Optical techniques for Mechanical Alignment – Robert Parks, Optical Perspectives Group

This tutorial will begin by discussing what optical alignment means as it is usually applied to optical instruments and setups, but will also address mechanical issues such as measuring straightness, perpendicularity and spatial relationships of mechanical features and datums.

Once the scope of the topic is defined we look at why optical methods are useful for making mechanical measurements. Optical methods work because light travels in straight lines. This is particularly useful for metrological purposes when light interacts with specular surfaces. We demonstrate methods of making rough surfaces appear specular through the use of simple tooling. We show how it is possible to transfer of optical datums that cannot be seen or tactilely probed to mechanical datums that are easily measured with familiar mechanical tooling.

Once some of the concepts of optical alignment are understood we describe the optical instruments used in alignment such as autocollimators, alignment telescopes, autostigmatic microscopes. Also we look at combinations of these optical instruments with precision bearing and encoders such as theodolites and laser trackers, and give a feel for the precision with which these instruments are capable. Along with the descriptions of these sophisticated instruments we look at some very simple tooling that extends the usefulness of these instruments such as laser point sources of light, spherical balls to simulate theoretical points and plug gauges to replicate axes, angle gauge blocks and sine plates, and optical grating structures ebeam written on photomask substrates as primary spatial standards.

The largest part of the tutorial will cover methods of using these tools to perform various aspects of alignment of both optical and mechanical systems. Alignment is either placing components in space in 6 degrees of freedom where a drawing specifies they should be, or to verify that a component is correctly positioned relative to some one or more physical datums. The explanation of alignment techniques and procedures will start with use of an autocollimator to compare angles and proceed on to using an alignment telescope to define an axis and coaxiallity with the axis.

The discussion will move on to using autostigmatic microscopes and precision stages including CMMs to define points in space when those points are relatively close together, and the use of laser trackers for points spread out over larger areas. Finally, the use of diffractive optical patterns will be discussed as a means of defining points and axes in space with high precision and stability.

Robert Parks, Optical Perspectives Group

Robert E. Parks has been active in the fields of optical fabrication and testing for the last 55 years beginning his career at Eastman Kodak Company as an optical engineer. From there he went to Itek Corp. and Frank Cooke, Inc., where he was introduced to optical fabrication. An opportunity to manage the optics shop at the Optical Sciences Center, University of Arizona led him to Tucson where he has lived ever since. For the last 20 years has worked in his consulting business, Optical Perspectives Group.