Design of a Triple Crossed Flexure Pivot With Minimized Parasitic Shift

Abstract

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 so-called 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 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 for given dimensions and material, which are valuable for its dimensioning towards practical applications. We expect this new pivot to become a competitive alternative to the crossed flexure pivot for applications where high accuracy and compactness are required.

Gravity-Compensation Design Approaches for Flexure-Pivot Time Bases

“…The evaluation of these approaches in terms of chronometric accuracy on designs and prototypes satisfying realistic mechanical watch specifications. This is demonstrated on two flexure-pivot oscillator architectures developed in previous research: the co-RCC [4,6,8] (Figure 1a) and the TRIVOT [10,21] (Figure 1b). For the co-RCC oscillator, watch-scale silicon prototypes are used to validate experimentally the presented approaches.…”

Zero Parasitic Shift Pivoting Kinematic Structures Based on Coupled n-RRR Planar Parallel Mechanisms for Flexure Pivot Design

“…In order to highlight the advantages of the new flexure pivots presented in this paper (i.e., the TRIOVOT, the QUADRIVOT and the HEXAVOT), we compare their mechanical properties with two existing planar flexure pivots with minimized parasitic shift, namely the co-RCC [14] and the TRIVOT [19].…”

“…A theoretically zero parasitic shift can be obtained for flexure pivots with rotational symmetry [9,19,20]. Nevertheless, most designs are either: underconstrained [4,9,21], implying internal vibrations; overcontrained [4,20], which can create a highly unpredictable restoring torque and a limited rotation angle; or non-planar [9,20], requiring assembly which can induce large assembly errors.…”

“…Nevertheless, most designs are either: underconstrained [4,9,21], implying internal vibrations; overcontrained [4,20], which can create a highly unpredictable restoring torque and a limited rotation angle; or non-planar [9,20], requiring assembly which can induce large assembly errors. Today, the only known rotationally symmetric pivot without underconstraint and slightly overcontrained is the triple crossed flexure named TRIVOT [19]. Nevertheless, its radial support stiffness appears to be relatively low [22].…”

A fast steering mirror with ultra-low geometric tilt-to-length coupling noise for space-borne gravitational wave detection

“…A cartwheel hinge (also known as Haberland hinge), shown in figure 3(b), consists of a pair of intersecting leaf springs. Cartwheel hinges have higher rotation accuracy than notched flexure hinges and are easier to process and install than cross-axis flexural pivots [16] and butterfly flexure pivots [17], which have been used in some precision optical machine structures in recent years [18]. Figures 3(c)-(e) exhibit a notched flexure hinge, a cross-axis flexural pivot, and a butterfly flexure pivot respectively.…”