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Slide 1
Touch-trigger probe technologies
Resistive simple
compact
rugged
Strain-gauge solid-state switching
high accuracy and
repeatability
long operating life
Piezo three sensing
methods in one probe
ultra-high accuracy
quill mounted
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Slide 2
Kinematic resistive probe operation
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Slide 3
Kinematic resistive probe operation
probe in seated positionAll kinematics
in contact
Motion of
machine
stylus makes contact with
component
contact force resisted by reactiveforce in probe mechanism
resulting in bending of the stylus
Reactive
force
Contact
force
stylus assembly pivots about
kinematic contacts, resulting in
one or two contacts moving apart trigger generated before
contacts separate
Contacts
separate
Pivots about
these
contacts
machine backs off surface and
probe reseats
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Slide 4
Kinematic resistive probe operation
lectrical s!itching
electrical circuit through
contacts
resistance measured
contact patches reduce in
sie as stylus forces build
Kinematicattache" to
stylus
Kinematics bon"e" to #an"
insulate" from$ probe bo"y
Current flo!s
throughkinematics
Contact patch shrinks as
stylus force balances
spring force
Resistance rises as area
re"uces #R % &A$
Close-up vie! of
kinematics'
lastic "eformation
Section through
kinematics'
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Slide !
Kinematic resistive probe operation
lectrical s!itching
resistance breaches
threshold and probe
triggers
kinematics are still in
contact when probetriggers
stylus in "efine"
position
current cut before
kinematics separate toavoid arcing
(orce on
kinematics
Resistance
Trigger
threshol"
Trigger
signal
generate"
(orce on kinematics
!hen stylus is in freespace
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Slide "
(actors in measurement performance
Pre-travel
stylus bending under contact
loads before trigger threshold is
reached
pre-travel "epen"s on (C an" )
trigger is generated a short
distance after the stylus first
touches the component
(C* ) % (S* R# and $Sare constant
(Cis proportional to R
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Slide %
(actors in measurement performance
Pre-travel variation - +lobing,
trigger force depends on probing
direction, since pivot point varies
$&is proportional to '
therefore, pre-travel varies around
the () plane
Top vie!
igh force
"irection'
Pivot
point
)o! force
"irection'
Pivot
point
R./ R0
(C./ (C0
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Slide *
(actors in measurement performance
Pre-travel variation - +lobing,
trigger force in + direction is higher than
in () plane
no mechanical advantage over spring
$& $S
kinematic resistive probes ehibit 3.
/()+0 pre-travel variation
combination of + and () trigger effects
low ()+ useful for contoured part
inspection
Test "ata'
S5 163"6-2 3. form
26 with !6 mm stylus7 486 m /686661" in0
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Slide 9
(actors in measurement performance
Probe calibration pre-travel can be compensated by probe
calibration
a datum feature /of known sie and position0 is
measured to establish the average pre-travel
key performance factor is repeatability
)imitations
on comple parts, many probing directions may
be needed
low means simple calibration can be usedfor comple measurements
if is significant compared to allowable
measurement error, may need to qualify the
probe : stylus in each probing direction
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Slide 16
(actors in measurement performance
Typical pre-travel variation () plane
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Slide 11
(actors in measurement performance
Repeatability the ability of a probe to trigger
at the same point each time
a random error with a ;ormal
distribution
for a given probe and probingcondition, repeatability is equal
to twice the standard deviation
/20 of the ;ormal distribution
9!< confidence level that all
readings taken in this mode
will repeat within =:- 2 from a
mean value
ysteresis error arising from the direction
of the preceding probing move
maimum hysteresis occurs
when a measurement follows a
probing moves in oppositedirections to each other in the
probe>s () plane
hysteresis errors increases
linearly with trigger force and
stylus length
kinematic mechanism
minimises hysteresis
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Slide 12
(actors in measurement performance
Ranke" in terms of importance repeatability
key requirement of any trigger probe
fundamental limit on system measurement performance
hysteresis contributes to measurement repeatability
pre-travel variation
can be calibrated, provided all probing directions are known
measurement accuracy will be reduced if probe used in un-qualified
direction and is high
increases rapidly with stylus length
hysteresis
small error factor for probes with kinematic mechanisms
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Slide 13
Kinematic resistive probe technology
Simple electro-mechanicals!itching
resistive probes use the probe
kinematics as an electrical trigger
circuit
pre-travel variation is significant dueto the arrangement of the kinematics
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Slide 14
Kinematic resistive probe characteristics
*tremely robust Compact
good part access
suitable for long etensions
1oo" repeatability
ecellent performance with shorter styli
low contact and overtravel forces minimise
stylus bending and part deflection
2niversal fitment
simple interfacing
Cost-effective
(inite operating life
electro-mechanical switching