Coordinate Measurement System Research Articles

The analysis of feature-based measurement error in coordinate metrology

Coordinate measurement systems (CMSs) dominate the dimensional control and diagnostics of various manufacturing processes. However, CMSs have inherent errors caused by the lack of a tracing ability for some of the measured part features. This is important for product inspection and process variation reduction in a number of automated manufacturing systems, such as for example the automotive body assembly process. The lack of a feature tracing ability means that instead of measuring a given feature, the CMS may actually measure the area around the selected feature. In this paper, a principle for the part feature tracing ability and the resultant feature-based measurement error analysis are developed to estimate the aforementioned deficiencies in the CMSs. The impact of feature type and part(s) positional variation on the feature-based measurement error is explored. The proposed approach is applicable to both contact and non-contact CMSs including both mechanical and optical coordinate measuring machines An analysis of the error for different measurement algorithms is presented. We show that the developed feature-based measurement error can have a significant impact on the measurement accuracy and hence on process control and the diagnostic algorithms currently used in manufacturing. A feature-based error map and error compensation approach are also developed and presented. Simulations, experimental results and two industrial case studies illustrate the proposed method.

A New Model of Binocular Stereo Coordinate Measurement System Based on Skew Ray Tracing

Two-CCD binocular stereo vision systems using pinhole model are attracting research interest in many important fields such as 3-D coordinate measurement. However, new system modeling is difficult because of lack of fundamental imaging formation theory. In this paper, in order to measure a 3-D surface, we demonstrate how a binocular stereo vision system can be modeled by the proposed skew ray tracing method to study the geometric relations between the binocular camera images and the 3-D surface. In order to investigate the overall accuracy and resolution of this system, the influence of infinitesimal camera reading errors on measured coordinate errors is determined by sensitivity analysis. Experimental verification demonstrates that the performance of the proposed system is excellent.

A Self-Organising Fuzzy Logic Controller for a Coordinate Machine

For a 3D coordinate measurement system, the dynamic accuracy of the moving table will influence the measuring accuracy directly. If a classical PID controller were designed for this measuring table without an accurate mathematical model, the gain parameters may need to be regulated frequently by trial-and-error to obtain the precise motion control objective, good adaptability, and robustness. In this paper, a model-free fuzzy controller and a self-organising fuzzy controller (SOFC) were employed to eliminate the above controller design problems and improve the tracking control accuracy. The control performances of these intelligent control strategies were compared, based on the experimental results. The SOFC has the best tracking accuracy and its learning ability significantly reduces the trial-and-error design effort of a traditional fuzzy controller.

Automatic camera calibration for a multiple-sensor integrated coordinate measurement system

An automatic camera calibration scheme that utilizes a coordinate measuring machine (CMM) and a camera calibration algorithm is presented for a multiple-sensor integrated coordinate measurement system. In the proposed calibration scheme, the touch probe tip carried by the CMM is employed to automatically generate high-precision calibration target points for camera calibration and sensor integration. A camera calibration algorithm with analytical formulations is developed to calibrate camera parameters in three stages without nonlinear minimization procedures. Simulations and experiments were performed to verify the proposed camera calibration algorithm. The precision of the automatic camera calibration scheme is also evaluated.

The question of spiral axes and brachiopod shell growth: a comparison of morphometric techniques

An example of actual shell growth in the pentameride brachiopodLycophoria nucella(Dalman) reveals that the axis-computing morphometric technique (Aldridge 1998; Van Osselaer and Grosjean 2000) produces hypothetical ideal logarithmic spirals that fail to morphometrically characterize the biological realities determined by the actual geometry of the shells to which the axis-computing technique is applied. In contrast, the actual-outline morphometric technique (McGhee 1980) links the measurement coordinate system directly to the ontogeny of the animal under analysis, and it yields morphometric parameterizations of geometric aspects of the shell of direct biological significance to the animal (the presence or absence of ontogenetic alterations in shell convexity, rates of change of shell convexity in the case of anisometric growth, and the nature of anisometric changes in shell convexity—i.e., whether the shell becomes increasingly more convex with growth, or whether the shell becomes increasingly flatter with growth).

The Threaded Dental Implant as a Reference Object for Image Alignment

This paper presents a method that uses the threaded dental implant as a reference object for the inter-image alignment necessary for digital subtraction radiography. The implant is furthermore used to define a measurement coordinate system and to automate the placement of reference areas used for contrast correction. The method is intended for studies of diffuse bone density changes in the vicinity of the implant. The method is shown to be insensitive to large variations in exposure time and geometry, and is together with the contrast correction method of Ruttimann et at., able to detect clinically invisible simulated bone density changes.

Multiple-sensor integration for rapid and high-precision coordinate metrology

The development of a multiple-sensor coordinate measuring system (CMM) is introduced and its applications to automated part localization and rapid surface digitization are experimentally demonstrated. The developed multiple-sensor CMM is characterized by an integrated use of a high-precision CMM equipped with a motorized touch probe, and a 3D active vision system, advanced computational software, and the associated electronics. The 3D active vision system is capable of digitizing surface coordinates of objects having multiple features; thus intelligent feature recognition algorithms can be applied to extract the global surface information of the object. The obtained information can be subsequently used to automatically guide the touch probe for rapid coordinate data acquisition and to strategically control the coordinate measuring machine for high precision sampling of critical surface area. In this paper, the information automation for the multiple-sensor integrated system is demonstrated in part localization.

A superfiber for position sensitive detectors

Scintillating fibers are being used more and more in science and medicine to provide precise coordinate measurement systems for elementary particles and X-ray detection. However, low light collection efficiency (3–4% per direction typically) is still the most limiting factor. In this paper we present results of Monte Carlo calculations to illustrate some peculiarities of light collection in round fibers. According to our analyses, by certain modifications light collection in round scintillating and waveshifting fibers could be increased to about 20% per direction.

The Reality of Experience: Gibson's Way

This paper considers some first principles that might provide a basis for an objective science of experience (presence or immersion). Dimensions that are considered include classical Newtonian measures of the distal stimulus, changes in neural mechanisms reflecting the proximal stimulus, information theoretic measures of the statistical properties of events, and functional properties related to intentions and abilities. Gibson's ecological framework is suggested as a promising functional approach for defining the reality of experience in relation to the problem of designing virtual environments. This approach emphasizes the tight coordination between perception and action and fixes the measurement coordinate system relative to the capacity for action.

Design considerations for a three dimensional fiber optic laser Doppler velocimeter for turbomachinery applications

Single headed three dimensional (3D) laser Doppler velocimetry (LDV) geometries generally rely upon the use of three Doppler difference channels, inclined at differing angles with respect to the mechanical axes of the probe. The transformation between the nonorthogonal measurement coordinate system and the Cartesian system can result in large errors in the calculated velocities. A theoretical analysis of the geometrically induced uncertainties in measurements produced by four single headed 3D LDV configurations is presented. These considerations have lead to the development of a single headed fiber optic 3D LDV probe based on the use of two Doppler difference channels to directly measure the transverse velocity components, and a reference beam channel to measure the on axis velocity component. The f/4 probe head has a working distance of 200 mm, designed to operate within the constraints of the limited optical access available in turbomachinery applications.

Hybrid optical-electrical overlay test structure

This paper describes the exploratory use of electrical test structures to enable the calibration of optical overlay instruments of the type used to monitor semiconductor-device fabrication processes. Such optical instruments are known to be vulnerable to hard-to-determine systematic process- and instrument-specific errors known as shifts. However, these shift errors generally do not affect electrical test-structure measurements extracted from the same features. Thus the opportunity exists to configure physical standards having overlay targets that can be certified by electrical means, thereby enabling estimates of the shifts prevailing in a particular application. In this work, a new hybrid test structure, meaning one from which overlay measurements can be extracted electrically, as well as by optical instruments, has been designed and fabricated with built-in overlay values ranging from -60 to +60 nm. A selection of structures constituting a test chip has been patterned in a single conducting film with CD (critical dimension) design rules ranging from 1.0 /spl mu/m to 2.0 /spl mu/m and fabricated and tested. Electrical overlay parameters, derived from multiple step-and-repeat die-site measurements, generally match the corresponding optical measurements to within several nanometers, subject to limitations of the pattern-replication process. This paper focuses on the extraction of overlay from the electrical measurements, the dependence of the measurements on CD design rules, and their comparison with the corresponding measurements made both by a commercial optical-overlay instrument and by a coordinate-measurement system having measurements traceable to absolute dimensional standards. It is presented as a first step toward the use of electrical measurements for advancing shift management in optical overlay of features patterned in separate lithographic processes.

Integrated real time compensation system for errors introduced by measurement probe and machine geometry in commercial CMMs

In this paper, an integrated real time compensation system has been proposed for the errors introduced by the probe and machine geometry in commercial CMMS. For efficient probe error mapping, a compact notation (ϵ, θ) for probing direction and corresponding concentric diagram is proposed. A set of integrated volumetric error equations are also proposed for the volumetric error map integrating the probe error and the machine geometric error. For the real time error compensation scheme, an interface box and an appropriate software driver have been designed and implemented between the CMM and machine controller. The data flow is intercepted and corrected according to the integrated volumetric error map without the controller being noticed. Thus the real time error compensation system has been successfully implemented for the machine with minimum interference to the existing coordinate measurement system. The developed system has been applied to a commercial CMM on the shop floor, and the measurement accuracy has been improved remarkably.

3D MEASUREMENT CONTROLLED BY A CAD MODEL-BASED MEASUREMENT PLANNING AND VISION SYSTEM

Optical coordinate measurement systems will benefit from developments similar to those taking place in robots, namely off-line programming capability and intelligent sensors. Research work towards these goals is reported here. An experimental system with CAD model-based measurement planning and vision control has been constructed and its feasibility demonstrated. The system comprises a measurement planning tool, a measurement robot with vision guidance and a means of visualizing and comparing the measured results with the design data. The measurement planning tool is based on a commercial CAD system and enables the use of existing CAD models of the objects to be measured as a basis for planning. It generates a measurement model file (MMF) containing instructions for controlling the measurement robot, which is an optical coordinate measurement device based on the laser rangefinder principle and supplemented with a vision system for guiding the measurement to planned target points. The measured coordinate values can be compared with design values either graphically or numerically. The performance of the experimental system was demonstrated and evaluated. In the demonstration case a measurement sequence was planned and saved in the form of a MMF, whereupon the measurement robot was able to execute the sequence reliably according to the MMF and measure the planned target points with vision guidance. The pointing repeatability of the vision guidance function was 0.019 mRad (standard deviation), which is equal to 0.19 mm at a distance of 10 meters, and the corresponding pointing accuracy was better than 0.04 mRad. The 3D measurement had an average repeatability of 0.3 mm (standard deviation), and the absolute accuracy of averaged measurement results was better than ±1 mm (for x, y and z) in 81% of the cases. The next phase of the work will include piloting the system in an industrial application.

Performance Measures for Geometric Fitting in the NIST Algorithm Testing and Evaluation Program for Coordinate Measurement Systems.

The Algorithm Testing and Evaluation Program for Coordinate Measurement Systems (ATEP-CMS) is a Special Test Service offered under the NIST Calibration Program. ATEP-CMS evaluates the performance of geometric fitting software used in coordinate measurement systems. It is a Special Test because it is a new type of NIST service, experimental in nature and unsupported by historical data. This report documents and explains the rationale of the performance measures used in ATEP-CMS and analyzes the uncertainties of those measures.

Multicamera vision-based approach to flexible feature measurement for inspection and reverse engineering

The vision-based coordinate measurement system, developed at the National Research Council Canada, is a multicamera passive system that combines the principles of stereo vision, photogrammetry, knowledge-based techniques, and an object-oriented design methodology to provide precise coordinate and dimension measurements of parts for applications such as dimensional inspection, positioning and tracking of objects, and reverse engineering. For a vision system to be considered for such applications, its performance and design parameters must be well understood. A description of the system, the techniques employed for calibration, a performance evaluation procedure, an accuracy analysis, and test results are presented.

Coordinate measurement system supported by image processor for emulsion plates

Central collisions of 32S and 16O with Pb at 200 GeV amu have been studied by the emulsion spectrometer in the CERN-EMU05 experiment. The emission angles, momenta and charge signs of the secondary particles are measured. The position of a track in an emulsion plate should be measured by using a microscope to determine the momenta of more than 500 charged secondaries in an event. A new coordinate measurement system has been developed by using a video image processor connected to the microscope. In this system, the position, direction and length of a track in a coated emulsion are expressed as a vector which is linked with the motion of micro X- Y stage and is superimposed on an emulsion image on a TV monitor. By using this system, the data acquisition rate has become about ten times faster than that by using only an emulsion image and the momentum resolution has become higher than that. Moreover, this system is effective for identifying tracks emitted in more than 45°.

Spherical coordinate automatic measurement (SCAM) system for robots' end-point sensing

To assess robots' end-point positioning accuracy and repeatability, a Spherical Coordinate Automatic Measurement (SCAM) system that is currently under development at the National Institute of Standards and Technology (NIST) formerly the National Bureau of Standards—is presented. The system has been designed to be interfaced with a personal computer for on-line analysis of three-dimensional static, as well as kinematic, positioning performance. The SCAM system has a spherical work envelope that is monitored by a built-in linear transducer with a resolution of 2.5 μm and two angular optical encoders of 0.005 accuracy. The measurement device is inexpensive and well-suited for calibration and diagnosis of small or medium-sized robots. Tests have indicated that the measurement system can sense the robot end effector with 34 μm accuracy and 32 μm repeatability. The SCAM system, when affixed to the robot end effector for testing, exerts an external load on the end effector (nature of the contact-type measurement technique). Because of this drawback, its applicability is limited; specifically, when no-load test condition results are desired. However, its reliability and simplicity in design make it a powerful and economical tool for robot positioning testing.

Creating a Standards Infrastructure for Co-Ordinate Measurement Technology in the UK

The National Physical Laboratory (NPL) is playing a leading role in the establishment of a standards framework to support the extensive use of co-ordinate measuring machines (CMMs) in UK industry. These activities are strongly specification standards oriented and are undertaken in close collaboration with the British Standards Institute in many cases. Such work includes (i) the formulation of specification standards for performance verification of complete co-ordinate measurement systems to ensure traceability to national primary standards. (ii) the provision of calibration facilities for reference artefacts, particularly those used in CMM systems acceptance-testing and (iii) developing various measurement sub-systems checking techniques including a software validation service. The paper describes the progress in these fields and more specifically the NPL work.

超音波多重位相差方式による３次元座標の測定

Development of three dimensional (3 D) measuring machines which are not equipped with axes; x, y, z axes and/or joint axes, is important because such machines do not suffer from the Abbe's errors, play and clearance of joint axes, and/or elastic deformation of mechanisms. This paper first introduces the principle of a new coordinate measurement system using ultrasonic waves in which : (1) some fixed receivers receive several kinds of ultrasonic signals from a movable transmitter, (2) from the phase shifts between the transmitted and received signals, distances of the transmitter from the receivers are calculated, and (3) from the distances, 3 D coordinates of the transmitter are determined by triangulation. Secondly, the paper explains a measuring setup. Some experimental results in a space of 300 mm×300 mm×1000 mm shows that the errors of 1 D measurements are less than 0.2 mm and those of 2 D and 3 D are less than 1 mm and 2 mm respectively. The causes of the errors are also discussed.

A simple and rapid coordinate measurement system for large-molecule oscillation photographs

A simple and rapid coordinate measurement system for large-molecule oscillation photographs