JPH07215498A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device which reduces the carrying load for the sheet after separation and feeding, prevents the excessive carriage of the succeeding sheets, and improves the separation and carriage performance of the sheet. CONSTITUTION:The rear end of the sheet P passes the nip area of a feeding roller 9 and a separating pad 10 based on the detected signal of a size detecting sensor and a sensor 20 before resist, and the timepoint is predicted when the succeeding sheet P comes as close as possible to the nip area of the feeding roller 9 and the separating pad 10, and the driving of the feeding roller 9 is controlled to stop.

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 or a printer, and more particularly to an image forming apparatus having a separating / feeding means for separating and feeding a plurality of stacked cut sheets. is there.

[0002]

2. Description of the Related Art Conventionally, in image forming apparatuses, particularly electrophotographic copying machines, there is a tendency to employ a method having a superior paper feeding performance with the spread of recycled paper. Since this recycled paper has unevenness in the waist or the cut state of the paper and the claw separation method that has been often used in copying machines in the past causes a paper feed failure or double feed, the paper feed roller and the paper feed roller 2. Description of the Related Art A copying machine that uses a Duplo type paper feeding device that separates sheets of paper one by one by a separation pad that uses a plate-shaped cork-containing urethane rubber or the like that is pressed against a paper roller is widely used.

FIG. 4 shows an example of a feeding device equipped in a copying machine. A transfer sheet 53 is loaded on an intermediate plate 52 provided in the paper feed cassette 51, and the intermediate plate 52 is urged upward in the direction of arrow A from the back side by an unillustrated pressing means such as a pressing spring. The upper surface of the transfer paper 53 is in contact with the paper feed roller 54. A separation pad 55 is in pressure contact with the paper feed roller 54. The separation pad 55 is urged in the direction of arrow C by a spring 55a to press the paper feed roller 54.

When the paper feed roller 54 rotates in the direction of arrow B, the transfer paper 53 enters the contact area between the paper feed roller 54 and the separation pad 55, and the separation pad 55 causes the transfer paper 53 on the uppermost side and below it. The transfer paper 53 is separated. For example, if two transfer sheets 53 enter this area, the first sheet (upper side)
Transfer paper 53 is fed to the feeding roller 54, and the second sheet (lower side)
The transfer paper 53 is blocked by the separation pad 55. Two
The transfer sheet 53 of the first sheet is about to be conveyed to the downstream side by the frictional force with the transfer sheet 53 of the first sheet, but since the frictional force with the separation pad 55 is larger, the transfer sheet 53 is blocked. Only the paper 53 is separated and fed.

After the transfer paper 53 is separated, the paper feed roller 54 is driven to convey the transfer paper 53 until the transfer paper 53 reaches the state shown by the one-dot chain line in FIG.
When the rear end 53a of 53 is located between the front end of the intermediate plate 52 and the separation pad 55 as shown in FIG. 4, the drive of the paper feed roller 54 is cut off. If the driving force is further applied and the paper feed roller 54 continues to rotate, the second and subsequent transfer papers 53 will be fed, and if the paper feed cassette 51 is tried to be pulled out in this state, the leading edge of the paper will be the main frame of the device. It is more likely to come in contact with and break.

Further, as described below, a force acts on the transfer paper 53 to prevent the registration roller 56 from trying to convey the transfer paper 53 at a constant speed. (1) The separation pad 55 comes into contact with the transfer paper 53, and the frictional force of these two members receives a force in the direction opposite to the conveying direction. (2) Transfer paper between the registration roller 56 and the separation pad 55
When 53 is pulled, transfer paper 53 is U-turn guide.
The transfer sheet 53 is pressed against 57, and the frictional force between the transfer sheet 53 and the U-turn guide 57 acts in the direction in which the transfer sheet 53 is not conveyed. (3) The paper feed roller 54 is pressed in the direction of arrow A from the side of the intermediate plate 52, and a large torque is required to rotate the paper feed roller 54 in the direction of arrow B. Transfer paper against this torque
53 must be transported by the paper feed roller 54.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above,
Since three large forces act on the transfer paper 53, the peripheral speed of the photosensitive drum 58 and the transfer speed of the transfer paper 53 differ due to fluctuations in the transfer speed of the registration roller 56, and the toner image on the drum 58 shakes. As a result, “transfer deviation” occurs in which the transfer is transferred to the transfer paper 53.

The item (3) has the greatest influence on the image formation as the cause. In the paper feeding device, the middle plate 52 in the paper feeding cassette 51 is the paper feeding roller.
The intermediate plate 52 constantly presses the transfer paper 53 of various types and various sizes to a certain pressure or more, for example,
A pressure of about 700 g is applied to the paper feed roller 54. While the paper feed roller 54 is being driven, the paper feed roller 54 conveys the transfer paper 53 against this pressing force, so that no problem occurs. However, if the drive is temporarily stopped, only the registration roller 56 is moved. The transfer paper 53 must be transported by. In this case, the pressure applied to the pair of rollers of the registration rollers 56 must be made very large, and in some cases the load torque of the registration rollers 56 may become too large and the rotation of the registration rollers 56 may become uncontrollable with an electromagnetic clutch or the like. there were.

Further, the drive of the paper feed roller 54 is rotated longer than necessary without being interrupted, and for example, the paper feed roller 54 and the separation pad are rotated.
If the paper feed roller 54 is rotated until the trailing edge 53a of the transfer paper 53 is completely removed from the nip with the transfer paper 53, the next transfer paper 53 jumps out of the nip. If the paper feed cassette 51 is pulled out in this state, the leading edge of the next transfer paper 53 may come into contact with the apparatus body frame and be damaged.

An object of the present invention is to solve the above-mentioned problems of the prior art, to reduce the conveyance load on a sheet after separating and feeding, prevent the next sheet from being excessively conveyed, and improve the sheet separating / conveying performance. And an image forming apparatus.

[0011]

A typical means for solving the above-mentioned problems of the prior art and applied to the embodiments described below is a sheet stacking means for stacking and storing sheets, and the sheet stacking means. Feeding means for feeding the stacked sheets, separating means for separating the sheets fed out by the feeding means one by one, and a sheet for detecting passage of sheet ends separated / fed by the separating means Edge detecting means, size detecting means for detecting the size of sheets stacked on the sheet stacking means, and image forming means for forming an image on the sheets fed by the feeding means according to image information. And a control means for controlling the drive stop timing of the feeding means according to the detection signals of the sheet edge detection means and the size detection means.

[0012]

According to the above means, the control means predicts the timing when the trailing edge of the sheet passes through the separating means based on the detection signals of the size detecting means and the sheet end detecting means, and stops the driving of the feeding means. To control.

[0013]

Next, an image forming apparatus according to an embodiment of the present invention to which the above means is applied will be described. This embodiment will be described using a copying machine as an example of an image forming apparatus. FIG. 1 is an explanatory diagram showing an operation sequence of the sheet feeding apparatus, and FIG. 2 is a sectional view showing a schematic configuration of a copying machine.

(Overall structure)

First, the schematic structure of the copying machine will be described with reference to FIG. In FIG. 2, reference numeral 1 denotes a document table glass for placing a document on which a document to be copied is placed. Reference numeral 2 denotes an exposure device which moves in the direction of arrow D while scanning the original placed on the original table glass 1 and scans the entire original surface.

The reflected light obtained by irradiating the original with the exposure device 2 is imaged on the photosensitive drum 5 via the first mirror group 3a, the zoom lens 4 and the second mirror group 3b. An electrostatic latent image is formed.

The photosensitive drum 5 is provided in a process cartridge 6 equipped with a plurality of process means for contributing to image formation on the periphery thereof, and a charging means 6a, a developing means 6b and a cleaning means are provided around the photosensitive drum 5. 6c and the like are provided. The electrostatic latent image formed on the photosensitive drum 5 is developed by the developing means and visualized.

A cassette 7 is a sheet stacking means for stacking and storing sheets P such as recording sheets, which is detachably mounted on the bottom of the apparatus main body. Inside this cassette 7, the middle plate 7
a is rotatably provided and pushes up the intermediate plate 7a by a not-shown pressing means provided on the back surface side, and the sheet P stacked on the intermediate plate 7a is a feeding roller 9 serving as a feeding means. It is configured to generate a frictional force between the two by being pressed against. Further, 10 is a separation pad as a separation means, which is pressed by the pressing spring 10a and is fed by the feeding roller 9
Is pressed against.

When the feeding roller 9 rotates, it is fed from the uppermost sheet P, and when passing between the feeding roller 9 and the separation pad 10, the sheets are separated and fed one by one. Then, it is conveyed through a reversing conveyance path formed between the feeding roller 9 and the reversing guide 11, then passes through the pre-registration guide 12 and is guided to the pair of registration rollers 13 that is temporarily stopped. The pair of registration rollers 13 synchronizes with the developed image formed on the photosensitive drum 5 and conveys the sheet P to the transfer portion.

A transfer roller 14 is in pressure contact with the photosensitive drum 5. The transfer roller 14 constitutes an image forming means for forming an image on the sheet P together with the process cartridge 6. That is, the pair of registration rollers
When the sheet P conveyed by 13 passes between the photosensitive drum 5 and the transfer roller 14, the developed image formed on the photosensitive drum 5 is transferred. The sheet P after the image transfer is
When transferred by the transfer device 15 and passing through the fixing device 16, heat and pressure are applied to fix the transferred image. Then, the sheet P after the image fixing is conveyed and discharged to the discharge tray 18 by the discharge roller pair 17.

(Description of Sheet Conveying Operation Sequence)

Next, a sheet conveying operation sequence by a controller (control means) not shown will be described with reference to FIG. Immediately before the registration roller pair 13, a sensor lever 19 and a pre-registration sensor 20 as a sheet edge detecting means are provided. When the sheet P passes, the sensor lever 19 rotates to turn on the pre-registration sensor 20 /
It is turned off. Further, in the cassette 7, the sheets P stacked and stored in the cassette 7 at a position not shown
A size detection sensor is provided as a size detection means for informing the apparatus body of the size of the.

Further, in FIG. 1, L ₁ indicates a sheet conveyance path length from the registration roller pair 13 to the downstream side from the nip between the feeding roller 9 and the separation pad 10. L ₂ represents the sheet conveyance path length from the pre-registration lenser 20 to the nip between the registration roller pair 13. L ₃ indicates the length of the sheet conveyance path conveyed downstream from the nip portion of the registration roller pair 13.

When the leading end of the sheet P hits the nip of the registration roller pair 13 which has been fed out by the feeding roller 9 and is stopped, a loop P'is formed, and skew feeding immediately after feeding is corrected. At this time, the loop amount (the amount by which the sheet P is additionally fed) L ₄ is expressed as follows. If the length of the sheet P existing in the region of L ₁ is L ₅ , then L ₄ = L ₅ −
It becomes L ₁ . Further, the sheet length data detected by a controller (not shown) by the output from the size detection sensor is P ₁ , and the sheet P held in the registration roller pair 13 is P.
The ON time of the registration roller pair 13 which is conveyed to the downstream side by the driving start of the registration roller pair 13 is t ₁ , and the sheet conveyance speed of the registration roller pair 13 is V ₁ . The operation sequence will be described under the above conditions.

The sheet P fed from the cassette 7 is separated only by the action of the feeding roller 9 and the separating pad 10, and is fed to the downstream side by the rotation of the feeding roller 9, When P rotates the sensor lever 19, the pre-registration sensor 20 is turned on. From this point,
By rotating the feeding roller 9 for (L ₂ + L ₄ ) / V ₁ hour, the sheet P abuts on the nip of the registration roller pair 13 whose front end is stopped to form a loop P ′. In this state, the driving of the feeding roller 9 is once stopped.

Next, the registration roller pair 13 starts to rotate at the timing of the optical system for scanning the original by the exposure device 2, and L ₃ = t ₁ V ₁ P ₁ = L ₃ + L ₁ + L ₄ = t _{1 V 1 + L 1 + L} 5 becomes a -L _1. Then, after the registration roller pair 13 rotates for t ₁ time, the rotation of the feeding roller 9 is stopped. The time t ₁ is calculated in advance by the controller, and as shown in FIG. 1, the trailing edge of the sheet P fed is separated from the nip region between the feeding roller 9 and the separation pad 10 to the downstream side. Has become. Further, the leading edge of the sheet P to be fed next is brought as close as possible to the nip region between the feeding roller 9 and the separation pad 10.

Therefore, the load on the sheet after separation and feeding is reduced, and when the registration roller pair 13 is driven to convey the sheet P to the image forming portion, the feeding roller and the separation pad are separated from each other as in the conventional case. Since the rear end is not pinched in the nip, it is possible to prevent transfer deviation and image disturbance due to insufficient conveyance force of the registration roller pair 13, and to maintain high image quality. Further, when the driving of the feeding roller 9 is stopped, the next sheet P is fed to the feeding roller 9 and the separation pad
It is also possible to prevent double feeding by adding it to the nip with.

[Other Embodiments]

Next, another example of the image forming apparatus will be described with reference to FIG.
Will be described with reference to. Incidentally, since the schematic configuration of the copying machine is the same, the same reference numerals are given to the same members, and the description is cited,
The following description will focus on the characteristic points.

In the above embodiment, the driving of the feeding roller 9 is stopped at the earliest possible timing when the trailing edge of the sheet P passes through the nip region between the feeding roller 9 and the separation pad 10. This is necessary in order to prevent excessive conveyance of the next sheet P, but when the last sheet P stored in the cassette 7 is the last sheet P, there is no next sheet P, so there is no problem. Therefore, it is not necessary to stop the driving of the feeding roller 9 at a very delicate timing.

Therefore, in this embodiment, as shown in FIG. 3, a remaining amount detecting sensor 21a as a remaining amount detecting means for detecting the remaining amount of the sheet P in the cassette 7 and a sensor lever 21b are provided, and the last sheet is installed. By feeding P, the middle plate 7
When the sensor lever 21b falls into the notch 7b provided in a, the remaining amount detection sensor 21a is cut off, and when a signal indicating that the sheet P is lost is transmitted to the controller, the controller performs the sequence shown in the above embodiment. The timing of further stopping and stopping the feeding roller 9 is delayed by a certain amount, and when the trailing edge of the final sheet P surely passes through the nip region between the feeding roller 9 and the separation pad 10, the feeding roller 9 is stopped. Stop driving.

According to the present embodiment, the last sheet P in the cassette 7 is reliably conveyed until it passes through the nip region between the feeding roller 9 and the separation pad 10, thereby reducing the conveyance load and the registration roller. It is possible to prevent transfer deviation and image disturbance due to insufficient conveyance force of the pair 13.

In each of the above-mentioned embodiments, the separating means of the friction separation type, which is composed of the separation pad 10 which is brought into pressure contact with the feeding roller 9, is used, but the sheet arranged downstream of the feeding roller 9 is fed. It is also possible to use a so-called retard roller type separating means including a separation roller that rotates in a direction and a reverse roller that is provided so as to be in pressure contact with the separation roller and that rotates in a direction in which the sheet is returned. Further, although the above-described embodiments have been described by using the copying machine, the image forming apparatus is not limited to this, and may be other devices such as a facsimile device and a printer.

[0034]

As described above, according to the present invention, the control means is
With the trailing edge of the sheet sent out by the feeding means separated from the downstream side of the separating means, and the leading edge of the next sheet to be fed as close as possible to separation, the drive stop timing of the feeding means is set. By controlling, the conveyance load on the sheet after separation and feeding is reduced, and when the sheet is conveyed to the image forming unit, the disturbance of the image is prevented from occurring,
High image quality can be maintained. Further, it is possible to prevent the next sheet from being over-conveyed and double-fed when the driving of the feeding unit is stopped.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a sheet conveying operation sequence of a copying machine.

FIG. 2 is a sectional view showing a schematic configuration of a copying machine.

FIG. 3 is an explanatory diagram showing a configuration of a sheet remaining amount detecting means according to another example.

FIG. 4 is an explanatory diagram showing a configuration of a conventional copying machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Original glass stand 2 ... Exposure device 3a ... 1st mirror group 3b ... 2nd mirror group 4 ... Zoom lens 5 ... Photosensitive drum 6 ... Process cartridge 7 ... Cassette 9 ... Feed roller 10 ... Separation pad 10a ... Pressing spring 11 … Reversing guide 12… Pre-registration guide 13… Registration roller pair 14… Transfer roller 15… Conveying device 16… Fixing device 17… Ejection roller pair 18… Ejection tray 19, 21b… Sensor lever 20… Pre-registration sensor 21a… Remaining amount detection sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G03G 15/00 518 21/14

Claims (4)

[Claims] 1. A sheet stacking means for stacking and storing sheets, a feeding means for feeding the sheets stacked on the sheet stacking means, and a sheet fed by the feeding means are separated one by one. Separating means; sheet edge detecting means for detecting passage of sheet edges separated and fed by the separating means; size detecting means for detecting the size of sheets stacked on the sheet stacking means; Image forming means for forming an image on the sheet fed by the means according to the image information, and controlling the drive stop timing of the feeding means according to the detection signals of the sheet edge detecting means and the size detecting means An image forming apparatus, comprising: 2. The control means controls to stop the driving of the feeding means when the trailing edge of the sheet fed by the feeding means has finished passing through the separating means. The image forming apparatus according to claim 1, wherein: 3. The sheet stacking means is equipped with a remaining amount detecting means for detecting the remaining amount of stacked and stored sheets, and the control means drives the feeding means in response to a detection signal from the remaining amount detecting means. The image forming apparatus according to claim 1, wherein the stop timing of the image forming apparatus is controlled. 4. The control means sets the drive stop timing of the feeding means more than usual when the remaining amount detecting means detects that the last sheet stacked and stored in the sheet stacking means has been fed. The image forming apparatus according to claim 3, wherein the image forming apparatus is controlled to be delayed.