GB2145523A - Coatings for contacts of a touch probe - Google Patents

Coatings for contacts of a touch probe Download PDF

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Publication number
GB2145523A
GB2145523A GB08421175A GB8421175A GB2145523A GB 2145523 A GB2145523 A GB 2145523A GB 08421175 A GB08421175 A GB 08421175A GB 8421175 A GB8421175 A GB 8421175A GB 2145523 A GB2145523 A GB 2145523A
Authority
GB
United Kingdom
Prior art keywords
probe
stylus
members
contacts
electrically conductive
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB08421175A
Other versions
GB8421175D0 (en
Inventor
Gregory Keith Campbell
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Valenite LLC
Original Assignee
GTE Valeron Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by GTE Valeron Corp filed Critical GTE Valeron Corp
Publication of GB8421175D0 publication Critical patent/GB8421175D0/en
Publication of GB2145523A publication Critical patent/GB2145523A/en
Withdrawn legal-status Critical Current

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Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H1/00Contacts
    • H01H1/02Contacts characterised by the material thereof
    • H01H1/021Composite material

Abstract

A probe for detecting contact with an object such as a workpiece includes a switch assembly having one or more point contacts 20,22 therein which develop a change in electrical resistance when the probe stylus moves from its rest position upon contacting the object. The contact members are coated with a homogeneous, chemically inert, and electrically conductive material to maintain precise mechanical repeatability and consistent electrical characteristics of the probe. Preferably, the coating material is selected from the group of titanium nitride and titanium carbide where the contacts are made of tungsten carbide. <IMAGE>

Description

SPECIFICATION Coatings for contacts of a touch probe Technical Field This invention relates to probes for detect ing contact with an object such as a work piece. More particularly, the invention in volves the construction of the contacts used in such probes that develop a change in electrical characteristics as a result of the probe touching the object.
Background Art Automatic machining systems and coordi nate measuring systems require a precise means for locating surfaces on workpieces.
One method of such measurement is to utilize a so-called "touch probe" in which a stylus is moved into a position where it touches the surface resulting in a movement of the stylus from its rest position. The probe includes one or more point contacts whose electrical characteristics, generally resistance, are changed as a result of movement of the stylus. This change in electrical characteristic is typically made by opening the point contacts and detecting the resultant change in electrical resistance by suitable electrical circuitry. The signal from the probe is used in conjunction with a determination of the X, Y and Z axes location of the table or machine spindle to calculate the position of the inspected workpiece surface.
The usefulness of these touch probes depends upon their extreme repeatability. It is often desirable to provide a probe that is capable of repeating its measurement to within about one micron or less. In other words, if the probe is used to make several measurements on the same workpiece surface, the calculated position thereof cannot deviate more than about one micron.
In order to provide and maintain touch probes with this kind of repeatability over a period of time there are two basic requirements. The first is that the contacts must return to exactly the same position whenever external contact force is removed from the probe stylus. This requirement is referred to as mechanical positional repeatability. The second requirement is the electrical resistance between the contacts remains constant whenever the stylus returns substantially to its rest position.
The mechanical repeatability requirement generally necessitates the use of one or more point contacts. Touch probes of the assignee of the present invention have utilized a spherical surface against a flat surface to define the point contacts (see, e.g. U.S. Serial No.
388,187, filed June 14, 1982 by Cusack entitled "Touch Probe"). Other types of touch probes utilize a spherical surface trapped by two converging spherical or flat surfaces (see, e.g. U.S. patent Nos. 4,155,171 to McMurtry; 4,270,275 to McMurtry and 4,301,338 to McMurtry).
Cemented carbide is typically used as the material for the contacts. Unfortunately, the grains of the binder metal do not have exactly the same electrical characteristics as the carbide particles. Thus, the electrical characteristics thereof may change if the location of the point contact changes from an area of binder metal to that of carbide. In addition, the binder metal has a tendency to oxidize creating an uneven surface even after polishing.
The oxidation rate is further increased when electrical current passes through the contacts.
Whether the surface roughness is created by oxidation or otherwise, it affects the mechanical repeatability of the probes using these contacts.
In an effort to overcome these problems the contacts have, in the past, been covered with a neutral pH value oil such as baby oil, mineral oil or the like. However, the oil has a tendency to become displaced from the contacts after a period of use so that the contacts again become exposed to the air and other sources of contamination. In addition,the oil is somewhat messy and can also flow over other parts in the probe. Consequently, this approach has not been entirely satisfactory in overcoming the problems noted above.
Summary of the Invention Pursuant to the present invention the contacts are coated with a homogeneous, chemically inert electrically conductive material. Preferably, the contacts are made of tungsten carbide and the coating material is selected from the group of titanium nitride and titanium carbide. These coatings are harder than the tungsten carbide and compatible therewith. Since the coating material is inert the contacts do not corrode and the aforementioned problems with mechanical repeatability are avoided. In addition, the homogeneous nature of the coatings maintain consistent electrical resistance characteristics for the contacts even after prolonged usage of the probes.Consequently, the problems associated with the prior art approach are substantially eliminated while at the same time avoiding the undesirable side effects resulting from the conventional practice of applying oil to the contacts.
Brief Description of the Drawing The various advantages of the present invention will become apparent to those skilled in the art upon reading the following specification and by reference to the drawings in which: FIGURE 1 is a plan view in partial cross section of a touch probe utilizing the teachings of the present invention; FIGURE 2 is a cross-sectional view along the lines 2-2 of FIGURE 1; FIGURE 3 is a partial cross-sectional view similar to that of FIGURE 1 depicting the probe stylus in a displaced position under a contact force; FIGURE 4 (A-B) are enlarged cross-sectional views of two probe contact members of the PRIOR ART; and FIGURE 5 is a cross-sectional view showing contact members made in accordance with the preferred embodiment of this invention.
Description of the Preferred Embodiment FIGURES 1 and 3 illustrate a touch probe 10 of the type in which the improvements of the present invention find particular utility.
The details of the construction of probe 10 are disclosed in U.S. Serial No. 388,187 filed June 14, 1 982 and assigned to the assignee of the instant invention. Therefore, only those details necessary to an understanding of the present invention will be described.
Probe 10 includes a stylus 1 2 projecting from one end of housing 14 through an aperture therein. The probe 10 also includes an adapter section 1 5 which may, for example, include a machine tool industry standard taper which is configured for receipt in a complimentary socket of a machine tool spindle. A variety of other adapter configurations is well within the knowledge of the skilled practioner and known in the art.
A diaphragm 1 6 surrounds stylus 1 2 in the area of the aperture to protect the internal components from contamination. The rearward end of stylus 1 2 is connected to a switch assembly generally designated by the numeral 1 8. The purpose of switch assembly 1 8 is to change an electrical characteristic whenever the stylus 1 2 contacts an object and moves from its rest position, i.e. when the stylus 1 2 contacts an object. In the illustrated embodiment, this is accomplished by way of three of point contacts, two of them bearing the reference numerals 20 and 22.
Each point contact is defined by a first electrically conductive member having a spherical surface and a second electrically conductive member opposing the first. In this embodiment, the contacts 20 and 22 are each defined by a ball 24 and a pad 26. The balls 24 are affixed to a pivot plate 30 connected to the rearward end of stylus 12. The pads 26, on the other hand, are mounted to a fixed reference surface provided by member 32.
A reed spring 34 is connected at one end to pivot plate 30 and at another end to member 32. The purpose of reed spring 34 is to urge the contacts together in the absence of contact force being exerted on stylus 1 2 as shown in FIGURE 1. A spring 36 may also be provided to give additional bias force parallel to the longitudinal axis of stylus 1 2 thereby urging plate 30 and member 32 into a rest position via engagement of the contacts.
As shown in FIGURE 3, deflection of the stylus 1 2 causes deflection of pivot plate 30 thereby displacing one of the contacts depending upon the direction of stylus movement. In FIGURE 3, contact 20 is shown displaced thereby opening the electrical connection defined by ball 24 and pad 26. This change in electrical characteristic can be detected in a variety of ways well within the knowledge of those skilled in the art. One such technique is disclosed in U.S. Serial No.
259,257 file April 30, 1981 and assigned to the same assignee as the present invention.
Basically, circuitry 40 is used to detect the opening of one of the contacts and initiate the transmission of an optical signal via infrared light emitting diode 42. The signal from diode 42 can be used by a machine controller to calculate the position of the probe and therefore the location of the surface that it contacted. The above-mentioned applications are hereby incorporated by reference. It should be understood, however, that various other probe contact arrangements and detecting schemes can also be utilized.
It can be appreciated that the accuracy of this general approach requires mechanical repeatability and consistent electrical characterisitcs developed between the contacts. Reference to FIGURE 4 will help in the understanding of some of the problems with the contact construction of the prior art. In FIGURE 4 the pad and ball making up the point contact of the prior art design bear a prime superscript.
The pad 26' is shown in exaggerated manner with uneven surface. As noted above, this uneven surface has a tendency to develop after a period of use of the probe due to such things as oxidation and the like. If the ball 24' contacts a peak in the surface of pad 26' as shown in FIGURE 4A, then the stylus 12 will be in a given rest position which is a function of the distance Y. If the ball 24' is contacting a carbide particle making up the peak of the pad 26' surface there will be a given electrical resistance developed therebetween. FIGURE 4B illustrates a situation in which the ball 24' has fallen into a valley in the uneven surface of pad 26'. In such situations the rest position of stylus 1 2 will be different from that shown in FIGURE 4A. This is represented by the difference in distances Y and Y'. Accordingly, the probe 10 cannot repeat the same measurement with the same results thereby disturbing its accuracy. Additionally, if the ball 24 is contacting dissimilar materials such as a binder metal then the electrical characteristics will also be different thereby further increasing the potential for inaccurate measurements.
Pursuant to the present invention, these and other problems are solved by coating the contact members with a homogeneous, chemically inert, electrically conductive material. preferably, the bodies of the contact members are made of cemented carbides, for example fine tungsten carbide particles bonded or cemented with a tough, comparatively soft binder metal, such as cobalt. It is to be understood that the term "cemented carbide" as used herein may, in addition to tungsten carbide, include commercially available materials in which the tungsten carbide is frequently supplemented or substituted by the carbides of titanium, tantalum, niobuim, chromium, vanadium, molybdenum or hafnium, independently or in combination, while the cobalt binder may similarly be alloyed with, or substituted by, nickel or nickel-molybdenum.One type of cemented carbide found suitable for the purposes of the invention is grade VC-2, commercially available from The Valeron Corporation, Troy, Michigan.
Preferably, the cemented carbide contact bodies are coated with a layer selected from the group of titanium nitride and titanium carbide. Titanium nitride is preferred because of its better electrical conductive characterisitics. As shown in FIGURE 5 the body 40 of ball contact 24 includes coating 42 and the body 44 of pad 26 includes coating 46.
Coatings 42 and 46 are characterized by extremely hard conductive surfaces exhibiting a Rockwell hardness in the C scale. The coatings 42 and 46 resist oxidation and thereby retain their smooth surface configuration. In addition, the homogeneity of the coatings insures consistent electrical resistance characteristics therebetween.
In producing the contact members the tungsten carbide bodies are preferably lapped to about 95% of their desired ultimate surface finish. For example, it is preferable to have an ultimate surface finish of about 2-3 RMS and, therefore, the carbide bodies are lapped to about a 5 RMS finish. The contact bodies are then coated with a layer about 2-3 microns in thickness. The bodies are preferably coated using a chemical or physical vapor deposition process. After the coatings have been applied the coated contact members can be lapped down to their final finish, if necessary. By using a physical vapor deposition process this latter lapping step may be eliminated.
Those skilled in the art can now appreciate the present invention may provide probes of these types with exceedingly long useful lives by fulfilling the dual requirements of mechanical repeatability and consistent electrical characterisitics for the contacts. It eliminates the conventional use of oil in the probe, an approach which has not proven to be entirely satisffactory in the long run. It should be understood that while this invention was described in connection with specific examples thereof, various modifications will become apparent to those skilled in the art after a study of the specification, drawings and following

Claims (9)

claims. CLAIMS
1. In a probe for detecting contact with an object, said probe including a stylus projecting from one end thereof having a tip adapted to touch the object resulting in movement of the stylus from a rest, position, and switch assembly means connected to the other end of the stylus for developing a change in electrical characteristic when the stylus moves from its rest position, the improvement wherein:: said switch assembly means includes at least one point contact defined by a first electrically conductive member having a nonplanar surface and a second electrically conductive member having a surface located generally opposite to that of the non-planar surface of the first member, one of the members being movable with the stylus and the other member being fixed, and said surfaces of the members being coated with a homogeneous, chemically inert, electrically conductive coating material to thereby maintain precise mechanical repeatability and consistent electrical characteristics of the probe.
2. The improvement of claim 1 wherein said members have bodies comprising cemented carbide particles in a binder metal and said coating material is selected from the group of titanium nitride and titanium carbide.
3. The improvement of claim 2 wherein one member is in the shape of a ball and the surface of the other member is generally flat.
4. The improvement of claim 2 wherein said members are coated with said coating material to a thickness of about 2-3 microns.
5. A method of making contact members for use in a touch probe, said method comprising: vapor depositing a coating of titanium nitride or titanium carbide onto bodies made of cemented carbide.
6. A method of making contact members for use in a touch probe, said method comprising: vapor depositing a homogeneous, chemically inert, electrically conductive coating material onto electrically conductive bodies.
7. A method of making contact members for use in a touch probe, such method being substantially as herein described with reference to the accompanying drawings.
8. A probe for detecting contact with an object, such probe being constructed and arranged substantially as herein described with reference to and as illustrated in the accompanying drawings.
9. A switch assembly for a probe, such switch assembly being constructed and arranged to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.
GB08421175A 1983-08-26 1984-08-21 Coatings for contacts of a touch probe Withdrawn GB2145523A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US52659383A 1983-08-26 1983-08-26

Publications (2)

Publication Number Publication Date
GB8421175D0 GB8421175D0 (en) 1984-09-26
GB2145523A true GB2145523A (en) 1985-03-27

Family

ID=24097966

Family Applications (1)

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GB08421175A Withdrawn GB2145523A (en) 1983-08-26 1984-08-21 Coatings for contacts of a touch probe

Country Status (6)

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JP (1) JPS6091201A (en)
BE (1) BE900428A (en)
DE (1) DE3431476A1 (en)
GB (1) GB2145523A (en)
IT (1) IT1237348B (en)
SE (1) SE8404219L (en)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2180404A (en) * 1985-09-06 1987-03-25 Ashley Accessories Ltd Switch having pivoted bridging contact
US5272817A (en) * 1991-02-28 1993-12-28 Renishaw Metrology Limited Signal conditioning circuit for trigger probe
US5319858A (en) * 1990-11-24 1994-06-14 Renishaw Plc Touch probe
WO2003035541A2 (en) * 2001-10-15 2003-05-01 Infineon Technologies Ag Probe needle for testing semiconductor chips and method for producing said probe needle
WO2004031684A1 (en) * 2002-10-07 2004-04-15 Marposs Società per Azioni Touch probe comprising a switch with contacts protected by inert gas
US7168179B2 (en) 2003-09-29 2007-01-30 Marposs Societa ' Per Azioni Touch probe comprising a switch with contacts protected by inert gas
DE102006012095A1 (en) * 2006-03-14 2007-09-20 Wolfgang Madlener Touch sensor for detecting movement of sensing stylus, has idle state mechanism with touch sensor holder having carrier unit and seat unit, where carrier and seat units are made of hard metal e.g. nickel
US8673213B2 (en) 2004-03-10 2014-03-18 Roche Diagnostics Operations, Inc. Test element analysis system with contact surfaces coated with hard material
US9835653B2 (en) 2014-05-13 2017-12-05 International Business Machines Corporation Solder bump array probe tip structure for laser cleaning

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0428740A1 (en) * 1989-05-10 1991-05-29 The Furukawa Electric Co., Ltd. Electric contact material, method of producing said material, and electric contact produced therefrom
JP4072282B2 (en) * 1999-04-07 2008-04-09 日新産業株式会社 Position detector and its contact needle

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1124822A (en) * 1964-08-15 1968-08-21 Hitachi Ltd Automobile electrical contacts for use in distributors and contact breakers for internal combustion engines
GB1242004A (en) * 1967-11-13 1971-08-11 Westinghouse Electric Corp Electrical contact assembly
GB1445977A (en) * 1972-09-21 1976-08-11 Rolls Royce Probes
GB1531209A (en) * 1976-10-01 1978-11-08 Bendix Corp Sensing probe
GB1586052A (en) * 1977-03-19 1981-03-18 Zeiss Stiftung Measurement head
GB1597842A (en) * 1977-02-07 1981-09-09 Rolls Royce Indexing mechanism
EP0074630A2 (en) * 1981-09-11 1983-03-23 Western Electric Company, Incorporated Apparatus including electrical contacts

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE622522C (en) * 1932-08-06 1935-11-29 Metallwerk Plansee G M B H Electrical contact material that contains one or more carbides in addition to one or more lower melting and softer metals
US2180956A (en) * 1937-09-29 1939-11-21 Mallory & Co Inc P R Electric contacting element
NL85511C (en) * 1954-03-31
DK653473A (en) * 1973-12-04 1975-07-21 Danfoss As
GB1593050A (en) * 1976-09-30 1981-07-15 Renishaw Electrical Ltd Contact sensing probe

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1124822A (en) * 1964-08-15 1968-08-21 Hitachi Ltd Automobile electrical contacts for use in distributors and contact breakers for internal combustion engines
GB1242004A (en) * 1967-11-13 1971-08-11 Westinghouse Electric Corp Electrical contact assembly
GB1445977A (en) * 1972-09-21 1976-08-11 Rolls Royce Probes
GB1531209A (en) * 1976-10-01 1978-11-08 Bendix Corp Sensing probe
GB1597842A (en) * 1977-02-07 1981-09-09 Rolls Royce Indexing mechanism
GB1586052A (en) * 1977-03-19 1981-03-18 Zeiss Stiftung Measurement head
EP0074630A2 (en) * 1981-09-11 1983-03-23 Western Electric Company, Incorporated Apparatus including electrical contacts

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2180404B (en) * 1985-09-06 1990-04-04 Ashley Accessories Ltd Electric isolater switch
GB2180404A (en) * 1985-09-06 1987-03-25 Ashley Accessories Ltd Switch having pivoted bridging contact
US5319858A (en) * 1990-11-24 1994-06-14 Renishaw Plc Touch probe
US5272817A (en) * 1991-02-28 1993-12-28 Renishaw Metrology Limited Signal conditioning circuit for trigger probe
US7212019B2 (en) * 2001-10-15 2007-05-01 Infineon Technologies Ag Probe needle for testing semiconductor chips and method for producing said probe needle
WO2003035541A2 (en) * 2001-10-15 2003-05-01 Infineon Technologies Ag Probe needle for testing semiconductor chips and method for producing said probe needle
WO2003035541A3 (en) * 2001-10-15 2003-08-14 Infineon Technologies Ag Probe needle for testing semiconductor chips and method for producing said probe needle
WO2004031684A1 (en) * 2002-10-07 2004-04-15 Marposs Società per Azioni Touch probe comprising a switch with contacts protected by inert gas
US7168179B2 (en) 2003-09-29 2007-01-30 Marposs Societa ' Per Azioni Touch probe comprising a switch with contacts protected by inert gas
US8673213B2 (en) 2004-03-10 2014-03-18 Roche Diagnostics Operations, Inc. Test element analysis system with contact surfaces coated with hard material
US9638655B2 (en) 2004-03-10 2017-05-02 Roche Diagnostics Operations, Inc. Test element analysis system with contact surfaces coated with hard material
DE102006012095A1 (en) * 2006-03-14 2007-09-20 Wolfgang Madlener Touch sensor for detecting movement of sensing stylus, has idle state mechanism with touch sensor holder having carrier unit and seat unit, where carrier and seat units are made of hard metal e.g. nickel
DE102006012095B4 (en) * 2006-03-14 2017-01-05 M & H Inprocess Messtechnik Gmbh feeler
US9835653B2 (en) 2014-05-13 2017-12-05 International Business Machines Corporation Solder bump array probe tip structure for laser cleaning
US10571490B2 (en) 2014-05-13 2020-02-25 International Business Machines Corporation Solder bump array probe tip structure for laser cleaning

Also Published As

Publication number Publication date
JPS6091201A (en) 1985-05-22
DE3431476A1 (en) 1985-03-07
IT1237348B (en) 1993-05-31
BE900428A (en) 1984-12-17
SE8404219D0 (en) 1984-08-24
SE8404219L (en) 1985-02-27
IT8422423A0 (en) 1984-08-24
GB8421175D0 (en) 1984-09-26

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WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)