US3306595A

US3306595A - Fixing unit for photocopy machines with improved guiding means

Info

Publication number: US3306595A
Application number: US347464A
Authority: US
Inventors: Burton D Eisner
Original assignee: American Photocopy Equipment Co
Current assignee: American Photocopy Equipment Co
Priority date: 1964-02-26
Filing date: 1964-02-26
Publication date: 1967-02-28
Anticipated expiration: 1984-02-28

Description

Feb. 28, 1967 B. D. EISNER 3,306,595 FIXING UNIT FOR PHOTOCOPY MACHINES WITH IMPROVED GUIDING MEANS Filed Feb. 26, 1964 5 Sheets-Sheet l INVENTOR. BURTON D. EISNER BY 57 W0%, MM,W LZ AQM Feb. 28, 1967 B. D. EISNER 3,306,595

FIXING UNIT FOR PHOTOCOPY MACHINES WITH IMPROVED GUIDING MEANS Flled Feb 26 1964 5 Sheets-Sheet 2 INVENTOR. BURTON D. EISNER BY 214%, MM, wwwm Feb. 28, 1967 B. D. EISNER 3,305,595

FIXING UNIT FOR PHOTOCOPY MACHINES WITH IMPROVED NS GUIDING MEA 5 Sheets-Sheet 5 INVENTOR.

A'rrvs.

Filed Feb. 26, 1964 United States Patent 3,306,595 FIXING UNHT FOR PHQTOCQPY MAtIHlNES WlTH IMPRQVED GUlDlNG MEANS Burton l). Eisner, Highland Park, IlL, assignor to American Photocopy Equipment Company, Evanston, Ill., a

corporation of Illinois Filed Feb. 26, 1964, Ser. No. 347,464 3 Claims. (Cl. 263-6) The present invention relates machines and, more particularly, guiding means for the fixing unit of an electrophotographic copying machine.

The electrophotographic printing process employed in office photocopy machines and the like generally comprises the steps of uniformly charging the surface of a photoconductive coating on a suitable photocopy sheet, focusing a light image on the charged surface so as to discharge the portions irradiated by the light rays while leaving the remaining portions in a charged condition, thereby producing a latent electrostatic image, developing the latent image by applying a developer powder which adheres selectively to the charged areas, and then fixing the developed image on the photocopy sheet, such as by heating the developer powder. The developer powder conventionally includes a minor proportion of a heat settable resin which, upon being heated, causes the powder to firmly adhere to the surface of the sheet. A suitable machine for carrying out such a copying process is described in detail in copending application Serial No. 209,122, filed July 11, 1962, now US. Patent No. 3,159,- 735, entitled, Fixing Unit for Photocopy Machines, and assigned to the assignee of the present invention.

While use of the apparatus referred to above is found to produce copies of a quality heretofore unattainable, it has been found that under some circumstances the photocopy paper has a tendency to buckle under the influence of the applied heat in the fixer unit. This problem may be encountered when the copy sheets have high and variable moisture content. For example, the copy sheets may pass through the machine smoothly during normal weather conditions, and then begin to buckle and hang up in the machine when the moisture content in the atmosphere increases above a certain level. This buckling of the sheets, which occurs in the fixing unit, not only jams the machine, With all the attendant production losses and maintenance costs, but also produces a potential fire hazard.

When attempts are made to restrict the curling or buckling of the copy sheet by the use of physical guides, one of the main problems encountered is that the guides which engage the face or image-bearing side of the copy sheet tend to mar or blemish the heat-softened coating. For example, in certain cases the guiding members may have a scraping effect which simply removes the softened coating from the areas engaged by the guides. Moreover, with certain types of rotating guides, it has been found that the guides develop tires of soft material which produce various types of longitudinal marks on the copy sheet. In some cases the soft material deposits on the copy sheet, producing black lines which deface the developed image; in other cases, the soft material in the tire picks up additional developer powder, producing blank lines running through the developed image.

It is, therefore, a main object of the present invention to provide an improved'fixing unit which effectively prevents buckling of the copy sheets under the influence of the applied heat. Accordingly, it is also an object to provide such a fixing unit which elfectively prevents machine jamming and avoids all the attendant production losses and maintenance costs. A related object is ,to

generally to photocopy to an improved paper provide such a fixing unit which passes the copy sheets smoothly and rapidly therethrough regardless of the moisture content in the copy sheets.

It is another object of the invention to provide a fixing unit having improved paper guiding means which prevent the heated copy sheets from buckling and becoming hung up in the machine. It is a further object to provide such guiding means which do not have any deleterious effect on the copy sheets. A more particular object is to provide such guiding means which do not produce any substantial undesirable marks or lines on the softened coating containing the developed image, and which does not remove or pick up any of the softened coating material. Another object is to provide such guiding means which do not distort or mar the developed image on the softened surface coating.

Still another object of the invention is to provide a fixing unit having improved paper guiding means which provides high interfacial tension and low thermal conductivity and substantially eliminates sliding friction between the copy sheet and the engaging surface of the guiding means. A related object is to achieve an extremely small area of engagement between the copy sheet and the guiding means. Another object is to provide such a guiding means which has a relatively low thermal capacity.

A further object of the invention is to provide an improved paper guide for fixing units which substantially improves both the overall reliability and production capabilities of the machine and the quality of the copies produced. In this connection, it is another object to provide such a guiding means which has a relatively simple construction and extremely long life, whereby replacement and maintenance costs are minimized.

Other objects and advantages of the invention will become apparent upon reading the attached detailed description and appended claims and upon reference to the drawings, in which:

FIGURE 1 is a simplified vertical section of an electrophotographic copying machine employing the present FIG. 2 is an enlarged vertical section taken through the fixing and finishing unit of the machine in FIG. 1 and showing the associated developing unit;

FIG. 3 is a side elevation view taken along line 3-3 in FIG. 2 and showing the paper guiding means which engage the image side of the vertical copy sheets;

FIGS. 4 and 5 are side and end elevation views, respectively, of the paper guiding assembly removed from the machine of FIGS. 1 through 3;

FIG. 6 is an enlarged perspective view of the guiding means which engage the back side of the copy sheet in the machine of FIG. 1; and

FIGS. 7, 8 and 9 are perspective, side, and end views, respectively, of the guiding emans which engage the front of the copy sheet in the machine of FIG. 1.

While the invention has been described in connection with a preferred embodiment, it will be understood there is no intention to limit the invention to the embodiment shown but, on the contrary, it is intended to cover the various modifications and alternatives included within the spirit and scope of the appended claims.

Turning now to FIG. 1 of the drawings, an electrophotographic copying machine intended for ofi'ice use includes a frame 11, a base 12, and a housing 13. At the front of the housing, two inlet slots are provided, a first slot 14 for the original and a second slot 15 for the copy sheet,with the two sheets, indicated at 16, 17, being fed in together, faceto-face. These sheets are separated in the machine, and the copy sheet passes through a charging unit 18 where the face of the sheet acquires an overall static electric charge.

The original 16 is fed into the illuminating station 19 at the same time that the copy sheet 17 is brought into the exposing station 20. Light from a source not shown illuminates the original, with the image thereon being refiected by a mirror and lens assembly (not shown) onto the moving copy sheet and with the speed of the original corresponding exactly to the speed of the copy sheet. Subsequently, the original is discharged into a return chute 22, while the copy sheet is conveyed upwardly by

transfer rollers

23, 24 forcing its way through .a flexible closure flap 25 which is in the bottom of the trough 26 of the developing unit 27. Such trough contains a charge of toner mix in the form of toner particles temporarily adherent to larger magnetic particles which act as a carrier. The mix clings to the surface of the developing cylinder 29 in the form of soft tufts or bristles by reason of the magnetism induced by an external permanent magnet.

Because of triboelectric phenomena, the toner particles are attracted to the charged areas on the sheet leaving behind the magnetic carrier particles, which latter particles, however, serve to prevent deposition of toner power in the uncharged areas on the sheet. Consequently, the copy sheet, with the developed image thereon, passes upwardly into the fixing and finishing unit 40.

The particular heating arrangement shown in the fixing unit 40 (see FIG. 2) utilizes back fixing, with the radiant heat source located at the back of the sheet, but it will be apparent that the invention is not limited thereto and includes the possibility of front fixing or a combination of the two. In the present instance, the heat source is in the form of an electrically heated radiation producing lamp 41 which extends lengthwise within a reflector 42. The surface of the reflector 42 is elliptical with the lamp 41 being positioned at one of the foci so that the heat tends to be concentrated on the paper over a narrow horizontal band. It will be apparent that the temperature and power dissipation of the lamp 41 may be optimized depending on the speed of transporting the copy sheet on a particular machine. While a transporting speed on the order of one inch per second may be used, studies show that the present fixing unit finishing arrangement is capable of operating at a speed of much higher than this and up to approximately three or even four inches per second. If desired, a reflector may be used opposite the heat source to reflect incident radiant heat back toward the face of the sheet. Extensions 45, 46 on the reflector are provided to maintain the fixing space at relatively high temperature throughout to provide what may be termed oven effec Means are, however, provided for preventing excess heat build up, particularly when the unit is operated over long periods of time. In the present instance, this is accomplished by forming the reflector 42 in a relatively massive reflector member 47 which is formed of aluminum or other good conducting material, and by providing an adjacent, close coupled heat sink 48 in the form of an internally finned chamber through which air is forced longitudinally under slight pressure. A corresponding heat sink 49 is provided on the opposite side of the fixing unit and is also supplied with a source of cooling air.

In order to press the fused particles of pigmented toner into the softened resinous coating on the copy sheet, a pair of smothly surfaced driven

rollers

50 and 51 of good conducting material are mounted for rotation in the frame plates 52 immediately adjacent the heat applying means. These

rollers

50, 51 have a nip 53 which lies in the path of the movement of the advancing sheet. More specifically, the rollers are arranged sufliciently close to the source of heat so that the toner in the surface of the paper are in the softened or yieldable state at the time of the engagement by the rollers, and the rollers are biased together with a force which is suflicient to press the toner into intimate engagement with the surface material.

In the practice of this invention, there is provided an improved guiding system including a first guiding means engaging the back of the copy sheet and a second guiding means engaging the face or image-bearing side of the copy sheet, the second guiding means being located sufficiently close to the first guiding means to restrict the buckling of the heated sheet whereby jamming of the machine is effectively prevented, the second guiding means comprising a plurality of rotatable guiding members having low thermal conductivity and mounted to rotate in the direction of movement of the copy sheet, the rotatable guiding members also having a very fine sheet-engaging edge, whereby high interfacial tension and low thermal conduction is provided between the face of the copy sheet and the rotatable guiding members. Thus, there is provided a first guiding means comprising an array of guide wires 54 engaging the back of the copy sheet adjacent the heat source, and a second guiding means comprising a plurality of spaced rotatable glass beads 55 shaped to provide a fine peripheral edge 55a which engages the heat-softened face of the copy sheet.

Turning attention first to the first guiding means, which engages the back of the copy sheet, there is provided in front of the reflector member 47 a plurality of spaced generally vertical guide wires 54 secured to top and

bottom headers

56 and 57, respectively, such as by welding. To maintain the wires 54 in position, the bottom header 57 is fitted into notches 58 in the frame plates, while the upper header 56 is secured by a spring clip 59. As will be apparent, this enables the entire assembly of guide wires 54 to be quickly removed for access to the fixing region, such as for replacement of the lamp. While it has been stated above that the wires 54 are generally vertical, it is preferred to arrange the wires in herringbone pattern as illustrated in FIG. 6, with the wires diverting somewhat outwardly and upwardly with respect to the center line. It has been found that this arrangement of the wires tends to keep the copy sheet flat, particularly where one of the corners of the advancing edge of the copy sheet has been turned over or is dog-eared and might, therefore, become caught on one of the wires or headers. The action of the diverging guide wires is to tend to straighten out the corner, keeping it flat in the plane of the sheet ready for engagement with the nipping rollers. Equally important, keeping in mind that the wires 54 are in the path of radiation, the heat transferred from the wires to the copy sheet tends to be distributed over the surface of the sheet rather than being concentrated along narrow longitudinal paths.

In accordance with one of the aspects-of the present invention, buckling or curling of the copy sheet 17 is effectively prevented by positioning the second guiding means, which engages the face or image-bearing side of the sheet, sufiiciently close to the first guiding means to maintain the copy sheet in a fixed vertical plane and thereby restrict any tendency of the sheet to buckle or curl as it is heated. The second guiding means comprises a plurality of guide members 55 rotatably mounted on brackets 60. In order to prevent the curling or buckling of any substantial portion of the copy sheet 17 as it passes through the fixing region, both the wires 54 and the guide members 50 must be located at spaced points across substantially the entire width of the sheet 17. The transverse space between the wires 54 and the peripheries of the guide members 55 must be sufliciently narrow to prevent the undesired curling or buckling, and this space may vary somewhat with diflerent applications.

Referring to FIGS. 3 to 9, the rotatable guide members 55 in the particular construciton illustrated are secured to axles 61 by means of clinch pins 62. The axles 61 are rotatably mounted in the supporting brackets 60 which, in turn, are riveted to a mounting plate 63, as by rivets 64. This entire assembly is then secured within the fixing region by bolting the mounting plate 63 to the wall of the heat drain, as by bolts 65. Since the axles 61 are loosely mounted in the brackets 60, the slightest grazing contact between the advancing copy sheet 17 and the rotatable guiding members 55 suflicies to rotate the members 55. Thus, there is practically no sliding friction between the image side of the copy sheet 17 and the rotatable guide members 55.

In the particular guiding system illustrated, the rotatable members 55 are arranged in two staggered horizontal series (see FIGS. 3 and 4). The lower series of members 55 is located at the lower portion of the fixing region and includes only one rotatable member 55' on each of four brackets 60, the brackets being spaced across the full width of the copy sheet 17. The upper series of rotatable members 55" is located at about the middle of the fixing zone and, since the temperature of the copy sheet is highest at that point, it includes two rotatable members 55" on each of the four brackets 100. Of course, it will be understood that additional horizontal series of rotatable guide members may be provided, or additional members may be provided in each horizontal series, depending on the size of the fixing region, the particular temperature employed, the type of paper employed, and the like.

In accordance with one aspect of this invention, there is provided a guiding member for engaging the softened coating on the image side of the copy sheet without producing any substantial deleterious marks or lines thereon, and without removing nor picking up any of the softened coating material thereon. Thus, there is provided a plurality of small spaced rotatable glass beads 55 made of a hard low-heat-conducting material such as glass, ceramic, or the like and mounted to rotate in the direction of movement of the copy sheet 17. The contacting surface of the glass beads 55, i.e., the surface which engages the softened coating on the image side of the copy sheet, should be extremely narrow or fine and is preferably discontinuous. In other words, the area of engagement between the copy sheet and the guiding glass beads should be as small as possible and also discontinuous. In the particular construction illustrated in the drawings, the small contact area is provided by employing beads which are beveled to a generally double conical shape so as to form a narrow contact ridge 55a (see FIGS. 6-8) around the middle of each bead in the common plane of the cone bases. The discontinuity is provided by employing beads which are faceted on the conical surfaces so that the contact ridge 55a has a serrated or serpentine edge which engages the copy sheet intermittently rather than continuously.

It has been found that when the insulating glass beads are used as guide members according to this invention, they completely eliminate buckling or curling of the copy sheet without any substantial marring of the developed image. Even in the case of copy sheets exhibiting extremely high buckling tendencies, the copies emerge from the machine with only sporadic minute dot marks appearing on the copy. Machine jamming is completely avoided, with resultant substantial increases in machine productivity and corresponding decreases in down time and maintenance cost.

Studies have been made in order to ascertain the reasons for the unexpected superior performance of the glass guiding members described above, and it is believed that the unusual effectiveness of this guiding system is due at least in part to the extremely low interfacial tension and low thermal conductivity between the copy sheet and the glass beads, and the low thermal capacity of the glass beads. Thus, the fine contact ridge of the glass guiding members, although in a region of high temperature, does not tend to maintain the high temperature on engaging the face of the sheet, but rather tends to immediately assume the temperature of the sheet. This is in contrast to the effect of a conductive guide member, such as a metal disc, which would have the effect of supplying heat of fusion to the image being fixed, portions engaging the back of the copy sheet and second 6 of the fused material being lifted off as the disc rotates for a progressive build up of a tire.

It will be apparent from the foregoing description that the nature of the guiding members which engage the image side of the copy sheets is much more critical than that of the guiding members which engage the back side of the copy sheets. Thus, if desired and without departing from the invention, the guide wires 59 may be dispensed with and the paper may be held forwardly by an air blast directed against the back side of the sheet from a series of horizontally arranged holes directly opposite the heat source; however, this requires a corresponding increase in capacity of the blower which is used for cooling purposes. Alternatively, a vacuum may be drawn in the C- shaped reflector by a vacuum line.

What is claimed is:

1. In a fixing unit for a photocopy machine of the type in which a coated copy sheet having the electrostatic image thereon is developed by application of a fusible pigmented powder to the charged areas, the combination comprising a heating unit for increasing the temperature of said fusible pigmented powder sufiiciently high to fuse said powder and fix the developed image, transporting mechanism for advancing the copy sheet past said heating unit, and a guiding system for directing the copy sheet through the fixing unit, said guiding system including first guiding means engaging the back of the copy sheet and second guiding means comprising a plurality of faceted double conical glass beads having serrated ridges formed by the bases of the cones, said serrated ridges engaging the softened powder on the copy side of the copy sheet, said first and second guiding means being located sufiiciently close to each other to restrict the buckling of the heated sheet whereby jamming of the machine is effectively prevented.

2. In a fixing unit for a photocopy machine of the type in which a coated copy sheet having a latent electrostatic image thereon is developed by application of a fusible pigmented powder to the charged areas, the combination comprising a heating unit for increasing the temperature of said fusible pigmented powder sufficiently high to fuse said powder and fix the developed image, transporting mechanism for advancing the copy sheet through a fixing region adjacent to said heating unit, and a guiding system within said fixing region for directing the copy sheet therethrough, said guiding system including first guiding means engaging the back of the copy sheet and second guiding means engaging the coated image-bearing side of the copy sheet, said first and second guiding means being located sufficiently close to each other to maintain said copy sheet in a fixed plane and to restrict the buckling of the heated sheet whereby jamming of the machine is effectively prevented, said second guiding means comprising a plurality of rotatable glass beads spaced both transversely and longitudinally along the path of said sheet through said fixing region, said beads being of generally double conical shape with the common plane of the bases of said double cones forming a narrow guiding edge around the periphery of said beads for engagement with said sheet, and the conical surfaces of said beads being faceted so as to provide discontinuous engagement between said guiding edge and said copy sheet.

3. In a fixing unit for a photocopy machine of the type in which a coated copy sheet having a latent electrostatic image thereon is developed by the application by a fusible pigmented powder to the charged areas, the combination comprising a heating unit for increasing the temperature of the said fusible pigmented powder sufiiciently high to fuse said powder and fix the developed image, transporting mechanism for advancing the copy sheet through a fixing region adjacent to said heating unit, and a guiding system for directing the copy sheet through said fixing region, said guiding system including first guiding means guiding means engaging the coated image-bearing side of the copy sheet, said first and second guiding means being located sufliciently close to each other to maintain said sheet in a fixed plane and to restrict the buckling of the heated sheet whereby jamming of the machine is effectively prevented, said vfirst guiding means comprising a plurality of laterally spaced guide wires oriented in the direction of movement of said sheet and interposed between the face of the sheet and said heating unit for defining a certain minimum spacing between the heat source and the back of the sheet, said second guiding means comprising a plurality of thermally insulating rotatable glass beads spaced both longitudinally and transversely along the path of said sheet said beads being of generally double conical shape with the common plane of the bases of said double cones forming a narrow guiding edge around the periphery of said beads for engagement with said sheet, and the conical surfaces of said beads being faceted so as to provide discontinuous engagement between said guiding edge and said copy sheet.

References Cited by the Examiner UNITED STATES PATENTS 3,055,229 9/1962 Mecham 198-230 X 3,159,735 12/1964 Eisner et al. 219347 3,190,643 6/1965 Taillie 27175 X 3,219,799 11/1965 Trumbull et a1. 219-216 X 3,239,220 3/1966 Lot et al 198167 X FREDERICK L. MATTESON, JR., Primary Examiner.

JOHN J. CAMBY, Examiner.

Claims

1. IN A FIXING UNIT FOR A PHOTOCOPY MACHINE OF THE TYPE IN WHICH A COATED COPY SHEET HAVING THE ELECTROSTATIC IMAGE THEREON IS DEVELOPED BY APPLICATION OF A FUSIBLE PIGMENTED POWDER TO THE CHARGED AREAS, THE COMBINATION COMPRISING A HEATING UNIT FOR INCREASING THE TEMPERATURE OF SAID FUSIBLE PIGMENTED POWDER SUFFICIENTLY HIGH TO FUSE SAID POWDER AND FIX THE DEVELOPED IMAGE, TRANSPORTING MECHANISM FOR ADVANCING THE COPY SHEET PAST SAID HEATING UNIT, AND A GUIDING SYSTEM FOR DIRECTING THE COPY SHEET THROUGH THE FIXING UNIT, SAID GUIDING SYSTEM INCLUDING FIRST GUIDING MEANS ENGAGING THE BACK OF THE COPY SHEET AND SECOND GUIDING MEANS COMPRISING A PLURALITY OF FACETED DOUBLE CONICAL GLASS BEADS HAVING SERRATED RIDGES FORMED BY THE BASES OF THE CONES, SAID SERRATED RIDGES ENGAGING THE SOFTENED POWDER ON THE COPY SIDE OF THE COPY