US3053962A

US3053962A - Xerographic fusing apparatus

Info

Publication number: US3053962A
Application number: US46503A
Authority: US
Inventors: Americo J Corasani; Joseph J Codichini
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1960-08-01
Filing date: 1960-08-01
Publication date: 1962-09-11
Anticipated expiration: 1979-09-11
Also published as: DE1165413B; GB999763A

Description

Sept. 11, 1962 Filed Aug. 1, 1960 A. J. CERASANI ET AL 3,053,962

XEROGRAPHIC FUSING APPARATUS 5 Sheets-Sheet 1 INVENTORS AMERICO J. CERASANI BY JOSEPH J. CODICHINI ATTORNEY Sept. 11, 1962 CERASANl L 3,053,962

' XEROGRAPHIC FUSING APPARATUS 5 Sheets-Sheet 2 Filed Aug. 1, 1960 INVENTORS AMERICO J.CERASANI BY JOSEPH J. CODICHINI Se t. 11, 1962 A. J. CERASANI ET AL 3,053,962

XEROGRAPHIC FUSING APPARATUS Filed Aug. 1, 1960 5 Sheets-Sheet 3 INVENTORS AMERICO J. CERASANI JOSEPH J. CODICHI N I fBY - ATTORNEY it rates 3,@53,96Z Patented Sept. 11, 1962 snssssz XERGGRAEi-HC FUSENG APPARATUS America I. Qerasani, Rochester, and Joseph J. Qodichini,

Fairport, N.Y., assignors to Xerox Corporation, a corporation of New York Filed Aug. 1, 196%, Ser. No. 465% 4 (Claims. (or. arm-rs) This invention relates to xerography and in particular to improved fusing apparatus for affixing a xerographic powder image onto a moving support surface. More specifically the invention relates to an improved fusing apparatus of variable capacity to aifix xerographic powder images onto moving support surfaces that may differ in thickness of stock and rate of movement.

In the process of xer-ography, for example, as disclosed in Carlson Patent 2,297,691, issued October 6, 1942, a xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the radiation intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is efiected with an electrostatically charged, finely divided material such as an electroscopic powder that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed xerographic powder image is usually transferred to a. support surface to which it may be fixed by any suitable means.

Xerography has gained wide commercial success as a convenient and accurate method for the reproduction of copy, producing copy of high resolution. One of the virtues of xerography is its ability to reproduce copy ontoa variety of support surfaces that are not sensitized in advance, as is done, for example, in photography. The application of heat to affix xerographic powder images to support surfaces has been extensively employed and typical fusing apparatus for afiixing powder images to moving support surfaces is disclosed in Crumrine Patent 2,852,651. Whereas fusers of the Crumrine type have been marketed in conjunction with xerographic equipment, it has a relatively low heating capacity limiting its use to applications of relatively slow moving light weight paper stock as, for example, a pound paper moving at approximately 20 feet per minute. Many ap plications currently being encountered in xerography require support surface speeds of approximately 65 feet per minute and above, and material employed for the support surface typically may vary from a vellum to a .012 inch cardboard stock.

The magnitude of heat or temperature necessary to effect powder image fixing is largely a function of the time available in which to bring the elements up to fusing temperature which in turn is a function of thickness of support surface on which the image is to be fixed and the rate of support surface movement past the fusing area. Under conditions in which either or both thickness and speed vary, a variable capacity is required of a fuser capable of functioning through substantially a complete range of projected operation for any combination of speed and thickness for a particular support surface. Furthermore, since the fixing capacity for any specific application is largely predicated on a predetermined rate of support surface movement, in the event movement of the support surface ceases for any reason, such as ordinary machine shutdown, precautionary measures are required to protect the support surface from immediate destruction from the residual radiation of the heating elements after being deenergized. In the apparatus of Crumrine, to protect the support surface when movement stops, a movable shutter arrangement is employed which when the fuser is operative is open to permit exposure of the heating elements to the support surface to effect fixing, but when movement stops instantly interposes a protective shield between the heating elements and the support surface. Whereas the shutter mechanism of Orumr-ine has provided the degree of protection required from the two heating elements employed therein, its mechanism is not practi cally applicable to a multiple element type fusing unit as described below for the fuser of the invention having considerably more heating surface from which to instantly prevent heat from radiating to the support surface.

The principal object of the invention is to improve fusing apparatus for amxing a xerographic powder image onto a moving support surface.

A further object of the invention is an improved powder image fusing apparatus having a variable capacity for use in xerography.

A still further object of the invention is to improve fusing apparatus for affixing xerographic powder images onto moving support surfaces of different thicknesses.

A still further object of the invention is to improve fusing apparatus for affixing xerographic powder images onto support surfaces which move at different rates.

Yet another object of the invention is a variable output fuser for use in xenography having improved means to protect a stopped support surface from heat destruction.

These and other objects of the invention are achieved by the improved fuser of the invent-ion having a plurality of heating elements which can be energized to variable magnitudes of capacity and are pivotally adapted to be positioned in effective fixing relation to a moving support surface but are instantly deenergized and pivotally positioned in ineffective relation when movement of the support surface is stopped.

A preferred embodiment of the invention is illustrated in the accompanying 'drawings in which:

FIG. 1 is a typical xerog-raphic machine incorporating the fusing apparatus of the invention;

FIG. 2 is an isometric view illustrating the fuser of the invention in non-fixing relation relative to a support surface and partially broken to facilitate an understanding of the structure;

FIG. 3 is a sectional elevation of the fuser apparatus of the invention taken substantially on line 33 of FIG. 2 but modified to illustrate the fuser in fixing relation;

FIG. 4 is an electrical diagram.

For a general understanding of the xerographic processing system in which the invention is incorporated, reference is had to FIG. 1 in which the various system components are schematically illustrated. As in all xerographic systems based on the concept disclosed in the above-cited Carlson patent, a radiation image of copy to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged developing material to form a xerographic powder image, corresponding to the latent image, on the plate surface. The powder image is then electrostatically transferred to a support surface to which it may be afiixed by a fusing device, whereby the powder image is caused permanently to adhere to the support surface.

The xerographic apparatus described herein typically may be of the type disclosed in copending application SN. 837,173, filed August 31, 1959, in the name of A. J. Cerasani, et a1. As in the apparatus of Cerasani, original copy to be reproduced is placed on a support tray 10 from which it is fed onto a feed apparatus generally designated 11. On the feed apparatus an original is moved on an endless belt 12, driven by motor 13, to pass the optical axis of projection lens system 14 that is illuminated by a projection lamp LMP-l. The image of the original is reflected by mirror 15 through an adjustable objective lens 16 and then reflected by mirror 17 downwardly through a variable slit aperture assembly 18 and onto the surface of a xerographic plate in the form of a drum 19.

Xerographic drum 19 includes a cylindrical member mounted in suitable hearings in the frame of the machine and is driven in a counterclockwise direction by a motor 24 at a constant rate that is proportional to the transport rate of the original, whereby the peripheral rate of the drum surface is identical to the rate of movement of the projected radiation image. The drum surface comprises a layer of photoconductive material on a conductive backing that is sensitized prior to exposure by means of a screened corona generating device 25, which may be an adaptation of the type disclosed in Walkup Patent 2,777,- 95 7, that is energized from a suitable high potential source.

The exposure of the drum to the radiation image discharges the photoconduotive layer in the areas struck by radiation, whereby there remains on the drum a latent electrostatic image in image configuration corresponding to the radiation image projected from the original. As the drum surface continues its movement, the electrostatic latent image passes through a developing station 26 in which a two-component developing material 27, which may be of the type disclosed in Waikup Patent 2,63 8,416, is cascaded over the drum surface by means of developing apparatus 28 which may be an adaptation of the type disclosed in copending application S.N. 393,058, filed November 19, 1953, in the name of Mayo et al.

In the developing apparatus, developing material is carried up by conveyor 29, driven by suitable drive means from motor 3%), and then released onto chute 31 wherefrom it cascades down over the drum surface. Toner component 32 of the developer that is consumed in developing is stored in dispenser 33 and is dispensed in amounts controlled by gate 34.

After developing, the xerographic powder image passes a discharge station 41 at which the drum surface is illuminated by a lamp LMP2, whereby residual charges on the non-image areas of the drum surface are completely discharged. Thereafter, the powder image passes through an image transfer station 42 at which the powder image is electrostatically transferred to a support surface web 43 by means of a second corona generating device 44 similar to corona charging device 25, mentioned above.

The support surface to which the powder image is transferred may be of any convenient type such as paper and may be obtained from a supply roll 4-5, fed over guide rolls 46 and 47 and over suitable tensioning rolls being directed into surface contact with the drum in the immediate vicinity of transfer corona generating device 44. After transfer, the support surface is separated from the drum surface and guided through the fusing apparatus of the invention, generally designated 48, wherein the powder image is permanently affixed to the support surface. Thereafter, the support surface may be fed over a further system of guide and tensioning rolls and onto a take-up roll 52 that is driven by motor 53.

After separation of the support surface from the drum, a corona generating device 54 which may be of the type described in copending application S.N. 845,482, now Patent No. 2,965,756, filed October 9, 1959, in the name of Vyverberg, directs electrostatic charge to a residual powder image on the drum surface and to the support surface before leaving guide roll 47.

Thereafter the Xerographic drum surface passes through a cleaning station 55 at which its surface is brushed by a cleaning brush assembly 56, rotated by a motor 57, whereby residual developing material remaining on the drum is removed. Thereafter, the drum surface passes through a second discharge station 58 at which it is illuminated by a fluorescent lamp LMP-3, whereby the drum surface in this region is completely flooded with light to remove any electrostatic charge that may remain thereon. Suitable light traps are provided in the system to prevent any light rays from reaching the drum surface, other than the projected image, during the period of drum travel immediately prior to sensitization by corona generating device 25 until after the drum surface is completely passed through the developing station 26. Plate 84- prevents removed powder from falling into corona generating device 54.

Referring to FIG. 2, the fuser 48 of the invention is isometrically illustrated in non-fixing or ineffective relation to a web support surface 43 which during operation of the xerographic apparatus is moved through the fuser substantially in a planar path accorded by platform pan 59.

For support of the components the fuser includes a frame 62, formed of a front and rear plate and a pair of side plates, and which in turn is suitably supported in the xerographic apparatus adjacent the path of movement of the support surface. A hood 71 covers the fuser and shields the conduction of heat from the fuser to the xerographic apparatus in which the fuser apparatus is incorporated.

In the drawings eight heating elements are shown for convenience, each designated 55 and four of which are supported on each of a pair of reflector assemblies generally designated 6t} and 61. The reflector assemblies are selectively movable, as described below, toward and away from platform pan 59 to place the heating elements thereon into fixing and non-fixing relation respectively with a web moving over pan 59. Fewer or more elements and/ or reflector assemblies, however, could be employed.

The wire 63 of the heating elements conveniently is comprised of a nickel alloy which is commercially marketed by the Wilbur B. Driver Co. of Newark, New Jersey, and referred to as Tophet A. The wire of each heating element is wound around a quartz rod 64 mounted in endclips 65 secured to angles 66. The angles are mounted on plate 67 but are separated therefrom by means of insulator blocks 74 which extend to

electrical terminals

84 and 85. Insulator blocks 63 maintain a separation between the heating elements for the purpose of circuitry described below.

The heating elements on each reflector assembly are arranged in a plane substantially parallel to each other and in front of a reflective surface 70. The elements are about 13 /4 inches long and approximately 1% inch on centers and are arranged to extend transverse to the direction of support surface movement although obviously other arrangements and dimensions of the heating elements could as effectively be employed. On the side of plate 67 opposite the heating elements is a bracing member 72 which bears against a resilient rubber cushion 73 when the fuser is in the non-fixing relation illustrated in FIG. 2.

Secured to plate 67 at each end thereof is a pair of end plates 69 that extend therefrom into the frame 62. Between the end plates is shouldered a shaft 75 extending therethrough and journaled in suitable bearings of support frame 62. Also shouldered between the end-plates is another shaft 76 the function for which is described below.

On the rear end-plates as viewed in FIG. 2, i.e., the side opposite the motor 91, there are studs 77 which extend from the end-plates and seat in grooves 78 of

follower arms

79 and 80. The follower arms are each bolted to frame 62 through their

respective slots

81 and 82 in a manner to permit their longitudinal movement in opposite directions by means of cam 96 described below. T 0 guide movement of the follower arms there is secured to the frame 62 a pair of flat rectangular bars 83 extending into each follower arm slot and providing a fiat surface on which the upper inside surface of a slot is miided to ensure arm movement substantially in a plane.

The reflector assemblies of the appaartus are urged to maintain the non-fixing relation illustrated in FIG. 2 by means of springs 86 and 37 each extended under tension and attached at one end to a shaft 76 of each reflector assembly and at the other end to a suitable stationary member of support frame 62.

To move the reflector assemblies from the non-fixing ineffective relation illustrated in FIG. 2 to the effective image-fixing relation illustrated in FIG. 3, a run switch SW-Z, located on the xerographic apparatus and shown schematically in the diagram of FIG. 4, when actuated initiates operation of motor 91 through circuitry described below. Motor 91 operates at approximately 3 rpm. and when operative its drive is transmitted from pulley 92, secured on the motor drive shaft, through belt 93 to pulley 94 secured to cam shaft 95. Cam 96 is secured to the cam shaft and on rotation the cam forces the follower arms '79 and 80 in opposite directions sufficiently far to pivot the reflector assemblies about shafts 75 until rea l1- ing the fixing relation illustrated in FIG. 3.

Closing of the run switch SW2 also effects, through circuitry described below, energizing of solenoid Sol-1 to withdraw its armature secured to pin 101 which, when the fuser is idled, is supported with its axis in a plane slightly above the lower periphery of shafts 109 and 119 (see FIG. 3). Pivotally secured to pin 101 are a pair of

positioning levers

102 and 103 that are integrally con nected to latch

assemblies

104 and 105 respectively. The latch assemblies are arranged to pivot on

shafts

109 and 110 such that on energizing solenoid Sol-1, pin 1&1 is withdrawn to push the levers outwardly and pivot the latch assemblies upward toward each other from the posi tion shown dashed and into a latch or detent position shown solid.

Since the latch assemblies reach their latch position substantially instantaneously by virtue of the solenoid operation as compared to the relatively slow positioning on the order of 5 seconds of the reflector assemblies operated from the cam, the latch assemblies are in position to latch and sustain the fixing relation of the reflector assemblies after the assemblies reaches that position.

The latch assemblies each have a front plate 111 secured to and inclined outward from a backing plate 112 whereby at its upper end the plate 111 is bent back toward the backing plate substantially at a right angle and is resiliently yieldable toward the backing plate when depressed. As may be understood from the position of components of FIG. 3, in positioning the reflector assembly shaft 76 swings through an are, shown dashed in FIG. 3, to deflect plate 111 when passing thereover into a pocket 113 formed by the arrangement of plate 111 to plate 112.

After positioning the reflector assemblies into fixing relation, motor 91 remains operative until cam 96 engages limit switch SLS, operation of which is described below, while the latch assemblies maintain the fixing relation of the reflector assemblies. Should the running circuit of the xerographic machine be interrupted for any reason solenoid Sol-1 is deenergized and springs 115 and 116 suitably secured between frame 62 and

positioning levers

102 and 103 respectively, immediately hoist the positioning levers to pivot the latch assemblies outwardly and away from latch position to release both shafts 76. When shafts 76 are released, springs 86 and 87 instantly restore the reflector assemblies to their ineffective position as illustrated in FIG. 2. Shock cushions, 73 and 88, the latter being in the form of a spring metal clip, absorb the shock of impact from stopping the reflector assemblies in their pivotally upward movement.

To remove excess heat from within the fuser during its operation fan blower 118, driven by motor 119, draws ambient air through the fuser into duct 117, wherefrom the heated air is discharged through duct 120 to any conenient location.

An electrical circuit for operation of the fuser is schematically illustrated in FIG. 4. Switch SW1, comprises a master switch for the xerographic unit and when closed a momentary closing of run switch SW-Z initiates operation of the fuser circuit. When the run switch is closed relay 1CR is actuated to close contact MIR-4 which energizes solenoid Sol-1, fan motor 119, and relay 4CR and energizes motor 91 through normally closed contact SLSB of limit switch SLS. After switch SW-Z is reopened, relay 1CR is maintained energized by a holding circuit formed through contact 1CR-1 and switch SW-1ll.

Motor 91 drives cam 96 and after the cam has moved the follower arms to their extreme positions, motor 91 is still operative and the cam continues rotating free of the followers until physically contacting limit switch 5LS to open normally closed contact SLSB and close normally open contact SLSA. Since normally closed contact 40R has previously been opened by energizing of relay 4CR, the motor circuit is interrupted and the motor is stopped when SLSB opens. Subsequent interruption of the circuit as by opening stop switch SW41, or by circuit external of that shown, breaks the holding circuit of contact lCR-l to deenergize relay lCR which in turn deenergizes solenoid Sol-1, fan motor 119 and relay 4CR. Because contact 4CR returns to normally closed position and is in series with closed contact ELSA, motor 91 is again operative for a short duration until cam moves sufiiciently to release limit switch 5L8 and return its contacts to normal positions. Although not shown, a time delay is frequently included to permit fixing the last developed image after the stop button is depressed and the apparatus other wise functions as above for an emergency shutdown.

The heating elements 50 are separately designated in FIG. 4 as R-1 through R-8 inclusive and are connected to a potential source in the manner schematically shown.

Closing of contacts 1CR3 and 1CR5, from operation of relay 1CR as above, applies line voltage to the heating elements plus the voltages of transformer secondaries T1B and T-1C of transformer T-1. For accelerated warmup of the elements line voltage is applied through normally closed contact ZCR-Z to the primary T-1A of transformer T-1 thereby to have a full secondary voltage at T1B and T1C that conveniently may be on the order of 16 volts each. However, closing of contact 1CR2 energizes timer motor lTR and, after expiration of a preset time, contact 1TR energizes relay ZCR opening normally closed contact ZCR-Z and closing normally open contact 2CR1 thereafter to connect the primary of T-1 to a variable voltage, center-tapped transformer T-Z. Since T-2 is connected across approximately 220 volts and T1 is connected across approximately volts, by varying the output of T-Z the primary voltage to T1 can be varied to line voltage in either phase. By this means the voltage on the heating elements can be varied from line voltage minus transformer secondary voltage to line voltage plus secondary voltage such that line voltage either aids or opposes the transformer secondary voltage. By this means and with the selected parameters, a 32 volt differential applied to each element is possible.

To provide a further variation in heating capacity double pole switch SW4- serves to connect more or fewer heating elements to the circuit. In a typical arrangement of the invention lowest heat output is obtained by connecting half the heating elements at line voltage minus secondary whereas maximum heat is obtained with all of the heating elements connected at line voltage plus secondary. By the circuitry thus described heating capacity of the elements can gradually be increased to approximately 350 percent of the minimum and can be pre-set to generate substantially any capacity between the extremes. In the embodiment of invention described, i.e., employing eight heating elements of the dimensions described, the fuser has an adjustable capacity range of approximately 1940 to 6800 watts.

When stop switch SW41 is opened the holding circuit of 1CR1 is interrupted and relay ICR is deenergized and its contacts 1CR-2, ICR-3 and 1CR5 are opened to deenergize the heating elements and permit timer motor lTR to return to starting position.

In operation, switch SW1 is first closed to effect operation of the xerographic machine by circuitry not shown in FIG. 4 momentarily depressing SW2 initiates operation of the fuser. Drum 19 is constantly rotated past corona charging unit 25, exposure aperture 18, developing station 26, discharge station '41, transfer station 42 and cleaning station 55 during which original copy being transported on belt 12 is xerographically reproduced onto a support surface 43 which typically may be moving at any preset rate between 5 feet per minute to approximately 65 feet per minute and may consist of paper Within the thickness range f vellum to approximately .012 cardboard stock.

As fuser operation is initiated solenoid Sol-ll is energized to effect pivoting of latch assemblies M4 and 105 into latch position. Simultaneously, motor 91 is operative to drive cam 96 and effect horizontal movement of follower arms 79 and 89 whereby to pivot reflector assemblies 6t and 61 from the non-fixing relation of FIG. 2 into image fixing relation with web 43 as illustrated in FIG. 3.

The heating elements of the reflector assemblies are immediately warmed at an accelerated rate effected through the operation of timer motor lTR which permits variable voltage transformer T2 to be bypassed and effect full line voltage onto the primary coil of transformer T-ll. After expiration of the timers preset period the primary coil of T-l is energized through T2 which includes an adjustment means to vary the magnitude and polarity of primary potential and effect secondary voltages on transformer T1 which either aid or oppose the line voltage connected to the heater elements in series with the transformer secondary coil. By the adjustment means of T2 the power input to the heating elements is effectively varied to vary the rate of heat generation therefrom and by means of switch SW-4 the number of operative heating elements can be selected to provide increased flexibility of the fuser heating capacity.

On interruption of power to the xerographic machine solenoid Soll is immediately deenergized to release the

latch assemblies

104 and 105 from latch position permitting the

reflector assemblies

60 and 61 to be instantly restored to non-fixing relation and thus prevent burning or destruction of the stopped web support surface. Shock cushions 73 and 8S absorb the shock from the sudden movement of the assemblies.

By the above description there is disclosed an improved fuser apparatus of variable capacity for fixing a xerographically formed powder image onto support surfaces which can arbitrarily be set to move at different rates and which may be selected within a wide range of stock thickness.

Since many changes could be made in the above con struction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a xerographic reproducing apparatus wherein powder images are loosely supported on a moving web support surface, a heat fuser for affixing a powder image to a moving web support surface, said fuser including in combination a support frame arranged adjacent to the path of movement of a Web support surface on which a powder image is loosely supported, a plurality of heating elements adapted to be electrically energized, at least one support member on which the heating elements are mounted, said support member being supported on said frame and adapted for movement selectively between an operative and inoperative position relative to said path of movement to place the heating elements thereon removably into fixing relation with a Web, means operative concomitantly with movement of a web, said last recited means including means to energize said heating elements, and means to move said support member and heating elements thereon into operative position relative to a web into fixing relation therewith; and means responsive on cessation of web movement to effect removal of said support member and heating elements to said inoperative position away from said fixing relation.

2. In a xerographic reproducing apparatus wherein powder images are loosely supported on a moving support surface, a heat fuser for aflixing a powder image to a moving web support surface, said fuser including in combination a support frame arranged adjacent the path of movement of a web support surface on which a powder image is loosely supported, a plurality of heating elements adapted to be electrically energized, means to vary the magnitude of energy to said elements, a plurality of support members on which the heating elements are mounted, said support members being pivotally supported on said frame and adapted for pivoting selectively between an operative and inoperative position relative to said path of movement to place the heating elements thereon removably into fixing relation with a web, means operative concomitantly with movement of a web, said last recited means including means to connect electrical potential to said heating elements, and means to pivot said support members and heating elements thereon into operative position relative to a web into fixing relation therewith; and means responsive on cessation of web movement to pivotally effect removal of said support members and heating elements to said inoperative position away from said fixing relation.

3. In a xerographic reproducing apparatus wherein powder images are loosely supported on a moving support surface, a heat fuser for aflixing a powder image to a moving web support surface, said fuser including in combination a support frame arranged adjacent to the path of movement of a web support surface on which a powder image is loosely supported, a platform member mounted in the support frame below said path of movement to provide a support plane for a moving web, a plurality of elongated heating elements adapted to be electrically energized, means to vary the magnitude of energy to said elements, at least one support member on which the heating elements are mounted, said support member being pivotally supported on said frame and adapted for pivoting selectively between an operative and inoperative position relative to a web moving over said platform member to place the heating elements thereon removably into fixing relation with a web, means operative concomitantly with movement of a web, said last recited means including means to connect electrical potential to said heating elements, means to pivot said support member and heating elements thereon into operative position relative to a Web into fixing relation therewith, and detent means to sustain the support member in said last recited relation; and means responsive on cessation of web movement to render said detent means inoperative whereby said support member and heating elements are pivotally removed to said inoperative position away from said fixing relation.

4. In a xerographic reproducing apparatus wherein powder images are loosely supported on a moving Web support surface, a heat fuser for aflixing a powder image to a moving web support surface, said fuser including in combination a support frame arranged adjacent to the path of movement of a web support surface on which a powder image is loosely supported, a platform member arranged in the support frame below said path of movement to provide a support plane for a moving web, a plurality of elongated heating elements adapted to be electrically energized, means to vary the magnitude of potential to be connected from a potential source to said heating elements, at least one support member on which the heating elements are mounted, said support member being supported on said frame and adapted for movement selectively between an operative and inoperative position relative to a web moving over said platform member to place the heating elements thereon removably into fixing relation with a web, resilient means operatively connected to said support member urging removal of said member to said inoperative position away from said fixing relation, means operative concomitantly with movement of a web, said last recited means including means to connect potential of preset magnitude to said heating elements, means to move said support member and heating elements thereon into operative position relative to a web into fixing relation therewith, and detent means to sustain the sup- 15 2,965,358

References Cited in the file of this patent UNITED STATES PATENTS 2,573,881 Walkup Nov. 6, 1951 2,624,652 Carlson Jan. 6, 1953 2,701,765 Codichini et a1. Feb. 8, 1955 2,852,651 Crumn'ne et a1 Sept. 16, 1958 Eichler Dec. 20, 1960