Paper Transporting Device for Image Forming Equipment

The present invention relates to a device incorporated in image forming equipment for transporting a paper sheet and, more particularly, to a paper transporting device having a plurality of paper feeding sections arranged one above and a common vertically extending transport path for transporting a paper sheet fed from any one of the paper feeding sections vertically therealong.

Many of modern image forming equipment such as copiers, facsimile transceivers and printers have a plurality of paper feeding sections each being loaded with paper sheets of particular size. In this type of equipment, a paper sheet fed from any one of the paper feeding sections is transported along a predetermined transport path to an image transfer station, so that a toner image formed on a photoconductive element may be transferred to the paper sheet. The space available in such equipment is becoming smaller and smaller due to the increasing demand for a miniature configuration. In light of this, Japanese Utility Model Laid-Open Publication No. 78629/1989, for example, discloses a paper transport arrangement wherein a single common transport path extends vertically upward to feed all the paper sheets fed from individual paper feeding sections to an image transfer station therealong. This arrangement has a plurality of transport rollers made of rubber and positioned along the vertical transport path at intervals which are smaller than the minimum paper size as measured in the intended direction of transport. Guide members each guides a paper sheet between nearby ones of the transport rollers. The transport rollers are driven by an exclusive drive mechanism. A drawback with this conventional arrangement is, however, that the coefficient of friction of the transport rollers made of rubber changes due to aging and thereby causes paper sheets to slip on the rollers. To eliminate such slippage, a pressure of 1 kgf to 3 kgf is constantly applied to the individual transport rollers. When the length of the transport path and, therefore, the number of transport rollers increases, such pressures act on the drive mechanism as heavy loads. Another drawback is that when a paper sheet is curled due to humid environment, it is often caught by the gap between the transport roller and guide plate which neighbor each other, jamming the transport path.

Generally, the transport of a paper sheet using a transport roller relies on the coefficient of friction of the roller surface, the pressure which the roller exerts on a paper sheet, the surface hardness of the roller which is made of rubber, etc. Since the area over which the roller and paper sheet can contact each other is limited, the paper sheet is apt to slip on the roller when a load acts on the paper sheet in the opposite direction to the transport direction. To eliminate this problem, it has been customary to locate a register roller in front of a paper sheet and to cause a paper sheet to abut against a rubber roller which is biased by a substantial pressure. Specifically, a paper sheet is caused to warp on abutting against such a rubber roller to correct a skew and is then driven by the register roller at a particular timing matching the operation of an image transfer device. This kind of implementation may achieve a satisfactory paper transport ability in the initial stage of use. However, the surface of the rubber roller sequentially wears to reduce the coefficient of friction as well as the diameter thereof. This, coupled with the fact that paper dust deposited on the roller surface reduces the contact area of the roller surface and paper sheet, critically lowers the paper transport ability.

It is therefore an object of the present invention to provide a paper transporting device for image forming equipment which surely and stably transports paper sheets fed out from any one of a plurality of vertically spaced paper feeding sections along a common vertically extending transport path.

It is another object of the present invention to provide a paper transporting device for image forming equipment capable of transporting paper sheets stably over a long period of time without exerting any noticeable load on a drive mechanism.

It is another object of the present invention to provide a paper transporting device for image forming equipment which eliminates paper jams ascribable to the changes in ambient conditions.

It is another object of the present invention to provide a paper transporting device for image forming equipment which reduces the cost by reducing the required number of component parts and elements.

It is another object of the present invention to provide a paper transporting device for image forming equipment which transports a paper sheet at a desired speed.

It is another object of the present invention to provide a generally improved paper transporting device for image forming equipment.

In accordance with the present invention, a device incorporated in image forming equipment for transporting vertically a paper sheet fed from any one of a plurality of paper feeding sections which are arranged one above another comprises an endless dielectric belt defining a common transport path for transporting vertically paper sheets which are selectively fed from the plurality of paper feeding sections, and a plurality of charging sections each for charging the belt at a particular position where paper sheets fed from one of the paper feeding sections are guided onto the common transport path.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which;

FIG. 1 is a section showing a first embodiment of the paper transporting device in accordance with the present invention;

FIG. 2 is a section showing a second embodiment of the present invention;

FIG. 3 is a section showing a third embodiment of the present invention;

FIG. 4 is a section showing a fourth embodiment of the present invention; and

FIGS. 5A and 5B are views demonstrating the operation of the fourth embodiment.

In illustrative embodiments which will be described, image forming equipment is implemented as an electrophotographic copier by way of example. The copier is assumed to have an endless dielectric belt for transporting a paper sheet fed out from any one of a plurality of vertically spaced paper feeding sections while attracting it electrostatically thereonto. The dielectric belt extends vertically to drive a paper sheet from a lower portion to an upper portion of the copier.

Referring to FIG. 1 of the drawings, a first embodiment of the paper transporting device in accordance with the present invention is shown and generally designated by the reference numeral 20. As shown, the device 20 is incorporated in a copier having paper feeding sections 12, 14 and 16 which have respectively paper cassettes 12a, 14a and 16a, and pick-up rollers 12b, 14b and 16b. The device has a drive roller 22, driven rollers 24, 26 and 28, and a dielectric belt 30 passed over the rollers 22 and 24 to 28. The belt 30 has a vertical extension, no numeral, part of which defines a junction 32 where the paths extending from the individual paper feeding sections 12, 14 and 16 join. A corona discharger 38 and a counter electrode 36 face each other with the intermediary of the belt 30 in the vicinity of the junction 32. The corona discharger is connected to a high-tension power source 38 while the counter electrode 36 is connected to ground and implemented as a metallic roller. A discharger 40 is located in close proximity to the drive roller 26 having a relatively small curvature. A paper sheet coming out of the junction 32 is attracted and transported by the belt 30 which has been charged by the corona discharger 34. At the position where the driven roller 26 is located, the paper sheet is discharged by the discharger 49 and thereby separated from the belt 30 to advance to a step which follows.

As stated above, the illustrative embodiment causes the belt 30 to transport a paper sheet fed from any one of the paper feeding section 12, 14 and 16 while attracting it electrostatically at the junction 32.

A second embodiment of the present invention will be described with reference to FIG. 2. In the figures, the same or similar parts and elements are designated by like reference numerals, and redundant description will be avoided for simplicity. As shown, the paper transporting device, generally 20A, has independent guides 12c, 14c and 16c associated with the paper feeding sections 12, 14 and 16, respectively. A corona discharger 34a and a counter electrode 36a, a corona discharger 34b and a counter electrode 36b, and a corona discharger 34c and a counter electrode 36c are respectively located in the vicinity of the guides 12c, 14c and 16c, each in the same positional relation as in the first embodiment. The corona dischargers 34a, 34b and 34c are respectively connected to exclusive high-tension power sources 38a, 38b and 38c, so that they may be individually controlled in synchronism with the movement of the paper sheet.

Referring to FIG. 3, a third embodiment of the present invention will be described. In the figures, the same or similar parts and elements are designated by like reference numerals, and redundant description will be avoided for simplicity. As shown, the paper transporting device, generally 20B, has metallic rollers 42a, 42b and 42c in addition to the corona dischargers 34a, 34b and 34c which are associated with the guides 12c, 14c and 16c, respectively. Specifically, the metallic rollers 42a, 42b and 42c are connected to ground and respectively located between the corona dischargers 34a and 34b, between the corona dischargers 34b and 34c, and between the corona dischargers 34c and 34a with respect to an intended direction of movement of the belt 30 which is indicated by arrows in the figure. The rollers, or grounding members, 42a, 42b and 42c each is held in contact with the inner surface of the belt 30. The roller 42c additionally plays the role of a driven roller over which the belt 30 is passed. The diameter of the roller 42c is selected to be as small as about 12 mm, so that a paper sheet may be separated from the belt 30 there. A separator in the form of a pawl 44 is located near the outer periphery of the roller 42c. In this embodiment, the belt 30 is made of rubber having a volume resistivity ranging from 10.sup.8 to 10.sup.13 .OMEGA..multidot.cm and a thickness of about 0.6 mm and is wider than the maximum paper size usable with the copier. Also, in the illustrative embodiment, the drive roller 22 for driving the belt 30 is made of ozone-resistive EPDM rubber and driven in a direction indicated by an arrow in the figure. The corona dischargers 34a, 34b and 34c are connected to a single high-tension power source 38.

In operation, when a paper sheet fed out from any one of the paper feeding sections 12, 14 and 16 arrives, the high-tension power source 38 feeds a current to all of the corona dischargers 34a, 34b and 34c at a predetermined time. As a result, the corona dischargers 34a, 34b and 34c discharge toward their associated counter electrodes or metallic rollers 36a, 36b and 36c to individually charge the belt 30. Since the belt 30 constantly moves, each charged portion thereof is moved upward. However, when a paper sheet does not exist on the part of the belt 30 that has been charged by, for example, the corona discharger 34c, the potential of such part of the belt 30 is lowered to ground level when it reaches the metallic roller 42b due to the particular volume resistivity of the belt 30, i.e., 10.sup.8 to 10.sup.13 .OMEGA..multidot.cm. This is also true with the part of the belt 30 that has been charged by the corona discharger 34. Hence, the belt 30 is lowered to ground level at all of the positions where the corona dischargers 34a, 34b and 34c are located. In this condition, despite that the high-tension power source 34 turns on the corona dischargers 34a, 34b and 34c at the same time, the belt 30 is free from incomplete attraction otherwise occurring due to charge saturation thereof. When a paper sheet is fed from the paper feeding section 16, for example, the paper sheet and the belt 30 are individually polarized by the corona discharger 34c between the belt 30 and the counter electrode 36c. As a result, this paper sheet and the belt 30 move upward together while attracting each other electrostatically. Even when the paper sheet and belt 30 reach the counter electrode 36a which is connected to ground, the former is not effected by the latter due to the electrostatic attraction thereof. As a result, the paper sheet and belt 30 move further upward while being charged to the same polarity. Likewise, a paper sheet fed from the paper feeding section 12 passes the corona discharger 34a and counter electrode 36a and then separated from the belt 30 by the pawl 44.

The volume resistivity of the belt 30 ranging from 10.sup.8 to 10.sup.13 .OMEGA..multidot.cm as mentioned previously was found to be adequate by experiments. Specifically, the volume resistivity of the belt 30 was excessively low, the belt 30 failed to obtain an electrostatic capacity and, therefore sufficient attraction. Conversely, when the volume resistivity was excessively high, the discharging ability of the metallic rollers 42a, 42b and 42c fell to cause the potential of the belt 30 to sequentially increase until corona discharge practically failed, i.e., until a paper sheet was prevented from being polarized and attracted.

While the illustrative embodiments have been described as using corona dischargers as discharging means, they are, of course, practicable even with bias rollers, charging brushes or any other suitable charging means.

Referring to FIG. 4, a fourth embodiment of the present invention is shown. In the figures, the same or similar parts and elements are designated by like reference numerals, and redundant description will be avoided for simplicity. As shown, the paper transporting device, generally 20C, has the paper feeding sections 12 and 14 which include the paper cassettes 12a and 14a, respectively. The paper cassettes 12a and 14a each is loaded with a stack of paper sheets S. The belt 30 is passed over the drive roller 22 and driven rollers 24, 26 and 28. The drive roller 22 is made of rubber having a large coefficient of friction. The driven roller 26 is made of metal and has an outside diameter as small as about 12 mm so as to readily separate the paper sheet S from the belt 30 due to the curvature thereof. The metallic roller 26 is connected to ground via the side panels of the equipment. The dielectric belt 30 is implemented as a rubber belt having a volume resistivity of 10.sup.10 to 10.sup.13 .OMEGA..multidot.cm and a thickness of 0.6 mm. The surface of the belt 30 is polished. The drive roller 22 is driven intermittently by an electromagnetic clutch, not shown.

Registration or paper separating sections I and II are respectively associated with and located in front of the paper feeding sections 12 and 14 with respect to the direction of paper feed from the paper cassettes 12a and 14a. Bias rollers 46a and 46b and counter electrodes 36a and 36b in the form of rollers are located to face each other with the intermediary of the belt 30 and respectively associated with the above-mentioned registration or paper separating sections I and II. A metallic roller 42a is interposed between the bias rollers 46a and 46b and held in contact with the inner surface of the belt 30. The roller 42a is connected to ground. The bias rollers 46a and 46b each is made up of a core made of stainless steel, and a conductive rubber layer provided on the core. A DC high voltage is applied from a high-tension power source 38 to the core of each bias roller 46a or 46b at a predetermined timing. Bearing portions provided at axially opposite ends of the bias rollers 46a and 46b are made of an insulating material such as polyacetal, so that the charge may be prevented from leaking to the side panels of the equipment. The counter electrodes 36a and 36b are made of stainless steel or similar conductive material and urged against the belt 30 by springs. The bearing portions of the counter electrodes 36a and 36b are made of highly conductive metal such as steel-based sintered metal and connected to ground.

An upper guide plate 12c and a lower guide plate 12d extend between the registration section I and the counter electrode 36a. Likewise, an upper guide plate 14c and a lower guide plate 14d intervene between the registration section II and the counter electrode 36b. Sheets made of Mylar 48a and 48b are respectively affixed to the lower guide plates 12d and 14d at one end thereof. Reflection type sensors 50a and 50b are respectively mounted on the upper surfaces of the upper guide plates 12c and 14c so as to monitor the running condition of the paper sheets S. Guide plates 12e and 14e are respectively disposed in the gap between the upper guide 12c and the Mylar sheet 48a and the gap between the upper guide 14c and the Mylar sheet 48b. A conductive discharge brush 40a is located at the rear of the metallic roller 26 which defines a position for separating the paper sheet S from the belt 30, as stated earlier. Further, a polyester film 52 is held in contact with the belt 30 in the vicinity of the drive roller 22 and inclined relative to the running direction of the belt 30.

In operation, one of the paper sheets S fed from the paper cassette 12a or 14a is separated from the others by the associated registration or paper separating section I or II. As shown in FIG. 5A, the paper sheet S is guided by the Mylar sheet 48a or 48b to the belt 30. At this instant, the sensor 50a or 50b senses the leading edge of the paper sheet S. At this stage of operation, the electromagnetic clutch, not shown, is not coupled to maintain the belt 30 in a halt. Hence, the paper sheet S slides on the surface of the belt 30 whose coefficient of friction is small to reach the gap between the belt 30 and the counter electrode 36a or 36b. As shown in FIG. 5B, the counter electrodes 36a and 36b each is constantly biased by a spring toward the belt 30. Therefore, the leading edge of the paper sheet S is stopped at the inlet of the gap between the belt 30 and the counter electrode 36a or 36b. As a result, the paper sheet S is caused to warp while urging the Mylar sheet 48a or 48b downward, whereby the skew of the paper sheet S is corrected.

The above-mentioned electromagnetic clutch, not shown, is coupled at a predetermined timing after the associated sensor 50a or 50b has sensed the leading edge of the paper sheet S. At the same time, a high voltage is applied from the power source 38 to the bias roller 46a or 46b of interest. Consequently, the paper sheet S is driven to between the belt 30 and the counter electrode 36a or 36b. At the same time, an electric field is developed between the bias roller 46a or 46b and the paper sheet S with the result that electrostatic attraction occurs between the belt 30 and the paper sheet S due to polarization. The paper sheet is, therefore, transported by the electrostatic attraction and the friction of the surface of the belt 30. The drive of the paper feeding section 12 or 14 from which the paper sheet S has been fed out is interrupted when the associated sensor 50a or 50b has sensed the leading edge of the paper sheet S. Hence, despite that the above-mentioned electrostatic attraction depends on the contact area of the belt 30 and paper sheet S, the paper sheet S is successfully transported by the electrostatic attraction and the surface friction of the belt 30 since the paper feed section 12 or 14 is not driven at that time. The belt 30 transports the paper sheet S to the metallic roller 26 while retaining the paper sheet S thereon by the electrostatic attraction. At this instant, the belt 30 is driven at the same peripheral speed as the photoconductive element or drum of an image transfer device located downstream of the device 20C.

On reaching the metallic roller 26, the paper sheet S is easily separated from the belt 30 since the roller 26 has a small diameter and a large curvature, as stated previously. Then, the paper sheet S is further driven toward the image transfer device. The discharge brush 40a dissipates the charge remaining on the paper sheet S. Further, the polyester film 52 removes paper dust and other impurities from the surface of the belt 30 which has released the paper sheet S. Hence, the part of the belt 30 having been brought to the gap between the bias roller 46b and the counter electrode 36b again is free from impurities and allows the bias roller 46a to generate the electrostatic attraction with ease.

The illustrative embodiment has two vertically spaced paper cassettes, as shown and described. Alternatively, three or more paper cassettes may be arranged one above another only if the number of charging sections, the number of bias rollers and the number of counter electrodes are increased accordingly.

In summary, it will be seen that the present invention provides a paper transporting device which causes a dielectric belt to transport a paper sheet vertically while attracting it electrostatically thereonto. This eliminates a jam ascribable to a paper sheet being caught by a gap between a transport roller and a guide plate, as often occurs in a conventional device of the type using such rollers and plates. In addition, the device of the present invention exerts a minimum of load even during long distance of transport and, therefore, exhibits a stable transport ability over a long period of time. In addition, since a paper sheet in transport contacts a belt over a substantial area, it is free from noticeable slippage and skew.

Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.