BACKGROUND

[0001] Calibration targets may include a substantially rigid plate on which is printed or otherwise provided a plurality of markers. The markers may be provided at intended locations with respect to each other. An image capture mechanism such as a three-dimensional (3D) image capture mechanism, may capture images of the markers and the locations of the markers in the captured images may be used to calibrate the image capture mechanism. In some instances, images of the calibration targets captured while the calibration targets are in various orientations may be used to calibrate the image capture mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Features of the present disclosure are illustrated by way of example and not limited in the following figure(s), in which like numerals indicate like elements, in which:

[0003] FIG. 1 shows a rear isometric view of an example apparatus that may apply a force onto a calibration target having markers and cause an area of the calibration target to become deflected beyond a predefined deflection level;

[0004] FIG. 2 depicts a front isometric view of the apparatus depicted in FIG. 1 ;

[0005] FIG. 3 shows a cross-sectional side view of an example apparatus and a calibration target, in which the calibration target is in an example load state; and

[0006] FIG. 4 shows a cross-sectional side view of an example apparatus and a calibration target, in which the calibration target is in an example load state. DETAILED DESCRIPTION

[0007] For simplicity and illustrative purposes, the present disclosure is described by referring mainly to examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be readily apparent however, that the present disclosure may be practiced without limitation to these specific details. In other instances, some methods and structures have not been described in detail so as not to unnecessarily obscure the present disclosure.

[0008] Throughout the present disclosure, the terms “a” and “an” are intended to denote at least one of a particular element. As used herein, the term “includes” means includes but not limited to, the term “including” means including but not limited to. The term “based on” means based at least in part on.

[0009] Calibration targets having markers may generally be formed of substantially rigid materials. However, the calibration targets may become deflected through the effect of gravity on the calibration targets. Particularly, when a calibration target is positioned in a horizontal orientation and is supported by the edges of the calibration target, a central area of the calibration target may be deflected to a greater extent than other areas of the calibration target. As a result, the locations of the targets on the calibration target may vary with respect to each other depending upon whether the calibration target is held vertically or horizontally as there may be greater deflection when the calibration target is positioned horizontally during image capture. The level of deflection may be reduced in some instances by increasing the thickness of the calibration target. However, such increases in thickness may result in increased manufacturing costs and processes as well as in increased difficulties associated with handling the calibration target due to the increased weight of the calibration target.

[0010] Disclosed herein are apparatuses that may reduce and/or prevent changes in levels of deflection that a calibration target may encounter when the calibration target is positioned at multiple orientations. Particularly, the apparatuses disclosed herein may apply a load, which may equivalently be termed a pre-load, a stress, or a pre-stress, onto the calibration target to cause the calibration target to be deflected to a level that reaches or exceeds a predefined deflection level. The predefined deflection level of the calibration target may be a deflection level that exceeds the level of deflection that the effect of gravity may have on the calibration target when the calibration target is, for instance, supported by its edges while the calibration target is positioned in a horizontal orientation.

[0011] Through implementation of the apparatuses disclosed herein, the calibration target may be deflected to a predefined level and may be maintained at that deflected level regardless of the orientation of the calibration target. As a result, the locations of the markers with respect to each other on the calibration target may remain the same regardless of the orientation of the calibration target. In one regard, therefore, the calibration target may be fabricated with a relatively thin plate, e.g., a plate having a thickness of between around 5 mm and 10 mm, which may reduce or minimize costs associated with fabrication of the calibration target as well as may facilitate simple handling and use of the calibration target, while enabling an optical coordinate measuring machine to accurately measure the positions of the markers on the calibration target while the calibration target is positioned at multiple orientations.

[0012] Reference is first made to FIGS. 1 and 2. FIG. 1 shows a rear isometric view of an example apparatus 100 that may apply a force onto a calibration target 102 having markers 104 and cause an area of the calibration target 102 to become deflected beyond a predefined deflection level. FIG. 2 shows a front isometric view of the apparatus 100 depicted in FIG. 1. It should be understood that the example apparatus 100 depicted in FIGS. 1 and 2 may include additional features and that some of the features described herein may be removed and/or modified without departing from a scope of the apparatus 100.

[0013] As shown, the apparatus 100 may include a frame 110 that may support a calibration target 102 having markers 104. The frame 110 may provide structural support for the calibration target 102. As such, for instance, the frame 110 may protect the calibration target 102 during, for instance, transportation of the calibration target 102. The frame 110 may also support the calibration target 102 during movement of the calibration target 102 into multiple orientations, as may occur during measurement of the markers 104 by an optical coordinate measuring machine (CMM). For instance, the optical CMM may measure the markers 104 while the calibration target 102 is positioned horizontally as the optical CMM may more accurately measure the locations of the markers 104 with respect to each other when the calibration target 102 is in the horizontal position. The CMM may also measure the locations of the markers 104 with respect to each other with the calibration target 102 being positioned at other orientations. In some examples, the measured locations of the markers 104 by the CMM may be used to calibrate an optical 3D scanner, a machine vision system, or the like.

[0014] In many instances, the calibration target 102 may be formed of a relatively thin sheet of material, e.g., with a thickness of between around 5 mm and around 10 mm, and may be formed of glass, quartz, metal (e.g., aluminum), carbon fiber, and/or the like. In addition, the markers 104 may be printed onto the calibration target 102 through screen printing, photolithography, or another manner. The calibration target 102 may be formed to be relatively thin to reduce or minimize the weight of the calibration target 102, which may result in costs associated with fabrication of the calibration target 102 being reduced or minimized. Additionally, the reduced or minimized weight of the calibration target 102 may make transportation and handling of the calibration target 102 relatively easier than may result without the reduced weight.

[0015] As the calibration target 102 may be relatively thin, when the calibration target 102 is positioned at an angle with respect to vertical, gravity may cause a portion of the calibration target 102 to become displaced with respect to other portions thereof. For instance, a central area of the calibration target 102 may experience a greatest level of displacement (e.g., deflection) when the calibration target 102 is positioned horizontally. For instance, the central area may deflect between around 50 microns when positioned horizontally. As a result, the effects of gravity may cause the measured positions of some of the markers 104 with respect to each other to differ depending upon the orientation at which the markers 104 are measured. [0016] As discussed herein, the apparatus 100 may include features that may apply a load onto the calibration target 102 such that an area of the calibration target 102 is deflected beyond a predefined deflection level. In some examples, the predefined deflection level may be a level at which the effects of gravity may not cause the calibration target 102 to become further deflected when the calibration target 102 is oriented in a horizontal position while being held at its edges. By way of particular example, the predefined deflection level may be between around 500 microns and around 700 microns.

[0017] As shown in FIGS. 1 and 2, the calibration target 102 may be inserted into the frame 110 through a rear of the frame 110 and may abut front support members 112 of the frame 110. Alternatively, some or all of the front support members 112 may be disengaged from the frame 110 and the calibration target 102 may be inserted from a front of the frame 110 and the support members 112 may be engaged with the frame 110 to support the calibration target 102. The front support members 112 may be engaged with the frame 110 through use of any suitable connection devices, such as mechanical fasteners, mating engagement features, an adhesive, welds, and/or the like.

[0018] The apparatus 100 may also include a structural component 114 that may extend from a first edge 116 to a second edge 118 of the frame 110. The structural component 114 may be formed of a rigid material that may have less flexibility than the calibration target 102. For example, the structural component 114 may be formed of a metal, a hard plastic, a ceramic, an alloy, and/or the like. In addition, or alternatively, the structural component 114 may be relatively thicker than the calibration target 102. In some examples, the structural component 114 may be formed integrally with other members of the frame 110 while in other examples, the structural component 114 may be formed separately from the other members of the frame 110 and the structural component 114 may be attached to the other members through, for instance, mechanical fasteners, adhesive, welds, and/or the like.

[0019] The structural components 114 may also include a through hole 120 and a loading member 122 that may extend through the through hole 120. As shown in FIG. 1 , the through hole 120 may be positioned at a central location of the structural component 114, while in other examples, the through hole 120 may be positioned at another location of the structural component 114. The through hole 120 and the loading member 122 may have mating engagement features such as grooves and threads that may enable a position of the loading member 122 to move with respect to the structural component 114 as the loading member 122 is rotated within the through hole 120 and to remain in the moved position. In other examples, the loading member 122 may be moved with respect to the structural component 114 and maintained in the moved position through other structural features.

[0020] According to examples, the loading member 122 may have an end portion (shown in FIG. 3) to apply a force onto a back surface of the calibration target 102. The back surface may be the surface opposite the surface on which the markers 104 are provided. In addition, the structural component 114 may maintain the end portion of the loading member 122 with respect to the structural component 114 to apply a load onto the calibration target 102 and cause an area of the calibration target 102 to become deflected with respect to other areas of the calibration target 102 beyond a predefined deflection level. For example, the loading member 122 may be rotated with respect to the structural component 114, in which the rotation of the loading member 122 may cause the distance between the end portion of the loading member 122 to vary. Thus, for instance, the loading member 122 may apply a load to a central area of the calibration target 102, in which a level of the load is to vary based on the varied distance between the end portion and the structural component 114.

[0021] Reference is now made to FIG. 3, which shows a cross-sectional side view of an example apparatus 200 and a calibration target 102, in which the calibration target 102 is in an example load state. It should be understood that the example apparatus 200 depicted in FIG. 3 may include additional features and that some of the features described herein may be removed and/or modified without departing from a scope of the apparatus 200.

[0022] As shown in FIG. 3, the apparatus 200 may include the same or similar features as the apparatus 100 depicted in FIGS. 1 and 2. However, the apparatus 200 is depicted as including additional elements. For instance, instead of a single loading member 122, the apparatus 200 may include a plurality of loading members 122 and the structural component 114 may include a plurality of through holes 120. Thus, for instance, the loading members 122 in the apparatus 200 may apply a more distributed and/or a greater load 202 on the calibration target 102 than the loading member 122 in the apparatus 100. As a result, the loading members 122 in the apparatus 200 may cause a greater load to be applied onto the calibration target 102 while reducing a possibility of damage to the calibration target 102 caused by the application of the load 202.

[0023] The apparatus 200 may also include a force distribution plate 204 that may be in contact with the back surface of the calibration target 102. The force distribution plate 204 may also be in contact with the end portions of the loading members 122 such that the force distribution plate 204 may act as a barrier between the end portions and the force distribution plate 204, which may prevent direct contact between the end portions and the force distribution plate 204 and may reduce a concentrated point load on the calibration target 102. The force distribution plate 204 may be a free floating piece of material, e.g., a spring steel, that may distribute force applied by the loading members 122 to a larger area of the calibration target 102. In addition, the force distribution plate 204 may have a relatively greater flexibility than the calibration target 102 such that the force distribution plate 204 may not prevent the calibration target 102 from reaching a predefined deflection level when the load 202 is applied by the loading members 122.

[0024] As shown in FIG. 3, when a sufficient load 202 is applied onto the calibration target 102, the calibration target 102 may become deflected, e.g., bowed, with respect to the structural component 114. The load 202 applied to the calibration target 102 may also be below a certain level, such as a level that may cause sufficient force to be applied onto the calibration target 102 to cause the calibration target 102 to reach or closely approach a fracture point of the calibration target 102. According to examples, the loading members 122 may be positioned with respect to the structural component 114 to apply a sufficient level of load 202 to cause a central area of the calibration target 102 to be deflected by a sufficient distance to prevent the calibration target 102 from being further deflected by the effects of gravity on the calibration target 102. In other examples, the loading members 122 may be positioned with respect to the structural component 114 to apply a level of the load 202 to cause the calibration target 102 to be deflected by an even greater distance.

[0025] As also shown in FIG. 3, the apparatus 200 may include a gasket 206 positioned between the calibration target 102 and the frame 110, e.g., the front support members 112. The gasket 206 may be formed of a compliant material such as an open-cell foam material, a rubber material, a plastic material, and/or the like. In addition, the gasket 206 may extend around the periphery of the calibration target 102 such that the gasket 206 may be positioned between the calibration target 102 and each of the front support members 112.

[0026] According to examples, the loading members 122 may be positioned with respect to the structural component 114 to cause a sufficient load 202 to be applied onto the calibration target 102 to compress the gasket 206 to a predefined compression level. By way of example, the predefined compression level may correspond to a compression level resulting from the calibration target 102 being deflected beyond the predefined deflection level. As another example, the predefined compression level may be a level at which the calibration target 102 is securely maintained within the frame 110. As a yet further example in which the gasket 206 is formed of an open-cell foam material, the predefined compression level may be a level in which the gasket 206 reaches a densification state of the open-cell foam material.

[0027] As still further shown in FIG. 3, the frame 110 may include a back plate 208 supported by, for instance, the members of the frame 110. The back plate 208 may provide additional structural support for the frame 110 and may include holes located in line with the through holes 120 such that the loading members 122 may extend through the back plate 208.

[0028] Reference is now made to FIG. 4, which shows a cross-sectional side view of an example apparatus 300 and a calibration target 102, in which the calibration target 102 is in an example load state. It should be understood that the example apparatus 300 depicted in FIG. 4 may include additional features and that some of the features described herein may be removed and/or modified without departing from a scope of the apparatus 300.

[0029] As shown in FIG. 4, the apparatus 300 may include the same or similar features as the apparatus 200 depicted in FIG. 3. However, the load 202 in the apparatus 300 depicted in FIG. 4 may be directed in an opposite direction. That is, the loading members 122 may pull the calibration target 102 toward the structural component 114 such that the calibration target 102 may be deflected toward the structural component 114 such that an area of the calibration target 102 may be deflected with respect to other areas of the calibration target 102 beyond the predefined deflection level. In addition, the gasket 206 may be positioned between the rear surface of the calibration target 102 and the frame 110.

[0030] In the example shown in FIG. 4, the force distribution plate 204 may be attached to the calibration target 102, for instance, through use of an adhesive. In addition, the loading members 122 may be rotatably attached to the force distribution plate 204 such that the loading members 122 may remain attached to the force distribution plate 204 while being rotated in a direction that causes the loading members 122 to move away from the calibration target 102.

[0031] Although described specifically throughout the entirety of the instant disclosure, representative examples of the present disclosure have utility over a wide range of applications, and the above discussion is not intended and should not be construed to be limiting, but is offered as an illustrative discussion of aspects of the disclosure.

[0032] What has been described and illustrated herein is an example of the disclosure along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration and are not meant as limitations. Many variations are possible within the scope of the disclosure, which is intended to be defined by the following claims - and their equivalents - in which all terms are meant in their broadest reasonable sense unless otherwise indicated.