Researchers and clinicians often desire to monitor pressure distributions on soft tissues at interfaces to mechanical devices such as prosthetics, orthotics or shoes. The most common type of sensor used for this type of applications is a Force Sensitive Resistor (FSR) as these are convenient to use and inexpensive. Several other types of sensors exist that may have superior sensing performance but are less ubiquitous or more expensive, such as optical or capacitive sensors. We tested five sensors (two FSRs, one optical, one capacitive and one fluid pressure) in a static drift and cyclic loading configuration. The results show that relative to the important performance characteristics for soft tissue pressure monitoring (i.e. hysteresis, drift), many of the sensors tested have significant limitations. The FSRs exhibited hysteresis, drift and loss of sensitivity under cyclic loading. The capacitive sensor had substantial drift. The optical sensor had some hysteresis and temperature-related drift. The fluid pressure sensor performed well in these tests but is not as flat as the other sensors and is not commercially available. Researchers and clinicians should carefully consider the convenience and performance trade-offs when choosing a sensor for soft-tissue pressure monitoring.

The ability to chronically monitor pressure at the prosthetic socket/residual limb interface could provide important data to the research and clinical communities. With this application in mind, we describe a novel type of sensor which consists of a MEMS pressure sensor and custom electronics packaged in a fluid-filled bubble. The sensor is characterized and compared to two commercially-available technologies. The bubble sensor has excellent drift performance and good sensing resolution. It exhibits hysteresis which may be due to the silicone that the sensor is molded in. To reduce hysteresis, it may be advisable to place the sensor between the liner and the socket rather molding directly into the liner.

This paper presents the design and assessment results of two types of miniature, high speed, low torque transmissions to be used in a partial hand, powered finger prosthesis. Transmissions enabling torque transfer across varied flexion angles of a finger joint can allow placement of a motor and a gearbox in adjacent phalanges, significantly decreasing space requirements for partial hand prostheses. Bevel gear-based and cable-based transmission designs for a variety of flexion angles are implemented and tested in comparison with a direct cascaded motor and gearbox (benchmark) configuration. The miter-gear transmission provided consistent operation at tested flexion angles, but demonstrated reduced efficiency in comparison with the benchmark configuration. Cable transmission matched efficiency of the benchmark configuration at low flexion angles but lacked mechanical durability at high loads and flexion angles. The designs presented complementary strengths and weaknesses, with the miter-gear design demonstrating better overall mechanical reliability, while the cable transmission excelled in secondary characteristics.

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