# Grasp Analysis for the Robot-Based Manipulation of Pre-Assembled Cables with Electrical Connectors
###### Abstract  
The mounting of pre-assembled cables with electrical connectors is mainly carried out manually in industry today. An exemplary application is the interconnection of battery modules. Automation of such assembly tasks offers the potential for increasing efficiency but requires the design of suitable gripper systems. This is challenging as the cable induces state-dependent forces and torques on the gripper system, which must be transmitted via the complex surface geometries of the plugs. Currently, the required grasp force cannot be determined in advance but only after prototypes have been manufactured and with elaborate physical experiments. To overcome these drawbacks, we present a methodology for the grasp analysis of pre-assembled cables with electrical connectors. The novelty of this approach is to combine a physics simulation for deformable linear objects with a contact model for non-planar grasping surfaces. The results indicate that the cable deformation significantly affects the required grasp force. In addition, each combination of contact surface and dynamic cable deformation results in an individual grasp force course. The methodology enables comparison of different electrical connectors and their grasping surfaces, as well as cables and their manipulation paths, efficiently and with little expert knowledge.  
gripper design; grasp force; deformable linear object; physics simulation; contact model +
Footnote †: journal: Applied Physics Letters  
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Footnote 1: email: [EMAIL_ADDRESS].  
on its current deformation state. In addition, these forces and torques have to be transmitted via complex surfaces [2].  
In automated gripper design, a core step is grasp analysis, which evaluates the quality of a grasp [1]. This commonly includes calculating the grasp force. The latter must neither be too low to hold the workpiece securely [3] nor too high, as, otherwise, the workpiece could be damaged [4] and the purchasing and operating costs will be unnecessarily high [5].  
In order to estimate the grasp force, the contact relation between the gripper jaws and the workpiece has to be modeled and the occurring forces and torques have to be determined. For common workpieces with planar grasping surfaces, e.g., polyhedra, the contact model is typically approximated by Coulomb's friction [3]. Furthermore, the forces considered are mostly based on the mass of the workpiece and inertia. If necessary, process forces, drag and rotational effects, such as the Euler and Coriolis forces, are also considered [4].  
However, an automated gripper design for pre-assembled cables with ECs requires consideration of non-planar grasping surfaces and the shape-dependent impact of cables. Therefore, we introduce a novel methodology that enables grasp analysis for ECs. The core part of our work is the combination of a contact model for robotic grasping with a physics simulation for DLOs. With the CAD data of the assembly task and the EC, as well as the cable specifications as the main user input, a physics simulation scenario of the cables involved is automatically generated and subsequently evaluated by the contact model. The methodology enables us to estimate the required grasp force for different pairs of grasping surfaces, from now on referred to as _surface pairs_. A user can, thus, observe to what extent the dynamic cable behavior affects the stability of the grasp simulatively with little effort and expert knowledge required. For this work, we consider the grasp force as the force that each gripper jaw exerts on a plug along the grasp axis [3]. Consequently, the _required grasp force_ is the lowest possible to hold the plug securely.