Optical measurement refers to noncontact measurement utilizing various light sources. It normally requires not less than one lens, a light source and a detector. It differs from other forms of inspection in that instead of using a tactile measurement method like a contact probe, it uses either a degree of reference (e.g. a crosshair) or a computer to calculate edge detection. Two of its greatest benefits are its capability to measure features too small or fragile to measure by contact, and the fact that it is faster compared to other forms of measurement.
The medical, plastics, aerospace and automotive industries are where optical measurement has, and will continue to have, significant impact. However, in reality, this form of noncontact detection applies to applications across most verticals and sectors. Adopters of modern optical measurement gadgets are looking for simple-to-use technology that helps the acquisition of more accurate data in less time. As a result, there’s a rising demand for in-line measurement and faster processing of acquired images as well as image stitching capability and bigger fields of view. There’s additionally a growing demand for innovative components like liquid lenses. However when deciding which—if any—optical measurement gadgets are right for you, all factors must be considered.
Profile Projectors/Optical Comparators
You possibly can think of this optical measuring system as a high-accuracy overhead projector similar to what schools used in the 1970s, ‘80s and ‘90s. It may accommodate objective lenses as much as 100x magnification, use either contour or surface illumination, and has either a microscope-fashion stage or metal stage with T-slots that can hold as much as a hundred lbs. The stage is married to high-accuracy linear scales, which provide positional feedback, and a crosshair is typically etched onscreen as a measurement reference point. Measurement throughput will be increased by adding edge detection, usually within the form of an onscreen fiber optic detector.
Operation is fairly straightforward, with a person putting a workpiece on the stage with the necessary fixturing, then bringing the workpiece into focus by adjusting the Z-axis position. As soon as there’s a centered image on screen, the consumer moves the stage so the onscreen reference reticle is aligned with the feature of interest. The consumer then can zero the scales on either the X- or Y-axis and move the stage to the next position on the feature. The scale readout will decide the gap traveled with elevated measurement repeatability made doable with the usage of edge detection software. Final data is stored and analyzed by an optional 2D processor.
Advantages: The design of the objective lens, coupled with a screen size that may measure 14 inches or larger, means profile projectors typically have a larger field of view. Having been a well-known staple for decades, they are one of many easiest measurement devices to use. Unlike a measuring microscope, profile projectors tend to inflict a low level of eye strain. And, general, they are usually the least expensive option while remaining one of the fastest.
Disadvantages: Profile projectors/optical comparators have a decrease optical decision compared to measuring microscopes as well as a lack of digital processing capability and low throughput. Lighting options are additionally limited, sometimes only including contour illumination.
Measuring Microscopes
It’s essential to point out that measuring microscopes are different from traditional microscopes. Unlike a traditional microscope, in a measuring microscope the stage is connected to linear scales that provide positional feedback, and a reticle is either constructed into the eyepiece itself or positioned in the light path as a reference level for measurement. In addition, a measuring microscope accommodates each in-line illumination for applications that require mirrored light and transmitted illumination that allows for contour or profile measurements.
When it comes to operation, measuring microscopes function in a similar manner to profile projectors. A workpiece is positioned on the stage, and an image of the function of interest is then introduced into focus by adjusting the coarse and fine focus knob. As soon as a transparent image is viewable, the consumer aligns the constructed-in reticle after which moves the stage to the following edge of the feature. The ensuing scale readout shows the gap traveled. As with profile projectors, edge detection software could be added to achieve larger accuracy and repeatability towards figuring out the precise edge of a part.
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