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Bleeding Edge: Flex Circuits as Robot Skin Sensors
Monday, May 15, 2006 | Robert Tarzwell with Ken Bahl - Sierra Proto Express

In today's increasingly robotic world, robots need more human-like features to integrate properly into our society. One example of improved sensory applications is the fingertips of a robotic hand, which require the ability to sense temperature, touch, pressure, pain and even air flow. Inventive applications of flex circuits and simple sensors can emulate a human's highly sensory fingertip systems.

To sense touch, we can use a resistive layer and connections to a microprocessor, which would be similar to a touch pad on your laptop. The resistor touch pad allows position of touch as well as some pressure sensing. The resistive layer is printed on a top flex layer with a skin-like, latex protective outer surface. To sense temperature, we can silkscreen or implant resistive sensors on the flex layers, connected to a microprocessor to measure temperature through resistive changes. The microprocessor compares the resistive reading to a lookup scaling chart, therefore generating an accurate temperature reading. When the fingers of our robot touch something hot, our robot can assess what it is holding and decide to suffer damage to save human life--unlike humans, who instinctively jump and drop the object. (Example: The robot is working in the lab and picks up a hot beaker of sulfuric acid. Rather than drop the acid and possibly hurt humans or damage property, the robot can simply place the hot object back down and walk over to the repair shop for new finger sensory pads.) To sense pressure, the flex circuit can have carbonized rubber pads attached to gold pads between the flex layers; as the finger pads press on an object, the resistance of the carbonized rubber decreases. As the softer carbon/rubber pressure sensors are compressed flatter with increasing pressure, a series of harder durometer rubber pads continues to react to stronger pressures--for example, your robot picking up your bowling ball versus a feather. 

 

For pain or damage sensors, a series of fine, 2mil-thin copper tracks on the outer-layer flex circuit would open if the finger pad were severely damaged. The tracks would be covered with a thin, soft silicon or latex rubber to act as a skin. The pain/damage tracks could be shaped similar to human fingerprints. The height of the pain tracks would cause the silicon to follow the pain-sensing tracks and protrude with a similar shape, allowing for robot identification. Should one run amok and rob a candy store, it would leave its fingerprints all over the store.


     

To make the robot more human-like, should it touch you, we need to heat the skin to 98.6* F. through a series of screen-printed carbon resistors placed on one of the flex layers, which, with a little current, will heat the silicon slightly to the touch. The temperature sensors allow the microprocessors to keep the skin heat constant and yet still measure contact temperature. The heat resistors also measure air flow; with a heated resistor, any air flow will cause a rise in current required to keep the temperature constant, and the sensors can measure air flow as human hair and skin do. If you order the new S.E.X. 3000-version personal-satisfaction robot, you will want as many tactility sensors as possible, as well as heated skin. Well, just kidding about the S.E.X. 3000 robot--but this article still shows that it's possible to use flex circuits for new purposes.

 

CLICK HEREto request additional info from Sierra Proto Express.

Robert Tarzwell is the director of technology at Sierra Proto Express

Ken Bahl is Sierra's CEO


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