Normally closed electrical switch

Abstract: A normally closed electrical switch (10) includes a first circuit board (12) having a first switch contact (22) thereon and an aperture (26) therethrough near the first switch contact. A second, flexible circuit board (14) has a second switch contact (28) aligned with the first switch contact of the first circuit board. A spacer sheet (16) separates the first and second circuit boards (12,14) and has an aperture (38) in registry with the aperture in the first circuit board. The switch contacts (22,28) extend toward each other through the aperture (38) in the spacer sheet (16) such that they are in normally closed condition. A movable cover (18) is provided on the first circuit board at least over the aperture therein. An actuator (50) is operatively associated with the cover and extends through the aperture (26) in the first circuit board (12), through the aperture (38) in the spacer sheet (16) and engageable with the second, flexible circuit board (14) for flexing the second circuit board and opening the switch contacts (22,28) in response to movement of the cover.

Description: This invention generally relates to the art of electrical switches and, particularly, to a normally closed membrane-type electrical switch. See for example US-A-4 302 647. Background of the Invention Membrane electrical switches are used in a wide variety of applications. Such switches often are called "touch" switches. In particular, such a switch includes a pair of flexible non-conductive substrates or membranes, such as of flexible plastic material, on which thin metallic contacts are bonded, such as of conductive metallic foil. In a normally open membrane switch, a spacer sheet is sandwiched between the pair of membranes, and the spacer sheet has an aperture aligned with the metallic contacts. When one of the membranes is depressed in the area of the aperture in the spacer sheet, the metallic contacts engage to close the switch. Usually, there are thin foil conductors or leads connected to the metallic contacts and bonded to the flexible substrates or membranes for facilitating connecting the switch contacts to external circuits. Such normally open membrane switches are conventional and have been commercially available heretofore as low profile, inexpensive alternatives for more complex mechanical switches. In order to make a membrane switch as a normally closed switch, the membranes must be adhered in close juxtaposition to maintain the foil contacts in normal engagement, and extraneous rigid support means must be provided to support the normally flexible membranes. Some means then must be provided for separating the membranes and their respective metallic contacts in order to open the switch. Such normally closed membrane switches have serious reliability problems. It can be readily understood that membrane switches are not as efficient and cost effective in a normally closed configuration than in the normally open configuration described above. Unfortunately, there are many switch applications wherein it would be desirable to use inexpensive normally closed membrane switches rather than more elaborate and expensive mechanical or mechanical/optical switches. For instance, vending machines, such as those that distribute beverage cans, must sense when a can which has been requested has been physically dispensed into and through a dispensing chute. If a particular selection is empty, a command to dispense that selection made by the machine's control system has no effect. In that instance, a sensing system informs the control system that no can was dispensed, whereby the customer can make an alternate selection or obtain a refund. Conversely, if the sensing system indicates that a can was dispensed, the control system terminates the opportunity for the customer to obtain a refund. Heretofore, such sensing systems typically employ optical sources and sensor combinations arranged such that a dispensed can breaks an optical beam from the source to the sensor as it passes through the dispensing chute. The broken beam signals an input of the control system. While such optical sensors function reasonably well, they are relatively expensive. The above vending machine example is but one example wherein an expensive sensing/switch system could be made much more efficient and cost effective by using membrane switches. In other words, a membrane switch simply could actuate under the weight of the beverage can rolling down the dispensing chute. It would be most desirable if the membrane switch is in a normally closed electrical condition. However, as described above in regard to membrane switches, the least complex and most cost effective membrane switches conventionally have normally open contacts. The present invention is directed to providing a membrane switch which is in a normally closed electrical condition but which still is extremely simple and cost effective. Summary of the Invention An object, therefore, of the invention is to provide a new and improved normally closed electrical switch, such as a normally closed membrane switch. In the exemplary embodiments of the invention, the normally closed electrical switch includes a first circuit board having a first switch contact thereon and an aperture therethrough near the first switch contact. A second, flexible circuit board has a second switch contact aligned with the first switch contact of the first circuit board. A spacer separates the first and second circuit boards and has an aperture in registry with the aperture in the first circuit board. The switch contacts extend toward each other through the aperture in the spacer such that they are in normally closed condition. A movable cover is provided on the first circuit board at least over the aperture therein. Actuator means are operatively associated with the cover and extend through the aperture in the first printed circuit board, through the aperture in the spacer and engageable with the second, flexible circuit board for flexing the second circuit board and opening the switch contacts in response to movement of the cover. As disclosed herein, the first and second circuit boards comprise plastic membranes, and the first and second switch contacts are metal foil contacts on the membranes. The spacer is generally rigid relative to the membranes. The cover is fabricated of deformable material and may include a switch button operatively associated with the actuator means. In one embodiment of the invention, the actuator means is integral with the switch button. In the preferred embodiment, at least one of the circuit boards is embossed to project through the aperture in the spacer such that the switch contacts are in normally closed condition. In one embodiment of the invention, the actuator means is provided by a plurality of actuator posts spaced around the switch contacts. In another embodiment of the invention, the actuator means is provided by a single actuator post, and a plurality of switches are spaced around the actuator post, with each switch including one of the switch contacts on each of the circuit boards. Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings. Brief Description of the Drawings The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with its objects and the advantages thereof, may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements in the figures and in which: FIGURE 1 is an exploded perspective view of a first embodiment of a normally closed electrical switch according to the invention; FIGURE 2 is a vertical section through the first embodiment, with the switch in normally closed condition; FIGURE 3 is a view similar to that of Figure 2, with the switch in open condition; FIGURES 4-6 are views similar to that of Figures 1-3, respectively, of a second embodiment of the invention; and FIGURES 7-9 are views similar to that of Figures 1-3, respectively, but of a third embodiment of the invention. Detailed Description of the Preferred Embodiments Referring to the drawings in greater detail, and first to Figures 1-3, a first embodiment of a normally closed electrical switch, generally designated 10, includes a first circuit board 12 and a second circuit board 14. A spacer sheet 16 is sandwiched between circuit boards 12 and 14. A cover 18 is disposed on top of first circuit board 12, and a backing sheet 20 is disposed beneath second circuit board 14. First circuit board 12 comprises a thin flexible plastic membrane or substrate having a first switch contact 22 on the underside thereof. The switch contact is provided by a thin metal foil contact pad adhered to the underside of the membrane, along with a foil lead 24 extending from the pad to an edge 12a of the circuit board for connection to appropriate circuit means (not shown). A plurality of apertures 26 through circuit board 12 are equally spaced around switch contact 22. Second circuit board 14 also is fabricated of a thin flexible plastic membrane or substrate having a second switch contact 28 on the top side thereof. Again, second switch contact 28 is provided by a thin metal foil having a lead 30 extending to an edge 14a of the circuit board, where the lead is connected to a conductor 32 of a flat electrical cable 34. As best seen in Figures 2 and 3, membrane 14 is embossed, as at 36, so that second switch contact 28 projects upwardly from the top surface of the membrane of second circuit board 14. Spacer sheet 16 has an enlarged aperture 38 therethrough. The aperture is large enough to surround all of apertures 26 in first circuit board 12, with first switch contact 22 in the center thereof. The spacer sheet is fabricated of appropriate material which is generally rigid in comparison to the thin plastic membranes of first and second circuit boards 12 and 14, respectively. Therefore, the spacer sheet effectively supports the membranes. Backing sheet 20 is similar to spacer sheet 16 in that it has an enlarged aperture 40 approximately the same size as aperture 38 in the spacer sheet. Backing sheet 20 also is generally rigid in comparison to the thin flexible membranes of circuit boards 12 and 14. Cover 18 is fabricated of elastomeric material and includes an integral switch button 42 projecting upwardly therefrom. The switch button is integrally formed with the cover by means of a peripheral web 44 entirely surrounding the switch button. As best seen in Figures 2 and 3, web 44 is thinner than cover 18 and switch button 42, so that when pressure is applied to the button in the direction of arrow "A" (Fig. 3) web 44 will deform because of the elastomeric material of the integral cover/web/switch button. Lastly, actuator means are operatively associated with cover 18, and particularly switch button 42, for flexing second circuit board 14 and opening switch contacts 22 and 28 in response to depressing switch button 42 of the cover. More particularly, as seen in Figure 2, a plurality of actuator posts 50 are formed integral with and project inwardly or downwardly from switch button 42 through apertures 26 in first circuit board 12. These actuator posts are effective for flexing second circuit board 14 and opening normally closed switch contacts 22 and 28 as described below. In operation of normally closed electrical switch 10, reference is made first to Figure 2 wherein it can be seen that apertures 38 and 40 in spacer sheet 16 and backing sheet 20, respectively, are in alignment transversely through the laminated switch. In addition, it can be seen that by embossing the flexible plastic membrane of second circuit board 14, as at 36, second switch contact 28 is elevated into engagement with first switch contact 22. In other words, embossing the membrane of the second circuit board accommodates for the thickness of spacer sheet 16. When a force is applied to switch button 42 in the direction arrow "A" as shown in Figure 3, web 44 between the switch button and cover 18 deforms, and actuator posts 50 are driven downwardly through apertures 26 in first circuit board 12, through aperture 38 in spacer sheet 16 and against the top surface of second circuit board 14. This pressure or force flexes the plastic membrane of second circuit board 14 into aperture 40 of backing sheet 20 and, thereby, separates or opens switch contacts 22 and 28. In essence, actuator posts 50 move switch contact 28 away from switch contact 22. The various laminates including cover 18, first circuit board 12, spacer sheet 16, second circuit board 14 and backing sheet 20 are held together as a laminate by appropriate adhesive. In fact, it should be understood that backing sheet 20 could be eliminated, with second circuit board 14 fixed to the more rigid spacer sheet 16 by an appropriate adhesive and still allow the second circuit board to be moved away from the first circuit board, opening the switch contacts, by depressing switch button 42 and driving actuator posts 50 against the top of the flexible second circuit board. The second embodiment of the normally closed electrical switch shown in Figures 4-6 operates substantially the same as the first embodiment described above and shown in Figures 1-3. Therefore, like numerals have been applied where appropriate in Figures 4-6 to designate like components described above in relation to Figures 1-3. There are two major differences in the second embodiment of Figures 4-6. The first major difference is that switch button 42 is joined to cover 18 by means of an oblique or angled web 44' as best seen in Figure 5. This angled web acts as a camming surface should the switch be used in applications as described in the "Background", wherein an item, such as a beverage can, might roll over the switch button in order to open the switch. Angled web 44' allows for easy rolling of such an item over the switch and down a chute of a beverage dispensing machine, for instance. The second difference in the second embodiment of Figures 4-6 is seen best in Figures 4 and 5 wherein actuator posts 54 project upwardly from second circuit board 14 rather than downwardly from the underside of switch button 42. In manufacture, the actuator posts 50' would be made as separate components appropriately adhered to the top of second circuit board 14 rather than being integral with the underside of switch button 42 as in the first embodiment of Figures 1-3. By not having the actuator posts as integral portions of the cover and/or switch button, the cover and switch button, along with angled web 44', can be simply and inexpensively fabricated of a uniform thickness of material. Figures 7-9 show a third embodiment of the normally closed electrical switch and, again, like numerals have been applied in Figures 7-9 to designate like components described above and shown in Figures 1-6. More particularly, the third embodiment of Figures 7-9 is similar to the second embodiment of Figures 4-6, in that switch button 42 is joined to cover 18 by an angled web 44', with the cover, web and button being fabricated of a material of uniform thickness. In addition, rather than having a plurality of separate actuator posts 50' as in the second embodiment of Figures 4-6, the third embodiment of Figures 7-9 employs a single, center actuator post 50". The post projects through a single aperture 26' in first circuit board 12. The third embodiment of Figures 7-9 also employs a plurality of pairs of normally closed switch contacts 22 and 28 surrounding the single actuator post 50". The flexible plastic membrane of second circuit board 14 again is embossed, as at 36, so that switch contacts 28 project upwardly through aperture 38 in spacer sheet 16 to normally engage switch contacts 22, and, thereby, compensate for the thickness of the spacer sheet. Again, single actuator post 50" is adhered to the top of second circuit board 14. Finally, although first and second circuit boards 12 and 14, respectively, along with spacer sheet 16, cover 18 and backing sheet 20 all are shown herein as being square sheets or portions of a laminated composite structure, it should be understood that these sheets may comprise only portions of much larger sheet-like components. In other words, first and second circuit boards 12 and 14, respectively, may be only portions of much larger circuit boards.

Claims: A normally closed electrical switch (10), comprising: a first circuit board (12) having a first switch contact (22) thereon and an aperture (26) therethrough near the first switch contact; a second, flexible circuit board (14) having a second switch contact (28) aligned with the first switch contact (22) of the first circuit board (12); characterised by a spacer (16) separating the first and second circuit boards and having an aperture (38) in registry with the aperture in the first circuit board; said switch contacts (22,28) extending toward each other through the aperture (38) in the spacer (16) such that they are in normally closed condition; a movable cover (18) on the first circuit board at least over the aperture therein; and actuator means (50) operatively associated with the cover and extending through the aperture (26) in the first circuit board (12), through the aperture (38) in the spacer (16) and engageable with the second, flexible circuit board (14) for flexing the second circuit board and opening the switch contacts (22,28) in response to movement of the cover. The normally closed electrical switch of claim 1 wherein said second, flexible circuit board (14) comprises a plastic membrane, and said second switch contact (28) comprises a metal foil contact on the membrane. The normally closed electrical switch of claim 2 wherein said first circuit board (12) comprises a plastic membrane, and said first switch contact (22) comprises a metal foil contact on the membrane. The normally closed electrical switch of claim 3 wherein said spacer (16) is generally rigid relative to said plastic membrane. The normally closed electrical switch of claim 1 wherein said cover (18) is fabricated of deformable material. The normally closed electrical switch of claim 1 wherein said actuator means (50) is integral with said cover (18). The normally closed electrical switch of claim 1 wherein at least one of said circuit boards (12,14) is embossed (36) to project through the aperture (38) in the spacer (16) such that the switch contacts (22,28) are in normally closed condition. The normally closed electrical switch of claim 1 wherein said cover (18) includes a movable switch button (42) operatively associated with said actuator means (50). The normally closed electrical switch of claim 1 wherein said actuator means comprise a plurality of actuator posts (50) spaced around the switch contacts (22, 28). The normally closed electrical switch of claim 1 wherein said actuator means comprise a single actuator post (50"), and including a plurality of switches spaced around the actuator post, each switch including one of said first switch contacts (22) and one of said second switch contacts (28).

Inventors: HESTER TODD A, KREGER DANIEL T, HESTER, TODD A., KREGER, DANIEL T.
Applicants: MOLEX INC, MOLEX INCORPORATED
Application year: 1997
Main classification: H01H13
IPC codes: H01H13