autocollimator

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1. AUTOCOLLIMATOR

Amity School Of Engineering & Technology

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AUTOCOLLIMATORS• Autocollimators are devices for precise measurement of small rotations around axes orthogonal to an opticalsighting axis.• Autocollimators are more often used as inspection devicesthan as integral parts of a sensor system for servo controlled machines.• Both manual and electronic autocollimators are available, although the latter are most widely used today.• An autocollimator is actually the marriage of a collimator to a telescope.


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A collimator takes diverging light (e.g., light from a bulb) and focuses it into a non diverging column of light (i.e., focus the light at infinity).A telescope, on the other hand, takes light from a source at infinity and focuses it onto a point: thus when the angle of incidence of the light from infinity on the telescope changes, the position of the focused image on the focal plane of the telescope also changes. Because one focus of the telescope is at infinity, the axial position of the target mirror does not affect the position of the focused image.


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An auto collimating telescope is an instrument that combines a collimator and telescope into a single unit.• The measured angle is independent of the distance of the target.


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COMPONENTS OF A TYPICAL ELECTRONICAUTOCOLLIMATOR SYSTEM:


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FUNCTIONING OF AUTOCOLLIMATOR


• The basic function of an autocollimator is to detect and measure a deviation in the position of a reference reflective surface. The autocollimator projects a collimated beam of light onto a reflective surface.• When a deviation in the position of that reflective surface occurs, a deviated beam of collimated light returns to the Autocollimator.

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Autocollimators provide a simple method to measure straightness or flatness of a surface. such as a bearing way or surface plate, a mirror mounted to a sled is incrementally moved along a straight path (linear or crisscross).

• At each incremental stop, the autocollimator is used to measure the slope from which elevations can then be derived.• Properly used, an autocollimator can check thestraightness or flatness of a surface to the 1/2-1/4 μm level.


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WORKING

• An autocollimator works by projecting an image onto a target mirror, and measuring the deflection of the returned image against a scale, either visually or by means of an electronic detector. A visual autocollimator can measure angles as small as 0.5 arc second, while an electronic autocollimator can be up to 100 times more accurate.

• Visual autocollimators are often used for lining up laser rod ends and checking the face parallelism of optical windows and wedges. Electronic and digital autocollimators are used as angle measurement standards, for monitoring angular movement over long periods of time and for checking angular position repeatability in mechanical systems.


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• Servo autocollimators are specialized compact forms of electronic autocollimators that are used in high speed servo-feedback loops for stable platform applications. the measurement with autocollimator is done with by formula.

h= 2af

Where

h= reading on collimator

a= angle

f= focal length of the collimator.


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APPLICATIONS OF AUTOCOLLIMATORS• Autocollimators provide a last, simple method to

measure straightness or flatness of a surface. such as a bearing way or surface plate, a mirror mounted to a sled is incrementally moved along a straight path (linear or crisscross).

• At each incremental stop, the autocollimator is used to measure the slope from which elevations can then be derived.

• Properly used, an autocollimator can check the straightness or flatness of a surface to the 1/2-1/4 μm level in an order of magnitude less time than would be required to set up a laser interferometer and a straightedge.Amity School Of Engineering & Technology

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• Measures minute angle deviations• Determines repeatability and accuracy of rotary

axes• Visible laser source allows rapid alignment


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AUTOCOLLIMATORAmity School Of Engineering & Technology

The Micro-Radian TL160 laser-based autocollimator

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2. STRAIGHTNESS AND FLATNESS ERROR


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STRAIGHTNESS ERROR

• A line is said to be straight over a given length, if the variation of the distance of its points from two planes perpendicular and parallel to the generation direction of the line remains within the specified tolerance limit.– The tolerance on the straightness of a line is

defined as the maximum deviation in relation to the reference straight line going the two extremities of the line under examination

– The reference plane being so chosen that their intersection is parallel to the straight line joining two points located on line to be tested.


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• The straightness error of a line is defines as the distance ‘e’ between two lines drawn parallel to the mean true line and enveloping the actual contour bypassing through the highest and lowest points on the measured line


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The mean true line should be chosen such that it passes through the maximum number of points measured and the sum of the areas above it must be equal to the sum of areas below it.

The maximum straightness error can then be graphically determined by measuring the normal distance (e) between the two straight lines drawn parallel to the mean true line, enveloping all measured points.

For measuring the straightness error the following instruments are used:

• Straight edge• Sprit level• Autocollimator


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FLATNESS ERROR

According to IS:2063-1962,surface is deemed to be flat within a given range of measurement when the variation of the perpendicular distance of its point from a geometrical plane(this plane should be exterior to the surface to be tested)parallel to the general trajectory of the plane to be tested remains below a given value

It is a well known that a surface can be considered to be composed of an infinitely large number of lines. The surface will be truly flat only if all the lines are straight and they lie in the same plane.


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• Flatness deviation (errors of flatness) are indicated as follows:

1. µ or mm per meter- when convexities are allowed as well as concavities

2. Concave to….. µ or mm- when, between the ends, only concave surfaces are allowed

3. Convex to….. µ or mm- when, between the ends, only convex surfaces are allowed.


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THANK YOU


SUBMITTED BY -:PURSHOTTAM SMONTEK SINGHHARSHIT AGARWALKULKEERTY SINGH

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autocollimator