Abstract
Soft grippers with soft and flexible materials have been widely researched to improve the functionality of grasping. Although grippers that can grasp various objects with different shapes are important, a large number of industrial applications require a gripper that is targeted for a specified object. In this paper, we propose a design methodology for soft grippers that are customized to grasp single dedicated objects. A customized soft gripper can safely and efficiently grasp a dedicated target object with lowered surface contact forces while maintaining a higher lifting force, compared to its non-customized counterpart. A simplified analytical model and a fabrication method that can rapidly customize and fabricate soft grippers are proposed. Stiffness patterns were implemented onto the constraint layers of pneumatic bending actuators to establish actuated postures with irregular bending curvatures in the longitudinal direction. Soft grippers with customized stiffness patterns yielded higher shape conformability to target objects than non-patterned regular soft grippers. The simplified analytical model represents the pneumatically actuated soft finger as a summation of interactions between its air chambers. Geometric approximations and pseudo-rigid-body modeling theory were employed to build the analytical model. The customized soft grippers were compared with non-patterned soft grippers by measuring their lifting forces and contact forces while they grasped objects. Under the identical actuating pressure, the conformable grasping postures enabled customized soft grippers to have almost three times the lifting force than that of non-patterned soft grippers, while the maximum contact force was reduced to two thirds.
Highlights
Softness and flexibility of constituting materials allow soft robotic grippers to be adaptive when interacting with objects (Hughes et al, 2016; Shintake et al, 2018)
We introduce design and fabrication methods to develop customized soft grippers with highly conformable pregrasping finger postures that outline the shapes of specified target objects (Figure 1) to reduce the contact pressure by increasing the contact area
The following outlines the fabrication process of a customized soft gripper: first, the thickness tuning plates are stacked inside the base mold of the constraint layer, according to the desired design; a pre-cured elastomer is poured into the assembled mold and cured; the fully cured constraint layer is bonded together with the air chamber section (Figure 8)
Summary
Softness and flexibility of constituting materials allow soft robotic grippers to be adaptive when interacting with objects (Hughes et al, 2016; Shintake et al, 2018). Design methodology for customized soft grippers that are matched to the shape outlines of target objects by patterning stiffness of constraint layers. Equilibrium between the moment generated by the air chambers and the constraint layer results in a bending angle that represents the initial steady state of the soft finger without any contact force. The following outlines the fabrication process of a customized soft gripper: first, the thickness tuning plates are stacked inside the base mold of the constraint layer, according to the desired design; a pre-cured elastomer is poured into the assembled mold and cured; the fully cured constraint layer is bonded together with the air chamber section (Figure 8). The resulting soft gripper achieves customized actuated postures with irregular bending curvatures at different pressures compared to their non-patterned counterparts (Supplementary Figure 6). Details are described in section Expand to Multiple Air Chambers of the Supplementary Material
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