OPTICAL COMPARATOR AND ITS WORKING

Optical Comparators have a high degree of precision and magnification is obtained with the help of light beams which have the advantage of being straight and weightless. Optical comparators , therefore, suffer less wear during usage than the mechanical type.

Optical comparators are used to magnify parts of very small size and of complex configuration that require accurate and enlarged profile. So they are widely employed in the inspection of many small parts such as needles, saw teeth , gear teeth , screw threads , etc. Since they check work to definite tolerances , they can be used to study wear on tools or distortion caused by heat treatment.

In an optical or projection comparator which is designed on the same principle as the ordinary projection lantern, an object is placed before a light source , and the shadow of the profile is projected at some enlarged scale on a screen where it is compared to a master chart or drawing. Interchangeable projection lenses which serve to magnify the image give accurate magnifications from 5 to 100 times.

Light is collected from a suitable source by a circular swiveling mirror placed at the left-hand side near the eyepiece. This light which is directed on to the 90 prism shown between H and E illuminates the scale incorporated in E and its image is reflected downwards by the mirror D through the lens onto the mirror B. This mirror , which is carried on a Pivot and rests on the top of the measuring finger A, reflects the image of the scale back the way it came. The mirror is so arranged that the return path offset slightly to enable it to be observed through the eye-piece H . In diagram C represents a fine adjustment ring for vertical position and G a final adjustment for zero setting.

In setting the comparator, the center zero on the scale is level with the zero mark in the eye piece. Any variation of the work causes the measuring finger A to tilt the mirror B and displaces the reflection of the scale from its mid position. The accuracy of measurement of this type of instrument is usually limited to 0.001 mm, and one of such division appears to occupy a space of about 2 mm. The scale movement provided (+) or (-) variation on each side of the zero is about 0.02 mm.

Working of Mechanical optical comparator

Other Common Types of comparators :

* Mechanical Comparators.

* Electrical Comparators.

* Pneumatic Comparators.

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Mechinopedia For Mechanical Engineers

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