US2956150A - Luminous ceiling construction - Google Patents

Description

R. A. D. SCHWARTZ ETAL 2,956,150

LUMINOUS CEILING CONSTRUCTION Oct. 11, 1960 5 Sheets-Sheet 1 Filed NOV. 29, 1956 INVENTORS ROBERT A. D. $CHW4RTZ STEPHEN W L/NDHE/M By W 771 Oct. 11, 1960 R. A. D. SCHWARTZ ETAL 2,956,150

LUMINOUS CEILING CONSTRUCTIbN Filed Nov. 29, 1956 5 Sheets-Sheet 2 fil NV NTORS ROBERT A. 0. 5 HMRTZ STEPHEN W L/NDHE/M A TTORNEY Oct. 11, 1960 R. A. D. SCHWARTZ ET AL 2,956,150

LUMINQUS CEILING CONSTRUCTION 5 Sheets-Sheet 3 Filed Nov. 29, 1956 ZM T/ WWW My M EH/ VCL v.m aw fl A E w m W 05 R A; w

A T YTORNEV Oct. 11, 196 R. A. D. SCHWARTZ ET AL LUMINOUS CEILING CONSTRUCTION Filed Nov. 29, 1956 5 Sheets-Sheet 4 a A m E m R STEPHEN W L/NDHE/M By W #77 A T TORNEV Oct. 11, 1960 Filed Nov. 29, 1956 [Olo R. A. D. SCHWARTZ ETAL 2,956,150

LUMINOUS CEILING CONSTRUCTION 5 Sheets-Sheet 5 /IF A 85 I llllillllllllllllllllllHllhlllllllllllHlIlllIIIIIIHHIillllllHYlJjI 107 i 1 us loo A02 IOI- IN V EN TORS ROBERT A. D SCHWARTZ STEPHEN W L/NDHE/M BY M [313, 7

A 7' TORNEV rates Patent fiice LUMINOUS CEILING CQNSTRUCTION Robert A. D. Schwartz, 1081 Annerley Road, Piedmont, Calif., and Stephen W. Lindheim, 1146 Keeler St., Berkeley, Calif.

Filed Nov. 29, 1956, Ser. N0. 625,065

6 Claims. (31. 240-9 This invention relates to a luminous ceiling and lighting construction of the type wherein a ceiling is provided which is transparent or translucent and above which are mounted lamps such as fluorescent lamps.

This application is a continuation-in-part of our copending applications Serial No. 457,844, filed September 23, 1954, now United States Patent No. 2,888,113, issued May 26, 1959, entitled Ceiling and Lighting Construc tion, and Serial No. 590,012, filed June 7, 1956, entitled Ceiling Framework.

In modern ceiling and lighting construction today, particularly in offices, markets, factories, public buildings and the like, there is a trend toward the use of so-called luminous ceilings. In this type of ceiling there is suspended from the roof structure (e.g., from permanent rafters) a ceiling which is translucent. Above the translucent ceiling are lamps, preferably fluorescent type lamps whose light shines down through the translucent ceiling. This type of ceiling is, therefore, illuminated from above and is referred to as a luminous ceiling. The term luminous ceiling is used herein to designate this type of construction and it refers to the translucent ceiling and the illuminating means.

It is an advantage of luminous ceilings that the light is spread more uniformly over the area of a room than from lighting fixtures suspended beneath a ceiling and visible from the room, such as chandeliers and conven tional fluorescent lighting fixtures.

it has been customary heretofore, in the art of luminous ceilings, for suppliers to provide standardized items such as extruded shapes for constructing the framework of luminous ceilings. Such standardized items have the disadvantage of inflexibility. Thus, commercially available parts may require a fixed, definite spacing of lamps without the possibility of varying lamp spacing to suit indi vidual needs except by expensive hand labor.

it is, therefore, one of the objects of the present invention to provide a luminous ceiling construction whereby prefabricated parts or elements can be provided which can be assembled very rapidly and economically on the job yet which allow variations, e.g., of lamp spacing, to suit individual requirements.

It is another object of the invention to provide an integrated type of ceiling and lighting construction wherein the lighting system can be varied independently of the ceiling, and vice versa, to permit a wide selection and variation of factors such as depth of ceiling, lamp spacing and type of ceiling (whether acoustical, egg crate, etc).

In luminous ceiling design it is desirable to avoid a shadow or band effect. By shadow effect or band effect is meant the appearance, to an observer beneath, at relatively bright bands interspersed with relatively dark In an extreme case, the illumination appears as narrow bands of intense illumination close to the rows of tubular lamps with wide, relatively dark areas between.

h prior practice, a shadow effect has been avoided as follows: Rows of fluorescent lamps are suspended above a light diffusing ceiling such as plastic panels or an open cellular or louvre structure. The rows of lamps are spaced apart a horizontal distance L which is not more than twice the vertical distance 1 between the lamps and the diffusing ceiling. V v

This design has provided luminous ceilings which are uniformly illuminated, but the maximum limit of 2-to-1 for the ratio L/ 1 has created problems. Thus a considerable depth is required for light diffusing ceilings. Thus, if the lamps are spaced on four foot centers, the difiusing ceiling must be two feet below the lamps. .This problem is aggravated in the case of the most recently available lamps of 13,000 lumen power compared to older lamps of 5000lumen power. To achieve a given light intensity, the former (13,000 lumen) lamps. must be spaced farther apart than the latter (5000 lumen) lamps. But the 2:1 ratio ofL/ 1 would require a much deeper diffusing ceiling, hence would be wasteful of space.

it is an object of the present invention to provide a ceiling and lighting design which obviates the need for a 2:1 ratio of L to 1.

It is a further object of the invention to provide a luminous ceiling design including tubular lamps and a diffusing ceiling wherein uniform ceiling illumination is achieved without the need for a 2-to-1 ratio of horizontal lamp spacing to depth of diffusing ceiling below the lamps.

These and other objects of the invention will be apparent from the ensuing description and the appended claims.

Certain forms of the invention are illustrated by way of example in the accompanying drawings, in which Figure 1 is a perspective-view of a luminous ceiling constructed in accordance with the invention, such ceiling including a lighting assembly above and a ceiling asserm bly below, both of which are suspended from a roof.

Figure 2 is a transverse section taken through one of the channel members of the lighting assembly.

Figure 3 is an end sectional view of the construction of Figure 1.

Figure 4 is a view similar to that shown in Figure 3 but illustrating a different type of ceiling panel.

Figure 5 is a perspective view of the preferred form of bracket for mounting sockets of fluorescent tubes.

Figure 6. is a perspective view of a ceiling and lighting assembly in which an acoustical and/or thermally insulating ceiling is located above the lamps and wherein light diffusing elements are located below the lamps.

Figure 7 is a fragmentary sectional view taken along the lines 7-7 of Figure 6.

Figure. 8 is a perspective view of a support bracket used in the construction of Figures 6 and 7 to support the light diffusers.

Figure 9 is a fragmentary perspective view showing a modified form of cross connection for the electrical wiring between the main raceways.

Figure 10 is. a fragmentary exploded view in'per'spective of yet'another form of cross connection.

Figure 11 is. a perspective view of an end of a cross connection such asshown in. Figure 1.0:

Figure 12 is a view in vertical section of a complete ceiling and lighting installation in accordance with the invention.

Referring now to the. drawings. and more particularly to Figures 1 and 2,. one formof our luminous ceiling construction is there illustrated and is generally designated by the reference numeral 10. It comprises a lighting assembly 11 and a ceiling assembly 12 which is. located below the lighting assembly. The ceiling assembly 12. is preferably of the type described and claimedin our copending application Serial No. 590,012 and it. prefer.- ably involves elements such as described in our copend Patented Oct. 11, 1960 3 ing application Serial No. 457,844 (now US. Patent No. 2,885,113).

Thus, the ceiling assembly 12 comprises longitudinal members 13 and transverse members 14. The transverse members 14 are T-bars, i.e. they are T-shaped in cross section, each having a vertical portion 15 and outwardly extending horizontal flanges 16 on opposite sides of the vertical portion. Each of the longitudinal members 13 is also of generally T-shaped cross section but has a modified construction. It includes a vertical portion 17, horizontal flanges 18 and two pairs of grooves 19 disposed on opposite sides of the vertical portion 17, each pair being arranged in a vertical plane. Connector clips are provided such as shown at 20. As described in detail in our copending applications abovementioned, it is a function of each connector clip 20 to fit within a pair of the grooves 19 and to connect with one end of a cross member 14. This type of connection possesses several advantages among which are the fact that the clip can be caused to slide along the length of a longitudinal member 13 to the desired position, then clamped in place by a simple crimping operation. Also each clip 20 serves to level the flanges 16 and 18 of the cross members 14 and longitudinal members 13, respectively.

It will be apparent that by this means there is provided a grid of modular construction, i.e., consisting of any desired number of identical units. As will be seen, a translucent ceiling panel is provided for each unit and is indicated by the reference numeral 25. Each panel 25 is supported by flanges 16 and 18. As will be seen from an inspection of Figure 3, the particular translucent or luminous ceiling panels shown at 25 are of a watfie type of design and may consist of spaced, translucent plastic halves joined together at the edges, thus providing a multiplicity of individual light transmitting and acoustical units or cells which are indicated individually by the reference numeral 25a in Figure 3.

The ceiling assembly thus described and illustrated and generally designated by the reference numeral 12, is suspended from the lighting assembly 11 by any suitable means such as rods, one of which is shown at 26 in Figures 1 and 3.

Referring now more particularly to Figure 2, the main or frame members of the lighting assembly 11 are channel members 27, one of which is shown in cross section and in detail in Figure 2. Thus each of the channel members 27 has a channel 28 formed by spaced vertical side walls 29 and a bottom portion 30. Horizontal flanges 31 are provided which extend outwardly from the bottoms of the side walls 29. A pair of aligned grooves 32 is provided on each side of the channel member 27 such grooves being arranged in vertical planes. Two pairs of horizontal grooves 33 and 34 are provided at the top of the channel members 27.

As explained in more detail in the aforesaid copending applications, the frame members 13 and 14 of the ceiling assembly 12 and the channel members 27 of the lighting assembly 11 may be constructed of any suitable material in any desired manner but, preferably, they are of aluminum alloy construction and are extruded shapes. As also explained in the aforesaid copending applications it is one of the functions of the vertical grooves '19 of the longitudinal members 13 of the ceiling assembly 12, and of the vertical grooves 32 of the longitudinal channel members 27 of the lighting assembly 11 to receive connector members (not shown) to provide connections between longitudinal members 13 or channel members 27 which are joined end-to-end.

The channel members 27 are suspended from a roof structure, e.g., rafters (not shown) by means of U-shaped hangers 35, each of which has inwardly projecting ears 35a to engage the bottom edges of the grooves 32 and to support the channel members. Each of the hanger members 35 in turn is supported by a rod 40 and a wire or cable 41. The rods 26 which serve to support the ceiling assembly 12, are suspended from the channel members 27 by means of hangers 42 which have grooved flanges 43 adapted to fit slideably over the flanges 31. It will thus be apparent that both of the assemblies 11 and 12 are easily and conveniently supported from the permanent ceiling, rafters or the like.

As described in detail in copending application Serial No. 457,844 (now US. Patent No. 2,888,113), the channels 28 of the channel members 27 serve as race- Ways for wiring for the fluorescent lights. As will be seen cover members 44 are provided which can be snapped into the grooves 34, whose shape is best shown in Figure 2 and is such as to facilitate a snap fitting. The lower, horizontal grooves 33 are intended to receive metal plates for other purposes as described in copending application Serial No. 457,844. Also shown in Figure 1' are such elements of a fluorescent lighting system as boxes 45 intended to house ballasts; connector boxes 46 to receive the ends of wires to make electrical connections; and angle shaped end plates 47. Also shown are tubes 48 extending between the connector boxes 46 and intended to carry the necessary wiring.

-Also shown in Figure l, and on a larger scale and in more detail in Figures 2 and 5, are angle brackets 49 which are bolted to the flanges 31 of the channel members 27 at suitably spaced intervals, e.g., on 2, or 2 /2 foot centers. Each bracket 49 is formed with a groove 49a to receive wires. To the vertical portion of each such braket is fixed a socket 50 intended to receive one end of an electric lamp, preferably a fluorescent type of lamp such as shown at 51.

It will be apparent from a consideration of Figures 1, 2 and 3 that certain very important advantages result from the construction there illustrated. Thus, a very simple means is provided for suspending both a ceiling assembly such as shown at 12 and a lighting assembly such as shown at 11 from a roof structure.

It is a distinct and very important advantage of this construction that the illuminating tubes 51 may be spaced as desired, either uniformly or nonuniformly; on wide, narrow or intermediate centers; and in any relation desired to modular units of the ceiling assembly 12.

Referring now to Figure 3, the illumination from one of the tubes 51 is there indicated by arrows radiating uniformly from such tube, thus indicating that the primary radiation emanates uniformly in all directions. Primary radiation which is directed upwardly is reflected down. It will be apparent that a very uniform type of illumination is achieved which avoids the disadvantage of illumination of the nonuniform, spotty type. Thus it is a disadvantage of many types of illumination, that the illumination proceeds downwardly with maximum intensity from certain scattered sources, and at eye level the intensity of illumination varies greatly from place to place about a room. It will be evident from an inspection of Figure 3 that this difficulty is avoided to a great degree and that a high degree of uniformity of illumination is achieved.

Referring now to Figure 4 a similar type of installation is there shown which is generally designated as 10a and which comprises a lighting assembly 11 which is identical, except as explained hereinafter, with the assembly 11 shown in Figure 1. Also shown is a ceiling assembly 12a of a somewhat different character than the ceiling assembly 12 shown in Figures 1 and 3.

The ceiling assembly 1211 may employ the same framework as the ceiling assembly 12, but instead of employing a plastic, waflie-type of ceiling panel such as shown at 25 in Figures 1 and 3, a metallic grid or egg crate" type of ceiling panel is employed which is generally designated by the reference numeral 52. Each grid panel 52 comprises a number of small, open cells 53, each formed by four vertical walls 54. Inasmuch as this open type of grid lacks some of the desirable light diffusing properties of the waffle-type grid shown at 25 in Figures l and 3, it is preferred to employ light deflecting means for each of the tubes 51, such light deflecting means being generally designated by the reference numeral 55. It comprises end sections 56 and rounded, downwardly convex shields 57.

The arrows in Figure 4 indicate the manner in which illumination is. diffused by this type of construction. Thus direct illumination through the open cells 53 directly beneath a tube 51 is prevented by the shields 57. Most or all of the radiation impinges upon the walls 54 of the panels 52. The result is that direct transmission of light downwardly through the cells 53 is reduced to a minimum, glare is eliminated, and a high degree of uniformity of illumination is achieved.

Referring now to Figure 6, a ceiling and lighting system is there shown which is generally designated by the reference numeral 65. In this system a lighting assembly is provided at 66 which comprises fluorescent tubes 51 supported by brackets 49 as described above. The system 65 also comprises a ceiling assembly 67 above the lamps 51 and light diffusing means 68 below the lamps. Longitudinal, channel members 27 are provided which constitute the main frame members of the system, which also serve as raceways for wiring and to which T-bars 14 are attached as described hereinabove. Ceiling panels 69 are supported by the flanges 16 and 31 of the T-bars 14 and channel members 27, respectively. The ceiling panels 69 may be acoustical panels and/or thermally insulating panels. Thus perforated panels of well known type and of porous, insulating composition may be used to provide a ceiling which has good acoustical properties and also good thermally insulating properties.

Cross channels are provided at 70 to provide conduits for cross wiring. As shown in Figure 10, these cross channels may be attached to. the longitudinal channels 27 by clips '71; angle brackets 72 and screws 73. A cover is provided at 74 for each channel 70 which has inwardly slanting flanges 75 to clip onto outwardly slanting flanges 8% on the channels 70. Also, U-shaped segments 81 are riveted to the covers 74 to bridge the ga s between cross channels 70. Each unpaired endof a cross channel 7f) may be closed by a modified segment 81a having an end flap 82, as shown in Figure 11.

Referring again to Figure 6, and also of Figure 7, a light diffuser is provided at 85 which supplements and complements that shown at 68. Each light diffuser 85 is an upwardly concave, translucent glass or plastic light diffusing element which is thickest at the middle and which tapers toward its edges. Thus. the diffuser 85, by reason of its tapered thickness, absorbs a greater proportion of light radiated directly downwardly than the light radiated outwardly. Thus, the diffuser 85 acts to distribute radiation which is directed in a general downward direction more uniformly, sothat an observer beneath who is looking up does not see a narrow band of intense illumination but, rather, sees a broad field of uniform illumination. To support the diffusers. 85, angle brackets are provided such as shown at- 86 which are formed with ears 87 (see Figure 8) to be received in grooves or slots formed in the diffusers 85. The light diffusing means 68 is of the egg crate type as in Figure 4 and is similarly suspended.

In the system shown in Figure 6, certain advantages are obtained. Thus, lamp spacing can be varied at will. The acoustical and/or thermally insulating ceiling 67 is independent of and. is concealed by the, light diffusing means 68. Therefore, less expensive, nondecorative panels 69 may be employed. The egg crate diffuser 68 acts to diffuse the illumination and make it uniform except to an observer looking up almost vertically. The

6 Referring now to, Figure 9, an alternative type of cross channel is there shown which is generally designated by the. reference numeral 95. Each cross channel has an upper, channel portion 96 and a lower, T-bar portion 97'. The T-bar portion is connected to longitudinal channels, such as shown at 27, by means of conhector clips such as shown at, 20.. The cross channels 95, therefore, serve not only as conduits, for cross wiring but also as stiffeners and structural members of the framework. The channel portions 96 are covered as in the case of the cross channels 70 in Figures 6.and 10.

Referring now to Figure 12, a complete ceiling and lighting system is there illustrated. A multiple story building is shown at 100' including a lower. room 101 having walls ltlZ'and an upper room. 101a separated at 103 by the floor of the upper room. The ceiling and lighting system installed in the lower room 101 is. that shown in Figure 6, including a ceiling assembly at 67 and an egg crate light diffusing structure at 68. A plenum or air space is provided at 104 vwithin which air ducts 105 communicate with a blower or other suitable air circulating device (not shown). An anemostat or air vent is shown at 106 which is supplied with air by the ducting and which delivers the air to the space 137 between the ceiling 67 and the egg crate 52. Thus air which has been suitably conditioned, e..g., heated, cooled, dehumidified, etc., is distributed uniformly over the entire upper surface of the room 101. Additionally, vents are provided at 108 and 109 in the ceiling 67 and wall 102 of the room 101. Hence, a desirable circulation of air is maintained. Also, sprinklers are provided at 11-5 and fans at 116.

Referring again to Figures 6 and 7 and also to Figure 12, another feature of importance will now be described. As explained above, it has been considered better practice heretofore to space the lamps, such as the fluorescent lamps 51 apart a distance not more, than twice the vertical distance between the lamps and the diffuser i.e., the egg crate difiuser 63 of Figures 6. and 12 or the plastic diffuser 25 of Figure l).

We have now found that this two-to-one ratio. is unnecessary provided auxiliary diifusers such as shown at 85 are used and provided also. that a light reflecting surface is located above the lamps, such as the panels 69 in Figures 6 and 12.

A system of this character, operates as follows: Referring to Figure 7' it will be apparent that the most intense illumination from an unshielded tubular lamp such as that shown at 51, 1'.e., the most intense illumination as seen by an observer beneath, will be in the form of a narrow band directly beneath the tube. It will also be apparent that the intensity of illumination asseen by an observer beneath, drops off laterally as the distance from the. tube increases. The function of the auxiliary did-user is to interpose a type of dispersive lens or light absorption medium whose light absorptive, capacity diminishes inversely as the light intensity. Thus the auxiliary diffuser 85 acts as a dispersive or divergent lens or equalizer. It is more efiective for this purpose if it is located in close proximity to the lamp, as illustrated in Figure 7. Preferably also-the difluserhas a tapered thickness such as that shown to accomplish the diffusing function. However, this may be accomplished by the application of paint, by the use of pigments or dyes in the material of the diffuser, or by other means, provided the light intensity is diffused to eliminate a bright line or band, of light as seen from beneath.

Even so, unless such lamps are spaced rather close together, bands of illumination will not be eliminated altogether. Instead the bands of illumination will be broadened out. To eliminate a band effect altogether, a light reflecting surface is provided above the lamps, such as that shown at 69 in Figures 6 and 12. By employing a light reflecting surface above the lamps, that portion of the light from the lamp 51 which is directed upwardly will strike the surface of the light reflecting ceiling 69 and will be reflected downwardly. Thus the light diffusers 85 and reflective ceiling 69 accomplish the object of uniform illumination. By employing a light diffusing ceiling beneath the lamps, a luminous ceiling is provided. The light diffusing ceiling may be located in close proximity to the lamps, thereby economizing in space. The 2:1 ratio of lateral lamp spacing to depth of light diffusing ceiling below the lamps, heretofore regarded as necessary, need not be employed.

The light diffusing ceiling is preferably an open, cellular or louvre type of structure such as shown at 68, because it facilitates the use of concealed sprinklers, facilitates air circulation and provides a'ceiling having a lesser intensity of illumination.

It will be apparent that the system shown in Figure 12 provides a number of advantages. Thus, it provides uniform, homogeneous illumination; it provides thermal and acoustical insulation; at provides air conditioning; and it conceals all unsightly objects such as ventilators, sprinkler heads and non-decorative insulating panels. The system can be installed in old as well as new buildings as an integrated unit tailored to particular requirements. It also occupies relatively little depth, thus economizing in height requirements.

It will, therefore, be apparent that a ceiling and lighting construction has been provided which satisfies the objects above stated. It is simple in its design from a manufacturing standpoint. It is readily assembled and mounted and, in case of need, it is readily disassembled. The construction provides a high degree of flexibility in that, for example, the spacing of the illuminating tubes can be adjusted at will and with great ease. The ceiling is adapted for closed, cellular types of ceiling panels and for panels in the form of open grids. It achieves the object of a high degree of uniformity of illumination. It provides integrated systems which can be installed in new or old buildings and which provide ef ficient, comfortable illumination, thermal and acoustical insulation, and efiicient air circulation.

We claim:

1. A luminous ceiling structure of the character described adapted to provide substantially uniform ceiling illumination without areas of substantially greater intensity and areas of substantially less intensity, said structure comprising: A light reflecting ceiling; at least one row of tubular lamps supported beneath said light reflecting ceiling in a manner to illuminate said ceiling and thereby illuminate the space beneath the lamps by reflected light from the ceiling and also by direct radiation from the lamps; a light-diffusing ceiling supported beneath said lamps which is adapted to diffuse said reflected light and said direct radiation and to produce a diffused ceiling illumination as seen from beneath the light-diffusing ceiling; and a light modifying element for and beneath each row of lamps, each said light modifying element being in the form of an elongated, translucent, light-absorbing member extending the length of its respective row of lamps, being centered in relation to the longitudinal axis of such row of lamps and having minimum light transmitting power along and adjacent its central longitudinal axis and having progressively greater light transmitting power laterally therefrom such that an intense band or hands of illumination are substantially eliminated.

2. The structure of claim 1 wherein said light modifying element is in the form of a translucent light-transmitting member having maximum thickness along its lonthroughout.

5. An integrated lighting, ceiling, air circulating and acoustical system comprising: (1) An enclosed space having walls and a permanent ceiling; (2) a light refleeting acoustical ceiling supported beneath said permanent ceiling and adapted to form a plenum between said permanent and acoustical ceilings, said acoustical ceiling being formed with air circulating openings to circulate air between said plenum and the space below; (3) a cellular light transmitting and diffusing ceiling supported below said acoustical ceiling and forming an intervening space between said acoustical and cellular ceilings; (4) illuminating means supported in said intervening space in the form of spaced, parallel rows of tubular lighting elements which illuminate said cellular ceiling, as seen from beneath, partly by reflection from said acoustical ceiling and partly by direct radiation; and (5) a light modifying element for each row of tubular lighting elements, said light modifying element comprising a translucent, light-absorbing member extending the length of its respective row of lamps, being centered in relation to the longitudinal axis of such row of lamps and having minimum light transmitting power lango and adjacent its central longitudinal axis and having progressively greater light transmitting power laterally therefrom such that an intense band or bands of illumination are substantially eliminated.

6. The system of claim 5 wherein said light modifying element is in the form of an elongated, translucent, transver'sely tapered and symmetrical light absorbing member supported beneath its respective row of tubular lighting elements, the thickness of said light absorbing member being greatest along its longitudinal axis and tapering symmetrically toward both edges, said taper being such as to effect a progressively decreasing light absorption and to bring about a light homogenizing effect.

References Cited in the file of this patent UNITED STATES PATENTS 2,277,468 Welch Mar. 24, 1942 2,476,109 Neitzel July 12, 1949 2,536,710 Baker Jan. 2, 1951 2,544,378 Cyr Mar. 6, 1951 2,583,939 French et a1. Jan. 29, 1952 2,659,807 Wakefield Nov. 17, 1953 2,680,502 Kurtzon June 8, 1954 2,680,805 MacDonald a- June 8, 1954 2,689,630 Drury Sept. 21, 1954 2,710,335 Wong June 7, 1955 2,730,942 Peterson Jan. 17, 1956 2,734,126 Kruger Feb. 7, 1956 2,742,122 Stanley Apr. 17, 1956 2,753,440 Wakefield July 3, 1956 2,767,815 Brandstetter et a1. Oct. 23, 1956 2,772,742 Sprankle Dec. 4, 1956 2,803,741 Guth Aug. 20, 1957 2,817,752 Florence Dec. 24, 1957 FOREIGN PATENTS 1,091,225 France Oct. 27, 1954

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