A straightness measuring interferometer characterised with different wedge prisms

Independently of the component used to introduce a divergence angle between the two probing beams of straightness interferometers, their uncertainty is limited by three main errors linked to each other: their resolution, the influence of refractive index gradients and the topography of the straightness reflector. The larger the divergence angle the higher is the resolving capability, but also the potential influence of the other two error sources. A fully fibre-coupled heterodyne interferometer was successively equipped with three different wedge prisms to investigate the optimal divergence angle under laboratory conditions. For that, the straightness interferometer was qualified with the Nanometer Comparator, which is a one-dimensional line scale interferometer with an additional straightness measurement capability. This feature is based on the traceable multi-sensor method, where an angle measurement embodies the “straightedge”. Therefore, the qualification of the straightness interferometer was also a comparison of two different straightness measurement methods. The influence of the refractive index gradients of air did not increase with interspaces between the probing beams larger than 11.3 mm. Therefore, over a movement range of 220 mm, the lowest uncertainty was realized with the largest divergence angle. The dominant uncertainty contribution arose from the uncorrected mirror topography determined with sub-nanometre uncertainty with the Nanometer Comparator

Range estimation system for powered wheelchairs

In this paper, we present a method to estimate a wheelchair’s power consumption and therefore its battery autonomy. The wheelchair powertrain is modeled to enable a virtual driving simulation. The use of a white box model enables an adaption to other systems and configurations. This model outputs the actual battery and motor currents within a simulation for a given route and speed profile. These currents affect the battery’s SoC, whose total charge depends on its temperature. To account changes of the available charge, a simplistic model of the battery’s temperature dependence is introduced, that has been acquired via discharge cycles within a climate chamber. Furthermore, an a priori simulation uses the model to estimate the SoC after the virtual completion of a route with a corresponding height and velocity profile. Finally, the paper compares the results of the simulation with real measurements using the recorded tracks and the generated virtual routes. Since the input for the a priori estimation relies on virtual routes, their quality is assessed as well