image forming apparatus such as a printer or a copying machine, and more particularly to a sheet conveying device for preventing image loss.

[0002]

2. Description of the Related Art In an image forming apparatus such as a laser printer, a toner image is formed on the surface of a drum-shaped or belt-shaped photosensitive member that rotates at a constant speed, and the toner image is conveyed at the timing of image formation. The image is transferred onto the paper.

At the time of this image transfer, if the timing of the sheet conveyance is wrong, the center of the image is deviated from the center of the sheet, or a part of the toner image is not transferred onto the sheet and the image is lost. Occurs.

Therefore, in such an image forming apparatus, a paper sensor is provided in the paper conveyance path, and the paper conveyance timing is controlled accurately based on the output of the paper sensor. .

In addition, in Japanese Patent Laid-Open No. 59-48344, for the purpose of detecting skew of the paper in addition to the timing of conveying the paper, the paper is conveyed on the paper conveying path at right angles to the paper conveying direction. At least one sheet detection unit is provided near both ends in the width direction, and the time from the start of sheet conveyance until the sheet detection unit detects the sheet is compared with a reference value. A recording device that issues a warning is disclosed.

[0006]

However, in the apparatus described in the above publication, it is necessary to dispose the sheet detecting means, that is, the sheet sensor, at both ends of the sheet in the width direction, so that it is possible to cope with sheets of various sizes. In order to do so, a large number of paper sensors must be provided for each size, which is not realistic.

An object of the present invention is to provide a sheet conveying device capable of detecting the sheet conveying timing and the sheet skew with a small number of sheet sensors.

[0008]

SUMMARY OF THE INVENTION A sheet conveying apparatus of the present invention is arranged in a sheet conveying path toward an image forming section in the vicinity of both widthwise ends of a smallest size sheet which is arranged in a direction orthogonal to the sheet advancing direction. And at least one sheet detecting means for detecting the time from the time when the sheet passes a certain reference point in the sheet conveying path to the time when the passage of the sheet is detected by the sheet detecting means. And a conversion unit for converting the time detected by the time detection unit into a value according to the size of the paper.

[0009]

1 is a schematic cross-sectional view schematically showing an image forming apparatus to which a sheet conveying apparatus of the present invention is applied. A charger 2, an exposure device 3, a developing device 4, a transfer device 5, a cleaning device 6 and the like are sequentially arranged around the drum-shaped photoreceptor 1. Further, below the photoconductor 1, paper feed cassettes 9a and 9b having paper feed rolls 7a and 7b and size sensors 8a and 8b, respectively, are arranged. Papers 10a and 10b of the same size or different sizes are stored in the paper feed cassettes 9a and 9b. Further, a registration gate 1 which is driven to open and close by a gate solenoid (not shown in FIG. 1) is provided in the vicinity of the facing portion of the photoconductor 1 and the transfer device 5.
1, register roll 12, and pair of paper sensors 13, 14
Is provided.

FIG. 2 is an explanatory view showing the relationship of the arrangement positions of the pair of sheet sensors 13 and 14 with respect to the sheet. The pair of paper sensors 13 and 14 are arranged at both widthwise end portions of the smallest size paper that can be conveyed. 2A shows the arrangement position of the sheet sensors 13 and 14 when the reference position of the sheet is one side edge in the width direction of the image formable range, that is, in the side registration method. (B) shows the arrangement position of the sheet sensors 13 and 14 when the reference position of the sheet is the center of the image formable range in the width direction, that is, in the case of the center registration method.

FIG. 3 is a block diagram schematically showing an electric circuit for controlling the operation of the above-mentioned image forming apparatus. The size sensors 8a and 8b and the paper sensors 13 and 14 shown in FIG. 1 are connected to the CPU 15. This CP
ROM1 in which control programs are written in U15
6, a RAM 17 used as a work area, etc., various buttons for giving various instructions to the image forming apparatus, and a user interface 18 including various lamps and a display device for displaying the operating state of the image forming apparatus are connected. Has been done. The various buttons in the user interface 18 include a print start button 18a, and the various lamps include an abnormality display lamp 18b. In addition, in FIG. 3, only the print start button 18a and the abnormality display lamp 18b are shown for simplicity.
Illustration of other parts is omitted. Further, an image forming control device 20 for controlling each image forming mechanism of the image forming apparatus is connected to the CPU 15 via an interface 19. The image formation control device 20 includes a cash register 1
It includes a gate solenoid 20a for driving the opening and closing of 1. Although the image forming control device 20 includes other components, only the gate solenoid 20a is shown here for the sake of simplicity.

Next, the operation of the above-described image forming apparatus will be described. FIG. 4 is a flowchart showing the operation of the image forming apparatus. Further, FIG. 5 is a timing chart for explaining the paper detection operation in the image forming apparatus.

First, when the paper feed cassettes 9a and 9b are inserted (step 101), the size sensors 8a and 8b for detecting the shape of the paper feed cassette, the identification member (identification pin) and the like determine the paper size (step). 102), the lead edge length is stored in the RAM 16. Next, when the print start button 18a of the user interface 18 is pressed to instruct to start printing, the image forming apparatus starts the image forming operation (step 103). That is, the photoconductor 1
Is uniformly charged by the charger, the surface of the photoconductor 1 is exposed by the laser light from the exposure device 3, and an electrostatic latent image corresponding to the image to be output is formed. This electrostatic latent image is developed. The toner image is formed on the surface of the photoconductor 1 by being developed by a container. On the other hand, the paper fed by the paper feed roll 7a or 7b from the paper feed cassette 9a or 9b is temporarily stopped at the registration gate 11. The registration gate 11 is opened in synchronization with the rotation of the photoconductor 1 at such a timing that the toner image on the photoconductor 1 is transferred onto the sheet (step 10).
4, refer to time t0 in FIG. 5 (a)). The registration gate solenoid 20a is turned on (gate closed) after a fixed time elapses from the start of sheet feeding. The paper starts to move at the same time when the gate is opened, and after passing through the registration roll 12, passes through two paper sensors 13 and 14 arranged near both ends of the smallest paper that can be carried in a direction orthogonal to the carrying direction, and the photoconductor 1 The upper toner image is transferred onto the sheet by the transfer device 5. 5B and 5C show the paper sensors 13 and 1.
4 shows an example of the output of FIG. The toner remaining on the photoconductor 1 is removed by the cleaning device 6 to prepare for the next image forming cycle.

At the time of this image formation and transfer, the times T1 and T2 from the gate opening to the passage of the paper through the paper sensors 13 and 14 are measured (step 105), and these values are measured at the center or both ends of the paper. The value is converted into a value (step 106), and a timing shift due to paper delay or advance is determined. At the same time, the skew (skew) of the paper is also determined, and if there is an abnormality in either one, the abnormality display lamp is turned on and printing is stopped.

Next, the above conversion method and determination method will be described.

Here, when the time measurement start timing is the paper feed start time, in the case of an apparatus having a plurality of paper feed cassettes like this embodiment, the reference value must be determined for each paper feed cassette. The inconvenience occurs. Therefore, the time measurement start timing is the operation start timing or operation end timing of the operation body located upstream of the paper sensors 13 and 14 after the conveyance paths are all merged, or the paper detection timing of the existing paper sensor. It is desirable to use. In the present embodiment, the time at which the registration gate 11, which is an operating body located on the upstream side of the sheet sensors 13 and 14 after the conveyance paths are all joined, is set as the time measurement start timing. However, the present invention is not limited to this, and it is also possible to use the outputs of the paper feed sensor and the registration sensor provided in the middle of the conveyance path, the on / off timing of the registration roll drive motor, and the like.

As described above, there are a side registration system and a center registration system as the paper conveyance type,
Both cases will be described.

[1] In case of side registration method The variables and symbols used here are defined as follows.

T1: Time from gate opening to ON of first paper sensor 13 T2: Time from gate opening to ON of second paper sensor 14 a: Distance from side register to first paper sensor 13 b: From side register Distance to second paper sensor 14 M: Center of leading edge of paper of arbitrary size P: Lead edge end of paper of arbitrary size (side registration side) Q: Lead edge end of paper of arbitrary size (side registration) Opposite side) TM: M is from gate open to first paper sensor 13-
Time until passing between the second sheet sensors 14 TP: P from gate open to first sheet sensor 13-
Time until passing between second sheet sensors 14 TQ: Q is from gate open to first sheet sensor 13-
Time until passing between the second sheet sensors 14 C: Length of lead edge of sheet of arbitrary size Since the conveyance speed of the sheet is constant, in the case of the side registration method, it is separated from the side registration by an arbitrary distance x. Letting T be the time from the gate opening to the point on the lead register passing between the first sheet sensor 13 and the second sheet sensor 14, T is a linear function of x, and T1, T2, a, and b are Can be used to represent:

[0020]

[Equation 1] This time T is converted to (1) the value at the center of the lead edge or (2) the value at both ends of the lead edge, as described below, in order to detect the timing shift and the skew shift. To be done.

(1) The central portion of the lead edge (x = C /
The time TM when converted into the value of 2) can be expressed as follows.

[0022]

[Equation 2] The difference when this TM is compared with the reference value TA, that is,
If ΔTM = −TA−TM− is smaller than the specified value ΔTA, it is determined that the timing shift due to the delay or advance of the paper is within the allowable range. If Δt = -T2-T1- is smaller than the specified value Δt0 of the skew, it is determined that the skew deviation is within the allowable range. If either of these conditions is not satisfied (steps 107 and 108), it is determined to be abnormal, and the abnormality display lamp is turned on (step 109) and printing is stopped (step 110). If there is no abnormality, printing is continued (step 11
1) When the printing is finished, the process is finished (step 112).

(2) Both ends of the lead edge (x = 0, x
= C), the times TP and TQ when converted into a value can be expressed as follows.

[0024]

(Equation 3) Differences when these TP and TQ are compared with the reference value TB, that is, ΔTP = −TB−TP−, ΔTQ = −T
If both B-TQ- are smaller than the specified value ΔTB, it is determined that the timing deviation is within the allowable range. Also,
Regarding skew, as in (1), Δt = −T2−
When T1− is smaller than the specified value Δt0 of the skew, it is determined that the deviation of the skew is within the allowable range.

[2] In the case of the center registration method As in the case of the side registration method, the relationship between the time T and the distance x can be expressed as follows.

[0026]

(Equation 4) In the center register method as well as in the side register method, from this time, the value at the center of the lead edge, or
The values are converted into values at both ends of the lead edge, and a timing shift and a skew shift are detected.

[0027]

As described above, in the present invention, the sheet conveyance timing detected by the pair of sheet sensors arranged at a predetermined position is converted into a value according to the size of the sheet, and the value after the conversion is converted. Is compared with the reference value to detect the timing shift and the skew shift, so that it is possible to detect the transport state of a large number of sheets of paper with a small number of paper sensors.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view schematically showing an image forming apparatus to which a sheet conveying device of the present invention is applied.

FIG. 2 is an explanatory diagram showing a relationship of arrangement positions of the pair of sheet sensors with respect to a sheet.

FIG. 3 is a block diagram schematically showing an electric circuit for controlling the operation of the image forming apparatus described above.

FIG. 4 is a flowchart illustrating an operation of the image forming apparatus.

FIG. 5 is a timing chart for explaining a sheet detection operation in the image forming apparatus.

[Explanation of symbols]

1 ... Photosensitive member, 2 ... Charging device, 3 ... Exposure device, 4 ... Developing device,
5 ... Transfer device, 6 ... Cleaning device, 7a, 7b ... Paper feeding roll, 8a, 8b ... Size sensor, 9a, 9b ... Paper feeding cassette, 10a, 10b ... Paper, 11 ... Registor,
12 ... Register roll, 13, 14 ... Paper sensor, 15 ... C
PU, 16 ... ROM, 17 ... RAM, 18 ... User interface, 19 ... Interface, 20 ... Image forming control device

Claims (5)

[Claims] 1. A paper detection means, wherein at least one paper detection unit is provided in the vicinity of both ends in the width direction of a minimum-size paper which is arranged in a direction orthogonal to the paper traveling direction in a paper conveyance path toward an image forming unit. A time detection means for detecting a time from the time when the paper passes a certain reference point in the paper conveyance path to the time when the paper detection means detects the passage of the paper, and the time detected by the time detection means And a conversion means for converting the value into a value according to the size of the paper. 2. The sheet conveying apparatus according to claim 1, wherein the converting means converts the detected time into a value in the widthwise central portion of the paper of each size. 3. The sheet conveying apparatus according to claim 1, wherein the converting means converts the detected time into a value at both widthwise end portions of a sheet of each size. 4. The sheet conveying apparatus according to claim 1, wherein the reference point is located on the upstream side of the sheet sensor after the plurality of conveying paths have all merged. 5. The sheet conveying apparatus according to claim 4, wherein the reference point is a position of a registration gate that determines a timing of feeding the sheet toward the image forming unit.