JP3441525B2 - Sheet feeder and image forming apparatus provided with the same - Google Patents

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 for electrophotography or the like, in which a sheet original for forming an image or a sheet of paper on which an image is formed is conveyed to a position for forming an image. The present invention relates to a sheet feeding device for a sheet and an image forming apparatus including the sheet feeding device.

[0002]

2. Description of the Related Art Conventionally, according to an image forming apparatus, a sheet-shaped recording sheet is conveyed to a position where an image is formed, an image is formed on the sheet-shaped recording sheet, and then the sheet is discharged outside the apparatus. . For example, an image of a document is projected onto a photoconductor, which is a recording medium, an electrostatic latent image is formed on the photoconductor, and the latent image is developed with toner, which is a colorant, in order to make it visible. Then, the toner image on the recording medium is transferred to a sheet-shaped sheet of paper that is conveyed to form a copy image, and the transferred sheet of paper is discharged from the apparatus through a fixing process. Also,
In the case of an original for forming the above-mentioned image on the photoconductor, if it is a sheet-like original, the originals are placed one by one in order to save the labor of manually placing them on an image forming position, for example, on a transparent original table. There is provided a device which is placed on a tray and is automatically fed to a document table which is an exposure position for forming images one by one.

Here, conventionally, in order to reliably feed sheets one by one to a target position, a separating means such as a separating material or a separating roller is provided separately from the sheet feeding roller to prevent double feeding. The sheets to be double-fed are forcibly separated so that only one sheet at the bottom or the top can be fed.

[0004]

According to the above-described paper feeding device, although the provision of the separating means to prevent the double feed is effective, the double feed is prevented in advance. There wasn't. That is, conventionally, in order to prevent the double feeding, the present invention is that the separating means has been devised so that the separating action by the separating means can be surely performed.

Further, it has been proposed that the sheet feeding device is provided with means for detecting double feeding, and when the double feeding is detected by the detecting means, the operation of the image forming apparatus itself is stopped. For example, Japanese Unexamined Patent Publication No. 6-40604 is equipped with an elevator mechanism (elevating mechanism) capable of raising and lowering a placing tray of a sheet feeding device, and the height (H1) of the placed uppermost sheet sheet before feeding. ) Is measured, the number of fed sheets is counted each time the paper is fed, and the height (H)
2) is measured, the difference (H1−H2) and the sheet thickness based on the value based on the count number are obtained, and the double feed is detected based on the sheet thickness.

However, even if the double feeding of the fed sheet sheets is detected, it does not prevent the double feeding of the sheet sheets, but merely stops the main body of the apparatus. Therefore, double feeding cannot be prevented in advance. Further, according to the technical content proposed in the above-mentioned publication, the thickness is measured in relation to the number of fed sheets based on the difference in the height of the uppermost portion after several sheets have been fed. ,
It was not possible to detect double feed during paper feeding. Therefore, after the sheet is fed, passed through the image forming area, and discharged to the outside of the apparatus, the preceding sheet may be detected as being double-fed.
Therefore, after the sheet is fed, if it is jammed in the image forming apparatus, it may be useless to detect whether the sheet is double-fed.

In view of this problem, it is an object of the present invention to provide an effective sheet feeding device capable of preventing double feeding in advance.

That is, the present invention is to effectively prevent the double feeding of sheets by detecting the thickness of the sheets and controlling the feeding speed according to the thickness.

Further, in the image forming apparatus provided with the sheet feeding device of the present invention, the sheet feeding speed is controlled, and at the same time, the image forming speed is controlled accordingly, thereby changing the sheet feeding speed. It is to surely perform control in accordance with the corresponding timing.

Further, in the present invention, the means for measuring the thickness of the sheet is used as it is, and when the sheet is fed from the uppermost portion, the position of the uppermost portion is maintained at a constant height. Although it is necessary, the purpose is to also serve as a means for keeping the height at a certain level.

[0011]

SUMMARY OF THE INVENTION In the sheet feeding apparatus of the present invention, in short, the distance to the uppermost portion placed on the placing tray is arranged so as to correspond to the rear end of the sheet surface to be fed. It detects by using the distance measuring sensor. This distance measuring sensor irradiates the light from the light emitting element to the target measurement object, causes the light receiving element to receive the reflected light at the irradiation point from the measurement object, and measures the distance according to the output state of the light receiving element. It is a thing. Therefore, the distance to the uppermost part before and after the fed sheet is measured by the distance measuring sensor, and the difference is calculated to measure the thickness of the fed sheet. Then, based on the measured thickness of the sheet, the thickness of the sheet is smaller than the predetermined thickness.
If it is thin, the paper feeding speed of the paper feeding device is controlled so as to slow the paper feeding speed.

According to the image forming apparatus equipped with the sheet feeding device of the present invention, the thickness of the sheet is measured in the case where the image is formed on the sheet fed by the sheet feeding device as described above. Then, the speed required for image formation is controlled according to the measured thickness. As the speed control, the speed of image formation is controlled together with the control of the sheet feeding speed. In particular, the conveyance speed for conveying the sheet to the image forming apparatus is controlled.

Here, the distance measuring sensor measures the position of the uppermost portion of the placed sheet, that is, the height. for that reason,
It can be processed as a signal for controlling the rise of the tray on which the sheet is placed according to the measurement distance, and the elevation of the above-mentioned placement tray is controlled based on this signal, and the position of the sheet is held at a determined height, Feed sheets.

[0014]

According to the sheet feeding apparatus of the present invention having the above-described structure, in response to the timing of feeding one sheet,
Each time, the distance (L2) to the sheet surface on the loading tray to the uppermost portion is measured by the distance measuring sensor. From the measurement result, the difference t (L2-L1) from the distance (L1) to the uppermost sheet surface measured before the sheet is fed is obtained. That is, since the distance to the uppermost portion when the sheet is fed is greater than the position where the distance measuring sensor is arranged, the distance L2 to the uppermost portion of the sheet after feeding is longer than the measured distance L1 before feeding the sheet. This difference t can be measured as the thickness t of the fed sheet. The paper feeding speed of the paper feeding means is controlled according to the thickness t. For example, the detected thickness t
However, if the thickness is smaller than the predetermined thickness ts, the paper feeding speed is reduced.

As a result, for example, when the sheet is thin,
Since the sheet feeding speed becomes slow, the sheet feeding force of the uppermost sheet to be fed becomes large. In addition, when the sheet feeding speed of the means for separating becomes slow, the separating action of the sheets to be double-fed becomes larger and the separating effect becomes higher. As a result, the effect of separating the multi-fed sheets is enhanced, and the multi-fed sheets are prevented, so that one sheet can be reliably fed.

On the other hand, when the sheet to be used has a thickness ts of a certain value or more, the sheet can be effectively separated by feeding at a normal sheet feeding speed due to the strength of the sheet itself and the action of the separating means. . However, when the fed sheet is sent to the image forming position, there is a high possibility that the sheet will be jammed in the conveying path. Even in such a state, it is possible to reduce the jam of the sheet after being fed in the image forming apparatus by controlling not only the feeding speed but also the conveying speed required for image formation, that is, slowing it.

When the sheet is fed from the uppermost portion, the distance measuring sensor measures the distance to the uppermost portion, that is, the height. Based on this measured distance, control can be performed to raise the uppermost sheet to a certain height. That is,
If the measured distance is less than the height of the sheet uppermost,
The elevating mechanism can be controlled so as to raise the loading tray so that the distance matches the determined height. As a result, the uppermost portion of the sheet can be held at a constant height, and the sheet feeding can be made more stable.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus equipped with a sheet feeding apparatus according to the present invention, particularly an electrophotographic copying apparatus will be described below with reference to the drawings. Further, although the electrophotographic copying apparatus will be described according to the present embodiment, it can be applied to all image forming apparatuses using the electrophotographic method. For example, it can be used for a sheet feeding device used in a laser printer, an LED printer, a liquid crystal printer, or the like.

FIG. 1 is a sectional view showing the outline of a copying apparatus provided with a sheet feeding apparatus according to the present invention. In the figure, an original table 2 made of transparent glass is provided on the upper surface of the copying apparatus main body 1, and an automatic original for supplying a sheet-like original to be copied to the original table 2 is provided on the original table 2. A feeding device 3, that is, a document is fed to an exposure position which is an image forming position of the document table 2, and after the exposure is finished, the document is circulated to the original document placement position again to circulate and feed the document (hereinafter referred to as RDH
Is described).

An optical system 11 is arranged below the original table 2. The optical system 11 includes a copy lamp (exposure lamp) 12 including a halogen lamp, a plurality of reflecting plates 4, 5, 6, 7, 8, 9 and a zoom lens 10. And the mirror 4 are installed on a movable optical system mounting table (not shown) which is movable along the document table 2, and the mirrors 5 and 6 move at a speed half that of the optical system mounting table. It is mounted on the second optical system mounting table. And a plurality of reflectors 4, 5, 6, 7, 8,
At 9, the light emitted from the copy lamp 12 is reflected by the document on the document table 2, and the reflected light image is projected on the photoconductor 13 along the optical path indicated by the alternate long and short dash line. For this projection, the zoom lens 10 is arranged on the optical axis of the optical path, and projects the image of the document on the surface of the photoconductor 13 at the set magnification.

Below the optical system 11, a photosensitive member 13 which is a cylindrical recording medium on which the above-mentioned reflected light image is irradiated is arranged, and a well-known image forming is provided around the photosensitive member 13. Means are arranged. That is, including the optical system 11 that constitutes the image forming unit, a charger 14 that charges the photoconductor 13 to a predetermined potential, and a developing process that attaches toner to the formed electrostatic latent image to make it visible as a toner image. A device 15, a transfer device 16 for transferring the toner image onto a transfer paper, and a static eliminator 17 for separating the sheet-shaped transfer paper from the photoconductor 13.
A cleaning device 18 for removing the residual toner after the transfer and a static eliminator 19 for removing the electric charge remaining on the photoconductor 13 are arranged.

In order to supply the transfer paper to the transfer position of the transfer device 16, the transfer paper, which is a sheet paper of various sizes, is accommodated and three paper feeding devices 20 for feeding the transfer paper of the selected size are provided. , 21, 22 are arranged on the right side of the main body of the copying apparatus. Since the toner image formed on the photoconductor 13 is transferred onto the transfer paper fed from any one of the paper feeding devices 20, 21, and 22, the transfer device is synchronized with the rotational position of the photoconductor 13. It is sent to the registration roller 23 for carrying to the position of 16.

After the toner image on the photoconductor 13 is transferred onto the transfer paper, the transfer paper is peeled off from the photoconductor 13 by the action of the static eliminator 17. On the peeling side, that is, on the left side of the photoconductor 13, a belt-shaped transport device 24 and a heat fixing unit 25 that melts and fixes an unfixed toner image via the device 24 are arranged to constitute a transfer paper transport system. ing. In addition, the heat fixing unit 2
The transfer paper passing through 5 is discharged to a discharge processing section 30 which is detachably provided in the copying apparatus main body 1 or an intermediate tray 2 provided for forming an image on both sides of the transfer paper.
Switching means 35 for switching the route for carrying out to 6
The direction can be switched with.

A transfer means 27 is provided in the switching path of the intermediate tray 26 by the switching means 35, and the intermediate tray 2 is provided.
A reversing / conveying unit 28 for carrying out the image formed on the transfer paper 6 to the upper side is arranged. Further, a sheet feeding means 29 is arranged for feeding the transfer sheet carried out to the intermediate tray 26 again to the image transfer position.

The discharge processing unit 30 temporarily stores a copy sheet of copy sheets in which the copy sheets are aligned in the page order of the original, and a stack of originals on the processing tray 31. A stapler 32 for stapling a corresponding copy sheet bundle, and a discharge tray 33 for the stapled transfer sheet bundle.
And a discharge unit 34 for discharging the discharge.

Further, the transfer paper feeding devices 20 and 2
Reference numerals 1 and 22 have the same configuration, and are vertically movable sheet mounting trays 202 and 212 for setting transfer sheets.
Paper feeding means 201, 211, 221 for supplying one sheet of the uppermost transfer sheet is provided corresponding to the uppermost transfer sheet. The paper feeding means 201, 211, 22
The transfer paper fed at No. 1 is a paper feed roller 201-8 and a separation roller 2 arranged in the next stage in order to prevent double feeding.
The sheet passes between 01-9 and is conveyed to the above-mentioned registration roller 23 through the confluence path 36 of the sheet feeding devices 20, 21 and 22. A transport path for the transfer paper fed from the intermediate tray 26 and a paper feed path for manually feeding the desired sheet-shaped transfer paper S are joined to the merge path 36.

In the copying apparatus having the above-described structure, in the present invention, the distance measuring sensor 37 for detecting the thickness of the sheet S in the sheet feeding device for feeding the sheet-shaped transfer sheet.
On the mounting trays 202, 212, 2 on which the transfer sheets are mounted.
It is arranged corresponding to the uppermost sheet on 22. The distance measuring sensor 37 for detecting the thickness of the sheet is provided as shown in the sheet feeding device of FIG. FIG. 2 shows the paper feeding device 2.
Although 0 is described as an example, other sheet feeding devices have the same configuration.

The distance measuring sensor 37 is, for example, the sheet feeding device 2.
The distance L1 to the uppermost portion of the sheets placed on the loading tray 202 of 0 is measured before feeding. By measuring the distance L2 from the measured distance L1 to the uppermost portion of the sheet after the sheet is fed, the difference t is calculated as L1-
The thickness t of the fed sheet can be measured by obtaining L2.

The measured thickness of the sheet is determined by the sheet feeding device 2
It is determined whether or not it is within the range of the predetermined thickness ts that can be processed at 0. According to this determination, if the measured thickness of the sheet is within the reference thickness ts, the sheet is fed at the normal feeding speed. That is, sheet feeding is performed at a processing speed capable of feeding one sheet having a thickness determined by the sheet feeding device. The speed of the sheet feeding device is determined under the design that can feed one sheet. It is designed to feed sheets of fixed thickness, which determines the speed. This paper feeding speed is set as a normal speed of the paper feeding device 20, for example.

Therefore, when the thickness of the sheet S is outside the range of the standard thickness ts that can be processed at the normal sheet feeding speed, for example, when it is thin (t <ts), the sheet feeding apparatus can treat the sheet normally. Depending on the paper speed, double feed, paper jam or misfeed may occur. Therefore, the sheet is fed at a feeding speed lower than the normal feeding speed. As a result, since double feeding is likely to occur when feeding thin sheets, the effect of preventing the occurrence of double feeding by slowing the feeding speed is obtained. You can reliably feed paper and eliminate jams and poor paper feed.

If the measured thickness t of the sheet is outside the range of the standard thickness ts and is thicker, even if double feeding by the sheet feeding device does not occur frequently, Paper feeding failure or paper feeding failure may occur. In other words, empty paper feed may be performed. It is also conceivable to jam the paper while it is being sent to the image forming position in the copying apparatus main body. For that reason, in terms of increasing the paper feeding ability,
The paper feeding speed is slowed down, the paper feeding power is improved, and reliable paper feeding is performed. Then, by slowing down the image forming speed in the image forming apparatus, it is possible to eliminate the risk of jam and perform reliable image formation.

An example of the construction of the sheet feeding device will be described with reference to FIG. The present invention is not limited to this paper feeding device. In the drawing, a sheet-like sheet, that is, a placing tray 202 on which the transfer sheet S is placed is provided so as to be able to move up and down
The mechanism for raising and lowering is configured such that the wire 203 fixed to both ends of the placing tray 202 is driven by a raising and lowering motor 206 that rotates forward and backward via each pulley 204 and a drive pulley 205.

A detection switch 207 for detecting the sheet to be placed is arranged on the loading tray 202, and the elevating motor 206 is driven, for example, in the normal direction in accordance with the detection of the loading to move the loading tray 202. When the uppermost sheet S reaches a predetermined height, the motor 206 is stopped. In this case, a limit switch for detecting the height of the top of the seat is arranged.

When the sheets on the loading tray 202 are used up, the loading tray 202 and the like are provided so that they can be pulled out from the copying apparatus 1 in order to replenish the sheets or replace the sheet size. In response to this pulling out, the lifting motor 206 is reversely driven, and the driving of the motor is stopped when the loading tray 202 is lowered to the lowermost position. Although not shown, a switch for detecting the state in which the mounting tray 202 is lowered to the lowermost position is appropriately arranged.

In order to feed the uppermost sheet S placed on the placing tray 202, the sheet feeding means 201 is arranged correspondingly. This paper feeding means 201
Is an air feeding unit in this example, which sucks the uppermost sheet by the action of air and feeds the sucked sheet. The paper feed unit 201 is not an air feeding may be a paper feeding means that by the friction roller.

The sheet feeding means 201 is a roller 201-for stretching a sheet feeding belt 201-1 for feeding the sheet S.
2, 201-3, the paper feeding belt 201-
The opening 201-5 of the intake duct 201-4 is arranged in the sheet feeding belt in order to suck the sheet. The intake duct 201-4 is connected to the fan device 208 and forms an air flow in the direction of the arrow. This allows
The uppermost sheet S is sucked onto the sheet feeding belt 201-1.

In addition to the air sucked together with the suction of the air, the air outlet 2 blows the air from the leading end in the paper feeding direction in order to separate the bundle of placed sheets.
01-6 are arranged so as to face each other, and the air outlet 201-
6 to the fan device 209 via the exhaust duct 201-7.
And forms a flow of air in the direction of the arrow. The blowout port 201-6 has a plurality of air blowing nozzles (not shown), ejects air near the uppermost sheet to float the sheet S to separate the stacked sheets, and there may be a plurality of sucked sheets. For example, it acts as an air knife that separates the lower sheet with air.

When sheet feeding is performed in the sheet feeding device 20 having the above configuration, first, air is ejected from the air outlet 201-6 to float the uppermost stacked sheet S,
Therefore, after the uppermost sheet S is sucked by the sheet feeding belt 201-1, the sheet feeding belt 201-1 is driven in the arrow direction to feed the uppermost sheet. Then, the paper feeding means 201
The sheet is fed to the above-mentioned registration roller 23 via the conveying path 36 via the feeding means including the feeding roller 201-8 and the separation roller 201-9 arranged on the front surface of the sheet. Paper feeding belt 2 including the feeding roller 201-8
The sheet feeding means 201 is constituted by 01-1.

Here, in the present invention, the loading tray 2
A distance measuring sensor 37 for measuring the height to the surface of the sheet to be placed on 02, that is, the distance, is arranged to face the sheet to be placed. The distance measuring sensor 37 is arranged corresponding to the rear end of the sheet to be fed, and has a sheet thickness t.
Measure the distance to the top of the seat to measure

Corresponding to the arrangement position of the sensor 37,
A pressing plate 38 for pressing the uppermost sheet is provided. The holding plate 38 is arranged corresponding to the position of a predetermined height of the sheet to be lifted, and in particular, after feeding the uppermost sheet, the solenoid 39 is pressed so as to push the next sheet to be fed from above.
Are connected. When the solenoid 39 depresses the uppermost sheet and the distance measurement sensor 37 completes the distance measurement, the energization state is deenergized so that the sheet feeding is not hindered, and the sheet feeding by the holding plate 38 is obstructed. In order to prevent this, the pressed state by the urging force of the spring 40 is released.

Therefore, the pressing plate 38 is pushed down to the uppermost sheet by the energization of the solenoid 39, and in this state, the distance measuring sensor 37 measures the distance. This distance is the distance from the position where the distance measuring sensor 37 is arranged to the upper surface of the holding plate 38. After the distance is measured, the energization of the solenoid 39 is deenergized, and the pressing plate 38 is separated from the sheet surface by the urging of the spring 40, and the sheet feeding operation is performed. At the timing when the sheet is fed and the trailing edge of the sheet passes the pressing plate 38, the solenoid 39 is passed and the pressing plate 38 presses the uppermost portion of the sheet. Since the distance measurement is performed at this point, the distance measurement is performed without being affected by vibrations during sheet feeding.

The sheet thickness t is obtained by this distance measurement, and the sheet feeding belt 201 serving as the sheet feeding means 201 is obtained.
The rotation (running) speed of -1 is controlled. Further, the fed sheet is fed to the next feeding roller 201-8 and separation roller 2
It is sent to the registration roller 23 by 01-9,
At that time, the feeding roller 201-8 and the separation roller 201-
The speed of 9 is also controlled accordingly to enhance the effect of controlling the speed of the feeding means and preventing double feeding of sheets.

FIG. 3 is a block diagram showing the control system of the copying machine according to the present invention. Microcomputer 4 comprising master CPU as control means constituting the control system
1 is provided. The master CPU 41 receives signals from various keys and sensors according to a program previously stored in the ROM 42, and controls a copying operation and a copying process related to projection scanning of an original by the optical system 11. Further, the RAM 43 for storing the data required each time the control is performed is connected like the ROM 42.

Further, the master CPU 41 controls the supply and stop of the supply of voltage to the copy lamp 12 of the optical system through the copy lamp drive circuit 44 in order to execute the copy control operation, and also applies the voltage to the copy lamp 12. The effective voltage level is adjusted and the light amount is controlled. Also,
The master CPU 41 controls the supply voltage of the charging device 14, the developing device 15, the transfer device 16 and the like via various drive circuits (including a driver and the like) 45. In addition, a series of copy control is executed through various drive circuits as necessary including the voltage supplied to the cleaning device 18, the static eliminator 19 and the like.

Further, the master CPU 41 receives the measurement signal from the distance measuring sensor 37 according to the present invention through the signal processing circuit 46, and measures or calculates the thickness t of the sheet. Based on this, in order to control the sheet feeding speed of the sheet feeding device 20 described above, the driving motor 4
8 speed control is performed. Further, in accordance with the distance measurement from the distance measuring sensor 37, the elevating motor 206 for positioning the uppermost position of the sheet placed on the placing tray 202 to a constant height is drive-controlled. This lifting motor 20
6 is driven in the forward and reverse directions via the driver circuit 56 in response to a command signal from the master CPU 41 in response to signals from the above-described various detection switches, etc., to raise and lower the loading tray 202. In this case, a signal from the rotary encoder 57 that outputs a signal indicating the rotational position such as the rotational angle of the lifting motor 206 is input to the CPU 41.

The speed of the drive motor 48 for driving the paper feeding means 201 of the paper feeding device 20 is controlled by the speed control circuit 49 via the driver circuit 50. In order to control the speed, the speed control circuit 49 inputs a signal from the rotary encoder 51 that outputs a signal corresponding to the motor rotation speed directly connected to the motor, thereby controlling the motor 48 at the speed set by the CPU 41. To drive.

Here, in FIG. 4, for example, in FIG.
An example of specifying the paper feeding process by the is shown. In FIG.
The sheet feeding device 20 is designed to be capable of feeding 75 sheets (sheets of A4 size in the lateral direction) per minute. In this case, when a sheet having a certain thickness is used, it is designed at a processing speed capable of feeding one sheet. This paper feeding speed is 450m
m / s. The sheet thickness t that can be processed at such a speed is in the range of 83 to 110 μm.

If the paper feeding speed is slower than the above speed, the range of sheet thickness that can be processed becomes large. For example, in the case of 277 mm / s (35 sheets / minute), the thickness of the sheet that can be processed is expanded to the range of 77 to 143 μm. Therefore, for a sheet with a thickness of 83 μm or more and 110 μm or less, it is 7 minutes per minute.
Even if you feed paper at a speed that can process 5 sheets, double feeding,
It can be processed with almost no paper feeding failure.

On the other hand, when the thickness of the sheet is out of the above range, for example, the sheet feeding speed is controlled to a sheet feeding speed capable of processing 35 sheets per minute. The speed of the copying process is also controlled at the same time according to the feeding speed at this time.

If it does not fall within the above range of 77 to 143 μm, it is sufficient to control the processing speed to be slower than the sheet feeding speed of 35 sheets per minute, for example, about 20 sheets, and more accurate. In order to increase the sheet feeding speed, a sheet feeding speed corresponding to each sheet thickness is set each time as shown in FIG. 4, and the sheet feeding speed is controlled.

Here, it is important to perform speed control of the copying process, that is, speed control for image formation at the same time as control of the paper feed speed. That is, by setting the copy speed that matches the paper feed speed, it is possible to easily match the timing of image formation on the fed sheet. For example, if the copying speed is maintained as it is by lowering the paper feeding speed, the timing of image formation on the fed sheet is deviated, and a problem such as processing as a jam occurs. Further, if the sheet is out of the range of the thickness suitable for the normal sheet feeding speed, a jam or the like may occur when the sheet is fed to the image forming position. Especially when the sheet is fed to a position facing the photoconductor, even if the thickness of the sheet is not a problem within a predetermined range, when the thicker sheet is conveyed to the photoconductor, Due to such a problem, there is a strong possibility that the sheet will be clogged at that position, and the photoconductor will be damaged at the leading edge of the sheet. Therefore, the above-mentioned problems can be solved by controlling the copying speed as well.

The distance measuring sensor 37 for measuring the sheet thickness according to the present invention has a light emitting element 37-1 for measuring the distance. Therefore, the master CPU4
In order to measure the distance of the distance measuring sensor 37, 1 drives the light emitting element 37-1 through the driver 47 at a predetermined timing, and the light receiving element 37-2 of the distance measuring sensor 37 at this time is set to the light receiving state. The signal output in response to the signal processing circuit 46
The sheet thickness t based on the measured distance is measured as described above according to the reception status, and the sheet feeding speed and the copying speed are also controlled based on this.

In order to control the copying speed, the main drive motor 52 that rotationally drives the photoconductor 13 is driven by the driver circuit 5.
The speed is controlled by the speed control circuit 54 via 3. That is, the photoconductor 13 is rotated in synchronization with the feeding speed and the carrying speed for carrying to the image forming position. When the main drive motor 52 rotates, the photoconductor 13 is rotated by a transmission unit such as a clutch when necessary, and the conveying unit is also rotated as needed. The rotation speed of the motor 52 is controlled based on a signal from the rotary encoder 55 that outputs a signal according to the rotation speed of the motor, when the speed control circuit 54 receives the speed command from the CPU 41.

Further, the above-mentioned input copy conditions are provided together with a copy condition, for example, a numeric key for numerically inputting the number of copies and an input key for designating copy magnification, copy density, and various functions such as double-sided or composite copy, trimming and masking. An operation panel 58 having a display unit for displaying the content of is connected.

Next, one specific example of the distance measurement by the distance measuring sensor 37 of the present invention will be described in detail. This distance measuring sensor 3
7 is, for example, the first in the "Sensor Technology" October 1992 issue.
Volume 2, No. 11 uses the “8-bit precision distance measuring sensor” described on pages 24 to 27. This distance measuring sensor is a PSD (Position Sensitive Detecto).
r) It is called a sensor, which measures the distance by irradiating the object to be measured with light from the light-emitting element and measuring the incident position of the reflected light from the object to the sensor.

This distance measuring sensor will be briefly described. This is a kind of PIN type photodiode, and as shown in FIG. 5, the silicon chip has ap ⁻ layer on the front surface, an n ⁺ layer on the back surface, and an intermediate layer therebetween. It is composed of an i layer, and electrodes A, B and C as shown in the figure are provided on the respective layers on the front surface and the back surface. An equivalent circuit of the PSD sensor having the structure shown in FIG. 5 is shown in FIG.

In FIG. 6, by supplying the bias voltage VB to the terminal of the electrode C, the resistances R1 and R2 change at the position of the light incident on the surface (spot position). For example, if light is incident on the midpoint (point d) between the electrodes A and B,
Although R1: R2 = 1: 1, the ratio of R1: R2 changes in proportion to the position of the incident light if the incident light deviates to one of the A and B electrodes. Now, assuming that the incident position of light is shifted to the B electrode side by x with respect to the center point d, and the length of the light receiving surface of the sensor (distance between A and B electrodes) is D, R1 + R2 = R0, R1 = R0 / 2 (1 + 2x / D) and R2 = R0 / 2 (1-2x / D).

Therefore, the current I extracted from the electrodes A and B in FIG. 6 is utilized by utilizing the above resistance change depending on the incident position (spot position) of the light on the light receiving surface of the PSD sensor.
1 and I2, and the current ratio I1 / I at this time
2 is, for example, proportional to the distance from the electrode B (inversely proportional to the distance from the electrode A). At this time, although the absolute values of the currents I1 and I2 change depending on the amount of light incident on the PSD sensor, since the incident position of light is proportional to the current ratio I1 / I2, the amount of light itself has no effect.

Therefore, in the relation of the current ratio I1 / I2, the position of the incident light on the light receiving surface on the PSD sensor can be specified, thus enabling accurate distance detection. In particular, when the current ratio becomes large, the incident light comes closer to the electrode A side of the PSD sensor, and conversely, when the current ratio becomes smaller, the electrode B side is irradiated with the incident light.

For example, as shown in FIG. 7, a light emitting element (infrared LED) 37-1 which constitutes the distance measuring sensor 37 of the present invention.
Is emitted to the object to be measured (sheet surface), and the reflected light is received by the light receiving section 37-2 of the PSD sensor constituting the distance measuring sensor 37 via the light receiving lens. The position x1 of the light receiving point (spot) at this time is obtained by x1 = A · f / Ls in the relationship shown in the figure. In the above formula, A is the distance between the centers of the light projecting lens and the light receiving lens, L1 is the distance from the light projecting lens to the object to be measured (the distance to the toner image surface according to the present invention), and f is the focal length of the light receiving lens. is there. Therefore, the position x1 of the light receiving spot on the light receiving surface of the PSD sensor becomes smaller and the position moves to the position x2 as the distance to the object to be measured increases. On the contrary, when the position x1 of the light receiving spot becomes large, the distance to the object to be measured becomes short.

The point x on the light receiving surface of the PSD sensor is the current ratio I1 / I2 obtained from the electrodes A and B as described above.
Therefore, the distance L from the light emitting element 37-1 to the object to be measured, that is, the distance to the light receiving portion 37-2 of the distance measuring sensor 37 can be easily measured according to the above equation.

Therefore, in the present invention, as shown in FIG. 3, the currents I1 and I2 obtained from the PSD sensor which is the distance measuring sensor 37 are converted into voltages V1 and V2 by the signal processing circuit 47, and the master CPU 41 is operated. Via the analog port input section (AN1, AN2) of. here,
The signal processing circuit 47 performs conversion processing as a voltage value equivalent to or equal to the obtained currents I1 and I2. The master CPU 41, based on this voltage value, I
The value corresponding to 1 / I2 is calculated to obtain the spot position (x) of the distance measuring sensor 37, and the distance between the sensors 37 to the top of the sheet can be calculated from the above equation for obtaining x.

Therefore, if necessary, the master CPU
Reference numeral 40 outputs a signal for driving the driver 32 to cause the light emitting element 28, which is an infrared LED, to emit light. Further, based on the output from the light receiving element 37-2 of the distance measuring sensor 37,
The sheet thickness is detected according to the obtained distance, and the sheet feeding speed and the speed of the copying process are controlled based on the detected thickness.

Here, in FIG. 7, the light receiving element 37-2
The effective length D of the light-receiving surface is 2 mm, the distance L2 between the distance measuring sensor 37 and the top surface of the sheet is 30 mm, the focal length f of the light-receiving lens is 5 mm, and the distance A between the light-projecting lens and the light-receiving lens is 20 mm. For example, the measurement limit distance L of the photoconductor surface
1 is obtained from the relational expression D = (1 / L1-1 / L2) · A · f, and the maximum distance L1 when the sheet is fed and reduced can be measured up to 18.75 mm. Therefore, the measurable distance difference ΔL (L2-L1) is 11.25 mm.
Becomes Therefore, when the analog data input through the terminals AN1 and AN2 on the CPU 41 side is processed as 8-bit data, the thickness t of the sheet can be measured in units of about 40 μm as the resolution. Therefore, if the distance L2 to the uppermost surface of the sheet is short and the distance measuring sensor 37 is arranged at a position of about 20 mm for the distance L2 from the distance measuring sensor 37 to the measuring surface, about 20 μm under the above conditions.
Can be measured in units. This may be set appropriately according to the thickness of the sheet to be handled.

An example of control according to the distance measurement of the distance measuring sensor 37 according to the present invention will be described below.

FIG. 8 shows an example of the control procedure by the master CPU 41 in the block diagram of FIG.
In particular, the paper feed speed and the speed of the copying process are controlled based on the detection of the sheet thickness.

When the power of the copying machine is turned on, the loading tray 202 such as the sheet feeding device 20 drives the lifting motor 206 to raise the uppermost sheet to a predetermined position, and a limit switch ( It is stopped in response to detection (not shown). This is because the CPU 41 inputs the detection signals from the above-mentioned various detection switches, and the lifting motor 206
Forward / reverse drive and stop control are performed.

In this state, if the copy switch for starting the copy operation is operated (n1), the distance measurement sensor 37 starts measuring the distance (L1) to the top of the sheet. Therefore, the light emitting element 37 of the distance measuring sensor 37-
1 is driven, and the reflected light from the uppermost part of the sheet receives the light receiving element 3
It is received by 7-2. At this time, the sheet pressing plate 38 is pressing the uppermost sheet, and the light receiving element 37-2 receives the reflected light from the upper surface of the sheet pressing plate 38. Therefore, the distance measurement is performed in a state in which the corrugation of the sheet, the vibration of the sheet mounting portion, and the like are prevented, and the distance measurement is very stable.

In particular, for the light receiving signal from the light receiving element 37-2, the analog signal from the signal processing circuit 46 is input to the analog input terminal of the CPU 41 to obtain the distance from the distance measuring sensor 37 to the above-mentioned sheet pressing plate 38. . Let this measured distance be L1, and this measured distance (L1)
It is temporarily stored in a predetermined storage area (M1) 43.

When this measurement is completed, the contents of the counter for counting the number of fed sheets are cleared (n
3) Do. After that, when the preparation for copying on the main body of the copying apparatus is completed, the sheet feeding operation is started by the sheet feeding command in order to feed the sheet (n4). As the paper feeding operation, in the configuration of FIG. 2, the fan device 20 is used for air feeding.
9 and 208 are driven to perform air suction and blowing, whereby the uppermost sheet is fed to the sheet feeding belt 201-1.
After the suction, the motor 48 is driven to rotate the sheet feeding belt 201-1 in the sheet feeding direction. The sheet is fed by this rotational drive.

The speed driven by the motor 48 is a preset speed that can be processed by the sheet feeding device, and the sheet thickness is such that the sheet can be processed at the maximum speed as shown in FIG. Treated as a sheet feed rate. When the sheet thickness is measured before the sheet is fed and the sheet thickness t is stored, the sheet feeding speed is set according to the thickness, and the sheet feeding speed Drive controlled.

Next, it is determined in n5 whether the time for feeding the trailing edge of the fed sheet has elapsed until the distance measuring sensor 37 can measure it. In particular, before performing the above distance measurement, the pressing plate 38 is placed on the solenoid 3 from the uppermost sheet.
It is in a state of being separated by the deenergization of 9 and the urging of the spring 40. Therefore, when the above time elapses, the holding plate 38
The solenoid 39 is energized in order to push the uppermost sheet.

With the pressing plate 38 pressing the uppermost portion of the sheet, the distance measurement by the distance measuring sensor 37 is restarted (n6). This measured distance is stored as L2 in the predetermined area (M2) of the RAM 43 described above.

When the above distance measurement is completed, the thickness t of the fed sheet is obtained. That is, the RAM 43 is first
The thickness t of the sheet being fed can be measured by obtaining the difference between the distances L1 and L2 stored in the predetermined areas M1 and M2 in L2-L1. The measured thickness t is similarly stored in a predetermined storage area (M3) of the RAM 43.

If the thickness t of the sheet being fed is 8 in the case of the sheet feeding device 20 having the characteristics shown in FIG.
The determination unit n8 determines whether the thickness ts is within the range of 3 to 110 μm. In this case, if the detected sheet thickness t is within the range, the paper feeding speed is maintained at n9 and the speed of the copying process is also maintained, and the copying operation is executed.

On the other hand, when the detected sheet thickness t does not exist in the range of the above-mentioned thickness ts, for example, if the sheet is thinner than 83 μm, the sheet is fed at a slower speed than the above-mentioned sheet feeding speed (n10). ). The speed of the copying process is also controlled to match this speed. For example, the feeding speed is set to 277 mm / s, and the rotation speed of the main drive motor 52 is controlled via the speed control circuit 54 at a speed commensurate with the rotation speed of the photoconductor 13 in accordance with the feeding speed. The document scanning speed is synchronized with the rotation speed of the photoconductor 13. Further, the rotation speed of the registration roller 23 that feeds the sheet to the transfer position of the photoconductor 13 is also controlled according to the rotation speed of the photoconductor 13.

Moreover, since the sheet feeding speed of the sheet, that is, the conveying speed becomes slow, the control temperature of the heat fixing portion is set to be somewhat low. This is because the conveyance speed of the sheet becomes slower,
Since a large amount of heat is applied to the sheet, an excessive amount of heat is applied when the set temperature is high, which is an effective means for preventing the phenomenon that the toner is transferred to the fixing roller at the same time as wasting power.

Here, regarding the paper feeding speed, for the first paper feeding, the paper feeding speed is driven at a normal speed, for example, 450 mm / s in the example of FIG. This is a predetermined speed that can be processed by the sheet feeding device, assuming that the thickness of the sheet to be processed is unknown. At the time of feeding at this speed, if the sheet thickness ts corresponding to the speed is within the range,
The probability of double feeding is extremely low, and the paper feeding is continued while maintaining the speed. However, when the sheets to be fed are thin, there is a high possibility that they will be double fed. Therefore, if it is determined that the measured thickness t of the sheet is thin, the sheet feeding speed is reduced at that time so that, for example, the lower sheet of the sheets to be double-fed is separated in air feeding. Since the separation time due to the air discharged from the blowout port is prolonged and the action of the separation roller 201-9 and the like is promoted, the lower sheet is returned and double feeding is prevented. It should be noted that the sheet feeding of the first sheet is maintained at the same speed, and the sheet feeding and the image formation are performed by the speed control according to the previously measured sheet thickness t in the sheet feeding of the second and subsequent sheets. May be.

Further, if the sheet is thick, even if double feeding does not occur at the time of feeding, the speed is high when a feeding failure occurs or when the sheet is sequentially conveyed to the copying process section. Since there is a high possibility of jamming, it is possible to eliminate jamming and the like at the time of contact with the photoconductor by slowing the speed accordingly.

The above is the thickness t of the sheet fed.
Is measured, and the control of the paper feed speed according to the measured thickness of the paper feed sheet and the speed control of the copying process relating to image formation are performed. Therefore, when the copied sheets are ejected, the number of the sheets is counted by the counter C, and it is determined whether or not the content of the counter C has reached the set number of sheets, so that a series of copying is completed. ,
Wait for the next copy. If copying has not been completed, the above-described operations of n4 and subsequent steps are sequentially repeated to start feeding.

On the other hand, if all the copying operations are not completed, the operations after n4 are repeated as described above, but it is possible to detect the double feeding of the sheets fed here. As an example of the detection, one sheet is fed, and the counter C counts +1 (n9), thereby driving the elevating motor 206 in the ascending direction to elevate the loading tray 202. And the loading tray 20
A detection switch for detecting the position of the uppermost part of the sheet 2 is provided corresponding to the uppermost part of the seat, and the driving of the lifting motor 206 is stopped while the detection switch is in operation.
At this time, the amount of increase l corresponding to the rotation speed of the motor 206 is compared with the previously measured sheet thickness t.

In the above comparison, the detected thickness t is 1
If the number of rotations of the motor 206 corresponding to the number of sheets is increased, it means that the number of sheets fed is one and the sheets are not double-fed. However, the detected thickness t is
When the amount of rise l corresponding to two sheets is rotated instead of one sheet, it is determined that the sheet is double-fed. in this case,
If the amount of increase is less than the detected thickness t, it means that the double-fed sheets have been fed in a state in which the double-fed sheets have been blocked, and that thin sheets have been fed. Become.

It is possible to detect the double feeding after the paper is fed as described above by detecting the raising of the loading tray 202. In this case, the motor 2 for raising one sheet
The number of rotations of 06 is stored as a reference value, and the double feed can be easily detected by comparing the stored data with the detected thickness t. In this case, the thickness of the sheet that can be processed by the sheet feeding device 20 is determined by the performance of the sheet feeding device.
Therefore, for example, in FIG. 4, when the loading tray 202 having a sheet thickness of about 83 to 110 μm is doubled or more is lifted, it is possible to determine that the sheet is double-fed, and for that purpose, a lifting motor corresponding to the above-described thickness is used. The number of rotations of 206 is stored as a reference value, and the double feed detection can be performed by comparing this with the thickness t.

Further, the sheet thickness t at the time of sheet feeding is compared with the sheet thickness tr at the previous sheet feeding without detecting the double feeding of the sheets in accordance with the raised state of the loading tray 202. If there is a difference of nearly double the thickness of the sheet feeding sheet, it can be determined that the sheet is double-fed. That is, it is possible to detect the double feeding of the fed sheets according to the detection status of the sheet thickness t. Even in this case, when the sheet thickness t that is about twice the sheet thickness 83 to 110 μm that can be processed in FIG.

Based on the detection of the double feed, the sheet feeding is temporarily stopped, and the operator is informed of the double feed through the notifying means.

As described above, the sheet thickness is detected every time the sheet is fed, and the speed of the copying process is controlled at the same time as the feeding speed according to the detected thickness t. However, in the sheet bundle loaded on the loading tray 202, the thickness of each sheet is usually constant. That is, the sheet has the same thickness in each specification, and the difference in the thickness of each sheet within the specification causes a serious problem in terms of quality, and is unlikely. Therefore, if the speed is first determined based on the thickness t detected when the sheet is fed, the object of the present invention can be sufficiently achieved by controlling the speed to be maintained thereafter.

Therefore, the timing for detecting the thickness t of the fed sheet at the time of feeding the sheet is such that when the sheet feeding device is selected, when the sheet is fed from the selected sheet feeding device. The thickness t is measured, and the sheet feeding speed and the copying process speed according to the detected thickness are controlled. After that, the measured thickness t is stored correspondingly in each sheet feeding device, and the first sheet feeding is performed at the sheet feeding speed according to the stored contents.

In this case, at the timing for measuring the sheet thickness t, the loading tray 202 is pulled out by replenishing or replacing the sheet in the sheet feeding device, the sheet is loaded on the loading tray 202, and this loading is performed. After storing the loading tray 202, the thickness t is measured by feeding the sheet in a state where the sheet feeding device is selected. The feeding speed and the copying process speed are controlled according to the measured thickness t, and thereafter, when the feeding device is selected, the thickness t is stored and the stored thickness t is stored. Paper is fed at a speed according to. In this case, if the sheet is replenished or the like, the sheet is newly filled in the placement tray 202 of the sheet feeding device, so that the thickness of the sheet can be predicted to change. Therefore, if sheet replenishment is detected, when the sheet feeding device is selected, the sheet thickness t is measured in advance, the measured sheet thickness t is stored, and the sheet feeding speed corresponding to the sheet thickness t is stored. And control the speed of the copying process. After that, if the sheet is not replenished,
Since the sheet thickness is not changed, the sheet may be fed at a speed according to the stored sheet thickness t. From the above, it is not necessary to perform the measurement by the distance measuring sensor 37 for each sheet feeding.

When the thickness of the sheet is measured and the thickness of the sheet cannot be processed by the sheet feeding device, not only the trouble due to the sheet feeding and the jam in the copying apparatus but also the exposure There is a risk of physical damage. Therefore, if the thickness t of the sheet that cannot be processed by the sheet feeding device is measured,
The operator is informed that a sheet that cannot be processed is loaded. This notification is performed by voice, display, or both, while the copying operation is stopped. As a result, it is possible to prevent poor paper feeding and damage in the copying apparatus.

The thickness t of the sheet that cannot be completely processed is 65 μm or less in the example shown in FIG.
Sheets of less than μm, more than 180 μm, especially 200 μm
If the sheet is more than m, it becomes difficult to feed the sheet.
It can be predicted that the transportation within the copying machine will be difficult. Therefore, when the thickness of such a sheet is measured in advance, the sheet feeding is prohibited at this point, the copying operation is prohibited, and the operator is informed to replace the sheet.

Here, the paper feeding device shown in FIG. 2 has been described as a device that feeds air, but instead of this air,
Even if the friction roller is used as the paper feeding means, the same operation can be performed. As means for using this friction roller, a paper feed roller in which a friction member such as rubber is formed in a roll shape is provided instead of the paper feed belt 201-1 in FIG.

When the uppermost sheet on the loading tray 202 is held at a certain height while the loading tray 202 is vertically movable, the paper feed roller can be moved up and down. And is configured to descend at the time of the paper feeding operation and press-contact with the uppermost sheet to perform the paper feeding. Then, when the feeding is completed, it rises and is separated from the fed sheet. At this time, the feeding roller 2 shown in FIG.
The sheet feeding by the sheet feeding roller is completed in a state where the leading edge of the sheet is fed between 01-8 and the separating roller 201-9.

Therefore, in the state where the paper feeding by the paper feeding roller is completed, the feeding roller 201-8 and the separating roller 201-
In the state in which the sheet leading edge is fed to the sheet feeding device 9 and the sheet feeding function that temporarily stands by in the sheet feeding state, when the preliminary feeding is completed, the maximum distance sensor 37 detects Measure the distance to the top. Based on this measurement result, the feeding roller 201-8 and the separating roller 201-8
It is possible to measure the thickness t of the sheet preliminarily fed up to -9. Depending on the measured thickness t, the feeding roller 201-
It is possible to set the feeding speed of No. 8 and the feeding speed of the separating roller 201-9, that is, the reverse rotation speed. This makes it possible to control the feeding speed of the sheet being fed and also to control the speed in the copying process.

Particularly, according to the paper feeding device as shown in FIG.
The fed sheet is fed to the position of the registration roller 23 without preliminary feeding, but when the distance from the sheet feeding device 20 to the registration roller 23 is very long, the feeding roller 201-8 And the separation roller 201-9 are preliminarily fed, and the feeding time to the registration roller 23 is shortened. Further, when the distance to the registration roller 23 is short, the trailing edge of the sheet may remain at the position of the loading tray 202 when the registration roller 23 is fed as described above.

Even in such a case, the distance is measured by the distance measuring sensor 37 after the preliminary feeding, the thickness of the sheet is measured, and then the registration roller 23 and the feeding roller 201-8 are used.
Even if the feeding speed is controlled according to the measured thickness t, the feeding control of the sheet being fed can be performed. After the measurement of the sheet thickness t, it is possible to control the speed of the sheet feeding roller in sheet feeding on the loading tray 202.

In the above embodiments, the sheet is fed from the uppermost part, but in the loading tray portion of the loading tray 202, that is, in the sheet feeding device that sequentially feeds the lowermost sheet. Can of course also be implemented. This is a sheet feeding belt 201-
1 is arranged so that the other sheet is not fed at the leading end portion of the sheet feed, and the opening is provided to allow the lowermost sheet to pass therethrough. In addition, the loading tray 20
On the front side of the paper feed 2, the feeding roller 2 for preventing double feeding
01-8 and the separation roller 201-9 are arranged in advance, the lower part is the feeding roller 201-8, and the upper part is the separation roller 201-8.
-9. The lowermost sheet is fed by the rotation of the sheet feeding belt or the rollers for feeding the sheet, and one sheet is fed by the action of the sheet feeding roller and the separating roller in the next stage. By measuring the distance to the top of the sheet with the distance measuring sensor 37 at the time of this sheet feeding, the thickness of the sheet can be measured by the difference from the distance before the sheet feeding. Based on this measurement result,
By controlling the speed of the sheet feeding belt or the roller, the same control as the sheet feeding from the uppermost portion can be performed.

Further, in the paper feeding device 20, the height of the uppermost sheet is placed in order to place the sheet-like sheet on the placing tray 202 and keep the placed uppermost sheet at a constant position. The example in which a switch (limit switch) for detection is separately provided has been described. However, even if the distance measuring sensor 37 is used, the position of the uppermost sheet of the sheet feeding device can be maintained at a constant height.

This is because when the power is turned on, the loading tray 202 moves the uppermost portion of the loaded sheet to a position corresponding to a certain height under the control of the CPU 41, and the lifting motor 2
06 is driven to rotate forward. The distance sensor 37 measures the distance to the uppermost portion of the seat when the vehicle is raised by this rotation.
As a result of this measurement, when the height of the uppermost portion of the sheet reaches a distance that matches the determined height, the driving of the motor 206 is stopped at that position. That is, the distance between the distance measuring sensor 37 and the uppermost portion of the seat, that is, the height is set as Lo, and when the measured distance L1 by the distance measuring sensor 37 becomes Lo = L1, the rotation of the lifting motor 206 is stopped. Good.

In this stopped state, when the sheet feeding device 20 is selected, in order to measure the thickness of the sheet to be fed as described above, the height to the top of the sheet after feeding the sheet, that is, The distance L2 is measured, and the thickness t of the fed sheet can be measured by the difference between this measurement and the previous measurement result L1. Then, the feeding speed can be controlled according to the measured thickness t. Also, speed control of the copying process can be performed at the same time.

This measurement is performed every time the sheet is fed, and when the uppermost portion of the sheet is lowered to a predetermined position, the lifting motor 206 is driven to rotate in the forward direction, and the measurement is performed according to the distance Lo described above. Raise to position. Although the thickness of the sheet can be measured even during this measurement, it is not considered that the sheets placed on the loading tray 202 have different thicknesses on the loading tray 202. If the thickness t measured at the time of the first sheet feeding selected by the sheet feeding device of the loading tray after replenishment is stored, the sheet feeding control is performed based on the stored thickness t. Good. Therefore, as the distance measuring sensor 37, the distance measuring sensor 37 also serves as a position detecting sensor for keeping the uppermost portion of the sheet at a constant height except that the timing of measuring the thickness of the sheet is set at the time of loading the sheet. it can. Therefore, more effective use can be achieved, it is not necessary to provide a separate switch, and the number of parts and cost can be reduced.

Although the position of the uppermost portion of the sheet can be held constant by using the distance measuring sensor 37, the stop position of the lifting motor 206 is based on the distance measurement of Lo, and the uppermost portion of the sheet is fed each time the sheet is fed. Height decreases, and the measurement distance increases. At this time, the loading tray 20 is fed every time one sheet is fed.
2 can be raised and always held at a fixed position Lo,
If the paper can be fed normally even if the uppermost position is lowered a little in the paper feeding operation, for example, 5 m from Lo.
It is also possible to perform control so that the ascending operation is performed under the condition that a position lower by about m is detected (the measuring distance becomes 5 mm longer).

In the above embodiments, in the example of feeding the sheet paper, the control of the feeding speed according to the sheet thickness and the speed control of the copying process have been described. However, the same can be applied to the case where the sheet document is sent to the exposure position. In other words, regarding the sheet original to be processed, depending on the processing speed according to the thickness of the sheet original, if the sheet is thin, there is a paper feed failure or double feed including a paper feed jam, and if it is thick, there is a paper feed failure or feeding Paper mistakes may occur.

Therefore, in the sheet document feeder shown in FIG. 9, after the sheet is fed by the action of the call-in roller 62 which feeds the sheet document on the loading tray 61 on which the sheet document can be placed, The uppermost sheet original is preliminarily fed to the position of the registration roller 65 by the feeding means having a double feeding prevention function by the 63 and the separating belt 64 which is the separating means. The above-mentioned call-in roller 62 and paper-feeding roller 63 constitute a paper-feeding means for feeding a sheet original. An automatic document feeder (ADF) 6 including the document feeder shown in FIG.
0 is provided on the document table 2 instead of the RDH 3 shown in FIG.

The registration roller 65 is for temporarily stopping the fed sheet original so that the timing of starting conveyance to the original table 2 is synchronized with the image forming operation.
Upon completion of the series of image forming operations of the previous sheet document, the temporarily stopped sheet document is sent to the document table 2. The sheet original conveyed by the registration rollers 65 is stopped by aligning the leading edge of the sheet original with a reference position by a conveyance belt 66 arranged so as to face the original table 2. A stopper 67 slightly protruding from the surface of the document table 2 is provided at this stop position, and the driving of the conveyance belt 66 is stopped a little later than the time when the sheet document is locked on the stopper 67, so that the stopper 67 is stopped. The leading edge of the sheet document comes into contact with the sheet, and the skew feeding can be stopped in a corrected state.

In this stopped state, preliminary feeding of the sheet original on the loading tray 61 to the registration roller 65 is performed. When the image formation of the sheet document on the document table 2 is completed, the sheet document is sent out from the document table 2 and carried out to the discharge tray 69, so that the stopper 67 is provided with a solenoid (not shown) at the same time when the conveyor belt 66 is started. It is rotated through a driving source such as the above and is sunk from the surface of the document table 2. As a result, the sheet document is sent out to the discharge tray 69 via the reverse conveyance path 68, and the sheet document waiting on the next registration roller 65 is sent to the document table 2.

In the ADF 60 having the above-described structure, the sheet original placed on the placing tray 61 is fed from the uppermost portion by the lowering of the vertically moving invocation roller 62, and the sheet feeding roller 62 and the separation belt 63 are fed. Sent in between. Due to the action of the separation belt 63, the lower sheet original document that is double-fed is fed back, and the double feeding is blocked. Then, when the uppermost sheet document is sent to the registration roller 65, when the leading edge of the sheet document is detected by the leading edge detection switch SW1, the feeding by the sheet feeding roller 62 is stopped after a predetermined time. In a state where the Yo I Do preliminary feeding is performed, the distance measurement by the distance measuring sensor 37-1 arranged corresponding to the rear end portion of the sheet document placed (L2) is carried out. The thickness t of the pre-fed sheet document can be measured by the difference between this measurement distance and the distance L1 measured before feeding.

The thickness t of the sheet original measured as described above
In accordance with the above, for example, if the sheet feeding characteristics shown in FIG.
The feeding speed may be controlled according to the thickness. In this case, in the preliminary paper feeding, the paper is always fed at a fixed speed, and the sheet feeding speed in the operation of the registration roller 65 after the preliminary paper feeding is controlled. Therefore, the measured thickness t
Is smaller than the determined thickness ts, the conveyance speed of the registration roller 65 is decreased at that time. At this time, the paper feed roller 62 is held rotatably, and the separation belt 63 is rotated in the reverse direction to slow its speed.
As a result, when the sheet originals are double-fed, the separation effect is further enhanced and one sheet can be reliably fed.

On the other hand, if the measured sheet thickness t is within the predetermined range of thickness ts, the registration roller 65
The feeding speed is driven at a normal determined speed, and the reverse rotation speed of the separation belt 63 is also driven at a normal speed.

Here, the registration roller 65 for the sheet original is used.
When controlling the feeding speed of the sheet document thereafter, the time for feeding the sheet document to the document table 2 changes. Therefore, the start timing of the copying process may be changed with respect to the change, and the sheet feeding speed and the copying process speed may be kept constant. However, there is no problem in controlling the sheet feeding speed at the same time as the sheet original feeding speed is reduced. However, when copying a sheet original into a plurality of sheets, it is only necessary to adjust the sheet feeding timing of the first sheet to the sheet original feeding time, and the subsequent sheet feeding is performed at the normal speed. Good.

Further, when the speed control according to the thickness of the sheet is performed on the side of the sheet feeding device 20 side, since the speed control including the copying process is performed, the feeding speed of the sheet original is high. However, there is no problem because the timing of starting copying is delayed, and therefore the feeding speed of the sheet document is slowed down to increase the certainty of feeding one sheet, so that more effective control can be performed. By doing so, if the copying speed becomes slow, there is no problem even if the speed of the sheet original is slowed down accordingly, and one sheet can be fed more reliably in feeding the sheet.

The feeding of the sheet original has been described in the ADF, but it can be similarly performed in the RDH 3 shown in FIG. The difference between this ADF and RDH3 is
In the RDH 3, the sheet document is fed from the loading tray, the sheet document is transported to the document table 2, and after the image formation of the sheet document is completed, the sheet is circulated and transported to the loading tray again as an ADF. Only different. Therefore, it is more effective in that double feeding due to controlling the conveying speed of the sheet original according to the thickness of the sheet original is eliminated and one sheet is reliably fed.

[0112]

According to the present invention described above, according to the present invention, to measure the thickness of the sheet to be fed, for controlling the sheet feeding speed corresponding to said thickness of the sheet is multi-fed double feeding the It can be blocked more effectively, and can reliably feed one sheet. Also the sheet is thin
Paper feed speed is slower, the top
The feeding power of the sheet is increased. Also for separation
When the paper feeding speed becomes slow, the means
The separating effect of the gut becomes larger and the separating effect becomes higher.
As a result, the separation effect of double-fed sheets is increased,
It is possible to reliably feed one sheet.

Further, by controlling the image forming speed in accordance with the paper feeding speed, the image formation on one fed sheet is surely performed, and the jam of the sheet in the apparatus causes the conveyance failure. Can be blocked in advance. Furthermore, the top of the sheet
It can be maintained at a certain height, which makes the paper feeding more stable.
The distance measuring sensor always maintains a constant height at the top of the seat.
It can be used also as a position detection sensor for
You can expect an effect.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an outline of an entire copying apparatus of an electrophotographic system provided with a sheet feeding device of the present invention.

FIG. 2 is a sectional view for explaining details of a sheet feeding device provided in the copying apparatus in FIG.

FIG. 3 is a block diagram showing a control system of the entire copying apparatus including the sheet feeding apparatus of the present invention.

FIG. 4 is a characteristic diagram showing an example of the relationship between the sheet thickness and the sheet feeding speed in the sheet feeding device of the present invention.

FIG. 5 is a PSD showing an example of a distance measuring sensor according to the present invention.
Sectional drawing of a sensor.

6 is an equivalent circuit diagram of the PSD sensor of FIG.

FIG. 7 is a diagram for explaining the principle of distance measurement and sheet thickness measurement according to the present invention using a PSD (distance measurement sensor) sensor.

FIG. 8 is a control flow chart showing an example of a paper feed speed control based on sheet thickness measurement by distance measurement according to the present invention.

9 is a cross-sectional view showing an example of a sheet document feeding device mounted in the copying apparatus in FIG.

[Explanation of symbols]

1 Copying device body 2 Platen 3 RDH (Original circulation type transport device) 11 Optical system 13 Photoconductor 20 (21, 22) sheet feeding device 201 paper feeding means 201-1 Paper feeding belt 201-8 Feed roller 201-9 Separation roller 206 Lifting motor 23 Registration roller 24 Conveyor belt 25 fixing roller 37 Distance measuring sensor 41 CPU (control circuit) 42 ROM 43 RAM 48 Feeder drive motor 52 Main drive motor 60 Automatic document feeder 61 Document loading tray 62 Call roller 63 paper feed roller 64 separation belt 65 Registration roller 66 Conveyor belt

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masanori Nakazawa 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture Sharp Corporation (56) References JP-A-49-73141 (JP, A) JP-A-4- 41349 (JP, A) JP-A-4-77758 (JP, A) JP-A-63-311360 (JP, A) JP-A-4-75945 (JP, A) JP-A-5-14640 (JP, A) JP 5-8903 (JP, A) JP 5-208755 (JP, A) JP 6-40604 (JP, A) JP 6-180213 (JP, A) JP 5-132194 (JP, A) JP-A-5-281874 (JP, A) JP-A-6-92514 (JP, A) Actual development Sho 63-190238 (JP, U) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) B65H 1 / 18,7 / 18,3 / 12 G05G 21/00 370

Claims (4)

(57) [Claims] 1. A sheet feeding apparatus comprising a sheet feeding unit for feeding a placed sheet and a separating unit for preventing double feeding of fed sheets, Distance measuring sensor that is placed opposite to the rear edge and measures the distance to the top of the placed sheet, and drives the distance measuring sensor before and after feeding the thickness of the fed sheet The thickness of the sheet fed by the difference in the measured distance, and the thickness of the sheet measured by the thickness measuring means is predetermined.
A sheet feeding device, comprising: speed control means for controlling the paper feeding speed of the paper feeding means so as to slow the paper feeding speed when the thickness is smaller than the predetermined thickness . 2. The sheet feeding according to claim 1, further comprising a double feed detecting unit that detects a double feed of sheets to be fed based on the thickness measured by the thickness measuring unit. apparatus. 3. A loading tray on which a sheet is placed so as to be fed from the uppermost portion of the loaded sheet is configured to be movable up and down, and the uppermost tray on the loading tray is based on the distance measured by the distance measuring sensor. 2. The sheet feeding apparatus according to claim 1, further comprising means for holding the upper sheet position at a constant height. 4. A sheet feeding device for feeding the placed sheet is provided, and the sheet fed by the sheet feeding device is conveyed to an image forming position to form an image on the sheet. In an image forming apparatus that forms an image, a distance measuring sensor that is arranged to face the trailing edge of the sheet to be fed and measures the distance to the top of the placed sheet, and A thickness measuring unit that drives the distance measuring sensor before and after feeding the sheet thickness to measure the thickness of the sheet, and measures the thickness of the fed sheet by the difference in the measured distance; A speed control means for controlling at least a speed required for image formation according to the thickness of the sheet measured by the thickness measurement means, and the control means is a speed for conveying the fed sheet to the image forming position. It was measured by the thickness measuring means sheet
If the thickness of the paper is less than the predetermined thickness, the paper is fed
An image forming apparatus provided with a sheet feeding device, which is controlled so as to reduce the speed .