A thin film strain gauge angular displacement sensor for measuring finger joint angles

An angular displacement sensor based on a thin-metal-film strain gage has been developed and evaluated in vitro. Gold or palladium films 2000-AA thick were vacuum-deposited on 127- mu m thick flexible polymide substrates and etched to produce a strain gage pattern. Individual strain elements were 100- mu m wide, and holes were placed in the substrate for mounting pins. Nominal resistances for this pattern were 200 Omega for gold and 750 Omega for palladium. Joint angle was measured by fixing one end of the sensor proximal to the joint using a velcro band while the other end slid in a guide attached to the digit distal to the joint. Flexing the joint caused the strain gage which was located on the convex surfaces to be in tension and resulted in a strain proportional to the angle of flexion. A mathematical model of the structure has predicted that the resistance change of this sensor would be sensitive to angle and not to the radius of curvature over which the sensor was bent.<>