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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