Patent Description:
Medical personnel, such as practitioners, have recently found benefit in using robotic systems to perform surgical procedures. Such a robotic system typically includes a moveable arm. The movable arm has a free, distal end that can be positioned with a very high degree of accuracy. A surgical instrument is attached to the free end of the arm. The surgical instrument is designed to be applied to a surgical site.

In early robotic systems, medical personnel rigidly fixed the patient in a surgical holder thereby fixing the surgical site in a static patient coordinate system. However, recent robotic systems employ surgical holders that allow slight movements of the patient. As such, modern surgical holders do not rigidly fix the surgical site in a static patient coordinate system.

One drawback of allowing movement of the surgical site is the possibility that the surgical site is too loosely secured during autonomous operation of the robotic system. In this situation, a position control loop of the robotic system continually attempts to reach a target at the surgical site while at the same time constantly pushing the target out of reach. As a result, the surgical instrument is positioned inaccurately at the surgical site, thereby adding unnecessary delay to the surgical procedure.

As such, it is desirable to develop a robotic system which can compensate for these conditions or prevent the condition altogether.

Document <CIT> may be construed to disclose a robotic system for steering a flexible needle during insertion into soft-tissue using imaging to determine the needle position. The control system calculates a needle tip trajectory that hits the desired target while avoiding potentially dangerous obstacles en route. Using an inverse kinematics algorithm, the maneuvers required of the needle base to cause the tip to follow this trajectory are calculated, such that the robot can perform controlled needle insertion. The insertion of a flexible needle into a deformable tissue is modeled as a linear beam supported by virtual springs, where the stiffness coefficients of the springs varies along the needle. The forward and inverse kinematics of the needle are solved analytically, enabling both path planning and correction in real-time. The needle shape is detected by image processing performed on fluoroscopic images. The stiffness properties of the tissue are calculated from the measured shape of the needle.

Document <CIT> may be construed to disclose a robotic system for flexible needle steering under ultrasound imaging. A robot is used to steer the needle along a predetermined curved trajectory by maneuvering the needle base. The needle tip position is detected by an ultrasound sensor and the tracking error of the needle tip from a predetermined needle path is input to a controller which solves the inverse kinematic based on the needle position, and the needle and tissue properties. The control algorithm uses a novel method to detect the elastic properties of the tissue by analyzing tissue motion at the region in front of the needle tip. The inverse kinematic solution may be performed on a model of the needle as a flexible beam having laterally connected virtual springs to simulate lateral forces exerted by the tissue elasticity. The system is able to direct the needle to a target within the tissue while circumventing forbidden regions.

Document <CIT> may be construed to disclose an automated vessel puncture device, methods of mapping three-dimensional views of subcutaneous vessels and methods for providing simultaneous real-time diagnostic assay.

Document <CIT> may be construed to disclose a technique to define objects with respect to images of an anatomy displayed using an image guided surgery system. For non-trivial objects, or those with complicated two or three dimensional forms, it may be difficult to present information in a manner that is simple for a user to understand. The local distance to a surface of interest, such as the surface of the defined object, or to a desired position, the local penetration distance of the surface of interest, or haptic repulsion force, often provides the most useful information for augmenting the interaction of the user with the image guided surgery system. The scalar value of the local distance may be conveyed to the user by visual, audio, tactile, haptic, or other means.

According to the present disclosure, there is provided a robotic system according to the independent claim. Further developments are set forth in the dependent claims.

Methods of treatment described here below are not claimed and are not part of the present invention.

In an example, a robotic system for manipulating anatomy of a patient during a surgical procedure is provided. A force-applying device is configured to apply force to the anatomy to generate a response by the anatomy. A response-measuring device is configured to measure the response of the anatomy. The anatomy has a characteristic and a controller is configured to calculate the characteristic of the anatomy based on the response. An instrument is configured to manipulate the anatomy. The controller autonomously controls the instrument in relation to the anatomy based on the calculated characteristic.

In an example, a method of controlling a robotic system for manipulating anatomy of a patient during a surgical procedure is provided. The anatomy has a characteristic. The robotic system includes an instrument and is configured to autonomously control the instrument. The method includes applying a force to the anatomy to generate a response by the anatomy. The response of the anatomy is measured and the characteristic of the anatomy is calculated based on the response. The method further includes autonomously controlling the instrument in relation to the anatomy based on the calculated characteristic.

In an example, a method of controlling a robotic system for manipulating anatomy of a patient during a surgical procedure is provided. The anatomy is secured by a support and the robotic system includes an instrument and is configured to autonomously control the instrument. A navigation system is configured to track the anatomy and the instrument. The method includes determining with the navigation system data representing the extent to which the anatomy moves relative to the support. The method further includes autonomously controlling the instrument in relation to the anatomy based on the data.

The system and method address situations in which the anatomy moves as the instrument is applied autonomously to the anatomy. By measuring the response and calculating the characteristic of the anatomy, the system and method account for such movement. Advantageously, the system and method are capable of autonomously controlling the instrument in relation to the anatomy based on the calculated characteristic. By autonomously controlling the instrument based on the calculated characteristic of the anatomy, the system and method account for movement of the anatomy with minimal to no intervention from medical personnel. Additionally, the system and method beneficially accounts for characteristics of the anatomy, thereby avoiding the problem of continually attempting to reach a target at the surgical site while at the same time constantly pushing the target out of reach. Instead, the system and method allows the target at the surgical site to be reached efficiently by taking the characteristic of the anatomy into account. As such, the system and method provide more accurate positioning of the surgical instrument at the surgical site and reduced delay during the surgical procedure.

Systems and methods are disclosed for controlling a robotic system to perform a surgical procedure. Referring to <FIG>, a robotic system <NUM> for performing the surgical procedure on a patient is shown.

Prior to the surgical procedure, medical personnel may collect preoperative data of the patient. Preoperative data may come from an x-ray, a CT scan, a MRI or any other modality that can collect preoperative data. The collected preoperative data may be saved and stored for use by the robotic system <NUM>.

In one embodiment, the patient is placed onto a support station <NUM> during the surgical procedure. The support station <NUM> has a support or surgical holder <NUM> that secures anatomy of the patient. The anatomy of the patient is identified by reference to A in <FIG>. The anatomy may be a femur F and/or a tibia T in some embodiments. It should be appreciated that the surgical holder <NUM> may be coupled to the support station <NUM> in any fashion.

In <FIG>, the support station12 includes an operating table <NUM> having a track <NUM>. The surgical holder <NUM> is coupled to the track <NUM> such that the surgical holder <NUM> may move along the track <NUM> on the table <NUM>. During the surgical procedure, medical personnel may slide the surgical holder <NUM> forward and backward along the track <NUM> to position the anatomy. The surgical holder <NUM> may lock in the track <NUM> such that the surgical holder <NUM> is in a fixed position. For example, the surgical holder <NUM> may lock in the fixed position when the anatomy is in an optimal position. One embodiment of a suitable surgical holder <NUM> is shown in <CIT> entitled "Multi-Position Limb Holder".

Although the surgical holder <NUM> may be in the fixed position, the anatomy is placed in the surgical holder <NUM> such that the anatomy may still move relative to the surgical holder <NUM>. For example, the anatomy may move relative to the surgical holder <NUM> in one or more degrees of freedom, including up to six degrees of freedom. In turn, the anatomy is effectively a dynamic member of the robotic system <NUM>. Still, the surgical holder <NUM> is configured to securely hold the anatomy in a manner that limits gross or major movements of the anatomy upon the application of force to the anatomy so that the robotic system <NUM> is able to treat the anatomy.

The robotic system <NUM> includes a manipulator <NUM> that may be used to manipulate a surgical instrument <NUM> to treat the anatomy. One embodiment of the manipulator <NUM> is described in <CIT>, entitled "Surgical Manipulator Capable of Controlling a Surgical Instrument in Multiple Modes".

The manipulator <NUM> includes a cart <NUM> and a pair of arms <NUM> extending from the cart <NUM> to a distal end. The instrument <NUM> is coupled to the distal end of the pair of arms <NUM>. It should be appreciated that the instrument <NUM> may be integrated with the manipulator <NUM> in any fashion. In one embodiment, the instrument <NUM> includes an energy applicator <NUM> extending from the instrument <NUM>. The energy applicator <NUM> may be an ultrasonic tip, bur, or any other treatment device for performing a surgical procedure. The surgical holder <NUM> is generally fixed relative to the manipulator <NUM>.

The manipulator <NUM> and the instrument <NUM> may also have one or more sensors and/or encoders for sensing position, force/torque, etc. The sensors and encoders may be of any form to those known in the art to provide physical data or other types of data associated with the manipulator <NUM> and the instrument <NUM>. One type of sensor is a force/torque sensor <NUM>, which can detect forces and torques applied to the instrument <NUM>. One embodiment of a suitable force/torque sensor <NUM> is shown in <CIT> entitled "Force/Torque Transducer".

The manipulator <NUM> also includes a manipulator controller <NUM>. The manipulator controller <NUM> communicates with the sensors and encoders, including the force/torque sensor <NUM>. The manipulator controller <NUM> is able to communicate with the force/torque sensor <NUM> such that the forces and torques sensed by the force/torque sensor <NUM> are communicated back to the manipulator controller <NUM>. The manipulator controller <NUM> further communicates with a navigation system <NUM>.

The robotic system <NUM>, and more specifically, the manipulator <NUM>, may be operated manually or autonomously. When operated manually, the robotic system <NUM> is operating in a manual mode. In the manual mode, medical personnel can manually position the instrument <NUM> by applying commands to the robotic system <NUM>. One example of applying commands includes the medical personnel grasping and applying forces/torques to the instrument <NUM>. Based on the commands applied by the medical personnel, the robotic system <NUM> actuates the arms <NUM> to cause corresponding and effectively simultaneous, real time, movement of the instrument <NUM> to the desired position.

The robotic system <NUM> is configured to autonomously control the instrument <NUM>. More specifically, the robotic system <NUM> autonomously controls the instrument <NUM> in an autonomous mode or a semi-autonomous mode of operation. In the autonomous or semi-autonomous modes, the manipulator controller <NUM> processes preloaded data, data from the navigation system <NUM> and data from the encoders to derive a path along which the instrument <NUM> will follow. The path may be preprogrammed or predetermined. The robotic system <NUM> actuates the arms <NUM> to cause autonomous movement of the instrument <NUM> along the path to treat the anatomy. The robotic system <NUM> performs the procedure with effectively no input from the medical personnel.

In the semi-autonomous mode, the robotic system <NUM> autonomously moves the instrument <NUM> along the path. However, medical personnel are able to assert commands to control the operation of the robotic system <NUM>. For example, the robotic system <NUM> may require that the medical personnel continually depress a control button or switch associated with the robotic system <NUM> to permit movement of the instrument. Upon the release of the button or switch by the medical personnel, the advancement of the instrument <NUM> temporarily halts. One suitable navigation system utilized in the autonomous or semi-autonomous mode is described in <CIT>, entitled "Navigation System Including Optical and Non-Optical Sensors". However, one should appreciate that other navigation systems may be used.

The navigation system <NUM> may include a computer cart assembly <NUM> that houses a navigation computer <NUM>. A navigation interface is in operative communication with the navigation computer <NUM>. The navigation interface allows the medical personnel to communicate with the robotic system <NUM>. The navigation interface includes at least one display <NUM>, <NUM>, and input devices <NUM>, <NUM> such as a keyboard and a mouse, to allow the medical personnel to communicate with the navigation computer <NUM>.

The navigation computer <NUM> cooperates with the manipulator controller <NUM> to control the manipulator <NUM>. The navigation computer <NUM> provides pose data of the instrument <NUM> to the manipulator controller <NUM> such that the manipulator controller <NUM> may direct motion of the manipulator <NUM>, and in turn, the instrument <NUM>.

A localizer <NUM> communicates with the navigation computer <NUM>. In the embodiment shown in <FIG>, the localizer <NUM> is an optical localizer <NUM> and includes a camera unit <NUM>. The camera unit <NUM> has an outer casing that houses one or more optical sensors <NUM>. In some embodiments, at least two optical sensors <NUM> are employed. In other embodiments, three or more optical sensors <NUM> may be used.

The navigation system <NUM> includes one or more trackers. The trackers may include a pointer tracker PT, an instrument tracker <NUM>, a first patient tracker <NUM>, and a second patient tracker <NUM>. The trackers include active markers <NUM>. The active markers <NUM> may be light emitting diodes or LEDs. In other embodiments, the trackers <NUM>, <NUM>, <NUM> may have passive markers, such as reflectors that reflect light emitted from the camera unit <NUM>. It should be appreciated that additional trackers may be incorporated into the navigation system <NUM> to track additional components that may be part of the robotic system <NUM>.

In the illustrated embodiment of <FIG>, the first patient tracker <NUM> is firmly affixed to the femur F of the patient P and the second patient tracker <NUM> is firmly affixed to the tibia T of the patient P. The patient trackers <NUM>, <NUM> are firmly affixed to sections of bone. In addition, the instrument tracker <NUM> is firmly attached to the instrument <NUM>. The trackers <NUM>, <NUM>, <NUM> may be fixed to their respective components in any manner which one may find useful.

Referring to <FIG>, each of the LEDs are connected to a tracker controller <NUM> located in a housing (not shown) of the associated tracker that transmits/receives data to/from the navigation computer <NUM>. The trackers <NUM>, <NUM>, <NUM> also include a <NUM>-dimensional gyroscope sensor <NUM> that measures angular velocities of the trackers <NUM>, <NUM>, <NUM>. The trackers <NUM>, <NUM>, <NUM> also include an accelerometer <NUM> to measure acceleration in the x, y, and z coordinate system.

The camera unit <NUM> includes a camera controller <NUM> in communication with the optical sensors <NUM> to communicate pose data from the active markers <NUM> of the trackers <NUM>, <NUM>, <NUM>. The camera controller <NUM> then communicates the pose data to the navigation computer <NUM>. The navigation computer <NUM> then processes the pose data with additional preoperative data, to communicate the pose of the instrument <NUM> and thus the energy applicator <NUM> in relationship to the anatomy of the patient. In one embodiment, the navigation interface communicates such data to the medical personnel. It should be appreciated that one of ordinary skill in the art may find other methods not described in the previous embodiments for the medical personnel to communicate with the robotic system <NUM>.

During a surgical procedure, it is desirable for the robotic system <NUM> to switch from the manual mode to the semi-autonomous or autonomous mode. In some procedures, such as bone cutting procedures, it is desirable for the anatomy to be securely located in the surgical holder <NUM> such that the anatomy does not move at the same rate as the instrument <NUM> when the instrument <NUM> engages the bone. Otherwise, the instrument <NUM> will be unable to cut any bone. In other words, it is desirable for the anatomy to have a certain minimum stiffness or other characteristic when secured in the surgical holder <NUM>. Additionally, there is a desire to control the robotic system <NUM> based on the value of certain characteristics, such as stiffness, to ensure that the anatomy moves at a lower rate than the instrument <NUM> when the instrument <NUM> is applied to the anatomy during the surgical procedure.

To account for movement of the anatomy as the instrument <NUM> is applied to the anatomy, the robotic system <NUM> is calibrated based on one or more characteristics of the anatomy. The one or more characteristics may be a stiffness characteristic (k), a damping characteristic (b), a mass (m), a damping ratio (ζ), a frequency response (ωn) and/or other characteristic. The stiffness characteristic (k) may be further defined as a spring constant. In another example, the characteristic includes data representing the extent to which the anatomy is secured by the surgical holder <NUM>. More specifically, the characteristic includes data representing the extent to which the anatomy moves relative to the surgical holder <NUM>.

<FIG> illustrates the basic steps of controlling the robotic system <NUM> for manipulating the anatomy of the patient P during the surgical procedure. A force is applied to the anatomy to generate a response by the anatomy in step <NUM>. The response of the anatomy is measured in step <NUM>. In step <NUM>, the characteristic of the anatomy is calculated based on the response. In step <NUM>, the instrument <NUM> is autonomously controlled in relation to the anatomy based on the calculated characteristic.

In order to apply the force to the anatomy at step <NUM>, a force-applying device is generally positioned adjacent to or against the anatomy. In one embodiment, the robotic system <NUM>, and more specifically, the manipulator controller <NUM>, actively moves the force-applying device toward the anatomy to apply the force. Alternatively, the robotic system <NUM> may be stationary and the force-applying device extends from the robotic system <NUM> toward the anatomy to apply the force. Such movement of the force-applying device may be made independent of the manipulator controller <NUM>. The force-applying device may have any suitable configuration. For example, the instrument <NUM> that manipulates the anatomy is the force-applying device. In another example, a device other than the instrument <NUM>, such as a sensor or gauge, acts as the force-applying device and is positioned against the anatomy. Any suitable device other than the instrument <NUM> may act as the force-applying device.

The medical personnel may provide input in the manual mode so that the robotic system <NUM>, and more specifically, the manipulator controller <NUM> positions the instrument <NUM>, or other force-applying device, against the anatomy. In some cases, the energy applicator <NUM> may be positioned against the anatomy. In other cases, the surgical instrument <NUM> is outfitted with a calibration probe (not shown) that has a non-invasive and biocompatible structure at its distal end to position against the anatomy.

In alternative versions, the robotic system <NUM> may be utilized in the semi-autonomous or autonomous modes to autonomously position the instrument <NUM> against the anatomy prior to applying the force in step <NUM>. The medical personnel may interact with the navigation interface to intervene during autonomous operation to direct positioning of the instrument <NUM> against the anatomy. It should be appreciated that the medical personnel may interact with the manipulator <NUM>, navigation system <NUM>, or any other component of the robotic system <NUM> in any way that one of ordinary skill in the art would find it useful to direct the position of the instrument <NUM>. Additionally, the medical personnel may switch between manual, autonomous, and/or semi-autonomous modes when positioning the instrument <NUM> against the anatomy.

The force is applied to the anatomy in step <NUM>. In one embodiment of step <NUM>, the instrument <NUM> applies the force to the anatomy. In another embodiment, the force- applying device other than the instrument <NUM> applies the force to the anatomy. In either instance, the force may be applied to the anatomy in the manual mode, autonomous mode and/or semi-autonomous mode. In one embodiment, the force is predetermined. Furthermore, the force may be applied in one degree of freedom. Alternatively, forces and torques may be applied in several degrees of freedom, such as six degrees of freedom.

In one embodiment, the force is applied to the anatomy according to a step function. In such instances, the force is applied at first level during a first interval and at a second level during a second interval that is consecutive to the first interval. The first level may be higher than the second level, or vice-versa. As such, the robotic system <NUM> may apply forces of various levels to the anatomy. The step function may include any suitable number of levels and intervals.

In another embodiment, the force is applied to the anatomy according to an impulse function F(t). In this embodiment, the force is applied to the anatomy and a signal is recorded to measure the reaction of the anatomy as a function of time.

In yet another embodiment, step <NUM> includes activating a calibration procedure. As such, applying the force to the anatomy occurs in response to activation of the calibration procedure. The calibration procedure may be a stored calibration program in the manipulator controller <NUM>. The stored calibration program may be stored in any medium that can store a computer program and is a part of the robotic system <NUM>. The navigation interface may prompt a user to start the calibration procedure. Alternatively, the calibration procedure may start automatically.

During the calibration procedure, the stored calibration program can cooperate with the manipulator controller <NUM> to instruct the instrument <NUM> to apply the force to the anatomy. In one embodiment, the force is applied to the anatomy such that that the instrument <NUM> maintains contact with the anatomy throughout the calibration procedure. Additionally or alternatively, the manipulator <NUM> may continue to increase force applied to the anatomy until a predetermined threshold force is reached.

The anatomy generates the response after the force is applied. As will be described in detail below, the generated response of the anatomy may take any combination of various forms. In one embodiment, the generated response of the anatomy is a mechanical response. For example, the generated response may be mechanical movement of the anatomy, or more specifically, displacement or rotational movement of the anatomy. Those skilled in the art will appreciate that the generated response of the anatomy may take non-mechanical forms. For example, the generated response may be an electrical response.

After the response by the anatomy is generated, the response is measured at step <NUM>. The response may be measured according to various methods. A response-measuring device measures the response. In one embodiment of step <NUM>, the response is measured using a force/torque sensor <NUM>. The force/torque sensor <NUM> may be associated with the instrument <NUM>. When the instrument <NUM> applies forces and/or torques to the anatomy, the force/torque sensor <NUM> may measure the forces and/or torques. Alternatively, the force/torque sensor <NUM> may be associated with a device other than the instrument <NUM>. The forces and/or torques may be measured as a function of time. In addition, the forces and/or torques may be measured discretely or continuously.

In another embodiment of step <NUM>, the response of the anatomy is measured by measuring a joint torque. The joint torque corresponds to the torque related to one of the joints of the manipulator <NUM>. Any suitable sensors and/or encoders may sense the joint torque. Additionally, more than one joint torque may be measured. In one embodiment, the joint torques are calculated and converted into tool center point (TCP) forces/torques using equation (<NUM>) below. In equation (<NUM>), (J') is the transpose of the Jacobian from the TCP to the joints and (t) is the vector of the joint torques. The joint torque may be calculated from the current drawn by motor controllers used to manipulate the instrument <NUM>, as shown in formula (<NUM>) below, where (kt) is the motor torque constant and (i) is the current. Additionally, an estimate of the joint torques may be determined using joint torque sensors. The joint torques may be measured according to various other methods. <MAT> <MAT>.

In yet another embodiment of step <NUM>, the response of the anatomy is measured by measuring a displacement of the anatomy. The displacement may be the distance that the anatomy moves because of having the force applied thereto. The displacement may be measured as a function of time. In addition, the displacement may be measured discretely or continuously. In some embodiments, the manipulator <NUM> may continue to apply the instrument <NUM> to the anatomy until a desired displacement is reached. Any suitable device or method may be utilized to measure the displacement of the anatomy. In one example, the navigation system <NUM> calculates the displacement by measuring changes in position of the trackers <NUM> and <NUM>. For instance, the navigation system <NUM> may determine an initial position of the anatomy prior to applying the force at step <NUM>. After the force is applied, the navigation system <NUM> may determine a displaced position of the anatomy. The navigation system <NUM> may then compare the displaced position relative to the initial position to determine the displacement.

When measuring the displacement, the robotic system <NUM> may record a final force and displacement measurement. In step <NUM>, the manipulator <NUM> may wait a defined settling time so that the anatomy and the instrument <NUM> reach an equilibrium point before the robotic system <NUM> records the final force and displacement measurement. Additionally, the manipulator controller <NUM> may calculate the displacement of the anatomy using the encoders and kinematic calculations. It should be appreciated that one of ordinary skill in the art may find alternative methods to calculate the displacement of the anatomy.

In measuring the response of the anatomy, the mass (m) of the anatomy may be considered. In one embodiment, the mass of the anatomy is estimated from the preoperative data. Additionally, the mass of the anatomy may be added to the mass of the surgical holder <NUM>. As such, the mass of the anatomy and the holder <NUM> may be considered in measuring the response of the anatomy. Furthermore, both the mass and the displacement may be taken into account when measuring the response.

The response of the anatomy may be measured according any combination of the aforementioned embodiments. In one embodiment, certain steps of the method occur at different times. For example, steps <NUM> and <NUM> occur at different times. More specifically, the force is applied to the anatomy before the response of the anatomy is measured. In another example, steps <NUM> and <NUM> occur at different times. Specifically, the force is applied to the anatomy prior to autonomous control of the instrument <NUM>. In such instances, the step <NUM> of applying the force to the anatomy occurs separately and distinctly from the step <NUM> of autonomously controlling the instrument <NUM>.

Alternatively, certain steps of the method may occur at the same time. For example, steps <NUM> and <NUM> may occur simultaneously such that the response of the anatomy is measured contemporaneously as the force is applied. In another example, step <NUM> occurs at the same time as step <NUM>. Specifically, the force is applied as the instrument <NUM> is autonomously controlled. In such instances, the step <NUM> of applying the force need not be executed prior to autonomously controlling the instrument <NUM>. That is, autonomous control of the instrument <NUM> may be initiated without having previously applied the force to the anatomy. Rather, during autonomous control of the instrument <NUM>, the force is continuously applied to the anatomy. Additionally, steps <NUM> and <NUM> may occur at the same time as step <NUM>. That is, the response of the anatomy may be measured and the characteristic of the anatomy may be calculated as the instrument <NUM> is autonomously controlled.

As described above, the characteristic of the anatomy is calculated based on the measured response of the anatomy at step <NUM>. The characteristic may be calculated according to various embodiments. In one embodiment, the characteristic is measured using a static approach. In this approach, a stiffness characteristic (k) of the anatomy is determined. The force applied to the anatomy is known and is represented by (F). The calculated displacement of the anatomy is also known and is represented by (x). The manipulator controller <NUM> processes the force (F) and the calculated displacement (x) by inputting the force (F) and the displacement (X) into equation (<NUM>) below, to solve for the stiffness characteristic (k) in step <NUM>.

In equation (<NUM>), the static deflection of the anatomy is measured. The stiffness characteristic (k) is the spring constant, which may be estimated under steady state conditions. It should be appreciated that one of ordinary skill in the art may find alternative static approaches for calculating the characteristic of the anatomy.

In another embodiment, the characteristic is measured using a dynamic approach. In this approach, a step or impulse response of the anatomy is measured. Parameters are estimated using the following characteristic equation (<NUM>) for a mass/spring/damper model: <MAT>.

In equation (<NUM>), (m) is the mass of the holder and/or anatomy, (b) is a damping characteristic, such as a damping coefficient, (k) is the spring constant, (x") is the second derivative with respect to time of displacement (e.g., acceleration), (x') is the first derivative with respect to time of displacement (e.g., velocity), and (x) is displacement. In equation (<NUM>), at least one of the parameters (m, b, or k) may be assumed or known to allow for easy estimation of the remaining parameters. For example, if two of the three parameters are known, this allows for an improved estimation of the third parameter. In one example, the mass is known or may be estimated from available clinical data. In another example, the spring constant (k) is computed and estimated through a static test. In either example, the remaining two variables may be calculated from the experimental data. Alternatively, the approach of both examples can be combined to provide for initial estimates for both (m) and (k) such that the damping characteristic (b) can be calculated from the experimental data.

In another embodiment of step <NUM>, calculating the characteristic includes estimating the resonant frequency (ωn) and the damping ratio (ζ) of the anatomy"s response from a displacement over time graph generated by the manipulator controller <NUM>. Using the estimated mass, and solving equation (<NUM>) and equation (<NUM>) below, the stiffness characteristic (k) and the damping characteristic (b) can be calculated. In other examples, the mass, the stiffness characteristic (k), and the damping characteristic (b) are estimated. <MAT> <MAT>.

In yet another embodiment, step <NUM> includes performing an iterative optimization routine to search for parameter values that minimize the mean square error between a calculated response, xc(t), and an experimental response x(t), as evaluated from the displacement versus time data. In this embodiment, the full transfer function for the mass, spring, damper model, H s<IMG> in equation (<NUM>), is utilized to calculate the value of the mass (m), the damping characteristic (b) and the stiffness characteristic (k).

In equation (<NUM>), a force input, f(t), is known and the Laplace transform of f(t) is calculated to solve for F(s). As such, F(s) in equation (<NUM>) is the Laplace transform of the force input. In equation (<NUM>), X(s) is the Laplace transform of a translation output, and s is the Laplace frequency variable. In equation (<NUM>), X(s) is solved using the calculated values of F(s) and the guessed values of (m), (k), and (b). Once X(s) is known, the inverse Laplace transform, as shown by equation (<NUM>) below, is used to convert X(s) from the frequency domain to the time domain as xc(t). The mean square error is then calculated between xc(t) and x(t). The process is then repeated by using updated guesses for (m), (k), and (b) until the mean square error converges within an acceptable margin. <MAT> <MAT>.

It should be appreciated that one of ordinary skill in the art could anticipate using alternative mathematical methods not stated above to calculate the characteristic of the anatomy.

As described, at step <NUM> the robotic system <NUM> autonomously controls the instrument <NUM> in relation to the anatomy based on the calculated characteristic. By doing so, the method takes the characteristic of the anatomy into account when autonomously controlling the instrument <NUM>. The manipulator controller <NUM> may control the placement of the instrument <NUM>, and in turn, the tip of the energy applicator <NUM> in relationship to the anatomy based on the calculated characteristic. According to one embodiment, autonomously controlling the instrument <NUM> includes utilizing the calculated characteristic to account for movement of the anatomy during the surgical procedure.

In another embodiment, the calculated characteristic is used as a factor in controlling a feed rate of the manipulator in the autonomous or semi-autonomous modes. The feed rate of the manipulator is described in <CIT>, entitled "Surgical Manipulator Capable of Controlling a Surgical Instrument in Multiple Modes".

In one example, the feed rate of the instrument <NUM> is adjusted based on the calculated characteristic. For example, the feed rate is adjusted such that the feed rate is faster than a rate at which the anatomy moves as the instrument <NUM> is applied to the anatomy during the surgical procedure. This way, the calculated characteristic is factored in to ensure that the feed rate of the instrument <NUM> is sufficient to allow the instrument <NUM> to contact anatomy that may be susceptible to movement in the surgical holder <NUM>.

In another example, feed rate is adjusted based on data representing the extent to which the anatomy is secured by the surgical holder <NUM>. More specifically, the feed rate is adjusted based on data representing the extent to which the anatomy moves relative to the surgical holder <NUM>. Such data may be derived by comparing an actual position of the instrument <NUM> to an intended position of the instrument <NUM> relative to the anatomy. The navigation system <NUM> tracks the anatomy and the instrument <NUM> to determine the actual position. The actual position may include a traversed cut path of the instrument <NUM>. The intended position may be predetermined and preloaded data representing an intended traversed cut path. The cut path of the instrument <NUM> may be determined at a plurality of discrete points. A profile error can be determined between the actual path and the intended path. The profile error may then be compared to a predetermined threshold. In one example, if the percentage of traversed cut path points having a profile error exceeding the threshold is deemed unacceptable, the feed rate is reduced and/or a notification is displayed. In some cases, the profile error target as well as the acceptable percentage could be adjusted or variable. Such an adjustment may be made, for example, depending on whether the cut is a rough or finish cut. Additionally, such an adjustment may be made based on criticality of the anatomy being cut. Undercuts may also have a different threshold than overcuts. In another example, the method described above is employed to compare actual bone removal by the instrument <NUM> to intended bone removal by the instrument <NUM>.

In another embodiment, autonomously controlling the instrument includes setting a maximum feed rate of the instrument <NUM> based on the calculated characteristic of the anatomy. In some instances, the robotic system <NUM> may designate a default maximum feed rate of the instrument <NUM> depending on the specific anatomy that is subject to the surgical procedure. In other words, the default maximum feed rate may be different depending upon the subject anatomy. However, depending upon the calculated characteristic, the robotic system <NUM> may set the maximum feed rate at or below the default maximum feed rate. For example, if the calculated characteristic indicates a relatively stiff anatomy, then the robotic system <NUM> may set the maximum feed rate at the default maximum feed rate. The robotic system <NUM> may maintain the maximum feed rate because there is less chance for inaccuracy in application of the instrument <NUM> when the anatomy is relatively stiff. Alternatively, for example, if the calculated characteristic indicates a relatively loosely secured anatomy, then the robotic system <NUM> may set the maximum feed rate of the instrument <NUM> below the default maximum feed rate or within a range of feed rates that are below the default maximum feed rate. The robotic system <NUM> may limit the maximum feed rate to counteract inaccuracies in application of the instrument <NUM> that may result from the anatomy being loosely secured. In other embodiments, the maximum feed rate is set simply as a function of the calculated characteristic notwithstanding a default maximum feed rate as described above.

In addition, autonomously controlling the instrument <NUM> based on the calculated characteristic may include applying the calculated characteristic in a simulation program. The simulation program may model the movement of the instrument <NUM>, and more specifically, the energy applicator <NUM>, in relationship to the anatomy during the surgical procedure. In one embodiment, the simulation models a bone milling procedure.

It should be appreciated that one of ordinary skill in the art may find uses for autonomously controlling the instrument <NUM> based on the calculated characteristic other than those described in the above embodiments without departing from the scope of the method.

Based on the calculated characteristic, the robotic system <NUM> may provide a message or notification <NUM>, as shown in <FIG> and <FIG>. The notification <NUM> aides the medical personnel during the surgical procedure. The notification <NUM> may be provided on any suitable medium, such as the user interface. In <FIG> and <FIG>, the notification <NUM> is provided on the display <NUM> of the navigation system <NUM>. The notification <NUM> may be provided by images, text, or a combination of images and text. Additionally, the notification <NUM> may be animated.

The notification <NUM> is provided based on the calculated characteristic. In one embodiment, the notification <NUM> is provided based on an assessment of the calculated characteristic. For example, the notification <NUM> may be provided based on a comparison of the calculated characteristic to a threshold related to optimal operation. The threshold may be a minimum threshold or a maximum threshold. If the calculated characteristic is above the maximum threshold or below the minimum threshold, the robotic system <NUM> provides the notification <NUM>. For example, a minimum threshold for the stiffness k (or a combination of parameters m, b, and k) may be determined. If the calculated stiffness is below the minimum threshold for the stiffness k, the robotic system <NUM> provides the notification <NUM> to the medical personnel that the procedure cannot continue until the anatomy is more securely fastened.

Alternatively or additionally, based on the calculated characteristic, the feed rate in the autonomous or semi-autonomous mode may be adjusted to a level needed to maintain machining accuracy. In one example, the feed rate is decreased until or unless the anatomy is more firmly secured. Specifically, the feed rate may be decreased until or unless the anatomy is more firmly secured in degrees-of-freedom exhibiting low stiffness. Adjustment of the feed rate may be automatic and passive such that medical personnel need not manually adjust the feed rate. Rather, the stiffness of the anatomy is adjusted if faster machining is desired. The robotic system <NUM> may thereafter display the notification <NUM> to the medical personnel that the feed rate may be increased if the anatomy is more securely fastened.

In other embodiments, the calculated characteristic is compared against a predetermined range of characteristics for optimal operation. If the calculated characteristic falls outside the range then the robotic system <NUM> may send the notification <NUM>. For example, if the robotic system <NUM> determines the calculated characteristic, such as the stiffness characteristic (k), falls outside the range for optimal operation, then the robotic system <NUM> may send the notification <NUM> warning the medical personnel of that the calculated characteristic has fallen outside the range or that the surgical procedure should be halted. On the other hand, if the stiffness characteristic (k) falls within the range of optimal operating characteristics and the robotic system <NUM> may notify the medical personnel that the surgical procedure may continue. Additionally, the aforementioned embodiment may be realized during a calibration procedure. For example, the calibration procedure may terminate when the calculated characteristic falls within the range of optimal operating characteristics.

In many instances, it is advantageous to provide the notification <NUM> with instructions on how to adjust the anatomy of the patient based on the calculated characteristic. The notification <NUM> may alert the medical personnel to reposition the anatomy in the surgical holder <NUM> such that the anatomy is more securely fastened. Repositioning of the anatomy is carried out by manipulating the surgical holder <NUM>. As such, the notification <NUM> may suggest instructions on how to manipulate (e.g., move/adjust) the surgical holder <NUM>. The position of the anatomy can be adjustably set along a plurality of degrees of freedom using the surgical holder <NUM>. The force applied to the anatomy generates the response by the anatomy with respect to each degree of freedom. For each degree of freedom, the response of the anatomy is measured. The calculated characteristic is determined for each degree of freedom. Based on the calculated characteristic, a determination can be made as to whether the anatomy should be adjusted with respect to any of the degrees of freedom. The determination can be made according to various methods, including whether the calculated characteristic has exceeded a predetermined threshold or a range. The magnitude or extent of the adjustment may also be determined.

The notification <NUM> provides suggestions that are derived from calculations based on the degrees of freedom of the anatomy. By determining which degrees of freedom of the anatomy require manipulation and the extent of such manipulation, the notification <NUM> provides suggestions to modify the position of the surgical holder <NUM>. By modifying the position of the surgical holder <NUM>, the position of the anatomy changes. The calculated characteristic changes as the position of the anatomy changes. As such, the notification <NUM> promotes repositioning of the anatomy to change the calculated characteristic.

As shown in <FIG> and <FIG>, the notification <NUM> may be displayed as an image or animation visually showing how to adjust the surgical holder <NUM>. The notification <NUM> indicates how to move the anatomy from a current position <NUM> to a suggested position <NUM>. The current position <NUM> of the anatomy is the real-time position of the anatomy. The suggested position <NUM> is derived from the calculated characteristic, as described above. In <FIG> and <FIG>, the current position <NUM> is illustrated by dashed lines and the suggested position <NUM> is illustrated by solid lines.

Suggestions provided by the notification <NUM> may depend on the configuration of the surgical holder <NUM>. In <FIG> and <FIG>, for example, the anatomy supported by the surgical holder <NUM> is a limb, such as a leg. The surgical holder <NUM> includes mechanisms for extending or flexing the anatomy. The surgical holder <NUM> is supported by a sled <NUM>, which moves along a support bar <NUM>. The notification <NUM> may suggest unlocking the sled <NUM> from the support bar <NUM> and moving the sled <NUM> along the support bar <NUM> to the suggested position <NUM>. The surgical holder <NUM> is then locked in the suggested position <NUM>. The direction of the suggested movement of the sled <NUM> in <FIG> is illustrated by an arrow for simplicity. The notification <NUM> may suggest movement of the leg from extension to flexion, or vice-versa. The notification <NUM> suggests movement of the anatomy along any given degree(s) of freedom. For example, in <FIG>, the notification <NUM> suggests rotating the surgical holder <NUM> medially (toward centerline of the patient). Alternatively, the notification <NUM> may suggest rotating the surgical holder <NUM> laterally (away from the centerline of the patient). In such instances, the notification <NUM> may suggest to move the surgical holder <NUM> laterally or medially. Furthermore, as shown in <FIG>, the surgical holder <NUM> may include at least one strap <NUM> for securing the anatomy. The notification <NUM> may suggest tightening the strap <NUM>.

Of course, the surgical holder <NUM> may have various other configurations and may be manipulated in various other ways not recited herein. Additionally, the notification <NUM> may suggest repositioning more than one feature of the surgical holder <NUM>. The notification <NUM> may also provide instructions through a single step or a series of steps. For example, the notification <NUM> may first display the suggestion shown in <FIG> as a first step and subsequently display the suggestion shown in <FIG> as a second step.

In some instances, the notification <NUM> is passive and merely suggests movement to the suggested position <NUM>. In such instances, the robotic system <NUM> generally does not determine whether the surgical holder <NUM> is moved to the suggested position <NUM>. In other instances, the notification <NUM> is active such that the robotic system <NUM> determines whether the anatomy and/or the surgical holder <NUM> have reached the suggested position <NUM>. The robotic system <NUM> may monitor movement of the anatomy and surgical holder <NUM> intermittently or continuously. The robotic system <NUM> may employ any suitable method or system for determining whether the anatomy and surgical holder <NUM> have reached the suggested position <NUM>. For example, the robotic system <NUM> may utilize the navigation system <NUM> and patient trackers <NUM>, <NUM> for determining the current and suggested positions <NUM> of the anatomy and/or surgical holder <NUM>.

Claim 1:
A robotic system (<NUM>) configured to interact with an anatomy held by a limb holder (<NUM>), the robotic system (<NUM>) comprising:
a force-applying device configured to apply a force to the anatomy held by the limb holder (<NUM>);
wherein the robotic system (<NUM>) is configured to:
measure an extent to which the anatomy moves relative to the limb holder (<NUM>) in response to the force applied to the anatomy by the force-applying device; and
the robotic system (<NUM>) further comprising:
a manipulator (<NUM>); and
a controller (<NUM>) configured to:
autonomously control the manipulator (<NUM>) based on the measured extent.