Three-axial force sensor with capacitive read-out using a differential relaxation oscillator

A silicon three-axis force sensor is designed and realized to be used for measurement of the interaction force between a human finger and the environment. To detect the force components, a capacitive read-out system using a novel relaxation oscillator has been developed with an output frequency proportional to differential capacitance. The sensor has a range of 2N in tangential- and normal force direction with an accuracy better than 1.5% of the full-scale. The sensor can be safely overloaded with a normal force of more than 30N.