1. A roller screw system comprising:

a main shaft comprising a helically threaded portion and defining a longitudinal axis about which the main shaft rotates;

a nut at least partially radially surrounding the helically threaded portion of the spindle, the nut including helical threads on an inner cavity wall thereof, the nut configured for selective longitudinal movement relative to the spindle in a first direction and a second direction opposite the first direction;

at least one non-helically grooved roller radially interposed between the spindle and the nut; and

a cage holding the at least one roller in position radially between the spindle and the nut, the cage supporting the at least one roller for rotational movement about a longitudinal axis of the at least one roller, the at least one roller maintaining a substantially constant longitudinal position relative to the cage during operation of the roller screw system; wherein the content of the first and second substances,

in response to the transfer of rotational motion from the spindle to the at least one roller and the translation of the rotational motion of the at least one roller to longitudinal motion of the nut, the nut moves in the first direction and the second direction during a duty cycle; and

both the home position of the nut relative to the spindle and the home position of the cage relative to the nut move longitudinally after a predetermined number of cycles of operation.

2. The roller screw system of claim 1, wherein the cage comprises first and second longitudinally spaced rings and a plurality of longitudinally extending rods, the cage configured to longitudinally retain the at least one roller between the first and second rings.

3. The roller screw system of claim 2, wherein at least one rod may be shaped to have different radial distances from the main axis at different longitudinal positions along the rod.

4. The roller screw system of claim 1, wherein the cage is configured to urge the spindle toward a radially centered position within the nut.

5. The roller screw system of claim 4, wherein the cage includes at least one biasing tab for biasing contact with a selected one of the nut and the spindle to urge the spindle toward a radially centered position within the nut.

6. The roller screw system of claim 1, comprising a selected one of a torsion spring and a compression spring mechanically interposed between the cage and the nut, the selected spring operable to maintain a longitudinal position of the cage relative to the nut during a sliding phase of operation and to allow the cage to move longitudinally relative to the nut when the at least one roller rotates during a motion transmitting phase of operation.

7. The roller screw system of claim 1, comprising a plurality of rollers, at least two rollers of the plurality of rollers being held at different longitudinal positions relative to the cage.

8. The roller screw system of claim 1, comprising ten rollers.

9. The roller screw system of claim 1, wherein the home position of the nut relative to the spindle moves longitudinally in the first direction after the predetermined number of cycles.

10. The roller screw system of claim 1, wherein the cage moves longitudinally in the second direction relative to the home position of the nut after the predetermined number of cycles of operation.

11. The roller screw system of claim 1, wherein the thread angle of the at least one roller is in the range of 15 ° to 45 °.

12. An electromechanical brake device comprising:

a housing defining a mechanism cavity;

the roller screw of claim 1, at least partially located within the mechanism cavity;

a brake pad operatively connected to the nut to be driven longitudinally thereby; and

a motor operably connected to the spindle to provide rotational motion thereto.

13. An electromechanical brake device comprising:

a housing defining a mechanism cavity;

a roller screw at least partially located within the mechanism cavity, the roller screw comprising

A main shaft comprising a helically threaded portion and defining a longitudinal axis about which the main shaft rotates;

a nut at least partially radially surrounding the helically threaded portion of the spindle, the nut including helical threads on an inner cavity wall thereof, the nut configured for selective longitudinal movement relative to the spindle in a first direction and a second direction opposite the first direction;

at least one non-helically grooved roller radially interposed between the spindle and the nut; and

a cage holding the at least one roller in position radially between the spindle and the nut, the cage supporting the at least one roller for rotational movement about a longitudinal axis of the at least one roller, the at least one roller maintaining a substantially constant longitudinal position relative to the cage during operation of the roller screw system; and

a brake pad operatively connected to the nut to be driven longitudinally thereby; in response to the transfer of rotational motion from the spindle to the at least one roller and the translation of the rotational motion of the at least one roller to longitudinal motion of the nut, the nut moves in the first and second directions during a duty cycle and moves the brake pads accordingly; and

a motor operably connected to the spindle to provide rotational motion thereto.

14. The electromechanical brake device of claim 13 wherein both the home position of the nut relative to the spindle and the home position of the cage relative to the nut move longitudinally after a predetermined number of cycles of operation.

15. The electromechanical brake device of claim 13 wherein the cage comprises first and second longitudinally spaced rings and a plurality of longitudinally extending rods, the cage configured to longitudinally retain the at least one roller between the first and second rings.

16. The electromechanical brake device of claim 13 wherein the cage is configured to urge the spindle toward a radially centered position within the nut.

17. The electromechanical brake device of claim 13 comprising a plurality of rollers, at least two of which are held at different longitudinal positions relative to the cage.

18. The electromechanical brake device of claim 14 wherein a home position of the nut relative to the spindle moves longitudinally in the first direction after the predetermined number of cycles of operation.

19. The electromechanical brake device of claim 14 wherein the cage moves longitudinally in the second direction relative to the home position of the nut after the predetermined number of cycles of operation.

20. The electromechanical brake device of claim 13 wherein a longitudinal position of the cage relative to the nut is maintained during a slip phase of operation and the cage is permitted to move longitudinally relative to the nut as the at least one roller rotates during a motion transfer phase of operation.

Background

Vehicle braking systems typically include a service brake having a service brake application mode and a parking brake system having a parking brake application mode. During service brake application, hydraulic pressure is applied to move the piston. In recent systems, during application of the parking brake, an electric motor and drive mechanism moves a piston by pressing brake pads against a rotor on the wheel to produce the parking brake application. Once the parking brake application is complete, the motor is turned off. Typically, a worm gear or some other threaded member (e.g., a lead screw) is located between the piston and the motor, which prevents the piston from driving the mechanism and motor backwards.

Disclosure of Invention

In one aspect, a roller screw system is described. The main shaft includes a helically threaded portion and defines a longitudinal axis about which the main shaft rotates. The nut at least partially radially surrounds the helically threaded portion of the main shaft. The nut includes a helical thread on its inner cavity wall. The nut is configured for selective longitudinal movement relative to the spindle in a first direction and in a second direction opposite the first direction. At least one non-helically grooved roller is radially interposed between the spindle and the nut. A cage radially retains the at least one roller in position between the spindle and the nut. The cage supports at least one roller for rotational movement about a longitudinal axis of the at least one roller. During operation of the roller screw system, at least one roller maintains a substantially constant longitudinal position relative to the cage. The nut moves in the first direction and the second direction during a work cycle in response to the transfer of rotational motion from the spindle to the at least one roller and the translation of the rotational motion of the at least one roller to longitudinal motion of the nut. Both the home position of the nut relative to the spindle and the home position of the cage relative to the nut move longitudinally after a predetermined number of cycles of operation.

In one aspect, an electromechanical brake device is described. The housing defines a mechanism cavity. The roller screw is at least partially located within the mechanism cavity. The roller screw includes a main shaft including a helically threaded portion and defining a longitudinal axis about which the main shaft rotates. The nut at least partially radially surrounds the helically threaded portion of the main shaft. The nut includes a helical thread on its inner cavity wall. The nut is configured for selective longitudinal movement relative to the spindle in a first direction and in a second direction opposite the first direction. At least one non-helically grooved roller is radially interposed between the spindle and the nut. A cage radially retains the at least one roller in position between the spindle and the nut. The cage supports at least one roller for rotational movement about a longitudinal axis of the at least one roller. During operation of the roller screw system, at least one roller maintains a substantially constant longitudinal position relative to the cage. A brake pad is operatively connected to the nut to be driven longitudinally thereby. In response to the transfer of rotational motion from the spindle to the at least one roller and the translation of the rotational motion of the at least one roller to longitudinal motion of the nut, the nut moves in the first and second directions during a duty cycle and moves the brake pads accordingly. A motor is operatively connected to the spindle to provide rotational motion thereto.

Drawings

For a better understanding, reference may be made to the accompanying drawings in which:

FIG. 1 is an exploded side perspective view of a roller screw system;

fig. 2-4 schematically depict an assembly sequence of the roller screw system of fig. 1;

FIG. 5 is a partial side view of an electromechanical brake device including the roller screw system of FIG. 1;

FIG. 6A schematically depicts the roller screw system of FIG. 1 in a first configuration of use;

FIG. 6B schematically depicts the roller screw system of FIG. 1 in a second configuration of use;

FIG. 7 is a disassembled view of the components of the roller screw system of FIG. 1;

FIG. 8 is a schematic partial side view of the roller screw system of FIG. 1 in a first exemplary configuration;

FIG. 9A is a partial side view of components of the roller screw system of FIG. 1;

FIG. 9B is a schematic partial side view of the components of FIG. 9A in an exemplary use configuration in the roller screw system of FIG. 1;

FIG. 10A is a partial side view of components of the roller screw system of FIG. 1;

FIG. 10B is a schematic partial side view of the components of FIG. 10A in an exemplary use configuration in the roller screw system of FIG. 1;

FIG. 11A is a partial side view of components of the roller screw system of FIG. 1;

FIG. 11B is a schematic partial side view of the components of FIG. 11A in an exemplary use configuration in the roller screw system of FIG. 1;

FIG. 12A is a partial side view of components of the roller screw system of FIG. 1;

FIG. 12B is a schematic partial side view of the components of FIG. 12A in an exemplary use configuration in the roller screw system of FIG. 1;

FIG. 13A is a partial side view of components of the roller screw system of FIG. 1; and

FIG. 13B is a schematic partial side view of the components of FIG. 13A in an exemplary use configuration in the roller screw system of FIG. 1;

this application includes the appendix that forms part of this application. Appendix a provides exemplary embodiments.

Detailed Description

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

As used herein, the singular forms "a", "an" and "the" may include the plural forms as well, unless the context clearly indicates that the plural form is not included. It will be further understood that the terms "comprises" and/or "comprising," when used herein, may specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.

As used herein, the term "and/or" may include any and all combinations of one or more of the associated listed items.

It will be understood that when an element is referred to as being "on," "attached to," "connected to," "coupled to," "contacting," "adjacent to" another element, etc., it can be directly on, attached to, connected to, coupled to, contacting or adjacent to the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, "directly on," "directly attached to," "directly connected to," "directly coupled to," "directly contacting" or "directly adjacent to" another element, there are no intervening elements present. It will also be appreciated by those of ordinary skill in the art that references to one structure or feature being "directly adjacent" another feature arrangement may have portions that overlap or underlie the adjacent feature, while one structure or feature being "adjacent" another feature arrangement may not have portions that overlap or underlie the adjacent feature.

Spatially relative terms, such as "below," "lower," "over," "upper," "proximal," "distal," and the like, may be used herein to facilitate describing the relationship of one element or feature to another element(s) or feature as illustrated in the figures. It will be understood that the spatially relative terms may encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features.

As used herein, the phrase "at least one of X and Y" may be interpreted to include X, Y or a combination of X and Y. For example, if an element is described as having at least one of X and Y, that element may include X, Y or a combination of X and Y at a particular time, the choice of which may vary from time to time. In contrast, the phrase "at least one of X" can be interpreted to include one or more X.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. Thus, a "first" element discussed below could also be termed a "second" element without departing from the teachings of the present disclosure. The sequence of operations (or steps) is not limited to the order presented in the claims or figures unless specifically indicated otherwise.

The invention includes, consists of, or consists essentially of the following features in any combination.

Fig. 1 depicts a roller screw system 100 including a main shaft 102 having a helically threaded portion 104 and defining a longitudinal axis L about which the main shaft 102 rotates. The term "longitudinal" is used herein to refer to a direction that is axially coincident with the main axis 102, and is substantially horizontal in the orientation of fig. 1.

The nut 106 at least partially radially surrounds the helically threaded portion 104 of the main shaft 102. Nut 106 includes a helical thread on its inner cavity wall 108. The nut 106 is configured for selective longitudinal movement relative to the spindle 102 in a first direction and in a second direction opposite the first direction. For example, the nut 106 may travel in a forward F direction and a rearward B direction, as shown in fig. 1.

At least one non-helically grooved roller 110 is radially interposed between the main shaft 102 and the nut 106. The cage 112 holds the at least one roller 110 radially in place between the main shaft 102 and the nut 106, as shown in FIG. 3. As referred to herein, a "radial" direction is a direction substantially perpendicular to the longitudinal direction and extending into and from the plane of the page in fig. 1-4.

The cage 112 supports the at least one roller 110 for rotational movement about a longitudinal axis LR of the at least one roller 110, as shown in the figures. During operation of the roller screw system 100, at least one roller 110 maintains a substantially constant longitudinal position relative to the cage 112. In other words, the roller screw system 100 shown and described herein is not of the recirculating type; instead, during operation of the roller screw system 100, the cage 112 holds the rollers 110 in at least the position shown in fig. 3. During operation of the roller screw system 100, the longitudinal position of the rollers 110 relative to the cage 112 is not displaced from the position shown in fig. 3.

The rollers 110, like the other components of the roller screw system 100, may have any desired specifications for a particular use environment. Various exemplary configurations of the various components of the roller screw system 100 are given in appendix a, which is incorporated herein by reference as an integral part of the present application. For example, the at least one roller 110 may have a thread angle in the range of 0 ° to 90 °, more specifically 10 ° to 60 °, and even more specifically 15 ° to 45 °. The term "thread angle" is used herein to refer to the angle between a reference plane taken substantially perpendicular to the longitudinal axis of the threaded rod (e.g., the LR of the roller 110) and the thread flanks. "thread angle" is the angle marked θ in the "Power screw" reference that can be on https:// roymech. org/usefull _ Tables/Cams _ Springs/Power _ screens _1.html (last visit 3/16/2020). It should be noted, however, that at least one of the rollers 110 is non-helically threaded. That is, a series of closed grooves are provided along the length of the roller 110, rather than a continuous "progressive" screw-type flight as in a "helical" screw member.

It is contemplated that the roller screw system 100 may include a plurality of rollers in the range of three to twenty, and more specifically, for certain use environments, ten rollers 110 will be provided.

It is contemplated that the cage 112 may include one or more shafts (not shown) that extend fully or partially into corresponding bores of one or more of the rollers 110 to facilitate holding the rollers 110 in place relative to the cage 112 and to facilitate rotation of the rollers 110 about their own longitudinal axes LR.

As shown in at least fig. 1-4, the cage 112 may include longitudinally spaced apart first and second rings 114 and a plurality of longitudinally extending rods 116. When present, the cage 112 may be configured to retain at least one roller 110 longitudinally between the first and second rings 114, and/or between a pair of adjacent rods 116 around the circumference of the roller 112.

As an exemplary use environment for the roller screw system 100, fig. 5 depicts an electromechanical brake 518. The electromechanical brake 518 includes a housing 520 defining a mechanism cavity 522. The roller screw system 100 is at least partially located within the mechanism cavity 522. The brake pad 524 is operatively connected to the nut 106, either directly or through one or more intermediate structures, to be longitudinally driven thereby. Nut 106 moves in first and second directions (forward F and rearward B, as viewed in fig. 5) and correspondingly moves brake pads 524 to selectively bring brake pads 524 into frictional contact with rotor 526 during parking and/or service brake use of electromechanical brake 518. Movement of the nut 106 (and thus the brake pads 524) occurs along the work cycle in response to the transfer of rotational movement from the spindle 102 to the at least one roller 110 and the subsequent conversion of the rotational movement of the at least one roller 110 to longitudinal movement of the nut 106. A motor (shown schematically at 528 in fig. 5) is operatively connected to the spindle 102 to provide rotational motion to the spindle. The motor 528 may be, for example, brushless or brushed dc current type. It is contemplated that in some use applications, a transmission unit (not shown) may be mechanically disposed between the motor 528 and the main shaft 102. It is also contemplated that for ease of installation and/or operation or for any other purpose, the roller screw system 100 may be at least partially enclosed by a screw housing that protects the roller screw system 100 within the housing 522, as desired.

In this context, a "duty cycle" is defined as an operating cycle of a machine that operates intermittently, rather than continuously. Here, the roller screw system 100 operates intermittently as part of an electromechanical brake 518. Roller screw system 100 is driven, for example, by motor 528 in a first rotational direction (e.g., counterclockwise) to cause movement of spindle 102 in a first or forward direction to push brake pad 524 longitudinally toward rotor 526 via the connection of nut 106 with brake pad 524. Roller screw system 100 may then be driven in a second rotational direction (e.g., clockwise), such as by motor 528, to cause movement of spindle 102 in a second or rearward direction to pull brake pad 524 longitudinally away from rotor 526, again via the connection of nut 106 with brake pad 524.

That is, the nut 106 may move in a first direction and a second direction (forward F and backward B as shown, respectively) during a work cycle in response to a transfer of rotational motion from the spindle 102 (rotating about the longitudinal axis) to the at least one roller 110 and a conversion of the rotational motion of the at least one roller 110 about its own longitudinal axis LR to the longitudinal motion of the nut 106. As schematically shown in fig. 6A-6B, both the home position of the nut 106 relative to the spindle 102 and the home position of the cage 112 relative to the nut 106 move longitudinally after a predetermined number of work cycles. The brake pads 524 may be directly attached to the nut 106, or any suitable type of intermediate structure may be provided to transfer longitudinal motion from the nut 106 to the brake pads 524.

Fig. 6A depicts the "original" configuration of the roller screw system 100 in a first stage of the life of the roller screw system 100. This first stage may be, for example, shortly after the roller screw system 100 is manufactured. When the roller screw system 100 is used in the electromechanical braking device 518, it may be in a first-stage original configuration when the brake pads 524 are fairly new and thickest. In this first stage original configuration, the first end 630 of the nut 106 may be directly and closely adjacent to the flange 632 of the main shaft 102, and the first end 634 of the cage 112 may be slightly spaced from the first end 630 of the nut 106. It should be noted that the distance and spacing may be small and it is not necessary to have the various components longitudinally aligned with one another; it should be emphasized that fig. 6A-6B depict the trend of motion only schematically and, like all the figures of the present application, are not drawn to scale. The nut 106 and cage 112 (and associated rollers 110) will reciprocate longitudinally during operation of the roller screw system 100, but the "original" configuration or position refers to the "at rest" position to which the roller screw system 100 returns when not in powered use.

At least in part because the roller screw system 100 is not of the recirculating type, the rollers 110 will tend to "climb" or shift relative to the nut 106 and/or spindle 102 during operation due to the natural interaction of the threads (helical and non-helical) of these components, even as they reciprocate in the first and second directions during a duty cycle of the roller screw system 100. Fig. 6B schematically depicts the "original" configuration of the roller screw system 100 in a second stage of the life of the roller screw system 100. The second phase may be, for example, after a predetermined number of duty cycles have elapsed, and may be associated with wear and subsequent thinning of brake pad 524 during use.

As shown in fig. 6B, the home position of the nut 106 relative to the spindle 102 has been moved longitudinally in a first direction after a predetermined number of cycles of operation. Meanwhile, after a predetermined number of cycles of operation, the home position of the cage 112 relative to the nut 106 has been moved longitudinally in the second direction. Also, this phenomenon tends to occur as the rollers 110 are progressively displaced relative to the nut 106 and spindle 102 over at least a predetermined number of cycles. For most use environments, this predetermined number will be very large, potentially thousands of thousands.

It should be noted that in the context of use of the electromechanical brake device 518, this longitudinal displacement may be designed by one of ordinary skill in the art to be very conveniently associated with wear on the brake pads 524 such that the roller screw system 100 may be "reset" to the first stage home position or configuration when the brake pads 524 are replaced. This is the use environment schematically shown in fig. 6A to 6B as an example. For example, the first end 634 of the cage 112 may be initially located in the first stage at a distance "a" (which may be about 15mm for some use configurations) from the first end 630 of the nut 106. Then, in a second stage, the first end 630 of the nut 106 may be located a distance 2A from the flange 632 of the spindle 102, which position will translate approximately 30mm in the mechanical arrangement depicted in fig. 6A-6B. Throughout this "travel" of the nut 106 and/or cage 112 relative to the spindle 102, the rollers 110 remain in their original longitudinal position relative to the cage 112 and move there as a single unit.

As previously described, the roller screw system 100 may include a plurality of rollers 110, wherein at least two rollers of the plurality of rollers 110 are maintained at different longitudinal positions relative to the cage 112. Fig. 7 schematically depicts a flattened "blank" that may be formed into cage 112 during manufacture of roller screw system 100. As is evident from fig. 7, longitudinally extending rods 116 are interposed between adjacent rollers 110 in the circumferential direction C, however, as can also be seen in fig. 7, the rings 114 may be "stepped" or "tapered" to maintain the rollers 110 at different longitudinal positions relative to the cage 112 during operation of the roller screw system 100. It is contemplated that the distance by which the longitudinal positions of one or more rollers 110 are offset from each other may be determined, taking into account, for example, the thread angle or other thread/groove characteristics of one or more components of the roller screw system 100.

Further, as schematically depicted in fig. 8, the cage 112 may be configured to urge the spindle 102 toward a radially centered position within the nut 106. For example, at least one rod 116 may be shaped to have different radial distances from the main axis 102 at different longitudinal positions along the rod 116. As a result, the cage 112 may be used to "space" or "push" at least one of the spindle 102 and the nut 106 against gravity in order to urge the spindle 102 and the nut 106 toward a substantially coaxial position. This may help avoid undesirable wear and imbalance issues within the roller screw system 100 or for any other reason.

The arrangement of the roller screw system 100 shown in fig. 8 uses a contoured or curved configuration of at least one rod 116 of the cage 112 in order to provide the spacing and centering functions just described. However, fig. 9A-13B schematically depict many different potential arrangements that may assist in such centering, pushing, and/or spacing functions and affect the radial position of the main shaft 102 relative to the nut 106. For example, as shown in the various exemplary configurations of fig. 9A-10B, the cage 110 can include at least one biasing tab 936 for biasing contact with a selected one of the nut 106 and the spindle 102 to urge the spindle 102 toward a radially centered position within the nut 106. As shown in these figures, one or more tabs 936 may also or alternatively be provided to selectively interact with the flange 632 of the spindle 102 and thereby act as a "bump stop" for returning the nut 106 toward the spindle 102 during a work cycle. This will help prevent jarring and forceful contact between the components of the roller screw system 100 during use.

Turning now to fig. 11A-13B, the roller screw system 100 may include one of a torsion spring (shown schematically as 1138 in fig. 11A-12B) and a compression spring (shown schematically as 1340 in fig. 13A-13B) mechanically interposed between the cage and the nut 106. When present, the torsion springs 1138 and/or compression springs 1340 are selected to operate to help maintain the longitudinal position of the cage 112 relative to the nut 106 during the sliding phase of operation. The compression spring 1340 and/or the torsion spring 1138 may also help to allow longitudinal movement of the cage 112 relative to the nut 106 as the at least one roller 110 rotates during the motion transfer phase of operation. Any desired flange, lip, tab, aperture, clip, or any other structure may be provided as desired to help retain the torsion spring 1138 and/or the compression spring 1340 in place relative to the other components of the roller screw system 100. In other words, the spring may help maintain the position of the cage 112 relative to the nut 106 during (allowed) slippage in the system, and then allow the cage 112 to rotate as the rollers 110 rotate under axial load.

While aspects of the present disclosure have been particularly shown and described with reference to the example aspects above, it will be understood by those of ordinary skill in the art that various additional aspects may be contemplated. For example, the particular methods described above for using the apparatus are merely illustrative; one of ordinary skill in the art may readily determine any number of tools, sequences of steps, or other means/options for placing the above-described apparatus or components thereof in a position substantially similar to that shown and described herein. Some of the repeated components shown are not specifically numbered in order to preserve clarity of the drawings, but one of ordinary skill in the art will recognize, based on numbered components, that element numbers should be associated with unnumbered components; and distinction between similar elements is not meant or implied solely by the presence or absence of element numbers in the figures. Any of the described structures and components may be integrally formed as a single unitary or monolithic piece, or be composed of separate sub-components, wherein any of these forms involve any suitable blank or customized component and/or any suitable material or combination of materials. Any of the described structures and components may be disposable or reusable as desired for a particular use environment. Any component may be provided with a user-perceptible marking to indicate a material, configuration, at least one dimension, etc. associated with the component, which potentially assists a user in selecting one component from an array of similar components for a particular use environment. The "predetermined" state may be determined at any time before the structure being manipulated actually reaches that state, the "predetermined" being reached at the latest just before the structure reaches that predetermined state. The term "substantially" as used herein refers to a substantial but not necessarily all amount, which means that the amount specified-a "substantial" amount, is allowed to include somewhat less than all non-quantitative terms. Although certain components described herein are shown as having a particular geometry, all structures of the present disclosure may have any suitable shape, size, configuration, relative relationship, cross-sectional area, or any other physical characteristic as desired for a particular application. Any structure or feature described with reference to one aspect or configuration may be provided to any other aspect or configuration, alone or in combination with other structures or features, as it would not be practical to describe each aspect and configuration discussed herein as having all the options discussed with respect to all other aspects and configurations. An apparatus or method incorporating any of these features should be understood to fall within the scope of the present disclosure as determined in accordance with the appended claims and any equivalents thereof.

Other aspects, objects, and advantages can be obtained from a study of the drawings, the disclosure, and the appended claims.