2020 September Speaker Series Agenda

Robotic Arm Compensation With Laser Trackers
Joseph Packer

Electroimpact uses laser trackers in the compensation of large-scale serial link robot arms to achieve a very high degree of positional accuracy using our “Accurate Robot Technology”. 3D laser tracker data is collected from hundreds of uncompensated robot positions using a special end-effector designed for metrology. This measured data is compared to the nominal commanded position of the robot. Using the data comparison, a compensated kinematic model that is calculated then applied to the robot’s CNC and verified once more using the tracker.

Simple Methods for Dynamically Testing Laser Trackers in the Field
David Parker

Laser trackers are typically evaluated under the ASME B89.4.19 standard using artifact standards under static conditions. Due to the requirements of the artifact standards, evaluations are typically beyond the capabilities of most laser tracker owners and are thus conducted by instrument manufacturers and standards laboratories. Instruments must be shipped to a lab for periodic evaluation, or following an incident that throws the performance in question. Moreover, the evaluations are under static conditions. There are no evaluation standards for the tracking and servo systems. Simple methods for testing, based on first principles, which are suitable for use in the field are proposed. For example, a plane pendulum is simply constructed by a beam, mass, and knife edge bearings. From first principles, it is known that the motions of a retroreflector attached to such a pendulum exhibit damped simple harmonic motions having a fixed period, T, and radius of curvature, r1. Given those two constraints, and the high accuracy clock capabilities of a laser tracker, it is possible to fit a series of measurements to a Fourier series of period T and higher harmonics. A secondary retroreflector, which could be used to simultaneously measure by a second instrument, would also have the same period, T, but in general a different radius, r2. While a smooth fit by relatively few terms does not guarantee good instrument performance—a poor fit is an indication of a possible problem. By strategically orienting the instrument under test with respect to the motion of the pendulum, the sensitivity of the distance meter or tracking and servo system can be emphasized or minimized. For example, to minimize sensitivity to the tracking and servo system and maximize sensitivity to the distance meter, orient the instrument in the plane of motion at the height of the retroreflector. To maximize sensitivity to the vertical servo system, orient the retroreflector looking downward and track the image of the retroreflector in a first surface mirror placed under the pendulum, i.e., virtually place the instrument looking up to the retroreflector. To maximize sensitivity to the horizontal servo system, orient the instrument perpendicular to the plane of motion. For added confidence, use two instruments simultaneously measuring to the two retroreflectors, in either opposite or orthogonal orientations. For higher frequency distance meter evaluations, such as vibration measurements, a retroreflector attached to a tuning fork could be used. Sources of error, such as the cyclic error, double path measurements due to stray reflections at the focal point of the columinating lens, servo lag, and software induced errors would be exposed.

A Case Study of an Automated Fuselage Pre-join
Robert Flynn

A recent fuselage join automation project gave the metrology team an opportunity to implement an automated metrology solution. This automation case study reviews a practical application of a single laser tracker solution. Limited access to the inside of the fuselage where the tracker sits adds an additional challenge to the problem, since it calls for perfection in the setup. Many challenges may be addressed successfully with mundane responses but a key to a satisfactory project solution is persistence in problem solving.

Integration of Laser Tracker Systems in BIW Measurement: A Case Study in Automotive Industry
Emre Bolova

Product and process quality assurance are challenging task due to increasingly narrowing product specifications. Coordinate measurement is one of the key technologies used in the area of dimensional control to inspect and improve the accuracy of produced components. Dimensional inspection tasks are often carried out on conventional coordinate measuring machines (CMMs). However, there are strong concerns about CMMs usage due to low measurement capacity, speed, flexibility, and limited accessibility to the underbody and inside the body measurement points. Besides, the agility requirement in diagnostic measurements in case of blocking quality problems is a critical task to be handled. In order to overcome these challenges, automotive companies are tending to adapt laser scanning technologies. However, according to the limited study to make a comparison in the literature, they are less accurate than the measurement with contact probe. In this study, the assessment of body geometry measurement capability was performed for off-line Leica laser scanning system through uncertainty and measurement system analysis (MSA) and compared with CMM. The obtained results demonstrated that the uncertainty and Gauge Repeatability & Reproducibility (GRR) values of laser scanning technology are very satisfactory for body geometry measurements. Besides, the measurement capacity due to increased speed, and the accessibility due to non-contact measurements are seriously improved compared to CMM.

CMM Verification of A Low Pressure Turbine Blisk Under Spin Testing Of A Small Turbofan Engine
Suneel Kumar

Spin testing testing of the integrated bladed rotors or blisks is being increasingly used for the better understanding and validation of life and integrity. The test is carried out in various steps and goes thorough rigorous monitoring and inspection during and after each set of testing cycles. The current paper gives an overview of the dimensional and geometrical verification on a Coordinate Measuring Machine (CMM) carried out at the pre-test and post-test levels. An overall measurement strategy and plan followed for the verification is explained. The measurement data obtained under the controlled conditions is analysed for deviations from the pretest values conditions for the validation.

From High-resolution Imaging to High-precision Metrology
Herminso Villarraga-Gómez

Today, X-ray microscopes (XRM) have the unique ability to achieve higher resolution, non-destructive imaging within larger parts than traditional X-ray micro computed tomography (μCT) systems. This unique capability—valued by researchers around the world—enables them to make new discoveries with XRM. This same unique capability is, more and more, of interest to industrial quality control entities as they grapple with small features in high precision manufactured parts for various industries such as automotive, electronics, aerospace, and medical devices, to name a few examples. However, many of today’s technology and manufacturing companies require traceable metrology, even at these high resolutions. This paper describes the development of a package—a solution consisting of hardware and software—for performing high-precision metrology using the high-resolution capabilities of ZEISS Xradia Versa 3D X-ray microscopes, which can attain spatial resolutions better than 1 μm (e.g., ~0.5 μm with the Versa 620 model). This new package, Metrology Extension (MTX) for Xradia Versa, includes a workflow designed to adjust and calibrate the XRM system to perform metrology tasks. Once the MTX calibration workflow is executed, the system can be used to measure small volumes, in in the order of (5 mm)3 or less, with high dimensional accuracy.

The MTX workflow (for dimensional metrology) has been tested in several XRM systems for metrological performance evaluation. The main results show that such systems can produce repeatable and reproducible measurements, with repeatability standard deviations in the order of 0.1 μm, reproducibility standard deviations of about 0.35 μm, and measurement accuracies comparable to those offered by tactile CMM (with deviations within the range of ±0.95 µm). Overall, the MTX is an advancement that converts a high-resolution instrument, the Xradia Versa, into a highly accurate instrument for dimensional measurements, enabling to extend further the imaging capabilities of XRM into the field of high-precision metrology.

Mobile Metrology AGV Within the Aerospace Industry
Doug Kappler

Large-volume, close-tolerance measurement presents unique challenges for aerospace manufacturers. Traditionally, metrology on large assemblies such as fuselages or wings has been performed using jigs, and the parts need to be moved to locations in the facility in which the measurements can be taken. However, this practice risks breakage to the parts and exposes them to security concerns during transport, which often necessitates them moving between hangars and other buildings.
In this paper, we will present an alternative mobile metrology option utilizing Nikon Metrology’s laser radar (LR) technology, which bounces light off a target and then uses a sensor to measure its reflection. Precise differences in the returned wavelengths can then be used to construct highly accurate 3D models of the target’s features. For the application we will be discussing, the LR system is mounted to an automated guided vehicle (AGV), which is a portable robot. This allows the measurement system to be brought to the part, as opposed to the part needing to be brought to the measurement system.
A large aerospace manufacturer employed this solution to overcome several limitations of their previous metrology system. We will examine these issues and describe in detail the technical means by which the LR mobile metrology solution solved them. We will then explore the lessons learned and potential uses for this application in additional industries.
Big parts can mean big problems for manufacturers; an LR system mounted on an AGV is an elegant solution to save time and money. This project demonstrated that metrology systems can utilize robotics in innovative ways to achieve breakthrough results for manufacturers.

An Investigation Into a Large Antenna Measuring System Based on Total Station and Vision Guidance
Zill Zhang | William Jansma

The deformation measurement and monitoring of large-scale antenna is very important for antenna users as well as manufacturers. This paper proposed a large antenna measuring method based on total station and vision guidance. Firstly, an automatic measuring model was established based on photogrammetry, precise distance measuring and angle measuring technology which used a camera to recognize the key points on the antenna and guide the total station to automatically aim at them and accomplish measurement. Then research was emphatically focused on automatic object recognition, calibration of spatial relationship between the camera and total station. Also collimation errors were compensated to improve the measuring accuracy. Finally experiments were carried out and the results indicated that the measuring error of the system could be within ±1mm in the measuring range of 60m which can meet the need of large antenna measuring demands in certain projects.

Beyond Best-Fit – Spatial Compensation of Metrology Data
Chris Jamison

Technological progress over the last decade has allowed metrology professionals to efficiently collect accurate and comprehensive datasets on large complex structures. With contemporary software, analysts distill meaningful results with unprecedented accuracy and speed. Specifically, automated feature extraction and cross sectional analysis allows analysts to report critical details efficiently. However, despite the increased speed and accuracy of the metrology technologies, the stiffness and stability of the structures limit our ability to achieve global tolerances without costly and time-consuming efforts.

To achieve the global best-fit tolerance requirements, these structures are typically inspected in either a manually adjusted support condition or on a costly holding fixture. Adjusting large, flexible structures to achieve global profile tolerances is notoriously expensive and time-consuming. When seeking to reduce this expense, two accepted metrology techniques are employed; profile at station lines and profile-per-unit-length (PPUL). Both techniques allow for verification in an indiscriminate support condition and can show an approximation of the optimally adjusted structure.

Profile at station lines locally fits cross sections extracted at incremental planes along the length of the structure. Unfortunately, these profiles are insensitive to potentially unacceptable deviations perpendicular to the station planes. These deviations can go undetected unless the global profile tolerance is controlled, which requires a return to costly global adjustment or fixturing. PPUL, where a structure is sectioned into locally-fit overlapping segments, can show lengthwise waviness and an approximation of the adjusted condition. However, the piecewise, rigid-body nature of the fit creates artificial discontinuities at the segment overlaps.

While the aforementioned techniques achieve acceptable results with mitigated cost and time commitment, they fail to explicitly address the flexibility of the structure. To solve this problem, our team has developed Spatial Compensation to produce a realistic simulation of a globally-adjusted structure independent of the global support condition. We have ensured validity by incorporating the structural characteristics (weight, area-moment of inertia and material stiffness) into the algorithm which compensates the measured data along the length of the structure.

The algorithm has degrees of freedom for fitting data in the local Y and Z axes and rotationally about the lengthwise X axis. Additional constraints can be applied to represent linear weight or clamping loads which, in combination with the physical properties of the structure, limit the solution to physical configurations achievable through manual adjustment. Empirical verification of the Spatial Compensation process was performed on a test article and the results are presented. The Spatial Compensation solution has been implemented through a user-interface within Spatial Analyzer.

Spatial Compensation successfully produces a simulation of the optimally adjusted support condition without masking deviations that would remain given realistic load limits. Spatially compensated metrology data is smooth and continuous while remaining sensitive to lengthwise waviness, resulting in higher quality results that expose subtle, often unidentified deviations. Spatial Compensation improves data quality while eliminating expensive holding fixtures or time-consuming adjustment operations, reducing cost and accelerating verifications.

Derivation and Guide to the Uncertainty in the Angle Between Two Planes
Jana Barker

Coordinate metrologists need to plan their measurements and estimate the resulting uncertainties before data collection in order to achieve needed precisions. We present the mathematical relationship between the calculated angle between two planes, least-square fitted from measurements of two surfaces, and the uncertainties in the employed measurements. Various types of measurement uncertainty are considered, including centering error, and instrument, network, and targeting uncertainties. Calculations assume that all uncertainties are small and normally distributed. We also provide a guide to the process of simulating the measurement uncertainties before the measurements are taken in order to plan the measurement and select instruments and tools.

X-Ray CT Measurement Study
Andrew Ramsey

World-class manufacturers have many metrology solutions at hand to help them ensure the quality of their parts and finished products. For many decades now, the “gold standard” for accuracy has been a fixed coordinate measuring machine (CMM). Increasingly, however, alternative metrology options are coming to the fore which can approach and often equal the performance of CMMs for dimensional measurement.

An option for an increasing number of manufacturers is X-ray computed tomography (CT), which uses penetrative radiation to provide three-dimensional images of a part. These systems can provide information in unique ways—by, for example, peering inside the part to analyze porosity, connection issues, or even the material layers in additive manufacturing processes.

In this paper, we will review the current state-of-the-art for X-ray CT, consider the environmental and application factors that can affect measurement results, and review the problems, solutions, and lessons learned from a specific project at a manufacturer utilizing the technology. In the final section, we will compare and contrast the performance and accuracy of CMMs and X-ray CT in a variety of settings and for different applications.

Industrial measurement is no longer a one-size-fits-all proposition. Although fixed CMMs will continue to have their place, as this testing and these projects demonstrate, X-ray CT can offer a wealth of options for manufacturers who understand their specific application and are looking for the best combination of outcomes for their given process.