Abstract
When people are asked to palpate a novel soft object to discern its physical properties such as texture, elasticity, and even non-homogeneity, they not only regulate probing behaviors, but also the co-contraction level of antagonistic muscles to control the mechanical impedance of fingers. It is suspected that such behavior tries to enhance haptic perception by regulating the function of mechanoreceptors at different depths of the fingertips and proprioceptive sensors such as tendon and spindle sensors located in muscles. In this paper, we designed and fabricated a novel two-degree of freedom variable stiffness indentation probe to investigate whether the regulation of internal stiffness, indentation, and probe sweeping velocity (PSV) variables affect the accuracy of the depth estimation of stiff inclusions in an artificial silicon phantom using information gain metrics. Our experimental results provide new insights into not only the biological phenomena of haptic perception but also new opportunities to design and control soft robotic probes.
Highlights
Physical examination of soft objects to identify hidden mechanical features can be seen in a variety of areas like minimally invasive surgery, medical physical examination, security, quality assurance in food industry, entertainment, etc
We use the controllable stiffness robotic probe described earlier to derive deeper insights into the influence of the variation of combinations of probe’s internal stiffness, indentation level, and probe sweeping velocity (PSV) on the real-time estimation of the depth of a hard nodule embedded in soft silicon phantom
We explore whether a probe with controllable stiffness, indentation level, and PSV can exploit its past experience of palpation by varying its own internal stiffness, indentation level, and PSV to estimate the depth of embedded nodule inside a soft silicon phantom
Summary
Physical examination of soft objects to identify hidden mechanical features can be seen in a variety of areas like minimally invasive surgery, medical physical examination, security, quality assurance in food industry, entertainment, etc. Manual examination involves variation of both behavioral and internal impedance levels of the fingers [1, 2], because the interplay between motor control and internal mechanics (muscles and reflexes) [3, 4] play an important role in both action and perception [5]. The notion—morphological computation—in soft robotics and biological systems views the mechanical circuits in the embodiment as a computational resource for both perception and action. Since the mechanical impedance of the embodiment changes the functionality of those mechanical circuits, it is important to understand its role in regulating perception and action of soft robots. Its applications have been largely limited to control of action than understanding its role in perception or action-perception coupling in biological systems. Impedance control principles have been widely applied in robotics for metastable walking [7], tele-operated excavation [8], safe interaction
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