glass scales and tempeature
Posted by
Elliot Burke
on 1999-08-29 10:41:57 UTC
About 20 years ago when I worked at Tinsley Labs, they had a metrology setup
to measure large lenses that was adapted from a Moore jig boring machine.
It had HP interferometers on the vertical and one horizontal axis, the other
horizontal axis was used for setup only. To make this thing work to the 1
millionth accuracy of the HP interferometers, it was necessary to keep it in
a fairly well temp controlled room.
It was possible to verify the machine's accuracy by measuring a known
surface, say a lambda/20 flat 20" in diameter tilted up on one edge by an
inch or so. The part was moved under the spindle, and a sapphire ball was
lowered to contact the surface, then picked up.
I don't recall if the interferometers was temperature and humidity
compensated, the room stability may have made this unnessary.
This is far from state of the art now. Diamond turning machines are rigid
lathes than can turn to surface roughness of a few nanometers, accuracy on
the order of 10 nanometers or so.
They are used for making lenses and mirrors from a variety of materials:
plastic, metal, and crystals.
Some of the technology is described in Foundations of Ultraprecision
Mechanism Design, by Smith and Chetwynd, ISBN 2-88124-840-3, 1992. There
are probably more current sources of information.
One of remarkable things about these machines is how stiff they must be.
The cutting force has some irreducable value, the deflection is limited to
nm, so the deflection and stiffness from cutting tool, mounts, ways,
bearings, etc difficult. They describe it as being equivalent to a 1 meter
cube of steel.
It may be that their technology has no points in common with ordinary CNC
machines, except that they do use G code.
They don't use glass scales.
Many measuring machines can't use glass scales because they don't want to
include the way errors in the measurement error. A method to avoid this is
to polish two edges of a square of glass, and use a flat mirror type
interferometer (also from HP) on the edges of the mirror. The
interferometer beams intersect at the point of work.
Elliot Burke
to measure large lenses that was adapted from a Moore jig boring machine.
It had HP interferometers on the vertical and one horizontal axis, the other
horizontal axis was used for setup only. To make this thing work to the 1
millionth accuracy of the HP interferometers, it was necessary to keep it in
a fairly well temp controlled room.
It was possible to verify the machine's accuracy by measuring a known
surface, say a lambda/20 flat 20" in diameter tilted up on one edge by an
inch or so. The part was moved under the spindle, and a sapphire ball was
lowered to contact the surface, then picked up.
I don't recall if the interferometers was temperature and humidity
compensated, the room stability may have made this unnessary.
This is far from state of the art now. Diamond turning machines are rigid
lathes than can turn to surface roughness of a few nanometers, accuracy on
the order of 10 nanometers or so.
They are used for making lenses and mirrors from a variety of materials:
plastic, metal, and crystals.
Some of the technology is described in Foundations of Ultraprecision
Mechanism Design, by Smith and Chetwynd, ISBN 2-88124-840-3, 1992. There
are probably more current sources of information.
One of remarkable things about these machines is how stiff they must be.
The cutting force has some irreducable value, the deflection is limited to
nm, so the deflection and stiffness from cutting tool, mounts, ways,
bearings, etc difficult. They describe it as being equivalent to a 1 meter
cube of steel.
It may be that their technology has no points in common with ordinary CNC
machines, except that they do use G code.
They don't use glass scales.
Many measuring machines can't use glass scales because they don't want to
include the way errors in the measurement error. A method to avoid this is
to polish two edges of a square of glass, and use a flat mirror type
interferometer (also from HP) on the edges of the mirror. The
interferometer beams intersect at the point of work.
Elliot Burke
Discussion Thread
Elliot Burke
1999-08-29 10:41:57 UTC
glass scales and tempeature
David Howland
1999-08-30 10:37:19 UTC
RE: glass scales and tempeature
PTENGIN@x...
1999-08-30 10:50:58 UTC
Re: glass scales and tempeature
Jon Elson
1999-08-30 13:14:32 UTC
Re: glass scales and tempeature