United States Patent [19J
`Marinaccio et al.
`
`[54] CONTACT DIGITIZER, PARTICULARLY
`FOR DENTAL APPLICATIONS
`
`[75]
`
`Inventors: Paul J. Marinaccio, East Orleans;
`Bruce Nappi, Reading; Khushroo M.
`Captain, Cambridge; Alan J. Lane,
`Lexington, all of Mass.
`
`[73] Assignee: Foster-Miller, Inc., Waltham, Mass.
`
`[21] Appl. No.: 682,001
`
`[22] Filed:
`
`Apr. 8, 1991
`
`Int. Cl.5 .............................................. A61C 19/04
`[51]
`[52] U.S. Cl . ...................................... 433/72; 128/776;
`33/503; 33/513
`[58] Field of Search ............... 433/72, 75, 76; 409/92,
`409/126, 98, 99, 103, 114, 121, 124; 364/474.03,
`474.29; 33/503, 504, 513, 514; 128/776
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`1,387,329 8/1921 Stark ..................................... 433/76
`4,575,805 3/1986 Moennann et al. ................ 364/474
`4,997,369 3/1991 Shafir .................................... 433/72
`5,017,139 5/1991 Mushabac ............................. 433/72
`
`FOREIGN PATENT DOCUMENTS
`0040165 11/1981 European Pat. Off ..
`0091876 10/1983 European Pat. Off ..
`0110797 6/1984 European Pat. Off. .
`1194061 5/1959 France.
`75885 7/1961 France .
`157456 1/1962 U.S.S.R ..
`2140308 11/1984 United Kingdom .................. 433/75
`
`OTHER PUBLICATIONS
`Brochure, "Announcernent-Procera Station Installed",
`Nobelpharma, Feb. 1991.
`
`I 111111111111111111111 IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIIII Ill lllll llll
`US005131844A
`5,131,844
`[11] Patent Number:
`[45] Date of Patent:
`Jul. 21, 1992
`
`Brochure, "DCS-Titansystem Dux 1 ", Girn-Alldent,
`Germany.
`Matts Andersson et al., "Clinical results with titanium
`crowns fabricated with machine duplication and spark
`erosion", Acta Odontol Scand 47, pp. 279-286 (1989).
`Brochure, "Capture 3-Dimensional Position Data In(cid:173)
`stantly From Any Object-The Perceptor", Micro
`Control Systems, Inc.
`Primary Examiner-Cary E. O'Connor
`Attorney, Agent, or Firm-Ostrolenk, Faber, Gerb &
`Soffen
`ABSTRACT
`[57]
`A dental surface tracer includes a probe with a tip that
`can be moved to trace a given dental surface, including
`a mounting device for mounting the tracer to a stable
`reference location and defining a base plane; a first
`plurality of links which are substantially coplanar and_
`define a plane of movement; the links being pivotably
`attached to the mounting device so that the plane of
`movement makes a variable angle with the base plane; a
`distal one of the first plurality of links being movable in
`t\VO dimensions within the plane of movement; circuitry
`for generating electrical signals representative of move(cid:173)
`ments of the probe tip, as a function exclusively of
`movements of the first plurality of links; a dental hand(cid:173)
`piece supporting the probe; and a second plurality of
`links which hold the handpiece and are attached to the
`first plurality oflinks; the second plurality oflinks hold(cid:173)
`ing the probe tip at all times at a fixed location in the
`plane of movement with respect to the distal link of the
`first plurality of links; and permitting the handpiece to
`move about three axes without moving the probe tip
`from the fixed location. The entire tracer exclusive of
`the handpiece is sized to be accommodated within the
`human mouth.
`
`31 Claims, 7 Drawing Sheets
`
`FIRST-+
`JOINT
`
`SIXTH
`JOINT
`
`Align EX1016
`Align v. 3Shape
`IPR2022-00144
`
`

`

`U.S. Patent
`U.S. Patent
`
`July 21, 1992
`July 21, 1992
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`Sheet 1 of 7
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`5,131,844
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`
`July 21, 1992
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`1
`
`5,131,844
`
`2
`Unfortunately, this commercial system is not suitable
`for use in the dental environment.
`
`Mechanical Dental Systems
`U.S. Pat. No. 4,182,312 is directed to a dental probe
`mechanism in which three-dimensional information is
`provided by a transducer mechanism connected to the
`probe. The probe has limited maneuverability and so
`cannot be used to noninvasively detect the contours of
`10 many tooth portions that are not readily accessible.
`Additional linkages and dental equipment of back(cid:173)
`ground interest are disclosed in the following U.S. pa(cid:173)
`tents:
`
`CONTACT DIGITIZER, PARTICULARLY FOR
`DENTAL APPLICATIONS
`
`ST A TEMENT AS TO RIGHTS TO INVENTIONS 5
`MADE UNDER FEDERALLY-SPONSORED
`RESEARCH AND DEVELOPMENT
`The United States has certain rights in this invention
`under the terms of Grant No. 1 R43 DEO7835-0l and
`Grant No. 2 R44 DEO7835-02 awarded by the National
`Institute of Dental Research (National Institutes of
`Health).
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`This application is related to U.S. patent application
`Ser. Nos. 07/364,017 (Rekow et al.); 07/364,270 (Riley
`~t al.); 07/365,139 (Riley et al.); and 07/365,140 (Erd(cid:173)
`man et al.); all filed Jun. 9, 1989, which are expressly 20
`incorporated by reference herein.
`
`15
`
`1,230.156
`1,831,390
`2,299,151
`2,701,915
`3,063,149
`3,226,828
`3,490,146
`3,943,913
`4,344.755
`4,445,857
`4,639.220
`
`1,387,329
`2,119.823
`2,447,287
`2,841,871
`3.152,401
`3,254,413
`3,564,717
`3,943,914
`4,390,028
`4,495,952
`
`1.799,528
`2,119,824
`2,566,903
`3,035,348
`3,218,624
`3,380,163
`3,777,740
`4,085.514
`4,402.326
`4,634,377
`
`See also U.S.S.R. Patent 157,456, French Patent of
`Addition 75,885, and French Patent 1,194,061.
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The invention relates to a probe system including an 25
`electromechanical digitizer, which can be traced over a
`surface for generating digital data representative of the
`configuration of such surface. A primary application of
`the digitizer is contemplated to be digitizing dental
`surfaces, either within the oral cavity, or outside the 30
`oral cavity, for example in a dental laboratory.
`It is expected that the data generated by the digitizer
`will be used with suitable computer modeling (e.g., line
`modeling, surface-skin modeling, or solids modeling)
`and computer-aided design techniques in various dental 35
`applications, such as orthodontics, prosthodontics and
`other restorative dentistry, forensics, and teaching.
`2. Background Art
`The application of computer modeling and mechani(cid:173)
`cal contact digitizing to dentistry is new and is yet un- 40
`proven from a practical standpoint.
`
`General Commercial Digitizers
`Three-dimensional digitizing devices have become 45
`common in the past few years and are used in the air(cid:173)
`craft, automotive, industrial and leisure fields. These are
`divided roughly into four areas:
`Mechanical contact
`Magnetic
`Ultrasonic
`Digital imaging.
`It appears that a mechanical contact system will be most
`workable in the dental field and will entail minimal
`changes in dental practices and the required level of 55
`dental skill.
`Microcontrol Systems (Vernon, Conn.) has intro(cid:173)
`duced a mechanical contact 3-D digitizer called the
`Space Tablet and the Perceptor 3-D. In operation, the
`stylus at the end of the Perceptor's arm is tracked over 60
`the solid object. Movement about 6 axes appears to be
`provided. A precision potentiometer housed in the ex(cid:173)
`tension arm computes the (x,y,z) coordinates of any
`position based on the angle of rotation and known arm
`length. As many as seven points per second can be 65
`recorded. In addition, four different digitization modes
`are switch selectable and resolution ranges between
`0.007 and 0.010 in.
`
`Optical Dental Systems
`The present inventors are aware of work in this field
`performed in France and the United States by Francois
`Duret. He has filed European and United States patent
`applications on imaging devices (EP O 040 165-Al; EP
`0 091 876-Al; and EP O 110 797-Al) and sparse refer(cid:173)
`ences have occurred in the trade journals to his work.
`His imaging device consists of a miniature black and
`white camera which obtains multiple views of the oral
`cavity.
`The Duret system has attempted to automate the
`production of restorations from obtaining the impres(cid:173)
`sion to producing the prosthesis. It is said to be capable
`of several functions:
`To produce a numerical data set that characterizes
`tooth or preparation surfaces by a nontraumatic, non(cid:173)
`contact optical probe.
`To present the tooth image in graphic form on a
`workstation allowing an operator to modify the model
`dynamically.
`To convert the surface data into a form which can
`50 direct an automatic milling machine to cut the form in a
`ceramic, restorative or biocompatible material.
`To measure the contours of the surface of a tooth or
`preparation, a pattern of alternating black and white
`lines is projected onto the surface. The pattern is
`viewed with a miniature TV camera from an angle
`away from the axis of projection of the lines. This al-
`lows surface relief to be measured.
`While the theory is straightforward, the implementa(cid:173)
`tion is very complex and not yet practical. Duret claims
`to have spent 7 years or more, working out this aspect
`of the system. It is the most difficult part of the system
`and requires a large computer to process the data. Some
`of the complications are:
`The teeth must be coated to obtain a consistent color.
`The surrounding soft tissues must be retracted to
`visually expose the marginal portions of the teeth.
`Multiple images are required to observe all of the
`surfaces. The program must in fact compute surface
`
`

`

`5,131,844
`
`15
`
`3
`segments and then link them together appropriately,
`removing any overlaps.
`The occlusal surface must be digitized with the jaws
`apart to allow the camera to fit. A calculation must be
`made to estimate where the occlusion will actually 5
`occur when the jaw is closed.
`To obtain sufficient resolution, it is believed each
`surface image must be viewed multiple times with the
`projected lines moved slightly so that a line edge is
`viewed every 25 microns across the surface. On this 10
`assumption, using lines I mm wide, spaced I mm apart
`(with the camera 2 cm from the surface), 40 separate
`images would be required to obtain the 25 microns of
`spacing.
`The system cannot handle visual artifacts such as
`reflections from saliva, poor line reflectivity on the skin,
`and line discontinuity near abrupt morphology.
`The calculations required to produce a suitable data
`set to use in the next step of the process take approxi- 20
`mately 2 min on a VAX computer running with 5 Mb
`core memory and 80 Mb hard disk. A library of stored
`tooth forms is used to generate the outer contour for
`missing teeth. This library is also used to help bound the
`range of surface locations which can be taken by the 25
`data. The dentist must select an appropriate tooth
`model from the library to work with.
`Once a tooth surface is determined, the surface is
`displayed in wire-mesh form on a workstation. The
`operator must then make decisions on the appropriate- 30
`ness of the model and make size, scaling and other
`changes where necessary. One of the areas requiring
`modeling is the occlusal surface. Another is surface
`element matching errors. Edge contouring may be re(cid:173)
`quired to avoid false sharp ridges.
`The completed computer model is used to generate a
`tool path data file for a particular machine and set of
`cutting tools (a Hennson miller with automatic tool
`changer is used in Duret's system). The milling machine
`then cuts a restoration. It typically takes 30 min to pro- 40
`duce the raw tooth. A trained dental technician then
`hand-polishes and colors the machined restoration. This.
`system appears to be unable to accomplish complete
`automation in an expeditious and cost-effective manner.
`Accordingly, it would be desirable to overcome the 45
`following disadvantages of the Duret system:
`The surface generation software should be simplified
`by providing a fixed reference point for digitizing a
`given tooth.
`The software should be able to run on a smaller com- SO
`puter.
`The surface generation software should be simplified
`by allowing each data point for the surface to be read
`directly from the digitizer sensors and not to require 55
`computation from multiple photo projections.
`The sampled data should be usable to form a continu(cid:173)
`ous surface and not require piecing segments together.
`Redundant data should not be collected, thereby
`reducing memory requirements, preferably by coordi- 60
`nation of surface contact data, quantizing the resolution
`of the accepted data, and real time sensor data process(cid:173)
`ing. These measures would permit storing only needed
`data.
`The contact probe should not be affected by reflec- 65
`tions from saliva or tooth transparency.
`The contact probe should be able to sense below the
`gum surface where the cameras cannot see.
`
`4
`The contact probe should be able to reach surfaces
`that are always shadowed from view by surrounding
`teeth.
`
`Other Optical Systems
`U.S. Pat. No. 4,575,805 discloses a system that is said
`to optically scan a dental surface, digitize and record its
`contour data, determine the necessary shape of a corre(cid:173)
`sponding dental implant, and then control a process for
`manufacturing the implant.
`Additional video systems of background interest are
`disclosed
`in U.S. Pat. Nos. 3,861,044; 4,324,546;
`4,611,288; 4,663,720; and 4,742,464.
`All prior art mentioned herein is expressly incorpo(cid:173)
`rated by reference.
`None of the prior art disclosed above addresses the
`specific dental applications we have identified, and
`more specifically,
`the digitizing system proposed
`herein.
`
`OBJECTS OF THE INVENTION
`This invention relates to a mechanical digitizer, par(cid:173)
`ticularly for use in the fields of restorative dentistry,
`forensic dentistry, orthodontics, and the teaching of
`dentistry practices.
`Restorative Dentistry-Current restorative
`tech(cid:173)
`niques in crown and bridge fabrication involve tooth
`preparation, impression procedures, construction of the
`restoration, and its insertion.
`Tooth preparation with exact replication of a die is
`the key to an accurately fabricated restoration. Cur(cid:173)
`rently, the state-of-the-art involves preparation of a
`tooth by a clinician, with subsequent gum retraction.
`The geometry of the preparation is then captured with
`35 impression material. These procedures lead to the mak(cid:173)
`ing of a die, which in turn is processed to wax a restora(cid:173)
`tion that is ultimately cast and sometimes veneered to
`aesthetically match the surrounding environment.
`Impression techniques are inconvenient,
`tedious,
`time-consuming, and, in general, unpleasant for the
`patient. Sometimes the making of an impression is not
`possible in certain individuals due to a highly sensitive
`gag reflex. The production of a highly accurate die is
`time-consuming and difficult to accomplish. For exam-
`ple, the dimensions of the die vary with the nature and
`type of impression material and the stone that is used.
`Mixing of impression material and timing of the pouring
`of the impression are other critical factors that influence
`die accuracy. All impressions are manually done and
`are subject to human working error. At times, impres(cid:173)
`sions need to be repeated, especially if care is not exer-
`cised initially in retraction and tissue control. Simplify(cid:173)
`ing these procedures while maintaining or improving
`upon their accuracy would be highly desirable and
`contribute beneficially to both the dentist and the pa(cid:173)
`tient. In addition, if these methods could improve resto-
`ration production, they would be widely embraced. Of
`even more importance is the fact that gingival retrac(cid:173)
`tion procedures may traumatize the gingival tissues,
`lead to gum recession, and result in a lack of definition
`of the marginal finish line as captured by the impression.
`The ability to digitize soft and hard tissues presents
`potential applications in other areas of dentistry and
`medicine where the use of impression-taking proce(cid:173)
`dures is currently disadvantageous or impossible:
`Oral Surgery-The impression-taking process in oral
`surgery procedures involving prosthetic appliance fab(cid:173)
`rication (implants, for example) for the maxilla or man-
`
`

`

`5,131,844
`
`6
`geometric data concerning the meshing of the occlusal
`surfaces, the resulting bite positions, and the geometri(cid:173)
`cally allowed range of comfortable bite positions. This
`will allow new diagnostic and treatment methods for
`5 orthodontics
`including
`temporal mandibular
`joint
`(TMJ)-related problems. Since these digital data are
`mathematically and geometrically precise, they can be
`used in new ways.
`The orthodontic methods disclosed herein will allow
`several significant improvements. First, the visual
`model produced can be used to assess the present situa(cid:173)
`tion by alJowing the dentist to view the entire cavity
`and each tooth position from many angles. Secondly, it
`will be possible to recalculate and redisplay each tooth
`position based on the treatment prescribed, prior to any
`work on the patient. This will allow the dentist to try
`out a proposed treatment and alter it before any actual
`treatment. Furthermore, the optimum placement of
`each tooth can be calculated for a given aesthetic effect
`and to efficiently maximize the spatial distribution of
`teeth in the cavity to obtain the best functional result. In
`addition, since the precise geometry is known ·before(cid:173)
`hand and the relative tooth positions can be determined
`with each subsequent visit, it will be possible to quanti(cid:173)
`tatively follow, for example, relative tooth positions, or
`the location of periodontal disease, over time, and to
`• calculate and display by computer any modification to
`the treatment schedule.
`One of the most important decisions made by the
`orthodontist is the exact placement of the brackets on
`each tooth in order to produce the necessary tooth
`movement. The computer geometric data base, coupled
`with the eventual mathematical capabilities of the com(cid:173)
`puter model, will assist in the calculation and display of
`the exact bracket position on each tooth to produce the
`required rate, type, and degree of movement. This will
`alJow a more exact functional result to be obtained. This
`alone will be a major improvement over present meth(cid:173)
`ods.
`Teaching-The teaching applications of a geometric
`data base coupled with the visual capabilities of solids
`modeling are numerous. The ability to rotate geome(cid:173)
`tries in three-dimensional space, to zoom in on areas for
`emphasis or inspection, and to change the viewing per(cid:173)
`spective give the instructor a tool that can increase the
`creativity of teaching methods. Man·ipulation of the
`visual display allows the frame of reference of the ob(cid:173)
`server to be readily changed. For example, it is possible
`to view the lower incisors both from the front and also
`from the lingual perspective, creating visual impres(cid:173)
`sions not now possible. Automatic teaching and grading
`of dental technique can also be provided, which will
`reduce the cost of education, increase the repeatability
`of grades by eliminating judgments by graders, and give
`the students the ability to get more practice and feed(cid:173)
`back when appropriate.
`Dentures-It may be possible to replicate soft tissue
`contours for complete and partial dentures with this
`digitizing system.
`
`20
`
`5
`dible is one example. It is very difficult to obtain a good
`bone impression of the mandible due to tissue manage(cid:173)
`ment problems, whereas digitization of the mandible
`may be obtained with little difficulty once the tissue is
`exposed.
`Forensic Applications-The oral cavity geometry,
`especially the occlusal surface, can be used for identifi(cid:173)
`cation purposes and is believed to be as unique for each
`individual as a fingerprint. A digitizing device can be
`used to create a computer data base from which a visual IO
`output can be generated. A quantitative comparison of
`geometry is possible via numerical methods, allowing
`the data base to be compared with any other data gener(cid:173)
`ated in the future, making exact identification possible
`simply from a comparison of geometric detail of intact 15
`enamel and its interruption with restorations. The abil-
`ity to capture the oral geometry via digitization and to
`make quantitative comparisons from that geometry
`offers an increase in the reliability and speed with which
`identifications can be made from dental information.
`Orthodontic Applications-A geometric data base of
`the oral cavity has many applications in orthodontics.
`Orthodontic applications are especially advantageous
`because of the desirability of having a quantitative data
`base from which changes over time can be determined. 25
`A quantitative geometric data base and the ability to
`generate three-dimensional displays and manipulate
`those displays will give the orthodontist capabilities
`that are not currently available. The visual display can
`be used to show before-and-after effects. The geometry 30
`can be tracked over time to show movement effects and
`to identify gumline changes, etc. More quantitative
`measurements and comparisons are possible than with
`present methods.
`A digital description of the oral cavity, using a me- 35
`chanical digitizing device, will have a major, if not
`revolutionary, impact on the procedures used for the
`diagnosis and treatment of orthodontic patients. The
`mechanical digitizing device can capture (x,y,z) coordi(cid:173)
`nates by point-to-point measurements of the oral cavity 40
`for manipulation by computer solids or surface model(cid:173)
`ing techniques. It will be possible, in real-time, to pro(cid:173)
`duce a visual computer model of a patient's teeth in full
`color and in three dimensions. This model can then be
`rotated in space, viewed from all angles, expanded, and 45
`in general, manipulated by the orthodontist in much the .
`same way as a study model is today. The system will
`detect changes in tooth position much earlier than with
`traditional methods. In time these methods may actualJy
`replace study models as the primary reference for pa- 50
`tient treatment. The orthodontist may in the future
`actualJy demonstrate the facial effects of treatment and
`show the patient before and after images of the tooth
`positions and resulting facial changes ..
`The significance of an accurate digital description of 55
`the oral cavity for orthodontic applications cannot be
`overemphasized. Present methods generalJy involve
`full face x-rays and measurements of relative tooth posi(cid:173)
`tions from these images. The orthodontist presently uses
`this information and clinical experience and judgment 60
`to generate a treatment schedule for the repositioning of
`each tooth. This involves precise bracket location and
`periodic follow-up during the course of treatment.
`The digital data wiJJ allow a precise model of the oral
`cavity to be produced mathematically and to be visualJy 65
`generated by computer solids or surface modeling tech(cid:173)
`niques. With this model available, the precise relative
`position of each tooth is known exactly along with the
`
`SUMMARY OF THE INVENTION
`In view of the foregoing possibilities, the central
`object of this invention is to develop a mechanical
`contact digitizer that will enable the geometry of a'
`tooth and its local environment to be digitized before
`being modeled by a computer.
`
`

`

`5,131,844
`
`7
`Another object is to permit the tooth and its local
`environment to be digitized in a few minutes (less than
`about 5-10 min.).
`A further object is to provide a digitizer whose over(cid:173)
`all accuracy is less than about 0.025 mm (25 microns). 5
`Yet another object of the invention is to provide a
`digitizer which can be affixed in the oral cavity by
`known attachment techniques.
`A further object is for the digitizer to have the feel
`and maneuverability of a dental exploration tool.
`Still another object is to provide a digitizer which
`both is compact enough to fit in the mouth, yet also can
`be extended to reach all parts of the oral cavity.
`A further object is for the digitizer to provide six
`degrees of freedom for the handpiece, so as to reach any 15
`oral surface with the probe tip, from any angle.
`Thease and other objects can be achieved, for exam(cid:173)
`ple by a dental surface tracer including a probe with a
`tip that can be moved to trace a given dental surface,
`comprising a mounting device for mounting said tracer 20
`to a stable reference location and defining a base plane;
`a first plurality of links which are substantially coplanar
`and define a plane of movement; said links being pivota(cid:173)
`bly attached to said mounting device so that said plane
`of movement makes a variable angle with said base 25
`plane; a distal one of said first plurality of links being
`movable in two dimensions within said plane of move(cid:173)
`ment; means for generating electrical signals representa(cid:173)
`tive of movements of said probe tip, as a function exclu-.
`sively of movements of said first plurality of links; a 30
`dental handpiece supporting said probe; and a second
`plurality of links which hold the handpiece and are
`attached to said first plurality of links; said second plu(cid:173)
`rality of links holding said probe tip at all times at a
`fixed location in said plane of movement with respect to 35
`said distal link of said first plurality oflinks; and permit(cid:173)
`ting said handpiece to move about three axes without
`moving said probe tip from said fixed location. Advan(cid:173)
`tageously, said entire tracer exclusive of said handpiece
`is sized to be accommodated within the human mouth. 40
`According to another aspect of the invention, a probe
`system may comprise: a probe; a linking arrangement
`supporting said probe and having a plurality of joints ·
`providing at least 6 degrees of freedom for the probe; a
`device for attaching said linking arrangement to a stable 45
`reference location; and a sensing system which mea(cid:173)
`sures all movements of said probe with respect to said
`reference location; wherein said linking arrangement
`comprises a first plurality of joints providing three de(cid:173)
`grees of freedom for said probe, movement of those 50
`joints being sensed by said sensing system; and wherein
`said linking arrangement comprises a second plurality
`of joints providing said probe with three degrees of
`freedom independently of said first plurality, movement
`of said second plurality of joints not being sensed. The 55
`attaching device is capable of attaching the linking
`arrangement to a work bench, or to a reference location
`on a given jaw.
`A gimbal-type arrangement of the second plurality of
`joints advantageously provides three degrees of free- 60
`dom for said handpiece while said probe tip remains at
`the same location with respect to said first through third
`joints, the probe tip remaining at all times at the com(cid:173)
`mon axis of rotation of said fourth, fifth and sixth joints.
`The sensing system comprises at least one Hall sensor 65
`and at least one magnet associated with said linking
`arrangement; advantageously first, second and third
`Hall sensors associated respectively with said first, sec-
`
`8
`ond and third joints, said first Hall sensor sensing rela(cid:173)
`tive movement of said first and second links, said second
`Hall sensor sensing relative movement of said second
`and third links, and said third Hall sensor sensing rela(cid:173)
`tive movement of said third and fourth links.
`Another aspect of the invention relates to linearizing
`means for receiving output signals from said Hall sen(cid:173)
`sors and improving the linearity thereof.
`According to another feature, the invention provides
`IO a dental surface tracer including a dental probe having
`six degrees of freedom, comprising: a mounting device
`which is capable of being mounted to a reference loca(cid:173)
`tion with respect to a given jaw and defining a base
`plane; a first link which is integral with said mounting
`device; substantially coplanar second, third and fourth
`links defining a plane of movement; said second link
`being pivotally mounted to said first link so that said
`plane of movement is movable above and below said
`base plane; first means for generating electrical signals
`representative of such movement; said second, third and
`fourth links being jointed together to have predeter(cid:173)
`mined ranges of relative angular motion so that a distal
`end of said fourth link is movable over a predetermined
`area in said plane of movement; whereby said distal end
`has three degrees of freedom; second means for generat(cid:173)
`ing electrical signals representative of such movement;
`a probe; and gimbal means supporting said probe and
`attached to said distal end of said fourth link, for permit-
`ting said probe to move with three degrees of freedom
`without any movement of said first through fourth
`links; whereby said probe can move with respect to said
`reference location with six degrees of freedom. All of
`said links and gimbal means are sized for being accom-
`modated within the human mouth. The second, third
`and fourth links are jointed to provide greater than 90"
`of relative angular motion between each pair of adja(cid:173)
`cent links, or more advantageously, substantially 100" of
`relative angular motion.
`Disclosed herein is a mechanical contact digitizing
`device which avoids the limitations of the prior art and
`is, therefore, suitable for the oral and dental environ(cid:173)
`ment or the dental lab. A perspective view is shown in
`FIG. 1. The device is small enough to fit entirely inside
`the mouth. Such a small size greatly facilitates achiev(cid:173)
`ing high accuracy by minimizing the bending of link-
`ages and maximizing the angular motion of the joint
`motion sensors. The linkages were designed such that
`they have optimum linear motion to reach all teeth and
`optimum rotational motion to maneuver the sensor tip
`to all tooth surfaces. The joint motion sensors are Hall-
`effect sensors. Every linkage and sensor was designed
`individually for an accuracy of0.0025 mm (2.5 microns)
`in order to achieve an overall digitizer accuracy of less
`than 25 microns or better. The joints are preloaded to
`reduce play and increase rigidity. Test data on joint
`rigidity and Hall-effect joint motion sensor accuracy
`and hysteresis indicate that an overall digitizer accuracy
`of less than 25 microns can be achieved.
`The disclosed mechanical contact digitizer enables
`the dentist or the lab to quickly and accurately digitize
`a tooth or a prepared tooth and i