Compact differential coaxial sensing force sensor

Abstract

The invention relates to a compact differential coaxial induced stress sensor. A variety of applications may include apparatuses and / or methods of providing an axial force transducer. Two coils coaxially wound relative to each other may be used with a magnet to determine a distance traveled based on application of an axial force to the instrument component. The two coils and magnets may be configured in a variety of ways relative to the instrument component. In various embodiments, the difference between the inductance associated with one of the two coils along with its relationship with the magnet and the inductance associated with the other of the two coils along with its relationship with the magnet may be used to determine an axial force on the instrument component, the axial force associated with the distance of travel. Additional apparatus, systems, and methods are disclosed.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 202080066153X (PCT / US2020 / 050696), titled "Compact Differential Coaxial Inductive Force Sensor", filed on September 14, 2020.

[0002] Related Applications

[0003] This patent application claims the benefit of priority and the filing date of U.S. Provisional Patent Application No. 62 / 901,729, titled "COMPACT, DIFFERENTIAL, COAXIAL INDUCTIVE FORCE SENSOR", filed on September 17, 2019, which is incorporated herein by reference in its entirety. This application is related to U.S. Provisional Patent Application No. 63 / 077,833, titled "Devices and Methods for Compact, Redundant Inductive Force Sensor", filed on September 14, 2020, which is incorporated herein by reference in its entirety. Technical Field

[0004] The embodiments described herein relate to force-sensing mechanical structures, and more particularly to medical devices, and still more particularly to instruments for minimally invasive surgery. More specifically, the embodiments described herein relate to medical devices including a force sensor unit that is coupled to the mechanical structure of the medical device and is configured to measure the axial force applied to the end effector of the medical device during a surgical procedure. Background Art

[0005] Minimally invasive medical techniques are designed to reduce the amount of tissue damaged during diagnostic or surgical procedures, thereby reducing patient recovery time, discomfort, and harmful side effects. Teleoperated surgical systems using robotic-assisted technology can be used to overcome the limitations of manual laparoscopy and open surgery. Advancements in telepresence systems provide the surgeon with a view inside the patient, increase the degrees of freedom of movement of the surgical tools, and provide the ability for long-distance surgical collaboration. In a teleoperated surgical system, a tool operator can actuate an input of a master control device to send a control signal to a mechanical control device located at a proximal portion of an elongate tool shaft to control the movement of a connector (e.g., a cable) or a connector-hypotube combination extending within the length of the shaft, thereby controlling the movement of an end effector located at a distal portion of the tool shaft. The control connector or connector-hypotube combination is typically pre-tensioned to enable the surgical tool at the surgical site to respond quickly and accurately to the actuation signal. Thus, direct natural force feedback to the tool operator is largely eliminated because such a tool user does not directly manually manipulate the tool.

[0006] For example, a force sensor can be disposed at or near the tool shaft to measure the clinical force applied to the patient tissue due to contact with the end effector during a medical procedure. For example, these force measurements at or near the tool shaft can be used to generate a haptic feedback force at an input of the master control device, thereby providing an indication to the user of the force applied by the tool to the patient tissue. Enhancement of the force sensor system can result in more accurate force measurements, which in turn can generate more accurate haptic feedback. SUMMARY

[0007] This Summary introduces certain aspects of the embodiments described herein to provide a basic understanding. This Summary is not an extensive review of the subject matter of the present invention and is not intended to identify key or important elements of the subject matter of the present invention or to delineate the scope of the present invention. In some embodiments, a device includes a mechanical structure and a force sensor unit coupled to the mechanical structure. The force sensor unit includes a rod, a magnet coupled to the rod, a first coil coupled to the mechanical structure, and a second coil coupled to the mechanical structure and coaxial with the first coil. The rod includes a distal portion and a proximal portion, and a central axis of the rod is defined between the proximal portion and the distal portion of the rod. The magnet translates along the central axis of the rod within the first coil and the second coil.

[0008] In some embodiments, the device further includes a shaft coupled to the mechanical structure, and the shaft is operatively coupled to the rod such that translational movement of the shaft relative to the mechanical structure causes the rod to move along the central axis of the rod. In some embodiments, the shaft includes a proximal end and a distal end, and a central axis of the shaft is defined between the proximal end and the distal end of the shaft. The shaft is coupled to the mechanical structure such that a linear displacement of the shaft along the central axis of the shaft is proportional to a force applied to the shaft in a direction along the central axis of the shaft.

[0009] In some embodiments, the central axis of the rod is in a direction parallel to the central axis of the shaft. In some embodiments, the shaft includes a proximal end and a distal end, and the central axis of the shaft is defined between the proximal end and the distal end of the shaft. The first signal generated by the first coil is associated with the position of the magnet relative to the first coil, and the second signal generated by the second coil is associated with the position of the magnet relative to the second coil. Wherein the first signal from the first coil and the second signal from the second coil are associated with the linear displacement of the shaft along the central axis of the shaft.

[0010] In some embodiments, the linear displacement of the shaft is proportional to the force applied to the shaft in the direction along the central axis of the shaft. In some embodiments, the shaft includes a proximal end and a distal end, and the central axis of the shaft is defined between the proximal end and the distal end of the shaft. In such an embodiment, the device further includes a spring coupled to the shaft, and the spring is configured to displace in proportion to the force applied to the shaft in the direction along the central axis of the shaft.

[0011] In some embodiments, the first signal generated by the first coil is associated with the position of the magnet relative to the first coil, and the second signal generated by the second coil is associated with the position of the magnet relative to the second coil. The force sensor unit includes a microprocessor coupled to receive the first signal and the second signal.

[0012] In some embodiments, the first signal has a first frequency, the second signal has a second frequency different from the first frequency, and the microprocessor is configured to execute instructions to determine the linear displacement of the shaft along the central axis of the shaft based on the first frequency and the second frequency.

[0013] In some embodiments, the device includes a first magnet and a second magnet. The first magnet is positioned to move within the first coil, and the second magnet is positioned to move within the second coil.

[0014] In some embodiments, a medical device includes: an instrument shaft including a proximal end and a distal end; a medical end effector coupled to the distal end of the shaft; a mechanical structure coupled to the proximal end of the shaft; and a force sensor unit coupled to the mechanical structure and the instrument shaft. The force sensor unit includes a first coil wound around a first coil axis, a second coil wound around a second coil axis and coaxial with the first coil axis, and a magnet. The instrument shaft axis is defined between the proximal end and the distal end of the instrument shaft, and the magnet is operably coupled to the instrument shaft and moves along the first coil axis as the instrument shaft moves along the instrument shaft axis.

[0015] In some embodiments, as the instrument shaft moves along the instrument shaft axis, the magnet moves within the first coil. In some embodiments, as the instrument shaft moves along the instrument shaft axis, the magnet moves within the first coil and within the second coil. In some embodiments, the force sensor unit includes a rod, and the rod is axially aligned with the first coil axis and couples the magnet to the instrument shaft.

[0016] In some embodiments, a first signal generated by the first coil is associated with the position of the magnet relative to the first coil, and a second signal generated by the second coil is associated with the position of the magnet relative to the second coil. The force sensor unit includes a microprocessor coupled to receive the first signal and the second signal.

[0017] In some embodiments, the first signal has a first frequency and the second signal has a second frequency. The microprocessor is configured to execute instructions to determine a measure of the force along the instrument shaft axis on the instrument shaft based on the first frequency and the second frequency.

[0018] In some embodiments, at a unique position of the magnet relative to the first coil and the second coil, the first signal is generated by the first coil and the second signal is generated by the second coil, and the first signal from the first coil and the second signal from the second coil are associated with a unique linear displacement of the instrument shaft along the instrument shaft axis.

[0019] In some embodiments, the medical device further includes a spring coupled to the shaft and a mechanical structure, and the spring is configured to displace in proportion to a force applied to the instrument shaft in a direction along the instrument shaft axis.

[0020] In some embodiments, the medical device includes an instrument support structure, an instrument shaft, and a force sensor unit. The instrument shaft includes a proximal end and a distal end, and the instrument shaft axis is defined between the proximal end and the distal end of the instrument shaft. The force sensor unit includes a first coil wound around a first coil axis, a second coil wound around a second coil axis and coaxial with the first coil axis, and a magnet at least partially within one of the first coil and the second coil. The first coil, the second coil, and the magnet are positioned such that translation of the instrument shaft relative to the instrument support structure along the instrument shaft axis causes relative movement between the magnet and the first coil along the first coil axis and relative movement between the magnet and the second coil along the second coil axis. In some embodiments, the first coil and the second coil are fixed relative to the instrument support structure.

[0021] In some embodiments, a medical device includes a proximal mechanical structure, a distal mechanism, and a connecting member. The distal mechanism is coupled to the distal end of an instrument shaft and includes a movable component. The proximal mechanical structure includes an instrument support structure and an actuator input that is mounted to move relative to the instrument support structure. The connecting member is coupled between the actuator input and the movable component of the distal mechanism and transfers a pulling force, a compressive force, or both a pulling force and a compressive force from the actuator input to the movable component of the distal mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] When read in conjunction with the Figure 1 accompanying drawings, various aspects of the present disclosure can be best understood from the following detailed description. It should be emphasized that, according to standard practice in the industry, the various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. Additionally, the present disclosure may repeat reference numerals and / or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations discussed.

[0023] Figure 1 is an illustrative plan view of a minimally invasive teleoperated surgical system for performing minimally invasive diagnostic or surgical procedures on a patient lying on an operating table according to various embodiments.

[0024] Figure 2 is a perspective view of a surgeon's console according to various embodiments.

[0025] Figure 3 is a perspective view of a patient-side cart of a minimally invasive teleoperated surgical system according to various embodiments.

[0026] Figure 4A is an illustrative side view of a medical device including a distal portion and a proximal mechanical structure, the distal portion and the proximal mechanical structure being coupled to each other by an elongate shaft defining an inner bore according to various embodiments.

[0027] Figure 4B is according to various embodiments Figure 4A of a medical device, showing a control surface of an input device.

[0028] Figure 4C is a schematic illustration of a medical device including a force sensor unit according to an embodiment.

[0029] Figures 5A - 5H Illustrates components of an exemplary force sensor unit according to various embodiments.

[0030] Figure 6A Shows a mechanical structure according to various embodiments, which can be coupled to as described with respect to Figures 5A - 5HThe instrument shaft under discussion.

[0031] Figure 6B illustrates, according to various embodiments, Figure 6A a mechanical structure in which a dual coil has a rod inserted therein, where the rod is fixed to a support base to be coupled to Figure 6A the instrument shaft.

[0032] Figure 7 is a block diagram of an exemplary force sensor according to various embodiments, which can be implemented to measure the axial force applied to the instrument shaft.

[0033] Figures 8A - 8C illustrates the measurement of the inductance of a magnet target and two coils relative to the target position according to various embodiments.

[0034] Figure 9 is a flowchart of the features of an exemplary method for determining the axial force according to various embodiments. Detailed Description

[0035] The following detailed description refers to the accompanying drawings, which illustrate, by way of example, various embodiments of the present invention. These embodiments are described in sufficient detail to enable those of ordinary skill in the art to practice these and other embodiments. Other embodiments may be utilized and structural, logical, mechanical, and electrical changes may be made. The various embodiments are not necessarily mutually exclusive, as some embodiments may be combined with one or more other embodiments to form new embodiments. Thus, the following detailed description should not be construed as limiting.

[0036] The embodiments described herein can be advantageously used in a variety of force sensor applications, such as for grasping, cutting, and manipulation operations related to minimally invasive surgery. The embodiments described herein can also be used in various non-medical applications, such as remote operating systems for search and rescue, remotely controlled diving devices, aviation devices, and automobiles, etc. The embodiments described herein can also be used to determine the force applied to (or exerted by) the distal portion of the instrument during use.

[0037] The medical device described herein includes a force sensor unit that includes a compact differential force sensor to measure the force axially applied to the end effector of the medical device along the z-axis direction. As described herein, two induction coils are coaxially wound around a cylinder, and a magnet (e.g., a ferrite bead, an EMI (electromagnetic interference) suppression bead, a nickel-zinc bead, etc.; the term "magnet" is described in more detail below) held by a rod is movably positioned within the coils. When the magnet moves axially within the coils, the inductance at each coil changes. The change in inductance at each coil can be used to measure the change in the position of the instrument shaft, which can be translated into a z-axis force measurement.

[0038] Figure 1 FIG. 4 is an exemplary illustrative plan view embodiment of a minimally invasive teleoperated surgical system 10 for performing minimally invasive diagnostic or surgical procedures on a patient 12 lying on an operating table 14. The system includes a surgeon's console 16 for use by a surgeon 18 during the procedure. One or more assistants 20 may also participate in the procedure. The minimally invasive teleoperated surgical system 10 further includes one or more patient-side carts 22 and an electronics cart 24. The patient-side cart 22 can manipulate at least one medical device 26 (such as a surgical instrument) through a minimally invasive incision in the patient 12, while the surgeon 18 observes the surgical site through the surgeon's console 16. Images of the surgical site can be obtained by an endoscope 28 (such as a stereoscopic endoscope), and the endoscope 28 can be positioned using a mechanical support arm 72 associated with the patient-side cart 22 to orient the endoscope 28 to capture images of the surgical site.

[0039] A computer processor located on the electronics cart 24 can be used to process images of the surgical site for subsequent display to the surgeon 18 through the surgeon's console 16. Additionally, the computer processor at the electronics cart 24 can be configured to process electrical or optical signals indicative of the force applied at the medical device. For example, the computer processor can generate haptic feedback at the surgeon's console 16. In various embodiments, stereoscopic images can be captured, which allows for the perception of depth during a surgical procedure. The number of single-use medical devices 26 typically depends on the diagnostic or surgical procedure and the spatial limitations within the surgical site and other factors. If it is necessary to replace one or more of the medical devices 26 being used during the surgical procedure, then the assistant 20 can remove the medical device 26 from the mechanical support arm 72 associated with the patient-side cart 22 and replace it with another medical device 26 in a tray 30 in the operating room.

[0040] Figure 2Is a perspective view of an embodiment of the surgeon's console 16. The surgeon's console 16 may include an observer display 31, which includes a left-eye display 32 and a right-eye display 34 for presenting a coordinated stereoscopic view of the surgical site to the surgeon 18, which view enables depth perception. The console 16 may also include one or more manually operated master control inputs 36, 38 to receive large-scale manual control movements. One or more slave medical devices 26 mounted for use at one or more corresponding mechanical support arms 72 of the patient-side cart 22 are capable of moving at a smaller scale distance that matches the large-scale manipulation of the one or more master control inputs 36, 38 by the surgeon 18. The master control inputs 36, 38 may provide the same mechanical degrees of freedom as the medical devices 26 associated with them to provide telepresence to the surgeon 18, or the master control input 36 is integrated with the slave medical device 26 so that the surgeon has a keen sense of directly controlling the tool 26. For this purpose, position, force, and / or tactile feedback sensors (not shown) may be employed to determine the tool position, and measure the force, and measure the tactile sensation at the tool 26. The determined tool position and force may be used to generate tactile feedback on the surgeon's hand through the control inputs 36, 38. An electrical or optical signal modulated based on the force detected at a force sensor (not shown) at the tool 26 may be processed by a processor at the electronics cart 24 to generate tactile feedback at the control inputs 36, 38, which may indicate the magnitude and direction of the detected force.

[0041] Figure 3FIG. 0 is a perspective view of an example embodiment of a patient-side cart 22 of a minimally invasive teleoperated surgical system 10. The patient-side cart 22 can include four robotic support arms 72. Each support arm 72 can include an articulated support arm segment 73 pivotally mounted end-to-end and a support forearm 74 pivotally mounted thereto. A respective medical device carriage 75 that includes a motor for controlling tool movement is mounted at each support forearm 74. Additionally, each of the support arms 72 can optionally include one or more fitting joints (e.g., passive and / or lockable) at the juncture of the support arm segment 73 and at the juncture with the support forearm 74, and the support forearm 74 can be used to position the attached medical device carriage 75 relative to the patient 12 undergoing surgery. Each medical device 26 can be removably coupled to the carriage 75. Although the patient-side cart 22 is shown as including four support arms 72, more or fewer support arms 72 can be used. Generally, at least one of the medical devices will include a vision system, which typically includes an endoscopic camera tool (not shown) for capturing video images and one or more video displays for displaying the captured video images, and the vision system can be coupled to one of the carriages 75.

[0042] The respective medical devices 26 and cannulas 27 can be removably coupled to the carriage 75, where the tool shaft portion 410 of the medical device 26 is inserted through the cannula 27. The carriage 75 can house a plurality of remotely operated actuators, such as motors (not shown), that impart motion to drive members, such as drive shafts and winches (not shown), which in turn drive connectors coupled to the end effector, and the medical device 26 translates the motion into various movements of the end effector on the medical device 26. In various embodiments, the remotely operated actuators in the carriage 75 can impart motion to various components of the medical device 26, e.g., such as end effector wrist movement or clamp movement.

[0043] The surgeon manipulates the master control input devices 36, 38 to control the tool end effector. Inputs (“master” commands) provided by the surgeon or other medical personnel to the control input devices 36 or 38 are translated by actuation of one or more remote motors into corresponding actions (“slave” responses) performed by the medical device 26. In some embodiments, a flexible cable-based force transmission mechanism or the like can be used to transfer the motion of each remotely located remotely operated motor to a respective tool docking winch (which serves as an actuator or actuator input) located at the carriage 75. In various embodiments, a mechanical adapter interface 76 mechanically couples the connector drive member within the tool 26 to the motor within the carriage.

[0044] The term "medical device" is used herein to describe a medical device for insertion into a patient and for performing a surgical or diagnostic procedure. A medical device typically includes an end effector associated with one or more surgical tasks, such as forceps, a needle driver, scissors, a bipolar cautery, a tissue stabilizer or retractor, an applicator, an anastomosis device, an imaging device (e.g., an endoscope or an ultrasound probe), and the like. In various embodiments, some medical devices may also provide articulating support for the end effector, sometimes referred to as a "wrist," so that the position and orientation of the end effector can be manipulated in one or more mechanical degrees of freedom relative to the axis 410 of the tool. Additionally, many surgical end effectors may include functional mechanical degrees of freedom, such as jaws that open or close, or a blade that translates along a path.

[0045] A surgical instrument suitable for use in one or more embodiments of the present disclosure may control its end effector with one or more connectors, which may be, for example, a rod and / or a flexible cable. In some examples, a rod, which may be in the form of a tube, may be combined with a cable to provide pull, push, or combined "push / pull" or "pull / pull" control of the end effector, where the connector provides flexible segments as needed. A typical slender tool axis 410 for a medical device is small, for example, having a diameter of five to eight millimeters. The small scale of the mechanisms in a surgical instrument creates unique mechanical conditions and problems related to the construction of these mechanisms, which are different from those found in similar mechanisms constructed at a larger scale because the forces and strengths of materials do not scale at the same rate as the size of the mechanism. The connector must fit within the slender tool axis 410 and be able to control the end effector through the wrist joint. The connector may be made of a variety of metal (e.g., tungsten or stainless steel) or polymer (e.g., high molecular weight polyethylene) materials.

[0046] Figure 4AAn illustrative side view of a medical device 26 that includes a distal portion 420 and a proximal mechanism 422, which are coupled to each other by an elongate shaft 410 that defines a bore. As used herein, the term "proximal" refers to a position closer to the body center or point of attachment, while the term "distal" refers to a position farther from the body center or point of attachment. For example, the term "proximal" refers to a position closer to the manipulator arm, while the term "distal" refers to a position farther from the manipulator arm. The mechanism 422 may include a support structure, which may include, for example, a housing 425 that supports an input device 429. The input device 429 may include an instrument control surface 427. In other embodiments, various support structures may optionally be used, such as a chassis, a frame, a bed, an overall surrounding outer body of the mechanism, and the like. The input device facilitates controlled adjustment of the end effector of the instrument via a connector that extends through the bore along the elongate tool shaft 410 and that serves as, for example, a tension member for actuating the end effector. In some embodiments, the connector may be a cable, a belt, or the like.

[0047] The control surface 427 provides a mechanical connection to other control features of the medical device 26. During use, the instrument control surface 427 is coupled to a medical device carriage 75 (see Figure 3 ), which provides a motor-driven rotational force to a steering input device 432 at the control surface 427 to control the medical device 26. The distal portion 420 of the medical device 26 may be secured to any of a variety of end effectors, such as the illustrated forceps 428, a needle driver, a cautery device, a cutting tool, an imaging device (e.g., an endoscope or an ultrasound probe), or a combination device that includes a combination of two or more different tools and imaging devices. Additionally, in the illustrated embodiment, the forceps 428 are coupled to the elongate tool shaft 410 by a wrist joint 430, which permits manipulation of the orientation of the forceps relative to the elongate tool shaft 424.

[0048] Figure 4B is Figure 4AExplanatory bottom view of an exemplary medical device, showing the control surface 427 of the input device 429. For example, the control surface 427 may rest on top of the carriage 75, which includes an actuator, such as a motor (not shown), controlled by control signals generated in response to user input at the control input devices 36, 38. As shown, the control surface 427 includes a plurality of steering input devices 432, each of which governs a different aspect of the movement through the wrist joint 430 and the forceps 428. Of course, more or fewer steering input devices 432 may be provided in different embodiments. When the control surface 427 is coupled to the tool carriage 75, each of the steering input devices 432 interfaces with an actuator (e.g., a servo motor, not shown) within the carriage 75 that drives the steering input device. In this example, the steering input devices 432 are configured to form a direct mechanical engagement with corresponding rotary actuators (e.g., servo motors) of the tool carriage 75. However, other suitable configurations for power transmission may also be used (e.g., indirect mechanical coupling, including speed changers and / or torque changers, hydraulic couplings, and / or electrical couplings). For example, each of the steering input devices 432 is part of a limited-slip winch and drive shaft assembly that operates a drive cable that controls the movement of an end effector, such as the forceps 428. In various embodiments, the mechanical structure 422 may be constructed as a rear housing that includes a force sensor unit 440 to detect axial forces at the distal end of the elongate shaft 410. The force sensor unit 440 may be disposed within the mechanical structure 422 in a number of arrangements. For example, a portion of the force sensor 440 may be disposed on the elongate shaft 410.

[0049] The design of a compact axial force sensor unit with components small enough to fit on the proximal end of the instrument shaft can be achieved using target materials related to a plurality of coils to generate signals that can be compared to determine the axial movement of the instrument shaft in response to an axial force applied to the distal end of the instrument shaft. The designs described herein are temperature stable, robust to cautery interference, and withstand autoclaving. The force sensor unit is frictionless and thus does not interfere with the force being measured.

[0050] In various embodiments, a dual-coil distance displacement sensor can be used in combination with a spring or flexure to determine the axial force applied to the instrument shaft. Since the force is bidirectional, the spring can be configured as a bi-directional spring. The axial direction can be taken as the z-axis direction. A z-direction force acting on the distal end of the instrument shaft causes the instrument shaft to axially displace in the proximal direction of the instrument shaft. In the case where the spring is operably coupled to the proximal portion of the instrument shaft, the distance of spring displacement is proportional to the z-direction force applied to the distal portion of the instrument shaft. The dual-coil displacement sensor can include a proximal coil and a distal coil, which are coaxially mounted at fixed positions on a support structure of a proximal mechanical structure to measure the axial displacement of the spring based on changes in the magnetic flux through the coils or the inductance within the coils, as described in more detail below.

[0051] The proximal end of the instrument shaft or a component coupled to the proximal end of the instrument shaft can include a magnet disposed thereon. Any magnet described herein can be, for example, a ferrite bead, an EMI suppression bead, a nickel-zinc bead, or any other suitable material. Thus, in one aspect, it should be understood that the term "magnet" as used herein can refer to any component or material coupled to the instrument shaft that can be used to provide a signal indicative of the position of the shaft within the coil when the magnet moves within the coil. The magnet can be in the form of a bead, but other forms can also be used. The magnet can be arranged or connected to the instrument shaft in a variety of ways. In the case where the magnet is connected to the instrument shaft, movement of the instrument shaft causes movement of the magnet. The proximal end of the instrument shaft (or an extension, rod, or the like of the instrument) with the magnet thereon extends through the dual windings such that there is an air gap between the instrument shaft (or rod) with the magnet thereon and the dual coils. When "at rest", in the absence of a z-direction force applied to the instrument shaft, the instrument shaft can be axially positioned such that the magnet is partially disposed within each coil. In some embodiments, equal portions of the magnet can be disposed within each coil in the absence of a z-direction force applied to the instrument shaft. Each coil is coupled to a separate LC circuit in which the coil acts as an inductor (L), and the inductance varies with the amount of magnet contained within the coil. The resonant frequency of each circuit changes with the change in the circuit inductance. Materials other than magnetic materials can be used, where these other materials contribute to or affect the inductance associated with the coils used in the LC circuit. For example, these other materials can be used in the configurations discussed with respect to Figures 5A - 9 the configurations discussed.

[0052] The inductance of each coil, and thus the resonant frequency of each circuit, varies with the z-axis force on the distal portion of the instrument shaft. In the case where a spring is operably coupled to the proximal portion of the instrument shaft, the spring displacement in response to a z-direction force on the distal portion of the instrument shaft corresponds to the amount of axial displacement of the instrument shaft and the amount of axial displacement of the magnet thereon. The amount of axial displacement of the magnet determines the portion of the magnet that extends into each coil. For example, a larger z-direction force results in more of the magnet being disposed within the proximal coil rather than the distal coil.

[0053] A frequency detection circuit can be used to detect the resonant frequencies of the circuit including the proximal coil and the circuit including the distal coil. Each of these two circuits will have a resonant frequency defined by its coil and magnet, where the contribution of the magnet is based on the z-direction distance of the magnet within the respective coil. When more of the magnet is disposed within the proximal coil rather than the distal coil, the resonant frequency of the circuit using the proximal coil will be different from the resonant frequency of the circuit using the distal coil. The resonant frequencies can be used to determine the axial displacement of the shaft, and thus the amount of displacement of the spring, whereby a measure of the z-direction force on the distal portion of the shaft can be determined accordingly.

[0054] Figure 4C is a schematic illustration of a medical device 326 according to an embodiment. In some embodiments, the medical device 326 or any component thereof is optionally part of a surgical system that performs a surgical procedure, and the surgical system can include a manipulator unit, a series of kinematic linkages, a series of cannulas, or the like as described above with reference to Figures 1 - 4B The medical device 326 and the medical devices described herein can include a mechanical structure 322 and a force sensor unit 340 coupled to or included within the mechanical structure 322, a shaft 310 coupled to the mechanical structure 322, and an end effector 328 coupled to the distal end of the shaft 310. The end effector 328 can include, for example, an articulating clamp or other suitable surgical tool coupled to a linkage 330. In some embodiments, the linkage 330 can be included within a wrist assembly having a plurality of articulated linkages. In some embodiments, the shaft 310 is also movably coupled to the mechanical structure 322 at the proximal portion. The mechanical structure 322 can include components configured to move one or more components of the medical device, such as, for example, the end effector 328. The mechanical structure 322 can be similar to the mechanical structure 422 described herein.

[0055] Generally, during a medical procedure, the end effector 328 contacts anatomical tissue, which can cause forces in the X, Y, or Z directions to be applied to the end effector 328 and can cause torques, such as, for example, Figure 4C the torque M about the y-direction axis as shown Y。In some embodiments, one or more strain sensors (not shown), which may be strain gauges, may be included in the medical device 326 to measure strain that can be used to determine forces applied to the end effector 328 in the X and Y axis directions. These X and Y axis forces are transverse (e.g., perpendicular) to the Z axis (which is parallel or collinear with the central axis of the shaft).

[0056] The force sensor unit 340 (and any force sensor unit described herein) can be used to measure the (one or more) axial forces (i.e., in the Z axis direction parallel to the central axis of the shaft) applied to the end effector 328. For example, an axial force applied to the end effector 328 in the Z axis direction may cause the shaft 310 to undergo axial displacement in the direction of the central axis C-A of the shaft 310. The axial force can be in the proximal direction (e.g., a reaction force generated by pushing tissue with the end effector), or it can be in the distal direction (e.g., a reaction force generated by pulling the grasped tissue with the end effector). As described herein, the shaft 310 can be coupled to the mechanical structure 322 via a biasing mechanism (e.g., a spring member) such that the amount of travel of the shaft 310 relative to the mechanical structure 322 can be correlated with the magnitude of the axial force applied to the end effector 328. In this way, measuring the distance that the shaft 310 moves relative to the mechanical structure 322 can be used to determine the axial force.

[0057] In some embodiments, the force sensor units described herein can include any suitable components to isolate the axial movement of the shaft (i.e., to constrain the shaft such that the measured movement is caused only by the axial force and not by transverse forces along the X and Y axes), and to limit the frictional force opposing the movement of the shaft (which may cause errors in determining the axial force). In some embodiments, the force sensor unit can include a coil assembly and a microprocessor.

[0058] As described herein, the coil assembly of the force sensor unit measures displacement along the z-axis and then converts this displacement into a force measurement. The coil assembly can include two inductive coils, each wound around a cylinder formed of a non-conductive material (e.g., PEEK). The two coils can be coaxially positioned relative to each other and coupled to or within a mechanical structure. In some embodiments, a rod is movable within the interior of the coils and is coupled to the instrument shaft of the medical device. In an alternative embodiment, the medical device may not include a rod, but rather the proximal portion of the instrument shaft is movable within the coils. The rod can include, for example, a core having a magnet coupled thereto, and the core moves with the rod within the coaxial coils. The core can be, for example, a glass core, a stainless steel core, or a core formed of another suitable material. The magnet and any magnet described herein can be, for example, a ferrite bead, an EMI suppression bead, a nickel-zinc bead, or any other suitable material. Thus, in another aspect, it should be understood that the term "magnet" as used herein can refer to any component or material coupled to a core that can be used to provide a signal indicative of the position of the core within the coils when the rod and core move within the coils. The rod is operably coupled to the shaft such that when the shaft moves axially due to a force applied to the distal end of the medical device, the rod moves with the shaft and within the coils. As the rod moves within the inductive coils, the inductance of each coil changes, which can be used to measure the change in the position of the instrument shaft. As described above, the change in the position of the shaft can be translated into a z-axis force measurement.

[0059] During use of the medical device, when a force is applied to the shaft in the z-direction, the shaft will travel along the z-axis, which in turn causes the rod to move along the z-axis. As the rod moves within the coils, each coil generates a signal associated with the position of the magnet on the rod within the coils. The microprocessor receives the signals from the coils. For example, in some embodiments, each coil generates a signal associated with the linear displacement of the shaft along the central axis of the shaft (e.g., along the z-axis). In some embodiments, the signals from the coils can include a first signal having a first frequency from the first coil and a second signal having a second frequency from the second coil. The microprocessor is configured to execute instructions to determine a measure of the force on the shaft along the central axis of the shaft based on the first frequency and the second frequency. Further details regarding the operation and interaction of the microprocessor are described below with reference to Figure 7 describe further details regarding the operation and interaction of the microprocessor.

[0060] Figures 5A - 5H illustrates the components of an example axial force sensor unit embodiment that can be included within a medical device. Since the components in the illustrated configuration can use some of the same materials, the component numbers in Figure 5A and Figure 5B are used in Figures 5C - 5H herein. Figure 5AA dual coil 545 is shown, which has a first coil 546 displaced from a second coil 548, where the first coil 546 and the second coil 548 are fixed to a tube 547. Each of the first coil 546 and the second coil 548 is made of a conductive material such as that of an antenna coil. These two conductive coils, namely the first coil 546 and the second coil 548, can be coaxially wound around the tube 547. The tube 547 can be a plastic tube, such as but not limited to a polyetheretherketone (PEEK) plastic tube for low-dimensional variations and temperature. The first coil 546 and the second coil 548 can be coated with silicone. Using a silicone coating on the coils allows the coils to remain substantially unaffected by high-pressure steam cleaning (withstand high-pressure steam cleaning).

[0061] The tube 547 can be coupled to a proximal mechanical structure, to which or within which an axial force sensor unit is coupled. Since the tube 547 is coupled to the mechanical structure, the first coil 546 is further away from the distal end of the instrument axis to which the axial force applied thereto is to be measured than the second coil 548. Thus, in the dual coil arrangement, the first coil 546 is the proximal coil and the second coil 548 is the distal coil. The proximal coil 546 has leads 546-1 and 546-2, which can be coupled to a capacitor to form part of an LC circuit, and this part can be coupled to a precision dual-inductance sensor that measures the inductance of this LC circuit. The distal coil 548 has a lead 548-1 and another lead (not shown), and the lead 548-1 and the other lead can be coupled to another capacitor to form part of another LC circuit, and this part can be coupled to a precision dual-inductance sensor that can effectively measure the inductance of this other LC circuit.

[0062] Figure 5B An arrangement 550 is shown having a rod 554 and a magnet 552 on the rod 554, which can be used with Figure 5A the dual coil 545. The rod 554 can also be referred to as a bar. Since the magnet 552 is a relatively small structure, the arrangement 550 can be referred to as a magnet-on-rod or a bead-on-rod. The rod 554 has a proximal portion, a distal portion, and a central axis, where the central axis extends between the proximal portion and the distal portion. The rod 554 can be, for example, a fiberglass rod or a stainless steel rod, but other embodiments can also be used. For example, the rod 554 can include materials such as but not limited to quartz, glass, silica, ceramic, and alumina. For example, these other materials for the rod 554 can be used in the arrangements discussed with respect to Figures 5A - 9 The magnet 552 can be disposed on the distal portion of the rod 554. The magnet 552 can be a ferrite structure, which can be implemented as a ferrite magnetic bead. The ferrite magnetic bead on the rod can be connected to the proximal end of the instrument axis whose axial force is to be sensed.

[0063] Figure 5C An embodiment is shown that illustrates an example of a magnet and a rod implemented with a dual coil. Figure 5B The configuration 550 can be implemented with Figure 5A a dual coil. The magnet 552 on the rod 554 can be inserted into the tube 547, and the proximal coil 546 and the axial coil 548 are coaxially wound around the tube 547. The magnet 552 can be a ferrite structure. The two conductive coils, the proximal coil 546 and the distal coil 548, can be coaxially wound around the tube 547. The tube 547 can be a plastic tube, such as but not limited to a polyetheretherketone (PEEK) plastic tube. The proximal coil 546 and the distal coil 548 can be coated with silicone.

[0064] The rod 554 can move within the proximal coil 546 and the distal coil 548; wherein the magnet 552 is disposed on the proximal portion of the rod 554. The magnet 552 can have such dimensions along the central axis of the rod 554 that are sized such that the magnet 552 can extend within a portion of the proximal coil 546 and within a portion of the distal coil 548 simultaneously. The magnet 552 can be disposed at an initial position centered along the z-axis between the distal coil 546 and the proximal coil 548. This initial position can be a position where no axial force is applied to the instrument shaft to which the rod is attached. This initial position can provide a zero reference that can be used to determine the distance by which the instrument shaft moves in response to a force applied to the distal end of the instrument shaft. The initial position can be a position corresponding to the center of the magnet 552 centered between the distal coil 546 and the proximal coil 548, wherein the magnet 552 extends within a portion of the proximal coil 546 and within a portion of the distal coil 548. In various embodiments, the initial position serving as the zero reference can be different from the magnet 552 centered between the distal coil 546 and the proximal coil 548. For example, the initial position can depend on the characteristics of the distal coil 546 and the proximal coil 548 along with the corresponding capacitors to which the distal coil 546 and the proximal coil 548 are coupled relative to the measurement arrangement.

[0065] The instrument shaft to which the rod 554 is attached can be coupled to a mechanical structure through a spring member ( Figures 5A - 5C not shown in). When a force is applied in the z-direction (see, for example, Figure 5C ) along the central axis of the instrument shaft to the distal end of the instrument shaft, the spring member is displaced in proportion to the force applied to the distal end of the instrument shaft. In the case where the distal coil 546 and the proximal coil 548 are coupled to a precision dual inductance sensor, the movement of the magnet 552 on the rod 554 within the tube 547 relative to the distal coil 546 and the proximal coil 548 can be detected. This detection can be based on the movement of the magnet 552 relative to the initial position.

[0066] The dual coils in the axial force sensor unit can be configured in various ways with respect to the instrument shaft to measure the axial force on the instrument shaft. For example,Figure 5D An embodiment showing an example of a magnet implemented with a dual coil is shown, where the magnet 552 is disposed at the proximal end of the instrument shaft 510 rather than on a rod (such as rod 554). The instrument shaft 510 may be coupled to a proximal mechanical structure via a spring member 560 such that the displacement of the spring member 560 is proportional to the force applied to the instrument shaft 510 in the direction along the central axis. Figure 5D The use of the dual coil may be similar to Figure 5C the use of the dual coil. The spring member 560 may also be configured in a different arrangement than Figures 5C - 5G shown.

[0067] The proximal end of the instrument shaft 510 may be used as Figure 5C the rod 554. The proximal end of the instrument shaft 510 with the magnet 552 thereon may extend through a dual winding consisting of a proximal coil 546 and a distal coil 548 in a tube 547 such that there is an air gap between the instrument shaft 510 with the magnet 552 disposed thereon and the tube 547 around which the dual coil is wound. When "at rest", in the absence of an axial (z - direction) force applied to the instrument shaft 510, the instrument shaft 510 may be axially positioned such that the magnet 552 is partially disposed within each coil. In some embodiments, with no z - direction force applied to the instrument shaft 510, equal portions of the magnet 552 may be disposed within each coil. Each coil 546 and 548 may be coupled to a separate LC circuit in which the coil acts as an inductor (L), and the inductance varies with the amount of magnetic material contained within the respective coil. The resonant frequency of each circuit varies as the inductance of the corresponding circuit changes.

[0068] Figure 5E An embodiment showing an example of a magnet implemented with a dual coil is shown, where the magnet 552 is disposed at the proximal end of the rod 554. The rod 554 may be attached to the instrument shaft 510, which may be coupled to a mechanical structure via a spring member 560 such that the displacement of the spring member 560 is proportional to the force applied to the instrument shaft 510 in the direction along the central axis. The rod 554 may be configured to be attached to the instrument shaft 510, where the rod 554 is inserted into the instrument shaft 510. Figure 5E The use of the dual coil may be similar to Figure 5C the use of the dual coil.

[0069] The proximal end of the rod 554 with the magnet 552 thereon can extend through the dual windings of the proximal coil 546 and the distal coil 548 in the tube 547, such that there is an air gap between the rod 554 with the magnet 552 disposed thereon and the tube 547 with the dual coils wound thereon. As the instrument shaft 510 moves, the rod 554 moves axially. When "at rest", without an axial (z-direction) force applied to the instrument shaft 510, the rod 554 attached to the instrument shaft 510 can be axially positioned such that the magnet 552 is partially disposed within each coil. In some embodiments, equal portions of the magnet 552 can be disposed within each coil without a z-direction force applied to the instrument shaft. Each coil can be coupled to a separate LC circuit, in which the coil serves as an inductor (L), and the inductance varies with the amount of magnetic material contained in the corresponding coil. The resonant frequency of each circuit varies with the change in the inductance of the corresponding circuit.

[0070] Figure 5F An embodiment is shown that illustrates an example of the magnet 552 implemented with dual coils, where the magnet 552 is disposed on the proximal end of the rod 554. The rod 554 can be attached to the instrument shaft 510, where the instrument shaft 510 can be coupled to a component 523 of the mechanical structure via a spring member 560 such that the displacement of the spring member 560 is proportional to the force applied to the instrument shaft 510 in the direction along the central axis. The rod 554 can be configured to be attached to the instrument shaft 510 using a support base 555 to secure the rod 554 to the instrument shaft 510. The central axis of the rod 554 can be aligned in a direction parallel to the central axis of the instrument. In the case where the rod 554 is attached to the instrument shaft 510 via the support base 555, as the instrument shaft 510 moves in its axial direction, the rod 554 moves in the axial direction parallel to the central axis of the instrument shaft 510. Figure 5F The use of the dual coils can be similar to Figure 5C the use of the dual coils.

[0071] The proximal end of the rod 554 with the magnet 552 thereon can extend through the dual windings of the proximal coil 546 and the distal coil 548 in the tube 547, such that there is an air gap between the rod 554 with the magnet 552 disposed thereon and the tube 547 with the dual coils wound thereon. When "at rest", without an axial (z-direction) force applied to the instrument shaft 510, the rod 554 attached to the instrument shaft 510 can be axially positioned such that the magnet 552 is partially disposed within each coil. In some embodiments, equal portions of the magnet 552 can be disposed within each coil without a z-direction force applied to the instrument shaft. Each coil can be coupled to a separate LC circuit, in which the coil serves as an inductor (L), and the inductance varies with the amount of magnetic material contained in the corresponding coil. The resonant frequency of each circuit varies with the change in the inductance of the corresponding circuit.

[0072] The dual coils and magnets can be arranged with the instrument shaft in other configurations. For example, the proximal coil 546 and the distal coil 548 can be fixed to the movable instrument shaft 510, where the magnet 552 is coupled to the stationary rear-end component 523 of the proximal mechanical structure, and the instrument shaft is coupled to the proximal mechanical structure through a spring 560, as Figure 5G shown. In another example, the coils 546 and 548 of the dual-coil configuration on the tube 547 can be relatively farther apart than the coils used in the Figures 5C - 5F configuration, where two magnets 552-1 and 552-2 are on the rod 547, as Figure 5H shown, with one magnet 552-1 close to the proximal coil 546 and the other magnet 552-2 close to the distal coil 548. Additionally, any of the dual-coil / magnet arrangements described herein can be coupled to the instrument shaft and / or within the proximal mechanical structure using any suitable linkage device, such as those shown and described in U.S. Provisional Patent Application No. 63 / 077,833, entitled "Devices and Methods for Compact, Redundant Inductive Force Sensor", which is incorporated by reference as described above.

[0073] Figure 6A The proximal mechanical structure 622 is shown, which can be coupled to the instrument shaft 610 as discussed with respect to Figures 5A - 5H . The mechanical structure 622 includes a dual coil 645 for measuring the axial force applied to the distal end of the instrument shaft 610. Figure 6B The mechanical structure 622 of Figure 6A is shown, where the dual coil 645 has a rod 647 inserted therein, and the rod 647 is fixed to the support base 655 to be coupled to the Figure 6A instrument shaft 610.

[0074] Figure 7 is a block diagram of an embodiment of an exemplary force sensor 700 that can be implemented to measure the axial force applied to the instrument shaft. The force sensor 700 can be arranged as an inductive z-axis force sensor. The axial force on the instrument shaft causes axial movement of the instrument shaft, which can be detected by the force sensor 700. The force sensor 700 can include antenna coils 746 and 748, where a magnet such as a magnetic bead 752 is on the rod 754. According to the present disclosure in relation to Figures 5A - 5H and Figures 6A - 6BIn any of one or more associated teachings, antenna coil 746 and antenna coil 748 can be configured as a proximal coil and a distal coil positioned coaxially relative to each other, where the magnet is on the shaft. In some embodiments, as described herein, the magnet is coupled to the instrument shaft instead of the shaft.

[0075] Antenna coil 746 can be coupled to multi-channel frequency detection 765 through capacitor C. Capacitor C can form an LC circuit with antenna coil 746, where the inductance contribution is based on the distance that magnetic bead 752 moves within antenna coil 746. Antenna coil 748 can be coupled to multi-channel frequency detection 765 through capacitor C. Capacitor C can form an LC circuit with antenna coil 748, where the inductance contribution is based on the distance that magnetic bead 752 moves within antenna coil 746. The LC circuits associated with antenna coil 746 and antenna coil 748 can be implemented with different capacitances, and such differences are taken into account. Since magnetic bead 752 is closer to antenna coil 746 than to antenna coil 748, the inductance contribution to the LC circuit associated with antenna coil 746 is greater than the inductance contribution to the LC circuit associated with antenna coil 748. That is, since magnetic bead 752 is centered within antenna coils 746 and 748, when magnetic bead 752 axially moves along the instrument shaft, the inductance of one coil increases while the inductance of the other coil decreases. The difference in the inductor values indicates the change in the force on the shaft. For these two coils, the temperature change, long-term aging, and burn interference pickup of the inductor are the same. Taking the difference cancels out these effects.

[0076] Multi-channel frequency detection 765 can be implemented as a precision dual-inductance sensor for measuring inductance. Since capacitor C forms an LC circuit with antenna coil 746 input to multi-channel frequency detection 765, multi-channel frequency detection 765 can output a first signal associated with the frequency of this circuit, such as the ratio of this frequency to a known reference frequency. Since capacitor C forms an LC circuit with antenna coil 748 input to multi-channel frequency detection 765, multi-channel frequency detection 765 can output a second signal associated with the frequency of this circuit, such as the ratio of this frequency to a known reference frequency. Multi-channel frequency detection 765 can output N digital signals to microprocessor 770. For two LC circuits, multi-channel frequency detection 765 can output two digital signals to microprocessor 770.

[0077] The microprocessor 770 may include or have access to an EEPROM 772 or other storage device that may include calibration values for implementing the magnetic beads 752 using the antenna coils 746 and 748. When determining the axial force on the instrument axis, the calibration values may be accessed to determine the distance of movement based on the frequencies received from the multi-channel frequency detection 765. The frequency difference may be stored in the EEPROM 772 as an inductance difference according to the distance. This distance difference may be cross-correlated with the reference position and the inductance difference. Using the distance selected from the measured inductance difference, this distance may be used with the spring constant stored in the EEPROM 772, where the spring constant is a property of the spring through which the instrument axis is coupled to the proximal mechanical structure on which the force sensor 700 may be deployed.

[0078] The force sensor 700 may include other components. For example, the microprocessor 770 may include a Universal Asynchronous Receiver / Transmitter (UART) interface 774 or other communication interface to transmit (TX) digital outputs and receive (RX) digital signals. The received signals may be used to update the calibration values in the EEPROM 772 of the microprocessor 770. A common-mode choke 780 may be used to reduce interference with other boards of the mechanical structure on which the force sensor 700 is deployed. Optionally, the force sensor 700 may include a magnet 762 located between the common-mode choke 780 and the microprocessor 770. The magnet 762 may be inserted to help reduce electromagnetic interference (EMI) radiation. The magnet 762 may be implemented as a ferrite bead. Other magnetic material formats may be implemented for the magnet 762.

[0079] Figures 8A - 8C The measured values of the inductance of the magnet target and two coils are shown compared to the target position, and the value of the axial force on the instrument axis is shown, which causes a small movement (±0.025 inches) of the axis relative to the mechanical structure. The target of the axis displacement (also known as the target position) is ±0.025 inches. Figure 8A It is a graph of the difference between two inductances labeled L3 and L2 compared to the position of the ferrite bead, and the ferrite bead position is attached to a micrometer. Curve 862 is the measured difference between the two inductances L3 and L2. Curve 861 is the ideal difference between the two inductances L3 and L2. The two vertical lines 863 and 864 represent distances of -0.025 inches and +0.025 inches from the center position of the bead, respectively.

[0080] Figure 8BIt is shown that for the difference in inductance compared to the micrometer (bead) position, the difference L3 - L2 is almost a straight line. Such measured values can be used to define the operating range from the sensor to the linear signal, since subtraction only works in the linear region. However, when the two coils drift equally and independently of temperature, the dual - coil method can also work, which can eliminate the use of subtraction of one from the other. Curve 872 is the measured difference between the two inductances L3 and L2. Curve 871 is the ideal difference between the two inductances L3 and L2. The two vertical lines 873 and 874 represent distances of - 0.025 inches and + 0.025 inches from the center position of the bead, respectively.

[0081] Figure 8C A plot of the inductances L3 and L2 versus the micrometer (bead) position is shown. Curve 876 is the measured inductance L3. Curve 878 is the measured inductance L2.

[0082] Figure 9 It is a flowchart of the characteristics of an embodiment of an example method 900 for determining axial force. At 910, a first signal having a first frequency is received at an electronic signal frequency detector from a proximal coil fixed to a proximal mechanical structure. At 920, a second signal having a second frequency is received at the electronic signal frequency detector from a distal coil fixed to the proximal mechanical structure and coaxial with the proximal coil. A rod movable within the proximal coil and the distal coil is used to provide the first frequency and the second frequency, wherein the rod has a magnet disposed on the proximal portion of the rod. The rod has a proximal portion, a distal portion, and a central axis, where the central axis extends between the proximal portion and the distal portion.

[0083] At 930, the first frequency and the second frequency are determined. At 940, the first frequency and the second frequency are used to determine a measure of the axial force on the instrument axis to which the rod is attached. Using the first frequency and the second frequency to determine a measure of the axial force on the instrument axis can include using the first frequency and the second frequency to determine the axial displacement of a spring member through which the instrument axis is coupled to the proximal mechanical structure.

[0084] Variations of method 900 or methods similar to method 900 may include multiple different embodiments that may be combined depending on the application of these methods and / or the architecture of the system in which these methods are implemented. Such methods may include converting a first frequency and a second frequency into a first inductance and a second inductance; and using the difference between the first inductance and the second inductance to generate an identification of a change in the force on the instrument axis. Such measurements can be used in the operating range from the sensor to the linear signal, since subtraction only works in the linear region. However, the dual-coil method can also work when the two coils drift equally and are temperature-independent, which can eliminate the use of subtraction of one from the other. The change in force is a measure of the axial force on the distal portion of the instrument axis to which the rod is attached. Since force is bidirectional, the measure of the axial force on the distal portion of the instrument axis is bidirectional.

[0085] Variations of method 900 or methods similar to method 900 may include: converting a first frequency and a second frequency into a first inductance and a second inductance; using the first inductance and the second inductance for a proximal coil and a distal coil to generate an identification of a change in the force on the instrument axis, the proximal coil and the distal coil being configured as equally-drifting temperature-independent coils.

[0086] A machine-readable storage device may include any non-transitory mechanism for storing information in a machine-readable form, such as, for example, a computer or a microprocessor, the task of which is to perform a specific function. For example, a machine-readable storage device may include a read-only memory (ROM), a random-access memory (RAM), a disk storage medium, an optical storage medium, a flash device, and other storage devices and media. In various embodiments, the non-transitory machine-readable medium may include instructions that, when executed by a set of processors, may cause the system to perform operations including: receiving, at an electronic signal frequency detector, a first signal having a first frequency from a proximal coil fixed to a mechanical structure; receiving, at the electronic signal frequency detector, a second signal having a second frequency from a distal coil fixed to the mechanical structure and coaxial with the proximal coil, wherein a rod is movable within the proximal coil and the distal coil, the rod having a proximal portion, a distal portion, and a central axis extending between the proximal portion and the distal portion, the rod having a magnet disposed on the proximal portion of the rod; determining the first frequency and the second frequency; and using the first frequency and the second frequency to determine a measure of the axial force on the instrument axis to which the rod is attached. In various embodiments, the non-transitory machine-readable medium may include instructions that, when executed by a set of processors, cause the system to perform operations including the features of method 900 or a similar method, and may include performing and associating functions associated with Figures 1 - 8C associated features.

[0087] In various embodiments, the system may include: an axial force transducer, wherein the axial force transducer includes a mechanical structure; a proximal coil fixed to the mechanical structure; a distal coil fixed to the mechanical structure, the distal coil being coaxial with the proximal coil; a rod having a proximal portion, a distal portion, and a central axis, the central axis extending between the proximal portion and the distal portion, the rod being movable within the proximal coil and the distal coil; a magnet disposed on the proximal portion of the rod; and an electronic signal detector for detecting a first signal from the proximal coil and a second signal from the distal coil. The electronic signal detector may be implemented as an electronic signal frequency detector to detect a first frequency of the first signal from the proximal coil and a second frequency of the second signal from the distal coil. The axial force transducer may be implemented as a system.

[0088] Variations of such a system may include a number of different embodiments that may be combined depending on the manner in which the system is designed. Such a system may include a magnet having a dimension along the central axis that is sized such that the magnet extends within a portion of the proximal coil and within a portion of the distal coil simultaneously. Such a system may include a magnet disposed at an initial position centered between the distal coil and the proximal coil.

[0089] Such a system may include a rod attachable to an instrument shaft, wherein the instrument shaft is coupled to the mechanical structure by a spring member for displacement proportional to a force applied to the instrument shaft in a direction along the central axis. The central axis of the rod may be configured in a direction parallel to the central axis of the instrument shaft. Such a system may include a rod that is a fiberglass rod, but other materials may be used for the rod. Such a system may include the axial force transducer according to claim 1, wherein the magnet disposed on the proximal portion of the rod is a ferrite structure.

[0090] Such a system may include a proximal coil and a distal coil coaxial wound around a plastic tube, but other materials may be used. The plastic tube may be a polyetheretherketone tube.

[0091] Such a system may include an axial force sensor having a microprocessor coupled to receive the first frequency of the first signal and the second frequency of the second signal, wherein the microprocessor is configured to determine a measure of the axial force on the distal portion of the instrument shaft to which the rod is attached based on the first frequency and the second frequency.

[0092] In various embodiments, an axial force transducer can include: a mechanical structure; a shaft having a proximal portion, a distal portion, and a central axis extending between the proximal portion and the distal portion; a spring member operatively coupled to the mechanical structure for displacement in proportion to a force applied to the shaft in a direction along the central axis; a proximal coil fixed to the mechanical structure; a distal coil fixed to the mechanical structure and coaxial with the proximal coil; a magnet disposed on the proximal portion of the shaft, wherein the magnet has a dimension along the central axis sized such that the magnet extends within a portion of the proximal coil and within a portion of the distal coil simultaneously; wherein the shaft extends within the proximal coil and the distal coil such that at least a portion of the magnet extends within at least one of the proximal coil and the distal coil; and an electronic signal frequency detector for detecting the frequency of an electrical signal within at least one of the proximal coil and the distal coil in which the magnet extends.

[0093] In various embodiments, an instrument having an axial force transducer can include: an instrument shaft; a mechanical structure; a spring member for coupling the instrument shaft to the mechanical structure for displacement in proportion to a force applied to the instrument shaft in a direction along the central axis; a proximal coil fixed to the mechanical structure; a distal coil fixed to the mechanical structure and coaxial with the proximal coil; a rod having a proximal portion, a distal portion, and a central axis extending between the proximal portion and the distal portion, the rod movable within the proximal coil and the distal coil; a magnet disposed on the proximal portion of the rod; and an electronic signal detector for detecting a first signal from the proximal coil and a second signal from the distal coil. The electronic signal detector can be implemented as an electronic signal frequency detector to detect a first frequency of the first signal from the proximal coil and a second frequency of the second signal from the distal coil.

[0094] Variations of such an instrument can include many different embodiments that can be combined depending on the manner of implementing the design of such an instrument. Such an instrument can include a magnet having a dimension along the central axis sized such that the magnet extends within a portion of the proximal coil and within a portion of the distal coil simultaneously.

[0095] Such an instrument can include a rod connected to the instrument shaft. The central axis of the rod can be in a direction parallel to the central axis of the instrument shaft.

[0096] Such an instrument may include a microprocessor coupled to receive a first frequency of a first signal and a second frequency of a second signal, wherein the microprocessor is configured to use the first frequency and the second frequency to determine a measure of an axial force on a distal portion of an instrument axis to which the stem is attached. The instrument may include a common-mode choke coupled to the microprocessor to reduce interference in determining the measure of the axial force. Such an instrument may include an additional magnet, wherein the additional magnet is disposed between the common-mode choke and the microprocessor to help reduce electromagnetic interference radiation. The additional magnet may include a ferrite bead.

[0097] Although specific embodiments have been illustrated and described herein, those of ordinary skill in the art will understand that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. Various embodiments utilize arrangements and / or combinations of the embodiments described herein. It should be understood that the foregoing description is intended to be illustrative and not restrictive, and the words or terms used herein are for the purpose of description. After studying the foregoing description, those skilled in the art will appreciate the combination of the above embodiments and other embodiments.

Claims

1. A device, comprising: a mechanical structure and a force sensor unit coupled to the mechanical structure; wherein the force sensor unit includes a rod, a magnet coupled to the rod, a first coil coupled to the mechanical structure, and a second coil coupled to the mechanical structure and coaxial with the first coil; wherein the rod includes a distal portion and a proximal portion, and a central axis of the rod is defined between the proximal portion and the distal portion of the rod; and wherein the magnet translates along the central axis of the rod within the first coil and the second coil.

2. The device according to claim 1, wherein: the device further includes a shaft coupled to the mechanical structure; and the shaft is operably coupled to the rod such that a translational movement of the shaft relative to the mechanical structure causes the rod to move along the central axis of the rod.

3. The device according to claim 2, wherein: the shaft includes a proximal end and a distal end; a central axis of the shaft is defined between the proximal end and the distal end of the shaft; and the shaft is coupled to the mechanical structure such that a linear displacement of the shaft along the central axis of the shaft is proportional to a force applied to the shaft in a direction along the central axis of the shaft.

4. The device according to claim 3, wherein: the central axis of the rod is in a direction parallel to the central axis of the shaft.

5. The device according to claim 2, wherein: the shaft includes a proximal end and a distal end; a central axis of the shaft is defined between the proximal end and the distal end of the shaft; a first signal generated by the first coil is associated with a position of the magnet relative to the first coil, and a second signal generated by the second coil is associated with a position of the magnet relative to the second coil; and the first signal from the first coil and the second signal from the second coil are associated with a linear displacement of the shaft along the central axis of the shaft.

6. The device according to claim 5, wherein: the linear displacement of the shaft is proportional to a force applied to the shaft in a direction along the central axis of the shaft.

7. The device according to claim 2, wherein: the shaft includes a proximal end and a distal end; a central axis of the shaft is defined between the proximal end and the distal end of the shaft; the device further includes a spring coupled to the shaft; and the spring is configured to displace in proportion to a force applied to the shaft in a direction along the central axis of the shaft.

8. The device according to claim 2, wherein: a first signal generated by the first coil is associated with a position of the magnet relative to the first coil, and a second signal generated by the second coil is associated with a position of the magnet relative to the second coil; and the force sensor unit includes a microprocessor coupled to receive the first signal and the second signal.

9. The device according to claim 8, wherein: the first signal has a first frequency; the second signal has a second frequency different from the first frequency; and The microprocessor is configured to execute instructions to determine a linear displacement of the axis along a central axis of the axis based on the first frequency and the second frequency.

10. The apparatus according to claim 1, wherein: the magnet includes a first magnet and a second magnet; the first magnet is positioned to move within the first coil, and the second magnet is positioned to move within the second coil.

Images