US2258355A - Test and focusing means for light signals - Google Patents

Description

Oct. 1941.

M. R. DOUGLASS TEST AND FOCUSING MEANS FDR LIGHT SIGNALS Filed Feb. 10, 1940 -HZS ATITORNEY Patented Oct. 7, 1941 Myrl R. Douglass, Edgewood, Pa., assignor to The Union Switch 8; Signal Company, Swissvale, Pa., a corporation Pennsylvania Application February 10, 1940, Serial No. 318,383

1 Claim.

Myinvention relates to testing and focusing means for :light signals.

In certain forms of light signals, such, for example, as that disclosed in Letters Patent f the United States, No. 2,230,853, grantedto Wesley B. Wells on February 4, 1941, for Light signals. a light projecting unit consisting of a lamp having a concentrated filament located at the focal point-of an ellipticalreflector is intended to be replaceably secured in place in the light signal by preadjusted means which insures that any similar unit will be accurately positioned relative to the other optical elements of the signal. The lamp employed in each light projecting unit is of the precision type, thatis to say, of the type which has its filament positioned relative to the lamp base with sufficient accuracy 50 that it can be interchanged with a similar, lamp without changing the optical characteristics of the light projecting unit, and in order thatthe units and lamps can both be interchangedin the intended manner and still maintain the maximum signal efllciency, it is essential that all reflectors and lamps should come up to a certain standard of excellence, and also that the sockets in which the lamps are mounted should oe positioned relative to the reflector during manufacture with .suflicient accuracy so that any lamp which is in service in the socket will have its filament located exactly at the focal point of the reflector.

One object of my present invention is to provide a device which will enable the lamps and reflectors of light projecting units of the type described to be quickly and conveniently tested to ascertain that they come up to the required degree of excellence, and which will also enable the lamp socket of any light projecting unit to be quickly and accurately located in the, position with respect to theassociated reflector in which all precision lampswhich are placed in the socket will have their filaments accurately located at the focal point of the reflector.

According to my invention, the device comprises a series of lenses and stop plates provided with peep holes all disposed in a frame between detachable mounting means for the light units and a light sensitive cell connected to a suitable meter, in such manner that the axes of all lenses, peep holes, and the light sensitive element of the light sensitive cell all coincide exactly with the axis of the reflector mounting means, whereby when a light unit is mounted on the mounting means with the lamp illuminated and the socket is adjusted to the position in which the lamp filament is located at the focal point of the reflector, a maximum meter reading will be obtained.

Other objects and characteristic features of my invention will appear as the description proceeds.

I shall describe one form of device embodying my invention, and shall then features thereof in the claim.

In the accompanying drawing, Figs. 1, 2 and 3 are front elevational, right-hand and left-hand end views, respectively, showing one form of device embodying my invention.

Similar reference characters refer to similar parts in all three views.

Referrin to the'drawing, the device in the form here shown comprises three parallel rods I, 2 and 3 disposed at the three corners of an isosceles triangle, and mounted at their .ends in spaced end plates 4 and 5 secured to a suitable base 5. Formed in the end plate 4 is an opening l which aligns axially with an opening 8 formed in the end plate 5, and provided on the outer side of the end plate-4 are suitable means which I will describe presently for supporting a light unit in a position to project the rays of light emerging from the unit through the opening 1 toward the opening 8 in an axial direction.

The light unit may assume a variety of forms, but inasmuch as the device embodying my invention is particularly suitable for, although in no. way limited to, use with a light unit of the type shown and described in the previously re- Ierre'd to Wells Patent No. 2,230,853, I have chosen to illustrate my invention in connection with this type of light unit.

This unit,,which is designated as a whole by the point out the novel reference character A, comprises an elliptical re-' flector 20 mounted in a metal case 2|," and an electric lamp 22, the filament of which is intended to be located at one of theconjugate foci of the reflector 20. The rear wall oi the casing 2| is provided with three rearwardly projecting studs 23, arranged in triangular'formation, and mounted on these studs betwecn compressed coil springs 24 which surround the shank portions of the studs and nuts 25 which are adjustably screwed onto the outer ends of the studs, is a plate 26. This plate carries a socket 21 which projects with some clearance through a hole 28 formed in the rear wall of the casing 21, and serves as a support for the previously referred to electric lamp 22. Mounted on the studs 23 outside of the nuts 25 are lock nuts 29 for securing the nuts 25 in adjusted positions. It will be apparent that by adjusting the nuts 25, the position of the lamp filament with respect to the reflector may be varied, thus enabling the lamp filament to be accurately positioned'atthe focal point of the reflector, and hence permitting the maximum efficiency to be obtained from the light unit.

The light unit further comprises three radial arms 38, 3| and 32 each of which is formed with 'a socket 33. These sockets are adapted to receive of the light issuing from the lamp 22 from strikingthelens l3.

As is well understood, the light emerging from the lens M will be in the form of a beam of parallel rays, and these rays are directed onto the lens l5. This lens is also of the clear glass planoconvex type, and is so arranged and so constructed that it will convert the parallel beam the studs and will be yieldably held in a flxed position. The studs are so adjusted that when the light unit is'in place on the studs and the filament of the lamp 22 is accurately located at the one focal point of the reflector, the other focal point will be located on the axial line extending between the two openings 1 and 8. For the purpose of holding the studs in their adjusted position lock nuts 4! are provided on the inner ends of the studs.

It will be apparent that with mounting means of the type shown the light units may be quickly secured to and removed from the end plate 4, whereby testing of the units is greatly facilitated.

A light sensitive cell 9 is secured to the end plate 5 in back of the opening 8, and is connected by means of a wire Illa to a meter l0 secured to the base plate 6 adjacent the light unit A. The light sensitive cell is so arranged that the axis of its light sensitive elementwill coincide with the axis of the opening 8, and that any light which passes through the opening 8 will strike this element,--wherebythe meter lflwill indicate the intensity of the light energy passing through the opening 8.

Supported by the rods l, 2 and 3 between the two'end plates 4 and 5 is a stop plate ll provided with an opening Ha, a stop plate I2 provided with an opening 12a, a lens l3 mounted in a plate i3a, a lens 14 mounted in a plate l4a, a lens I5 7 mounted in a plate I5a, and a vided with an opening lBa.

The two lenses l3 and I4 are of the well-known clear glass plano-convex'type, and together form a doublet which is identical with that-employed in actual practice in light signals of the type in which the light projecting unit A is intended to be used. The axis of the doublet coincides with the axis of the openings I and 8 in the end plates 4 and 5, and thedoublet is so positioned that when the light unit A is in place on the studs 35, 38 and 31, the focal point X of the doublet will coincide exactly with the conjugate focus of the reflector of the light unit.

The two stop plates II and '12 are disposed on opposite sides of the focal point X, and the plate II is so located and has its opening Ha of such size that the cone of light which is concentrated bythe reflector at the point X will'just pass through the opening. The plate I! is so located and has its opening l2a of such size that only a sufficient amount of light passing through the focal point X to exactly cover the lens Hi can pass through the opening. It will be seen, therefore, that the two stop plates H and I! serve to prevent the greater portion of the direct rays stop plate I6 proback into a cone of light having a focal point Y located on the axis passing through the openings 1 and 8 a little in front of the opening 8.

The stop plate It is so located that its opening 16a which is relatively small, usually about inch in practice, coincides exactly with the focal point of the lens l5. The light after it passes throughthe focal point Y passes through the opening 8 and impinges on the light sensitive element of the light sensitive cell, the parts being so proportioned that the light will just cover the light sensitive element of the cell.

In explaining the operation of the device, I will first assume that it is desired to position the filament of a lamp 22 in a light unit at the focal point of the reflector. is snapped into place on the studs 35, 36 and 31 and the lamp is illuminated. This causes the light emitted from the reflector to follow the path indicated by the broken lines I! and I8 in the drawing, thereby concentrating the light rays on the photo electric cell, and hence causing meter H) to read. The reading of the meter ID will, of course, vary with the intensity of the light, it being necessary in order to produce the maximum reading that all of the light emitted by the reflector should pass through the opening in and strike the light sensitive cell. Due to the location and arrangement of the parts, before all of the light will pass through the point Y it must first be concentrated at the focal point X, and this will only happen when thefllament of the lamp is accurately located at the other focal point of the reflector. The position of the lamp may be varied by means of the adjusting nuts 25, and the operator will adjust these nuts until a maximum meter reading is obtained, whereupon he -observe the meter reading for each lamp, discarding those lamps which produce a lower meter reading than that of the standard lamp.

Kit is desired to test reflectors, the operator will provide a standard light unitwith a stand ard lamp which is properly focused in-relation to a standard reflector, and will observe the meter reading. He will then replace this standard reflector with those reflectors which are to be tested, and will observe the meter readings for each reflector, discarding those reflectors which give a smaller reading than that provided by the standard reflector. I

One advantage of a device embodying my invention is that it takes up very little room.

Another advantage of a device embodying my invention is that it provides a means for deter-' mining when the sockets are accurately located inthe reflector assembly, thereby producing a light source for Searchlight signals which will give the maximum obtainable in beam intensity.

To do this, the light unit- Although I have herein shown and described only one means for testing and focusing light signals it is understood that various changes and modifications may be made therein within the scope of the appended claim without departing from the spirit and scope of my invention.

Having thus described my invention what I claim is:

A testing device for use with a light unit comprising a reflector having conjugate foci and an electric lamp the filament of which is adapted to be accurately located at one of the foci of said reflector, said device comprising a plurality of parallel rods mounted in two spaced end plates, a doublet mounted on said rods between said end plates and having a focal point adjacent one end plate and capable of emitting a beam of parallel rays toward the other end plate when a light source is disposed at said focal point, means on said one end plate for detachably securing said light unit thereto in a position in which its axis aligns with the axis of said doublet and its other focus coincides exactly with the focal point of said doublet, a first stop plate mounted on said rods between the focal point of said doublet and said one end plate and provided with an opening of such size that the cone of light emitted from the reflector will just pass through said opening, a second stop plate mounted on said rods between said doublet and its focal point and provided with an opening of such size that only enough light to fill the lenses of the doublet is permitted to pass said second plate, a condensing lens mounted on said rods in the beam of light emitted by said doublet and arranged to concentrate the light rays at a point adjacent said other end plate, a third stop plate mounted on said rods and provided with a relatively small opening which coincides exactly with the point of light from said condensing lens, a photo electric cell secured to said other end plate in a position to receive the light rays after they pass through said third stop plate, and a meter connected with said light sensitive element and responsive to the intensity of the light striking said element, said intensity being a maximum when said lamp is on focus.

MYRL R. noUGLAss.

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