Patent Publication Number: US-11653988-B2

Title: Mitigating electromagnetic field distortion for a surgical robotic system

Description:
BACKGROUND 
     Field 
     Embodiments related to robotic systems are disclosed. More particularly, embodiments related to surgical robotic systems are disclosed. 
     Background Information 
     Endoscopic surgery involves looking into a patient&#39;s body and performing surgery inside the body using endoscopes and other surgical tools. For example, laparoscopic surgery can use a laparoscope to access and view an abdominal cavity. Endoscopic surgery can be performed using manual tools and/or a surgical robotic system having robotically-assisted tools. 
     A surgical robotic system may be remotely operated by a surgeon to control robotically-assisted tools and at least one camera located at an operating table. The surgeon may use a computer console located in the operating room, or it may be located in a different city, to command a robot to manipulate the surgical tool and camera. The robot uses the surgical tools to perform surgery, with the visualization aid provided by the camera. 
     Control of the surgical robotic system may require control inputs from the surgeon. For example, the surgeon may hold in her hand a user input device such as a joystick or a computer mouse that she manipulates to generate the signals for the control commands that control motion of the surgical robotic system components, e.g., the surgical tool or the camera. 
     SUMMARY 
     Surgical robotic systems including a user console for controlling a surgical robotic tool are described. The user console can communicate with a user interface device (UID) to detect a position, orientation, or both, of the UID within an electromagnetic (EM) tracking space. The detected position or orientation of the UID may be correlated to control of a surgical robotic tool, by for example mimicking the motion of the UID at the tool. Detection of the position or orientation, however, may be disrupted by distortion of an EM field within the EM tracking space. The surgical robotic system can include one or more response mechanisms to reduce the likelihood that such EM distortion will disrupt operation of the UID or control of the surgical robotic tool. 
     In an embodiment, a surgical robotic system includes a user console used to control a surgical robotic system in accordance with motion of a UID. More particularly, the user console provides control signals to control one or more actuators and/or surgical tools of the surgical robotic system in accordance with motion of the UID. The control signals represent spatial state signals that may be produced by an EM tracking subsystem, and in particular received from the UID, in response to movement of the UID within an EM field of an EM tracking space. To reduce the likelihood that the UID EM readings are disrupted by a distortion within the EM field, the user console can include a witness sensor mounted at a particular location, and a reference sensor. The reference sensor may be mounted adjacent to the witness sensor, or on the UID. The witness sensor can sense or measure a witness EM reading of the EM field. The witness EM reading can reflect a distortion of the EM field. The reference sensor can sense or measure a non-electromagnetic event, such as a deformation of the user console at the location of the witness sensor. The distortion that is reflected in the witness EM reading and the deformation that is reflected in the deformation reading may coincide in time, partially or wholly. The deformation reading can be used to validate the witness EM reading events. For example, when the witness EM reading and the deformation reading do not “match”, e.g. coincide in time, it may be determined that the distortion reflected in the witness EM reading results from an actual EM distortion and not a mechanical vibration of the witness sensor. When the witness EM reading is validated, the user console can have several responses. For example, the user console can generate a notification of the detected distortion to cause an alert (e.g., visual, audible, or both, in terms of being perceived by a user of the surgical robotic system) indicating an existence of the distortion, a location of the distortion, or a cause of the distortion. The user console can also adjust or pause motion of an actuator and/or surgical tool of the surgical robotic system, e.g., immediately in response to the validation. 
     In an embodiment, the cause of distortion within the EM field is known (e.g., hypothesized). For example, the distortion may originate from actuation of a haptic motor incorporated in the UID. The user console may alter a manner in which actuation pulses are input to the haptic motor, or a manner in which UID EM readings are sampled from the UID, to reduce the likelihood that the actuation-caused distortion will affect the spatial state signal samples. For example, the user console may not actuate the haptic motor (e.g., prevents actuation of the haptic motor) while it is sampling spatial state signals (that are being used in real-time to control the motion of an actuator and/or a surgical tool of the surgical robotic system during a surgical operation). Alternatively, the user console may ignore spatial state signals (samples) received while the haptic motor is being actuated. The user console may interlace the spatial state and actuation pulse signals by for example controlling the timing of the actuation pulses, generating an actuation pulse for the haptic motor only during the time interval between samples of a spatial state signal. Accordingly, the user console can adjust the actuation to reduce the likelihood that the EM distortion will disrupt surgical tool control. 
     The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment of the invention in this disclosure are not necessarily to the same embodiment, and they mean at least one. Also, in the interest of conciseness and reducing the total number of figures, a given figure may be used to illustrate the features of more than one embodiment of the invention, and not all elements in the figure may be required for a given embodiment. 
         FIG.  1    is a pictorial view of a surgical robotic system in an operating arena, in accordance with an embodiment. 
         FIG.  2    is a side view of a user interface device, in accordance with an embodiment. 
         FIG.  3    is a sectional view of a user interface device, taken about line A-A of  FIG.  2   , in accordance with an embodiment. 
         FIG.  4    is a perspective view of a user console, in accordance with an embodiment. 
         FIG.  5    is a pictorial view of an electromagnetic tracking space, in accordance with an embodiment. 
         FIGS.  6 A- 6 C  are pictorial views of a witness sensor and a reference sensor mounted on a user console, in accordance with an embodiment. 
         FIG.  7    is a flowchart of a method of detecting and responding to distortions in an electromagnetic tracking field in a surgical robotic system, in accordance with an embodiment. 
         FIG.  8    is a flowchart of a method of monitoring spatial state signals from a user interface device and outputting actuation pulses to a haptic motor of the user interface device, in accordance with an embodiment. 
         FIG.  9    is a graph of spatial state signal samples received from a user interface device and actuation pulses output to a haptic motor of the user interface device, in accordance with an embodiment. 
         FIG.  10    is a graph of spatial state signal samples received from a user interface device and actuation pulses output to a haptic motor of the user interface device, in accordance with an embodiment. 
         FIG.  11    is a block diagram of a computer portion of a surgical robotic system, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe a surgical robotic system having a user console for controlling a surgical robotic system. The user console may, however, be used to control other systems, such as interventional cardiology systems, vision systems, or aircraft systems, to name only a few possible applications. 
     In various embodiments, description is made with reference to the figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions, and processes, in order to provide a thorough understanding of the embodiments. In other instances, well-known processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the description. Reference throughout this specification to “one embodiment,” “an embodiment,” or the like, means that a particular feature, structure, configuration, or characteristic described is included in at least one embodiment. Thus, the appearance of the phrase “one embodiment,” “an embodiment,” or the like, in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The use of relative terms throughout the description may denote a relative position or direction. For example, “left” may indicate a first direction away from a reference point, e.g., to the left of a seat. Similarly, “right” may indicate a location in a second direction opposite to the first direction, e.g., to the right of the seat. Such terms are provided to establish relative frames of reference, however, and are not intended to limit the use or orientation of a surgical robotic system to a specific configuration described in the various embodiments below. 
     In an aspect, a surgical robotic system includes a user console for controlling a surgical robotic tool. The surgical robotic system has one or more electromagnetic (EM) field distortion responses to reduce the likelihood that distortions occurring in an EM field of the user console will affect control signals transmitted to the surgical robotic tool. In an embodiment, the user console includes reference sensors paired with respective witness sensors to determine whether a distortion reflected in a witness EM reading from a witness sensor is an actual EM distortion or an artifact of a mechanical movement of the witness sensor. When the witness EM reading from the witness sensor is validated by the reference sensor as reflecting a real distortion, the user console can initiate several responses, including: alerting an operator about the distortion, providing guidance to the operator about how to correct the distortion, or pausing teleoperation of the surgical robotic tool. The distortion can be from a known, e.g., hypothesized, source, such as from actuation of a haptic motor of a user interface device used to control the surgical robotic tool. Accordingly, the user console can take actions to mitigate the effect of the known distortions such as, but not limited to: not actuating the haptic motor when surgical operations are being performed, ignoring control signals from the user interface device when the haptic motor is actuated, supplementing controls signals from the user interface device with control signals from other sensors that are unaffected by the distortion, or interlacing the control signals received from the user interface device with the actuation signals sent to the user interface device. These response signals and others described below may be used by the user console to reduce the likelihood that EM distortion will disrupt surgical tool control. 
     Referring to  FIG.  1   , this is a pictorial view of an example robotic system in an operating arena. A surgical robotic system  100  includes a user console  120 , a control tower  130 , and one or more surgical robotic arms  112  at a surgical robotic platform  111 , e.g., a table, a bed, etc. The system  100  can incorporate any number of devices, tools, or accessories used to perform surgery on a patient  102 . For example, the system  100  may include one or more surgical tools  104  used to perform surgery. A surgical tool  104  may be an end effector that is attached to a distal end of a surgical arm  112 , for executing a surgical procedure. 
     Each surgical tool  104  may be manipulated manually, robotically, or both, during the surgery. For example, surgical tool  104  may be a tool used to enter, view, or manipulate an internal anatomy of patient  102 . In an embodiment, surgical tool  104  is a grasper that can grasp tissue of patient  102 . Surgical tool  104  may be controlled manually, by a bedside operator  106 ; or it may be controlled robotically, via actuated movement of the surgical robotic arm  112  to which it is attached. Robotic arms  112  are shown as a table-mounted system, but in other configurations the arms  112  may be mounted in a cart, ceiling or sidewall, or in another suitable structural support. 
     Generally, a remote operator  107 , such as a surgeon or other operator, may use the user console  120  to remotely manipulate the arms  112  and/or surgical tools  104 , e.g., by teleoperation. The user console  120  may be located in the same operating room as the rest of the system  100 , as shown in  FIG.  1   . In other environments, however, the user console  120  may be located in an adjacent or nearby room, or it may be at a remote location, e.g., in a different building, city, or country. The user console  120  may comprise a seat  122 , foot-operated controls  124 , one or more handheld user interface devices, UIDs  126 , and at least one user display  128  that is configured to display, for example, a view of the surgical site inside patient  102 . In the example user console  120 , remote operator  107  is sitting in seat  122  and viewing the user display  128  while manipulating a foot-operated control  124  and a handheld UID  126  in order to remotely control the arms  112  and surgical tools  104  (that are mounted on the distal ends of the arms  112 ). Foot-operated control(s)  124  can be foot pedals, such as seven pedals, that generate motion control signals when actuated. User console  120  may include one or more additional interface devices ( FIG.  11   ) such as a keyboard or joystick, to receive manual inputs to control operations of user console  120  or surgical robotic system  100 . 
     In some variations, bedside operator  106  may also operate system  100  in an “over the bed” mode, in which bedside operator  106  (user) is now at a side of patient  102  and is simultaneously manipulating a robotically-driven tool (end effector attached to arm  112 ), e.g., with a handheld UID  126  held in one hand, and a manual laparoscopic tool. For example, the bedside operator&#39;s left hand may be manipulating the handheld UID  126  to control a robotic component, while the bedside operator&#39;s right hand may be manipulating a manual laparoscopic tool. Thus, in these variations, bedside operator  106  may perform both robotic-assisted minimally invasive surgery and manual laparoscopic surgery on patient  102 . 
     During an example procedure (surgery), patient  102  is prepped and draped in a sterile fashion to achieve anesthesia. Initial access to the surgical site may be performed manually while the arms of the robotic system  100  are in a stowed configuration, e.g., under platform  111 , or withdrawn configuration (to facilitate access to the surgical site). Once access is completed, initial positioning or preparation of the robotic system including its arms  112  may be performed. Next the surgery proceeds with the remote operator  107  at the user console  120  utilizing the foot-operated controls  124  and the UIDs  126  to manipulate the various end effectors and perhaps an imaging system, to perform the surgery. Manual assistance may also be provided at the procedure bed or table, by sterile-gowned bedside personnel, e.g., bedside operator  106 , who may perform tasks such as retracting tissues, performing manual repositioning, and tool exchange upon one or more of the robotic arms  112 . Non-sterile personnel may also be present to assist remote operator  107  at the user console  120 . When the procedure or surgery is completed, the system  100  and/or user console  120  may be configured or set in a state to facilitate post-operative procedures such as cleaning or sterilization, and healthcare record entry or printout via user console  120 . 
     In one embodiment, remote operator  107  holds and moves UID  126  to provide an input command to move a robot arm actuator  114  in robotic system  100 . UID  126  may be communicatively coupled to the rest of robotic system  100 , e.g., via a console computer system  110 . UID  126  can generate spatial state signals corresponding to movement of UID  126 , e.g., position and orientation of the handheld housing of the UID, and the spatial state signals may be input signals to control a motion of the robot arm actuator  114 . Robotic system  100  may use control signals derived from the spatial state signals to control proportional motion of actuator  114 . In one embodiment, a console processor of console computer system  110  receives the spatial state signals, also referred to herein as UID EM readings, from UID  126  and uses the UID EM readings to generate the corresponding control signals. Based on these control signals, which control how the actuator  114  is energized to move a segment or link of arm  112 , the movement of corresponding surgical tool  104  that is attached to the arm may mimic the movement of UID  126 . For example, console processor can pause motion of a corresponding actuator when UID  126  is within a range of a detected distortion in an EM field, as described below. Similarly, interaction between remote operator  107  and UID  126  can generate for example a grip control signal that causes a jaw of a grasper of surgical tool  104  to close and grip the tissue of patient  102 . 
     Surgical robotic system  100  may include several UIDs  126 , where respective control signals are generated for each UID that control the actuators and the surgical tool (end effector) of a respective arm  112 . For example, remote operator  107  may move a first UID  126  to control the motion of actuator  114  that is in a left robotic arm, where the actuator responds by moving linkages, gears, etc., in that arm  112 . Similarly, movement of a second UID  126  by remote operator  107  controls the motion of another actuator  114 , which in turn moves other linkages, gears, etc., of the robotic system  100 . Robotic system  100  may include a right arm  112  that is secured to the bed or table to the right side of the patient, and a left arm  112  that is at the left side of the patient. An actuator  114  may include one or more motors that are controlled so that they drive the rotation or linear movement of a joint of arm  112  to, for example, change relative to the patient an orientation of an endoscope or a grasper of the surgical tool that is attached to that arm. Motion of several actuators  114  in the same arm  112  can be controlled by the spatial state signals generated from a particular UID  126 . UIDs  126  can also control motion of respective surgical tool graspers. For example, each UID  126  can generate a respective grip signal to control motion of an actuator, e.g., a linear actuator, that opens or closes jaws of the grasper at a distal end of the surgical tool to grip tissue within patient  102 . 
     In some aspects, the communication between platform  111  and user console  120  may be through a control tower  130 , which may translate user commands that are received from user console  120  (and more particularly from console computer system  110 ) into robotic control commands that are transmitted to arms  112  on robotic platform  111 . The control tower  130  may also transmit status and feedback from platform  111  back to user console  120 . The communication connections between the robotic platform  111 , user console  120 , and control tower  130  may be via wired and/or wireless links, using any suitable ones of a variety of data communication protocols. Any wired connections may be optionally built into the floor and/or walls or ceiling of the operating room. Robotic system  100  may provide video output to one or more displays, including displays within the operating room as well as remote displays that are accessible via the Internet or other networks. The video output or feed may also be encrypted to ensure privacy and all or portions of the video output may be saved to a server or electronic healthcare record system. 
     Referring to  FIG.  2   , a side view of a user interface device is shown in accordance with an embodiment. Remote operator  107  may hold and move an ungrounded user interface device (UID)  126  to provide an input command to the console computer system  110 . In an embodiment, UID  126  includes a device body  204  extending in a longitudinal direction along a central axis  206 . For example, device body  204  may extend longitudinally from a proximal end  208  that is normally cupped within a hand of remote operator  107  during use. Device body  204  may extend to a distal end  210  having a forward-facing surface. UID  126  can be considered to be ungrounded because it is capable of being held and moved freely in space by a user. More particularly, UID  126  may not be connected to an external frame, link, or support, but rather motion of UID  126  may be constrained only by a range of motion of the user&#39;s arms. 
     UID  126  may be communicatively coupled to actuator  114 , e.g., via console computer system  110 . For example, UID  126  can generate spatial state signals corresponding to movement of the UID  126 , and the spatial state signals can be transmitted to console computer system  110  through an electrical cable  202 . The spatial state signals from the UID  126  can be used to control various elements of surgical robotic system  100 , depending on a mode of operation. More particularly, UID  126  may be used in a surgery mode or a non-surgery mode to control different system functions. 
     When UID  126  is used in the surgery mode, spatial state signals from UID  126  can control proportional motion of a corresponding actuator  114 . Actuator  114  may be coupled to a corresponding surgical tool  104 , e.g., via arm  112 , and thus, the corresponding surgical tool  104  may be moved by the corresponding actuator  114  based on the spatial state signals. Similarly, interaction between remote operator  107  and UID  126  can generate a grip signal to cause a jaw of a grasper of surgical tool  104  to close and grip the tissue of patient  102 . For example, when user squeezes UID  126  between two or more fingers, the jaw may mimic the motion of the fingers and squeeze the tissue. 
     When UID  126  is used in a non-surgery mode, UID  126  can control elements of user console  120 . For example, spatial state signals from UID  126  can control a graphical user interface displayed on console computer system  110 . More particularly, spatial state signals can control a cursor element on display  128  of console computer system  110 . Movement of UID  126  in the non-surgery mode may be characterized as coarse movement and movement of UID  126  in the surgery mode may be characterized as fine movement because a speed or magnitude of UID movement in the non-surgery mode may be greater than a speed or magnitude of UID movement in the surgery mode. 
     The surgical robotic system may include several UIDs  126 . Each UID  126  can generate a respective control signal. For example, remote operator  107  may move a first UID  126  to control a function of a first actuator  114  or a first GUI element of console computer system  110 . Similarly, movement of a second UID  126  (not shown) can control function of a second actuator  114  or another GUI element of console computer system  110 . Accordingly, the surgical robotic system can include one or more UIDs  126  having the structure described below. 
     Referring to  FIG.  3   , a sectional view of a user interface device, taken about line A-A of  FIG.  2   , is shown in accordance with an embodiment. Device body  204  can have an outer surface  302  extending around central axis  206 . Outer surface  302  of device body  204  may surround a cavity. The cavity within device body  204  can receive a tracking sensor  304  used to track movement of UID  126 . More particularly, tracking sensor  304  may be mounted within device body  204 . Tracking sensor  304  can be fixed to a device member  306 . Device member  306  can be attached to device body  204 . Thus, tracking sensor  304  may experience the same movement as device body  204 . 
     Tracking sensor  304  can be an EM sensor configured to generate spatial state signals that are UID EM readings of the EM field. For example, the UID EM sensor can generate a spatial state signal in response to movement of device body  204 . Tracking sensor  304  can detect a position and/or orientation of device body  204  when user moves UID  126 . For example, tracking sensor  304  may detect translation, rotation, or tilting of device body  204  within a workspace. In an embodiment, tracking sensor  304  generates the spatial state signal in response to movement of UID  126  within the EM field of the workspace. 
     UID  126  can include other sensors to detect movement of device body  204 . For example, UID  126  can include an inertial measurement unit (IMU)  308 . IMU  308  can be mounted on a printed circuit board  310  in or on device body  204  of UID  126 . IMU  308  may include an accelerometer and/or a gyroscope or other inertial sensors. IMU  308  may generate a second spatial state signal in response to movement of UID  126 . That is, IMU  308  may generate the second spatial state signal that corresponds to the same movement of UID  126  tracked by tracking sensor  304 . Accordingly, UID  126  may simultaneously generate the spatial state signal from tracking sensor  304  and the second spatial state signal from IMU  308  to control function(s) of the robotic system. 
     In an embodiment, UID  126  can include a haptic motor  312  capable of generating a haptic cue  314  when actuated. Haptic cue  314  can be a mechanical vibration to indicate to remote operator  107  that a haptic trigger event has occurred. Haptic cue  314  can be generated in response to energizing haptic motor  312 , which may include an electromechanical transducer such as a rotary motor, a linear motion motor, or other suitable vibrational or other tactile feedback motor. Haptic motor  312  may be controlled to provide haptic feedback to remote operator  107  in the form of tactile feedback. For example, a controller may actuate haptic motor  312  to drive a rotating eccentric mass and generate a vibration that communicates the occurrence of the haptic trigger event. Haptic cues  314  may be generated using other known haptic technologies. Different patterns, e.g., duty cycle, pattern of an irregular on-off cycle, speed, etc., may indicate different haptic trigger events to remote operator  107 . For example, a haptic trigger event may be when remote operator  107  has moved UID  126  in a direction to a predetermined limit of the workspace, e.g., to a boundary of the workspace. Haptic cue  314  may be emitted to alert remote operator  107  that UID  126  must be repositioned within the workspace to continue movement in the direction. Other examples of events triggering haptic feedback to remote operator  107  include actuation of an end effector, e.g., firing of a cauterization tool, loss of communication with UID  126 , e.g., due to power loss, misalignment of UID  126  relative to a calibrated or known reference frame, or detection of potential collision between components of the robotic system, e.g., between arms  112 . 
     UID  126  may include a feedback mechanism capable of generating other feedback cues. For example, UID  126  may include an electroacoustic transducer to generate an audio cue such as a tone, warning, etc. UID  126  may include an electro-optical transducer, e.g., a light emitting diode or a display, to generate a visual cue such as an error code or other visual information. The visual or audio cues can be considered to be a type of haptic cue  314 , and accordingly, the electroacoustic transducer and electro-optical transducer can be considered to be a type of haptic motor  312 . 
     Referring to  FIG.  4   , a perspective view of a user console is shown in accordance with an embodiment. User console  120  can include a base  402  to support seat  122  and display  128  of the surgical robotic system. Remote operator  107  may sit on seat  122  while viewing display  128  during a surgical procedure. User console  120  can include a tracking subsystem to monitor movement of UID  126 . For example, the tracking subsystem can be an optical tracking subsystem including components to monitor movement of UID  126  based on detection of a marker on UID  126 . The marker may be identifiable in an image to determine a position or orientation of UID  126 . The tracking subsystem may be an EM tracking subsystem having an EM source. The EM source can generate an EM tracking space  408 , and remote operator  107  can hold UID  126  within EM tracking space  408  to cause movement of surgical tool  104  during the surgical procedure. More particularly, EM tracking space  408  may be the workspace within which remote operator  107  may move UID  126  to generate the spatial state signal. 
     User console  120  may include a source of an EM field (not shown). The source can be an EM generator mounted on user console  120 . The EM generator may include a field generator to generate a position varying magnetic field that is used to establish a coordinate space. Accordingly, the EM generator can generate the EM field of the workspace within which UID  126  is manipulated. The EM field can be EM tracking space  408 . 
     Tracking sensor  304  can be a magnetic tracking probe capable of measuring six degrees of freedom within EM tracking space  408 . Tracking sensor  304  can be a sensor containing coils in which current is induced via the EM field. Tracking sensor  304  can have a known response to the EM field, and the response may be measured. By measuring the coil behavior, a position and orientation of tracking sensor  304 , and thus UID  126 , can be determined. The measured response may be output as the spatial state signal (UID EM readings) representing movement of UID  126  within EM tracking space  408 . 
     Distortion of the EM field can cause inaccuracies in the spatial state signal generated by UID  126 . For example, metals entering or passing near EM tracking space  408  can cause a distortion  401  in the EM field. When the EM field is distorted, the spatial state signal may be inaccurate and may not accurately control movement of surgical tool  104 . For example, when distortion  401  is collocated with UID  126  in the EM field, the spatial state signal may erroneously represent a movement of UID  126  and cause actuator  114  to move surgical tool  104  even when remote operator  107  has held UID  126  stationary. 
     The surgical robotic system can include one or more witness sensors  410  mounted on user console  120  at respective locations. The witness sensors  410  can be EM sensors, and can communicate respective witness EM readings to the console processor of user console  120 . As described below, the witness EM readings can reflect a distortion in the EM field, and thus, the console processor can process the witness EM readings to detect a distortion event within the EM field of EM tracking space  408 . 
     Each witness sensor  410  may be configured to generate a witness EM reading of an EM field within EM tracking space  408 . Witness sensor  410  can be an EM sensor in order to monitor the quality of the EM field. More particularly, the witness sensor(s)  410  can measure the EM field at known locations within or near EM tracking space  408 . The witness EM reading can be a sensor signal containing real-time variation of a sensed environmental quantity, e.g., the quality of the EM field. The sensed data stream can reflect events or occurrences within the EM field. For example, the witness EM readings can reflect distortion  401  of the EM field. Since the tracking sensor  304  relies on the quality and stability of the EM field, when the witness EM reading from witness sensor(s)  410  reflect the distortion event, the spatial state signal from tracking sensor  304  can be handled differently by the console processor so as to prevent inaccurate movement of surgical tool  104 . 
     Referring to  FIG.  5   , a pictorial view of an EM tracking space is shown in accordance with an embodiment. Witness sensors  410  may be vulnerable to false triggers. User console  120  can include a first witness sensor  502  mounted on user console  120  at a first location  504 , and a second witness sensor  506  mounted on user console  120  at a second location  508 . By way of example, first location  504  may be on a left armrest of seat  122 , and second location  508  may be on a right armrest of seat  122 . Second witness sensor  506  can generate a second witness EM reading of the EM field. The second witness EM reading can reflect a quality of the EM field around second witness sensor  506 . First witness sensor  502  and second witness sensor  506  are assumed to be static, and thus, a distance  510  between witness sensors  502 ,  506  is known and expected to be constant (as determined by the console processor, which is communicatively coupled to both witness sensors  502 ) when there is no distortion of the EM field. When the witness EM readings from witness sensor  502  and second witness sensor  506  reflect a change in distance  510  between the witness sensors, the console processor can determine that a distortion occurred in the EM field. Accordingly, detecting distortion  401  of the EM field by the console processor may include detecting the distance change between first location  504  and second location  508 . The detected distance change, however, may actually result from a mechanical movement of witness sensors  502 ,  506  relative to each other, rather than being caused by an EM field distortion. For example, the armrests can move if remote operator  107  shifts in seat  122 . The movement of the armrests may be inaccurately detected as the distortion  401 . 
     Mechanical vibrations of witness sensors  410  may be one source of unreliable witness EM readings. Aberrant witness EM readings can also be caused by localized temperature changes at the location where witness sensor  410  is mounted. More particularly, heating or cooling of first witness sensor  502  can trigger false reflections of a distortion in the witness EM reading when there is no actual distortion of the EM field. 
     To avoid false detections of EM field distortion, the surgical robotic system may include a reference sensor  420  mounted on user console  120  adjacent to each witness sensor  410 . Each reference sensor  420  may generate a deformation reading in response to a non-EM event occurring at the location where the adjacent witness sensor  410  is mounted. Accordingly, as used herein, the term “adjacent” can refer to any distance at which reference sensor  420  can detect the non-EM event occurring at the mounting location of witness sensor  410 . For example, a first reference sensor  512  may be mounted on the left armrest adjacent to first witness sensor  502 , and a second reference sensor  514  may be mounted on the right armrest adjacent to second witness sensor  506 . A first reference sensor  512  can be mounted on the left armrest to detect a deformation or movement of user console  120  at the location where the adjacent first witness sensor  502  is mounted, e.g., when remote operator  107  shifts in seat  122 . Alternatively, first reference sensor  502  may be mounted on seat  122  below the left armrest and detect a temperature change at the location where the adjacent first witness sensor  502  is mounted. Accordingly, data from first witness sensor  502  and first reference sensor  512  may be fused to determine whether a distortion reflected in a witness EM reading from the witness sensor is real, or whether the reflected distortion results from the non-EM event, e.g., a mechanical deformation or a temperature change of user console  120 . The deformation reading from first reference sensor  512  can therefore validate the witness EM reading from first witness sensor  502 . 
     Reference sensors  420  may include a non-EM sensor for detecting mechanical movement. For example, first reference sensor  512  may include an IMU to generate a time-varying signal containing data reflecting mechanical deformation of the mounting location. More particularly, detecting the deformation may include measuring a movement of the IMU adjacent to the mounting location. Reference sensors  420  may include a non-EM sensor for detecting temperature. For example, first reference sensor  512  may include a temperature sensor to measure a temperature change at first location  504  when the heating or cooling is applied. More particularly, detecting the temperature change can include measuring a temperature change adjacent to the mounting location. Reference sensor  420  may include other non-EM sensors for measuring non-EM events within or near the EM field. Data from the non-EM sensors can be used to validate data from EM witness sensors  410 . 
     In an embodiment, one or more references sensors  420  are mounted on UID  126 . For example, reference sensor  420  can be contained within device body  204  as one of the other sensors described above. IMU  308  may be reference sensor  420 , and may be mounted on and/or inside of UID  126  adjacent to tracking sensor  304  such that movement of device body  302  in free space causes corresponding movements of the UID EM sensor  304  and reference sensor  420 . 
     User console  120  may include witness sensors  410  and reference sensors  420  around a boundary of EM tracking space  408 . For example, a third witness sensor  516  and a third reference sensor  518  may be collocated on base  402  near a left foot rest. Similarly, a fourth witness sensor  520  and a fourth reference sensor  522  may be co-located on base  402  near a right foot rest. Each pair of sensors may monitor a respective region of EM tracking space  408 . More particularly, when the fused data from witness sensor  410  and reference sensor  420  of a pair indicates that a true distortion of the EM field has occurred, the distortion may be within a range  524  of the location where the witness sensor  410  is mounted. Range  524  of each pair of sensors, may be predetermined. For example, sensor pairs located at the corners of a lower plane of a cube-shaped volume of interest may have a spherical range  524  with a predetermined radius  526 . As described below, console computer system  110  may identify a location of the distortion relative to user console  120 , and appropriately handle spatial state signals received from UID  126  within a range of the location. For example, when a metal object passes near first witness sensor  502 , distortion  401  may occur within range  524  of first witness sensor  502 , and spatial state signals generated by UID  126  located within the range  524  may be ignored until the distortion is eliminated. 
     Referring to  FIGS.  6 A- 6 C , a pictorial view of a witness sensor  410  and a reference sensor  420  mounted on a user console  120  is shown in accordance with an embodiment. The illustrated examples are described using first witness sensor  502 , first reference sensor  512 , second witness sensor  506 , and second reference sensor  514 , mounted on user console  120  at distance  510  from each other. It will be appreciated, however, that the description applies similarly to any grouping of sensor pairs. Furthermore, although reference sensors in each of  FIGS.  6 A- 6 C  detect motion, e.g., the reference sensors are IMUs, the description applies similarly to reference sensors that measure other non-EM events, e.g., temperature changes. 
     In  FIG.  6 A , a static scenario is illustrated in which distance  510  between first witness sensor  502  and second witness sensor  506 , as reflected in the witness EM readings from the witness sensors, is constant. Similarly, neither of the deformation readings from first reference sensor  512  nor second reference sensor  514  reflect motion. That is, first location  504  on user console  120  and second location  508  on user console  120  are stable and fixed relative to each other. In the static scenario, the witness sensors  410  may not generate a witness EM reading  602  indicating a distortion of the EM field. Similarly, motion data from the reference sensors may indicate that there is no motion between first location  504  and second location  508 , or that any motion between the locations is less than a predetermined deformation threshold. 
     In  FIG.  6 B , a static scenario is illustrated in which a distortion  401  occurs within the EM field. When distortion  401  occurs, e.g., when a metallic object passes near first witness sensor  502 , a relative distance  510  between first witness sensor  502  and second witness sensor  506  as detected by user console  120  may change. First witness sensor  502  may generate a witness EM reading  602  indicating an existence of distortion  401 . By contrast, user console  120  may be stable and first reference sensor  512  may remain stationary when the distortion occurs. Accordingly, relative readings of first witness sensor  502  and first reference sensor  512  may differ. Sensor readings that do not “match,” e.g., contain data representing a distance change and a deformation that coincide in time, can indicate that the witness EM reading  602  indicating the distortion is accurate. 
     In  FIG.  6 C , a dynamic scenario is illustrated in which no distortion occurs within the EM field. The scenario may be dynamic because the location where first witness sensor  502  and second witness sensor  506  are mounted may move. For example, remote operator  107  may shift in seat  122  and cause the armrest to jostle. When the armrest moves, a relative distance  510  between first witness sensor  502  and second witness sensor  506  as detected by user console  120  may change. First witness sensor  502  may generate witness EM reading  602  indicating the existence of a distortion (that does not actually exist). Similarly, the deformation readings from first reference sensor  512  may reflect movement of armrest (or a change in another non-EM property at the location) and generate a deformation reading  604  representing the movement. Accordingly, relative readings of first witness sensor  502  and first reference sensor  512  may be the same. Sensor readings that “match,” e.g., contain data representing a distance change and a deformation that coincide in time, can indicate that the distortion is falsely represented by first witness sensor  502 , and witness EM reading  602  actually representing a system vibration, a mechanical movement, or another non-EM effect at the mounting location of first witness sensor  502 . 
     Based on witness EM reading  602  and deformation reading  604 , user console  120  can notify remote operator  107  of a potential distortion in the EM field. Furthermore, user console  120  can determine a likely location of the distortion, and notify remote operator  107  of the location. Additionally, given that a position of UID  126  relative to witness sensors  410  is known by the EM tracking system, user console  120  can determine when the detected distortion will affect the system. More particularly, user console  120  can notify remote operator  107  when UID  126  is near a witness sensor  410  measuring the distortion and/or pause teleoperation of surgical tool  104  by UID  126  when UID  126  comes within a predetermined proximity of the detected distortion. Accordingly, as described further below, user console  120  can provide a warning to remote operator  107  before the distortion affects performance of the system, and in some cases, may provide guidance to remote operator  107  to remove a cause of the distortion. 
     Referring to  FIG.  7   , a flowchart of a method of detecting and responding to a distortion in an EM tracking field in a surgical robotic system is shown in accordance with an embodiment. The surgical robotic system can include a processor in communication with witness sensor  410  and reference sensor  420  of user console  120 . For example, the processor may be a console processor ( FIG.  11   ) contained in console computer system  110 . The processor may be configured to respond, e.g., generate a distortion response signal, in response to a detected distortion. The processor can detect the distortion based on witness EM reading  602  and deformation reading  604 . The response may include notifying remote operator  107  or otherwise altering control of the surgical robotic system when the distortion occurs within the EM field. The processor can execute instructions contained in a non-transitory computer-readable medium to cause the surgical robotic system to perform the method described below. 
     At operation  702 , the processor receives UID EM readings of the EM tracking field. UID  126  generates the spatial state signals that are received by the processor. The spatial state signals provide the UID EM readings of the EM field. Accordingly, the console processor of user console  120 , which is communicatively coupled to UID  126 , can track one or more of position, orientation, or movement of UID  126  based on the UID EM readings. 
     At operation  704 , the processor receives witness EM reading  602  of the EM tracking field from witness sensor  410 . A stationary witness sensor  410 , e.g., mounted on user console  120 , generates witness EM reading  602  of the EM field. Witness EM reading  602  can reflect a distortion of the EM field. Accordingly, the console processor of user console  120 , which is communicatively coupled to witness sensor  410 , can detect distortion  401  within EM tracking space  408  of user console  120  based on witness EM reading  602 . 
     At operation  706 , the processor receives deformation readings  604  from reference sensor  420 , e.g., mounted adjacent to witness sensor  410  on user console  120 . Reference sensor  420  generates deformation readings  604  in response to a non-EM property or event at the mounting location. For example, deformation readings  604  may reflect a deformation of user console  120  at the location. Accordingly, the console processor of user console  120 , which is communicatively coupled to reference sensor  420 , can detect the deformation of user console  120 . 
     At operation  708 , the processor detects the distortion of the EM field based on one or more of the UID EM readings, the witness EM readings  602 , or the deformation readings  604 . 
     In an embodiment, the processor is communicatively coupled to witness sensor  410  and reference sensor  420 , and the processor is configured to detect the distortion of the EM field based on both the witness EM readings  602  and the deformation readings  604 . For example, the processor can generate the distortion response signal when, as shown in  FIG.  6 B , witness EM reading  602  and deformation reading  604  do not match. The processor may be configured to generate the distortion response signal when witness EM reading  602  from witness sensor  410  reflecting the presence of a distortion and deformation reading  604  indicates that there is disproportionately less deformation at the mounting location than witness EM reading  602  would otherwise indicate. More particularly, deformation reading  604  may indicate some movement at the location, such as movement corresponding to ambient noise or vibration. The deformation, however, may be less than a predetermined deformation threshold. Thus, deformation reading  604  may indicate movement by reference sensor  420  that is less than the detected relative movement between first witness sensor  502  and second witness sensor  506  resulting from the distortion. Deformation reading  604  can validate witness EM reading  602  to trigger the distortion response signal. More particularly, the processor can detect the distortion when witness EM readings  602  reflect the distortion in the EM field and deformation readings  604  reflect that the deformation is less than the predetermined deformation threshold. 
     At operation  710 , the processor responds to the detected distortion. For example, the processor can generate a distortion response signal based on the received witness EM reading  602  and deformation reading  604 . 
     Generation of the distortion response signal in response to the detected distortion can include adjusting one or more of a tracked position, orientation, or movement of UID  126  based on the detected distortion. For example, as described above, UID EM sensors  304  can generate UID EM readings that are used by the console processor to track one or more a position, an orientation, or a movement of UID  126 . The console processor can be configured to adjust the tracking data reflecting the position, orientation, or movement of UID  126  based on witness EM readings  602  that measure or describe the distortion. Several examples of such adjustments are described immediately. 
     Adjustment of the one or more tracked position, orientation, or movement of UID  126  can be based on whether the detected distortion is below a distortion threshold. When the detected distortion is less than a certain amount of distortion, it may be assumed that the distortion will not have a significantly negative effect on the operation being performed. For example, a minor distortion may cause a cursor to skip slightly when the current operation is controlling a cursor on a display. Such skipping may be inconsequential to the procedure, and thus, not adjusting the one or more tracked position, orientation, or movement of UID  126  based on the detected distortion can conserve computing resources without negatively impacting the surgical procedure. Accordingly, the distortion may be ignored when the distortion value is below a distortion threshold. 
     Adjustment of the one or more tracked position, orientation, or movement of UID  126  can be based on whether UID  126  is within a range of the detected distortion. The processor can determine the location based on the predetermined range  524  of witness sensor  410 . For example, when distortion  401  is detected based on a witness EM reading from first witness sensor  502 , the processor can determine that the distortion  401  is within the predetermined range  524 . The processor can also determine a location of UID  126  based on the UID EM readings, and thus, the processor can determine whether UID  126  is within the range of the detected distortion. In an embodiment, when UID  126  is within the range of the detected distortion and the deformation is less than the predetermined deformation threshold, the processor can adjust the one or more tracked position, orientation, or movement of UID  126 . 
     In an embodiment, adjusting the one or more tracked position, orientation, or movement of UID  126  includes skipping the one or more tracked position, orientation, or movement of UID  126 . For example, the console processor can skip the tracking of UID  126 , e.g., ignore the UID EM readings while UID  126  is within the range of the distortion. By skipping the tracking, teleoperation of a corresponding actuator  114  may be paused regardless of the spatial state signal received from tracking sensor  304 . 
     As described above, the console processor can use deformation readings from the reference sensor  420  to validate witness EM readings from the witness sensor  410 . The validated readings can cause a distortion to be detected. In an embodiment, however, the console processor can ignore the distortion. For example, the console processor may ignore the distortion in response to the deformation being more than a predetermined threshold. More particularly, when the deformation is too large, it can be determined that the distortion reading is faulty, and thus, the console processor may responsively not make adjustments based on the distortion. 
     Generation of the distortion response signal in response to the detected distortion can include generating a notification of the detected distortion. For example, user console  120  can include an alert mechanism in communication with the processor, and the processor can generate the notification to cause the alert mechanism to indicate one or more of an existence of the distortion, a location of the distortion, or a cause of the distortion. For example, the alert mechanism may be display  128  of user console  120 . Display  128  can present the notification or warning to remote operator  107 . Alternatively, the alert mechanism may be a speaker used to emit a sound notifying remote operator  107  of the distortion. The alert mechanism may be configured to generate an alert in response to receiving the distortion response signal from the processor. 
     In an embodiment, the alert generated in response to the distortion response signal is a warning to remote operator  107 . The warning may be a visual warning, an audible indicator, a haptic cue, etc. The alert may indicate to remote operator  107  that distortion  401  exists within the EM field. Remote operator  107  may pause movement of UID  126  until the warning ends. The surgical robotic system may automatically pause teleoperation of surgical tool  104  in response to the warning. For example, spatial state signals from UID  126  may be disregarded by console computer system  110 , or control signals based on spatial state signals withheld, to prevent movement of surgical tool  104  until the warning ceases. 
     In an embodiment, the alert provides an indication of the location where the distortion is detected. The processor can determine the location based on the predetermined range  524  of witness sensor  410 . For example, when distortion  401  is detected based on a witness EM reading from first witness sensor  502 , the processor can notify remote operator  107  that the distortion is likely near the left armrest. 
     In addition to determining the likely location of the distortion, the processor may monitor a position of UID  126  to determine whether UID  126  is within range  524  of the location. The processor may receive the spatial state signal from tracking sensor  304  to determine a position of UID  126  within EM tracking space  408 . When UID  126  is within a range  524  of the mounting location of witness sensor  410  that measures the distortion, the distortion response signal may be generated. The distortion response signal can pause motion of surgical tool  104  based on whether UID  126  is close enough to the distortion. If UID  126  is near witness sensor  410  measuring the distortion, this may indicate an error in the spatial state signal. Accordingly, when the system detects UID  126  is within the range  524  of the location, motion of a corresponding actuator  114  may be paused by the distortion response signal regardless of the spatial state signal received from tracking sensor  304 . By contrast, the system may notify remote operator  107  of the presence of the distortion, but may take no action to pause the surgery when UID  126  is not within range of the location. That is, the distortion response signal may not pause teleoperation when UID  126  is outside of range  524  of witness sensor  410  that measures the distortion. 
     In an embodiment, the distortion response signal can trigger the alert to provide an indication of a cause of the distortion. The alert can provide guidance as to where the distortion is coming from. For example, the alert may be a visual notification that a cause of the distortion is a metal cart passing near the left armrest of user console  120 . The processor can determine possible causes of the distortion using reference distortion values, such as quality readings or relative errors. The processor can perform machine learning to identify the likely cause based on the reference distortion values. When the processor identifies a likely cause, the distortion response signal can trigger an alert to suggest to remote operator  107  what may be causing the distortion. Furthermore, the alert can provide guidance or suggestions to reduce the effect. For example, the alert may instruct remote operator  107  to move metal cart  526  outside of range  524  of witness sensor  410  that measures the distortion. Teleoperation of surgical tool  104  may be disengaged while the guidance is provided to remote operator  107 . When the cause of the distortion is removed, remote operator  107  may continue teleoperation of surgical tool  104  to perform the surgery. 
     An EM tracking system is susceptible to magnetic distortion from external objects, such as metal carts, and from sources within the EM tracking space  408 . For example, a motor of UID  126 , e.g., haptic motor  312 , can distort the EM field and degrade the tracking accuracy of the EM tracking system. Actuation of the motor may be the cause of distortion, and thus, the surgical robotic system may include features to minimize the effects of the EM distortion from the known source. 
     In an embodiment, a structure of UID  126  may reduce the EM distortion caused by actuation of the electronics or the motor within UID  126 . For example, the electronics or the motor may be spaced apart from tracking sensor  304  by a distance sufficient to reduce the distortion to a sufficient level. Similarly, the distortion may be reduced to a sufficient level by reducing metallic or non-shielded electronics in UID  126 . For example, parts of UID  126  may be fabricated from plastic, silicone, or another non-metallic material. In an embodiment, the electronics or the motor of UID  126  may be shielded to prevent distortion of the EM field. For example, a Faraday cage or another EM shielding structure may be mounted within UID  126  to surround haptic motor  312  and to contain the EM field of haptic motor  312  such that the field does not disrupt operation of tracking sensor  304 . The shielding itself may cause distortion, however, a constant consistent distortion may be acceptable for operation of tracking sensor  304 . That is, tracking sensor  304  may be monitored to determine relative motion, and not absolute position, and thus, a constant offset of tracking sensor  304  within EM tracking space  408  may not affect performance of surgical tool  104 . 
     In addition to mitigating distortion from the electronics or the motor of UID  126  using structural features, the surgical robotic system may control a manner of sampling data from UID  126  and/or actuating haptic motor  312  of UID  126  to reduce the likelihood that the distortion from haptic motor  312  will affect the spatial state signal. The surgical robotic system can include the processor in communication with tracking sensor  304  and haptic motor  312  of UID  126 . For example, the processor may be a console processor ( FIG.  11   ) contained in console computer system  110 . The processor may be configured to sample spatial state signal from tracking sensor  304 . The processor may also be configured to control actuation of haptic motor  312 , e.g., by generating and applying several actuation pulses to haptic motor  312 . The processor can execute instructions contained in a non-transitory computer-readable medium to cause the surgical robotic system to perform the methods described below to reduce the likelihood that sampled data is disrupted by distortions caused by the motor actuation. 
     Referring to  FIG.  8   , a flowchart of a method of monitoring spatial state signals from a user interface device and outputting actuation pulses to a haptic motor of the user interface device is shown in accordance with an embodiment. At operation  802 , the processor samples the spatial state signal from tracking sensor  304  of UID  126 . Tracking sensor  304  can generate the spatial state signal in response to movement of UID  126  within the EM field of EM tracking space  408 , as described above. At operation  804 , the processor can determine whether UID  126  is being used in the surgery mode or the non-surgery mode. As described above, UID  126  is used in the surgery mode to control proportional motion of a corresponding actuator  114 . UID  126  may be in the non-surgery mode when, for example, remote operator  107  is using UID  126  to control a graphical user interface element on display  128  of user console  120 . At operation  806 , based on whether UID  126  is being used in the surgery mode or the non-surgery mode, the processor can actuate haptic motor  312  in a particular manner. More particularly, the processor can control actuation of haptic motor  312  during a time interval in a manner to reduce the likelihood that the actuation will disrupt spatial state signal samples. At operation  808 , the processor selects a portion of the spatial state signal samples obtained during the time interval based on whether the user interface device is being used in the surgery mode or the non-surgery mode. More particularly, the processor can select the portion of the spatial state signal samples that are unaffected by the actuation of haptic motor  312 , or that are affected but will not disrupt control of surgical tool  104 . 
     The method illustrated in  FIG.  8    can be adapted to include several operations that respectively reduce the likelihood that sampled data is disrupted by distortions from the motor actuation. In an embodiment, the processor can trigger haptic cues  314  based on whether remote operator  107  is using UID  126  to control coarse movement or fine movement of a controlled element. Coarse movement may correspond to the non-surgery mode and fine movement may correspond to the surgery mode. 
     The processor may determine that UID  126  is being used in the non-surgery mode based on a velocity of UID  126 . The processor can use spatial state signal samples from tracking sensor  304  to determine the velocity. The processor may determine that UID  126  is being used in the non-surgery mode when the velocity is greater than a predetermined velocity threshold. By contrast, the processor may determine that UID  126  is being used in the surgery mode when the velocity is less than the predetermined velocity threshold. 
     The predetermined velocity threshold may be selected to correspond to a speed at which remote operator  107  moves UID  126  during surgical operations. For example, velocities lower than the predetermined velocity threshold may be consistent with the fine movements made by remote operator  107  when grasping tissue of patient  102 . By contrast, velocities higher than the predetermined velocity threshold may be consistent with the coarse movements made by remote operator  107  when using UID  126  to move a cursor on display  128 . 
     The processor may disallow or withhold haptic cues  314  in response to the haptic trigger event when UID  126  is used in the surgery mode. The haptic trigger event can occur during the time interval when the processor gathers spatial state signal samples from tracking sensor  304 . Accordingly, the processor may not actuate haptic motor  312  during the time interval when the processor determines that UID  126  is being used in the surgery mode. 
     The processor may allow or cause haptic cues  314  in response to a haptic trigger event when UID  126  is used in the non-surgery mode. The haptic trigger event can occur during the time interval when the processor gathers spatial state signal samples from tracking sensor  304 . Accuracy of spatial state signals may be less important when controlling a cursor element as compared to controlling surgical tool  104 , and thus, any error introduced into spatial state signals by haptic motor  312  during the non-surgery mode may be acceptable. Accordingly, the processor may actuate haptic motor  312  during the time interval when the processor determines that UID  126  is being used in the non-surgery mode. 
     Referring to  FIG.  9   , a graph of spatial state signal samples received from a user interface device and actuation pulses output to a haptic motor of the user interface device is shown in accordance with an embodiment. The processor may select spatial state signal samples  902  that are known to be undisrupted by actuation of haptic motor  312 . Similarly, the processor may not select spatial state signal samples  902  that may be disrupted by actuation of haptic motor  312 . To avoid using spatial state signal samples  902  that are distorted by haptic motor  312 , the processor may ignore EM tracker readings while haptic motor  312  is actuated by actuation pulses  906 . 
     As shown in the graph, spatial state signal samples  902  are selected outside of time interval  904  when haptic motor  312  is not being actuated. That is, the selected portion of the spatial state signal from tracking sensor  304  may be none of the spatial state signal samples  902  during the time interval  904 . The processor may disregard the spatial state signal samples  902  when UID  126  is being used in the surgery mode. By ignoring one or more of the spatial state signal samples  902  obtained during the time interval  904 , surgical tool  104  is controlled by samples obtained when there can be no disruption of the EM field by actuation pulses  906  that are generated and transmitted to haptic motor  312  by the processor. 
     In an embodiment, the ignored spatial state signal samples  902  from tracking sensor  304  may be supplemented by another sensor of UID  126 . For example, the processor may sample a second spatial state signal from IMU  308  of UID  126 . Second spatial state signal samples  908  can represent motion of UID  126  irrespective of the EM tracking space  408 . For example, the second spatial state signal may include data representing a change in position or orientation of UID  126  without regard to a position of UID  126  within the coordinate space. The processor can select a portion of the second spatial state signal samples  908  during the time interval  904  to control proportional motion of a corresponding actuator  114 . The processor may select the portion based on whether UID  126  is being used in the surgery mode or the non-surgery mode. For example, the processor can ignore spatial state signal samples  902  during time interval  904  and select second spatial state signal samples  908  during time interval  904  when UID  126  is being used in the surgery mode. 
     The processor may employ an algorithm to weight spatial state signal samples  902  and second spatial state signal samples  908  for use in controlling proportional motion of a corresponding actuator  114 . Rather than entirely ignoring samples of the spatial state signal from tracking sensor  304 , the processor can fuse the data from tracking sensor  304  with the data received from IMU  308  of UID  126 . That is, the processor can select samples from both the spatial state signal and the second spatial state signal during the time interval  904 . The fusion of data can occur when UID  126  is being used in the surgery mode. Combining tracking data can provide reliable tracking of UID  126  within the EM tracking space  408  when haptic motor  312  is actuated. 
     The weighting of the data may give more importance to some data over other data. More particularly, the processor may assign respective levels of confidence to the spatial state signal samples  902  and the second spatial state signal samples  908  during the time interval  904 . For example, the level of confidence assigned to the second spatial state signal samples  908  may be higher than the level of confidence assigned to the spatial state signal samples  902  when haptic motor  312  is actuated. The level of confidence afforded to second spatial state signal samples  908  can be higher because actuation of haptic motor  312  may affect the sensor readings of IMU  308  less than the sensor readings of tracking sensor  304 . The weighting of data from each sensor can allow both spatial state signals to be used, i.e., can allow some use of EM tracking signals during actuation of haptic motor  312 . 
     Referring to  FIG.  10   , a graph of spatial state signal samples received from a user interface device and actuation pulses output to a haptic motor of the user interface device is shown in accordance with an embodiment. Rather than ignore or devalue the spatial state signal samples  902  received during the time interval  904 , the processor may coordinate the timing of sampling and actuation to reduce the likelihood that actuation pulses  906  will disrupt spatial state signal samples  902 . In an embodiment, the processor generates and transmits actuation pulses  906  to UID  126  between sampling of spatial state signal samples  902 . More particularly, the processor can sample EM tracking data at a same frequency at which haptic motor  312  is actuated. The spatial state signal may be sampled at a sampling frequency, which may be known and constant during operation of the EM tracker. The processor can generate actuation pulses  906  at an actuation frequency. The actuation frequency can be a driving frequency of haptic motor  312 . That is, the actuation frequency can be a frequency at which actuation pulses  906  are delivered to haptic motor  312  to generate haptic cues  314 . The actuation frequency can be equal to the sampling frequency. The actuation pulses  906  can be interjected between samples gathered from tracking sensor  304 . For example, the processor may apply a phase shift between the actuation signal and the sample time. Each actuation pulse  906  may begin after a preceding spatial state signal sample  902 , and may end before a next spatial state signal sample  902 . Thus, the actuation pulses  906  can be interlaced with the spatial state signal samples  902 . 
     Referring to  FIG.  11   , a block diagram of a computer portion of a surgical robotic system is shown in accordance with an embodiment. The exemplary surgical robotic system  100  may include a user console  120 , a surgical robot  1102 , and a control tower  130 . The surgical robotic system  100  may include other additional hardware components; thus, the diagram is provided by way of example and not limitation to the system architecture. 
     As described above, the user console  120  comprises console computers  110  and one or more UIDs  126 . User console  120  can include console actuators  1104 , displays  128 , a UID tracker  1106 , foot pedals  124 , and a network interface  1108 . A user or surgeon sitting at the user console  120  can adjust ergonomic settings of the user console  120  manually, or the settings can be automatically adjusted according to the user profile or preference. The manual and automatic adjustments may be achieved through driving the console actuators  1104  based on user input or stored configurations by the console computers  110 . The user may perform robot-assisted surgeries by controlling the surgical robot  1102  using two master UIDs  126  and foot pedals  124 . Positions and orientations of the UIDs  126  are continuously tracked by the UID tracker  1106 , and status changes are recorded by the console computers  110  as user input and dispatched to the control tower  130  via the network interface  1108 . Real-time surgical video of patient anatomy, instrumentation, and relevant software apps can be presented to the user on the high resolution 3-D displays  128  including open or immersive displays. 
     Unlike other existing surgical robotic systems, the user console  120  disclosed herein may be communicatively coupled to the control tower  130  over a single fiber optic cable. The user console also provides additional features for improved ergonomics. For example, both an open and immersive display are offered compared to only an immersive display. Furthermore, a highly-adjustable adjustable seat for surgeons and master UIDs tracked through EM or optical trackers are included at the user console  120  for improved ergonomics. To improve safety, eye tracking, head tracking, and/or seat swivel tracking can be implemented to prevent accidental tool motion, for example, by pausing or locking teleoperation when the user&#39;s gaze is not engaged in the surgical site on the open display for over a predetermined period of time. 
     The control tower  130  can be a mobile point-of-care cart housing touchscreen displays, computers that control the surgeon&#39;s robotically-assisted manipulation of instruments, safety systems, graphical user interface (GUI), light source, and video and graphics computers. As shown in  FIG.  11   , the control tower  130  may comprise central computers  1110  including at least a visualization computer, a control computer, and an auxiliary computer, various displays  1112  including a team display and a nurse display, and a network interface  1114  coupling the control tower  130  to both the user console  120  and the surgical robot  1102 . The control tower  130  may also house third-party devices, such as an advanced light engine  1116 , an electrosurgical generator unit (ESU)  1118 , and insufflator and CO2 tanks  1120 . The control tower  130  may offer additional features for user convenience, such as the nurse display touchscreen, soft power and E-hold buttons, user-facing USB for video and still images, and electronic caster control interface. The auxiliary computer may also run a real-time Linux, providing logging/monitoring and interacting with cloud-based web services. 
     The surgical robot  1102  comprises an articulated operating table  111  with a plurality of integrated arms  112  that can be positioned over the target patient anatomy. A suite of compatible tools  104  can be attached to or detached from the distal ends of the arms  112 , enabling the surgeon to perform various surgical procedures. The surgical robot  1102  may also comprise control interface  1122  for manual control of the arms  112 , table  111 , and tools  104 . The control interface can include items such as, but not limited to, remote controls, buttons, panels, and touchscreens. Other accessories such as trocars (sleeves, seal cartridge, and obturators) and drapes may also be needed to perform procedures with the system. In some variations the plurality of arms  112  include forearms mounted on both sides of the operating table  111 , with two arms on each side. For certain surgical procedures, an arm mounted on one side of the table can be positioned on the other side of the table by stretching out and crossing over under the table and arms mounted on the other side, resulting in a total of three arms positioned on the same side of the table  111 . The surgical tool can also comprise table computers  1124  and a network interface  1126 , which can place the surgical robot  1102  in communication with the control tower  130 . 
     The following statements of invention are supported by the above description. In an embodiment, a user console includes a user interface device incorporating a tracking sensor and a haptic motor. The tracking sensor generates a spatial state signal in response to movement of the user interface device within an EM field of an EM tracking space. The haptic motor is capable of generating a haptic cue when actuated. The user interface device is used in a surgery mode and a non-surgery mode, and the spatial state signal is used in the surgery mode to control proportional motion of a corresponding actuator. A processor is configured to sample the spatial state signal from the tracking sensor. The processor is configured to determine whether the user interface device is being used in the surgery mode or the non-surgery mode. The processor is configured to control actuation of the haptic motor during a time interval based on whether the user interface device is being used in the surgery mode or the non-surgery mode. The processor is configured to select a portion of the spatial state signal samples during the time interval based on whether the user interface device is being used in the surgery mode or the non-surgery mode. In one embodiment, the processor is configured to determine a velocity of the user interface device based on the spatial state signal samples. The processor is configured to determine that the user interface device is being used in the non-surgery mode when the velocity is greater than a predetermined velocity threshold. The processor is configured to determine that the user interface device is being used in the surgery mode when the velocity is less than the predetermined velocity threshold. In one embodiment, the processor is configured to not actuate the haptic motor in response to a haptic trigger event during the time interval when the processor determines that the user interface device is being used in the surgery mode. The processor is configured to actuate the haptic motor in response to the haptic trigger event during the time interval when the processor determines that the user interface device is being used in the non-surgery mode. In one embodiment, the selected portion is none of the spatial state signal samples during the time interval when the processor determines that the user interface device is being used in the surgery mode. In one embodiment, the user interface device further includes an inertial measurement unit to generate a second spatial state signal in response to movement of the user interface device. The processor is configured to sample the second spatial state signal from the inertial measurement unit. The processor is configured to select a portion of the second spatial state signal samples during the time interval based on whether the user interface device is being used in the surgery mode or the non-surgery mode. In one embodiment, the processor selects samples from both the second spatial state signal and the spatial state signal during the time interval when the user interface device is being used in the surgery mode. In one embodiment, the processor is configured to assign respective levels of confidence to the spatial state signal samples and the second spatial state signal samples. The level of confidence assigned to the second spatial state signal samples is higher than the level of confidence assigned to the spatial state signal samples during the time interval. In one embodiment, the processor controls actuation of the haptic motor by generating a plurality of actuation pulses. In one embodiment, the processor is configured to generate the plurality of actuation pulses between sampling spatial state signal samples. In one embodiment, the processor is configured to generate the plurality of actuation pulses at an actuation frequency. The processor is configured to sample the spatial state signal at a sampling frequency equal to the actuation frequency. The plurality of actuation pulses are interlaced with the spatial state signal samples. 
     In an embodiment, a method includes sampling, by a processor, a spatial state signal from a tracking sensor of a user interface device. The tracking sensor generates the spatial state signal in response to movement of the user interface device within an EM field of an EM tracking space. The method includes determining, by the processor, whether the user interface device is being used in a surgery mode or a non-surgery mode. The user interface device is used in the surgery mode to control proportional motion of a corresponding actuator. The method includes controlling, by the processor, actuation of a haptic motor within the user interface device during a time interval based on whether the user interface device is being used in the surgery mode or the non-surgery mode. The method includes selecting, by the processor, a portion of the spatial state signal samples during the time interval based on whether the user interface device is being used in the surgery mode or the non-surgery mode. 
     In an embodiment, a non-transitory computer-readable medium including instructions, which when executed by a processor of a user console, cause the user console to perform a method including sampling, by a processor, a spatial state signal from a tracking sensor of a user interface device. The tracking sensor generates the spatial state signal in response to movement of the user interface device within an EM field of an EM tracking space. The method includes determining, by the processor, whether the user interface device is being used in a surgery mode or a non-surgery mode. The user interface device is used in the surgery mode to control proportional motion of a corresponding actuator. The method includes controlling, by the processor, actuation of a haptic motor within the user interface device during a time interval based on whether the user interface device is being used in the surgery mode or the non-surgery mode. The method includes selecting, by the processor, a portion of the spatial state signal samples during the time interval based on whether the user interface device is being used in the surgery mode or the non-surgery mode. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.