CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to United States Provisional Patent Application No. 61/438,505 filed February 1, 2011 under the title HAPTIC DEVICE.

[0002] The content of the above patent application is hereby expressly incorporated by reference into the detailed description hereof.

TECHNICAL FIELD [0003] The present application relates to a device for sensing and generating forces on a body in space, and specifically to a haptic force- feedback device for exchanging forces with the body of a user.

BACKGROUND

[0004] The field of haptics generally relates to the human sense of touch and technology for communicating with users through this sense. A number of haptic devices have been designed to sense the forces exerted by a user on a rigid body and to provide force feedback in response to the user through the rigid body. One application for such devices is to provide a user interface for the navigation or manipulation of virtual or remote environments.

[0005] These devices typically provide between th ree and six degrees of freedom for a user to manipulate the rigid body, the six possible degree of freedom comprising three positional coordinates and three rotational coordinates for the body. Devices have been designed to both sense and generate forces acting on a body in one or more of these various positional and rotational dimensions, using sensors and motors attached to various joints of a mechanism attached to the rigid body. SUMMARY OF THE INVENTION

[0006] A haptic device forms one aspect of the invention. The device comprises a base, a parallel-bar mechanism, and an end effector.

[0007] According to another aspect of the invention, the device comprises a base; a parallel-bar mechanism having a proximal end pivotally attached to the base and a distal end, the parallel-bar mechanism comprising at least four links operatively joined to each other by revolute joints to move within a plane, wherein four of the at least four links form a parallelogram structure within the plane; and an end effector attached to the distal end of the parallel-bar mechanism.

[0008] According to another aspect of the invention, the parallel-bar mechanism comprises a waist piece pivotally mounted to the base and extending substantially away from the base, the waist piece defining a first mounting point and a second mounting point; a short drive arm having a first end and a second end, the first end being pivotally mounted to the first mounting point of the waist piece; a swing link having a first end and a second end, the first end being coupled to the second end of the short drive arm by a revolute joint; a lever link having a first end, an elbow, and a second end, the first end being coupled to the second end of the swing link by a revolute joint and the elbow being coupled to the second mounting point of the waist piece by a revolute joint; a long drive arm having a first end and a second end, the first end being pivotally mounted to the second mounting point of the waist piece; a passive arm having a first end and a second end, the first end being coupled to the second end of the lever link by a revolute joint; and an outer arm having a first end and a second end, the first end defining a first mounting point proximal to the first end and a second mounting point farther from the first end than the first mounting point, the first mounting point being coupled to the second end of the passive arm by a revolute joint and the second mounting point being coupled to the second end of the long drive arm by a revolute joint.

[0009] According to another aspect of the invention, the end effector comprises a rigid body having a first end and a second end, the first end being connected to the second end of the outer arm of the parallel-bar mechanism by a joint having at least two degrees of freedom.

[OOIO] According to another aspect of the invention, the device further comprises at least one counterweight affixed to the parallel-bar mechanism such that the parallel-bar mechanism is statically balanced with the end effector attached over the entire range of movement of the device.

[0011] According to another aspect of the invention, the links of the parallel-bar mechanism comprise a swing link pivotally mounted to a drive arm in addition to the at least four links forming a parallelogram structure within the plane.

[0012] According to another aspect of the invention, the device further comprises at least one motor attached to at least one joint of the parallel-bar mechanism operative to drive movement of the parallel-bar mechanism.

[0013] According to another aspect of the invention, the at least one motor comprises a first motor operative to pivotally drive the short drive arm at its first end; a second motor operative to pivotally drive the long drive arm at its first end; and a third motor operative to pivotally drive the waist piece relative to the base.

[0014] According to another aspect of the invention, the device further comprises at least one rotation sensor attached to at least one joint of the device operative to sense rotation of the joint to which it is attached.

[0015] According to another aspect of the invention, the device has two parallel-bar mechanisms, and the end effector is joined to the distal end of each parallel-bar mechanism by a joint having at least two degrees of freedom.

[0016] According to a further aspect of the invention, the device has three parallel-bar mechanisms, and the end effector comprises a rigid body having three corners, each corner being attached to a distal end of one of the parallel-bar mechanisms by a joint having three degrees of freedom. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which :

[0018] FIG. 1 is a perspective view of a first embodiment of the device with a single parallel-bar mechanism .

[0019] FIG. 2 is a perspective view of the embodiment from FIG. 1 shown from a different viewing angle.

[0020] FIG. 3 is a side view of the embodiment from FIG. 1 showing the left side. [0021] FIG. 4 is a side view of the embodiment from FIG. 1 showing the right side.

[0022] FIG. 5 is a perspective view of the embodiment from FIG. 1 shown from a different viewing angle.

[0023] FIG. 6 is an enlarged partial perspective view of the embodiment from FIG. 1 showing the details of the mechanism close to the base.

[0024] FIG. 7 is an enlarged partial side view of the embodiment from FIG. 1 showing the details of the mechanism close to the base.

[0025] FIG. 8 is a perspective view of a second example embodiment of the device with two parallel-bar mechanisms.

[0026] FIG. 9 is a perspective view of the embodiment from FIG. 8 shown from a different viewing angle.

[0027] FIG. 10 is a perspective view of the embodiment from FIG. 8 shown from a different viewing angle. [0028] FIG. 11 is a perspective view of the embodiment from FIG. 8 shown from a different viewing angle. [0029] FIG. 12 is a perspective view of a third example embodiment of the device with three parallel-bar mechanisms.

[0030] FIG. 13 is a partial perspective view of the embodiment from FIG. 12 shown from a different viewing angle. [0031] FIG. 14 is an exploded side view of the arms and links of an example parallel-bar mechanism used by the above-illustrated embodiments.

[0032] FIG. 15 is a detailed side view of an example waist piece and motors used by a further example embodiment. [0033] FIG. 16 is a perspective view of an example base and base motor used by the example embodiment of FIG. 15.

[0034] FIG. 17 is a further detailed side view of a waist piece, motors, and clamp used by example embodiments.

[0035] FIG. 18 is a perspective view of a waist piece, motors, and sensors used by example embodiments.

[0036] FIG. 19 is a perspective view of an example design of a short drive arm.

[0037] FIG. 20 is a perspective view of an example design of a long drive arm. [0038] FIG. 21 is a foreshortened side view of an example design of a long drive arm.

[0039] FIG. 22 is a perspective view of an example design of an outer arm.

[0040] FIG. 23 is a perspective view of an example design of a passive arm.

[0041] FIG. 24 is a perspective view of an example design of a lever link. [0042] FIG. 25 is a perspective view of an example design of a swing link.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0043] The present application is d irected to a haptic device. In one example embodiment, the device provides a statically-balanced, low-inertia mechanism for sensing and generating forces acting on an end effector within a three-dimensional workspace. In at least some example embodiments, the device keeps its motors and sensors close to a grounded base, thereby further reducing inertia and minimizing the need for rebalancing when different motors, sensors, and/or end effector attachments are swapped in and out. In addition, in at least some example embodiments, the design of the device simplifies the kinematic calculations necessary to sense and control the rotation and position of the end effector relative to other designs. Furthermore, in at least some example embodiments, the structure and components of the device are relatively straightforward, allowing it to be manufactured and assembled easily.

[0044] Turning to the drawings, FIG. 1 to FIG. 5 show a first example embodiment, in which the device comprises a parallel-bar mechanism 114 mounted at one end to a base 102 and having mounted at its other end an end effector 10 that can be positioned and rotated in space and/or manipulated by a user. The parallel-bar mechanism 114 exhibits three degrees of freedom, allowing the user to position the end effector 10 at any point in the three-dimensional workspace defined by the extension of the parallel-bar mechanism 114 from the base 102. The parallel-bar mechanism 114 in combination with the base 102 provides a five-bar mechanism . The end effector 10 is further attached to the end of the parallel-bar mechanism 114 by a universal joint 164 having two degrees of freedom, and the end effector 10 includes a rotatable element 16 thereby providing a sixth degree of freedom. This embodiment therefore provides a full six degrees of freedom for the manipulation of the end effector 10 in the workspace by a user. It also provides active motor control and force feedback over three degrees of movement of the end effector 10 by means of three motors 112, 170, 172. A detailed description of the components of this example embodiment and how they work together follows below.

[0045] In this embodiment, the base 102 is a rigid L-shaped anchoring structure intended for mounting to a grounded surface. It has a horizontal top portion 106 and a vertical side portion 108, the latter of which includes holes 104 to allow mounting to a grounded surface by means of screws or other fasteners. The top portion 106 of the base 102 defines a circular aperture through which is mounted a base motor 112.

[0046] FIG. 6 and FIG. 7 provide a detailed view of the structure proximal to the base 102. The motor 112 has a motor shaft 110 extending upward with a vertical rotational axis, on which is mounted a waist piece 116 of metal or a similar rigid substance. FIG. 7, FIG. 4, and FIG. 15 detail this waist piece 116 as being formed as a single piece of metal having two horizontally oriented circular apertures 118, 120 joined by a narrow elongate aperture 121. As shown in FIG. 17, a clamp 123 is situated within the narrow elongate aperture 121 which serves to compress the two halves of the waist piece 116 around driving motors 170, 172. The first circular aperture 118 accommodates a long arm driving motor 170 and the second circular aperture 120 accommodates a short arm driving motor 172. A motor shaft 182 of the short arm driving motor 172 extends and engages with the end of a short drive arm 122 at a first end 124 of the short drive arm 122, thereby allowing the action of the motor 172 to pivot the arm 122. A second end 126 of the short driving arm 122 is pivotally joined to a first end 130 of a swing link 128 by means of a revolute joint 184. This swing link 128 has a second end 132 pivotally joined to the first end 136 of an L-shaped lever link 134 by means of a revolute joint 186. The lever link 134 has an elbow 140 which is pivotally joined to a motor shaft 190 of the long arm driving motor 170 by a revolute joint 188, allowing the lever link 134 to freely rotate about the motor shaft 190 independent of the operation of the motor 170. The drive motor shafts 190, 182 are parallel, having horizontal rotational axes.

[0047] Closer to the long arm driving motor 170, the motor shaft 190 is actively engaged to the first end 144 of a long driving arm 142, thereby allowing the motor 170 to exert pivotal force upon the long driving arm 142. Thus, the driving arm 142 can be driven by the motor 170 while the lever link 134 pivots freely using the motor shaft 190 as an axle.

[0048] Pivotally joined to the second end 138 of the lever link 134 by means of a revolute joint 192 is the first end 150 of a passive arm 148. Both the long driving arm 142 and the passive arm 148 extend away from the base 102. As shown in FIG. 5, the second end 146 of the long drive arm 142 and the second end 152 of the passive arm 148 are joined by means of revolute joints to an outer arm 154. The passive arm 148 attaches to the outer arm 154 at revolute joint 194 at a first end 156 of the outer arm 154, while the long driving arm 142 attaches at a revolute joint 196 at a location spaced from revolute joint 194 somewhat further from the first end 156 of the outer arm 154.

[0049] The second end 158 of the outer arm 154 attaches to a universal joint 164 supporting the end effector 10. The universal joint 164 in this embodiment has a Y-shaped fork 166 joined by means of a revolute joint 198 at its center to the second end 158 of the outer arm 154. The two arms of the fork 166 are joined by a further revolute joint 200 to an insert 168, which in turn attaches to the end effector 10 by means of a revolute joint 22 allowing the rotatable portion 16 of the end effector 10 to rotate relative to the insert 168. This embodiment shows the end effector as an elongate body with a first end 12 proximal to the insert 168 and a second end 14 distal from the insert 168.

[0050] In operation, the parallel-bar mechanism 114 in the illustrated embodiments always maintains a parallelogram structure regardless of the position of the end effector 10. This parallelogram is formed, on two sides, by the passive arm 148 parallel to the long drive arm 142, and on the other two sides by the outer arm 154 parallel to the segment of the lever link 134 between its elbow 140 and its second end 138. Thus, in the illustrated embodiment, the parallel-bar mechanism 114 is defined by four links (passive arm 148, long drive arm 142, outer arm 154, and lever link 134) which are joined by revolute joints 192, 188, 194, 196. Th is parallelogram structure contributes to the static balance of the device. It also results in relatively uniform forces acting on the device over its entire workspace, thereby simplifying the kinematic calculations necessary for providing haptic feedback or for other sensing or manipulating applications.

[0051] It will be appreciated that the parallel-bar mechanism 114 consists generally of multiple components that pivot within a single vertical plane perpendicular to the top portion 106 of the base 102, mounted on a motor that rotates the mechanism 114 relative to the base 102. This plane, which can rotate about a vertical axis relative to the base 102, defines the parallelogram structure of the mechanism 114. It will further be appreciated that the base motor 112 exerts torque on the mechanism 114 relative to the base; while the long arm driving motor 170 and the short arm driving motor 172 work in conjunction to exert angular forces on the mechanism within its plane of operation, as well as extending or retracting forces by changing the angle of collapse of the parallelogram .

[0052] The mechanism 114 uses two counterweights to maintain static balance across the entire workspace of the device 2. As shown in FIG. 6, a first, large counterweight 180 is attached at the extreme end of the first end 144 of the long drive arm 142, closer to the tip of the arm 142 than the point where it engages with the motor 170. A second, small counterweight 178 is attached at the second end 138 of the lever link 134. These counterweights are placed and scaled to balance the weight of the long driving arm 142, passive arm 148, outer arm 154, and end effector 10 along with any other end attachments. By statically balancing the structure, no motor torque is required to cancel the effect of gravity at the end effector 10, allowing all motor power to be used in providing force feedback to a user. A further consequence of static balance, combined with the direct coupling of the motors 112, 170, 172 to the mechanism 114 to yield a 1 : 1 mechanical advantage, is that the motors provide very high-fidelity control over the device. In alternative embodiments, the motors might be situated so as to provide greater mechanical advantage, with the possible loss of some fidelity.

[0053] By placing all three motors 112, 170, 172 and both counterweights 178, 180 close to the base 102, the perceived inertia of the device 2 at the end effector 10 is minimized. However, some embodiments could employ motors or counterweights positioned elsewhere depending on the intended application and operating environment of the device. Furthermore, in alternative embodiments, the mass and/or location of the counterweights could be changed while keeping them proximal to the base 102. For example, static balance could be achieved with the small counterweight 178 repositioned from the lever link 134 to the passive arm 148 and the mass of the small counterweight 178 adjusted accordingly. In some embodiments, one or both of the counterweights 178, 180 might be omitted altogether, with static balance achieved through other weighted elements.

[0054] In the illustrated embodiments, the design of the waist piece 116 and its orientation at approximately a 45 degree angle away from the base 102 contributes to the static balance of the device by balancing the two motors 170, 172 against each other, with one on either side of the base motor 112.

[0055] While the illustrated embodiment of FIG. 1 to FIG. 7 shows three motors 112, 170, 172 for exerting forces in three spatial dimensions, other embodiments could include additional motors or other actuators to exert torque on the end effector 10. For example, motors could be attached to one or more of the revolute joints 198, 200, 22 defining the three degrees of rotational freedom of the end effector 10, thereby increasing the degrees of active force feedback provided by the device 2 from three (in the illustrated embodiment) to four, five, or six. It will be appreciated that attaching one or more motors proximal to the end effector 10 would introduce significant weight at the most distal point of the mechanism 114, thereby requiring significant increases in the mass of the counterweights 178, 180.

[0056] While not shown in the illustrated embodiment 2, rotation sensors could be placed on one or more of the motor shafts and/or revolute joints of the mechanism 114 to record the rotation of various components and thereby derive the position and/or rotation of the end effector 10. Example embodiments incorporating these sensors are shown in FIG. 15, FIG. 16, and FIG. 18, wherein a base motor sensor 113 is placed on the end of the base motor 112, a first motor sensor 169 is placed on the end of the long arm driving motor 170, and a second motor sensor 171 is placed on the end of the short arm driving motor 172. Placement of a rotation sensor on the shaft of each of the three motors 112, 170, 172 would allow the derivation of the position of the universal joint 164 at the end of the outer arm 154. An additional three sensors on the three revolute joints 198, 200, 22 would allow further derivation of the three degrees of rotation of the end effector 10. In some embodiments, sensors other than rotation sensors could be used to derive the same information. The sensors could be in electrical communication with electronic components attached to the device, such as circuitry built into or attached to the base 102. This same circuitry could control the activity of the motors 112, 170, 172. By processing information from the sensors and activating motors in response to the sensor data and/or other data sources (such as virtual reality environmental data), a force -feed back system could be implemented using the device 2. One of the advantages of this embodiment of the device 2 is that rotational sensor data from the shafts of the three motors 112, 170, 172 translates into positional data via relatively straightforward mathematical equations.

[0057] While the lever link 134 is embodied as a substantially L-shaped boomerang link in the example embodiment 2, it could be bent at different angles, or even straight, depending on the placement of the other components. In the illustrated embodiments, which use an L-shaped boomerang link as the lever link 134, the swing link 128 is generally equal in length to the distance between the shafts of the two motors 170, 172. Similarly, the length of the short drive arm 122 in these embodiments is equal in length to the distance from the first end 136 of the lever link 134 to the elbow 140 of the lever link 134.

[0058] In the described embodiment 2, the various links and arms of each parallel-bar mechanism are formed from a rigid material, such as aluminum or carbon fiber. The long drive arm 142, passive arm 148, and outer arm 154 may be formed from lightweight materials, such as hollow tubes of aluminum or carbon fiber, to minimize the inertia of the device, whereas the short drive arm 122, swing link 128, lever link 134, and waist piece 116 may be formed from a stronger material, such as solid aluminum, owing to their smaller size and the greater stresses upon some of them in operation . However, different metals, polymers, or other materials can be used for some or all of these components depending on the needs of a given embodiment based on its operating environment or application.

[0059] A second example embodiment is illustrated by FIG. 8 to FIG. 11. This embodiment is a device 4 having two parallel-bar mechanisms 114, 214 substantially identical in design to the single parallel-bar mechanism 114 from the first embodiment 2 described above. This device 4 has an end effector 30 having a first end 32 attached by a universal joint 164 to the first parallel-bar mechanism 114 and a second end 34 attached by a universal joint 264 to the second parallel-bar mechanism 214. The end effector 30 has a rotatable element 36, which has a plurality of holes 38 drilled through it to allow the attachment of additional attachments. [0060] This device 4, compared to the first device 2, provides more degrees of active control of the end effector 30 using only the base motors 112, 212, long arm driving motors 170, 270 and short arm driving motors 172, 272. The end effector 30 can be subjected to directional force in three degrees, and also torque in two additional degrees, by the use of these motors alone, thereby giving five degrees of active control to the motors mounted at the bases 102, 202 of the device 4. Similarly, rotational sensors mounted at each of these motors 112, 212, 170, 270, 172, 272 would provide five degrees of passive sensing, leaving only the rotation of the rotational element 36 of the end effector 30 unknown. Alternative embodiments could provide active and/or passive capability to the sixth degree of freedom of the device 4 by attaching a motor and/or a rotational sensor to one of the revolute joints 44, 46 upon which the rotational element 36 rotates. This additional motor could be situated within one of the hollow outer arms 154, 254 of the mechanisms 114, 214, thereby centering its mass and making it easier to counterbalance using weighted elements proximal to the base 102, 202.

[0061] Maintaining static balance in this second device 4 may require that the small counterweight 178 and large counterweight 180 of each of the parallel-bar mechanisms 114, 214 differ in mass from their counterparts in the first device 2, depending on the weight of the end effector 30 and any attachments thereto. It will be appreciated that distributing the weight of any end attachments over two sets of counterweights gives this device 4 greater capacity for static balancing of large end attachments than the previous embodiment 2 having only a single set of counterweights.

[0062] A third embodiment is shown in FIG. 12 to FIG. 13. This embodiment is a device 6 having three parallel-bar mechanisms 114, 214, 314. Each parallel-bar mechanism 114, 214, 314 is joined at its distal end by a universal joint 164, 264, 364 to a platform 50 having three corners 52, 54, 56. The platform 50 has holes 58 for mounting additional attachments.

[0063] This th ird device 6 allows for a full six degrees of active force to be exerted upon the platform 50 by means only of the motors mounted proximal to the bases 102, 202, 302 of each parallel-bar mechanism 114, 214, 314. Similarly, rotational sensors attached to each of these motors would provide six degrees of passive sensing of the position and rotation of the platform 50. Thus, there is no need in this device 6 for any sensors or motors attached to the end platform 50, thereby minimizing the mass and bulk of the platform 50 with which a user directly interacts and which is statically balanced by the counterweights attached to each parallel-bar mechanism 114, 214, 314. This feature further reduces the inertia of the device 6.

[0064] In alternative versions of any of the three described embodiments 2, 4, 6, the universal joints attaching the end effector 10, 30 or platform 50 to the parallel-bar mechanisms could take alternative forms, such as gimbals. In particular, in the third example embodiment 6, because there is no need to sense or control the rotation of any of the joints of the universal joints 164, 264, 364 attached to the platform 50, these joints 164, 264, 364 could in alternative embodiments take the form of ball joints or any other joint with three degrees of freedom. Similarly, either of the other two example embodiments 2, 4 could also replace one or more of the universal joints 164, 264 with ball joints or other joint types, although some of these alternative designs could interfere with the ability to detect or exert torque on the end effector 10, 30. Further alternative embodiments of a single-arm device could omit this universal joint altogether, rigidly coupling the distal end of the outer arm to an end effector.

[0065] While the example embodiments 2, 4, 6 have been described as having motors to exert forces on the end effector and having sensors to sense forces on the end effector, in some embodiments the device could be employed entirely passively to record user manipulation of an end effector or entirely actively to manipulate an end effector in space using motors. In a purely passive embodiment, or in any other embodiment not using the motors to drive the short drive arm and/or long drive arm, the short drive arm and/or long drive arm may not operate as drive arms; accordingly, the term "drive arm" as used herein can be understood to identify a part within the structure and not necessarily its function in every embodiment.

[0066] Additionally, while the participation of a human user has been implied in the above descriptions of example embodiments, the device could be deployed as a sensor and/or manipulator without a user being involved.

[0067] In the example embodiment shown in FIG. 1 to FIG. 5, the end effector 10 is embodied as a pen or other elongate, rotatable body meant to be grasped by a user's fingers. Some embodiments may incorporate a button or other element by which a user can provide additional input to a sensor incorporated into the device. In other possible embodiments, the end effector 10 can take different rotatable and non-rotatable forms, such as a thimble for a single finger, a depressible syringe, or any other object intended for manipulation . Similarly, the end effector 30 of the two-arm device 4 shown in FIG. 8 to FIG. 11 can be embodied in any of a number of forms, including the example end effector 30 depicted in the drawings with an additional object attached via the holes 38 in the rotatable element 36 of the end effector 30. The platform 50 of the three-arm device 6 depicted in FIG. 12 and FIG. 13 is similarly capable of embodiment as a number of different objects, including the platform 50 as depicted with another object attached by means such as the holes 58 in the platform 50. [0068] Alternative embodiments may also vary the shape and design of the base 102. In FIG. 15 and FIG. 16, an alternative embodiment uses a base comprising only a single vertical support, with the shaft of the base motor extending horizontally away therefrom. In other embodiments, the base could take the form of a case or box containing additional components, such as circuitry for controlling the motors and processing input from the sensors. In such an embodiment, the case could also be situated to encompass the body of the base motor 112.

[0069] In the illustrated embodiments, the motors 170, 172 attached to the waist piece 116 can be adjusted as to their standoff height relative to the waist piece 116 by loosening the clamp 123 compressing them within the waist piece 116. This allows the center of mass of the parallel-bar mechanism 114 (which may vary depending on the use of end attachments and the weight of the motors 170, 172) to be adjusted to line up with the base axis. This adjustment is illustrated in FIG. 18 by the bi-directional arrow at the right side of the figure. In alternative embodiments, other means could be provided for clamping or securing these motors.

[0070] The drawings in FIG. 19 to FIG. 25 illustrate details of the shapes used in example embodiments for the various links and arms of the parallel-bar mechanism 114. FIG. 19 shows an example short drive arm 122. FIG. 20 and FIG. 21 show an example long drive arm 142 with large counterweight 180. FIG. 22 shows an example outer arm 154. FIG. 23 shows an example passive arm 148. FIG. 24 shows an example lever link 134 with small counterweight 178. FIG. 25 shows an example swing link 128. [0071] The various embodiments presented above are merely examples and are in no way meant to limit the scope of this disclosure. Variations of the innovations described herein will be apparent to persons of ordinary skill in the art, such variations being within the intended scope of the present application. In particular, features from one or more of the above-described embodiments may be selected to create alternative embodiments comprised of a sub-combination of features which may not be explicitly described above. In addition, features from one or more of the above-described embodiments may be selected and combined to create alternative embodiments comprised of a combination of features which may not be explicitly described above. Features suitable for such combinations and sub-combinations would be readily apparent to persons skilled in the art upon review of the present application as a whole. The subject matter described herein and in the recited claims intends to cover and embrace all suitable changes in technology.