Laser Measurement Enables Closed-Loop Centerless Grinding

This laser measurement system not only measures ground part diameters, but can also signal a grinder's control to make process adjustments on the fly.

Routine part measurement adds no value to workpieces. It does, however, offer a means to track machining accuracy so that equipment can be adjusted to ensure that parts are produced to tolerance. If a process could adjust itself on the fly, then it would be unnecessary to interrupt production to make such adjustments manually. According to Freedom Technologies, headquartered in East Glastonbury, Connecticut, such a closed-loop centerless grinding process is possible with its Grindline laser measurement system.

The Grindline system allows non-contact laser measurement of ground part diameters ranging from 0.004 to 3.15 inches to 1-micron accuracy. Based upon that measurement data, the system’s software can then signal the grinder’s control to make the necessary adjustments (such as re-positioning wheels as they wear) in real time.

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The system can be used with both through-feed and plunge-type centerless grinders. Its main components include a parts conveyor, part cleaning fixture, laser micrometer and dedicated controller. The conveyor receives parts as they exit the centerless grinder and transports them to the cleaning fixture. This fixture uses compressed air to clean parts prior to laser measurement. After cleaning, the conveyor delivers the parts to the laser micrometer to measure their diameters as they pass in front of the beam.

For each new job, users enter a nominal diameter, tolerance control band and out-of-spec tolerance limits. The control band is a safe range within the out-of-spec tolerance limits that allows shops to perform trending analysis. Users can specify the number of times the measured part diameter is permitted to fall outside the control band before the software signals the machine to make the necessary adjustments.

Users can also set up discrete measurement zones to find localized errors that may be caused by a chipped wheel or other similar problem. For example, a 6-inch-long part could be divided into six individual measurement zones along its length. The Grindline software will average the diameter measurements for each zone, rather than over the entire part length, to catch the small error. The software can also determine overall shaft straightness, as well as generate a detailed statistical report for each job.

The Grindline T-Series is designed for through-feed centerless grinders in which parts will have only one nominal diameter. The P-Series can measure multiple diameters for parts ground on plunge-type centerless grinders. Both versions are self-calibrating and can automatically compensate for fluctuating environmental conditions.

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