Soft robotic fingers can safely grasp fragile or variable form objects, but their force capacity is limited, especially with less contact area: precision grasps and when objects are smaller or not spherical. Current research is improving force capacity through mechanical design by increasing contact area or stiffness, typically without models which explain soft finger force limitations. To address this, this paper considers two types of soft grip failure, slip and dynamic rotational stability. For slip, the validity of a Coulomb model investigated, identifying the effect of contact area, pressure, and relative pose. For rotational stability, bulk linear stiffness of the fingers is used to develop conditions for dynamic stability and identify when rotation leads to slip. Together, these models suggest contact area improves force capacity by increasing transverse stiffness and normal force. The models are validated on pneumatic fingers, both custom PneuNets-based and commercially available. The models are used to find grip parameters which increase force capacity without failure.

翻译：软体机器人手指能够安全抓取易碎或形状多变的物体，但其施力能力有限，尤其在接触面积较小的情况下（如精密抓取以及抓取非球形或尺寸较小的物体时）。当前研究通过增加接触面积或提高刚度等机械设计手段来提升施力能力，但通常缺乏解释软手指受力限制的模型。针对这一问题，本文研究了两种软体抓取失效模式：滑移与动态旋转稳定性。针对滑移，探究了库仑模型的适用性，明确了接触面积、压力及相对位姿的影响。针对旋转稳定性，利用手指的体线性刚度建立了动态稳定条件，并确定了旋转导致滑移的临界状态。综合这些模型表明，接触面积通过提高横向刚度与法向力来增强施力能力。通过定制化PneuNets气动手指与商用气动手指对模型进行了验证，并利用模型找到了在不发生失效前提下提升施力能力的抓取参数。