JPH01217470A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the missing of a copied image and the appearance of black in the back of sheet by controlling a timing in the way that the copied image leading edge of an original first page and the leading edge of sheet front are made coincided, and the copied image trailing edge of an original second page and sheet back trailing edge are made coincided when the measured value of original total length is shorter than standard length. CONSTITUTION:The total length 2L1 of an original 2a put on an original platen 1 is measured, and the measured value 2L1 is compared with the specified standard length 2L. If the measured value 2L1 is shorter than the standard length 2L, the copied image leading edge of the first page of the original 2a and the leading edge of the sheet front are made coincided, and an exposure timing and a sheet feeding timing are controlled in the way that the copied image trailing edge of the second page of the original 2a and the sheet back trailing edge are made coincided. Thus, in a mode in which page-continuous copying and both-side copying are performed, the missing of the copied image of the second page of sheets and the black of the right side edge of the image of said page can be prevented even if originals are book-styled, and high copying quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus, and particularly to an image forming apparatus equipped with a continuous page copying function.

[Conventional technology]

Conventionally, in an image forming apparatus such as a copying machine, two pages of W and O placed on a document table are copied onto two copy sheets or one or both sides of one sheet of paper by one copy command operation. A so-called "page continuous copying machine" that does this is well known.

FIG. 7 shows an outline of this type of conventional image forming apparatus (hereinafter referred to as the apparatus).

In FIG. 7, a first page document 2 and a second page document 2 □ having a predetermined standard length are placed on the document table 1. After pressing the page continuous copy switch (not shown),
When the copy switch (not shown) is pressed, the light i3 starts slit exposure scanning of the first page of the original 2 from the initial position (home position) HP. Manuscript 2. The reflected light from
．． Second. Third mirror 4,5. ．． After being sequentially reflected by 52, the light enters the imaging lens system 6, and then is further reflected by the fourth mirror 7 and projected onto the photoreceptor drum B. Since the surface of the photoreceptor tram 8 has already been charged by the charger 10, an electrostatic latent image is formed by the projection light, and if necessary, the charge is removed by the eraser 11 from portions that do not require development. The eraser 11 is a device in which small lamps are continuously arranged in a direction perpendicular to the rotation direction of the photoreceptor drum 80, and by controlling the blinking of each lamp, the charge on the photoreceptor drum 8 is removed or left behind. This is a well-known method.

A developing device 12 develops a charged portion of the photosensitive drum 8 into a visible image.

Copy sheets (hereinafter referred to as paper) are supplied in parallel with these image forming processes.

That is, the paper of the standard length accommodated in the paper feed cassette 23 of the first paper feed section is fed and stopped by the registration roller pair 25 which is stopped by the paper feed roller 91.

Next, at the timing when the leading edge of the image on the photosensitive drum 8 and the leading edge of the paper coincide, the pair of registration rollers 25 starts rotating, and the paper is re-fed, and the paper is fed again to the transfer section 1.
3, after the toner on the photoreceptor drum 8 is transferred to the paper, the paper is separated from the photoreceptor drum 8 by the separation corona 14, passed through the conveyance section 16, and fixed by the fixing section 17, and then transferred to the paper ejection roller. It is discharged from the device by pair 18. Note that the paper in the paper feed cassette 24 of the second paper feed section is also processed in the same way as the paper in the paper feed cassette 23. By the way, the light source 3 is the original 2. After completing the exposure scan for the right end of , or after completing the exposure scan for the document 22 , it returns to the initial position HP.

Next, the copying operation of the second page of the original 22 is started. That is,
The light source 3 moves along the original platen 1, and the second page original M4
After performing 22 exposure scans, it returns to the initial position HP.

Single-sided copying is performed in the page continuous copying mode as described above, but in the case of double-sided copying, the paper on which the copy image of the first page of the original 21 is formed is inverted and transferred to the intermediate tray 2.
The second page of the original 22 is placed on the back of the paper.
This is accomplished by forming a copy of the image and then discharging it from the apparatus. Specifically, a sheet of paper on which a copy image of 8% 21 of the original page of the first page is formed is fixed by the fixing unit 17, and then
The paper is conveyed to the paper ejection roller pair 18, but before the trailing end passes through the paper ejection roller 18, the paper ejection roller pair 18 begins to rotate in the reverse direction. At this time, since the flapper 19 is at the position indicated by the broken line in the figure, the paper is transferred to the intermediate tray 20 by a conveying means (not shown).
will be loaded on.

Next, the second page original M422 is exposed and scanned at a timing such that the leading edge of the visible image on the photoreceptor drum 8 of the second page original M42□ matches the leading edge of the paper stored in the intermediate tray 20;
The paper is re-feeded by the paper re-feeding means 21 from the intermediate tray 20, the transport roller pair 22° and the registration roller 25 are operated,
Transfer operation 1 in the transfer section 13 Separation operation in the corona section 14.

Double-sided copying in page continuous copying mode is performed by carrying out a carrying operation by the carrying means 16, a fixing operation by the fixing unit 17, and then discharging the paper to the outside of the apparatus.

In the above explanation, there is a length of 2 on the document placement table 1.
It has been described that copying in page continuous copying mode cannot be performed because a long sheet of paper is fed from the paper feed cassette 23 based on a sheet of original placed on the sheet, but this can be done as follows. achieved. As shown in the explanatory drawing for document length measurement in FIG. 8, the original 8I
In order to receive the reflected light from the photometer 2, a photometry means 26 is provided in which a light receiving section 27 made of a CCD is supported by a support member 28. A part of the light irradiated from the light source 3 is irradiated onto the original 2 via the original placing table 1. Second. Third mirror 4,5. ．． 52 and enters the light receiving section 27. The reflected light incident on the light receiving section 27 is converted into an electrical signal and amplified. This amplified electrical signal is compared with a reference signal for determining the presence or absence of a document, and it is determined whether or not there is a document at the center position where the light source 3 irradiates light.

FIG. 9 is an explanatory diagram of a method for detecting the presence or absence of a document and the length of the document.

In FIG. 9, the horizontal axis X corresponds to the scanning distance of the light source 3,
The vertical axis V represents the output voltage of the photometric means 26 (FIG. 8) corresponding to the amount of light incident on the photometric means 26, and Vo represents the threshold voltage for determining the presence or absence of a document. Note that the X-axis is actually a time axis, or since the speed of the light source 3 is constant during scanning, it corresponds to the traveling distance.

To explain the X axis in FIG. 9, the initial position of the light source 3
Home position) HP is X=XO, and the reference position of the original placed on the original placing table 1 is x=X2. Xo
<XI <X2 (7) The relationship X=X is determined, and from X=X to , from X=X
The area between 2 and 2 is a white area, so the photometry means 26
The output voltage of is as shown in FIG.

In the case of the output waveform shown in FIG. 9, it is determined that there is a document at the value of X where the output voltage V exceeds the threshold voltage v0. length 1
2 and Ru J2 fl = X 3X 2 or fl
It is determined that a document of jQ/2 is placed on the document table 1.

(Problem to be Solved by the Invention) However, copying using the conventional page continuous copying mode as described above is not convenient for operation because copy images of two sheets (two pages) of the original are automatically obtained. However, when the original is in the form of a book, the resulting copied image has the following problems.

Figure 10 is the manuscript mounting table! FIG. 7 is a diagram illustrating the state of the book-like document above.

In FIG. 10, for example, when the number of pages of the object to be copied is large, the book-shaped original 2a is placed on the original placing table 1.
When placed on top, the total length of the original is 2, as shown in the figure.
It does not become L, but becomes 2 L+ (2L+ < 2 L). Copy sheets obtained when such a document is copied in the continuous page copying mode are as shown in (1) and (2) in FIG. 11, for example. In other words, the copy image on the back side of the copy paper has its copy reference at a position L (first position) from the front reference line.
0), a part of the image (the letter J in Figure 11 (2)) is missing, and the right edge is the reflected light from the document pressure plate that is separated from the document placement table 1. , the color becomes dark (the shaded area in FIG. 11(2)), which is unfavorable in terms of copy quality.

The present invention has been made in order to solve the above-mentioned problems of the conventional method, and in page continuous duplex copying mode, even when the original is a book-like original, the copied image on the back side of the copy paper may be missing. It is an object of the present invention to provide an image forming apparatus that can prevent partial darkening of an image (for example, the right edge) and obtain good copy quality.

[Means to solve the problem]

An image forming apparatus that obtains one double-sided copy image from a two-page original placed on a document placement table, the apparatus comprising: a measuring means for measuring the total length of the document placed on the document placement table; a comparison means for comparing the measured value of the means with a predetermined reference length, and when the measured value is shorter than the reference length, the leading edge of the copied image of the first page of the original document is made to coincide with the leading edge of the paper surface; The above object is achieved by having a control means for controlling exposure timing, paper feeding timing, or both timings so that the trailing edge of the copied image of the second page of the document coincides with the trailing edge of the back surface of the paper. That is.

(Function) According to the image forming apparatus of the present invention as described above, the leading edge of the copied image of the first page of the document formed on the photoreceptor and the leading edge of the paper, and the trailing edge of the copied image of the second page of the document and the back side of the paper. Since the rear edge of the paper is controlled so as to coincide with the trailing edge of the paper, it is possible to prevent copying images from being missing, darkening, etc. on the back side of the paper.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1(a) is an explanatory diagram of an embodiment of an image forming apparatus according to the present invention. In the figure, the same or equivalent components as those in the conventional example FIG. is omitted. In FIG. 1(a), 2a is a book-shaped manuscript placed on the manuscript table 1, and the length of each person on the table 1 when two arbitrary pages are unfolded is as follows. It is shorter than the predetermined reference length L. The coordinate in the scanning direction from the initial position HP of scanning by the light source 3 is defined as X (scanning distance ll!), and the position of the leading edge of the document on the mounting table 1 is indicated by X=X2.

FIG. 1(b) is a block diagram showing the configuration of the apparatus according to the present invention. In the figure, the output of the document length measuring means is input to the CPU, and the document length and folds are detected. Further, an optical unit position detection sensor Ilo and a clock timer are connected to the CPU.

The present invention is implemented by controlling the optical motor, main motor, registration roller clutch, etc. using the above Ilo.

Next, the operation in this embodiment is shown in FIGS. 1(a) and (b).
This will be explained using FIGS.

FIG. 2(a) is an operation sequence flowchart in one embodiment of the present invention, and FIG. 2(b) is a flowchart of the operation sequence in one embodiment of the present invention.
12 is a flowchart of subroutine B in step 7 of FIG.

First, when a page continuous copying switch (not shown) is turned on (step 1), the first page continuous copying switch (not shown) is turned on (step 1). The size of paper stored in the cassettes 23 and 24 installed in the second paper feed section is detected (step 2). This detection may be performed by a known method, for example, by detecting an optical read mark corresponding to the paper size stored in the cassette or a mechanical notch row corresponding to the paper size using a microswitch or the like. In an apparatus according to an embodiment of the present invention (referred to as the present apparatus), paper sizes A-a, A4, B
4, B5, or the 1st cassette. Second
It can be installed in the paper feed section.

Next, when a print switch (not shown) is turned on (step 3), preliminary exposure scanning, which is means for measuring the total length of the document, is started (step 4). The preliminary exposure scan is a step of detecting the size of the original placed on the original placing table 1, and since the specific optical detection method is as described above, the explanation will be omitted.

In this step 4, a white plate 30 having a length of 2 from the document leading edge reference (X=X2 in FIG. 1) of the document placing table 1 is
This is an embodiment in which the document tray 1 is disposed on the lower surface of the document table 1.

A method of detecting the length of the document and the position of the leading edge of the document in FIG. 3 will be explained.

Each dimension L ra, L 2111 L 3 in Fig. 3
a+L 411 are each as shown.

FIG. 4 is an operation sequence flowchart for the example of FIG. 3 of the step 4 preliminary exposure scan of FIG. 2.

In FIG. 1(a), the light source 3 started from the initial position HP has a length of ! from the reference position of the leading edge of the document in FIG. , the white plate 30 is exposed and scanned, but depending on whether the leading edge of the document is on the white plate, it is determined whether the position can be detected. (Step 4.1) in Figure 4 is a step that shows this, and when the leading edge of the original is detected, the difference between the leading edge position and the trailing edge position is the total length of the original 2L.
2. = L I-L 3a is determined (step 4.
2). If the leading edge of the document is not detected, that is, the white plate 3
If it is above 0, proceed to step 4.3.

For convenience of explanation, a case will be described here in which an A4-sized book-like document is spread open as shown in FIG.

In step 4.3, the detection position Ula of the trailing edge of the document is
Determine whether it is longer or shorter than the total length of A3 (420 mm). If Lla≧A3, go to step 4.4, L, a<
In the case of A3, proceed to step 4.10. Step 4.4
In order to predict the total length of the original placed on the original placing table 1 and the position of the leading edge of the original, changes in the intensity of light reflected from the original in the scanning direction are observed.

In FIG. 5, as shown in FIG. 3, there is a length 1. 9 is an example of a characteristic diagram corresponding to FIG. 9, showing the relationship between the scanning distance X and the intensity V of reflected light when the white plate 30 of FIG.

In Fig. 5, x=xo is the initial position (home position), and the intensity V of the reflected light at this time is
The distance up to X I 2, that is, the reference position of the leading edge of the document, is kept almost constant. X = X, from position 2 to X −
Since there is a white plate 30 between the positions X l 3, the strength V
is a nearly constant value. X = X I 3 to X = X,
The values up to 5 are values due to reflected light from the original.

Figure 5 shows the positions where the reflected light V sharply decreases between X=XI3 and x=x15.
, 5, it is determined whether X=X, 4 is a fold line of the book-like document. Specifically, the third
See also figure, distance between X=X, 4 and X=X+s is L 4
5, assuming that the leading edge and trailing edge of the original are equidistant from the center of the fold, the condition that the leading edge of the original is on the white plate is 0≦
L ,, -2L4゜≦I+, and in this relationship
If there is a position of =X, it is assumed that a fold of the document has been detected. If a crease is detected, the leading edge of the document
It is located at L311=L, a-2L4a from the document leading edge reference position, and the total length of the document is 2 L2. = 2 L4a (step 4.5). Next, in step 4.4, if no change due to reflected light is detected at the position where 0≦L, a-2L4a≦Il, as shown by X-XI4 in FIG. Length of the copyable portion of the original placed on table 1 L 5Il= L +a
42 + (step 4.6).

Next, in step 4.7, the length of LI,a is compared with the original standard length A3, and if Lea≧A3,
The leading edge of the manuscript is L3. , = 0, and the total length of the manuscript is 2L2
゜=l, , 9 and processed FL (step 4.8), also L
5. < In the case of A 3, the leading edge of the document, = L, a
-A3, and the total length of the document is processed as 2L2a=A3 (step 4.9).

In the step 4.3, if Lla<A3, that is, if the length of the document placed on the document table 1 is shorter than the standard document length A3, the process proceeds to step 4, IO. In step 4.10, step 4.4
Similarly, this is a step of predicting the total length and center of the original or the placement position of the original on the original placing table 1 based on changes in the intensity of reflected light from the original, and in FIG.
Reflected light input V between 13 and X = X + s
At the position X = X l 4, where
Based on the position of I5, it is determined whether X = X, , is a fold. That is, as above, 0
The subsequent steps are determined depending on whether L+4a exists that satisfies ≦L, a-2L, , ≦II-+ (FIG. 3). When a fold is detected, the leading edge position L3a of the document is L3a=L, a-2L, a, and the total length 2L2a of the document is 2L2. = 2 L4° (step 4.11), and if no crease is detected, L
3. =0,2L2. =L1. Step 4.1
2).

From the above explanation of step 4 in FIG. 2, the total length and placement position of the original placed on the original placing table l are determined.

The determined document length is compared with a plurality of reference document lengths in step 5 of FIG. 2 (comparison means).

Here, the multiple standard document lengths (predetermined standard lengths) are BS and A4.
Explained as size. In step 5, the length L is half of the total length LA of the document measured in the preliminary exposure scan in step 4.
It is determined whether the length is A/2 or between B5 and A4 sizes.

That is, this is a step in which it is determined whether or not an A4-sized book-shaped original 2a is placed on the MM placing table 1.

In step 5, if YES, that is, it is determined that an A4 size book-shaped original is placed, the process proceeds to subroutine A, and if NO, the process proceeds to step 17. First, subroutine A in the case of YES will be explained. Step 6 is the first step performed in step 2 above. This is a step of determining whether or not the detection result of the size of the paper stored in the second paper feed section indicates that A4 size paper exists. If there is A4 size paper, subroutine B (
Proceed to step 7), and if there is no A4 size paper, proceed to step 9.

First, subroutine B shown in FIG. yj2 (b) will be explained. In step 100, if the selected mode is not the double-sided copy mode, the process advances to step 101. Two sheets of paper are fed from the paper feed unit that stores A4 size paper, and images of two pages of each document placed on the document tray 1 are formed on the paper by continuous page copying. However, at this time, the exposure scan corresponds to the first scan in step 101 and the second scan in step 102''.

Further, in step 100, if the selected copy mode is double-sided copying, the first page of the document is scanned in parallel with feeding one sheet of A4 size paper (step 103). ), after the first page image is formed on the paper and fixed, the intermediate tray 20 in FIG.
(step 104).

Next, the second page of the original is scanned (step tOS).
, the original image is fed from the intermediate tray 20 (step 1
06) The image is transferred to the back side of the paper and discharged to the outside of the fixing layer.

The positional relationship between the copy image on the photosensitive drum 8 and the paper in the first scan and second scan in this double-sided copying mode will be explained with reference to FIG. 6(a) (control means).

First, in the first scan, the first page, that is, FIG.
Align the leading edge of the copied image (original image) on the photosensitive drum 8 of the left original in a) with the leading edge of the paper (transfer paper) surface,
In the second scan, control is performed so that the trailing edge of the copied image on the photosensitive drum 8 of the second page, that is, the right-hand document, is aligned with the trailing edge of the back surface of the paper.

Specifically, the timing of paper feeding or refeeding of the registration roller 25 in FIG. 1(a) is controlled;
Alternatively, this can be realized by controlling the scanning start timing of the light source 3, or by controlling the timing of both.

Note that the control referred to here refers to the leading edge of the copied image on the first page, the leading edge of the paper surface, and the end of the copied image on the second page when the original length of the original placed on the document mounting table 1 is set to 2. Compared to the timing when the edge coincides with the trailing edge of the back sheet, it shows a slight timing control such that the technical problem of the present invention is achieved.

Note that in order to change the relative position of the copy image formed on the photosensitive drum 8 and the paper, timing control of the start of scanning of the registration roller 25 or the light source 3 is a known method.

After the copying operation of double-sided copying or single-sided copying is performed in this manner, the process proceeds to step 8 in FIG. 2(a). After completing step 7, turn over the next page of the book-like manuscript,
After placing the original on the original table 1 again, turn on the print switch (not shown) (step 8), the process returns to step 3 and the copying operation starts again, but after step 7 is completed, the print switch is turned on. If it is not pressed for a certain set time,
Page continuous shooting mode is automatically canceled.

Next, if NO in step 6, that is, if there is no A4 size paper, it will be displayed that there is no suitable paper (
Step 9). For example, the display unit that displays A4 size paper may be made to blink. If the appropriate size paper is loaded and detected within the set time after the warning that there is no paper of the appropriate size in step 9 is started, and the print stitch is turned ON again, the process advances to subroutine B. However, the print switch was turned on again within the set time.
The flow differs depending on whether or not paper with an area twice the proper size, that is, A3 size in this case, is loaded (step 11). First A3
If the A3 size paper is loaded, the A3 size paper is selected and the copy image is formed on it.

In this case, even though page continuous copying mode is selected, the exposure scan on the original is done once, and the exposure scanning distance is for two pages, so the image of the original for two pages is printed on the paper. (Step 12).

In this case, the timing of the start of rotation of the registration roller 25 or the timing of the start of scanning of the light source 3 is controlled so that the position of the original image formed on the paper coincides with the center of the paper and the image. In step 11, if A3 size paper is not loaded, the process advances to step 13.

Step 13 is the closest size to A4 size,
Furthermore, sheets whose orientation with respect to the copying device is the same are selected.

In this device, A4. B5 size paper is loaded so that its horizontal direction is perpendicular to the paper traveling direction, and Aa and B< size paper are loaded so that the vertical direction is perpendicular to the paper traveling direction. It is determined whether or not the size paper can be copied (step 13). If there is no BS size paper, that is, if B4 size paper is loaded (if B4 size paper is not loaded) If this is the case, it means that there is no paper that can be loaded in the device, and the process does not proceed to the preliminary exposure scan in step 4), the process proceeds to step 15, and as in step 12, page continuous shooting mode is specified. Despite the fact that the document is exposed once, the exposure scan distance is two pages, and two pages of the document image are formed, and the document image formed on the paper is different from the document image formed on the paper. The timing of the start of rotation of the registration rollers 25 or the timing of the start of exposure scanning of the light [3 is controlled so that the centers of each sheet coincide.

However, in step 15, based on the total length of the document measured in step 4, the mirror 5 in FIG. The position of the lens 6 is changed, and methods for changing these positions are known.

In step 13, if there is BS size paper, the process advances to step 14, subroutine Ba. Subroutine Ba in step 14 differs from subroutine B in step 7 in some steps. The difference arises from the difference in paper size of the object to be copied. Each step resulting from the difference in paper size will be explained below.

In step 100, if the selected mode is not the double-sided copy mode, the process advances to step 101. Then, two sheets of paper are fed from the paper feed unit containing BS size paper, and images of two sides of the original placed on each document mounting table 1 are formed on the paper by continuous page copying. . At this time, exposure scanning is performed by a first scan in step 101 and a second scan in step 102.

However, the exposure scanning in steps 101 and 102 in the subroutine Ba in step 14 is performed as shown in FIG. 2(a) in order to copy on BS size paper as described above.
A reduced image is formed on the paper according to the ratio of the document length to the paper size measured in the preliminary exposure scan of step 4. After the copying operation in one page continuous copying mode is performed in this way, the process proceeds to step 16, where the book-like original i
If the print switch is pressed after turning over the page 2a and completing the preparation for the next copy, the process returns to step 3 and the copying operation is repeated.Also, if the print switch is not pressed for a certain period of time after copying is completed in page continuous copying mode, the page Continuous shooting mode is canceled.

Returning to step 5, if LA is the total length of the document measured in the preliminary exposure scan of step 4, then B5<LA/
If 2≦A4, proceed to step 17, or in step 17, if LA/2≦BS, proceed to step 18.
If not, the process advances to step 19 to display that there is no paper of the appropriate size.

First, step 18 will be explained. Basically, the operation shown in subroutine A is performed, but some of the steps in subroutine A are different depending on the document length. That is, the paper size A4 in steps 6 and 10 is set to BS, and the paper size A3 in step 11 is set to 8.
4, the paper size B5 in step 13 is changed to A4, and in the step of subroutine Ba in step 4, the copy magnification is determined by the ratio of half the original length to the length of A4 size paper. The difference is that the paper size selected in step 15 for copying is A3.

Subroutine A in step 20 also basically performs the operations shown in subroutine A, but some of the steps in subroutine A differ depending on the document length. That is, in step 12, reduced copying is performed, which is determined by the ratio of the document length to the length of A3 size paper, and in step 14, subroutine Ba
Step 101 of subroutine B shown as Step 102. Step 103. Enlarged copying is performed in which the copying magnification in steps 104 and 105 is determined by the ratio of half the original length to the length of Bs size paper,
Further, in step 15, an enlarged copy determined by the ratio of the length of the original document to the length of B4 size paper is performed.

As described above, according to the image forming method of this embodiment, as shown in FIG. ) (Back side) There is no missing copy image as shown on the left side, and there is no darkening on the right side, and of course, Figure 6 (1) (Front side)
A copy image of good copy quality was obtained with no missing images.

In this embodiment, in FIG. 6(a), the left side document is the first page, and the right side document is the second page, but the present invention is not limited to this, and the right side document is the first page. If the first page and the original on the left side are the second page, then the copy image corresponding to the first page formed on the photosensitive drum 8? It is easy to imagine that the control would be performed so that the rear edge of the sheet coincides with the rear edge of the sheet, and the leading edge of the copy image corresponding to the second page formed on the photosensitive drum 8 coincides with the leading edge of the sheet. It is.

〔Effect of the invention〕

As explained above, according to the present invention, there is provided an image forming apparatus that obtains one double-sided copy image of two pages of original placed on the original placing table, wherein a measuring means for measuring the total length of the original; a comparing means for comparing the measured value of the measuring means with a predetermined reference length; Control for controlling exposure timing, paper feeding timing, or both timings so that the leading edge of the front surface of the paper coincides with the leading edge of the front surface of the paper, and the trailing edge of the copied image of the second page of the document coincides with the trailing edge of the back surface of the paper. In the continuous page double-sided copying mode, even if the original is a book-like original, the second page (back side) of the copied image is prevented from being lost, and the rightmost image of the same page is prevented from being lost. It has the effect of preventing darkening and obtaining good copy quality.

[Brief explanation of the drawing]

FIG. 1(a) is an explanatory diagram of an embodiment of an image forming apparatus according to the present invention, FIG. 1(b) is a block diagram showing the configuration of the apparatus according to the present invention, and FIG. 3(b) is an operation sequence flowchart in one embodiment of the present invention, FIG. 3 is a side view of the document table with a white plate disposed on the lower surface, and FIG. 4 is the third step of the step 4 preliminary exposure scan in FIG. FIG. 5 is a characteristic diagram showing an example of scanning distance versus reflected light intensity; FIGS. 6(a) and (b) are a book-like original on the original placing table and a quick copy in this embodiment, respectively. A diagram of a sheet image, FIG. 7 is a schematic diagram of a conventional image forming apparatus, FIG. 8 is an explanatory diagram of document length measurement, FIG. 9 is an explanatory diagram of a method for detecting the presence or absence of an original and document length, and FIG. 10 is an illustration of a document FIG. 11, which is a diagram showing the state of a book-shaped original on a mounting table, is an image of a double-sided copy sheet of a book-shaped original in a conventional example. 1...Original MIIit stand 2.2a...Book-like original 8...Photosensitive drum 23.24-...Paper feed cassette 26...・Photometering means

Claims (1)

[Claims] An image forming apparatus that obtains one double-sided copy image from a two-page original placed on a document placement table, the apparatus comprising: a measuring means for measuring the total length of the document placed on the document placement table; a comparison means for comparing the measured value of the means with a predetermined reference length, and when the measured value is shorter than the reference length, the leading edge of the copied image of the first page of the original document is made to coincide with the leading edge of the paper surface; Image formation characterized by comprising a control means for controlling exposure timing, paper feeding timing, or both timings so that the trailing edge of the copied image of the second page of the original document matches the trailing edge of the back surface of the paper. Device.