MEASUREMENT

A New Paradigm for

Multisensor Metrology With so many tools, it's not work-it's fun. BY KENNETH L. SHEEHAN

Imagine having a complete toolbox in your garage-one of those big red roll-

ing toolboxes with drawers

sible features. Need to access features on all faces of a part or features at

odd angles? Wrists and rotary tab les and compartments every-where. Every w rench and ratchet, screwdriver and socket is neatly organ ized and available to be used. Just the right tool for every task.

This is the world of modern multisensor mea-surement. Need speed to measure thousands of small features on a surface? Digital video systems gather thousands of measurement points in fractions of a second. Need high density points to characterize a 3-D surface? High speed laser sensors scan part surfaces down to sub-micrometer uncertainty. Have features

manipulate the system to create the perfect part/

»The move to visual interfac-es for the most fundamental sensor relationship.

T H I S

steps of automatic measure- When you have a com-plete set of tools, there ment area is a giant step

forward in truly bringing 3-D multisensor metrology soft-ware to the shop floor user.

»Although 3-D metrology software has closed the gap with current display technology for the moment, there is much more than can and should be done.

»True three-dimensional , perhaps holographic, displays will eventually become available, opening up new frontiers in 3-D metrology software.

is virtually no feature dimension that can't be measured. With a tool-box so well equipped, it's not work-it's fun.

HOW IT BEGAN Multisensor metrology systems have been in use for over 25 years. The world's first multisensor coordinate measuring system was featured on this magazine's cover in 1988. Since those early days, multisensor systems quickly evolved to measure

that present access problems such as bores or slots? Touch probes, both single point and scanning, are avai lable to probe and scan the most inacces-

full 3-D geometries, combining data from touch probes, scanning probes, point and wide scan lasers as well as a variety of optical/video sensors.

But throughout a quarter century of 3-D multisensor evolution, measure-ment softwa re itself did not become truly "3-D" in the visua l sense-it relied on 2-D video images and 2-D "models" to represent the measured part. It might fairly be said that system and sensor technology out-stripped the ability of software and display technol-ogy to conveniently a nd easily inform and empower the user.

As parts are increasingly designed using 3-D CAD, and the purpose of advanced metrology evolves to "con-firm design intent" and perform "what if? analysis" rather than merely offer-ing go/no-go evaluation, it follows that multisensor systems ought to use the origina l 3-D CAD model as the essen-tial basis for conducting and display-ing measurements.

Of course today's multisensor mea-suring software does use 3-D CAD models as the basis of measurement projects, but the latest software tech-nology goes a step further in extending the 3-D model concept to other key aspects of the man-machine interface. These new visual interface techniques address the most cumbersome aspects ofCMM programming. By creating an imated, visual models that let the user see exact ly what's happening "inside" the software, the most difficult

Figure 1: A 3-D Kinematic model of a multisensor measuring system with a part staged in a rotary indexer. Source: QVI

Figure 2 : Part coordinate system superimposed on the 3-D CAD model. Source: QVI

24 QUALITY I October 2014 www.qualitymag.com

Figure 3: The 3-D Kinematic model showing the part's coordi-nate axis system graphically superimposed on the part model. Source: QVI

Figure 4: This is a 3-D part model with 3-D optical measure-ment range superimposed. Note the range shows both X,Y measuring area and Z-axis depth of focus for the current

aspects of training and start-up experi-ence can be transformed. What once took many days of training now takes new users just a few minutes.

The first of these visual devices is the full multi-axis kinematic display.

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lens arrangement. Source: QVI

This model is an animated 3-D view of part and machine with all axes and sensors shown "live." If the user moves the joystick or deploys a sensor, the model instantly changes to reflect the commanded motion in real time.

The virtual world presented on the kinematic display matches the real world of the machine, including all its sensors and the part being measured. Whether working on-line with the machine or off-line on a stand-alone computer,

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MEASUREMENT

the kinematic model demystifies the relationships of all the working parts of the system, allowing intuitive and easy interaction. With new metrology soft-ware, 3-0 animations include the optical field of view, laser capture range and touch probe reach within the measur-ing volume. The ability to visualize the relation hips between optics, sensors and the measured part makes setting up new routines vastly more efficient.

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Three-dimensional visual anima-tions can also be used to simplify the most challenging aspect of learning to use a multisensor coordinate measur-ing system-setting up alignments. Alignments are a difficult concept for new users to grasp, primarily because there is no tangible result of creating an a lignment. A stage move or mea-surement is obvious because there is a corresponding machine action for each

programmed step, but datum set-ups have no such obvious action.

That problem is solved using ani-mated alignments to graphically show the coordinate reference frame super-imposed on the 3-D part model. The guesswork of creating alignments is eliminated, because there is tangible evidence of the current datum set up shown right on the screen. This real time visual reminder greatly increases the user's confidence. A user that is not constantly "double checking" to assure him or herself that the system is doing what they want it do lives in a world of lower stress and higher efficiency.

The next area in which 3-D anima-tions are used is in the appLication of Geometric Dimensioning & Tolerancing (GD&T). Three-dimensional animations show the user all degrees of freedom specified by the feature control frames for all features and datapoints. Now the relationships of nominal features, toler-ance zones and datum constraints are shown visually. When datapoints are measured, they are added to the anima-tion, allowing one to easily see the part condition compared to the design.

Another common measurement function which is vastly simplified by using animations are feature construc-tions. Most parts carry numerous dimensions that are actually distances or relationships between two or more physical features of a part. The mea-suring system's sensors measure the features, and the software "constructs" the dimension from them. In many measuring system's software, construc-tions are a tedious process involving many-sometimes counterintuitive-steps. Animated constructions make the process obvious-just "point and click" on features in the model to con-struct their relationship.

BENEFITS The benefits of using 3-D anima-tion s as the principal user interface scheme in 3-D measuring software are many.

3-0 visualization of the measuring system and part gives users complete understanding and confidence in the datum set-up and lets them act intui-tively with the measuring system.

Less training is required to begin using the system productively, and users can work with greater confidence.

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Shorter time is needed to stage parts and begin programming or measurement.

CAD Model based programming streamlines the verification process, allowing measurements to be com-pared directly to the original part design rather than an interpretation of the original part model.

Advanced features such as "apply to similar" allow one programming step to be assigned to any or all features in the CAD model which share the same characteristics-effectively leveraging the CAD database to best advantage.

All in all, the move to visual interfaces for the most fundamental steps of auto-matic measurement are a giant step for-ward in truly bringing 3-D multisensor metrology software to the shop floor user.

Where do we go from here? Although 3-D metrology software

has closed the gap with current display technology for the moment, there is much more than can and should be done. True three-dimensional, perhaps holographic, displays will eventually become available, opening up new fron-tiers in 3-D metrology software. We'll

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Figure 5: Here Is a 3-D part model with 3-D laser measurement zone superimposed. The laser range depicts the spot center, capture range, and return angle. Source: QVI

all go back to the drawing board (what's a drawing board?) to develop even rich-er, more intuitive user experiences. Q

Kenneth L. Sheehan is new product development manager at Optical Gaging Products. He has over 30 years in the 3-D Metrology Industry and has

been a member of the ASME Y14.5.1 Committee on the Mathematical Definition of Dimensioning and Tolerancing Principles since its inception. An avid yacht racer, he served as chief metrologist for the 2003 New York Yacht Club America's Cup campaign. For more information, email kls@qvii. com or visit www.qvii.com.

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