Hongzhe Zhao

Analysis of annulus-shaped compliant pivot with series–parallel leaves

Annulus-shaped compliant pivot, formed by well-proportioned compliant modules between the outer ring and inner ring, can be employed in precision mechanical systems due to good performances. Especially for the multi-series leaves in one module, the annulus-shaped compliant pivot can fulfill a large displacement range without any axial drift in theory. In the design of the annulus-shaped compliant pivot, the load–displacement behavior and the stress analysis with analytical forms are important consideration. However, in the literature, there is few detailed work. In this article, a general annulus-shaped compliant pivot model formed by series–parallel leaves is first analytically established for the load–displacement behavior and the stress prediction. These calculations are based on accurate approximation of a beam flexure. Firstly, a loaded moment is decomposed into universal loads by combining the geometric compatibility condition. The stiffness accurate approximation is then analytically obtained, which provides a simple design strategy. Furthermore, the stresses in every leaf are obtained so that the annulus-shaped compliant pivot with large motion range can be actualized by stress checking. Lastly, the analytical model has been verified by commercial finite element analysis software ANSYS.

The Accurate Modeling and Performance Analysis of Cross-Spring Pivot as a Flexure Module

The load-displacement behavior of a cross-spring pivot as a kind of rotational element or module in compliant mechanisms is a subject of keen interest for many researchers. The model allowing not only quick design but also characteristics capture is pursued. This paper addresses some accurate closed-form results via approximations. These expressions are simple for a designer to understand the parameters without resorting to a tedious iterative procedure. The rotational displacement and center shift of the pivot are analyzed both qualitatively and quantitatively, with a general-purposed load applied including bending moment, horizontal and vertical forces. Meanwhile, a concise expression for center shift without approximations is proposed. The validity of the model is verified by finite element analysis (FEA). The relative error of the rotational displacement is less than 1.8% even if the rotational angle reaches ±20° the relative errors for the two components of center shift are less than 6% and 4% respectively, in the case of typical but general configurations and loads.Copyright

Research of Performance Comparison of Topology Structure of Cross-Spring Flexural Pivots

Cross-Spring Flexural Pivot (CSFP) has some advantages compared with rigid bearing. However, this kind of flexural pivot is limited in the field of precision positioning due to its small motion stroke, large axis drift, and sensitivity to temperature, etc. In this paper, topology structures of the CSFP were analyzed through defining different geometric parameters λ, spring crossing angle α, and spring number N. Characteristics of stiffness, axis drift, maximum stress, and temperature drift were compared and summarized by the Finite Element Analysis (FEA). Ultimately, a class of flexural pivots, called Inner and Outer Ring Flexural Pivots (IORFP), were selected for their excellent comprehensive performances. This type of flexural pivots has some significant advantages, such as large stroke, approximate zero axis drift and no temperature drift. Finally, the stiffness characteristic of IORFP with different geometrical parameters λ was compared by FEA, and law of stiffness variation was obtained. When λ is 0.1273, the IORFP has linear stiffness characteristics.© 2014 ASME

Analytical Modeling and Analysis of an Annulus-Shaped Flexural Pivot

Annulus-shaped flexural pivots (ASFP), composed of three or more identical leaves that are symmetrically arrayed in an annulus, can be used widely in compliant mechanisms for their excellent performances. This paper proposes the accurate load-rotation models of ASFP with three straight leaves, which include the load cases of bending moment combined with horizontal force and vertical force. Firstly, the load-rotation models of ASFP are derived based on the Beam Constraint Model (BCM). Then, the rotational stiffness and buckling characteristics are analyzed based on the derived models. Finally, the accuracy of the models is validated by the finite element analysis (FEA). The relative error of the load-rotation models is within 7% for various load cases even if the rotational angle reaches 0.07 (4°). The results show that the models are accurate enough to be used for initial parametric designing of ASFP.Copyright