A Standard Methodology to Characterize the Intrinsic Material Properties of Compliant Test Stimuli

Abstract

Understanding how we perceive differences in material compliance, or 'softness,' is a central topic in the field of haptics. The intrinsic elasticity of an object is the primary factor thought to influence our perceptual estimates. Therefore, most studies test and report the elasticity of their stimuli, typically as stiffness or modulus. However, many reported estimates are of very high magnitude for silicone-elastomers, which may be due to artifacts in characterization technique. This makes it very difficult to compare the perceptual results between the studies. The work herein defines a standardized and easy-to-implement way to characterize test stimuli. The procedure involves the unconstrained, uniaxial compression of a plate into cylindrical substrates 10 mm tall by 10 mm diameter. The resultant force-displacement data are straightforwardly converted into stress-strain data, from which a modulus is readily derived. This procedure was used to re-characterize stimuli from prior studies. The revised results from the validated method herein are 200-1,100% lower than modulus values either reported and/or approximated from stiffness. This is practically significant when differences of 10-15% are perceptually discriminable. The re-characterized estimates are useful in comparing prior studies and designing new studies. Furthermore, this characterization methodology may help more readily bridge studies on perception with those designing technology.

Visuo-Haptic Discrimination of Viscoelastic Materials

“…Hence, care should be given to their mechanical characterization. Nevertheless, so far, mechanical characterization of these specimens for the psychophysical investigation of haptic perception has been nonstandard, and the recent work by Gerling et al is an important step towards solving this problem [74]. More specifically, tuning the viscoelastic properties of a silicone rubber while controlling its material nonlinearities is a challenge that has not been solved yet.…”

Role of indentation depth and contact area on human perception of softness for haptic interfaces

“…However, a clear picture has yet to emerge from this work because both tactile cues believed to be important in the perception of softness (i.e., indentation depth and contact area) are affected simultaneously by the mechanical properties (e.g., Young’s modulus, stiffness). In a critical review, Gerling et al ( 20 ) found several instances in which the relationships between the mechanical properties of test objects and the participant’s responses to them were unclear. In some studies, it was difficult to connect participant responses with mechanical properties because of the unreliable control over the mechanical properties of samples ( 20 ).…”

“…In a critical review, Gerling et al ( 20 ) found several instances in which the relationships between the mechanical properties of test objects and the participant’s responses to them were unclear. In some studies, it was difficult to connect participant responses with mechanical properties because of the unreliable control over the mechanical properties of samples ( 20 ). In other instances, some studies were regarded as ambiguous because it was assumed that controlling the intrinsic mechanical properties would automatically control the extrinsic properties such as the indentation depth and contact area on the finger ( 20 ).…”

Switching Between Objects Improves Precision in Haptic Perception of Softness

“…We produced softness stimuli with different elasticity by mixing a two-component silicon rubber solution (AlpaSil EH 10:1) with different amounts of silicon oil (polydimethylsiloxane, viscosity 50 mPa/s) and pouring it into cylindrical plastic dishes (75 mm diameter × 38 mm height). We produced in total 10 To characterize the elasticity of the stimuli we adopted the standard methodology proposed by [22]. From the solution mixed for every stimulus a portion was poured into a small cylinder (10 mm thick, 10 mm diameter) to obtain standardized substrates of the same material for the measurement.…”