Five National Metrology Institutes (NMIs) worked together to validate the assessment of laser tracker's (LT) uncertainty for large scale dimensional metrology in subsequent measurements using the network method. The LT uncertainty is assessed by measuring a set of a fixed network of targets from different LT positions. Afterward, we must perform a "bundled adjustment" of all the measurements to determine the transformations of the LT positions that minimize the residuals (differences) between a computed "virtual" group of targets, called composite points, and the redundant targets coming from the LT positions transformed to a unique LT position. Each residual is weighted with the LT's Maximum Permissible Error (MPE) specified by the LT manufacturer. The standard deviation of the weighted residuals becomes LT uncertainty. Afterward, with Monte-Carlo simulation, we propagate the LT uncertainty to the position of every target in the network and 3D distances between them. LT uncertainty is valid if 3D distance's uncertainties computed with composite points is greater than the error computed with these distances minus the same distances calibrated with the line of sight method (LOS) or if the absolute normalized error is less or equal to one. LOS method uses only the LT's interferometer for calibration, which dispense the use of a calibrated scale bar. Based on the network method, the NMIs developed two methods to improve LT geometry error parameters. The first improves the LT geometry error parameters by fitting the composite points to the LT geometry error model. The second evaluates the parameters placing the LT geometry error model in the minimization of the bundled adjustment's residual. LT geometry error parameters are valid if the parameter's uncertainties are negligent.

A method is described to select the location and number of fiducials used in point-based, rigid-body registration of two coordinate frames. Two indices are introduced which are used to search for the optimum configuration of fiducials. They can be used to quickly evaluate a large number of configurations because no actual registration is involved in their calculation. Furthermore, configurations yielding small values of the indices correlate well with configurations which result in optimum registrations. Three registration performance metrics are discussed, and it is shown that optimization of different metrics leads to different selection of fiducial configurations. If an optimized configuration is selected as a starting configuration of fiducials, the addition of extra fiducials does not significantly improve the registration in most cases. This work is based on 3D data acquired with three different instruments, each having different noise and bias characteristics.

Many experimental biological techniques utilize hollow glass needles called micropipettes to perform fluid extraction, cell manipulation, and electrophysiological recordings For electrophysiological recordings, micropipettes are typically fabricated immediately before use using a "pipette puller", which uses open-loop control to heat a hollow glass capillary while applying a tensile load. Variability between manufactured micropipettes requires a highly trained operator to qualitatively inspect each micropipette; typically this is achieved by viewing the pipette under 40-100x magnification in order to ensure that the tip has the correct shape (e.g., outer diameter, cone angle, taper length). Since laboratories may use hundreds of micropipettes per week, significant time demands are associated with micropipette inspection. Here, we have automated the measurement of micropipette tip outer diameter and cone angle using optical microscopy. The process features repeatable constraint of the micropipette, quickly and automatically moving the micropipette to bring its tip into the field of view, focusing on the tip, and computing tip outer diameter and cone angle measurements from the acquired images by applying a series of image processing algorithms. As implemented on a custom automated microscope, these methods achieved, with 95% confidence, ±0.38 µm repeatability in outer diameter measurement and ±5.45° repeatability in cone angle measurement, comparable to a trained human operator. Accuracy was evaluated by comparing optical pipette measurements with measurements obtained using scanning electron microscopy (SEM); optical outer diameter measurements differed from SEM by 0.35 ± 0.36 µm and optical cone angle measurements differed from SEM by -0.23 ± 2.32°. The algorithms we developed are adaptable to most commercial automated microscopes and provide a skill-free route to rapid, quantitative measurement of pipette tip geometry with high resolution, accuracy, and repeatability. Further, these methods are an important step toward a closed-loop, fully-automated micropipette fabrication system.

We present on a simple yet effective method for creating an invisible stylus from which a non-contact 3-D coordinated measuring system (the PiCMS) is realized. This invisible stylus dubbed a Pixel Probe is created through the orthographic projection of a spherical mounted reflector (SMR) through a trifocal camera system. Through this, a single point in space that is linked to a laser tracker world frame is mapped to a unique set of pixel coordinates in the trifocal camera creating the Pixel Probe. The system is constructed through the union of a Pixel Probe, a laser tracker, and calibrated stage, and does not require contact to obtain a measurement. In the current configuration, system resolution and accuracy better than is demonstrated on objects in the meso/micro scale that are well below the range of a laser tracker alone. A simple single-point coincidence condition allows the user to specify a measurement coordinate by pointing-and-clicking in the images captured by the Pixel Probe. We describe this system using multi-view geometry vision theory and present proof of concept measurement examples of 2-D and 3-D objects.