TECHNOLOGY OVERVIEW
 

Texzec has discovered a proprietary method of trapping ultrasonic energy in localized regions of virtually any metal, glass or ceramic, and in some plastics. Once trapped this concentration of acoustic energy is sensitive to a touch on the front surface from a finger or glove, but insensitive to water, grease and other common contaminants. The trapped energy is localized in areas about the size of a fingertip, so touch positions can be spaced in a manner similar to those of any keyboard or membrane switch. Simple electronics are used to detect which location has been touched, up to sixteen positions per square inch in metal up to 3/8" thick.

Illumination can be provided by clear epoxy filled channels formed in the metal in the center or adjacent to each switch position, or by a light guide plastic overlay bonded onto the top surface. Rear mounted LED's are the illumination source.

Tactility can be enhanced by recessing the switch position, striking the metal plate with an actuator when a switch is activated, or with an inexpensive overlay if switch travel is specified. Braille legends and other locating aids for the disabled are easily implemented.

The switch operates with ultrasonic energy and the metal plate acts as a very effective shield, thus radiated electromagnetic energy levels are low.

PRINCIPALS OF OPERATION

When the surface of a switch plate is contoured, as in Figure 1, it creates raised regions that trap ultrasonic energy, in accordance with energy trapping theory.

Texzec has discovered that when a raised region is set into vibration by a properly positioned ultrasonic transducer, a twisting motion, confined to the shape of a cylinder, is induced, extending through the thickness of the metal, as in Figure 2. This twisting motion, known as a trapped torsional mode, is the key to the technologies unprecedented performance and is proprietary to Texzec, Inc.

When the raised region is set into vibration at around 1 MHz by the transducer, it subsequently rings down like a bell that has been struck. (Figure 3) A finger or gloved hand touching the front surface at the end of a vibrating cylindrical region dampens the vibration and reduces ring down time. This reduction in ring down time is detected with an inexpensive microcontroller, which is easily multiplexed for multiple switch positions.

 

SOFT FAILURES, FAILURE PREDICTION AND FAILURE REPORTING

The touch detection microcontroller first sets the switch into resonance with a short series of pulses. The resonator part of the switch then rings down at the resonant frequency with it's amplitude in the form of an exponential decay. We detect this exponentially decaying signal and count the number of cycles to a predetermined amplitude.

As long as the processor gets the count and the number is between preset limits, the switch has to work and the micro reports out switch status to a monitoring system. Should the micro fail, a periodic status signal will not be received by the monitoring system so all aspects of the switch are monitored.

Using a simple algorithm, the count and the rate of change of the count with time are stored and compared to predetermined limits. This enables us to predict imminent as well as actual failures and report these to a monitoring system.

 

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