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Abstract
In this thesis, a journey of development of newer tactile sensors and sensing techniques is presented. The characterisation of a novel capacitance-based, tactile sensor designed to measure shear forces is discussed. The sensor design is targeted for use in robotic and prosthetic hands, where haptic feedback or the ability to detect shear forces associated with slip are critical. Sensors with a full-scale displacement range of ±0.525 mm were produced and the differential capacitance, when measured at each fixed interval, was found experimentally to have a maximum standard deviation of 0.428 fF over a ±2 N range. A maximum standard deviation of 1.35 fF was measured across the full scale sensor range of ±4 N. Due to the capacitive nature of the sensor, it suffers from low dynamic frequency response and a higher standard deviation in output under larger deformation.
The design and fabrication of a polyvinylidene fluoride (PVDF) based, mouse (or rodent) whisker mimicking, tactile sensor is also presented, which overcomes some of the limitations of the capacitance-based, shear sensing tactile sensor. Unlike previous designs reported in the literature, this sensor mimics the mouse whisker not only mechanically, but it also makes macro movements, just like a real mouse whisker in a natural environment. With the control system developed for this sensor, the whisker can vibrate between 5 to 236 Hz, similar to a real mouse whisker. The minimum standard deviation in sensor output, in terms of frequency is 0.649 Hz at 200 Hz, while minimum standard deviation in terms of voltage amplitude of sensor output is 0.0012 V at 200 Hz. The sensor has high bandwidth of 200Hz, but is limited to dynamic sensing only.
To achieve both static and dynamic sensing, with high bandwidth, another design was conceived using a novel technique employing PVDF. Results show that within a test range of 0-12 N, applied static forces can be discriminated with a 95% level of confidence. Maximum standard deviation of 0.0074 V was observed at 1 N.
The capacitance and both PVDF-based sensor designs, feature ease of mass production, low per-unit-cost, novel overload protection and a low wire count, while still preserving the ability to achieve reasonable spatial resolutions and array densities. Along the way, advantages and limitations of designs are discussed in detail and recommendations for future work are put forth.