Hi Fred, can you define what you mean as a precision guidance transport?
Hi, is this Chris K?
Anyway, the term comes from the field of web guidance, an obscure segment of mechanical engineering that deals with continuous web processes seen in manufacturing plants like textiles, light gauge sheet steel and paper mills. Many old-time newspaper printing plants also employed continuous web (offset) printing, where a roll of paper perhaps thousands of feet long runs through the presses (or transits through the web) only to be cut into pages at the very end, after all the printing is performed.
For the mechanical engineer who is designing continuous web processing equipment, making it all work without wrinkles (in the literal sense here) is hardly trivial. A fundamental principle in this discipline is that there can be but a single plane of reference for the alignment of all of the rolling elements in the system. This reference plane must be invariable and immensely stable. And each and every one of the rolling elements then needs to be rigidly fixed to that plane absolutely normal. (That means with perfect perpendicularity.) Perfectly perpendicular, not to the degree, not to some minutes of the degree. But down to seconds of the degree.
In terms of tape transport guidance types, we basically see only two: those of forced guidance and those of precision guidance.
Do they force the tape to follow a path that is defined by the placement of (typically edge) guides? This is forced guidance and it is seen in over 99.9 percent of all tape machines.
Or, is the tape free to follow its own natural path through the web system, with no forced guidance at all? This is precision guidance. It is seen mainly on the better one and two-inch multichannel tape machines.
Attend an operator training class someday at ATL / ATAE and you'll see all this possibly better explained with some tape transport hardware examples that we pass around the classroom. We might first show you an Ampex AG-440 transport foundation casting (a TFC, or "a top plate", in the old Ampex California factory jargon) that was once used in a very popular, force-guided, commercial machine.
Then maybe we'll show you the equivalent part from an Ampex ATR-102. Often at that point, participants examining the ATR 100 part will say "Oh, much, much better. Much more stable and precise!"
Then we'll pass around the TFC from a Studer A80.
And we hear quiet gasps. Or, OH MY GOD!
Lastly to come out is the TFC from an A820.
I won't disclose the reaction that part gets. But if you happen to know much about manufacturing, you'll immediately recognize that it isn't fiction that Studer precision guidance transports cost way over fifteen times what it cost to build an entire Ampex.
Jay McKnight (of Ampex and MRL) has a very good paper on web guidance in tape machines. I'm not sure it is presently linked from his MRL site. You may ask Jay about it on the Studer list.