JP2011126675A - Paper feeder and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a paper feeder and an image forming device mounted with the same, capable of surely carrying at a high speed, for carrying a sheet material up to the next carrying means, while keeping carrying force. <P>SOLUTION: A distance α in the carrying direction of a sheet sucking surface on the periphery of an endless belt 19, is set longer than a distance β up to the next carrying means 8 on and after a sucking-separating means from a contact position with the sheet bundle S tip on the periphery of the endless belt 19 (α>β). Thus, the sucking surface of the endless belt 19 with a sheet material S1 before carrying a sheet, can surely carry the sheet material S1 at a high speed up to the next carrying means 8 composed of carrier roller pairs while keeping the required carrying force without losing the carrying force of the sheet material S1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sheet feeding device that separates and conveys a sheet material from a stack of stacked sheet materials (hereinafter, a sheet material bundle), and further relates to an image forming apparatus using the same.

  Pickup member formed as a roller or belt made of a material having a high friction coefficient such as rubber as a sheet feeding device for recording paper or the like used in an image forming apparatus such as an electrophotographic copying machine, a facsimile, or a printer Friction paper feeding method is widely adopted.

  However, although the friction feeding method is simple in configuration, it is necessary to press the pickup member against the sheet surface with a spring or the like in order to obtain a large frictional force, and a material having a high friction coefficient such as rubber is used over time. Since the friction coefficient of the surface changes due to various changes and environmental influences, the paper feeding performance is not stable.

  In particular, printers are using not only plain paper but also various types of recording paper such as coated paper and label paper due to the diversification of user usage patterns. Tend to. Recording paper for such applications has various characteristics and conditions, such as those with extremely small surface friction coefficients, those whose frictional force changes with temperature, and sheets that are stacked due to moisture absorption. There are many cases where it is difficult to separate the conventional friction separation method alone.

  Even in the case of a sheet material that is difficult to separate by friction as described above, there are cases where it is possible to solve the problem by an air suction method in which a negative pressure portion is created by suction of air and the sheet material is sucked and conveyed.

  This method has a stable paper feeding performance compared to the friction paper feeding method, but the noise at the time of air suction is large, the equipment becomes large and not only the product cost but also the operating cost increases. There is a difficulty as a device to be used in such as.

  In addition, there is a method in which air is blown from the direction facing the end surface in the traveling direction of the stacked sheet bundle, the sheet material is separated, and the uppermost sheet material is separated and conveyed by a friction roller. There is a problem with cost.

  As a separation method different from the above, there is a method of separating by adsorbing paper using static electricity. As an example of this method, there is an endless dielectric belt that moves in the paper feeding direction facing the upper surface of the stacked sheet bundle, and a member that applies an alternating voltage to the surface of the endless dielectric belt is provided. A device having a charging function that forms an alternating charge pattern on the surface of the endless belt and a discharging function that neutralizes the endless dielectric belt. An attracting force is generated by the electric field, and the uppermost sheet can be separated from the sheet bundle and moved in the sheet feeding direction. In addition, comb-like electrodes are continuously formed in a state where they are alternately meshed with a certain gap, and an electric field is generated by applying positive and negative voltages between the electrodes, and adsorption is performed in the same manner as described above. There is also known an apparatus that can generate a force to separate the uppermost sheet from the sheet bundle and move it in the sheet feeding direction.

  For example, in Patent Document 1, the eccentric roller is held in advance at a position where the circumferential portion farthest from the eccentric shaft is upward, and when the eccentric shaft rotates, a charge pattern is applied to the surface of the sheet feeding belt and the sheet bundle is The lower traveling side travels in the sheet feeding direction and approaches the sheet bundle, and the uppermost sheet is electrostatically attracted to the sheet feeding belt by the attracting force generated by the charge pattern of the sheet feeding belt. The uppermost sheet adsorbed on the sheet feeding belt is fed downstream in the sheet feeding direction as the sheet feeding belt further rotates. Further, the distance from the leading edge of the sheet bundle to the nip of the pair of conveying rollers is a half of the circumferential length of a circle whose radius is a value obtained by adding the thickness of the dielectric endless belt to the radial length of the eccentric roller. The length is set to 1 or less. Conventionally, the circumferential length of the eccentric roller that rotates and moves the belt up and down and the distance from the leading edge of the sheet to the next conveying means are defined. In the present invention, from the charging position of the belt to the leading edge of the sheet, the leading edge of the sheet The position from the edge to the next conveying means is defined.

  In Patent Document 2, by applying a voltage to an endless belt stretched around a plurality of support members, the sheet is electrostatically attracted to the lower surface of the endless belt and conveyed, and the endless belt attracted with the sheet However, the suction of the sheet is continued until the direction starts changing along the predetermined support member of the plurality of support members.

  Further, in Patent Document 3, in a sheet feeding / separating apparatus for an image forming apparatus that separates and feeds sheets one by one from a stack of stacked cut sheets, a flat plate that comes into contact with a sheet and has a dielectric portion, and the flat plate Means for reciprocating the plate, means for bringing the flat plate into and out of contact with the sheet surface of the stacked sheets, and means for applying a voltage so as to generate an attracting force on the flat plate.

  In the case of a system in which an electric field generated on an endless dielectric belt acts on a sheet to generate an adsorption force, an adsorption force necessary for separation and conveyance may be generated depending on environmental conditions and the resistance value of the sheet material. If it is not possible, or after a contact between the endless dielectric belt and the sheet, for a certain period of time, not only the uppermost sheet but also a plurality of stacked sheets may generate an attractive force due to an electric field. There is a problem. And when the necessary suction force cannot be obtained, sheet non-feed occurs, and when the endless dielectric belt is moved in the paper feeding direction with the suction force acting on a plurality of sheets, Double feed occurs and reliable separation cannot be performed.

  In order to cope with this problem, after measuring the physical property value of the sheet to be separated, according to the measured value, the charge amount applied to the endless dielectric belt, the distance between the charges, and the adsorption time are controlled, An invention that minimizes the attractive force acting on the second and subsequent sheets, and an endless dielectric belt that is sandwiched by the sheet material feeding path and is movable or can move in the direction opposite to the feeding direction. Various inventions such as an invention having a blocking member, and an invention in which an operation is performed after a certain period of time elapses from when the endless dielectric belt and the sheet are brought into contact to when the sheet is separated and fed are proposed.

  However, in the method of controlling the charge state of the endless dielectric belt based on the physical property value of the sheet to be separated, it is necessary to measure after separating the sheet, and control is performed on the first sheet material. It becomes impossible. Moreover, it cannot cope with the mixed loading of sheet materials having different physical properties.

  Further, in the method of providing the blocking member pressed against the endless dielectric belt, the adsorption force due to the electric field is also generated at the tip of the plurality of sheet materials, so that the sheet is surely secured by the blocking member. Separation is difficult considering a wide range of conditions. In addition, when the operation is performed after a certain period of time has elapsed from the contact between the endless dielectric belt and the sheet until the sheet is separated and fed, if the contact time is long, the productivity is reduced and the sheet is reduced. There is a possibility that the material separating and feeding apparatus may lack commercial properties.

  In this case, the operation is performed after a predetermined time has elapsed from the contact between the endless dielectric belt and the sheet until the sheet is separated and fed. In this case, the alternating charges + σ and −σ applied to the endless dielectric belt The smaller the interval, the faster the time for which the suction force acting on the first sheet of the sheet material bundle is maximized, and the shorter the time for the suction force acting on the second and subsequent sheets of the sheet material bundle to be minimized. However, it can be easily proved by calculating the Maxwell stress for each time working on each sheet material.

  However, when the interval between the alternating charges + σ and −σ is small, the adjacent potentials are close to each other, and the charges between the adjacent charges cancel each other, so that the interval between the alternating charges + σ and −σ is constant. If it is set below, it will not be possible to obtain an attractive force. Further, when adjacent potentials are close to each other, the electric field distance in the stacking direction generated on the sheet side is also shortened, and the distance at which the suction force can be applied to the sheet is also shortened. Therefore, the smaller the interval between the alternating charges + σ and −σ, the weaker the sheet is in the direction of peeling from the endless dielectric belt, and the adsorptive power is lost with a slight peeling. For these reasons, a certain amount of time for adsorbing and waiting for the sheet material is required.

  By the way, if the configuration is such that the adsorbed sheet material is moved by rotating the belt, the new belt always contacts the sheet material at the rear end side in the conveying direction as the sheet material is conveyed. An area will be generated. When a new contact area is generated in this way, when a sheet material is conveyed at a high speed, a necessary adsorption time cannot be secured, and a necessary adsorption force cannot be obtained, which causes a conveyance failure.

  In view of the above-mentioned conventional drawbacks, difficulties, and problems, the present invention has a relatively simple configuration, is stable against environmental fluctuations and fluctuations with time from a stack of stacked sheets, and is reliably one sheet at a time at high speed. An object of the present invention is to provide a highly reliable paper feeding apparatus and image forming apparatus capable of separating and feeding materials.

  A sheet feeding device according to a first aspect of the present invention includes a sheet stacking member for stacking several sheet materials, a dielectric wound around a plurality of rollers, an endless belt that moves around, and the endless belt. In a sheet feeding device that includes a charging member that gives alternating charge to the surface of the sheet, and that separates and feeds the uppermost sheet from the plurality of sheets on the sheet stacking member by the endless belt, The distance in the conveyance direction of the sheet suction surface on the circumference of the endless belt is determined from the distance from the contact position with the front end of the sheet on the circumference of the endless belt to the sheet conveyance means disposed after the adsorption separation means in the sheet material conveyance direction. It is characterized by being made longer.

  According to a second aspect of the present invention, in the paper feeding device according to the first aspect, the charging device includes a partial charging unit that charges only a portion of the surface of the endless belt that contacts the stacked uppermost sheet material. .

  According to a third aspect of the present invention, in the paper feeding device of the second aspect, the partial charging means is arranged at regular intervals with markings readable by a sensor outside the charging area on the endless belt, and the markings are read. Further, the endless belt travel distance is measured by a signal from the sensor, and the charging voltage is turned on / off according to the distance from the charging member to the adsorption surface of the sheet material, thereby allowing an arbitrary range of the endless belt. It is characterized in that it forms a charged portion.

  According to a fourth aspect of the present invention, in the paper feeding device according to the second or third aspect, a charge eliminating member is provided on the endless belt, and the charge is removed for each circumference of the endless belt.

  According to a fifth aspect of the present invention, in the sheet feeding device according to the second or third aspect, when performing another type of rotation that is not a charging operation of the endless belt, a voltage is applied to the charging member to neutralize the endless belt. It is characterized by doing.

  An image forming apparatus according to a sixth aspect includes the paper feeding device according to any one of the first to fifth aspects.

  According to the present invention, the sheet material can be conveyed to the next conveying means while maintaining the conveying force, and high-speed and reliable conveyance is possible.

1 is a schematic configuration diagram of an example of a sheet feeding device and an image forming apparatus that can include the sheet feeding device according to an embodiment of the present invention. The perspective view which shows the structural example of the paper feeder concerning the implementation object of this invention The perspective view which shows the electrostatic adsorption separation part Side view showing the electrostatic adsorption separation unit Side view showing the electrostatic adsorption separation unit Side view showing the electrostatic adsorption separation unit Side view showing a conventional electrostatic adsorption separation unit The figure which shows the example of the voltage waveform for electrification and static elimination in a paper feeder Side view showing another conventional electrostatic adsorption separation unit The perspective view which shows the other conventional electrostatic attraction separation part 1 is a side view of an electrostatic adsorption separation unit, a stacked sheet leading end portion, and a next conveying unit of a sheet feeding device according to a first embodiment of the present invention The perspective view of the electrostatic adsorption separation part of the paper feeder which concerns on 2nd Example of this invention

  The present invention is based on the premise that the distance from the downstream end in the transport direction of the contact surface between the electrostatic attraction belt and the paper to the next transport means position is longer than the length in the transport direction of the contact surface between the electrostatic suction belt and the paper. A sheet material stacking member for stacking sheets of sheet material, an endless belt made of a dielectric wound around a plurality of rollers, and a charging member for applying an alternating charge to the surface of the endless belt, In a sheet feeding device that separates and feeds the uppermost sheet material from a plurality of sheet materials on the sheet material stacking member by an endless belt, the conveyance direction distance of the sheet adsorption surface on the circumference of the endless belt is The distance between the contact position with the front end of the sheet on the circumference of the endless belt and the sheet conveying means after the suction separating means is longer than the distance.

  Further, the sheet feeding device of the present invention charges only the portion of the endless belt surface that contacts the stacked uppermost sheet material. The charged part can be arbitrarily set. Therefore, charging of unnecessary portions can be prevented, and energy saving and belt life can be improved (belt fatigue due to charging can be reduced).

  Further, by mounting the sheet feeding device of the present invention as described above, an image forming apparatus that can be used under a wide range of conditions can be realized.

  Embodiments of a paper feeding device and an image forming apparatus using the same according to the present invention will be described below with reference to the drawings.

  First, a sheet feeding device and an image forming apparatus that are targets of the present invention will be described.

  1 is a schematic configuration diagram of a sheet feeding device and an image forming apparatus including the sheet feeding device, FIG. 2 is a perspective view illustrating a configuration of the sheet feeding device, and FIG. 3 is an electrostatic adsorption separation unit of the sheet feeding device. FIG. 5 to FIG. 7 are side views showing the electrostatic adsorption separation unit of the sheet feeding device, and FIGS. 8A to 8D are voltage waveforms for charging and discharging the sheet feeding device. FIG. 9 is a side view showing an electrostatic adsorption separation unit of the paper feeding device, and FIG. 10 is a perspective view showing another example of the electrostatic adsorption separation unit of the paper feeding device. Note that the image forming apparatus to be implemented in the present invention is not limited to the one shown in the figure, and the image forming apparatus such as a copying machine, a facsimile apparatus, an apparatus having a function of a multifunction machine having a copying function and a facsimile function, etc. Various types of apparatuses that perform the above are targeted. Note that the present invention is not limited to the sheet feeding device and the image forming apparatus according to this description.

  In FIG. 1, a copying machine 100 as an image forming apparatus separates a document from a bundle of documents placed on a document tray 110a and automatically feeds the document to a contact glass on a document reading unit 120. Then, the original reading unit 120 that reads the original conveyed on the contact glass by the automatic original conveying apparatus 110 and the image read by the original reading unit 120 are formed on the sheet material fed from the paper feeding unit 130. An image forming unit (image forming unit) 140 and a sheet bundle S in which a plurality of sheet materials are stacked, and a sheet material S1 positioned at the top of the sheet bundle S is fed to the image forming unit 140. Part 130. In this embodiment, the image forming unit 140 and the paper feeding unit 130 can be divided, but a configuration other than that may be used.

  The sheet feeding unit 130 is a sheet feeding cassette 150 (see FIG. 2) serving as a sheet stacking member on which a plurality of sheet materials S1 are stacked, and a sheet positioned at the top of the plurality of sheet materials S1 on the sheet feeding cassette 150. And a sheet separating and feeding device 160 that separates and conveys the material.

  The sheet material S1 separated and fed by the sheet separating and feeding device 160 is transported on the transport path 170, and the sheet material S1 transported on the transport path 170 is transported by the transport roller pair 180. Then, the toner image formed in the image forming unit 140 is transferred by the transfer roller 190, this toner image is thermally transferred by the fixing device 200, and discharged to the discharge tray 220 by the discharge roller pair 210.

  The image forming unit 140 includes four image forming units 230 (230Y (yellow), 230C (cyan), 230M (magenta), 230BK (black)), an intermediate transfer belt 240 that is a transfer belt, and an exposure device 250. It is configured.

  The exposure apparatus 250 converts color-separated image data input from a personal computer, a word processor, or the like, or image data of a document read by the document reading unit 120 into a signal for driving a light source, and accordingly, each laser light source unit. The semiconductor laser is driven to emit a light beam.

  The image forming units 230Y, 230C, 230M, and 230BK form images of different colors (toner images), and the image forming units 230Y, 230C, 230M, and 230BK are rotated in the clockwise direction. The image forming apparatus includes a photosensitive member 260 (260Y, 260C, 260M, and 260BK) that is an image carrier, a charging unit 270, a developing unit 280, a cleaning unit 290, and the like disposed around the photosensitive member 260.

  The photoreceptor 260 is formed in a cylindrical shape and is driven to rotate by a drive source (not shown). A photosensitive layer is provided on the outer peripheral surface portion of the photoconductor 260, and a light beam indicated by a broken line emitted from the exposure apparatus 250 is spot-irradiated on the outer peripheral surface of the photoconductor 260, whereby the outer peripheral surface of the photoconductor 260 is exposed. The electrostatic latent image corresponding to the image information is written.

  The charging unit 270 uniformly charges the outer peripheral surface of the photoconductor 260, and a contact type is used for the photoconductor 260. The developing unit 280 supplies toner to the photosensitive member 260, and the supplied toner adheres to the electrostatic latent image written on the outer peripheral surface of the photosensitive member 260, whereby the electrostatic latent image on the photosensitive member 260 is changed. A toner image is visualized, and a non-contact type is used for the photoreceptor 260.

  The cleaning unit 290 cleans residual toner adhering to the outer peripheral surface of the photoconductor 260 and employs a brush contact type in which a brush contacts the outer peripheral surface of the photoconductor 260.

  The intermediate transfer belt 240 is composed of an endless belt formed using a resin film or rubber as a base, and the toner image formed on the photosensitive member 260 is transferred to the intermediate transfer belt 240. The toner image is transferred to the sheet material S1 by the transfer roller 190.

  In addition to the electrophotographic system, for example, other systems such as an ink jet system may be adopted as the copying machine 100. Besides the configuration of the copying machine 100, a printer device, a facsimile device, a printing machine, or You may comprise from a multifunction machine.

  As illustrated in FIG. 2, the sheet feeding device 5 includes a sheet feeding tray 16 on which the sheet bundle S is stacked, and includes an electrostatic adsorption separation unit 14 as the separation unit 7. In FIG. 2, the electrostatic adsorption separation unit 14 is short with respect to the stackable paper width and is disposed near the center. However, this may be the same or longer than the stackable paper width. Further, although one is shown near the center in FIG. 2, there may be a case where a plurality are arranged in the paper width direction.

As shown in FIG. 3A, the electrostatic adsorption separation unit 14 includes an endless belt 19 made of a dielectric material wound around a driving roller 17 and a driven roller 18. The belt 19 is made of a dielectric material having a resistance of 10 ⁸ Ω · cm or more, for example, a film of polyethylene terephthalate having a thickness of about 100 μm. Further, a blade-shaped charging electrode 21 is in contact with the belt 19. Further, as shown in FIG. 3B, the electrode may be a roller-shaped charging electrode 60.

As shown in FIG. 4, the belt 19 has a two-layer structure including a surface layer 20a made of a dielectric having a resistance of 10 ⁸ Ω · cm or more and a back layer 20b made of a conductor having a resistance of 10 ⁶ Ω · cm or less. This is suitable for forming a good charged state. The charging electrode 21 uses the back layer 20b of the belt 19 as a grounded counter electrode. Therefore, the charging electrode 21 may be provided anywhere as long as it is in contact with the surface layer 20a of the belt 19 in terms of giving a charge to the belt. . Further, the position of the sheet bundle S is also set to a position where a sufficient suction area can be obtained with respect to the belt 19.

The surface of the driving roller 17 is composed of a conductive rubber layer having a resistance value of about 10 ⁶ Ω · cm, and the surface of the driven roller 18 is composed of metal. The driving roller 17 and the driven roller 18 are grounded. The driving roller 17 has a small diameter suitable for separating the sheet material S1 from the belt 19 by the curvature. That is, by setting the diameter of the driving roller 17 to be small and increasing the curvature, the sheet material S1 attracted to the belt 19 and separated and conveyed is separated from the driving roller 17 by the guide member 26 on the downstream side in the conveying direction. It is possible to enter the formed conveyance path 50.

  In the present embodiment, the charging electrode 21 is disposed so as to contact the belt 19 near the position where the belt 19 is wound around the driving roller 17. The charging electrode 21 is connected to a charging power source 24 that generates alternating current. On the upstream side of the charging electrode 21 in the rotation direction of the belt 19 and on the downstream side of the separation position of the sheet bundle S and the belt 19, the static elimination electrode 22 connected to the static elimination power source 25 that is an alternating power source contacts the belt 19. Or they are installed close together. The charging power source 24 and the neutralizing power source 25 are controlled such that the suction force on the belt 19 is removed at a position where the leading end of the sheet material S1 contacts the next conveying unit 8 including a pair of conveying rollers. The static elimination electrode 22 is not always necessary and can be omitted. The following description will be made assuming that the static elimination electrode 22 is not provided.

  A method for contacting and separating the belt 19 and the sheet bundle S will be described. As shown in FIG. 5, the belt 19 is positioned at the upper front end of the uppermost sheet material S1 of the sheet bundle S on the bottom plate 28 pushed up by the push-up member 27b with the driving roller 17 as an axis. It arrange | positions so that contact with material S1 is possible. The bottom plate 28 urges the sheet material S1 to the belt 19 by lifting the other end so that the bottom plate 28 is rotated by the push-up member 27b with the rotation fulcrum 28d as a fulcrum. The belt 19, the driving roller 17, and the driven roller 18 are supported so that their postures can be changed as indicated by arrows 51 in accordance with changes in the inclination of the bottom plate 28.

  As shown in FIG. 6, the bottom plate 28 may be configured to move up and down while being kept parallel by a rack-and-pinion type sheet push-up portion 29b. In that case, the position of the belt 19, the driving roller 17, and the driven roller 18 may be fixed in the paper feeding device 5. In addition, the sheet feeding device 5 includes a sensor 30 that detects the position of the uppermost sheet material S1 in the vertical direction, and can appropriately control the interval and the contact pressure between the belt 19 and the sheet material S1. It has become.

  With reference to FIG. 7, an example of a conventional technique for turning the sheet material S1 tip will be described for reference. The bottom plate 28 may be either moved up and down while being kept parallel by a rack-and-pinion type sheet push-up portion 29b, or may be fixed while being kept parallel. Is configured to move up and down as indicated by an arrow 52. Further, there is also a type in which the driven roller 18 side moves as indicated by an arrow 53 around the driving roller 17 to perform a sheet material turning operation.

  In the sheet feeding device 5 configured as described above, the drive roller 17 is rotationally driven by a sheet feeding signal, and an alternating voltage is applied from the charging power source 24 to the belt 19 that has started to rotate. On the surface of the belt 19, an alternating charge pattern is formed at a pitch (pitch should be about 2 mm to 15 mm) according to the AC power supply frequency and the circumferential speed of the belt 19. The charging power source 24 may be an alternating current or a direct current having a high and low alternating potential. In this embodiment, the charging power supply 24 has an amplitude of 3 to 4 KV (± 1.5 to ± 2) with respect to the surface of the belt 19. AC is applied.

  That is, as shown in FIG. 8A, charging and discharging can be performed by controlling the voltage, and the charge pattern on the belt 19 is removed by lowering the applied voltage. FIG. 8B is an example in which the suction force based on Maxwell stress of the belt 19 is reduced by increasing the power supply frequency to reduce the pitch of the charge pattern formed on the belt 19. These are rectangular waves in which a DC power supply is alternated, but the same applies when a sine wave is used as shown in FIGS. 8 (C) and 8 (D).

  Since the belt 19 on which the charge pattern is formed is in contact with the upper surface front end portion of the uppermost sheet material S1 at a position wound around the driven roller 18, the surface of the belt 19 is placed on the sheet material S1 which is a dielectric. Maxwell stress works due to the unequal electric field formed by the electric charge pattern, and only the uppermost sheet material S1 is attracted, held and conveyed to the belt 19, and then separated from the belt 19 by the curvature and fed out in the conveying direction. Then, the sheet is conveyed to the image forming unit 3 by the next conveying unit 8 through the conveying path 50 formed in the guide member 26.

  The adsorption force due to the charge pattern acts on the sheet material S1 other than the uppermost sheet material for a certain time from the moment of adsorption, but only on the uppermost sheet material S1 after the certain time has elapsed. It does not act on the sheet material S2 or lower. That is, by taking time, the uppermost sheet material S1 can be separated from the sheet bundle S even if the double feed blocking member 31b is not provided. The linear speeds of the next transport unit 8 and the belt 19 are the same, and when the next transport unit 8 is intermittently driven at a timing, the belt 19 is also controlled to be intermittently driven.

  The belt 19 prevents the second sheet material S2 from being attracted to the belt 19 before the rear end of the sheet material S1 reaches the position facing the driven roller 18. Further, separation of the sheet from the belt 19 at the portion of the driving roller 17 is based on curvature separation, but a separation claw 32 may be provided as shown in FIG. 9 in order to further ensure separation. The sheet material S <b> 1 is conveyed by only the conveying force of the next conveying unit 8 without being influenced by the belt 19 after being sandwiched by the next conveying unit 8. Further, the belt 19 may have a cleaning mechanism (not shown) in order to prevent paper dust and other dust from adversely affecting the adsorption operation of the electrostatic adsorption separation unit 14.

  Further, in the above description, in order to obtain the electrostatic attraction force, an electric field is generated on the belt 19 by applying an electric charge to the belt 19 with a blade-like electrode. However, the present invention is not limited to this, and the roller-shaped electrode 60 may be brought into contact with the belt 19, and the sawtooth-shaped electrode may be arranged in a state separated from the belt 19 by a minute distance. However, with the roller-shaped electrode, as described above, it is difficult to reduce the pitch of the alternating charging interval. In the case of a sawtooth electrode, since the belt 19 has a minute wave or the like, it is difficult to accurately maintain the distance from the electrode, and thus there is a possibility that stable charging cannot be performed.

  Further, FIG. 10 shows a system different from the above as a system for generating electric lines of force on the belt. The positive and negative comb-like electrodes 40 are arranged on the belt 19 so as to face each other in a direction orthogonal to the moving direction of the belt 19. At both ends of the belt 19, there are power-supplied portions 41 with exposed patterns, and an electric field is generated by applying a positive or negative voltage to the electrodes 40 by the positive and negative high-voltage power sources 42 through the power-supplied portions 41. Thus, a force for adsorbing the sheet material S1 is generated. However, this method is difficult to maintain the insulation between the electrodes, is not suitable for a small pitch, loses the flexibility of the belt, and is relatively less expensive than the above-described method of applying charge to the belt. There are problems such as high cost, and it is not very popular as a paper transport device.

  The drive roller 17 is provided with a drive transmission cutoff mechanism such as a clutch (not shown) via a drive shaft and a drive source (not shown), and after the sheet material S1 reaches the next conveying means 8, the drive is cut off. Thus, the rotation is free, and the load on the drive source generated by the separation unit 7 is reduced.

  In addition, in order to charge the static electricity separating unit 14 to the belt 19 or to remove static electricity, it is necessary to rotate the belt 19, and in this case, if the belt 19 is in contact with the sheet material bundle, There is a possibility that the uppermost sheet material may be sent out during the static elimination operation, which may cause a malfunction. Therefore, a contact / separation mechanism is provided so that contact and separation between the belt 19 and the sheet material bundle can be arbitrarily controlled.

  Here, a control method of the electrostatic adsorption separation unit 14 will be described. The electrostatic adsorption separation method employed by the electrostatic adsorption separation unit 14 is that it takes time to obtain the necessary adsorption force when the electrical resistance of the sheet material S1 is high, or the second sheet material S2. There is a problem that it takes time to reduce the attractive force acting below, and there is a problem that the attractive force is small when the electric resistance of the sheet material S1 is low.

  The detection of the environmental condition can be realized by, for example, incorporating a thermo-hygrometer in the paper feeding device 5, and by controlling the charging pitch, charging voltage, adsorption time, etc. based on the temperature-humidity condition, Adsorption and separation conditions suitable for the environmental conditions can be obtained. Further, acquisition of information on the material of the sheet material S1 can be realized by a user performing an input operation or a selection operation from an operation unit (not shown).

<Example 1>
A first embodiment of a paper feeding device according to the present invention will be described below with reference to FIG. Since the configuration from the sheet separating and conveying means 16 to the next conveying means 8 is the same as that described so far, the description thereof is omitted.

  In FIG. 11, the transport direction distance (α) 61 of the sheet suction surface on the circumference of the endless belt 19 is the next transport means after the suction separation means from the contact position with the tip of the sheet bundle S on the circumference of the endless belt 19. It is shown that the distance to 8 is longer than (β) 62 (α> β).

  That is, the distance from the downstream end in the conveyance direction of the contact surface between the electrostatic adsorption belt and the sheet to the position of the next conveyance means is longer than the length in the conveyance direction of the contact surface between the electrostatic adsorption belt and the sheet material. A sheet stacking member for stacking a plurality of sheet materials, an endless belt made of a dielectric wound around a plurality of rollers, and revolving, and a charging member for applying an alternating charge to the surface of the endless belt. A sheet feeding device that adsorbs and separates and feeds a sheet material positioned at the top of a sheet bundle composed of a plurality of sheet materials on a sheet stacking member by an endless belt, the endless belt The distance in the conveyance direction of the sheet material adsorption surface on the circumference of 19 is longer than the distance from the contact position with the front end of the sheet material on the circumference of the endless belt 19 to the sheet conveyance means after the adsorption separation means, Thus, the suction surface of the sheet material S1 before the sheet conveyance and the endless belt 19 ensures the sheet material S1 at high speed to the next conveyance means while maintaining the necessary conveyance force without losing the conveyance force of the sheet material S1. Transport to.

<Example 2>
A second embodiment of the paper feeding device according to the present invention will be described below with reference to FIG. In this example as well, the configuration from the sheet separating and conveying means 16 to the next conveying means 8 is the same as that described so far, and the description thereof is omitted.

  As shown in FIG. 12, the sheet separating and conveying means 16 has, for example, black and white markings 63 arranged at equal intervals outside the charging area on the illustrated endless belt 19 and a sensor 64 that can read the markings. It is assumed that the moving distance of the endless belt 19 can be measured by a signal from the sensor 64 disposed on the marking 63. With this configuration, the distance from the charging member 60 to the adsorption surface of the sheet material can be monitored. Therefore, a charged portion is formed in an arbitrary range of the endless belt 19 by turning on and off the charging voltage. It is possible to charge only the portion in contact with the stacked uppermost sheet material S1.

  Furthermore, once the endless belt 19 is charged, the electric charge remains on the endless belt 19 unless it is discharged through the conductive member. This prevents the above-mentioned partial charging. A charge eliminating member (not shown) may be provided to eliminate the charge every rotation of the endless belt 19, or a method of removing the charge by applying a minute voltage to the charging member 60 during a rotation different from the charging operation.

<Comparison with prior art documents>
In the invention disclosed in Patent Document 1, which is a prior art, the suction surface is returned to the original position by one rotation by the eccentric roller, so that the positional relationship with the next conveying means is inevitably determined. The distance to the next conveying means can be set to some extent freely depending on the length, and the sheet material can be conveyed at high speed with a relatively simple configuration. In the invention disclosed in Patent Document 2, the sheet material is continuously adsorbed until the predetermined sheet material support member is reached in order to prevent the image transfer portion from shifting. The front end of the sheet material reaches the next conveying means until the surface adsorbed on the sheet disappears. That is, the suction belt is required up to the intended conveying means, but in the present invention, it is only necessary to have a guide plate, so the cost is reduced. Further, in Patent Document 3, the suction means is a flat plate, and the flat plate on which the sheet material is sucked is moved to the next transport unit to transport the sheet material. Transport to transport means. That is, the present invention does not require a complicated mechanism for moving the flat plate, and can be transported at a high speed with a relatively simple configuration.

S: Sheet bundle S1: Sheet material S2: Second sheet material α, β: Distance 3: Image forming unit 5: Paper feeding device 7: Separating unit 8: Next conveying means 14: Electrostatic adsorption separating unit 16: Feeding Paper tray 16: Sheet separating and conveying means 17: Driving roller 18: Driven roller 19: Endless belt 20a: Belt surface layer 20b: Back layer 21: Blade-shaped charging electrode 22: Discharge electrode 24: Charge power source 25: Discharge Power supply 26: Guide member 27b: Push-up member 28: Bottom plate 28d: Rotating fulcrum 29b of the bottom plate: Push-up portion 30: Sensor 31b: Double feed blocking member 32: Separation claw 40: Comb-like electrode 41: Power-supplied portion 42: High-voltage power supply 50: conveying path 60: roller-shaped charging electrode 63: marking 64: sensor

JP-A-5-139548 JP 2004-217414 A JP-A-6-40583

Claims (6)

A sheet stacking member configured to stack a plurality of sheet materials; a dielectric wound around a plurality of rollers; an endless belt that circulates; and a charging member that applies an alternating charge to the surface of the endless belt. In the sheet feeding device configured to suck and separate and feed the uppermost sheet from the plurality of sheets on the sheet stacking member,
The conveyance direction distance of the sheet suction surface on the circumference of the endless belt,
It is longer than the distance from the contact position with the sheet tip on the endless belt circumference to the sheet conveying means disposed after the adsorption separation means in the sheet material conveying direction.
A paper feeder characterized by that. The paper feeding device according to claim 1.
A partial charging means for charging only a portion of the surface of the endless belt that comes into contact with the uppermost stacked sheet material;
A paper feeder characterized by that. The paper feeding device according to claim 2.
The partial charging means;
Marks readable by a sensor are arranged at regular intervals outside the charging area on the endless belt, the moving distance of the endless belt is measured by a signal from the sensor that has read the marking, and the sheet from the charging member A charging portion is formed in an arbitrary range of the endless belt by turning on and off the charging voltage according to the distance to the adsorption surface of the material.
A paper feeder characterized by that. The paper feeding device according to claim 2 or 3,
A static elimination member is provided on the endless belt, and static elimination is performed every round of the endless belt.
A paper feeder characterized by that. The paper feeding device according to claim 2 or 3,
When performing another type of rotation that is not a charging operation of the endless belt, the endless belt is neutralized by applying a minute voltage to the charging member;
A paper feeder characterized by that. An image forming apparatus comprising the paper feeding device according to claim 1.