I. Introduction
The grasp stability is essential for evaluating the grasping posture for an object. Hence, the external disturbances that can be balanced for this posture are often used as quality metrics. These metrics require accurate contact information, such as the maximum frictional force and torque. This information is especially important for grasping easily breakable objects or deformable thin-walled bottles, such as plastic cups. If the applied force becomes too large, the object might be damaged caused by the grasp, or the content of an open bottle might spill due to an excessive deformation. For these objects, gripper fingers with soft pads are widely used to prevent such damage and to increase the stability of grasps due to the larger contact area achievable with deformable jaws. In this paper, we focus on grasp planning for deformable objects which are grasped with a parallel gripper equipped with passive soft foams, such as the visuo-haptic gripper (VH gripper) in [1]–[3]. We simulate the contact using the Finite Element Method (FEM) and study the friction model of a non-planar contact area caused by the soft foam, as shown in Fig. 1. The friction model is then used to determine grasp quality measures.