US2813447A - Vibrator exciting action - Google Patents

Description

Y Nov. 19; 1957 B. F. MlEss'NER 2,813,447

l vIBRAToR EXCITING ACTION Filed Aug. 26, 1955 I -8 ad 7 E; l. Arm sys atent @ffice 2,813,447 Patented Nov. 19, f9.5??

visitaron axcrrrNG ACrioN Eeniamin F. Miessner, Harding Township, Morris County, N. J., assigner to Miessner Inventions, Inc., Harding ovvnship, Morris County, N. J., a corporation of New ersey Application August 26, 1953, Serial No. 376,543

13 Claims. (Cl. 845-236) This invention relates to musical instruments of the type wherein tuned vibrators are impulsively excited by mechanical means, and more particularly to key-actuated vibrator exciting actions of novel construction affording touch-responsive control of the vibrators vibration amplitude and including simple and improved means for preventing spurious excitation of the vibrator.

Striker mechanisms of the type contemplated by this inention are generally known as piano actions but the use herein of this or similar terms is not to be construed as limiting the scope or application of the novel mechanisms disclosed. Such an action must perform three functions, namely (1) to convey to the striker or hammer a motion which shall carry it toward the vibrator for the purpose of inflicting a blow thereon, (2) to release the hammer just before its actual contact with the vibrator so ythat it may instantly rebound without blocking the vibration and without re-rebounding to deliver any second, unintended blow, and (3) to permit the repetition of the hammer blow upon re-operation of the key without a complete release thereof from a prior operation. Standard actions for performing `these required functions are of relatively great cornplexity in that they require the use of a sensitive escapement mechanism anda complicated assembly of adjustable tensioning and motion-limiting devices, all delicately balanced to respond to a relatively weak key operation yet sturdy enough to withstand the effects of strong blows applied to the key.

In my United States Patents Nos. 2,469,568, 2,594,967, 2,533,830 and 2,535,503 I disclose key and hammer arrangements wherein the hammer is driven directly by the key and wherein unwanted multiple striking of the vibrator in response to a single operation of the key is avoided by suitable devices which absorb the energy of the hammer after it contacts and leaves the vibrator, yet which leave the hammer quite free for repetitive use. It is an i object of this invention to provide improvements and simplications of such actions as are disclosed in those patents.

It is an object to provide a generally improved keyoperated vibrator-exciting action. It is a further object to provide ya generally simplified such action.

it isa more specic object to provide improved `and simplified arrangements for the absorption of the energy of the rebounding hammer.

Other and allied objects will more fully appear from the following description and the appended claims.

ln the description of my invention hereinafter set forth reference is had to the vaccomuna-Dying drawings, of which:

.Figure 1 is a longitudinal sectional view showing a conventional piano key in its normal position;

Figure 2 is a view similar to Figure 1 but showingfthe position of the key relative to the balance-rail pin when the forward end of the key has been struck with considerable force;

Figure 3 is alongitudinalsectional view of an action in accordance with the present invention, including a showing of the hammer and, by way of example, a vibrator in the form of a tuned reed;

Figure 4 is a fragmentary plan View of the central portion of the key;

Figure 5 is an elevation, drawn to an enlarged scale, of the balance-rail pin;

Figure 6 is a view similar to Figure 3 but showing the key in its depressed o r operated position; and

Figures 7 kand 8 are fragmentary longitudinal sectional views of another embodiment of the invention showing the key in the normal and operated positions, respectively.

Reference is now made to Figure 1 which shows a base or key-frame 5 carrying a rear-rail cloth 6, ka balance rail 7 supporting a fulcrum pad 8, a balance-rail pin 9, a front-end guide pin 10 and a down-stop pad 11. The playing key 12 is provided with a tapered hole 13 affording pivotal movement of the key about the balance-rail or guide pin 9, with a guide slot 14 cooperating with the pin 10, and with suitable weights 15. A conventional top piece 16 is carried by the upper surface of the key and includes a tapered hole aligned with the similar hole 13 of the key proper. The mechanism thus far described is of conventional construction and the key is shown in its normal or at-rest position, to which it is gravity-biased by the weights 15.

I have found that a playing key such as above described having a static unbalance of 1 to 3 ounces in favor of the rear end will jump up along the guide pin 9 when struck at its front or playing end. This jumped-up position of the playing key is shown, on an exaggerated scale, in Figure 2. Actually the key 12 jumps out of Contact with the fulerum pad 8 a distance dependent on the striking velocity imparted to the front end of the key by the finger of the performer. Such key jump is brought about by the momentum or inertia of the upwardly Amoving rear end of the key, and the key will drop back into Contact with the fulcrurn pad 8 in response to gravity, or to gravity augmented by the downwardly acting force of the hammer when the hammer is thrown back bythe vibrator in rebound therefrom. I have found, however, that with no hammer present to Vaid in restoring the key into contact with the pad 8, and with a maintenance of strong fiuger pressure on the outer tip of the key, the key can be retained in its raised position out of contact with the fulcrum pad. A considerable and abnormal continuing pressure on the key is required so to hold up the rear end of the key because a new fulcrum is now in effect, namely of the down-stop pad 11 that is spaced only about onehalf inch in from the front end of the playing key. Dynamically, the performers finger, being more or less stiflly coupled to the mass of the playing hand and forearm by the tension of the various involved muscles, always relaxes to some extent after it has struck the key and while it retains the key in the depressed or operated position. Once the desired initial velocity has been imparted to the playing key the maintenance of the initial high nger tension is no longer required and, in fact, would be unduly tiring. As a result of this relaxation of finger tension, the playing key drops back into contact with its normal fulcrum and thereafter yonly a relatively small finger pressure is required to overcome the key unbalance arising by reason of the weight carried by the inner end of the key.

In one of its aspects the present invention utilizes the dynamic, or jump, characteristic of the playing key to absorb the energy of the rebounding hammer, and thereby to suppress re-rebounding tendencies Without need of conventional complicated escape mechanisms and associated tensioning and motion-restricting devices.

Reference is now made to Figure 3 which is a longitudinal sectional viewsimilar to vFigures 1 and 2 and including a hammer and vibrator. The base or key frame Ztl carries a rear-end stop pad 21, a balance rail 22 supporting the fulcrum pad 23, a balance-rail pin 24, a front-end key guide pin and a front down-stop pad 26. These parts correspond to the similar parts of the conventional key arrangement shown in Figures l and 2. in order to achieve the full object of my novel design i have secured to the base 20 an intermediate fulcrum rail 27 carrying the fulcrum pad 28 and positioned somewhat rearwardly from the rear end of the finger-contacting surface 30 of the playing key. The full purpose of the added fulcrum rail and pad will be apparent as the description proceeds.

The playing key K is provided with a metal member 31 that carries a pad 32 preferably of an anti-rebound or energy-absorbing nature (though it is to be understood that it is not upon this element that any primary reliance is placed for the suppression of re-rebounding tendencies according to the present invention), the member 31 being secured to the playing key as by the screw 33 and resting on the down-stop pad 21 when the key K is in its normal position as shown in Figure 3. 31 may provide the normal unbalance of the key or, alternatively, the key may be provided with an additional conventional balance weight 15 for this purpose. The balance-pin hole 35, passing transversely up and down through the key K, is circular at the bottom and rectangular at the top surface, as shown in Figure 4, in order to provide ample space to the front and rear of the guide pin 24 for the required angular movement of the key about the intermediate fulcrum pad 28. The rectangular sides of the hole 35 are covered with a thin felt cloth, as is common practice in this art, such cloth extending through the top piece 36. A novel element P, in the form of a thin friction pad, is cemented to the rear wall of the hole 35 for purposes described in detail hereinbelow.

Except for the supplementary fulcrum pad 28 and the friction pad P, the structure described to this point is conventional, the member 31 being used for convenience both to provide the rear-end static weight for the playing key and to permit lowering of the key-drive point for the hammer, the latter being desirable to reduce the overall height of the instrument when tuned reeds are employed as vibrators. The pad P may be made of a tough frictional material such for example as felt or leather impregnated with a stable, somewhat sticky Visco-elastic resin, vinylite plastic of a soft rubber-like consistency, or the like.

Positioned to the rear of the playing key is a rail 4@ secured to the base 20 in any suitable manner, and a hammer flange 41 is secured to the rail 40 as by the screw 42. A hammer butt 43 is pivotally attached to the flange 41 by a felt-bushed pin 44 and has secured thereto the hammer stem 45 that carries the felt-covered hammer head 46 adapted to strike the vibrator here shown as a tuned reed V.

The supplementary fulcrum pad 28 is of such height that when the key K is bottomed on the down-stop pad 26 the pad 28 forms the effective key fulcrum and the key will be raised up off the pad 23 by a maximum separation of about 1/16 to 1A; of an inch, at which point the friction pad P will be pressed against the adjacent surface of the guide pin 24. In this position, as shown in Figure 6, the frictional engagement between the pad P and the pin 24 is sufiicient to retain the key removed from the pad 23 with relatively low finger pressure maintained on the finger surface 30 of the key. The circular grooves in the upper portion of the guide pin 24, as shown more clearly in the elevational View of Figure 5, may be provided to increase the effectiveness of the frictional engagement. The pin 24 is preferably bent forward slightly, as shown, for best operation.

Of course, upon the release of finger pressure on the front end of the key the key will rotate in a counterclockwise direction as seen in the figures, iirst on the fulcrum pad 28 and then on the fulcrum pad 23, as a Such member result of gravity and will come back to rest on the rear down-stop pad 21, as shown in Figure 3.

The extent of the up-jump of the center of the key, away from the pad 23, is determined by the key velocity when struck. The initial movement of the key is purely angular about the fulcrum pad 23, as is the case when the outer end of the key is depressed slowly. However, with increasing velocity of key depression the key develops increasing kinetic energy or momentum which causes its center to slide vertically up on the guide pin 24 after the pad P has come into contact with the pin. Such sliding contact, under pressure, between the pad and the pin frictionally retains the key in the raised position which it reaches until the key is released by a release of finger pressure thereon, or until the key is forced back into Contact with pad 23 by a force applied thereto by the hammer as it rebounds from the vibrator V.

The adjustments of the lever arm of the hammer butt, the arc of travel of the hammer head, and the extent of key depression are such that when the extension plate 31 has reached its maximum uppermost position (such as achieved by removing the hammer butt 43 from contact with the plate 31 and applying a maximum striking force to the front end of the key) the head of the hammer will be spaced from that position of the vibrator which corresponds to the maximum vibration amplitude, as shown by the dotted line Va in Figure 6. Thus there can be no blocking of the vibrator Vibrations by repeated actuations of the hammer. If desired, the maximum angular rotation of the key K under any conditions may be defined by a resilient pad 50 spaced from the upper surface of the key and carried by a rail 51 disposed transversely across the entire complement of playing keys.

As shown in Figure 3 all parts are in the normal at-rest positions with the key unoperated. The arc a indicates the path of travel of the hammer head; the point X indicates the position of the hammer-head felt covering when the key has been depressed slowly into contact with the fulcrum pad 28, and the point Y indicates the approximate position of the hammer-head felt covering when the key has been forcefully bottomed at high keydepression velocity on the down-stop pad 26, in each case before the hammer butt has yet left contact with the pad 32.

The maximum reed-vibration amplitude in the direction of the hammer head is shown by the dotted line Va. Thus in the actual dynamic operation of the device when the key is struck and held down on the pad 26 the hammer is directly driven toward the vibrator by reason of the physical contact between the hammer butt 43 and the pad 32 carried by the plate 31. Even assuming a high-velocity operation of the key, such direct driving of the hammer takes place only until the front edge of the hammer head reaches the point Y on the arc a, by which time the center of the playing key has jumped out of contact with the normal fulcrum pad 23 and is frictionally held in raised position by the action of the pad P against the guide pin 24. Now the hammer flies toward the reed under its own momentum and strikes the reed, defiecting it to the leftshown dotted-line position. At this point all of the hammers kinetic energy has been conveyed to the reed, where it is stored momentarily by the reeds compliance.

Then the reeds compliance drives the reed and hammer toward the right as illustrated, at about the same velocity as the original hammer-striking velocity against the reed, until the reed reaches its extreme right-shown deflection, following which the reed leaves the hammer head to repeat the reed-vibration cycle as a free vibrator. The hammer now flies in a clockwise direction as illustrated until the forward tip thereof reaches the approximate point e. g., Y) at which the hammer butt left contact with the pad 32 during the driving of the hammer by the key, whereupon the butt again comes into contact with that pad. When `such contact is re-established the entire key K is `forced downwardly against the frictional resistance provided between the pad P and the guide pin 24, as well as against the compliance of pad 28, so that the kinetic energy of the clockwise-dying, or rebounding, hammer is principally transferred to the key, from which it is in turn absorbed by the friction attendant on the movement of the pad P along and in contact with pin 24. Therefore the hammer butt, after having forced the key back into its normal contact with the fulcrurn pad 23, comes to rest on the pad :t2-even though that pad remains raised as a result of continued depression of the front end of the key by the player-without appreciable tendency to rerebound from the pad 32 toward the reed.

The arrangement is so completely eiective that extremely highvelocity key depressions such as may be produced by striking the key with the players closed iist, followed by key hold-down, cause no spurious contact with the vibrator even with a hammer of conventional weight. It may further be pointed out that the tendency of the front end of the depressed key to raise slightly as the rebounding hammer drives the center of the key downwardly into contact with the fulcrum pad 23 (which tendency may be minimized by suitable choice of the characteristics of the fulcrum pad 23) have proven unobjectionable.

Since the construction includes no hammer spring the action is extremely sensitive to low-velocity key depressions. When the key is bottomed at low velocity with continuing low pressure on the pad 2d, the hammer stern is substantially in a vertical position so that a very low velocity of angular motion suffices to carry the hammer over its gravitational `dead center into contact with the vibrator. Such spring-free construction is not to be construed as limiting, as it is apparent that if the pivoted hammer device is of light construction a weak spring, biasing the hammer device in a clockwise direction, may be used, if desired, to increase the repetition speed of the action.

Since there is no escapement mechanism (which in conventional actions requires the key to move upward to about 2/3 of its depth of depression before the jack can again engage the hammer), the hammer is always in operative association with the playing key, which provides for fast repetition by a Very shallow release of the key from its down, or operated, position.

lt may here be pointed out that the fulcrum pad 23 may advantageously be made of a Visco-elastic material with a high viscosity factor and only enough elasticity to cause a very slow recovery from its deformed state (here compression) compared, for example, with rubber or felt.

It will be noted that the playing key has freedom of angular rocking movement about the pad 23 within the elastic limits provided by the pads 2l, 23, 28 and 26, `and by the pad P in cooperation with the pin 24. lt will also be noted that there can be only an insignificant longitudinal motion of the playing key due to the close t of the lower end of the hole 3S about the guide pin 24. Also, the motion of the friction pad P, so long as the key remains in Contact with the fulcrum pad 23, is almost wholly horizontal since that pad is then the center of its rocking action.

The normal spacing of the pad P from the adjacent side of the pin 24 is such that the pad contacts the pin when the key bottoms initially on the pad 28. As the pad 28 is compressed more and more by thc key K the friction pad P is compressed more and more against the pin 24. Under the increasing momentum developed in the rear end of the key by the increasingly forceful key blows the key climbs up more and more along the pin 24-and remains in its position of highest climb, with only a small key-holding down-pressure, until the hammer drives it back down into Contact with the pad 23. rl`he absorption of the rebound energy of the hammer is, therefore, selfadjusting. For a weak key blow the key rises but little from the fulcrum pad 23, and the weak energy of the hammer rebounding from the vibrator is absorbed by the friction attendant on driving the key back this relatively small distance. For stronger and stronger key blows, with their increasing hammer velocities, the key automatically rises higher and higher from the pad 23, and for the resulting higher and higher hammer-rebound energies there is automatically available the friction attendant on driving the key back through greater and greater distances. In other words the hammer-rebound energy varies directly with the force of key depression, and that force has automatically set up a potential energy-absorbing power of likewise varying magnitude to absorb that energy. It will thus be clear that the rebound-energy absorption of an action according to the invention is fully effective at all keyoperation velocities.

While I have shown a conventional playing-key construction in the Figures 3-6 embodiment of the invention I do not intend this as a limitation. For example, the front guide pin 26 may be xed in the key K rather than in the base Ztl in which case the cooperating felt-hushed hole would be formed in the base. Likewise the guide pin 24 may be fixed in the key in which case the slot for this pin and the friction pad P would be located in the base. Also, the playing key may be biased downwardly on its rear end by a suitable spring.

lt may be mentioned that the Visco- elastic pads 32, 23 and 255 should have a high viscosity yet these should not be subject to cold ilow. The latter consideration tends to be most important with respect to the pads 32 and 23 which normally carry the downward pressures of the hammer and key, respectively.

Reference is now made to Figures 7 and 3 for a description of another embodiment of my invention. In Figure 7 the playing key is shown in its normal at-rest position. Here a wood rail 6G, spaced from the key, is suitably disposed in fixed position and extends transversely across the keys, one face of the rail being serrated, if desired, as shown. A bendable wire rod 6i is secured to and eX- tends upwardly from the key, the rod carrying a wood head 61a that is covered with a friction material such as the leather 62. When the playing key is in the normal position the hammer butt 43 rests upon the Visco-elastic pad 63 that is cemented to the reduced-thickness rear end of the key. As explained hereinabove, when 'the outer end of the playing key is struck the central portion thereof moves upwardly along the guide pin 2d. Such rocking and upward movement of the key brings the friction member 62 into contact with the surface of the rail 6b, as shown in Fioure 8. The sliding frictional pressure between these members is suiicient to retain the key in its raised position as long as the forward end of the playing key is retained in depressed or operated position. When the finger pressure on the forward end of the key is released the key drops back to its original, normal position. When, however, the key is struck vigorously, and retained in depressed position as by a reduced finger pressure, the key is returned into contact with the pad 23 by the rebounding hammer butt. The energy of the rebounding hammer is absorbed analogously to its absorption in the case of the earlier embodiment, excepting that the interengageable frictional energy-absorbing elements are now the members 6b and 62 instead of the members P and 24 of the earlier embodiment.

The rod dll may be somewhat elastic, yet bendable, for adjusting the relationship between the friction material 62 and the rail 6i?, somewhat in the nature of the normal adjustments of the back-check device used for cooperan tion with the tail of the hammer in conventional piano actions.

it may here be pointed out that in the illustrated embodiments of the invention the pad 2S, serving as a second fulcrum for the playing key upon `a predetermined rotation of the key, is positioned to the rear of the playing key surface 30. Thus linger pressure applied at the rearrnost extremity of the surface 3i) will still hold the center of the playinU key spaced from the primary luicrum formed by the pad 23, so that the frictional engagement and relative movement of the pad P and pin 24 in the first embodiment, and of the material 62 and rail 60 in the second, are effective for their described purposes regardless of the actual point of contact of the performers finger on the playing key surface 3ft.

it will be appreciated that in both the illustrated embodiments of the invention the rear portion of the key may be considered as an element moved by the key to a certain position (that occupied by the key when on a very slow depression or operation of the key it has just contacted the front downstop Z6, at which time the hammer-head surface will have arrived at a certain point between X and Y on the arc a), beyond which that element is subject to further displacement in response and in proportion to its own inertia acquired during key op eration, and from which further displacement it tends to be restored by the rebounding hammer coupling thereto or impinging thereon. It will further be appreciated that in the first embodiment the members P and 24, and in the second embodiment the members 6@ and 62, may be considered as a brake connected with the inertia element and effective thereon at least throughout the time the key remains depressed-this brake being then effective (a) on the further displacement of that element to retard and limit that displacement, (b) on that element to maintain that further displacement which it attains, and (c) on the restoration of that element, from that further displacement, by the hammer in its rebound from the vibrator.

lt will further be appreciated that the provision of the second fulcrum 2S for the key results, late in the downstroke or operation of the key, in an alteration of the leverage which the operated, or front, end of the key exerts Aon the hammer-operating rear end of the key. This, both in connection with and independently of the rebound-energy-absorption function hereinabove detailedly described, is a feature of utility. ln itself, it provides an increase in acceleration of the hammer on stronger key blows, thereby tending to increase the range `of velocities with which the hammer may be propelled into contact with the vibrator -by key depressions confined within a given range of velocities.

This application is a continuation-in-part of my co pending application Serial No. 292,096, filed lune 6, 1952, and entitled Vibrator Exciting Action now forfeited. Further, the invention herein disclosed has certain features in common with the invention disclosed in my co-pending application Serial No. 291,830, filed i une 5, 1952, and similarly entitled, now U. S. Patent No. 2,767,608, dated October 23, 1956.

While I have disclosed my invention in terms of particular embodiments thereof, l intend no unnecessary limitations thereby. Modifications in many respects will be suggested by my disclosure to those skilled in the art, and such modifications will not necessarily constitute departures from the spirit or scope of the invention, which I undertake to define in the following claims.

I claim:

l. A vibrator-exciting action operated by a limitedly movable key, said action comprising a pivoted hammer moved by the key to strike the vibrator and rebound therefrom, and frictional resistance means for dissipating the rebound energy of the hammer, said frictional resistance means comprising a first member carried by the playing key, and a second member fixed in spaced relationship to the key and the first member, one of said members having a relatively high coefficient of resistance and the two members being adapted for sliding pressure contact to an extent depending on the velocity of key movement.

2. A vibrator-exciting action operated by a limitedly movable key and comprising a pivoted hammer moved by the key to a relatively small spacing from the vibrator and thereafter moved by its Vown momentum to strike the vibrator and rebound therefrom through said spacing, and frictional resistance means to vary the said spacing in accordance with the motional velocity of the key and to dissipate the rebound energy of the hammer, said frictional resistance means comprising a fixed member spaced from the key and a second member carried by the key and normally spaced from the first member, one of the said members having a high coefficient of friction and the two members being adapted for sliding pressure contact that varies directly with the velocity of key movement.

3. A vibratoreexciting action comprising a playing key, pivot means supporting the key for rotational movement in response to a relatively weak depression force applied to the front end of the key, means effective to space the key from the pivot means when the depression force applied to the front end of the key exceeds a predetermined magnitude, frictional resistance means retaining the key in said spaced position while the front end of the key remains depressed, and a pivoted hammer actuated by the rear end of the playing key to strike the vibrator and rebound therefrom.

4. The invention as recited in claim 3, wherein the said frictional resistance means comprises a guide pin passing through a transverse hole in the key and a pad of material having a relatively high coeflicient of friction secured within said hole and normally spaced from said pin.

5. The invention as recited in claim 3, wherein the said frictional resistance means comprises a fixed member normally spaced from the key and a member secured to the key, one of said members having a relatively high coefficient of resistance.

6. The invention as recited in claim 3, wherein the means effective to space the key from the pivot means comprises a stop pad limiting the movement of the key front end and said stop pad is disposed between the said pivot point and the front edge of the key.

7. The invention as recited in claim 3, including a stop pad limiting the downward movement of the front end of the playing key, and a fulcrum pad disposed between the said pivot means and the stop pad, said key contacting the fulcrum pad as the key rotates about the pivot means in response to the depression force.

8. A vibrator-exciting action comprising a playing key, a first fulcrum supporting the playing key at a point intermediate of the ends of the key; a second fulcrum disposed between the first fulcrum and the front end of the key, said second fulcrum being effective to space the key from the first fulcrum a distance depending upon the magnitude of a depression force applied to the front end of the key; friction means ineffective as the key rotates about the first fulcrum and effective to retain the key spaced from the first fulcrum when the key rotates about the second fulcrum; and a pivoted hammer moved by the rear end of the key to a relatively small spacing from the vibrator and thereafter moved by its own momentum to strike the vibrator and rebound therefrom through said spacing.

9. The invention as recited in claim 8, including a stop pad limiting the downward movement of the front end of the playing key and means restricting lateral movement of the playing key relative to the first fulcrum.

l0. In a system having a Vibrator and a vibrator-exciting action therefor comprising a hammer and a key for propelling and receiving the rebound of the hammer, said key having hammer-engaging means, finger-engaging means and intermediate pivot means on which said key normally rests, the improvement comprising a fulcrum means intermediate said intermediate pivot means and said finger-engaging means, said fulcrum means being spaced below the bottom of said key when said key is in rest position and forming a substituted pivot means about which said key pivots when said finger-engaging means has been depressed at relatively high velocity.`

11. The improvement claimed in claim 10, further including an element coupled to the key, and a stationary member positioned to be engaged and frictionally moved against by said element during pivoting of said key about said fulcrum means.

12. The improvement claimed in claim 10, further including means comprising cooperating elements, one coupled to the key and the other fixed in stationary position, for damping the pivoting of the key about said fulcrum means.

13. The improvement claimed in claim 10, further including means rendered eective by the pivoting of the key about said fulcrum means for dissipating the energy of the rebounding hammer.

References Cited in the tile of this patent UNITED STATES PATENTS 115,782 Steinway June 6, 1871 2,505,806 Stein May 2, 1950 2,535,503 Miessner Dec. 26, 1950 FOREIGN PATENTS 21,993 Great Britain Oct. 27, 1913 230,390 Great Britain Mar. 12, 1925

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