Bal-tec™ introduces: The unistraint calibration artifact

Laser Tracker Calibration Device
Articulating Arm Calibration Device
Portable Arm Calibration Device
Giant ball-bar Like Calibration Devices

Unistraint, marker for scale.


The Unistraint is a very unique concept in long calibration artifacts (patent #86325970).

This concept is based on simple principles of physics.

All of the falderal about the original camber or waviness of the artifact and all of the smoke screen of stiffness to weight ratios become poppy cock.

The difference with Unistraint is that it is not based on constraint, or for that matter over-constraint, but on the simple principal that “if it doesn’t bend it doesn’t matter.” We call the new doctrine: Unistraint.

The basic design is based on the resistance of very thick sections of material to bending. In the case of Unistraint it is the resistance of four, huge, sixteen-inch thick sections of aluminum to bend due to the minor load imparted by change in the force of gravity when the ball-bar-like structure is moved from vertical to Horizontal, and of course any interim position.


Unistraint stand


The fact that the sixteen-inch thick sections are only 0.020 inches thick has very little effect on the bending moment generated. This brings us back to the original premise that “if it doesn’t bend it doesn’t matter.”

The feature that entirely eliminates the influence of the original geometry of the artifact is that the invar bar that forms the body of the ball-bar or trihedral nest, is encapsulated in a high stiffness foam 25000 P.S.I. that connects all elements of the artifact together to form a pseudo-monolithic structure.

There have always been serious problems with slippage in the rotary position of large calibration artifacts during use. This dilemma has been entirely eliminated through the application of two gear-tooth-like Hirth plates that form a preloaded coupling, which both locates the artifact at a very accurate incline and also lock it there without even microinches of movement.


Unistraint tilt


We are building these giant calibration artifacts in two off-the-shelf standard lengths.

We have the really giant two-point-three meter (90.5512”) long version, ┬áthat is part number US-2.3-B for ball-bar version, and US-2.3-TH for laser-tracker version. And there is a shorter fifty-inch long version (1,270mm), part number US-1.27-B (for ball-bar version) and US-1.27-TH (for Laser Tracker version).

One of the two standard designs is a simple standard ball-bar. The body of this ball-bar is invar with its almost zero rate of thermal expansion and contraction and unlike carbon and glass fiber composites it has absolutely zero sensitivity to moisture. This ball-bar is equipped with one-inch diameter balls of either hard stainless steel or zirconium-oxide ceramic.

The second standard, off-the-shelf configuration has the same general construction but with a magnetically preloaded trihedral nest on each end to hold a spherical retro reflector (SMR), for use in calibrating laser-trackers. This standard configuration is setup for one and one-half-inch diameter spherical retro reflectors, but we can also supply a version that is compatible with seven-eighths of an inch or one-half-inch diameter SMR’s.

A super bonus with the design of the Unistraint ball-bar is that the version used to calibrate laser-trackers can be converted to a standard ball-bar by just screwing accessory ball-bar ends, part number ABB-1, into the trihedral mounts.

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