U.S. patent application number 13/279480 was filed with the patent office on 2012-04-26 for ergonomic handpiece for laparoscopic and open surgery.
This patent application is currently assigned to SRA DEVELOPMENTS LIMITED. Invention is credited to Christopher John LEAVER, Peter James MANLEY, Nicholas Charles WRIGHT, Michael John Radley YOUNG.
Application Number | 20120101495 13/279480 |
Document ID | / |
Family ID | 43365455 |
Filed Date | 2012-04-26 |
United States Patent
Application |
20120101495 |
Kind Code |
A1 |
YOUNG; Michael John Radley ;
et al. |
April 26, 2012 |
ERGONOMIC HANDPIECE FOR LAPAROSCOPIC AND OPEN SURGERY
Abstract
A surgical tool having an elongate shaft, with a directional
operative element at its distal end, is provided with a mechanism
to rotate the shaft and the operative element about a longitudinal
axis shaft. This allows the operative element to be aligned with an
element of tissue without excessive hand movement by the user. In a
preferred version, the mechanism is electrically powered and is
regulated to produce smooth, controlled, accurate motion between
selected rotational positions. The mechanism may include a linear
magnetic motor drive to move a drive element longitudinally along
the tool. This drive element is engaged with a helical formation on
a drive shaft, such that longitudinal motion of the drive element
is converted to rotational motion of the drive shaft, and of the
shaft and operative element, to which the shaft is mounted.
Inventors: |
YOUNG; Michael John Radley;
(South Devon, GB) ; LEAVER; Christopher John;
(South Devon, GB) ; WRIGHT; Nicholas Charles;
(South Devon, GB) ; MANLEY; Peter James; (South
Devon, GB) |
Assignee: |
SRA DEVELOPMENTS LIMITED
South Devon
GB
|
Family ID: |
43365455 |
Appl. No.: |
13/279480 |
Filed: |
October 24, 2011 |
Current U.S.
Class: |
606/41 |
Current CPC
Class: |
A61B 2090/0811 20160201;
A61B 17/29 20130101; A61B 17/00234 20130101; A61B 90/08 20160201;
A61B 2017/00398 20130101; A61B 18/04 20130101; A61B 2017/320093
20170801; A61B 2017/2929 20130101; A61B 2017/320098 20170801; A61B
2017/00017 20130101; A61B 2017/320094 20170801 |
Class at
Publication: |
606/41 |
International
Class: |
A61B 18/18 20060101
A61B018/18 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2010 |
GB |
1017968.7 |
Nov 22, 2010 |
GB |
1019794.5 |
Dec 6, 2010 |
GB |
1020672.0 |
Feb 4, 2011 |
GB |
1102034.4 |
Claims
1. A surgical tool comprising an elongate member having a distal
end and a proximal end, the elongate member being provided adjacent
the distal end with an effector defining a plane of operation, a
manipulable handpiece disposed adjacent the proximal end of the
elongate member, and a rotation mechanism adapted controllably to
rotate the elongate member and the effector together about a
longitudinal axis of the elongate member so as to align said plane
of operation of the effector in a desired orientation, wherein the
rotation mechanism comprises at least two elements co-operably
moveable relative to one another.
2. A surgical tool as claimed in claim 1, wherein the rotation
mechanism comprises a geared transmission mechanism.
3. A surgical tool as claimed in claim 1, wherein the rotation
mechanism comprises an electromagnetic drive mechanism.
4. A surgical tool as claimed in claim 1, wherein the rotation
mechanism comprises a powered rotation mechanism provided with a
hand-operable activation member.
5. A surgical tool as claimed in claim 4, wherein said
hand-operable activation member is operable by a finger of a hand
holding the handpiece.
6. A surgical tool as claimed in claim 5, wherein said
hand-operable activation member is operable by finger-tip
pressure.
7. A surgical tool as claimed in claim 4, wherein the rotation
mechanism comprises a first hand-operable activation member and a
second hand-operable activation member, operation of which causes
rotation in opposite directions, respectively.
8. A surgical tool as claimed in claim 1, wherein the elongate
member comprises an elongate energy transmission member, through
which energy is transmissible to activate the effector.
9. A surgical tool as claimed in claim 8, wherein the tool is
adapted to be activated by ultrasonic vibrations, and said elongate
energy transmission member comprises an elongate waveguide adapted
to transmit ultrasound.
10. A surgical tool as claimed in claim 9, also comprising a source
of ultrasonic vibrations.
11. A surgical tool as claimed in claim 1, wherein the elongate
member comprises an elongate support member for a
mechanically-operable or electrically-operable effector.
12. A surgical tool as claimed in claim 1, wherein the elongate
member comprises an elongate optical transmission element, the
effector thereof comprising a directional viewing element.
13. A surgical tool as claimed in claim 1, comprising an operating
mechanism for the effector, said operating mechanism extending
between the handpiece and the effector.
14. A surgical tool as claimed in claim 1, wherein the rotation
mechanism comprises a longitudinally-displaceable driving element
operatively engaged with a rotatable driven element through
helically-symmetrical engagement means.
15. A surgical tool as claimed in claim 14, wherein the
helically-symmetrical engagement means comprises a body protruding
from a first of the driving and driven elements and received within
a helically-extending groove of a second of the driving and driven
elements.
16. A surgical tool as claimed in claim 14, further comprising a
linear drive adapted controllably to displace the
longitudinally-displaceable driving element.
17. A surgical tool as claimed in claim 16, wherein said linear
drive comprises a linear electromagnetic motor.
18. A surgical tool as claimed in claim 17, wherein said linear
electromagnetic motor comprises an electromagnet fixedly mounted to
the handpiece of the surgical tool and a permanent magnet so
mounted to the driving element that activation of the electromagnet
urges the driving element to move longitudinally of the tool.
19. A surgical tool as claimed in claim 1, wherein the rotation
mechanism comprises a permanent magnet and a selectively
energisable electromagnet, so mounted that energising the
electromagnet urges the permanent magnet and the electromagnet
means to rotate with respect to one another.
20. A surgical tool as claimed in claim 1, wherein the rotation
mechanism comprises a driveable first gear operatively engaged with
a driven second gear.
21. A surgical tool as claimed in claim 1, wherein the rotation
mechanism comprises a longitudinally manually displaceable first
connecting element engaged with a helical second connecting element
on a rotatable body.
22. A surgical tool as claimed in claim 8, wherein the rotation
mechanism acts on an energy generation means or an energy
conversion means of the surgical tool, to which said elongate
energy transmission member is mounted.
23. A surgical tool as claimed in claim 1, wherein the surgical
tool comprises a detector to detect a rotational position of the
elongate member and the effector.
24. A surgical tool as claimed in claim 23, wherein said detector
to detect a rotational position of the elongate member and the
effector comprises a potentiometer arrangement producing an
electrical signal proportional to said rotational position.
25. A surgical tool as claimed in claim 23, wherein the surgical
tool comprises a controller to govern rotational movement of the
elongate member and the effector.
26. A surgical tool as claimed in claim 25, wherein the controller
to govern the rotational movement of the elongate member and the
effector includes or is operatively connected to the detector to
detect a rotational position of the elongate member and the
effector.
27. A surgical tool as claimed in claim 25, wherein said controller
to govern rotational movement is adapted to regulate a rotational
velocity of the elongate member and the effector on the basis of at
least a current rotational position thereof and a target rotational
position selected by a user.
28. A surgical tool as claimed in claim 27, wherein said controller
regulates said rotational velocity on a continuous basis.
29. A surgical tool as claimed in claim 25, wherein said controller
to govern rotational movement provides power to the rotation
mechanism by a pulse width modulated signal.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of United Kingdom
applications GB1017968.7 filed on Oct. 23, 2010, GB1019794.5 filed
on Nov. 22, 2010, GB1020672.0 filed on Dec. 6, 2010, and
GB1102034.4 filed on Feb. 4, 2011, the entire contents of all of
these applications being hereby incorporated by reference
herein.
BACKGROUND ART
[0002] The present invention relates to a surgical tool, and to a
mechanism for its operation. More particularly, but not
exclusively, it relates to such a tool having improved ease of
manual control.
[0003] Over the past 20 years, much effort has been applied to the
development of specialised surgical instruments which allow complex
procedures to be performed with predictable outcome. (For example,
see U.S. Pat. No. 6,887,252; U.S. Pat. No. 6,056,735; U.S. Pat. No.
6,063,050 and U.S. Pat. No. 6,468,286). Many of these devices are
designed to manipulate and dissect biological tissues. These
devices may be manually operated or alternatively may incorporate a
powered element designed to deliver an enhanced tissue cutting
performance with significant haemostasis: see for example U.S. Pat.
No. 5,938,633; U.S. Pat. No. 5,322,055 and U.S. Pat. No. 6,352,532.
Both ultrasound and RF electrical currents are commonly used to
energise such instruments. The above instruments also embody
ergonomic features associated with basic hand instruments providing
core surgical needs.
[0004] A review of modern clinical trends related to the field of
general surgery indicates an expectation on the part of specialists
in minimal invasive surgery that any instruments offered in the
future will incorporate significantly enhanced handpiece designs,
in order to enable the surgeon successfully to undertake long,
intricate procedures without experiencing fatigue, which could
compromise the surgical outcome.
[0005] There have been past attempts to provide relevant
functionalities addressing the requirements for controlling the
cutting plane orientation, combined with accurate tissue targeting.
These have been limited by inadequate mechanism designs, which
impose physical constraints on the surgeons' ability to operate
freely. For example, mechanisms have been proposed in which the
cutting plane of the surgical tool is rotated by pushing with the
surgeon's fingertip. Accurate control is difficult, and even the
most dextrous surgeons find that they can rotate the cutting plane
in one direction but not rotate it back in the other direction.
BRIEF SUMMARY OF THE INVENTION
[0006] It is hence an aspect of the present invention to provide a
surgical tool and a mechanism for a surgical tool having enhanced
ergonomic features which obviate the above problems and contribute
to the above surgical requirements.
[0007] In a first aspect of the invention, special attention is
paid to means of controlling the orientation of a
cutting/coagulating plane of a surgical tool with respect to the
manually held instrument handle
[0008] According to a first aspect of the present invention, there
is provided a surgical tool comprising an elongate member provided
adjacent its distal end with an effector defining a plane of
operation, a manipulable handpiece disposed adjacent a proximal end
of the elongate member, and a rotation mechanism adapted
controllably to rotate the elongate member and the effector
together about a longitudinal axis of the elongate member so as to
align said plane of operation of the effector in a desired
orientation.
[0009] Preferably, the rotation mechanism comprises a geared
transmission mechanism.
[0010] Preferably, the rotation mechanism comprises a magnetic
drive mechanism.
[0011] Preferably, the rotation mechanism comprises a powered
rotation mechanism operatively connected to hand-operable
activation member.
[0012] The hand-operable activation member may be operable by a
finger of a hand holding the handpiece.
[0013] The hand-operable activation member may be operable by
finger-tip pressure.
[0014] The hand-operable activation member may be operable by
finger-tip contact.
[0015] Advantageously, the hand-operable activation member
comprises first and second hand-operable activation members,
operation of each of which produces rotation in opposite
directions.
[0016] Preferably, the elongate member comprises an elongate energy
transmission member, through which energy is transmissible to
activate the effector.
[0017] Advantageously, the surgical tool is adapted to be activated
by ultrasonic vibrations.
[0018] The elongate energy transmission member may then comprise an
elongate waveguide adapted to transmit ultrasound.
[0019] The surgical tool advantageously then also comprises a
source of ultrasonic vibrations.
[0020] The source of ultrasonic vibrations may comprise a source of
any one of torsional mode ultrasonic vibrations, longitudinal mode
ultrasonic vibrations, flexural mode ultrasonic vibrations, and a
combination of any two or more of said modes of ultrasonic
vibrations.
[0021] The source of ultrasonic vibrations may comprise an
amplifying horn to which the energy transmission member is mounted,
and which may optionally also act as a conversion horn to produce a
desired vibrational mode.
[0022] The handpiece of the tool may contain an ultrasound
generator operatively linked to a proximal end of the
waveguide.
[0023] Alternatively, the elongate member of the surgical tool may
comprise an elongate support member for a mechanically-operable or
electrically-operable effector.
[0024] The elongate member may additionally or alternatively
comprise an elongate optical transmission element, the effector
thereof comprising a directional viewing element, such as that of a
laparoscope.
[0025] Preferably, the surgical tool comprises an operating
mechanism for the effector extending operatively between the
handpiece and the effector.
[0026] The effector may comprise an effecting mechanism controlled
by the operating mechanism to move within the plane of
operation.
[0027] The effecting mechanism may comprise a clamp adapted to
grasp an element of tissue.
[0028] The clamp may comprise a jaw member moveable by the
operating mechanism.
[0029] The clamp may be adapted to hold an element of tissue to the
effector so that the effector may act thereon.
[0030] The effector may transmit energy from the energy
transmission member into tissue adjacent the effector.
[0031] Preferably, the operating mechanism comprises a sleeve
extending coaxially around the elongate member.
[0032] Advantageously, the sleeve is rotatably displaceable
relative to the elongate member.
[0033] Alternatively or additionally, the sleeve may be
longitudinally displaceable relative to the elongate member.
[0034] In a first embodiment, the rotation mechanism comprises a
permanent magnet and a selectively energisable electromagnet, so
mounted that energising the electromagnet urges the permanent
magnet and the electromagnet to rotate with respect to one
another.
[0035] The permanent magnet may be mounted to a first one of the
handpiece and the elongate member and the electromagnet may be
connected to a second one of the handpiece and the elongate
member.
[0036] The permanent magnet may be mounted to the handpiece and the
electromagnet to the elongate member, such that energising the
electromagnet causes rotation of the elongate member relative to
the handpiece.
[0037] In alternative embodiments, the rotation mechanism comprises
means directly to drive said rotation.
[0038] In a second embodiment, the rotation mechanism comprises a
driveable first gear operatively engaged with a driven second
gear.
[0039] Advantageously, the driveable first gear is mounted to the
handpiece and the driven second gear is mounted to the elongate
member.
[0040] The first gear may be driven by a selectively operable
motor.
[0041] In a third embodiment, the rotation mechanism comprises a
longitudinally displaceable first connecting element engaged with a
helical second connecting element on a rotatable body.
[0042] Advantageously, the first connecting element is mounted to
the handpiece and the rotatable body comprises the elongate
member.
[0043] The first connecting element may comprise a pin, optionally
a ball, held within a helical slot, said helical slot comprising
said second connecting element.
[0044] In a fourth embodiment, the rotation mechanism acts on an
energy generation means or an energy conversion means of the
surgical tool, to which said elongate energy transmission member is
mounted.
[0045] Preferably, part of the energy generation or conversion
means also comprises part of the rotation mechanism.
[0046] In a fifth embodiment, the rotation mechanism comprises a
longitudinally-displaceable driving element operatively engaged
with a rotatable driven element through helically-symmetrical
engagement means.
[0047] Preferably, the helically-symmetrical engagement means
comprises a body protruding from a first of the driving and driven
elements and received within a helically-extending groove of a
second of the driving and driven elements.
[0048] Alternatively, the helically-symmetrical engagement means
may comprise a helically-extending rib protruding from a first of
the driving and driven elements and received within a slot of a
second of the driving and driven elements.
[0049] The protruding body preferably comprises a ball, optionally
held freely rotatably to said first of the driving and driven
elements.
[0050] Advantageously, the protruding body is mounted to the
driving element and the helically-extending groove is located on
the driven element.
[0051] Preferably, the surgical tool comprises a linear drive
adapted controllably to displace the driving element.
[0052] The linear drive may comprise a linear electromagnetic
motor.
[0053] The linear electromagnetic motor may comprise an
electromagnet fixedly mounted to the handpiece of the surgical tool
and a permanent magnet so mounted to the driving element that
activation of the electromagnet urges the driving element to move
longitudinally of the tool.
[0054] The driven element is preferably fixedly mounted to energy
generation means of the surgical tool, optionally to an energy
conversion means thereof
[0055] The elongate member may then comprise an elongate energy
transmission member mounted to the energy generation means,
optionally to the energy conversion means thereof.
[0056] The energy generation means may comprise a source of
ultrasonic vibrations, and the energy conversion means may then
comprise an ultrasound amplification/conversion horn.
[0057] The driven element preferably comprises an integral portion
of one of the energy generation means and the energy conversion
means.
[0058] The driven element is advantageously joined to one of the
energy generation means and the energy conversion means adjacent a
nodal plane of oscillations therein.
[0059] The oscillations may comprise ultrasonic vibrations.
[0060] Preferably, the surgical tool of any of the above
embodiments is provided with a detector to detect a rotational
position of the elongate member and the effector.
[0061] Advantageously, the detector to detect a rotational position
comprises a potentiometer arrangement, whereby a rotational
position is converted to an electrical signal.
[0062] Preferably, the surgical tool comprises a controller to
govern the rotational movement of the elongate member and the
effector.
[0063] The controller to govern the rotational movement of the
elongate member and the effector may comprise the detector to
detect a rotational position thereof
[0064] The controller to govern rotational movement may be adapted
to select a rotational velocity of the elongate member and the
effector based on a current rotational position thereof and a
target rotational position input by a user, optionally on a
continuous basis.
[0065] The controller to govern rotational movement may regulate a
supply of power to the rotation mechanism in order to produce a
selected rotational velocity, optionally by means of a pulse width
modulated signal.
[0066] According to a second aspect of the present invention, there
is provided a handpiece for a surgical tool comprising a
manipulable handpiece member mountable to a proximal end of an
elongate member having adjacent its distal end an effector defining
a plane of operation, and a rotation mechanism adapted controllably
to rotate such an elongate member and effector together about a
longitudinal axis of the elongate member so as to align said plane
of operation of the effector in a desired orientation.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0067] Embodiments of the present invention will now be more
particularly described by way of example and with reference to the
accompanying drawings, in which:
[0068] FIG. 1a shows, schematically, an exploded perspective view
of components of a first handpiece of an ultrasonically-activatable
surgical tool embodying the present invention, including cross
sections of juxtaposed elements of its acoustic system;
[0069] FIG. 1b is a cross-sectional plan view of the handpiece of
FIG. 1a, showing acoustic elements;
[0070] FIG. 1c is a cross-sectional side elevation of the handpiece
of FIG. 1a, showing the acoustic elements;
[0071] FIG. 1d shows vibrational displacement characteristics of
the acoustic elements shown in FIG. 1b and 1c;
[0072] FIG. 2 is a side elevation of the handpiece shown in FIG.
1a;
[0073] FIG. 3a shows, schematically, an exploded perspective view
of components of a second handpiece of an
ultrasonically-activatable surgical tool embodying the present
invention, including cross sections of juxtaposed elements of its
acoustic system;
[0074] FIG. 3b is a cross-sectional side elevation of the handpiece
of FIG. 3a, showing the acoustic elements;
[0075] FIG. 4a shows, schematically, an exploded perspective view
of components of a third handpiece of an ultrasonically-activatable
surgical tool embodying the present invention, including cross
sections of juxtaposed elements of its acoustic system;
[0076] FIG. 4b is a cross-sectional side elevation of the handpiece
of FIG. 4a, showing the acoustic elements;
[0077] FIG. 5 is a schematic cross-sectional side elevation of a
fourth handpiece of an ultrasonically-activatable surgical tool
embodying the present invention;
[0078] FIG. 6 is shows, schematically, an exploded perspective view
of components of a fifth handpiece of an ultrasonically-activatable
surgical tool embodying the present invention;
[0079] FIG. 7 is a cross-sectional side elevation of the assembled
handpiece components of FIG. 6;
[0080] FIG. 8 is a cross-sectional side elevation of an operating
mechanism of a sixth, preferred handpiece of an
ultrasonically-activatable surgical tool embodying the present
invention;
[0081] FIG. 9 is an exploded perspective view from a first
direction of the operating mechanism shown in FIG. 8;
[0082] FIG. 10 is an exploded perspective view from a second
direction of the operating mechanism shown in FIG. 8; and
[0083] FIGS. 11a to 11d are schematic flow charts of portions of a
control method for the operating mechanism shown in FIG. 8.
DETAILED DESCRIPTION
[0084] Referring now to the Figures and to FIG. 1a in particular,
an acoustic system for an ultrasonically-actuable surgical tool
comprises a transducer 12, a waveguide 3 operatively connected
thereto, and a distal end effector 3e. An isolating sleeve 6 is
mounted to the acoustic system within a handpiece casing 1 (for
which, see FIG. 2). The acoustic system is mounted within casing
components 12a and 12b. Coupling sleeve 14 and its extension
components 14a and 14b is attached to an inner tube 15b of a contra
rotatable tube-set 15 extending coaxially around the waveguide 3.
The tube-set 15 comprises said inner tube 15b, an outer tube 15a
and an outer tube collar 15c; a helical slot 15d extends around the
outer tube collar 15c.
[0085] The outer tube collar 15c is either integral with, or
mouldably attached to, said outer tube 15a, so as to cause pivoting
movement of a distally-mounted hinged jaw 15e in the direction of
arrows C and C.sup.1 when the outer tube collar 15c is reciprocally
rotated in the direction indicated by arrows D and D.sup.1. (A
variety of mechanisms to convert rotational movement of the outer
tube 15a to pivoting movement of the jaw 15e are known from the
above references and elsewhere.) The outer tube collar 15c is urged
to rotate by a slide ring 16 provided with a drive pin 16a which
engages with said helical groove 15d of the outer tube collar 15c
through an axial slot 14c in extension component 14b. This slide
ring 16 is in turn moved longitudinally in the direction of arrows
A and A.sup.1 by manual movement of a trigger 17 pivotally mounted
about axis 17a and engaged at its inner tip with a circumferential
groove 16b extending around the slide ring 16. Manual movement of
the trigger 17 thus causes corresponding rotation of jaw 15e
according to arrows C and C.sup.1. The plane defined by the
end-effector 3e and the travel of the jaw 15e comprises a cutting
plane of the tool.
[0086] The rotation of the acoustic system and attached isolating
elements, 6, 14, 14a, and 14b, relative to the handpiece casing 1,
about the longitudinal axis of said acoustic system, may be
achieved by several exemplary means.
[0087] An advantageous embodiment is shown schematically in FIGS.
1a to 1c. The acoustic system, comprising the transducer 12, the
waveguide 3, and its end effector 3e, together with the jaw 15e
adjacent to the end effector 3e and pivotable into engagement
therewith, has the integrally or clamped compressively coupled
isolating sleeve 6 positioned between an ultrasonic horn 10 and a
proximal section 3b of the waveguide 3, at an annular interface 3a.
The isolating sleeve 6 has a vibrational displacement node 6d (see
FIG. 1d) located at a distance from interface 3a corresponding to
one quarter of a wavelength of ultrasonic vibrations therein.
[0088] A circumferential flange 6a is integral with the isolating
sleeve 6 and co-incidental with nodal plane 6d, said flange 6a
containing a plurality of "hard" permanent magnets 6c inserted
radially and at regular circumferential intervals around the flange
6a. Said magnets may be made of NdFeB or other suitable magnet
material.
[0089] As shown in FIG. 1a, a "soft" magnetic stator core 18
comprises a plurality of electromagnet elements 18a, disposed
coaxially around the flange 6a, with a radial gap 18b between them.
The stator core 18 is firmly held stationary within the handpiece
casing 1. An even number of permanent magnets 6c inserted into the
flange 6a is matched by an equal number of electromagnetic elements
18a in the fixed stator ring 18. Electromagnet windings are coiled
around each electromagnet element 18a, and may controllably be
supplied with direct current through the housing 12a, 12b of the
transducer 12, coupled via a cable 30 to a generator or other DC
source 31 (see FIG. 1c).
[0090] Said electromagnet windings are connected in radially
opposed pairs so as to provide alternating magnetic polarity
between adjacent windings when current is passed therethrough,
causing a magnetic interaction with the permanent magnets 6c in the
nodal flange 6a. Pulsed activation of selected electromagnet
winding coils is produced by control circuitry in the electrical
generator 31. This activation is supplied in response to pressure
on one or other of two switches 26a and 26b of a switch unit 26
conveniently mounted to an exterior of the handpiece 1 for
fingertip access (see FIG. 2). Respective switches 26a, 26b reverse
the direction of rotation of the acoustic system and functionally
associated components.
[0091] In a preferred variation of this embodiment, the relative
positions of the permanent magnets 6c, and of the stator core 18
and its electromagnetic elements 18a are reversed. Thus a ring of
permanent magnets 6c would be mounted to the (static) handpiece 1
casing 12a, encircling a ring of electromagnet elements 18a
arranged around the flange 6a on the (rotatable) isolating sleeve
6. When the windings around each electromagnet element 18a are
energised, this arrangement works in the same way as that described
above. A benefit of this preferred arrangement is that the
handpiece 1 casing 12a, 12b is usually disposable (since it cannot
be sterilised by autoclaving), and so it is preferable to mount the
simple, cheap permanent magnets 6c to this component of the tool,
and to mount the more complex electromagnet elements 18a to the
autoclavable acoustic system.
[0092] The principle described above in respect of the embodiment
shown in FIGS. 1a to 1c may be implemented as described by
deploying a circumferential array of permanent magnets 6c around
electromagnet elements 18a. Alternatively, a configuration based on
that disclosed in U.S. Pat. No. 4,841,189 may be employed. The
configuration of U.S. Pat. No. 4,841,189 comprises annular pole
pieces having interleaved individually formed poles and permanent
magnet rotor, but in the present invention may be transposed so
that the electromagnet structures (hitherto described as the stator
winding) is arranged to rotate within an array of permanent magnets
mounted around its periphery.
[0093] Furthermore, any of the above structures may be mounted at
different locations within a surgical instrument, in order to
effect the required rotation, as will be described below and shown
in FIG. 5. In this fourth embodiment, a distal portion of the drive
assembly of the handpiece of the tool comprises fixed stator
windings 40, mounted to a manually-graspable handle 5 of the tool,
while magnetic rotor elements 41 are attached to a
distally-extending handpiece member 2 (which may comprise the
waveguide 3 or an equivalent energy transmission member) and a
proximally-extending transducer 12 through a connecting mechanism
45. The member 2, the magnetic rotor elements 41, the connecting
mechanism 45 and the transducer 12 may thus be rotated about a
longitudinal axis in the sense of arrow 42, relative to the handle
5 and a remainder of the casing 1 of the handpiece.
[0094] Alternatively, electromagnetic elements 50 may be
incorporated into the casing 12a, 12b of the transducer 12, and are
capable of generating a rotational torque by magnetic interaction
with a permanent magnet array 49 fixed within the casing 1 of the
handpiece, which is held by the handle 5 by a surgeon or other
user.
[0095] This particular electromagnetic mechanism may be applied to
any such tool or instrument requiring an electrical coupling to a
power source/controller (such as generator 31 in FIG. 1c). This
would include electrosurgical devices in which the ultrasonic
components described herein would be substituted with electrodes
carrying controlled electrical currents to an end-effector at the
distal operative tip of the tool for tissue treatment.
[0096] An alternative means of rotation of the cutting plane of the
tool may be effected by the second embodiment illustrated in FIGS.
3a and 3b. The aforementioned isolating sleeve 6, with its same
nodal plane 6d, is provided with a raised circumferential flange
having a profile comprising a gear ring 6g. A tangentially-mounted
electric motor 11, fixed to handpiece casing 1 has a gearbox 11b
operatively connected thereto, provided with an output worm gear
11a, which is operatively engaged with said gear ring 6g. The motor
11 is activated by switches 26a and 26b on the exterior of the
handpiece casing 1 and conveniently positioned for digital
access.
[0097] In the tools illustrated, which contain `L-shaped`
transducers 12 adapted to produce torsional mode ultrasonic
vibrations, rotation of the cutting plane would be limited to
.+-.90.degree. about a neutral plane. If an alternative
axisymmetric transducer 12 were used, both the above approach and
that described in the context of FIGS. 1a to 1c would be capable of
360.degree. rotation of the cutting plane.
[0098] A third embodiment of an arrangement for rotating the
cutting plane is shown in FIGS. 4a and 4b. The acoustic isolating
sleeve 6 is provided with a helically-extending slot 6h, within
which is held a hardened ball 6k (see FIG. 4a). The ball 6k is
compelled to move in a direction parallel to the longitudinal axis
of the waveguide 3 by slideable knob 9b, which is constrained to
travel within a longitudinal slot 9a in an outer sleeve 9.
Slideable knob 9b is provided with a protruding socket 9c, which
receives part of the ball 6k and which also passes through a
longitudinal slot 7c in an inner slide sleeve 7. Longitudinal
movement of the knob 9b, in the direction of arrows E and E.sup.1,
thus causes a corresponding rotational displacement of said
acoustic isolator 6, and hence the transducer 12 and waveguide 3
connected thereto, as indicated by arrows D and D.sup.1. The inner
slide sleeve 7 is operatively connected at its distal end to tube
holder 14, and at its proximal end to the transducer casing 12a, in
order to achieve effective positional movement of all the
components which control the orientation of the cutting plane.
[0099] A fifth embodiment of an arrangement for rotating the
cutting plane is shown in FIGS. 6 and 7. This arrangement is
believed to be particularly effective, both in the
magnetically-driven variant described in detail below and in a
pneumatically-driven variant, which is described in outline
only.
[0100] The arrangement of FIGS. 6 and 7 employs a linear magnetic
drive, the longitudinally movable component of which is coupled to
a cylindrical sleeve comprising part of the acoustic horn of the
ultrasound generation/conversion system. A ball, pin or the like is
held by the movable component of the linear magnetic drive and
travels within a helical groove extending around an outer surface
of the cylindrical sleeve, such that longitudinal motion of the
linear magnetic drive causes rotational motion of the cylindrical
sleeve and the acoustic horn of which it forms part. A conventional
elongate waveguide is mounted to the acoustic horn, such that the
entire acoustically-vibratable assembly rotates about its
longitudinal axis, rotating the cutting plane of the end effector
located at a distal end of the waveguide.
[0101] Looking at this embodiment in more detail, with reference to
FIGS. 6 and 7, a transducer stack 12c is eccentrically mounted to
an ultrasound conversion/amplification horn ("ultrasonic horn") 10.
An elongate waveguide 3 is mounted coaxially extending from the
ultrasonic horn 10 and has adjacent its remote distal end an end
effector 3e. The end effector 3e may comprise a cutting edge
defining a surgical plane, or may comprise part of a jaw mechanism
as shown in FIG. 1, co-operating with a pivotable jaw 15e. The end
effector 3e and jaw 15e would then define the surgical plane
between them. The waveguide 3 and ultrasonic horn 10 between them
define a longitudinal axis 71 of the surgical tool.
[0102] A hollow cylindrical sleeve element 60 extends distally from
the horn 10, coaxially enclosing a proximal end 3b of the waveguide
3 and the annular interface 3a between the horn 10 and the
waveguide 3, across which ultrasonic vibrations are transmitted to
the waveguide 3.
[0103] An annular flange 10a extends outwardly from the horn 10
adjacent the junction of the horn 10 and a proximal end of the
cylindrical sleeve element 60. The annular flange 10a and the
junction of the sleeve element 60 are located at or closely
adjacent to a nodal plane 10a of the ultrasonic vibrations in the
horn 10, and so the annular flange 10a and the sleeve element 60
are isolated from said vibrations. Ideally, the annular flange 10a
and the sleeve element 60 are formed integrally with the horn
10.
[0104] One or more helical grooves 67 extend around an outer face
of the cylindrical sleeve element 60. These helical grooves 67
extend almost from end to end of the cylindrical sleeve element 60,
but are closed at each end.
[0105] A hollow cylindrical drive member 63 coaxially encircles the
cylindrical sleeve element 60, and is free to slide longitudinally
along the outer surface of the cylindrical sleeve element 60. The
drive member 63 holds one or more low-friction balls 63c in
respective recesses on its internal cylindrical surface 63d, such
that the or each ball 63c is also received engagingly in a
respective helical groove 67 on the outer cylindrical surface of
the cylindrical sleeve element 60 of the horn 10. The ball or balls
63c thus operatively connect the drive member 63 and the
cylindrical sleeve element 60.
[0106] The cylindrical drive member 63 is provided with two or more
annular permanent magnet rings 63a coaxially encircling its outer
surface, the permanent magnet rings 63a being spaced apart by soft
magnetic rings 63b.
[0107] The permanent magnet rings 63a preferably comprise a
magnetic composition containing neodymium, or a similar rare earth
composition.
[0108] The cylindrical drive member 63 is in turn coaxially
encircled by a phased array of electromagnetic coils 65; an even
number of said coils 65 is preferred. When the phased array of
coils 65 is energised by passage of electrical current
therethrough, the array 65 interacts with the permanent and soft
magnet rings 63a, 63b on the drive member 63 to form a linear
magnetic drive. The drive member 63 can thus be controllably driven
back and forth, longitudinally of the array 65 and of the sleeve
element 10, as shown by arrows 69.
[0109] This longitudinal motion of the drive member 63 causes the
sleeve element 10 to move, being engaged by means of the balls 63c
travelling in the helical grooves 67. The sleeve element 10 thus
rotates about the longitudinal axis 71 of the tool. As a result,
the entire ultrasonic horn 10, together with the transducer stack
12c and the waveguide 3, is driven to rotate about the longitudinal
axis 71. This in turn rotates the surgical plane of the end
effector 3e located at the distal end of the waveguide 3.
[0110] The array of electromagnetic coils 65 is held in a casing
70, which is fixedly mounted to a casing (not shown in FIGS. 6 and
7) of the handpiece. The casing 70 contacts the drive member 63 and
the annular flange 10a of the horn 10 sufficiently closely to
maintain the respective coaxial alignment of the various
components, while allowing the drive member 63 to slide freely,
longitudinally, and the annular flange 10a (and the horn 10,
transducer stack 12c, sleeve element 67 and waveguide 3) to rotate
freely within the handpiece.
[0111] This arrangement produces smooth, controlled and continuous
rotational movement of the surgical plane of the end-effector,
activated by any desired form of control element (although
fingertip controls 26, as shown in FIG. 2, should be particularly
convenient to a user).
[0112] It is envisaged that the linear magnetic drive described
above could be replaced by a pneumatic drive mechanism, the casing
70 representing an outer casing of a piston arrangement, and the
drive member 63 the piston itself, driven to move longitudinally
back and forth. The same arrangement of balls 63c in helical
grooves 67 would be used to convert linear motion of the drive
member 63 into rotational motion of the sleeve element 10a, horn 10
and so forth.
[0113] The generator 31, indicated schematically in FIG. 1c, has a
primary function of controlling power delivery to the acoustic
system, comprising the transducer 12, the waveguide 3, and its end
effector 3e. The generator 31 may also incorporate circuitry
designed to control cutting plane rotation and to regulate the
timing of plane rotation in relation to acoustic activation.
[0114] FIGS. 8 to 10 show a sixth, preferred embodiment of an
arrangement for rotating the cutting plane. This is similar in
principle to that shown in FIGS. 6 and 7, but also comprises a
mechanism for detecting the current rotational position of the
cutting plane and for producing a controlled and smooth rotational
motion between positions of the cutting plane.
[0115] As in the fifth embodiment of FIGS. 6 and 7, this sixth
embodiment employs a linear magnetic drive in conjunction with a
helically-grooved transmission arrangement to convert the
longitudinal motion of the linear magnetic drive to rotational
motion of the stack, transducer, acoustic horn, waveguide and end
effector.
[0116] The sixth embodiment also comprises a mechanism for
detecting a current rotational position of these elements which
employs a potentiometer mechanism to produce an electrical signal
having a magnitude directly related to the rotational position.
This signal is used as the basis for a control sequence (described
in more detail below in respect of FIGS. 11a to 11d) for the drive
that produces rapid, accurate, smooth and controlled motion between
selected rotational positions.
[0117] A transducer stack 12c is mounted eccentrically to an
ultrasound conversion/amplification horn ("ultrasonic horn") 10. An
elongate waveguide 3 is mounted to extend coaxially from the
ultrasonic horn 10, through a central axis of the drive mechanism
88, and has an end effector 3e at its distal end. This end effector
3e may comprise a cutting edge defining an operative plane. It may
also comprise part of a jaw mechanism as shown in FIG. 1,
cooperating with a pivotable jaw 15c, the operative plane being
defined by the end effector 3e and the plane through which the jaw
15c is swept.
[0118] The drive mechanism 88 is centred around an elongate hollow
cylindrical drive shaft 80, which is mounted at its proximal end to
an annular flange 10a, extending radially outwardly from the
ultrasonic horn 10 adjacent its junction with the waveguide 3. The
annular flange 10a is located at or near a nodal plane in the
ultrasonic vibrations set up in the horn 10 and waveguide 3, so as
to isolate the drive mechanism from these vibrations.
[0119] Towards a distal end of the drive shaft 80, a set of three
helical grooves 87 extend around its outer surface. The helical
grooves 87 each have a part-circular cross-sectional profile to
receive a respective one of three low-friction ceramic balls 84,
which are thus free to travel along their respective helical
grooves 87.
[0120] A hollow cylindrical permanent magnet 83 encircles the drive
shaft. On its inner surface, a coaxial non-magnetic ring 86 (not
shaded for clarity) holds the three ceramic balls 84 in respective
part-spherical recesses, leaving the balls 84 free to rotate within
each recess. The cylindrical permanent magnet 83 is free to travel
longitudinally back and forth along the drive shaft 80 and
waveguide 3, as shown by arrow 81.
[0121] The permanent magnet 83 has three straight grooves 82
extending longitudinally along its outer surface, spaced at
120.degree. to each other around its circumference. These each
receive a pair of additional low-friction ceramic balls 89. Each of
the additional ceramic balls 89 is also held in a part-spherical
recess in an inner surface of a coaxially extending cylindrical
outer casing 90 of the drive mechanism 88.
[0122] The outer casing 90 acts as a former for a set of
circumferential electromagnet coils 85, which thus encircle the
permanent magnet 83. The electromagnetic coils 85 extend along
substantially a whole length of the drive mechanism 88, such that
the permanent magnet 83 is still encircled thereby at any point
along its longitudinal motion 81.
[0123] This mechanism is preferably controlled using a two-button,
forward/reverse arrangement, similar to that shown in FIG. 2. Thus,
when the electromagnetic coils 85 are energised, the permanent
magnet 83 will be driven distally or proximally within the drive
mechanism 88, depending on the direction of the current within the
coils 85. The ceramic balls 89 are constrained to travel only
within the straight longitudinal grooves 82 on the outer surface of
the permanent magnet 83, and so in turn constrain the permanent
magnet 83 to purely longitudinal back and forth motion.
[0124] Meanwhile, the ceramic balls 84 bridge between the inner
surface of the hollow cylindrical permanent magnet 83 and the
helical grooves 87 on the drive shaft 80. Longitudinal motion of
the permanent magnet 83 thus constrains the ceramic balls 84 to
travel longitudinally, but since they are also constrained to
travel within the helical grooves 87, the drive shaft 80 must
therefore rotate to allow this, and with it the stack 12c, horn 10,
waveguide 3 and effector 3e.
[0125] This structure effectively defines a gearing arrangement
between the linear magnetic motor and the rotatable portion of the
drive mechanism. Selection of a suitable "stroke length" for the
movement of the permanent magnet 63, together with the number and
pitch of the helical grooves 87, ensures that the effective gear
ratio of this arrangement is sufficient to drive the rotatable
portion to rotate without significant resistance, as well as
ensuring that the full "stroke length" of the movement of the
magnet 83 produces a sufficient rotation of the rotatable portion.
A total rotational range of slightly less than a full circle is
preferred, for constructional and control reasons. If necessary,
the surgeon can supply the last few degrees of adjustment by hand
movements, without significant inconvenience or fatigue.
[0126] The sixth embodiment also comprises a potentiometer sensor
arrangement for determining the exact rotational position of the
drive shaft stack, transducer, horn, waveguide and end effector. In
essence, a conductive element is held stationary while bridging a
conductive track and a resistive track, which rotate along with the
waveguide, etc. An electrically conductive path is thus set up
along the conductive track, across the stationary conductive
element and back along the resistive track, and the resistance of
this path depends on exactly where the conductive element bridges
to the resistive track. Hence, a potential across this conductive
path is directly related to the relative rotational positions of
the tracks and the stationary conductive element.
[0127] One implementation of this approach is shown in FIGS. 8 to
10. The outer casing 90 of the drive mechanism 88 is fixed to the
handpiece of the surgical tool (not shown) and thus does not
rotate. An end plate 91 of the drive mechanism 88 is provided with
a recess 94 which holds a permanent locating magnet 93 (the
function of which is described below).
[0128] A low-friction bearing ring 98, made of PTFE
(polytetrafluoroethylene) or the like, is located between the end
plate 91 and a front plate 97 of the sensor arrangement, so that
the sensor arrangement may rotate freely with respect to the drive
mechanism 88. The sensor front plate 97 supports two spring loaded
contact pins 95 in respective sockets 96, which contact two
corresponding part-circular contact tracks 92 inset into the end
plate 91 of the drive mechanism 88. This is a convenient
arrangement for electrical power to be supplied to the
electromagnet coils 85 of the drive mechanism 88. (The main power
lead of such surgical tools generally leads to the transducer stack
12c, i.e. power is supplied to the rotatable components, so special
contact arrangements are required for the coils of the drive
mechanism which do not rotate).
[0129] A hollow cylindrical sensor housing 99 and a sensor back
plate 107 (actually forming part of the proximal end of the drive
shaft 80 in this example) cooperate with the sensor front plate 97
to enclose the sensor arrangement itself (in some embodiments, the
interior of the sensor arrangement is filled with oil to reduce
friction).
[0130] A generally annular printed circuit board 100 is almost
completely divided into an outer annulus 101 and an inner annulus
102 by an almost-circular slot 103. The outer annulus 101 bears a
circumferential resistive track, while the inner annulus 102 bears
a corresponding circumferential conductive track around its
surface.
[0131] A sliding contact 104 comprises a conductive flat plate with
a permanent ferromagnet 105 extending from its centre, and several
sprung contact pins 106 at its periphery. The permanent ferromagnet
105 extends through the slot 103 in the printed circuit board 100
and is strongly coupled to the permanent locating magnet 93 on the
drive mechanism 88. This urges the contact pins 106 into contact
with the respective tracks on the outer and inner annuli 101, 102
of the printed circuit board 100. When the printed circuit board
100 rotates with the sensor arrangement, this magnetic attraction
holds the sliding contact 104 stationary, so it contacts the tracks
at a different point. The sliding contact 104 thus provides the
conductive bridge between the conductive and resistive tracks,
required for the potentiometer arrangement referred to above.
[0132] The sensor back plate 107 carries a range of PCB tracks,
electrical connections and so forth, connected to internal wiring,
leading for example to the contact pins 95 and the drive mechanism
80, as well as to the printed circuit board 100 and other tool
controls. This circuitry is of conventional form and so is not
shown, for clarity.
[0133] In an alternative potentiometer arrangement (not shown), the
sliding contact plate 104 is replaced by a magnetic conductive
sphere. The resistive track still extends around an outer margin of
the printed circuit board 100, but the conductive track extends
around an adjacent portion of an inner surface of the sensor
housing 99. The sphere is magnetically held in alignment with the
permanent magnet 93 on the drive mechanism 88, which also holds it
in contact with both tracks. The sphere thus remains stationary
while the tracks and the sensor arrangement rotate, providing a
conductive bridge for the conductive path of the potentiometer
arrangement.
[0134] Both arrangements produce a simple voltage output that is
accurately dependent on the current rotational position of the
sensor arrangement, and hence of the other rotatable components of
the surgical tool. This has been found to be superior to optical
methods of identifying the rotational position (e.g. with a
stationary photo-cell responding to black lines on an otherwise
white rotating element). The optical arrangement only indicates
when the rotation has already reached a desired point, for example,
necessitating a crash stop to avoid an overshoot. The
potentiometric arrangement allows the position to be tracked
continuously, permitting far more effective and subtle control.
Merely rotating between estimated positions by dead reckoning is
far too inaccurate.
[0135] It should be noted that in each case, the surgical tool is
set up for the rotatable elements to index between a relatively
small number of pre-set rotational positions. This is much easier
to control than a system allowing infinite variations of position,
while the surgeon can easily adjust the angle of the tool by a few
degrees if an indexed position is not quite ideal.
[0136] The control procedure for the rotation of the stack, horn,
waveguide and end effector follows the sequence set out in FIGS.
11a to 11d. FIG. 11a shows the whole sequence of operation; FIG.
11b expands the structure of the MAIN PROGRAM LOOP from FIG. 11a;
FIG. 11c expands the structure of the CALCULATE CONTROL SIGNAL step
from FIG. 11b; and FIG. 11d expands the structure of the MOVE MOTOR
step from FIG. 11b.
[0137] Referring to FIG. 11a, when the equipment is switched on, a
PIC (Peripheral Interface Controller) chip is activated. This is
conveniently located within a control unit for the ultrasound
generator of the surgical tool. The PIC is set up, and variables
described below are set to their default initial values.
[0138] In particular, the variable TARGET, indicating the desired
rotational position of the surgical tool, is set to MIDPOINT,
corresponding to the midpoint of the possible rotational travel
range of the stack, transducer, horn, waveguide and end-effector
assembly. Thus, a surgeon will always start with the surgical tool
set at this midpoint position and able to rotate in either
direction as required.
[0139] The sequence then comprises repeated passes around the MAIN
PROGRAM LOOP until the surgeon has completed use of the surgical
tool.
[0140] Referring to the expanded structure of the MAIN PROGRAM LOOP
in FIG. 11b, the first step is to check the FORWARD button of the
controls provided. If a signal has been received from operation of
this button by the surgeon, the variable TARGET is incremented,
indicating that the desired rotational position is
forwards/clockwise from the current potential position.
[0141] The next step is to check the REVERSE button of the
controls. If a signal has been received, the variable TARGET is
decremented, indicating that the desired rotational position is
backwards/anti-clockwise from the current rotational position.
[0142] The third step is to check the ACTIVATE button, which is to
activate the ultrasound generator to energise the stack,
transducer, horn, waveguide and end-effector. If the ACTIVATE
button is being operated, a master PIC controller activates the
ultrasound generator, and the FORWARD and REVERSE buttons of the
controls are inhibited. It is undesirable for the end-effector to
be turning during operation of the tool, particularly if it is
grasping or otherwise targeting a specific element of body tissue.
Accidental operation of the FORWARD and REVERSE buttons is thus
prevented.
[0143] The fourth step is to check the TOGGLE button, which alters
the intensity of the ultrasound generated between pre-set levels.
Again, operation of the TOGGLE button causes the master PIC
controller to alter the intensity, while the FORWARD and REVERSE
buttons are inhibited to prevent accidental operation.
[0144] The fifth step, CALCULATE CONTROL SIGNAL, is at the heart of
the sequence, and is shown in more detail as a series of sub-steps
in FIG. 11c.
[0145] The rotational position detector/sensor arrangement of the
surgical tool is interrogated in the first sub-step to give the
variable CURRENT for the present instantaneous rotational position
of the surgical tool.
[0146] In the second sub-step, the variable TARGET is retrieved
from memory, including any increments or decrements resulting from
the first two steps of the MAIN PROGRAM LOOP.
[0147] A set of further variables are then calculated. The variable
ERROR, in the third sub-step, is set to the (vector) difference of
the TARGET and CURRENT variables, indicating how far the surgical
tool is from the desired rotational position.
[0148] The variable PROPORTIONAL, in the fourth sub-step, is set to
the (vector) difference between the TARGET and CURRENT variables,
multiplied by a pre-set constant, K1.
[0149] The variable SPEED, in the fifth sub-step, is set to the
(vector) difference between the CURRENT variable and the PREVIOUS
variable multiplied by a second pre-set constant, K2. (The PREVIOUS
variable corresponds to the value of CURRENT from the previous pass
around the MAIN PROGRAM LOOP).
[0150] The variable INTEGRAL, in the sixth sub-step, is set to the
value of INTEGRAL from the previous pass around the MAIN PROGRAM
LOOP, incremented or decremented by the value of ERROR, and then
multiplied by a third pre-set constant, K3.
[0151] The seventh sub-step comprises the calculation of the
CONTROL SIGNAL variable from the sum of the variables PROPORTIONAL,
SPEED and INTEGRAL. The value of CONTROL SIGNAL (as described
below) governs the speed and direction of rotation of the
mechanism. There is a pre-set maximum value for CONTROL SIGNAL to
prevent excessive speed of rotation.
[0152] In the eighth sub-step, the variable CONTROL SIGNAL is
returned. The net sign of CONTROL SIGNAL indicates whether a
FORWARD/clockwise rotation or a REVERSE/anti-clockwise rotation
will be produced. The magnitude of CONTROL SIGNAL naturally
indicates the amount of power sent to the mechanism. At this
sub-step, the magnitude of CONTROL SIGNAL is compared to a pre-set
minimum threshold value. If it is below this threshold value,
CONTROL SIGNAL is instead set to zero. This prevents the sequence
producing a series of small jittery correcting movements,
particularly when sufficiently close to a desired TARGET rotational
position as to make no practical difference to the surgeon.
[0153] Control then transfers to the sixth step of the MAIN PROGRAM
LOOP, which is set out in sub-steps in FIG. 11d.
[0154] In the first sub-step, if CONTROL SIGNAL is positive, the
signal to the drive mechanism is set up to be in the
FORWARDS/clockwise direction. In the second sub-step, if CONTROL
SIGNAL is negative, this signal is set up to be in the
REVERSE/anticlockwise direction. An asymmetric compensation
coefficient may be used to adjust the FORWARD/REVERSE signals to
ensure similar motion characteristics in both directions, should
physical parameters of the equipment (e.g. an asymmetry in the
resistance along the resistive track) cause them to differ.
[0155] In the third sub-step, the signal to the drive mechanism is
generated as a PWM (pulse width modulated) current. The ON time of
the PWM current is proportional to the magnitude of CONTROL SIGNAL.
In the fourth sub-step, the drive mechanism, here indicated as
MOTOR DRIVE, moves in response to the PWM current supplied. After a
pre-set time interval, the MOTOR DRIVE is stopped and the control
returns to the start of the MAIN PROGRAM LOOP. This loop will be
followed, repeating the above steps and sub-steps, until the TARGET
position is reached (or the position is sufficiently close that
CONTROL SIGNAL is set to zero anyway).
[0156] The benefit of the above control sequence is to produce a
smooth, controlled, accurate and proportionate rate of rotation of
the mechanism. The rotation will be faster for larger position
changes, but the rotation will gradually be slowed as the TARGET
position is approached, coming to a controlled rest (rather than a
jerky stop as soon as the system "realises" that it has arrived).
Adjustment of constants K1, K2 and K3 should allow adjustment of
the exact speed profiles produced, depending on the requirements of
a particular tool, or even of a particular user.
[0157] Although the above examples are ultrasonically-vibratable
surgical tools for minimally-invasive surgical techniques, the
mechanisms shown for rotating an element of a tool about its axis
should be applicable to a wide range of other surgical tools, and
possibly even similar tools for non-surgical purposes. For example,
tools are used in minimally-invasive surgery which employ directed
RF (radio frequency) electric currents to cut or cauterise tissue;
other tools used in minimally-invasive techniques comprise an
elongate shaft with a tissue stapling attachment at the distal end.
Both would benefit from mechanisms such as those described above.
Such surgery is usually carried out under visualisation using a
laparoscope, requiring the surgeon also to manipulate the
laparoscope, in order to see clearly the exact point where he or
she is operating. Smooth and controlled redirection of the viewing
lens at the distal end of the laparoscope would be highly
beneficial.
* * * * *