PRESSURE SENSING – 21110

Robotic pressure sensing devices detect and measure force, and can in some instances tell where the force is applied.

In a basic pressure sensor, a pressure-sensitive transducer tells a robot when it collides with something.Two metal plates are separated by a layer of nonconductive foam. This forms a capacitor. The capacitor is combined with a coil (inductor). The coil/capacitor circuit sets the frequency of an oscillator. The transducer is coated with plastic to keep the metal from shorting out to anything. If an object hits the sensor, the plate spacing changes. This changes the capacitance, and therefore the oscillator frequency.When the object moves away from the transducer, the foam springs back, and the plates return to their original spacing. This device can be fooled by metallic objects. If a good electrical conductor comes near the transducer, the capacitance might change even if contact is not made.

Conductive foam, rather than dielectric foam, can be placed between the plates, so that the resistance changes with pressure. A direct current is passed through the device. If something bumps the transducer, the current increases because the resistance drops. This transducer will not react to nearby conductive objects unless force is actually applied.

The output of a pressure sensor can be converted to digital data using an analog-to-digital converter. This signal can be used by the robot controller. Pressure on a transducer in the front of a robot might cause the machine to back up; pressure on the right side might make the machine turn left.