Using an accelerometer sensor to measure human hand motion

Microfabricated accelerometer sensors have been developed to measure acceleration in a variety of applications, including automobile airbag crash sensors and seismic activity monitors. For this thesis a three-dimensional accelerometer sensor has been created for measuring involuntary human hand motion. The sensor uses three single-axis accelerometers fabricated at the MIT Microsystems Technology Laboratory (MTL). The size and mass of the sensor were limited to avoid altering hand motion being measured. The MTL fabricated accelerometers have a proof mass restricted to motion along a single axis and constrained by angular springs. Acceleration of the sensor forces displacement of the proof mass, and the displacement is sensed using differential capacitors. The accelerometer dies were packaged in leadless chip carriers (LCCs), and the LCCs were arranged in a three-axis configuration. A circuit was constructed to convert the differential capacitance signal into an analog signal and then into a digital signal before being read into a computer. The data acquisition program allows real-time analysis of the acceleration data, as well as storage of the data for more sophisticated subsequent analysis. There are several sources of error in the accelerometer sensor system that limit the accuracy of measurement. Analog electrical noise limits the precision to ± 2.5 mg. There is a nonlinearity between the acceleration input and the analog voltage output of at least ± 7 mg. A third error source is cross-sensitivity, arising from movement in accelerometer proof masses from acceleration perpendicular to the intended axis of motion, and is 3.75% with this accelerometer sensor. The three-dimensional accelerometer sensor has been demonstrated in the intended application of measuring human hand motion. Thesis Supervisor: Charles G. Sodini Title: Professor of Electrical Engineering