Wearable elongation sensors for human posture analysis

Type: Master thesis
Student: Christof Kueng
Advisor: Corinne Mattmann
Project: Backmanager

The scope of this master thesis was the design, fabrication and evaluation of wearable elongation sensors.

The recognition of a person's posture, the analysis of human motions, the measurement of joint angels and other parameters are of great interest in rehabilitation, sports and health care. The goal of the research currently in progress at the Wearable Computing Group is to build systems which can carry out such tasks, while the systems are truly wearable, i.e. all parts are unobtrusively integrated into garments (Motion Aware Clothing).

Measurement of the stretch which occurs in a close fitting garment worn by a person provides valuable information about posture and movements. Therefore wearable elongation sensors are needed.

The following materials were evaluated for their usefulness as resistive transducers:

• Stretchable electroconductive fabrics: Metallized fabrics and a carbon fabric.
• Electroconductive elastomers: A carbon filled silicone rubber product, several carbon filled thermoplastic elstomer fibers and a fluoroelastomer coating.

It was found, that all these materials show sever shortcomings:

• Drift of resistance or dependence of resistance on strain history.
• High electrical hysteresis
• High transient times
• Resistance depends on speed of deformation

While these are only the problems common to all materials, most materials show further peculiar deficiencies. Their advantage is however the high compatibility with textiles. Hence, sensors made by utilizing these materials would be very unobtrusive.

Regarding the mentioned problems, the step was made from using transducer materials alone to structures built onto the fabric. The following sensors were built and investigated:

• A sensor which utilizes an electroconductive fluid in a rubber tube integrated into the fabric.
• A sensor which makes use of the changing light transmission through a fabric when it is stretched.

It was found, that the transducer performances of these two sensors are outstanding compared to the performance of the materials described above, yet they are not as unobtrusive.

These sensors are a useful basis for research in the fields mentioned at the beginning.