The Design Challenge

Imagine for a moment that you are asked to design a pushbutton switch for the most challenging applications. The pushbutton needs to be extremely rugged, capable of surviving abuse and vandalism. It needs to function perfectly in extreme temperatures, in desert heat, driving rain, or snow and ice. Immunity to dusty environments and sand storms is required. Vibration cannot harm it, and it should be able to survive direct hammer blows. It must be corrosion proof, waterproof, explosion resistant, and submersible to 200 meters. It should be low-profile, flush mounted. It must be permanent, never needing to be replaced, and must carry a lifetime product warranty. And it must have no moving parts. That would be a very challenging assignment.

Now imagine that switches with these characteristics have already been engineered for you, and there are dozens of selectable options perfectly designed for your application. These are the ActiveMetal switches, part of the new Illinois Tool Works ActiveTouch line of switch products. They are designed “Beyond Durable.”

Imagine the Applications

Imagine, for a moment, in what applications such a switch might be ideally applied. Military and aerospace applications are the first applications that come to mind, followed by mining, petroleum exploration, refining and other hazardous environments. Industrial and process controls might be other viable applications. Municipal facilities, elevators, public transportation and outdoor kiosks such as ATMs and vending machines offer other possibilities, as the costly damage of vandalism can be avoided. Access security applications, especially those in prisons, might be another likely application. The technology could also extend the lifetime of pushbuttons used in the gaming industry.

Would it surprise you then, if you were to discover that sterile environments were one of the first applications? Medical facilities and equipment require steam sterilization, as do pharmaceutical manufacturing facilities and clean rooms. Food processing plants require frequent cleaning with hot water and steam hoses. Commercial laundry applications are also possible, as these make extensive use of steam, hot water and dry cleaning chemicals. From these applications it is a very short step to providing waterproof hot tub, whirlpool, and other spa controls.

Recreational marine and automotive applications come to mind too; whether underwater, for rugged off-road vehicles. Earth movers, mining equipment and farm machinery also have similar requirements of durability.

Yet one of the first unique applications was the custom creation of a solid QWERTY keyboard for use in sterile environments. An audible tone provides feedback to the user for each keystroke.

Solid ActiveTouch keyboard created for a sterile environment
A solid ActiveTouch keyboard created for a sterile environment.
How it Works

The unique, patented technology behind the ActiveMetal pushbutton switch employs a low-voltage subminiature transducer. The transducer generates a Megahertz frequency vibration to the pushbutton a thousand times a second, and detects the decay or ring-down of that tiny vibration. Forming the pushbutton into a concave or convex shape, by machining, embossing, or debossing, creates a resonant cavity that provides a drumhead effect. When the button surface is touched by a bare finger or gloved hand the ultrasonic vibration is dampened (as illustrated in Figure 2 below) and the transducer detects this change in resonance within milliseconds.    

The intelligence of the firmware built into the PCB of the microprocessor includes the capability to identify and predict problems, like foreign material interference within the active switch area, and adapts to the change. This function performs continuously and automatically.

In mission critical applications, the ActiveTouch technology can not only sense abnormal operation or imminent malfunction, but can even notify the user via a selected communication protocol (RS232, USB, CANbus, etc.) or transfer the activation area to a backup switch location.  

Imagine the Service Requirements

There are no service requirements. There is no need to inventory quantities of spare parts around the country, or to dispatch repair services to reconcile switch problems. The savings of this advantage can be easily calculated. 

For additional information on the products and technologies discussed in this article, see ITW Switches.