Optimising electromechanical whisker design for contact localisation

Abstract

Electromechanical whiskers are inexpensive and useful tactile sensor systems for robotic mapping tasks within environments problematic to image and range sensors. This research aims to quantify the effect of the whisker's mechanical properties on its ability to achieve accurate contact localisation. Using mechanical beam theory, a model relating the rate of change of a whisker's strain as a result of the location of a radial contact was derived. A more practical linear approximation of this model was then created with an operating range for which a whisker was theoretically capable of performing contact localisation within 0.1% error. These models facilitated the design of theoretically optimal whiskers. It was discovered that the longer the whisker, and the closer the strain-measuring sensor was placed towards the whisker base, the greater the required taper. For larger whisker widths and faster contact speeds, a smaller taper was required. Additionally, whiskers tapered in 2 dimensions required larger tapers than one-dimensional tapers to achieve optimal performance. The presence of a central hollow region (medulla) did not have a practical effect on the required taper or the performance of the whisker. Experimental results showed that a 200 mm whisker with an optimal taper derived from our model was able to measure the location of contacts with an error less than the target 0.1% anywhere in the distal 58 mm, with a response time of 0.1 s. Tapering electromechanical whiskers to their derived optimal value enhances the accuracy and efficiency of whisker-based robotic mapping.