Angular displacement sensing and joint position localization using stretchable fiber-optic sensors in soft flexo-structures

The measurement of the exact state of an actuator is necessary to use it reliably in any situation especially in interaction with humans. Traditional rigid encoders would not be very useful since they limit the functionality of the actuator and hence a system of stretchable optic-fibres is proposed as a sensing mechanism to determine the location of the bending axis and the exact rotation achieved along it. Stretchable fiber optic is constrained in a flexo-structure to increase sensitivity in certain sections and achieve two sensing sections with different range of operations. Various fiber configurations are tested to optimise the linearity, sensitivity, range of operation and resolution in a simple bending test of a flexo-structure with a single fiber optic sensor. It was observed that increased sensitivity is observed for the constrained (stick) section compared to a free (slip) section of fiber. Two potential sensors (TOF and light amplitude modulation based) are created and calibrated for angle measurement. This system could be used in on-board, non-hysteretic, non-electric, soft sensing in robots or devices with limited sensing capabilities like a soft prosthetic glove. The application of this system is demonstrated in a small glove to measure the bending at two joint locations