CA2195983A1 - Articulated arm for medical procedures - Google Patents

Abstract

An articulated arm is disclosed which can be used to firmly support and position a variety of medical tools, including surgical or diagnostic instruments flexibly in space. Though some of its sub-assemblies may be computer controlled, thus autonomous in accordance to some pre-programmed sequence, manual control is also possible. When its sub-assemblies are suitably controlled using computer software, and with a suitable cutting instrument, the arm is capable of generating a barrel shape cavity or, for that matter, any desired shape of cavity (or treatment volume) that is within the work envelope of the arm. The ideal position of the focal point is dynamically variable as required, either with respect to the tool or the absolute frame of reference, during an intervention. A suitable type of intervention is minimally invasive surgery (MIS). Apart from cutting (or resection), the articulated arm, by virtue of its robotic nature, can also be used to perform such tasks as biopsies and radiation seed implantation, where positional accuracy and repeatability are highly desirable. The articulated arm is a universal computer assisted holder for a wide range of medical tools, in particular endoscopes for treatment of urological disorders.

Description

AT~rT~m~Al~Rn ATM FOR M~nT~r, ~k~ ~.IIIKr~.;

FTT~T.n OF ~ ~ b~v ~ nN
This invention relates to an articulated arm for ~n~nCt; ng medical pLv~eduLe8 and relates particularly, though not OE clu8ively, to a robotic system which is suitable for use in medical applirat;~n~, whether it be 8urgical, therapeutic or diagnostic. The articulated arm may be used to provide a firm support for a range of surgical or diagnostic tools.

0 BAI.~ K(III- -I TO ~I~T.' ,L~V~
C~ r;~ r-rh;n~ and robotic technology have been used very successfully in many industries, especially where repetitive (hence laborious), accurate or hazardous tasks are to be handled with speed. The positional repeatability, certainty, accuracy and precision of a robot has recently found application in positioning surgical tools in the operating theatre. In particular, m;n;~-lly invasive procedures have great potential to exploit robotic technology.
It is known in the art that non-invasive surgeries, such as E5WL ~extracorporeal shockwave lithrotripsy) and high intensity ultrasound, for the fra~ ;on of kidney stones, or otherwise, have employed computer assisted positioning systems to place the target, which is in the patient, in line with the firing line of the treatment tool which is outside the patient.
However, most m;n;r-lly invasive surgery (MIS) procedures require the use of a tool or a number of macroscopic scale tools called endoscopes, which can be rigid or fl OEible, enter through small natural, or incised, openings on the patient, to treat the diseased portions of an organ ; nt~rn~l to the body. ~n~cor~ for MIS yloeedures usually carry optic fibres for the delivery of cool light for viewing the operating site. Such views can be seen through an eyepiece, or shown on a TV monitor (called video surgery), W097100649 1 9S9~3 F~

for comfortable and enlarged viewing. These views (direct ~n~ngroric viaion), however, only provide sight on the ~ P operating environment. The surgeon does not have a clear idea of what lies out8ide this view. It often requires his/her skills and experience to identify his~her whereabouts in the patient when new tissues unfold as a result of cutting, which can be ~Ll~yeluus~
Modern medical imaging modalities, such aa,- ~Pr t~ y (CT), magnetic r~nn~nre imaging (MRI) and ultrasound ~US) offer the po~;h;1;ty of a c ~Pr-~ tPd three-~; -ion~l view, by displaying on a flat monitor a 3D
image of the organ under treatment or observation. This image i6 capable of being superimposed onto the patient as seen through a pair of speri~11y ~,e~aLed goggles, to guide the surgeon during an MIS. In this manner, the time ~ULI~ ~
in resection and suturing can be cut down by a clear view of the operating site. 3D data, composed by the _ Pr can also be used directly, in addition to display, by suitable supervisory or control ~uLLd~Lle of a motion control system, to control the v ~ of the cutter/pn~n~cope carried by a robot of suitable configuration. This way, the surgeon and the computing system know what is beyond the ; ~i~te operating environment.
~xamples of active robotic intervention in MIS
~uuedules are numerous, ;nr~ ;ng TURP (transurethral resection of the pro8tate), automated colu-.08uu~y, stap~ , and ENT (ear-noae-throat) procedures. An example of an open procedure that has been demonstrated with robotic intervention is cementless hip bone implant/replacement, where a precise cavity to fit a pre-selected implant is milled both locationally and dimensionally accurately in the femur by an industrial robot that carries the milling cutter.
EP 0,416,863 (WICKHAM) describes a frame for positioning and guiding a medical implement such as a resectoscope, which can be used for the non-invasive surgical treatment of the prostate. The frame comprises an annular . _ _ . .. _ . , , .. . . _ . , _ . _ . _ _ _ _ _ . _ _ ~195983 frame member (10,50) and an annular ring (15,57) held captive and rotatable about its axia in a plane parallel to that of the frame member. An arcuate bow (18,65) extends acros6 the ring and carries a i ;ng block (20,66) for the implement, the ~ ,v ' of which is controlled by moving the block along the bow and by moving the ring relative to the frame member.
The radius of the ring, the radius of curvature of the bow and the distance of the tip of the medical implement from the bow are selected such that , ~. t of the implement around the ring and across the bow will sweep out two gubgt~nt;~l1y conical regions on the side of the ring remote from the bow.
In the case where the medical implement is a resectoscope, the smaller conical region is that of the material to be removed to leave a conical orifice in the prostate. One form of the frame may be mounted to a table by means of a clamp, whilst another form of the frame may be secured to an overhead mounting. Motor drives may be provided for rotating the annular ring, traversing an ~ t mounted across the bow and for operating the implement.
The frame of EP 0,416,863 is not readily ~ ';f;~
to perform operation6 other than TURP or other cutting modalities for TURP than electrocauteri6ation. In particular, the mounting block ~20,66) is not easily adapted to carry other types of medical tool and the annular ring (15,57) also places a constraint on the type of medical tool that can be mounted on the frame because of the limited area for r Vl of the tool within the circumference of the annular ring. Also, the frame of EP 0,416,863 must be mounted on or in connection with the operating table which further restrict6 the ease with which it can be used or modified for performing other medical procedure5. 5et up of the frame in the operating theatre is extremely difficult.
An assistant is needed to manually carry the entire frame (weighing about 8 kg), rr~nf;nPd to the ball joint8 of the , t;ng frame, to engage the , ;ng block (20,66) with a bracket on the r~rertosrope. The assi8tant has to manually lock two ball joint~ when ~ny~ is ~ h~d. The ~19~3 WO 97/0061~9 PCT/SG95/00009 assistant's presence can cause problems and ob~LLuuLion to the ateriliaed area. Also the frame does not allow for ~uick ;, yell~y manual takeover. With the motorised version, wires cannot be properly hArnP~P~, due to the frame design, and therefore cause obatruction and are a safety hazard.
Complete sterility of the frame cannot be achieved.
The present invention was developed with a view to providing an articlllAtPd arm which can be readily adapted to carry a wide range of medical tools for performing various medical procedures.

~UMMARY OF TXE Iwv According to the present invention there is provided an articulated arm for performing medical pLuceduLes with a medical tool, the arm comprising:
an arcuate member slidably mounted on a first movable support member;
a tool holder for holding the medical tool in an operational position, said tool holder being carried by the arcuate member; and, a first drive assembly provided on said firat support member for alidably moving aaid arcuate member with said tool holder, wherein 8aid tool holder can be moved along an arcuate path 80 as to alter the operational position of the tool in a predetermined manner.
Preferably the articulated arm further comprises a second drive assembly provided in rnnnP~t; nn with said tool holder for moving said tool holder along a linear path, said linear path intersecting an axis passing through the centre of curvature of said arcuate path. The arcuate member may be removably mounted on said firat support member, and wherein another arcuate member having a different radius of curvature can be slidably mounted on the first support member if desired.

~ 219~9v3 W097/00649 . PCT/SG95/00009 Preferably the articulated arm further comprises a third drive assembly , -hAn;cAlly coupled to said first support member for pivoting said first support member about a first drive axis, whereby said tool holder carried by the arcuate member can also be pivoted about said first drive axis.
Advantageously said first support member is coupled to said third drive assembly by means of a ron~ling adapted to produce an offset between said first drive axis and a longitudinal axis of said first support member whereby, in use, a central axis of the medical tool held in the tool holder intersects said first drive axis so as to define a pivot point of the tool.
Preferably said coupling is a removable coupling which can be replaced with a different r~nr1;nS to produce a different offset 80 as to A~ - a te a different medical tool.
Preferably the articulated arm further comprises a second support member for supporting said third drive assembly, said second support member being provided with a fourth drive assembly for moving said third drive assembly in a linear direction whereby, in use, said tool holder together with the arcuate member can also be moved in said linear direction.
The following description will be given with particular reference to the use of the articulated arm in a plv~eduL~ commonly known as TURP (tL~ uLèthral resection of the prostate), which has been regarded as the gold standard in treating Benign Prostate Hyperplasia ~BPH). The cutting modality assumed is the electro~AIlt~r;~Ation technique. The medical tools employed in TURP are urological endoscopes, in particular, a resectoscope which comprises a telescopic lens, an electrode, an outer sheath and a working element equipped with a spring loaded handle of standard configuration. It is to be understood that the ~ticulated arm can be used equally ~cc~sfnl1y in many other medical procedures, and is not limited in its application to TURP. Fur~l e~ the 219~983 W097/00649 ; pcT/sGssloooo9 articulated arm is capable of holding a wide variety of other medical tools and is not restricted to urological endoscopes.

B~IEF ~1~L_ OF T~E
In order to enable the current invention to be more readily understood, reference will now be made to the ~rl_ ying figures which illustrate, by way of example only, an : ' '; of the articulated arm, and in which:
Figure 1 is an isometric view of the articulated arm showing its various Enh~
Figure 2 is an isometric view of the articulated arm and count~rh~lAnre support system as it would be used in an operating room to perform T~oRP;
Figure 3 illustrates a preferred pivot length drive sub-assembly of~the articulated arm, including a preferred tool holder;
Figure ~ illustrates a C-bracket sub-assembly employed with the tool holder of Figure 3;
Figure 5 illustrates how a LL~#uLethral ultrasound probe can be mounted onto the tool holder of the pivot length drive assembly;
Figure 6 illustrates how a transrectral ultrasound probe can be mounted onto the tool holder of the pivot length drive assembly;
Figure 7 is a peL~e~Live view of the arch drive 8ub-assembly of the art; e~ t~d arm;
Figure 3 is a section view through an arch drive sub-assembly of the articulated arm;
Figure 9 illustrates one form of ring rotation sub-assembly of the artic~ t~d arm;
Figure 10 illustrates one form of conrl ;ng that maybe employed with the arti~nlat~ arm;
Figure 11 illustrates one form of head travel sub-assembly of the articulated arm;
Figure 12 ahows a main column assembly including a pulley system and b~l ~n~;ng weights;
Figure 13 depicts a ronnt~hAl~n~e support W097io0649 213 ~ 9 8 3 r~ll~G)s~c structure used with the articulated arm;
Figure 14 illustrates a r~n~;n~ ly lockable cable system used in the X, Y and Z arma of the counl-~h;~l;7n~e support system;
Figure 15 shows schematically the tracing of a barrel shape contour beyond a focal point by a resectoscope held by the art;rlll;7t~f7 arm;
Figure 16 shows the modular structure of the surgeon interface ~oCL~dLe, which is designed to allow self- i guided event driven operation of the articulated arm; and, Figure 17 is a flln~ j~n;71 block diagram of the overall system, showing , p~nen~C7 of the system, their inter-relationE and control.

nRT~ Tr.~Rn r~ OF ~r r ~
A preferred ' ~';~ of the articulated arm according to the invention is illustrated in Figure 1. The arm comprises an arcuate member in the ~orm of an arch 124 (see=Figure 7) slidably mounted on a first movable support member in the form of an-arch support 300. A tool holder in the form of a carriage 137 (see Figure 3), for holding a medical tool in an operational position, iE carried by the arch 124. A first drive assembly in the form of arch drive aEsembly 302 (see Figure 8) is provided on said arch support 300 for slidably moving the arch 124 with said carriage 137 so that the carriage can be moved along an arcuate path so as to alter the operational position of the tool in a predetermined manner. A second drive assembly in the form of a pivot length drive assembly 304 is provided in connection with the carriage 137 for moving the carriage along a linear path. Advantageously, the linear path along which the carriage 137 can move intersects with the centre of curvature of the arch 124.
The arch drive support 300 of the articulated arm is in turn carried by a second movable support men7ber in the form of a vertical support column 84 by means of a coupling 275 The support column 84 is provided with a third drive 219 ~3 W097/00649 ~ PCT/SG95/00009 assernbly in the form of a ring drive assembly 306 in cnnn~c~;on therewith, for pivoting the cQ--rling 275 about a ring drive axis 180. The rollrling 275 creates an offset 272 between a longitudinal axis 308 of the arch support 300 and the axis of rotation 180 of the ring drive assembly 306. The ring drive assembly 306 is in turn mounted in r~nn~ct;on with a fourth drive assembly in the form of a head travel drive assembly 310 (see Figure 11) provided at the base of support column 84. The head travel drive assembly is adapted to move the ring drive assembly 306 and all of the previously ;rm~ drive ~rr ' li~5 together with the arch support 300 and arch 124 along a linear path in a generally horizontal direction.
The articulated arm of the preferred '~~;
provides freedom- of motion in four in~ nr1~ directions.
They are namely the head travel direction 1, the pivot length direction 2, the arch r v. direction 3, and the ring rotation 4. The art;cnlat~ arm typically has a pivot point 182 (Figures 1 and 15), which is the centre of ~uLv~LULe of the arch 124 of the arch drive asse~bly 302. The pivot point, through which a central axis of the tool carried by the arm preferably passes, advantageously lies on the ring rotational axis 180. This is achieved by having the arch displaced at an offset 272 from the arch drive assembly 302.
Surgical or diagno8tic tool8 can be ~tt~ch~d onto the articulated arm via the carriage 137, (Figure 3). It is usually desirable that the central, or desired, axis of the~e tools can be arranged to pass through the pivot point at all times and all configurations. This way, the tool axis forms the radial axis of the arch. Though the pivot point is fixed with respect to the arch 124, its position with respect to the tool body is variable. This is desirable in optimising the cutting strategy to be described later.
The pivot length drive assembly 304 (Figure 3) is the nearest to the patient. It consists of the carriage 137, a motor housing 144, a servo motor 139, a printed circuit board 140, guide rails 145, ball bnrh;ng~ 143, locking levers _ _ _ _ _ _ . . . . _ ~ wO97/00649 219 ~ ~ 8 3 PCT/SC9S/0oO09 g _ 150, a pair of set screws 147, and a rack 135 and pinion 136.
The carriage is shaped in such a way that clearances/offsets 134 are provided to clear the penis head and the resectoscope body. The centre line, which is also the central axis of the resectoscope, is arranged to align with the ring rotational axis 180.
The carriage 137 is supported on the guide rails 145 using ball bllRh;ngR 143 housed in the motor hou~ing. As i8 clearly illuatrated in Figure 3, the servo motor 139 i8 partly enclosed in its housing, with its shaft protruding m~rnf-~th. The rack and pinion a~ .y~ 135, 136 allows the motor 139 to drive the carriage and move it back and forth. The motor housing 144 remains stationary and is secured firmly by means of slot 142 onto an ear 299 milled on the arch 124, via three screws 298 (see Figure 7). Any - ~, of the arch will carry the entire pivot length drive assembly 304 with it.
The printed circuit board 140 houses a differential line driver for the encoder signals to make them less susceptible to noise. The board is properly shielded to suppress ele~L~ 3n~tic interference (notably from a electro-cauterisation unit commonly u8ed in the operating theatre), and is mounted beside the motor housing 144. this board allow8 ea8y r~rl~f t of the motor, by providing electrical ~nnn~rtnrs on board.
The carriage 137 has two, or more, pairs of grooves 138 cut in a manner shown in Figure 3. A selected pair of these grooves can be used to engage a C-bracket 151. The choice of groove depends on the desired location of the pivot point 182 with respect to a resectoscope body 179. The C-bracket lSl (see Figure 4) is secured semi-permanently, using screws, onto a suitable portion of the resectoscope 179 and is sterilised together with the resectoscope. The C-bracket 151 forms one part of a bracket assembly, with another bracket 157. With a 81ight gap between the two parts of the bracket assembly, a suff;ri~ntly firm grip can be nht~;nr~
when they are assembled onto a cylindrical portion of a tool W097/00649 ~ 9 8 3 PCT~G95loO009 such a3 an ~n~srope. Other forms of brackets may be readily made to fix onto other tools whose bodies are not cylindrical.
A protruding section on the bracket 157, as shown in Figure 4, has a slot 159 through which a spindle 154, of corr~pnn~;ng diameter can pass. Recesses 160 are made on both sides of the thickness of the protruding section. A set of locking keys 156, constituting two halves, can be pushed manually, or under spring action, toward the slot 159 or away from it (see Figure 4). The spindle 154 already mounted on the tip of a retractor (for example, a Greenberg retractor), is slid into the slot 159 of the protruding section. The entrance of the slot is slightly chamfered to ease entry.
The spindle 154 is provided with a keyway 155. The spindle, or the C-bracket, can be rotated 90 that the keyway is directly in the path of the locking keys 156. Once aligned, the locking keys are pushed (manually) down to engage with the keyway 155 milled on the spindle, or, the spring action pushes the locking keys 156 into the keyway 155. This removes two degrees of freedom, 286 and 287 (see Figure 4), so that there is no relative v~ between the endoscope and the tool holder. ~ence the endoscope can only be --n;r~ t~ in ways permitted by the holder. To remove the endO8COpe i8 achieved simply by lifting the locking key8 156 upward 80 that they are not in the keyway 155. The spindle, and the holder it ~tt~h~ onto, can now be removed from the protruding section; and ~t~h~d from the ~n~ ope Semi-circular grooves 152 cut on the C-bracket 151 are for the purpose of locking the bracket assembly when the C-bracket is engaged into grooves 138 cut on the carriage 137. The locking levers 150 have a flat 149 milled over a suitable length of its body. The levers are inserted into drilled holes 146 whose centres are offset 80 that the levers can be rotated to a poaition where the flat is flush with the grooves 138. When flush, the C-bracket can be inserted. The locking levers are prevented from dropping out by the set screws 147. Once the C-bracket is in place, the locking ~ 2~9~gg3 WO 97/00649 ~ r~.~s~.~s,~

levers are turned 90 degrees or more 80 that the rounded portion of the levers now fill the grooves lS2 cut on the C-bracket, thus locking it to the carriage 137.
One ' ~';~ of an arch drive assembly is 5 illu5trated in Figure 8. As can be seen in Figure 8, the arch drive consist8 of a drive shaft 130, bearing supports 118 and 129, a differential optical encoder 106 (or other form of position sensor), an ele~:LL~ _ ~ ;c brake 131 (preferably of normally locked type~, bearing housing 117 and p~~nAimn 113, and a servo motor 119. The bearing housing ~-117 and extension 113 together form the arch support 300.
Axial grooves (not shown in Figure 8) are cut on the annular surface of the housing 117 for the passage of wires. These wires, from the arch drive motor 119, encoder 106, brake 131, 15 and from the arch 124 itself (limit switches or other additions), are collected at the recess where another branch of wires, (from the pivot length drive), t~orm;nRte via an electrical connector 108. The wires 116 leading to the pivot length drive are bundled in a highly flexible insulated 20 conduit 115, and with extra overhang to allow r ,vc t of the arch 124.
Wires collected within a recess 288 are all arranged to pass through a central hole 112 in the housing extension 113 at the end of which is another ~1 ~ctr; mAl 25 C.~,nn_~t~~ir 109. The use of connectors, as described above, is to facilitate changing of the .~Qllpl ;ng 275 to accommodate different ~1; t~r offsets 272 and tool lengths. From the end of the housing extension 113 ~Figures 7 and 8), another flexible insulated and shielded conduit 107, with overhang to 30 allow for ring rotation, bundles the wires and leads them to the vertical column 84 (Figure 4) where it enters with a stress relief.
The arch drive assembly 302 carries and drives the - ~-arch 124 in the arch assembly (see Figures 7 and 8). The 35 arch assembly consists of the arch 124 which has an external gear profile 120 cut on its circumference and is in the shape of an arc of a circle (of suitable radius and subtended W097/00649 219 ~ 9 g ~ PCT/SG95/00009 angle), stiffeners 121 and 125, a cross shaft 126, a bevel gear set 128, a stopper 297, bearings 123, bearing tPn~inninrJ
screws 301, limit switches 294 (inside the stiffener 125, not visible), and a bearing housing 127. As v ~nnPd before, the arch 124 has an ear 299 for the ; ng of the pivot length drive assev.,bly. When the arch drive motor 119 rotates the drive shaft 130, the motion is transmitted via the bevel gear set, 128 and 120, to the arch 124. The tool, mounted on the carriage 137 of the pivot length drive assembly, is caused to move along an arcuate path and the pivot point, formed by the centre of curvature of the arch, is at a suitable location along the tool body. This location can be adjusted either by moving the carriage 137 using the pivot length drive or by placing the tool with the C-bracket manually onto another available pair of grooves 138 on the carriage.
In the manual option, one can select the right pair of grooves 138 on the carriage, which can be one of several pairs limited by the length of the carriage, to engage the C-bracket. The other option is motorised and . _~Prised, inthat the pivot length drive can move the tool it carries with respect to the arch and hence its centre. Furthermore, the ol~te position of the pivot point in space can be adjusted by moving the head travel drive assev.,bly 310 after the articulated arm is locked onto the c~llntrrh~l ~nr~ support system.
The stiffeners 121, 125 act to strengthen the arch support and to give bearing surfaces for the smooth sliding ~ t of the arch 124. The arch has a series of holes 293 and 294 cut on its body at specific radial distances or intervals. The holes 293 allow the screwing on of a hard stop to positively prevent the arch 124 from overrun. Two hard stops are preferably provided to limit the arch travel in both directions. One stop is fixed, the rl~ of the other into the holes is ~PpPn~Pnt on the size of the target and is le ~P~ by the YofL~Le. The total arch travel is therefore adjustable. If a larger travel is needed, an . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ =

219~983 w~s7~00649 arcuate member of larger subtended angle and/or having a different radius of euLvdLuLe can be used. Indeed, the arcuate member may have a radius of ~uLvdLuLe from anywhere between 5cm to ;nf;n;tP (in the latter case the arcuate mernber is aubs~nt;~lly straight so that the tool holder will be movable along a linear path). The optimum travel for treating the prostate, using electro-TURP is zero to 40 degrees with a radius of euLvdLuLe of 250 to 300 mm.
An alternative means of ac -' ~;ng different radii, rather than using an arcuate mernber having a different radius of eULVd8ULe, is to use a tool holder or carriage 137 that has ~ n~d length to provide more slots 138. Each of these slots carries the tool at a different radius of curvature.
A preferred ~~' '; ' of a ring drive assembly will now be described with reference to Figure 9. The ring drive consists of a motor 96, bearings 98 and 105, a housing 94, tr~n ~si~n shafts 97 and 100, a position sensor 103, a gear train 95 and 102, and a brake 104. The ring drive assembly carries the arch support 300, the arch 124 and hence the pivot length drive, via a rollrl;ng 275 (Figure lo). The rota~i~n~l r ~. provided by the ring drive is limited to +/- 180 degrees. As the ring drive rotates the arch drive assernbly and pivot length drive as~ernbly, it brings the tool to address different angular positions 181 with respect to the patient ~Figure 15). Wires 289 from the ring drive join a separate insulated and ~h;~ d conduit 290 and t~nmin~te at the lower portion of the column 84.
The arch drive axis 308 together with the pivot length drive axis, are arranged to be c~nf;n~d in a plane 285 (Figure 1). This is to save space. When the ring drive operates, this plane rotates and forms an angle with a plane 284 that c~nt~;n~ the head drive and ring drive axea. The planes are ~;~plac~d by an offset 272 which can be alterable.

The offset 272 is alterable by means of the coupling 275 illustrated in Figure 10. The P~n~;~n 113 of i~ ~ 9 ~ ~ ~3 W097/00649 rc.,~ sc~ 3 arch support 300 is non-rotatably received in recess 274 of ~onrl;ng 275, whilst the tr~nr~ inn shaft 100 of the ring drive assembly i8 non-rotatably received in the recess 273 of the collrl; ng, Hence, rotation of shaft 100 will produce a pivoting - VG ' of the coupling 275, which in turn produces an orbital motion of the arch support and its associated ass ~l;~r about the ring drive axis 180. The radius of orbit, corresponding to the offset 272 can be altered simply by replacing rollrlinrJ 275 with another rollrl;ng of different length. Alternatively~ an adjustable offset of variable length may be employed The length of the ~t~n~inn arm 113 of arch support 300 can be altered to ac ' ~e different tool lengths. A
telescopic arm can be used. The rOllrl; ng void 274 can a~ te a limited difference in length7 by sliding the arm in it Also, 113 is made modular 80 that a different length of 113 can be selected. However, too long an arm will not be desirable as the bending r v~ about the bail joint 163 will be great. Although 163 can be modified dimensionally and/or texturally to suit the need, h~n~l ;ng the art;~nl~t~ arm becomes prohibitively difficult.
Finally, the head travel drive assembly 310, which is provided at the bottom of column 84, will be described with reference to Figure 11. The head travel drive assembly consists of a motor 89, a po8ition encoder (not shown), a rack 81 and pinion 91, a guide rail 79, ~n~rl~t~ 87, housing 83, limit switches 86 and base plate 88 (Figure 11). The head travel drive moves all the as8emblies described in the preceding p~L~yl~hs in a horizontal fashion, sagitally 1 (Figure 1) with respect to the patient. This allows different prostate lengths to be administered. All conduit~
and wires t~r~;n~ing at the column 84 are connected to four or five sockets 291 at the upper end of the column.
Co.,~ ;nrJ plugs affixed on the Y-arm of the count~rh~l ~nre support system can be connected to these sockets to prepare the robot for use.
At the upper end of the column 84, a bolt with a ~ ~19Sg~3'''' W097/00649 PcT~GsS/OOOOs spherical head 164 i8 secured firmly. The spherical head 164 is to engage into a ball joint assembly 312 ~P~ignPd to facilitate rapid rnnnPrtinn/~;~rnnnpct;nn of the art;c~ tP~
arm to a ~o~ntPrh~l~n~P support 6ystem (see Figure 13). The head travel has a movable limit 6tops 78 that poaitively (by way of jam bolts 85 and limit switches 80) prevents the tool, being carried by the arm, from going beyond a safe limit, even when there is a di~L~cu~y in the software driving the head travel motor.
lo AdvAnt~geou~ly, the pivot length drive is 6elf-cnnt~;nPd and can be ~Pt~hPd for a stand alone ~ppliratinn It is therefore capable of being held by a -~h~n; ~P~ holder such as, but not limited to, an Flmed retractor to perform such useful tasks as urodynamics study where the diagnostic probe, usually ultrasound, has to be moved at fixed and accurate intervals. These lineari v. l'~ can be delivered by the pivot length drive alone. The same argument extends to other axes of the articulated arm, either individually or in , - n~t; nn, aa they are modular by design.
In a preferred '~'i-- of the current invention, the articulated arm is sn~pPn~Pd on a rountPrh~llnnP support system (Figure 13) via a ball joint 164 (Figure l) which is manually lockable by means of a handle 168. The conntPrh~l~nre support system provides three degrees of linear freedom, 8 (X), 7 (Y) and 6 (Z), plus a rot~t;nn~l swing 5 (R). The latter allows a quick swing away of the robot when human intervention is ~PcP~ry in an . yGn~y.
The Z I ~G ' 6 is collntPrh~l~nrPd by a suitable number of deadweights 248 hidden in the main column 28. (see Figure 12). The conntPrh~l~nre support system ;n~ P~ a horizontal Y-arm 17, a horizontal X-arm 18 from which the art;~nl~tPd arm is suspended, and a vertical main column 28.
When ~L~Liately tuned, the total weight of the Y-arm 17, X-arm 18 and the art;rnlite~ arm (Figure 2) is h~lAncPd.
Hence, very little effort is required by the human operator in order to move the ~r- ' 1 i PS during a setup pL~ceduLG.
The X, Y and Z , v. '~ of the conntPrh~l~nee .... .. . ~

lgS~3 '"
WO 97/00649 ~ PCT/.~:C:9 ~ 9 support system provide cnnt;nnm~C -- v. along the respective axes. The physical aL-_ _ is such that the X arm 18 is carried by the Y arm 17 which is in turn carried by a column rotation aasembly, which in turn is carried by the Z arm ~on the main column 28) via a swing bracket aasembly 19 (see Figure 13). The load being carried ride9 on a bearing guide 30a and 30b (Figure 12), 240a and 240b (Figure 14) which is able to with~t~n~ the bending moment and torsional torques. In the swing bracket assembly 19, the Y
arm 17 rotates on a sliding bearing about a awivel shaft 29, (Figure 13). Unlike the linear axes, the rot~tinn~l axis has intermittent steps of rotation. A plunger 36 is spring loaded and falls into a series of tapered holes 39 to give very positive locking action. To unlock, either a solenoid 35 i8 activated, or the plunger button 32 is compressed, both lift the plunger off its seat, thus allowing swivel action of the horizontal Y-arm 17. (Figure 13).
Within each of the X arm 17, Y arm 18 and main column 28 means ior slidably moving the art;cnl~ted arm in the X, Y and Z directions respectively are provided Figure 14 provides a cut away view of the X arm 18 illustrating a preferred means of effecting the sliding - v. . A cable and pulley system is used comprising an endless cable loop 239 received on guide pulleys 237 provided at both ends of the arm. A bearing mounted slide unit 240b is slidably mounted on a linear guide 240a and is provided with a ball joint atta~' 241 to which the ball joint assembly 312 is connected. The slide unit 240b is fixed to the cable 239, and its sliding , ,v. t on the linear guide 240a is limited by rubber stoppers 243. Along the cable path, one or two locking r -hAn;l can be ;nct~llP~, ~PpPn~;ng on the stroke length. As a fail safe feature, the cable, and hence the load being carried, is normally prevented from moving. Thi8 is accomplished by a cl _; n5 lever 268, pivot pin 266 and spring 269, the cable 239 is gripped by the lever under the spring force acting at a pivot distance 265. To unlock the cable, the solPnnid 236 (Figure 14) can be activated _ _ _ _ . _ _ _ _ _ _ . _ . .. . .. . . . . ..

~ 2195g~:3',,' W097/00649 PCT/sG95loouos electrically, which pulls the lever away from the cable, thus freeing it. A manual override lever 34 is provided to allow manual override, in case of power failure or unforr~e~hle circumstances. The cable and pulley aLL_ , is repeated in all the linear axes, with slight alterations, particularly stroke length. (see Figure 12, solenoid 249 and manual lever 247).
In the illustrated : ' ' t of the current invention, the nn-lnt~rh~l~nr~ support system is in the form o~ a trolley system that can be wheeled around for transportation or storage purpose. The trolley is equipped with shelves 25, 26 and 27 (Figure 13) for the housing of personal ~ ~r systems, surgical in~LLl t ~ and a motion control system. The trolley has a base 24 that can be lowered such that the entire system, including the robot, rests on the floor on four footings. The weight of the system ensures that, even with the d~yare~ ve~ g of the Y-arm the system is sufficiently rigid and stable with respect to the patient tl~uuylluuL an op~rAt;nn or np~n~t;r,n~.
When the operation is complete or not required, the robot and its trolley (rollnt~h~l~nre support) system can be wheeled away. This is achieved by applying a force on a foot pedal 254 to lift up the base and have the wheels 257 engage with the floor and bear the weight of the overall system.
In a setup procedure for TURP, the target to be est~hli~hPd as the reference position of the robot is the ve-l , which is the junction of the ej~nnl~tory duct and the prostatic urethra. The veL, ~nnm is i~nt;~;r~
under direct endoscopic vision. When it is found, the endoscope/cystoscope/resectoscope is fixed in space by an iate holder such as a Greenberg retractor or an Elmed retractor. It should be appreciated that the orientation of ~ the endoscope is arbitrary when the veL, t: is found.
When the endoscope i5 fixed, the art;c~leted arm is then brought into ~nga~ with the ~ ~n~r~pe.
Moving the nri~ntat;r,n and position of the art~rnl~t~ arm, relative to the patient who is fixed under

2 ~ 8 3 his o~n weight or with some suitable method of strapping (see Figure 2), is facilitated by the ~-mlnt~rh~l~n~ support 8y8tem, mainly by its three linear axes which must first be nnlorkPd by activating the corr~pn"~;ng solenoids, such as 8o1Pnn;~q 236, 249 and the ball joint. In the first ~y~l~a~h~ the surgeon ~-n;rlll~tP~ the articulated arm, lifting it or lowering it, ahifting it ~;.d I y~ swivelling it about the ball joint, until the C-bracket 151 enters into the grooves 138 cut on the carriage 137 of the art~rnl~tPd arm, ~see Figure 3). Alternatively, to avoid the use of a passive holder, the articulated arm and the tool holder are brought close to the endoscope, which is then engaged onto the carriage 137, disturbing it slightly from the reference position; followed by moving the articnl~tP~ arm together with the Pn~n~cope (as one body without moving the robot's axes) to re-establish the V~L ' ~ lo~t;nn~ These two approaches are both valid, their use depending on the surgeon~ 8 preference and skill.
The rmlntPrh~l~n~e gantry can be provided with a plurality of cameras at the same level as the x-arm 18. Thi~
is to enhance the safety of the art;rlll~t~ arm during an operation. The cameras are to observe markers or stripes strlt~g;r~lly placed on to the robot and are properly calibrated 80 as to obtain optimal accuracy. Knowing directly the joints rotation or tr~n~lat;nn using machine vision, and with known k;r ~~;C~ and geometry of the arm, the tip of the cutter can be ensured to always move within a prP~Pf;nPd safe working envelope. Any r~ t outgide this envelope will trigger a suspension of motion and an alarm to warn the user.
The C-bracket 151 is previously fastened onto the resectoscope/endoscope and sterilised together with it.
Securing of the C-bracket 151, hence the resectoscope, is achieved by turning the two levers 150, preventing it from dropping out of the grooves 138 of the c~rr;~ge 137. The X, Y, z and R axes of the countprh~l~n~p support system are then locked by de-activation of their respective solenoids 236, w097/00649 2 i 9~ ~ PCT~C95/oooog 249 and 35. This is a fail safe feature in that the axes are normally locked when the s~l~nni~ are not powered. The retractor i9 then removed by l~nl nr~; n~ the lever 156 and sliding the pin 154 away from the C-bracket. The setup procedure is then , ~lete. Although the vc~ ~mlm has been used in the above ~ yL~phs to show a setup procedure for TURP, it should be appreciated that other targets, to be i~nt;f;~ ~n~n~copjcally and referenced, or other kinds of intervention, can benefit from the same setup yl~ed~L~
The articl~1~teA arm, like other known robot systems, may be controlled by a motion controller 47 which in turn is supervised by a portabie personal c ~r 48, via RS232 communication 76 (see Figure 17). Motorisation 73 of the respective axes (positioning, velocity, acceleration, and coo~dination) are controlled using a conv~ntinn~l PID control loop impl~ t~ digitally on a state of the art microprocessor based multi-axis motion control system 47.
Position sensors, such as, but not limited to, a differential optical encoder 71, can be employed to provide both positional and velocity ;nfor~-t;nn for the control loop.
The motion control system is also capable of a number of signal input and output functions 59. These 80 called l/o functions are normally used to capture the status of limit switches, 74 and 75, for the purpose of ~homing~', turn on or off ~q~ working in conjunction with the robot send off alarm or light ;n~;cat;nn to serve as a warning of danger or other important events etc.. The above r ~; nn~d motion control system is well known and is widely available commercially and will not, therefore, be described in detail here.
sarrel cavity g~n~t;nn/ as shown in Figure 15, is a typical form of resection capable of being performed by the articulated arm design. In this cutting strategy, one or more axes of ~ ,vc are involved at any one time.
Coordinated , ~. ' of the arch and pivot length drive to trace a, 80 called, sagittal line 185 being the ideal.
~ ~ reconstruction of ultrasound images facilitates the 2195~g3 w097/0~9 ~ ,j r~

fl~t~rm;nA~inn of a series of sagittal lines in a round the clock fashion 181. The ring axis brings the r~nertn~ope to address each of these ~agitt2l lines. In the case of ele~L~ r;n2t~nn, tracing, and hence cutting, along the sagittal line is repeated clockwise and counter-clockwise and progres8ively outwards till the surgical capsule 279 (Figure 15) i8 reached. In the case of Laser T~RP (such as VLAP, vi8ual laser ~hl2t;nn of the Prostate), the speed of withfl 1 of the laser fibre and its spatial power pattern can be controlled on the fly (i.e. dyn~m;rAlly) so as to achieve optimal cutting, not guite possible by a human operator. Similar ~L' ' extends to TUNA (transurethral needle Ahlat; nn of the Prostate) where the needles are to protrude/retract at different clock positions to different depths and the power setting is to be controlled in a manner quite cumbersome for a human operator.
Figure 17 is a circuit block diagram showing typical ~ _ ~nt n which the linked arm can work in conjunction with to carry out useful and safe activities.
These , ~ n are:
An nn;nt~rruptable power supply 45 to supply power to the system cnnt;nllAlly. It sustains the system to operate for at least 10 minutes (fl~pPnfl;ng on the capacity of standby battery 44) in the event of a power failure.
A 4-axis motion controller 47 with input-output functions 59, that can be interrupt driven. The motion controller can be stand alone or mounted on an ~p2nRi~n slot in a personal computer 48. r ;cat;on with the PC in the stand alone case is via a RS232 line, while the latter is via a local bus.
A personal c ~ ~r 48 with a usual di8play monitor 56, hard disk 58, floppy disk drive, RAM and ROM operating memories, op~rAt;ng system, printer 57, and optional e~rn2l storage devices such as a compact disk drive 60, and an optical di~k drive 61.
A diagnostic ultrasound 8~Ann;ng 8ystem 49. Either transrectal or LL~.su,~thral probe or both can be used. A

_ _ _ _ _ _ _ _ _ _ _ ~ .. . . : .. . .. . _ ... _ . . _ . . .

~ ~195~3 W097/00649 PcTlsGs5/oooos frame grabber 62, ;n#tAllr~ on the PC 48, captures the ultrasound images from the ultrAAolln~ scanner via a set of co-axial video signal cables. Communication between the ultrasound scanner and the ~r is optional, but can be~ estAhl;Ah~ using the GPIB standard conformed to IEEE 488,77.
A video rAAsette recorder 50, to archive ultrasound and/or endoscopic images, intra, pre- or postop~rAt;vely.
A remote light source 51, supplying cool light via optical fibres to the operating site and the scene u~8uL~d by CCD (charged coupled device) camera 69, for maximum efficiency. The image, in the form of electronic signals, can be processed and ~nh~nred and finally displayed onto an endoscopic monitor screen 70.
Energy source 52 for cutting. In the case of electlu~uly~Ly, this is the 80 called ~;~th~rmy unit. In the case of laser surgery, this will be a gQn~rAtor for high intensity laser light source.
A hard logic safety monitor 53, r~t~;nR
yLuyL hl e logic arrays that will monitor logic status of critical paL ~rs and send out interrupting signals to suspend the robot action, or warning signals to alert the user of any untoward events during an operation.
The personal computer ~cnt~A an interface ~ uL~w~Le 191, called APUI (~lt~ t~ Pro8tAtect~ y U8er Tnt~rfAre), which carries out tasks as ol~tl~n~d in Pigure 16.
Each task to be performed by the user interface is designed to occupy a page of screen display, with pop-up windows and pull down menus to offer versatile s~lertl~nA.
Support 192, displays a acreen with control buttons and status boxes to control the activation ~or deactivation) of locks of the colmtQrh~lAnre support sygtem, in, ';n~tirn or individually. It also displays the lock status of each of the axes of the rrllnt~rhalance support system, (except B, 200) X, 201, Y, 202, A, 203, R, 204, which correspond to the axes of the collnt~rhAlAnre support system (Figure 13), 8, 7, 5 and 6 respectively.
A homing seguence of the robot, after or before the . . . _ _ _ _ _ w097/00649 219 5 ~ ~ 3 r~ ,3 setup procedure i8 accomplished, i8 carried out by a subroutine in the interface called HOME, 193. This routine brings each of the axes of the robot to a suitable reference poaition ;nf1u~nr~d by the size and orientation of the target that i8 to be addressed by the robot. HOME occupies a screen display page, again with pop-up windows and pull down menus to f~r;1;tate a~lert;nn of a large variety, including redefinition of home poaition of the axes.
A frame grabber board F.GR3 62 and biaxial cable take and tran8fer image8 respectively from the ultrasound scanner. A state-of-the-art ~fLw~le for image processing, together with customised software routine3, process the images. The end results are used to guide the operation to be performed by the articulated arm.
The desired~ v~ t., or ~ ~;n~t;nn Of to achieve the ;nt~n~ed work envelope within the patient, and events like switching, adjusting the power setting, etc , are f- l~t~d into 'R understood by the motion controller and sent to it by the personal ~ ~ ~r via RS232 (or serial) lines ~6. The s~f LW~Le routines that handle this translation are grouped under BARRE~ 198.
The articulated arm is also capable of manual control where ~oysticks, foot or finger switches, at dp~L~iate location8, are provided for fl~;hl~ control of the ~ s of the robot manually. To interpret the controls from joysticks and the like, routines in MAN 199 undertake the tr~n~]at;~n~
Patients' biodata are ~LuLed u8ing PAT 196, of the APUI. These data can be the amount of tissue removed, 30 time taken, age of patient, etc., which are of interest to researchers. St~t;~t;r~l tools, either standard or customised, can be integrated with PAT 196.
Power supply to the robot system is monitored by PWR.M 197, of the APUI. It P~L~LI.~ the n~c~ ry actiona to ensure cont;nnrl~ operation of the robot ayctem without ~ t;nn, in the event of a power failure. Graceful degradation of the system will be ;n;t;~t~ after a _ _ _ _ _ _ _ . . . _ . _ w097/OO~g 2 1 ~ 5 9 8 3 . ~ 93,~ ~

pr~f;nPd period of time.
ERROR hAn~l; ng routines 195 are to handle both foreseeable (normal error h2n~l;ng - for example, memory overflow, 1088 of communication etc.) and nn~Y~ct~d (exception hAn~l ;ng) errors. Recovery procedures will be activated for the first type of errors to restore system operation. Attempts to recover will be activated for nn~rected errors, but will generally lead to a graceful shutdown. In addition, 195 also comprises safety monitoring routines. For example, when the tool holder axis is not moving, cutting power will not be allowed to switch on.
In order to place the.work envelope of the cutting tool, or other forms of implement carried by the robot, in a desired location within the patient, and to know the limit of the work envelope, it is desirable that some form of image guidance be used for the articulated arm. Ultrasound imaging, both transrectal and tL~n~u~èLhral, have been found adequate and safe for such a task. To avoid the problem of patient registration, that is the r-tnh;ns of pre- and intra-( ~ even post-) operative data, it is best that the imaging process shares the same reference frame as the robot system. This means the imaging process has to be done intraoperatively with some form of adaptor for the imaging probe and the cutting tool (or other implements). seing intraoperative, ~i ~;nn~l and lo~t;nnAl mea~u~ ~ of the target have to be accomplished quickly 80 that the process does not add significantly to the overall operating time. ~his can be achieved by using computer image processing techniques.
To facilitate the above method, it is a preferred aspect of the current invention that provision is allowed for both transrectal and transurethral intraoperative scanning of the target to be treated. Transurethral scanning is possible by leaving the outer sheath of the ~Ldosc~pe, which is attached to the carriage (or tool holder) of the articulated arm, in the patient. In the place of the usual working element is the t~ u-ethral ult~A~olln~ probe 186 (see Figure 219~983 w097/00649 ~ 9 5). During srAnn;ng, only the head travel i8 moved, bringing the probe in and out of the patient to obtain the needed tl~nnv~L~e scan data. The probe is replaced by the working element when the scanning is completed, thus sharing of the 3ame frame of reference is realised. The arch stays put at its zero degree, or horizontal, position t~Luu~huuL the 8~nnn; ng process.
Tran8rectal scanning is pon~;hle by way of an ~ttA~' ~ (8ee Figure 6), which has an extension 188 with one end adapted to the outer sheath of the Pn~nnrope and the other a holder 187 for the probe body 190. The extension is adjustable 80 that the ~ntrAnre~ governed by the offset 189, to the rectum is fairly level. Grabbing of the probe body is variable along its length to ic_ ~t~ different setup conditions and pAt;Pntn. As in the case of tL~"nuL~thral scanning, only the head travel is moved, and the probe and extension are replaced by the working element when g~nn;ng is complete.
In a TURP, or procedure to address sPH, the information to be oh~;n~d in an ultrnno~n~ scanning is the coordinates of the boundary known as a surgical capsule.
Cutting beyond the surgical capsule is ~ t desirable as it can lead to ;nr~nt;nPnre~ impotence or torrential bleeding.
The first two cûmplications are due to nerve endings, a fair amount of which lie just behind the capsule, being damaged as a result of cutting. The reason for torrential bleP~;ng is obvious - big vessels are usually situated outside the capsule.
It is not i ~ tPly obvious in a transver8e ultrasound scan where the capsule boundary is. It requiree a trained eye to pick it up and very often not ~ _let~1y and precisely. The articulated arm can perform an ;ntn~pPrative ultrasound sc~nn;n~ either semi-~nt: t;~nlly or automatically. ~ t; n~s in 194 cater for this purpose. In semi-auto scanning, the surgeon has to outline the boundary using a digiti8er 8uch a8 a mou8e. In auto srAnn;ng, the image analysis algorithms will do the job (of course to be W097/00649 219 ~ 9 8 3 PCT~G9S/00009 ~

ay~L-Jved by the silrgeon when done). The choice of which mode of Er~nn;ng to use is a matter of convenience versus safety.
Both must not add ~i~n;f;r~ntly to the operating time.
Preferably all the drive ~r ~ 3 can be draped in a sterilised bag just prior to an npPrat;nn~ The bag can be conveniently fastened onto the column structure 84 of the head drive assembly. It has ample sag room to allow .v~ S of the articulated arm during an operation yet preserving sterility. The entire system is best arranged in a manner shown in Figure 2 where the robot is ghown gnsp~n~
on the connt~rhAl~n~ e support structure which, with its trolley platforms 25, 26 and 27, also houses the computing and surgical ~ l; t ~n~ngrrp;c view is shown on a monitor 259 suitably supported 21 to give comfortable viewing.
To ensure maximum safety and convenience of operation of the system a control panel 218 is placed next to the computer console 258 on the trolley platform (see Pigure 2) . There are visual ;n~;c3tnrs on the control panel to di8play operating status of each axis of the motion controller. When activated, an ;~ ~el.ey switch cuts off power supply to the motors and cutting power sources only, leaving all other system l , -n~5 still functional. Even 80, this is a more drastic measure compared to the keyboard interrupt feature installed in the user interface routine.
The keyl)~Jald interrupt feature is enabled once any, or a number of motors, is set into motion. By hitting any key on the ~ r keyboard, all motor I v~ n~r can be killed or suspended.
Although it has been shown that an I~Y~ nt target for the articulated arm is the prostate gland, it should be appreciated that it can also be used for other targets, for example, the bladder, the womb, etc. Furthermore, the treatment modality is not limited to electrocauterisation, but may include other modalities such as laser, high intensity ultrasound, TUNA (Trans Urethral Needle Ablation), etc. The articulated arm is ~.or;gn~d so as to be capable of ~19~983 W097/00649 PcT/sGgs/oooos holding a wide range of medical tools and to facilitate more precise and ~rCllrRte medical interventions in an operating theatre. With the help of ~ _ ~rised motion control, the system is able to carry the tools, one at a time and to conduct useful medical interventions. In 80 doing, it assists the surgeon to perform his/her task better in terms of time rnnl _Lion, skill, accuracy and hence safety. These may lead to additional benefits such as low mortality, low morbidity, $ewer assistants and nursing staff, less cnn, hl~fi~ and lower risks by avoiding prolonged operating time.
The arm is typically made such that the drive Rr_ ~lies are modular. This allows an entirely different k; n t; r configuration to be nhtR;n~ by replacing the existing drive and support mer.,bers with new ones. Wires are self c~ntR;n~ in a drive and connector~ are provided to enable control and drive signals to reach and leave the drive.
Now that a preferred rmho~; of the articnl~tr~
arm has been described in detail, numerous variations and ';f;r~t;nnr will 8uggest themselves to persons skilled in the relevant arts, in addition to those already described, without departing from the basic inventive concepts. All such variations and r ';~irat;rnC are to be rnnr;~red within the scope of the pre8ent invention, the nature of which is to be ~rtrrm;n~d from the foregoing description and the Rpp~n~
claims.

Claims (20)

1. An articulated arm for performing medical procedures with a medical tool, the arm comprising:
an arcuate member slidably mounted on a first movable support member;
a tool holder for holding the medical tool in an operational position, said tool holder being carried by the arcuate member; and, a first drive assembly provided on said first support member for slidably moving said arcuate member with said tool holder, wherein said tool holder can be moved along an arcuate path so as to alter the operational position of the tool in a predetermined manner.

2. An articulated arm as defined in claim 1, further comprising a second drive assembly provided in connection with said tool holder for moving said tool holder along a linear path, said linear path intersecting an axis passing through the centre of curvature of said arcuate path.

3. An articulated arm as defined in claim 1 or claim 2, wherein said arcuate member is removably mounted on said first support member, and wherein another arcuate member having a different radius of curvature can be slidably mounted on the first support member if desired.

4. An articulated arm as defined in claim 1, wherein said tool holder comprises a slidable carriage provided with a pair of grooves adapted to receive a removable tool mounting bracket therein, each groove having an associated locking lever for locking the tool mounting bracket to the carriage, said locking levers having a flat provided along a longitudinal edge thereof whereby each of the locking levers can be rotated to a position where the flat is flush with the respective groove to facilitate insertion or removal of the tool mounting bracket.

5. An articulated arm as defined in claim 4, wherein said pair of grooves are one of a plurality of pairs of grooves provided in the carriage to allow the location of tool mounting bracket to be varied to vary the operational position of the medical tool.

6. An articulated arm as defined in claim 4, wherein said tool mounting bracket is in the form of a C-bracket forming one half of a bracket assembly, the other half of the bracket assembly being in the form of a clamping bracket adapted to clamp the C-bracket to a body of a medical tool.

7. An articulated arm as defined in claim 4, wherein said carriage is slidably mounted on a pair of guide rails and is provided with a rack and pinion arrangement for sliding movement of the carriage along said guide rails, the tool holder further comprising a motor for driving the rack and pinion arrangement to effect said sliding movement of the carriage.

8. An articulated arm as defined in claim 1, wherein said first support member is provided with first and second stiffening members between which said arcuate member is slidably supported.

9. An articulated arm as defined in claim 8, wherein said arcuate member is provided with an external gear profile and said first drive assembly includes a motor that engages with said external gear profile to slidably move the arcuate member along said arcuate path.

10. An articulated arm as defined in claim 2, further comprising a third drive assembly mechanically coupled to said first support member for pivoting said first support member about a first drive axis, whereby said tool holder carried by the arcuate member can also be pivoted about said first drive axis.

11. An articulated arm as defined in claim 10, wherein said first support member is coupled to said third drive assembly by means of a coupling adapted to produce an offset between said first drive axis and a longitudinal axis of said first support member whereby, in use, a central axis of the medical tool held in the tool holder intersects said first drive axis so as to define a pivot point of the tool.

12. An articulated arm as defined in claim 11, wherein said coupling is a removable coupling which can be replaced with a different coupling to produce a different offset so as to accommodate a different medical tool.

13. An articulated arm as defined in claim 10, further comprising a second support member for supporting said third drive assembly, said second support member being provided with a fourth drive assembly for moving said third drive assembly in a linear direction whereby, in use, said tool holder together with the arcuate member can also be moved in said linear direction.

14. An articulated arm as defined in claim 13, wherein each of said first, second, third and fourth drive assemblies include an electric drive motor and wherein each of said drive assemblies are under the control of a microprocessor based multi-axis motion control system.

15. An articulated arm as defined in claim 13, wherein said second support member is suspended on a counterbalance support system providing at least four degrees of freedom of movement X, Y, Z and R. R is to allow quick manual takeover in an emergency for the articulated arm.

16. An articulated arm as defined in claim 15, wherein said counterbalance support system is provided with first and second mutually perpendicular support arms allowing X and Y axis movement respectively of the articulated arm, and a vertical support column allowing Z axis movement of the articulated arm.

17. An articulated arm as defined in claim 16, wherein said articulated arm is slidably mounted on said first support arm by means of said second support member, said first support arm is slidably mounted on said second support arm, and said second support arm is slidably mounted on said support column, and wherein each of said first and second support arms and said second support member can be locked in position by respective first, second and third locking means.

18. An articulated arm as defined in claim 17, wherein sliding movement of each support arm of the counterbalance support system is effected by a cable and pulley system, and wherein said locking means comprises a cable clamp.

19. An articulated arm as defined in claim 16, wherein said slidable mounting of the second support arm is provided with a swing bracket assembly to enable the second support arm to pivot horizontally about its slidable mounting on the support column.

20. An articulated arm as defined in claim 19, wherein said counterbalance support system further comprises a trolley forming a base on which the vertical support column is mounted, and having a plurality of shelves provided thereon for supporting other equipment.