Auto-Collimator & its applications
Auto-Collimator
Auto-collimator is
an optical instrument
used for the
measurement of small angular differences, changes or
deflection, plane surface inspection etc. They are typically used to align
components and measure deflections in optical or mechanical systems. 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 minute (0.15 rad), while an
electronic autocollimator can have up to 100 times more resolution.
Basic principle:
If a light source is placed in the flows
of a collimating lens, it is projected as a parallel beam of light. If this
beam is made to strike a plane reflector, kept normal to the optical axis, it
is reflected back along its own path and is brought to the same focus. The
reflector is tilted through a small angle‘0’. Then the parallel beam is
deflected twice the angle and is brought to focus in the same plane as the
light source.
Working of auto-collimator:
There are three
main parts in auto-collimator.
1. Micrometer microscope.
2. Lighting unit and
3. Collimating lens.
Figure
shows a line diagram of a modern auto-collimator. A target graticule is
positioned perpendicular to the optical axis. When the target graticule is
illuminated by a lamp, rays of light diverging from the intersection point
reach the objective lens via beam splitter. From objective, the light rays are
projected as a parallel rays to the reflector.
A flat reflector placed infront of the
objective and exactly normal to the optical axis reflects the parallel rays of
light back along their original paths. They are then brought to the target
graticule and exactly coincide with its intersection. A portion of the returned
light passes through the beam splitter and is visible through the eyepiece. If the
reflector is tilted through a small angle, the reflected beam will be changed its
path at twice the angle. It can also be brought to target graticule but linearly
displaced from the actual target by the amount 2θ x f. linear displacement of
the graticule image in the plane tilted angle of eyepiece is directly
proportional to the reflector. This can be measured by optical micrometer. The
photoelectric auto- collimator is particularly suitable for calibrating
polygons, for checking angular indexing and for checking small linear
displacements.
Applications
1.
Measuring the difference in height of length standards.
2.
Checking the flatness and straightness of surfaces.
3.
Checking squareness of two surfaces.
4.
Precise angular indexing in conjunction with polygons.
5.
Checking alignment or parallelism.
6.
Comparative measurement using master angles.
7.
Measurement of small linear dimensions.
8.
For machine tool adjustment testing.
