Variable roughness soft gripper fingertip with pneumatically deployable microspike array

초록

This paper presents a pneumatically actuated variable-roughness fingertip that reversibly switches a single polydimethylsiloxane (PDMS) contact surface between flat and spike modes. Under negative pressure, the internal chamber contracts, retracting the spikes beneath the cover to form a flat contact state. Conversely, under positive pressure, the chamber expands and deploys the spikes, creating a contact state in which the microstructures can engage the counter surface directly. The protruding geometry in the spike mode can deteriorate under increasing normal load; therefore, we encapsulated a resin-based medial axis tree support structure inside the PDMS spikes to enhance the load-bearing capability and preserve the deployed shape. Friction tests performed on glass, paper, and sandpaper revealed that the friction coefficient was higher in the flat mode on glass, while it was higher in the spike mode on paper and sandpaper, indicating a crossover in the preferred mode based on surface conditions. Grasping tests confirmed the same trend: on glass, the gripping force in the flat mode was 35.8% higher, while on sandpaper, the gripping force in the spike mode was 23.9% higher. These results demonstrate that the performance advantage of flat versus spike contact can be reversed with surface roughness, highlighting the utility of a switchable contact interface for mixed-roughness environments.

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