Non-contact measurement and inspection is a fundamental practice in many manufacturing environments and QC Labs. With the ever-increasing evolution of video technology, PC capabilities and other technological factors, understanding and selecting the best solution for a given application involves a process of continuous learning.

In addition to the requirements of the application, budget, the current level of a user's expertise, and training requirements must also be considered.

Microscopes
At the entry level, optical microscopes are broadly used by toolmakers and in other manufacturing applications, as well as in research and education. The most common types used in manufacturing are stereo and toolmakers' microscopes.

Toolmakers' microscopes typically utilize a single optical path and a shallow depth of focus which is better for measuring. They also utilize an XY stage for moving the work piece into the field of view and making measurements to a reference line.

On the high end, “zoom stereo scopes” combine two separate optical paths through individual zoom lenses. They provide a clear, rich image with an extended depth of focus for visual inspection.

Microscopes and video microscopes are often designed in a modular fashion so they can be tailored to the application by adding lenses, illumination and work holding devices. They continue to offer more capabilities. For example, simple LED displays have evolved into “smart digital readouts” that can include specialized computation functions such as measuring of features with complex geometric shapes. Another potential benefit is a significant increase in throughput when measuring multiples of the same part.

Optical Comparators
The optical comparator offers an easy-to-use solution with a well-established track record. Comparators provide a combination of excellent image quality and a full range of features. These include superb optics, readout devices, software interfaces, geometric measuring capabilities and screens that range in size from 12 inches all the way to 40 inches.

Light path options are available in horizontal or vertical orientations as determined by the application. In recent years many optical comparators have been configured with optical edge detection. These systems are small, powerful and affordable. (To find out more, click here to see the extensive article about Optical Comparators in the Winter 2007 edition of “Last Word”.

Vision Systems
If an application demands brighter surface illumination and higher magnification, a manual vision system should be considered.  Vision systems offer excellent surface illumination and the versatility of a zoom lens with magnification ranging from 10x to 240x.  Inspectors that know how to use a comparator generally find a manual vision system easy-to-learn.

Compact manual vision systems are available with live video camera feed and automatic edge detection via digital readouts. This type of system is an ideal video based measurement solution for general-purpose QA inspection, manufacturing and R&D non-contact measurement applications.

Features can include image archival with the ability to add text and upload data to a flash memory device. Also, the digital readout can provide video edge detection that automatically detects and targets edge points. This is easily achieved by scanning the image area within a circle around the crosshairs on the display. Its major benefit is that it eliminates operator subjectivity. 

Multi-Sensor Systems
Today, non-contact inspection has evolved into “the vision metrology field”, in which systems are effectively “precision coordinate positioning platforms” that can utilize a variety of sensor technologies from zoom optics and video, to lasers and touch probes. These are more commonly known as “multi-sensor” systems.  Multi-sensor systems are very flexible, enabling a variety of measurement work with one system.

For parts with complex contoured 3-D features, laser sensing can be a good choice. This method provides an extensive set of data points that precisely define a complex shape.  A touch probe can work well for larger parts with many recesses.  However when a touch probe will not reach critical areas, and/or when fine detail and magnification is essential, video is the best solution. The best method of measuring some complex parts involves several of these methods in a single program. 

The Future – More Technology Integration & Greater Capabilities
Video measurement applications will continue to evolve at a steady pace in the future. Future trends include more intuitive systems that require minimal measurement programming, systems with higher resolution field of view measuring capabilities and an increase in automated inspection solutions.

Increasingly, users require inspection of more complex and/or smaller components, the need to remove operator error or subjectivity and to increase accuracy and throughput volume. 

From microscopes to optical, vision and multi-sensor systems, there are many ways to employ a variety of techniques for measurement and inspection. The key is to evaluate your applications and options carefully, then utilize the methodology, technology and expertise to guide you to the most effective solution.

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