Optical Alignment

[Optic Eyes]

I have used jig transits and optical levels for paper and film machines. typically 60 to 120" wide film has some stretch ability and changes length as it cools, so if uneven drying happens one side of web can be tighter than the other.

Tipical alignment is .005" per 60" although if idling rollers are farther apart the alignment tolerance can often tolerance .010" or more.

We run field calibration tests to make sure jig transit calibration is in normal operating condition.

Typical range is a crosshair width of 4 to 10 arc seconds, at 100 feet a 10 arc second wide cross hair is .060" wide, 5 arc second .030" wide.
heat waves at distances over 50 feet the air can shimmer like looking far distances in a desert or highway on a hot summer day.

also structural steel building columns against a outside wall on a hot sunny day the columns can grow .030 or longer ovea 6 hour period.

just saying holding repeatable tolerances there are many variables.

I have even seen floor points on either side of a floor expansion joint side shift considerable amounts as temperature changes.

Leveling machinery is not only temperature changes but a floor can easily go down if a fork truck is parked nearby, or as machine sections are stacked on top of another.
The weight can cause machine base to go down unevenly. especially if machine is
not centered on structural steel supporting floor.

Optically levels require a peg test to check calibration.

Dial indicators and precision spirit levels are normally used for short range alignment especially 40" or less.
Optical more for long range alignment.


Sometimes plumb bobs from a roller 10 feet above are put in cups of water to steady and the plumb bobs strings are optically shot.

I used industrial sewing thread for string or fishing line.

This is similar to drill holes down into a tunnel to check
tunnel straightness. If tunneling underground it would be easy to slowly drift far off course unless tunnel drilling progress is checked periodically.

Obviously if 1 to 5 feet off center per mile that could be a problem.

 

[Optic Eyes]

An alignment telescope and an autocollimator are both optical devices that can be used for different purposes:

Alignment telescope

Used to establish an accurate line of sight. The telescope has a very straight line of sight and a reticle, or crosshair, that defines the center of the line of sight. In alignment telescope mode, the field of view is often measured in minutes horizontally.

Autocollimator

Used to measure angular tilts or rotation of an object. The autocollimator projects a crosshair pattern out to the object being monitored. The device under test is placed in the optical path and reflects the light back into the autocollimator, which can then be inspected via the telescope functionality. In autocollimator mode, the horizontal measurement range is often measured in minutes.

What is the difference between alignment telescope and Autocollimator?



The basic difference between the two modes is that the autocollimator measures tilt or rotation of the object while the alignment telescope measures lateral displacement. Also, lateral displacement can be given as either a linear value or an angular displacement, depending on the set-up.

 

[Eddyde]

Thanks for enlightening us on a subject most do not know of, yet is so critically important!