Uniform scaling of haptic actuators

Abstract

The present application relates to uniform scaling of haptic actuators, and provides a surgical system comprising: an input device; a first actuator and a second actuator; a controller for controlling the first actuator and the second actuator, the controller being configured to apply a first scaling factor to a first command output of the first actuator and a second command output of the second actuator, respectively, when the first command output would fall outside a first predetermined working range of the first actuator, wherein the first scaling factor adjusts the first command output to be within the first predetermined working range.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 201780006284.7, filed January 12, 2017, entitled "Uniform Scaling of Haptic Actuators."

[0002] CLAIM OF PRIORITY

[0003] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62 / 277,827, filed January 12, 2016, which is incorporated by reference herein in its entirety. TECHNICAL FIELD

[0004] The present invention relates to systems and methods for providing haptic feedback to an operator of a surgical system, and more particularly to maintaining an intuitive haptic profile for the user when a haptic feedback actuator reaches a performance limit. BACKGROUND

[0005] Teleoperated surgical systems are often intended to improve a surgeon's precision and / or reduce patient trauma during a medical procedure. In such systems, the surgeon interacts with an input device (sometimes referred to as a "master" or "master controller") to control a surgical instrument actuated by a drive mechanism, such as a motor. Because the surgeon does not directly manipulate the surgical instrument, it can be beneficial to sometimes provide haptic feedback at the input device that indicates or replicates an interaction force (e.g., felt at the surgical instrument, other elements of the surgical system, and / or virtual or synthetic elements / features generated by the surgical system). Note that the force feedback presented to the user can be a sum of feedback from sensors, from algorithms, from user interface cues, collision detection, model interaction, etc.

[0006] To provide a good user experience, the surgeon would ideally experience a seamless haptic experience through system state and configuration changes. However, this can be difficult to achieve, for example, where actuators used to provide haptic feedback have different performance limits, or where different actuators reach their performance limits at different times. In such cases, the haptic feedback presented to the user can not be properly aligned with the perceived user experience (e.g., actual forces sensed at the surgical instrument or visual representations of interactive objects), resulting in a confusing or unintuitive user experience.

[0007] For example, motor torque limits (i.e., saturation limits) are often imposed in software for robotic interfaces. These performance limits can arise for a variety of reasons, including protecting the motors from overheating, limiting the forces applied to the surgeon / patient, and / or keeping the motors within their ideal torque operating range. Limiting the torque at the motors can create non-isotropic force saturation at the interface (e.g., the handle of an input device or the tip of an instrument). This means that, when you are trying to render a force at an interface that involves two or more motors, if one motor is constrained by a motor torque limit, the direction of the force can be incorrect.

[0008] This can be particularly problematic when giving force (haptic feedback) to a user at an input device. The user can be feeling a force in a given direction, but as the force applied to the user increases and reaches the torque limit of any motor associated with giving force to the user, the direction of the force exhibited to the user starts to rotate, which can be confusing and / or disorienting to the user.

[0009] Accordingly, it is desirable to provide a system and method for ensuring haptic feedback that is consistent with the force environment at a surgical instrument. SUMMARY

[0010] To minimize the difference between the intended force direction and the haptic force feedback direction, the output of the haptic feedback actuators is scaled whenever one or more actuators reach a predetermined output threshold, thereby maintaining proper haptic feedback directionality when individual actuators would otherwise be commanded to operate outside of their precise performance range. Such scaling can change the overall haptic feedback magnitude, but allows the haptic feedback direction to be properly maintained.

[0011] In some embodiments, where software limits the output of any actuator, the monitoring process can determine when the output of an actuator will exceed a maximum threshold output (at or below the software-defined output limit), and at that point scale down the output of at least one of the other actuators so that the intended direction of the total output (e.g., force or torque) is maintained. In some embodiments, the monitoring process can additionally or alternatively determine when the output of an actuator will fall below a minimum output threshold (below which the actuator output can be too low to accurately generate), and at that point scale up its output and the output of at least one of the other actuators so that the intended direction of the total output (e.g., force or torque) is maintained. In some embodiments, all actuators are scaled when one actuator reaches its threshold output, while in other embodiments only the concurrently active actuators are scaled. In some embodiments, the output thresholds of the actuators are fixed, while in various other embodiments the output thresholds of the actuators can vary over time or based on actuator and / or system state.

[0012] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide a further explanation of the disclosure as claimed. Additional aspects, features, and advantages of the present disclosure will become apparent to those skilled in the art upon consideration of the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0013] Aspects of the present disclosure can be best understood with reference to the following detailed description when read in conjunction with the accompanying drawings. It should be emphasized that various features are not to scale. In fact, the dimensions can be arbitrarily increased or decreased for the sake of discussion. Additionally, the present disclosure can repeat the use of reference characters in the various figures to denote particular elements throughout the figures. Such repetition of reference characters is for the sake of simplicity and clarity and does not necessarily signify a common function among the various embodiments of the disclosure discussed.

[0014] Figure 1 A method of providing consistent haptic feedback to a user of a surgical system when a maximum output of an actuator is reached is shown in accordance with various embodiments of the present disclosure.

[0015] Figure 2A And Figure 2B Exemplary haptic force vector outputs when actuator output maximum is ignored versus resolved are shown.

[0016] Figures 3A-3B An exemplary surgical system providing haptic force feedback in response to an actuator output maximum threshold is shown in accordance with various embodiments of the present disclosure. DETAILED DESCRIPTION

[0017] In the following detailed description of aspects of the application, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. However, it will be apparent to one skilled in the art that embodiments of the present disclosure can be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the embodiments of the present disclosure. Moreover, for the purpose of clarity, one or more components or acts can be described as being used or performed in a certain way, but this is not meant to be limiting, as the components or acts can be used or performed in any way that is suitable for the purpose.

[0018] To minimize the difference between the desired haptic force feedback direction (e.g., sensed or modeled by the surgical system) and the actual haptic force feedback direction, the output of the haptic feedback actuators is scaled whenever the commanded output of one or more actuators falls outside of a predetermined operating range for that actuator. The predetermined operating range can be defined by a maximum output threshold equal to or less than the output limit of the actuator, and / or a minimum output threshold equal to or greater than the minimum precise output level of the actuator. Such scaling can reduce the overall haptic feedback magnitude, but allows the haptic feedback direction to be suitably maintained, which is often the more critical aspect of haptic feedback.

[0019] Figure 1 An exemplary method for providing directionally consistent haptic feedback when actuator output limits are exceeded is shown. In a step 110 of providing haptic feedback, a surgical system allows a user (e.g., a surgeon) to control a surgical instrument (and / or other elements of the surgical system, such as a robotic arm, a mounting structure, or a positioning element such as a boom or cart) via an input device(s) (e.g., a control stick(s), a clamp(s), a joystick(s), or any other structure capable of receiving user input) and then provides force feedback to the input device based on a desired haptic feedback profile (a set of one or more haptic feedback effects that at least partially recreate or represent the physical experience of a real or virtual / modelled interaction). The haptic feedback profile can be based on any haptic model input, such as forces sensed at the instrument (e.g., tissue or other instrument interaction) or the robotic arm (e.g., arm collision with a structure or person), user guidance devices (e.g., haptic stop devices, guard devices, or other profiles for providing guidance to the user to move the input device(s) along a desired path or trajectory), and user interface (UI) elements (e.g., presenting a virtual handle or steering wheel to the user). The haptic feedback can be anything from a direct copy of the haptic feedback profile to a scaling of the haptic feedback profile, to a non-linear modification or any other transformation of the haptic feedback profile applied (e.g., force scaling that varies according to one or more other factors such as instrument state / speed, observation magnification, etc.).

[0020] The actual force feedback provided at the input device is generated by two or more actuators (e.g., motors, drivers, or any other powered elements) that work cooperatively to provide feedback of varying force and direction. For example, an input device with pitch and yaw capability can be coupled to a first pair of actuators that apply force in opposite directions about a pitch axis and a second pair of actuators that apply force in opposite directions about a yaw axis. The two or more pitch actuators and yaw actuators can then be used simultaneously to provide force feedback that is offset from the pitch and yaw axes.

[0021] Because actuators do not typically have exactly the same performance characteristics, either due to inherent performance limits or due to operational constraints / effects (e.g., thermal constraints, mechanical constraints). For example, one of the haptic feedback actuator group will typically reach its maximum output level before the others. Any commanded output that exceeds the maximum output level will not result in any increased output, and thus haptic feedback involving the actuator that is maxed-out will likely deviate from the intended force feedback direction. Additionally, when the output falls below a certain level, the actuator will likely begin to produce noisier (less accurate) output, such that haptic feedback below a certain level can also deviate from the intended force feedback direction.

[0022] Figure 2A An example of this haptic deviation is graphically depicted, where the output of a first actuator and a second actuator (respectively "Actuator 1" and "Actuator 2") are represented by the horizontal and vertical axes of the graph, respectively. The output limits OL1 and OL2 for the first and second actuators are also indicated on the axes of the graph, representing the output limits of the first and second actuators, respectively.

[0023] As noted above, an actuator cannot exceed its output limit, which can be static (e.g., defined by the inherent performance characteristics of the actuator), or dynamic (e.g., based on current parameters of the actuator, such as temperature, or physical constraints such as the kinematic configuration of a driven structure that places the actuator in a mechanically disadvantageous position).

[0024] A problem arises if the commanded output of an actuator exceeds its output limit, such as indicated by the desired (commanded) feedback force FD. To generate the desired feedback force FD, actuator 1 receives a commanded output CO1, and actuator 2 receives a commanded output CO2. The commanded output CO1 is less than the output limit OL1, and thus the commanded output CO1 can be provided by actuator 1. However, because the commanded output CO2 is greater than the output limit OL2, the actual output of actuator 2 will be limited to the output level OL2, resulting in an overall feedback force FO that is both less than and deviated from the desired feedback force FD. While slight changes in haptic feedback magnitude can typically be accommodated by a user with little effort, a deviation in force direction can cause considerable confusion to the user, and can result in the user making an inappropriate control action in response.

[0025] Returning to Figure 1To mitigate this force feedback offset problem, in step 120 of actuator threshold detection, any command output to an actuator that exceeds the maximum output threshold of that actuator is identified. Note that while in some embodiments the maximum output threshold of an actuator can be defined as the output limit of that actuator, in various other embodiments the maximum output threshold can be set at a level lower than the output limit to provide a buffer for detecting actuator limits and / or applying a scaling factor (as described in more detail below) before any output limit is reached. Further note that as described above, the maximum output threshold of a haptic feedback actuator can be static or dynamic, and can be individualized or universal across actuators.

[0026] Then, in step 130 of global actuator scaling, a common scaling factor is applied to the command outputs of the actuators. The scaling factor is selected to keep the output of the identified actuators (i.e., the actuators identified in step 120 as having a command output greater than their output threshold) less than their output limit. Because the scaling factor is applied to the command output of each actuator, the direction of the overall force is maintained, with the overall magnitude reduced. Note that in some embodiments, if multiple actuators would receive a command output that exceeds their output limit, the scaling factor would be based on the command output that exceeds the output threshold of its associated actuator by the greatest amount, i.e., the scaling factor would be based on the “worst” output discrepancy.

[0027] Figure 2B The illustration depicts an example of haptic scaling with respect to the same first and second actuator features (output limits OL1 and OL2, respectively) and a desired feedback force FD. However, rather than allowing the output limit associated with actuator 2 to pull the overall haptic force away from the desired force direction as shown in Figure 2A the scaling factor is applied to command outputs CO1 and CO2 to proportionally reduce both to adjusted command outputs CO1’ and CO2’, respectively. The scaling factor is selected such that adjusted command output CO2’ is reduced at least to the output limit OL2, although in various other embodiments the scaling factor can be selected such that adjusted command output CO2’ is less than output limit OL2 by some increment.

[0028] In some embodiments, actuator 1 and actuator 2 can additionally or alternatively exhibit reduced output accuracy at low output levels. In such embodiments, if either of command outputs CO1 and CO2 is less than the minimum output threshold of actuator 1 or actuator 2, respectively, a scaling factor can be applied to command outputs CO1 and CO2. The scaling factor then increases adjusted command outputs CO1’ and CO2’ above the level at which output accuracy is reduced. Note that as described above, the minimum output threshold of a haptic feedback actuator can be static or dynamic, and can be individualized or universal across actuators.

[0029] In any case, application of the scaling factor results in an overall scaled feedback force FS that is directionally aligned with the original desired feedback force FD. As noted above, as long as directional consistency of force feedback is maintained, a consistent haptic experience can be provided even if the magnitude of the force changes.

[0030] Returning to Figure 1 In various embodiments, when it is detected in the optional actuator sub-threshold detection step 140 that the (un-scaled) command output of the actuator identified in step 120 will exceed the output threshold of that actuator (e.g., exceed the maximum output threshold or fall below the minimum output threshold), the scaling factor applied to all command outputs in step 130 is removed (or set to 1) in the optional global actuator de-scaling step 150. Returning to step 110, unscaled haptic feedback is provided.

[0031] As noted previously, in some embodiments, the output threshold of a haptic feedback actuator can be dynamic, i.e., the particular value can change depending on actuator operating parameters, input device kinematic configuration, or various other factors. In such embodiments, the output threshold(s) applied in step 120 can have different values during the course of operation of the surgical system. Additionally, in various other embodiments, different actuators can trigger step 120 during the course of operation of the surgical system.

[0032] Figure 3A and Figure 3B A surgical system 300 incorporating haptic feedback at an input device 330 is shown, as well as a method for providing a user with a haptic experience as described above with respect to Figure 1 , Figure 2A and Figure 2BA block diagram of an apparatus to describe a consistent haptic experience. The surgical system 300 includes an instrument 310 for performing a surgical task (e.g., forceps, cutter, retractor, vessel sealer, needle driver, catheter, etc.), an input device 330 for receiving input from a user (e.g., a surgeon) (e.g., joystick(s), clamp(s), joystick(s), or any other structure capable of receiving user input), and a controller 320 for receiving input instructions from the input device 330, correspondingly controlling the actions of the instrument 310 via a manipulation structure 313, and providing instructions to a haptic feedback actuation mechanism 340 to provide haptic feedback to the input device 330 according to a desired haptic feedback profile. In various embodiments, the manipulation structure 313 can include any number of systems and structures for motorizing, positioning, actuating, or otherwise controlling the behavior of the instrument 310, including robotic arm(s) / manipulator(s), assembly structure(s), and / or positioning element(s) such as booms or carts, etc. The controller 320 can include any combination of hardware, software, firmware, and other modalities for generating, managing, controlling, and implementing the actions described herein. In various embodiments, the controller 320 can be integrated with the instrument 310, the input device 330, and / or discrete control hardware (e.g., independent processing units or computing platforms).

[0033] For illustrative purposes, Figure 3A A distal end effector 311 is shown grasping a portion of tissue 390 (e.g., retracting) at the end of a shaft 312 of the instrument 310. This results in a force FM at the distal end effector 311 that, in an ideal case, would be delivered at the input device 330 as a desired haptic feedback profile force FD. The actual haptic feedback delivery is achieved by the haptic feedback actuation mechanism 340, which includes a plurality of actuators that attempt to provide the haptic feedback profile force FD to present to the surgeon a“feeling” of the resistance provided by the tissue 390 as it is being retracted.

[0034] While the haptic feedback profile force FD is described as originating from a force FM sensed at the distal end effector 311 of the instrument 310 for illustrative purposes, in various other embodiments, the force FM can be sensed at any vantage point where a corresponding haptic feedback at the input device 330 would be beneficial, such as at an interaction at the shaft 312 or any other element of the manipulation structure 313 (e.g., a collision with a structure or a person’s arm).

[0035] In various other embodiments, the force FMmay be defined in terms of non-physical parameters, such as guidance or user interface features. For example, in some embodiments, the surgical system 300 can include a display 350 (e.g., a monitor(s), a head-in viewer(s), a projector, video glasses / headset, and / or any other graphical representation element). In various embodiments, the display 350 can present virtual or synthetic elements 361 that can be interacted with via the input device 330. In some embodiments, the synthetic elements 361 can serve as a supplemental interface for interacting with the physical components of the surgical system 300. For example, as shown, the synthetic elements 361 can be virtual handles or knobs that can be "grabbed" and dragged around using the input device 330 to reposition the instrument 310 at the surgical site. In other embodiments, the synthetic elements 361 can provide purely virtual interaction elements, such as dials, knuckles, joysticks, or any other structure for controlling the surgical system 300. In any case, by generating a haptic feedback profile based on a model force FMl associated with interacting with the synthetic elements 361 (e.g., a radial outward resistance force generated by grabbing a circular knob), the controller 320 can then attempt to provide an appropriate haptic feedback profile force FDat the input device 330. Figure 3A

[0036] In various other embodiments, the surgical system 300 can provide guidance to the user regarding movement of the instrument 310 and / or the input device 330. For example, a desired motion of the instrument 310 (e.g., a target or safe dissection path, a desired retraction movement, or any other beneficial articulation) can optionally be defined as a trajectory 362. By generating a haptic feedback profile based on a model force FM2associated with maintaining the position of the instrument 310 along the trajectory 362 (e.g., an inward force generated upon deviating from the trajectory 362), the controller 320 can then attempt to provide an appropriate haptic feedback profile force FDat the input device 330.

[0037] Figure 3B An exemplary block diagram of the actuation mechanism 340 is shown, which includes a plurality of actuators 341 that apply components of the haptic feedback force to the input device 330. Note that although four actuators are depicted driving the input device 330 via cables or tendons for purposes of description, in various other embodiments, the actuation mechanism 340 can include any number and type of actuators (e.g., rotary actuators, linear actuators, hydraulic, and / or piezoelectric, vibrotactile, or fluidic actuators) and / or force transmission mechanisms (e.g., direct drives, linkages, transmissions, etc.).

[0038] ​Various actuators 341 in combination with each other provide actuation output (e.g., torque or force) in an effort to produce a desired haptic feedback profile force FD. However, if the desired haptic feedback profile force FD requires output from one of the actuators 341 that falls outside of its operating range, attempting to use the command output for that actuator 341 without modification will result in an unmodified haptic feedback force FO that has a magnitude and a direction different from the desired force FD, as described above with respect to Figure 1 and 2A The operating range of an actuator can be defined by a maximum output threshold (e.g., at or below the output limit of the actuator) and / or a minimum output threshold (e.g., at or above the minimum reliable output level of the actuator), as described above.

[0039] Accordingly, when the controller 320 detects that the command output for any actuator 341 will exceed the output threshold defined for that actuator (as described above with respect to step 120 in Figure 1 It applies a common scaling factor to the command output supplied to each actuator 341 such that the command output for all actuators 341 remains within their predetermined operating ranges (as described above with respect to step 130 in Figure 1 This has the effect of proportionally changing the output of all actuators 341, which in turn results in a scaled haptic feedback force FS that, while different in magnitude relative to the desired feedback force FD, remains directionally aligned with the desired feedback force FD (as described above with respect to Figure 2B

[0040] In various embodiments, when the controller 320 detects that the unscaled command output will no longer exceed the output threshold defined for any actuator 341, the scaling factor can be eliminated (or set to 1), thereby allowing the unscaled haptic feedback to resume at the input device 330 (as described above with respect to steps 140 and 150 in Figure 1

[0041] While certain example embodiments of the application have been described and shown herein in order to elucidate the general principles of the application, it is to be understood that the embodiments are merely illustrative of the general principles of the application and are not to be limiting nor is the application to be limited to the specific constructions and arrangements shown and described since various modifications can occur to those skilled in the art upon the reading of the description of the application.​​

Claims

1. A surgical system comprising: a surgical instrument user control and user haptic feedback input device; a haptic feedback mechanism comprising a first actuator coupled to the input device and a second actuator coupled to the input device; and a controller coupled to receive input commands from the input device and provide commands to the haptic feedback mechanism; wherein an operating range of the first actuator is defined at least in part by an upper output limit of the first actuator; wherein the controller is configured to determine a first commanded output haptic feedback force for the first actuator to provide to the input device and a second commanded output haptic feedback force for the second actuator to provide to the input device; wherein in the event that the first commanded output haptic feedback force would be greater than the upper output limit of the first actuator, the controller generates a scaled first commanded output feedback force for the first actuator to provide to the input device by applying a common scaling factor to the first commanded output haptic feedback force, the controller generates a scaled second commanded output feedback force for the second actuator to provide to the input device by applying the common scaling factor to the second commanded output haptic feedback force, and the controller provides user haptic feedback at the input device by providing the scaled first commanded output feedback force to the first actuator and the scaled second commanded output feedback force to the second actuator; and wherein the common scaling factor adjusts the first commanded output haptic feedback force to be at or below the upper output limit of the first actuator.

2. The surgical system of claim 1, wherein: the operating range is further defined by a lower output limit; and the lower output limit is at or above a minimum reliable output level force of the first actuator.

3. The surgical system of claim 2, wherein: the common scaling factor adjusts the first commanded output haptic feedback force to be at or below the upper output limit of the first actuator and at or above the lower output limit.

4. The surgical system of claim 1, wherein: the upper output limit is associated with a maximum output threshold force of the first actuator.

5. The surgical system of claim 1, wherein: the upper output limit is dynamic and based on a kinematic configuration of the input device.

6. The surgical system of claim 2, wherein: the lower output limit is dynamic and based on a kinematic configuration of the input device.

7. The surgical system of claim 1, wherein: the common scaling factor is associated with any one of an instrument state, an instrument velocity, or an observed magnification.

8. The surgical system of claim 3, wherein: the common scaling factor is variable.

9. The surgical system of claim 1, wherein: In the event that the first command output haptic feedback force would fall within the working range of the first actuator, the controller removes the common scaling factor from the first command output haptic feedback force and the second command output haptic feedback force.

10. The surgical system of claim 1, wherein: the working range of the second actuator is defined at least in part by an output upper limit of the second actuator; and the common scaling factor adjusts the second command output haptic feedback force to be within the working range of the second actuator.

11. The surgical system of claim 10, wherein: the condition that the first command output haptic feedback force would be greater than the output upper limit of the first actuator is a first condition; the common scaling factor is a first common scaling factor; in the event that the first common scaling factor applied to the first command output haptic feedback force would result in a second condition in which the second actuator outputs a force outside of the working range of the second actuator, the controller applies a second common scaling factor to the first command output haptic feedback force and the second command output haptic feedback force; and the second common scaling factor adjusts the second command output haptic feedback force to be within the working range of the second actuator.

12. A method for operating a surgical system, the surgical system comprising a surgical instrument user control and user haptic feedback input device, a haptic feedback mechanism comprising a first actuator coupled to the input device and a second actuator coupled to the input device, and a controller, the first actuator having a working range defined at least in part by an output upper limit of the first actuator, the method comprising: determining, via the controller, a first command output haptic feedback force for the first actuator to provide to the input device and a second command output haptic feedback force for the second actuator to provide to the input device; detecting, via the controller, a condition in which the first command output haptic feedback force would be greater than the output upper limit of the first actuator; generating, via the controller, a scaled first command output feedback force for the first actuator to provide to the input device by applying a common scaling factor to the first command output haptic feedback force; generating, via the controller, a scaled second command output feedback force for the second actuator to provide to the input device by applying the common scaling factor to the second command output haptic feedback force; providing user haptic feedback at the input device by providing, via the controller, the scaled first command output feedback force to the first actuator and the scaled second command output feedback force to the second actuator; and adjusting, via the common scaling factor, the first command output haptic feedback force to be at or below the output upper limit of the first actuator.

13. The method of claim 12, wherein: the working range is further defined by an output lower limit; the common scaling factor is a first common scaling factor; in the event that the first common scaling factor applied to the first command output haptic feedback force would result in a second condition in which the second actuator outputs a force outside of the working range of the second actuator, the controller applies a second common scaling factor to the first command output haptic feedback force and the second command output haptic feedback force; and the second common scaling factor adjusts the second command output haptic feedback force to be within the working range of the second actuator. the output lower bound is at or above a minimum reliable output level force of the first actuator; and adjusting the first command output haptic feedback force includes adjusting the first command output haptic feedback force via the common scaling factor to be at or below the output upper bound of the first actuator and at or above the output lower bound.

14. The method of claim 13, wherein: the output lower bound is dynamic and based on a kinematic configuration of the input device.

15. The method of claim 12, wherein: the output upper bound is dynamic and based on a kinematic configuration of the input device.

16. The method of claim 12, wherein: the common scaling factor is associated with any one of an instrument state, an instrument velocity, or an observation magnification.

17. The method of claim 12, wherein: the common scaling factor is variable.

18. The method of claim 12, wherein: the method further includes detecting, via the controller and after adjusting the first command output haptic feedback force via the common scaling factor, a condition that the first command output haptic feedback force will fall within the working range of the first actuator; and the method further includes removing, via the controller and after detecting the condition that the first command output haptic feedback force will fall within the working range of the first actuator, the common scaling factor from the first command output haptic feedback force and the second command output haptic feedback force.

19. The method of claim 12, wherein: a working range of the second actuator is defined at least in part by an output upper bound of the second actuator; and the common scaling factor adjusts the second command output haptic feedback force to be within the working range of the second actuator.

20. The method of claim 19, wherein: the condition that the first command output haptic feedback force will be greater than the output upper bound of the first actuator is a first condition; the common scaling factor is a first common scaling factor; the method further includes detecting, via the controller, a second condition that application of the first common scaling factor to the first command output haptic feedback force will cause the second actuator to output a force outside of the working range of the second actuator; and the method further includes applying, via the controller, a second common scaling factor to the first command output haptic feedback force and the second command output haptic feedback force to adjust the second command output haptic feedback force to be within the working range of the second actuator.

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