Optical measurement refers to noncontact measurement utilizing various light sources. It usually requires at the least one lens, a light supply and a detector. It differs from different forms of inspection in that instead of utilizing a tactile measurement methodology like a contact probe, it makes use of either a point of reference (e.g. a crosshair) or a pc to calculate edge detection. Two of its greatest benefits are its capability to measure options 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 proceed to have, significant impact. However, in reality, this form of noncontact detection applies to applications throughout most verticals and sectors. Adopters of recent optical measurement devices are looking for straightforward-to-use technology that helps the acquisition of more accurate data in less time. In consequence, there’s a rising demand for in-line measurement and faster processing of acquired images as well as image stitching capability and larger fields of view. There’s also a growing demand for innovative parts like liquid lenses. However when deciding which—if any—optical measurement gadgets are best 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 just like what schools used within the 1970s, ‘80s and ‘90s. It can accommodate goal 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 up to one 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 can be elevated by adding edge detection, normally in the form of an onscreen fiber optic detector.
Operation is pretty straightforward, with a person putting a workpiece on the stage with the required fixturing, then bringing the workpiece into focus by adjusting the Z-axis position. As soon as there’s a targeted image on screen, the person moves the stage so the onscreen reference reticle is aligned with the function of interest. The person 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 increased measurement repeatability made potential with the use 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 can measure 14 inches or larger, means profile projectors typically have a larger subject of view. Having been a familiar staple for decades, they are one of many best measurement gadgets to use. Unlike a measuring microscope, profile projectors are likely to inflict a low level of eye strain. And, total, they are usually the least expensive option while remaining one of many fastest.
Disadvantages: Profile projectors/optical comparators have a lower optical resolution compared to measuring microscopes as well as a lack of digital processing capability and low throughput. Lighting options are also limited, sometimes only including contour illumination.
Measuring Microscopes
It’s important 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 contains both in-line illumination for applications that require reflected light and transmitted illumination that permits for contour or profile measurements.
In terms of operation, measuring microscopes perform in a similar method to profile projectors. A workpiece is positioned on the stage, and an image of the feature of interest is then introduced into focus by adjusting the coarse and fine focus knob. As soon as a transparent image is viewable, the person aligns the built-in reticle after which moves the stage to the next fringe of the feature. The resulting scale readout shows the space traveled. As with profile projectors, edge detection software could be added to achieve better accuracy and repeatability towards determining the precise fringe of a part.
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