Showing papers on "Rotation published in 2022"

Vortex induced vibrations of a cylinder at low mass ratio

Abstract: We used the Lattice Boltzmann Method (LBM) to study the vortex-induced vibrations of a circular cylinder in an incompressible flow with a restoring force. The cylinder has three degrees of freedom, two for translation and one for rotation. Results with a wide range of relevant parameters are presented in high resolution simulations. The three detected branches in cross-flow amplitudes were related with flow and cylinder’s dynamics in the limit of low mass ratios. The transition regions between these branches were related with regions where several solutions exist depending on the initial conditions, this solution space is increased with the inclusion of the rotational degree of freedom.

A novel error mapping of bi-directional angular positioning deviation of rotary axes in a SCARA-type robot by “open-loop” tracking interferometer measurement

Abstract: To further extend the application of an industrial robot to e.g. the machining, it is crucial to ensure its three-dimensional (3D) positioning accuracy over its entire workspace. Numerous past works presented numerical compensation based on the robot kinematic model containing position and orientation errors of rotary axes average lines, widely known as Denavit-Hartenberg (D-H) parameters. This paper presents two novel contributions. First, this paper proposes a kinematic model with the angular positioning deviation “error map” of each rotary axis, which is given as a function of command angular positions. Furthermore, to model the backlash influence, it is modelled dependent also on the direction of rotation. The second contribution is on the proposal of the “open-loop” tracking interferometer measurement to indirectly identify the angular positioning deviation of each rotary axis. It measures the distance from the retroreflector, fixed on the table, to the robot's end effector at many points over the entire workspace by using a laser interferometer attached to the robot's end effector. The identified kinematic model's accuracy is experimentally investigated, and is compared to the conventional D-H model.

Geodetic model for teaching motion on the Earth’s spheroidal surface

Abstract: We explore the forces that shape our spheroidal earth and the forces that govern the motion of a puck that slides without friction on its surface. The earth's stable spheroidal shape (apart from small-scale surface features) is determined by balancing the gravitational forces that hold it together against the centrifugal forces that try to tear it apart. The motion of a puck on its surface differs profoundly from motion on a sphere because the earth's spheroidal deformations neutralize the centrifugal and gravitational forces on the puck, leaving only the Coriolis force to govern the motion. Yet the earth's spheroidal deformations are small and difficult to see in scale drawings. To assist students in exploring the crucial role of these deformations for motion on the earth's surface, we develop a model of uniformly rotating homogeneous earth-like planets with arbitrary eccentricities and arbitrary angular speeds of rotation, derive equations of motion for a puck sliding on the frictionless surface of such a planet, and introduce CorioVis software for visualizing this motion. By construction, this model replicates the rotational properties of the reference spheroid that is used in terrestrial cartography, geodesy, and the global positioning system.