Jaw-Dropping Facts in Motion Control #4 & #5
December 3, 2020
Continuing the story of how the motion control feedback industry is enabling technologies to perform absolutely incredible feats, today we focus on angle measurement. One usually does not encounter extreme angle measurement in their everyday life, but it is so important and fundamental to the way we live, explore and progress. Here is the third installment of this 2020 column.
By Kevin Kaufenberg, Business Development and Product Manager, Electronics Industry
In the world of spinning hard drives — which are still mainstream today and not going away any time soon due to price point vs. data storage capacity — angle encoders are used as the critical measurement source needed to write the base data tracks on them. These base tracks are important so that the hard drive can continue to write itself offline in order to be ready for consumer use.
The angle encoders that are often used to write those base tracks start with an analog signal period of 360,000 lines on a diameter of 108mm. Then after interpolation of the analog signals, the machines used in writing the base tracks can have resolutions of down to 2 nanoradians or 0.00041 arc seconds. To provide a perspective on how small that angle is, if you were to project the vertex of that angle starting from the center of the Earth outward toward the surface of the Moon, the angle width would be only about 0.7m across!
Absolute angle encoders provide a unique serial word or bit sequence for every position reported. Their advantage is that when a machine starts up, it automatically knows where it is along the travel distances and does not have to spend time referencing the motion system. HEIDENHAIN offers the highest resolution absolute angle encoders, which are used in a variety of industries including machine tool rotary tables, grinding axes, large astronomical telescopes, and radar dishes.
The latest model of HEIDENHAIN’s RCN 8000 absolute angle encoder series can report an astounding 29 bits of absolute information; each position is unique for all 536,870,912 positions around a 360-degree circle! Large structures like astronomical telescopes that weigh tens of tons or more can and do use this positioning technology to achieve incredible pointing accuracies and tracking capabilities that help find extra-solar planets, faint asteroids that may be worrisome or other interesting objects in the universe.