NU 2011-006

Inventor

Steven Jacobsen*

Short Description

An optical contact micrometer that measures part dimensions to extremely high precision across sample contact points

Abstract

Northwestern researchers have invented an Optical Contact Micrometer that measures part dimensions to extremely high precision across sample contact points.  The user is able to “look through” the contact points to examine and precisely choose where the thickness measurement is made.  The current prototype demonstrates +/-0.05 micrometer resolution or better – a 20 X improvement over the +/-1.0 micrometer precision provided by existing non-optical micrometers.  The Optical Contact Micrometer combines special tooling with commercially available components including a laser interferometer and standard optical microscope.  A custom-built linear stage brings two hard spheres into point contact with a test sample.  The spheres, which are transparent, act as “contact lenses” through which to view contact points under user control.  The linear translation stage is open by a manual micrometer drive, and retraction of the stage is accomplished by adjustable spring to allow for force control, depending upon the sample being measured.  The sample floats on a flexible wire to allow for self-alignment between the contact spheres.  One sphere is fixed, while the other is driven by the micrometer.  The moveable sphere is attached to a plane mirror, which is tracked by any commercial heterodyne interferometer to readout absolute thickness of the part or sample with optical precision. 

Applications

• Small-scale Metrology
• Geological Metrology

Advantages

• 20X improvement in metrology precision, down to +/-0.05 micrometers or better
• Measures across specific contact points
• Contact points are under user control, as they are readily viewable through a standard microscope
• A product can be built with currently available commercial technologies. 
• Prototype has been made.

IP Status

Issued US Patent No. 8,810,904