Made to measure softly

If asked to measure the surface of a contact lens, would you use a contact or non contact method? Both have a limited dynamic range and resolution and the contact method also has the problem of probe force on the scanned surface.

The SoftProbe is a new automatic surface topography system developed by 3D Digital Design and Development and the National Physical Laboratory to overcome these limitations and to provide an accurate method of surface measurement without any damage to the surface being scanned. The developers expect the SoftProbe to be most powerful where soft materials such as optical components have to be scanned for surface topography analysis, including telescope mirrors, semiconductor substrates and contact lenses.

The device has an active servo-driven force transducer which, together with its integrated electronics, can maintain the stylus force to within a few milligrams, irrespective of the dynamic range of the system.

The load applied to any surface is totally under the operator or host computer control, and can be as low as 20 milligrams. Enough force is used to keep continuous contact between the probe tip and the surface over the full dynamic range of the instrument. A gantry supports the probe to allow the workpiece to be located under the tip. The probe incorporates the force transducer, geared servo-motor and height sensor.

A motorised XY stage provides raster scanning, using stepper motors with a movement of one micron per step over the working area of 100mm x 100mm.

Scan data can easily be transported to signal analysis software packages using ASCII or spreadsheet data format. The system supports data analysis for various surface parameters such as wear volume, Ra, Rq and surface detrending.

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