Armstrong Optical - Radius of Curvature Measurement

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Spherometers for radius of curvature measurement Spherometers are in use in hundreds of optical companies and laboratories worldwide and have become an industry standard for ultra-accurate radius measurement and calibration of test glasses. The long term accuracy and automated features make TRIOPTICS spherometers the preferred instruments for laboratory and production environments.

Super Spherotronic for high-precision measurements

Super-Spherotronic is an automatic three ball contacting spherometer designed to meet the highest test plate calibration requirements. Being the most accurate instrument of our line of spherometers, Super-Spherotronic can measure the radius of curvature to an accuracy of 0.01%. To ensure that the highest available accuracy values of radius measurement are obtained, all Super-Spherotronic components have been optimized and perfected so that residual errors are negligible:

The mainframe components locating the probe are made of massive stainless steel, hardened and fine ground on machine-tools to the highest achievable accuracy. Concentricity of mainframe components to the probe is less than 1 micron (0.00004“).

The spherometer rings represent one of the key components of the Super-Spherotronic including an incredible amount of work to eliminate any possible error source. Made of heat-treated high quality stainless steel, the rings are machined on high accuracy grinding machine-tools and finally fine-lapped. An ingenious design combined with a special electro-erosion procedure allows the ball and the ball location site to be matched with highest accuracy. Each ring is delivered with a calibration certificate. The measuring accuracy is directly traceable to NIST standard.

The supporting balls are also concentrically positioned with an extreme accuracy of less than 1 micron (0.00004“). This highly accurate positioning of the ring balls is an essential and distinctive feature of the Super-Spherotronic, ensuring excellent repeatability. To avoid any thermal and mechanical deformation, the supporting balls are made of wolfram carbide (an extremely hard metal), while the probe center is an ultra-precision ruby ball. This completely eliminates any errors introduces by metallic probe centers used in other spherometers.

The probe itself is a high precision Heidenhain encoder, specifically selected for this use, having a total systematic and random error of less than 0.2 microns (0.000008“).

The test plates used for calibration of the instrument are manufactured to high quality standards to an accuracy better than 1/10 wave for sphericity. The test plates are certified by NIST of USA, so that the accuracy of Super-Spherotronic is directly traceable to international standards.

Ultra Spherotronic - unsurpassed accuracy for test plate calibration

The Ultra-Spherotronic, the latest addition to our line of automatic spherometers, is the response to increased accuracy requirements in measurement of radii of curvature of optical components. The heart of the new spherometer is a special linear encoder featuring the highest measurement accuracy worldwide.

Under constant temperature conditions the absolute measurement error of the linear encoder is less than 0.05µm. The resolution is selectable : 0.01/0.05/0.1µm.

The typical high quality mechanical components and the stability of TRIOPTICS spherometers have been further optimized and perfected during the development of the Ultra-Spherotronic.

The probe is a ruby ball centered precisely to the encoder spindle. The use of ruby ball probe excludes the accidental damage of valuable test plates during measurement. The precise centering of the ruby ball is a key factor in obtaining the high repeatability of the Ultra-Spherotronic.

When accuracy really counts, there is no replacement for Ultra-Spherotronic: the unsurpassed accuracy of the linear encoder combined with the high quality of the mechanics leads to new levels of accuracy of radius measurement.

Depending on the diameter of the spherometer ring used, a radius measurement accuracy of approx. 0.005% and a repeatability of 0.001% are achievable.

SpheroCompact

SpheroCompact is an extremely accurate and easy to use instrument designed for sagittal measurement of both concave and convex surfaces.

It is the first hand held spherometer with a high precision linear encoder which features bright digital readout, micron resolution and excellent absolute accuracy.

The calibrated rings have precision ground reference surfaces and are machined of high quality stainless steel. Ultra-precision RUBY BALLS guarantee highest hardness and unsurpassed thermal stability. The deviation from sphericity is less than 1/10 of a micron.

The diameter of each ring is Certified and the instrument is calibrated using test plates with Certified Radius, traceable to NIST. The calibration is done for both concave and convex spherical surfaces. The radius difference between the concave and convex test plates used in calibration is smaller than lambda/10.

Easily removable rings of different diameters increase the versatility of the instrument and feature a very large measuring range covering almost all applications in optical manufacturing. The Spherocompact can be used either as a hand-held instrument to take measurements directly on the machine or as a stand-alone instrument in the laboratory.

Please download the generalSpherometer pdf