Self-contained electromagnetic tracking unit

Abstract

An electromagnetic tracking system includes a magnetic transmitter configured to output a magnetic field, a receiver responsive to the magnetic field, an electronic component having a conductive element that causes distortion of the magnetic field, and an output mechanism configured to output a position of the receiver relative to the magnetic transmitter, wherein the magnetic emitter has at least one winding arranged around a hollow ferromagnetic core made of an electrically conductive material through which an electric current is passed by the electronic device, and wherein the electronic component is at least partially contained within a hollow portion of the hollow ferromagnetic core. A method of manufacture includes shaping a wall into a hollow shell to enclose an electronic component, covering the hollow shell with a ferromagnetic material, inserting the wrapped hollow shell into a plastic bobbin, and winding the plastic bobbin with a coil wire to produce three orthogonal windings.

Description

[0001] This application is a divisional application of the Chinese invention patent application with application number 202080013914.5, application date January 7, 2020, and invention name “Self-contained electromagnetic tracking unit”.

[0002] Priority claim

[0003] This application claims the benefit of U.S. Patent Application Serial No. 16 / 242,765, filed on January 8, 2019. The entire contents of the aforementioned U.S. Patent Application are hereby incorporated by reference. Technical Field

[0004] The present invention relates to a self-contained electromagnetic tracking unit. Background Art

[0005] To increase the field strength, the wire coils used in electromagnetic (EM) tracking systems are wrapped around a ferromagnetic core. The resulting assembly is heavy and requires separate connections to external drive circuits and signal processing. Summary of the invention

[0006] The electronics in an EM tracking unit must be shielded from the magnetic fields generated by the windings of wire (or coils) arranged around its ferromagnetic core. New lightweight core materials have become available that allow the EM unit to eliminate the core, or even be completely hollow. The EM tracking unit transmitter described herein takes advantage of the empty space now available inside the core to contain all the necessary drive circuitry for the coils. The coil drive circuitry is contained within the core to achieve a smaller, lighter combined unit than previous units, while utilizing shielding from the ferromagnetic layer. The shielding reduces distortion of the magnetic field generated by the windings arranged around the hollow ferromagnetic core. This reduced distortion improves the accuracy of the position output by the electromagnetic tracker.

[0007] In some embodiments, an electromagnetic tracking system includes a magnetic transmitter configured to output a magnetic field, a receiver responsive to the magnetic field, an electronic component having a conductive element that causes distortion of the magnetic field, and an output mechanism configured to output the position of the receiver relative to the magnetic transmitter, wherein the magnetic transmitter has at least one winding arranged around a hollow ferromagnetic core composed of a conductive material, an electric current passes through the electronic component to cause the electric current to flow through the ferromagnetic core, and wherein the electronic component is at least partially contained within a hollow portion of the hollow ferromagnetic core.

[0008] Embodiments may include one or more of the following features. An electronic component is completely contained within the hollow portion of the hollow ferromagnetic core. The hollow ferromagnetic core includes a flexible ferromagnetic material. The flexible ferromagnetic material includes a fabric. The ferromagnetic core includes an adhesive layer and a backing layer attached to the fabric. The electronic component is printed on a flexible circuit, which is contained within the hollow portion of the ferromagnetic core. A plastic bobbin surrounds the flexible circuit. The flexible circuit has a folding feature that allows the flexible circuit to be folded into a rectangular parallelepiped shape. The folding feature defines a wall portion and a central support portion. The central support portion is configured to rest on two wall portions. The hollow ferromagnetic core includes a rigid ferromagnetic material. The rigid ferromagnetic material is a formed ferrite. The rigid ferromagnetic material is a sintered ferrite / adhesive composite.

[0009] In some embodiments, a method of manufacturing a magnetic transmitter includes forming a wall into a hollow shell to surround an electronic component, covering the hollow shell with a ferromagnetic material, inserting the wrapped hollow shell into a plastic bobbin, and winding the plastic bobbin with coil wire to produce three orthogonal windings.

[0010] Implementations may include one or more of the following features. The wall includes a flexible circuit that includes electronic components, and forming the wall includes folding the flexible circuit into a portion including a central portion and four wall portions. Forming the wall into a hollow shell includes supporting an edge of the central portion between two wall portions. Forming the wall into a hollow shell includes folding the flexible circuit, wherein the electronic components on one side of the flexible circuit face the interior of the hollow shell. Forming the hollow shell circuit includes folding the flexible circuit into a cuboid shape. Covering the hollow shell includes wrapping a rigid sintered ferrite material around the hollow shell.

[0011] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1A is an exemplary embodiment of an electromagnetic tracking (EMT) system.

[0013] Figure 1B Another example of an EMT system is shown.

[0014] Figure 2 is used for Figure 1A and Figure 1B Assembly of a self-contained tracking unit of the EMT system.

[0015] Figure 3A-3B is used for Figure 2 A view of the flexible circuit of the unit.

[0016] Figures 4A-4C It is used to manufacture Figure 2 Steps for a self-contained tracking unit.

[0017] Figure 5 is shown for manufacturing Figure 2 Flowchart of the steps of a self-contained tracking unit.

[0018] Like reference numbers in the various drawings indicate like elements. DETAILED DESCRIPTION

[0019] Electromagnetic tracking (EMT) systems can be used in gaming and / or surgical devices to track devices (e.g., game controllers, head-mounted displays, medical equipment, robotic arms, etc.), allowing users of the system to know the three-dimensional position and orientation of the devices. Augmented reality (AR) and virtual reality (VR) systems also use EMT systems to perform head, hand, and body tracking, for example, to synchronize the user's movements with AR / VR content. Such EMT systems use magnetic transmitters close to magnetic sensors to determine the position and / or orientation of the sensors relative to the transmitters. The sensors used in such systems provide accurate position and orientation information to medical professionals.

[0020] Figure 1A 1 is an exemplary embodiment of an EMT system 100 that can be used, for example, for image-guided medical procedures performed on a patient 102. The system 100 can include a freely movable medical instrument 104, which can include any form of surgical tools and equipment used in medical treatment. The system 100 allows for the targeting of anatomical organs, structures, blood vessels, etc. for visualization, diagnosis, intervention, etc.

[0021] The apparatus used in the EMT system 100 may include one or more magnetic sensors including one or more coils. For example, the apparatus 104 may include a three-axis sensor 106 including a set of concentric, juxtaposed sensor coils. The sensor 106 may be embedded in a channel, fixed to the tip of the apparatus 104, etc. The specific sensor used by the system 100 may be determined by the type of procedure and / or the measurement performance requirements. The sensor 106 is connected to a computing device (e.g., a computer 108).

[0022] Under control of the circuitry for energizing the magnetic field, the sensor 106 measures its instantaneous position (x, y, z) and orientation angles (azimuth, altitude, roll) in three-dimensional space with reference to the transmitter 110. As with the sensor 106, the particular transmitter 110 employed by the system 100 may be determined by the type of procedure, measurement performance requirements, etc. In some embodiments, the transmitter 110 may be a three-axis transmitter including a set of concentric, juxtaposed transmitter coils. The transmitter 110 is typically fixed in space beside, above, or below the patient or on medical equipment, where it serves as a spatial reference frame for the measurements provided by the sensor 106.

[0023] In some embodiments, the computer 108 is an imaging computer configured to provide imaging capabilities to the system 100. The imaging computer 108, which can communicate with the sensor 106 and the transmitter 110 by wire or wireless communication, is configured to store pre-acquired images or intraoperative images of the patient 102 in an image database. Such images can then be input into the imaging software for registration and visualization purposes. During the medical procedure, the three-dimensional position of the instrument 104 can be tracked relative to the anatomy of the patient 102, and the pre-acquired images or intraoperative images are presented in real time on the display of the computer 108. When the instrument 104 advances toward a target of interest in the patient 102, the transmitter 110 can be activated and energized, thereby generating electromagnetic signals sensed by the sensor 106 and represented as signals (e.g., voltage signals). These signals are processed and the three-dimensional position is calculated for transmission to the computer 108. In some embodiments, the computer 108 includes a guidance electronic unit configured to process the voltage signal to provide a three-dimensional position.

[0024] Figure 1B It shows that it can be used as a VR / AR or other system (e.g., such as Figure 1A Another example of an EMT system 120 that is part of a medical system or gaming system (such as a head mounted display (HMD) 122). The EMT system 120 includes a head mounted display (HMD) 122 that includes a magnetic sensor 132 and a controller 124 that includes a magnetic transmitter 134. The HMD 122 and the controller 124 are configured to track position and orientation in three-dimensional space relative to each other. For example, the transmitter 134 of the controller 124 is configured to track the sensor 132 of the HMD 122 relative to a reference frame defined by the position and orientation of the transmitter 134, or the sensor 132 of the HMD 122 is configured to track the transmitter 134 of the controller 124 relative to a reference frame defined by the position and orientation of the sensor 132. The specific sensors 132 and transmitters 134 employed by the EMT system 120 can be determined by the process it is being used for, the measurement performance requirements, etc.

[0025] The position and orientation of the HMD 122 and controller 124 may be tracked relative to each other within the tracking volume 126. Although the tracking volume 126 is shown as a defined space, it should be understood that the tracking volume 126 may be any three-dimensional space, including a dimensionless three-dimensional space (e.g., a large indoor and / or outdoor area, etc.).

[0026] In some embodiments, the transmitter 134 includes three orthogonally wound magnetic coils, referred to herein as x, y, and z coils. The current traveling through the three coils causes the coils to generate three orthogonal magnetic fields at three frequencies (e.g., three different frequencies) for FDM (frequency division multiplexing) applications, or to generate three pulses (e.g., three different time slots) for TDM (time division multiplexing) applications. The three frequencies can be three closely spaced frequencies, such as 34KHz, 34.25KHz, and 34.5KHz, but other frequencies may also or alternatively be used. In some embodiments, the coils can generate magnetic fields of the same frequency, but used, for example, in a TDM manner. The sensor 132 also includes three orthogonally wound magnetic coils, referred to herein as x, y, and z coils. In response to the magnetic field sensed by magnetic induction, a voltage is induced in the coils of the sensor 132. Each coil of the sensor 132 generates an electrical signal for each magnetic field generated by the coil of the transmitter 134; for example, the x-coil of the sensor 132 generates a first electrical signal in response to the magnetic field received from the x-coil of the transmitter 134, generates a second electrical signal in response to the magnetic field received from the y-coil of the transmitter 134, and generates a third electrical signal in response to the magnetic field received from the z-coil of the transmitter 134. The y and z-coils of the sensor 132 similarly generate electrical signals for each magnetic field received from each coil of the transmitter 134. The sensor may also include other sensing elements that measure magnetic fields, such as Hall effect elements, etc.

[0027] The data from the sensor 132 may be represented as a data matrix (e.g., a 3×3 matrix) that may be decomposed into the position and orientation of the sensor 132 relative to the transmitter 134, and vice versa. The electronic devices incorporated into the HMD 122 are configured to determine the position and orientation of the controller 124 relative to the HMD 122 based on the characteristics of the magnetic field generated by the transmitter 134 and the various electrical signals generated by the sensor 132. As described above, the computer system 128 may also be configured to determine the position and orientation of the sensor and / or transmitter.

[0028] Electronics within an EM tracking unit, such as transmitter 110 or transmitter 134, must be shielded from the magnetic field generated by the wire windings disposed around the core of the unit. New lightweight core materials have become available that allow the EM transmitter unit to be removed and even completely hollow. The EM transmitter described herein utilizes the empty space inside the core to contain all necessary drive circuitry for the surrounding coils. The coil drive circuitry is contained within the coil to achieve a smaller, lighter combined unit than previous units, and the coil drive circuitry is shielded using a ferromagnetic layer. The shielding reduces distortion of the magnetic field generated by the coils disposed around the hollow core. This reduced distortion improves the accuracy of the position output by the electromagnetic tracker.

[0029] Figure 2 A tracking unit 200 is shown that can be used as transmitter 110 or transmitter 134. Tracking unit 200 has a wall shaped as a shell surrounding a hollow core. The wall can be a flexible circuit 210 that is conductive and contains the electronic circuitry 214 (in Figure 3A and Figure 3B 2). The flexible circuit 210 is folded upon itself into a cuboid configuration to provide structural rigidity to the additional components surrounding the flexible circuit 210. These components include a ferromagnetic fabric material 220 covering the flexible circuit 210, which is inserted into a plastic bobbin 230 around which the coil wire 240 is wound. The coil wire 240 is terminated by soldering to an exposed portion 212 of the flexible circuit 210. The coil drive circuit 214 is thus contained within the coil wire 240 for a compact and lightweight unit.

[0030] refer to Figure 3A and Figure 3B , the flexible circuit 210 includes a first side 222 and a second side 224. The first side 222 may include folding features 226 that simplify folding of the flexible circuit 210 into a desired final (e.g., cuboid) shape. These folding features 226 may be, for example, etched lines or other reduced thicknesses that allow the flexible circuit 210 to bend along the folding features 226. In the example shown, the folding features 226 divide the flexible circuit 210 into at least five portions, including a central portion 216 and four wall portions 218. The second side 224 includes electronic circuitry 214 for signal transmission. In some examples, the exposed portion 212 of the flexible circuit 210 is attached to the ends of the four wall portions 218 opposite the central portion 216.

[0031] Figures 4A-4C Steps for forming a tracking unit 200 that can be used as transmitter 110 or transmitter 134 are shown. Figure 4AIn the embodiment of the present invention, the flexible circuit 210 is folded upon itself into a cuboid configuration. The second side 224 including the electronic circuit 214 is folded so that the circuit points toward the empty interior of the cube. The four wall portions 214 provide a support surface for additional components surrounding the flexible circuit 210. The central portion 216 is bent diagonally within the four wall portions 214 to provide additional structural rigidity.

[0032] exist Figure 4B , the ferromagnetic fabric material 220 is then placed around the folded flexible circuit 210 by wrapping the ferromagnetic fabric material 220 around the outside of the folded circuit (e.g., the first side 222 of the folded circuit, now facing outward from the core). The fabric material 220 can be wrapped around the circuit so that there is no gap or only a small gap remains between the inner core of the folded circuit and the outside of the fabric material.

[0033] The wrapped flexible circuit 210 is then inserted into the spool 230, Figure 4C The bobbin 230 holds the ferromagnetic material 220 in place around the flexible circuit 210. For low cost and ease of manufacturing, the bobbin can be made of plastic. The wall of the bobbin has a small thickness that is sufficient to hold the fabric in place and prevent the assembly from collapsing due to tension from the surrounding wires 240. In some examples, the order of steps can be modified, for example, the bobbin 230 can be placed directly around the flexible circuit 210 and then covered with the ferromagnetic fabric material 220. In such an arrangement, the ferromagnetic fabric material 220 is mounted to the outer surface of the bobbin 230.

[0034] Once the plastic bobbin 230 contains the wrapped flex circuit, the partially assembled unit is then wrapped with coil wire 240 to create three orthogonal windings and provide Figure 2 The construction shown. The thickness and number of windings of the coil wire are determined by the intended application of the tracking unit 200. The coil drive circuit 214 and its electronic components are thus contained within the coil wire 240 and within the ferromagnetic portion of the core. The coil drive circuit communicates with an exposed portion 212 of the flexible circuit 210 that is located external to the wire 240 and the core. The result is a compact and lightweight tracking unit 200.

[0035] The ferromagnetic fabric material 220 may include an adhesive backing layer that secures the ferromagnetic portion of the material sheet to the bobbin 230 or some other structure within the coil. Without an adhesive and backing material, the thickness of the ferromagnetic material may be between 0.1 and 0.3 millimeters. With an adhesive and backing material, the thickness increases by about 0.2 mm.

[0036] The ferromagnetic fabric material 220 may include iron, nickel, cobalt, and alloys thereof. The material may be formed into sheets, rods, wires, or powders and applied to cover and / or surround the hollow flexible circuit 210. In some instances (e.g., using wire), ferromagnetic components may be embedded in non-ferromagnetic fabrics.

[0037] In some embodiments, the ferromagnetic material is a sintered ferromagnetic material having a suitable magnetic permeability to operate within the frequency range used for the final transmitter unit. Instead of a flexible fabric, the ferromagnetic material can be formed from a ferrite having a rigid sintered structure. The rigid sintered material can additionally or alternatively include a ferrite / binder matrix or composite material, and the formed ferrite can be formed into one or more elements that are conveniently arranged to form a hollow core surrounding the transmitter circuit. Typically, the binder is a polymer. The ferrite / binder mixture can be molded (in liquid form) or thermoformed (into sheets or strips) around the electronic device. In this arrangement, the bobbin can be omitted because the formed ferrite provides sufficient structural integrity for the final unit. The unit can instead have the form of an open-ended cube with or without end caps enclosing the electronic device.

[0038] High permeability sheets or strips may be used in place of ferromagnetic materials. For example, sheets of Permalloy 80 (a highly magnetic nickel-iron-molybdenum alloy) are available in a thickness of 0.0025 mm; these sheets can be cut into strips and wound or formed in a similar manner to the ferrite fabric described above.

[0039] The ferromagnetic transmitter core described herein is hollow, and some portion of the electronic device (e.g., all of the electronic device) is disposed within the hollow portion, which provides significant advantages. The ferromagnetic material shields the electronic device from the magnetic field generated by the windings disposed around the hollow ferromagnetic core. The shielding provides the advantage of reducing the distortion of the magnetic field generated by the windings disposed around the hollow ferromagnetic core. The reduced distortion improves the accuracy of the position output by the electromagnetic tracker. At the same time, the hollow unit is lightweight and compact, and is simple to manufacture.

[0040] Figure 5Steps of a method 400 for forming a tracking unit 200 that can be used as a transmitter 110 or a transmitter 134 are shown. In step 402, the walls are formed into a hollow shell to enclose the electronic components, such as by folding the flexible circuit 210 onto itself into a cuboid configuration, wherein the second side 224 including the electronic circuit 214 points toward the hollow interior of the cube. The folding may include bending the central portion 216 within the four wall portions 214 and supporting the edge of the central portion 216 between two wall portions 214 to provide additional structural rigidity. In step 404, the hollow shell of the flexible circuit 210 is covered with a ferromagnetic material such as a flexible ferrite fabric material 220 by wrapping the ferromagnetic material around the flexible circuit 210 on the first side 222 of the flexible circuit 210. In step 406, the wrapped hollow shell is then inserted into a plastic bobbin 230. The plastic bobbin is then wrapped with coil wire 240 to produce three orthogonal windings and provide a final configuration, step 408.

[0041] A number of embodiments of the present invention have been described, however, it will be appreciated that various modifications can be made without departing from the spirit and scope of the invention.

[0042] For example, the tracking unit shown in the figure is represented as having a rectangular parallelepiped shape. However, other shapes are possible, such as non-rectangular prisms, spheres, cylinders, etc. Therefore, although the flexible circuit 210 is described as being folded into five parts, other numbers of parts are possible (e.g., less than five or more than five).

[0043] In some embodiments, the flexible circuit 210 may not be folded, but may be assembled from several different parts. For example, four or six wall parts may be joined together to form an open (eg, Figure 4A The connection can be performed by gluing, welding, fusing, etc. The wall portion forms the wall of the hollow core and protects the internal circuit.

[0044] The exposed portion 212 of the flexible circuit 210 may be integral with the flexible circuit 210, or may be separate therefrom. For example, the exposed portion 212 may be attached to the remainder of the flexible circuit 210, such as by soldering, before or after assembly of the rest of the unit.

[0045] In some examples, the electronic circuit 214 is located on a single section of circuit material (e.g., one of the five sections described above). The section can form a wall (with the electronic device pointing inward), or be a separate section that is placed (e.g., diagonally) within a hollow core formed by folding the flexible material without the circuit.

[0046] Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A magnetic transmitter, comprising: Electronic components having conductive elements; as well as at least one winding disposed about the hollow ferromagnetic core, the at least one winding being comprised of an electrically conductive material capable of causing an electric current to flow through the electronic component, wherein the electronic component is at least partially contained within a hollow portion of the hollow ferromagnetic core, Wherein, the electronic assembly includes a flexible circuit contained in the hollow portion of the hollow ferromagnetic core, the flexible circuit being folded to provide structural support to the ferromagnetic material of the magnetic transmitter.

2. The magnetic transmitter according to claim 1, wherein: The electronic components are completely contained within the hollow portion of the hollow ferromagnetic core.

3. The magnetic transmitter according to claim 1, wherein: The ferromagnetic material comprises a flexible ferromagnetic material, and the hollow ferromagnetic core comprises the flexible ferromagnetic material.

4. The magnetic transmitter according to claim 3, wherein: The flexible ferromagnetic material comprises fabric.

5. The magnetic transmitter according to claim 4, wherein: The hollow ferromagnetic core includes an adhesive layer and a backing layer attached to the fabric.

6. The magnetic transmitter of claim 1 including a plastic bobbin surrounding the flexible circuit.

7. The magnetic transmitter according to claim 1, wherein: The flexible circuit has a folding feature that allows the flexible circuit to be folded into a rectangular parallelepiped shape.

8. The magnetic transmitter according to claim 7, wherein: The fold features define a wall portion and a central support portion.

9. The magnetic transmitter according to claim 8, wherein: The central support portion is configured to rest against two of the wall portions.

10. The magnetic transmitter according to claim 1, wherein: The flexible circuit is folded such that the electronic circuitry of the flexible circuit is directed toward the hollow interior of the folded shape of the flexible circuit.

11. The magnetic transmitter according to claim 1, wherein: The ferromagnetic material comprises a rigid ferromagnetic material, and the hollow ferromagnetic core comprises the rigid ferromagnetic material.

12. The magnetic transmitter according to claim 11, wherein: The rigid ferromagnetic material is a formed ferrite.

13. The magnetic transmitter according to claim 11, wherein: The rigid ferromagnetic material is a sintered ferrite / binder composite material.

14. An electromagnetic tracking system comprising: a magnetic transmitter configured to output a magnetic field, the magnetic transmitter comprising at least one winding disposed about a hollow core of the magnetic transmitter and a foldable circuit located within the hollow core, the foldable circuit being folded to provide structural support to a material of the magnetic transmitter, the material being located between the foldable circuit and the at least one winding; as well as A receiver is responsive to the magnetic field.

15. The electromagnetic tracking system according to claim 14, wherein: The material comprises a flexible ferromagnetic material, and the hollow core comprises the flexible ferromagnetic material.

16. The electromagnetic tracking system according to claim 15, wherein: The flexible ferromagnetic material comprises fabric.

17. The electromagnetic tracking system according to claim 14, wherein: The foldable circuit has a folding feature that allows the foldable circuit to be folded into a cuboid shape.

18. The electromagnetic tracking system according to claim 17, wherein: The fold features define a wall portion and a central support portion.

19. The electromagnetic tracking system according to claim 18, wherein: The central support portion is configured to rest against two of the wall portions.

20. The electromagnetic tracking system of claim 14, wherein: The foldable circuit is folded such that the electronic circuit system of the foldable circuit is directed toward the empty interior of the folded shape of the foldable circuit.

21. A method of manufacturing a magnetic transmitter, the method comprising: forming the wall into a hollow shell to surround the electronic component; covering the hollow shell with a ferromagnetic material; Insert the covered hollow shell into the plastic spool; as well as The plastic bobbin is wound with coil wire to produce three orthogonal windings.

22. A method comprising: folding the flexible circuit into a cuboid configuration such that one or more components of the flexible circuit are located on one or more interior surfaces of the folded flexible circuit; disposing a ferromagnetic material on one or more exterior surfaces of the folded flexible circuit; inserting the folded flexible circuit into a spool; as well as At least one magnetic coil is disposed about the folded flexible circuit and the ferromagnetic material such that the folded flexible circuit is disposed within a hollow core of the at least one magnetic coil.

23. A method comprising: generating one or more electromagnetic signals by a transmitter of the tracking system; 07508-0184CN1_div sensing the one or more electromagnetic signals by a sensor of an instrument of the tracking system; as well as The three-dimensional position of the instrument in a three-dimensional environment is determined by a computer of the tracking system based on the one or more electromagnetic signals, wherein at least one of the transmitter or the sensor includes at least one magnetic coil, an electronic device at least partially disposed within a hollow core of the at least one magnetic coil, and a shielding layer disposed between the electronic device and the at least one magnetic coil.

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