JP2003276905A - Sheet detecting device, sheet detecting method, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet detecting device capable of improving a reading speed to realize high speed POD products. <P>SOLUTION: An image reading part 205 in a CIS 204 has a plurality of chips 1-n each of which incorporates a group of light receiving elements and a shift register. Based on a shift pulse inputted from the outside as a trigger, all the data in the chips 1-n are loaded to the shift registers 211b-218b. Synchronized with an external clock, the shift register 211b outputs set data outside through an output channel 1, and the shift register 218b outputs them outside through an output channel 218b. In the case image data are outputted through the output channel 1, the detection time for one chip is (operating clock) ×(the number of the light receiving elements per chip). When the number of the chips is n, detection action is completed in time of 1/n as compared to conventional devices. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet for detecting the presence / absence of a sheet to be conveyed in a print position adjusting mechanism of an image forming apparatus such as an LBP (laser beam printer) or a copying machine using an electrophotographic technique. The present invention relates to a detection device, a sheet detection method, and an image forming apparatus.

[0002]

2. Description of the Related Art First, a sheet detecting method in a print position adjusting mechanism of a conventional image forming apparatus will be described. FIG. 19 is a side view showing a print position adjusting mechanism in a conventional image forming apparatus. 20 is a plan view showing a part of the print position adjusting mechanism of FIG. In the figure, 1301 is a photosensitive drum. A laser 1302 forms a latent image on the photosensitive drum 1301. Reference numeral 1303 denotes a registration clutch (registration roller) that determines the paper feed timing.

Reference numeral 1304 is a paper sensor for detecting the leading edge of the conveyed paper. Reference numeral 1305 denotes a deviation amount detection sensor that detects the deviation amount of the lateral edge in the direction perpendicular to the sheet feeding direction. Further, 1401 is an output sheet. 1403 indicates the paper feeding direction.

In the conventional print position adjusting mechanism (conventional example 1) having the above structure, the CPU (not shown) acquires the vertical position (lateral edge position) of the sheet detected by the shift amount detection sensor 1305. The vertical (main scanning direction) writing timing of the laser 1302 is adjusted by the difference between the vertical position of the sheet detected by the shift amount detection sensor 1305 and the theoretical vertical position of the sheet. Here, as the deviation amount detection sensor 1305, a mechanical flag that is driven in the transport direction, or an image sensor such as CCD or CIS is used. Further, the CPU is the paper sensor 130.
Acquire the paper position in the paper feed direction detected by 4.
The data request signal is output to the image control circuit (not shown).

Then, the image control circuit transfers the image data to a laser control circuit (not shown) for driving the laser 1302 in accordance with the timing of the data request signal.
The laser 1302 rotates the photosensitive drum 13 rotating in the direction of the arrow in the drawing at the timing when the paper reaches position P in the drawing.
Write the image to 01. This writing position coincides with the beginning of the image formed when the leading edge of the sheet is conveyed to the Q position in the figure. Further, the distance from the position of the paper sensor 1304 to the P position corresponds to the distance that the paper advances within the processing time such as setting in the laser control circuit. The paper sensor 1304 has
A mechanical flag or a reflection type optical sensor is used.

FIG. 21 is a side view showing a print position adjusting mechanism in another conventional image forming apparatus. This print position adjusting mechanism (conventional example 2) is not provided with a paper sensor for detecting the paper position in the paper feeding direction, as compared with the print position adjusting mechanism of FIG. Other configurations such as the shift amount detection sensor are the same as those in FIG.

In this print position adjusting mechanism, the conveyed sheet temporarily waits in the registration clutch 1303.
The registration clutch 1 is activated by an ON signal from the conveyance control unit.
303 is connected and paper conveyance is restarted. After the lapse of a predetermined time of this ON signal, the image data is transferred from the image control circuit to the laser control circuit that drives the laser 1302.

When the paper transport speed is constant, the time Treg during which the paper is transported from the position of the registration clutch 1303 to the P position is fixed, and the processing time Tal for setting the laser control circuit is also fixed. Therefore, the transfer timing of the image data with respect to the laser 1302 is determined from the ON signal of the registration clutch 1303 to (Treg + Ta
l) It will be after hours.

FIG. 22 is a diagram showing how an image is formed at a desired position on a sheet by the print position adjusting mechanism of the above-mentioned conventional examples 1 and 2. In the figure, 901 indicates a desired position on the sheet 1401, and 902 indicates an image.

[0010]

However, the above-described sheet detecting method in the conventional print position adjusting mechanism has the following problems, and its improvement has been demanded. In other words, as the speed of image forming apparatuses has increased in recent years, the speed at which the paper is conveyed has also increased, so the reading performance of the paper sensor that detects the position of the paper in the conveying direction has become a problem. With an inexpensive mechanical sensor, the error is large, and the reading error appears as a deviation of the image position.

The optical sensor as the paper sensor 1304 shown in Conventional Example 1 generally has a rise time of several msec.
It is on the order, and in a high-speed image forming apparatus, the detection accuracy is greatly affected.

On the other hand, as shown in the conventional example 2, when the timing control is performed by the ON signal of the registration clutch 1303, the variation of the coupling time due to the variation of the element is 10 msec or more even in the clutch component single item level, and the image forming apparatus has a When incorporated, the mounting accuracy and variations due to increased load due to paper dust and the like are added as an error as they are, so that the detection accuracy is significantly reduced.

FIG. 23 is a diagram showing a decrease in printing accuracy caused by a detection error. Transport speed is 800 mm / s
ec, if the error in the detection time of the paper sensor 1304 in the paper transport direction is ± 2 msec, the printing error of the paper is
800 mm / sec x (± 2 msec) = ± 1.6 mm
Becomes FIG. 24 shows (A) no error, (B) error: +1.
It is a figure which shows each output image in 6 mm and (C) error: -1.6 mm. High-speed POD (print on demand)
In the market, the printing accuracy is required to be at least within ± 0.2 mm, and the sheet detection method in the conventional print position adjusting mechanism cannot achieve the printing accuracy particularly in the paper transport direction. Furthermore, with mechanical or optical sensors, there is flutter due to chattering,
There is a problem that the time for performing the removal processing by software is not a high-speed machine.

For the above reason, a method of detecting the sheet position in the sheet conveying direction by using a CCD or CIS image sensor is also proposed, but in the case of CCD, at the present stage, an optical reduction system CCD is formed in the conveying path. This is physically difficult, resulting in a significant cost increase.

FIG. 25 is a block diagram showing the structure of a conventional CIS. CIS is an emitter follower circuit (output section)
1316 and a plurality of chips (1 to n) 1311 to 13
It is composed of 14. Light receiving element groups 1311a to 1314a and shift registers 1311b to 1314b are incorporated in the chips 1311 to 1314, respectively. In this CIS, the light receiving element groups 1311a to 1314
a converts the received light energy into analog data (potential), and uses a load signal input from the outside as a trigger to shift all data from chips 1 to n to the shift register 1311.
b to 1314b. Shift register 1311
b to 1314b shift the set data to the output side in synchronization with the external clock (CLK). The output value of the chip 1 becomes the input signal of the shift register of the adjacent chip 2. The shift operation is normally continued until the transfer of all the data to the output unit 1316 including the emitter follower circuit is completed.

This CIS (contact image sensor)
In this case, the operating clock frequency of the sensor itself is about 5.5 MHz at the maximum, so the reading speed is 1 mse.
c / line, which is slow. Therefore, the printing error is 800
mm / sec × (± 1 msec / line) = ± 0.8
mm, which cannot satisfy the demands of the high-speed POD market.

Recently, in order to improve the CIS reading speed, the apparent operating speed is increased by dividing the internal chips evenly into N and outputting them in parallel.
FIG. 26 is a diagram showing parallel output of CIS in which the internal chip is divided into N. C consisting of 8 internal chips (N = 8)
The IS is evenly divided into 4: 4, and two channels are output in parallel by setting the reading range of chips 1 to 4 as output 1 and the reading range of chips 5 to 8 as output 2. CIS has emerged that can read about twice as fast as the channel output type.

However, even in the case of this CIS, the reading speed is on the order of msec, and the maximum is 600 μse.
It is about c / line. Therefore, the printing error is 80
0mm / sec × (± 600μsec) = ± 0.48m
m, which cannot meet the demands of the high-speed POD product market. It is assumed that the resolution of the CIS is 600 dpi.

Even if the reading gradation is sacrificed,
It is presumed that a considerable amount of technical force will be required from the viewpoints of the storage time of the light receiving element and the residual charge of the reading element in order to develop a custom CIS with an operating clock frequency of several tens of MHz. Leads to up,
Furthermore, the cost is increased because it is a custom product.

Therefore, according to the present invention, the reading speed can be improved and a high-speed POD product can be realized without making difficult or complicated changes such as increasing the CIS operation clock speed. An object is to provide a forming device.

[0021]

In order to achieve the above object, a sheet detecting apparatus of the present invention is a sheet detecting apparatus for detecting the presence or absence of a conveyed sheet based on a signal from a reading means, The reading means comprises a plurality of light receiving elements, and a plurality of chips each incorporating a light receiving element group that outputs a signal according to external light and a shift register that sequentially transfers the signals output from the light receiving element group. Then
The plurality of chips have a first detection area for detecting that the conveyed sheet has reached a predetermined position, and a number of chips larger than the number of chips in the first detection area, Is divided into a plurality of regions including a second detection region for detecting the lateral end position of the, and a signal output from the shift register at the final stage in the first detection region,
A signal output from the final stage shift register in the second detection area is output to the outside through the second transfer means and is output to the outside through the first transfer means. Detecting that the conveyed sheet has reached a predetermined position based on the output signal,
The lateral edge position of the conveyed sheet is detected based on a signal output from the second transmission unit.

The image forming apparatus of the present invention generates the print start timing in accordance with the sheet detection means for detecting the presence or absence of the conveyed sheet based on the signal from the reading means and the detection signal from the sheet detection means. In the image forming apparatus provided with a timing control means for performing, and an image forming means for forming an image at a predetermined position of the conveyed sheet in accordance with the print start timing, the reading means includes a plurality of light receiving elements, It has a plurality of chips each incorporating a light receiving element group that outputs a signal according to external light and a shift register that sequentially transfers the signals output from the light receiving element group, and the plurality of chips are carried by the carrier. A first detection area for detecting that the sheet has reached a predetermined position, and a number of chips larger than the number of chips in the first detection area And a second detection area for detecting the lateral edge position of the sheet, and is divided into a plurality of areas, and a signal output from the final stage shift register in the first detection area is The signal output from the final stage shift register in the second detection region is output to the outside through the second transmission unit, and the sheet detection unit outputs the signal to the outside through the first transmission unit. Based on the signal output from the first transmission means, it is detected that the conveyed sheet has reached a predetermined position, and the second sheet is detected.
The lateral edge position of the conveyed sheet is detected based on the signal output through the transmission means.

The sheet detecting method of the present invention comprises a plurality of light receiving elements, and a light receiving element group for outputting a signal according to external light,
And a sheet detecting method for detecting the presence or absence of a conveyed sheet based on a signal from a reading unit having a plurality of chips each having a built-in shift register for sequentially transferring signals output from the light receiving element group. , The plurality of chips has a first detection area for detecting that the conveyed sheet has reached a predetermined position, and a number of chips larger than the number of chips in the first detection area, The sheet is divided into a plurality of areas including a second detection area for detecting the lateral edge position of the sheet, and a signal output from the shift register at the final stage in the first detection area is transferred to the first transmission area. A first output step of outputting to the outside through a means;
Based on the second output step of outputting the signal output from the final stage shift register in the detection area of No. 2 to the outside through the second transfer unit, and the signal output from the first transfer unit. A first detecting step of detecting that the conveyed sheet has reached a predetermined position, and a second detecting step of detecting a lateral end position of the conveyed sheet based on a signal output through the second transmission means. And a detection step of.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a sheet detecting device, a sheet detecting method and an image forming apparatus of the present invention will be described with reference to the drawings.

[Overall Configuration] FIG. 1 is a diagram showing the configuration of an image forming apparatus according to an embodiment. The image forming apparatus includes an image forming apparatus main body 10, a folding device 40, and a finisher 50. In addition, the image forming apparatus main body 1
Reference numeral 0 is composed of an image reader 11 for reading a document image and a printer 13.

The image reader 11 includes a document feeder 1
2 is installed. The document feeder 12 feeds the documents set upward on the document tray 12a one by one in the left direction in the figure from the first page, and conveys them onto the platen glass through a curved path to a predetermined position. The original is read by stopping at the position and scanning the scanner unit 21 from the left side to the right side in this state. After reading, the document is discharged toward the external discharge tray 12b.

The reading surface of the original is the scanner unit 21.
The reflected light from the document is guided to the lens 25 via the mirrors 22, 23 and 24. The light that has passed through the lens 25 is the image sensor 2
An image is formed on the image pickup surface of 6.

Then, while the image of the original is read by the image sensor 26 line by line in the main scanning direction, the entire image of the original is read by conveying the scanner unit 21 in the sub scanning direction. The optically read image is converted into image data by the image sensor 26 and output. The image data output from the image sensor 26 is subjected to predetermined processing in an image signal control unit (image processing circuit) (not shown), and then input as a video signal to an exposure control unit (laser control circuit) (not shown) of the printer 13. To do.

The exposure controller of the printer 13 modulates the laser light output from the laser element (not shown) based on the input image data, and the modulated laser light is scanned by the polygon mirror 27. , Lens 28,
It is irradiated onto the photosensitive drum 31 via 29 and the mirror 30.

An electrostatic latent image corresponding to the scanned laser beam is formed on the photosensitive drum 31. The electrostatic latent image on the photosensitive drum 31 is visualized as a developer image by the developer supplied from the developing device 33. In addition, at the timing synchronized with the start of laser light irradiation, each of the cassettes 34, 3
Paper is fed from 5, 36, 37, the manual paper feed unit 38, or the double-sided conveyance path, and conveyed to the image forming unit via the registration rollers.

This paper is composed of the photosensitive drum 31 and the transfer roller 3.
The developer image formed on the photosensitive drum 31 by being conveyed to and from the transfer roller 9 is transferred onto the paper fed by the transfer roller 39. The sheet on which the developer image has been transferred is conveyed to the fixing unit 32, and the fixing unit 32 fixes the developer image on the sheet by heat-pressing the sheet. The paper that has passed through the fixing unit 32 is
The paper is ejected from the printer 13 to the outside (folding device 40) via the flapper and the ejection roller.

Here, when the sheet is discharged with the image forming surface thereof facing downward (face down state),
The sheet that has passed through the fixing unit 32 is temporarily guided into the reversing path by the flapper switching operation, and after the trailing edge of the sheet has passed the flapper, the sheet is switched back and ejected from the printer 13 by the ejection roller.

When a hard paper such as an OHP sheet is fed from the manual paper feed section 38 and an image is formed on this paper, the image forming surface is directed upward without guiding the paper to the reversing path ( Discharge with the discharge roller in the face-up state.

Further, when double-sided recording for forming images on both sides of the sheet is set, the sheet is guided to the reverse path by the switching operation of the flapper and then conveyed to the double-sided conveyance path, and then to the double-sided conveyance path. The fed paper is fed again between the photosensitive drum 31 and the transfer portion at the timing described above.

The sheet discharged from the printer 13 is sent to the folding device 40. The folding device 40 performs a process of folding a sheet into a Z shape. For example, in case of A3 size or B4 size sheet and folding process is specified,
Folding processing is performed by the folding device 40, and in other cases, the sheet discharged from the printer 13 passes through the folding device 40 and is sent to the finisher 50. The finisher 50 is provided with an inserter 90 for feeding a special sheet such as a cover sheet or a slip sheet to be inserted into a sheet on which an image is formed. The finisher 50 performs various processes such as bookbinding, binding, and punching.

Although the photosensitive drum is used as the image carrier of the image forming apparatus here, it may be a photosensitive belt.

[Paper feeding timing and image writing timing] FIG. 2 is a diagram showing a print position adjusting mechanism arranged in a paper conveying path to the photosensitive drum. In the figure, 205
Is a paper transport path. Reference numeral 31 is the photosensitive drum described above. A laser element 202 forms a latent image on the photosensitive drum 31. The layout of the laser element 202 is drawn for convenience, and differs from the actual layout. Reference numeral 203 denotes a paper carrying roller (registration roller), which temporarily abuts the paper sent along the paper carrying path 205 against the registration roller 203 and causes the paper to stay therein, and then, at a predetermined paper feeding timing, the photosensitive drum 31. Send to the side. An image reading sensor (image sensor) 204 reads an image to detect the position of the sheet, and is composed of a photoelectric conversion element array such as CCD or CIS. In this embodiment, a CIS (contact image sensor) is used. This CIS20
4 is disposed on the photosensitive drum side, which is separated from the registration roller 203 by a distance L1 (see FIG. 3).

FIG. 3 is a diagram showing the relationship between the paper feed timing and the image forming timing. When performing the image forming operation,
As described above, the paper sent out from the registration roller 203 is conveyed to the photosensitive drum 31 side along the paper conveyance path 205. At this time, the sheet fed from the registration roller 203 is controlled to irradiate the photosensitive drum 31 with laser when the sheet advances by L1 + L2. For example, after the registration roller 203 is turned on, the sheet is L1 + L
A timer counts the time corresponding to the time of two steps, and the laser is applied to the photosensitive drum 31 as the time elapses.

In order to adjust the write start position with higher accuracy, the timing of the paper in the paper feed direction (for convenience, referred to as the sub-scanning direction) and the direction perpendicular to this paper feed direction (for convenience, referred to as the main scanning direction). ), It is necessary to control the writing by laser light.

That is, the start time of image formation is determined after the leading edge position of the paper is detected by the CIS 204, and the writing by the laser is started when the paper advances by the distance L2. You can adjust the export position. Therefore, the distance L2 is the timing at which the CIS detects the leading edge of the sheet and then detects the deviation between the sheet feeding direction and the direction perpendicular to this sheet feeding direction, and the laser light writing timing in each direction. It is necessary to have at least a distance corresponding to the time to set.

Further, in a normal image forming apparatus, since the sheet conveying speed and the rotation speed of the photosensitive drum 31 are set to be equal, the nip position between the transfer roller 39 and the photosensitive drum 31 is advanced from the position advanced from the CIS 204 by the distance L2. This means that the distance to the transfer position on a certain sheet is equal to the circumferential distance on the photosensitive drum 31 from the laser writing position to the transfer position on the sheet.

When the CIS 204 detects the lateral edge position (horizontal registration) of the paper, the beam detector (BD)
At a distance L3 from 108 to the lower end of CIS 204, CI
The distance (x + L3) is calculated by adding the distance x from the lower edge of S204 to the lateral edge position of the paper, and the beam detector 108
After the laser light is detected by the method, the laser light is shaken in the main scanning direction by the calculated distance, and then the writing by the laser is started, whereby the writing position of the image in the main scanning direction can be adjusted.

The timing control unit (TCU) 105, which will be described later, adjusts the writing position of the image in the sub-scanning direction and the main-scanning direction by the laser light. That is, the TCU 105 turns on the registration roller 203 to start the conveyance of the sheet, and then the CCU
The writing start timing is output to the laser control circuit 27 based on the detection signal from the IS 204. Laser control circuit 2
Reference numeral 7 drives the laser element 202 based on an image signal sent from an image processing circuit (not shown) in synchronization with the writing timing output from the TCU 105.

[CIS Configuration] FIG. 4 is a diagram showing the configuration of the CIS 204. The CIS 204 is the image reading unit 2
05 and the LED light emitting section 206. The image reading unit 205 includes a plurality of chips (1 to n) 211 to 2 in which a light receiving element group and a shift register are built in one chip.
18 and outputs two signals to the outside through the output channel 1 of the chip (1) 211 and the output channel 2 of the chip (8) 218.

In the CIS 204, the received light energy is converted into analog data (potential), and a load signal input from the outside (TCU 105 described later) is used as a trigger to store all data in the chips 1 to n.
11b-218b. Shift register 21
1b shifts the set data in synchronization with an external clock (CLK), and its output signal is output to the outside through an output channel 1. On the other hand, the shift register 212
The outputs of b to 217b are respectively connected to the shift registers of the next stage, and the shift registers 212b to 218b shift the data set therein to the output side in synchronization with the external clock (CLK), and the shift register of the final stage. The output signal from 218b is output to the outside through the output channel 2.

In this embodiment, when the output signal output through the output channel 1 is used, the detection operation for one chip can obtain the same effect as the detection operation for one line. The detection time is 1 operation clock (CLK)
It is the number of light receiving elements per chip. Therefore, assuming that the number of chips is n, compared to the conventional CIS shown in FIG.
The detection operation is completed in 1 / n time. When the number of CIS chips is "8", the standard of the detection time is 1/8 =
0.125msec / line, PS = 800m
800 mm / sec × 0.12 even in the case of m / sec
It becomes 5 msec = 0.1 mm, and it becomes possible to sufficiently meet the demand of the POD market.

In this embodiment, eight chips are provided (n = 8). The light receiving element group in each chip is provided with 1000 reading pixels.

Of the 8,000 effective pixels to be read in the entire CIS, the chip (1) 2 located at the beginning is read for reading in the sub-scanning direction (leading edge and skew detection which will be described later).
1000 read pixels in 11 are used. On the other hand, for reading in the main scanning direction (lateral edge detection described later),
7000 in the remaining 7 chips (2-8) 212-218
Read pixels are used. Note that the total number of effective pixels of the plurality of chips is an example, and is not particularly limited and may be any number. Also, chip division,
The number of divisions is not limited to 1: (n-1) in this embodiment, and may be any number.

As described above, in the image reading section 205, when the leading edge is detected, the image signal detected by the light receiving element group 211a is the load signal (CIS-S) from the TCU 105.
H) once read to the shift register 211b, and then sequentially output from the shift register 211b to the outside as CIS data through the output channel 1 in accordance with the clock (CLK) from the TCU 105.

When the lateral edge detection is performed, the image signal detected by each of the light receiving element groups 212a to 218a is TCU1.
The shift signal from the shift register 2
12b to 218b, the shift register 2 is sequentially read according to the clock (CLK) from the TCU 105.
12b to 218b are output to the outside as CIS data through the output channel 2.

On the other hand, the LED light emitting section 206 includes an LED section 22 in which a plurality of LED groups connected in series are connected in parallel.
1 and connected to the cathode side of each LED group, each LE
LED current adjustment circuit 222 that adjusts the current flowing through the D group
Composed of. The LED current adjustment circuit 222 is a TCU.
According to the light amount control data from 105, the LED unit 2
The total LED light emission of 21 is adjusted.

FIG. 5 is a timing chart showing changes in the clock (CLK), load signal (CIS-SH) and image signal of the CIS 204 when the leading edge detection, the skew feeding detection and the lateral edge detection are performed. In the case of tip detection and skew detection (A and C in the figure), the light receiving element group 211a used is 1
This is for the chip, and the charge accumulation time repeatedly read by the load signal (shift pulse) becomes short. In this case, according to the light quantity control data from the TCU 105, LE
By setting the LED current value by the D-current adjustment circuit 222 to be high and increasing the LED light emission amount, a decrease in the S / N ratio of the read image is prevented. On the other hand, in the case of the lateral edge detection (B in the figure), the number of light receiving element groups 212a to 218a used is seven, and the charge accumulation time repeatedly read by the load signal becomes relatively long. In this case, TCU10
The S / N ratio of the read image can be maintained even if the LED current value by the LED current adjusting circuit 222 is set low by the light amount control data from 5, and the LED light emission amount is reduced.

Thus, in this embodiment, the CIS 20
4 is composed of 8 chips divided into 1: 7,
The area (Area) A corresponding to the chip 1 is assigned to the output channel 1, and the area (Area) B corresponding to the chips 2 to 8 is assigned to the output channel 2. Therefore, in the case of the leading edge detection and the lateral edge detection (area A), the frequency of the load signal (shift pulse) is eight times that of the conventional one, but in the present embodiment, the output channel 1, Since the configuration is such that 2 is switched, the reading speed for each line is half the frequency of the shift pulse, that is, 4 times faster than the conventional one.

FIG. 6 shows the CIS 20 for the paper passage area.
It is a figure which shows arrangement | positioning of No. 4. CIS 204 is paper 107
The reading pixels are arranged so as to be perpendicular to the transport direction of. In addition, one end of the CIS 204 is located at a substantially central position of the paper 107 passing therethrough, and the other end is located at a position beyond the lateral edge of the paper 107 passing therethrough.
Is placed. The chip (1) 211 is located on the substantially center side of the sheet 107 of the CIS 204, and the chip (8) 218 is located on the side beyond the lateral edge.

Then, in the case of the leading edge detection, as will be described later, by selecting the output channel 1 (area A) at the timing when the leading edge of the sheet approaches the CIS 204, the number of effective pixels is small and the edge of the sheet is short. Detect the part. Further, when the leading edge detection is completed, the output channel 2 (area B) is selected in order to perform the lateral edge detection for detecting the deviation amount of the sheet in the main scanning direction. The edge portion of the paper is detected at long intervals close to the number of effective pixels.

FIG. 7 is a diagram showing the leading edge detection area and the lateral edge detection area in the CIS 204. As described above, the leading edge (skew) detection region is included in the light receiving element group 211a in the CIS 204 located substantially on the center side of the sheet 107.
Corresponding to 000 pixels, the remaining read pixels in the CIS are not used while the leading edge (skew) is being detected (indicated by x in the figure). On the other hand, the lateral edge detection area is CIS204.
7 included in the remaining light receiving element groups 212a to 218a in
This corresponds to 000 pixels, and 1000 pixels of the light receiving element group 211a used for tip detection are not used during horizontal edge detection (indicated by x in the figure).

In this way, for the leading edge detection and the lateral edge detection, processing is performed so as to fetch only the necessary pixel data of the read pixels of the CIS 204, which are suitable for the respective detections, and data unnecessary for the respective detections is made as much as possible. I try not to capture it.

FIG. 8 is a diagram showing the maximum detection width of the CIS 204. The maximum paper width used in the image forming apparatus is Lma
x and the minimum paper width is Lmin, the maximum detection width X
Is approximately 1/2 (Lmax-Lmin), and it can be seen that the CIS 204 having such a maximum detection width X may be used.

Here, the usefulness when the CIS is used for tip (oblique) detection will be described. For example, the paper feed speed (P
S) is 800 mm / S, maximum detection width (X) is 100 m
m, main scanning / sub scanning resolution Ph and Pv are each 0.0
When set to 5 mm, the reading cycle of one sensor line = P
S / Pv = 16 KHz, sensor pixel number = X / Ph = 20
It becomes 00 dots, and VC is
LK = 16 KHz * 2000 dot = 32 MHz. That is, a sensor capable of operating at 32 MHz is required.

However, in the method shown in this embodiment, VCLK = 16 KHz by temporarily setting the number of pixels used for reading in the sub-scanning direction to 200 dots, which is 1/10.
* 200dot = 3.2MHz. That is, 3.2
A sensor operable at MHz can be used, and an inexpensive CIS can be adopted. Further, in the reading in the main scanning direction, since the clock VCLK is set to 3.2 MHz, it can be detected only once while the distance of 10 lines advances, but it may be delayed because it is the lateral edge detection.

Further, since a plurality of pixels are used in the main scanning direction as the pixel data used for the leading edge detection and the skew detection, as compared with the conventional single optical sensor or mechanical paper detection sensor, Since the sensor for detecting the leading edge is not required, the image forming apparatus can be made more compact by reducing the number of parts.

Then, by performing the lateral edge detection after the detection of the leading edge detection and the skew feeding detection, different methods can be adopted as the respective detection methods, and the detection accuracy is improved by the adoption of the detection methods suitable for the respective detections. It becomes possible to do.

In particular, in the leading edge detection, using the data of a part of a plurality of pixels in the main scanning direction contributes to the improvement of the detection accuracy. This is because the reading cycle is shorter and the pixel data density in the paper transport direction is higher than in the case where a plurality of all pixels are read with the same reading clock, and as a result, the detection accuracy is improved.

In the sequence, although the leading edge of the sheet is first detected by the CIS, if the leading edge detection and the lateral edge detection are simultaneously performed without first processing the sheet leading edge detection, the lateral edge is detected. For this purpose, it is necessary to read a plurality of all pixels of the CIS, and the cycle of tip detection becomes long, so that the tip cannot be detected with high accuracy. Therefore, processing in the order of detecting the horizontal edge after detecting the leading edge (detecting skew) is
Enables more accurate tip detection.

Furthermore, by separately performing the leading edge detection and the lateral edge detection, the detection processing can be set to the shortest time at each optimal detection cycle. Therefore, the conveyance distance corresponding to L2, which is the distance between the registration roller and the image forming unit. Can be shortened and the device can be made compact.

[Outline of Paper Detection Process] Here, an example of the paper detection process is shown. The image data read by the light receiving element group of the CIS 204 is transferred to the shift register by the load signal (shift pulse) according to the detection function as a trigger, and is shifted to the output channels 1 and 2 in synchronization with the operation clock (CLK). Will be done.

In the case of detecting the sub-scanning direction, image data is transferred from the light receiving element group 211a in the chip 1 to the shift register 211b by the shift pulse, and is shifted to the output channel 1. On the other hand, in the case of detecting the main scanning direction,
Image data is transferred from the light receiving element groups 212a to 218a in 8 to the shift registers 212b to 218b, and is shifted to the output channel 2 in the order of chip 8, chip 7, ..., Chip 2.

FIG. 9 is a diagram showing an example of a processing circuit from image reading by CIS to paper detection. CI
The image data sequentially read in S204 and output through the output channels 1 and 2 are sequentially transferred to the analog processor 701 in the control circuit, and the analog processor 7
A sample and hold circuit 702 inside 01 converts each pixel into analog level pixel data. further,
When the pixel data is converted into a digital value by the A / D conversion circuit 703, the main scanning direction averaging circuit 704 performs averaging processing in the main scanning direction.

FIG. 10 is a diagram showing an averaging process in the main scanning direction in the main scanning direction averaging circuit 704. In the figure,
An array of pixel data for one line output from the A / D conversion circuit 703 is shown. Here, the first pixel value is Data (1), the second pixel value is Data (2),
The xth pixel value is represented by Data (x). For example, the averaging process in the main scanning direction is performed for each line by averaging the pixel values in the x-th to (x + Hn) -th pixel range. Further, the main scanning average value HaveData
By the sub-scanning direction averaging circuit 705.
By averaging with, the sub-scanning average value VAveDat
get a. Then, according to the control signal 710, the selector 709 selects either the main scanning average value HaveData / the sub-scanning average value VAveData. In this embodiment, the control signal 710 is a detection function mode signal.

In the case of detection in the sub-scanning direction, the comparison circuit 706.
The main scanning average value HaveData is compared with the threshold Th which is the white level of the paper. On the other hand, in the case of detection in the main scanning direction, similarly, the comparison circuit 706 compares the sub-scanning average value VAveData with the threshold value Th which is the white level of the paper. In either case, the average value Ave
If Data> Th, the presence of paper is detected and AveD
When ata <Th, it is detected that there is no paper.

The averaging process is a process for removing noise and dust pixels to improve the detection reliability. However, since it is a process for a predetermined time, it does not cause a variation in timing control, and thus is performed in the present embodiment. It does not impose any restriction on the detection of the form paper. Further, the processing circuit shown in FIG. 9 is an example, and it goes without saying that it may be configured by other circuits as described later.

As described above, in this embodiment, one CI is used.
Using S204, it is possible to detect the leading edge of the paper in the sub-scanning direction and detect the lateral edge of the paper in the main scanning direction in a very short time. Then, by notifying the control circuit of the sub-scanning timing and the main scanning position information, it becomes possible to accurately record the image on the output paper.

Here, the usefulness in the case of the sub-scanning direction detection will be described. Paper feed speed (PS) is 800mm / S
And the maximum detection width (X) is 100 mm, and the main scanning resolution (Ph) / sub scanning resolution (Pv) are both 0.05 mm.
(600 dpi). Further, the CIS operation clock (CLK) is set to 5 MHz, which is considered to be the fastest among the current general-purpose products, and the number of pixels per chip (Pchi
p) is 800 pixels, the number of chips (Cv, Ch) is divided into 1 chip and 7 chips, and the number of output channels (Ou
Let t) be channel 2.

Conventionally, the reading speed of one line (Vo
ld) is 1 / CLK * Pchip * (Cv + Ch) /
Out = 0.64 msec / line. On the other hand, in the present embodiment, the reading speed (Vnew) is 1 / CL
K * Pchip * Cv = 0.16 msec / line.

Therefore, the detection accuracy improvement rate is Vold.
/ Vnew = 4, and the sub-scanning detection resolution (Dv) is
It becomes Vnew * PS (about 230 dpi). As described above, in the present embodiment, it is possible to improve the detection accuracy four times in the sub-scanning direction and to achieve high-precision detection with a resolution of 0.13 mm (about 230 dpi).

Regarding the main scanning reading, the reading speed (Vh) of the chips 2 to 8 is approximately Ph = 0.05.
mm, and can be detected with high accuracy regardless of the transport speed. The sub-scanning direction accuracy (Dh) when detecting the main scanning direction
Is Dv * Ch / Cv = 0.91 mm (about 33 dpi)
The output accuracy is required at the time of this detection is Vh (0.05 mm), and Dh does not have to be accurate.

[Configuration of Control Circuit] FIG. 11 is a block diagram showing the configuration of the control circuit. The control circuit 51 has an image processing circuit 52, a laser control circuit (V-CNT) 27, and a timing control unit (TCU) 105. The image processing circuit 52 stores an image memory (P) in which image data read by the image sensor 26 is stored.
-MEM) 56, and a CPU 57 that processes the image data stored in the image memory 56.

The laser control circuit 27 includes an image processing circuit 52.
A drive signal is output to the laser element 202 on the basis of a signal output in accordance with the image data. The drive signal is output to the laser element 202 in synchronization with the timing signal from the TCU 105. TCU105 is CIS204
The CIS control signal is output to, and the CIS data read by the CIS 204 is input, and a timing signal is output to the laser control circuit 27 based on the CIS data. This timing signal includes the vertical synchronization signal VSY.
NC, clock VCLK, horizontal sync signal HSYNC, a laser writing signal, a signal for driving the registration roller 203 (registration ON signal), and the like are included.

FIG. 12 is a block diagram showing the structure of the TCU 105. The TCU 105 has a counter (count).
r) 61, registration ON section 62, leading edge detecting section 63, lateral edge detecting section 64, CIS controller 65, CIS leading edge detecting short cycle setting section 66, leading edge error detecting section 67, CIS lateral edge detecting long cycle setting section 68. , A lateral edge error detection unit 69 and a sequence end setting unit (SEQ END) 70.

A counter 61 is activated by a sequence start signal (SEQ START) and counts clocks having a constant cycle. Cash register ON section 62
Turns on / off the driving of the registration roller 203.
The tip detection unit 63 uses the CIS input from the CIS 204.
The leading edge position of the paper is detected based on the data. The lateral edge detection unit 64 similarly detects the lateral edge position of the sheet based on the CIS data input from the CIS 204.

The CIS controller 65 uses the CIS204
In contrast, load signal (CIS-SH), clock (CI
S-CLK), selector signal, light quantity control data, etc.
Output the S control signal. In the CIS front end detection short cycle setting unit 66, a short cycle TS of the load signal (CIS-SH) input to the CIS 204 when the front end of the sheet is detected is set. On the other hand, in the CIS lateral edge detection long cycle setting unit 68, the long cycle TL of the load signal (CIS-SH) input to the CIS 204 is set when lateral edge detection of the paper is performed. In the present embodiment, this long cycle TL is 7 of the short cycle TS.
It's twice as long.

The leading edge error detecting section 67 includes a leading edge detecting section 63.
When the leading edge position of the sheet detected by is out of the predetermined range, an error signal (ERR) is generated. Similarly, the lateral edge error detector 69 generates an error signal (ERR) when the lateral edge position of the sheet detected by the lateral edge detector 64 is out of the predetermined range. Sequence end setting unit 70
Is set to the count value of the sequence for ending the printing of one sheet.

FIG. 13 is a block diagram showing the structure of the leading edge detector 63. The leading edge detection unit 63 has a plurality of edge circuits (EDDGE) 81, a timing generation circuit 82, a counter 83, and a skew feed amount setting unit 84. Each edge circuit (EDDGE) 81 includes a light receiving element group 2 of CIS204.
A register signal (REG1 that specifies the pixel position in 11a)
~ REGn) is input together with the CIS data. Then, when "paper out → paper is present" is detected at the pixel position designated in synchronization with the count signal from the counter 83, the edge circuit (EDDGE) 81 thereof detects an edge (EDDGE).
1-n) generate signals.

Timing generation circuit (TIMING) 82
Averages the generated plurality of edge (EDDGE1 to n) signals and outputs a leading edge detection signal (VREQ), and outputs the generated plurality of edges (EDDG).
The skew feeding amount is detected by using the E1 to n) signals, and the detected skew feeding amount is set in advance in the skew feeding amount setting unit 84 (RE).
If it is larger than G), the skew error signal (skew ER
R) is output. It should be noted that when performing tip detection, only a specific pixel may be used, but in the present embodiment, as described above, the influence of noise or the like is removed by using a plurality of pixels. Further, since a plurality of pixels are used in the tip detection, the tip detection accuracy is further improved as compared with the conventional single optical sensor or mechanical sensor.

The counter 83 has a load signal (CIS-S
H) and the clock (CIS-CLK), the count signal is output to the plurality of edge circuits (EDDGE) 81.

Since the skew feed amount of the sheet is detected based on the data representing the leading edge of the sheet read out from the plurality of read pixels by the leading edge detection means, the skew amount of the sheet is calculated and the leading edge position of the sheet is detected. They can be executed simultaneously and the processing time can be shortened.

Therefore, it is possible to accurately detect the skew feeding before the image is formed on the sheet, and it is not necessary to output the sheet on which the image of low print quality is formed by the skew feeding.

[Paper Feed / Image Forming Sequence] FIG. 14 is a timing chart showing the operation of the TCU 105.
The sheet 107 is conveyed to the registration roller 203 along the sheet conveyance path 205, and the registration roller 203 causes the sheet 10 to be conveyed.
The sheet feeding / image forming sequence of the present embodiment starts in the state where 7 is retained. Sequence start signal (S
(EQ START) is input to the counter 61, the counter 61 starts measuring a clock with a constant cycle. When the count value of the counter 61 reaches the timing a, the cash register O
The N section 62 sets the registration signal to the H level and the registration roller 2
Drive 03 on.

Then, when the count value reaches the timing b, the operation of the leading edge detection mode in the CIS 204 is started. In the leading edge detection mode, the TCU 105 outputs a load signal (CIS-SH) to the CIS 204 at the short cycle TS set in the CIS leading edge detection short cycle setting unit 66. As a result, the tip detection unit 63 reads only the CIS data from the light receiving element group 211a in the CIS 204.

When the leading edge of the sheet is detected when the count value reaches the timing c, the leading edge detection section 63 outputs the leading edge detection signal VREQ to the CIS controller 65 and starts the operation of the CIS 204 in the lateral edge detection mode. Let CIS controller 65 detects the tip detection signal VR
When the vertical synchronizing signal VSYNC corresponding to the EQ is output to the laser control circuit 27, the laser controlling circuit 27 takes the vertical margin into consideration based on the vertical synchronizing signal VSYNC from the CIS controller 65 and writes the position in the sub-scanning direction by the laser. Adjust. FIG. 15 is a diagram showing the writing start position adjustment by the laser. The count value is the timing c '(c'
If the leading edge position of the sheet is not detected even when the condition of &gt; c is reached, the CIS controller 65 outputs a leading edge error signal (leading edge ERR).

In the lateral edge detection mode, the TCU 105
Long cycle TL set in the S horizontal edge detection short cycle setting unit 68
Outputs a load signal (CIS-SH). As a result, the lateral edge detection unit 64 reads only the CIS data from the light receiving element groups 212a to 218a in the specific area within the CIS 204.

When the lateral edge position of the paper is detected when the count value reaches the timing d, the CIS controller 6
5 stops the operation of the CIS 204, and the horizontal synchronization signal H
The SYNC and the clock VCLK are supplied to the laser control circuit 27.
Output to. The laser control circuit 27 uses the horizontal synchronization signal HS.
Based on YNC and the clock VCLK, the write start position in the main scanning direction by the laser is set (see FIG. 15).
If the horizontal edge position is not detected even when the count value reaches the timing d ', a horizontal edge error signal (horizontal edge ERR) is output.

[Skew Detection] Next, the case where the skew amount is detected at the same time when the leading edge of the sheet conveyed by the CIS 204 is detected will be described. In the skew amount detection of the sheet, only the light receiving element group 211a in one chip of the CIS 204 is used similarly to the sheet leading edge detection. That is, CIS2
Of the 8000 pixels included in the entire detection area 04, 1000 pixels in the specific area are used to detect the front end and the skew amount. Hereinafter, the skew feed amount by such tip detection will be referred to as the tip skew feed amount.

FIG. 16 is a diagram showing the amount of skew of the leading edge obtained from the image read by the leading edge detection of the CIS 204. In the figure, the horizontal axis represents the conveyance distance in the sub-scanning direction, and the vertical axis represents the arrangement of pixels in the main scanning direction. Each read image divided into squares represents the average value of the images read from the read pixels having an arbitrary number of pixels (for example, 10 to 100 pixels). In the figure, the black image portion indicates that the paper is read. Indicates that The inclination of the boundary portion of the square shown in the black image indicates the amount of skew of the tip, as described later,
The value is represented by dH / dV.

Here, when the CIS 204 is attached so that the reading pixels are accurately aligned in the vertical direction with respect to the sheet conveyance direction, the calculated leading edge skew amount is equal to the skew amount of the sheet. Become. However, in practice,
The CIS 204 is not always correctly attached, and if the arrangement of the read pixels is slightly deviated from the vertical direction described above, it is necessary to perform the correction to calculate the front skew amount. Therefore, in this embodiment, it is assumed that the lateral edge detection of the paper is performed at at least two places, and the skew feeding amount (horizontal edge skew feeding amount) calculated from the lateral edge detection is an accurate skew feeding amount of the paper. , The skew amount at the tip is corrected based on that value. Then, after the correction value is obtained, the accurate skew feeding amount of the sheet is calculated only by the skew feeding amount by the leading edge detection.

FIG. 17 is a diagram showing a lateral edge skew amount obtained by lateral edge detection of the CIS 204. When at least two lateral edge positions are detected by the lateral edge detection of the sheet, the lateral edge positions X1 and X2 and the transport distance L between the lateral edge detections are used, and the lateral edge skew amount is (X1-X2). ) / L.

Using this lateral edge skew amount, a correction value for the tip skew amount due to the CIS mounting angle error is calculated, and when the calculated mounting angle error is equal to or greater than a predetermined value, the CIS mounting is adjusted again. To do. As described above, the skew amount detection is performed by the CIS.
This is done during the adjustment of the mounting angle or in the adjustment mode.

After the CIS mounting angle is adjusted, if the corrected leading edge skew amount obtained by detecting the leading edge of the paper is equal to or greater than a predetermined amount, a warning is issued to the operator and the subsequent image forming operation is performed. To stop.

Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations of these embodiments, and the functions shown in the claims or the configurations of the embodiments are not limited thereto. Any structure can be applied as long as it can achieve the function it has.

For example, in the above embodiment, the case where the chip division ratio is 1: 7 has been shown, but the present invention is not limited to this, and it goes without saying that any division ratio such as 2: 6, 3: 5 may be used. Is.

FIG. 18 is a diagram showing the structure of an image reading unit in another CIS. In the figure (A), the chip division ratio is 2:
The case of 2 is shown. Further, FIG. 3B shows the case where the chip division ratio is 1: 3. In the image reading unit of FIG. 1B, in addition to the shift pulse 1 for the chip 1,
The shift pulse 2 for the is added. This makes it possible to set the reading cycle of the read image data independently. Further, the change of the image reading section from the same figure (A) to the same figure (B) is realized relatively simply by changing the connection between each chip and the output channel and adding a shift pulse separately. Therefore, general-purpose product C
Since IS can be used, problems such as a longer development period and higher costs do not occur.

Further, in the present embodiment, the plurality of chips in the CIS are divided into two and the image data is output through the two channels. However, the plurality of chips are divided into three or more and the number of channels is increased. The image data may be output through the present invention, and the present invention is similarly applicable.

Further, in the above embodiment, the image forming timing in the sub-scanning direction is acquired by detecting the leading edge of the sheet by CIS. However, depending on the configuration of the apparatus, instead of detecting the leading edge, the trailing edge of the sheet is detected by CIS. The image forming timing in the sub-scanning direction may be acquired by.

Further, although the paper feed / image forming sequence is realized by the hardware circuit, it may be realized by software control by the CPU executing the program instead of the hardware circuit.

[0105]

According to the present invention, since the reading range of the reading means is set to an appropriate area according to the purpose of detection, it is possible to increase the detection speed in the paper transport direction. That is, even in a high-speed printing machine, the printing position accuracy can be guaranteed with high resolution.

Further, since the same reading means detects the conveyance direction of the sheet and the direction perpendicular to the conveyance direction, the number of parts can be reduced.

Further, the reading range can be changed only by changing the division ratio of the internal chip. For example, when the image reading unit is changed from 4: 4 to 2: 6, the distance between each chip and the output channel is changed. Since it can be realized relatively easily by simply changing the wiring, the general-purpose CIS can be used, and problems such as a longer development period and higher costs do not occur.

Further, by making the chip for performing the sheet detecting operation in the sheet conveying direction the minimum unit, the detecting speed can be maximized as much as possible.

As described above, the reading speed can be improved and a high-speed POD product can be realized without making difficult or complicated changes such as increasing the CIS operation clock speed.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an image forming apparatus according to an embodiment.

FIG. 2 is a diagram showing a print position adjusting mechanism arranged in a paper conveyance path leading to a photosensitive drum.

FIG. 3 is a diagram showing a relationship between a paper feed timing and an image forming timing.

FIG. 4 is a diagram showing a configuration of a CIS 204.

FIG. 5 is a clock (CLK) and load signal (CI) of the CIS 204 at the time of performing leading edge detection, skew feeding detection, and lateral edge detection.
5 is a timing chart showing changes in (S-SH) and image signals.

FIG. 6 is a diagram showing an arrangement of the CIS 204 with respect to a paper passage area.

FIG. 7 is a diagram showing a leading edge detection area and a lateral edge detection area in the CIS 204.

FIG. 8 is a diagram showing the maximum detection width of the CIS 204.

FIG. 9 is a diagram showing an example of a processing circuit from image reading by CIS to paper detection.

10 is a diagram showing an averaging process in a main scanning direction in a main scanning direction averaging circuit 704. FIG.

FIG. 11 is a block diagram showing a configuration of a control circuit.

FIG. 12 is a block diagram showing a configuration of TCU 105.

FIG. 13 is a block diagram showing a configuration of a tip detection unit 63.

FIG. 14 is a timing chart showing the operation of the TCU 105.

FIG. 15 is a diagram showing a writing start position adjustment by a laser.

FIG. 16 is a diagram showing a skew amount of the leading edge obtained from a read image by the leading edge detection of CIS 204.

FIG. 17 is a diagram showing a lateral edge skew amount obtained by lateral edge detection of CIS 204.

FIG. 18 is a diagram showing a configuration of an image reading unit in another CIS.

FIG. 19 is a side view showing a print position adjusting mechanism in a conventional image forming apparatus.

20 is a plan view showing a part of the print position adjusting mechanism of FIG. 19. FIG.

FIG. 21 is a side view showing a print position adjusting mechanism in another conventional image forming apparatus.

FIG. 22 is a diagram showing how an image is formed at a desired position on a sheet by the print position adjusting mechanism of Conventional Examples 1 and 2;

FIG. 23 is a diagram showing a decrease in printing accuracy caused by a detection error.

FIG. 24 (A) No error, (B) error: +1.6 m
It is a figure which shows each output image in m, (C) error: -1.6 mm.

FIG. 25 is a block diagram showing a configuration of a conventional CIS.

FIG. 26 is a diagram showing parallel output of CIS in which an internal chip is divided into N parts.

[Explanation of symbols]

27 Laser control circuit 31 photosensitive drum 52 image processing circuit 62 cash register section 63 Tip detector 64 Horizontal edge detector 65 CIS controller 66 CIS Tip detection short cycle setting section 68 CIS horizontal edge detection long cycle setting section 82 Timing generation circuit 105 Timing Control Unit (TCU) 107 sheets 202 laser 203 Registration roller (registration clutch) 204 CIS (contact image sensor) 211-218 chips 211a to 218a Light receiving element group 211b-218b shift register

Claims (13)

[Claims] 1. A sheet detection device for detecting the presence / absence of a sheet to be conveyed based on a signal from the reading means, wherein the reading means comprises a plurality of light receiving elements, and outputs a signal according to external light. And a plurality of chips each having a shift register for sequentially transferring a signal output from the light receiving element group, the plurality of chips being such that the conveyed sheet has reached a predetermined position. A plurality of first detection areas for detecting the number of chips in the first detection area and a plurality of second detection areas for detecting the lateral edge position of the sheet having a number of chips larger than the number of chips in the first detection area. The signal output from the shift register at the final stage in the first detection area is output to the outside through the first transmission means, and the signal of the final stage in the second detection area is divided. Shift A signal output from the transistor is output to the outside through the second transmission unit, and based on the signal output from the first transmission unit, it is detected that the conveyed sheet has reached a predetermined position, A sheet detection apparatus, which detects a lateral edge position of the conveyed sheet based on a signal output from the second transmission unit. 2. The sheet detecting apparatus according to claim 1, wherein the plurality of chips are divided so that the number of chips in the first detection region is a minimum unit. 3. The reading unit is installed on a sheet conveying path so that the plurality of chips are arranged in a direction perpendicular to a sheet conveying direction, and the reading unit is configured to detect the conveyed sheet in the first detection area. The sheet detection device according to claim 1, wherein the leading edge is detected. 4. A detection operation based on a signal output from the first transmission means and a detection operation based on a signal output from the second transmission means while the conveyed sheet passes. The sheet detecting apparatus according to claim 1, wherein the sheet detecting apparatus is switched between the operation and the operation. 5. The sheet detecting apparatus according to claim 3, wherein skew feeding of the conveyed sheet is further detected in the first detection area. 6. The contact image sensor according to claim 1, wherein the reading unit includes a light projecting unit that projects light onto the conveyed sheet, and receives a reflected light from the sheet. The sheet detection device according to any one of 1. 7. A sheet detecting means for detecting the presence / absence of a conveyed sheet on the basis of a signal from the reading means, and a timing control means for generating a print start timing according to the detection signal from the sheet detecting means, In an image forming apparatus including an image forming unit that forms an image at a predetermined position of the conveyed sheet according to the print start timing, the reading unit includes a plurality of light receiving elements, and a signal corresponding to external light. And a plurality of chips each incorporating a shift register for sequentially transferring signals output from the light receiving element group, wherein the plurality of chips are such that the conveyed sheet reaches a predetermined position. And a first detection area for detecting that the number of chips in the first detection area is larger than the number of chips in the first detection area. And a second detection area for detecting a position, the signal output from the final stage shift register in the first detection area is output to the outside through the first transmission means. In addition to outputting, the signal output from the final stage shift register in the second detection area is output to the outside through the second transmission unit, and the sheet detection unit is output through the first transmission unit. Detecting that the conveyed sheet has reached a predetermined position based on a signal that is transmitted, and detecting the lateral edge position of the conveyed sheet based on a signal that is output through the second transmission means. An image forming apparatus characterized by. 8. A plurality of chips each comprising a plurality of light receiving elements, each of which includes a light receiving element group that outputs a signal according to external light, and a shift register that sequentially transfers signals output from the light receiving element group. A sheet detection method for detecting the presence / absence of a conveyed sheet based on a signal from a reading unit having, wherein the plurality of chips are configured to detect a fact that the conveyed sheet reaches a predetermined position. It is divided into a plurality of areas including one detection area and a second detection area having a number of chips larger than the number of chips in the first detection area and for detecting the lateral edge position of the sheet. A first output step of outputting a signal output from the final stage shift register in the first detection area to the outside through a first transmission means, and a final stage shift in the second detection area From register A second output step of outputting the output signal to the outside through the second transmission means, and the conveyed sheet having reached a predetermined position based on the signal output through the first transmission means. And a second detection step of detecting a lateral edge position of the conveyed sheet based on a signal output from the second transmission unit. Sheet detection method. 9. The sheet detection method according to claim 8, wherein the plurality of chips are divided so that the number of chips in the first detection region is a minimum unit. 10. The reading unit is arranged so that the plurality of chips are arranged in a direction perpendicular to a sheet conveying direction.
It is installed on the sheet conveying path, and in the first detection area,
The sheet detecting method according to claim 8, wherein the leading edge of the conveyed sheet is detected. 11. While the conveyed sheet is passing,
9. The sheet detection method according to claim 8, wherein the detection operations of the first detection step and the second detection step are switched. 12. The sheet detecting method according to claim 10, wherein skew feeding of the conveyed sheet is further detected in the first detection area. 13. The contact image sensor according to claim 8, wherein the reading unit includes a light projecting unit that projects light onto the conveyed sheet, and a contact image sensor that receives reflected light from the sheet. The sheet detection method according to any one of 1.