Retro-reflective marking with uniformly distributed micro-elements

Abstract

An apparatus includes a retro-reflective section. The retro-reflective section includes an outer surface, an inner surface, and a plurality of retro-reflective microelements. One or more of the plurality of retro-reflective microelements includes a plurality of reflective surfaces. Each of the plurality of retro-reflective micro-elements extends from the inner surface at a different position than the positions of the other retro-reflective micro-elements, and each of the plurality of retro-reflective micro-elements includes a central axis extending in a direction corresponding to a surface normal of the outer surface.

Description

[0001] Claiming priority

[0002] This application claims priority under 35 U.S.C. § 119(e) to U.S. Patent Application No. 63 / 525,382, filed on July 7, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to retro-reflective markings, and in particular to retro-reflective markings having uniformly distributed retro-reflective microelements. Background Art

[0004] Tracking systems (eg, optical tracking systems) may rely on an object having one or more markers attached.

[0005] The optical tracking system typically includes a plurality of retro-reflective markers located at different locations with corresponding orientations to achieve retro-reflection. The retro-reflective markers typically include a plurality of microelements having a characteristic size that is significantly smaller than the retro-reflective markers or the tools or devices on which the markers are positioned. The microelements are typically retro-reflective so that an incident optical signal traveling along an incident path may be reflected along a path that is substantially opposite to the incident path.

[0006] Optical tracking systems with retro-reflective markers can have a variety of applications. For example, optical tracking systems can capture the motion or movement of one or more objects, which can be used for animation, motion analysis, medical research, surgery, etc. Optical tracking systems can also be implemented in augmented reality (AR) and virtual reality (VR), biomechanics, robotics, and computer vision. Summary of the invention

[0007] A device is described herein for use as a retro-reflective marker or at least a portion of a retro-reflective marker for a tracking system configured to determine the position of a tracked object in an environment by estimating the pose (e.g., position and orientation) of one or more markers attached to the tracked object. Manufacturing techniques for producing three-dimensional (3D) markers (e.g., having a curved surface) from two-dimensional (2D) retro-reflective markers (e.g., a 2D sheet containing many markers) may result in 3D markers having unevenly distributed small reflective elements (e.g., microelements) and, in some cases, deforming the microelements. As a result, the brightness of the retro-reflective optical signals generated by these markers having curved surfaces becomes less consistent for optical signals incident at different angles of incidence, thereby reducing the tracking accuracy of the tracking system.

[0008] In sharp contrast, the devices described herein can be manufactured as a single structure, such as by injection molding or other applicable techniques, that provides a desired distribution (e.g., uniform distribution) of retro-reflective microelements. The desired distribution can be predetermined according to different retro-reflective tasks and obtained by one or more manufacturing techniques (e.g., injection molding), etc. With the desired distribution provided, undesirable variations in the desired distribution are reduced, undesirable deformations are reduced, etc.

[0009] More specifically, the device described herein has a retro-reflective segment for reflecting an incident optical signal along a direction substantially parallel to its corresponding incident direction (or at a corresponding angle of incidence). The retro-reflective segment may include one or more coupling mechanisms for coupling the retro-reflective segment with one or more other retro-reflective segments of a corresponding device to form an assembly. The device or an assembly consisting of one or more devices can be used as a retro-reflective marker for a tracking system. The retro-reflective segment includes an outer surface and a corresponding inner surface. The outer surface is typically curved and smooth and defines a surface normal with a varying direction. The inner surface may have a corresponding topology as the outer surface (and optionally a corresponding surface normal).

[0010] The retro-reflective section also includes a plurality of retro-reflective micro-elements, which are generally smaller than the size of the retro-reflective section or the mark. For example, the retro-reflective micro-elements may have a characteristic length of one or more millimeters, less than one millimeter, etc. The retro-reflective micro-elements may have one or more shapes, such as microbeads or microspheres, micro-angle cubes, micro-prisms, etc. Each retro-reflective micro-element extends from the inner surface at a position different from other retro-reflective micro-elements. Each retro-reflective micro-element includes a central axis extending in a direction corresponding to the surface normal of the outer surface. The alignment between the central axis and the surface normal improves the consistency of the retro-reflective brightness. Since the surface normal has a corresponding direction at different positions, and the central axes of different retro-reflective micro-elements are roughly aligned with the surface normal, the central axes at different positions extend along the corresponding directions corresponding to the surface normal. In some cases, the central axis may extend in a direction offset by a predetermined offset angle relative to the direction of the surface normal.

[0011] The retro-reflective segment may also include a reflective coating deposited on the surface of the plurality of retro-reflective microelements to enhance the retro-reflective effect. For example, having a reflective coating may slightly reduce brightness and provide a wider viewing angle for retro-reflection. Whether to deposit a reflective coating on the retro-reflective segment depends on the retro-reflective requirements. For example, for applications that do not require a wider retro-reflectivity, the retro-reflective segment may provide retro-reflection without a reflective coating. The reflective coating may include one or more materials, such as silver, aluminum, or any other similar reflective material. In addition, one or more of the plurality of retro-reflective microelements may have a plurality of reflective surfaces to reflect or retro-reflect incoming light.

[0012] For example, the first retro-reflective microelement may have two reflective surfaces to reflect or retro-reflect incident light.

[0013] In a general aspect, this document describes a device including a retro-reflective segment. The retro-reflective segment includes an outer surface, an inner surface, and a plurality of retro-reflective microelements. Each of the plurality of retro-reflective microelements extends from the inner surface at a position different from the positions of the other retro-reflective microelements. Each of the plurality of retro-reflective microelements includes a central axis extending along a direction corresponding to a surface normal of the outer surface. The device also includes a reflective coating deposited on the surface of the plurality of retro-reflective microelements.

[0014] Implementations may include one or more of the following features.

[0015] One of the plurality of retro-reflective microelements may be a micro-prism.The retro-reflective segment may further include a coupling mechanism to couple the retro-reflective segment with one or more other retro-reflective segments.

[0016] In some embodiments, the retro-reflective segment can form at least a portion of a retro-reflective marker having a hollow spherical, hollow conical, or hollow cylindrical shape. In some cases, the retro-reflective segment can form one or more retro-reflective markers.

[0017] The geometry and arrangement of the plurality of retro-reflective microelements may be predetermined for use in manufacturing the retro-reflective segment. In some embodiments, the retro-reflective segment may be manufactured by injection molding.

[0018] Each edge of one of the plurality of retro-reflective microelements may have a length of less than 1 mm. Each of the plurality of retro-reflective microelements may define a microprism center, and two adjacent retro-reflective microelements of the plurality of retro-reflective microelements may be spaced apart by a distance of less than 1 mm between the corresponding microprism centers.

[0019] In some embodiments, the central axis may extend in a direction parallel to a surface normal of the outer surface and offset relative to the surface normal by an offset. The offset may be determined by applying a randomization algorithm to the plurality of retro-reflective microelements.

[0020] In some embodiments, the retro-reflective segment may include a polymer that is transmissive in the near infrared (NIR) spectral band. The reflective coating may be deposited on the surface of the plurality of retro-reflective microelements by vapor deposition. The reflective coating may include a metallic material.

[0021] In addition, the retro-reflective segment may form part of the body of the tool for optical tracking. Alternatively, the retro-reflective segment may form part of a marker configured to be mounted to a tool for optical tracking. In some cases, the retro-reflective segment may include a first retro-reflective segment and a second retro-reflective segment. The first retro-reflective segment may form part of the body of the tool for optical tracking, and the second retro-reflective segment may form part of a marker configured to be mounted to the tool.

[0022] In another aspect, the marker includes a first portion including one or more retro-reflective segments coupled to each other. One of the one or more retro-reflective segments includes an outer surface, an inner surface, and a plurality of retro-reflective microelements. Each of the plurality of retro-reflective microelements extends from the inner surface at a position different from the positions of the other retro-reflective microelements, and each of the plurality of retro-reflective microelements includes a central axis extending in a direction corresponding to a surface normal of the outer surface. The one retro-reflective segment also includes a reflective coating deposited on a surface of the plurality of retro-reflective microelements.

[0023] The marker also includes a second portion including a connection mechanism configured to connect the first portion to a device.

[0024] On the other hand, an apparatus includes a device for optical tracking and a retro-reflective marker. The retro-reflective marker is attached to the device by a connecting mechanism of the retro-reflective marker. The retro-reflective marker includes one or more retro-reflective segments connected to each other. One of the one or more retro-reflective segments includes an outer surface, an inner surface, and a plurality of retro-reflective microelements. Each of the plurality of retro-reflective microelements extends from the inner surface at a position different from the positions of other retro-reflective microelements, and each of the plurality of retro-reflective microelements includes a central axis extending in a direction corresponding to a surface normal of the outer surface. A retro-reflective segment also includes a reflective coating deposited on the surface of the plurality of retro-reflective microelements.

[0025] The embodiments described herein can provide various technical benefits. For example, the described devices and markers (including assemblies consisting of multiple devices) can improve the uniformity of optical signals retro-reflected along different angles, thereby further improving the tracking accuracy of tracking systems using the described devices and markers. Since the described devices are manufactured using techniques such as injection molding controlled by predetermined geometries and parameters, the distribution and shape of the retro-reflective microelements are substantially the same as those controlled for the injection molding process. Thus, the brightness of the reflected optical signals generated by the described devices and corresponding markers is substantially uniform and controllable.

[0026] Furthermore, the described techniques for manufacturing markers are robust and efficient for different tracking tasks. Since the described devices are manufactured using injection molding and include one or more coupling mechanisms configured to couple themselves to one or more other devices, the geometry of the described devices (e.g., size, shape, or both), the geometry of markers assembled using one or more of the described devices, and the arrangement of retro-reflective microelements on the described devices or markers (e.g., size, shape, distribution, etc.) can be predetermined or adjusted or both according to different requirements for different tracking tasks. Furthermore, the ability to utilize injection molded retro-reflective segments and to design different assemblies consisting of multiple retro-reflective segments can reduce the time and cost of researching and developing new configurations of retro-reflective markers.

[0027] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 An example of a retro-reflective section in a device is shown.

[0029] Figure 2A , Figure 2B and Figure 2C is a bottom view of an exemplary retro-reflective segment.

[0030] Figure 3 An example of a building block with cube angle variation is shown.

[0031] Figure 4A is a perspective view of a retro-reflective building block formed on a plane and having a rectangular geometry with varying cube angles.

[0032] Figure 4B Exemplary retro-reflective building blocks formed on a plane and having different cube angles are shown.

[0033] Figure 4C Another exemplary retro-reflective building block positioned on a plane and having different cube angles is shown.

[0034] Figure 5A , Figure 5B and Figure 5C is a perspective view of an exemplary retro-reflective building block formed on a curved surface and having different cube angles.

[0035] Fig. 6A and Figure 6B An exemplary marker including a retro-reflective component connected to a base is shown respectively.

[0036] Figure 7 is a perspective view of a tracking system that optically tracks an object using three markers attached to the object.

[0037] Figure 8 It is shown that it is possible to use, for example Figure 1 , Figure 2A -C. Figure 3 , Figure 4A -C. Figure 5A -C. Fig. 6A , Figure 6B and Figure 7 An exemplary tracking system for a marker.

[0038] Fig. 9 A schematic diagram of an exemplary computing system is shown.

[0039] The same reference numbers and names in different drawings represent the same elements. DETAILED DESCRIPTION

[0040] This article describes a device that can be used by a tracking system for optically tracking a variety of objects in an environment (e.g., an optical tracking tool used in an operating room). In some embodiments, the device can be used to produce a marker (e.g., a retro-reflective marker) that can be used by the tracking system. The tracking system is generally configured to determine the posture (e.g., position and corresponding orientation) of the tracked object present in the environment. The tracked object generally includes one or more retro-reflective markers that can be similar or different (e.g., similar in structure, different in ability, etc.). These retro-reflective markers are configured to receive an incident signal beam (e.g., a light beam) along one or more directions (e.g., from a signal source) and provide a reflected signal to the tracking system. One or more sensors included in the tracking system are positioned near the signal source and are configured to receive a signal reflected by the retro-reflective marker. Once received by the sensor, the reflected signal can be processed (e.g., based on the optical path of the incident signal and the reflected signal and the reflection position) to determine the posture information associated with the tracked object, and in some cases, the posture information can be further processed to obtain more information about the tracked object. In one example, the tracking system is configured to estimate the position of the marker in the environment based on the position where the reflected signal is detected. The pose of the tracked object is then determined based on a predetermined relationship between the poses of each marker.

[0041] In some embodiments, the tracking system can be an optical tracking system operating in the optical portion of the electromagnetic spectrum, and the signal source can emit optical signals having various wavelengths (e.g., visible light beams, invisible light beams (e.g., infrared, ultraviolet, etc.)). The retro-reflective capability of the marker allows the optical signal to be reflected back to the signal source along a parallel path (e.g., the reflected optical signal propagates along a path parallel to the path of the incident optical signal). Various devices, techniques, etc. can be used by the system to detect the reflected optical signal. For example, a sensor or multiple sensors (e.g., similar or different sensors) (e.g., one or more cameras) can be configured to detect retro-reflections (e.g., flashes) from one or more markers.

[0042] The described devices and corresponding markers can be used in various applications, such as medical applications, industrial metrology, navigation, fields using medical devices, etc. For example, the markers described herein can be connected to a medical device for tracking the posture of the medical device during a procedure (e.g., a surgical procedure).

[0043] Retro-reflective markers may include 2D markers whose shapes are primarily two-dimensional (e.g., 2D flat plates with retro-reflective capabilities), 3D markers (e.g., markers and related structures having 3D geometric shapes (e.g., spherical, conical, cylindrical, etc.)), combinations of 2D markers and 3D markers, etc.

[0044] 2D markers and 3D markers have retro-reflective microelements on at least one side (or surface). Microelements generally refer to small components or units included in retro-reflective markers, a portion of a marker, etc. to provide reflective properties. For example, the average edge size of a microelement may be less than 1 mm. Microelements are generally designed to redirect incident optical signals back to their signal source along substantially the same path. Microelements may take various forms, such as microprisms (also known as micro-corner cubes), microbeads (also known as micro cat's eye elements or microspheres), etc., and are generally arranged in a specific pattern or configuration to maximize the retro-reflective effect. Typically, a 2D marker may have a plurality of microelements attached to one surface of a 2D marker. Similarly, a 3D marker may have a plurality of microelements attached to one or more surfaces (e.g., inner surface, outer surface, or both) of a 3D structure.

[0045] For some manufacturing technologies, 3D markers are produced by forming a 3D structure from a corresponding 2D marker sheet. For example, a 2D marker having a plurality of retro-reflective microelements is heated (e.g., by a heating system) and placed on a mold having a desired geometry. The 2D marker sheet is processed into the desired geometry by external pressure. For example, one or more vacuums (referred to as vacuum forming) may be applied to form the 2D marker sheet into a 3D marker. However, such a process may change the individual microelements, the distribution of the microelements, etc., and other aspects of the 2D marker sheet. The resulting 3D marker may have an undesirable distribution of microelements (e.g., an uneven distribution of retro-reflective microelements). In addition, one or more microelements of the 2D marker sheet may be deformed from its desired shape during production (e.g., a manufacturing process). Changes in the distribution of microelements, changes in the shape of the 2D marker sheet, and changes in the shape of the microelements in the 2D marker may reduce the tracking accuracy of a tracking system for a resulting 3D marker using conventional techniques. Another conventional technique includes producing a label comprising a 3D structure having one or more retro-reflective microelements attached to the structure (e.g., attached to at least one side or surface of the structure). However, the attachment process may be inefficient, expensive, and the uniformity of the microelement distribution is difficult to control.

[0046] One or more techniques may be used to produce a 3D retro-reflective marker comprising one or more retro-reflective segments manufactured using injection molding. By using injection molding, the retro-reflective segment described may have a plurality of retro-reflective microelements that are evenly distributed and precisely oriented in a predetermined manner, which results in a more consistent brightness of the retro-reflective optical signal (e.g., light beam) generated by the retro-reflective segment from light incident at different angles of incidence and from different directions. The consistent uniformity of brightness at different angles of incidence improves the tracking accuracy of a tracking system using the device or one or more corresponding markers. In some embodiments, the injection molding techniques described herein may also be used to manufacture 2D markers.

[0047] Typically, injection molding includes injecting molten molding material into a mold. The mold is formed into a desired 3D structure with a predetermined micro-element arrangement (e.g., the shape, size, orientation, and distribution of micro-elements). In some arrangements, the mold is subsequently cooled to solidify the molding material. Once the molding material is fully solidified, the retro-reflective section is removed from the mold, and the retro-reflective micro-elements located on the retro-reflective section should have the shape and desired distribution provided by the mold. The molding material can include various types of materials, such as polymers (acrylic acid, silicone, etc.) that can be transmissive in near-infrared (NIR) spectral bands. The molding material can attenuate optical signals in the visible spectrum (e.g., 400-740nm). In this way, the molding material can filter visible light and be compatible with the light source in the NIR spectral band. However, as long as the molding material is compatible with the light source for tracking an object, the molding material can be selected to filter the optical signals in different spectral bands.

[0048] Figure 1 An example of a retro-reflective segment 105 in a device 100 is shown. In this example, the retro-reflective segment 105 has the geometry of a spherical body segment; however, it should be noted that the geometry and shape of the device 100 are for illustration purposes and for ease of illustration. Other geometries and shapes of the device 100 may be utilized.

[0049] As described above, the retro-reflective segment 105 can be manufactured using injection molding. The retro-reflective segment 105 can be part of a 3D marker having a specific geometry. For example, the retro-reflective segment 105 can form part of a 3D marker having a hollow spherical shape (e.g., Fig. 6A One or more other geometric shapes may be used, for example, a retro-reflective segment 105

[0050] A portion of a 3D marker having a cylindrical shape may be formed (e.g. Figure 6B cylindrical mark 650).

[0051] The retro-reflective segments can be assembled together to form a 3D marker (e.g., Fig. 6A Mark 600 and Figure 6B In general, a coupling mechanism refers to a mechanism or structure capable of attaching or connecting one or more retro-reflective segments. Common examples of coupling mechanisms include adhesives, heat seals, adhesives, mechanical connectors (e.g., joints, hooks and loops), etc. By using coupling mechanisms, multiple retro-reflective markers can be coupled to each other to form a more complex and larger marker structure. A corresponding 3D marker can be formed by assembling more than one retro-reflective segment (e.g., two, five, ten, or other appropriate number of retro-reflective segments) using one or more coupling mechanisms provided by each retro-reflective segment.

[0052] For example, the retro-reflective marker 105 of the device 100 can include a coupling mechanism 170 on at least one side. For example, the coupling mechanism 170 can include a joint for interlocking the corresponding joint of another retro-reflective segment. The joint may include a dovetail joint (not shown), which includes a trapezoidal groove, and the corresponding dovetail joint of the corresponding retro-reflective segment may include a corresponding protrusion or protrusion (extrusion), which is configured to be assembled into the trapezoidal groove to form an interlocking connection. In some cases, each retro-reflective segment may include a groove on each of one or more sides for receiving a corresponding protrusion from other retro-reflective segments, and a protrusion on each of one or more other sides to be received by other retro-reflective segments. In addition, the dovetail coupling mechanism ensures a reliable and firm connection between different retro-reflective segments, and allows rapid assembly and disassembly when needed, which helps to produce a universal retro-reflective marker with an adjustable configuration to adapt to different tracking tasks and requirements. In some embodiments, heat sealing can be applied to join or seal two or more retro-reflective segments (e.g., thermoplastic materials) that can be deformed due to heat. Heat sealing generally refers to a technique that uses heat to join two or more materials together. For example, a welding technique such as friction welding or ultrasonic welding can be used to generate friction heat between the retro-reflective segments to soften and bond the segments. Alternatively or additionally, one or more laser sources can be used to heat the retro-reflective segments. In some embodiments, one or more materials can be used as a bonding or interface material for welding the retro-reflective segments.

[0053] The retro-reflective segment 105 also includes a retro-reflective segment 110. The retro-reflective segment 110 includes an outer surface 115, an inner surface 120, and a plurality of retro-reflective microelements 130. The outer surface 115 defines a surface normal in a direction extending away from and perpendicular to a local tangent to the outer surface 115. Typically, except for a flat surface, the surface normal of the outer surface 115 is typically different at different locations on the outer surface 115. For example, the surface normal 150 of the outer surface 115 may change orientation at different locations on the outer surface 115. Similarly, the inner surface 120 defines a surface normal in a direction extending away from and perpendicular to a local tangent to the inner surface 115. When the inner surface 120 and the outer surface 115 have a common curvature profile, the surface normal of the inner surface 120 may correspond to the surface normal of the outer surface 115. On the outer surface

[0054] In embodiments where face 115 and interior surface 120 do not share a common curvature profile, the surface normals of the corresponding surfaces are generally not aligned with each other.

[0055] The outer surface 115 and the inner surface 120 are generally smooth to obtain better retro-reflection. However, in some embodiments, a portion of the outer surface 115, a portion of the inner surface 120, or a portion of both may be non-smooth (e.g., having a rough surface). The level of non-smoothness, the location of non-smoothness, the size of non-smooth area, etc. are determined according to different requirements of the retro-reflection task.

[0056] In this example, the retro-reflective segment 105 includes a plurality of retro-reflective microelements 130 extending from the inner surface 120 at different locations. Each of the plurality of retro-reflective microelements 130 defines a central axis 140 extending along a corresponding direction corresponding to a surface normal 150 of the outer surface 115. Retro-reflective microelements each having a central axis aligned with the surface normal 150 improve the retro-reflectivity (e.g., consistency of retro-reflective brightness) of the segment 105. Typically, the central axis of the retro-reflective microelement is represented by a vector passing through the geometric center of the retro-reflective microelement. For situations where the retro-reflective microelement is asymmetric (e.g., having different edge sizes, non-vertical internal angles, or being skewed, etc.), the central axis of the retro-reflective microelement is defined as an axis passing through the geometric center that is at the same angle to all edges formed by two adjacent surfaces of the retro-reflective microelement. Similarly, the central axis is at the same angle to the normals of all surfaces of the retro-reflective microelement. In the case where the retro-reflective micro-element is a corner cube with the same edge length, the central axis of the retro-reflective micro-element may be an axis passing through the geometric center and perpendicular to the base 155 of the retro-reflective micro-element.

[0057] In some embodiments, the microelement 130 can be designed to have a central axis 140 extending in a direction parallel to the surface normal of the inner surface 120. By aligning the central axis 140 and the surface normal 150, the retro-reflective segment 105 can improve the brightness uniformity of the generated retro-reflected optical signal (indicated by the graphical arrow 165) that propagates in a direction (indicated by the graphical arrow 160) that is parallel to (but in the opposite direction of) the propagation direction of the incident optical signal.

[0058] In addition, the retro-reflective segment 105 also includes one or more coatings, such as a reflective coating 180 deposited on the surface of the plurality of retro-reflective microelements 130. The reflective coating 180 can increase the retro-reflectivity of the microelements 130. The reflective coating 180 can include one or more materials (e.g., silver, aluminum, etc.), which can be deposited individually or in combination. The reflective coating 180 can be applied to the surface of the microelements using various techniques. An exemplary technique described herein involves vapor deposition. Typically, vapor deposition is a process of applying a thin layer of a reflective coating using a vacuum-based deposition technique. For deposition, at least a portion of the retro-reflective segment 105 (e.g., a plurality of microelements 130) is placed in a vacuum-sealed deposition chamber. The coating material is vaporized by heating and provided to the deposition chamber. Once the vaporized coating material hits the target surface (e.g., the surface of the microelements 130), the vaporized coating material quickly condenses and forms a thin layer of reflective material on the target surface. There is no air gap between the reflective coating and the surface of the microelements.

[0059] In some embodiments, the reflective coating may be bonded to the retro-reflective surface using other techniques (eg, chemical deposition, spraying using a spray gun or atomizer, etc.).

[0060] The thickness of the reflective coating can be controlled by adjusting parameters such as deposition time, vapor temperature, distance between the coating source and the surface, etc. Typically, the temperature of the reflective coating can be specifically designed to obtain a reflectivity of at least 85% and above at all locations on the outer surface of the retro-reflective segment. Since the surface normal of the micro-element varies across the retro-reflective segment, the thickness of the reflective coating varies accordingly to obtain the desired retro-reflectivity. For example, the thickness can be 10 micrometers (um), 20um, 50um, 100um, 200um, 500um, 1mm, or other applicable values. In some cases, the thickness of the reflective coating in the valleys between the micro-elements can be higher than the thickness on the surface of the micro-elements, so that enough reflective coating can be applied to the surface of the micro-element to obtain the desired level of retro-reflectivity.

[0061] As described above, whether to deposit a reflective coating on the retro-reflective layer depends on the requirements for retro-reflectivity. For example, a retro-reflective segment without a reflective coating can provide a "brighter" area under the incident optical signal, while a retro-reflective segment with a reflective coating can provide a wider viewing angle for the incident optical signal. In the case where a wider retro-reflective viewing angle is not required or desired, the retro-reflective segment 105 can provide retro-reflection through multiple reflective surfaces of the micro-element without depositing a reflective coating on the reflective surface ( Figure 1 ). In these cases, the reflective surface is the surface of multiple microelements. For example, the microelements can have two surfaces that act as reflective surfaces to reflect or retro-reflect the incident visual signal. Therefore, the retro-reflective segment 105 can have a lower manufacturing cost, but has a slightly smaller retro-reflective viewing angle.

[0062] In addition, one or more retro-reflective microelements may be provided from the outer surface 115 at different locations ( Figure 1 115 ) rather than extending from the inner surface 120. In these cases, the retro-reflective microelements must be further covered by a reflective coating deposited on the surface of the retro-reflective microelements 130 to ensure or improve the retro-reflectivity. More specifically, the surface without the reflective coating generally does not retro-reflect an incident optical signal traveling from a medium with a lower refractive index to a medium with a higher refractive index (e.g., from air to a polymer). In addition, for the case where the retro-reflective microelements extend from the outer surface 115, as described above, depositing a reflective covering on the surface of the retro-reflective microelements 130 can provide a wider retro-reflective viewing angle.

[0063] Furthermore, since these retro-reflective microelements 130 are located on the outer surface 115, liquids and dust in the environment may get stuck in the gaps between them, thereby compromising the retro-reflectivity of the marker 105. Therefore, the marker 105 may be further protected by a transparent or translucent cover so that the retro-reflective microelements are shielded from contamination caused by liquids or dust in the environment.

[0064] In some embodiments, the retro-reflective segment 105 forms the entire 3D marker (eg, a hollow sphere, cone, or cylinder). In these embodiments, the retro-reflective segment 150 may not have any coupling mechanism 170 .

[0065] Figure 2A , Figure 2B and Figure 2C Each presents a method that can be used on a device (e.g. Figure 1A bottom view of different exemplary retro-reflective segments used alone or together in a device 100 of the present invention. The devices described herein may include a plurality of retro-reflective microelements extending away from the inner surface of the device. Generally speaking, the retro-reflective microelements may have different geometries and shapes. For example, the retro-reflective microelements may be microbeads (also referred to as microspheres or cat's eye shapes) or microprisms (also referred to as pyramids). Figure 2A , Figure 2B and Figure 2C Each includes a bottom view of a different microprismatic geometry in a corresponding retro-reflective segment.

[0066] like Figure 2A As shown, the retro-reflective section 205 (e.g., device) includes a two-dimensional array (referred to as array 210) consisting of retro-reflective microprisms 210a, b, c, d, e, f, g, h, i, j, k, l, m, n, p extending from the inner surface 207 of the retro-reflective section 205. In this configuration, each microprism has a top vertex 220 and three bottom vertices 225. Each microprism 210a-p includes a plurality of edges 230 (e.g., three sides and three bottom edges). Each of the three sides connects the top vertex 220 and one of the three bottom vertices 225, and each of the three bottom edges connects two adjacent bottom vertices 225. Since the retro-reflective section 205 may have a curvature, the three bottom edges 225 are not necessarily straight lines. For example, the three bottom edges 225 can be curved edges. The bottom edges usually form a triangle. The spatial angle between adjacent side surfaces 235 of the microprism can be approximately 90 degrees to form a cube corner. More specifically, a cube corner (also known as a corner reflector) typically includes three planes that intersect at right angles to each other. It is configured to reflect the optical signal back to the light source in a direction parallel to the incident direction but with a position offset. The shape of the three intersecting surfaces of the cube corner reflector is typically square. For microprisms, depending on different retro-reflective tasks, the spatial angle between the connecting surfaces can include other applicable degrees in addition to 90 degrees. For example, the spatial angle can vary between 75 degrees and 105 degrees to take into account the situation where one or more light sources are offset relative to one or more optical sensors.

[0067] A number of parameters associated with the retro-reflective microelements can be adjusted to control the brightness and uniformity of the retro-reflective signal. These parameters may include the total number of microelements, the size of each microelement, the internal angle of the microelement, etc. In some cases, the microprisms 210a-p are designed such that each edge 230 is less than 1 mm, and the distance D between two adjacent top vertices 220 (e.g., Figure 2A shown) is less than 1mm.

[0068] Obtaining an accurate and uniform surface form in a microprismatic structure is critical to optimizing retro-reflective performance. Irregularities or defects in the surface form can result in reduced retro-reflective efficiency or scattering of optical signals. In order to control the brightness difference of the retro-reflected optical signal to up to 15 degrees, the surface form of each microprism 210a-p is molded to have a surface finish of less than 1um. The term "surface form" generally refers to the magnitude of the deviation from the desired or expected shape of the retro-reflective micro-element. As an example, the surface form can characterize defects or deviations in the radius, curvature, etc. of the surface of the retro-reflective micro-element. As another example, the surface form can also characterize the deviation of the angle of the adjacent side surface from the desired angle. The term "surface finish" generally refers to the accuracy and quality level of the surface of the retro-reflective micro-element. Surface finish can be represented by parameters such as roughness, waviness, paving, etc. of the surface of the micro-element. Since the surface form is generally related to the deviation from the desired shape or specified tolerance, the surface finish is related to the texture, quality and characteristics of the outermost layer of the surface. Surface form defects are also called "low frequency deviations" and surface finish defects are called "high frequency deviations".

[0069] In order to improve the overall consistency of the brightness of the retro-reflected light, and optionally increase the range of incident angles of retro-reflection, the microprism array 210 can be designed to offset the direction of the central axis. More specifically, one or more microprisms can be selected to perturb the direction of their respective central axes so that these central axes deviate from corresponding predetermined offset values ​​relative to their corresponding surface normal directions. The process for offsetting the direction of one or more central axes can be performed using a randomization algorithm, which is configured to sample the central axis according to a predetermined distribution once executed, and perturb the direction using a value within a predetermined range. Although the overall brightness of the retro-reflected optical signal may be reduced due to the offset value, the overall viewing angle is increased. And because the sampling and perturbation are controlled using a randomization algorithm, the described technology ensures uniform brightness loss and prevents high brightness gradients in different local areas throughout the retro-reflection segment, resulting in improved brightness consistency in different orientations. Reference Figure 3 , Figure 4A , Figure 4B , Figure 4C , Figure 5A , Figure 5B and Figure 5C Describes the details of the randomization algorithm and corresponding examples.

[0070] In addition, other parameters of the microprisms 210a-p can be perturbed to improve the functionality of the retro-reflective segments. For situations where the light source is not coaxially oriented with the optical sensor (e.g., parallel offset), in order to further improve the overall brightness consistency of the retro-reflective segments at different positions between the retro-reflective segments and the corresponding optical sensors, a similar randomization algorithm can be applied to perturb the spatial angle of the retro-reflective micro-elements. Taking microprisms 210a-p as an example, the spatial angle between the side surface 235 and the overall size of different microprisms 210a-p can be sampled and given a perturbation within a predetermined range to improve the overall brightness consistency of the retro-reflective segments, at the expense of a slight decrease in the overall brightness of the retro-reflective optical signal. Figure 2B Another exemplary microprism geometry is shown. Again, the retro-reflective segment 245 includes a two-dimensional array of microprisms. Each microprism includes a top vertex 240 and six bottom vertices. Each microprism includes multiple edges 250 (e.g., three side edges and six bottom edges). Since the retro-reflective segment 245 typically has a curvature, the bottom edges are not necessarily straight lines; they can be curved edges. The bottom edges typically form a hexagon. The spatial angle between adjacent side surfaces of each microprism can be approximately 90 degrees to form a cube angle. In some embodiments, the spatial angle between the connecting surfaces can include other applicable degrees depending on different retro-reflective tasks. In order to obtain the desired brightness level, the length of each edge is less than 1 mm, and the distance D between two adjacent top vertices 240 is less than 1 mm. In addition, Figure 2B The geometry of one or more microprisms in the embodiment may be similar to that of the embodiment of the present invention. Figure 2A Sampling and perturbation are performed in a similar manner as described.

[0071] Figure 2C Another exemplary microprism geometry is shown. Again, the retro-reflective segment 265 includes a two-dimensional array of microprisms. Each microprism includes a top vertex 270 and five bottom vertices. Each microprism includes multiple edges 280 (e.g., three side edges and six bottom edges). Since the retro-reflective segment 265 typically has a curvature, the bottom edges are not necessarily straight lines; they can be curved edges. The bottom edges typically form a rectangular shape. The spatial angle between adjacent side surfaces of each microprism can be approximately 90 degrees to form a cube angle. In some embodiments, the spatial angle between the connecting surfaces can include other applicable degrees depending on different retro-reflective tasks. In order to obtain the desired brightness level, the length of each edge is less than 1 mm, and the distance D between two adjacent top vertices 270 is less than 1 mm. In addition, Figure 2C The geometry of one or more microprisms in the embodiment may be similar to that of the embodiment of the present invention. Figure 2A Sampling and perturbation are performed in a similar manner as described.

[0072] In some embodiments, more or fewer bottom vertices (e.g., four, seven, ten, or other appropriate number of vertices) may be included. The bottom edge may form any applicable polygon, or even a circle. In addition, although the bottom view of the bodies 205, 245, and 265 is shown as a rectangle for ease of illustration, the shape and size of the retro-reflective segment may include any applicable form. The arrangement, quantity, and size of the microprisms may vary according to different retro-reflective tasks.

[0073] The randomization algorithm described herein for perturbing the spatial angle of the retro-reflective microelement can be performed on a building block of a retro-reflective segment. Typically, a building block can include at least a subset of the retro-reflective microelements in the retro-reflective segment. For simplicity, the following description assumes that the spatial angles in the retro-reflective microelements are the same, which is referred to as the cube angle of the retro-reflective microelement.

[0074] Once executed, the randomization algorithm will disturb the cubic angle of each retro-reflective micro-element in the building block. The perturbation pattern of the cubic angle generated by the randomization algorithm for the building block (hereinafter also referred to as cubic angle variation) can be repeatedly replicated to disturb the cubic angle of other retro-reflective micro-elements in the retro-reflective segment (or those in the retro-reflective mark assembled by a plurality of retro-reflective segments). In this way, the retro-reflective mark or segment can include one or more building blocks with the same cubic angle variation. These building blocks can substantially cover the inner surface of the retro-reflective mark or segment. In some embodiments, these building blocks can be arranged adjacent to each other without overlap and gap. As an alternative, these building blocks can be arranged in a manner adjacent to each other and spaced apart by a gap. For example, the gap can be a size from 0um to a size comparable to the size of the building block.

[0075] Figure 3 An example of a building block 300 having cube angle variations is shown. For purposes of illustration and simplicity, Figure 3 is a top view of the building block 700 in the coordinate system 380. Each micro-element in the building block 300 has a Figure 2B The hexagons described are similar to hexagons. Note that building block 300 and the corresponding cube corner variations can be applied to flat or curved surfaces. Figure 4A , Figure 4B and Figure 4C Describes examples applied to planes and references Figure 5A , Figure 5B and Figure 5C Describes examples applied to surfaces.

[0076] like Figure 3As shown, building block 300 has an N by M array of retro-reflective microelements. Here, building block 300 has 8 by 8 retro-reflective microelements. Note that building block 300 can include other suitable numbers of microelements for edge 360 ​​or 370, for example, three, four, five, nine, eleven, or other suitable numbers of microelements.

[0077] Each microelement defines a cube angle to be perturbed by the randomization algorithm. For example, microelement 310 defines three intersecting planes or surfaces A, B, and C. In the enlarged view 315 of microelement 310, digital identifier 320 refers to surface A in microelement 310, digital identifier 330 refers to surface B in microelement 310, and digital identifier 340 refers to surface C in microelement 340. In addition, two different surfaces define corresponding plane angles at corresponding intersections. As shown in the enlarged view 315 of microelement 310, surfaces 320 and 330 define plane angle 325, surfaces 330 and 340 define plane angle 335, and surfaces 320 and 340 define plane angle 345. For simplicity, the description herein assumes that plane angles 325, 335, and 345 are the same, which are also referred to as cube angles, as described above. Thus, when executed, the randomization algorithm described herein perturbs the cube angles of each micro-element in the building block such that each micro-element has a corresponding perturbed cube angle.

[0078] A randomization algorithm for perturbing the cubic angles of microelements in a building block can be implemented using a random seed and bins. More specifically, a system implementing the randomization algorithm (e.g., a computer system having a processor) can receive data for perturbation from a user. The data can include a basic cubic angle, an angular perturbation range, a perturbation distribution, a random seed for reproducibility, and a plurality of bins for controlling the interval size of the perturbation within the range. For example, the basic cubic angle can be 90 degrees, and the range of the angular perturbation can be 1 degree, 2 degrees, 4 degrees, or other applicable degrees. As another example, the distribution for generating a random seed can include a Gaussian distribution, a Poisson distribution, or other applicable distributions or combinations of distributions. As another example, the random seed can be based on the current machine time or other applicable mechanisms.

[0079] After receiving the user data, the system may first divide the angular perturbation range into a plurality of intervals, each of which represents a corresponding portion of the perturbation range. For example, a perturbation having a range from 0 to 2 degrees may be divided into eight intervals, namely, [0, 0.25) degrees, [0.25, 0.5) degrees, [0.5, 0.75) degrees, [0.75, 1) degrees, [1, 1.25) degrees, [1.25, 1.5) degrees, [1.5, 1.75) degrees, and [1.75, 1] ​​degrees. Alternatively, the perturbation may include negative degrees, for example, a change from negative one degree to positive one degree. In this

[0080] In some cases, the system may determine the interval to start from a minimum disturbance value (eg, negative one degree) to a maximum value (eg, positive one degree).

[0081] For each of the plurality of intervals, the system generates a random number from a particular distribution using one of the received random seeds. The random number may be a real number between 0 and 1. The system then scales the random number to accommodate the range of variation allowed by the interval. For example, if the random number for the interval [0.5, 0.75) is 0.3, the output perturbation is 0.575 degrees. As another example, if the random number for the interval [1.25, 1.5) is 0.7, the output perturbation is 1.425 degrees. The system then applies the output perturbation value to a base cube angle value (e.g., 90 degrees as described above) to determine the perturbed angular value of the microelement. For example, the perturbed cube angle value may be 90.575 degrees, 91.425 degrees, 89.425 degrees, 88.575 degrees, or other applicable degrees.

[0082] The system repeats the above process for each microelement in the building block to determine all angular perturbations. Once the angular perturbations for all microelements are determined for a building block, the system can replicate the cubic angle variation in the building block to cover the surface of a retro-reflective segment or the entire retro-reflective mark.

[0083] As described above, the cube angle variations generated by the randomization algorithm can be applied to flat or curved surfaces. Figure 4A is a perspective view of a retro-reflective building block formed on a plane and having a rectangular geometry with varying cube corners. Building block 410 is presented according to coordinate system 430. Figure 4A As shown, building block 410 has an eight by eight array of retro-reflective microelements, and each edge 415 or 420 has eight arrays of microelements along the corresponding edge direction.

[0084] Note that although for ease of illustration, Figure 4AAn eight by eight array of building blocks 410 is shown, but building blocks can be used in arrays with different sizes depending on the different requirements for cube angle variation. For example, the building blocks can have a five by five array of microelements, a six by six array of microelements, a ten by ten array of microelements, or other suitable sizes. In some embodiments, the building blocks can have a rectangular array, where the building blocks can have more microelements along a first edge than a second edge. For example, the building blocks can have a four by six array of microelements, a seven by three array of microelements, or other suitable sizes.

[0085] Figure 4B An exemplary retro-reflective building block formed on a plane and having varying cube angles is shown. Figure 4B , both building blocks 440 and 450 are presented in a top view. Both building blocks 440 and 450 include retro-reflective microelements extending from respective inner surfaces (or bottom surfaces), and respective reflective coatings on respective outer surfaces (or top surfaces). Building block 450 has a darker appearance than building block 440 because building block 450 is placed in a different orientation relative to ambient lighting. Building block 440 has a different arrangement of retro-reflective microelements than building block 450. For example, building block 440 may have a different number of microelements, microelements with different cube angles, different gaps between adjacent microelements, microelements with different sizes, etc.

[0086] Figure 4C Another exemplary retro-reflective building block positioned on a plane and having a varying cube angle is shown. Building blocks 460 and 470 both correspond to Figure 4B The invention relates to building blocks 440 and 450 of the present invention, except that neither building blocks 460 nor 470 have a reflective coating. Building block 460 has the same micro-component pattern as building block 440, except for the reflective coating. Likewise, building block 470 has the same micro-component pattern as building block 450, except for the reflective coating.

[0087] Cubic angle perturbations can be applied to arc-shaped building blocks. For example, Figure 5A , Figure 5B and Figure 5C is a perspective view of an exemplary retro-reflective building block formed on a curved surface and having a varying cube angle. Here, building blocks 510, 540, and 570 are different perspective views of the same curved building block. Retro-reflective microelements extend from the inner surface of the building block. Each microelement in the building block (e.g., microelement 520, 550, or 580) has a corresponding perturbed cube angle determined by the randomization algorithm described above.

[0088] In addition, the tracking system can implement the randomization algorithm described herein to perturb other parameters. For example, the system can implement the randomization algorithm to perturb the spacing between two adjacent micro-elements. As another example, the tracking system can further implement the randomization algorithm to perturb the position, size, shape or other parameters of each micro-element in the building block and use the building block for the retro-reflective segment or mark to propagate this perturbation.

[0089] Here are some examples of the above perturbations. The characteristic size (e.g., edge length) of the microcomponent varies between 20 μm and 30 μm, and can be perturbed by up to 1 μm. The microcomponent can be rotated from -20 degrees to +20 degrees, and the rotation can be perturbed by up to 1 degree. The spacing between microcomponents can be varied so that each microcomponent is 10-50 μm away from its nearest neighbor, and can be perturbed by up to 1 μm.

[0090] Fig. 6A and Figure 6B Examples of markers 600, 650 are shown, respectively, each including a retro-reflective component that is respectively connected to a base.

[0091] like Fig. 6A As shown, the marker 600 includes a first portion 610 (also referred to as a retro-reflective component) that includes retro-reflective segments (e.g., segments 615, 620, 625, and 630) disposed on the first portion 610. Fig. 6A ). In this example, one or more retro-reflective segments 615, 620, 625, and 630 can be coupled to each other by a coupling mechanism of the corresponding segments. An exemplary coupling mechanism may include a joint that includes a groove or a corresponding protrusion. The assembled retro-reflective segments 615, 620, 625, and 630 of the first portion 610 generally form a hollow spherical marker.

[0092] The marker 600 also includes a retro-reflective section 635 having a connection mechanism to connect the first portion 610 of the marker 600 to the device 645 for retro-reflective tracking. For example, the connection mechanism is configured to connect the first portion 610 of the marker 600 to the base 640. The connection mechanism may include threads, grooves, etc. to engage with corresponding threads, guides, and channels on the base 640 of the marker. In some embodiments, the second portion 635 may include a screw having threads at both ends for connecting the corresponding threads in the first portion 610 and the base 640.

[0093] The base 640 is attached to the device 645 using different techniques. For example, the base 640 can be connected to the device 646 using a joint so that the first portion 610 of the marker 600 can be allowed to rotate about the joint formed between the base 640 and the device 645.

[0094] and Fig. 6A The hollow sphere in the Figure 6B A marker 650 having a hollow cylindrical shape is shown. Likewise, the marker 650 includes a first portion 660 (also referred to as a retro-reflective component) that includes one or more retro-reflective segments 665, 670, 675, and 680. As described above, one or more retro-reflective segments 665, 670, 675, and 680 may be coupled to each other by a coupling mechanism of the corresponding segments. An exemplary coupling mechanism may include a joint that includes a groove or a corresponding protrusion.

[0095] The marker 650 also includes a second portion 685 having a connection mechanism to connect the first portion 660 of the marker 650 to the device 695 for retro-reflection tracking. For example, the connection mechanism is configured to connect the first portion 660 of the marker 650 to the base 690. The connection mechanism may include threads, grooves, etc. to engage with corresponding threads, guides, and channels on the base 690 of the marker. In some embodiments, the second portion 685 may include a screw having threads at both ends for connecting the corresponding threads in the first portion 660 and the base 690.

[0096] Similar to the above combination Fig. 6A As described, the base 690 may be attached to the device 695 using a joint such that the first portion 660 of the marker 650 is allowed to rotate about the joint formed between the base 690 and the device 695 .

[0097] Although for ease of explanation, Fig. 6A and Figure 6B Markers with spherical and cylindrical shapes are shown, respectively; however, the marker can have other individual shapes (or shapes) that are different from or deviate from spherical or cylindrical shapes to accommodate different requirements for retro-reflectivity. For example, the marker can have a hollow cone shape (not shown). As another example, the marker can have a shape slightly different from a standard sphere or cylinder, such as an ellipsoid or other suitable shape.

[0098] Figure 7 is a perspective view of an exemplary tracking system 700 that employs three markers 702, 704, and 706 that are attached to an object for optical tracking. The markers 702, 704, and 706 are respectively equivalent to or similar to Fig. 6A Mark 600 and Figure 6B Marking 650. Markings 702, 704 and 706 can be represented by Figure 1 The retro-reflective section 105 and Figure 2A-C device 200 is formed. For ease of illustration, markers 702, 704, 706 are depicted as hollow cylinders. However, other shapes and geometric figures can also be used for different retro-reflective tasks. In some embodiments, the object for optical tracking can include a reference tool placed near the patient during surgery, and the reference tool establishes fixed coordinates or reference coordinates for optical tracking. In addition, the object for optical tracking may also include a positioning tool used during surgery, and the marker can be used to determine the position and orientation of the positioning tool based on the reference coordinates.

[0099] like Figure 7 As shown, the exemplary tracking system 700 includes a tracked object 716, markers 702, 704, and 706, an optical sensor 708 (e.g., a camera), an optical signal source 718, and a computing system 720. The tracking system 700 is configured to determine the position of the tracked object 716 in the environment by determining the pose of each marker 702, 704, and 706. Figure 7 As shown, the tracked object 716 includes a crossbar structure, wherein one end of a first beam is coupled to a middle portion of a second beam. Mark 704 is located at a free end of the first beam and is spaced apart from the middle portion of the second beam by a distance L2. Marks 702 and 706 are located at both free ends of the second beam and are spaced apart by a distance L1.

[0100] The optical signal source 718 is placed near the optical sensor 708 and may include a light emitting device such as a light emitting diode (LED), an LED array, or any other such source in the NIR spectrum. The optical sensor 708 may include a sensing device such as a CCD or CMOS optical sensor and is configured to capture electromagnetic waves (e.g., optical signals) reflected from the markers 702, 704, and 706 attached to the tracked object 716. Due to the highly retro-reflective nature of the markers 702, 704, and 706, the markers appear as bright spots (optical signatures) in the captured image at certain wavelengths of electromagnetic waves. The captured sensor data is provided to the computing system for further processing.

[0101] The computing system 720 can determine the pose of the tracked object 716 using the received sensor data, predetermined parameters (e.g., position) of the optical sensor 708, and the initial positions and poses of the markers 702, 704, and 706. In some embodiments, the computing system 720 is configured to analyze a predetermined relationship between the markers 702, 704, 706 and their corresponding retro-reflection centers to determine the pose of the tracked object 716. In some embodiments, the computing system 720 can estimate offset values ​​of the retro-reflection centers based on the geometry of the different markers.

[0102] Tracked object 716 may include any object to be tracked by tracking system 700, but typically includes a rigid or semi-rigid object such that markers 702, 704, and 706 do not move relative to each other in space during tracking. Tracked object 716 is typically configured to support multiple markers. Although for ease of illustration, Figure 7 In FIG. 7 , three markers 702 , 704 , and 706 are coupled to the tracked object 716 , but other numbers of markers may also be coupled to the tracked object 716 .

[0103] In some embodiments, the tracked object 716 includes tools for use during surgical tasks. In addition, or as an alternative, the tracked object can be used in other applications and industries, such as industrial metrology or navigation. For example, the tracked object can include a digitized probe for, for example, full-field and / or tactile measurements, an optically trackable scanner, a scale for photogrammetry and laser tracker applications, or other applicable devices. In addition, the markers described herein can be attached to devices used in other industries that also utilize medical devices and other devices. In some embodiments, the markers described herein can be attached together to one or more medical devices or other types of devices.

[0104] Additionally, tools for various applications (e.g., surgical tracking, industrial metrology, or navigation, etc.) may be manufactured with a body such that a portion of the body is manufactured to be retro-reflective (e.g., at least a portion of the body is made of Figure 1 Thus, the tool does not need to be attached to a device formed by one or more retro-reflective segments (e.g., Figure 1 That is, in some embodiments, a tool for optical tracking can be manufactured so that in addition to the retro-reflective segment forming at least a portion of the tool body, the tool can also be attached to a mark formed by one or more retro-reflective segments to enhance the retro-reflectivity.

[0105] Figure 8 It is shown that it is possible to use, for example Figure 1 , Figure 2A -C. Figure 3 , Figure 4A -C. Figure 5A -C. Fig. 6A , Figure 6B and Figure 7 An exemplary tracking system 800 (e.g., an optical tracking system) for a marker. For example, the marker may be similar to Figure 1 Retro-reflective section 105, Fig. 6A Retro-reflective marker 600, Figure 6B The retro-reflective mark 650 and Figure 7 The tracking system 800 includes an illumination / image capture unit 802, in which a marker sensing device (e.g., a camera, a camera array 804a-b, etc.) and a marker illumination device 818a-b (e.g., an electromagnetic wave source) are rigidly mounted. In this example, the illumination device 818a-b emits electromagnetic waves, such as visible light, infrared light, etc. The electromagnetic waves are directed to a portion of the image capture unit 802 including one or more retro-reflective markers (e.g., Fig. 6A Mark 600 or Figure 6B In the region of the marker 650), the one or more retro-reflective markers are attached to the medical device (or object). Figure 8 In the context shown, the medical device (or object) can be a tool 808 (e.g., a surgical tool, a medical device for treating a patient, etc.). The object is sometimes referred to as a tracked object. The retro-reflective marker is configured to have a retro-reflectivity to reflect the incident electromagnetic wave in a direction parallel to and opposite to the incident direction. The camera 804a-b captures one or more images of the illuminated retro-reflective marker. Due to the highly retro-reflective nature of the retro-reflective marker, each marker appears as a relatively bright point in the captured image, and the system can determine spatial coordinates (e.g., Cartesian coordinates, spherical coordinates, cylindrical coordinates, etc.) and intensity values ​​representing, for example, the brightness of each corresponding position. Since the range of incident angles provided by the retro-reflective marker is large, the marker can remain visible in different postures or at different positions relative to the light source. The data is provided to a computing device (e.g., a processor) of the computing system 810. The computing device is configured to determine the position of the retro-reflective marker (and the corresponding object to which they are attached) relative to the area or environment where the camera 804a-b is located.

[0106] Typically, the computing device is part of a computer system 810 that is connected to the camera array 804a-b via a communication link 812 (e.g., a wired communication link or a wireless communication link). In some examples, the computing device is located within the camera mounting unit 802. The computing system 810 may include one or more of various forms of digital computers, including, for example, laptops, desktops, workstations, personal digital assistants, servers, blade servers, mainframes, and other appropriate computers. The computing system 810 may include one or more of various forms of mobile devices, including, for example, personal digital assistants, tablet computing devices, cellular phones, smart phones, and other similar computing devices. The components shown here, their connections and relationships, and their functions are intended to be examples only and are not intended to limit the implementation of the techniques described and / or claimed herein.

[0107] Given the known positions of the cameras 804a-b included in the array and the retro-reflective markers (e.g., Fig. 6A Mark 600 or Figure 6B Based on the position of the markers 650 of the object 808, the computing device can calculate the position and / or orientation of the object 808. In addition, based on the known relationship between the position of each retro-reflective marker and the position of the tool end 820 of the object 808 in the working volume (e.g., the tool coordinate system), the computing device can calculate the coordinates of the tool end 820 in space. When the tool 808 is operated by a user (e.g., a surgeon 814) and the tool end 820 is pressed against a surface (e.g., a patient's body 816) or otherwise in contact with the surface, the coordinates of the tool end 820 correspond to the coordinates of the position where the tool end 820 contacts the surface.

[0108] Many embodiments of the subject matter have been described. However, it should be understood that various modifications may be made without departing from the spirit and scope of the subject matter disclosed herein. For example, the positions of the retro-reflective marker and the tracked object may change over time. The computing device may be configured to automatically detect which bright spots in the image are identified as retro-reflections provided by the retro-reflective marker at a first time and a first position, and which bright spots in the image are identified as retro-reflections provided by the retro-reflective marker at a second time and a second position. Therefore, other embodiments are within the scope of the appended claims.

[0109] Some embodiments of the subject matter and operations described in this patent specification may be implemented in digital electronic circuitry, or in computer software, firmware, or hardware (which includes the structures disclosed in this patent specification and their structural equivalents), or in a combination of one or more of them. For example, in some embodiments, tracking system 800 and computing system 810 may be implemented using digital electronic circuitry, or in computer software, firmware, or hardware, or in a combination of one or more of them.

[0110] Some embodiments described in this patent specification may be implemented as one or more groups or modules of digital electronic circuits, computer software, firmware, or hardware, or in a combination of one or more of them. Although different modules may be used, each module need not be different, and multiple modules may be implemented on the same digital electronic circuit, computer software, firmware, or hardware, or a combination thereof.

[0111] Some embodiments described in this patent specification may be implemented as one or more computer programs (i.e., one or more modules of computer program instructions) encoded on a computer storage medium for execution by a data processing device or for controlling the operation of a data processing device. For example, a computing system (e.g., computing system 810) may be used in a tracking system to control the operation of a transmitter and process images captured by an image sensor. A computer storage medium may be or may be included in a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. In addition, while a computer storage medium is not a propagated signal, a computer storage medium may be a source or destination address of a computer program instruction encoded in an artificially generated propagated signal. The computer storage medium may also be one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices), or be included therein.

[0112] The term "data processing equipment" includes all types of equipment, devices and machines for processing data, for example, including a programmable processor, a computer, a system on a chip, or a plurality of or a combination of the above. In some embodiments, the computing system 810 includes a data processing device as described herein. The device may include a dedicated logic circuit, for example, an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). In addition to hardware, the device may also include code for creating an execution environment for the computer program in question, for example, code constituting a processor firmware, a protocol stack, a database management system, an operating system, a cross-platform runtime environment, a virtual machine, or a combination of one or more of them. The device and the execution environment may implement different computing model infrastructures, such as web services, distributed computing, and grid computing infrastructures.

[0113] A computer program (also referred to as a program, software, software application, script, or code) may be written in any form of programming language, including compiled or parsed languages ​​and declarative or procedural languages. A computer program may, but need not, correspond to a file in a file system. A program may be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files storing one or more modules, subroutines, or portions of code). A computer program may be deployed for execution on one computer or on multiple computers located at one site or distributed across multiple sites and interconnected by a communications network.

[0114] Some of the processes and logic flows described in this patent specification can be performed by one or more programmable processors that execute one or more computer programs to perform actions by running input data and generating output. The processes and logic flows can also be performed by, and the device can be implemented as, a dedicated logic circuit (e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit)).

[0115] For example, processors suitable for executing computer programs include general and special purpose microprocessors, and processors of any type of digital computer. Typically, the processor will receive instructions and data from a read-only memory or a random access memory or both. A computer includes a processor for performing actions according to instructions and one or more memory devices for storing instructions and data. The computer may also include one or more large-capacity storage devices (e.g., magnetic disks, magneto-optical disks, or optical disks) for storing data, or be operatively connected to receive data from it or transmit data to it or both. However, the computer need not have such a device. Devices suitable for storing computer program instructions and data include all forms of non-volatile memory, media, and storage devices, including, for example, semiconductor storage devices (e.g., EPROM, EEPROM, flash memory devices, etc.), magnetic disks (e.g., internal hard disks, removable disks, etc.), magneto-optical disks, and CD-ROM and DVD-ROM disks. The processor and memory may be supplemented by or incorporated into a dedicated logic circuit.

[0116] To provide for interaction with a user, operations may be performed on a computer having a display device (e.g., a monitor or another type of display device) for displaying information to the user, and a keyboard and pointer device (e.g., a mouse, trackball, tablet, touch-sensitive screen, or another type of pointer device) through which the user can provide input to the computer. Other types of devices may also be used to provide for interaction with a user; for example, feedback provided to the user may be any form of sensory feedback, such as visual feedback, auditory feedback, or tactile feedback; and input from the user may be received in any form, including acoustic, voice, or tactile input. In addition, a computer may interact with a user by sending documents to and receiving documents from a device used by the user; for example, by sending a web page to a web browser on a user's client device in response to a request received from the web browser.

[0117] A computer system may include a single computing device or multiple computers that are close to each other or generally remote from each other and generally interact through a communication network. Examples of communication networks include local area networks ("LAN") and wide area networks ("WAN"), interconnected networks (e.g., the Internet), networks including satellite links, and peer-to-peer networks (e.g., ad hoc peer-to-peer networks). The relationship of client and server may arise through computer programs running on the respective computers and having a client-server relationship to each other.

[0118] Fig. 9 An exemplary computer system 900 (e.g., similar to or including Figure 8 The system 900 is a computer system 810, which includes a processor 910, a memory 920, a storage device 930, and an input / output device 940. Each of the components 910, 920, 930, and 940 can be interconnected, for example, by a system bus 950. The processor 910 is capable of processing instructions for execution within the system 900. In some embodiments, the processor 910 is a single-threaded processor, a multi-threaded processor, or another type of processor. The processor 910 is capable of processing instructions stored in the memory 920 or on the storage device 930. The memory 920 and the storage device 930 can store information within the system 900.

[0119] The input / output device 940 provides input / output operations for the system 900. In some embodiments, the input / output device 940 may include one or more of a network interface device (e.g., an Ethernet card), a serial communication device (e.g., an RS-232 port), and / or a wireless interface device (e.g., an 802.11 card, a 3G wireless modem, a 4G wireless modem, an 8G wireless modem, etc.). In some embodiments, the input / output device may include a driver device configured to receive input data and send output data to other input / output devices (e.g., a keyboard, a printer, and a display device 960). In some embodiments, a mobile computing device, a mobile

[0120] Mobile communication devices and other devices.

[0121] Although this patent specification contains many details, these details should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features unique to a particular example. Certain features described in this patent specification in the context of a single embodiment may also be combined. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments, either alone or in any applicable subcombination.

[0122] Thus, specific embodiments of optical tracking systems and retro-reflective markers and methods of tracking retro-reflective markers using the optical tracking systems have been disclosed. However, it should be apparent to those skilled in the art that many more modifications are possible in addition to those already described without departing from the inventive concepts herein. Therefore, the subject matter of the present invention is not limited except in the spirit of the present disclosure. In addition, when interpreting the present disclosure, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms "include" and "comprising" should be interpreted as referring to elements, parts or steps in a non-exclusive manner, indicating that the referenced elements, parts or steps may exist or be used or combined with other elements, parts or steps that are not explicitly referenced.

[0123] Where a range of values ​​is provided, it is understood that, unless the context clearly dictates otherwise, each intermediate value (to one tenth of the unit of the lower limit) between the upper and lower limits of the range and any other stated or intermediate values ​​within the range are included in the subject matter disclosed herein. The upper and lower limits of these smaller ranges may be individually included in the smaller ranges, which are also included in the subject matter disclosed herein, subject to any specifically excluded limitations in the ranges. Where the range includes one or two limitations, ranges excluding one or both of these included limitations are also included in the subject matter disclosed herein.

[0124] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the subject matter, a limited number of exemplary methods and materials are described herein.

Claims

1. A device comprising: A retro-reflective section, the retro-reflective section comprising: External surface, The inner surface, and A plurality of retro-reflective microelements, the plurality of retro-reflective microelements comprising a plurality of reflective surfaces, wherein each of the plurality of retro-reflective microelements extends from the inner surface at a position different from positions of other retro-reflective microelements, and each of the plurality of retro-reflective microelements comprises a central axis extending in a direction corresponding to a surface normal of the outer surface.

2. The device according to claim 1, wherein: One or more of the plurality of reflective surfaces are formed by depositing a reflective coating on a surface of the plurality of retro-reflective microelements.

3. The device of claim 2, wherein: The reflective coating is deposited by vapor deposition on the one or more of the plurality of reflective surfaces of the plurality of retro-reflective microelements.

4. The device of claim 2, wherein: The reflective coating includes a metallic material.

5. The device of claim 1, wherein: One or more of the plurality of reflective surfaces are formed without depositing a reflective coating on surfaces of the plurality of retro-reflective microelements.

6. The device of claim 1, wherein: One of the plurality of retro-reflective microelements is a microprism.

7. The device of claim 1, wherein: The retro-reflective segment also includes a coupling mechanism to couple the retro-reflective segment with one or more other retro-reflective segments.

8. The device of claim 1, wherein: The retro-reflective segment forms at least a portion of a retro-reflective marking having a hollow spherical shape.

9. The device of claim 1, wherein: The retro-reflective segment forms at least a portion of a retro-reflective marking having a hollow cylindrical shape.

10. The device of claim 1, wherein: The retro-reflective segment forms at least a portion of a retro-reflective marking having a hollow cone shape.

11. The device of claim 1, wherein: The retro-reflective segment forms a retro-reflective marking.

12. The apparatus of claim 1, wherein: The geometry and arrangement of the plurality of retro-reflective microelements are predetermined for manufacturing the retro-reflective segment, which is manufactured by injection molding.

13. The apparatus of claim 1, wherein: The length of each edge of one of the plurality of retro-reflective microelements is less than 1 mm.

14. The apparatus of claim 1, wherein: Each of the plurality of retro-reflective microelements defines a micro-prism center, and two adjacent retro-reflective microelements of the plurality of retro-reflective microelements are spaced apart by a distance of less than 1 mm between the corresponding micro-prism centers.

15. The apparatus of claim 1, wherein: The central axis extends in the direction parallel to the surface normal of the outer surface and offset with respect to the surface normal by an offset amount.

16. The device of claim 15, wherein: The offset is determined by applying a randomization algorithm to the plurality of retro-reflective microelements.

17. The apparatus of claim 1, wherein: The retro-reflective segment comprises a polymer that is transmissive in the near infrared (NIR) spectral band.

18. The apparatus of claim 1, wherein: The retro-reflective section forms part of the body of a tool for optical tracking.

19. The apparatus of claim 1, wherein: The retro-reflective segment forms a portion of a marking configured for being mounted to a tool for optical tracking.

20. The apparatus of claim 1, wherein: The retro-reflective segment comprises a first retro-reflective segment and a second retro-reflective segment, the first retro-reflective segment forming part of a body of a tool for optical tracking and the second retro-reflective segment forming a part of the tag configured to be mounted to the tool.

21. A label, comprising: A first portion, the first portion comprising one or more retro-reflective segments coupled to each other, one of the one or more retro-reflective segments comprising: External surface, The inner surface, and a plurality of retro-reflective microelements comprising a plurality of reflective surfaces, wherein each of the plurality of retro-reflective microelements extends from the inner surface at a position different from positions of other retro-reflective microelements, and each of the plurality of retro-reflective microelements comprises a central axis extending in a direction corresponding to a surface normal of the outer surface; and A second portion includes a connection mechanism configured to connect the first portion to a device.

22. The marking of claim 21, wherein: One or more of the plurality of reflective surfaces are formed by depositing a reflective coating on surfaces of the plurality of retro-reflective microelements.

23. The marking of claim 22, wherein: The reflective coating is deposited by vapor deposition on the one or more of the plurality of reflective surfaces of the plurality of retro-reflective microelements.

24. The marking of claim 21, wherein: The marker has a hollow spherical shape, a hollow cylindrical shape or a hollow conical shape.

25. The marking of claim 21, wherein: One of the plurality of retro-reflective microelements is a microprism, and each edge of the microprism has a length of less than 1 mm.

26. An apparatus comprising: means for optical tracking, and A retro-reflective marker attached to the device by a connecting mechanism of the retro-reflective marker, wherein the retro-reflective marker comprises one or more retro-reflective segments coupled to each other, one of the one or more retro-reflective segments comprising: External surface, The inner surface, and A plurality of retro-reflective microelements, the plurality of retro-reflective microelements comprising a plurality of reflective surfaces, wherein each of the plurality of retro-reflective microelements extends from the inner surface at a position different from positions of other retro-reflective microelements, and each of the plurality of retro-reflective microelements comprises a central axis extending in a direction corresponding to a surface normal of the outer surface.

27. The apparatus of claim 26, wherein: One or more of the plurality of reflective surfaces are formed by depositing a reflective coating on a surface of the plurality of retro-reflective microelements.

28. The apparatus of claim 27, wherein: The reflective coating is deposited by vapor deposition on the one or more of the plurality of reflective surfaces of the plurality of retro-reflective microelements.

29. The apparatus of claim 26, wherein: The retro-reflective marker has a hollow spherical shape, a hollow cylindrical shape or a hollow conical shape.

30. The apparatus of claim 26, wherein: One of the plurality of retro-reflective microelements is a microprism, and each edge of the microprism has a length of less than 1 mm.

Images