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Advanced Imaging Magazine

Updated: January 12th, 2011 10:01 AM CDT

The Growth of Optical Measuring Systems

Three-dimensional measuring system based on computer vision and photogrammetry
figure 1
© General Logic and Opto Engineering
Figure 1: An axonometric view of the measuring head, trinocular version, via EyeGauge.
Figure 2
© General Logic and Opto Engineering
Figure 2: A sample metal sheet with well-recognized cuts of various shapes using uniform illumination.
Figure 3
© General Logic and Opto Engineering
Figure 3: Cloud of points from a high relief on smooth surfaces using shaped illumination, instead of uniform.
A typical pattern projector
© General Logic and Opto Engineering
A typical pattern projector, which can can manage objects exhibiting well recognizable edges, like cut metal sheets—even bent or cast—and smooth surfaces just by varying the type of illumination, which is uniform in the first case and ‘shaped’ (light blades) in the second.
OptoEngineering projector
© General Logic and Opto Engineering
Acquisition of details on an automotive parts by pattern projection with an OptoEngineering projector.
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By Daniele Lugli, General Logic srl

In recent years, 3D optical measuring systems have been spreading at an increasing rate and beginning to erode the market of traditional contact-measuring systems. A comparison of their features will show why this is happening.

Acquisition rate (throughput): Contact measurement ranges from less than one point per second (for single contact machines) to thousands of points per second (for scanning), while optical measurement ranges from thousands to millions of points per second. Less time spent in measurement means more productivity and often the possibility of verifying 100 percent of the production instead of sampling.

Measuring volume: Contact measuring machines (CMM) usually have a fixed measuring volume, that is the size of measurable objects is limited. Portable contact measuring machines can be displaced to measure large objects, but patching together results obtained in different positions is not a trivial task. On the other hand, optical measurements easily can be patched together (by means of "markers," for example), and laser trackers can have measuring ranges up to kilometers.

Complexity and reliability: A contact measuring machine has many moving parts that are subject to wear, and several different subsystems, including mechanical, pneumatic, electric and, electronic. Optical measuring machines have few or no moving parts; their complexity lies mainly in software and their failure probability is low.

Safety: No contact and no moving parts means no possibility of damaging the object being measured or injuring the operator.

Precision: Contact measurement ranges from submicron to tens of microns, while optical measurement ranges from microns to millimeters. While only a minority of applications need micron or submicron precision, in most cases, the precision delivered by optical measurement is more than sufficient.

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