US2720613A

US2720613A - Switching systems for lighting control boards

Info

Publication number: US2720613A
Application number: US309542A
Authority: US
Inventors: Lustig Edgar
Original assignee: Century Lighting Inc
Current assignee: Century Lighting Inc
Priority date: 1952-09-13
Filing date: 1952-09-13
Publication date: 1955-10-11
Anticipated expiration: 1972-10-11

Description

Oct. 11, 1955 E. LUSTIG SWITCHING SYSTEMS FOR LIGHTING CONTROL BOARDS Filed Sept. 13, 1952 2 Sheets-Sheet l (Ittorneg Oct. 11, 1955 E. LU-STI G SWITCHING SYSTEMS FOR LIGHTING CONTROL BOARDS Filed Sept. 13, 1952 2 Sheets-Sheet 2 Snnentor EDGAR LusT/e Qttorneg United States Patent Ofiice SWITCHING SYSTEMS FGR LIGHTING CGNTROL BOARDS Edgar Lustig, New York, N. Y., assignor to Century Lighting, Inc., New York, N. Y., a corporation of New York Application September 13, 1952, Serial No. 3,54-2

7 Claims. (Cl. 317-99) This invention relates to switching systems for lighting control boards of the type employed in theaters and television studios.

These boards are constructed to supply power to a very large number of lighting loads which customarily are not utilized all at once. Ordinarily the intensity of lighting is controlled by varying the voltage applied to the loads and for this purpose voltage regulators of different kinds are employed. Since all the loads are not simultaneously energized and since voltage regulators are expensive, the number of regulators almost invariably is less than the number of lighting loads. However, since it is desirable to be able to regulate substantially any of the loads when and as required and since on occasion a special voltage regulator may be needed for one or more loads, the voltage regulators and loads should be capable of any desired type of interconnection; i. e. it should be possible to con nect any one of the voltage regulators to any one or more of the loads. Lighting boards of the type to which the present invention basically relates are employed as a switching element for the foregoing purpose.

At the present time two types of lighting boards are conventionally employed, these being the jack-and-plug board which resembles a PX telephone switchboard, and the rotary selector board.

In the jack-and-plug board each voltage regulator is connected to several different jacks and each load is connected to a different plug so that the plug of any selected load can be inserted in the jack of any selected regulator. Although this type of board is quite compact, is relatively inexpensive and is speedy in operation the cords are prone to tangle and become extremely confused. Moreover, a plug can be inserted or withdrawn from a jack while the load is drawing current thereby creating undesirable and dangerous arcing. In addition a jack-and-plug board has high voltage elements accessible, although with difficulty, from the front of the board so that a careless operator can injure himself.

The rotary selector type of board eliminates the tangling of cords, the opening and closing of circuits under load and the placement of live elements in operator-accessible locations. However, it is quite large, is relatively expensive and is slow in operation.

Neither type of board gives a clear cut, quickly cognizable, visual indication, other than physical location of the plugs and physical orientation of the handles, of the set-up of the board at any given instant.

It is an object of the present invention to provide a lighting control board having the advantages of the jack and plug and rotary selector, but the drawbacks of neither.

More specifically it is an object of the invention to provide a lighting control board of the character described which is compact and inexpensive, does not open and close the control board contacts under load, has no confusing array of elements such as plug cords, and will at a glance indicate the switching set-up.

It is another object of the invention to provide a light- 2,720,613 Patented Get. 11, 1955 ing control board of the character described whose operation is particularly simple and can be easily and quickly mastered.

It is another object of the invention to provide a lighting control board of the character described which can be readily expanded to accommodate additional lighting loads.

It is another object of the invention to provide a lighting control board of the character described in which the movable switch elements in the board for each lighting load have a minimum of wiring, in the specific embodiment of the invention shown herein, only two wires.

It is another object of the invention to provide a lighting control board of the character described which cannot be manipulated to short circuit or cross phase through the board.

It is an ancillary object of the invention to provide a multiple push button control board of such construction that all the actuated buttons can be ascertained at a glance.

Other objects of the invention will in part be obvious and in part will be pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements and arrangements of parts which will be exemplified in the device hereinafter described and of which the scope of application will be indicated in the appended claims.

In the accompanying drawings in which is shown one of the various possible embodiments of my invention,

Fig. 1 is a vertical front-to-back sectional view through a lighting board constructed in accordance with the invention;

Figs. 2 and 3 are sectional views taken substantially along the lines 2-2 and 33 of Fig. 1;

Fig. 4 is a schematic wiring diagram showing the manner in which the board is connected in circuit; and

Fig. 5 is a reduced front view of said board.

Referring now in detail to the drawings, the reference numeral 1% denotes a lighting control board embodying the present invention. In general said unit comprises a stationary rack 12 and a plurality of vertically elongated narrow push button switching sub-assemblies 14 hereinafter referred to as sticks.

The rack includes a suitable supporting frame 16 whose front is covered by a face plate 18, A plurality of tracks 29 are carried on the top of the frame and a similar number of tracks 22 are located on the bottom of the frame. The tracks extend from the front toward the back of the frame, each upper track being in vertical registry with a different lower track. Each pair of registered tracks is adapted to slidably receive a different stick 14 when the face plate, which is detachably held in place, is removed.

A plurality of horizontal line buses 24 extend across the back of the frame, said buses being vertically stacked and suitably insulated as with fiber tubes 26. Each of the buses 24 is connected to the hot side of a different source of power supply, preferably to the hot side of a different voltage regulator. The number of buses therefor coincides with the number of voltage regulators available in the operation of the board 10. Each tube 26 has a plurality of forwardly extending fibrous sleeves 28 in line with the pairs of registered

tracks

20, 22. That is to say, every tube 26 has several sleeves 28, one associated with every stick 14. A contact button 30 is located in each sleeve 28, the button being electrically and physically connected to the associated line bus 24.

A plurality of vertical load buses 32 are provided, a different bus 32 being atfiliated with each stick 14. The load buses are disposed in the spaces between the vertical rows of sleeves 28. The load buses mount a plurality of contacts 34, each load contact being horizontally registered with the associated line contact 30. Thus, there is associated with each stick a vertical row of pairs of horizontally spaced

contacts

30, 34.

The frame 16 also carries a plurality of double blade sockets 36, there being one socket associated with each stick 14. Each socket is suitably supported on a mounting bracket 38 which by way of convenience is located above the line of paired contacts 39, 34 for the associated stick.

All the sticks 14 are of identical construction and accordingly only one will be described in detail.

Said stick constitutes a front retaining bar 40 and a rear retaining bar 42 which are connected at their upper and lower ends by top and

bottom mounting plates

44, 46, thereby forming a framework F on which the operative elements of the stick are supported. Said framework is slidable between any pair of registered top and bottom tracks 24), 22. If desired, suitable stops 43 may be provided to limit insertion of the sticks and suitable retaining means, for example, angle brackets 45 may be employed to removably block the front ends of the tracks and thereby lock the sticks in place against accidental shifting.

The stick also includes a plurality of switch operating means which are carried by the framework in vertical alignment. Inasmuch as all of these means are the same, only one will be described. Said means constitutes a fiat push bar 48 on whose forward end there is mounted a push button 50. The push button freely extends through a matching opening 52 in the face plate 18.

In accordance with a feature of the invention the push button includes a forward portion 54 and a rear portion 56. These portions meet at a vertical plane which lies within the face plate or forwardly thereof when the button is in its idle position and which lies in back of the face plate when the button is actuated. The rear portion 56 .is made of an opaque material and the front portion of a transparent or translucent material. Desirably the front portion is made of a water white clear material such as a synthetic resin and preferably a resin as a polyacrylic resin, e. g. methyl methacrylate, which has an edge lighting, i. e. a light piping, characteristic. A source of light such as a cold cathode tube 58 is located in back of the face plate but forwardly of the front retaining bar 40. Said tube is held in conventional sockets (not shown) supported by the stationary rack 12. One cold cathode tube is located between each pair of sticks, so that there are half as many cold cathode tubes as there are sticks.

Thus when any push button is moved from idle to actuated position, the light from the tube will shine through the button in front of the face plate so that the button seems to glow. But as long as a button is in idle position the opaque rear portion 56 will block passage of light through the face plate so that only the actuated buttons will emanate light. Desirably each button bears some identifying mark, as, for instance, a numeral which conveniently may be imprinted on the front face of the button in opaque material so that it will be clearly and distinctly visible against the transparent forward portion whether or not the button is actuated.

The front retaining bar 40 is formed with a vertically elongated slot 60 to slidably receive the push bar 48 and guide the same for front-to-back reciprocation. The rear retaining bar 42 is formed with a similar slot 62 for like reception of the push bar.

Means is included to lock any given push bar in actuated position and to release any actuated push bar as another push bar subsequently is actuated. Said means includes a vertically extending trip bar 64 having a plurality of slots 66, the upper edge of each of which constitutes a follower for slidably engaging a different push bar 48. The trip bar is guided for vertical movement by rollers 68 mounted on braces 70 near the top and bottom of the stick framework.

The portion of the push bar which extends through the trip bar has its upper edge in the shape of a sloped cam 72. The cam rises toward the front of the push bar. Thus, as the push bar is moved from idle toward actuated position it will raise the trip bar. A dwell 74 located in back of the cam 72 terminates at a notch 76. Said notch is in registry with the slots 66 when the push bar is in actuated position whereby in such position the trip bar will drop to lock the push bar and hold it locked until the trip bar subsequently is raised upon actuation of another push bar.

A helical coil spring 78 is wrapped about the push bar, being held under compression between the rear retaining bar 42 and an abutment 80 on the push bar. Accordingly, when the push bar is moved rearwardly the spring will be compressed so that when later the trip bar is raised the energy stored up in the spring will snap the push bar back to idle position. To cushion the impact of the push bar as it is released a rubber grommet 82 is secured to the push bar, being so located that the grommet will strike the front retaining bar 40 as the push bar reaches idle position.

The rear end of the push bar carries a contact supporting button 84 of electrically non-conductive material, e. g. a phenolic condensate. The button is aligned with the line and

load contacts

30, 34 associated with the push bar. Said contact includes a ledge 86 which extends rearwardly from the lower corner of the back wall of the contact button. Slidable along said ledge is an electrically conductive bridge 88 in the form, for example, of a metal strip whose lower edge slidably engages the top surface of the ledge. The bridge is provided with a central aperture 98 that slidably passes a headed post 92 extending rearwardly from the back of the contact supporting button. A helical spring 94 wrapped about the post 92 is held under compression between the bridge and the contact supporting button whereby said bridge is resiliently supported and is biased rearwardly. The bridge has mounted on it a line bridge contact 96 and a load bridge contact 98 which respectively are aligned with the line contact 30 and the load contact 34. When the push bar is in idle position the movable bridge contacts are spaced from the

stationary contacts

30, 34. When the bridge bar is moved to actuated position the movable contacts engage and thereby bridge the stationary contacts, thus connecting to a voltage regulator or other similar voltage control mechanisms, the load associated with the stick 14.

If two push bars simultaneously were actuated, two voltage regulators would be connected to the same load bus 32 and thereby cause short-circuiting or cross-phasing. Suitable means is provided to prevent such an occurrence.

Said means includes a mechanical lockout 100 which prevents more than one button 50 from being depressed at any given time. The mechanical lockout comprises a vertical elongated hollow column 102 of rectangular cross-section in which a series of slugs 104 are stacked. The front corners of all the slugs are generously rounded. The column is formed with a plurality of deep slots 106 which extend from one side across the front to the other side thereby permitting elements to be slid into the column from the front. The column is located in the stick with its front edge alongside of and near the side central portions of the contact supporting buttons 84. Each of these buttons includes a laterally extending finger 108 which preferably is formed of metal and has its base imbedded in the button. The fingers are aligned with slots 106. Thus when a push button 50 is pressed the finger 108 associated therewith will enter the corresponding slot 106-. The slugs are of such height that when all buttons are idle, the planes of abutment are aligned with the slots 106 and fingers 108. Hence when a finger enters a slot it will separate the adjoining slugs. The base of the column is closed immediately beneath the lowermost slug and the top of the column is closed a short distance above the uppermost slug. The distance between the uppermost slug and the top closure for the column is less than the height of two fingers 108. Accordingly, if one finger has been inserted in the column there will be insuificient space for the Slugs to separate enough to permit insertion of a second finger.

Although manipulation of the board by means of the push buttons isolates the high voltage from the operator, nevertheless it is desirable for the purpose of fire prevention and maintenance to prevent opening and closing of the high voltage, high amperage contacts in open air, i. e. to prevent hot patching. This is accomplished in the present board, that is, cold patching is achieved, by providing a switch which, each time a button is depressed, opens an enclosed contactor series-connected in the load circuit, there being one such contactor for each stick.

More specifically, I mount on each stick a snap action momentary switch 110 such as a Micro or Mu switch. Conventionally this switch has a pair of terminals 112 which run to contacts C located within the switch casing. The switch is normally closed, that is to say, when the switch is idle the contacts connected to the switch 112 are in engagement. When the switch is actuated the contacts are spaced apart. Standard actuating means for said switch constitutes a small pin 114 which extends through a side of the casing. Depressing the pin actuates the switch and causes the terminals 112 to be disconnected within the casing. As soon as pressure is removed from the switch the pin will spring out again and cause the contacts to be reclosed.

A yoke 116 is mounted on the switch casing near the pin 114. A spindle 118 extends between the arms of the yoke. Journalled on the spindle is a control lever 120. A torsion spring 122 presses one end of the lever against the tip of the pin 114 with sufiicient pressure to actuate the switch, i. e. to open the contacts within the casing. In this manner I convert the switch from a normally closed switch to a normally open switch. That is to say when the control lever 12% is idle the switch contacts will be open, being maintained open by the spring 122. However, when the far end of the control lever is depressed (moved towards the switch casing) the action of the spring 122 is neutralized. Thereupon the pin 114 will move away from the casing and the contacts within the casing will close to connect the terminals 112.

The far end of said control lever is located directly above the top of the trip bar 64. It now will be appreciated that depressing any one of the buttons 56 raises the trip bar and closes the contacts of the switch 110.

To simplify wiring, the switch 110 is connected to the switching circuit by a mechanism which permits the stick to be inserted in or withdrawn from the supporting framework without wiring the switch up each time the stick is inserted or disconnecting the wiring each time the stick is withdrawn.

Said means includes the double blade socket 36 hereinbefore described and a two prong plug 124 carried by the stick in position to be inserted in the socket when the stick is slid along the top and

bottom mounting plates

44, 46. A lead wire 126 connects one terminal 112 to one of the plug prongs and a lead wire 1255 connects the other terminal to the other prong of the plug. A lead wire 13% connects one of the blades of the socket 36 to a source of current, such for instance as an A. C. source 132. The lead 130 is connected only to the hot side of the source, the return connection optionally being made through a neutral wire. This source of A. C. preferably is of comparatively low voltage, for example, 110 volts. Said voltage is used only for control so that if desired a lower voltage or a D. C. voltage can be em- 6 ployed. A lead wire 134 runs from the other blade socket 36 to an enclosed contactor 136.

In the preferred form of my invention this contactor is of the mercury type, that is, it is a contactor in which a pair of contacts are located within an envelope in which a pool of mercury is disposed. By a suitable mechanism, e. g. a plunger P, the pool can be arranged either to close the gap between the two contacts or to leave it open. Said contactor 136 is a normally closed contactor which when unenergized has a pool of mercury closing the space between its contacts, and which when energized has the pool lowered by withdrawal of the plunger to open the electrical connection between the contacts. Many kinds of enclosed contactors are well known to the trade and the specific type shown in the drawings has been illustrated here only by way of example.

Said contactor has an actuating coil 138. The lead wire 134 is connected to one end of said coil and the other end of the coil runs to ground. Thus it will be seen that when any push button 50 is depressed it will close the snap switch so as to energize the coil 13-3 and thus open the contacts of the contactor 136. A lead wire 14% connects one of the contacts of the contactor to a load 142. Another lead wire 144 from the contactor runs to the load bus 32. Thereby when the contactor is idle and its contacts closed, the load is connected to the load bus but as a push button 56 is depressed and moves between its idle and actuated positions, the trip bar 64 will raise and open the circuit between the load and the load bus for the stick corresponding to the button being depressed. When the button is fully depressed the trip bar will fall into the notch 76 thereby reopening the switch 110 and thus causing the contactor to reclose and reconnect the load 142 to the load has The cam 72 and notch 76 are spaced apart sufficiently so that the contactor is energized as the

contacts

96, 98 approach the

contacts

36, 34 and remains energized until said contacts engage one another. Moreover, the cam 72 is shaped to release any previously engaged push bar while the switch 116 is closed. That is, during the moment of engagement and during the moment of separation of the line and

load contacts

30, 34, 96, 98, the contactor 136 is open and the making or breaking of the patch is cold.

Each stick also may include a cancel push button 146 which controls a push bar 148. Said bar and the elements associated therewith are similar to the push bar 48 and its associated elements except that the cancel push bar has no notch 76 and carries no contacts. Thus the only purpose of the cancel push bar is to release any previously engaged push bars.

It will be appreciated that each time a new load is to be connected it merely is necessary to add one stick and one load bus. This stick then can connect that load to any of the voltage regulator buses 24 already in place. The only wiring that need be done is the wiring to connect the double bladed socket to the load bus through a contactor and also to connect said socket to a source of control energization. No wiring whatsoever is needed for the patch switches constituting the

contacts

30, 34, 96, Q8. Likewise if an additional voltage regulator is to be employed it simply is necessary to add another bus 24 with its associated contacts 34 It thus will be seen that there is provided a device which achieves all the objects of the invention and is well adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention, and as various changes might be made in the embodiment above set forth, it is to be understood that all matter herein described, or shown in the accompanying drawings, is to be interpreted as illustrative and not in a limiting sense.

Having thus described the invention, there is claimed as new and desired to be secured by Letters Patent:

1. A lighting control board comprising a stationary rack, a plurality of sticks, said rack including a plurality of guide means for detachably receiving said sticks side by side, a plurality of line buses carried by said rack in back of and crossing the sticks, a plurality of load buses carried by said rack, each stick having only one associated load bus directly in back of the same, each stick including a plurality of buttons arranged in a row parallel to the associated load bus, a push bar associated with and controlled by each button, a bridge carried by each push bar, a pair of contacts on the bridge, contacts on the load and line buses, each pair of bridge contacts in the same stick being registered with a contact of a diiterent line bus and with a contact of the associated load bus, means biasing each push bar away from the line and load buses whereby the bridge contacts normally are spaced from the load and line contacts, means to latch the push bar in a position in which the bridge contacts engage the load and line contacts, and means to release the latching means upon actuating any idle push button.

2. A lighting control board comprising a stationary rack, a plurality of sticks, said rack including a plurality of guide means for detachably receiving said sticks side by side, a plurality of line buses carried by said rack in back of and crossing the sticks, a plurality of load buses carried by said rack, each stick having only one associated load bus directly in back of the same, each stick including a plurality of buttons arranged in a row parallel to the associated load bus, a push bar associated with and controlled by each button, a bridge carried by each push bar, a pair of contacts on the bridge, contacts on the load and line buses, each pair of bridge contacts in the same stick being registered with a contact of a diiferent line bus and with a contact of the associated load bus, means biasing each push bar away from the line and load buses whereby the bridge contacts normally are spaced from the load and line contacts, means to latch the push bar in a position in which the bridge contacts engage the load and line contacts, means to release the latching means upon actuating any idle push button, and means to prevent simultaneous actuation of any two push buttons.

3. A lighting control board comprising a stationary rack, a plurality of sticks, said rack including a plurality of guide means for detachably receiving said sticks side by side, a plurality of line buses carried by said rack in back of and crossing the sticks, a plurality of load buses carried by said rack, each stick having only one associated load bus directly in back of the same, each stick including a plurality of buttons arranged in a row parallel to the associated load bus, a push bar associated with and controlled by each button, a bridge carried by each push bar, a pair of contacts on the bridge, contacts on the load and line buses, each pair of bridge contacts in the same stick being registered with a contact of a difierent line bus and with a contact of the associated load bus, means biasing each push bar away from the line and load buses whereby the bridge contacts normally are spaced from the load and line contacts, means to latch the push bar in a position in which the bridge contacts engage the load and line contacts, means to release the latching means upon actuating any idle push button, a pluraiity of normally closed contactors each of which is adapted to be series-connected between a different load bus and load, a plurality of normally open electric switches each associated with and carried by a difierent stick, a plurality of trip bars each associated with a different stick, said push bars having cam surfaces engaging followers on the trip bar, each trip bar being positioned to actuate the associated switch when any one of the push buttons is actuated,- and circuit means interconnecting each switch and its associated contactor whereby as a push button is pressed the normally open switch will be closed causing the contactor to open so that as the bridging contacts engage the load and line contacts the load is disconnected, said push bars including detent portions which engage the trip bar followers at the end of an actuating stroke to open the switch and reclose the contactor after the bridging contacts have engaged the load and line contacts.

4. A lighting control board comprising a stationary rack, a plurality of sticks, said rack including a plurality of guide means for detachably receiving said sticks side by side, a plurality of line buses carried byrsaid rack in back of and crossing the sticks, a plurality of load buses carried by said rack, each stick having only one associated load bus directly in back of the same, each stick including a plurality of buttons arranged in a row parallel to the associated load bus, a push bar associated with and controlled by each button, a bridge carried by each push bar, a pair of contacts on the bridge, contacts on the load and line buses, each pair of bridge contacts in the same stick being registered with a contact of a different line bus and with a contact of the associated load bus, means biasing each push bar away from the line and load buses whereby the bridge contacts normally are spaced from the load and line contacts, means to latch the push bar in a position in which the bridge contacts engage the load and line contacts, means to release the latching means upon actuating any idle push button, a panel having a plurality of apertures through which the buttons protrude, each button including a forward transparent portion and a rear opaque portion meeting at a plane forwardly of the rear surface of the panel and a source of light immediately in back of said panel.

5. A lighting control board comprising a stationary rack, a plurality of sticks, said rack including a plurality of guide means for detachably receiving said sticks side by side, a plurality of line buses carried by said rack in back of and crossing the sticks, a plurality of load buses carried by said rack, each stick having only one associated load bus directly in back of the same, each stick including a plurality of buttons arranged in a row parallel to the associated load bus, a push bar associated with and controlled by each button, a bridge carried by each push bar, a pair of contacts on the bridge, contacts on the load and line buses, each pair of bridge contacts in the same stick being registered with a contact of a different line bus and with a contact of the associated load bus, means biasing each push bar away from the line and load buses whereby the bridge contacts normally are spaced from the load and line contacts, means to latch the push bar in a position in which the bridge contacts engage the load and line contacts, means to release the latching means upon actuating any idle push button, a plurality of switches, each switch being associated in common with all the push bars of a dififerent stick, each said switch being disposed to be actuated by the associated trip bar as any one of the push bars on the associated stick is actuated.

6. A lighting control board comprising a stationary rack, a plurality of sticks, said rack including a plurality of guide means for deatchably receiving said sticks side by side, a plurality of line buses carried by said rack inback of and crossing the sticks, a plurality of load buses carried by said rack, each stick having only one associated load bus directly in back of the same, each stick including a plurality of buttons arranged in a row parallel to the associated load bus, a push bar associated with and controlled by each button, a bridge carried by each push bar, a pair of contacts on the bridge, contacts on the load and line buses, each pair of bridge contacts in the same stick being registered with a contact of a different line bus and with a contact of the associated load bus, means biasing each push bar away from the line and load buses whereby the bridge contacts normally are spaced from the load and line contacts", means to latch the push bar in a position in which the bridge con tacts engage the load and line contacts, means torelease the latching means upon actuating any idle push' button,

a plurality of switches, each switch being associated in common with all the push bars of a different stick, each said switch being disposed to be actuated by the associated trip bar as any one of the push bars on the associated stick is actuated, a plug member, a socket member, one of said members being mounted on the rack and the other of said members being mounted on the stick, said members being disposed to be engaged when the stick is received in the guide beams and lead wires connecting each switch with the associated member.

7. A lighting control board comprising a stationary rack, a plurality of sticks, said rack including a plurality of guide means for detachably receiving said sticks side by side, a plurality of line buses carried by said rack in back of and crossing the sticks, a plurality of load buses carried by each rack, each stick having only one associated load bus directly in back of the same, each stick including a plurality of buttons arranged in a row parallel to the associated load bus, a push bar associated with and controlled by each button, a bridge carried by each push bar, a pair of contacts on the bridge, contacts on References Cited in the file of this patent UNITED STATES PATENTS 2,232,582 Woods Feb. 18, 1941 2,234,405 Hall Mar. 11, 1941 2,338,757 Curran Jan. 11, 1944 2,442,984 Paris June 8, 1948 2,482,998 Andersson Sept. 27, 1949 2,581,053 Thomas Jan. 1, 1952 2,616,941 Lasko Nov. 4, 1952 FOREIGN PATENTS 195,564 Great Britain Apr. 5, 1923 839,592 France June 22, 1938