Abstract. Compliant mechanisms in precision weighing technology are highly sensitive mechanical systems with continuously rising demands for performance in terms of resolution and measurement uncertainty. The systematic combination of adjustment measures represents a promising option for the enhancement of weighing cells which is not yet fully exhausted. A novel adjustment concept for electromagnetic force compensated weighing cells designed for 1 kg mass standards is introduced. The effect on the mechanical behavior is analyzed in detail using a planar compliant mechanism with semi-circular flexure hinges. Design equations for a first layout of the mechanical system are derived from a linearized rigid body model. Existing adjustment concepts for the stiffness characteristic and the sensitivity to quasi-static ground tilt are included. They are extended by the novel approach to attach trim weights to the levers of the linear guide. Based on this concept, an optimal design for the weighing cell is determined. The comparison with a finite element model reveals further effects given by the more precise description of the mechanical behavior. By parametric studies of the adjustment parameters in the mechanical models, it is shown that the stiffness and tilt sensitivity can be reduced significantly compared to the non-adjusted weighing cell. The principal correlation of the trim weights and their effect on the mechanical properties is experimentally verified using a commercially available weighing cell.

Abstract. This paper describes the new adjustment concept of novel planar, monolithic, high-precision electromagnetic force compensation weighing cells. The concept allows the stiffness and the tilt sensitivity of the compliant mechanisms that are dependent on the nominal load on the weighing pan to be adjusted to an optimum. The new mechanism is set up and adjusted according to the developed mechanical model. For evaluation of the concept the system is tested on a high-precision tilt table and under high vacuum conditions in the environment of a commercially available mass comparator.

The aim of this work was to validate a novel methodology for high-resolution, repetitive measurements of mass dynamics of biological processes and structures in a closed plant-earth ecosystem consisting of Mammillaria vetula and microorganisms. To perform these experiments, the living system was materially welded into a newly developed Titanium Weighing Hollow Body (TWHB) with a laser. Three non-vital, also hermetically welded and high-vacuum suitable, externally identical TWHBs, filled with sand, served as controls. All TWHBs were equipped with a feedthrough and integrated light source. LEDs generated continuous light in all four bodies, which drove the photobiological processes in the vital test body and allowed long-term growth. Mass differences of the TWHBs were measured with a vacuum mass comparator at four points in time three months apart against two stainless steel mass standards. The expanded measurement uncertainty of the mass increase of the vital TWHB was calculated according to the Guide to the Expression of Uncertainty in Measurement (GUM) in each of the three independent experiments. The mass gain of the vital over the three nonvital TWHBs over the total experimental period of 9 months was +18 μg with the expanded measurement uncertainty 30 μg. The resulting mass gain would have had to be > 48 μ g $ > 48\enspace {\mu}\mathrm{g}$ to be considered statistically significant with a confidence level of 97.7%; time intervals over three and six months were also not significant. The study validates for the first time a methodology capable of measuring mass dynamics of living matter over time, when statistically sound conclusions with measurement uncertainties in the microgram range are required. This opens up a new level of precision mass measurements, which makes the methodology a candidate, e.g., for the verification of the principle of mass conservation in the life-sciences.

The following paper presents the development of a novel magnet system for use in a 1 kg Planck balance. For this purpose, several preliminary theoretical and experimental investigations were carried out and an optimized prototype magnetic system was modeled, designed and built based on the results. Initial measurements showed that the magnet system with an outer diameter of 104mm and a height of 50mm achieved a constant average value of 85.25NA−1 at a range of motion of ±0.6mm.

Further improvements in high precision mass comparison are a recent issue in the dissemination chain of the mass standard. One of the most precise methods of mass comparison is achieved by the use of high precision electromagnetic force compensated (EMFC) weighing cells as part of mass comparators. The mechanics of EMFC weighing cells are based on compliant mechanisms with concentrated compliances in form of flexure hinges. Total mechanical stiffness and tilt sensitivity are limiting factors with regard to the resolution of EMFC weighing cells. In order to optimize their performance, the stiffness and the tilt sensitivity of the systems need to be minimized. Due to manufacturing restrictions and robustness requirements, a further reduction of the thickness of the pivots is not desirable. In this paper, an alternative to reduce stiffness and tilt sensitivity by adding trim weights in combination with an astasizing adjustment is presented. Based on the results of the investigations, a new planar monolithic mechanism for an EMFC weighing cell is designed, providing the possibility to adjust trim masses. The new mechanism is set up and adjusted according to the developed mechanical model. A parameter combination for a total stiffness slightly above zero and a tilt sensitivity close to zero is found. For the evaluation of the adjustment success and the vacuum compatibility, the system is tested under high vacuum conditions.