JP2015057361A - Sheet feeder and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable sheet feeder capable of lessening a charge pitch, and of surely at high speed, feeding sheets one by one from a sheet bundle loaded on a sheet loading member even in various sheet types stabilizing with respect to environmental and time-lapse variations, and to provide an image formation device comprising the sheet feeder.SOLUTION: A sheet feeder comprises a paper feeding cassette 15, an endless belt 2 and a charging roller 1, and a sheet S1 is adsorbed and fed by the endless belt 2. The charging roller 1 and the endless belt 2 form a nip part 72, and the micro-gaps G which impart a prescribed charge on the surface of the endless belt 2 by an electric discharge at the upstream and downstream sides of the nip part 72 in a circumferential movement direction. The sheet feeder is configured so that the basic charge width H joined a nip width and the width of the micro-gap G in the upstream and downstream sides of the nip part 72 is smaller than the charge width W with respect to the circumferential movement direction of an identically polar charge charged on the surface of the endless belt 2 in the downstream side of the nip part 72 in the circumferential movement direction.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet feeding apparatus and an image forming apparatus, for example, a sheet feeding apparatus that uses static electricity to attract and separate a sheet on an endless belt, and an electrophotographic apparatus including the sheet feeding apparatus. The present invention relates to an image forming apparatus including a copying machine, a facsimile apparatus, a printer apparatus, an inkjet apparatus, and the like.

  As a sheet feeding device for an image forming apparatus such as an electrophotographic copying machine, a facsimile apparatus, a printer apparatus, an ink jet apparatus, etc., friction by a pickup member formed as a roller or belt made of a material having a high friction coefficient such as rubber. The paper feeding method is widely adopted.

  The friction feeding method is simple in structure, but in order to obtain a large frictional force, it is necessary to press the pickup member against the sheet surface with a spring or the like, and a material having a high friction coefficient such as rubber is Since the friction coefficient of the surface changes depending on the environment, the paper feeding performance is not stable.

  In particular, in printer devices, recording sheets having various functions such as coated paper and label paper have been used due to diversification of users, such as coated paper and label paper. It is in. Such special-purpose sheets have various characteristics and conditions, such as those with extremely small friction coefficients on the surface, those whose frictional force changes with temperature, and sheets that are stacked due to moisture absorption. However, there are many cases where it is difficult to separate the conventional friction separation system alone.

  Even in the case of such a sheet that is difficult to separate by friction, there are cases where it is possible to solve by an air suction method in which a negative pressure part is created by suction of air and the sheet is sucked and conveyed. Although the paper feeding performance is stable as compared with the method, the noise at the time of air suction is large, the apparatus becomes large, and the cost is high.

In addition, there is a system in which air is blown from the direction facing the end surface in the traveling direction of the stacked sheet bundle, the sheet is separated, and the uppermost sheet is separated and fed by a friction roller. There is a problem with the cost.
As a separation method different from the above, there is a method of separating by adsorbing a sheet using static electricity.

  As an example of a method for attracting and separating sheets using static electricity, an endless belt made of a derivative and moving in the sheet feeding direction is provided on the upper surface of a stacked sheet bundle. A sheet feeding apparatus having a charging member for applying an alternating voltage to the surface of the belt-like belt, a charging function for forming an alternating charge pattern on the surface of the endless belt, and a discharging function for discharging the endless belt. By applying a charge on the endless belt and bringing the sheet into contact with the dielectric belt, the potential of the sheet is increased, and a charge having a polarity opposite to that of the endless belt is formed on the sheet to generate an adsorption force. Thus, it is known that 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 a positive and negative voltage between the electrodes, and adsorption is performed in the same manner as described above. An apparatus that can generate a force, separate the uppermost sheet from the sheet bundle, and move it in the sheet feeding direction has already been invented.

  However, in the case of the above-described method in which the electric field generated on the endless belt acts on the sheet to generate the suction force, the suction force necessary for separation paper feeding cannot be generated due to environmental conditions, the sheet resistance value, and the like. In some cases, after a contact between the endless belt and the sheet, an adsorbing force due to an electric field may be generated not only on the uppermost sheet but also on a plurality of stacked sheets.

  When the necessary suction force cannot be obtained in this way, sheet non-feed occurs, and when the endless belt is moved in the paper feeding direction with the suction force acting on a plurality of sheets, Double feeding occurs, and reliable separation and feeding cannot be performed.

  In order to cope with such a point, after measuring the physical property value of the sheet to be separated, the charge amount applied to the endless belt, the distance between the charges, and the adsorption time are controlled according to the measured value. A member that minimizes the attractive force acting on the second and subsequent sheets (see, for example, Patent Document 1), a blocking member that is provided with an endless belt sandwiching the sheet conveyance path and is movable in the stationary or counter-feeding direction (For example, refer to Patent Document 2), or one that performs an operation after a certain period of time has elapsed from when an endless belt and a sheet are brought into contact with each other to be separated and fed.

  However, in the device described in Patent Document 1, it is necessary to measure a sheet physical property value after separating a sheet, and it becomes impossible to control the first sheet. Moreover, it cannot cope with the mixed loading of sheets having different physical properties.

  Moreover, since the thing described in patent document 2 has provided the blocking member press-contacted to the endless belt, since the adsorption | suction force by said electric field has also generate | occur | produced also at the front-end | tip of a several sheet | seat It is difficult to reliably separate the sheet with the blocking member in consideration of a wide range of conditions.

  In addition, when the operation is performed after a certain period of time has passed from the contact between the endless belt and the sheet to the separation and feeding, if the contact time is long, the productivity is lowered. As a sheet feeding apparatus, there is a risk that the merchantability is lacking.

  Here, the operation is performed after a certain period of time has passed from the contact between the endless belt and the sheet until the sheet is separated and fed. In this case, the interval between the positive charge and the negative charge applied to the endless belt is small. As the time required for the suction force acting on the first sheet of the sheet bundle to become maximum is earlier and the time required for the suction force acting on the second and subsequent sheets in the sheet bundle to be minimized, each sheet works. Known based on hourly Maxwell stress.

  However, in the case where the electrode for applying the charged charge on the endless belt is a charging roller, there is a problem in reducing the pitch between the positive charge and the negative charge (charge pitch).

  Specifically, when the charging electrode is, for example, a charging roller, as shown in FIG. 16, a contact portion between the charging roller 1 and the endless belt 2 (hereinafter, this contact portion is referred to as a nip width N). Exists with a certain width, and there are two small gaps G for discharging between the endless belt 2 and the charging roller 1 (immediately before the charging roller 1 and the endless belt 2 come into contact with each other). And immediately after the charging roller 1 and the endless belt 2 are separated from each other), when an alternating voltage is applied to the charging roller 1, the charge charged on the endless belt 2 is schematically shown on the endless belt 2 as shown in FIG. Charges of the same polarity are alternately charged with a certain charging width W.

  Here, if the diameter D of the charging roller 1 is larger than the charging width W so that the basic charging width H constituted by the minute gap G and the nip width N is larger than the charging width W, charging is performed within the nip width N. Since the roller 1 has a medium resistance or a low resistance, when a potential having a polarity opposite to the charge charged on the endless belt 2 is applied to the charging roller 1 (a positive voltage is applied to the charging roller 1, The negative charge is charged by the charging width within the nip width N), and there is a possibility that the charged charge moves on the endless belt 2 so as to be surrounded by the symbol A.

  Further, the charging roller 1 and the endless belt 2 are considered to have a portion that is in contact with a portion that is not in contact with the charging roller 1 and a portion that is not in contact with the endless belt 2. From this, it is conceivable that when a reverse polarity potential is applied as described above, a discharge phenomenon occurs and the endless belt 2 is charged with a reverse polarity so as to be surrounded by the symbol A. For this reason, there is a possibility that the electric charge charged on the charging width W on the downstream side in the circumferential movement direction of the endless belt 2 with respect to the nip width N may be reduced as surrounded by the symbol B.

  Further, in the minute gap G immediately before the charging roller 1 and the endless belt 2 come into contact with each other and immediately after the charging roller 1 and the endless belt 2 are separated from each other, the above-described 2 A discharge phenomenon occurs in the minute gap G at the location.

  For this reason, when a positive voltage is applied to the charging roller 1, a positive charge is given by the charging width W located in the minute gap G on the upstream side with respect to the circumferential movement direction R of the endless belt 2. Although the negative charge having the opposite polarity is charged with the charging width W corresponding to the minute gap G on the downstream side of the endless belt 2, the charging width W corresponding to the minute gap G on the downstream side is positive. There is a possibility that the electric charge is charged.

  As a result, there was a possibility that a fine alternating charge could not be applied, and a phenomenon that a sufficient adsorption force for adsorbing the sheet to the endless belt 2 could not be obtained occurred.

  The present invention has been made to solve such a problem, and can reduce the charging pitch. Even in various sheet types, the sheet bundle loaded on the sheet stacking member can be used against environmental fluctuations and temporal fluctuations. And a highly reliable sheet feeding apparatus and image forming apparatus capable of feeding one sheet at a time at high speed and reliably.

  In order to achieve the above object, a sheet feeding apparatus according to the present invention includes a sheet stacking member that stacks a plurality of sheets, an endless belt that is wound around a driving roller and a driven roller, and rotates in a circumferential movement direction. A charging roller that periodically charges positive and negative charges on the surface of the endless belt, and the endless belt is used to position the uppermost sheet from the plurality of sheets on the sheet stacking member. A sheet feeding apparatus that sucks and feeds the charging roller and the endless belt, wherein the charging roller and the endless belt include a nip portion in which an outer peripheral portion of the charging roller is in contact with an arbitrary position on a surface of the endless belt; A gap for applying a predetermined charge to the surface of the endless belt by discharge is formed on the upstream side and the downstream side of the nip portion in the movement direction, and the nip width of the nip portion in the circumferential movement direction The basic charging width that combines the width of the gap on the upstream side and the downstream side of the nip portion is the same polarity that is charged on the surface of the endless belt on the downstream side in the circumferential movement direction with respect to the nip portion. The charge is smaller than the charge width in the circumferential movement direction.

  As described above, the charging pitch can be reduced, and even for various types of sheets, one sheet is reliably stabilized at high speed from the sheet bundle stacked on the sheet stacking member with respect to environmental variations and temporal variations. It is possible to provide a highly reliable sheet feeding apparatus capable of feeding the sheet one by one and an image forming apparatus including the sheet feeding apparatus.

1 is a diagram illustrating a first embodiment of a sheet feeding apparatus and an image forming apparatus according to the present invention, and is a schematic configuration diagram of a copying machine. 1 is a perspective view of a sheet feeding unit according to a first embodiment of a sheet feeding device and an image forming apparatus according to the present invention. 1 is a diagram illustrating a first embodiment of a sheet feeding apparatus and an image forming apparatus according to the present invention, and is a perspective view of the sheet feeding apparatus. 1 is a diagram illustrating a first embodiment of a sheet feeding apparatus and an image forming apparatus according to the present invention, and is a schematic view of a side view of the sheet feeding apparatus and an apparatus for charging an endless belt. 1A and 1B are diagrams illustrating a first embodiment of a sheet feeding device and an image forming apparatus according to the present invention, in which FIG. 1A illustrates a separation mechanism that separates sheets, and FIG. 2B illustrates separation from an endless belt; It is a figure which shows the state which pulled apart the mechanism. 1A and 1B are diagrams illustrating a first embodiment of a sheet feeding apparatus and an image forming apparatus according to the present invention, and FIG. 5A is a schematic diagram of a positional relationship between a charging blade and an endless belt, and electric charges charged on the charging belt. FIG. 6B is a diagram showing the waveform of the voltage applied to the charging blade, and FIG. 5B is a diagram showing the positional relationship between the tip of the charging blade and the endless belt, the minute gap G, the basic charging width H, and the nip width N. . 1 is a diagram illustrating a first embodiment of a sheet feeding apparatus and an image forming apparatus according to the present invention, and is a diagram illustrating waveforms of a charging voltage and a discharging voltage. FIG. 1 is a diagram illustrating a first embodiment of a sheet feeding apparatus and an image forming apparatus according to the present invention, and is a diagram illustrating a state of a sheet due to electric charges formed on an endless belt. 1 is a diagram illustrating a first embodiment of a sheet feeding apparatus and an image forming apparatus according to the present invention, the positional relationship between a charging blade and an endless belt, a schematic diagram of charges charged on the charging belt, and application to the charging blade It is a figure which shows the other waveform of the voltage made, respectively. FIG. 3 is a diagram illustrating a first embodiment of a sheet feeding device and an image forming apparatus according to the present invention, and a side view illustrating another shape of the sheet feeding device. 2 is a diagram illustrating a first embodiment of a sheet feeding device and an image forming apparatus according to the present invention, and is a perspective view illustrating another shape of the sheet feeding device. FIG. FIG. 3 is a diagram illustrating a first embodiment of a sheet feeding device and an image forming apparatus according to the present invention, and a side view illustrating another shape of the sheet feeding device. FIG. 13 is a diagram illustrating a second embodiment of the sheet feeding apparatus and the image forming apparatus according to the present invention, and is a side view of the sheet feeding apparatus illustrating a state in which a topmost sheet turning operation is performed from the state illustrated in FIG. 12. is there. FIG. 5 is a diagram illustrating a second embodiment of the sheet feeding apparatus and the image forming apparatus according to the present invention, and is a perspective view of the sheet feeding apparatus. FIG. 4 is a diagram illustrating a second embodiment of a sheet feeding device and an image forming apparatus according to the present invention, the positional relationship between a charging blade and an endless belt, a schematic diagram of charges charged on the charging belt, and application to the charging blade It is a figure which shows the waveform of the voltage to be respectively performed. It is a schematic diagram of the positional relationship between a conventional charging blade and an endless belt and the electric charge charged on the charging belt.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
1 to 13 are diagrams showing a first embodiment of a sheet feeding apparatus and an image forming apparatus according to the present invention, and show an example in which the image forming apparatus is applied to an electrophotographic copying machine. .
First, the configuration will be described.
In FIG. 1, a copying machine 10 as an image forming apparatus separates one document from a bundle of documents placed on a document tray 11 a and automatically feeds the document to a contact glass on a document reading unit 12. A document reading unit 12 that reads a document conveyed on the contact glass by the automatic document conveyance device 11 and an image that forms an image read by the document reading unit 12 on a sheet fed from the sheet feeding unit 13 A forming unit (image forming unit) 14, a sheet bundle S having a sheet bundle S in which a plurality of sheets are stacked, and a sheet feeding unit 13 that feeds the sheet S 1 positioned at the top of the sheet bundle S to the image forming unit 14; It has. In the present embodiment, the image forming unit 14 and the paper feeding unit 13 can be divided.

  The sheet feeding unit 13 separates a sheet feeding cassette 15 (see FIG. 2) as a sheet stacking member on which a plurality of sheets S1 are stacked, and a topmost sheet from the plurality of sheets S1 on the sheet feeding cassette 15. And a sheet separating and feeding device 16 as a sheet feeding device to be conveyed.

  The sheet S1 separated and fed by the sheet separating and feeding device 16 is conveyed on the conveying path 17, and the sheet S1 conveyed on the conveying path 17 is conveyed by the conveying roller pair 18, The toner image formed in the image forming unit 14 is transferred by the transfer roller 19, this toner image is thermally transferred by the fixing device 20, and is discharged to the discharge tray 22 by the discharge roller pair 21.

  The image forming unit 14 includes four image forming units 23 (23Y (yellow), 23C (cyan), 23M (magenta), 23BK (black)), an intermediate transfer belt 24 as a transfer belt, and an exposure device 25. It is configured.

  The exposure device 25 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 12 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 23Y, 23C, 23M, and 23BK form images of different colors (toner images), and the image forming units 23Y, 23C, 23M, and 23BK are rotated in the clockwise direction. The photosensitive member 26 (26Y, 26C, 26M, 26BK), which is an image carrier, and a charging unit 27, a developing unit 28, a cleaning unit 29, and the like disposed around the photosensitive member 26 are configured.

  The photosensitive member 26 is formed in a cylindrical shape and is rotationally driven by a driving source (not shown). A photosensitive layer is provided on the outer peripheral surface portion of the photosensitive member 26, and a light beam indicated by a broken line emitted from the exposure device 25 is spot-irradiated on the outer peripheral surface of the photosensitive member 26. The electrostatic latent image corresponding to the image information is written.

  The charging unit 27 uniformly charges the outer peripheral surface of the photoconductor 26, and a contact type is used for the photoconductor 26. The developing unit 28 supplies toner to the photoconductor 26, and the supplied toner adheres to the electrostatic latent image written on the outer peripheral surface of the photoconductor 26, whereby the electrostatic latent image on the photoconductor 26 is changed. A toner image is visualized and a non-contact type is used for the photoreceptor 26.

The cleaning unit 29 cleans the residual toner adhering to the outer peripheral surface of the photoconductor 26 and employs a brush contact type in which a brush contacts the outer peripheral surface of the photoconductor 26.
The intermediate transfer belt 24 is composed of an endless belt formed with a resin film or rubber as a base, and the toner image formed on the photosensitive member 26 is transferred to the intermediate transfer belt 24. The toner image is transferred to the sheet S1 by the transfer roller 19.

  In addition to the electrophotographic system, for example, other systems such as an ink jet system may be adopted as the copying machine 10, and besides the configuration as the copying machine 10, a printer device, a facsimile device, a printing machine, or You may comprise from a multifunction machine.

  As shown in FIG. 2, the sheet feeding unit 13 includes a sheet feeding cassette 15 that stacks a sheet bundle S composed of a plurality of sheets S <b> 1 and a sheet separating and feeding device 16. The sheet S1 is shorter than the width of the sheet S1 and is disposed near the center in the width direction of the sheet S1.

  The sheet separating and feeding device 16 may be equal to or longer than the width of the sheet S1. In FIG. 2, only one sheet separating / feeding device 16 is provided near the center in the width direction of the sheet S1, but a plurality of sheet separating / feeding devices 16 may be arranged in the width direction of the sheet S1.

  As shown in FIG. 3, the sheet separating and feeding device 16 includes an endless belt 32 made of a dielectric material wound around a driving roller 30 and a driven roller 31. The endless belt 32 is made of a dielectric having a resistance of 108 Ω · cm or more, for example, a film of polyethylene terephthalate having a thickness of about 100 μm. The endless belt 32 is in contact with a charging blade 33 extending in a predetermined direction as a charging member.

  As shown in FIG. 4, the endless belt 32 has a two-layer structure including a surface layer 32a made of a dielectric having a resistance of 108 Ω · cm or more and a back layer 32b made of a conductor having a resistance of 106 Ω · cm or less. Therefore, it has a good charged state.

  Since the charging blade 33 uses the back layer 32b of the endless belt 32 as a grounded counter electrode, the charging blade 33 may be in a position in contact with the surface layer 32a of the endless belt 32 in order to give charge to the endless belt 32. , Any position on the endless belt 32 may be provided. Further, the endless belt 32 is set at a position where the suction area of the uppermost sheet S1 with respect to the sheet bundle S can be sufficiently taken.

  The surface of the driving roller 30 is composed of a conductive rubber layer having a resistance value of about 106 Ω · cm, and the surface of the driven roller 31 is composed of metal. The drive roller 30 and the driven roller 31 are both grounded.

  The drive roller 30 has a small diameter suitable for separating the sheet S1 from the endless belt 32 by the curvature. That is, by setting the diameter of the driving roller 30 to be small and increasing the curvature, the sheet S1 that is attracted to the endless belt 32 and separated and fed is separated from the driving roller 30 and downstream in the conveyance direction of the sheet S1. It can be transported to a pair of guide members 34 that form the transport path 17 provided.

  The charging blade 33 is disposed so as to be in contact with the endless belt 32 near the position where the endless belt 32 is wound around the driving roller 30, and the charging blade 33 is connected to a charging power source 35 that generates an alternating current. ing.

  Further, on the upstream side in the circumferential movement direction R of the endless belt 32 of the charging blade 33 and on the downstream side with respect to the separation position of the sheet bundle S and the endless belt 32, the charging blade 33 is connected to a static elimination power source 36 which is an alternating power source. The neutralizing electrode 37 is placed in contact with or close to the endless belt 32.

  The charging power source 35 and the neutralizing power source 36 are controlled so that the suction force on the endless belt 32 is removed at the position where the leading edge of the sheet S1 separated by the conveying roller pair 18 contacts. In the present embodiment, the static elimination electrode 37 is not necessarily required and can be omitted. In the following description, it is assumed that the static elimination electrode 37 is not provided.

  As shown in FIG. 5A, a bottom plate 38 is provided between the bottom surface of the sheet feeding cassette 15 and the sheet bundle S. The bottom plate 38 has a tip portion that swings around a swing fulcrum 38a. It is free to move. Further, a push-up spring 39 is provided between the bottom plate 38 and the bottom surface of the paper feed cassette 15, and the push-up spring 39 is arranged so that the sheet bundle S abuts against the endless belt 32 through the bottom plate 38. Is biased upward.

  Further, the bottom plate 38 is swung about a swinging fulcrum portion 38a as a fulcrum by an actuator such as a solenoid (not shown) provided in the sheet feeding cassette 15. Further, the endless belt 32 is configured so that the driven roller 31 swings in the vertical direction as indicated by an arrow R1 with the drive roller 30 as a swing shaft, and when the bottom plate 38 is pushed up by the push-up spring 39, The endless belt 32 is pushed up by the bottom plate 38, and the driven roller 31 is moved upward with the drive roller 30 as a swing shaft. For this reason, in a state where the endless belt 32 is not pushed up by the bottom plate 38, the driven roller 31 is positioned below by its own weight with the driving roller 30 as a swing shaft.

  On the other hand, as shown in FIG. 6, the tip 33a of the charging blade 33 is in contact with the surface layer 32a, which is the surface of the endless belt 32, and forms a nip portion together with the endless belt 32. The contact portion is configured. The width of the nip portion is hereinafter referred to as nip width N.

  Further, the charging blade 33 is provided so as to be inclined obliquely upward to the right with respect to the endless belt 32, and by discharging between the charging blade 33 and the endless belt 32, It has a minute gap G that forms a discharge region for applying a charge to the surface.

  The nip width N is set in consideration of the elastic modulus and pressing force of the charging blade 33, the bending of the endless belt 32, and the like, and the size of the minute gap G is given from the charging power source 35 to the charging blade 33. It is determined in consideration of the applied voltage, the thickness of the endless belt 32, the dielectric constant, and the like.

  Then, the nip width N of the tip 33a of the charging blade 33 and the endless belt 32 and the width of the minute gap G as the discharge region (hereinafter, the width obtained by combining the nip width N and the width of the minute gap G is the basic charging width H. Is configured to be smaller than the charge width of charges of the same polarity charged in the circumferential movement direction R of the endless belt 32.

  Specifically, in FIG. 6, when the positive charge and the negative charge attached to the surface layer 32a of the endless belt 32 are schematically shown, the charge width W of the surface layer 32a charged with the positive charge and the negative charge is shown. The basic charging width H is formed small.

  Further, a cycle in the circumferential direction of the endless belt 32 of a charge pattern of positive charges and negative charges attached to the surface layer 32a of the endless belt 32 by a voltage (here, a sine wave) applied from the charging power source 35 to the charging blade 33. Is defined as a charging pitch P, the basic charging width H is set to be smaller than a half of the charging pitch P.

  In the paper feeding unit 13 configured as described above, the driving roller 30 is rotationally driven by a paper feeding signal, and the endless belt 32 that has started rotating is alternately connected by the charging power source 35 via the charging blade 33. A voltage is applied to the surface layer 32a of the endless belt 32 by discharge from the minute gap G of the charging blade 33, and a pitch (pitch is about 2 mm to 15 mm) according to the AC power source frequency and the circumferential movement speed of the endless belt 32. An alternating charge pattern is formed (see FIG. 6A).

  The charging power source 35 may be one in which alternating current or alternating direct current is changed to high and low potentials. In the present embodiment, 3 to 4 KV (± 1.5 to ± 2) with respect to the surface layer 32 a of the endless belt 32. An alternating current having an amplitude of is applied (see FIG. 6A).

  Here, when charging and discharging are performed by controlling the voltage, the charge pattern on the endless belt 32 is removed by lowering the applied voltage, as shown in FIG. As shown in (b), by increasing the power frequency, the pitch of the charge pattern formed on the endless belt 32 can be reduced, thereby reducing the adsorption force based on the Maxwell stress of the endless belt 32. Conceivable.

  FIGS. 7A and 7B are rectangular waves in which a DC power source is alternated. However, as shown in FIGS. 7C and 7D, the same applies when using a sine wave. In the embodiment, a sine wave shown in FIG. 7 (c) or (d) is used.

  The endless belt 32 in which a charge pattern in which positive and negative polarities are alternately charged is formed on the surface layer 32a is in contact with the front end of the upper surface of the uppermost sheet S1 at a position wound around the driven roller 31. Therefore, Maxwell stress acts on the sheet S1 which is a dielectric material due to an unequal electric field formed by the charge pattern on the surface of the endless belt 32, and only the uppermost sheet S1 is adsorbed and held on the endless belt 32. Paper is fed.

Here, the principle of electrostatically attracting the sheet S1 to the endless belt 32 will be described with reference to FIG.
When the surface layer 32 a of the endless belt 32 is charged with positive and negative charges by the charging blade 33, electric lines of force are generated on the surface of the endless belt 32 from the positive charge on the endless belt 32 toward the negative charge. Occur.

Due to the influence of the electric lines of force, a charge having the same polarity is induced on the side of the sheet S1 that contacts the endless belt 32 that is in contact with the endless belt 32 and the opposite side. The density of electric lines of force (indicated by phantom lines) on the side that contacts the endless belt 32 in the sheet S1 is high, and the density on the non-belt contact surface side that does not contact the endless belt 32 is sparse.
At this time, a difference in charge is generated between the lower side and the upper side of the sheet S1, and the difference acts as a force in the direction in which the endless belt 32 is adsorbed. This is called Maxwell stress, and occurs at the boundary between positive and negative polarities.

  In FIG. 8, for convenience of explanation, one positive charge and one negative charge are shown alternately, but in actuality, the positive and negative charges have a constant pitch (charging width W) in the circumferential movement direction of the endless belt 32. As the charging width is smaller, adjacent potentials are closer to each other, so that the electric field distance in the stacking direction of the sheet bundle S generated on the sheet S1 side is shortened, and the sheet S1 is given an attractive force. The distance that can be shortened. For this reason, it is conceivable that the adsorption force based on the Maxwell stress of the endless belt 32 is reduced as the charging width is smaller.

  On the other hand, the sheet S1 adsorbed to the endless belt 32 is separated from the endless belt 32 by the curvature, is fed out in the transport direction, passes through the transport path 17 formed by the pair of guide members 34, and reaches the transport roller pair 18. It is pinched. The sheet S <b> 1 sandwiched between the conveying roller pair 18 is conveyed toward the image forming unit 14 only by the conveying force of the conveying roller pair 18 without being affected by the endless belt 32.

  The drive roller 30 is connected to a drive transmission cut-off mechanism such as a clutch (not shown) via a drive shaft and a drive source (not shown), and after the sheet S1 reaches the conveying roller pair 18, the drive is performed. It is cut off and free to rotate, so that the load on the drive source generated by the sheet separating and feeding device 16 is reduced.

  Here, the suction force due to the charge pattern acts on the sheet S1 other than the uppermost sheet S1 for a certain period from the moment when the sheet S1 is attracted to the endless belt 32, but after the certain period of time, the uppermost sheet S1. The contact time of the endless belt 32 becomes longer, the suction force for the uppermost sheet S1 increases, and the suction force for the sheets S1 other than the uppermost sheet S1 decreases.

  That is, by increasing the contact time of the uppermost sheet S1, the uppermost sheet S1 can be separated from the sheet bundle S without providing a double feed blocking member. For this reason, the linear speeds of the conveying roller pair 18 and the endless belt 32 are made the same, and the endless belt 32 is also controlled to be intermittently driven when the conveying roller pair 18 is intermittently driven with timing. By doing so, the contact time between the uppermost sheet S1 and the endless belt 32 can be increased.

  The endless belt 32 prevents the second sheet S1 from being attracted to the endless belt 32 before the trailing end of the sheet S1 reaches the position facing the driven roller 31.

  Here, when the endless belt 32 of the sheet separating and feeding device 16 is charged or neutralized, it is necessary to make the endless belt 32 go around. Therefore, when the endless belt 32 goes around, If the endless belt 32 is in contact with the bundle S, the uppermost sheet S1 may be sent out during the charging operation and the discharging operation.

  In the present embodiment, as shown in FIG. 5B, an actuator such as a solenoid is actuated to push down the bottom plate 38 against the urging force of the spring 39 around the swing fulcrum 38a. The bundle S is separated from the endless belt 32.

  In the state where the endless belt 32 is not pushed up by the bottom plate 38, the driven roller 31 is positioned below by its own weight with the driving roller 30 as a swinging shaft. However, the amount of downward movement of the driven roller 31 is as follows. By limiting the endless belt 32 so as not to contact the sheet bundle S via the driven roller 31, the endless belt 32 and the uppermost sheet S1 are prevented from coming into contact with each other. It is possible to prevent the sheet S1 from being sent out.

  As described above, in the present embodiment, the charging blade 33 has the tip portion 33 a that contacts the endless belt 32 and forms the nip portion together with the endless belt 32, and between the charging blade 33 and the endless belt 32. By carrying out the discharge, the surface of the surface layer 32a of the endless belt 32 has a minute gap G that gives an electric charge, and the basic charging width H composed of the nip width N and the minute gap G is set to the circumferential movement direction of the endless belt 32. Less than the width of half of the period (P) of the alternating charge applied from the charging blade 33 to the endless belt 32 so that it is smaller than the charging width W of the charge of the same polarity charged to Since the discharge is performed on the upstream side of the charging blade 33 with respect to the circumferential movement direction of the endless belt 32, the endless belt 3 has a nip width N between the charging blade 33 and the endless belt 32. It is possible to suppress the movement of the charged electric charge on the upper surface, to prevent the endless belt 32 from being charged with a reverse polarity charge, and to change the polarity of the electric charge charged to the endless belt 32. On the other hand, it is possible to prevent reverse polarity charging from occurring on the downstream side of the charging blade 33. For this reason, the entire charging width W of the endless belt 32 can be maintained in a normal charged state without being affected by the movement of charges or charging with the opposite polarity.

  For this reason, it is possible to reduce the charging pitch of the alternating charges and generate a sufficient attracting force on the endless belt 32.

  Accordingly, it is possible to accelerate the increase in the suction force with respect to the sheet S1 positioned at the top of the sheet bundle S stacked in the sheet feeding cassette 15, and to quickly decrease the suction force acting on the second and subsequent sheets S1. Thus, the time required for the separation operation can be shortened, and the productivity can be improved by the separation operation of the sheet S1.

  Note that the electrostatic adsorption separation method employed by the sheet separating and feeding device 16 takes time to obtain the required adsorption force when the electric resistance of the sheet S1 is high, and the second sheet S1 and below. However, when the electrical resistance of the sheet S1 is low, there is a problem that the adsorption force is small. However, in the present embodiment, as described above, Since the charging pitch of the alternating charge can be reduced, as described above, the increase in the suction force with respect to the sheet S1 positioned at the top of the sheet bundle S stacked on the sheet feeding cassette 15 can be accelerated, and 2 It is possible to accelerate the decrease in the attractive force acting on the first and subsequent sheets S1.

  As a result, even for various sheet types, the sheet bundle S loaded in the sheet feeding cassette 15 is stable against environmental fluctuations and fluctuations with time, and can be reliably separated and fed one by one at high speed. A sheet separating and feeding device 16 having high performance can be realized.

  The detection of the environmental condition can be realized, for example, by incorporating a temperature / humidity meter in the paper feeding unit 13. Further, acquisition of information on the material of the sheet S1 can be realized by a user performing an input operation or a selection operation from an operation unit (not shown).

  In the present embodiment, dust, dirt, discharge products, and the like accumulated on the surface of the surface layer 32 a of the endless belt 32 are pressed by pressing the tip 33 a of the charging blade 33 against the endless belt 32. Since the cleaning effect to be removed can be obtained, the surface of the surface layer 32a of the endless belt 32 can be kept in a normal state without adding a new cleaning member, and a decrease in the adsorption force due to a change with time can be suppressed. Can do.

  In addition, as a voltage applied to the charging blade 33, as shown in FIG. 9, a rectangular wave in which a DC power source is alternated may be used. In this case, the period of the alternating charge applied from the charging blade 33 to the endless belt 32 (less than the charging width W of the charge of the same polarity charged in the circumferential movement direction of the endless belt 32 ( The width may be smaller than 1/2 of P).

  In the present embodiment, the sheet S1 is separated from the endless belt 32 of the drive roller 30 by curvature separation. However, in order to further ensure the separation, as shown in FIG. 41 may be provided.

  Further, in the present embodiment, in order to obtain an electrostatic attraction force, an electric field is generated on the endless belt 32 by applying a charge to the endless belt 32 using the charging blade 33 extending in a predetermined direction. However, the method of applying an electric charge to the endless belt 32 is not limited to this, and the sawtooth electrode may be arranged in a state separated from the endless belt 32 by a minute distance.

  Further, as shown in FIG. 11, two positive and negative comb-like electrodes 51 may be arranged on the endless belt 32 so as to face each other in a direction orthogonal to the circumferential movement direction of the endless belt 32. . In this case, power-supplied portions 52 with exposed patterns are provided at both ends in the width direction of the endless belt 32, and positive or negative voltage is applied to the electrode 51 through positive and negative high-voltage power sources 53 and 54 through the power-supplied portion 52. By applying the electric field, an electric field may be generated, and a force for attracting the uppermost sheet S1 from the sheet bundle S may be generated.

  Further, as shown in FIG. 5, the sheet bundle S can be separated from the endless belt 32 in place of the one using an actuator such as a bottom plate 38, a push-up spring 39 and a solenoid, as shown in FIG. Good.

  That is, as shown in FIG. 12, a bottom plate 61 is interposed between the bottom surface of the sheet feeding cassette 15 and the sheet bundle S, and a rack 62 is provided on the back surface of the bottom plate 61. A pinion 63 that is rotationally driven by a motor that is not engaged is engaged with the rack 62. For this reason, the bottom plate 61 is moved up and down by the rack 62 and the pinion 63 while keeping parallel.

  In this case, the endless belt 32, the driving roller 30, and the driven roller 31 may be in a state in which positions are fixed in the paper feeding unit 13. The sheet feeding unit 13 includes a sensor 64 that detects the vertical position of the uppermost sheet S1, and a motor control circuit (not shown) controls the motor based on detection information from the sensor 64. Appropriateness is controlled for the distance and contact pressure between the endless belt 32 and the uppermost sheet S1.

  The bottom plate 61 is attached to the paper feed cassette 15 by slidably engaging the rack 62 with a cylindrical portion protruding from the bottom plate 61 so that the bottom plate 61 is interposed via the rack 62. Or the bottom plate 61 is slidably engaged with the side plates at both ends in the width direction of the paper feed cassette 15 so that the bottom plate 61 is attached to the paper feed cassette 15 via the rack 62. do it. The motor may be provided between the bottom plate 61 and the bottom surface of the paper feed cassette 15.

  Further, as shown in FIG. 13, the drive roller 30 is used as a swing shaft, and the driven roller 31 is swung as indicated by an arrow R2, and the drive roller 30 is separated when the uppermost sheet S1 is separated from the sheet bundle S. The driven roller 31 may be swung as indicated by an arrow R2 with 30 as a rocking shaft.

  In this way, as shown in FIG. 12, the drive roller 30 is swung by moving the bottom plate 61 downward as shown in FIG. 13 from the state in which the endless belt 32 attracts the uppermost sheet S1. The driven roller 31 can be swung counterclockwise as an axis to turn the uppermost sheet S1 from the sheet bundle S. As a result, the uppermost sheet S1 can be reliably separated from the sheet bundle S and the sheet S1 can be reliably prevented from being double fed.

(Second Embodiment)
FIGS. 14 and 15 are diagrams showing a second embodiment of the sheet feeding apparatus and the image forming apparatus according to the present invention. In this embodiment, the charging blade of the first embodiment is used as a charging member. Instead of this, a charging roller 71 is used, and the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  14 and 15, a charging roller 71 as a charging member includes an outer peripheral portion 71a that contacts the endless belt 32 and forms a nip portion together with the endless belt 32. The outer peripheral portion 71a includes a contact portion. Is configured. The width of the nip portion 72 is hereinafter referred to as a nip width N.

  As shown in FIG. 15, the charging roller 71 discharges between the upstream side and the downstream side of the charging roller 71 with respect to the circumferential movement direction R of the endless belt 32, thereby It has two minute gaps G that form a discharge region for applying a charge to the surface.

  The nip width N is set in consideration of the elastic modulus and pressing force of the charging roller 71, the bending of the endless belt 32, and the like, and the size of the minute gap G is given from the charging power source 35 to the charging roller 71. It is determined in consideration of the applied voltage, the thickness of the endless belt 32, the dielectric constant, and the like.

  Then, the nip width N of the outer peripheral portion 71a of the charging roller 71 and the endless belt 32 and the width of the minute gap G as the discharge region (hereinafter, the width obtained by combining the nip width N and the width of the minute gap G is the basic charging width H. Is configured to be smaller than the charge width of charges of the same polarity charged in the circumferential movement direction R of the endless belt 32.

  Specifically, the diameter D of the charging roller 71 is formed to be smaller than the charging width W, and the cycle of the voltage waveform (here, a sine wave) applied from the charging power source 35 to the charging roller 71 is defined as the charging pitch P. In this case, the diameter D of the charging roller 71 is set to be smaller than a half of the charging pitch P. As a result, the basic charging width H becomes smaller than the charging width W.

  In the sheet separating and feeding apparatus 16 configured as described above, the charging roller 71 has an outer peripheral portion 71 a that contacts the endless belt 32 and forms a nip portion together with the endless belt 32, and the charging roller 71. A basic charging width having a small gap G that gives electric charge to the surface layer 32a of the endless belt 32 by discharging between the upstream side and the downstream side of the charging roller 71, and the outer peripheral portion 71a of the charging roller 71 and the minute gap G. The diameter D of the charging roller 71 is made smaller than the charging width W so that H becomes smaller than the charging width W of the charge of the same polarity charged in the circumferential movement direction of the endless belt 32, and the charging roller The diameter D of 71 was made smaller than the width of 1/2 of the charging pitch P.

  For this reason, when an alternating voltage is applied to the charging roller 71, the movement of the charged charge on the endless belt 32 in the nip width N between the charging roller 71 and the endless belt 32 is suppressed, or the endless belt 32 is prevented from being charged with a reverse polarity charge, and a reverse polarity charge is generated in the minute gap G on the downstream side of the charging roller 71 with respect to the polarity of the charge charged on the endless belt 32. Even in this case (in FIG. 15, the charge discharged in the upstream minute gap G is indicated by reference numeral 72, and the charge discharged in the downstream minute gap G is indicated by reference numeral 73), the endless belt 32 Thus, the regular charge state can be maintained without being affected by the charge transfer or the reverse polarity charge.

  For this reason, the charging pitch of the alternating charges can be reduced, and a sufficient suction force can be generated on the endless belt 32.

  Accordingly, it is possible to accelerate the increase in the suction force with respect to the sheet S1 positioned at the top of the sheet bundle S stacked in the sheet feeding cassette 15, and to quickly decrease the suction force acting on the second and subsequent sheets S1. Thus, the time required for the separation operation can be shortened, and the productivity can be improved by the separation operation of the sheet S1.

As a result, even for various sheet types, the sheet bundle S loaded in the sheet feeding cassette 15 is stable against environmental fluctuations and fluctuations with time, and can be reliably separated and fed one by one at high speed. A sheet separating and feeding device 16 having high performance can be realized.
In addition, a cleaning mechanism may be provided on the endless belt 32 in order to prevent paper dust and other dust from adversely affecting the suction operation of the sheet separating and feeding device 16.
The case where N = 0 is also included in these embodiments. When N = 0, non-contact charging is performed, and a region discharged by the minute gap G is the basic charging width H.

  As described above, the sheet feeding apparatus and the image forming apparatus according to the present invention can reduce the charging pitch, and even in various sheet types, environmental fluctuations and temporal fluctuations from the sheet bundle loaded on the sheet stacking member. The sheet feeding device and the image forming apparatus including the sheet feeding device can be provided with high reliability and the ability to reliably feed one by one at a high speed. An image comprising a sheet feeding device that uses static electricity to attract and separate a sheet onto an endless belt, and an electrophotographic copying machine, a facsimile machine, a printer device, an ink jet device, and the like equipped with the sheet feeding device It is useful as a forming device or the like.

10 Copying machine (image forming device)
14 Image forming unit (image forming means)
15 Paper cassette (sheet stacking member)
16 Sheet separation and feeding device (sheet feeding device)
32 Endless belt 33 Charging blade (charging member)
33a Tip (contact part)
71 Charging roller (charging member)
71a Outer peripheral part (contact part)
S Sheet bundle S1 Sheet G Micro gap H Basic charge width W Charge width

Japanese Patent No. 3927833 Japanese Patent Laid-Open No. 2002-21777

Claims (4)

A sheet stacking member for stacking a plurality of sheets;
An endless belt that is wound around a driving roller and a driven roller and rotates in a circumferential movement direction;
A charging roller that periodically charges positive and negative charges on the surface of the endless belt,
A sheet feeding device that sucks and feeds the uppermost sheet from the plurality of sheets on the sheet stacking member by the endless belt;
The charging roller and the endless belt are:
A nip portion where an outer peripheral portion of the charging roller contacts an arbitrary position on the surface of the endless belt;
Forming a gap for applying a predetermined charge to the surface of the endless belt by discharge on the upstream side and the downstream side of the nip portion in the circumferential movement direction;
The basic charging width obtained by combining the nip width of the nip portion with respect to the circumferential movement direction and the width of the gap on the upstream side and the downstream side of the nip portion is the downstream side in the circumferential movement direction from the nip portion. A sheet feeding apparatus configured to be smaller than a charging width of charges of the same polarity charged on the surface of an endless belt in the circumferential movement direction.   The sheet feeding apparatus according to claim 1, wherein the basic charging width is smaller than a half period width of an alternating charge applied from the charging roller to the endless belt.   The sheet feeding apparatus according to claim 1, wherein a diameter of the charging roller is smaller than the charging width. The sheet feeding device according to any one of claims 1 to 3,
Image forming means for forming an image on the sheet fed by the sheet feeding device;
An image forming apparatus.

Images