Grasping posture estimation for a two-finger parallel gripper with soft material jaws using a curved contact area friction model | IEEE Conference Publication | IEEE Xplore

Grasping posture estimation for a two-finger parallel gripper with soft material jaws using a curved contact area friction model


Abstract:

We present a friction model for the curved contact area between a deformable object and soft parallel gripper jaws for grasping posture estimation. We show that the assum...Show More

Abstract:

We present a friction model for the curved contact area between a deformable object and soft parallel gripper jaws for grasping posture estimation. We show that the assumption of a planar contact area leads to an overestimation of the frictional force and torque, which might cause the object to slip. We simulate the contact with the Finite Element Method, then compute the friction wrenches, which are fitted with two limit surface models: an ellipsoid and a convex 4th-order polynomial. Despite a slightly higher fitting error, the ellipsoid limit surface is chosen to compute the grasp quality because of its simplicity. We compare the limit surfaces of our friction model with the planar contact model and show the improved accuracy obtainable with our model. We then apply the presented model for grasping posture estimation by simulating the contact for all grasp candidates. We show a grasp quality map (quality of all grasp candidates) and the best possible grasp location for several deformable objects.
Date of Conference: 29 May 2017 - 03 June 2017
Date Added to IEEE Xplore: 24 July 2017
ISBN Information:
Conference Location: Singapore

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.

References

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