Soft robotic fingers can safely grasp fragile or non-uniform objects, but their force capacity is limited, especially with less contact area: objects which are smaller, not round, or where an enclosing grasp is not feasible. To improve force capacity, this paper considers two types of grip failure, slip and dynamic rotational stability. For slip, a Coulomb model for soft fingers based on total normal and tangential force is validated, identifying the effect of contact area, pressure, and grip position on effective Coulomb coefficient, normal force and transverse stiffness. For rotational stability, bulk stiffness of the fingers is used to develop conditions for dynamic stability about the initial grasp, and a condition for when the rotation leads to slip. Together, these models suggest contact area improves grip by increasing transverse stiffness and normal force. The models are validated in a range of grasp conditions, shown to predict the influence of object radius and finger distance on grip stability limits.

翻译：软体机器人手指能够安全抓取脆弱或不规则物体，但其力承载能力有限，尤其在接触面积较小时表现更为突出：例如抓取体积较小、非圆形物体，或无法实现包络抓取的情形。为提升力承载能力，本文研究了两种抓取失效模式——滑移与动态旋转稳定性。针对滑移问题，基于总法向力和切向力建立了软体手指的库仑模型，验证了接触面积、压力及抓取位置对有效库仑系数、法向力和横向刚度的影响。在旋转稳定性方面，利用手指体刚度建立了初始抓取状态的动态稳定性条件，并推导了旋转导致滑移的临界条件。综合模型表明，接触面积通过提升横向刚度和法向力增强抓取能力。通过多种抓取条件下的实验验证，模型成功预测了物体半径和手指间距对抓取稳定性极限的影响。