CA1226351A - Apparatus for detecting the position of a probe relative to a workpiece - Google Patents

Abstract

APPARATUS FOR DETECTING THE POSITION OF A PROBE
RELATIVE TO A WORKPIECE

ABSTRACT
Apparatus for detecting the position of a probe relative to a workpiece, for example probe contact with the workpiece, is disclosed. The apparatus includes atransducer for converting probe contact to an electrical signal and a plurality of light emitting semiconductors for wirelessly transmitting an indication of the occurrence of the signal via infrared radiation. The apparatus is particularly suitable for operation with a mechanical switch type probe transducer. The apparatus is easily adapted to transmit the occurrence of probe contact by either amplitude modulation or frequency modulation of the emitted infrared radiation.

Description

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.

-3-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 -3b-~,~

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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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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 Z635~
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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, 2;~635~
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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.

Claims (18)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for detecting a position of a probe relative to an object comprising;
a probe body surface whose position relative to an object 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 said position, and detector means coupled to the means coupled to the probe bodysurface, operative to generate an indicator signal at a transducer means output indicative of said characteristic change;
modulator means having a first input coupled to the oscillator means output 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 control input coupled to the modulator means output, operative to emit optical radiation having a characteristic determined by the modulation means output.

2. Apparatus as set forth in Claim 1 wherein the modulator means is operative to alter the frequency of the reference alternating current signal upon receipt of the indicator signal.

3. Apparatus as set forth in Claim 1 wherein the modulator means is operative to alter the amplitude of the reference alternating current signal upon receipt of the indicator signal.

4. Apparatus as set forth in Claim 1 wherein the transducer means further comprises first and second reference potential sources; wherein the means coupled to the probe body surface comprises a plurality of switch contacts 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, said comparator having a first input coupled to the first reference potential source,and a second input coupled via the series circuit of switch contacts to the second reference potential in a manner such that signal levels at the first and second inputs to the comparator will approach substantial equality whenever any one of the switch contacts begins to exhibit an altered inpedance thereacross, thereby enabling the comparator to generate the indicator signal at its output.

5. Apparatus as set forth in Claim 4 wherein the modulator means includes;
a programmable divider having an input providing the modulator means first input for receipt of the reference alternating current signal, and a frequency determining input providing the modulator means second input for receipt of the indicator signal, operative to divide the frequency of the reference alternating current signal by a first number whenever the indicator signal is not present and by a second number whenever the indicator signal is present and to present the resultant divided frequency signal at a programmable divider output; and means for coupling the divider output to the modulator means output.

6. Apparatus as set forth in Claim 4 wherein the modulator means comprises logic gate means having a first input coupled to the modulator means first input for receipt of the reference alternating current signal, a second input coupled to the modulat?
means second input for receipt of the indicator signal, and an output providing the modulator means output the logic gate means operative to alter the amplitude of the reference alternating current signal in accordance with the status of the indicator signal and to present the altered amplitude signal at the logic means output.

7. Apparatus as set forth in Claim 6 wherein the logic gate means is operative to reduce the amplitude of the reference alternating current signal to zero whenever the indicator signal is generated.

8. Apparatus as set forth in Claim 6 wherein the logic gate means is operative to reduce the amplitude of the reference alternating current signal to zero whenever the indicator signal is not generated.

9. Apparatus as set forth in Claim 1 wherein the emitted optical radiation is in the infrared frequency spectrum.

10. Apparatus as set forth in Claim 9 further comprising:
a housing for the apparatus having an exterior surface portion; and wherein the optical source includes a plurality of infrared light emitting diodes mounted at the surface portion such that infrared radiation is emitted in a preselected pattern.

11.Apparatus as set forth in Claim 10 wherein the exterior surface portion s substantially cylindrical and the plurality of diodes is mounted about the cylindrical surface so as to emit infrared radiation in a substantially full circular pattern.

12.Apparatus as set forth in Claim 1 further comprising an elongate stylus coupled to the transducer means at one end thereof; and wherein the probe body surface comprises a contact element coupled to a second end of the elongate stylus.

13.Apparatus as set forth in Claim 1 wherein the position relative to the workpiece comprises physical contact between the probe body surface and the workpiece.

14.Touch probe apparatus for detecting contact between 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 at an oscillator output;
at least three serially connected normally closed switch contacts coupled to a second end of the stylus so as to initiate opening of at least one of the switch contacts whenever the contact element touches the object;
a comparator having first and second inputs and an output, a reference potential coupled to the first comparator input; a voltage source coupled to oneend of said serially connected switch contacts, with the other end of the switchcontacts being coupled to ground potential; said one end of the switch contacts being coupled to the second comparator input whereby the resistance presented bythe switch contacts increases as at least one of the contacts begins to open thereby increasing the potential at the second comparator input from essentiallyground potential to a potential greater than the reference potential to thereby provide a touch indicator 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 comparator output, operativeto alter the reference alternating current signal and to present the altered 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 radiation 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.

15. Apparatus as set forth in Claim 14 wherein the modulator means comprises:
a programmable divider operative to divide the frequency of a signal coupled to an operand input of the divider by one of two divisors respectively determined by the presence and absence of a programming signal at a programming input of the divider and further operative to present the division result at a divider output, with the operand input coupled to the crystal controlled oscillator output and the programming input coupled to the comparator output; and means for coupling the divider output to the control input of the infrared radiation source.

16.Apparatus as set forth in Claim 15 wherein the means for coupling the divider output comprises a logic AND gate having first and second inputs and an output coupled to the control input of the radiation source;
wherein frequency modulation of the reference alternating current signal is effected in a first optional configuration by coupling the comparator output to the programming input, coupling the first AND gate input to the divider output, and coupling the second AND gate input to a logic TRUE signal level so as to maintain the AND gate in an enabled state; and wherein amplitude modulation of the reference alternating current signal is effected in a second optional configuration by coupling the comparator output to the second AND gate input, disconnecting the programming input from the comparator output, and coupling the first AND gate input to the divider output.

17.Apparatus as set forth in Claim 14 wherein said reference potential is developed by coupling one end of a series connection of two fixed resistors to said voltage source and coupling the other end thereof to ground potential, withthe first comparator input being connected between the two resistors.

18.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 switchcontacts exhibiting a change in electrical characteristics when the stylus contacts the object, the improvement wherein the probe further comprises:
optical transmission means including at least one selectively energizable infrared light emitting device on the housing, operative to transmitinformation 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 said modulated infrared light can be detected by a remote receiver spaced from the probe to thereby detect stylus contact with the object.l9.The improvement of Claim 18 wherein said optical transmission means comprises a plurality of infrared light emitting diodes.
20.The improvement of Claim 19 wherein said probe housing includes a cylindrical portion and the light emitting diodes are mounted thereon in substantially a full circular pattern.
21.The improvement of Claim 18 wherein said electrical circuit means includes:
first means for providing an alternating current signal having a preselected frequency at an output thereof;
second means coupled to the first means for altering the frequency of the signal from the first means when the probe stylus contacts the object; and means for coupling the alternating current signal to said optical transmission means whereby the optical transmission means transmits an optical signal of a first frequency when the stylus is not touching the object and transmits an optical signal of a second frequency when the stylus contacts the object.

22.The improvement of Claim 18 wherein said electrical circuit means includes:
first means for providing a reference alternating current signal having a preselected frequency at an output thereof;
second means coupled to the first means, operative to change the amplitude of said reference signal at an output thereof when the stylus contactsthe object; and means for coupling the output of said second means to said optical transmission means whereby said optical transmission means transmits an optical signal of a first amplitude when the stylus is not contacting the object and transmits an optical signal of a different amplitude when the stylus contacts the object.
23.The improvement of Claim 22 wherein said second means includes logic gate means adapted to remove the reference signal from said optical transmissionmeans when the stylus contacts the object so that no optical signal is transmitted during periods of stylus contact with the object.
24.A method 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, said probe having a housing with at least one infrared optical transmission device located thereon and wherein the stylus projects from one endof the housing, said stylus being coupled to a plurality of switch contacts whose electrical characteristics are adapted to change when the stylus contacts an object;
using said optical transmission device to transmit an optical signal which is modulated at a first frequency to a remote receiver;
using the machine to move the probe relative to the object until the stylus contacts the object thereby creating a change in electrical characteristic of at least one of said switch contacts; and altering a characteristic of the transmitted optical signal in response to stylus contact with the object.
25.The method of Claim 24 wherein the characteristic of the transmitted optical signal is its frequency and it is altered by shifting the frequency thereof.