Dynamic Comparison of a 3-Degrees-of-Freedom Parallel Manipulator With Multiple Dry Clearance Joints and With Lubricated Joints

This paper compares the dynamic response of a 3-degree-of-freedom (3-DOFs) parallel manipulator with multiple dry clearance joints and with lubricated joints. For this purpose, a methodology developed on Newton–Euler equations is proposed to study lubricated joints in the parallel manipulator, which involves the hydrodynamic forces and impact forces in the constrained equations. Specifically, the hydrodynamic forces are based on the Reynolds’ equation of an infinitely long lubricated joint. Dynamic simulations are presented through the dynamic parameters of a planar parallel manipulator (3-PRR, the underline of the P represents the actuated joint, P and R represents prismatic and revolute pairs respectively), which has six revolute clearance joints and three ideal prismatic joints. The results of the comparison show that the lubricant makes significant difference and greatly improves the dynamic performance of the parallel manipulator with multiple revolute joints. More periodic states are observed from the dynamic behavior of the parallel manipulator with lubricated joints, making the manipulator easier to drive. All results demonstrate the usage of the procedures which contain the hydrodynamic force model of multiple lubricated joints in non-linear DAEs of a 3-DOFs parallel manipulator.

Dynamics and lubrication analyses of a planar multibody system with multiple lubricated joints

In order to ensure the mechanical systems a better performance, most of their joints are designed to operate with lubricant. The differently located lubricated joints interact with each other, influencing the total performances of the system. This study proposes a numerical approach for the multibody system modeling with the consideration of the interactions among the multiple lubricated joints to investigate the dynamics and tribological performances of the mechanism. This approach couples the lubrication model of both translational and revolute joints with the dynamics model of the multibody system, and is performed on a four-stroke gasoline engine with the lubricated piston skirt-liner subsystem and lubricated big-end bearing of the connecting rod. The multibody dynamics model is built with Lagrange’s method. The lubrication models are built based on the average Reynolds equation, and solved with finite element method to derive the hydrodynamic forces according to the motion of the system. The piston skirt profile, pin offset and the effects of surface roughness on the lubrication performances are taken into account. The simulation results reveal that there are obvious interactions between the differently located lubricated joints, and the larger clearance can pronounce the interactions.

Ancient origin of lubricated joints in bony vertebrates

Synovial joints are the lubricated connections between the bones of our body that are commonly affected in arthritis. It is assumed that synovial joints first evolved as vertebrates came to land, with ray-finned fishes lacking lubricated joints. Here, we examine the expression and function of a critical lubricating protein of mammalian synovial joints, Prg4/Lubricin, in diverse ray-finned fishes. We find that Prg4 homologs are specifically enriched at the jaw and pectoral fin joints of zebrafish, stickleback, and gar, with genetic deletion of the zebrafish prg4b gene resulting in the same age-related degeneration of joints as seen in lubricin-deficient mice and humans. Our data support lubricated synovial joints evolving much earlier than currently accepted, at least in the common ancestor of all bony vertebrates. Establishment of the first arthritis model in the highly regenerative zebrafish will offer unique opportunities to understand the aetiology and possible treatment of synovial joint disease.