An Improved Dynamic Model of the Mecanum Wheel for Multibody Simulations

Mobile robots and autonomous guided vehicles have become an indispensable part of modern industrial environments and are used for a wide range of handling operations. To fully use the potential of mobile platforms, omnidirectional platforms are a good choice. A prominent and widely used variant in the industry are Mecanum wheels, which allow arbitrary movement in any direction in the plane. In most applications only the kinematics is considered, however, dynamic models that take the geometry of the rollers into account are still missing. In this paper two models for Mecanum wheels with different degrees of detail are derived. The detailed model considers the rollers as single bodies undergoing contact and friction with the rolling plane. As the wheel consists of multiple rollers, a complex contact situation with temporal overlapping and additional vibrations occurs. The simplified model reproduces the overall kinematics of the rollers with orthotropic friction and only one rigid body for the wheel, thereby being computationally more efficient. Both models are well suited to reproduce essential dynamic effects of a mobile robotic platform, which can not be described by the conventional kinematics model. We implement and compare both models with experimental results, showing the good performance of both models.

Theoretical and numerical studies of the slip resistance of main cable clamp composed of an upper and a lower part

Cable clamps are important connection members widely used in suspension bridges and cable structure buildings. The clamps are usually tightened on the cable through pre-stressed bolts and resist cable axial component of the external load by friction. Current relevant standards provide slip resistance formulas for anti-slip design of the clamps but are conceptive and simple, lacking explicit and quantitative mechanical derivation. This paper develops an analytical model and proposes a novel slip failure criterion based on the slippage amount, aiming at understanding the force state and estimating the slip resistance of the main cable clamp composed of an upper and a lower part. Finite element analyses then validate that the analytical model can correctly reveal the influences of the multiple factors including hanger tensile force and orthotropic friction on the force state of the cable-clamp system. Moreover, the original Coulomb-friction-law-based slip resistance formula is briefly revised by introducing a partial factor in order to take the nonlinearity of the connection system into account. The revised slip resistance formula implies its promising applicability in obtaining reliable and flexible solution to anti-slip problem of the clamp with different level of safety redundancy.