Patent ID: 12239385

DETAILED DESCRIPTION OF EMBODIMENTS

Overview

During a medical procedure performed using an augmented reality system, a tool used in the procedure, such as a screwdriver used for pedicle screws, typically needs to be tracked, so that images presented to a medical professional using the system correctly register with the tool and with the patient undergoing the procedure. In order to track the tool, a marker is typically connected to the tool, and the marker is tracked by the system. However, in the case of tools such as screwdrivers that need one or more rotations, or even a partial rotation, the marker must stay within the field of view of the tracking system so that tracking is maintained. Furthermore, to eliminate tracking errors, total indicated runout should be minimized.

Embodiments of the present invention provide a solution that overcomes both of these problems by attaching a tool adapter having the marker to the tool, and configuring the tool adapter to be able to rotate about the tool without changing the spatial relationship of the tool to the marker.

The tool adapter comprises an adapter arm which terminates at a proximal end in a connection to the marker, and at a distal end in a circular opening. A tool grip is rotatingly connected to the circular opening so as to permit rotation of the tool grip about an axis defined by the opening, the tool grip being configured to fixedly retain a tool along the axis.

The tool grip typically comprises a collet housed in a collet holder, and the collet is configured to grip the tool when the collet is compressed. Use of a collet firmly and stably holds the tool in a centered location. The collet holder is held in the circular opening, and the combination of the collet, collet holder, and circular opening means that the shaft of the tool remains accurately along the axis of the opening during rotation, and that there is very low total indicated runout (TIR) during all rotations. The inventors have found that in contrast to prior art systems that have a TIR of the order of 100 microns, embodiments of the present invention have a TIR of the order of 10 microns, and thus substantially improve the accuracy of tracking of a gripped tool.

System Description

In the following, all directional references (e.g., upper, lower, upward, downward, left, right, top, bottom, above, below, vertical, and horizontal) are only used for identification purposes to aid the reader's understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of embodiments of the invention.

Reference is now made toFIG.1, which schematically illustrates use of a tool adapter18in an augmented reality system20, according to an embodiment of the present invention. By way of example and for simplicity, in the following description system20is assumed to be used by a medical professional22in a medical procedure wherein adapter18is attached to a cylindrical tool16, for example a screwdriver, using a wrench180, as is explained in more detail below. While the description herein assumes a medical procedure, it will be understood that embodiments of the present invention may be used in non-medical situations.

System20is operated by medical professional22, who wears, by way of example, an augmented reality assembly24, described in more detail below with respect toFIG.2, which tracks tool adapter18. It will be understood that assembly24is but one type of tracking system, that is able to track the tool holder, and that the scope of the present invention comprises any tracking system able to track tool adapter18.

Assembly24comprises, inter alia, an image capturing device72, also termed herein a camera72, that has a field of view74and that is configured to capture images in the visible spectrum. Assembly24and functions of system20, processor26, and device72are described below. An assembly similar to augmented reality assembly24, and its operation, are described in U.S. Pat. No. 9,928,629, to Benishti, et al., whose disclosure is incorporated herein by reference.

While assembly24may be incorporated for wearing into a number of different retaining structures on professional22, in the present description the retaining structure is assumed to be similar to a pair of spectacles. Those having ordinary skill in the augmented reality art will be aware of other possible structures, such as incorporation of the augmented reality assembly into a head-up display that is integrated into a headset worn by the user of system20, and all such structures are assumed to be comprised within the scope of the present invention.

System20comprises and is under overall control of a processor26. In one embodiment processor26is assumed to be incorporated within a stand-alone computer28, and the processor typically communicates with other elements of the system, including assembly24, wirelessly, as is illustrated inFIG.1. Alternatively or additionally, processor26may use optical and/or conducting cables for communication. In further alternative embodiments processor26is integrated within assembly24, or in the mounting of the assembly. Processor26is typically able to access a database40, wherein are stored images and other visual elements used by system20. Software enabling processor26to operate system20may be downloaded to the processor in electronic form, over a network, for example. Alternatively or additionally, the software may be provided on non-transitory tangible media, such as optical, magnetic, or electronic storage media.

The medical procedure exemplified here is on a patient30, and during the procedure a position marker14is incorporated into tool adapter18. As described below, marker14is trackable by processor26, so that the processor is able to track also the tool adapter to which the marker is attached, and a tool16held by the adapter.

FIG.2is a schematic diagram illustrating assembly24, according to an embodiment of the present invention. As stated above, assembly24is configured, by way of example, as a pair of spectacles50mounted on a frame54.

At least one image capturing device68is attached to frame54. Typically, devices68comprise cameras configured to capture images of scenes viewed by the professional's eyes, including images of marker14in the visible spectrum.

As stated above assembly24also comprises camera72, which is configured to capture images of elements of a scene, including marker14, in front of assembly24. The images are produced from radiation projected by a projector73that is in the spectrum detected by camera72. Projector73is located in close proximity to camera72, so that radiation from the projector, that has been retroreflected, is captured by camera72. The camera typically has a bandpass filter configured to block other radiation, such as that projected by surgical lighting. Typically, camera72and projector73operate in a non-visible region of the spectrum, such as in the near infra-red spectrum. As is described below, at least some retroreflected radiation is typically received from marker14, and processor26uses the image of the marker produced by camera72from the received radiation to track the marker, and thus the position and orientation of adapter18and of tool16.

FIG.3is a schematic diagram illustrating tool adapter18and tool16,FIG.4is a schematic exploded view of the tool adapter and the tool, andFIG.5is a schematic cross-section of the tool adapter and the tool, according to an embodiment of the present invention. Tool adapter18is formed from an adapter arm102, which terminates at an upper or distal end of the arm in a circular opening104, and which terminates at a lower or proximal end of the arm at a connection110which fixedly connects the arm to marker14. A marker similar to marker14is described in U.S. patent application Ser. No. 16/199,281 to Messinger et al., which is incorporated herein by reference.

In a disclosed embodiment arm102is formed as a single unit. However, in an alternative embodiment arm102may be formed as two or more units fixedly connected together. For example, opening104may be formed as a separate unit from the remainder of arm102, and the opening may be fixedly connected by any convenient means to the remainder of the arm.

A tool grip32fixedly holds tool16, as is described in more detail below, and the tool grip is rotatingly connected to circular opening104, so that tool16rotates with respect to the opening as the grip rotates.

Circular opening104comprises an internal cylindrical surface106having a diameter that is typically in a range 10 mm-50 mm, and the surface defines an axis of symmetry114of the opening. Tool Grip32comprises a rigid collet holder120, having an external cylindrical surface112with a diameter slightly smaller than that of internal cylindrical surface106, that fits into opening104. Except as described below, collet holder120is able to freely rotate within opening104.

After assembling collet holder120into opening104, the holder is held, so that it cannot translate along axis114, by an upper circular washer130and a lower locking nut132. Locking nut132acts as a washer due to its geometry and the material from which it is formed. The washer and nut are typically formed from a low friction material such as PEEK, and act as friction bearings, preventing the holder from translating along axis114while allowing the holder to rotate about the axis. Upper washer130is held in place between a circular protruding ridge136fixedly formed on surface112and an upper edge140of opening104.

Lower locking nut132is threaded and is configured to mate with a threaded lower region144of holder120, and is dimensioned to mate with a lower edge148of opening104. The lower locking nut is held in place in region144by adhesive between the nut and the region, and with a set screw152that screws into region144. Systems other than set screw152for holding the locking nut in place, such as a dowel pin, will be familiar to those having ordinary skill in the art, and all such systems are assumed to be comprised within the scope of the present invention.

As is described below, in some embodiments the locking nut may be used to limit, in a controlled manner, the freedom of rotation of arm102around collet holder120.

A collet150fits within collet holder120. Collet150has an upper external portion154that is cylindrical, and a lower external portion158that is conical. Collet150also has a central cylindrical aperture162that is dimensioned to accept tool16when the collet is uncompressed, and to grip the tool when the collet is compressed. An embodiment of the invention comprises a set of collets, each collet of the set being able to accept tools with a range of diameters.

Collet holder120has an internal upper cylindrical surface166and a lower conical surface170, the two internal surfaces being dimensioned to mate with the external surfaces of collet150(FIG.5).

Collet150is held in place within the collet holder by a retaining spring174, the retaining spring being sprung against a dedicated groove in upper cylindrical surface166. A collet fastening head178is configured to screw onto a threaded outer surface182of collet holder120. Fastening head178is configured internally to mate with spring174, so that when the head is screwed on surface182so as to move towards the collet holder, it pushes on spring174and thus pushes and compresses collet150.

An internal cylindrical tube190is fixed to an upper surface of collet fastening head178, the tube having an internal diameter larger than the external diameter of cylindrical tool16. An outer surface of fastening head178is configured to be able to be gripped by wrench180so that the wrench is able to turn the fastening head. By way of example, in one embodiment the outer surface has protuberances194, and wrench180mates with the protuberances so that the wrench is able to rotate the fastening head.

Once tool16is positioned within adapter18, so that it traverses tube190, rotation of collet fastening head178pushes on a flat edge of collet150causing the collet to be compressed, and thus to grip tool16. It will be appreciated that while the tool is gripped by the collet, adapter arm102is able to rotate around the tool.

From review of the above description, it will be appreciated that tool grip32comprises collet holder120, and other elements described herein that are connected to the collet holder and collet150, apart from arm102and tool16.

In some embodiments arm102comprises a locking mechanism200. Mechanism200comprises an operating button204, which is configured to toggle, via a spring and a connecting rod, a pin208of the mechanism to mate with or disengage from one of holes212in collet holder surface112. Use of the locking mechanism facilitates attachment of tool16to tool adapter18, by preventing the free rotation of collet holder120around the center axis of the tool while wrench180rotates fastening head178.

In some embodiments circular opening104has holes that align with holes212. The holes in opening104may be used by professional22to align mechanism200with holes212, and may also facilitate flushing of liquids and avoidance of residual liquid when adapter18is cleaned.

As stated above marker14is fixedly attached to lower-connection110. In an illustrated embodiment marker14comprises optical elements12formed on marker14. Elements12may be formed as a plurality of apertures21in an upper marker section15, the apertures being backed by a retroreflective sheet17that is held in place with respect to the apertures by a lower marker section23fixed to the upper marker section. Marker14is fixedly connected by a screw19to lower connection110.

Elements12are typically configured to have no rotational or reflective axis of symmetry, so that processor26is able to use the image of marker14, including the images of elements12acquired by image capturing device68and/or camera72of assembly24, to track the marker, i.e., to determine the location and orientation of the marker in a frame of reference defined by the assembly.

In some embodiments, typically on production of adapter18, locking nut132may be used to limit, in a controlled manner, the freedom of rotation of arm102around collet holder120. In this case the locking nut acts as a torque limiting device. (With no limitation on its rotation, during a procedure professional22may inadvertently cause the arm to rotate. While, as described herein, inadvertent rotation of the arm does not affect the functioning of system20, such rotation may be undesired.)

With no limit on the arm rotation, it will be understood that once tool16has been clamped by collet150to collet holder120, and the tool is held horizontal, the weight of arm102, i.e. the force on the arm due to gravity, will cause the arm to rotate about axis114to a vertical “6 o'clock” position. As stated above, locking nut132may be adjusted to counteract the force of gravity, so that when tool16is held horizontal, arm102does not rotate but is also horizontal, in a “3 o'clock” position. The locking nut acts to provide a countervailing torque to the torque generated by gravity. The countervailing torque, herein also termed a threshold torque, does not completely prevent rotation of arm102, but reduces inadvertent rotation of the arm, since rotation only occurs when the threshold torque is exceeded.

It will be understood that the threshold torque provided by locking nut132prevents adapter18from rotating due to the force of gravity, but does not apply too much friction that could prevent smooth rotation of tool16by professional22. For an arm and marker having a mass of 80 g, and a center of mass 100 mm from axis114, the threshold torque applied to arm192is approximately 8 N·cm.

In addition to acting as a torque limiting device, locking nut132also acts as a controller of the amount of total indicated runout (TIR) of a tool gripped by adapter18. If locking nut132is set to have a threshold torque of 8 N·cm, then the TIR is approximately 60 microns or less.

FIG.6is a schematic diagram illustrating a tool adapter418and tool16, according to an alternative embodiment of the present invention. Apart from the differences described below, the operation of adapter418is generally similar to that of adapter18(FIGS.1-5), and elements indicated by the same reference numerals in both adapters18and418are generally similar in construction and in operation.

In contrast to adapter18, in adapter418three substantially similar blind holes420are formed in collet holder120. Blind holes420are distributed symmetrically about axis114, and are orthogonal to the axis.

Three substantially similar springs428are inserted into holes420, and three substantially similar pins424are inserted into the springs. Each pin424has a terminal shoulder432which has an outer diameter that fits to the diameter of its hole420.

In addition, the springs and pins are dimensioned so that after insertion each spring lower end contacts the base of its blind hole, the spring upper end contacts shoulder432, and an exposed surface436of the shoulder slightly protrudes from surface112, as illustrated inFIG.6.

After assembly of adapter418, each surface436pushes against internal surface106of opening104with a force that is a function of parameters of spring428, i.e., the spring constant of the spring as well as its changed length.

The pushing force in turn generates a frictional force on opening104when the opening rotates, or attempts to rotate, about axis114, and the frictional force provides the threshold torque referred to above.

It will be understood that the threshold torque may be set to the value of 8 N·cm cited above, or to a value above or below this value, by selecting a spring with appropriate parameters, as well as by selecting the materials from which pin424and opening104are formed. Thus, any desired threshold torque may be implemented by these selections, without undue experimentation.

To assemble tool grip32, springs428and pins424are first positioned in their blind holes. Opening104of the holder arm are then slid over collet holder120, and over pin shoulders432. Finally, locking nut132is screwed onto holder120.

In contrast to adapter18, wherein, as described above, locking nut132acts to set values of TIR and the threshold torque, in adapter418the two parameters can be set independently. I.e., in adapter418locking nut132is used to set the value of TIR, and springs428and pins424are used to set the value of the threshold torque.

The description above assumes that there are three sets of springs428and pins424distributed symmetrically about axis114. However, it will be understood that any other convenient plurality of springs and pins distributed symmetrically about the axis, such as two, four, or five springs and pins, may be used as a torque limiting device.

FIG.7is a flowchart of steps performed in using tool adapter418with augmented reality system20(FIG.1), according to an embodiment of the present invention. Those having ordinary skill in the art will be able to adapt the description below, mutatis mutandis, for tool adapter18.

In an initial step300tool adapter418is assembled, as described above with reference toFIGS.3,4,5and6. The assembly typically includes adjusting locking nut132to provide a pre-determined TIR, and positioning pins424and springs428as described above. Also marker14is attached to connection110of arm102.

In a tool insertion step304, cylindrical tool16is inserted through aperture162of collet150. Since the tool is to be used in the medical procedure referred to above on patient30, tool16is inserted so that tip16T of tool16is below the level of marker14.

In a collet activation step308, wrench180is used to rotate collet fastening head178so as to compress collet150, the compression causing the collet to grip tool16. While wrench180is being used, locking mechanism200should be activated to lock collet holder120in place, as described above, so as to facilitate the compression of collet150.

As described above, processor26is able to track marker14. Thus, in a calibration step310, professional22positions tool termination16T on a predefined location, and processor26acquires an image of marker14. From the acquired image, the processor calculates a position of the marker, i.e., its location and orientation, and forms a vector correspondence between the marker position and tool termination16T and the orientation of tool16. I.e., the processor “learns” how to translate the marker position to tool termination16T and to the direction of axis114. It will be understood that the vector correspondence is unchanged if arm102rotates around axis114, since the marker is fixed to the arm.

In a tool insertion step316, tool16is inserted into patient30while processor26tracks marker14. The tracking of the marker provides the processor with the location and orientation, i.e., the marker position, of the marker. From the marker position the processor is able to find, using the vector correspondence found in step310, the location of tool termination161and the orientation of tool16. The processor is able to use the orientation of tool16and the location of tool termination16T in presenting correctly registered images in assembly24.

In one embodiment tool16comprises a screwdriver, which is inserted into patient30so that professional22is able to adjust a pedicle screw. It will be appreciated that while the screwdriver is turned, processor26is still able to track the screwdriver orientation and its termination, using the vector correspondence found in calibration step310, so long as marker14is tracked.

Alternatively or additionally, during the procedure positioning marker14may obstruct the professional's view of the patient, and/or the view of the patient as acquired by devices68and/or camera72. In any of these events, professional22may rotate arm102about axis114, applying a torque greater than the threshold torque applied in step300, so that marker14no longer obstructs the view, but while processor26continues to track the marker. Since marker14continues to be tracked, the processor is able to use the new tracked location of the marker to continue tracking tool16and termination16T of the tool, since the spatial relationships, i.e., the vector correspondence, between the tool and the marker, and between the tool termination and the marker, are unchanged by the tool adapter rotation about axis114.

It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.