Patent Application
20080202911
The field of the invention is membrane switches.
Membrane switches have at least one contact that is on, or made of, a flexible substrate, i.e. a membrane layer. There is always a second layer against which the membrane layer is pressed, and that second layer can be either static or flexible.
Although it is possible to produce membrane switches that rely upon capacitive, ferrite core, or hall effect, membrane switches typically utilize a direct (Ohmic) contact in which the poles of the switch make transient physical contact. Thus, pressure on the membrane layer physically closes a circuit by contacting one electrical trace to another, and upon release these “poles” separate as the flexing membrane returns to its original position.
The momentary type of action, ready accommodation to visual design feature, low cost, and relatively high reliability, all cooperate to provide applicability in innumerable applications. Among other things, membrane switches are very commonly used in DC logic-level circuits such as those used in computer keyboards, on medical equipment, and in television and other hand-held controllers.
Although membrane switches are fairly reliable, they are known to fail. Failures can occur for any number of reasons, including operator error, moisture, excessive use, manufacturing defects, and so forth. In some applications failure carries an extremely high cost, and it is therefore necessary to utilize some sort of self check that identifies a switch as being defective, or at least allows the switch to continue functioning with a defect. Exemplary applications requiring failsafe operation include pressure sensing floor mats used for security purposes, and operational controls on life support equipment.
As used herein the term failsafe device means that the device can be interrogated at all times to detect a failure. Failsafe capabilities appear to be unknown in membrane switches. Existing membrane technology generally relies upon orthogonally parallel traces upon opposing surfaces. In normal operation the traces do not touch each other, and there is only a single lead from each trace. Such designs are not conducive to failsafe operation because there is no way to test the integrity of the traces. Indeed, Touch-Sensor™ advertises their TouchCell™ switches (which are not membrane switches) as the only “touch technology” switches that are recognized by UL as failsafe switches. (http://www.touch sensor.com/ faq.html). The Touch Sensor™ web page, as well as all other patents, applications, web sites, articles and the like referenced herein are incorporated by reference in their entirety. Where a definition or use of a term in a reference, which is incorporated by reference herein, is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
U.S. Pat. No. 5,175,443 to Tabuchi (December 1992) does teach a membrane switch that can detect a false positive (always on) condition. There, a membrane switch has closely disposed duplicate traces. When the switch is operating normally, pressure sufficient to establish a circuit in one of the duplication traces is assumed to concurrently establish a circuit in the close duplicate. If one of the switches becomes defective because one of the traces has peeled away from its base, a logic circuit can detect the failure by comparing the current in the duplicate traces. Unfortunately, devices using to the '443 technology are only able to detect false positive situations—they are unable to detect false negative situations, in which the switch fails to record a proper “on” situation. Such switches are not considered failsafe as the term is used herein because the integrity of apparently viable traces cannot be tested.
Existing membrane circuits are also designed to detect pressure at a given point, on the membrane, or pressure on the membrane at any point. And such circuits merely detect on-off. Membrane circuits are apparently unknown that detect sizes and shapes (i.e., footprints) or weights. Significantly, it is exactly in detection of sizes, shapes and weights that failsafe operation is so critical.
Thus, there is still a need for additional development of failsafe membrane switches, especially for membrane switches that detect sizes, shapes and/or weights
The present invention provides apparatus, systems and methods for novel classes of membrane switches. Novel classes include switches using: (a) failsafe four-wire series circuits; (b) failsafe two-wire circuits; (c) ladder circuits (two- and four-wire non-failsafe); (d) multi-zone; and (e) weight detecting technology.
In other aspects of the inventive subject matter, a failsafe membrane switch serving as safety mat can be manufactured much thinner than prior art failsafe safety mats—on the order of no more than ¼ inch thickness, or no more than ⅙ inch, as opposed to ⅜″ to ½″. As used herein the term “mat” is intended to be interpreted broadly, to include mats upon which one would stand, as well as mats on tables and other surfaces upon which one would not ordinarily stand.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components.
In
It is highly preferred that integrity testing can be accomplished while the switch is deployed in a useful operational setting other than merely testing itself. One could do this continuously without interrupting the useful function, by passing a low voltage alternating current along the trace being testing. One could also test the switch discontinuously by passing any suitable AC or DC voltage along the current a periodic intervals. Suitable intervals can range from less than a second to every minute, once every hour, or even less frequently.
In
In
In
In
In
A related improvement over the prior art involves modification of the spacers to detect differences in weight or depth. In
The ability to close different circuits as a function of the applied pressure has many uses, including weighing. Thus, a security mat may be designed to send one signal when it experiences a relatively small load (such as a bird), another signal with a medium load (such as a person), and another signal with a heavy load (such as a cart with boxes). The technology can also be useful in many other areas, such as in computers, where different signals can be sent depending on how hard a key I pressed. Thus, in a QWERTY keyboard, pressing the “A” key lightly may be associated with a small letter “a”, but pushing the same key with greater force may be associated with the capital letter “A”, and pushing even harder may be associated with a common word such as “Anderson”.
Depending on the spacing of the traces and spacer dots (not shown) it is contemplated that membrane switches can be used to detect object sizes as low as ¼ inch (6.35 mm) or even ⅛ inch or 1/16th inch in diameter, length, etc. Similarly, it is contemplated that membrane switches can be used to detect object sizes as low as 6 mm, 3 mm or 1.5 mm. On the upper end, it is contemplated that floor mat type detectors could have a diameter or edge of at least 6 inches, 12 inches, 18 inches, and in rectangular form could be as large as 24 inches by 48 inches, 36 inches by 72 inches, or even 48 inches by 96 inches. Roughly corresponding metric measurements are 0.6 meters by 1.3 meters, 0.9 meters by 1.8 meters, and 1.3 meters by 2.6 meters. The types of shapes that can be detected include solid shapes (round, rectangular, oval, polygonal, etc) as well as donuts and other shapes with open areas, and irregular shapes.
Another aspect of the inventive subject matter involves embossing. It is common to place a trace on the underside of a dimpled up embossment. Thus, in prior art
In
A major improvement of the various failsafe designs contemplated herein is that they can be much thinner than the ⅜-½ inch thick (10 to 13 mm) failsafe floor mats currently available. In preferred embodiments the inventive switches can readily be produced at least as thin as 1/16 inch (1.6 mm). This improvement arises in part because a second lead line to each trace is all that is needed within the contacting portion of the switch to effectuate failsafe testing. The improvement can also arise as a function of embossing at least one of the active layers.
Materials suitable for the inventive switches include all previously known membrane switch materials, including especially Lexan™ or other polycarbonate resin. To reduce thickness and improve moisture and water resistance, the switch can be conformally coated with polyurethane or other spray. Such coatings can provide water resistance to at least 3 atmospheres.
Thus, specific embodiments and applications of failsafe and other membrane switches have been disclosed. It should be apparent, however, to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended proposed claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.
| Number | Date | Country | |
|---|---|---|---|
| 60681633 | May 2005 | US |
