Many people are familiar with the four “C’s” used to help determine the quality of a diamond: Clarity, Carat, Color and Cut. The problem is, the traditional 4C standard does not really differentiate a superior diamond from an inferior one.

What really makes a diamond eye catching is the way it plays with light-its “light performance”-which can be much harder to quantify. With this problem in mind, GemEx Systems Inc. (Mequon, WI) created what it calls its BrillianceScop analyzer, an imaging spectrophotometer that measures the ability of a diamond to refract and focus light.

In operation, the system measures each gem in a controlled lighting environment from a number of different lighting angles. Using complex optic technology, the device measures three types of light as they pass through the diamond’s upper portion, or “crown”: white light, colored light and scintillation (commonly known as the “sparkle”). Superior performance in any one of these light categories results in a high quality diamond.

To examine a particular stone, an operator first positions it inside a 3-inch integrated sphere. After taking an initial set of measurements, a stepper motor then moves a 2.5-inch ring light through five preset stations, so that the system can measure the diamond’s performance from five different light angles.

Not surprisingly, system accuracy depends heavily on the precise movement of the ring light. The smallest inconsistency will affect the light angle and, as a result, the final analysis of the diamond. Repeatability is absolutely essential.

To ensure the necessary precision, GemEx co-founder Kurt Schoeckert first designed his own in-house system using a U-shaped piece of sheet metal, a 3/16-inch-diameter drive screw and a power nut with bearings on the end.

Unfortunately, this system failed to provide the accuracy GemEx needed, so Schoeckert implemented a ScrewRail-model lead screw assembly from motion control equipment manufacturer Kerk Motion Products Inc. (Hollis, NH). This approach has since made it possible for the BrillianceScop to achieve repeatability of ±5 percent-more than sufficient to ensure the validity of the test results.

Each ScrewRail consists of a drive screw with a concentric rail, a combination nut and bushing, and a robust support component. The system provides wear-compensating performance, with low-drag torque and high axial stiffness. A proprietary Kerkote TFE coating, used on the system’s lead screw and nut, provides efficient self-lubrication.

The result has been a motion system that is compact and reliable to the point where operators don’t even bother checking it anymore in the event a BrillianceScope develops any kind of performance problems.

“The motion of the rail is about as smooth and precise as it can possibly be. We’re confident that the rail system is the most efficient part of the machine,” Schoeckert says.

For more on linear motion, call 603-465-7227 or visit www.kerkmotion.com.