The present disclosure generally relates to calibration systems, and more particularly, to systems and methods for calibration of tracking systems.
Demand for tracking systems with heightened performance is increasing, including with the growth of electronic virtual reality and augmented reality systems and other electronic devices. Virtual reality systems typically envelop a wearer's eyes completely and substitute a “virtual” reality for the actual view (or actual reality) in front of the wearer, while augmented reality systems typically provide a semi-transparent or transparent overlay of one or more screens in front of a wearer's eyes such that actual view is augmented with additional information. In many virtual reality and augmented reality systems, the movement of a wearer of such a head mounted display may be tracked in various manners, such as via sensors in the head mounted display and/or external to the head mounted display, in order to enable the images being shown to reflect user movements.
Calibration of precise tracking systems such as optical tracking systems or acoustic tracking systems can be challenging, at least because tolerances on calibration equipment are often greater than the expected errors in the tracking systems. A less-precise tracking system can be calibrated by comparing its results to results of a more-precise tracking system, but this leaves the challenge of calibrating the more precise tracking system.
Applicant has discovered that it is possible to move objects carrying optical, acoustic, or other emitters or detectors in a circle with extreme precision, which can provide a “ground truth” condition useful for calibrating tracking systems. For example, with the knowledge that a calibration object such as an optical or acoustic emitter or detector has moved in a perfect circle while measurements are obtained, errors in a manufactured tracking system, such as those that result from manufacturing imperfections, can be accurately measured and then adjusted for, providing a measure of the precision or accuracy of the tracking system and ultimately improving the performance of the tracking system.
A calibration system may be summarized as comprising: a stationary support element; and a sensor assembly rotatably coupled to the stationary support element, the sensor assembly includes at least one photodetector constrained to rotate about an axis of rotation of the sensor assembly. The sensor assembly may include a dome-shaped outer surface and each of the photodetectors may be positioned within the dome-shaped outer surface of the sensor assembly. The at least one photodetector may include a plurality of photodetectors.
Each of the photodetectors may be arranged on the sensor assembly such that no two of the photodetectors are aligned with one another along a radial axis extending radially outward from the axis of rotation. Each of the photodetectors may be arranged on the sensor assembly such that the photodetectors are radially spaced apart from one another with respect to the axis of rotation. Each of the photodetectors may be arranged on the sensor assembly such that the photodetectors are uniformly radially spaced apart from one another with respect to the axis of rotation. Each of the photodetectors may be arranged on the sensor assembly such that no two of the photodetectors sweep out circular paths within a single geometric plane. Each of the photodetectors may be arranged on the sensor assembly such that a clear line of sight exists from a location of an optical system to be calibrated by the calibration system to each of the photodetectors along an entirety of a path of each of the photodetectors.
A calibration system may be summarized as comprising: a stationary support structure; and a plurality of sensor assemblies including a first sensor assembly rotatably coupled to the support structure and a second sensor assembly rotatably coupled to the support structure, the first sensor assembly includes a first plurality of photodetectors constrained to rotate about a first axis of rotation of the first sensor assembly, the second sensor assembly includes a second plurality of photodetectors constrained to rotate about a second axis of rotation of the second sensor assembly.
The support structure may include: a first panel located at a center of a segmented dish and having a hexagonal shape including a first edge, a second edge, a third edge, a fourth edge, a fifth edge, and a sixth edge; a second panel having a trapezoidal shape including a smaller base coupled to the first edge of the first panel; a third panel having a trapezoidal shape including a smaller base coupled to the second edge of the first panel and a first leg coupled to a first leg of the second panel; a fourth panel having a trapezoidal shape including a smaller base coupled to the third edge of the first panel and a first leg coupled to a second leg of the third panel; a fifth panel having a trapezoidal shape including a smaller base coupled to the fourth edge of the first panel and a first leg coupled to a second leg of the fourth panel; a sixth panel having a trapezoidal shape including a smaller base coupled to the fifth edge of the first panel and a first leg coupled to a second leg of the fifth panel; and a seventh panel having a trapezoidal shape including a smaller base coupled to the sixth edge of the first panel, a first leg coupled to a second leg of the sixth panel, and a second leg coupled to a second leg of the second panel.
The plurality of sensor assemblies may include two sensor assemblies rotatably coupled to each of a plurality of the panels of the support structure. Each of the two sensor assemblies rotatably coupled to each of the plurality of panels may include twenty photodetectors constrained to rotate about an axis of rotation of the respective sensor assembly. The calibration system may further comprise: a first motor assembly coupled to the first sensor assembly to actuate the first sensor assembly to rotate about the first axis of rotation; and a second motor assembly coupled to the second sensor assembly to actuate the second sensor assembly to rotate about the second axis of rotation.
A method of calibrating an optical system may be summarized as comprising: moving a first photodetector coupled to a stationary support element along at least a portion of a first circular path; moving a second photodetector coupled to the stationary support element along at least a portion of a second circular path; generating light at the optical system; recording measurements of the generated light taken by the first and second photodetectors; and using the recorded measurements to calculate at least one calibration factor for the optical system.
Using the recorded measurements may include providing the recorded measurements and a specified geometry of the optical system to a non-linear solver. Using the recorded measurements may include providing the recorded measurements and a specified pattern of the generated light to a non-linear solver. Using the recorded measurements may include providing the recorded measurements and a constraint that the photodetectors moved along circular paths to a non-linear solver. The at least one calibration factor may be representative of a deviation of the actual geometry of the optical system from a specified geometry of the optical system.
A method of calibrating an optical system may be summarized as comprising: positioning the optical system at a focal point of a segmented dish formed of a plurality of panels; moving a first photodetector coupled to a first one of the panels along at least a portion of a first circular path; moving a second photodetector coupled to a second one of the panels along at least a portion of a second circular path; generating light at the optical system; recording measurements of the generated light taken by the first and second photodetectors; and using the recorded measurements to calculate at least one calibration factor for the optical system.
The method may further comprise: using the optical system in a virtual reality system; communicating the at least one calibration factor to a component of the virtual reality system; and using the calibration factor to correct measurements of the location of the component. The component may be a headset or a controller.
A calibration system may be summarized as comprising: a stationary support element; and a first light assembly rotatably coupled to the stationary support element, the first light assembly includes at least one light-emitting device constrained to rotate about an axis of rotation of the first light assembly.
The first light assembly may include a plurality of light-emitting devices. The calibration system may further comprise: a second light assembly rotatably coupled to the stationary support element, the second light assembly includes at least one light-emitting device constrained to rotate about an axis of rotation of the second light assembly. The at least one light-emitting device may include at least one light emitting diode.
A calibration system to calibrate a tracking system that includes one of an emitter or a detector may comprise: a stationary support element; and a calibration assembly rotatably coupled to the stationary support element, the calibration assembly includes at least one of the other of an emitter or a detector constrained to rotate about an axis of rotation of the calibration assembly.
The tracking system may include an optical emitter and the calibration assembly may include an optical detector. The tracking system may include an optical detector and the calibration assembly may include an optical emitter. The tracking system may include an acoustic emitter and the calibration assembly may include an acoustic detector. The tracking system may include an acoustic detector and the calibration assembly may include an acoustic emitter.
In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not necessarily drawn to scale, and some of these elements may be arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn are not necessarily intended to convey any information regarding the actual shape of the particular elements, and may have been solely selected for ease of recognition in the drawings.
In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed implementations. However, one skilled in the relevant art will recognize that implementations may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with the technology have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the implementations.
Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprising” is synonymous with “including,” and is inclusive or open-ended (i.e., does not exclude additional, unrecited elements or method acts).
Reference throughout this specification to “one implementation” or “an implementation” means that a particular feature, structure or characteristic described in connection with the implementation is included in at least one implementation. Thus, the appearances of the phrases “in one implementation” or “in an implementation” in various places throughout this specification are not necessarily all referring to the same implementation. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more implementations.
As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its broadest sense, that is, as meaning “and/or” unless the context clearly dictates otherwise.
The headings and Abstract of the Disclosure provided herein are for convenience only and do not limit the scope or meaning of the implementations.
The panel 12 is arranged and oriented with a first major surface thereof facing forward toward the platform 14, and is positioned within a field of view of the optical system 16. The panel 12 includes a sensor assembly 18 rotatably coupled to a central portion of its first major surface. The sensor assembly 18 includes a central hub 20, which is rotatably mounted to the panel 12, and which rotatably couples the rest of the sensor assembly 18 to the panel 12.
The sensor assembly 18 also includes an arm 22 that extends radially outward from the central hub 20 and a head portion 24 that extends forward from the arm 22. The head portion 24 includes one or more photodetectors facing forward from the outer surface of the head portion 24. When the sensor assembly 18 is actuated to rotate about its axis of rotation 26 at the center of its central hub 20, its head portion 24, and each of the one or more photodetectors, travel in a circular path (as used herein, the term “circular path” can refer to either at least a portion of a circle or at least an entirety of a circle) about the axis of rotation 26. In at least some implementations, the optical system 16 is designed and configured to emit light, such as infrared light, according to a predetermined pattern, including various pulses and sweeps of the infrared light across its field of view.
A method of using the calibration system 10 to calibrate the optical system 16 includes controlling the sensor assembly 18 to rotate about its axis of rotation 26, controlling the optical system 16 to emit light according to the predetermined pattern, and measuring the light emitted by the optical system 16 and received by each of the one or more photodetectors of the sensor assembly 18 as it rotates about its axis of rotation 26. Once these measurements have been taken and recorded, they are fed into or provided to a non-linear solver, along with the specified geometry of the optical system 16, the predetermined pattern for the emitted light, and a constraint that each of the individual photodetectors of the sensor assembly 18 moved along a perfect circular path in three-dimensional space.
Using such input information, the non-linear solver then computes and outputs numerical values representative of errors in the actual geometry of the optical system 16 or the deviation of the actual geometry of the optical system 16 from its specified geometry. The numerical values are then stored or used as correction or calibration factors within the optical system 16.
Due to the relatively tight tolerances in commercially available rotational bearings, it is relatively straightforward, using off-the-shelf components, to fabricate the calibration system 10 so that the circular path of the photodetectors of the sensor assembly 18 is highly precise. Specifically, in at least some implementations the calibration system 10 is fabricated so that the circular path of the photodetectors of the sensor assembly 18 is sufficiently precise to detect deviations in the light emitted by the optical system 16 from the predetermined pattern to within an accuracy of, or better than, 0.1 mm at a distance of one meter away from the optical system 16, for example.
As used herein, words such as “front,” “forward,” and other similar terminology refer to a feature being located in the direction of the rotatable platform 110 along an axis extending through the centers of the segmented dish 102 and the rotatable platform 110, while words such as “back,” “rearward,” “behind,” and other similar terminology refer to a feature being located in the direction of the segmented dish 102 along such an axis. As used herein, terms such as “right” and “left” refer to locations as viewed in a direction from the rotatable platform 110 toward the segmented dish 102 along such an axis. As used herein, terms of relative elevation, such as “top,” “bottom,” “upper,” lower,” “above,” “below,” “up,” and “down,” are used in their ordinary sense, that is, with respect to a direction of a gravitational force, such that liquids are drawn by gravity to flow from a first location toward a second location below the first location.
As illustrated in
As illustrated in
As illustrated in
Each of the second, third, fourth, fifth, sixth, and seventh panels 104b-104g has an overall trapezoidal, and specifically a convex isosceles trapezoidal, shape, with the shapes of each of the second, third, fourth, fifth, sixth, and seventh panels 104b-104g being the same as one another. Each of the panels 104b-104g is coupled to the first panel 104a at its respective smaller base side of its trapezoidal shape. Further, each of the panels 104b-104g is coupled to another one of the panels 104b-104g at a first leg of its trapezoidal shape and to another one of the panels 104b-104g at a second leg of its trapezoidal shape.
In particular, the second panel 104b is coupled at the legs of its trapezoidal shape to respective legs of the trapezoidal shapes of the third panel 104c and the seventh panel 104g. The third panel 104c is coupled at the legs of its trapezoidal shape to respective legs of the trapezoidal shapes of the fourth panel 104d and the second panel 104b. The fourth panel 104d is coupled at the legs of its trapezoidal shape to respective legs of the trapezoidal shapes of the fifth panel 104e and the third panel 104c. The fifth panel 104e is coupled at the legs of its trapezoidal shape to respective legs of the trapezoidal shapes of the sixth panel 104f and the fourth panel 104d. The sixth panel 104f is coupled at the legs of its trapezoidal shape to respective legs of the trapezoidal shapes of the seventh panel 104g and the fifth panel 104e. The seventh panel 104g is coupled at the legs of its trapezoidal shape to respective legs of the trapezoidal shapes of the second panel 104b and the sixth panel 104f.
The first panel 104a is held by the support frame 106 so that it is arranged and oriented vertically, with a first major surface thereof spanning between its six outer edges facing forward toward the rotatable platform 110. In particular, a longitudinal axis 118 extending through and perpendicular to the center of the first major surface of the first panel 104a is horizontal and intersects with a first one of the optical systems 112a that is closest to the segmented dish 102. Each of the panels 104b-104g extends from its respective smaller base, coupled to a respective outer edge of the first panel 104a, radially outward from the first panel 104a and forward in a direction aligned with the axis 118 toward the rotatable platform 110, to its respective longer base. In some implementations, the panels 104b-104g extend forward at an angle of about 30 degrees, or between 20 and 40 degrees, or between 10 and 50 degrees, with respect to the first panel 104a, such that the segmented dish forms a truncated hexagonal pyramid with an angle between opposing sides of about 120 degrees, or between 100 and 140 degrees, or between 80 and 160 degrees. A resulting front edge of the segmented dish 102 is hexagonal and formed by the longer bases of the panels 104b-104g.
The segmented dish 102 therefore has an overall concave dish shape when viewed from the rotatable platform 110 and optical systems 112, and covers a field of view of the optical system 112a. As illustrated in
The first optical system 112a, which is to be calibrated by the calibration system 100, is located at a focus or focal point of the segmented dish 102. As used herein, this means that each of an axis extending through and perpendicular to the first panel 104a, an axis extending through and perpendicular to the second panel 104b, an axis extending through and perpendicular to the third panel 104c, an axis extending through and perpendicular to the fourth panel 104d, an axis extending through and perpendicular to the fifth panel 104e, an axis extending through and perpendicular to the sixth panel 104f, and an axis extending through and perpendicular to the seventh panel 104g intersect with the optical system 112a.
In some implementations, an axis extending through a location at or proximate a center of, and perpendicular to, the first panel 104a, an axis extending through a location at or proximate a center of, and perpendicular to, the second panel 104b, an axis extending through a location at or proximate a center of, and perpendicular to, the third panel 104c, an axis extending through a location at or proximate a center of, and perpendicular to, the fourth panel 104d, an axis extending through a location at or proximate a center of, and perpendicular to, the fifth panel 104e, an axis extending through a location at or proximate a center of, and perpendicular to, the sixth panel 104f, and/or an axis extending through a location at or proximate a center of, and perpendicular to, the seventh panel 104g intersect with the optical system 112a.
In some implementations, the platform 110 is a part of a larger system that carries optical systems 112 toward and away from the platform 110. For example, the optical system 112a can be carried to the platform 110 and positioned on one of the pedestals 122, such as the pedestal 122 located farthest from the segmented dish 102, by the larger system. The arms 124a, 124b can be actuated to grasp the optical system 112a and hold it in place with respect to the platform 110. The platform 110 can then be actuated to rotate about its own central longitudinal axis 128, such as on a bearing 126, to carry the optical system 112a to the position illustrated in
Thereafter, the platform 110 can be actuated to rotate about its own central longitudinal axis 128, such as on the bearing 126, to carry the optical system 112a to the position farthest from the segmented dish 102. The arms 124a, 124b can be actuated to release the optical system 112a, and the larger system can carry the optical system 112a away from the platform 110. The larger system can then carry another optical system 112 to the platform 110 and position the optical system 112 on the emptied pedestal 122, to repeat the testing and calibration process.
The platform 110 can carry four different optical systems 112 at a time. Thus, the unloading and re-loading of optical systems from a first one of the pedestals 122 can take place as another optical system 112 positioned on a second one of the pedestals opposite to the first is tested or calibrated using the calibration system 100. Nevertheless, unloading and re-loading of optical systems from the pedestals 122 may not occur while another optical system 112 is tested or calibrated, to minimize potential interference of any resulting movements or vibrations caused by the unloading or re-loading process. Throughout the remainder of this disclosure, reference to the optical system 112a means the optical system 112 that is positioned closest to the segmented dish 102 for testing or calibration by the calibration system 100.
The sensor assembly 130 also includes an arm 138 that extends radially outward from the central hub 132 and a head portion 140 having an overall shape comprising a dome or a portion of a sphere that extends forward from the arm 138. The head portion 140 includes a plurality of (e.g., twenty) photodetectors 142 facing forward from the dome-shaped outer surface of the head portion 140. When the sensor assembly 130 is actuated to rotate about its axis of rotation at the center of its central hub 132, its head portion 140, and each of its photodetectors 142, travel along a circular path about the axis of rotation.
In at least some implementations, the photodetectors 142 are arranged on the surface of the head portion 140 such that no two photodetectors 132 are aligned with one another along a radial axis extending radially outward from the axis of rotation of the sensor assembly 130. The photodetectors 142 may also be arranged so that they are spaced apart from one another, such as uniformly spaced apart from one another, in a radial direction from the axis of rotation, which allows each of the photodetectors 142 to sweep out a different circular path as it rotates about the axis of rotation at the center of the central hub 132. Further, the photodetectors 142 are arranged on the dome shape of the head portion 140 such that no two photodetectors 142 sweep out circular paths within the same geometric plane, and so that there is a clear line of sight from the optical system 112a to each of the photodetectors 142 throughout the entirety of their respective circular paths. Such features improve the overall performance of the calibration system 100.
As illustrated in
The sensor assemblies 130 are mechanically coupled to the input shafts 152, 154 by their respective hubs 132. Due to the relatively tight tolerances in commercially available rotational bearings, it is relatively straightforward, using off-the-shelf components, to fabricate the calibration system 100 so that the circular paths of the photodetectors 142 of the sensor assemblies 130 are highly precise. Specifically, in at least some implementations the calibration system 100 is fabricated so that the circular paths of the photodetectors 142 of the sensor assemblies 130 are sufficiently precise to detect deviations in the light emitted by the optical system 112a from the predetermined pattern to within an accuracy of, or better than, 0.1 mm at a distance of one meter away from the optical system 112a.
As also illustrated in
The optical system 112a is designed and configured to emit light, such as infrared light, according to a predetermined pattern, including various pulses and sweeps of the infrared light across its field of view. For example, the optical system 112a includes a plurality of infrared light emitting diodes (LEDs) and a plurality of infrared laser systems, as well as a plurality of adjustable mirrors and a plurality of adjustable lenses to direct the light across the field of view of the optical system 112a.
The optical system 112a can be used in a virtual or augmented reality system by emitting such light according to the predetermined pattern and thereby allowing a head mounted display unit of the virtual or augmented reality system to determine its position and/or orientation within its environment using photodetectors to detect the emitted light. In order for the optical system 112a to be used in such implementations, it is desirable for the light emitted by the optical system 112a to conform to the predetermined pattern to within an accuracy of, or better than, 0.10 mm at a distance of one meter away from the optical system 112a, for example.
Given that the manufacturing tolerances for the optical system 112a are non-zero, however (i.e., the actual geometry of the optical system 112a, including the positions and orientations of the LEDs, laser systems, mirrors, and lenses, differs from the specified geometry of the optical system 112a), overall performance of the virtual or augmented reality system can be improved by measuring, testing, analyzing, and/or calibrating the optical system 112a prior to shipment to an end-user.
In particular, as illustrated in
Controlling the optical system 112a to emit light according to the predetermined pattern may take only a few (e.g., between two and five or between three and four) seconds, and the photodetectors take measurements of the light they receive at a rate of between 50 and 100 Hz, or between 60 and 80 Hz, such that the total number of measurements taken by the calibration system 100 over the course of the emission of the light according to the predetermined pattern is about 60,000. Once these measurements have been taken and recorded, they are fed into or provided to a non-linear solver, along with the specified geometry of the optical system, the predetermined pattern for the emitted light, and a constraint that each of the individual photodetectors 142 moved along a perfect circular path in three-dimensional space, at 210. Geometric data identifying the location of each of the photodetectors 142 could also be fed into or provided to the non-linear solver, but is not needed for the performance of the non-linear solver.
Due to the arrangement of the photodetectors 142 within each of the sensor assemblies 130, the photodetectors 142 capture many data samples along circular paths that are adjacent to each other, which produces data in the form of a plurality of concentric circles. Using such input information, the non-linear solver then computes and outputs numerical values representative of errors in the actual geometry of the optical system 112a or the deviation of the actual geometry of the optical system 112a from its specified geometry, at 212. As examples, the non-linear solver can output numerical values representative of deviations in the shape and orientation of a spreader lens, in the shape and orientation of an optical sheet, in the speed of a rotor, or in the dynamic behavior of one or more components of the optical system 112a. The numerical values are then stored or used as correction or calibration factors within the optical system 112a, at 214, a measure of overall system accuracy when using the correction factors is computed, at 216, and the optical system 112a is then shipped to an end-user for use in a virtual or augmented reality system, at 218.
Once the end-user begins using the optical system 112a in a virtual or augmented reality system, at 220, the optical system 112a communicates the correction factors to a headset of the virtual or augmented reality system, at 222, and the headset uses the correction factors to correct its measurements of its position and orientation within its environment, based on its detection of the light emitted from the optical system 112a, at 224.
While the calibration system 100 has been described as being used to calibrate an optical system 112a for use within a virtual or augmented reality system, the calibration system 100 could be used to calibrate an optical system 112a, an acoustic (e.g., ultrasound) tracking system, or any other suitable system for use within a three-dimensional tracking system. For example, the calibration system 100 can be modified to include acoustic detectors in place of the photodetectors 142 to be used to calibrate an acoustic emitter in place of the optical system 112a.
Further, while the calibration system 100 has been described as being used to calibrate a light-emitting optical system 112a by using photodetectors moving along circular paths to detect the emitted light, the principles described above for the calibration system 100 could be used to calibrate a light-detecting optical system such as a photodetector, a camera, etc., by using light-emitting devices such as LEDs moving along circular paths. Similarly, the principles described above for the calibration system 100 could be used to calibrate an acoustic detector rather than an acoustic emitter, by using acoustic emitters moving along circular paths.
The various implementations described above can be combined to provide further implementations. These and other changes can be made to the implementations in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific implementations disclosed in the specification and the claims, but should be construed to include all possible implementations along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.
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