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The heart of optical measuring systems are the quality of the optics and the rigidity of the mountings.
Be very cautious when purchasing the systems. If you make purchasing decisions solely
on the stated specifications you may be in for long term disappointments. Dim images with edge distortions along with very frequent and expensive calibrations can be your
long term costs. As with any high end measuring system, insist on demonstrated capability on your products, preferrably utilizing your people. Get several quotations and
contact current owners to review ease of use, calibration and reliability (support) for the systems.
Our Vision System information is at our HiRes Displacement section.
Measuring Microscopes are in a couple of classes. The simplest and least expensive
contain a precision scale in the reticle (or one of the reticles of a binocular microscope). This works out well if the feature to be measured can be contained in the field of view
and the reloution of the optic scale is satisfactory for the required precision of measurement. The very simple hand held units under 30 power with a scale resolution
of 0.05 mm are typically under $200. The larger binocular units run around $1200 and offer a broader field of view with a brighter image. Adding another $1000 provides a
video camera. When the features to be measured do not fit into the field of view, another approach is needed. Two micrometer stages are put on the base which holds
the item to be measured. One stage moves in and out, the other left and right. Measurement is accomplished by positioning one feature under the cross hairs of the
reticle, noting the micrometer readings, then using the micrometer screws to move the item until the other feature is aligned with the cross hairs and noting the change in the
micrometer readings. The change in the micrometer readings is the distance. A system such as this with two inch stage travel length, grey scale camera, cross hair generator
and light source is around $7000. Resolution is in the 0.0005" range. Toolmaker's microscopes typically have much higher resolution and larger stage travel (at least on
one axis) and are generally cost in the $10,000 range.
A truely video based measuring system goes far beyond the capabilities of a measuring
microscope. The units have a camera system but incorporate high precision motors and scales on the stage that holds the item to be measured. They are generally
controlled by a computer system which can be used to calculate relationships between features such as positions, straightness, roundness, angles. Additionally, the higher end
units have the ability to save measuring routines for repetitive measurments of parts. The lighting can be programmed to allow very accurate feature edge detection.
Additionally the units have a scale system on the focus of the camera to enable detecting variations in the distance to the target point. All in all, it is essentially a
coordinate measuring machine - enabling precised measurements in 3 axis (X, Y and Z). These units cost around $40,000.
Optical comparators, on the most basic level, do what the name suggests, compare two
items optically. The item being evaluated is placed on the stage. A high intensity light source is on one side of the item and which produces a profile along the edge of the
item being evaluated. On the other side of the item, a lens system captures the profile and magnifies it. This magnified image is then projected onto the translucent glass
screen where the comparison can take place. Sometimes this screen if fitted with a transparent scale system graduated in length and angular units - the graduations on the
scale match the magnification of the comparator. Other times the screen if fitted with a transparent template matching complicated required contour of the part. The actual
contour of the magnified image of the item being measured is then compared to the template. Enhancements to the basic comparator include motorized stages with
encoders, surface reflection, interchangable lens systems, edge detection, computer interface for storing repetitive or complicated measurement sequences. The costs for
the systems vary considerably. A small lightweight comparator for occasional lightweight use may be as low as $5000 while a decent motorized system with a 24 inch
screen is in the $30,000 range. Prices go up from there depending on features but more on the screen size
SOURCES:
.OGP - Optical and Video Measuring Equipment
Mitutoyo - Measuring Microscope
Nikon - Optical and Video Measuring Equipment, Measuring Microscopes
Deltronic - Optical and Video Inspection Equipment
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