Self-illuminated fibre optic switch

Abstract: A fibre optic switch (10) for controlling the electrical power to a load or for logical applications is disclosed in which the switch has a secondary guided light beam (34) to provide status indicator light (30). The moulded plastic components of the switch are used to provide the means for light transmission and control.

Description: FIELD OF THE INVENTION This invention relates to the field of switches for electrical controls, and more particularly to switches which operate through fibre optic or light guided systems. BACKGROUND OF THE INVENTION In certain applications, such as airplane cockpits, illuminated indicators are required for electrical switches to allow the operator to determine whether the switch is in an "on" or "off" state. Conventional switches have used incandescent lamps to provide such indicator lights. In large numbers, however, such incandescent lights produce a large quantity of heat which is inefficient and potentially unsafe in closed environments such as airplanes. In the past it has been known to use fibre optic controls to control the functioning of electrical devices to provide a safer system for use in wet, hospital, explosive or other hazardous environments. For example see United States Patent No. 3,999,074 which describes a fibre optic electric power control device, and United States Patent No. 4,704,656 which discloses a fibre optic switch for controlling a wall receptacle. Such devices use the fibre optic switch to provide a light signal to a photo-electric device which in turn controls the electrical circuit. In this way the fibre optic control can be made remote from the electrical circuit. For example, see also United States Patent No. 4,315,147 which describes a mechanical actuator interposed between two fibre optic lines to reversibly block light travelling from one line to the other and European Patent No. 12,274, which discloses a device where the light switch in which the actuator is a reflecting member affixed to a magnetic guide made movable in response to current applied to an electro-magnet. None of these devices have a light guide incorporated into the casing of the unit itself for ease of manufacturing. Finally, none of the known prior devices have utilized a simple mechanical actuator to switch the light into and away from an optical path. The invention as claimed is intended to remedy these problems. It provides light director in a mechanical actuator to direct light into or away from an output optical path depending on the position of the actuator. Coupling between an optical input and output path or paths are provided by a fibre optic or light-guided control system incorporated at least partly in a mechanical actuator. The switched light is used to control electrical circuits and to control the incidence of switched light onto a light indicator. According to one aspect of the invention, the light guide is formed by the casing of the switch itself. The advantages of the invention over conventional electrical control systems are less complexity, greater reliability, reduced heat generation and lower costs. BRIEF DESCRIPTION OF THE DRAWINGS Specific embodiments of the invention will now be described by way of example only with the use of drawings in which: Figure 1, is a diagrammatic partially sectional side view of a first embodiment of the optical switch according to the invention; Figure 2 is a diagrammatic plan sectional view of the switch of Figure 1 taken along line II-II of Figure 1; Figure 3 is a view of the latching mechanism used in the invention; Figure 4 is an enlarged view of the area VI of Figure 3; Figure 5 is a vertical cross-section of another embodiment of the invention; and Figure 6 is a cross-sectional view taken along lines VIII-VIII of Figure 5. Figure 7 is a cross-sectional view of a first slide switch variant according to the invention; DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, an optical switch is illustrated generally at 10 in Figure 1. It comprises a housing lla which is made up of a casing 11 mounted on a switch base 12 and a pushbutton 13 mounted within the casing 11 and being operable to move vertically relative to the casing 11. All of the components are plastic and are moulded using injection moulded techniques. An illumination light is provided through a waveguide 34 mounted in switch base 12. Referring now to Figure 3, the latching mechanism generally illustrated at 40. Latching mechanism 40 comprises a latch groove 41 in the form of a heart, a latch 42 and a leaf spring 43 between the housing 11 and the latch 42. A compression spring 44 is positioned between the pushbutton 13 and the switch base 12. OPERATION In operation, it will be assumed that the position of the optical switch illustrated in Figure 1 is the condition under which the circuit is in a positive condition. That is, the circuit is operating. In this condition, the signal light source which passes through the waveguide 33 and input optical path as waveguide 15 is reflected off the planar surfaces 31 and is received by waveguide 14. Waveguide 14 is operatively connected to a sensor (not shown), the existence of light indicating to the sensor that the circuit is operating. Likewise, the illumination light source is transmitted through waveguide 34 to illumination waveguide 23 and is transmitted off mirror 24 to illumination waveguide 25 which extends as indicated to the top of pushbutton 13. The top 30 simply comprises a transparent plastic material, having two sections 27 and 28 with one color, green, indicating that the illumination waveguide 25 is being travelled by light and thereby indicating the circuit is operational and a second color, red, indicating that the illumination waveguide 26 is being travelled by light and thereby indicating that the circuit is not operational. In this condition, the latch 42 of Figure 4 will be in the position indicated. That is, it will be positioned in the upper apex of the heart shaped latch groove 41. The compression spring 44 will be compressed as illustrated in Figure 3. It will now be assumed that the operator desires to interrupt the operation of the circuit. To do so, he will push downwardly on the pushbutton 13. As he pushes downwardly, the latch groove 41 will move downwardly relative to the latch 42 and the compression spring 44 will be further compressed until the latch 42 is positioned in the upper area of the heart shaped latch groove 41. The pushbutton 13 will then be in the maximum downwards position and it will then be released. The pushbutton 13 will tend to move upwardly when released under the influence of compression spring 44. As it moves the latch groove 41 will move upwardly relative to the latch 42 until the latch 42 is received by the bottom apex 50 of the latch groove 41 which will retain the pushbutton 13 in this "up" position. In this position and again with reference to Figure 1, the signal light will be transmitted through waveguide 15, reflected off planar surfaces 32 and out through waveguide 16. The signal received by the aforementioned optical sensor from waveguide 14 will cease. A further optical sensor may be positioned to receive the new signal from waveguide 16 if desired, thereby to indicate a new circuit condition. With the pushbutton in the "up" position as described, the illumination light, rather than being transmitted through waveguide 25, is transmitted to the top 30 of the pushbutton 13 through waveguide 26. The top 27 above the waveguide 26 may be, for example, red plastic transparent material, thus indicating to the operator the condition of the interrupted circuit. When it is again desired to activate the circuit, the operator will again press the pushbutton 13 until the latch 42 is retained at the uppermost position 51 of the latch groove 41 where it is released. The pushbutton 13 will move upwardly under the influence of compression spring 44 until the position illustrated in Figure 4 is again assumed by the latch 42 and the latch groove 41. Figure 5 discloses an embodiment of the invention in which the plastic of the casing, plunger and base form the light guide for the system. A plastic base 72 receives the input fibre optic cables 70 and 71. Cable 70 carries the light for the cap indicator illumination, whereas cable 71 carries a signal light beam. The rectangular casing 76, base 72 and plunger 78 are moulded from an optical grade acrylic plastic. The central rectangular plunger 78 is latched by latch 88 as previously described. Cap 80 attached to plunger 78 has transparent coloured indicator sections 86 and 87. Figure 5 shows the plunger in the "off" position. In this position light entering cable 70 passes through collimating lens 90 and strikes angled shoulder 77 which causes the light beam to be internally reflected for the most part at an angle of 90 degrees. The light beam proceeds into the centre of clear acrylic plunger 78 and strikes surface 75 which causes the beam to be reflected a second time at a 90 degree angle. With the plunger in the lower position the beam strikes the cap 80 at a point in the region of coloured section 87 and accordingly illumination indicating "off" status is perceived by the user. When the switch is in the "on" position, latch 88 allows the plunger, biassed upwardly by spring 44, to move upwardly, and this causes the surface 75 to be moved upwardly within the casing of the switch. Consequently, the light beam is directed to impinge upon transparent coloured section 86 and the user will see a light indicating "on" status. Similarly the operation of the signal beam can be seen with reference to Figures 5 and 6. When the switch is in the "off" position, the light beam travelling along fibre optic cable 71 travels into the casing through a collimating lens 90 which prevents dispersion of the light beam. The beam is then reflected off internal reflecting surface 91 and travels in the path shown in Figure 6. The beam reflects off internal retroreflective surfaces 92 so that it returns in a parallel but opposite and offset direction from the incoming beam and travels similarly out of the casing and through output fibre optic cable 94. A light signal carried on this cable indicated to the electrical circuit that the circuit is in the "off" postion. When the plunger is released to the "on" position, the plunger moves upwardly in the casing and incoming light beam impinges on the lower reflecting surface 95, shown in dotted outline in Figure 6, which causes the reflected path of the beam to be directed to output cable 96. A light signal on output cable 96 indicates to the electrical circuit that this circuit is "on". Collimating lenses 90 are moulded in the casing or base of the switch to prevent dispersion of the light and allow the switch to operate without separate fibre optic cables which would increase the manufacturing cost of the switch. This factor results in significantly decreased manufacturing costs for the present invention. The reflecting surface 75 in the plunger is moulded as an internal reflecting surface in the plunger and needs no mirror surface. A first slide switch variant is shown in Figure 7 in which a light guide 100 is formed at the bottom of a slide actuator 112 which moves into or out of the paper as shown. The two prism reflectors of guide 100 are offset so that when in a first position light is reflected from input fibre 103 to output fibre 105 while in a second position it is reflected into output fibre 107. Due to the geometry of the switch, the manufacturing tolerances for the parts of the switch need not be exact. While the critical tolerances required for operation of the switch are maintained by precise moulding of the optical and mechanical reference surface, the fit between the moving parts need not be precise. This permits simple and inexpensive manufacturing and assembly. As will be apparent to those skilled in the art, a number of variations of the invention as described in the preferred embodiment are possible. It is possible to substitute coated reflecting surfaces for the internal uncoated surface described. Further, a single input optical fibre may be used both for the signal and indicator lights. This would require a beam-splitting surface within the light switch body to generate the two beams. Also, other mechanical equivalents for the reciprocating motion of the plunger will be apparent, such as through use of rotary, rocker, slide, toggle or paddle switches. The scope of the invention is to be construed, however, in accordance with the following claims.

Claims: A switch for switching a beam of light, comprising, (a) a housing (11a,76) (b) an actuator (13) reversibly moveable in said housing (11a) between a first and a second position; (c) an input and two output optical paths (33,15,71,103; 14,16,94,96,105,107); and (d) two light directing means (31,32,92,95) each having at least two reflecting faces, characterised in that said light directing means are positioned on said actuator (13) such that in each of the actuator's positions a different one of said directing means is arranged so as to direct light from said input optical path (15,33,71,103) to a corresponding different one of said output optical paths (14,16,94,96,105,107). A switch according to claim 1, wherein said two directing means are prisms. A switch according to claim 2, wherein the reflecting faces of each of said prisms are orthogonal. A switch according to claim 2, including an input collimating lens (90) positioned so as to collimate light from said input optical path (71) onto one face of one of said prisms (92,95) so that the light is reflected onto another face of said one of said prisms and an output collimating lens positioned so as to collimate light from said another face into one of said output optical paths (94). A switch according to claim 1, wherein said housing (11a) is transparent. A switch according to claim 1, including latch means (40) for releasably holding said actuator (13) in each of said positions. A switch according to claim 1, including means for biasing said actuator (13) towards each of said positions. A switch according to claim 1, further including (a) an indicator optical input path (23,34); (b) an indicator optical output path (25) positioned to receive light from said indicator optical input path (23,34) when said actuator (13) is in a first position and not positioned to receive such light when said actuator (13) is in a second position; and (c) an indicator (28) on said actuator (13) responsive to indicate the incidence of light thereon and positioned to receive light from said indicator optical input path (23,34) via said indicator optical output path (25) when said actuator (13) is in the first position; such that said indicator (28) becomes illuminated when said actuator is in the first position. A switch according to claim 8, wherein said indicator (28) is translucent. A switch according to claim 1, futher including: (a) an indicator optical input path (34,70) in said housing (11a,76); (b) two indicator optical output paths (25,26) positioned to receive light from said indicator optical input path (34,70) when the actuator (13) is in a respective one of said positions, and (c) two indicators (28,27) on said actuator (13,78) responsive to indicate the incidence of light thereon and positioned to receive light from respective ones of said indicator optical output paths (25,26).

Inventors: KIDDER JOHN S, MONTGOMERY DEREK, KIDDER, JOHN S., MONTGOMERY, DEREK
Applicants: KIDDER JOHN S, KIDDER, JOHN S.
Application year: 1989
Main classification: G02B26
IPC codes: G02B6