What you should consider before purchasing an optical measurement device
by Fritz Jordaan
Due to the extensive range of products available in the market, optical measuring devices range from stereo microscopes, measuring microscopes, and profile projectors, to 2D and 3D vision systems both manual and CNC.
When you are in need of an optical measuring device the following should be taken into consideration.
What material is the part composed of? Customers in need of an optical inspection device usually have features on parts where a mechanical tool is not able to measure these features. In most cases, softer materials and/or smaller features, where a mechanical tool is not able to access the feature and need to be magnified, are reasons to choose an optical inspection device.
Different optical devices measure different parts or features
Stereo microscopes are used to inspect small components. There is typically no need to perform any feature measurements.
Measuring Microscopes aid in measuring small features on parts, by incorporating an X Y travel table. Using a reticle in the eyepiece, or a camera and software to project the image onto a monitor, software can aid in measuring specific features. Measuring microscopes are available in various table and travel sizes, and offer objective lenses to suit optical needs
Shadow graphs and profile projectorsare used to project an image on a screen where it measures the part either by using an overlay chart, or by a counter that can measure more complicated parameters such as diameters, angles, distances, and other geometrical parameters.
Manual and CNC vision systemsare used when many complex features need to be measured on a part. Options vary from manual move XY stages, to fully automated systems that allow customers to change machine parameters such as lighting, various objection lenses, and complex tools to ensure proper feature measurement.
Features on vision systems could include Laser Auto Focus, which is optimal for high speed height measurement, and programmable illumination systems, which ensure measuring edges are properly defined. Where complex surface detail is involved and focusing becomes an issue, multi-auto focus tools can be incorporated to ensure that the correct location is in focus. This is especially important when focusing on transparent or mirror-like surfaces where focusing could be difficult. Projecting a pattern onto the surface of the feature, and allowing the camera to focus on the image of the pattern, will assist in the feature measurement.
CNC Vision systems can be incorporated into manufacturing cells to ensure that the production process is not producing defective parts due to bottlenecks in quality control. Measurement results can be obtained instantaneously and decisions relating to the production process can be made immediately.
The choice in optical measuring systems relies on many factors relating to accuracy, complexity of parts, part material, inspection frequency, throughput and cost. Choosing the correct equipment will ensure that the measurement results being obtained will meet your customer’s measurement results.
Fritz Jordaan, is service manager, Mitutoyo Canada Inc., Mississauga, ON.