Artificial Finger Quantifies Touch Sensations

Researchers have developed an artificial finger that can sense the fineness, roughness and slipperiness of a surface.

AsianScientist (Apr. 21, 2015) – Our sense of touch is used extensively every day, in simple tasks such as picking a pen up or maintaining a firm grip on a glass wet with condensation while having a cold drink on a hot day. Yet the complexities behind interpreting this type of subjective feedback are so profound that they vary extensively between human beings. Tactile sensations are all the more appreciated by professions requiring sensitive haptic feedback such as surgery.

In a study published in Tribology Letters, researchers have attempted to express the sense of touch in an objective, measurable form. By breaking down the sensation of touch into three defining dimensions—fineness, roughness and slipperiness of a surface—and starting with eight measurable features of the surface, Dr. Tang Wei and colleagues from the China University of Mining and Technology studied the features which best correlate to tactile dimensions.

To do so, they utilized an artificial finger attached to a tribometer fitted with sensors to measure the eight features and conducted sliding and contact (pressing) tests against thirty-eight different surfaces. This was then compared with human subjective tests from a sample of 20 humans, spread across the ages of 20-60 and evenly divided between male and female, who were trained to identify and score the three dimensions on a scale of 0 to 100.

To sense these eight features—expressed by the team as the spatial centroid, peak number, three different variations of vertical deviations (distinguished as V1, V2, and V∞), peak ratio, coefficient of friction and average power—the team also had to account for noise in the frequency as well as the no-load condition on the artificial finger/tribometer.

One interesting discovery from the research was that the artificial finger’s sliding velocity appeared to play a larger part in the sensitivity of the measurements. This was attributed to a number of factors, including the viscoelasticity of the skin on the “finger” and the deformation of the ridges on the “finger”. These factors in turn affect the real contact area and adhesive forces between the “finger” and the surface–factors that are known to affect the coefficient of friction.

By comparing the ratings given by the human volunteers and the measurement of the features from the artificial finger, the team then discovered a strong correlation between three of the features and the three dimensions—spatial centroid, one method of calculation of vertical deviation (V1) and the coefficient of friction—and the dimensions of fineness, roughness and slipperiness respectively, indicating that the qualities of a surface can indeed be interpreted by sensors and correctly compared between a variety of surfaces.

The implications of this study are far-reaching—if computers can interpret such surfaces and replay them to another human being, robot-assisted surgery may gain newfound popularity, with recent developments in haptic feedback technology as surgeons can now receive tactile feedback instead of having to rely purely on visual cues, bringing a whole new level of sensitivity to intricate surgical processes.

This article can be found at: Tang et al. (2015) Characterization Of Tactile Perception And Optimal Exploration Movement.

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Copyright: Asian Scientist Magazine; Photo: Kevin Dooley/Flickr/CC.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Jonathan Leong graduated from the NUS-Imperial College Joint PhD Programme at the National University of Singapore. He is interested in all things related to friction, but particularly at the micro- or nano-scale. He is a lecturer at SIM University.

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