Exhibit 1009
`
`Exhibit 1009
`
`
`Mako Surgical Corp. Ex. 1009
`
`

`
`United Statesv Patent [191
`Glassman et al.
`
`US005408409A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,408,409
`Apr. 18, 1995
`
`[54]
`
`[75]
`
`[73]
`
`[21]
`[22]
`
`[51]
`[52]
`
`[53]
`
`[56]
`
`IMAGE-DIRECT ED ROBOTIC SYSTEM FOR
`PRECISE ROBOTIC SURGERY INCLUDING
`REDUNDANT CONSISTENCY CHECKING
`Inventors: Edward Glassman, New York, N.Y.;
`William A. Hanson, Mountain View,
`Calif.; Peter Kazanzides, Davis,
`Calif; Brent D. Mittelstadt,
`Placerville, Calif; Bela L. Musits,
`Hopewell Junction, N.Y.; Howard A.
`Paul, Loomis, Calif.; Russell H.
`‘Taylor, Ossining, N.Y.
`Assignee: International Business Machines
`Corporation, Armonk, N.Y.
`Appl. N0.: 170,540
`Filed:
`Dec. 20, 1993
`
`Related US. Application Data
`Division of Ser. No. 761,720, Sep. 18, 1991, Pat. No.
`5,299,288.
`__
`Int. Cl.6 ....................... .. B23Q 15/14; A61B 6/00
`US. Cl.
`......................... .. 364/413.13; 395/80;
`395/94
`Field of Search ............. .. 395/80, 94; 364/4l3.14,
`364/413.l3, 413.02; l28/653.1, 782
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,150,326 4/1979 Engelberger et al. ............ .. 318/563
`4,485,453 11/1984 Taylor .................... .. 364/571
`4,506,393 3/1985 Murphy
`128/653 1
`4,618,978 10/1986 Cosman ..... ..
`128/303 B
`4,691,694 9/1987 Boyd et a1. ..
`128/25 R
`
`4,704,686 ll/1987 Aldinger . . . . .
`
`4,750,487 6/ 1988 Zanetti
`4,791,934 12/1988 Brunnett
`4,858,149 8/ 1989 Quarendon ..
`
`. . . . . . .. 364/414
`
`128/303 B
`128/653
`364/522
`
`. . . .. 128/6531
`4,873,707 10/1989 Robertson . . . . . . .
`364/4l3.13
`4,945,914 8/1990 Allen ..................... ..
`4,979,949 12/ 1990 Matsen, III et a]. ................ .. 606/53
`4,984,157 1/1991 Cline et a1. ................... .. 364/413.l3
`4,991,579 2/1991
`5,007,936 4/ 1991
`5,078,140 1/1992
`5,079,699 l/ 1992
`5,097,839 3/ 1992
`5,098,426 3/ 1992
`
`5,170,347 12/1992 Tuy m1. ..................... .. 364/413.22
`5,274,565 12/1993 Reuben ....... ..
`.. 364/413.15
`5,279,309 1/1994 Taylor et a]. .... ............... ..12s/7s2
`FOREIGN PATENT DOCUMENTS
`114505 8/1984 European Pat. Off. .
`0326768 8/ 1989 European Pat. Off. .
`3447365 12/1984 Germany .
`59-157715 9/1984 Japan .
`60-231208 11/1985 Japan .
`2094590 9/ 1982 United Kingdom .
`OTHER PUBLICATIONS
`' Balogh et al., “Simulation and error analysis for stereo
`tactic pointing system”, IEEE Bug. in Medicine & Biol
`ogy Society 11th Annual Int. Conf. 1989. H
`(List continued on next page.)
`Primary Examiner-Allen R. MacDonald
`Assistant Examiner—George Davis
`Attorney, Agent, or Firm-Perman & Green
`[57]
`ABSTRACT
`A robotic surgical system (10) includes a multiple de
`gree of freedom manipulator arm (14) having a surgical
`tool (22). The arm is coupled to a controller (24) for
`controllably positioning the surgical tool within a three
`dimensional coordinate system. The system further
`includes a safety monitoring processor (38) for deter
`mining the position of the surgical tool in the three
`dimensional coordinate system relative to a volumetric
`model. The volumetric model may be represented as a
`constructive solid geometry (CSG) tree data structure.
`The system further includes an optical tracking camera
`system (28,32) disposed for imaging a region of space
`that includes at least a portion‘ of the manipulator arm.
`An output of the camera system is coupled to the pro
`cessor (38) that processes the volumetric model for
`determining if the surgical tool is positioned outside of
`the volumetric model. The system further includes a
`strain gage (40) for detecting slippage in three dimen~
`sions between an immobilized tissue, such as bone, and
`a reference point (44). The system also includes multiple
`and redundant safety features for suspending a motion
`of the surgical tool to prevent the tool from operating i
`outside of the predetermined volume of space.
`
`10 Claims, 4 Drawing Sheets
`
`Page 1
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`Mako Surgical Corp. Ex. 1009
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`

`
`5,408,409
`Page 2
`
`OTHER PUBLICATIONS
`“Computer Assisted Surgery”, IEEE Computer
`Graphics and Applications, vol. 1, No. 3, May 1990
`(IEEE) pp. 43-51.
`'
`“Robotic Total Hip Replacement Surgery in Dogs”, R.
`Taylor et al., IEEE Engineering in Medicine & Biology
`Society 11th Annual International Conf. Nov. 9-12,
`1989.
`“A Robotic System for Cementless Total Hip Replace
`ment Surgery in Dogs”, by R. Taylor et al., Proc. 2nd
`IARP Workshop on Medical & Healthcare Robotics,
`OK Sep. 5-7, 1989.
`'
`“An Articulated Neurosurgical Navigation System
`Using MRI and CT Images” by R. Kosugi et al., IEEE
`Transactions on Biomedical Engineering vol. 35, No. 2,
`Feb. 1988.
`“A Robot with Improved Absolute Positioning Accu- _
`racyfor CT Guided Stereotactic Brain Surgery”, by Y.
`Kwoh et al., IEEE Trans. on Biomedical Engin., vol.
`35, No. 2, Feb. 1988.
`“A New System for Computer Assisted Neurosur
`gery”, by S. Lallee, Adv. Topics in Birobotics,
`0926-IEEE Engineering in Medicine & Biology Soci
`ety 11th Annual International Conf., Nov. 9-12, 1989.
`“S.M.O.S.: Stereotaxical Microtelemanipulator for Oc
`ular Surgery”, A. Guerrouad et al., Medical Applica
`tions of Robotics, IEEE Engineering in Medicine &
`Biology Society, 11th Annual Int’l. Conf. Nov. 9-12,
`
`1989.
`“The United Kingdom Advanced Medical Robotics
`Initiative”, P. Finlay, Medical Applications of Robot
`ics, IEEE Engineering in Medicine & Biology Society
`11th Annual International Conf. Nov. 9-12, 1989.
`“Computer Assisted Medical Interventions”, by P. Cin
`quin et al., Proc. 2nd IARP Workshop on Medical &
`Healthcare Robotics, OK Sep. 5-7, 1989.
`“Use of Puma 560 Robot in Biopsies” by M. Thorn et
`al., Use of Robots as an Aid to Deskilling the Taking of
`Biopsies, Dept. of Electrical & Electronic Engineering
`Hudders?eld Polytechnic Sep. 5-7, 1989.
`“A Surgeon Robot for Prostatectomies”, by B. Davies
`et al., Proc. 2nd IARP Workshop on Medical & Health
`care Robotics, OK Sep. 5-7, 1989.
`School of Medicine, University of California UC Davis
`Medical Background, Feb. 11, 1988.
`. IBM, University of California “Developing Robot-As
`sisted Surgical Procedure”, Feb. 11, 1988.
`“IBM Robotics Technology Background”, Feb. 11,
`1988.
`“Robotic Instrumentation in Total Knee Arthroplasty”
`by J. L. Garbini et al., 33rd Annual Meeting, Orthopae
`dic Research Society, Jan. 1987, Calif, p. 413.
`“Watchdog Safety Computer Design and Implementa
`tion”, by R. D. Kilmer et al., presented at the RI/SME
`Robots 8 Conference, Jun. 1984, pp. 101-117.
`“Bilateral Control for Mainpulators with Different
`Con?gurations”, to Arai et al.
`
`Page 2
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`Mako Surgical Corp. Ex. 1009
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`

`
`US. Patent
`
`Apr. 18, 1995
`
`Sheet 1 of 4
`
`5,408,409
`
`tOwwwuOtl
`
`
`
`@235.“ 503
`
`\rmmé
`
`000
`
`Page 3
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`Mako Surgical Corp. Ex. 1009
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`

`
`US. Patent
`
`Apr. 18, 1995
`
`Sheet 2 of 4
`
`5,408,409
`
`'
`
`FIG. 3b
`CS6 TREE
`
`IMPLAN T
`
`PROXIMA L
`POR TION
`
`APPROACH
`VOLUME
`
`' /PROXIMAL
`
`PORTION
`
`I
`
`Page 4
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`Mako Surgical Corp. Ex. 1009
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`

`
`US. Patent
`
`Apr. 18, 1995
`
`Sheet 3 of 4
`
`5,408,409
`
`F/G.4
`
`F A
`
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`2
`.
`
`L _€@E5_Z€_ _
`I MOTION
`
`_ ._
`
`j;
`:’
`
`F/G.5 A
`PRE-SuRGIcAL
`PLANNING
`INFORMATION
`FLOW
`
`CT/MRI‘
`DATA
`
`E
`A
`'
`
`3-0 IMAGE
`PROCESSING AND
`TISSUE CLASS.
`
`B
`
`[E
`MODELLING
`I
`
`C
`f
`IMPLANT
`CHOICE AND
`PLACEMENT
`
`D
`/
`IMPLANT
`DESIGNS
`LIBQARY
`
`ANALYSIS OF
`IMPLANT-BONE
`SYSTEM
`
`CUSTOM
`DESIGN '
`
`SURGICAL
`DATA
`FILE
`
`Page 5
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`Mako Surgical Corp. Ex. 1009
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`

`
`US. Patent
`
`Apr. 18, 1995
`
`Sheet 4 of 4
`
`5,408,409
`
`1/‘
`
`‘
`
`"Z
`
`BONE
`WITH REFERENCE
`INDICATORS
`
`cusrglés ‘1845mm
`‘
`BQEG r- ———
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`T
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`PRE-SURGICAL
`PLANNING
`
`IMPLAN T
`DESIGNS
`UBRARY
`
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`
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`(:QQRgIgMET/ECS
`
`CALIBRATION DATA
`IMPLANT SHAPE DATA
`IMPLANT PLACEMENT
`
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`
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`SAFETY
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`\\ curs
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`POSITION
`5/‘
`
`Page 6
`
`Mako Surgical Corp. Ex. 1009
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`

`
`IMAGE-DIRECTED ROBOTIC SYSTEM FOR
`PRECISE ROBOTIC SURGERY INCLUDING
`REDUNDANT CONSISTENCY CHECKING
`
`1 This is a divisional of application Ser. No. 07/761,720
`?led on Sep. 18, 1991, US. Pat. No. 5,299,288.
`
`FIELD OF THE INVENTION
`This invention relates generally to robotic systems
`and, in particular, to a robotic system that integrates an
`interactive Computed Tomagraphy (CT)-based presur
`gical planning component with a surgical system that
`includes a multiple-degree of freedom robot and redun
`dant motion monitoring. An illustrative application is
`presented in the context of a system that prepares a
`femoral cavity to have a shape precisely determined for
`receiving a cementless prosthetic hip implant.
`
`20
`
`30
`
`35
`
`40
`
`45
`
`BACKGROUND OF THE INVENTION
`It has been found that computed tomagraphy (CT)
`7
`imaging and computer modelling methods provide a
`precision for pre-surgical planning, simulation, and cus
`tom implant design that greatly exceeds the precision of
`subsequent surgical execution. For example, approxi
`25
`mately one half of the 300,000 total hip replacement
`operations performed each year use cementless im
`plants. Stability of the implant, uniform stress transfer
`from the implant to the bone, and restoration of the
`proper biomechanics critically affect ef?cacy and, in
`turn, are signi?cantly affected by the proper placement
`of the implant relative to the bone. An important factor
`in achieving proper placement of the implant is the
`accuracy with which the femoral cavity is prepared to
`match the implant shape.
`Recently reported research con?rms that gaps be
`tween implant and bone signi?cantly affect bone in~
`growth. One study of the standard manual broaching
`method for preparing the femoral cavity found that the
`gaps between the implant and the bone is commonly in
`the range of one millimeter to four millimeters and that
`the overall resulting hole size was 36% larger than the
`broach used to form the hole. As a result, only 18-20
`percent of the implant actually touches bone when it is
`inserted into such a hole. Furthermore, the placement
`of the implant cavity in the bone, which affects restora
`tion of biomechanics, is as much a function where the
`broach “seats” itself as of any active placement decision
`on the part of the surgeon.
`Typically, precise surgical execution has been limited
`to procedures, such as brain biopsies, for which a suit
`able stereotactic frame is available. However, the incon
`venience and restricted applicability of these devices
`has led some researchers to explore the use of robots to
`augment a surgeon’s ability to perform geometrically
`precise tasks planned from CT or other image data.
`Safety is an obvious consideration whenever a mov
`ing device such as a robot is used in the vicinity of a
`patient. In some applications, the robot does not need to
`move during the “in-contact” part of the procedure. In
`these applications the robot moves a passive tool guide
`or holder to a desired position and orientation relative
`to the patient. Brakes are then set and motor power is
`turned off while a surgeon provides whatever motive
`force is needed for the surgical instruments. Other sur
`gical applications rely on instrumented passive devices
`to provide feedback to the surgeon on where the instru
`ment is located relative to an image-based surgical plan.
`
`60
`
`65
`
`1
`
`5,408,409
`
`2
`In an IBM Research Report (RC 14504 (#64956)
`3/28/89) R. H. Taylor et al. describe a robotic system
`for milling a correctly shaped hole into a femur for
`receiving a cementless hip implant. The system com
`putes a transformation between CT-based bone coordi
`nate data and robot cutter coordinates. The transforma
`tion is accomplished in part by a combination of guiding
`and tactile search used to locate a top center of each of
`three alignment pins that are pre-surgically affixed to
`the femur and CT-imaged. This robotic system includes
`a vision subsystem to provide a redundant check of the
`robot’s motion to ensure that the tool path does not
`stray outside of a planned work volume. An online
`display is provided for the surgeon to monitor the
`progress of the operation. Proximity sensors may be
`positioned to detect any subsequent motion of- the pins
`relative to a robot base.
`
`SUMMARY OF THE INVENTION
`The invention discloses a robotic surgical system that
`includes a multiple degree of freedom manipulator arm
`having a surgical tool. The arm is coupled to a control
`ler for controllably positioning the surgical tool within
`a three dimensional coordinate system. The system
`further includes apparatus for determining the position
`of the surgical tool in the three dimensional coordinate
`system relative to a volumetric model. The determining
`apparatus includes a device for detecting a location of
`the surgical tool, such as an optical tracking system
`disposed for imaging a region of space that includes at
`least a part of the manipulator arm. An output of the
`tracking system is coupled to a processor that processes
`the volumetric model for determining if the surgical
`tool is positioned outside of a predetermined volume of
`space. The system further includes redundant safety
`checks including a strain gage for detecting in three
`dimensions any slippage between an immobilized tissue,
`such as bone, and a reference point and also a force
`sensor coupled to the surgical tool. The multiple and
`redundant safety devices are employed for suspending a
`motion of the surgical tool to prevent the tool from
`operating outside of the volumetric model. The coordi
`nates and structure of the volumetric model are deter
`mined during a pre-surgical planning session wherein a
`surgeon interactively selects and positions a suitably
`shaped implant relative to images of the bone within
`which the implant is to be installed.
`
`BRIEF DESCRIPTION OF THE DRAWING
`The above set forth and other features of the inven
`tion are made more apparent in the ensuing. Detailed
`Description of the Invention when read in conjunction
`with the attached Drawing, wherein:
`FIG. 1 is a block diagram showing a presently pre
`ferred embodiment of a surgical robotic system;
`FIG. 2a illustrates a human hip prosthetic implant;
`FIG. 2b illustrates the implant of FIG. 2a implanted
`with a femur, the Figure also showing the placement of
`three alignment pins upon the femur;
`FIG. 3a illustrates a method of determining a cutter
`work volume for the implant of FIG. 2a;
`FIG. 3b is a CSG tree representation of the cutter
`work volume of FIG. 30;
`FIG. 4 is a graph of measured force, resolved at the
`cutter tip, as a function of time, the graph further illus
`trating ?rst and second force thresholds;
`FIG. 5 illustrates information ?ow during pre-surgi
`cal planning; and
`
`Page 7
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`

`
`5,408,409
`3
`FIG. 6 is a block diagram showing in greater detail
`the pre-surgery system and the coupling of the pre-surg
`ery system to the robot controller and on-line display.
`
`20
`
`25
`
`4
`proximately 3 kgf (L2) result in arm power being re
`moved, an arm 14 “shutdown” condition. The force
`sensor 20 is effective in detecting such conditions as the
`cutter 22 stalling, encountering improperly excised soft
`tissue, and changes in bone hardness such as that which
`occurs between trabecular and cortical bone.
`Also coupled to the controller 24 is a hand-held pen
`dant 26 for use by the surgeon as an input terminal as
`will be described.
`A motion monitoring subsystem includes, in the pres
`ent embodiment, an optical tracking system having a
`camera 28 with three spatially separated image sensors
`30a, 30b and 30:. Coupled to camera 28 is a camera
`processor 32 that visually tracks in three dimensions the
`position and orientation of a plurality of infrared (IR)
`beacons, such as LEDS 34, that are mounted on a refer
`ence plate 36 coupled to the robot end effector. The
`optical tracking system is but one of several redundant
`motion detecting systems employed during the cutting
`phase of the surgery to verify that the cutter 22 tip does
`not stray more than a speci?ed amount outside of a
`de?ned implant volume. In a presently preferred em
`bodiment of the invention the optical tracking system is
`a type known as Optotrak that is manufactured by
`Northern Digital, Inc. The three image sensors 3012-300
`are line-scan devices mounted in a rigid frame which
`track the position of IR LEDs 34 in three dimensional
`space to an accuracy of 0.1 ‘mm/m3.
`In the present embodiment the reference plate 36
`includes eight LEDs 34 which function as positional
`beacons. Camera processor 32 software is employed to
`compute a camera-based coordinate system from the
`beacon locations. Robot-to-camera and cutter-to-refer
`ence plate transformations are computed by a least
`squares technique from data taken with the robot arm
`14 fn various known positions, using appropriate linear
`ized models.
`An output 32a of the optical tracking system is cou
`pled to a safety monitoring processor 38 that has as one
`function a task of verifying that the cutter 22 remains
`within the predetermined spatial volume associated
`with the selected implant. Processor 38 receives a coor
`dinate transformation (Top) of the reference plate 36
`relative to camera 28 from the camera processor 32. In
`an alternative embodiment, processor 38 receives the
`coordinates of LEDS 34 from camera processor 32 and
`computes the coordinates of reference plate 36 itself.
`During a calibration phase prior to surgery, robot
`controller 34 moves the robot to a plurality of positions
`and orientations. After each motion, robot controller 24
`transmits the position and orientation of the robot’s
`cutter 22 to processor 38 over a communication bus 240.
`Processor 38 uses this information, together with the
`reference plate 36 coordinates relative to the camera 28,
`to compute the coordinate transformation (Trc) be
`tween the camera coordinate system and the robot co
`ordinate system and also to compute the coordinate
`transformation (Tpk) between the cutter 22 and the
`reference plate 36. As a result, processor 38 is enabled to
`determine the coordinate transformation (Trk) of the
`robot’s cutter 22 relative to the robot from the relation
`ship
`’
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`FIG. 1 is a block diagram illustrating a present em
`bodiment of a surgical robotic system 10. System 10
`includes a robot 12 having a manipulator arm 14 and a
`base 16. The arm 14 has at least S-axes of motion and
`includes a plurality of joint (J) motors J1, J2, J3 and J4
`that provide four degrees of motion and, in the present
`embodiment, a pitch motor (PM) 18 that provides the
`?fth degree of motion. In the present embodiment of the
`invention the robot 12 is a four-degree of freedom IBM
`7575 or 7576 SCARA manipulator having an additional
`pitch axis (IBM is a registered trademark of the Interna
`tional Business Machines Corporation). The PM 18 is
`presently implemented with a stepper motor having an
`encoder, primarily for stall detection, that is controlled
`with a commercially available indexer of the type that
`accepts a user provided acceleration, velocity and dis
`tance commands. Each of the manipulator arm joints
`has an associated controlling microprocessor.
`The robot 12 further includes a six degree-of-freedom
`wrist-mounted force sensor 20. One suitable force sen
`sor is known as a Lord Force/Torque Wrist ‘Sensor,
`Model F/T-30/10O having a maximum force limit of 30
`pounds and a resolution of l/40 pound. The force sen
`sor 20 is coupled via a serial or a parallel interface to a
`robot controller 24.
`The robot 12 further includes an end effector having
`a cylindrical high-speed (65000 rpm) pneumatic surgical
`cutting tool 22. During surgery all but the robot’s end
`effector are covered by a sterile sleeve, the end-effector
`being separately sterilized. The robot 12 is positioned
`relative to an operating table such that it has ready
`access to the surgical region. The robot controller 24
`provides servocontrol, low-level monitoring, sensor
`interfaces, and higher-level application functions imple
`mented in the AML/2 language. The controller 24 is
`presently embodied in an industrial IBM Personal Com
`puter AT data processor herein low~level servo control
`and force sensor interface is provided by suitable
`printed circuit cards that are plugged into the processor
`45
`bus (Personal Computer AT is a registered trademark of
`the International Business Machines Corporation). Con
`troller 24 includes an AML/ 2 Language Interpreter and
`also Motion Control System (MCS) software. A com
`mercial version of this software is described in “AML-2
`Language Reference Manual”, Manual #G7X1369 and
`in “AML-2 Manufacturing Control System User’s
`Guide”, Manual #G67X1370, both of which are avail
`able from IBM Manufacturing Systems Products, Boca
`Raton, Fla.
`55
`In the present embodiment the AML/2 software is
`modi?ed to accommodate the operation of the PM 18
`and the force sensor 20. During surgery, the force sen~
`sor 20 is employed in conjunction with a Force Moni
`toring Processor (FMP) 53 to support redundant safety
`checking, tactile searching to locate aligning pins, and
`compliant motion guiding by the surgeon.
`The FMP 53 is interfaced to the wrist-mounted force
`sensor 20 and computes forces and torques resolved at
`the utter 22 tip. As can be seen in the graph of FIG. 4 if
`any cutter 22 tip force component greater than approxi
`mately 1.5 kgf (L1) is detected, the robot controller 24
`is signalled to freeze motion. Forces greater than ap
`
`35
`
`40
`
`60
`
`65
`
`Trk =Trc ‘Tcp*Tpk.
`
`(1)
`
`In the presently preferred embodiment, the calibra
`tion for Tpk is accomplished by placing plate 36 in
`many orientations with respect to camera 28 with the
`
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`5,408,409
`5
`tool tip being maintained in the same location. This may
`be accomplished either by reliance on the robot-to-tool
`calibration or preferably by means of a tactile search
`procedure using force sensor 20 to locate the cutter tip
`at a known constant position relative to a calibration pin
`or post 54. Alternative embodiments include the use of
`other sensing means either for direct measurement of
`the cutter tip position or as feedback allowing the robot
`controller 24 to place the cutter tip in a known position
`relative to a reference landmark or coordinate system.
`In other embodiments of the invention the position of
`the manipulator arm 12 may be tracked in three dimen
`sions by, for example, magnetic sensing devices or by an
`ultrasonic ranging system. That is, the practice of the
`invention is not limited to use with an arm motion de
`tector that relies on detecting optical beacons.
`During surgery processor 38 receives inputs over
`communication bus 240 from the robot controller 24
`specifying, for this embodiment,‘ a Constructive Solid
`Geometry (CSG) tree representation of the volume to
`20
`be checked (“check volume”) and the coordinates of
`this volume relative to the robot 12. Processor 38 re
`peatedly receives reference plate coordinates (Tcp)
`from camera processor 32 or, alternatively, receives the
`coordinates of LEDS 34 and computes (Tcp). Proces
`sor 38 computes Trk and determines if the cutter 22 is
`within the speci?ed check volume.
`~
`Processor 38 also monitors a bone slippage detector
`which, in accordance with an aspect of the invention, is
`comprised of strain gages 40 which are physically cou
`pled to a tissue, such as a bone 42, that is being surgi
`cally altered. The strain gages 40 are disposed to mea
`sure in three dimensions any displacement of the bone
`42 relative -to a bone ?xator 44, the ?xator 44 being
`rigidly coupled to the robot base 16. The strain gages 40
`are interfaced through appropriate circuitry, including
`an analog-to-digital converter, to the processor 38.
`It has been demonstrated that motions on the order of
`0.1 mm are readily detectable in this manner. Further
`more, it has been determined that with a suitable ?xator
`40
`44, such as a device that employs screw-type connec
`tions made directly to the bone, that even rather large
`forces (5 kgf) produce only a few microns of motion.
`Bone motion of this small magnitude is negligible in the
`context of this application. Thus, although no signi?
`cant bone motion is expected during surgery, the strain
`gages 40 provide an immediate indication if any bone
`slippage should occur.
`If slippage of the bone is detected at least two options
`are available. A ?rst option is to recalibrate the system
`by relocating the position of the bone in space by locat
`ing the three pins 46 with the robot effector in accor
`dance with a procedure described below. A second
`option is employed if the slip sensor is accurately cali
`brated. The second option involves a mathematical
`determination of the amount of bone slippage to derive
`a compensation factor that is applied to subsequent
`robot motions. The ?rst option is preferred for simplic
`ity.
`Further in accordance with the invention, and as
`illustrated in FIGS. 3a and 3b, the safety monitoring
`processor 38 employs a volumetric processing tech
`nique to verify that the cutter 22 tip does not stray by
`more than a predetermined tolerance beyond a spatial
`envelope that corresponds to the three dimensional
`implant model. The present embodiment of the inven
`tion employs the above mentioned CSG tree “check
`volumes”, corresponding to shapes resulting from im
`
`6
`plant and cutter selection, that are constructed from
`primitives bounded by quadric surfaces located at a
`de?ned distance, such as one millimeter, outside of the
`furthest nominal excursions of the cutter 22. In FIG. 3a
`the volume of space that corresponds to a selected im
`plant shape is determined by partitioning the implant
`shape into a plurality of primitive shapes that corre
`spond to (a) a cutter approach volume, (b) an implant
`proximal portion and (c) an implant distal portion. The
`inner dashed line corresponds to the maximum cutter 22
`excursion as measured from the center (X) of the cutter
`22. The cutter 22 outer edge is thus-coincident with the
`outer, solid envelope of the implant volume. In practice,
`the “cutter center (X) is uniformly offset away from a
`longitudinal axis of the implant shape by the predeter
`mined cutter excursion tolerance, such as one millime
`ter.
`In accordance with CSG technique the implant prim
`itive shapes are organized into a tree structure (FIG.
`3b). A CSG tree has internal nodes that represent Bool
`ean operations and rigid motions while the leaves of the
`tree represent solid primitives, here representative of
`the implant proximal and distal portions and the ap
`proach volume. The robot controller 24 can specify the
`check volumes to the safety monitoring processor 38 in
`at least two manners. A ?rst approach speci?es a check
`volume for each major phase of the surgery, such as
`specifying the check volume for the approach volume,
`then the proximal portion of the implant and subse
`quently specifying the check volume for the distal por
`tion. A second approach increases the number of leaves
`of the CSG tree by disassociating each major portion
`into its constituent required cutting motions and speci
`fying a check volume for each cut (CUTl-CUTn). A
`combination of these two approaches can also be used.
`Furthermore, each check volume may be speci?ed im
`mediately prior to use or may be speci?ed at any time
`after the robot-to-bone transformation has been com
`puted and stored for subsequent selection and use.
`During surgery the position of the LED beacons are
`observed and, via the transformations discussed above,
`the location of the center of the cutter 22 is determined
`relative to the implant volume by searching and pro
`cessing the CSG tree structure by known techniques. If
`the cutter 22 is determined to stray outside of the im~
`plant volume a command is sent by the safety monitor
`ing processor 38 to the robot controller 24 to freeze
`motion. This command is preferably sent via a minimum
`latency path 240, such as an optically isolated digital
`port. After freezing motion the robot controller 24
`interrogates the safety control processor 38 via the
`serial communication link 24a for more detailed infor
`mation regarding the “out-of-bounds” condition.
`It has been determined that this technique reliably
`detects a motion that crosses a predetermined CSG
`threshold to within approximately 0.2 mm precision
`with constant orientation, and approximately 0.4 mm
`precision with cutter reorientation. Cutter motion
`checking rates of approximately 3-4 Hz are obtained
`using the present embodiment. At typical bone cutting
`speeds a total cutter excursion before motion is frozen is
`approximately two millimeters, after all system laten
`cies are accounted for.
`The surgeon-system interface further includes an
`online display system that includes a high resolution
`monitor 48 coupled to a display processor 50. The dis
`play processor 50 receives information from the robot
`controller 24, the safety monitoring processor 38 and a
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`7
`CT pre-surgery system 52. This information is com
`bined by the display processor 50 to visually depict the
`progress of the cutting procedure by superimposing the
`CT-derived bone images and a corresponding cross-sec
`tional view of the selected implant shape. The CT im
`ages may include both transverse and longitudinal im
`ages of the femur having appropriate cross-sectional
`views of the selected implant superimposed thereon. A
`particular cross-sectional bone image that is selected for
`display typically corresponds to the current depth of
`the cutter 22 within the femur.
`The pendant 26 is a gas-sterilized hand-held data
`terminal that allows the surgeon to interact with the
`system 10 during the course of the operation. Menus
`invoked from the pendant 26 and displayed on the dis
`play 48 permit the surgeon to interrogate system 10
`status, to select local actions such as manual guiding or
`withdrawal of the cutting tool, to continue a present
`motion, to discontinue or repeat a present step of the
`surgical procedure, or to restart the procedure from
`some earlier step altogether. One very common case is
`a simple “pause” function that inhibits further forward
`motion of the cutter 22 to allow the surgeon to satisfy
`himself that all is well or to permit the performance of
`some housekeeping function such as re?lling an irriga
`tion bottle. Pendant 26 also supports an emergency
`power on/off function and may also be employed to
`control the overall sequence of application steps and to
`select appropriate pre-programmed error recovery pro
`cedures should the need arise. -
`Each of the major system components, that is the
`robot controller 24, FMP 53 and safety monitoring
`processor 38, are enabled to freeze (inhibit) all robot
`motion or to turn off manipulator and cutter power in
`response to recognized exception conditions. If _one of
`these conditions occurs the surgeon must explicitly
`re-enable motion from the hand-held pendant 26.
`During surgery the principal safety monitoring re
`quirements are (1) that the robot 12 should not “run
`away”; (2) that it should not exert excessive force on the
`patient; (3) that the cutter 22 should stay within a pre
`speci?ed positional envelope relative to the volume
`being cut; and (4) that the surgeon be able to intervene
`at any time to stop the robot 12. Once robot motion is
`stopped the surgeon is able, via the pendant 26, to query
`the robot’s status, to manually guide the effector, to
`select an appropriate recovery procedure to continue
`the surgery, or to completely terminate use of the robot
`l2 and continue manually with the surgery.
`As a part of the redundant safety monitoring of the
`system 10 the robot controller 24 itself routinely per- ,
`forms many safety and consistency checks, including
`such functions as determining position and velocity
`deadbands of the joint servos, monitoring of external
`signals, and the maintenance of a safety timeout monitor
`(STM) 24b which removes arm 14 power if the control
`ler 24 does not af?rmatively verify system integrity at
`predetermined intervals. In a presently preferred em
`bodiment the interval is 16 ms. In addition to a robot
`power-enable relay (not shown) the controller 24 soft
`ware provides facilities for disabling manipulator
`power, for “freezing” motion, for resuming interrupted
`motions, and for transferring control to predetermined
`recovery p