US2844674A - Snap switch - Google Patents

Description

July 22, 1958 c. P. ANDERSON SNAP SWITCH Filed March 22, 1954 INVENTOR. CARL E AuoznsoN ATTO RNEYS United tates Patent SNAP swrrcn Carl P. Anderson, Evanston, iiL, assignor to Kleinschmidt Laboratories, Inc, Deerlield, Ill., a corporation of Delaware Application March 22, 1954, Serial No. 417,548

22 Claims. (Cl. 260-6116) This invention relates to electric toggle switches of the snap action variety in which a pivoting contact bearing rocker member is employed cooperating with a pair of stationary contacts.

More specifically this invention concerns snap switches of the class in which a contact member is biased by a coil spring in one direction or another when moved past a dead center by the switch actuating member.

The present invention was developed for use in printing-telegraph-sending-receiving-machine to control a sig nal circuit indicating the exhaustion of tape on a supply reel. Available snap action switches were not sensitive enough to insure the rapid opening of contacts for slow movement of the operating handle and resulted in burning of contacts.

Tests on available snap action switches have disclosed that the lever directly controlling movement of the contact moved a very small amount and so slowly and the spring force holding the contacts together had decreased, that prior to complete separation of the contacts by rapid snap action, Vibration of the machine upon which the switches were tested caused the contacting points to vibrate and separate a small amount thus contributing to arcing with a resultant rapid burning away of the contacts.

The present invention disengages the contacts very rapidly and eliminates the initial momentary slow separation prior to the snap action present in the prior art switches. By increasing the contact pressure during the major portion of the operating handle throw, positive abutment of the contacts is assured up to the point of actual snap action to immediately rapidly separate the contact points.

With these and other considerations in view a primary object of this invention is to provide a two position switch which has increased speed of throw thus minimizing arcing at the contacts.

Another object of the invention is to provide an electrical snap switch in which the contacts are held tightly closed until the instant they are disengaged, and wherein the pressure between the contacts is greatest just prior to the instant of separation.

Another object of the invention is to provide a two position snap switch in which the contacts are maintained completely engaged until the instant of separation even though the switch control lever or handle is gradually moved to the point at which it operates.

Another object is the provision of a novel movable contact carrier and means to make an electrical connection thereto.

A still further object is the provision of a molded mounting base of improved design in which the electrical leads are well shielded from one another.

Another object is the provision of a switch of the above described class, the movable parts of which are designed to reduce wear to a minimum thus insuring a long troublefree life.

A still further object is to incorporate in a telegraph 2 machine, provisions whereby the condition of a tape reel can be mechanically transferred to actuate a rapid acting snap switch to control the circuit to an indicating device.

Another object is to provide a follower mechanism responsive to the condition of a telegraph machine tape reel connected through an overthrow safety device to a fast action snap switch controlling a circuit of a device for indicating the tape reel condition.

Another object is to provide a condition responsive mechanism responsive to a slowly changing condition, having an operative connection to a snap-action switch designed to transfer the resultant slow movement of the condition responsive mechanism to a rapid positive separation of the switch contact points upon the condition reaching a certain predetermined value.

Still further objects and advantages will become apparent from the following detailed description taken in conjunction with the accompanying drawings in which,

Figure l is a perspective view of the switch with its cover removed.

Figures 2 and 3 are views of the same switch mechanism in two different positions, and

Figure 4 is an enlarged View of the contact rocker con struction.

Figure 5 is a perspective view of the switch utilized in an indicating circuit.

Referring to Figure l, the numeral 10 designates an insulating base structure molded from any suitable dielectric. Formed in this base structure 10 are channels 12, 14 and 16 for receiving and positioning the terminal bars 18, Ztl and 22. The terminal bars are made of good conducting material and are formed to fit the chanels 12, 16 and respectively in order to locate their contact ends 24, 26 and 28 in proper operating relation. Each terminal bar is fastened to base it) in its respective channel by suitable means such as rivets 29. Contacts 24 and 26 are disclosed as right angular bent ends of the bars 18 and 20 respectively but may be formed of separate elements riveted on the bent ends of bars 18 and 20. The end 2%; of terminal bar 22 is bent back on itself to form a thicker cross section to efiiciently hold a screw 30 which fastens a leaf spring 32 on bar 22 to form a common electrical conductor for the movable contact which will presently be described.

Fixed in the base in is a post 34 having in its outer end an annular groove 36 to receive a snap Washer 38. Pivoting upon the post 3 2 is an operating arm 40 and a contact rocker 42. Operating arm 44? has its lower end doubled back in U-shape to form two spaced bearings 011 pivot post 34. The cross member 44 at the lower end of arm 40 is of arcuate cross section containing a hole 46 centrally located.

Rocker 42 (Figure 4) pivotally mounted on post 34 between the two spaced bearings of arm at is molded of a dielectric and has contacts 48 and 5d suitably mounted at its ends by means such as riveting. Connecting the contacts 48 and 50 is a strip of electrical conducting material 51 which lies in a channel 52 formed along the top surface of rocker 42. Leaf spring 32 is resiliently biased against strip 51 at a tangent of the arc of the rocker pivot and thus completes an electric circuit between terminal bar 22 and the two movable contacts 48 and 50. g

The under side of the rocker 42 has a recess generally indicated at 53, to receive a roller 54 and to define its motion. A raised rib 56 extending longitudinally of the recess 53 is formed integral with the dielectric material of which rocker 42 is formed midway of the width of recess 53. An annular groove 58 in the roller 54 receives rib 56 thus preventing axial movement of the roller 54 with respect to rocker 42, Recess 53 constitutes a track for roller 54 the specific configuration of which will be described in greater detail hereinafter.

The roller 54 is operatively connected to the arm by a rod generally indicated at 60. Rod 60 is a flat strip having an enlarged concave tip 62 which rides in the annular groove 58 of roller 54. The opposite end of rod 60 passes freely through hole 46 in cross member 44. A compression coil spring 64 surrounds the rod 60 and is held between a shoulder 66 on the rod 60 and a washer 68 slidably mounted thereon and abutting the cross member 44. The pressure of the spring 64 between the cross member 44 of the operating arm and the shoulder 66 holds concave tip 62 in the roller groove 58 to thereby hold the roller against the arched recess 53 of rocker 42.

The two extremeties of the recess 53 define arcs having radii substantially equal to the radius of the roller 54. However, the arcs are not tangent to the curved path of the control portion of the recess but are recessed a slightly greater amount to form slight indentations 55 at each end of the recess to prevent the free rolling of the roller 54 from its position at one end or the other.

End positions of the arm 40 are defined by a stop 70 best seen in Figures 2 and 3, which is formed as a raised portion of the base 10. Stop 70 projects on both sides of the center of the pivot post 34 and has angular faces to coact against arm 40 and thus define the two limiting positions.

Operation of the above disclosed invention will now be described:

The leads from a three wire circuit was connected to the three terminals 18, 2t) and 22, the terminal 22 being the common side of the circuit. Referring to Figures 2 and 3, the arm 49 has just been thrown from its previous left hand position, phantom lines of Figure 2, in which position a circuit through the contact 26, the contact of the rocker 42, the conducting strip 51, the leaf spring 32 and the terminal 28, is closed. The movement of the arm 40 to the right will move the lower end with cross member 44 to the left. The spring 64 will be compressed and the roller 54 will remain in its position until the hole 46 of the cross member 44 has traveled to a point far enough past the dead center of a line drawn between the edge of the indentation 55, the center of the roller 54 and the hole 46, to cause the roller 54 to be thrust to the right out of the indentation 55. The inertia of the roller 54 and the rod 60, plus the expansion of the spring 64 will rock the member 42 counterclockwise thus breaking the electrical connection between contacts 50 and 26 and connecting the electrical circuit between contacts 48 and 24, Figure 3.

The washer 68 which holds the spring 64 against the cross member 44 will always be tangent to the curved surface of the member 44 thus maintaining a square abutting surface for the spring 64 for all positions of the rod 60. i

As the member 40 moves from one of its limit positions toward its opposite limit position, spring 64 is gradually compressed and the line of action of the force exerted thereby, which may be considered to be coincident with the axis of rod 60, gradually pivots about the axis of roller 54 until it intersects the line of intersection of the curve of arcuate notch 55 in which the roller 54 is resting with the curve of the main or intermediate arcuate portion of the recess 53. At the instant the line of action of the force exerted by this spring 64 reaches the intersection of those two curves, a critical condition of the mechanism is reached. At that position the force exerted by the spring consists of two components, one biasing the closed contacts together and the other biasing the roller 54 towards its opposite limit position. Once the line of action of the force exerted by the compressed spring 64 passes this critical position, the component force tending to shift roller 54 is no longer opposed and 4 the roller 54 is shifted rapidly to its opposite limit position as the spring 64 expands.

As the switch mechanism approaches this critical position, the line of action of the spring becomes so directed that it has one component maintaining engagement of the closed contacts which is gradually increased up to the critical position due to further spring compression and a second component directed to produce, when released, movement of the mechanism toward its opposite limit position. This second component gradually increases up to the limit position due both to the further compression of the spring and to the change in angularity of the line of force exerted thereby. This fact assures not only that the engaged contacts will remain engaged up to the critical position of the mechanism but that the mechanism will be shifted very rapidly toward its opposite limit position once the critical position is past. This feature constitutes a marked improvement over prior art switches of which applicant has knowledge and is one important feature of the present invention. Further, since the critical position of the mechanism is established by engagement of roller 54 with the line of intersection of arcuate recess 53 with arcuate recess 55, the dead center position of the mechanism is a highly unstable one assuring that the mechanism will move to one limit position or the other. The slight inertia of the rocker 42 and the roller 54 assure that, in operation, even when slowly actuated by the gradual increase or decrease in accumulation of tape upon a reel in a telegraph tape handling apparatus, the line of action of the spring will not be normal to the arc of the main notch 53 and intersect the axis of the rocker pivot post 34 simultaneously, the only other possible dead center position of the mechanism. The present invention thus assures that not only will the closed contacts remain closed up to the critical position but that the mechanism will be shifted rapidly and positively toward its opposite limit position to fully open those contacts once the critical position is past.

One of the many uses of this type of switch is for controlling a signal circuit for indicating exhaustion of tape on a tape supply reel such as used in telegraph machines. Figure 5 illustrates such a signal circuit and the associated mechanism to actuate the switch. A tape reel is diagrammatically illustrated in solid lines 72 as exhausted and in phantom lines 74 as full. A follower arm 76 pivoted to the telegraph machine frame on post 78 bears against the periphery of the tape reel 72. Wire spring 80 located on pivot post 78 has two legs 82 and 84 resting in hooked lugs 36 and 88 formed on a portion of the follower arm 76 offset from the pivot post 78. The ends of the spring legs 82 and 84 are bent for a purpose to be presently described. The arrangement of spring 80 on post 78 and hooked in lugs 86 and 88 of arm 76 is such that the two spring legs act as a forked lever operated in conjunction with follower arm 76.

A snap switch of the type described is suitably mounted on the frame of the machine with the operating arm 40 situated between the bent ends of spring legs 82 and 84. In the tape exhausted position of follower arm 76 the lower spring leg 84 bears against switch arm 40 to position it at one of its limits whereby the rocker of the switch internally connects terminals 18 and 22 to.

complete a circuit to an indicator light 94 As may readily be seen, the s ring mechanism 80 will allow an overthrow of follower arm 76 to prevent damage to the switch.

The circuit may be wired to indicate a full take-up reel 74, where the spring 84), will position the switch arm 49 at the opposite position to complete a circuit between terminals 20 and 22, wherein the indicator light circuit will include the dotted connection 2 and omit the connection 94, to thereby flash a signal light when the takeup reel is full. The stationary contact 24 or 26 not connected to the signal light will be connected to control the tape advancing mechanism, as for example in series with the motor magnets of the mechanism disclosed in copending application Serial No. 355,002.

In this type of installation the switch arm is gradually moved from one position to the other as the tape reel slowly becomes exhausted. In prior art switches tested for use in this type of circuit the switch contacts vibrated with the machines and the decreased spring pressure on the contact just prior to the snap action from a closed position to a positively opened position failed to positively hold the contacts together and resulted in arcing and burning of the contacts.

Although this switch was designed specifically for use in a telegraph machine, its application to other circuits is multifold and results in a switch capable of longer continued use, before replacement, than other prior art switches known to the applicant, because of the decreased arcing with resultant decrease in burned contacts.

It can be plainly seen from the foregoing description that the objects hereinbefore set forth have been accomplished and that a more efiicient switch has been invented wherein one position of the contacts is held until maximum compression has been given to the spring to throw the switch to the other contact position with greatly increased momentum, and such action results regardless of the rate of movement of the switch operating arm.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In an electric snap switch, an insulating block, a stationary electrical contact secured thereto, a rocker member pivoted on said block, a contact carried on said rocker member engageable with said stationary contact, an operating lever for rocking said rocker member to engage and disengage said contacts, and means in engagement with said member and said operating lever for producing continually increasing engaged contact pressure between initiation of contact disengagement and the instant of disengagement, upon movement of said operating lever.

2. In an electric snap switch, an insulating block, electrical contacts secured thereto, a rocking member pivoted on said block, contacts secured on said rocking member adapted to engage associated contacts on said block, means for placing pressure on engaged ones of said contacts, and operating means adapted to rock said rocking member to disengage one set of contacts and to engage another set of contacts, said operating means including said pressure applying means and arranged to produce, through said pressure applying means, continually increasing engaged contact pressure between initiation'of contact disengagement and the instant of disengagement.

3. In an electric snap switch, an insulating block, contacts secured to said block, a rocker member, contacts on said rocker member adapted to individually engage an associated contact on said block, operating means for rocking said rocker member to disengage one set of contacts and engage another set of contacts, said operating means including an arched recess in said rocker member, a roller movable from one end of said arched recess to the other end, and indentations in the ends of said recess for delaying the movement of said roller.

\ 4. In an electric snap switch, an insulating block, contacts secured to said block, a rocker member, contacts i on said rocker member adapted to engage an associated contact on said block, operating means for rocking said rocker member to disengage one set of contacts and engage another set of contacts, said operating means including an arched recess in said rocker member, a roller movable from one end of said arched recess to the other end, and spring means associated with said roller to place said engaged contacts under pressure, and indentations in the ends of said arched recess for delaying the movement of said roller and thereby increasing the contact pressure until the instant of disengagement.

5. In an electric switch, a grooved insulating block and a pivot post projecting from one face thereof, said grooves being provided with electric leads having angularly bent ends forming a pair of stationary contacts and a terminal, a rocker member and an operating arm both pivoting upon said pivot post, contacts at each end of said rocker member, a strip of conducting material bridging said second set of contacts, a leaf spring attached to said terminal and engaging said strip, an arched recess in said rocker, a roller to be actuated from one end of said arched recess to the other, a forked rod engaging said roller at one end and said operating arm at the other, a coil spring surrounding said rod and exerting pressure between said operating arm and said roller to hold said roller against said arched recess, means at each end of said arched recess tending to retain said roller at one or the other of said ends as said forked rod is swung by said operating arm.

6. In an electric switch as defined in claim 5, said retaining means at each end of said arched recess being slight indentations in the curve of the arch, said indentations'being formed by the arcs of circles with radii substantially equal to that of said roller.

7. In an electric switch, a grooved insulating block and a pivot post projecting from one face thereof, said grooves being provided with electric leads terminating in a set of stationary contacts and a terminal, a rocker member and an operating arm both pivoting upon said pivot post, contacts at each end of said rocker member, electrical connection between said terminal and said second mentioned contacts, an arched recess in said rocker, a roller to be actuated from one end of said arched recess to the other, connecting means including a compression spring between said operating arm and said roller, means consisting of indentations at the ends of said arched recess tending to retain said roller at one end or the other of said ends as the position of said connecting means is changed.

8. In a snap switch, a pair of stationary contacts, a rocker member, a pair of movable contacts one at each end of said rocker member, electrical connection between the last two mentioned contacts, means to rock said rocker member to cause one or the other of its contacts to engage one or the other of said stationary contacts, said means comprising a roller engaging said rocker member a spring pressing said roller against said rocker member and actuating mechanism to shift the direction of spring force on said roller, and detent means on said rocker member to prevent rolling of said roller on said rocker member during initial shifting of the direction of spring force on said roller by said mechanism.

9. In an electric switch, a grooved insulating block and a pivot post projecting from one face thereof, said grooves being provided with electric leads having angularly bent ends forming a pair of stationary contacts and a terminal, a rocker member and an operating arm both pivoting upon said post, means actuated by said operating arm to rapidly pivot said rocker member, contacts at each end of said rocker member, a strip of conducting material mounted upon a surface of said rocker and bridging said second set of contacts, a leaf spring attached to said terminal and engaging said conducting strip adjacent the pivot of said rocker to form a continuous electrical connection between said terminal and said second set of contacts as said rocker is actuated by said operating arm, said continuous electrical connection having a small amount of frictional engagement wherein enough wear is caused to keep said electrical connection clean.

10. In an electric snap switch, an insulated base structure, a plurality of stationary contacts and a terminal mounted on said base, a rocker member and an actuating arm pivotally mounted upon said base, contacts at the extremities of said rocker and movable therewith, electrical connection between said terminal and said movable contacts, a recess in said rocker having extremity portions and a continuous concave arch between said extremity portions, a roller riding in said recess, spring means between said actuating arm and said roller to thrust said roller from one end of said recess along said concave arch to the other when said actuating arm is pivoted past the center of said arched recess.

11. In an electric toggle switch, a molded insulating base block with a post projecting from one face thereof, channels in said face for mounting electric leads, a pair of contacts and a terminal integrally formed with said leads, an actuating arm pivotally mounted on said post, a raised section of said base block adjacent said post, said raised section having angular faces projecting on either side of said post and said faces being angular and displaced from one another by an amount which is the supplement of the predetermined angle of throw of said actuating arm, and switching means operable by said actuating arm to control a circuit through said contacts and terminal.

12. In a snap acting switch: a base member; a'plurality of contacts disposed on said base member; a rockable member pivotally disposed on said base member, having two spaced recesses formed therein and a third recess shallower than and connecting said spaced recesses; at least one contact disposed on said rockable member and in continuous electrical conductive engagement with one of said plurality of contacts and adapted to engage with another of said plurality of contacts when said rockable member is rocked from a first position to a second position; resiliently biased actuating means having a portion engaging said rockable member in one of said spaced apart recesses when the rockable member is in said first position and adapted to pass over said shallower recess to rock said rockable member to said second position and to engage in the other of said recesses when said actuating means are actuated.

13. In a snap action switch as set forth in claim 12, wherein said base member comprises a dielectric material having a face with grooves formed therein to receive said plurality of contacts and having a raised portion cooperating with said actuating means to limit its actuating movement.

14. A snap action switch as set forth in claim 12, wherein said rockable member comprises a dielectric material having an arched recess in one side thereof with deeper arcuate recesses at either end of the first mentioned recess.

15. A snap action switch as set forth in claim 14, wherein said portion of the actuating means is a roller and said arched recess forms a track whereby the roller is guided from a position in one of said deeper recesses to a position in the other of said deeper recesses.

16. In a telegraph machine of the type having a tape reel for holding a tape, the improvement consisting of: means for indicating the condition of the tape reel, said means comprising; a lever member cooperating with the tape wound on said reel and positioned in relation to the amount of tape on the reel; an electric indicating circuit including a snap switch comprising an insulating block, a stationary electrical contact secured thereto, arocker member pivoted on said block, a contact carried on said rocker member engageable with stationary contact, an operating means for rocking said rocking member to 8 engage and disengage said contacts including means for increasing the contact pressure until the instant of disengagement; connecting means between said lever member and said operating means to actuate said indicating circuit when the tape on the reel reaches a predetermined position.

17. A telegraph machine tape reel condition indicating device comprising: means cooperating with said tape reel to determine the condition of the tape; a positive snap-action switch having a spring actuated movable contact, a stationary contact and an operating arm that can he slowly repositioned almost the extent of its travel prior to switch actuation with means between said arm and said movable contact to increase contact pressure until actual switch actuation occurs, structurally cooperating with and positioned by said means; and an indicating circuit controlled by said switch.

18. In an apparatus having a slowly changing condition,'the improvement comprising: first means responsive to said slowly changing condition; a snap-switch includ ing an operating arm, circuit making contacts, and means actuated by said arm to increase contact engaging pressure as said arm is slowly moved from one position to approach a second position and to rapidly separate said contacts just prior to said arm reaching said second position; said arm being engaged by said first means to be slowly moved toward said second position by said switch lever in accordance with said slowly changing condition.

19. In a snap-action switch having a rocker contact member with a biasing spring track therein and a movable biasing spring having one end guided in the rocker member track, the improvement comprising: means at an end of said track for preventing the guided end of said spring from moving along said track until a component of the spring force is acting on the guided end of said spring in a direction to force it along the track.

20. In a snap acting switch, an actuating member and a member-to-be-actuated each pivoted about an axis for movement between predetermined limit positions, a spring compressed between opposed portions of said members, the end of said spring remote from the pivot axis of said actuating member being pivoted on said actuating member, the other end of said spring, adjacent the axis of said member-to-be-actuated, being mounted for movement in a predetermined path relative to said memberto-be-actuated between predetermined limit positions in which the respective lines of action of the force exerted thereby are directed on opposite sides of the pivot axis of the member-to-be-actuated, said predetermined path of movement of said other end of said spring being such that movement of, said actuating member between its said limit positions is effective to further compress said spring until the line of action of the force exerted thereby reaches a predetermined critical position, and means so locating the critical positions of the line of action of the force exerted by said spring that as said spring approaches said critical position the spring becomes so positioned relative to said members that the force exerted thereby contains a component of gradually increasing magnitude so directed as to impart movement to said spring other end toward its opposite limit position.

21. A snap acting switch comprising: a stationary contact and a movable contact; an actuating member and a rocker member each pivoted about an axis for movement between predetermined limit positions, and said rocker member carrying said movable contact and causing said contacts to engage when in one of its limit positions and to be disengaged when in the other of its limit positions; a spring compressed between opposed portions of said members; means pivotally retaining one end of said spring on a portion of said actuating member remote from its said axis; means guiding the other end of said spring on said rocker member for movement in a predetermined path between predetermined limit positions on said rocker member, said predetermined path of movement of said other end of said spring being such that movement of said actuating member between its said limit positions is effective to further compress said spring until the line of action of the force exerted thereby reaches a predetermined critical position; and means so locating the critical positions of the line of action of the force exerted by said spring that as said line of spring action approaches said critical position the spring becomes so positioned relative to the members that the force exerted thereby contains a component of gradually increasing magnitude so directed as to impart movement to said other end of the spring toward its opposite limit position on said rocker member to thereby pivot said rocker member from one limit position to the other limit position.

22. A snap acting switch comprising: a stationary contact and a movable contact; an actuating member and a rocker member each pivoted about an axis for movement between predetermined limit positions, said movable contact being disposed on said rocker member for engagement or disengagement with said stationary contact dependent upon the limit position of said rocker member; an arched recess portion of said rocker member facing toward a portion of said actuating member ofiset from its pivot axis with an indentation at each end of said arched recess; a spring compressed between said portions of said members; means pivotally retaining one end of said spring on the oifset portion of said actuating lever; and means on the other end of said spring shaped to fit in said indentations and guided for movement along said arched recess from one indentation to the other, said other spring end when at an end of said arched recess being retained at that end during actuation of said actuating member to move said pivoted end of said spring to a critical position from one of the actuating member limit positions during which movement said spring is further compressed and its line of force is so directed to increase the force maintaining the rocker member in one of its limit positions and at said critical spring position a component of the line of spring force becomes so directed to move said other end of the spring from the indentation at said end of the arched recess and along said arched recess to the other indentation whereupon the line of spring force is abruptly shifted to rock the rocker member to its other limit position.

References Cited in the file of this patent UNITED STATES PATENTS 1,239,275 Keen Sept. 4, 1917 1,343,676 La Montaine June 15, 1920 1,619,148 Miller et al. Mar. 1, 1927 1,799,099 Johnson Mar. 31, 1931 1,838,944 Ives Dec. 29, 1931 1,858,242 Hodgson -1 May 17, 1932 2,015,399 Grothe Sept. 24, 1935 2,095,174 Douglas Oct. 5, 1937 2,174,232 Baker Sept. 26, 1939 2,252,853 I Hoover Aug. 19, 1941 2,359,724 Fried Oct. 3, 1944 2,377,134 Dietrich May 29, 1945 2,400,984 Dyer et al May 28, 1946 2,550,623 Teruzzi Apr. 24, 1951 FOREIGN PATENTS 536,611 France Feb. 15, 1922

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