UPSTREAM NOZZLE SENSOR FOR INJECTION MOLDING APPARATUS AND METHODS OF USE

Abstract

A strain gauge nozzle adapter that may be placed between a barrel end cap and a nozzle body of an injection molding system, the strain gauge nozzle adapter having a strain gauge pin that measures strain within the strain gauge nozzle adapter for use in approximating conditions within an injection molding system, such as pressure or the location of a melt flow front. The strain gauge nozzle adapter may include a plurality of strain gauge pins. An alternative material insert in the strain gauge nozzle adapter may surround a strain gauge pin to amplify meaningful measurements obtained by the strain gauge pin so that noise measurements do not compromise the accuracy of approximation of conditions within a mold.

Claims

1. An external sensor nozzle adapter for an injection molding system comprising: a melt flow inlet attachable to a barrel end cap; a melt flow outlet attachable to a nozzle body; a melt flow conduit extending between the melt flow inlet and the melt flow outlet, the melt flow conduit having an internal melt flow conduit wall and an external melt flow conduit wall; an aperture for an external sensor on the external melt flow conduit wall, the aperture having a bottom that is at least a minimum distance from the internal melt flow conduit wall; and an external sensor in the aperture.

2. The external sensor nozzle adapter of claim 1, wherein the external sensor is a strain gauge pin.

3. The external sensor nozzle adapter of claim 1, wherein the minimum distance is at least 0.5 mm.

4. The external sensor nozzle adapter of claim 1, wherein the external sensor nozzle adapter includes an alternative material insert surrounding the aperture, the alternative material insert made from a material that amplifies the strain experienced by the external sensor nozzle adapter.

5. The external sensor nozzle adapter of claim 4, wherein the alternative material insert has a lower flex modulus than the surrounding external sensor nozzle adapter.

6. The external sensor nozzle adapter of claim 5, wherein the alternative material insert is made of brass and the minimum distance is at least 0.5 mm.

7. The external sensor nozzle adapter of claim 6, wherein the alternative material insert is made of aluminum and the minimum distance is at least 0.5 mm.

8. The external sensor nozzle adapter of claim 1, wherein the external sensor nozzle adapter has a plurality of apertures and each of the plurality of apertures has an external sensor in it.

9. The external sensor nozzle adapter of claim 8, wherein the plurality of apertures are located in the same circumferential plane of the external sensor nozzle adapter.

10. An injection molding apparatus, comprising: a mold comprising one or more mold cavities; a ram arranged to form a shot of molten thermoplastic material; a strain gauge nozzle adapter including a strain gauge pin attached between the ram and a nozzle arranged to inject the shot of molten thermoplastic material into the mold cavities; a controller communicatively connected to the ram and nozzle and the strain gauge pin; and a virtual cavity sensor, implemented as a set of instructions that are stored on a non-transitory machine-readable medium, to determine at least one of an approximate pressure or melt flow front location using an output of the strain gauge pin, wherein the injection molding apparatus adjusts an operation of the ram in view of the determined approximate pressure or melt flow front location.

11. The injection molding apparatus of claim 10, wherein the strain gauge nozzle adapter includes an aperture for the strain gauge pin.

12. The injection molding apparatus of claim 11, wherein the strain gauge nozzle adapter includes an alternative material insert surrounding the aperture, the alternative material insert made from a material that amplifies the strain experienced by the strain gauge nozzle adapter.

13. The injection molding apparatus of claim 11, wherein the alternative material insert has a lower flex modulus than the surrounding external sensor nozzle adapter.

14. The injection molding apparatus of claim 13, wherein the alternative material insert is one of aluminum and brass.

15. The injection molding apparatus of claim 12, wherein the aperture has a bottom and the strain gauge nozzle adapter has a melt flow conduit having an internal melt flow conduit wall, and wherein the distance between the bottom of the aperture and an internal melt flow conduit wall is a minimum distance necessary to prevent cracking or leakage.

16. The injection molding apparatus of claim 15, wherein the minimum distance is at least 0.5 mm.

17. The injection molding apparatus of claim 11, wherein the strain gauge nozzle adapter has a plurality of apertures and each of the plurality of apertures has an external sensor in it, and wherein the controller determines at least one of an approximate pressure or melt flow front location using an output of each external sensor, wherein the injection molding apparatus adjusts an operation of the ram in view of the determined approximate pressure or melt flow front location.

18. The injection molding apparatus of claim 17, wherein the plurality of apertures are located in the same circumferential plane of the strain gauge nozzle adapter.

19. The injection molding apparatus of claim 11, further comprising a secondary sensor, and wherein the controller determines at least one of an approximate pressure or melt flow front location using an output of the strain gauge pin and the secondary sensor, wherein the injection molding apparatus adjusts an operation of the ram in view of the determined approximate pressure or melt flow front location.

20. A method of injection molding, comprising: measuring, using a strain gauge pin, the change in strain in a strain gauge nozzle adapter; approximating at least one of a pressure or a melt flow front location within the mold cavity based on the change in strain; comparing the approximated pressure or melt flow front location to a trigger point; and, if the approximated pressure or melt flow front location equals or exceeds the trigger point, activating a virtual cavity sensor, wherein upon activation, the virtual cavity sensor causes a controller to perform an action.

21. The method of injection molding of claim 20, and amplifying a change in an alternative material insert of the strain gauge nozzle adapter.

22. The method of injection molding of claim 20, wherein measuring the change in strain in a strain gauge nozzle adapter includes using a plurality of strain gauge pins.

23. The method of injection molding of claim 20, wherein measuring the change in strain in a strain gauge nozzle adapter includes using a secondary sensor.

24. An injection molding apparatus, comprising: a mold comprising one or more mold cavities; a ram arranged to form a shot of molten thermoplastic material; a strain gauge feed system adapter including a strain gauge pin attached between the nozzle and the mold; a controller communicatively connected to the ram and nozzle and the strain gauge pin; and a virtual cavity sensor, implemented as a set of instructions that are stored on a non-transitory machine-readable medium, to determine at least one of an approximate pressure or melt flow front location using an output of the strain gauge pin, wherein the injection molding apparatus adjusts an operation of the ram in view of the determined approximate pressure or melt flow front location.

25. The injection molding apparatus of claim 24, wherein the strain gauge feed system adapter includes an aperture for the strain gauge pin.

26. The injection molding apparatus of claim 25, wherein the strain gauge feed system adapter includes an alternative material insert surrounding the aperture, the alternative material insert made from a material that amplifies the strain experienced by the strain gauge feed system adapter.

27. The injection molding apparatus of claim 26, wherein the alternative material insert has a lower flex modulus than the surrounding strain gauge feed system adapter.

28. The injection molding apparatus of claim 26, wherein the alternative material insert is one of aluminum and brass.

29. The injection molding apparatus of claim 25, wherein the aperture has a bottom and the strain gauge feed system adapter has a melt flow conduit having an internal melt flow conduit wall, and wherein the distance between the bottom of the aperture and an internal melt flow conduit wall is a minimum distance necessary to prevent cracking or leakage.

30. The injection molding apparatus of claim 29, wherein the minimum distance is at least 0.5 mm.

31. The injection molding apparatus of claim 24, wherein the strain gauge feed system adapter has a plurality of apertures and each of the plurality of apertures has a strain gauge in it, and wherein the controller determines at least one of an approximate pressure or melt flow front location using an output of each strain gauge, wherein the injection molding apparatus adjusts an operation of the ram in view of the determined approximate pressure or melt flow front location.

32. The injection molding apparatus of claim 31, wherein the plurality of apertures are located in the same circumferential plane of the strain gauge feed system adapter.

33. The injection molding apparatus of claim 24, further comprising a secondary sensor, and wherein the controller determines at least one of an approximate pressure or melt flow front location using an output of the strain gauge pin and the secondary sensor, wherein the injection molding apparatus adjusts an operation of the ram in view of the determined approximate pressure or melt flow front location.

34. A method of injection molding, comprising: measuring, using a strain gauge pin, the change in strain in a strain gauge feed system adapter; approximating at least one of a pressure or a melt flow front location within the mold cavity based on the change in strain; comparing the approximated pressure or melt flow front location to a trigger point; and, if the approximated pressure or melt flow front location equals or exceeds the trigger point, activating a virtual cavity sensor, wherein upon activation, the virtual cavity sensor causes a controller to perform an action.

35. The method of injection molding of claim 34, and amplifying a change in an alternative material insert of the strain gauge feed system adapter.

36. The method of injection molding of claim 34, wherein measuring the change in strain in a strain gauge feed system adapter includes using a plurality of strain gauge pins.

37. The method of injection molding of claim 34, wherein measuring the change in strain in a strain gauge feed system adapter includes using a secondary sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that is regarded as the present disclosure, it is believed that the disclosure will be more fully understood from the following description taken in conjunction with the accompanying drawings. Some of the figures may have been simplified by the omission of selected elements for the purpose of more clearly showing other elements. Such omissions of elements in some figures are not necessarily indicative of the presence or absence of particular elements in any of the exemplary embodiments, except as may be explicitly delineated in the corresponding written description. None of the drawings are necessarily to scale.

[0012] FIG. 1 is a front elevation view of an injection molding system;

[0013] FIG. 2 is a front elevation view of an injection molding system including a strain gauge nozzle adapter of the present disclosure including a single strain gauge pin;

[0014] FIG. 3 is a front elevation view of an injection molding system including a strain gauge nozzle adapter of the present disclosure including multiple strain gauge pins in the strain gauge nozzle adapter and a secondary sensor;

[0015] FIG. 4 is an orthogonal view of a portion of an injection system and a mold assembly of an injection molding system, illustrating (exploded from the injection system) a porous metal insert and strain gauge pin for use in a strain gauge nozzle adapter of the injection system;

[0016] FIG. 5 is a longitudinal cross-sectional view of a strain gauge nozzle adapter of the present disclosure;

[0017] FIG. 6 is an enlarged view of the strain gauge pin aperture depicted in the cross-sectional view of a strain gauge nozzle adapter of FIG. 3;

[0018] FIG. 7 is a top view of a strain gauge nozzle adapter of the present disclosure;

[0019] FIG. 8 is a cross-sectional view taken along lines 8-8 in FIG. 7 of a strain gauge nozzle adapter of the present disclosure; and

[0020] FIG. 9 is a front elevation view of an injection molding system including a strain gauge feed system adapter of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Referring to the figures in detail, FIG. 1 illustrates an exemplary injection molding apparatus 10 for producing thermoplastic parts in high volumes (e.g., a class 101 injection mold, or an “ultra-high productivity mold”, a class 102 (medium-to-high productivity mold), or class 103 (a medium productivity mold)). The injection molding apparatus 10 generally includes an injection system 12 and a clamping system 14. A thermoplastic material may be introduced to the injection system 12 in the form of thermoplastic pellets 16. The thermoplastic pellets 16 may be placed into a hopper 18, which feeds the thermoplastic pellets 16 into a heated barrel 20 of the injection system 12. The thermoplastic pellets 16, after being fed into the heated barrel 20, may be driven to the end of the heated barrel 20 by a ram, such as a reciprocating screw 22. The heating of the heated barrel 20 and the compression of the thermoplastic pellets 16 by the reciprocating screw 22 causes the thermoplastic pellets 16 to melt, forming a molten thermoplastic material 24. The molten thermoplastic material is typically processed at a temperature of about 130° C. to about 410° C.

[0022] The reciprocating screw 22 forces the molten thermoplastic material 24, toward a nozzle 26 to form a shot of thermoplastic material, which will be injected into a mold cavity 32 of a mold 28 via one or more gates. A check ring 38 is provided within the barrel toward a tip end of the reciprocating screw 22. The check ring 38 is coupled (e.g., attached) to a portion of the reciprocating screw 22, preferably at a position proximate a tip end of the screw 22. The check ring 38 is generally configured to prevent, or at least limit, a backflow of molten thermoplastic material 24 from flowing in a direction from the nozzle 26 toward the hopper 18. The molten thermoplastic material 24 may be injected through a gate 30, which directs the flow of the molten thermoplastic material 24 to the mold cavity 32. In other embodiments the nozzle 26 may be separated from one or more gates 30 by a feed system (not shown). The mold cavity 32 is formed between first and second mold sides 25, 27 of the mold 28 and the first and second mold sides 25, 27 are held together under pressure by a press or clamping unit 34. The press or clamping unit 34 applies a clamping force during the molding process that is greater than the force exerted by the injection pressure acting to separate the two mold halves 25, 27, thereby holding the first and second mold sides 25, 27 together while the molten thermoplastic material 24 is injected into the mold cavity 32. In a typical high variable pressure injection molding machine, the press typically exerts 30,000 psi or more because the clamping force is directly related to injection pressure. To support these clamping forces, the clamping system 14 may include a mold frame and a mold base.

[0023] Once the shot of molten thermoplastic material 24 is injected into the mold cavity 32, the reciprocating screw 22 stops traveling forward. The molten thermoplastic material 24 takes the form of the mold cavity 32 and the molten thermoplastic material 24 cools inside the mold 28 until the thermoplastic material 24 solidifies. Once the thermoplastic material 24 has solidified, the clamping unit 34 releases the first and second mold sides 25, 27, the first and second mold sides 25, 27 are separated from one another, and the finished part may be ejected from the mold 28. The mold 28 may include a plurality of mold cavities 32 to increase overall production rates. The shapes of the cavities of the plurality of mold cavities may be identical, similar or different from each other. (The latter may be considered a family of mold cavities).

[0024] FIG. 2 illustrates an injection molding system 10 of the present disclosure that includes a strain gauge nozzle adapter 42 and strain gauge pin 52. A controller 50 is communicatively connected with a strain gauge pin 52 and a screw control 36. The strain gauge pin 52 is located on in a strain gauge adapter 42, discussed in greater depth with respect to FIG. 3. The controller 50 may include a microprocessor (or another suitable processing unit, or several such units), a non-transitory memory, and one or more communication links.

[0025] The strain gauge pin 52 senses strain experienced by the strain gauge nozzle adapter 42. Data from the strain gauge pin 52 may be communicated to a processor that calculates the change in the strain of the strain gauge nozzle adapter 42. Electric signals 54 from the strain gauge pin 52 may travel along one or more electrical paths, such as wires 54, depicted in FIG. 1 in solid lines, ranging in strength from −10 to 10 Volts. The controller 50 may be connected to the screw control 36 via wired connection 56. In other embodiments, the controller 50 may be connected to the screw control 36 via a wireless connection, a mechanical connection, a hydraulic connection, a pneumatic connection, or any other type of communication connection known to those having ordinary skill in the art that will allow the controller 50 to communicate with the screw control 36.

[0026] The controller 50 may use the change in strain calculated from the information provided by the strain gauge pin 52 to approximate conditions, such as pressure or melt flow front position, within the mold cavity or, in certain molds, particularly in which the ratio of the length of the flow channel to the thickness of the molded part is large, at the melt flow front of the molten thermoplastic material 24. These approximations may then be used to adjust the injection molding process. For example, the amount of pressure within the mold cavity 32 may be approximated and compared to a maximum permissible mold cavity pressure in order to ensure that the mold cavity 32 is not damaged by excessive mold cavity pressure. If the amount of pressure within the mold cavity 32 is approximated to be dangerously close to the maximum permissible mold cavity pressure, or even in excess of a safety threshold well below the maximum permissible mold cavity pressure, the controller 50 may direct the screw control 36 to cease injecting molten thermoplastic material. Other approximations may be used to control the molding process, such that variations in material viscosity, mold temperatures, melt temperatures, and other variations influencing filling rate, can be used to trigger adjustments to the injection molding system by the controller 50. These adjustments may be made immediately during the molding cycle, or corrections can be made in subsequent cycles. Furthermore, the approximations may be averaged over a number of cycles and then used to make adjustments to the molding process by the controller 50.

[0027] Additionally, the controller 50 is in communication with a virtual cavity sensor 51, which is implemented as a program, or a set of software instructions. More generally, however, a virtual cavity sensor can be implemented in hardware (e.g., as an application-specific integrated circuit (ASIC)), firmware, software, or any suitable combination thereof. In this disclosure, the term “virtual cavity sensor” can refer to a module that determines the value of a process variable, such as pressure, without directly measuring this process variable. For purposes of this application, determines” means “compares the signal indicative of the output from each external sensor to a stored database that correlates that signal value to an approximate pressure or melt flow front location and outputs a signal indicative of that approximate pressure or melt flow front location corresponding to the external sensor signal value.” The strain gauge pin 52 and the virtual cavity sensor 51 together form a pressure controlling system that generates data relevant to strategic controlling of the pressure within the mold cavity 32. As used herein, the term “pressure controlling system” refers to any suitable group of components, which can include both software-implemented and hardware-implemented components, that generate a signal indicative of a condition within a mold cavity based on a signal indicative of another process variable.

[0028] For example, if based on the strain information provided by the strain gauge sensor 52, a processor associated with the controller 50 determines that pressure within the mold cavity exceeds a trigger point (or is outside of a predetermined acceptable range), the virtual cavity sensor 51 signals the controller to adjust the screw control 36 to bring the pressure within the mold cavity back to a level below the trigger point (or within the predetermined acceptable range). As another example, if based on the strain information provided by the strain gauge sensor 52, a processor associated with the controller 50 detects that changes in plastic pressure have progressed beyond a trigger point (which may correlate to a percentage of the mold that has been filled), the virtual cavity sensor 51 signals the controller to adjust the screw control 36 to bring the pressure within the mold cavity to a predetermined acceptable finalizing pressure or range, which may involve a reduction in pressure to avoid over-packing a mold cavity, and thereby prevent unwanted flashing.

[0029] FIG. 3 illustrates an injection molding system 10 having a strain gauge nozzle adapter 42 with multiple strain gauge pins 52. In the embodiment depicted in FIG. 3, the strain gauge nozzle adapter 42 has two strain gauge pins 52 arranged in the same circumferential plane, both of which are connected to the controller 50. In other embodiments within the scope of this disclosure, more than two strain gauge pins 52 may be included in the strain gauge nozzle adapter 42 and their location may be spread out along the length of the strain gauge nozzle adapter 42. FIG. 3 also depicts the injection molding system 10 including a secondary sensor 76. The secondary sensor 76 is depicted as a pressure sensor in the mold cavity 32, but in other embodiments within the scope of the present disclosure, the sensory sensor 76 may be another type of sensor, such as a strain gauge sensor, and may be located in another location. In addition, more than one secondary sensor 76 may be connected to the controller 50. The controller 50 provides the signals received from the strain gauge pins 52 and any secondary sensor 76 to the virtual cavity sensor 51.

[0030] Turning to FIG. 4, a region of the injection molding apparatus 10 of the present disclosure is illustrated, with the mold 28 at the lower left and a portion of the injection system 12 at the upper right in the drawing figure. The heated barrel 20 is provided with a barrel end cap 40. A strain gauge nozzle adapter 42 projects from the barrel end cap 40. A strain gauge aperture 43 is provided in the strain gauge nozzle adapter 42. The strain gauge aperture 43 receives a strain gauge 44 therein, which is secured by friction fit in the embodiment depicted. In other embodiments, the strain gauge 44 may be secured in place by screwing a screw into the walls of strain gauge aperture above the strain gauge 44. While a single strain gauge aperture 43 is illustrated, it is understood that the strain gauge nozzle adapter 42 may be provided with a plurality of strain gauge apertures 43, each having a strain gauge 44 secured therein as discussed above.

[0031] The strain gauge nozzle adapter 42 is provided between a barrel end cap 40 and a nozzle body 48 having a nozzle provided at an end thereof. While the embodiments illustrated in the drawings show the strain gauge nozzle adapter 42 as a distinct component from the strain gauge nozzle body 48, the strain gauge nozzle adapter 42 is considered part of what is referred to herein as the nozzle assembly, and could be formed integrally with the nozzle body 48 and still be considered within the scope of the appended claims. The nozzle body 48 is in fluid communication with at least one of the mold cavity 32, a gate, a runner, or a manifold of the injection molding system.

[0032] FIG. 5 illustrates a cross-sectional view of an embodiment of a strain gauge nozzle adapter 42 of the present disclosure. The strain gauge nozzle adapter 42 includes a melt flow inlet 60, a melt flow outlet 62, and a melt flow conduit 64 extending between the inlet 60 and outlet 64. The strain gauge aperture 43 is provided on an external melt flow conduit wall 66. In some embodiments, the longitudinal axis of strain gauge aperture 43 is perpendicular to the axis of the melt flow conduit 64. A minimum distance 68 must be maintained between the bottom 70 of the strain gauge aperture 43 and an internal melt flow conduit wall 74 to avoid cracking or leaking through the internal melt flow conduit wall 66. In some embodiments within the scope of the present disclosure, the minimum distance 68 is 0.5 mm.

[0033] In some embodiments within the scope of the present disclosure, the strain gauge aperture may be formed in an alternative material insert 72 that is made of a different material than the rest of the strain gauge nozzle adapter 42. An expanded view of an alternative material insert 72 is depicted in FIG. 6. In some embodiments, the strain gauge nozzle adapter 42 is made from stainless, pre-treated steel while the alternative material insert 72 is made from aluminum, brass, or another material that will better amplify the strain for detecting by the strain gauge pin 44. In some embodiments, the alternative metal insert is formed from a modified metallurgy that expands at the same rate as steel. The minimum distance 68 may vary depending upon the material forming the alternative material insert.

[0034] FIG. 7 illustrates a top view of a strain gauge nozzle adapter 42. One of the benefits of a strain gauge nozzle adapter 42 is that it is easily compatible with various injection molding systems without the need for modifications to the injection molding systems. For example, most injection molding systems may be connected to the melt flow inlet 60 and melt flow outlet 62 of the strain gauge nozzle adapter 42 by a universal thread. FIG. 8 provides a cross-sectional view of the strain gauge nozzle adapter 42 depicted in FIG. 6. The strain gauge pin 44 described in the present application could be chosen from a variety of commercially available strain gauge sensors. For example, the Kistler “Miniature Longitudinal Measuring Pin M5” Type 9247A would be suitable for use in embodiments within the scope of the present invention.

[0035] FIG. 9 illustrates an injection molding system 10 having a strain gauge feed system adapter 142 with a strain gauge pin 152. The strain gauge feed system adapter 142 works identically to the strain gauge nozzle adapter 42 discussed with respect to FIG. 2, except that strain is experienced by the strain gauge feed system adapter 142 and measured by the strain gauge pin 152 at a location along the feed system of the injection molding system 10 rather than at the nozzle 26. Specifically, the strain gauge feed system adapter 142 may be attached to the injection molding system 10 between the nozzle 26 and the mold 28.

[0036] A person having skill in the art would recognize that many of the features provided in a strain gauge nozzle adapter 42 could also be provided in a strain gauge feed system adapter 142. The strain gauge feed adapter 142 may include an aperture for the strain gauge pin 152, and an alternative material insert may surround the aperture and amplify the strain experienced by the strain gauge feed system adapter. The alternative material insert may have a lower flex modulus than the surrounding external sensor feed system adapter, and the alternative material insert may be one of aluminum and brass. The aperture of the strain gauge feed system adapter has a bottom, and the strain gauge nozzle adapter may have a melt flow conduit having an internal melt flow conduit wall. The distance between the bottom of the aperture and an internal melt flow conduit wall may be a minimum distance necessary to prevent cracking or leakage, such as 0.5 mm.

[0037] The strain gauge feed system adapter 142 may have a plurality of strain gauge pins 152 provided in a plurality of apertures, and the controller may determine at least one of an approximate pressure or melt flow front location using an output of each strain gauge pin and adjust the operation of the ram in view of the determined approximate pressure or melt flow front location. The plurality of apertures may be located in the same circumferential plane of the strain gauge feed system adapter. In some embodiments within the scope of the present disclosure, a secondary sensor may be used in conjunction with the strain gauge feed system adapter 142. The controller may determine at least one of an approximate pressure or melt flow front location using an output of the strain gauge pin and the secondary sensor, and the injection molding apparatus 10 adjusts an operation of the ram in view of the determined approximate pressure or melt flow front location.

[0038] The strain gauge feed system adapter may be used in a method of injection molding. The method may include measuring, using a strain gauge pin, the change in strain in a strain gauge feed system adapter. The method may further include approximating at least one of a pressure or a melt flow front location within the mold cavity based on the change in strain and comparing the approximated pressure or melt flow front location to a trigger point. If the approximated pressure or melt flow front location equals or exceeds the trigger point, the method may include activating a virtual cavity sensor, wherein upon activation, the virtual cavity sensor causes a controller to perform an action.

[0039] The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”

[0040] Every document cited herein, including any cross referenced or related patent or application and any patent application or patent to which this application claims priority or benefit thereof, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

[0041] While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.