US2925464A

US2925464A - Machine for producing a facsimile reproduction

Info

Publication number: US2925464A
Application number: US507701A
Authority: US
Inventors: Raible Albert Oskar
Original assignee: Individual
Current assignee: Individual
Priority date: 1954-05-14
Filing date: 1955-05-11
Publication date: 1960-02-16
Anticipated expiration: 1977-02-16
Also published as: CH308004A; GB781714A; FR1130263A

Description

A. O. RAIBLE Feb. 16, 1960 MACHINE FOR PRODUCING A FACSIMILE REPRODUCTION 5 Sheets-Sheet 1 Filed May 11, 1955 A. O. RAIBLE Feb. 16, 1960 MACHINE FOR PRODUCING A FACSiMIL-E REPRODUCTION 0 e m O r w n O m 5 H w w 5 3 4 9 O e 4 3 7 6667 .m 9 8 A 7 6 S .l 7 F WV 5 1 F 7 9 2 5 2 6 I 8 7 :l 5 4 F oo 7 3 v 0 U "U o 7 M M 8 72/ u 0 i! M 4 W U flu 2 8 8 O 5 O f I 5 7 Q. 3 a 9 7 8 'l/ 8 7 5V 9 5 8 5 5 5 9 1 L 1 m v 0 m L w 6 1- F Feb. 16, 1960 A. o. RAIBLE 2,925,464

MACHINE FOR PRODUCING A FACSIMILE REPRODUCTION Filedllgy 11, 1955 20 5 Sheets-Sheet 3 L Fig. 8

v ,4'11 m m 23 23 440 A. o. RAIBLE 2,925,464

MACHINE FOR PRODUCING A FACSIMILE REPRODUCTION Feb. 16, 1960 5 Sheets-Sheet 4 Filed May 11, 1955 m @N Wl'l'l M WI b 5 mm on H. fl oq mm 3 m. 2 IIIIILH'IIIIIIII ILIIIICI. L CFC... 2:2:- llll mm 3 8 mm N? Filed May 11, 1955 Feb. 16, 1960 A. o. RAIBLE 2,925,464

MACHINE FOR PRODUCING A FACSIMILE REPRODUCTION 5 Sheets-Sheet 5 Fig."

MACHINE FOR PRODUCING A FACSIMILE REPRODUCTION Albert Oskar Raible, Zurich, Switzerland Application May 11, 1955, Serial No. 507,701 Claims priority, application Switzerland May 14, 1954 '3 Claims. (Cl. 178-6.6)

The present invention relates to a method and a machine for producing a facsimile clich having a printing surface constituted by a screen or grid of elongated picture elements of variable widths left between adjacent grooves. It is the object of the present invention to provide a method and a machine of this type permitting to produce the printing plate by copying the pattern automatically, employing simple and reliable means resulting in a printing plate having a screen or grid of excellent qualities ready for use in a printing machine and requiring no variable controlling impulse representative of the tone of the spot of the pattern scanned at any time and simultaneously cutting generally parallel continuous grooves into the surface of the printing plate controlling the local width of said grooves in dependence on said controlling impulse to thereby produce a printing surface constituted by a grid of elongated picture elements of variable widths left between adjacent grooves.

This method is preferably carried out by a machine which, according to the invention, comprises a first support for the pattern, photoelectrical scanning means associated with said first support and adapted to scan said pattern, a second support for the printing plate, cutting means associated with said second support and adapted to cut a groove into the surface of said printing plate, actuating means adapted to produce synchronized simultaneous relative movements between said supports and said associated means along generally parallel paths, control means including an amplifier connected to and controlled by said scanning means and adapted to produce a variable controlling impulse representative of the tone of the spot scanned at any time, and means controlled by said control means and connected with said cutting means and adapted to cause the same to cut a groove into the surface of said printing plate, the local width of said groove depending on said controlling impulse, to thereby produce a printing surface constituted by a grid of elongated picture elements of variable widths left between adjacent grooves.

. Further objects of the invention will apear from a detailed description following hereinafter of a preferred embodiment of the present invention, and the features of novelty will be pointed out in the claims. It is to be understood, however, that such detailed description serves the purpose of illustrating the invention rather than that of restricting or limiting the same. In the drawings Fig. l is a top View of the novel machine for producing a relief printing plate of the screen type,

Fig. 2 is a transverse section taken along the line 2'-2 of Fig. l,

Fig. 3 is another transverse section taken through the machine along the line 3-3 of Fig. 1,

United States atent Fig. 4 is an axial section on an enlarged scale taken through the photoelectrical scanning head shown in Figs. 1 and 3,

Fig. 5 is an axial section on an enlarged scale taken through the cutting head shown in Figs. 1 and 2,

Fig.6 is a diagrammatic section taken through the finished printing plate illustrating the function of the cutter,

Fig. 7 is a section similar to that of Fig. 6 taken through a portion of the printing plate representing a highlight zone of the image, the scale being still larger than that of Fig. 6,

Fig. 8 is an elevation of the central portion of the machine shown in Fig. 1 showing various manipulating elements,

Fig. 9 is a semi-diagrammatic representation of the machine illustrating the function thereof,

Fig. 10 illustrates on an enlarged scale part of a transmission included in the central portion of the machine shown in Fig. 1,

Figs. 11, 12 and 13 are sectional views of the transmission, the sections being taken along the lines XI--XI, XIIXII, and XIIi-XIII respectively of Fig. 10,

Fig. 14 is a view on an enlarged scale of a detailed shown in Fig. 8 and represents mechanism shown in Fig. 13 and viewed from the right, and

Fig. 15 illustrates a cutter head provided with a milling tool and driving means therefor adapted to produce freely projecting autotypes.

In a transmission box 20 (Fig. 1) forming part of the housing 21 of the machine a shaft 22 is rotatably mounted, its ends projecting'out of the box 20 and being provided with clutch portions 23. In the axial direction A--A of this shaft 22 two additional stud shafts 24 are mounted each of which is provided with a clutch portion and a knob 25 and is shiftable in axial direction. With the aid of the knob each shaft 24 may be pulled outwardly from the position shown in Fig. l contrary to the action of a restoring spring, not shown, to thereby disengage a pair of supports formed by

cylindrical drums

26 and 27 which are normally located between and engaged by the clutch portions 23 and the clutch portions of the stud shafts 24. In this manner the drums may be removed and replaced by spare drums. The drum 26 on the left hand side of the machine constitutes a support for a flexible printing plate of zinc or copper which may be attached to the drum in a known manner. The drum 27 on the right hand side of the machine constitutes a support for a pattern displaying the photography, picture, drawing, or written or printed matter to be copied,

such pattern being so arranged that it will be copied on the printing plate in the desired manner.

The two

drums

26 and 27 are preferably rotated with the same speed. On its periphery the clich drum 26 or the drum 27 is provided with a V-belt groove 30 engaged by a V-belt 31 which is driven by a motor, not shown, directly or through a transmission.

On the left hand side of the machine a threaded spindle 32 is journalled to extend parallel to the drum axis AA and is adapted by means to be described later to be intermittently driven by the shaft 22 at an adjustable rate of speed. The threads of the spindle 32 engage the .internal thread of a carriage 33 (Figs. 1 and 2) which electrical cell.

. 3 face of the printing plate are constituted by a cutter head 40 provided with a cutting blade 41. The rear end of lever 39 carries an adjustable counterweight 42. Hence, the cutting blade will be fed in axial direction along the drum 26 throughout the length thereof at a speed depending on the rotary speed of the threaded spindle 32 causing the cutting blade to cut'generally parallel shaft portion 19. The spindle 43 (Figs. 1 and 3) engages internal threads of a nut fixed to a carriage 44 which is provided with a sleeve 45 slidably accommodating the tube 46 of a'microsc'ope. The carriage 44 is guided by and. mounted on a shaft 4 7' and is additionally guided V by a shaft 48, both

shafts

47 and 48 being mounted 'in the machine frame to extend parallel to the drum 27.

Rollers 49 and 50 mounted on the lower portion of the carriage 44 straddle the shaft 48 resiliently engaging the same. An additional threaded spindle 51 may be mounted in the machine frame so as to extend parallel to the

guide shafts

47 and 48. The spindle 51 is mounted for shifting movement in its axial direction and is adapted to actuate an electrical control contact, not shown. Two split nuts 52 are adjustable on the spindle 51' and adapted, when the carriage 44 moves in one direction or the other, to be engaged by stops 53 provided on the carriage 4 to thereby shift the spindle 51 for actuation of the control contact. The control contact constitutes an end switch adapted to stop the driving motor when the carriage dd arrives at a selectable position depending on the disposition of the pattern.

The microscope carried by the carriage 44 constitutes photoelectrical scanning means associated with the support 27 of the pattern. The objective lens of the microscope is shown at 54. It projects a beam of light upon a screen 55 constituting a photoelectrical cell mounted in the rear upper portion of the tube 46. A dispersing lens 56 serves the purpose of distributing the light of the beam over the entire area of the screen 55. The source of light is formed by a lamp 57 mounted together with a condensor lens system 58 in a transverse tube 68 communicating with the tube 46. The beam of light produced by the lamp 57 and the condensor lens system 58 is reflected by an inclined annular mirror 59 upon an annular lens system 65 which projects the beam uniformlyupon the spot of the pattern to be scanned at any time, such spot being located below the objective lens 54.

A synchronous motor 61 of a vibrationless type is mounted on the carriage 44 and imparts rotation to a slotted disk 62 which projects into a transverse slot of the tube 68 to intermittently interrupt the beam of light emitted by the lamp 57. The microscope is so adjusted that its objective lens will be focussed upon the pattern mounted on the drum 27 and will project an enlarged picture of'a restricted spot of the pattern upon the photoelectric screen 55. Hence, the light only that is reflected by the restricted spot will be projected upon the photo- Because of the intermittent interruption of the beam of light by the slotted disk 62 the photoelectrical cell will produce an alternating control current, the amplitude of which depends on the local tone of the pattern. When the section of the pattern scanned at any time is a solid shadow section, the amplitude of the alternating current produced will be a minimum. When the section of the pattern scanned at any time is a highlight section, the amplitude of the alternating current will be a maximum. When the section of the pattern scanned is a middle tone, the amplitude will have a median value. 7

Theproduced control current pulsating at about 800 to 2,000 cycles per second is supplied to an amplifier 63 brass.

(Fig. 9). The amplified output which may be a pulsat ing direct current is supplied to a potentiometer 65.

The cutting means 40 (Figs. 1, 2 and 5) include an electromagnet adapted to elfect adjustment of the cutting tool in radial direction with respect to the printing form drum 26. In the embodiment shown in Fig. 5 the electromagnetic device includes a coil 64 movable in the air gap of the electromagnet. This coil is supplied with the variable controlling impulse which is produced by the photoelectrical scanning means and is representative of the tone of the spot of the pattern scanned'at anytime. To this end, one end of the coil is connected by an electrical wire to the grounded terminal of the potentiometer 65 while the other end of the coil 64 is connected by a wire to the sliding contact of the potentiometer 65. By adjustment of the potentiometer 65 the maximum value of the'impulseis adjustable.

The cutting means will now be described in detail with reference to Fig. 5. The cutter head 46 comprises'a frame portion 66 of a non-magnetic material, such as A pair of spaced yoke elements 67- and 68 of magnetic material is secured to the frame portion 66. The elements carry a substantially cylindrical permanent magnet 69 between them. The yoke portion 67 is provided with a hollow core 70 of magnetic material the upper end of which includes an annular gap with the yoke portion 68, the flux flowing radially through such gap. A rod 71 of non-magnetic material extends through the hollow core 70 and is guided therein for axial displacement by a pair of parallel leaf springs 73 extending between the frame portion 66 and the ends of rod 71. A plate 72 of non-magnetic material is secured to the upper end of the rod 71 and carries the cylindrical coil 64 which surrounds the upper end of the core '70. A hook 74 is secured to the plate 72 and engages over the free end of an arm 75 which is swingably mounted by means of a leaf spring 76 on a frame portion 77. The latter is rigidly connected with the frame portion 66.

'The bottom of the arm 75 is engaged by the upper end of a tool carrier 82 which is mounted for vertical up and down movement by means of a pair of parallel leaf springs 79 and 8t) fixed to the frame portion 77, and

the yoke element 67 respectively. The tool support 82 is formed by a hollow sleeve adapted to adjustably accommodate a cutting blade 81 clamped in position by a screw 83. In this manner the cutting blade 81 may be readily exchanged.

The hook 74 is surmounted by a bridge portion 84 secured to the yoke member 63 and provided with a threaded bore engaged by an adjusting screw 85. The end of the screw 85 acts as an adjustable abutment limiting the movement of the cutting tool away from the clich support 26.

From the foregoing description it will appear that the cutting tool 81 is mounted on the

frame

66, 67 for axial displacement towards and away from the clich support 26 and that oscillations will be imparted to the tool 81, the amplitude being proportional to the impulse current supplied to the coil 64. In this manner, the tool will cut generally parallel continuous grooves into the surface of the printing plate. The local width of such grooves will be controlled in dependence on the impulse current. In this manner a printing surface will be produced which is constituted by a grid or screen of elongated picture elements of variable widths left between adjacent grooves. Since the tool 81 has a wedge-shaped point, the width of the groove depends on its depth. In this manner a picture is formed on the printingv plate and may be directly printed from the plate without any preparatory treatment other than the inking of the printing plate.

The transmission in the box 20 will now be described. It permits an adjustment of the fineness of the picture screen by means of a handle shown in Figs. 8, l3 and 14.

A spiral cam 90 (Fig. 11) is securedto the shaft 22 and. cooperates with a follower roller 91 mounted on a follower lever 92. The latter is pivotally mounted on astationary shaft93 mounted in the transmission box 20, The end offthe lever 92 is connected to a chain 94 which extends around a pair of sprockets including a sprocket 95 which is freely rotatably mounted on shaft 19. The chain is kept taut by a spring 96 attached to its end. Hence, it will appear that continuous rotation of the shaft 22 results in an oscillatory rotation of sprocket 95. The latter is rigidly connected with a disk 97 carrying a. pawl 98 held by a spring 99 in engagement with a ratchet wheel 100 splined to shaft 19. Hence, it will appear that the follower lever 92 operable by the cam 9.0 is connected with the pawl 93 to reciprocate the same and to impart intermittent rotation to the shaft 19 and to the threaded

spindles

32 and 43 connected therewith.

'An adjustable stationary stop is provided for limiting the reciprocatory motion of the follower 92. For that purpose, a sprocket 102 is freely rotatably mounted on shaft 19 adjacent to the pawl-carrying disk 97' and is connected by a chain 103 with a sprocket 104. The latter is rotatably mounted in the transmission box 20' near the front wall thereof on a shaft 106 and is con.- nected for common rotation with a bevel gear 105 which meshes with a bevel gear 107 secured to a shaft 108. This shaft is mounted in the front wall of the box 20 and extends out thereof and carries the handle 110.cooperating with a graduationlll. The. handle 110 may beturned to any one of a plurality of positions and is. arrested therein by a suitable detent pin 113' adapted to engage holes112 provided in the front wall of the box 20. In. this manner, the operator may turn the sprocket102 to any one of a plurality of angular posi-' tions. This sprocket 102 and the disk 97'carry cooperating stopsllS and 116. In this manner the .reciprocato ry motion of the disk 97, the sprocket 95, .the chain 94' and the follower lever 92 may be limited.

The. operation of the machine is as follows: The motor, not shown, imparts rotation to the shaft 22 by the belt running in groove 30. Therefore, both the clich. drum 26 and the pattern drum 27 revolve. The pattern formed by a picture or the like is mounted on the drum 27 whereasthe clich printing plate is mounted on the. cylinder 26. The photoelectric scanning head associated'with the pattern support 27 and'the cutting means 40 associated with the clich support 26 are so adjusted that they may commence their function in registering positions. Rota tionofshaft 22 is imparted to the cam 90 (Fig. 11') whereby the follower lever 92 isrocked once at any revolution and pulls the chain 94 tensioningthespring 9.6. When that happens, however, the shaft 19 rests since the sprocket 95 and the disk 97 fixed thereto are freely rotatably mounted on the shaft 19. As soon as thefollower roller 91 drops from the step 90a of the cam, it will be moved under'action by the spring 96 towards shaft 22, and the sprocket 95 and the disk 97 will be turned in clockwise direction through a limited angle. During this partial rotation the pawl 93 will connect the disk97 with the ratchet gear 100 and the shaft 19. In this manner both the

spindles

32 and 43 willbe turned through a certain angle.

From the foregoing description it will appear that while the

drums

26 and 27 revolve continuously, the

carriages

33 and 44 will be moved-step by step performing one step for every revolution of the drums. The length of the step depends on the angle of rotation of the disk 97 which may be determined by suitable adjustment of the handle 110. As a result, any revolution of the shaft 22 causes the threaded

spindles

32 and 43 to be intermittently-turned a predetermined amount. The size of the drum 26, thedrum 7, the pattern, and the clich printing plate is so chosen that when the pattern and the printing plate are placed on the respective drum a distance is left between .the leading edge and the trailing edge of the pattern, or clich plate respectively. This. distance is made use of to eifect the stepwise axial displacement of the scanning head and the cutting head by the intermittent rotation of the threaded

spindles

32 and 43. As a result, the pattern is scanned along generally parallel circumferential paths and will cause the cutting means to cut generally parallel peripheral continuous grooves into the surface of the printing plate.

The adjustment of the handle 110 determines the. fineness of the screen or grid within predetermined limits; In the embodiment shown, a screen may be cut including between 17 and elongated picture elements or lines per centimeter. When it is desired; for instance, to produce a screen of 25 lines per centimeter, the operator must so adjust the handle 110 (Fig. 14) that its detent pin may engage the hole 112 bearing the serial number 25. The handie 110 is operative by means of the

gears

107, 105, the shaft 106, the sprocket 104, and the chain 103 to turn the sprocket 102 to a predetermined angular position, When the follower roller 91 drops from the step 90a ofthe cam 9i? permitting the spring 96 to contract, the rotation of the disk 97 will be stopped by engagement of" its stop 115 with the stop 116 of the sprocket 102. Such engagement will stop the disk 97 and the ratchet gear 10%. That means that the spring 96 will not be permitted to contract completely. The angular distance through which the disk 97 carrying the pawl 98 is permitted to travel is so chosen that the pawl will turn the ratchet gear 100 through an angle sufficient to move the scanning means and the cutting means a distance corresponding tothe screen 25. Hence, it will appear that the ratchet gear 100 and the disk 107 will oscillate between an initial position and the stop 13.6 of the sprocket 102, the amplitude of such oscillation determining the desired fineness of the screen.

A predetermined cutting depth is coordinated to any degree of fineness of the screen. This cutting depth is adjusted in dependence on the adjustment of the handle 110 by manually turning the screw 85*(Fig. 5).

As stated hereinbefore, the lower end of the screw 85 engages the hook 74 and limits the upper position of the hook and of the rod 71. The amplitude of the oscillation of'the latter is transferred by the arm 75 to the cutting blade 81. Where highlight sections of the pattern are scanned, the controlling impulse current produced'will cause the cutting blade 81 to cut a deep groove, and where a solid shadow section of the pattern is scanned, the depth of the cut will be reduced substantially to zero. As a result, the elongated picture elements left between adjacent grooves will have a variable width depending on the tone of the scanned spot beneath theobjective lens 54 of the scanning head. Since the blade 81 has converging cutting edges, the cutting of grooves of a small depth results in wider picture elements than the cutting of deep grooves, as will appear from Fig. 6.

In order that the printing clich may be easier made ready for print, it is highly desirable that the highlight zones thereof, that is to say the zones where the picture elements have a minimum width, be located at a lower level than the picture elements of greater width requiring a more powerful pressure in the printing operation in order to produce a brilliant imprint. The method and the machine described offer a possibility to so cut the grooves that they will overlap at highlight sections, as shown in Fig. 7 in dotted lines. As a result, the grid so formed will be located at a lower level spaced by the distance a'below the level of the normal picture elements. This is illustrated in Fig. 7 on an exaggerated scale. In this manner the highlight sections of the print will be formed by extremely thin lines andwill thus appear particularly bright.

Moreover, the invention aifords a possibility of producing a printing plate having insulated projecting auto types; For thispurpose a rotary milling tool 120" is than;

rotary mining toollZtl is cooperatively connected with.

a motor 121 which is mounted by means of a bracket 122 on the frame of the cutter head 49. For producing autotypes freely projecting from the base of the printin'g plate, the following method is employed. First, the; entire pattern is scanned and the printing plate is cut in the manner described. Then all areas of the pattern which are to be printed are blackened out by a suitable black mask or otherwise. Then the milling tool 129 is substituted for the cutting blade 81 and the pattern so blackened is again scanned by the scanning liead. During this operation the milling tool 12% is fed by the magnetic device into the printing plate whenever the non-blackened portions of the patternare sensed to there by remove a surface layer from the printing plate under control by the controlling impulse which is produced by scanning the non-blackened areas of the pattern. After the milling tool will thus have removed all picture elements corresponding to the non-blackened areas of the pattern, the remaining areas of the printing plate will be left in insulated positions projecting from the base of the printing plate.

In the embodiment shown, the pattern drum 27 and the clich drum 26 revolve synchronously. Since the scanning head and the cutting head are intermittently moved equal steps of a length corresponding to the desired degree of fineness of the screen, the picture-elements successively cut in the printing plate will ultimately produce a print of the same scale as the pattern representing a mirror image thereof and having the same surface tones graduated from solid shadows to highlights. Preferably, a clich printing plate is employed which is protected from oxydization by a thin coat. This offers the. additional advantage that the engraved finished image is immediately visible since the zinc of the plate differs form the coat of the picture elements by its color.

Moreover, it is possible without requiring any adjustment of the elements of the machine to cut the elongated picture elements at any desired angle with respect to the edges of the printing plate. For this purpose the pattern and the printing plate must be so mounted on their respective supporting drums that the edges extend obliquely thereto. This advantage may be utilized for the reproduction of colored patterns. For that purpose component patterns are first produced photographically or manually representing the different color components of the original pattern. Then a clich plate is produced from any component pattern, the different clich plates differing by the angular position of the picture elements with respect to the edges thereof. Then registering imprints of difierent colors are made from the component clich plates. In this composite print the elementary lines of different colors will cross each other thus avoiding any undesirable moire.

As the pattern not only a photography may be used but also a fabric or a fabric with pictures mounted thereon. As stated heretofore, the cutting depth is adjusted by means of the screw 85. It is possible, however, to cooperatively connect the setting elements for the cutting blade with the setting element for the degree of fineness of the screen. The cliches produced in the manner described do not require any subsequent treatment, such 'as etching, but may be used for the printing operation immediately after the completion of all picture elements.

For plural color printing, the pattern and the clich plate may be mounted on their respective supporting drums in normal position, and then the individual clich may be printed one above the other in crosswise manner. While the invention has been described in connection with a preferred embodiment thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or

adaptations of theinventionjfollowing, in general, the principles of the invention and including such departures from the present invention as come within known or customary practice in the art to which the invention pertains, and as fall within the scope of the' invention or the limits of the appended claims.

What I claim is: l. A machine for producing a relief printing plate from a pattern comprising a first rotary drum for supintermittent equal axial displacements between said drums and the respective means associated therewith along generally parallel paths, one of said spindles being adapted to effect relative axial displacement between said first drum and said photoelectric scanning means and the other threaded spindle being adapted to effect relative axial displacement between said cutting means and said second drum, a transmission comprising a rotatable disc on said shaft portion and means for alternately rotating said disc in opposite directions, said disc being adapted to actuate said shaft portion during rotation in only one of said directions to impart an intermittent rotation to said spindles control means including an amplifier connected to and controlled by said scanning means and adapted to produce a variable controlling impulse representative of the tone of the spot scanned at any time, means controlled by said control means and connected with said cuttingmeans and including an electromagnet adapted to effect said radial adjustment of said cutter in dependence on said controlling impuse to cause same to cut a groove into the surface of said printing plate, the local width of which depends on said controlling impulse, whereby to produce a printing surface constituted by a grid of elongated picture elements of variable widths left between adjacent grooves, and adjustable means operatively associated with said actuating means for varying the amount of said axial displacements between said drums and their respective scanning and cutting means to adjust the fineness of said grid within predetermined limits, said adjustable means being operable to vary the rotation of said disc in said one direction A 2. Machine as claimed in claim 1, in which said transmission further comprises a ratchet gear secured to said shaft portion, said rotatable disc has a pawl thereon adapted to operatively engage and actuate said ratchet gear during rotation of said disc in said one direction, and said means for alternately rotating said disc comprises a cam connected to said drums for common rotation therewith and a follower operable by said cam and operatively connected with saiddisc.

3. Machine as claimed in claim 1,. in which said adjustable means comprises a manually positionable stop engageable with a stop provided on said rotatable disc.

References Cited in the fileof this patent UNITED STATES PATENTS 7 461,152 Soblik Oct. 13, 1891 2,047,851 Bennett July 14, 1936 2,063,614 McFarlane Dec. 8, 1936 2,520,761 can Aug. 29,1950 2,574,872 Jarvis Nov. 13, 1951 t FOREIGN PATENTS 468,177 France Apr. 17, 1914