BACKGROUND
5 It is known to use robots for assisting and performing surgery. Figure 1 illustrates a typical
surgical robotic system. A surgical robot 100 consists of a base 102, an arm 104 and an
instrument 106. The base supports the robot, and may itself be attached rigidly to, for
example, the operating theatre floor, the operating theatre ceiling or a cart. The arm extends
between the base and the instrument. The arm is articulated by means of multiple flexible
10 joints 108 along its length, which are used to locate the surgical instrument in a desired
location relative to the patient. The surgical instrument is attached to the distal end of the
robot arm. The surgical instrument penetrates the body of the patient at a port so as to access
the surgical site. The surgical instrument comprises a shaft connected to a distal end effector
110 by a jointed articulation. The end effector engages in a surgical procedure. In figure 1,
15 the illustrated end effector is a pair of jaws. A surgeon controls the surgical robot 100 via a
remote surgeon console 112. The surgeon console comprises one or more surgeon input
devices 114. These may take the form of a hand controller or foot pedal. The surgeon console
also comprises a display 116.
20 A control system 118 connects the surgeon console 112 to the surgical robot 100. The control
system receives inputs from the surgeon input device(s) and converts these to control signals
to move the joints of the robot arm 104 and end effector 110. The control system sends these
control signals to the robot. Joint controllers on the robot arm 104 drive the joints 108 to
move accordingly.
25
30
Power for driving the joints of the robot arm 104 is provided to the robot arm from the
surgeon console 112 via power cables. In the event of a power failure, it is known to use a
mechanical brake to hold the joints of the robot arm 104 in position, and for the surgical
instrument 106 to be removed from the patient manually.
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SUMMARY OF THE INVENTION
According to an aspect of the invention, there is provided a surgical robot comprising: a
surgical robot arm comprising: a series of joints extending from a base to a terminal end for
attaching to a surgical instrument for inserting through a port into a patient's body to a
5 surgical site, the series of joints comprising a first set of joints, wherein for each joint of the
first set of joints, there is a configuration of the surgical robot arm for which that joint
experiences a gravitational torque or force and a movement of that joint complying with the
gravitational torque or force would cause the surgical instrument to advance into the
patient's body towards the surgical site; and joint motors for driving the series of joints; and
10 a robot arm controller configured to send drive signals to drive the joint motors, wherein the
surgical robot arm controller is configured to, in response to detecting a power loss, send
drive signals to drive the joint motors so as to hold the position of each joint of the first set of
joints against gravity, thereby preventing the surgical instrument from advancing into the
patient's body towards the surgical site due to movement of one or more joints of the first
15 set of joints under gravity.
20
The series of joints may comprise a second set of joints, wherein for each joint of the second
set of joints, there is no configuration of the surgical robot arm for which that joint
experiences a gravitational torque or force.
Ofthe first and second sets of joints, the robot arm controller may be configured to only send
drive signals to drive the joint motors so as to hold the position ofthe first set of joints against
gravity in response to detecting a power loss.
25 The second set of joints may be adjacent to the base of the surgical robot arm.
The second set of joints may be between the base of the surgical robot arm and the first set
of joints.
30 The series of joints may comprise a third set of joints, wherein for each joint of the third set
of joints, there is a configuration of the surgical robot arm for which that joint experiences a
gravitational torque or force but no movement of that joint alone complying with the
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gravitational torque or force would cause the surgical instrument to advance through the port
towards the surgical site.
Of the first and third sets of joints, the robot arm controller may be configured to only send
5 drive signals to drive the joint motors so as to hold the position ofthe first set of joints against
gravity in response to detecting a power loss.
Of the first, second and third sets of joints, the robot arm controller may be configured to
only send drive signals to drive the joint motors so as to hold the position of the first set of
10 joints against gravity in response to detecting a power loss.
The third set of joints may be successive joints adjacent to the terminal end of the surgical
robot arm.
15 The third set of joints may be between the terminal end ofthe surgical robot arm and the first
set of joints.
The series of joints may consist of in order from the base of the surgical robot arm: a first roll
joint, a first pitch joint, a second roll joint, a second pitch joint, a third roll joint, a third pitch
20 joint, a first yaw joint, and a fourth roll joint.
The first set of joints may consist of the first pitch joint, the second roll joint and the second
pitch joint.
25 The second set of joints may consist of the first roll joint.
The third set of joints may consist of the third roll joint, the third pitch joint, the first yaw joint,
and the fourth roll joint.
30 The detected power loss may be loss of power to the surgical robot arm from a back-up
battery supply.
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The robot arm controller may be configured to detect a loss of power to the surgical robot
arm from a primary power supply prior to detecting the loss of power to the surgical robot
arm from the back-up battery supply.
5 The robot arm controller may be configured to, prior to detecting the loss of power from the
primary power supply, control the surgical robot arm and attached surgical instrument to
move according to inputs received from a remote surgeon input device.
10
The robot arm controller may be integrated into the surgical robot arm.
The surgical robot arm may be mounted on a support structure, and the robot arm controller
may be integrated into the support structure.
According to an aspect of the invention, there is provided a control method for controlling a
15 surgical robot arm comprising a series of joints extending from a base to a terminal end for
attaching to a surgical instrument for inserting into a patient's body to a surgical site, the
series of joints comprising a first set of joints, wherein for each joint of the first set of joints,
there is a configuration of the surgical robot arm for which that joint experiences a
gravitational torque or force and a movement of that joint complying with the gravitational
20 torque or force would cause the surgical instrument to advance into the patient's body
towards the surgical site, the surgical robot arm further comprising joint motors for driving
the series of joints, the method comprising: sending drive signals to drive the joint motors,
wherein the surgical robot arm controller is configured to, in response to detecting a power
loss, send drive signals to drive the joint motors so as to hold the position of each joint of the
25 first set of joints against gravity, thereby preventing the surgical instrument from advancing
into the patient's body towards the surgical site due to movement of one or more joints of
the first set of joints under gravity.
BRIEF DESCRIPTION OF THE FIGURES
30 The present invention will now be described by way of example with reference to the
accompanying drawings. In the drawings:
Figure 1 illustrates a surgical robotic system for performing a surgical procedure;
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Figure 2 illustrates a surgical robot arm;
Figure 3 illustrates an exploded view oft he joints of the surgical robot arm of figure 2;
Figure 4 is a schematic diagram illustrating the control system of a surgical robotic
system;
5 Figure 5 illustrates operating modes of a surgical robot arm and the transitions
permitted between them; and
Figures 6, 7, 8, 9, 10, 11 and 12 are flowcharts illustrating control methods of a robot
arm controller during a power failure.
10 DETAILED DESCRIPTION
The following describes a surgical robotic system of the type illustrated in figure 1. The
surgical robotic system comprises one or more surgical robot arm and surgical instrument,
along with a remote surgeon console. The remote surgeon console is connected to the
surgical robot arm(s) via a control system. The control system includes a central controller
15 located remotely from the surgical robot arm(s). The control system may also include a robot
arm controller per surgical robot arm co-located with that surgical robot arm.
The control system and methods described in the following are done so with respect to a
surgical robot arm holding a surgical instrument having an end effector at its distal end for
20 manipulating tissue of a patient at a surgical site. The end effector may be, for example, a
pair of jaws, scalpel, suturing needle etc. However, the same surgical robot arm, control
system and methods apply equally to a surgical instrument which is an endoscope having a
camera at its distal end for capturing a video feed of a surgical site.
25 Figure 2 illustrates an exemplary surgical robot 200. The robot comprises a base 201 which is
fixed in place when a surgical procedure is being performed. Suitably, the base 201 is
mounted to a support structure. In figure 2, the support structure is a cart 210. This cart may
be a bedside cart for mounting the robot at bed height. Alternatively, the support structure
may be a ceiling mounted device, or a bed mounted device.
30
A robot arm 202 extends from the base 201 ofthe robot to a terminal end 203 for attaching
to a surgical instrument 204. The arm is flexible. It is articulated by means of multiple flexible
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joints 205 along its length. In between the joints are rigid arm links 206. Suitably, the joints
are revolute joints. The robot arm has at least seven joints between the base and the terminal
end. The robot arm 200 illustrated in figure 2 has eight joints in total between the base 201
and the terminal end 203. The robot arm illustrated in figure 2 has only eight joints between
5 the base and the terminal end. The joints include one or more roll joints (which have an axis
of rotation along the longitudinal direction of the arm links on either side ofthe joint), one or
more pitch joints (which have an axis of rotation transverse to the longitudinal direction of
the preceding arm link), and one or more yaw joints (which also have an axis of rotation
transverse to the longitudinal direction of the preceding arm link and also transverse to the
10 rotation axis of a co-located pitch joint). In the example of figure 2: joints 205a, 205c, 205e
and 205h are roll joints; joints 205b, 205d and 205f are pitch joints; and joint 205g is a yaw
joint. The order of the joints sequentially from the base 201 of the robot arm to the terminal
end 203 of the robot arm is: roll, pitch, roll, pitch, roll, pitch, yaw, roll. There are no
intervening joints in figure 2.
15
The joints of the surgical robot arm of figure 2 are illustrated on figure 3. The robot arm is
articulated by eight joints. Roll joint J1 205a is adjacent to the base 201, and is followed by a
pitch joint Jz 205b. The pitch joint Jz has a rotation axis perpendicular to the rotation axis of
the roll joint h. Roll joint h 205c is adjacent to the pitch joint Jz, and is followed by a pitch
20 joint J4 205d. The pitch joint J4 has a rotation axis perpendicular to the rotation axis of the
roll joint h Roll joint Js 205e is adjacent to the pitch joint J4, and is followed by a pitch joint
J5205f and a yaw joint h 205g, followed by a roll joint Js 205h. The pitch joint J5 and yaw joint
hform a compound joint, which may be a spherical joint. The pitch joint J5 and the yaw joint
h have intersecting axes of rotation.
25
The end of the robot arm distal to the base can be articulated relative to the base by
movement of one or more of the joints of the arm. The rotation axes of the set of distal joints
Js, h, hand Jsall intersect at a point on the surgical robot arm. Reference is made to a wrist.
Suitably, the wrist is a portion of the robot arm which rigidly couples to the distal end of an
30 instrument when that instrument is attached to the robot arm. The wrist has a position and
an orientation. For example, the position of the wrist may be the intersection ofthe rotation
axes of Js, J5, h and Js. Alternatively, the position of the wrist may be the intersection of one
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or more rotation axes of joints of the instrument. Alternatively, the position of the wrist may
be the intersection of one or more rotation axes of the distal joints of the robot arm and one
or more rotation axes of joints of the instrument. The surgical robot arm illustrated in figures
2 and 3 has a redundant joint. For a given position of the wrist relative to the base of the
5 surgical robot arm, there is more than one configuration of the joints h to h Thus, the
surgical robot arm can adopt different poses whilst maintaining the same wrist position.
The surgical robot arm could be jointed differently to that illustrated in figures 2 and 3. For
example, the arm may have fewer than eight or more than eight joints. The arm may include
10 joints that permit motion other than rotation between respective sides of the joint, for
example a telescopic joint.
Returning to figure 2, the surgical robot arm comprises a set of motors 207. Each motor 207
drives one or more of the joints 205. Each motor 207 is controlled by a joint controller. The
15 joint controller may be co-located with the motor 207. A joint controller may control one or
more of the motors 207. The robot arm comprises a series of sensors 208, 209. These sensors
comprise, for each joint, a position sensor 208 for sensing the position of the joint, and a
torque sensor 209 for sensing the applied torque about the joint's rotation axis. The torque
applied about a joint's rotation axis includes any one or combination of the following
20 components: torque due to gravity acting on the joint, torque due to inertia, and torque due
to an external force applied to the joint. One or both of the position and torque sensors for
a joint may be integrated with the motor for that joint. The outputs of the sensors are passed
to the control system.
25 The surgical instrument 204 attaches to a drive assembly at the terminal end of the robot arm
203. This attachment point is at all times external to the patient. The surgical instrument 204
has an elongate profile, with a shaft spanning between its proximal end which attaches to the
robot arm and its distal end which accesses the surgical site within the patient's body. The
surgical instrument may be configured to extend linearly parallel with the rotation axis of the
30 joint 205h of the arm. For example, the surgical instrument may extend along an axis
coincident with the rotation axis of the joint 205h of the arm.
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The proximal end of the surgical instrument and the instrument shaft may be rigid with
respect to each other and rigid with respect to the distal end of the robot arm when attached
to it. An incision is made into the patient's body, through which a port is inserted. The surgical
instrument may penetrate the patient's body through the port to access the surgical site.
5 Alternatively, the surgical instrument may penetrate the body through a natural orifice of the
body to access the surgical site. At the proximal end ofthe instrument, the shaft is connected
to an instrument interface. The instrument interface engages with the drive assembly at the
distal end of the robot arm. Specifically, individual instrument interface elements of the
instrument interface each engage a respective individual drive assembly interface element of
10 the drive assembly. The instrument interface is releasably engageable with the drive
assembly. The instrument can be detached from the robot arm manually without requiring
any tools. This enables the instrument to be detached from the drive assembly quickly and
another instrument attached during an operation.
15 At the distal end ofthe surgical instrument, the distal end ofthe instrument shaft is connected
to an end effector by an articulated coupling. The end effector engages in a surgical
procedure at the surgical site. The end effector may be, for example, a pair of jaws, a pair of
monopolar scissors, a needle holder, a fenestrated grasper, or a scalpel. The articulated
coupling comprises several joints. These joints enable the pose of the end effector to be
20 altered relative to the direction of the instrument shaft. The end effector itself may also
comprise joints. The end effector illustrated in figures 2 and 3 has a pair of opposing end
effector elements 307, 308. The joints of the end effector are illustrated on figure 3 as a pitch
joint 301, a yaw joint 302 and a pinch joint 303. The pitch joint 301 is adjacent to the shaft of
the instrument and rotates about an axis perpendicular to the longitudinal axis of the
25 instrument shaft. The yaw joint 302 has a rotation axis perpendicular to the rotation axis of
the pitch joint 301. The pinch joint 303 determines the spread of the end effector elements.
In practice, the pinch joint 303 may be another yaw joint which has the same rotation axis as
the yaw joint 302. Independent operation of the two yaw joints 302, 303 can cause the end
effector elements to yaw in unison, and/or to open and close with respect to each other.
30
Drive is transmitted from the robot arm to the end effector in any suitable manner. For
example, the joints of the instrument may be driven by driving elements such as cables, push
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rods or push/pull rods. These driving elements engage the instrument interface at the
proximal end of the instrument. The drive assembly at the terminal end of the robot arm
comprises instrument drive joints which transfer drive from the surgical robot arm to the
instrument interface via the respective interface elements described above, and thereby to
5 the instrument joints. These instrument drive joints are shown on figure 3 as joints Jg, Jw and
Jn. Figure 3 illustrates three instrument drive joints, each one of which drives one of the
three joints of the instrument.
Suitably, the instrument drive joints are the only means by which drive is transferred to the
10 instrument joints. The robot arm may have more or fewer than three instrument drive joints.
The surgical instrument may have more or fewer than three joints. The instrument drive
joints may have a one-to-one mapping to the instrument joints that they drive, as shown in
figure 3. Alternatively, an instrument drive joint may drive more than one instrument joint.
15 The surgeon console is located remotely from the one or more surgical robot arms of the
surgical robotic system. The surgeon console comprises one or more surgeon input devices
and a display. Each surgeon input device enables the surgeon to provide a control input to
the control system. A surgeon input device may, for example, be a hand controller, a foot
controller such as a pedal, a touch sensitive input to be controlled by a finger or another part
20 of the body, a voice control input device, an eye control input device or a gesture control
input device. The surgeon input device may provide several inputs which the surgeon can
individually operate.
For example, the surgeon input device may be a hand controller connected to the surgeon
25 console, for example by a gimbal arrangement. This enables the hand controller to be moved
with three degrees of translational freedom with respect to the surgeon console. Such
movement may be used to command corresponding movement of the end effector of the
instrument. The hand controller may also be rotated with respect to the surgeon console.
Such movement may be used to command corresponding rotation of the end effector of the
30 instrument.
5
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The surgeon console may comprise two or more surgeon input devices. Each surgeon input
device may be used to control a different surgical instrument. Thus, for example, a surgeon
may control one surgical instrument using a hand controller in his left hand, and control
another surgical instrument using a hand controller in his right hand.
A control system connects the surgeon console to the one or more surgical robots. Such a
control system is illustrated in figure 4. The surgeon console 401 is connected by a bidirectional
communications link to a central controller 402. Specifically, the surgeon input
device(s) of the surgeon console 401 are communicatively coupled to the central controller
10 402. The central controller 402 is connected by a bi-directional communications link to an
arm controller 403, 404, 405 of each surgical robot arm of the surgical robotic system. Each
arm controller is co-located with a surgical robot arm. The arm controller may be located in
the surgical robot arm. Alternatively, the arm controller may be located in the support
structure which supports the surgical robot arm, for example in the cart of the arm. The
15 central controller is remotely located from at least one of the surgical robot arms. Suitably,
the central controller is remotely located from all the surgical robot arms in the surgical
robotic system. The central controller may be located at the surgeon console. Alternatively,
the central controller may be co-located with one of the arm controllers. The central
controller may be located remote from both the surgeon console and all the arm controllers.
20
25
30
The central controller comprises a processor 406 and a memory 407. The memory 407 stores,
in a non-transient way, software code that can be executed by the processor 406 to cause the
processor to control the surgeon console and the one or more surgical robot arms and
instruments in the manner described herein.
Each ofthe arm controllers comprises a processor 408 and a memory 409. The memory 409
stores, in a non-transient way, software code that can be executed by the processor 408 to
cause the processor to control the surgeon console and the one or more surgical robot arms
and instruments in the manner described herein.
The central controller 402 receives commands from the surgeon input device(s). The
commands from the surgeon input device indicate a change in the desired position and/or
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pose of a distal end of a surgical instrument. The control system converts the commands
received from the surgeon input device to drive signals. This conversion is carried out by one
or a combination ofthe central controller and the surgical robot arm controller ofthe surgical
robot arm associated with the surgeon input device. The robot arm controller sends the drive
5 signals to the joint controllers ofthe surgical robot arm and/or surgical instrument associated
with the surgeon input device. Those joint controllers respond by driving the joint motors
accordingly. The joints are thereby driven to cause the end effector to adopt the desired
position and/or pose commanded by the surgeon input device. Manipulation of the surgical
instrument is thereby controlled by the control system in response to manipulation of the
10 surgeon input device.
The control system receives inputs from the position and torque sensors on the joints of the
surgical robot arms. The control system determines the current configuration of a surgical
robot arm using the known sequence of joints and links in the arm, and the sensed joint
15 positions. From the current configuration ofthe surgical robot arm and the attached surgical
instrument, and the known mass and dimensions of the links and joints of the robot arm and
instrument, the control system determines the torque due to gravity acting on each joint. The
control system sends gravity compensating drive signals to the joint controllers of the robot
arm. The joint controllers respond by driving the joint motors so as to counteract the force
20 of gravity acting on each joint. In other words, each joint motor applies a torque which exactly
opposes the calculated gravitational force acting on the joint. In the absence of commands
from the surgeon input device and/or external forces (other than gravity) acting on the robot
arm, the robot arm is thereby held in position against gravity. It does not droop under the
force of gravity. In practice, each drive signal sent by the control system to a joint controller
25 for driving a joint motor may be resolved into a component which drives the joint in
accordance with the input received from the surgeon input device, and a component which
counteracts gravity. In some modes, as discussed below, the drive signal may also comprise
a component which drives the joint to conform with an external force applied to the robot
arm.
30
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A surgical robot arm is operable in a number of different operating modes. Figure 5 illustrates
some exemplary operating modes of the surgical robot arm, and the transitions permitted
between those operating modes.
5 Figure 5 illustrates a calibration mode 501. In the calibration mode 501, the surgical robot
arm is driven to conform to external forces applied to the robot arm. Specifically, the torque
sensors 209 detect external forces applied to the robot arm. The external force may be, for
example, a member of the bedside team applying a force to the robot arm (for example by
pushing the robot arm). As described above, the sensed torque about a joint's rotation axis
10 includes any one or combination of the following components: torque due to gravity acting
on the joint, torque due to inertia, and torque due to an external force applied to the joint.
The control system deducts the torques due to gravity and inertia from the sensed torque
about a joint to determine the component of the torque about that joint due to an external
force. The control system then determines drive signals to drive the joint so as to conform
15 with the external force. The control system sends the drive signals to the joint controller
controlling that joint. The joint controller controls the motor of that joint to drive the joint as
commanded by the control system. In this way, when an external force is applied to a joint,
that joint is driven to comply with that force. Thus, the robot arm is compliant to the force
applied to it by an operator.
20
In the calibration mode 501, the control system drives the robot arm to oppose the
gravitational torques acting on the robot arm as described above. Thus, in the calibration
mode 501, a member of the bedside team can manoeuvre the robot arm into position by
pushing or pulling any part of the robot arm in a desired position, and that part will stay in
25 that position notwithstanding the effect of gravity on it and on any parts depending from it.
In the calibration mode 501, the control system does not convert detected manipulation of
the surgeon input device(s) to drive signals for moving joints of the robot arm. Any inputs the
control system receives from the surgeon input device are not converted to movement of the
30 robot arm.
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The calibration mode 501 is primarily used during setup of the surgical robotic system prior
to the beginning of an operation. For example, a surgical instrument may be attached to the
robot arm during the calibration mode 501 and a member of bedside staff may manoeuvre
the robot arm so as to insert the surgical instrument into the port in the patient's body along
5 the desired direction to reach the surgical site. Should a robot arm and its support structure
be moved, or relocated during an operation, the calibration mode 501 is used again to
manoeuvre the robot arm into position.
During setup of the surgical robotic system, the calibration mode is used to determine a
10 virtual pivot point. The virtual pivot point is the natural centre of rotation of an instrument
having a rigid shaft as that instrument moves in the patient's body. The virtual pivot point is
a fulcrum about which the surgical instrument pivots when the configuration of the surgical
robot arm is altered whilst inside the port in the patient's body. A port is inserted into the
abdominal wall of the patient. The port is of the order of 2-10cm long. The instrument is
15 inserted into the patient's body through the port. The virtual pivot point lies along the length
of the port. The exact location of the virtual pivot point depends on the patient's anatomy,
and hence differs from patient to patient.
The virtual pivot point can be determined using the following method. With the instrument
20 located in the port, an operator moves the distal end of the robot arm in directions generally
transverse to the instrument shaft. This motion causes the port to exert a lateral force on the
instrument shaft where it passes through the port, with the result that the instrument applies
a torque to the joints of the arm -in this case joints J6 205f and h 205g- whose axes are
transverse to the longitudinal axis of the instrument shaft. The position of each arm joint is
25 measured by its associated position sensor 208, and this sensed position is output to the
control system. The torque at each arm joint is measured by its associated torque sensor 209,
and this sensed torque is output to the control system. Thus, as the operator moves the distal
end of the robot arm laterally the control system receives sensed inputs indicating the
position and forces on the arm joints. That information allows the control system to estimate:
30 (a) the position of the distal end of the robot relative to the fixed base and (b) the vector of
the instrument shaft relative to the distal end of the robot. Since the instrument shaft passes
through the passageway of the port, the passageway of the port must lie along that vector.
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As the distal end of the robot arm is moved, the controller calculates multiple pairs of distal
end positions and instrument shaft vectors. Those vectors all converge, from their respective
distal end position, on the location of the virtual pivot point in the passageway of the port.
By collecting a series of those data pairs and then solving for the mean location where the
5 instrument shaft vectors converge, the control system determines the virtual pivot point
relative to the base.
Once the virtual pivot point is determined in the calibration mode 501, it is set for the
remainder oft he modes illustrated on figure 5. The virtual pivot point is stored by the control
10 system. In each of the other modes illustrated in figure 5, the surgical robot arm is always
driven such that the longitudinal axis of the shaft of the attached surgical instrument
intersects the virtual pivot point (whether or not the instrument is actually attached to the
robot arm). The longitudinal axis of the shaft of the surgical instrument has a known
relationship to the longitudinal axis of the terminal end of the robot arm. For example, as
15 shown in figure 2, the longitudinal axis of the shaft of the surgical instrument may be
coincident with the longitudinal axis ofthe terminal end of the robot arm.
From the calibration mode, the surgical robot arm can transition to the locked mode 502. In
the locked mode 502, the control system holds the surgical robot arm in a fixed position. That
20 fixed position is the position that the surgical robot arm was in at the time that it transitioned
from the calibration mode to the locked mode 502. In the locked mode, the control system
drives the joints of the robot arm to compensate for gravity (as described above). Otherwise,
the control system does not convert any manipulation ofthe surgeon input device or external
forces applied to the robot arm to drive signals for driving the joints ofthe robot arm.
25
From the locked mode 502, the surgical robot arm can transition to the instrument adjust
mode 503. In the instrument adjust mode 503, the control system drives the surgical robot
arm to conform to external forces applied to the robot arm (as described above with respect
to the calibration mode), whilst retaining the intersection of the longitudinal axis of the shaft
30 of the surgical instrument with the virtual pivot point determined in the calibration mode.
The instrument adjust mode 503 can be used to adjust the position of the instrument within
the patient's body. For example, the instrument adjust mode 503 may be used to enable a
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member of the bedside team to push the instrument into the patient's body such that the
end effector reaches the surgical site, following setting of the virtual pivot point in the
calibration mode. In the instrument adjust mode 503, the control system drives the joints of
the robot arm to compensate for gravity (as described above). In the instrument adjust mode
5 503, the control system does not convert any manipulation of the surgeon input device to
drive signals for driving the joints of the robot arm.
From the instrument adjust mode 503, the surgical robot arm can transition to the surgical
mode 504 or the instrument change mode 505. In the surgical mode 504, the control system
10 responds to inputs received from a surgeon input device by converting those inputs to control
signals for controlling the motion of the surgical robot arm and/or surgical instrument
associated with that surgeon input device (as described above). The end effector of the
surgical instrument thereby moves as commanded by the surgeon input device. When
performing the conversion, the control system maintains an intersection between the
15 longitudinal axis of the shaft of the surgical instrument and the virtual pivot point.
The surgical mode 504 may comprise a clutch mode. The clutch mode may be initiated by the
surgeon console, for example via an input on the surgeon input device. Alternatively, the
clutch mode may be initiated by an input on the surgical robot arm or the support to which
20 the surgical robot arm is mounted. In the clutch mode, manipulation of the surgeon input
device is temporarily disconnected from the robot arm. When receiving an input indicating
that the clutch mode has been engaged, the control system does not convert manipulation
of the surgeon input device to control signals for driving joints of the robot arm. The clutch
mode is used by the surgeon in order to move the surgeon input device to a more comfortable
25 location in the workspace of the surgeon input device without transferring that motion to the
end effector of the surgical instrument. The clutch mode is also used by the surgeon to
temporarily disengage one surgical instrument whilst the surgeon concentrates on a surgical
instrument being manipulated by another surgeon input device.
30 The surgical mode 504 may be a semi-compliant mode. In other words, the robot arm may
exhibit some compliant behaviour towards external force applied to the robot arm. For
example, in the surgical mode 504, the control system may respond to a sensed external force
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applied proximal to the elbow joint 205d by controlling the motors driving the elbow joint
205d and the surrounding joints of the arm to drive those joints to comply with that sensed
external force. In this way, a member of the bedside team can push the elbow joint 205d or
a part of the arm proximal to the elbow joint out of the way to enable them to access the
5 patient during the surgical mode. In order to implement this, the control system may define
a permitted area/volume for one or more parts of the robot arm that are designated as
compliant such that movement of those parts in response to externally applied forces is
confined within the permitted area/volume. The permitted area/volume is defined such that
movements within that area/volume in response to externally applied forces do not cause
10 the configuration of the instrument to be affected. The robot arm is only semi-compliant in
the surgical mode 504 because the control system does not respond by conforming to an
external force applied to any part of the robot arm other than the parts designated as
compliant.
15 From the surgical mode 504, the surgical robot arm can transition to the instrument adjust
mode 503 or to the instrument change mode 505. The instrument change mode 505 is
engaged in order to remove and/or insert the instrument from/into the patient's body. In the
instrument change mode 505, the control system drives the surgical robot arm to conform to
the component of a sensed external force applied to the robot arm along the longitudinal axis
20 of the surgical instrument towards or away from the surgical robot arm. Whilst in the
instrument change mode 505, the control system retains the intersection of the longitudinal
axis of the shaft of the surgical instrument with the virtual pivot point determined in the
calibration mode. The control system conforms to the sensed external force in the same
manner as described above with respect to the calibration mode, the only differences being
25 that (i) the control system only conforms to the component of the sensed force in the
specified directions (i.e. along the longitudinal axis of the surgical instrument towards or away
from the surgical robot arm), and (ii) the control system maintains intersection of the surgical
instrument with the virtual pivot point.
30 At the end of an operation when surgical instruments are being removed from the surgical
site, or mid-operation when a surgical instrument is being exchanged for another one, a
member of the bedside team uses the instrument change mode 505 to enable them to pull
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the instrument out of the patient's body, and then insert another instrument into the
patient's body. In the instrument change mode 505, the control system prevents force
applied by the member of the bedside team in any direction other than the longitudinal axis
of the surgical instrument towards or away from the surgical robot arm from being converted
5 to corresponding movement of the surgical robot arm. Thus, no lateral force applied by the
member of the bedside team is converted to corresponding movement of the surgical robot
arm. This ensures that extraction ofthe surgical instrument is along the line of entry between
the port and the surgical site, thus avoiding damage to tissue away from this line.
10 In the instrument change mode 505, the control system limits the conversion of force applied
by the member of the bedside team along the longitudinal axis of the surgical instrument
towards the patient's body to corresponding movement of the surgical robot arm. This limit
is such that the end effector of the attached instrument cannot advance further into the
patient's body than the end effector ofthe instrument at the time that the instrument change
15 mode was entered. This limit applies to the same instrument that was attached to the arm
at the time that the instrument change mode was entered during instrument extraction. This
limit also applies to the newly attached instrument which is inserted into the patient's body
following instrument change. This ensures that the surgical instrument cannot be pushed
further into the patient's body causing damage to the surgical site.
20
25
In the instrument change mode 505, the control system drives the joints of the robot arm to
compensate for gravity (as described above). In the instrument change mode 505, the control
system does not convert any manipulation of the surgeon input device to drive signals for
driving the joints of the robot arm.
From the instrument change mode 505, the surgical robot arm can transition to the
instrument adjust mode 503 or the surgical mode 504.
From each of the locked mode 502, instrument adjust mode 503, surgical mode 504 and
30 instrument change mode 505, the surgical robot arm can transition to a standby mode 506.
From that standby mode 506, the surgical robot arm can transition back to the one of the
locked mode, instrument adjust mode, surgical mode and instrument change mode that it
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was previously in. From the standby mode 506, the surgical robot arm can also transition to
the calibration mode 501.
The surgical robot arm, or the support structure to which the robot arm is mounted, may
5 comprise one or more interfaces. These interfaces may be a button or set of buttons. The
interfaces can be actuated, for example by a member of the bedside team, to transition
between the operating modes described with respect to figure 5. The surgeon's console may
comprise one or more interfaces which can be actuated, for example by the surgeon, to
transition between the operating modes described with respect to figure 5.
10
Power is required by the surgical robot arm to power the joint motors to drive the joints, as
well as to power all the circuitry in the surgical robot arm including the robot arm controller
and the joint controllers. The surgical robot arm is generally operated in a full power mode
in which it is powered by a primary power source. This primary power source is sufficient to
15 sustain the power requirements of the surgical robot arm throughout a surgical procedure.
For example, the primary power source may be an electrical supply such as an electrical mains
power supply. Power may be routed from the primary power source to the surgical robot
arm through the surgeon's console.
20 The surgical robot arm may also be operable in a reduced power mode in which it is powered
by a secondary power source. In this reduced power mode, fewer operating modes of the
surgical robot arm are available for use. Referring to figure 5, the locked mode 502,
instrument adjust mode 503, surgical mode 504 and instrument change mode 505 may only
be available in the full power mode. They are not available in the reduced power mode. The
25 calibration mode 501 and standby modes 506 may be fully available in the full power mode
and partially or fully available in the reduced power mode.
The secondary power source may comprise one or more batteries. These batteries may be
local to the surgical robot arm. For example, each oft he one or more batteries may be located
30 in the surgical robot arm itself, or in the support structure to which the surgical robot arm is
mounted. The secondary power source may comprise two batteries. The first battery may
be a rechargeable battery and the second battery may be a non-rechargeable battery. The
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first battery, when fully charged, can provide sufficient power to drive the motors of the
surgical robot arm to hold the position ofthe surgical robot arm against gravity for at least N
minutes. For example, 5 < N < 30. For example, N = 5. The second battery can provide
sufficient power to drive motors of the surgical robot arm (as described below) to hold the
5 surgical robot arm for at least T seconds. For example, 20 < T < 180. For example, T = 30. N
and Tare estimations of how long the batteries can provide the described power for. These
estimations may be based on typical discharge v. time graphs for the batteries, or
mathematical models ofthe ideal discharge of the batteries overtime. The remaining battery
life of each battery may be estimated by measuring the voltage, current or power output of
10 the battery over time, and comparing those voltage/current/power readings against a typical
battery life graph of voltage v. battery capacity. The maximum capacity of the first battery
may be between 5000 and 6000 mAh. The maximum capacity of the second battery may be
between 300 and 600 mAh.
15 A surgical robot arm may only be able to be powered up for use if it is connected to the
primary power source in the full power mode. A robot arm controller on the surgical robot
arm detects that sufficient power is being received from the primary power source to power
the functions of the surgical robot arm. On detecting a power failure of the primary power
source, the robot arm controller switches the surgical robot arm to the reduced power mode.
20 In the reduced power mode, the robot arm controller controls the surgical robot arm to be
powered from the secondary power source. For example, initially in the reduced power
mode, the robot arm controller may control the surgical robot arm to be powered from the
first battery. If the first battery becomes depleted, then the robot arm controller may control
the surgical robot arm to be powered from the second battery. The robot arm controller may
25 detect power failures, detect restoration of power following a power failure, and enable and
disable the full power mode and the reduced power mode.
Control methods which may be carried out by the control system in response to detection of
a power failure to a surgical robot arm are now explained with reference to figures 6 to 12.
30 Suitably, these control methods are performed by the robot arm controller of the surgical
robot arm which has lost power.
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Starting with figure 6, at step 601, the surgical robot arm is being operated in a full power
mode with power being provided to the surgical robot arm by the primary power source. At
step 602, the control system operates the surgical robot arm in surgical mode. At step 603,
the control system determines whether a power failure to the surgical robot arm has been
5 detected. If no power failure has been detected, the control system returns to step 602 where
it continues to operate the surgical robot arm in the surgical mode. If a power failure has
been detected at step 603, then the control system responds by enabling a reduced power
mode at step 604 and entering a standby mode at step 605. The standby mode is a locked
mode in which the control system sends control signals to the joint controllers of the robot
10 arm commanding them to control the joint motors to drive the joints so as to hold the joints
of the surgical robot arm locked in place. The control method then moves on to step 606,
wherein it determines whether full power has been restored, i.e. whether the power failure
has ceased. If the answer is NO, then the control system retains the surgical robot arm in the
standby mode 605. If the answer is YES, then the control system moves to step 607. At step
15 607, the control system responds to detecting the cessation of the power failure by disabling
the reduced power mode and re-enabling the full power mode. The control system then
returns to the surgical mode 602.
Steps 604 and 605 could be implemented in the order shown in figure 6, the other way
20 around, or concurrently. Step 607 could be implemented concurrently with a return to the
surgical mode 602.
Although described with respect to the surgical mode, the method of figure 6 applies to any
of the operating modes of the surgical robot arm described with respect to figure 5, i.e. the
25 locked mode, instrument adjust mode and instrument change mode.
The control method of figure 6 is useful for surgical robot arms which do not have a
mechanical brake, but are instead braked electrically. In the event of a loss of power from
the primary power source, the control method of figure 6 ensures that the surgical robot arm
30 is held locked in its current position in the standby mode. This prevents the surgical robot
arm from drooping under gravity, which would otherwise happen if the robot arm is not
powered to counteract the gravitational torques acting on the robot arm's joints. By holding
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the robot arm in position on a back-up battery supply, time is provided for restoring full power
to the robot arm or removing the surgical instrument attached to the robot arm safely from
the patient's body.
5 The control method of figure 6 aids in setting up the operating theatre for a procedure and
tearing down the operating theatre after a procedure. Generally, several surgical robot arms
and other equipment needs to be appropriately located around the patient's bedside and
setup prior to a surgical operation commencing. The control method of figure 6 enables the
power cable to a surgical robot arm to be intentionally unplugged, so as to enable other
10 equipment to be wheeled past the surgical robot arm without having to be wheeled over the
power cable. The power cable can then be re-p lugged in, and the surgical robot arm returned
to the operating mode it was previously in without having to re-perform any calibration
procedures. During the time that the power cable is unplugged, the robot arm is held in
position. The control method of figure 6 is also useful mid-operation to enable other
15 components to be wheeled through the path of the power cable attached to the surgical
robot arm.
In order for the surgical robot arm to return to the surgical mode once full power is restored,
the virtual pivot point determined during the calibration mode is stored by the control system.
20 The virtual pivot point continues to be stored by the control system during the reduced power
mode. On returning to the surgical mode following the power failure, the virtual pivot point
is retrieved from memory by the control system and used by the control system in
determining the drive signals to send to the joint controllers to drive the joint motors of the
robot arm. In this way, no re-calibration is required following the power failure. In order for
25 no re-calibration to be required, the support structure of the surgical robot arm must remain
stationary during the standby mode. If the support structure moves, for example by unbraking
and re-braking the cart on which the robot arm is mounted, then the virtual pivot
point will change. Hence the stored virtual pivot point will no longer be valid for use following
restoration of full power to the surgical robot arm.
30
Figure 7 illustrates a modification to the control method of figure 6. Steps 601 to 606 are the
same as for figure 6. Following detecting that full power has been restored at step 606, the
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control system moves on to step 701. At step 701, the control system determines whether
there is more than a threshold battery capacity available from the secondary power source.
For example, the control system may determine whether there are more than P seconds of
power available from the secondary power source. lfthere is more than the threshold battery
5 capacity available from the secondary power source, then the control system proceeds to
step 607, where the control system disables the reduced power mode andre-enables the full
power mode. From step 607, the control system returns to the surgical mode at step 602. If
there is less than the threshold battery capacity available from the secondary power source,
then the control system returns to the standby mode of step 605. If there is less than the
10 threshold battery capacity available from the secondary power source, then the control
system may raise an alarm at step 702. The control system may output an alarm signal as an
indicator on the surgical robot arm. For example, an audio alarm signal output from a speaker
on the robot arm and/or a visual indicator such as a flashing light on the robot arm. The
control system may also send an alarm signal to the remote surgeon's console. This alarm
15 signal may be output on the surgeon's console as an audio alarm signal from a speaker on the
console or a visual indicator on the surgeon's console display screen.
The control method of figure 7 introduces an additional safety element beyond the control
method of figure 6. Specifically, the control method of figure 7 ensures that, on full power
20 being restored, there is still sufficient battery power available to hold the surgical robot arm
in position for at least P seconds before allowing the surgical robot arm to return to the
surgical mode. Thus, if full power is lost again, the surgical robot arm will be held in position
using power from the battery for long enough that the bedside team is able to remove the
instrument from the patient's body.
25
In the case that the secondary power source comprises a first rechargeable battery and a
second non-rechargeable battery as described above, P may be the same as T. In this case,
step 701 of figure 7 determines whether the first rechargeable battery was fully discharged
and the second non-rechargeable battery depleted to below T seconds of remaining power
30 for holding the surgical robot arm. If so, the only battery power available is the remaining
power of the second non-rechargeable battery which, if below T seconds, is not deemed long
enough to be able to safely remove the surgical instrument from the patient's body. If greater
5
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than T seconds of power are remaining, then the second non-rechargeable battery and/or the
first rechargeable battery have sufficient power available to enable the bedside team to safely
remove the surgical instrument should another power failure of the primary power source
occur.
Figure 8 illustrates a control method in which the surgical robot arm enters the standby mode
605 as described with reference to steps 601 to 605 of figure 6. Having entered the standby
mode, at step 801, the control system determines whether a command has been received
from a user input to change to a calibration mode. The user input may be an interface located
10 on or adjacent to the surgical robot arm. For example, the interface may be located on the
surgical robot arm or its support structure. The user input may be an interface located on the
surgeon's console. In either case, the interface may take the form of a button, switch, slider,
touch sensitive input, voice control input, eye control input or a gesture control input.
15 If at step 801, the control system determines that the user input has not been received, then
the control system returns to the standby mode at step 605. If at step 801, the control system
determines that the user input has been received, then the control method moves onto step
802. At step 802, the control system responds to the command from the user input by
transitioning control of the surgical robot arm from the standby mode to the calibration
20 mode.
The method of figure 8 allows the bedside team or surgeon to, upon detecting a power failure
of the primary power supply, safely end the surgical robot arm's part in the surgical
procedure. Upon receipt of the user input, the control system transitions the robot arm to a
25 calibration mode in which the robot arm is driven to comply with external force applied to
the robot arm. Thus, the bedside team can move the robot arm and its support structure out
of the way of the patient's bed.
Figure 9 illustrates a modification to the control method of figure 8. Steps 601 to 801 are the
30 same as for figure 8. Following detecting that a command has been received from a user
input to change to a calibration mode at step 801, the control method moves on to step 901.
At step 901, the control system determines whether there is more than a threshold battery
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capacity available from the secondary power source. For example, the control system may
determine whether there are more than P seconds of power available from the secondary
power source. If there is more than the threshold battery capacity available from the
secondary power source, then the control method proceeds to step 902. At step 902, the
5 control system transitions control of the surgical robot arm from the standby mode to the
calibration mode. If at step 901, the control system determines that there is less than the
threshold battery capacity available from the secondary power source, then the control
method either returns to the standby mode of step 605 or transitions to step 903, where the
instrument is manually removed. lfthere is less than the threshold battery capacity available
10 from the secondary power source, then the control system may raise an alarm at step 904.
The control system may output an alarm signal as an indicator on the surgical robot arm as
described above with reference to figure 7. The control system may also send an alarm signal
to the remote surgeon's console as described above with reference to figure 7. In the case
that the secondary power source comprises a first rechargeable battery and a second non-
15 rechargeable battery as described above, P may be the same as T.
At step 903, the bedside team may manually remove the instrument by detaching the
instrument from the robot arm, manually open the jaws of the instrument so as to release
any tissue grasped therebetween, manually straighten the instrument by manipulating the
20 instrument interface elements, then pull the instrument out of the patient. No tools are
required to perform this function.
Figure 10 illustrates a modification to the control method of figure 8. Steps 601 to 801 are
the same as for figure 8. Following detecting that a command has been received from a user
25 input to change to a calibration mode at step 801, the control method moves on to step 1001.
At step 1001, the control system determines whether there is a surgical instrument attached
to the surgical robot arm which is inside the patient's body. This condition is not satisfied if
either: (i) there is no surgical instrument attached to the surgical robot arm, or (ii) there is a
surgical instrument attached to the surgical robot arm but that surgical instrument has not
30 been inserted in a port in the patient's body. If the control system determines there is no
surgical instrument attached to the surgical robot arm that is located in the patient's body,
then at step 1002, the control system transitions from the standby mode to the calibration
5
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mode. If at step 1001, the control system determines that there is a surgical instrument
attached to the surgical robot arm which is located in the patient's body, then the control
method moves either (i) to step 605 where the control system maintains the surgical robot
arm in the standby mode, or (ii) to step 1003 where the instrument is manually removed.
Figure 11 illustrates a modification to the control method of figure 8 including both the
modifications of figures 9 and 10. Steps 601 to 901 are the same as for figure 9. If, at step
901, the control system determines that less than the threshold battery capacity is available
from the second power source, then the control system either (i) maintains the surgical robot
10 arm in standby mode 605, or (ii) at step 1103 the instrument is manually removed. In either
case, an alarm may be raised at step 903.
If, however, at step 901 the control system determines that more than the threshold battery
capacity is available from the second power source, then the control system moves to step
15 1101. At step 1101 the control system determines whether there is a surgical instrument
attached to the surgical robot arm which is inside the patient's body. If the control system
determines there is no surgical instrument attached to the surgical robot arm that is located
in the patient's body, then at step 1102, the control system transitions from the standby mode
to the calibration mode. If at step 1101, the control system determines that there is a surgical
20 instrument attached to the surgical robot arm which is located in the patient's body, then at
step 1103, the control system either (i) maintains the surgical robot arm in the standby mode
at step 605, or (ii) the instrument is manually removed at step 1103.
Steps 901 and 1101 could be implemented in the order shown in figure 11, the other way
25 around, or concurrently.
As with figure 6, although the methods of figures 7, 8, 9, 10 and 11 are described with respect
to the surgical mode, they apply equally to any of the operating modes of the surgical robot
arm described with respect to figure 5, i.e. the locked mode, instrument adjust mode and
30 instrument change mode. These modes all have the common feature that when the surgical
robot arm is in them, the control system constrains motion of the surgical robot arm so as to
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maintain an intersection between the longitudinal axis of the shaft of the surgical instrument
and the virtual pivot point.
Following a power failure, the battery supply to the surgical robot arm may become
5 sufficiently depleted that the robot arm controller causes the surgical robot arm to enter a
minimum power mode in which power is used only to maintain the position of the surgical
robot arm so as to prevent the surgical instrument from advancing any further into the
patient's body.
10 The surgical robot arm can be considered to consist of three sets of joints. Each set of joints
comprises one or more joints. These three sets of joints will now be described.
For each joint of the first set of joints, there is a configuration of the surgical robot arm when
the base is sat on a horizontal surface for which that joint: (i) experiences a gravitational
15 torque or force, and (ii) movement of the joint complying with the gravitational torque or
force would cause the surgical instrument attached to the surgical robot arm to advance into
the patient's body towards the surgical site. To satisfy this definition, there need only be one
configuration of the surgical robot arm in which the joint satisfies both the first and second
condition. It may be the case that that same joint does not satisfy the first and second
20 condition for some other configurations of the surgical robot arm. The joints of a specific
surgical robot arm which satisfy this definition are dependent on the specific structure of that
surgical robot arm including the sequence of joints of that surgical robot arm.
Movement of a joint of the first set of joints complying with the gravitational torque or force
25 may cause the surgical instrument to advance through the port into the patient's body by
more than a threshold distance K. For exam pie, that threshold dista nee K may be in the range
O.lcm < K