JP2003012197A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve conveying efficiency of sheets. SOLUTION: A copying machine 7 calculates a difference between a real time required from detecting the tip of the sheet by writing reference sensor 140 arranged between a position wherein tip of the sheet passes at starting an optical operation on a photoreceptor drum 12 by a laser section 5 and a register-upstream roller pair 107, until detecting the tip of the sheet by a regist sensor 132 and an allowable longest required time from detecting the tip of the sheet the writing reference sensor 140 until detecting the tip of the sheet by the regist sensor 132. By presses the sheet against the regist roller pair 106 stopped in rotation by the register-upstream roller pair 107 for forming a loop on the sheet. The register-upstream roller pair 107 and the regist roller pair 106 are stopped for the time difference calculated to see the conveying timing of the sheet to be conveyed to the photoreceptor drum 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and a composite machine of these.

[0002]

2. Description of the Related Art Conventionally, a copying machine 6 which is an example of an image forming apparatus shown in FIG. 6 is provided with an original table 2 made of a fixed transparent glass plate on an upper part of a main body 1 of the copying machine 6. Platen 2
The document is automatically fed by the document feeding device 3. The document sent to the document table 2 is read by the reading unit 4. The image information read by the reading unit 4 is written on the photosensitive drum 12 by scanning the photosensitive drum 12 uniformly charged by the charger 13 with the laser light emitted from the writing laser unit 5. ing.

The sheet supply unit 8 is a main body 1 of the copying machine 6.
The decks 30 and 31 built in and the decks 30 and 3
Deck sheet supply units 34 and 35 for feeding the sheets S stored in 1 to the image forming unit 9 described later, and decks 30 and 3
The sheet cassettes 32 and 33 are disposed below the sheet cassette 1, and the sheet feeding units 36 and 37 that feed the sheets S stacked on the sheet cassettes 32 and 33 to the image forming unit 9.

The image forming unit 9 includes a photosensitive drum 12, a charger 13 for uniformly charging the surface of the photosensitive drum 12, and light emitted from an optical system onto the surface of the photosensitive drum 12 charged by the charger 13. The developing device 14 that develops the electrostatic latent image formed by the image into a toner image, the transfer charger 19 that transfers the toner image developed on the surface of the photosensitive drum 12 to the sheet S, and the toner from the photosensitive drum 12 It is composed of a separation charger 20 for separating the sheet S on which the image is transferred, a cleaner 26 for removing the toner remaining on the photosensitive drum 12 after transferring the toner image, and the like.

On the downstream side of the image forming section 9, a conveying section 21 for conveying the sheet S on which the toner image is transferred, and a fixing device for fixing the image on the sheet S conveyed by the conveying section 21 to the sheet as a permanent image. 22, a discharge roller pair 24 for discharging the sheet S having the toner image fixed by the fixing device 22 from the apparatus body 1 of the copying machine 6, and a discharging roller pair 24 outside the apparatus body 1 of the copying machine 6. A discharge tray 25 or the like for receiving the discharged sheet S is provided. The entire copying machine has a control unit 150.
Is controlled by.

From the deck sheet supply section 34 to the image forming section 9
Sheet supply to the machine will be described.

The pickup roller 101 is a deck 30.
The sheet S set at is sent to the sheet supply roller 102. At this time, the sheets may be overlapped and delivered from the deck 30. Therefore, the lower sheet, which overlaps the uppermost sheet, moves in synchronization with the pickup roller 101, the sheet supply roller 102, and the sheet supply roller 102 that is provided so as to face the sheet supply roller 102 and is conveyed in a constant torque direction. It is separated from the uppermost sheet and returned to the deck 30 by the separating roller 103 which receives the force of rotating in the opposite direction. Therefore, the deck sheet supply unit 3
4 is deck 3 only for the top sheet (first sheet)
Send from 0.

Next, the vertical path sensor 104 detects the leading edge of the first sheet. Then, the first sheet is passed to the first transport roller 105. After that, the front edge of the first sheet is detected by the pre-registration sensor 130. The control unit 150 determines that the trailing edge of the first sheet is the sheet supply roller 1 based on the detection operation of the pre-registration sensor 130.
The pickup roller 101 is actuated at the time of exiting 02. The pickup roller 101 is the deck 30
Then, the supply of the second sheet is started. by this,
In the sheet supply unit 8, the sheet interval becomes a predetermined interval X.

In FIG. 7, the laser section is considered to have reached the image writing point 131 at the leading edge of the first sheet with reference to the time when the pre-registration sensor 130 detects the first sheet. 5 is a laser beam for the photosensitive drum 12
Start scanning over. The first sheet is further conveyed by the first conveying roller 105 (FIG. 6) and sent to the pre-registration roller pair 107. Then, the sheet is conveyed to the registration roller pair 106 by the pre-registration roller pair 107. During this time, the registration sensor 132 detects the leading edge of the sheet.

When the sheet is fed into the registration roller pair 106, the rotation of the registration roller pair 106 is stopped. Therefore, the first sheet hits the nip N of the registration roller pair 106 and stops. However, the pre-registration roller pair 107 continues to rotate. Therefore, since the leading end of the first sheet is stopped and the sheet is conveyed from the intermediate portion onward, the intermediate portion rises and curves. That is, a loop is formed on the first sheet.

The pre-registration roller pair 107 feeds the first sheet by feeding a predetermined amount B after the middle portion of the first sheet to form a predetermined amount of loops on the first sheet, and then conveys the first sheet. Stop. When the first sheet is skewed, it is straightened by forming a loop. After that, the registration roller pair 106 starts rotating and sends the sheet to the photosensitive drum 12.

[0012]

By the way, in the conventional copying machine 6, as described above, the sheet pre-registration sensor 130 is used.
The laser unit 5 starts scanning the photosensitive drum 12 with the laser light at the time when the leading edge of the sheet is considered to have reached the image writing point 131, based on the time when the sheet is detected. On the other hand, when the pre-registration sensor 130 detects the sheet and then the sheet enters the pre-registration roller pair 107 and is conveyed, the writing point 131 is reached depending on the thickness of the sheet, the material of the sheet, the curled state of the sheet, and the like. There was an error in the time to run.

Therefore, the copying machine 6 does not eliminate this error, forms a predetermined amount of loops on the sheet, and then sends the sheet to the photosensitive drum 12 by the rotation of the registration roller pair 106. The position of the toner image transferred onto the sheet deviates by the amount of the above error and cannot be formed at a predetermined position.

Then, as a method for dealing with this problem,
It is conceivable to eliminate the error by changing the amount of the loop formed on the sheet according to the above error. That is, when the sheet is conveyed early, the loop amount is increased to stop the sheet for the time that is fed earlier, and when the sheet is conveyed later, the loop amount is decreased to reduce the sheet stop time. It is conceivable to shorten it and catch up with the delay.

However, with this method, the copying machine 6
When the sheet is conveyed late, the loop amount is formed to be small. Therefore, when the sheet is skewed, it is sent to the photosensitive drum 12 by the registration roller pair 106 before the sheet cannot be straightened. Sometimes. As a result, the copying machine 6 shifts the sheet with respect to the toner image and cannot transfer the toner image to a predetermined position on the sheet. If the loop amount is too large, the seat will buckle and break.

Therefore, at the time of manufacturing, the longest allowable time (maximum allowable time T1max) from the detection of the sheet by the pre-registration sensor 130 to the detection by the registration sensor 132 is assumed (by experiment). The time is often obtained) is stored in the control unit 150 in advance. The control unit 150 determines the difference C1 (= T1max-T1p) between the maximum allowable time T1max and the time from the pre-registration sensor 130 to the registration sensor 132 (actual transfer required time T1p) for each sheet that is actually conveyed. After forming the predetermined loop on the sheet, the registration roller pair 106 continues to be stopped for the time C1 and the pre-registration roller pair 10 that has been rotated so far to form the loop on the sheet.
The rotation of 7 was also stopped. That is, when the sheet reaches the registration sensor 132 early, the time C1 is lengthened, and when the sheet arrives late, the time C1 is shortened. The photosensitive drum 12 continues to rotate during the time C1.

Accordingly, the conventional copying machine 6 eliminates the above error by stopping the sheet for the time C1 and transfers the toner image to a predetermined position on the sheet. That is, the conventional copying machine 6 stops the sheet for the time C1 other than the time for forming the loop on the sheet.

Therefore, in the conventional copying machine 6, the distance G1 between the sheets sent to the photosensitive drum 12 is G1 = X + C1 · F when the sheet conveying speed is F, as shown in the diagram of FIG. , Roller pair before cash register 107
In order to eliminate the sheet conveyance error caused by (1), it is necessary to increase the sheet interval by (C1 · F).

Therefore, the conventional copying machine 6 has a poor image forming efficiency.

In FIG. 7, the distance D is the distance from the irradiation point 134 on the photosensitive drum 12 to the transfer point 133 for transferring the image onto the sheet. The distance E is
It is the distance from the transfer point 133 to the writing point 131. If B is the loop amount, these distances are
There is a relation of E = D−B− (C1 · F).

An object of the present invention is to provide an image forming apparatus having excellent sheet conveying efficiency.

[0022]

In order to achieve the above object, the image forming apparatus of the present invention comprises an electrostatic latent image formed by optical scanning of a scanning means on a uniformly charged image carrier and developing means. In an image forming apparatus that transfers a developed image to a sheet after developing the developed image into a sheet, a sheet conveying unit that is arranged on the upstream side of the image carrier to convey the sheet, and the image bearing by the scanning unit. A sheet detection unit that is disposed between the position where the leading edge of the sheet passes and the sheet transporting unit when the optical scanning of the body is started and that detects the leading edge of the sheet transported by the sheet transporting unit. A pair of resist rotators capable of receiving the leading edge of the sheet conveyed by the sheet conveying means in a stopped state, and then conveying the sheet to the image carrier, and the sheet detecting unit. Means for detecting the leading edge of the sheet between the means and the pair of resist rotators, and from the detection of the leading edge of the sheet by the sheet sensing means to the detection of the leading edge of the sheet by the resist sensing means And a control means for storing the maximum allowable time required for the sheet transporting means and for stopping the pair of resist rotators to form a loop on the sheet while the sheet conveying means is operating. After forming a loop on the sheet by obtaining the difference between the actual required time for feeding from the detection means detecting the leading edge of the sheet to the detection of the leading edge of the sheet and the allowable maximum required time The sheet conveying means and the pair of resist rotators are stopped for the difference time.

In the image forming apparatus of the present invention, the sheet conveying amount of the sheet conveying means corresponding to the difference time is within the permissible range of the loop amount capable of correcting the skew of the sheet received by the pair of resist rotators. It is set within.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION A copying machine which is an image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings. The present invention is applicable not only to copying machines, but also to printers, facsimiles,
The present invention can be applied to a multi-function machine and the like, and is not limited to a copying machine.

The copying machine 7 is provided with an original table 2 made of a fixed transparent glass plate on the upper part of the main body 11 of the copying machine 7. A document is automatically fed to the document table 2 by the document feeder 3. The document sent to the document table 2 is read by the reading unit 4. The image information read by the reading unit 4 scans the photosensitive drum (image carrier) 12 uniformly charged by the charger 13 with the laser light emitted from the writing laser unit (scanning unit) 5. It is adapted to be written on the photosensitive drum 12.

The sheet supply unit 8 is the main body 1 of the copying machine 7.
Deck 30, 31 built in 1 and this deck 30,
Deck sheet supply units 34 and 35 for feeding the sheet S stored in 31 to the image forming unit 9 described later, the deck 30,
Sheet cassettes 32 and 33 arranged below 31;
The sheet cassettes 32 and 33 are composed of cassette sheet feeding units 36 and 37 that feed the sheets S stacked in the image forming unit 9.

The image forming unit 9 includes a photosensitive drum 12, a charger 13 for uniformly charging the surface of the photosensitive drum 12, and light emitted from an optical system onto the surface of the photosensitive drum 12 charged by the charger 13. A developing device 14 (developing means) that develops the electrostatic latent image formed by the image into a toner image, a transfer charging device 19 that transfers the toner image developed on the surface of the photosensitive drum 12 to the sheet S, and a photosensitive member. A separation charger 20 for separating the sheet S on which the toner image is transferred from the drum 12 and a cleaner 26 for removing the toner remaining on the photosensitive drum 12 after the toner image is transferred are configured.

On the downstream side of the image forming section 9, a conveying section 21 for conveying the sheet S on which the toner image is transferred, and a fixing device for fixing the image on the sheet S conveyed by the conveying section 21 to the sheet as a permanent image. 22, a discharge roller pair 24 for discharging the sheet S having the toner image fixed by the fixing device 22 from the apparatus main body 11 of the copying machine 7, and a discharge roller pair 24 outside the apparatus main body 11 of the copying machine 7. A discharge tray 25 or the like for receiving the discharged sheet S is provided. The entire copying machine is controlled by a control section (control means) 151.

In FIG. 2, the writing reference sensor (sheet detecting means) 140 is located upstream of the image writing point 131 in the registration roller pair (register rotation member pair) 1.
06 and the pre-registration roller pair (sheet conveying means) 107.

From the deck sheet supply section 34 to the image forming section 9
Sheet supply to the machine will be described.

The pickup roller 101 is the deck 30.
The sheet S set at is sent to the sheet supply roller 102. At this time, the sheets may be overlapped and delivered from the deck 30. Therefore, the lower sheet, which overlaps the uppermost sheet, moves in synchronization with the pickup roller 101, the sheet supply roller 102, and the sheet supply roller 102 that is provided so as to face the sheet supply roller 102 and is conveyed in a constant torque direction. It is separated from the uppermost sheet and returned to the deck 30 by the separating roller 103 which receives the force of rotating in the opposite direction. Therefore, the deck sheet supply unit 3
4 is deck 3 only for the top sheet (first sheet)
Send from 0.

Next, the vertical path sensor 104 detects the leading edge of the first sheet. Then, the first sheet is passed to the first transport roller 105. After that, by the pre-registration sensor 130 and the writing reference sensor 140,
The leading edge of the first sheet is detected one after another. Control unit 151
Operates the pickup roller 101 when the trailing edge of the first sheet leaves the sheet supply roller 102 based on the detection operation of the pre-registration sensor 130. The pickup roller 101 starts supplying the second sheet from the deck 30. As a result, the sheet supply unit 8
Thus, the sheet interval becomes a predetermined interval X.

In FIG. 2, the laser unit 5 is supposed to reach the image writing point 131 at the leading edge of the first sheet with reference to the time when the writing reference sensor 140 detects the first sheet. Is a laser beam on the photosensitive drum 1
2. Start scanning over. The first sheet is further conveyed by the first conveying roller 105 (FIG. 1) and sent to the pre-registration roller pair 107. Then, the sheet is conveyed to the registration roller pair 106 by the pre-registration roller pair 107. During this time, the registration sensor (registration detection means) 132 detects the leading edge of the sheet.

When the sheet is fed into the registration roller pair 106, the rotation of the registration roller pair 106 is stopped. Therefore, the first sheet hits the nip N of the registration roller pair 106 and stops. However, the pre-registration roller pair 107 continues to rotate. Therefore, since the leading edge of the first sheet is stopped and the sheet is conveyed from the intermediate portion onward, the intermediate portion rises and is curved. That is, a loop is formed on the first sheet.

The pre-registration roller pair 107 conveys the first sheet by feeding a predetermined amount B after the middle portion of the first sheet and forming a predetermined amount of loop on the first sheet. Stop. When the first sheet is skewed, it is straightened by forming a loop. After that, the registration roller pair 106 starts rotating and sends the sheet to the photosensitive drum 12.

By the way, in the copying machine 7 of the present embodiment, the laser unit 5 emits a laser beam at the time when it is considered that the leading edge of the sheet reaches the image writing point 131 with reference to the time when the writing reference sensor 140 detects. It is supposed to start scanning on the photosensitive drum 12.

Therefore, in the copying machine 7 of the present embodiment, the sheet rushes into the pre-registration roller pair 107, and the sheet conveying speed varies relatively due to the thickness of the sheet, the material of the sheet, the curled state of the sheet, and the like. Since the writing reference sensor 140 detects the leading edge of the sheet after the occurrence of the error, the image writing point 131 is detected after the leading edge of the sheet is detected by the writing reference sensor 140.
The error in the time to reach is smaller than that of the conventional copying machine 6.

However, even if the error is reduced, it is necessary to eliminate the error as long as there is an error. Therefore, at the time of manufacturing, assuming the longest allowable time (allowable maximum required time T2max) from the detection of the sheet by the writing reference sensor 140 to the detection by the registration sensor 132 (which can be obtained by an experiment). And the time is stored in the control unit 151 in advance. The control unit 151
The maximum allowable time T2m for each sheet actually conveyed
C2 between ax and the time from the writing reference sensor 140 to the registration sensor 132 (actual transfer required time T2p)
(= T2max−T2p) is determined, and after a predetermined loop is formed on the sheet, the registration roller pair 106 is continuously stopped for the time C2, and the register that has been rotated so far is formed to form the loop. The rotation of the front roller pair 107 is also stopped. That is, the control unit 151 eliminates the above error by increasing the time C2 when the sheet reaches the registration sensor 132 early and shortening the time C2 when the sheet arrives late.

Therefore, in the copying machine 7 of the present embodiment, the distance G2 between the sheets sent to the photosensitive drum 12 is G2 = X + C2 · F when the sheet conveying speed is F, and the pre-registration roller pair 107 is used. In order to eliminate the sheet conveyance error, it is necessary to increase the sheet interval by (C2 · F).

However, the time C2 in the copying machine 7 of this embodiment is shorter than the time C1 in the conventional copying machine 6. That is, in the copying machine 7 of the present embodiment, as described above, the sheet rushes into the pre-registration roller pair 107, and the sheet conveying speed is relatively high depending on the sheet thickness, the sheet material, the curled state of the sheet, and the like. Since the writing reference sensor 140 detects the leading edge of the sheet after the occurrence of the variation, the error in the time from when the leading edge of the sheet is detected by the writing reference sensor 140 to when the image writing point 131 is reached. Is less than the conventional copying machine 6. Therefore, the time C2 of the copying machine 7 of the present embodiment is shorter than the time C1 of the conventional copying machine 6.

FIG. 4 shows time C2 of the copying machine 7 of this embodiment.
And a time C1 of the conventional copying machine 6 are obtained by experiments. The upper part of the table of FIG. 4 shows the time C of the conventional copying machine 6.
1 and the lower part shows the time C2 of the copying machine 7 of the present embodiment. According to the table of FIG. 4, the copying machine 7 of the present embodiment
The time C2 of the conventional copying machine 6 is about 5 ms.
1 is about 16 ms. Therefore, the allowable maximum required time is reduced by about 11 ms.

As a result, the copying machine 7 of the present embodiment is G2
Since the relationship of (= X + C2) <G1 (= X + C1) is satisfied, it is possible to reduce the sheet interval and convey the sheet, and accordingly, the sheet conveying efficiency can be improved.

Further, when the sheet conveyance amount of the pre-registration roller pair 107 corresponding to the time C2 is received by the registration roller pair 106 and is within the allowable range of the loop amount capable of correcting skew of the sheet, the time C2 is provided. Even without it, the above error can be eliminated while forming the loop on the sheet.

FIG. 5 shows a case where a loop is formed on a sheet.
It is the table which calculated the permissible range which can carry out skew correction by experiment. According to FIG. 5, the loop amount is about 6 mm to about 11 mm
If so, skew feeding of the sheet can be corrected. That is, even if there is an error of about 5 mm (= 11 mm-6 mm) in the loop amount, skewing of the sheet can be corrected.
On the other hand, according to FIG. 4, the time C2 of the copying machine 7 of the present embodiment.
The sheet conveyance amount corresponding to is about 2.5 mm. Therefore, the sheet conveyance amount (about 2.5 mm) corresponding to the time C2 of the copying machine 7 of this embodiment is included in the loop amount error (about 5 mm) when correcting the skew of the sheet. Become.

As described above, when the sheet conveyance amount of the pre-registration roller pair 107 corresponding to the time C2 is set within the allowable range of the loop amount capable of correcting the skew feeding of the sheet, the time C2 is obtained as shown in the diagram of FIG. Even if the sheet is not provided, the above error can be eliminated while the loop is formed on the sheet, and the sheet conveyance interval is G2 (= X) <G1 (= X + C
It becomes the relationship of 1).

The actual stop time H2 of the pre-registration roller pair in this case is specifically the number of copies per minute (PPM).
Is calculated by the control unit 151 from the rotation start timing (generally about 590 ms with a margin of about 10 ms in a 100 PPM copying machine) allocated by the registration roller pair 106 earlier than the first sheet. If the writing reference sensor 140 comes to the eye,
The stop time H2 becomes large, and when it is late, the time C2 is set to zero because it is within the allowable range of the loop amount.
At this time, a pair of registration rollers and a sheet conveying interval G2 behind
Becomes G2 = X (FIG. 3).

In the copying machine 7 of the present embodiment, the sheet intervals can be packed further than before, and the sheets can be conveyed, and the sheet conveying efficiency can be improved accordingly.

In FIG. 2, the distance D is the distance from the irradiation point 134 on the photosensitive drum 12 to the transfer point 133 for transferring the image onto the sheet. The distance E is
It is the distance from the transfer point 133 to the writing point 131. These distances are E = D−B− (C2 ·
F).

[0049]

In the image forming apparatus of the present invention, the control means is
After forming a loop on the sheet by obtaining the difference between the actual required time for feeding from the detection of the leading edge of the sheet by the sheet detecting means to the detection of the leading edge of the sheet by the resist detecting means and the allowable maximum required time, the difference is calculated. Since the sheet conveying means and the pair of resist rotators are stopped only during the period of time, it is less affected by the variation in the sheet conveying speed by the sheet conveying means, and the sheet conveying interval can be reduced accordingly. Therefore, it is possible to improve the sheet conveying efficiency.

If the sheet conveying amount of the sheet conveying means corresponding to the above difference is set within the permissible range of the skew amount of the sheet received by the pair of registration rotators, the sheet conveying means can be corrected. The sheet conveyance interval can be set without considering the variation in the sheet conveyance speed due to the above, and the sheet conveyance efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a schematic front sectional view of a copying machine that is an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a portion related to the present invention in FIG.

3 is a diagram showing a sheet conveyance state between a pre-registration roller pair and a registration roller pair in the copying machine of FIG.

FIG. 4 is a table obtained by an experiment for a difference in a register section of the copying machine of FIG. 1 and a difference in a register section of a conventional copying machine.

5 is a table obtained by an experiment for a permissible range in which skew feeding can be corrected when a loop is formed on a sheet in the copying machine of FIG.

FIG. 6 is a schematic front sectional view of a copying machine which is a conventional image forming apparatus.

7 is a partial enlarged view for explaining a problem in the copying machine of FIG.

8 is a diagram showing a sheet conveyance state between a pre-registration roller pair and a registration roller pair in the copying machine of FIG.

[Explanation of symbols]

S sheet G2 sheet interval F sheet conveying speed B sheet feed amount for forming a loop on a sheet 5 laser unit (scanning unit) 7 copying machine (image forming apparatus) 9 image forming unit 11 apparatus body 12 of copying machine Photosensitive drum (image bearing member) 14 Developing device (developing means) 106 Registration roller pair (registration rotating body pair) 107 Pre-registration roller pair (sheet conveying means) 132 Registration sensor (registration detection means) 140 Writing reference sensor (sheet detection means) ) 151 control unit (control means)

Continued front page    F term (reference) 2H072 AA07 AA16 AA29 AB08 CA01                       CB05 JA02                 3F048 AA02 AA04 AA05 AB01 BA05                       BB02 CC03 CC17 DA06 DB07                       DC00 EA15 EB24 EB30                 3F049 AA10 DA12 EA24 EA27 LA02                       LA05 LA07 LB03                 3F102 AA02 AA10 AA11 AB01 BA02                       BB02 CA01 CB07 DA08 EA03                       FA08

Claims (2)

[Claims] 1. An image forming method in which an electrostatic latent image formed by optical scanning of a scanning means on a uniformly charged image carrier is developed into a visible image by developing means, and then the developed image is transferred to a sheet. In the apparatus, a sheet conveying unit that is arranged on the upstream side of the image carrier and conveys a sheet, and a position where the leading end of the sheet passes when starting optical scanning of the image carrier by the scanning unit, A sheet detection unit that is disposed between the sheet conveyance unit and detects the leading end of the sheet conveyed by the sheet conveyance unit, and a leading end of the sheet conveyed by the sheet conveyance unit in a stopped state. Once the sheet is received, the leading edge of the sheet is detected between the pair of resist rotators capable of transporting the sheet to the image carrier and between the sheet detection unit and the pair of resist rotators. The resist detecting means and the maximum allowable time from the detection of the leading edge of the sheet by the sheet detecting means to the detection of the leading edge of the sheet are stored, and the sheet conveying means is operated. As it is, the control means for stopping the pair of resist rotators to form a loop in the sheet, the control means, after the sheet detection means detects the leading edge of the sheet, the registration detection means After forming a loop on the sheet by finding the difference between the actual feed required time until the leading edge of the sheet is detected and the allowable maximum required time, the sheet conveying means and the resist rotating body pair are stopped for the time of the difference. An image forming apparatus characterized by being kept. 2. The sheet conveying amount of the sheet conveying unit corresponding to the difference time is set within an allowable range of a skew amount correctionable loop amount of the sheet received by the pair of registration rotators. The image forming apparatus according to claim 1, wherein: