Optical tooling
Optical Alignment Fundamentals
Optical instruments increase alignment accuracy and decrease measurement time — all while providing stable, repeatable reference lines with no deviation. The science of optical metrology and alignment, using optical tools, makes it possible to achieve the highest degree of accuracy when aligning precision systems that are straight, flat, plumb or square.
Direct precision measurements are made rapidly and consistently. It is no longer necessary to extrapolate readings, or to make constant adjustments and calculations.
The three methods of optical alignment
In optical alignment there are three methods. Which one you need depends on what you are trying to prove about the setup.
Collimation
The instrument sights a distant reference line and measures the deviation of your setup from it. Because the reference is effectively at infinity, the result does not change with distance, so a telescope can be placed wherever it is convenient to work from.
Useful for proving a long run is straight, or that a machine sits square to its neighbours, without occupying the space between them.
Auto-reflection
A front-surface mirror returns the line of sight back along itself. Anything that should be perpendicular or flat can then be checked by looking at the return image and reading the deviation directly.
Useful for proving perpendicularity and flatness — the usual application for optical mirrors, targets, and adhesive targets.
Auto-collimation
A collimating eyepiece or an autocollimator projects a target onto a surface and reads back the angle at which the surface returns it. This measures small angular deviations very close to the working surface, without needing a distant reference.
Useful for fine angular work at the machine itself — see auto-collimating eyepieces and electronic digital levels.
What optical tooling replaces
The straight-edge, the square and the surface table are the basic tools of the engineer, and each has a counterpart in optical alignment. The difference is that the mechanical version has to be placed, read and moved by hand; the optical version gives the same answer directly.
| Engineer's tool | Optical counterpart | What you are proving |
|---|---|---|
| Straight-edge | Alignment telescopes | That a run is straight to a stated tolerance |
| Square | Optical inclinometers, drum clinometers | That surfaces are perpendicular or level |
| Surface table | Micrometers and adapters, targets | Position, height and flatness to fine limits |
Background
Sighting methods are ancient. Aligning stones by line of sight is credited with the David altars at Stonehenge and with the pyramids of Egypt, and the use of a mirror to set out squareness by in-line pinholes has been known for centuries.
The working principle has not changed. What modern tooling changes is the reading: instead of a person judging whether two images appear to line up, a graduated scale or a sensor reports the deviation directly and repeatably.