Download TECHNIQUES FOR PRECISION AIR TEMPERATURE CONTROL

PRECISION AIR
TECHNIQUES FOR PRECISION
AIR TEMPERATURE
TEMPERATURE CONTROL
CONTROL
Hans J.
J. Hansen
Hans
Division, Lawrence
Lawrence Livermore
Livermore National
National Laboratory
Laboratory
Materials Fabrication Division,
808, LL-330,
P.
P. 0.
0. Box 808,
-330, Livermore,
Livermore, California
California 94550
Abstract
for minimizing
High quality
temperature control
control can
can provide
provide an
an excellent
excellent means
means for
minimizing the
the .thermal
thermal drift
drift of
of
quality air temperature
High
air
in air
practical. Improvements in
not practical.
are not
means are
other means
when other
instruments when
machine tools
inspection instruments
and inspection
tools and
careful
the careful
one byby the
to one
ten to
as ten
much as
as much
by as
areas by
machining areas
several machining
in several
improved in
been improved
has been
temperature control
control has
theory.
control theory.
classical control
fundamental classical
some fundamental
of some
application of
the application
and the
loads and
heat loads
identification of heat
identification
Introduction
usually .
are usually
part are
produce aa part
can produce
tool can
machine tool
which aa machine
to which
accuracy to
the accuracy
govern the
which govern
errors which
of errors
kinds of
The kinds
that
reported that
has reported
(1.) has
errors. Donaldson (1.)
nonrepeatable errors.
and nonrepeatable
categories: repeatable and
into two
broken
broken into
two categories:
result,
and asas aa result,
small, and
very small,
are very
errors are
nonrepeatable errors
the nonrepeatable
to the
compared to
when compared
errors when
repeatable errors
the repeatable
frequently the
large
large improvements
improvements in
in machine
machine performance
performance can
can often
often be
be obtained
obtained by
by trying
trying to
to decrease
decrease the
the nonrepeatable
nonrepeatable
is changing
the most common
that the
indicates that
He also
errors.
also indicates
common cause
cause of
of nonrepeatability
nonrepeatability is
changing temperature
temperature and
and the
the
errors.
structure.
machine structure.
the machine
of the
deformation of
consequent thermal
thermal deformation
the
to the
solutions to
long plagued
has long
Thermal
Thermal distortion
distortion has
plagued the
the areas
areas of
of precision
precision machining
machining and
and gaging.
gaging. Past
Past solutions
day/night
to day
respect to
with respect
processes with
of processes
scheduling of
careful scheduling
included careful
have included
problem have
/night ambient
ambient temperature
variations,
variations, construction
construction of
of subterranean
subterranean inspection
inspection facilities
facilities (2.)
(2.) and
and machine
machine temperature
temperature control
control by
by
In many
flooding. In
liquid
many cases
cases the
the thermal
thermal distortion
distortion problem
problem could
could have
have been
been minimized
minimized adequately
adequately if
if air
air
liquid flooding.
flood cooling
applications of flood
successful applications
Examples of successful
cooling
enough. Examples
well enough.
controlled well
been controlled
have been
temperature could have
temperature
for
for temperature
temperature control
control have
have been
been proven
proven by
by Bryan
Bryan at
at LLNL
LLNL on
on Diamond
Diamond Turning
Turning Machines
Machines #1
#1 and
and #2
#2 (3.)
(3.) and
and on
on
nearly 1010toto 1 1
factor ofof nearly
by aa factor
stability by
thermal stability
in thermal
improved in
was improved
which was
machine which
#3 measuring machine
aa modified Moore #3
increased cost
in production and increased
cost
both inconvenience in
solutions, although sufficient have caused both
(4.). These solutions,
(4.).
utilized onon-off
have utilized
solutions have
the solutions
of the
required. In
facilities required.
the facilities
and the
the product and
of
In addition,
addition, many of
-off
of both
both the
for the
changes. An alternate approach provides for
load changes.
heat load
to heat
sensitive to
controls
controls and
and have been consequently sensitive
remove
to remove
used to
is used
cooling is
liquid cooling
closed liquid
scheme, closed
In this
this scheme,
control. In
temperature control.
air temperature
and air
use
use of
of both
both liquid and
localized
localized heat
heat from
from the
the machine,
machine, while
while aa light
light air
air shower
shower is
is used
used to
to maintain
maintain the
the temperature
temperature of
of the
the
slide drive
spindle drive
superstructure. Localized
Localized heat would
would include
include heat
heat produced
produced by
by the
the spindle
drive motor
motor and
and slide
drive
the machine
on the
loads on
heat loads
are heat
there are
if there
that if
is that
desirable is
sometimes desirable
is sometimes
this approach is
that this
machine
motors. The reason that
motors.
air alone
if air
transfer if
heat transfer
necessary heat
required to
are required
velocities are
air velocities
high air
substantial, high
which are substantial,
to provide
provide the
the necessary
alone
operator. The combined
the operator.
for the
as well
be unpleasant as
well as
as unhealthy
unhealthy for
high air velocities can be
The high
used. The
is
is used.
LLNL.
at LLNL.
machines at
turning machines
precision turning
several precision
on several
implemented on
approach
approach is
is being implemented
insufficient
that insufficient
is that
difficult is
be difficult
to be
temperature control
The main thing that makes precision air temperature
control appear to
control
temperature control
the temperature
of the
dynamics of
the dynamics
present, the
sources present,
heat sources
the heat
of the
analysis of
the analysis
to the
attention
attention is
is paid to
static
on static
designed on
are designed
systems are
control systems
temperature control
air temperature
Most air
implemented. Most
control implemented.
of control
system
system and
and to
to the
the mode of
steady or
loads are
loads with
and cooling
heating and
such as
criteria such
criteria
as maximum heating
cooling loads
with no
no regard
regard to
to whether the
the loads
are steady
or
in many
is ever
variable. Very
Very little attention
attention is
ever paid
paid in
many cases
cases to
to the
the type
type of
of controller
controller used
used since
since the
the
type
simpleonon-off
result simple
as aa result
and as
applications and
precision applications
high precision
for high
designed for
not designed
are not
systems are
of systems
majority of
majority
-off type
suffice.
will suffice.
controls will
controls
considerations
load considerations
Heat load
heat
net heat
the net
affects the
nothing which affects
as nothing
long as
equilibrium as long
thermal equilibrium
static thermal
at static
be at
will be
tool will
A machine tool
not cause
rate will
constant rate
at aa constant
heat from aa machine at
remove heat
or remove
supply or
which supply
Things which
changes. Things
will not
cause
it changes.
transfer to it
the
the temperature
temperature distribution
distribution of
of the
the machine
machine to
to change
change after
after it
it has
has been
been allowed
allowed to
to reach
reach thermal
thermal equilibrium
equilibrium
heat at
remove heat
or remove
supply or
hand, things
the other hand,
sinks. On the
or sinks.
sources or
those sources
in
in the
the presence
presence of those
things which supply
at
thermal
resulting thermal
with aa resulting
time with
in time
vary in
to vary
distribution to
temperature distribution
the temperature
cause the
variable rates
rates will
will inevitably
inevitably cause
variable
drift.
drift.
sinks beyond
sources or
heat sources
necessary to
not necessary
is not
it is
that it
is that
conclusion is
primary conclusion
The primary
The
to worry
worry about constant heat
or sinks
beyond
ensuring that
that the
the static
static heating
heating or
or cooling
cooling capacity
capacity of
of the
the room
room is
is adequate
adequate to
to handle
handle the
the net
net heat
heat input
input or
or
ensuring
to be
is to
distribution is
temperature distribution
if aa constant temperature
that if
is that
conclusion is
secondary conclusion
The secondary
room. The
be
the room.
removal
removal from the
removed or
sources or sinks
the machine,
throughout the
maintained throughout
maintained
machine, variable
variable sources
sinks must
must be
be either
either removed
or their
their effects
effects reduced
reduced
distribution.
temperature distribution.
machine temperature
in machine
change in
tolerable change
a tolerable
level which
which produces a
to aa level
Constant
Constant sources
sources of
of heat
heat typically
typically include
include things
things like
like CNC
CNC units,
units, lights
lights (which
(which are
are left
left on
on day
day and
and
Variable
constantly. Variable
operates constantly.
which operates
room which
the room
as the
space as
same space
night)
night) and
and any
any other
other equipment
equipment within the same
drive
machine drive
and machine
temperature, and
air temperature,
varying air
temperatures, varying
wall temperatures,
varying wall
sources include
include people,
people, open
open doors,
doors, varying
sources
able to
be able
should be
system should
control system
temperature control
air temperature
units
designed air
speeds. A well
varying speeds.
at varying
well designed
operate at
which operate
units which
wall
varying wall
personnel, varying
of personnel,
effects of
the effects
minimize the
and minimize
temperature, and
constant temperature,
sufficiently constant
provide air at sufficiently
doors.
open doors.
and open
temperatures and
temperatures
84
Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms
A useful
useful technique
technique for
for representing
representing heat
heat load
load information
information is
is the
A
the generation
generation of
of aa heat
heat load table
the
table for the
space
in question.
question. It
It is
is aa list
list of
heat loads
space occupied
occupied by
by the
the machine
machine in
of all
all of
of the
the heat
loads present
present and
and an
an indication
indication
of their
their nature
nature (i.e.
(i.e. steady
steady or
or variable).
variable). In
In addition
addition it
it includes
includes totals
totals for
for heating
heating and
of
and cooling
cooling loads
loads
which
are useful
useful for
for determining
determining necessary
necessary system
system capacity.
capacity. An example
which are
example for
for aa typical
typical machining area
area is
is
given inri Table
ldu ' e 1.
Table!.
Table 1.
Sample Heat Load Table
Winter
Load
Type
Type
Latent
Sensible
Summer
Total
Total
Latent
Sensible
BTU/HR
BTU /HR
Total
BTU/HR
BTU /HR
Conduction
To
Inside Spaces
To Inside
Spaces
DN
ON
0
0
00
0
0
0
0
00
00
Conduction
Thru
Thru North Wall
Wall
DN
ON
0
0
-15092
-15092
0
0
14063
14063
Conduction
Roof
Thru Roof
ON
ON
0
0
-31040
-31040
0
0
69134
69134
Conduction
Conduction
Thru Floor
SS
00
00
00
0
0
00
00
6132
3000
9132
6132
6132
3000
9132
Personnel
Personnel
Heat Load
DN
Air Handler
7-1/2
7
-1/2 BHP
BHP
SS
00
19100
19100
19100
00
19100
19100
Infiltration
S
S
00
-10780
-10780
0
0
0
0
0
Make-Up
Make -Up Air
Air
(7000
SCFM Max)
Max)
(7000 SCFM
VV
00
-332640
-332640
00
279720
279720
0
0
Lighting
sS
0
28700
28700
00
28700
28700
c
(
Machine Tools
Machine
V
00
12804
12804
12804
12804
00
12804
12804
S
0
0
59633
59633
00
59633
59633
59633
6132
6132
-266315
-260183
6132
486154
486154
492286
6132
6132
*66325
*72i457
*72457
6132
*206434
*212566
{(
TOTALS
**
Includes
of Separate
Separate System
System for
Includes Effect of
for Makeup
Makeup Air
Air
The idea
idea of
heat load
load table
table of
of this
this kind
kind is
is not
not uncommon
The
of making
making aa heat
however, most
most
uncommon to
to the HVAC
HVAC profession;
profession; however,
tables
the nature
nature of
of the
the loads.
loads. Time
tables do
do not
not present
present the
Time history
history information
information is
is useful
useful in
in the
the design
design of
of the
the
control system
system for
for determining
determining the
the kind
kind of
of disturbance
disturbance rejection
rejection which
control
which will
will hebe necessary.
necessary. In
In addition
addition the
the
results of
results
of the
the heat
heat load
load table
table will
will indicate
indicate what
what modes
modes of
of conditioning
conditioning are
are required,
required, whether
whether heating
heating or
or
cooling or
or both.
both. It
It is
desirable from
from aa controls
cooling
point of view
is desirable
controls point
view to
to only
only have
have heating
heating or
or cooling
cooling since
since it
it is
is
difficult
for precision
precision applications
applications which
difficult to
to find
find controls
controls for
which can
can control
control both
both processes.
processes.
Control system
system considerations
considerations
Control
There
are two
two common
common control
control problems
problems one
one or
or both
both of
There are
of which
which many
many systems
systems are
are plagued
plagued with.
with. The first
first
problem is
is steady
steady oscillation
oscillation of
of air
air temperature
temperature with
problem
with respect
respect to
to time.
time. The
The most
most common
common cause
cause of
of this
this is
is the
the
on-off
on -off controllers
controllers frequently
frequently used.
used. Their
very nature
nature is
is destabilizing
destabilizing from
Their very
from aa controls
controls point
point of
To
of view.
view. To
be
specific, the
the on
on-off
be more
more specific,
-off action
action introduces
introduces aa non
non linearity
linearity to
to the
the system
system which
which usually
usually results
results in
in aa
limit cycle
limit
cycle condition. Almost
all heat
heat transfer
transfer devices
devices are
are nonlinear
nonlinear to
to begin
begin with
Almost all
-off
with and
and an
an on
on-off
controller
the whole
whole system
system more
more so.
controller just
just makes
makes the
so. Most
Most adjustments
adjustments made
to the
the system
system will
will only
made to
only vary
vary the
the
amplitude
of the
the oscillation.
oscillation. The
amplitude and
and frequency
frequency of
The discussion
discussion should
should not
not be
be construed
construed as
as that
that no
no oscillation
oscillation
of
kind is
is acceptable.
acceptable. McClure
of any
any kind
(5.) demonstrated
demonstrated that
that machine
McClure (5.)
machine tools
tools do demonstrate
demonstrate aa thermal
thermal frequency
frequency
response, and
for ambient
ambient temperature
temperature variations
variations above
response,
and that
that for
above some
some frequency
frequency characteristic
characteristic ofof the
the machine,
machine,
it's
response in
in terms
terms of
of drift
drift is
it's response
is negligible.
negligible.
The
appears quite
quite often
often in
The second
second problem
problem which
which appears
/night
in air
air temperature
temperature control
control systems
systems isis aa day
day/night
temperature
variation. This
This is
temperature variation.
is an
an indication
indication that
that the
the system
system has
has aa relatively
relatively poor
poor disturbance
disturbance rejection
rejection at
at
low frequency,
obviously, that
that some
some low
low
frequency, and
and more
more obviously,
low frequency
frequency disturbance
disturbance is
is present.
present. The
The changes
changes in
in
disturbance
disturbance are
are caused
caused by
by both
both changes
changes in
in outside
outside air
air temperature
temperature and
and also
also by
by changes
changes in
in the
the temperatures
temperatures
and
and heating
heating fluids
and pressures
pressures of
of the
the cooling
cooling and
fluids used
used in
in the
the control
control system.
system.
Both
Both of
of the
the above
above problems
problems can
can often
often be
be dealt
dealt with
with by
by being
being more
more attentive
attentive to
to the
the interaction
interaction of
of the
the
controller
heating and
and/or
controller with
with the
the heating
/or cooling
cooling device
device and
and in
in general
general by
by being
being more
more careful
careful in
in the
the selection of aa
controller.
In
controller.
heating and
and/or
In the
the case
case of
of the
the heating
/or cooling
cooling devices
devices it
it is
is desirable,
desirable, whenever
whenever possible
possible to
to
consider
static heat
heat transfer
transfer characteristics,
characteristics, but
consider not
not only
only their
their static
but their
their dynamic
dynamic characteristics
characteristics asas well.
well.
Sometimes
devices which are
are inherently
inherently easier
Sometimes it
it leads
leads to
to devices
easier to
to control.
control.
Controllers
in most
cases need
need not
not be
be much
much more
more sophisticated
Controllers in
most cases
sophisticated than
than to
to have
have proportional
proportional and
and integral
integral
actions
actions although
although it
it usually
usually costs
costs no
no more
more once
once proportional
proportional and
and integral
integral are
are present
present to
to get
get derivative
derivative
action
as well.
well. Proportional
action as
action is
is linear
linear in
in contrast
contrast to
to on
on-off
Proportional action
-off action
action and
and the
the integral
integral action
action is
all
is all
85
85
Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms
that is
is normally
normally required
required to
to remove
remove day
day/night
that
/night temperature
temperature variations
variations given adequate system capacity.
capacity. With
With
the
the advent
advent of
of the
the microprocessor,
microprocessor, many
many control
control manufacturers
manufacturers are
are offering
offering digital
digital controllers
controllers with
with PID
PID
action, suitable
suitable for
for air
air temperature
temperature control
control systems
systems for
action,
for less
less than
than $1000.
$1000.
Application
of the
the principles
principles
Application of
BODTM
enclosure
BODTM enclosure
The
BODTM (Baby
(Baby Optics
Optics Diamond
Diamond Turning
Turning Machine)
Machine) (6.)
(6.) is
is aa small
small tt-based
The BODTM
-based machine which has
has shown
shown the
the
capability
of producing
producing parts
parts to
to 20
20 microinch
microinch size
size and
and contour
contour tolerances
tolerances using
capability of
-process gaging with
using post
post-process
feedback.
feedback. A
factor contributing
contributing to
to the
the capability
capability of
of the
A major
major factor
which is
is
the machine is
is its
its high repeatability
repeatability which
made
by minimizing
minimizing thermal
thermal distortion.
made possible
possible by
distortion. Two
Two efforts
efforts are
are made
made to
to control
control the
the distortion.
distortion. One
One is
is the
the
application
application of
of closed
closed flow
flow cooling
cooling to
to the
the spindle
spindle drive
drive motor
motor and
and the
the other
other is
is maintaining.good
maintaining good control
control of
of
the ambient
ambient air
air temperature.
temperature. The
the
was originally
originally housed
housed in
in an
an inspection
inspection laboratory
laboratory with
The machine
machine was
with ++_ .20°
.20° FF
temperature
control. When
programmatic needs
temperature control.
needs demanded
demanded that
that the
When programmatic
the machine
machine be
be moved to
to a
with ^2.0°
+-2.0° FF air
air
a shop
shop with
temperature
temperature control,
control, the
the problem
problem of
of how
how to
to provide
provide adequate
adequate air
air temperature
temperature control
control materialized.
materialized
In response,
small temporary
In
response, aa small
temporary enclosure
enclosure was
was constructed
constructed to
to house
house the
the machine
machine which
which would
would be
be capable
capable of
of
providing air
air temperature
temperature control
control commensurate
commensurate with what existed
existed in
providing
in the
the machine's prior habitat.
habitat. The
The
control scheme
scheme involved drawing
drawing air from the shop
control
2.0° FF variations
variations and heating
shop which had
had ++ 2.0°
heating it
it at variable
variable
rates
the necessary
necessary control
rates in
in order to provide the
control accuracy.
accuracy. TFe
resulting conditioned
conditioned air
air was
was blown
blown over
over the
the
The resulting
machine and
and then
then returned
returned to
to the
the surrounding
surrounding shop.
machine
shop. Figure 11 shows
of the
the enclosure.
shows the
the configuration of
enclosure.
Blowers
Air
Air
Proportional
controller
Clear plastic curtains
Figure
1. BODTM
BODTM enclosure
Figure 1.
enclosure design
design
The air
air temperature
temperature was
heated by
by arrays
of standard
standard 100
The
was heated
arrays of
100 WW light
light bulbs
bulbs which
which received
varying amounts
amounts of
of
received varying
power depending
depending upon
upon the
the output
output signal
signal of
of the
the temperature
temperature controller.
power
controller. The
latter was
was aa basic
basic commercial
commercial
The latter
proportional control
it's input
proportional
control which
which had
had as
as it's
input aa thermistor
thermistor type
type temperature
temperature probe
probe located
located within
within the
the
enclosure near
near the
the slides
slides of
of the
the machine.
machine. Light
enclosure
bulbs were
were chosen
chosen for
for their
their fast
fast thermal
thermal response
response as
Light bulbs
as well
well
as availability.
availability.
as
Several efforts
in order to
Several
efforts were
were made in
to attempt to
to reduce
reduce the
the effects
effects of
of the
the surroundings
surroundings on
on the
the
temperature
the enclosure.
temperature within the
enclosure. The
first thing
thing that
that was
was done
done was
was to
to equip
equip the
The first
the enclosure
enclosure with
with transparent
transparent
plastic curtains
curtains to
to contain
contain the
the conditioned
conditioned air
air and
and minimize
minimize the
the infiltration
plastic
infiltration of
of outside
outside air.
air. The
net
The net
positive pressure
pressure provided
provided inside
inside by
by the
the blowers
blowers also
also helped
helped to
positive
to inhibit
inhibit the
the entry
entry of
of outside
outside air.
air. The
The
second
to design
design the
the enclosure
enclosure to
to limit
limit the
second thing
thing which
which was
was done
done was
was to
the entry
entry of
of the
the operator
operator to
to the
the minimum
minimum
requirement
hands, and
and hence
hence reduce
reduce the
the amount of
of variable
variable heat
heat contribution
requirement of
of arms
arms and
and hands,
contribution by
by the
the operator.
operator.
86
86
Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms
0.3° FF while
to +_+ 0.3°
inside to
air temperature
the air
of maintaining
capable of
is capable
The
crude, is
maintaining the
temperature inside
while
although crude,
enclosure, although
The enclosure,
from
recording from
temperature recording
sample temperature
F. A sample
2.0° F.
as ++_ 2.0°
much as
as much
varies as
shop varies
surrounding shop
the surrounding
the
the temperature
temperature in
in the
can
enclosure can
the enclosure
since the
that since
is that
the design
design is
The main caveat of the
2. The
Figure 2.
in Figure
given in
is given
enclosure is
the enclosure
within the
within
The
only provide
provide heating,
heating, the
the temperature
temperature inside
inside can
can only
only be
be held
held higher
higher than
than the
the outside
outside shop
shop temperature.
temperature. The
only
different
with aa different
area with
an area
in an
inspected in
are inspected
parts are
the parts
if the
that if
is that
first is
The first
twofold. The
are twofold.
consequences
consequences of
of this
this are
be
generally be
can generally
problem can
this problem
However, this
present. However,
be present.
doubt be
no doubt
will no
discrepancies will
temperature, size
size discrepancies
temperature,
accommodated by
by simply
simply taking
taking into
into account
account the
the coefficient
coefficient of
of thermal
thermal expansion
expansion of
of the
the part
part material
material and
and the
the
accommodated
that
is that
consequence is
second consequence
environments. The second
inspection environments.
and inspection
machine and
the machine
between the
temperature difference
temperature
difference between
since
the enclosure
enclosure temperature
temperature is
is linked
linked to
to the
the outside
outside shop
shop temperature,
temperature, if
if the
the latter
latter should
should depart
depart
since the
widely from
from the
the set
set point
point temperature
temperature within
within the
the enclosure,
enclosure, control
control will
will be
be either
either lost
lost or
or severely
severely
widely
(under
low cost
rapid, low
for aa rapid,
design provided
the design
of the
simplicity of
note, the simplicity
On aa more
more positive note,
provided for
cost (under
degraded. On
degraded.
the
of the
downtime of
reliability, downtime
In terms
terms of
of reliability,
BODTM. In
on BODTM.
problem on
control problem
temperature control
the temperature
for the
solution for
$5000)
$5000) solution
completion.
enclosure has
has been
been less
less than
than one
one week
week in
in the
the one
one year
year of
of continuous
continuous operation
operation since
since it's
its completion.
enclosure
15 min
hH
-I -
1-F
temperature
Sample temperature
2. Sample
Figure
Figure 2.
enclosure
BODTM enclosure
from BODTM
recording from
recording
enclosure
PERL enclosure
PERL
turning
small turning
is aa small
LLNL is
at LLNL
under construction at
now under
The
(PERL) now
Research Lathe (PERL)
Precision Engineering Research
The Precision
between the
differences between
the major
of the
machine. One
BODTM machine.
One of
major differences
the
aforementioned BODTM
the aforementioned
to the
ways to
many ways
machine
in many
similar in
machine similar
is
it is
When it
BODTM 1 s. When
than BODTM's.
higher than
magnitude higher
of magnitude
order of
an order
accuracy an
design accuracy
has aa design
two machines
machines is
is that the PERL has
two
shop as
finished
it is
is slated
slated to
to operate in
in the
the same
same shop
as the
the BODTM
BODTM and
and therefore
therefore some
some means
means will
will be
be required
required to
to
finished it
for
variation for
temperature variation
air temperature
design air
The design
temperature. The
constant temperature.
at constant
it at
around it
temperature around
the air temperature
maintain the
F.
0.25° F.
as ++_ 0.25°
specified as
is specified
the machine
the
machine is
and the
considered and
pitfalls of
the pitfalls
of the
all of
During the design
design of the
of the
the BODTM
BODTM enclosure
enclosure were
were considered
the
the enclosure all
During
design:
subsequent design:
the subsequent
improve the
to improve
made to
were made
decisions were
following
following decisions
1.
1.
decreased.
be decreased.
temperature would
air temperature
shop air
outside shop
on outside
would be
enclosure on
the enclosure
The dependence of the
and
curtains and
through curtains
to work
have to
not have
2.
would not
work through
so that the operator would
be configured so
2. The enclosure would be
face.
her face.
or her
his or
past his
air past
enclosure air
escaping enclosure
of escaping
flow of
the flow
to the
would
exposed to
be exposed
not be
would not
by
acceptance by
improve acceptance
to improve
enclosure to
the enclosure
of the
aesthetics of
3.
the aesthetics
upon the
placed upon
be placed
3. More emphasis would be
operators.
operators.
inside
stand inside
can stand
the operator
that the
so that
designed so
is designed
and is
flow and
air flow
operator can
closed air
features closed
resulting enclosure features
The resulting
covered
formica covered
and formica
members and
structural members
aluminum structural
extruded aluminum
features extruded
machine. Construction features
the machine.
to the
next to
next
attenuation
noise attenuation
and noise
insulation and
thermal insulation
it's thermal
for it's
design for
the design
in the
used in
panels. Some wood was used
panels.
finds
commonly finds
one commonly
what one
to what
similar to
curtains similar
plastic curtains
of plastic
made of
are made
enclosure are
the enclosure
of the
walls of
The walls
characteristics. The
characteristics.
the
inhibiting the
access while
for ease
provide for
ease of
of operator
operator access
while inhibiting
supermarkets. They provide
in supermarkets.
cases in
refrigeration cases
on
on refrigeration
3.
Figure 3.
in Figure
depicted in
is depicted
enclosure is
the enclosure
of the
design of
The design
air. The
outside air.
infiltration of
infiltration
of loosely
loosely controlled
controlled outside
as
almost as
areas almost
face areas
plenums with
large plenums
by two
the machine by
of the
top of
the top
Air
two large
with face
over the
distributed evenly over
is distributed
Air is
U-shaped
through aa Ureturned through
is returned
air is
shaped return
return duct
duct which
which exists
exists
itself. The air
enclosure itself.
the enclosure
large
large as
as the
the area
area of
of the
of about
rate of
back. AA 1/2
it's back.
across it's
and across
along both
both sides
sides of the machine and
1/2 HP
HP blower
blower draws
draws the
the air
air at
at the
the rate
about
along
700
700 CFM
CFM and
and forces
forces it
it through
through aa conventional
conventional furnace
furnace filter
filter and
and through
through aa small
small water
water to
to air
air heat
heat exchanger
exchanger
plenums.
supply plenums.
the supply
before
before the
the air
air arrives
arrives at
at the
87
Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms
machine
Perl
Perl ntachine
9'0"
7'-6"
7' -6'
90.00
- Water
Water to
to air
air
heat exchanger
9'-0'
"(108.00)
-- 1108.00)
- Supply
ductwork
II
___ JL-JL-I
1
6'-9"
6' -9'
(81.00)
`TE -- -1 i`-;
J
jdM
Blower
*i,1I
plenums
air plenums
-Return air
J
plastic
Clear
Clear p
astic
curtains
cu
tains
3.
Figure
Figure 3.
Return air
plenumsplenums
design
enclosure design
PERL enclosure
PERL
slides. The
the machine
near the
located near
sensor located
type sensor
thermistor type
by aa thermistor
sensed by
is sensed
air is
the air
temperature of
The
The temperature
of the
machine slides.
controller. The
PID controller.
digital PID
available digital
comrnercially available
to aa commercially
sent to
is sent
conditioning, is
after conditioning,
signal
signal from
from the
the sensor,
sensor, after
turn modulate
in turn
solenoid valves
controller
controller has
has aa time
time proportioning
proportioning output
output and
and operates
operates solenoid
valves which
which in
modulate the
the flow
flow of
of
the
showing the
diagram showing
schematic diagram
water-to-air
the water
through the
water through
50°
50° FF chilled
chilled water
-to -air heat
heat exchanger.
exchanger. A schematic
interconnections
interconnections of
of the
the sensor,
sensor, conditioner,
conditioner, controller,
controller, valves
valves and
and the
the heat
heat exchanger
exchanger is
is shown
shown in
in Figure
the
at the
right
available
always
is
water
cold
fresh
that
ensure
first
to
used
are
valves
solenoid
Two
4.
Two
solenoid
valves
are
used
to
first
ensure
that
fresh
cold
water
is
always
available
right
at
4.
hammer.
water hammer.
of water
effect of
the effect
minimize the
to minimize
second to
and second
exchanger and
exchanger
Digital PID
Digital
PID control
control with
time
Thermtstor
time proportioning
proportioning output
output Thermistor
signal conditioner
signal
conditioner
}
r
Thermistor
Solenoid
valve control
Solenoid
valves
0.6 sec
rWater to air
heat exchanger
Solenoid
valves -
Flowmeter
£
50- chilled
Chilled
water
supply
water
4.
Figure 4.
Figure
|+ 15
15 min
return
0.1
0.1
system
control system
PERL
PERL enclosure
enclosure control
FF
--
temperature
Sample
Sample temperature
enclosure
PERL enclosure
the PERL
from the
recording from
recording
5.
Figure 5.
Figure
Proportional
Proportional and
and integral
integral actions
actions have
have been
been used
used on
on the
the control
control to
to provide
provide +_+ 0.08°
0.08° FF air
air temperature
temperature
5. The
Figure 5.
in Figure
given in
is given
recording is
temperature recording
sample temperature
variation. A sample
day/night
visible day
no visible
with no
control with
control
/night variation.
variation
variation in
in temperature
temperature has
has an
an oscillatory
oscillatory nature
nature which
which appears
appears at
at this
this time
time to
to be
be as
as aa result
result of
of the
the
find a low cost means
are now under way to find
action. Efforts are
valve action.
solenoid valve
means of
of
the solenoid
by the
introduced by
nonlinearity
nonlinearity introduced
nonlinearity.
of nonlinearity.
introduction of
less introduction
with less
flow with
the flow
modulating the
modulating
88
88
Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms
CBN
room
CBN room
The Cubic
Cubic Boron
Boron Nitride
Nitride (CBN)
(CBN) machine
machine is
is aa tt-based
The
-based precision
precision turning
turning and
and boring
boring machine currently
currently under
under
construction at
at LLNL.
LLNL. It
construction
It has
has aa design
design disc
disc check
check accuracy
accuracy on
on the
the same
same order
order as
as LLNL's
LLNL's existing
existing diamond
diamond
turning
turning machines
machines but
but is
is designed
designed to
to be
be stiffer
stiffer and
and hence
hence more
more suitable
suitable for
for use
use with
with cubic
cubic boron
boron nitride
nitride
cutting tools.
tools. The
The machine
is built
built around
around the
the base
base of
of aa 920
920 EXCELLO
EXCELLO for
for an
an indication
indication of
cutting
machine is
of the
the size
size of
overall
size.
overall machine
machine size.
Due to
to the
involved, close
close air
air temperature
temperature control
Due
the accuracies
accuracies involved,
control was
was deemed
deemed necessary.
necessary. The design
design control
control
level
0.1° F.
F. Since
the machine
level was
was 68
68 4+ 0.1°
Since the
machine was
was fairly
fairly large
large it
it was
was more
more reasonable
reasonable to
to put
put it
it in
in aa room
with
room with
good temperature
temperature control
good
control as
as opposed
opposed to
to constructing
constructing an
an enclosure
enclosure around
around it
it as
as in
in the
the cases
cases of
of BODTM
BODTM and
and
PERL.
No room
room with
the necessary
necessary temperature
PERL.
temperature control
existed within
No
with the
control existed
within MFD's
MFD's machining complex,
was
complex, so one was
specially
designed.
specially designed.
The
room was
the objective
objective of
of providing
providing close
The room
was designed
designed with
with the
close air temperature control
control by
minimizing the
by minimizing
the
effects
variable heat
heat sources.
sources. Since
Since the
the variable
variable heat
effects of
of variable
heat sources
sources on
on the
the machine all
all have closed flow
flow
liquid cooling,
heat remaining
radiation from
liquid
cooling, the
the primary
primary sources
sources of
of variable
variable heat
remaining are
are conduction
conduction and
and radiation
walls,
from the walls,
heat
and infiltration
infiltration of
of air
air by
heat generation
generation by
by the
the operator
operator and
by leaks
leaks and
and the
the makeup
makeup air
air system.
system.
In order
In
order to
to minimize
minimize the
the contribution
contribution from
from the
the walls
walls supply
supply and
and return
return registers
registers were
were constructed
constructed around
around
the
the perimeter
perimeter of
of the
the room
room and
and adjusted
adjusted to
to provide
provide aa relatively
relatively high
high velocity
velocity curtain
curtain of
of air
air around
around the
the
perimeter. Velocities
are on
on the
the order
order of
of 100
100-150
FPM along
along the
the walls.
walls. Air is
perimeter.
Velocities are
-150 FPM
is also
also distributed
distributed over
over the
top
top of
of the
the machine
machine by
by two
two large
large plenums
plenums with
with exit
exit areas
areas slightly
slightly larger
larger than
than the
the projected
projected area
area of
of the
the
machine. Air
Air velocities
velocities out
out of
of the
the plenums
plenums averages
averagesbetween
machine.
-40 FPM.
between3030-40
FPM. This
This air
air returns
returns along
along with the
the
high
high velocity
velocity perimeter
perimeter air
air through the perimeter
perimeter registers.
registers. The
The air
air distribution
distribution scheme
scheme is
is shown
shown in
in Figure
6.
6.
-High
High velocity
velocity supply
supply registers
registers -
Laminar flow
plenums.
18"
,)
138"
J
Raised
computer
Return
grills
1
III I
18"
248"
Figure
Figure 6.
6.
CBN
scheme
CBNroom
roomair
airdistribution
distribution scheme
AA unique
unique feature
design is
is the
feature of
of the
the design
the configuration of the
the return
return ducting.
ducting. The
height of
the machine
The height
of the
machine
spindle
spindle centerline
centerline made
made it
it necessary
necessary to
to construct
construct aa raised
raised floor
floor around
around the
the machine
machine to
to facilitate
facilitate operator
operator
access. The
floor is
access.
is actually
floor and
and provides
The floor
actually aa computer
computer floor
provides for
for about 18 inches
inches of clearance between
between the
the
bottom of
the raised
raised floor
floor and
and the
the floor
floor on
bottom
of the
on which
which the
the machine
machine rests.
rests. The
The clearance
clearance space
space serves
serves as
as the
the
return duct,
some cost
cost savings
savings in
in sheet
sheet metal
return
duct, providing
providing some
metal work.
work.
The
same as
The control
control scheme
scheme implemented
implemented is
is the
the same
as that implemented
on the
the PERL
PERL enclosure
enclosure with
with the
the exception
exception
implemented on
that
that the
the air
air flow is
is increased
increased to
to 10,000
10,000 CFM.
CFM. Only
Only cooling
cooling is
is required
required since
since there
there are
are enough
enough heat
heat sources
sources
present
the year
to maintain
maintain 68°
68° F.
F.
present throughout
throughout the
year to
89
Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms
has been
it has
that it
the 66 months
for the
68 ++ 0.05°
providing 68
0.05° FF control
control for
months that
been
of providing
has been capable of
the system has
Thus far the
variation
temperature variation
later temperature
7. The
giveninin~Tigure
The later
recording isis given
A sample
-Figure 7.
temperature recording
sample temperature
produces
2.0 nicroinch
microinch thermal
thermal drift
drift between
between the
the two
two slides
slides of
of the
the machine
machine measured
measured at
at tool
tool height,
height, even
even
produces aa +_+ 2.0
base
the base
around the
cooling around
liquid cooling
flow liquid
room. Closed
the room.
Closed flow
leaving the
and leaving
entering and
when two 0E-three
are entering
or three machinists are
when
further.
even further.
drift even
the drift
reduce the
to reduce
expected to
is expected
the machine is
of the
in operation.
operation.
15 min
T
H h--
0.1°F --{
0.1°F
temperature
Sample temperature
7. Sample
Figure 7.
room
CBN room
from CBN
recording from
recording
upgrade
shop upgrade
Numerical control
control shop
Numerical
needs, the
programmatic needs,
to meet
in order
Long range
planners within MFD have
order to
to continue
continue to
meet programmatic
the
have projected that in
range planners
Long
temperature control
control in
in the
the shops
shops which
which house
house it's
it's precision
precision turning
turning and
and boring
boring machines
machines will
will have
have to
to be
be
air temperature
best way
the best
determine the
to determine
order to
in order
study was
F. A study
was conducted
conducted in
way
0.25° F.
to +^ 0.25°
improved from its
2.0° FF to
its current ++_ 2.0°
improved
load
heat load
preparing aa heat
included preparing
study included
The study
requirement. The
improvement requirement.
magnitude improvement
of magnitude
to meet the
order of
the almost order
to
table for
for the
the shops,
shops, identification
identification of
of the
the current
current control
control scheme,
scheme, reviewing
reviewing present
present air
air temperature
temperature control
control
table
system.
current system.
the current
with the
experiments with
some experiments
technology and conducting some
technology
was
temperature was
Air temperature
follows: Air
as follows:
operated as
system operated
the system
that the
revealed that
A brief
system revealed
review of the existing system
brief review
located. The
The
sensed by
by aa thermistor
thermistor type
type sensor
sensor located
located about
about 20
20 feet
feet above
above where
where the
the turning
turning machines
machines are
are located.
sensed
solenoid
switched aa solenoid
deadband. The
of deadband.
The controller
controller switched
0.3° FF of
about 0.3°
signal
-off controller
controller with
with about
on-off
an on
into an
fed into
signal was fed
water
chilled water
The chilled
valve which
which modulated
modulated the
the flow of
of air
air to
to aa pneumatically
pneumatically operated
operated chilled
chilled water
water valve.
valve. The
valve
in
located in
exchanger located
water-to-air
througha awater
waterthrough
chilled water
valve was used to
-to -air heat
heat exchanger
flow ofof chilled
the flow
modulate the
to modulate
valve
shop
the shop
of the
temperature of
air temperature
the air
to modulate
used to
was used
modulate the
heat exchanger was
shop. The heat
ductwork on
on the roof
the shop.
of the
roof of
ductwork
below.
below.
digital
with aa digital
it with
replace it
and replace
the onon-off
replace the
to replace
was to
A simple
-off control
control and
conducted was
was conducted
which was
experiment which
simple experiment
other
any other
Without any
room. Without
CBN room.
the CBN
in the
and in
enclosure and
PERL enclosure
the PERL
in the
PID control
control the same as
used in
those used
as those
PID
of
cost of
total cost
F. The
0.5° F.
to ++_ 0.5°
2.0° FF to
from _++ 2.0°
The total
shop went
the shop
in the
modification,
went from
fluctuation in
temperature fluctuation
modification, the air temperature
$1000.
under $1000.
the change was under
the
the
between the
delay between
transport delay
second transport
60 second
was aa 60
there was
that there
was that
Another discovery resulting from
study was
the study
from the
in
that in
which meant
effect which
is aa destabilizing
sensor. This
This is
destabilizing effect
meant that
feedback sensor.
temperature feedback
the temperature
heat exchanger and the
heat
that
was that
result was
The result
decreased. The
be decreased.
had to
system had
the system
of the
gain of
loop gain
the loop
order to
to be
stability, the
to obtain system stability,
disturbance rejection
rejection had
had to
to be
be compromised
compromised and
and therefore
therefore the
the quality
quality of
of the
the temperature
temperature control
control was
was limited
limited
disturbance
F.
0.5° F.
to
to ++ 0.5°
system is
In
order to
to meet
meet the
the temperature
temperature control
control requirement
requirement of
of +_
+ 0.25°
0.25° FF aa control
control system
is being
being built
built for
for
In order
few
only aa few
located only
be located
probe will
first feedback
probes. The first
feedback probe
will be
feedback probes.
temperature feedback
the shop
shop which
which has two
two temperature
the
The
feet downstream
downstream from
from the
the heat
heat exchanger
exchanger and
and the
the second
second will
will be
be located
located down
down near
near the
the turning
turning machines.
machines. The
feet
loop
its loop
and its
sensor and
first sensor
the first
of the
purpose of
8. The
Figure 8.
in Figure
form in
diagram form
control
The purpose
block diagram
in block
shown in
is shown
control scheme is
exchanger.
heat exchanger.
the heat
from the
temperature from
air temperature
immediate outlet
the immediate
over the
will
outlet air
control over
tight control
fairly tight
to provide fairly
be to
will be
travels
it travels
as it
air as
the air
of the
temperature of
the temperature
in the
detect changes
to detect
is to
loop is
and loop
The purpose
of the
the second sensor
changes in
sensor and
purpose of
occur
changes occur
temperature changes
latter temperature
the latter
that the
shown that
have shown
made have
Measurements made
second. Measurements
from the
the first
first sensor to
the second.
to the
from
fairly slowly
slowly and
and hence
hence will
will not
not be
be that
that difficult
difficult for
for the
the second
second sensor
sensor loop
loop to
to correct
correct for.
for.
fairly
Second temperature
temperature probe
Second
machines near machines
is down near
is
7
First
First temperature probe
isis near
nearcooling
coolingcoil
coil--
r/-Temperature
Temperature
setpoint
Valve /coil
Delay
+t
Disturbance
--1K21
K2
8.
Figure 8.
Figure
upgrade
shop upgrade
NC shop
for NC
Control scheme
scheme for
Control
90
Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms
The
The control
control system
system is
is being
being configured
configured around
around aa small
small personal
personal computer,
computer, not
not because
because the
the control
control scheme
scheme
requires
requires significant
significant computing
computing power,
power, but
but because
because it
it will
will also
also be
be used
used to
to log
log temperatures
temperatures at
at various
various
locations in
in the
the shop
shop simultaneously.
simultaneously. The
latter function
function will
be performed
so that the
The latter
will be
performed so
the performance of
of the
the
locations
air temperature
temperature control
control system
system can
can be
be continually
continually and
and conveniently
conveniently observed
observed by
by shop
shop supervisors.
supervisors. The
The system
system
air
will
will be
be capable
capable of
of displaying
displaying temperature
temperature time
time histories
histories graphically
graphically on
on its
its monitor
monitor at
at the
the discretion
discretion of
of
whoever
is operating
the keyboard.
keyboard. It
It will
will also
also be
be able
able to
to store
store several
several days
days worth
worth of
of temperature
temperature data
data on
on
whoever is
operating the
disk. AA layout
system is
layout of
of the
the system
is shown
shown in
in Figure
Figure 9.
disk.
Plotter
printer
Multiple
temperature
Data
storage
disk
Temperature
setpoint
(68" F I
Room
temp
I
i-+r
sensors
P+l
I
Signal
averaging
r
Control
signal
I
to
cooling
P+l
-J
Scanner
Duct air temp
I
valve
J
Computer
Figure 9.
9. Computer
Computer based
based temperature
temperature control
control and
and data
data logging
logging system
system
Conclusions
Conclusions
Precision
Precision air
air temperature
temperature control
control can
can be
be an
an excellent
excellent way
way of
of improving
improving the
the accuracy
accuracy capability
capability of
of
machines
by removing
removing one
one of
of the
the largest
largest sources
sources of
of nonrepeatability.
nonrepeatability. Work
Work at
at LLNL
LLNL has
has demonstrated
demonstrated that
that
machines by
achievement of
achievement
of close
close temperature
temperature control
control can
can be
be obtained
obtained by
by careful
careful identification
identification of
of heat
heat sources
sources and
and the
the
application
classical control
control theory.
theory. The
The work
work has
has also
also demonstrated
demonstrated that
that large
large
application of
of some
some fundamental
fundamental classical
improvements
improvements in
in the
the performance
performance of
of temperature
temperature control
control systems
systems do
do not
not necessarily
necessarily have
have to
to be
be complicated
complicated or
or
expensive.
expensive.
Acknowledgments
Acknowledgments
The author
author wishes
Fairley and
The
wishes to
to thank
thank D.
D. C.
C. Thompson,
Thompson, C.
C. R.
R. Fairley
and J.
J. W.
W. Roblee
Roblee for their support
support in
the
in the
development
in this
this paper.
paper.
development of
of the
the systems
systems discussed
discussed in
"Work
the auspices
auspices of
of the
the U.S.
U.S. Department
Department of
"Work performed
performed under
under the
of Energy
Energy by
by Lawrence
Lawrence Livermore
Livermore National
National
Laboratory
underContract
ContractW-W-7405-ENG-48."
Laboratory under
7405- ENG -48."
References
1.
Donaldson, R.
R., "Repeatability,
"Repeatability, aa Key
R. R.,
", American
-59
Key to
to Accuracy
Accuracy",
American Machinist,
Machinist, January
1.
January 8,
8, 1983,
1983, 5757-59
2. Moore,
W. R.,
R., Foundations
Foundations of
2.
Moore, W.
Mechanical Accuracy,
Accuracy, Moore
Tool Company,
Bridgeport, Connecticut
of Mechanical
Moore Special
Special Tool
Company, Bridgeport,
Connecticut
Bryan, J.
3.
Bryan,
J. B.,
Donaldson, R.
3.
B., Donaldson,
McClure, E.
W., A Practical
Practical Solution
Solution to
to the
Thermal
R. R.,
R., McClure,
E. R.,
R., Clouser,
Clouser, R.
R. W.,
the Thermal
Stability
in Machine
Tools, Lawrence
Lawrence Livermore
Livermore National
National Laboratory,
Stability Problem
Problem in
Machine Tools,
73577,
Laboratory, Report
Report Number
Number UCRLUCRL-73577,
Revision 1,
1, Livermore,
Livermore, California
Revision
4.
4. Bryan,
Bryan, J.
J. B.,
B., Carter,
Carter, D.
D. L.,
L., Clouser,
Clouser, R.
R. W.,
W., Hamilton,
Hamilton, J.
J. H.,
H., An
An Order
Order of
of Magnitude
Magnitude Improvement
Improvement in
in
Thermal Stability
Stability with
Use of
of Liquid
Liquid Shower on
on aa General
Purpose Measuring
Thermal
with Use
General Purpose
Measuring Machine,
Machine, S.M.E.
S.M.E. Precision
Precision
Machining Workshop,
Workshop, June
June 66-10,
Machining
-10, 1982,
1982, St.
St. Paul,
Paul, Minnesota,
Minnesota, Society
Society of
of Manufacturing
Manufacturing Engineers paper no.
no.
IQ82-936.
IQ82
-936.
5.
5.
McClure, E.
E. R.,
R., Manufacturing
Manufacturing Through
Through the
the Control
McClure,
Thesis, Lawrence Livermore
Control of
of Thermal
Thermal Effect,
Effect, PhD
PhD Thesis,
National
Report Number
Number UCRLUCRL-50636,
Livermore, California
National Laboratory,
Laboratory, Report
50636, Livermore,
California
6.
Thompson,
6.
Thompson, D.
D. C.,
C., Chrislock,
Chrislock, J.
J. L.,
L., Newton,
Newton, L.
L. E.,
E., "Development
"Development of
of an
an Inexpensive,
Inexpensive, High
High Accuracy
Accuracy Diamond
Diamond
Turning Machine
Machine",
Turning
", Precision
Precision Engineering,
-77
Engineering, 1982,
1982, Vol.
Vol. 1,1, Number
Number4,4,7373-77
DISCLAIMER
document vas
was prepared
prepared as
as an
an account
account of work
work sponsored
sponsored by
an agency
This document
by an
agency of
of
the
States Government.
United
the United
l; sited States
Government. Neither
Neither the
the I.
sited States
States Government
Governmentnor
nor the
the
University
of California
Californianor
t niversity of
norany
anyofoftheir
theiremployees,
employees, makes
makes any
any warranty, exexpress
assumes any
responsibility for the
the acacpressor
or implied,
implied, or
or assumes
anylegal
legalliability
liability or
or responsibility
curacy,
completeness, or
curacy, completeness,
or usefulness
usefulnessofofany
anyinformation,
information, apparatus,
apparatus, product,
product, or
or
process
disclosed,
or
represents
that
its
use
would
not
infringe
privately
owned
process disclosed, or represents that its use would not infringe privately owned
rights. Reference
Reference herein to any
any specific commercial
commercial products,
products, process,
process, or
or service
service
by
trade name,
name, trademark, manufacturer,
manufacturer, or
or otherwise,
otherwise, does
does not
not necessarily
necessarily
by trade
imply its
its endorsement,
endorsement, recommendation,
constitute or imply
recommendation, or
or favoring
favoring by
by the
the United
United
States
The views
views and
States Government
Governmentororthe
the University
University of
of California.
California. The
and opinions
opinionsof
of
expressed herein
authors expressed
herein do
do not
not necessarily
necessarilystate
stateororreflect
reflect those
thoseof
of the
the United
United
States
and shall
be used
product enenStates Government
Government thereof,
thereof, and
shall not be
used for
for advertising or product
dorsement
purposes.
dorsement purposes.
91
Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms