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Integrating Smart Materials and Adhesion Mechanics for Soft Gripping Mechanisms
AuthorMohammadi Nasab, Amir
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Surfaces comprised of soft elastomeric materials can adhere to a broad range of substrates and thus have applications in transfer printing, handling in automated manufacturing processes, and climbing robots. Polydimethylsiloxane (PDMS) and Ecoflex-50 are among the most commonly used elastomers in soft robotics due to their manufacturability and desirable mechanical properties. Previous studies have shown that the inclusion of a stiffness tunable core in a cylindrical PDMS pillar can enhance the dry adhesion strength of the pillar to an opposing rigid surface significantly. Here, I investigate three different approaches to enhance the dry adhesion of soft gripping mechanisms integrating smart materials and adhesion mechanics. First, the effect of the cross-sectional geometry on enhancing the dry adhesion strength of soft composite elastomeric structures is examined. Second, the effect of inserting a thin serpentine channel of a low melting point alloy (LMPA) close to the interface of an elastomeric post for dynamical dry adhesion tuning is investigated. Third, a cylindrical soft homogenous elastomeric structure is designed with a hollow annular chamber embedded close to the edge of the structure to dynamically tune its dry adhesion strength with varied pneumatic pressure. The dry adhesion is tuned in all the approaches because the stress distribution at the adhered interface is altered. For the latter two approaches, dynamic dry adhesion tuning is achieved, either through subsurface stiffness modulation (SSM), or through subsurface pressure modulation (SPM). In the first approach, the dry adhesion strength of relatively stiff PDMS pillars terminated with a compliant Ecoflex layer at the tip with circular, square and rectangular cross-sections are explored through experiments and Finite Element (FE) simulations. Experiments show that the adhesion strength can be tuned up to ~65 kPa via the manipulation of the thickness of the Ecoflex layer for all these three pillar cross-sectional shapes. Stress distribution simulations show that the crack initiation site shifts from the edge to the center of the adhered interface and finally to an internal point at the adhered interface as the compliant tip layer thickness decreases. In the second approach, the dry adhesion strength of the rectangular PDMS posts embedded with serpentine channel of LMPA is tuned dynamically almost two times when the LMPA layer is softened using electrical voltages. In the third approach, the dry adhesion strength of the pressure-operated device against multiple types of substrates for different sealing layer thicknesses of the device and different chamber pressures is characterized and FEA has been used to explain the mechanics behind it. Results show that the dry adhesion strength of the device can be tuned up to ~1.5σ0, and as low as ~0.05σ0, depending on the dimensions of the device, where σ0 is the adhesion strength of the device in the non-pressurized state.