B7.4 - Novel Method for Determining the Mechanical Stiffness of Weighing Cells
- Event
- SMSI 2023
2023-05-08 - 2023-05-11
Nürnberg - Band
- Lectures
- Chapter
- B7 - Kibble and Planck balances II
- Author(s)
- M. Wittke, M. Darnieder, R. Theska, M. Torres Melgarejo - Technische Universität Ilmenau, Ilmenau (Germany)
- Pages
- 139 - 140
- DOI
- 10.5162/SMSI2023/B7.4
- ISBN
- 978-3-9819376-8-8
- Price
- free
Abstract
Weighing cells with electromagnetic force compensation are frequently used in precision balances and mass comparators. The kinematic structure is given by a compliant mechanism with concentrated compliances. Thin flexure hinges enable highly reproducible motion but limit the sensitivity to mass changes due to their rotational stiffness. To achieve the desired sensitivity, the stiffness of the mechanism must be further reduced by mechanical adjustments. To optimize the adjustment parameters, the initial stiffness of the mechanism needs to be characterized accurately. For this purpose, a novel self-testing method was developed. It allows accurate determination of the elastic stiffness of the weighing cell and the geometric stiffness caused by the masses of the linkages. The method uses static stiffness measurements in three orientations. The gravity vector must be orthogonal to the plane of motion to characterize the elastic stiffness. Determining the geometric stiffness requires the system to be in the working orientation. The upside-down orientation is used to confirm the results. This paper considers the novel method analytically and simulates using a rigid body model and the finite element method. The measurement of the stiffness of a weighing cell prototype is taken to validate the method.