Patent Grant
8474811
1. Field of the Invention
Example embodiments relate to a sheet feeding device that separates and conveys the uppermost sheet from a sheet stack using electrostatic attraction method, and an image forming apparatus including the sheet feeding device.
2. Discussion of the Related Art
Background sheet feeding devices that separate and convey the uppermost sheet from a sheet stack include those that separate and feed stacked sheets, such as documents and recording sheets, by using frictional force, those that separate and feed sheets by air suction.
In background sheet feeding devices using the frictional separation method, which separates sheets by using frictional force, a material such as rubber is used to form feeding rollers. Therefore, a change over time in the condition of the feeding rollers due to abrasion or the like results in a change in the frictional force exerted by the feeding rollers, that is, consequent deterioration of feeding performance. Further, when separating and feeding sheets having unequal coefficients of friction due to variations from sheet to sheet, or when separating and feeding sheets having inherently different coefficients of friction in the same feeding operation, the frictional force acting between the feeding rollers and the sheets changes. In some cases, therefore, the separation of sheets fails, or multiple feeding occurs in which a plurality of sheets are fed together. Further, the feeding rollers need to be pressed against the sheets in order to function and in some cases the sheets are dirtied or damaged as a result.
By contrast, background sheet feeding devices using the air suction method, which separates sheets by air suction, employ a non-frictional separation method not relying on the frictional force acting between the feeding rollers and the sheets, and thus the above-described problems do not arise. However, the sheet feeding device requires a blower and a duct for the air suction. As a result, the sheet feeding device is increased in size, and the sound accompanying the air suction constitutes noise. Therefore, this type of sheet feeding device is not suitable for use in an office environment.
In view of the above, as one non-frictional separation methods, an electrostatic attraction separation method has been proposed which generates an electric field in a dielectric belt and brings the dielectric belt into contact with a sheet to attract and separate the sheet from other sheets.
Specifically, a background sheet feeding device according to the electrostatic attraction separation method first applies an alternating charge to an endless dielectric belt wound around a plurality of rollers, and swings or translates the dielectric belt relative to a sheet stack such that the dielectric belt approaches or contacts the sheet stack. Then, the sheet feeding device causes the dielectric belt to stand by for a predetermined time to attract the uppermost sheet of the sheet stack, and thereafter moves the dielectric belt away from the sheet stack, thereby, separating the uppermost sheet and conveying it from the sheet stack.
The sheet feeding device using the electrostatic attraction separation method is advantageous in preventing not only the abrasion of the feeding rollers and the damage to the sheets, which occur in the frictional separation method, but also the increase in device size and the noise generation, which occur in the air suction method.
When separating and feeding relatively thick sheets or sheets difficult to attract due to the electrical characteristics thereof, however, sheet feeding devices using the electrostatic attraction separation method need to extend the predetermined time for causing the dielectric belt to stand by to have the attraction force thereof act on the uppermost sheet. As a result, the productivity suffers.
Example embodiments disclose a novel sheet feeding device. In one example embodiment, a sheet feeding device includes a sheet carrying unit, an attraction separation device, a sheet conveying device, and a lifting and lowering device. The sheet carrying unit is configured to carry thereon a sheet stack. The attraction separation device is configured to electrostatically attract the uppermost sheet of the sheet stack and separate the uppermost sheet from the sheet stack. Further, the attraction separation device includes a plurality of rollers, an endless belt formed by a dielectric material and stretched over the plurality of rollers, and an elastic member provided inside the belt and configured to bring the belt into contact with the uppermost sheet. The sheet conveying device is configured to convey the uppermost sheet separated by the attraction separation device. The lifting and lowering device is configured to lift and lower the sheet stack carried on the sheet conveying device. The sheet feeding device causes the lifting and lowering device to lift the sheet stack to a lift position at which the uppermost sheet comes into contact with the attraction separation device, causes the attraction separation device to stand by for a predetermined time to attract the uppermost sheet, and causes the attraction separation device to start, after the lapse of the predetermined time, conveying the uppermost sheet with the sheet stack kept at the lift position.
Example embodiments further disclose a novel image forming apparatus. In one example embodiment, an image forming apparatus includes the above-described sheet feeding device.
A more complete appreciation of the invention and many of the advantages thereof are obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing the example embodiments illustrated in the drawings, specific terminology is employed for the purpose of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so used, and it is to be understood that substitutions for each specific element can include any technical equivalents that operate in a similar manner.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, example embodiments of the present invention will be described.
The configuration of an example embodiment of the present invention will be first described. As illustrated in
The sheet 1a fed by the sheet feeding device 104 is conveyed by a conveying roller pair 108. Then, a toner image formed by the image forming unit 103 is transferred onto the sheet 1a by a transfer device 109 and thermally transferred and fixed to the sheet 1a by a fixing device 110. Thereafter, the sheet 1a is discharged onto a sheet discharging tray 112 by a sheet discharging roller pair 111.
The image forming method employed by the image forming apparatus 101 is not limited to the electrophotographic method. Thus, the image forming apparatus 101 may employ another method, such as the inkjet method, for example. Further, the image forming apparatus 101 is not limited to the copier, and thus may be configured as a facsimile machine, a printer, a multifunctional machine, and so forth.
As illustrated in
The separation unit 107 includes a downstream roller 5, an upstream roller 6, and an endless belt 2 formed by a dielectric material and wound around the downstream roller 5 and the upstream roller 6.
The upstream roller 6 is configured as a drive roller which receives drive force from a not-illustrated drive source. The downstream roller 5 is configured as a driven roller which is driven to rotate in accordance with the rotation of the upstream roller 6 via the belt 2. The drive force from the not-illustrated drive source is transmitted to the upstream roller 6 via an electromagnetic clutch 16. The electromagnetic clutch 16 is activated in accordance with a sheet feeding signal to intermittently drive the upstream roller 6.
A surface of the upstream roller 6 is formed by a conductive rubber layer having a resistance value of approximately 106 Ω·cm (ohm centimeters). Meanwhile, a surface of the downstream roller 5 is made of metal. The upstream roller 6 and the downstream roller 5 are electrically grounded. The downstream roller 5 has a relatively small diameter suitable for separating the sheet 1a from the belt 2 in accordance with the curvature thereof. That is, the downstream roller 5 is set to have a relatively small diameter to increase the curvature thereof. With this configuration, the sheet 1a attracted, separated, and conveyed by the belt 2 is allowed to separate from the downstream roller 5 and enter between a guide plate pair 10 located downstream in the sheet conveying direction.
The downstream roller 5 and the upstream roller 6, which respectively serve as the driven roller and the drive roller, are arranged such that a lower tangent line of the belt 2 formed by the downstream roller 5 and the upstream roller 6 is on a level with the upper surface of the sheet 1a.
As illustrated in
That is, the elastic member 20 provides elasticity to the contact surface of the belt 2 such that the belt 2 comes into elastic contact with the sheet 1a. Therefore, even if the surface of the sheet 1a has irregularities, has a bump caused by multiple feeding thereof, or has a curled or undulated portion due to a phenomenon such as moisture attraction, it is possible to secure the area of contact between the belt 2 and the sheet 1a, and thus to ensure the attraction force for attracting the sheet 1a toward the belt 2, irrespective of the characteristics of the sheet 1a.
As illustrated in
With each of the elastic member pieces 20a to 20f formed by the contact member 21 and the spring 22, it is possible to easily change the elastic force by changing the spring 22, irrespective of the physical properties of the material forming the contact member 21 which comes into contact with the belt 2. Accordingly, the elastic force changes for each of the elastic member pieces 20a to 20f. Therefore, even if the state of the surface of the sheet 1a substantially changes due to irregularities or undulations thereof, it is possible to secure the area of contact between the belt 2 and the sheet 1a, and thus to ensure the attraction force for attracting the sheet 1a toward the belt 2.
As illustrated in
With this configuration, the plurality of elastic member pieces 20a to 20f forming the elastic member 20 are capable of expanding and contracting independently of one another in accordance with respective elastic forces. With the elastic member pieces 20a to 20f having different amounts of expansion and contraction, therefore, even if the state of the surface of the sheet 1a substantially changes due to irregularities or undulations thereof, it is possible to secure the area of contact between the surface of the belt 2 and the sheet 1a, and thus to ensure the attraction force for attracting the sheet 1a toward the belt 2.
Further, the elastic member 20 is divided in a direction perpendicular to the conveying direction of the sheet 1a. Therefore, there is no change in elastic force in the conveying direction of the sheet 1a and thus no burden on the sheet conveying operation. Further, even if the sheet 1a is undulated or curled in the direction perpendicular to the sheet conveying direction, the divided elastic member 20 brings the belt 2 into contact with the sheet 1a. Accordingly, it is possible to secure the area of contact between the surface of the belt 2 and the sheet 1a, and thus to ensure the attraction force for attracting the sheet 1a toward the belt 2.
The belt 2 is formed by a dielectric material having a resistance of at least approximately 108 Ω·cm. The dielectric material forming the belt 2 may include, for example, a film made of polyethylene terephthalate or the like having a thickness of approximately 100 μm (micrometers).
The belt 2 is stretched over the downstream roller 5 and the upstream roller 6, slacking downward to a degree not causing the upstream roller 6 to spin around without rotating the belt 2. With the downward slacking belt 2 brought into contact with the sheet 1a, it is possible to secure the area of contact of the belt 2 with the sheet 1a, even if the sheet 1a is undulated.
In the present embodiment, the belt 2 is stretched over two rollers of the downstream roller 5 and the upstream roller 6. The belt 2, however, may be stretched over a larger number of rollers, and one of the rollers located most upstream in the sheet conveying direction may be configured as a drive roller.
The belt 2 is placed between the rear end position and the central position in the sheet conveying direction of the sheet stack 1 located at a sheet carrying position and having the minimum sheet size compatible with the sheet feeding device 104. For example, if the size of the sheet 1a compatible with the sheet feeding device 104 ranges from A5 to A3, the belt 2 is arranged such that the leading end of the belt 2, which corresponds to the position of contact of the downstream roller 5 with the sheet 1a, is located between the center of the length in the sheet conveying direction of the sheet 1a having the minimum sheet size A5 (i.e., 210 mm) and the rear end position of the sheet 1a, i.e., between a position apart from the leading end of the sheet 1a by 105 mm to a position apart from the leading end by 210 mm.
Further, the belt 2 is placed at the center in a direction perpendicular to the sheet conveying direction. That is, as for the width direction perpendicular to the sheet conveying direction, i.e., the depth direction in
The guide plate pair 10 for guiding the conveyance of the sheet 1a and the sheet feeding roller pair 9 for conveying the sheet 1a entered between the guide plate pair 10 are provided downstream in the sheet conveying direction of the belt 2.
Inside portions of side edges of the belt 2 are provided with ribs 17. The ribs 17 of the belt 2 engage with respective side surfaces of the downstream roller 5 and the upstream roller 6. With this configuration, the belt 2 is prevented from moving in the width direction thereof and coming off the downstream roller 5 and the upstream roller 6.
On the upstream side in the sheet conveying direction of the separation unit 107, a feeler sensor 18 is provided which detects that the uppermost sheet 1a of the sheet stack 1 lifted by the bottom plate lifting arms 8 is located at a sheet feed position at which the sheet 1a comes into contact with the belt 2. The feeler sensor 18 is placed at a position corresponding to an end portion in the width direction of the sheet stack 1, and thus does not come into contact with the belt 2 placed on the upstream side in the sheet conveying direction.
At a position at which the belt 2 is wound around the upstream roller 6, a charging roller electrode 3 is provided which comes into contact with the outer circumferential surface of the belt 2 and is driven to rotate in accordance with the rotation of the belt 2. The roller electrode 3 is connected to an alternating-current power supply 4.
At a position upstream of the roller electrode 3 in the rotation direction of the belt 2 and downstream of the position at which the sheet stack 1 and the belt 2 separate from each other, a discharging roller electrode connected to a not-illustrated discharging power supply, which is an alternating power supply, may be provided such that the discharging roller electrode comes into contact with the belt 2 and is driven to rotate in accordance with the rotation of the belt 2. In this case, the charging roller electrode 3 and the discharging roller electrode are controlled such that the attraction force of the belt 2 has been removed by the time the leading end of the sheet 1a comes into contact with the sheet feeding roller pair 9. The discharging roller electrode is not necessarily required, and thus may be omitted. In the description of the present embodiment, therefore, the sheet feeding device 104 is assumed to include the charging roller electrode 3 but not to include the discharging roller electrode.
Subsequently, the operations of the sheet feeding device 104 will be described. As illustrated in
After the charging of the belt 2, the bottom plate lifting arms 8 start lifting the lowered bottom plate 7. The bottom plate lifting arms 8 stop lifting the bottom plate 7 when the feeler sensor 18 detects that the uppermost sheet 1a of the sheet stack 1 has reached a lift position at which the sheet 1a comes into contact with the belt 2 (i.e., the sheet feed position). In the lifting of the bottom plate 7, the lift amount of the bottom plate 7 may be determined on the basis of the calculation of the difference in height between the lower surface of the belt 2 and the position of the upper surface of the sheet 1a prior to the lifting of the bottom plate 7, which has previously been detected by the feeler sensor 18.
Then, as illustrated in
Immediately after the contact between the belt 2 and the uppermost sheet 1a, the electric field generated by the non-uniform charging of the belt 2 acts on a plurality of sheets of the sheet stack 1 on the basis of the action of the Maxwell stress, and thus attraction force for attracting the plurality of sheets is generated. After the lapse of the predetermines time, however, free electrons in the uppermost sheet 1a gather toward the belt 2 to cancel the electric field of the belt 2. Therefore, the attraction force of the belt 2 acts only on the uppermost sheet 1a.
Then, as illustrated in
Then, as illustrated in
Then, as illustrated in
The power supply 4 is not limited to the alternating-current power supply, and may provide a direct-current voltage alternated between high and low potentials. Further, the waveform of the voltage may be either a rectangular wave or a sine wave. In the present embodiment, the surface of the belt 2 is applied with a rectangular-wave voltage having an amplitude of approximately 4 kV (kilovolts).
If the sheet feeding device 104 includes a discharging roller electrode, the charge of the charged belt 2 can be removed by an alternating voltage applied to the belt 2 by the discharging roller electrode. Specifically, when the outer circumferential surface of the belt 2 is brought into contact with the discharging roller electrode and applied with a direct-current voltage by a direct-current power supply, the belt 2 is not charged by the applied direct-current voltage, if the direct-current voltage does not reach a predetermined voltage. The predetermined voltage is referred to as the charge start voltage. The charge start voltage value V0 varies depending on, for example, the thickness and the volume resistivity of the belt 2.
It has been confirmed that, if the discharging roller electrode is applied with an alternating voltage having the charge start voltage value V0 as the peak value thereof, the surface potential of the charged belt 2 is discharged to substantially 0 V. This indicates that the applied voltage having the charge start voltage value V0 as the peak value thereof is not capable of charging a dielectric object to be charged, but is capable of discharging the object with force for moving the space charge of the object. Further, the applied voltage used here alternates, and thus has the discharging effect whether the dielectric object is positively charged or negatively charged. If the applied voltage does not reach the charge start voltage, however, insufficient discharging is caused. Meanwhile, if the applied voltage exceeds the charge start voltage, charging is caused with an applied frequency of 120 Hz (hertz) and a period (i.e., wavelength=velocity/frequency) of 1 mm, and thus the charge is not discharged to 0 V. It is therefore preferred that the alternating voltage applied to the discharging roller electrode be controlled to have the charge start voltage of the belt 2 as the peak value thereof.
As described above, the sheet feeding device 104 according to the present embodiment includes the bottom plate 7 for carrying thereon the sheet stack 1, the separation unit 107 for electrostatically attracting and separating the uppermost sheet 1a from the sheet stack 1 and conveying the separated sheet 1a, and the bottom plate lifting arms 8 for lifting and lowering the sheet stack 1 carried on the bottom plate 7. Further, the sheet feeding device 104 causes the bottom plate lifting arms 8 to lift the sheet stack 1 to the lift position at which the uppermost sheet 1a comes into contact with the separation unit 107, causes the separation unit 107 to stand by for a predetermined time to attract the uppermost sheet 1a, and causes the separation unit 107 to start, after the lapse of the predetermined time, conveying the sheet 1a with the sheet stack 1 kept at the lift position. Further, the separation unit 107 is configured to include the downstream roller 5, the upstream roller 6, the endless belt 2 formed by a dielectric material and stretched over the downstream roller 5 and the upstream roller 6, and the elastic member 20 placed inside the belt 2 to bring the belt 2 into contact with the uppermost sheet 1a.
With this configuration, the contact surface of the belt 2 with the sheet 1a is provided with elasticity. Therefore, even if the surface of the sheet 1a has irregularities, has a bump caused by multiple feeding thereof, or has a curled or undulated portion due to a phenomenon such as moisture attraction, it is possible to secure the area of contact between the belt 2 and the sheet 1a, and thus to ensure the attraction force for attracting the sheet 1a toward the belt 2. Accordingly, the sheet feeding device 104 employing the electrostatic attraction separation method achieves relatively high productivity irrespective of the characteristics of the sheet 1a.
Further, in the sheet feeding device 104 according to the present embodiment, the elastic member 20 is divided into the plurality of elastic member pieces 20a to 20f. With this configuration, the plurality of elastic member pieces 20a to 20f forming the elastic member 20 are capable of expanding and contracting independently of one another in accordance with respective elastic forces. With the elastic member pieces 20a to 20f having different amounts of expansion and contraction, therefore, even if the state of the surface of the sheet 1a substantially changes due to irregularities or undulations thereof, it is possible to secure the area of contact between the surface of the belt 2 and the sheet 1a, and thus to ensure the attraction force for attracting the sheet 1a toward the belt 2.
Further, in the sheet feeding device 104 according to the present embodiment, the elastic member 20 is divided into the plurality of elastic member pieces 20a to 20f in a direction perpendicular to the conveying direction of the sheet 1a. With the elastic member 20 divided in a direction perpendicular to the conveying direction of the sheet 1a, therefore, there is no change in elastic force in the conveying direction of the sheet 1a and thus no burden on the sheet conveying operation. Further, even if the sheet 1a is undulated or curled in the direction perpendicular to the sheet conveying direction, the divided elastic member 20 brings the belt 2 into contact with the sheet 1a. Accordingly, it is possible to secure the area of contact between the surface of the belt 2 and the sheet 1a, and thus to ensure the attraction force for attracting the sheet 1a toward the belt 2.
Further, in the sheet feeding device 104 according to the present embodiment, each of the elastic member pieces 20a to 20f is formed by the contact member 21 which comes into contact with the belt 2 and the spring 22 which biases the contact member 21 toward the belt 2. With each of the elastic member pieces 20a to 20f formed by the contact member 21 and the spring 22, therefore, it is possible to easily change the elastic force by changing the spring 22, irrespective of the physical properties of the material forming the contact member 21 which comes into contact with the belt 2. Therefore, the elastic force changes for each of the elastic member pieces 20a to 20f. Accordingly, even if the state of the surface of the sheet 1a substantially changes due to irregularities or undulations thereof, it is possible to secure the area of contact between the belt 2 and the sheet 1a, and thus to ensure the attraction force for attracting the sheet 1a toward the belt 2.
Further, the image forming apparatus 101 according to the present embodiment includes the above-described sheet feeding device 104. Accordingly, the image forming apparatus 101 achieves relatively high productivity irrespective of the characteristics of the sheet 1a.
The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements at least one of features of different illustrative and exemplary embodiments herein may be combined with each other at least one of substituted for each other within the scope of this disclosure and appended claims. Further, features of components of the embodiments, such as the number, the position, and the shape, are not limited the embodiments and thus may be preferably set. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-269845 | Nov 2009 | JP | national |
This application is a Continuation of U.S. application Ser. No. 12/926,515 filed Nov. 23, 2010, which claims priority pursuant to 35 U.S.C. §119 from Japanese Patent Application No. 2009-269845, filed on Nov. 27, 2009 in the Japan Patent Office, which is hereby incorporated by reference herein in its entirety.
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| Number | Date | Country | |
|---|---|---|---|
| 20120193861 A1 | Aug 2012 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12926515 | Nov 2010 | US |
| Child | 13443295 | US |
