Microfabricated Shear -Sensitive Tactile Sensor: Development and Application

Abstract

This research includes the sensor design, fabrication, modeling, characterization, and application. The sensor design is based on a silicon diaphragm structure instrumented with four piezoresistors. A square mesa on top of the diaphragm is used to convert an applied force into stress. Each of the four resistors is designed as an independent strain gage to allow the sensor to resolve both normal and shear forces. The sensor is fabricated using integrated circuit (IC) and MEMS technologies. KOH etching is used to make the diaphragm. Low-temperature wafer bonding is used to seal the cavities. EPON su-8 is used to construct the mesa. Silicon isotropic etching is used to release PI/Al/PI leads to realize flexible package. An analytical model is developed for describing applied forces, induced stress, the resistance variation, and their relationships. Bench characterization is performed with a 0--3 N force applied at elevation angles of 0°, 30°, 45° and 60°. At each elevation angle, the sensor is rotated from 0° to 360° at increments of 30°. The bench characterization results demonstrate shear-force sensing ability. The characterization of the sensor on human subjects is performed with 5--40 N shear and 0--30 N compressive hand grasping forces applied. The results demonstrate the sensor's capability of measuring forces at human-object interfaces. Finally, the sensor is used to measure the finger forces during cylinder grasping. The normal and shear forces are measured at torque levels of 6.9, 11.5, 16.1, 20.7, and 25.3 kg-cm. for three segments of the middle fingers on six subjects. The results show that both normal and shear forces vary linearly with torque. The shear force is dominant in the cylinder grasping. The distal phalanx played the major role in the turning activity, whereas the middle phalanx played the major role in holding activity.