GB1564859A

GB1564859A - Document copying apparatus

Info

Publication number: GB1564859A
Application number: GB3815077A
Authority: GB
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1976-11-18
Filing date: 1977-09-13
Publication date: 1980-04-16
Also published as: AU2942877A; AU516348B2; CA1106900A; FR2371369B1; JPS5364041A; DE2744959A1; JPS6143710B2; FR2371369A1

Description

(54) DOCUMENT COPYING APPARATUS (71) We, INTERNATIONAL BUSINESS MACHINES CORPORATION, a Corporation organized and existing under the laws of the State of New York in the United States of America, of Armonk, New York 10504, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to document copying machines, and more particularly to arrangements for transporting copy paper from the transfer station to the fusing station of a transfer type copier.

In document copier machines, rotating drums are frequently used to support a photoreceptive material onto which an electrostatic image of an original document is placed. That electrostatic image is then developed by the application of developing material to the image and in the continued rotation of the drum that developed image is transferred to receiving material, typically a sheet of copy paper. After transfer of the developed image, the photoreceptive material is cleaned and charged in order to be ready to receive the next image of an original document.

The paper path for the copy paper begins with a paper supply area which may be a paper bin holding cut sheets of copy paper or a large roll of paper which is cut as it is unwound. In either case, the sheet of copy paper is fed from the supply area to the transfer station and placed in direct contact with the developed image. A corona is provided which attracts the developing material from the drum to the paper so that when the paper is stripped from contact with the drum, the image remains on the paper. The paper is then transported to a fusing apparatus which, through application of heat, fixes the developer material to the paper. Developing materials in current use include toner powders which rest on the copy paper after transfer and can be easily dislodged before fusing with resultant destruction of the image with the slightest jar of the copy paper or physical contact with the unfused side of the paper. As a consequence, one of the problems of document copier machines is to provide a mechanism for transporting the copy paper with the developed image thereon from the transfer station to a fusing station without jarring the copy paper or physically contacting the side of the paper with the developed image.

According to the invention, there is provided a document copying machine of the transfer type including copy sheet transport means comprising a transport surface, means for generating a gaseous stream and directing it along the surface under the Coanda effect, and means for directing sheets from the image transfer station of the machine towards the surface for passage along the surface, but spaced therefrom by gaseous stream therebetween, towards the fusing station of the machine.

In order that the invention can be fully understood, preferred embodiments thereof will now be described with reference to the accompanying drawings, in which: FIGURE 1 is a perspective view of a document copier machine embodying the present invention; FIGURE 2 is a side view of the Figure 1 machine: and FIGURE 3 is a side view of a further machine embodying the present invention.

FIGURE 1 shows the paper path of a typical document copier such as that described above under background of the invention, showing a drum 10, a developer 11, a transfer station 12 with its associated corona 13, a charging corona 14, and a preclean corona 15. The drum 10 rotates in the direction A and carries a photoreceptive material thereon which receives an electrostatic charge from the corona 14. An image of an original document is placed on the charged photoreceptive material by apparatus not shown prior to the arrival- of the photoreceptive material at the developer 11.

The developer deposits developing material such as a powder on the surface of the photoreceptor to develop the electrostatic image thereon. The continued rotation of the drum 10 in the direction A carries the developed electrostatic image to the transfer station 12 where the image is mated with a copy paper 17, and the developing material is transferred to the copy paper 17 under the influence of an electrostatic field generated by the corona 13. The continued rotation of the drum carries the photoreceptive material through a preclean corona 15 and a cleaning station which may be combined with the developer 11. In that manner the photoreceptive material is made ready for the application of the next image.

FIGURE 1 shows a compact document copier machine in which the copy paper 17 is receiving a developed image at transfer station 12, while at the same time the developed image is being fused to the copy paper 17 in the nip of the fuser rolls 18 and 19, wherein the hot roll is 18 and the backup roll is the roll 19.

One embodiment of this invention is shown in FIGURE 1 for transporting the paper from the transfer station 12 to the fuser rolls 18 and 19. In this case a deflector plate 20 is positioned as shown and air is blown over the deflector by the fan 21. The moving surface of air provides an air cushion to guide the paper along the deflector into the nip of the fuser rolls.

Guide 20a acts on the underside of the paper to prevent a deflection of the paper downwardly into backup roll 19. This embodiment of the invention will be explained further with respect to FIGURE 2.

In FIGURE 2 the drum 10 is shown with transfer station 12. Copy paper 17 is shown with the trailing edge extending just beyond transfer station 12 and the leading edge far beyond the fuser rolls 18 and 19 just entering a pair of pinch rolls 22 and 23. A mechanical sheet stripping finger 24 is shown in its rest position and in phantom in the position it takes before the leading edge of the copy paper 17 strikes it. The finger 24 is positioned against or closely adjacent to drum 10 in the position shown in phantom so that as the leading edge of the copy paper 17 leaves transfer station 12, it is captured in the notch 25 of finger 24, and thus drives the finger back around its pivot 32. In that manner the leading edge of the paper is stripped away from drum 10 and pushes finger 24 in an arcuate path to a position shown approximately at 26.

At that point the finger 24 is accelerated away from the leading edge of the copy paper, for example, by an overcenter spring, not shown, and the guidance of the leading edge of the copy paper is taken over by the influence of an airstream shown by dotted lines adjacent to the deflector plate 20. As discussed above, this airstream moves along the surface of the deflector plate 20 according to the Coanda effect and guides the paper 17 while keeping that paper apart from contact with the deflector 20. In actuality, the air acts as a bearing or cushion to guide the paper along the deflector surface but does not allow the paper to come into contact with the deflector surface. In that manner, the leading edge of the copy paper is guided by the deflector 20 and the associated airstream into the nip of the rollers 18 and 19. The actual path of the leading edge of the paper may be guided by guide 20a to strike the backup roller 19 just ahead of entrance into the nip of the rollers, so as to form a gentle curve in the paper as part of an "S" shape. It is the entrance into the nip of the rollers 18 and 19 which can create a mark on the paper at transfer station 12 by virtue of the driving effect on the paper which takes place when the rollers 18 and 19 grasp the paper and begin to move it. Any jarring effect of that entrance into the nip is dissipated in the curves of an "S" shape in the length of the copy paper between the nip of the fuser rolls and transfer station 12 due to the fact that the paper is at no point solidly attached to any transport mechanism. The "S" shape is formed in the paper by properly positioning the deflector 20.

FIGURE 3 shows another embodiment of the invention wherein the plate over which air is blown is placed on the underside of the copy paper rather than on the toned but unfused side as shown in FIGURE 2. In FIGURE 3 the copy paper 17 once again is positioned with the trailing edge still to reach transfer station 12 but with the leading edge already beyond the fusing rolls 18 and 19 and entering pinch rolls 22 and 23. A sheet stripping finger 24 is provided and operates, as discussed above, to strip the copy paper from the drum 10 and guide that paper in an arcuate path into proximity with the airstream. At that point the finger 24 accelerated away from the leading edge of the paper and the paper is held to the airstream by forces produced in accordance with the Bernoulli principle, and carried by the airstream along the surface of the plate 20 into the nip of the fuser rolls. Note that in this embodiment of the invention, the deflector plate 20 imparts an "S" shape to the copy paper so that when the leading edge of the paper enters the nip of the fuser rolls any shock from that entrance is dissipated in the bends of the "S" and does not reach backward to the transfer station 12.

In both FIGURES 2 and 3 a centrifugal fan or centrifugal blower 21 is shown feed ing a plenum 30. A tube 31 extends out of the plenum 30 to carry the airflow to the deflector plate 20. In referring to FIGURE 1 it can be seen that the plenum 30 and the tube 31 extend across the width of the paper such that a uniform distribution of airflow is present from one side of the paper path to the other.

An interesting aspect of the Coanda effect phenomenon is that by virtue of the moving airstream a low pressure area is present in and near the airstream such that the paper "adheres" to the airstream by virtue of the Bernoulli principle. Thus, the transport of this invention takes advantage of both the Coanda effect and the Bernoulli principle to move paper across the surface of the deflector without contacting it. Very small air pressures are suitable, for example, as low as 004 inches water pressure appears adequate but optimally over 008 inches.

These low air pressures correspond approximately to a minimum required airstream velocity of 50 inches-per-second. The thickness of the airstream is a function of the width of the tube 31 and it has been found that if the thickness of the airstream drops under 005 inches there will be insufficient viscous forces to the airstream to keep the paper out of contact with the deflector plate. Similarly, if the thickness of the airstream is increased above 0 25 inches the internal viscous forces weaken and the airstream does not follow the plate, i.e. the Coanda effect breaks down. Thus, it appears that the best range of values is between those two extremes and optimally somewhat less than 0-15 inches thick.

WHAT WE CLAIM IS: 1. A document copying machine of the transfer type including copy sheet transport means comprising a transport surface, means for generating a gaseous stream and directing it along the surface under the Coanda effect, and means for directing sheets from the image transfer station of the machine towards the surface for passage along the surface, but spaced therefrom by the gaseous stream therebetween, towards the fusing station of the machine.

2. A machine as claimed in claim 1 in which the surface is positioned above the paper path.

3. A machine as claimed in claim 2 in which a powder image carried by a sheet being transported faces said surface.

4. A machine as claimed in claim 1 in which the surface is positioned below the paper path.

5. A machine as claimed in claim 4 in which a powder image carried by a sheet being transported faces away from said surface.

6. A machine as claimed in any of the previous claims in which said surface is curved in the direction of transport of sheets.

7. A machine as claimed in claim 6, in which the surface is positioned such that a copy sheet assumes a serpentine shape as it passes from the transfer station to the fusing station.

8. A machine as claimed in any of the previous claims in which a sheet being transported is maintained in spaced relation to the surface under the Bernoulli principle.

9. A machine as claimed in any of the previous claims in which the thickness of the gaseous stream is between 0.05 inches and 0-25 inches.

10. A document copying machine substantially as described herein with reference to Figures 1 and 2 of the accompanying drawings.

11. A document copying machine substantially as described herein with reference to Figure 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ing a plenum 30. A tube 31 extends out of the plenum 30 to carry the airflow to the deflector plate 20. In referring to FIGURE 1 it can be seen that the plenum 30 and the tube 31 extend across the width of the paper such that a uniform distribution of airflow is present from one side of the paper path to the other. An interesting aspect of the Coanda effect phenomenon is that by virtue of the moving airstream a low pressure area is present in and near the airstream such that the paper "adheres" to the airstream by virtue of the Bernoulli principle. Thus, the transport of this invention takes advantage of both the Coanda effect and the Bernoulli principle to move paper across the surface of the deflector without contacting it. Very small air pressures are suitable, for example, as low as 004 inches water pressure appears adequate but optimally over 008 inches. These low air pressures correspond approximately to a minimum required airstream velocity of 50 inches-per-second. The thickness of the airstream is a function of the width of the tube 31 and it has been found that if the thickness of the airstream drops under 005 inches there will be insufficient viscous forces to the airstream to keep the paper out of contact with the deflector plate. Similarly, if the thickness of the airstream is increased above 0 25 inches the internal viscous forces weaken and the airstream does not follow the plate, i.e. the Coanda effect breaks down. Thus, it appears that the best range of values is between those two extremes and optimally somewhat less than 0-15 inches thick. WHAT WE CLAIM IS:

1. A document copying machine of the transfer type including copy sheet transport means comprising a transport surface, means for generating a gaseous stream and directing it along the surface under the Coanda effect, and means for directing sheets from the image transfer station of the machine towards the surface for passage along the surface, but spaced therefrom by the gaseous stream therebetween, towards the fusing station of the machine.