One of the hottest high-tech words today is nanotechnology. It is so popular that many companies are adding the prefix nano to their names. The real questions are: "Do we really know what nano is all about?" and "What are its implications in the controls area?" First of all, let's size things up. A nanometer is a thousandth of a micrometer (µm).
One of the hottest high-tech words today is nanotechnology. It is so popular that many companies are adding the prefix nano to their names. The real questions are: "Do we really know what nano is all about?" and "What are its implications in the controls area?" First of all, let's size things up. A nanometer is a thousandth of a micrometer (
Now that we have a few definitions, let's calibrate to a few physical items with which most of us are familiar like a human hair, a grain of sand, or even an atom. The diameter of a human hair can vary significantly, but a nominal value for it is approximately 100a hair. If we were to stack one million hair diameters, we would get a stack 100 m high (think of a football field resting vertically on one end).
Now that we have a feel for a nanometer, let's talk about controlling systems to a nm. What will this take? To do this, let's review a few key definitions, in particular: accuracy, precision, repeatability, and resolution. Accuracy is a quantitative measure of the degree of conformance to recognized standards of measurement. Repeatability is a measure of the ability of a machine to position a tool in the same location or the ability of a process to duplicate a measurement under similar conditions. Resolution is the least increment of a measuring device; the least significant bit on a digital machine.
Precision is often used as a synonym for repeatability; however, it is an obsolete term. So if you were target shooting, accuracy would be your ability to center on the bulls eye regardless of the spread on the target, repeatability would be your ability to cluster your shots tightly regardless of their location on the target, and precision would be the size of the holes that you put in the target.
With that in mind, let's consider controlling a couple of very impressive machines. The first is the Large Optics Diamond Turning Machine (LODTM) at the Lawrence Livermore National Laboratory. LODTM can produce a part with a diameter of 1.5 m while holding an accuracy of 25 nm. That means the machine is being controlled to one part per 100 million—similar to holding a tolerance of 0.001NIST's Web site states, "after refinement, M3's anticipated capability is akin to being able to locate two widely separated grains of sand in a 2,500 square-kilometer (960 square-mile) patch of desert and measure the distance between them to within one sand-grain diameter." Now that is impressive, and it is facilities like these that are keeping the U.S. in the forefront of developing manufacturing and controls technology.
Big innovations will be required to overcome the nanometer's sub-microscopic size. It is a small unit that will put significant demands on applied technology, and certainly those engineers working in the precision control areas have a hard-earned and significant respect for this little distance.
Thomas R. Kurfess is a professor at Georgia Tech's George W. Woodruff School of Mechanical Engineering.