Note: Descriptions are shown in the official language in which they were submitted.
~37~
This invention generally relates to workpiece
in~pection system~ and, more particularl~, to the u~e of probes
in automated machine tools to contact the workpieoe and provide
information relating thereto. Related material i~ disclosed in
applicant's U.S. Patent No~. 4,401,945, 4,545,106 and 4,578,874
issued August 30, 1983, October 8, 1985 and April 1, 198~,
respectively.
~ackground Art
Automated machine tool 3y9tem9 require a precise mean~
of locating surfaces on workpieces. One of t`he most common
methods is to have the machine move a probe into contact with a
workpiece and to record the probe position when contact is
made. Probes of this type are known as touch probes. They
generally include a stylus for contacting the workpiece and
circuitry which operates to generate an electrical signal when
the stylus contacts the part. ~he machine controller can
calculate information about the shape or location of the part
from the X, Y and Z axes positional data of the probe when the
stylus contact generates the electrical signal.
One of the problems encountered with the use of many
of these types of probing systems is in the method by which the
signal indicating contact by the probe i8 tranemitted back to
the controller. It is often impractical to rely on conventional
~iring to carry the ~ignal since the wire~ may interfere wibh
normal machining operations.
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~37~78
The patent literature di~closes several probe designs
~hich are adap-ted to be used in an automatic Machining center
where the probe~ are temporarily stored in a tool magazine and
are connected and removed from the spindle by an automatic tool
changer mechanism. Representative examples of patent~
disclosing these probes include U.S. Patent No. 4,339,714 to
Ellis; U.S. Patent No. 4,118,871 to Kirkham; and U.S. Patent No.
4,401,945 to Juengel.
The Kirkham approach is disadvantageous because its
radio frequency signals are susceptible to electromagnetic
interference and must be used within a relatively short
transmission distance between the probe and a receiver. Among
the problems with the probe system of the Ellis patent is that
great care mu~t be taken to align the probe and a specially
constructed detector on the spindle head in order for the
reactive coupling therebetween to operate properly. The
infrared transmission approach disclosed in the Juengel patent
is far more advantageous. However, it does require that the
probe, in most circumstances, contain its own power 30urce.
It has also been proposed to use touch probes in
turning centers such as lathes, as well as in machining
centers. Turning centers differ from machining or milling
centers in that the workpiece is rotated instead of the tooI.
In most turning centers, the tool holders are mounted at spaced
locations about a turret which operates to selectively advance
one of the tools towards the workpiece to perform work thereon.
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general, tools for performing outer dimension worlc on
the workpiece are mounted in slots within the ~urret
whereas inner diameter tools such as boring bars are
held in an adapter mounted to the turret.
5Touch probes used in turning centers have a
somewhat different set of problems to overcome than
probe used in machining centers, although the rnethod of
transmitting the probe signal back to the controller
remains a common concern. One of the problems unique ~o
10turning center application is that the probes remain
fixed to the turret even when not in use unlike the
situation with the machining centers where the probes
are inserted in the spindle only when they are needed to
be used. Consequently, it is not possible to rely on
15the probe insertion operation to activate the electronic
circuitry therein.
One prior touch probe technique for turning
centers utilizes inductive tr~a~smission modules to
transmit the probe signal through the turret to the
20controller. See, e.g., LP2 Probe System literature of
Renishaw Electrical Limited. Unfortunately, this
technique requires a substan~ial modification of the
turret in order to utilize the systemO Consequently,
this approach does not lend itself to be easily used in
25existing machines without requiring the expense and
machine down time to perform the retrofitting operation.
Also related to this invention, al~hough less
directly, is that prior art concerned with wireless
transmission o dimensional gauging data such as dis-
closed in U.S. Patent No. 3,670,243 to Fougere; U.S.
Patent No. 4,130,941 to Amsbury and U.S~ Patent No.
4,32~,623, to Juengel et al.
Disclosure of the Invention
The present invention is directed tv appar~tus
and a method of performing workpiece probing operations
in a manner so as ~o prolong the life of the power
sources used in these types of probes. According to one
embodiment of the present invention the probe is pro-
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vided with a detector that serves to connect the powersource to the probe signal ~ransmission circuitry when
the detector receives a given siynal. Means are pro-
vided remotely loca~ed from the probe for generating
this "turn on~ signal and wirelessly transmitting it to
the detector in the-probe. This signal i~ generated
prior to anticipated use of the probe to inspect the
workpiece and may be initiated by the controller in an
automated ~achine tool. Later, the power source is
disconnected. Power is thus drained from the source
only when necessary. This approach is espe~ially advan-
tageous when the probes are used in turning centers
where they remain fixed to the turret even though not
always used for inspecting operations. However, the
broad concepts of this invention have applicability in a
wide variety of other probingand machine tool system
applications.
In the preferred em^~diment, the machine
controller initiates a flash of infrared radiation from
a head mounted at a convenient location on the machine.
As a result, the probe transmission circuitry is enabled
and generates an IR signal of a given frequency to
indi~ate that the pro~e is opera~ing properly and ready
for use. The controller then proceeds with the
inspection operation. When the probe s~ylus contacts
the workpiece, the frequency o~ the IR transmission
shifts. This shift in frequency is remotely detected
and used by the controller to derive useful inforJnation
about of the workpiece. The probe circui~ry preferab~y
includes a timer which shuts off power to the circuit
components after a predetermined time period has elapsed
from the initial power up cycle or s~ylus contact.
Advantageously, the head may serve the dual
purpose of transmitting the flash turn on signal and
receiving the ~R ra-diation from the probe~ ~he head
includes an internally contained optical flash device
and a photodetector. An outer face of the head housing
preferably includes a lens with an IR filter~ The IR
filter serves to fil~er out light in the visible spec-
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~Z371~8
trum from the flash during probe turn on procedure. The
lens operates to focus the IR radiation from the probe
onto the photodetector in the head.
In an alternative embodiment, power to the
probe circuitry is initially applied when the stylus
contacts a reference s~rface. In operation, the machine
moves the probe so that the stylus contacts the
reference surface to initialize the power up cycle. The
probe is then used to inspect the workpiece, with the
probe operating to transmit signals relating thereto
back to a remote receiver head.
Brief Description of the Drawings
These and various other advantages o~ the
present invention will become apparent to one skilled in
~15 the art upon reading the following specification and by
reference to the drawings in which:
FIGURE 1 is an environi~ntal view showing a
probin~ system made in accordance with the teachings
of this invention in use with an automated machine tool;
FIGURE 2 is a perspective view illustrating
the of a probing system utilizing a flash turn 011
techrique according to one embodiment of this invention;
EIGURE 3 is a perspective view illusLratirlg
the use of a probing system with a touch turn on
technigue according to an alternative embodiment,
FIGU~E 4 illustraLes a cross sectional view
along the lines 4-4 of FI~URE 2 of a probe construction
according to one embodiment of this invention;
FIGURE 5 is a cross-sectional view along the
lines 5-5 of FIGURE 4;
FIGURE 6 is an exploded perspectiye view of
the probe shown in FIGURE 4;
FIGURE 7 is a perspective view of a
flash/receiver head used in one embodiment of this
invention;
FIGURE 8 is a cross sectional view alon~ the
lines B-8 of FIGURE 7;
FIGURE 9 is a top plan vi~w of a circuit
~237~7~3
~ 6 --
board used in the flash/receiver head of FIGURE 7;
FIGURE 10 is a schematic diagram of circuitry
used in the flash/receiver head;
FIGURE ll is a schematic diagra~n of circuitry
used in the probe of one embodiment of this invelltion
that utilizes the fla~h turn on technique; and
FIGUR~ 12 is a schematic diagram of circuitry
used in a probe utilizing the touch turn on technique.
Description of the Preferred Embodiments
I. Overview
FIGURE 1 illustrates, in simplified form, a
typical machine tool system utilizing various aspects of
the inventive features to be described. A n~merically
controlled turning center 10 is shown therein together
with a controller 12 for automatically controlling
turning operations on a workp;ec~l4 according to pro-
grammed instructions. Turning center 10 typically in-
cludes a rotating chuck 1~ with jaws 18 thereon for
holding the workpiece 14. Mounted to a turret 20 are a
plurality of tools 22 - 24 for performing work on the
inner diameter (ID) of workpiece 14. Typically, ID
tools of this sort include an elongated shank portion
which are held in place in turret 20 by way of adapters
- 26 - 28. In accordance with the present invention, a
~5 w~rkpiece inspection probe 30 is mounted to turret 2~ in
the same manner as tools 22 - 24~ In this embodiment,
probe 30 i5 mounted to turret 20 by way of adapter 32
which is identical to adapters 26 - 28.
As is known in the art, controller 12, among
other things, operates to rotate turret 20 to bring the
desired tool into the appropriate work position and then
moves turret 20 until the tool contacts the workpiece
and performs its desired machining operation thereon.
Probe 30, on the other hand, is used to inspect the
workpiece 14. In this specific exarnple~ probe 30 is
known in the industry as a touch probe in that it gen-
erates an output signal when the probe stylus contact a
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~'~3~7~7~
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surface of the workpiece or other object. Suitable
resolvers, digiti7ers or the like are used to provided
signals to controller 12 indicating the position of the
probe 30. Consequently, when the signal from probe 30
indicates contact with the workpiece controller 12 can
derive useful information about workpiece dimensions,
appropriate positioning thereof within the chuck, etc;
A. Flash Turn On
~ ro~e 30 contains its own battery power source
for supplying energy to its signal transmission
circuitry. Batteries, unfortunately, have limited
useful lives. Thus, there is a real need for some means
of preserving bat~ery life as long as possible. This is
especially true for smaller sized probes used in turning
centers. Smaller probes are also restricted in the size
of the batteries they can use and thus conservation of
energy is very important. ~
One aspect of this invention provides two
way optical communication between probe 30 and a
2~ flash~receiver head 40. Head 40 is connected to con-
troller 12 through an interface 42. When controller 12
determines that it is time ~o use probe 30 for a probing
operation it generate~ a signal over llne 44 to inter-
face 42, which in t~rn generates a control signal on
2~ line 46 to cause head 40 to transmit a given op~ical
signal to probe 3~. In the preferred embodiment, this
optical signal is a high intensity flash of infrared
radiation. This flash is sensed by a suitable detector
48 in probe 30 ~see ~IGURE 23. The flash causes de-
tector 48 to couple the battery power to the probetransmission circuitry. Preferably, probe 30 respon~s
to the flash by transmitting IR radiation at a given
frequency back to head 40 via light emitting diodes
- (LEDls) 50 - 54. This I~ radiation is received by head
40 which, in turnJ supplies a signal to oontroller 12
via interface 42 indicating ~hat the probe 30 is
operating properly and ready to perform Its lnspection
operation.
.
~.;2371~3
Controller 12 then causes turret 20 to advance
probe 30 until the stylus 56 contacts worlcpiece 1~.
Probe ~0 responds to stylus contact by creating a shift
in the frequency of the IR radiation transmitted by
LEDIs 50 54. The shift in frequency is detected by
interface ~2 and communicated to controller 12. The
workpirce inspection operation continues as desired,
with probe 30 transmitting frequency shifted IR radia-
tion t~ head 40 every time the stylus makes contact.
Probe 30 includes timing means therein which
will disconnect the battery supply from the transmission
circui~ry after a predetermined period of ti~e. This
time period begins when battery power is initially
applie~ to the circuitry and is reset every time ~;he
1~ stylus contacts the workpiece. Thus, after the probing
operation is finished the time period will eventually
lapse and the battery power is disconnected from the
transm~ssion circuitry. Accordi~!ly, the ba~tery power
is onl~ used during periods of anticipated probe usage.
Whenever the probe is not in use the battery power is
discon~ected and thus, conserves energy prolonging
periods belween battery replacement.
B. Touch Turn On
FIGURE 3 illustrates an alternative method of
prolon~ing battery life. In this example, battery
power ~s first connected to the probe transmission cir-
cuitry ~y touching the probe stylus 56 against any known
refere~ce surface 60. Reference surface 60 can be any
fixed point within machine 10 whose location is known by
3~ contro~ler 12. Probe contact with surface 60 couples
the ba~teries to the probe transmission circuitry and
initia~es the transmission from LEDIs 50 - 54 to head
40~ ead 40' is like head 40 previously described
except ~hat it does not need the flash means therein,
nor do~ probe 30' req~ire the photodetector 48. O~her-
wise, t~e two embodiments operate substantially
identicially. After initialization, the probe is moved
into p~sition for inspecting workp;ece 14, with probe
~h237~L78
g
30' transmitting frequency shifted signals to head 4~'
whenever stylus contact is made. After a predetermined
period of time from the last stylus contact, the
batteries are disconnected from the probe transmission
circuit.
II. Probe Construction
FIGURES 4 - 6 illustrate in more detail the
construction of probe 3~. The probe housing is
characterized by a generally cone-shaped middle portion
~0 and a rearwardly projecting shank or cylindrical
portion 72 of reduced cross-sectional diameter. In this
specific embodiment, cylindrical portion 72 is hollow
measuring about 4 and 1/4 inches in length~ with an
outer diameter of about 1.4 inches.
The outer dimensions of cylindrical portion 72
are chosen to generally correspond with the dimensions
of the bodies or shanks of tools 22-24. Consequently,
probe 30 may be used in place o,~- one of the tools in
turret 20 and held in adapter 32 ln the same manner. As
shown most clearly in FIGURE 4, this may be accomplished
by sliding cylindrical portion 72 into the pocket 74 of
adapter 32 until the rear wall 76 of housing portion 70
abuts the front face 78 of adapter 32. This procedure
thereby insures that the tip of stylus 56 is spaced at a
2~ known posi'ion with turret 20~ Consequently, controller
12 may accurately rely upon the position of the stylus
56 during the probe inspection operation~ O~ course,
other conventional means may be used to position st~lus
tip 56 at the appropriate spacing. For example, scme
machine tool systerns utilize a set screw tnot shown)~or
other means within the rear of pocket 74 to adjust the
stylus spacing.
Cylindrical portion 72 advantageously serves
the dual purpose of providing a battery co~partment as
well as t~ provide an easy to use mounting mem~er. The
elongated cylindrical shape of portion 72 enables the
use of long life ~cylindricalU batteries resemblirlg
typical flashlight batteries in shape for powering the
probe transmission circuitry. Preferably, two "C~ cell
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lithium batteries 80, 82 are employed. The ability to
use cylindrical batteries, instead of smaller batteries
such as button or disc cells, provides the probe with an
exceedingly long operational life at low cost.
Batteries 80, 82 are slid into the interior of
portion 72. A spring loaded cap 84 is then threaded
onto the end of portion 72, with spring 86 urging the
positive or male terminal 88 against board 90O The
lower surface of board g0 incl~des a circular conductive
layer 92. Board 90 is secured within a well 94 in an
interior surface of wall 76 by way of screws 96. An
insulated lead 98 makes elect.ical connection with con-
ductive layer 92 by way of a plated through hole in
board 90. 1`he opposite end of lead 98 is connected co
circuit board 100 containing the probe circuitry. A
description of the electrical schenatic for the cir-
cuitry will be described later h~erein. Circuit board
100 is generally circular in shape containing electrical
components mounted on both sides thereof. Circuit board
100 is mounted within the interior of middle por~ion 70
by way of suitable fasteners 102 passing through
standoffs 104. The board 100 also includes a centrally
located aperture 106 therein ~hrough which various leads
can pass to facilitate connection to the appropriate
areas of circuit board 100.
Photodetector 48 and its associated sub-
assem~ly is mounted in the outer sloping surface 1100f
middle housing portion 70O ~hotodetector 48, in thi~s
- particular example, is a PI~ diode such as par' No~
DP104 available from Telefunken. Photodetector 48 fi's
within a countersunk bore and is held in place by way of
a bezel 112 having a window therein. Interposed between
bezel 112 and photodetector 48 are layers of transparent
plastic 114, an infrared fil~er layer 116 and an O-ring
118. Suitable fasteners 120 sandwich all of these com-
ponents into a subassembly mounted within the counter-
sunk bore~ The leads from photodetector 48 pass through
aperture 106 and are connected to suitable points on
circuit board 100O
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~l23~7~78
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LED's 50-59 are mounted adjacent to photode-
tector ~8. LEDs 50-54 are designed to emit optical
signals in the infrared radiation band, i.e. light which
is not normally visible to the human eye. LED's 50-54
may comprise, for example, component Nos. OP290 avail-
able from TRW, Inc. It should be noted at this point
that the arrangement of LED's 50-54 and photodetector
48, taken together with the configuration of the sloping
probe surface to which they are mounted combine to
optimize several important advantayes. For example, by
mounting LED's 50-54 onto the sloping surface 110 of the
probe, the infrared radia'ion that is emitted thereby is
directed forwardly of turret 20 at angles at which the
radiation may be easily picked up by vaiious locations
of head 40. The probe construction enables the user to
rotate the probe into a position where the LED's 50 -54
and photodetector 98 are pointing in the general direc--
tion of head 40. Thus, it is not necessary to mount
~ead 40 at any absolute spatial~location relative to
probe 30 giving the system great flexibility for use in
different 0achine tool systems. Reliable optical com-
munication between probe 30 and head 40 is thereby
obtained while at the same time minimizing the number of
light emitting devices within probe 30. By keeping the
number of light emitting devices to a minimum the energy
drain from the batteries is kept as small as possiblec
thereby further prolonging battery life.
Rounding out the assembly of middle portion
70, the wall 76 is affixed ~o rearward portions of
por~ion 70 by way of suitable fasteners 122. O-r~ngs,
such as ring 124, are advantageously used to seal the
interior of the probe 30 from the somewhat adverse
conditions that the probe may encounter during use in
the machine tool system.
An annular nosepiece 130 includes a threaded
male member 132 which mates with threads formed in a
bore 134 in the front face of middle housing portion 70.
O-ring 136 is again employed for sealing purposes~
Nosepiece 130 may be made in various legnths to increase
12 - ~æ~7~
or decrea,~e the relatlve ~pacing of ~tylue tip 56 as may
be desired. Due to the -threaded fastening engagemen-t
with the middle housing portion 70, a variety 0~3uch
no~epieces can be made and interchanged with one ~mo-ther
for u~e in different applications.
A swi-tch unit 140 is removably attached to
nosepiece 130. Switch unit 140 includes a circular whLotle
no-tch ond con~truction 142 including a surrounding O-ring
146 which is press fit into -the internal passageway 146
within nosepiece 130. One or more set screws 148 extending
orthogonally through nosepiece 130 clamps the switch unit
140 i.n place. Swi-tch unit 140 can be a variety of
conqtructions that operate to open or break one or more
electrical contacts therein when stylus 56 i~q moved from its
rest position. ~hooe skilled in the art are aware of a
variety of construction~ tha-t fulfill this general purpo~e.
One suitable switch construction is disclosed in detail in
applicant's Canadian Patent ~o. 1,198,188, is~ued
December 17, 1985. Priefly, this construction employs a
wobble plate with three equally spaced ball contacts
thereon. The wobble plate is spring biased so that the
balls are normally pres~qed against three corresponding
electrically conductive inserts. The three ball-insert
pairs serve as switches (referred to later herein as
switches Sl-S3) and are connected together in series. The
wobble plate is connected to stylus 56. Whenever stylu~ 56
moves, the wobble pla-te -tilts and lifts one of the ball
contacts from its corresponding in~ert -thereby breaking the
electrical connection therebetween.
The three switche~ in unit 140 are connected to
circuitry on board 100 by way of cable 150. lhe other end
of cable 150 include~ a miniature coa~ connector 152 or
o-ther suitable connector -that ma-tes with a connector on the
end of replaceable ~witch unit 140. ~hose skilled in the
. art appreciate that these typeo of swi-tch units are very
sensitive and may need to be
~23~
replaced. The construction of the present invention
enables such replacement to be made quickly and easily.
Various shapes and sizes of styli may be used
in connection with probe 30. For example, instead of
the straight stylus 56 shown in the drawings, a stylus
may be used in which the tip thereof is offset from the
major l~ngitudinal axis of probe 30O The various styli
are in~erchangeable with switch unit 1~0 and may be
attache~ thereto by the use of suitable fastening mealls
such as set screws.
_I . FLi~SH TURN ON
A. Flash/Receiver Head
The mechanical details of flash/receiver head
4~ are ~hown most clearly in FIGURES 7 - 9. Head ~0
employs a generally rectangular container 160 having an
openin~ 162 formed ln a front face 1~4 thereofO One or
more c~rcuit boards 166 are moun~ed within container
lfi0. Circuit board 166 includes a variety of electrical
componer~ts 'hereon for carrying out the functions to be
described later in detail. Two of the most important
components are shown in these drawings~ ~hey are
xenon f~ash tube 16~ and photodetector 170. As noted
before, the purpose of flash tube 168 is to generate a
high intensity light pulse of short time duration to
2~ initiate probe operation. Xenon is preferred because it
generates light that is rich in infrared radia~ion. In
the preEerred embodiment, flash tube 168 is a part No.
BUB ~64~ xenon flash tube available from Siemens. It is
capable of generatins a flash or light pulse lasting
about S0 microseconds with an intensity of 100
watt/seconds. Other types of suitable light sources~ o~
course, can be employed.
Although not absolutely necessary, the visible
light generated by flash tube 168 is preerably
elimina~ed so as not to distract the operator or o~hers
in the shop where machine tool 10 is being used. To
this end, an infrared filter 172 coverinq opening 162 is
r
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~l237:~78
employed. IR filter 172 serves to block out visihlc
light but passes infrared radiation therethrough
generated by flash tube 168.
The purpose of photodetector 17~, on the other
hand, is to detect in~rared radiation transmitted by
probe 30. In this embodiment, photodetector 170 is a
PIN diode and operates in a similar manner as pho~o-
detect:or 48 in probe 30. A convex lens 174 is advan
tageously used in opening 162 to concentrate the IR
radiation from probe 30 onto photodetector 170 which is
located at the focal point of lens 174. Rounding out
the construction of head 40, there is supplied a
transparent face plate 176. ~ace plate 176 covers
opening 162 and is suitably attached to front face 164
havinq a gasket 178 sandwiched therebe'ween.
B. Flash/Receiver Head Circuitry
FIGURE 10 illustrates the circuitry used in
the flash/receiver head 40 of t~e preferred embodiment.
As noted bef~re, head 40 is coupled to interface 42 over
one or more conductor lines generally indicated by the
reerence numeral 46~
A 26 volt alternating current ~AC) signal is
dpplied to the primary of step u~ transformer Tl.
Energy from transformer Tl is stored across capacitors
C8 and C9 which are, in turnl coupled across the posi-
tive and negative electrodes of xenon flash tube 168
In this embodiment, capacitors C~ and C9 store abo~t
250-300 volts DC when fully charged.
To cause tube 168 to flash, controller 12 via
interface 42 generates an appropriate signal level on
the lines labeled ~controlU to cause LED 171 to conduct
and emi light. LED 171 is part of an optical isolation
package containing silicon controlled rectifier (SCR)
173. S~R 173 is connected in a series circuit wi~h the
primary of transformer T~ and capacitor C10. Capacitor
C10, like capacitor C8 and C9 is charycd due to the
action of transformer Tl. When LED 171 is activa~ed,
SCR 173 conducts and dumps the charge of ~apacitor C10
. .
~;Z 3~7~3
- 15 -
across the primary of transformer T2. This charye i.5
stepped up fo about 4,000 volts by transformer T2 whose
secondary is connected to the trigger electrode 175 o~
flash tube 168. Trigger electrode 175 is capacitively
coupled to tube 168 and the high voltage thereon is
sufficient to ionize the gas within the tube. The
ionized gas is sufficiently conductive to permit the
energy from capacitors C8 and C9 to discharge across the
positive and negative electrodes to create a very hiqh
intensity flash of short duration. After tube lG8
flashes the capaci,ors begin to recharge until s~ch time
as another flash initiating control signal is supplied
from interface 42.
The probe 30 responds to the flash by
transm~tting the IR signal which is picked up by the
photodetector 170 in head 40. Photodetector 170 i5
- coupled to a tuned tank circuit comprising variable
induct~r Ll and capacitor C2. By the way of a specific
example~ probe 30 will generate IR radiation pulsed at a
~requency of abou~ 150 kilohertz until the probe stylus
contac~s an object at which time the frequency will
shift t~ about 138 kilohertz. The tank circuit in head
40 is t~ned to approximately the average of these two
frequencies so that the head circuitry can detect eith~r
one of these probe frequencies but will ilter out
extraneous frequencies outside a preselected range or
band wi~th~
The remaining circuitry in FIGURE 10 is used
to ampl~y the detected signal transmitted from probe 30
which is coupled over the ~output" line to interface 42.
Brieflys the head amplification circuitry employs a
field e~fect transistor Ql whose high input impedence
matches that of the tuned circuit so as to avoid
loadin~ problems. Transistor Q2 in cooperation with
transis~or Ql amplifies the received signal and couples
it to an emitter follower network employing transistor
Q3. The amplified slgnal is coupled to interface 42
over the output line through DC filter capacitor C6 and
resister R7 coupled to the emitter of transistor Q3.
,
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`` ~ Z37~7~3
In-terE~ce 42 has circuitry therein -that operates to
d~tect theae selec~cd probe s~gnal frequencies and will generate
outputs to controller 12 in response thereto. A first signal is
generated to indicate that the probe is operating properly and a
second signal is generated when the probe stylus contacts an
object. Suitable circuitry for detecting the frequency shift is
disclosed in U.S. Patent No. 4,545,106. ~riefly, such circuitry
employs a phase locked loop circuit to perform a frequency shift
keying operation on the received signals and activates relays
upon detection of either of the selected frequencies. ~lowever,
a variety of other methods of detecting the probe signals is
within the skill of the ordinary practitioner.
_ Probe Circuitry
FIGURE 11 is an electrical schematic diagram of the
circuitry within probe 30. PNP transistor Q10 operates as a
switch to selectively connect or disconnect power from batteries
80, 82 to the components used to generate IR radiation from
L~D's 50-54. ~ransistor Q10 is normally in a nonconducting
state and thus, the batteries 80, 82 effectively see an open
circuit so that energy is not drained from the batteries.
However, when head 40 generates its flash of IR radiation,
photodetector 48 conducts current from the batteries through
inductor Ll for the duration of the flash.
~ he very fast rise time associated with the light
pulse from the xenon flash tube provides a unique signal which
can be easily discriminated from other light sources in the area
of the machine tool. The IR filter at the head 40 excludes most
of the visible spectrum so that the flash cannot be seen and
become an aggravation to nearby per30ns. When the fast rise
time
_ 16 -
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~L~3 717 !3
light ~ulse reaches the photodetector 48, it is con-
verted to an electrical pulse across the inductor coil
L10. The coil L10 serves as a high pass filter and e~~
cludes steady state or low frequency light pulses such
as flourescent lights in the area may produce.
The surge of current through photodetector 48
during the flash creates a ~rinqing~ phenomenon in in-
ductor L10 as is knownin the art. ~his ringing
phenomenon is basically a damped oscillation that lasts
approx~mately 500 microseconds in response to the flash
light pulse of about 50 microseconds. The oscillations
from inductor Ll are amplified and inverted by invert7ng
amplif~er 200. The output of amplifier 200 is connected
to the base of transistor Ql~o The momentary ringing in
inductor Ll caused by the flash creates a forward bias
across the base-emitter junction of transistorQ10 and
causes it to conduct. The conduc~ion of transistor ~10
connec~s the power from bat~eri~e~,~s, 80, 82 to the power
inputs of the circuit components labled ~V in the
drawings. When power is applied to oscillator 202 it
begins supplying pulses to a time out counter 204
Counte~ 204 is reset to initialize its time out period
when t~e flash is received from head 40. This ls
accomp~~ished by way of an inverter 206 which inverts tne
output of amplifer 202 to a positive signal which is
shaped by the RC time constant of capacitor C20 and
resist~r R2~ into a pulse. This pulse is connected to
the re~et input of counter 204 through OR gate means
208. A~ will appear9 time out counter 204 is also reset
whenever the probe stylus 56 contacts an object re-
flecte~ hy the opening of one of switches Sl-S3.
Time out counter 204 is designed so ~ha~ i~
will pr~vide a logical lo~ signal on its output line ~10
as long as it is counting, i.e. not timed out~ The
logical low signal on line 10 is inverted by inverter
212 wh~ch, in turn, is connected through diode D20 to
the inp~t of amplifier 200. As a result~ the outpu~, of
amplifier 200 is latched Lo a low state t~.ereby keeping
transis~or Q10 in a conductive state providing power to
~237 1~t~
- 18 -
the circu.it components until such time as counter 209
times ~ut. The time out period for counter 204 is
chosen to be of sufficient length to allow the ~on-
troller 12 to begin the actual inspection process with
the probe stylus con~acting the workpiece. In general,
a time period of sevèral minutes is sufficient for this
purpose. The time out period may be adjusted by way of
potentiometer P20 defilling the oscillation frequency ~or
time delay oscillator 202. Higher frequency oscilla-
tioJIs from oscillator 202 cause counter 204 to count
faster and thus, time out in a shorter time, and vice
versa~ The generation of various ti~e delays is, Gl
course 5 well within the skill of the ordinary
practitioner.
Carrier oscillator 220 and divider 222
cooperate ~o define the frequency at which LEDs 50 - 54
transm~t their IR radiation back to head 40~ Conv~n-
tional~y, oscillator 220 uses a`~crystal 224 having a
known r~sonant frequency as a master clOckr Osci 1 lator
220 ope~ates to shape the oscillations from crystal 224
into a ~orm suitable for providing clock pulses to a
conventional digital divider such as divider 222.
Divider 222 ser-~es as a convenient means for shifting
the fre~uency transmitted by LEDs 50 - 54 when the probe
stylus contacts an object. In this particular example,
divider ~22 operates to divide 1.8 M~3z pulses from
carrier oscillator 222 by the number 12 and thus pro
vides at its output signal frequencies of about 150 Kr-lz.
The output of divider 222 is coupled to a driver
transistor Q12 or other suitable circ~itry for driving
LEDs S0 - 54 at the freguency defined by the divider
output. Thusf in this example, when head ~0 initiates
the flash turn on sequence, probe 30 responds by
starting the transmission of IR radiatlon at a given
frequency. ~he probe.transmission is detected by photo-
detector 170 in head 40 which, in turn, supplies a
indication to controller 12 that the probe 30 i.s
operati~g properly and is ready to initiate the probing
sequence. If probe 30 does not respond in such manner
~237 17~
- 1'3 -
suitable precautionary measures can be taken.
When the probe stylus 56 contacts an object,
one of the three switches Sl-S3 in probe unit 140 will
open. The opening of one of the switches Sl-S3 causes
two things to happen. First, it resets time out counter
201 to the beginning of its time out sequence.
Secondly, it creates a shift in the frequency trans-
mitted by LEDs 50 - 54. This may be accomplished in a
variety of manner. However, in the preferred embodi-
ment, the opening of one of the switches Sl-S3 causes
comparator 228 to go high. The output of comparator
228 is coupled to the reset input of counter 204 through
OR gate 208 and thus, resets the counter. In addition,
the output of comparator 228 is coupled to a frequency
shift keying input of divider 222 over line 229 to
cause it to divide the clock pulses from carrier
oscillator 220 by a different number, here by the number
13. The output signals from di~ 222 thereby changed
in ~requency to about 13~ KHz. Thus, the frequency of
the I~ radiation transmitted by LEDs 50 - 54 is shifted
in comparison to the frequency transmitted when the
probe was initially turned on. This shift of frequenc~
is detected by photodet~ct~r 170 and transmitted to
controller 12 to indicate stylus contact with an object,
normally a workpiece surface~ Controller 12j by knowing
the posi'ion of stylus 56 when this signal is received,
can accurately calculate the dimensions of the workpiece
or derive other useful information.
Controller 12 may move the probe 30 to contact
other workpiece surfaces, each time the probe responding
by a shift in IR radiation transmitted from the probe.
The timeout period of timeout counter 204 is chosen so
that it is longer than the time that would elapse be-
tween stylus contacts. When the probing operation is
completed, controller 12 may go forward with other ma-
chining operations as may be desired. There is no need
to generate any further signals to turn of the probe
since energy from the ba~teries will be automatically
disconnected once counter 204 times out. In such case,
.~ .
lZ37 'L78
- 20 -
its ou~put line 210 would go high ultimately resulting
in the reverse biasing of the base -emitter junct1On of
transistor Q10. This places transistor Q10 in a non-
conducting state. In this manner the only drain on the
batteri~s 80, 82 is the leakage current of the semicon~
ductors and the photocurrent of photodetector 48
Typically, this current can be very small, of~en less
than 3~0 microamps. Consequently, the more power de-
manding components are disconnected from the battery
supply until actually needed for anticipated probe use.
Preferably these components are made from CMOS semi-
-onduct~r technology to even further conserve drain on
the ba~'eries when used.
By way of a nonlimited example, carrier
oscill,ator 220 is formed by a crystal controlled
transislor Component No. 2N2222, divider 222 is an
LM4526 available from National Semiconductor/ time delay
oscillator 202 is formed from on,~e~,,,,half of an integrated
circuit LM2903 available from National Semiconduc~or,
and ti~e out counter 204 is an LM4040 also available
from National Semiconductor.
IV. T~UCH TURN ON
The touch turn on technique previously
descri~ed in connection with FIGURE 3 may be used 2S an
2~ altern~tive to the flash turn on technique described in
sectio~ III. soth techniques have the same general
ob3ect-,1ve, i.e,. to conserve battery life. To a larye
extent the prob~ construction and circuitry for both
techni~ues are similar. A schematic diagram of ~he
probe circuitry or the touch turn on ~echnique is shown
in FI~RE 12. This circuitry is like that of ~IGURE 11
and th~s, common reference numerals will be used to
reference common componentsO
A comparison of the two figures will reveal
that the major difference is the deletion of photo~
detector 48 and associated ind~ctor coil L10 in favor of
resist~r R50 and capacitor C50. This circuit also
differs in that it includes a line 231 conne~ted between
~LZ37~Lt78
- 21 -
the probe switches Sl-S3 and node N1 coupled to the
input of inverting amplifier 200. Transistor Q10 is
kept in a nonconducting state until such time as one of
the switches Sl-S3 opens as a result of the stylus 56
contacting reference surface 60 (FIGUR~ 3). This is
because the switches-Sl-S3 keep the input to amplifier
200 at substantially ground level as long as they are
closed; i.e. when the probe stylus is not contactiny
anything. However, when stylus 56 contacts the
reference surface 60 one of the switches S1-S3 opens and
causes capacitor C50 to begin charging. Preferably, the
values of resistors R50 and R18 as well as capacitor C5~
are chosen to provide an RC time constant that delays
the time at which capacitor C50 is charged to a vol~age
sufficient to turn on transistor Q10 after being in-
verted by amplifier 200 This requires that the con-
troller 12 hold the probe stylus 56 against the refer-
ence surface 60 for a definite period of time, for
example, about a second. This procedure will insure
that accidental bumps against the probe stylus or other
extraneous factors such as electrical noise will not
erroneously trigger activation of the probe.
Once capacitor C50 has been sufficiently
charged the transistor Q10 will turn on and ~upply po~er
~rom batteries 80, 82 to the probe transmission com-
ponents. The counter 204 will be reset and supply its
output signal over line 210 to latch the transistor Ql~
in its conducting state . In this embodiment, the
divider will initially generate the lower of the two
output frequencies due to the tripping of comparator 2~8
while the probe stylus 56 is contacting the reference
surface. The controller 12, however, can be suitably
programmed to consider this initial probe signal as an
indicator that the probe has properly turned on and is
ready to proceed with inspecting the workpiece.
Controller 12, knowing that the probe 30' is
operating properly, then moves on to the workpiece in~
spection procedure with the stylus 56 contacting various
workpiece surfaces. Once the stylus 56 is moved away
,,
.
37~L7~
- 22 -
from the reference surface 60 the switches Sl~S3 close
causing divider 222 to drive the LED's 50-54 at t~e
other frequency. As soon as the stylus contacts a
workpiece surface, one of the switches Sl-S3 opens again
tripping comparator 228. This results in the resetting
of counter 204. The tripping of comparator 28 also
provides an output over line 229 to divider 222 to cause
its output and therefore the outputs of LED's 50 - 54 to
shift in frequency. This procedure continues until
such time as the workpiece piece inspection procedure is
finished, with the battery supply being automatically
disconnected from the probe circuitry once timer 204
times ou~
SUMMARY
I5 From reading the foregoing specification,
those skilled in the art will come to appreciate that it
discloses several significant advances in the workpiece
inspection art. Each of the embodiments have been
described in connection with the best mode that is
currently contemplated for carrying out their inventive
techniques. No attempt, however, has been made to list
all of th~ various alternatives or modifications to the
general concepts thereof. Such modifications or
improvements should become apparent to the skilled
2S practitioner after a study of the drawings, specifica
tion and claims. For example7 it should be apparent
that the flash turn on or touch turn on techniques can
be used with di;fferent types of probes other than the
one specifically illustrated. Therefore, while this
invention has been described in connection ~ith a par-
ticular example thereof, its true scope Should be
measured in light of _he following claims and equiva-
lents thereto.
'
