Polymer-Based Optical Waveguide Tactile Sensing Method for 3-D Surfaces

At present, most tactile sensors are fabricated based on the flat surface, which greatly limits their applications in the 3-D scenario. To deal with the bottleneck, this article proposes a polymer-based optical waveguide sensing method. The waveguide can be integrally formed along a channel within a 3-D surface. Microbending light loss of a waveguide is the sensing principle. By studying the linearity between the degree of microbending and light loss, the feasibility analysis of spherical tactile sensing element (tactile) was completed, as well as the basis for size selection of it. In addition, the key to layout on 3-D surface of the proposed sensing method is that the bending radius of the waveguide is within the critical angle of total internal reflection (TIR). By normalizing the ratio of the side length of the cross Section to the bending radius, it is shown that the light loss does not increase when the proportionality coefficient is less than 0.3. The experiment is validated by embedding four tactiles in a 3-D surface. The cross Section of the waveguide is $1.5\times1.5$ mm. We demonstrated that the static hysteresis error for a tactile is less than 16% within 595 kPa, the best sensing sensitivity is ${1}.{42} \times {{10}}^{-{5}} {}{\text {kPa}}^{-{1}}$ , and the maximum measurement range is from 0 to 850 kPa. As for the dynamic measurement, the tactile can rapidly response the signal change with given frequencies (the maximum is 10 Hz). The average delay time is around 12 ms.