Application of a new conformal contact force model to nonlinear dynamic behavior analysis of parallel robot with spherical clearance joints

Contact and friction phenomena in clearance joint adversely affect mechanical performance and may even result in chaos within the mechanism. Analysis of nonlinear characteristics of mechanical systems with clearance joints in which accurate description of contact is a key challenge. To accurately predict nonlinear dynamic behavior of parallel robots, a new conformal contact force model of spherical clearance joints is developed by combining elastic foundation theory, FEM, and least squares methods and verified it through ABAQUS simulation. A nonlinear dynamic model of the parallel robot with conformal contact of spherical clearance joints is derived. Initial qualitative identification of motion state of the parallel robot is achieved by employing dot density pattern and Poincare mapping. Largest Lyapunov exponent and bifurcation diagrams are used as numerical chaotic indicators to uncover attractor evolution rule. Analysis shows that new model has a reasonable physical meaning and good predictive power. As movement instability increases, one can observe remarkable differences in nonlinear characteristics description of the parallel robot between conformal and non-conformal contact models, but they are not sufficient to alter motion state of system.