JP2003076081A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately position an image without being influenced by the dimensional error and the dimensional variance of paper size in a transfer type image forming device. SOLUTION: This image forming device is provided with a passing detection means S1 for detecting the passing of the leading edge of paper and a passing detection means S2 and S3 for detecting the passing of the trailing edge of paper on the upstream side of a transfer point A where the image is transferred to paper P, and the timing of the image is made coincident with that of the paper based on a signal from either passing detection means at the image forming time. Then, the timing of the image is made coincident with that of the paper based on a passing signal from the passing detection means different between the first surface and the second surface at the double-sided image forming time.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrophotographic photoreceptor,
Can be formed on an image carrier such as an electrostatic recording dielectric, a magnetic recording magnetic material, or an intermediate transfer member by an appropriate image forming method (image forming process) such as an electrophotographic method, an electrostatic recording method, or a magnetic recording method. The present invention relates to an image forming apparatus such as a copying machine or a printer that uses a transfer method to obtain an image formed product by transferring a transferred image onto a sheet (recording medium).

[0002]

2. Description of the Related Art For example, in a transfer type electrophotographic image forming apparatus, a toner image formed on an image bearing member such as a photosensitive drum is transferred to a sheet, and then the toner image is fixed on the sheet by a heat fixing means to form an image. Obtaining formations (copy, print).

Further, in order to transfer the toner image to a predetermined position on the paper at the transfer position, the paper is conveyed to the transfer position at the timing when the toner image on the image carrier reaches the transfer position.

Conventionally, in such an image forming apparatus,
A transport roller pair for transporting the paper to the transfer position is provided upstream of the transfer position, and the timing of arrival of the paper at the transfer position is controlled by stopping, rotating, shifting, etc. of the transport roller pair.

Here, the timing at which the paper reaches the transfer position is defined by the paper passage signal when the leading edge of the paper in the sheet conveying direction passes the paper passage sensor provided on the upstream side of the transfer position, and the image position. It is determined based on the position of the toner image on the carrier. The position of the toner image on the image carrier is the image formation operation start signal on the image carrier, or the toner of the toner image passage sensor that detects the passage of the toner image on the upstream side of the transfer position on the image carrier. It is defined based on the image passing signal.

Further, even when the intermediate transfer belt is used as the image carrier and the timing at which the image on the image carrier reaches the transfer position varies due to the expansion and contraction of the belt, the image position on the image carrier is changed. There is also proposed an image forming apparatus which improves the accuracy of the timing adjustment of the image reaching the transfer position and the paper by providing a means for detecting the paper and using it together with the paper passage sensor (JP-A-11-194).
561).

On the other hand, in the image forming apparatus equipped with an automatic double-sided mechanism in which the image is formed on the second side by reversing the sheet inside the apparatus after the image formation on the first side is completed, conventionally, in the conveying direction, A switchback type front / back reversal method of reversing the front / rear direction of a sheet is widely used.

[0008]

In the image forming apparatus such as the above-mentioned conventional example, a standard size cut sheet (sheet) is widely used as a sheet. Normal,
The standard for cut paper size allows a dimensional error of about ± 2 mm from the regular size, and there are many errors and variations in the size of the paper actually distributed. In addition, paper shrinkage due to drying and moisture absorption also causes errors and variations in paper dimensions.

Further, as described above, the sheet position for determining the timing of arrival of the sheet at the transfer position is defined by the sheet passage signal when the leading edge of the sheet in the sheet conveying direction passes the sheet passage sensor. That is, the toner image is transferred to a position with the leading end of the sheet in the transport direction as a reference.

Therefore, as shown in FIG. 13, when the length dimension L1 of the sheet P in the carrying direction includes the dimension error E1 with respect to the standard size L0 (L1 = L0 + E1),
Position B of image Z with reference to front end PT of sheet P in the transport direction
T11 coincides with the image information generated according to the regular-sized sheet P0 shown in FIG. 14 (BT11 = BT),
The position BE11 of the image Z with respect to the rear end PE of the sheet P in the transport direction is displaced (BE11 ≠ B).
E).

Particularly, in an image forming apparatus equipped with an automatic double-sided mechanism, as a result of the front and back reversal of the leading end position in the sheet conveyance direction, which is the image positioning reference, the reference edge of the sheet serving as the image and image positioning reference is the first surface. Different on the second side. That is, as shown in FIG. 15, the trailing edge PE1 of the first side in the sheet conveying direction is
Is located at the position of the leading edge PT2 of the second surface in the sheet conveying direction, even if the relative positions of the first surface image Z1 and the second surface image Z2 are the same in the image information, as shown in FIG. A relative positional deviation of E1 occurs. Further, the dimensional change of the paper caused by the influence of fixing at the time of image formation on the first side also causes a relative image position deviation at the time of double-sided image formation.

Further, when a plurality of output images are bundled and cutting or bookbinding is performed with the trailing end side in the sheet conveying direction as a reference, in the case where there are variations in sheet sizes, inconveniences such as uneven image positions occur. Will end up.

The present invention has been made in order to solve the above problems, and its object is to perform image positioning with high accuracy without being affected by errors and variations in paper size dimensions. An image forming apparatus is provided.

[0014]

The present invention is an image forming apparatus characterized by the following means.

(1) an image carrier, transfer means for transferring an image formed on the image carrier to a sheet at a transfer position,
A transfer conveyance unit that conveys a sheet to a transfer position, a sheet passage detection unit that detects a passage timing of the sheet before reaching the transfer position at a predetermined position, and a transfer position based on the sheet passage timing that is detected by the sheet passage detection unit. In an image forming apparatus having a transfer / conveyance control means for controlling the transfer / conveyance means so as to match the arrival timing of the paper to the image position formed on the image carrier, the paper passage detection means is provided at the leading end of the paper in the conveyance direction. A transfer leading control means is provided according to image information, an image forming sequence, etc., provided with a sheet leading edge passage detecting means for detecting a passage timing and a sheet trailing edge passage detecting means for detecting a passage timing of a trailing edge of the sheet in the conveying direction. Controlling the transfer / conveyance means based on the detection result of either the leading edge passage detecting means or the trailing edge passage detecting means. An image forming apparatus comprising.

(2) The sheet passage detecting means is characterized in that either one of the sheet leading edge passage detecting means or the sheet trailing edge passage detecting means is selected according to the direction of the image transferred on the sheet. The image forming apparatus described in (1).

(3) Fixing means for fixing the image transferred on the paper on the downstream side of the transfer position, fixing conveyance means for conveying the paper from the transfer position to the fixing means, and conveyance of the paper on the downstream side of the fixing means. The image forming apparatus according to (1) or (2), which includes a double-sided conveyance unit that reverses the front and rear ends of the direction and the front and back sides and conveys the sheet to the transfer conveyance unit again.

(4) One of the sheet leading edge passage detecting means and the sheet trailing edge passage detecting means is selected, and the sheet passage detecting means is selected differently for the first side and the second side during double-sided image formation. The image forming apparatus according to (3).

(5) The image forming device has a belt-like image carrier and an image passage detecting device for detecting the passage timing of the image formed on the image carrier at a predetermined position before reaching the transfer position. The image forming apparatus according to any one of (1) to (4), wherein the transfer / conveyance unit is controlled based on the detection results of the image passage detection unit and the sheet passage detection unit.

(6) The image forming apparatus according to any one of (1) to (5), further comprising moving means for moving the sheet passage detecting means to a desired position.

[0021]

1 is a schematic view of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus of this embodiment is
The digital full-color copying machine has a printer function and a copying function and forms a full-color image from image information transmitted from the controller or the image reading unit 100.

(1) Overall Schematic Structure of Copying Machine The digital full-color copying machine shown in FIG. 1 includes: a: an image reading unit 100; b: an image forming unit 101 for performing laser exposure to forming a toner image; c: an image transfer unit 102 that superimposes the toner image formed by the image forming unit on the transfer belt 11 and then primary-transfers it, and then second-transfers it to the paper; d: paper cassettes C1 and C2 and paper cassette C1,
A sheet feeding unit 103 that feeds a sheet from C2, and e: a transfer conveying unit 1 that conveys the sheet to the secondary transfer point A
04, f: a fixing device 105, g: a fixing conveyance unit 106 that conveys the sheet after the secondary transfer to the fixing device 105, h: a reversing device 107 that reverses the front and back sides of the sheet when forming images on both sides And a double-sided conveyance unit 108 that conveys the paper to the transfer conveyance unit 104 again, and i: eject the fixed paper to the outside of the machine or the double-sided conveyance unit 108.
And a paper discharge unit 109 for switching the route to.

In the image forming unit 101, magenta (M), cyan (C), yellow (Y), black (K) transmitted from a controller (not shown) or the image reading unit 100.
Laser exposure devices 5M and 5 corresponding to the four color separation images
Laser light LM, LC emitted from C, 5Y, 5K
LY and LK are turned over to folding mirrors 6M, 6C, 6Y and 6K
After developing the electrostatic latent image obtained by forming an image on the photosensitive drums 1M, 1C, 1Y and 1K which are rotated in the direction of the arrow after being reflected by the developing devices 3M, 3C, 3Y and 3K. To form a toner image. In addition, the primary charger 2 is provided around the photosensitive drums 1M, 1C, 1Y and 1K.
M, 2C, 2Y, 2K and cleaning devices 4M, 4
C, 4Y, and 4K are arranged.

In the image transfer section 102, the intermediate transfer belt 11 as an image carrier is composed of three belt supporting rollers 12, 1.
3 and 14, supported at a constant speed V0 in the direction of arrow 18 in the figure.
Driven by. Further, the photosensitive drums 1M, 1C, 1Y,
Primary transfer rollers 15M, 15C, 15Y and 15K are arranged at positions facing each other with the 1K intermediate transfer belt 11 interposed therebetween, and the photosensitive drums 1M, 1C, 1Y and 1K and the primary transfer rollers 15M, 15C, 15Y and 15K are arranged. At the opposing primary transfer points, the photosensitive drums 1M, 1C, 1Y,
The toner images of the respective colors on 1K are transferred one after another onto the intermediate transfer belt 11 at the same timing so that the image positions coincide with each other.

The image transferred on the intermediate transfer belt 11 is superimposed on the image on the intermediate transfer belt 11 at the secondary transfer point A where the belt support roller 13 and the secondary transfer roller 16 facing the belt support roller 13 are in contact with each other. The second transfer is performed on the sheet P conveyed from the transfer conveyance unit 104 at the same timing.

The sheet P on which the image has been transferred is fixed and conveyed by the fixing and conveying section 10.
The sheet 6 is conveyed to the fixing device 105.

In the image transfer section 102, an image position detection sensor S0 for detecting the position of the image on the intermediate transfer belt 11 and a residual toner on the intermediate transfer belt 11 are cleaned at a position facing the belt support roller 14. The transfer cleaner 17 is provided.

On the other hand, the transfer / conveyance unit 104 detects the passage timing of the sheet P by the sheet passage detection sensors S1, S2 and S2.
S3 and conveyance roller pairs 21, 22, 23 for conveying the sheet P toward the secondary transfer point A are provided.

The sheet P on which the image has been fixed after passing through the fixing device 105 is discharged to the outside of the apparatus or is sent to the double-sided transport section 108 according to the operation sequence via the sheet discharge section 109.

When the sheet P is sent to the double-sided conveying section 108, it is turned upside down by the reversing device 107 in the direction in which the front and rear ends of the conveying direction are reversed, and the transfer conveying section 104 is again turned on.
Then, the image is formed on the second surface.

Further, as shown in FIG.
Sheet passing detection sensors S1, S2, S3 are arranged on 04, S1 is a passage detecting sensor at the leading edge of the sheet, S2 is a trailing edge detecting sensor for a small size sheet such as A4, and S.
Reference numeral 3 denotes a trailing edge passage detection sensor for large size paper such as A3, which is secondary-transferred based on any one detection result selected according to image information and operation sequence and the detection result of the image position detection sensor S0. Positioning of the paper and the image at point A is performed.

(2) Image and Image Position Detection Formed on Intermediate Transfer Belt 11 FIG. 2 shows an outline of the image and image position detection formed on the intermediate transfer belt 11. The image Z is formed at a distance from the leading edge ZT of the sheet to the leading edge margin BT based on the image information. In the non-image area on the leading edge side of the image, the reference image Z for image position detection is located at a position BD from the leading edge ZT of the paper on the image information.
D is formed. Then, the distance D from the secondary transfer point A of the sheet front end ZT on the image information when the image position detection sensor S0 detects the passage of the front end edge of the reference image ZD.
From 0 and the moving speed V0 of the intermediate transfer belt 11, the time T0 until the sheet front end ZT on the intermediate transfer belt 11 reaches the secondary transfer point A is calculated as follows.

T0 = D0 / V0 (1) In this embodiment, since the drive control is performed so that the running speed V0 of the intermediate transfer belt 11 is always constant, T0 is set for each image. Is a constant value.

(3) Positioning Control of Paper and Image Here, as shown in FIGS. 3 and 4, the leading edge margin BT1 and the trailing edge margin BE1 are set in accordance with the standard size L0 of the standard size of the sheet P. The alignment of the image Z1 and the sheet P will be described in detail by taking as an example the case where the image Z1 is transferred to the sheet P (FIG. 4) having the dimension L1 having the dimension error E1 with respect to the regular dimension L0 to form an image.

As shown in FIG. 3, on the intermediate transfer belt 11, an image Z1 based on the image information (the leading end margin BT1, the image length G1, the trailing end margin BE1) that matches the regular size L0 of the paper P is formed. The reference image ZD is formed.

On the other hand, the paper P is a paper passage detection sensor S1,
The passage detection is performed by one sensor selected from S2 and S3, but when the sheet leading edge passage detection sensor S1 is selected, as shown in FIG.
When T reaches the distance D1 from the secondary transfer point A, it is detected by the sheet leading edge passage detection sensor S1. At this time, the time difference ΔT between the timing at which the image position detection sensor S0 detects the passage of the leading edge of the reference image ZD and the timing at which the sheet leading edge passage detection sensor S1 detects the leading edge PT of the sheet P is calculated from the equation (1). Paper sheet P from T0
The time T1 required for the leading edge PT to reach the secondary transfer point A at the timing of the image Z1 is calculated as follows.

T1 = T0-ΔT (2) In this embodiment, as shown in FIG. 5, the paper P is conveyed at a speed V1 faster than the running speed V0 of the intermediate transfer belt 11, and the paper P The leading edge PT is the sheet leading edge detection sensor S
After being detected by 1, at a predetermined timing TC until reaching the secondary transfer point A, the transfer speed is reduced to the same transport speed V0 as the intermediate transfer belt 11 at a constant acceleration,
Secondary transfer is performed at a constant speed. Here, the timing at which the leading edge PT of the paper P reaches the secondary transfer point A is controlled by changing the deceleration timing TC according to T1 calculated by the equation (2).

Even when the timing at which the sheet P arrives at the sheet leading edge detection sensor S1 varies due to slipping of rollers during sheet feeding, the deceleration timing T
If C is changed according to T1, the timing of the image Z1 reaching the secondary transfer point A and the timing of the front end PT of the paper P can be accurately adjusted, and as shown in FIGS. 6 (a) and 6 (b), An output image in which the image Z1 is transferred at a position with the front end PT of the paper P as a reference is obtained. In FIG. 6A, L1> L
0 and (b) are respective output images when L1 <L0.

Further, in this embodiment, the timing at which the leading edge PT of the paper P reaches the secondary transfer point A is controlled by changing the deceleration timing TC of the transport speed of the paper P according to T1. As shown in FIG. 7, after the leading edge PT of the sheet P is detected by the sheet leading edge passage detection sensor S1, the conveyance of the sheet P is temporarily stopped at a predetermined timing TS, and the restart timing TD is changed according to T1. The timing at which the leading edge PT of the sheet P reaches the secondary transfer point A may be controlled. further,
Even when the conveyance speed of the paper P is accelerated or decelerated at an arbitrary speed according to T1, the timing at which the leading edge PT of the paper P reaches the secondary transfer point A can be controlled.

Next, with reference to FIG. 8, a case will be described in which the trailing edge passage detection sensor S2 of the small size sheet is selected for the passage detection of the sheet P. Here, the paper P is a small size paper such as A4 size, and the paper length L1 has a dimensional error E1 with respect to the regular size L0. Also, L1> L0.

The arrow 30 is formed by the pair of conveying rollers 21 and 22.
The passage of the sheet P conveyed in the conveying direction V1 in the direction is detected by the trailing edge passage detection sensor S2. FIG. 8 shows that the trailing edge PE of the sheet P has passed and the trailing edge detection sensor S2
Shows the position of the paper P at the timing detected by. The position of the sheet P and the image Z1 is aligned with the position PS on the leading end side of the distance L0 from the rear end PE of the sheet P as a reference point.
That is, the trailing edge passage detection sensor S2 detects passage of the trailing edge PE of the paper P at the timing when the reference point PS reaches the position of the secondary transfer point A to D2.

Assuming that the time difference from the detection of the passage of the leading edge of the reference image ZD by the image position detection sensor S0 to the detection of the trailing edge PE of the sheet P by the trailing edge passage detection sensor S2 is ΔT2. The arrival time T2 of the point PS at the secondary transfer point A is calculated by the following equation.

T2 = T0-ΔT2 (3) Then, based on T2, the paper P is adjusted so that the reference point PS and the arrival timing of the paper front end ZT on the image information to the secondary transfer point A coincide with each other. Transport control is performed.

In this way, by performing the positioning control of the sheet P and the image Z1 with reference to the passage timing of the trailing edge PE of the sheet P, as shown in FIG. An output image in which the image Z1 is transferred can be obtained.

When a large size sheet of A3 or the like is used to align the image with reference to the passage timing of the trailing edge of the sheet, the large size rear edge passage detection sensor S3 is selected. The same positioning control may be performed.

In the digital full-color copying machine of this embodiment, the paper passage detection sensors S1, S2, S3 are selectively switched according to the vertical and horizontal directions of the image obtained from the image information. Specifically, when the paper conveyance direction and the vertical direction of the image match, the paper edge in the upper direction of the image is used as a positioning reference, and when the paper conveyance direction and the horizontal direction of the image match, the image The paper passage detection sensor is selectively switched so that the left edge of the paper becomes the positioning reference. For example, the length L1 (= L0 + E1, E1>
When image formation is performed on the small size paper P of 0) such that the paper transport direction is the vertical direction of the image, the paper leading edge passage detection sensor S1 is used for the image Za whose top direction is the leading edge side in the paper transport direction. On the other hand, in the case of the image Zb in which the upper side is the trailing edge side in the sheet conveying direction, the sheet trailing edge passage detection sensor S2 is selected.

As a result, as shown in FIGS. 10 (a) and 10 (b), an output image positioned on the paper P in accordance with the vertical direction of the image is obtained. The combination of the image direction and the sheet passage detection sensor selected according to the image direction can be arbitrarily set as needed.

Further, in the digital full-color copying machine of the present embodiment, by manually providing the paper passage detection sensor selecting means, the image positioning reference can be selected according to the positioning method in the post-processing step such as bookbinding. It has become.

Further, at the time of image formation on both sides of the paper, 1
Different paper passage detection criteria are selected for the first and second sides.

In FIG. 11, the length L1 (= L0 + E1, E
1> 0) Small size paper P, first surface image Z1
(Image length G1, leading edge margin BT1, trailing edge margin BE1) and second side image Z2 (image length G2, leading edge margin BT2, trailing edge margin BE2) are prepared from the image information so that the relative positions of them coincide with each other. An output image when an image is formed is shown.

At this time, the sheet leading edge passage detection sensor S1 is selected on the first side, and the sheet trailing edge passage detection sensor S2 is selected on the second side to form images on both sides.

In this case, the sheet front edge passage detection sensor S1 detects the image on the first side and the first side image Z1 is detected.
The leading end PT1 of the paper P in the conveyance direction, which is used as the positioning reference of
It is reversed by the reversing device 107, and becomes the rear end PE2 in the transport direction when the image is formed on the second surface.

Therefore, by selecting the sheet trailing edge passage detection sensor S2 at the time of forming the image on the second side and positioning the second side image Z2 with reference to the passage timing of the trailing edge PE2 of the sheet P, the first side and the second side are detected. Since the same sheet edge serves as the image positioning reference, the relative positions of the first side image Z1 and the second side image Z2 can be aligned with high accuracy.

Further, in the case of a large size sheet such as A3, the sheet trailing edge passage detection sensor S3 is selected at the time of the image formation of the second side and the image formation is performed.

Here, the first surface is selected as the front end passage detection sensor S1 and the first surface is selected as the rear end passage detection sensors S2, S3. However, if necessary, the first surface is selected as the rear end passage detection sensor S2. , S3, the second surface is a tip passage detection sensor S
It is also possible to switch settings such that 1 is selected and image formation is performed.

Up to this point, the paper size error E1> 0
Although the case has been mainly described, the image can be similarly positioned even when E1 <0.

FIG. 12 shows a block diagram of the above control system. Reference numeral 200 denotes a transfer / conveyance control means (control circuit), and the transfer / conveyance control means 200 includes a paper front end detection sensor S1 and a paper rear end detection sensor S2.
The detection result of 3 and the detection result of the image position detection sensor S0 are input. The transfer / transport control unit 200 performs the above-described arithmetic processing based on the input detection result, and the transfer / transport is performed so that the timing of arrival of the paper P at the transfer position A is aligned with the image position formed on the image carrier 11. The transfer / conveyance unit 104, which is a unit, is controlled, that is, the driving of the pair of conveyance rollers 21 to 23 is controlled to control the conveyance of the paper P.

(4) Others 1) In the digital full-color copying machine of this embodiment,
As a paper detecting means for detecting the passage timing of paper 1
Although the front end passage detection sensor S1 and the two rear end passage detection sensors S2 and S3 are provided, if the passage of the front end and the rear end of the paper can be detected at a predetermined timing, the paper size to be used. It is also possible to increase or decrease the number of detection sensors according to the image forming operation, or to additionally provide means for moving the detection sensors to a desired position.

2) Furthermore, in the digital full-color copying machine of this embodiment, the image position on the intermediate transfer belt 11 is detected by the image position detection sensor S0, and the arrival timing T0 of the image at the secondary transfer point A is determined. Although calculated, T0 may be calculated from the irradiation timing of the laser beam onto the photosensitive drum, etc., if the drive control is performed so that the intermediate transfer belt 11 travels at a constant speed.

3) In the present embodiment, the present invention is applied to a digital full-color copying machine which employs an intermediate transfer belt as an image carrier, but image formation in which a toner image formed on a photosensitive drum is directly transferred to a sheet. Also in the apparatus, the present invention can be applied to any image forming apparatus that detects the passage timing of the sheet before reaching the transfer point and aligns the sheet and the image.

4) Even in an image forming apparatus such as an electrostatic recording system or a magnetic recording system using an electrostatic recording dielectric or magnetic recording magnetic material as an image carrier, the sheet passage timing before the transfer point is reached. The present invention can be applied to any image forming apparatus that detects a sheet and aligns a sheet and an image.

[0062]

As described above, in the image forming apparatus of the present invention, the sheet leading edge passage detecting means for detecting the passage timing of the leading edge of the sheet in the conveying direction and the sheet trailing edge detecting means for detecting the passage timing of the trailing edge of the sheet in the conveying direction. An edge passage detecting means, and controls the transfer conveying means based on the detection result of either the sheet leading edge passage detecting means or the sheet trailing edge passage detecting means selected according to the image information and the image forming sequence. Since the image is aligned with the paper, the image position with respect to the desired reference of either the leading or trailing edge of the paper in the paper transport direction is not affected by paper dimensional errors, variations, or dimensional changes. Can be matched with high precision. Further, the relative image positions of the first side and the second side during double-sided image formation can be adjusted with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a digital full-color copying machine that is an embodiment.

FIG. 2 is an explanatory diagram of image position detection on the intermediate transfer belt (No. 1)

FIG. 3 is an explanatory diagram of image position detection on the intermediate transfer belt (Part 2).

FIG. 4 is an explanatory diagram of paper leading edge detection.

FIG. 5 is an explanatory diagram of paper conveyance speed control.

FIG. 6 is an explanatory diagram of an image position transferred on a sheet.

FIG. 7 is an explanatory diagram of paper transport speed control.

FIG. 8 is an explanatory diagram of trailing edge detection of a sheet.

FIG. 9 is an explanatory diagram of an image position transferred on a sheet.

FIG. 10 is an explanatory diagram of an image direction and an image position.

FIG. 11 is an explanatory diagram of image positions during double-sided image formation.

FIG. 12 is a block diagram of a control system

FIG. 13 is an explanatory diagram of an image position in a conventional example.

FIG. 14 is an explanatory diagram of image information in a conventional example.

FIG. 15 is an explanatory diagram of image positions during double-sided image formation in the conventional example.

[Explanation of symbols]

100 ... Image reading unit, 101 ... Image forming unit, 102
..Image transfer section, 103..Paper feeding section, 104 .. Transfer transfer section, 105..Fixing device, 106..Fixing transfer section, 1
07..Reversing device, 108..Double-sided transport unit, 109 ..
Paper ejection section, A ... Secondary transfer point, S0 ... Image position detection sensor, S1 ... Paper leading edge detection sensor, S2, S
3 ・ ・ Paper trailing edge passage detection sensor, C1, C2 ・ ・ Paper cassette

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/16 103 G03G 15/16 103 3F100 21/14 21/00 372 F term (reference) 2H027 DA21 DC04 DE01 DE07 DE09 EC02 EC06 EC07 EC09 ED16 ED24 ED25 EE04 EE05 2H028 BA06 BA16 BB02 BB04 BB06 2H072 AA13 AA24 AA32. PB15 PB25 PB36 3F048 AA02 AA05 AB01 BA05 BA07 BB02 CA08 CC03 CC04 DA06 DA07 DB01 EA15 EB30 EB33 3F100 AA02 BA17 CA13 CA15 EA03 EA05

Claims (6)

[Claims] 1. An image carrier, a transfer unit for transferring an image formed on the image carrier to a sheet at a transfer position, a transfer conveying unit for conveying the sheet to a transfer position, and a sheet before reaching the transfer position. A sheet passage detection unit that detects the passage timing at a predetermined position, and adjusts the sheet arrival timing at the transfer position to the image position formed on the image carrier based on the sheet passage timing detected by the sheet passage detection unit. In an image forming apparatus having a transfer / conveyance control means for controlling the transfer / conveyance means, the paper passage detection means includes a paper front end passage detection means for detecting a passage timing of a front end of the paper in the conveyance direction and a rear end in the conveyance direction of the paper The transfer conveyance control means is provided with a paper trailing edge passage detecting means for detecting timing, and the transfer conveying control means selects the paper leading edge passage according to image information and an image forming sequence. Image forming apparatus and controls the transfer and transport means based on either detection result of intellectual means or the trailing edge of the sheet passage detecting means. 2. The sheet passage detecting means is characterized in that either one of the sheet leading edge passage detecting means or the sheet trailing edge passage detecting means is selected in accordance with the direction of the image transferred onto the sheet. The image forming apparatus according to item 1. 3. A fixing unit for fixing an image transferred onto a sheet at a downstream side of a transfer position, a fixing conveying unit for conveying a sheet from the transfer position to the fixing unit, and a sheet conveying direction at a downstream side of the fixing unit. 3. The image forming apparatus according to claim 1, further comprising a double-sided conveyance unit that reverses the front and rear ends and the front and back sides and conveys the sheet to the transfer conveyance unit again, and is capable of double-sided image formation. 4. The paper passage detecting means for selecting either the paper leading edge passage detecting means or the paper trailing edge passage detecting means is characterized in that different selections are made for the first side and the second side during double-sided image formation. The image forming apparatus according to claim 3. 5. A transfer carrier control means comprising: a belt-shaped image carrier; and an image passage detecting means for detecting passage timing of an image formed on the image carrier at a predetermined position before reaching the transfer position. 5. The image forming apparatus according to claim 1, wherein the transfer / conveyance unit is controlled based on the detection results of the image passage detection unit and the sheet passage detection unit. 6. The image forming apparatus according to claim 1, further comprising moving means for moving the sheet passage detecting means to a desired position.