Triple Crossed Flexure Pivot Based on a Zero Parasitic Center Shift Kinematic Design

Thanks to their absence of play, absence of contact friction and possible monolithic fabrication, flexure pivots offer advantages over traditional bearings in small-scale, high accuracy applications and environments where lubrication and wear debris are proscribed. However, they typically present a parasitic center shift that deteriorates their rotational guidance accuracy. Existing solutions addressing this issue have the drawbacks of reducing angular stroke, prohibiting planar design, or introducing overconstraints or underconstraints. This article introduces a new triple crossed flexure pivot called TRIVOT that has a reduced parasitic center shift without overconstraints nor internal mobility, while allowing either optimal stress distribution in the flexures or a planar design. The new architecture also makes it possible to place the center of rotation outside of the physical structure, which is not the case with traditional bearings. Based on finite element simulations, we show that the parasitic shift is reduced by one order of magnitude in comparison to the widely used crossed flexure pivot. We also derive and validate formulas for the rotational stiffness and angular stroke limit of the TRIVOT. Finally, we show that a high support stiffness can be achieved with a lowest uwanted eignenfrequency 13.5 times higher than the first eigenfrequency. We expect this new pivot to become a competitive alternative to the crossed flexure pivot for applications where high accuracy and compactness are required.

Rotordynamics of an Improved Face-grinding Spindle: Rotational Stiffness of Thrust Bearing Increases Radial Stiffness of Spindle

The support is a key factor affecting performance of face-grinding spindle. However, advantage of traditional rolling element bearing is not highlighted when it is for large-size face grinding. This technical brief aims to develop a combined support for the face-grinding spindle consisting of a water-lubricated hydrostatic thrust bearing and two types of radial rolling bearings, and the flexible rotor dynamics of the spindle with the combined support is analyzed using the modified transfer matrix method. The results show that the rotational stiffness of water-lubricated hydrostatic thrust bearing can increase the radial stiffness of the face-grinding spindle, so the small-size rolling bearings can be utilized as the radial support for the spindle by aid of such rotational stiffness. A comparative study of comprehensive performance between the spindle supported by rolling bearings and the replacement spindle designed with our proposed combined support shows that the proposed one has technical advantage of large axial load-carrying capacity, low frictional power loss, low temperature rise and etc.

Rotational Stiffness and Carrying Capacity of Timber Frame Corners with Dowel Type Connections

With the development of wooden structures and buildings, there is a need to research physical and numerical tests of wood-based structures. The presented research is focused on construction and computational approaches for new types of joints to use in wooden structures, particularly glued lamella elements made of wood and wood-based composites. This article focuses on improving the frame connection of a wooden post and a beam with the use of fasteners to ensure better load-bearing capacity and stiffness of the structure. In common practice, bolts or a combination of bolts and pins are used for this type of connection. The aim is to replace these commonly used fasteners with modern ones, namely full thread screws. The aim is also to shorten and simplify the assembly time in order to improve the load-bearing capacity and rigidity of this type of frame connection. Two variations of the experimental test were tested in this research. The first contained bolts and pins as connecting means and the second contained the connecting means of a full threaded screw. Each experiment contained a total of two tests. For a detailed study of the problem, we used a 2D or 3D computational model that models individual components, including fasteners.

Analysis of Changes in Parameters of Free Vibration of Single and Multi-span Girders with Semi-rigid Joints

This study presents the analysis carried out for changes in parameters of free vibrations of single-span corrugated web girders with a semi-rigid joint at midspan and multi-span girders with spans connected by semi-rigid joints. Based on the experimental tests and the theoretical analysis, the behavior of six simply supported girders with the semi-rigid joint at midspan was analyzed. They were straight and double-slope girders with a span of 6.02 m, made of corrugated web sections WTA 500/300x15 with different types of semi-rigid end plate joints. It was demonstrated that the variable rotational stiffness Sj of the joint affected the equivalent concentrated mass of the girder mz, the frequency of damped free vibrations α, damping ρ, and the frequency of free vibrations ω. The theoretical analysis was conducted for a change in the equivalent concentrated mass of the single-span girders fixed at both ends and of the multi-span girders. It was described how the change in the support stiffness in the single-span girders fixed at both ends and the change in joint stiffness of spans affected the equivalent concentrated mass mz as a function of non-dimensional stiffness k. The equivalent concentrated mass mz of the girder was found to affect the values of maximum vibrations in the structure. A continuous change in the rotational stiffness of joints was taken into account from the pinned to the rigid joint.

STRESS RESPONSE AND INITIAL STIFFNESS OF SIDE PLATE CONNECTIONS TO WCFT COLUMNS

To study the mechanism of load transfer in double-side-plate connections between I-beams and wall-type concrete-filled steel tubular columns, a pseudo-static experiment and finite element analysis were conducted for two full-scaled specimens. The results revealed that the primary load was transmitted along an S-shaped path in the side plate, and the primary strain occurred in an X-shaped region between the left and right steel beam flanges. The shear force in the steel beam web was transmitted first to the side plate centre and then to the joint area, where the side plate, steel tube web, and concrete all resisted the internal force. Based on principal component methods, a calculation formula was established for initial rotational stiffness that comprehensively considers the influence of the tensions, compression, and shear deformation of the cover plate, side plate, and web. Comparing this formula with an existing model showed that the proposed formula is suitable for new types of side plate joints. Moreover, it can accurately calculate the initial rotational stiffness of the joint, thus providing a reliable basis for future engineering design.