l~Z6351
BACK ROUND OF TIE INVENTION
IRE LAl Elm f~PPI IC~TIONS
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3~ield ox e invention:
The invention generally relates to position detection apparatus for use in
measuring and gaging systerns. More particularly the Inventiorl concerns probe contact
detection apparatus for providing an indication of probe contact with a worl<piece.
description of the Prior Art: -
l l<nown touch probe opera-tes by arranging the probe stylus to severely
attenuate a radio frecluency signal lJpOIl contac-t of the probe s-tylus wi-th a metallic
worlcpiece. One such pr ior art device is taught in U.S. Patent 4,118,871 l~irkham. S-lcll
arrangements are prone to electromagnetic noise interEerence with the raclia-tecl raclio
frequency signal, ancl this interference can lead to faJse indications of probe contact
with a worlcpiece.
Also related to this inven tion is that prior ar t concerned with wireless
transmission of dimensional gaging data such as disclosed in U.S. Pa ten t 3,670~243
Fougere et al., U.S. Patent 4,130,9~ Amsbury, and U.S. Patent 4,328,623 assigned to
the same assignee as the ins-tan t invention.
A need has arisen fot touch detection apparatus with high resolution and
immunity to electromagnetic noise, capable of wireless transmission of an indication o:E
2~ the occurrence of probe contact with a workpiece. A need also has been demonstrated
for touch detection apparatus with -the addecl capability of accepting a variety of
position determining transducers. One SllCh approach to fulfilling this need is disclosed
in U . S . Patont No . 4, 401, 945 - Juengel wherein either a
curren-t transformer or a mechanical switch type transducer is used in conjunction with a
voltage con-trolled oscillator to produce frecluency modulated infra-red signals whenever
the probe assumes c7 preselecLed position relative to a workpiece.
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SUMMARY OF THE INVENTION
There is provided according to the invention an apparatus
for detecting a position of a probe relative to a workpiece
comprising:
a probe body surface whose position relative to a workpiece
is -to be detected;
oscillator means for providing a reference alternating
current signal having a preselected frequency at an output thereof;
transducer means including means coupled to -the probe body
surface so as to exhibit a change in electrical characteristic
whenever the probe body surface assumes the position, and de-tector
means coupled to the means coupled to -the probe body surface,
operative to generate an indicator signal at a transducer means
output indicative of -the characteristic change;
modulator means having a first input coupled to the
oscillator means outpu-t and a second input coupled to the transducer
means output, operative to alter the reference alternating current
signal and -to present the altered signal at a modulator means output
whenever the indicator signal is generated; and
a source of optical radiation having a con-trol input
coupled to the modulator means ou-tput, operative to emit optical
radia-tion having a characteristic determined by the modulation means
output.
The modulator means may be operative to alter the frequency
or the ampli-tude, or both, of the reference alternating current
signal upon receipt of the indicator si.gnal.
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According to another aspect of the inven-tion, there is
provided an apparatus wherein the transducer means further comprises
first and second reference po-ten-tia] sources; wherein the means
coupled to the probe body surface comprises a plurality of switch
contac-ts coupled in a series circuit between the first and second
potential sources; and wherein -the detection means comprises a
comparator having an output providing the transducer means output,
the comparator having a first input coupled -to the first reference
poten-tial source, and a second input coupled via the series circui-t
of switch contacts to the second reference potential in a manner
such -that signal levels a-t the first and second inputs to the
comparator will approach substantial equality whenever any one of
the switch con-tacts begins to exhibit an altered inpedance
thereacross, -thereby enabling -the compara-tor to generate -the
indica-tor signal a-t i-ts outpu-t.
According to another aspect of -the invention there is
provided a touch probe apparatus for de-tecting contact be-tween a
probe stylus and an object comprising:
a contact element coupled to one end of the probe stylus;
a crystal controlled oscillator for providing a reference
alternating current signal having a preselected frequency a-t an
oscillator output;
at least three serially connected normally closed switch
con-tacts coupled -to a second end of the stylus so as to initiate
opening of at least one of the swi-tch contacts whenever the contact
element touches the object;
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a comparator having first and second inputs and an ou-tput,
a reference potential coupled to the first comparator input; a
voltage source coupled to one end of the serially connected switch
contacts, with the other end of the switch contac-ts being coupled to
ground potential; the one end of the switch contac-ts being coupled
to the second comparator input whereby the resistance presented by
the switch con-tac-ts increases as at least one of the con-tacts begins
to open thereby increasing the potential at the second comparator
input from essentially ground poten-tial to a potential greater -than
the reference potential to thereby provide a touch indica-tor signal
at the output of the comparator;
modulator means having a first input coupled to -the crystal
controlled oscillator output and a second input coupled to the
compara-tor output, operative to alter the reference al-ternating
current signal and to present the al.tered signal at a modulator
means output in accordance with -the status of the touch indicator
signal at the second modulator means input; and
a source of infrared radia-tion having a control input
coupled to the modulator means output, operative to emit infrared
radiation having a magnitude and frequency determined by the
magnitude and frequency of -the altered signal.
In an apparatus for detecting contact with an object, said
apparatus including a probe having a housing and a stylus projecting
from one end of -the housing, the opposite end of the stylus being
connected to a plurality of switch contacts exhibiting a change in
electrical characteristic when the stylus contacts the object, there
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is provided according to one aspec-t of the invention the improvement
wherein the probe further comprises:
optical transmission means including at leas-t one
selectively energizable infrared light emitting device on -the
housing, opera-tive to transmi-t informa-tion to a remote receiver;
electrical circuit means for modulating the energization of
the infrared device according to a first predetermined manner when
the stylus is in a rest position, and being further operative to
modulate the energization of -the infrared device in a second manner
when the stylus contacts -the object; and
whereby the modula-ted infrared ligh-t can be detected by a
remote receiver spaced from -the probe to thereby de-tec-t s-tylus
con-tac-t with the objec-t.
There is fur-ther provided according -to the invention a
me-thod of detecting -the position of an object by using a probe
having a moveable stylus, said method comprising:
inserting the probe into a machine capable of moving the
probe relative to the object, the probe having a housing with at
least one infrared optical -transmission device loca-ted thereon and
wherein -the stylus projects from one end of -the housing, the stylus
being coupled to a plurali-ty of switch contacts whose elec-trical
characteristics are adap-ted to change when the stylus con-tacts an
object;
using -the optical transmission device to transmit an
optical signal which is modulated a-t a first frequency to a remo-te
receiver;
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using -the machine to move the probe relative to -the object
until the stylus contacts -the object -thereby creating a change in
elec-trical characteristic of at leas-t one of the switch contacts;
and
altering a characteris-tic of the transmitted op-tical signal
in response to stylus contact with -the object.
DRAWING
The invention will be more clearly understood from a
reading of a detailed description of a preferred embodiment, taken
in conjunction with the drawing, in which:
FIG. 1 is a schematic diagram of position de-tection
apparatus arranged in accordance wi-th -the principles of the
invention; and
FIG. 2 is a perspec-tive view of a housing for a probe and
position determining apparatus therefor, sui-table for use in
accordance with the principles of the invention.
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DETAILED C3FSCRIPTION
With reference -to Fig. 17 a preferrecl embodimen-t for the circuitry employecl
to eEfect the inventlon is shownO A quartæ crystal 100 is coupled between reverence
ground potential and an input 110 of controlled oscillator 101. Crystal 100 may be
5 selected from a variety of commercially available (e.g. from Interna$ional Crystal
Manufacturing Co.) components tc provide a preselected reference frequency source.
element 101 is a type MC 4001 (Motorola) gate configured as an oscillator.
output lll of controlled oscillator 101 is coupled to input 112 of
programmable divider 102, which may be comprised of a Motorola type MC 4526 divider.
Output l l3 of divider 102 is coupled to a first input of logic AND gate 104.
A reference potential source YREF is coupled via resistor 121 to input 115 of
comparator 103 and to input 116 of comparator 103 via resistor 120. Comparator 103
could, for example, comprise type LM 2903, commercially available from National
Semiconductor. Input 115 of comparator 103 is additionally coupled to reference ground
potential via resistor 122, while comparator input 116 is additionally coupled to a first
end of a serial connection of three normally closed contacts 130A, 130B, and 130C of a
mechanical switch type transducer 130. A second end of the serial connection is coupled
to reference ground potential.
With contacts 130A, 130B and 130C electrically coupled in a series circuit as
shown in Fig. 1, any contact beginning to open will cause the voltage seen at comparator
input 116 to approach that voltage appearing at comparator input 115 thereby causing an
indication of the contact movement at output 117 of comparator 103. A contact need
not fully open to generate an output at 1179 but need only be8in to show increasing
electrical impedance.
( ontacts 130A, 130B and 130C are mechanically arranged so as to reflect the
movement of a probe stylus, or other probé contact type surface, such as contactelement 331 of stylus 330 of Fig. 2. This mechanical arrangement is not specifcically
shown herein, but sucl- arrangements are known to those skilled in the art and are
disclosed, for example, in U.S. Patent 4,138,823- McMurtry or U.S. Patent 4,153,998-
McMurtry. A more recent particularly advantageous mechanical arrangement suitable
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for use with contac-ts 130A, 130B ancl 130C is disclosed ;n Canadian patent
application Serial No. 430,330, filed 14 June, 1983.
Re$urnirlg to fig 1, the inclication signal at comparator outpu-t 117 is utilized
S to alter the programmable divider output as seen at output 119 of AND gate 104 in one
of two ways, depending upon whether ampli-tude or iErequency modulation is to be usecl
with the transrnitted optical output signal of the position detection probe of the
invention.
When using the probe with frequency modulation, jumpers FM are employed
to couple the comparator output 117 to a frequency determining input 114 of
programmable clivider 102 and to couple a reference source ~Vlj representing the logic
ONEor TRUEs-tate, to input 118of ANDgate 104.
When the probe apparatus is used with amplitude modulation, jumper f\M is
connected as shown and jumper F;M removed, thereby coupling comparator outpu-t 117 to
AND gate input 118 and Icavillg frequency determining input 11l~ unconnected As will
be apparent to those skillecl in the art, input 114 of divider 102 may be recluired to be
grounded to prevent damage to the divider in the ALA mode rather than simply left open
circuited, especially where divider 102 is comprised of a MOSFET~type integrated circuit
device. One approach which would avoid option jumper strappingj would- be to
permanently tie input 114 -to ground via a relatively high valued lesis-tor Also apparent
to those skilled in lhe art, divider 102 could be removed in the AM option, with the
output of a suitably driven oscillator 101 coupled directly to AND gate 104.
The control input to LEr~ array 600 is coupled to the output 119 of a
modulator comprising divider 102 and AND gate 104 at node 620 and is then coupled to
inputs of inver-ters 601 and 602.
on output ox inverter 601 is coupled via resistor 610 to a gate electrode of
MOS~ET 605. The ga te elec trocle of MOSFET 605 is also coupled to a collec tor
electrode of ga-Le driv e current regulating NPN transistor 603, whose emitter electrode
is couplecl to ground potential. A base electrode oL transistor 603 is coupled to a source
electrc,de of iv~oSFET 605 and to a Eirs-t terminal of drive current sensing resistor 612. A
second lerminal of resistor 612 is coupled -to ground potential. A drain electrocle oI
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MOSFET 605 is coupled to a cathode electrode of infrared light emitting diode 607A,
whiclI is series connec-tecl witll tllree aclclitional Lids 60713-D. An anocle electrode of
607D is coupled to DC source Vl. Transistor 603 is utilized as configured to main-tain a
substantially constant drive current via ~lOSFET 605 to light emitting diodes 607A-D at
5 an optimum opera-ting level for such cliodes.
Circuitry identical -to that described above in conjunction with MOSFET 605
is coupled between an output of inver~er 602 and four serially connected infrared l elms
608A-D. It will be apparen t there:fore, that node 620 may be multipled to as many
inverter inputs as necessary to provide a desired total number of ligiIt emitting diodes,
10 clriven in serially connec-tecl groups of four
With reference to I~ig. 2, housing 10 for a probe, such as probe stylus 330 of
Fig. 2, is shown in perspective. Housing 10 contains all -the apparatus described above in
conjunction with fig 1. The infra-red LED's of Fig. 1 are shown at 607, 608 of Fig. 2 as
a circular array, moun-ted to substantially cylindrical exterior housing surface 12, and
l capable of emitting infrared radiation in a full 360 clegree pattern. it an encl of housing
10 opposite the probe rmo-lnting end, a suitable aclaptor 14 is provided. The adaptor 14
shown in Fig. 2 ailows housinE 20 to be incorporated into an NC macl-ining center in the
same way as a typical cutting tool. Alternatively, housing.10 could be hand-held by a
human operator or an appropriate hous;ng adaptor or extension could be provided
20 enabling use of the housing by the "hand" or gripping elemen-t of an automaton, such as
an industrial robot.
Elongate s-tylus 330 may be equipped at i-ts end contacting terminus with a
suitably shaped contact element 331. ale commonly useful shape is a spherical surface.
element 331 may advantageously be fashioned from a wear resistant material, such as
25 cemented carbide. Stylus 330 is couplecl to a follower element, or wobble plate, within
housh~g 10 in a manlIer describecl in the above referenced pending application Serial No.
430, 330.
Wi lh tl-e compolIen ts of lie position cle tec tion appara tus arrangeci as describ-
ed above, the general operation in the frecluency moclula-tion mode is as follows. A
30 sui-table quart crystal is chosen to provide the base driving frequelIcy for controllecl
oscillator 101. In the rest sta-te, wi-tl- no probe contact inclication frorn cornparator 103,
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a carrier frequency is derived from the output of programmable divider 102 and coupled
to optical source 600 via AND gate 119. The preferred range of output frequency from
divider 102 is 150 kHz to 500 kHz, which will provide an infrared signal having a
frequency high enough to be easily distinguishable from background light source noise,
5 yet low enough to be used eEficiently with commercially available light-emitting diodes
607, 608 and PIN diodes at the remote receiver snot shown. Divider 102 divides the
input signal frequency at input i 12 by a first number, e.g. 12, when no indication signal is
present at frequency determining input 114, and by a second number, e.g. 13, ~,vhenever
the indicator signal indicative of probe contact is presented to input 114 by comparator
10 output 117 and an FM jumper connected as shown in Fig. 1. The other FM jumper in Fig.
I will maintain AND gate 104 in the enabled state to pass a signal having one of two
frequencies determined by divider 102 to the input of optical source 600.
Operation of the probe apparatus in the AM mode of Fix. 1 is as follows.
Divider 102 will pass a carrier of a fixed frequency iince no connection in this mode is
15 made to frequency determining input 11~. Hence, when no indicator signal is present at
comparator output 117, AND gate 10~ will be disabled thereby cutting off the carricr
signal from optical source 600. whenever the probe stylus assumes the position relative
a workpiece to be detected, AND gate 104 will be enabled by comparator output 117 to
pass the carrier signal through the source 600. If the opposite signaling convention is
20 desired, i.e. to provide carrier except when the probe stylus assumes -the detectable
position, then a logical invertor, or NOT gate, could be coupled between comparator
output 1 17 and input 1 18 of AND gate 104.
It should be noted that the invention described herein has been illustrated
with reference to a preferred embodiment. It is to be understood that many details used
25 to facilitate the description of sucl- an embodiment are chosen for convenience only and
without limitation on the scope ox the invention as set forth in the appended claims.
