Stab-connectable sister hook

Abstract

Sister hook type tool assemblies comprise mating arms having C shape lower ends grip portions that terminate in jaws. The arms preferably are held between two spaced apart housings. The arms, and housings when present, are held together by a fastener at the upper end of the assembly. The arms pivot relative to one another and to the mated housings. Each housing has a pair of forks at one end which define a U shape opening. An object received in the opening is retained when the jaw ends arms overlappingly close the fork opening, due to action of spring. The V shape lower end contour of the mated arms and inclined surfaces of the fork tips cause a rigid object to open the jaws when the tool is thrusted at the object. The jaws then close under spring force, capturing the object. Optional locking means are used to keep the jaws from unintentionally opening.

Claims

1. A tool for gripping an object, having a lengthwise center axis and, running perpendicular thereto, a pivot axis, a locking axis, and a stop axis, the tool comprising: a first arm; a second arm, abutting the first arm; each arm having in the lengthwise axis direction a pivot end, a shank connected to the pivot end, and a grip end connected to the shank, the grip end comprising a jaw that is at the terminal end of the arm, the grip end C shaped and defining a concavity which is open-sided; wherein each arm pivot end is configured for pivot motion about said pivot axis, enabling the arm to pivot from an arm home position to an arm open position; wherein at said home position the jaw and concavity of one arm respectively overlap the jaw and concavity of the other arm, and the mated concavities thereby define a space within which said object may be gripped; wherein when the jaws are in said open position the jaws are spaced apart sufficiently to allow an object to enter said overlapping concavity space; at least one spring for urging said arms to the home position; a first housing; a second housing spaced apart from the first housing and connected to the first housing by a fastener running along said stop axis; wherein said arms are pivotably and slidably contained in the space between the housings; wherein a portion of the shank of each arm extends laterally from said space between the housings, to enable manual pressing on the arm to move the arm in the direction of said open position, against the force of said spring; each housing having in the lengthwise axis direction a first end positioned along said pivot axis, a mid-body, and a second end; the second end comprising a pair of forks defining a U shape opening which aligns with said overlapping concavity space when the arms are in the home position; each fork having a tip.

2. The tool of claim 1 further comprising a fastener running between the housings along the stop axis, the fastener optionally within a spacer; wherein each arm has a tab extending from the grip section in a generally lengthwise direction away from the pivot end for contacting said fastener and limiting the extent of arm pivot motion at said arm open position.

3. The tool of claim 1 wherein each arm has a mirror-shape of the other arm and each housing has a similar external shape.

4. The tool of claim 1 wherein each arm has a tab extending lengthwise from said shank into the concavity of said C shape grip end; and wherein the pivot motion of each arm during opening of the jaws is limited by contact of the tab with said fastener.

5. The tool of claim 1 further comprising a spacer positioned around said fastener, wherein each arm has a tab extending lengthwise from said shank into the concavity of said C shape grip end; and wherein the pivot motion of each arm during opening of the jaws is limited by contact of the tab with said spacer.

6. The tool of claim 1 further comprising a pin, hollow rivet, or fastener running through holes in the pivot end of each arm and the first end of each housing.

7. The tool of claim 1 wherein the arms in home position have overlapping jaws with contoured surfaces that form a V shape contour surface facing in the direction of said terminal end of the tool.

8. The tool of claim 7 wherein the tip of each fork has a surface which is angled relative to the central length axis, to guide any said object contacted by the tool terminal end into the U shape opening of the fork pair.

9. The tool of claim 1 wherein each housing has a hole aligned with the locking axis, and the shank of each arm has a hole that is aligned with the locking axis when the arms are in home position; further comprising a removable pin running along the locking axis and passing through all said holes.

10. The tool of claim 1 further comprising: a first nub on the grip part of each arm near the shank, the first nub projecting generally in the lengthwise direction toward the pivot end of the arm; and, a locking bar running transverse to the length of the tool and between lengthwise slots in the opposing side housings, the locking bar movably positionable in the tool lengthwise direction for selectively engaging the first nub or each arm and thereby locking the movement of the arms when the arms are in the home position.

11. The tool of claim 10 further comprising at least one button connected to the end of the locking bar, the at least one button configured for latching engagement with the housing when in closest proximity position to a pivot end of a housing.

12. The tool of claim 11 further comprising a second nub projecting laterally toward the centerline of the tool for a shank of each arm at an elevation nearer to the pivot end than is the lock bar when each arm is in home position, each second nub configured to contact the locking bar when the arms approach open position, and thereby move the locking bar away from the pivot ends of the housings.

13. The tool of claim 1 wherein each arm has an integral pin on the shank portion, each pin extending generally in a direction transverse to said length axis, and wherein said spring runs between said pins.

14. The tool of claim 1 wherein each arm has a nub extending from the C shape section in the general direction of the arm pivot end, further comprising: a movable locking bar running between the housings; each end of the locking bar guided for lateral motion of the locking bar along the central lengthwise axis of the tool by a feature of at each housing, wherein the locking bar is resiliently biased in the direction of the U shape housing openings; and wherein engagement of the nubs with the locking bar keeps the arms in the home position; and wherein manual movement of the locking bar against the spring bias enables the arms to more to the open position.

15. A tool for gripping an object, having a lengthwise center axis and, running perpendicular thereto, a pivot axis and a locking axis, the tool comprising: a first arm; a second arm, abutting the first arm; each arm having in the lengthwise axis direction a pivot end having a pivot hole, a shank connected to the pivot end, and a grip end connected to the shank, the grip end comprising a jaw that is at the terminal end of the arm, the grip end C shaped and defining a concavity which is open-sided; a fastener running along the pivot axis and through the pivot hole of each arm; wherein each arm pivot end is configured for pivot motion about said pivot axis, enabling the arm to pivot from an arm home position to an arm open position; wherein at said home position the jaw and concavity of one arm respectively overlap the jaw and concavity of the other arm, and the mated concavities thereby define a space within which said object may be gripped; wherein when the jaws are in said open position the jaws are spaced apart sufficiently to allow an object to enter said overlapping concavity space; at least one spring for urging said arms to the home position; mating stop features on the arms to limit said arm open position; and, a linkage connecting the arms to limit said arm home position.

16. The tool of claim 15 wherein the arms in home position have overlapping jaws with contoured surfaces that form a V shape contour surface facing in the direction of said terminal end of the tool.

17. The tool of claim 15 wherein the shank of each arm has a hole that is aligned with the locking axis when the arms are in home position; further comprising a removable pin running along the locking axis and passing through said aligned holes

18. The tool of claim 15 further comprising a first housing and a second housing, each housing having a pivot end, wherein the first arm and the second arm are contained between the housings.

19. A method of engaging a tool with an object which comprises: providing a tool in accord with claim 1, with the arms in the home position; thrusting the tool at a said object so the terminal end of the tool and contour surface of the jaws contacts the object with sufficient force to cause each arm to pivot about the arm pivot end, thereby causing the jaws to separate and allowing the object to enter said mated concavity space; and, allowing the spring to cause the arms to return to the home position.

20. A method of engaging a tool with an object which comprises: providing a tool in accord with claim 13, with the arms in the home position; thrusting the tool at a said object so the terminal end of the tool and contour surface of the jaws contacts the object with sufficient force to cause each arm to pivot about the arm pivot end, thereby causing the jaws to separate and allowing the object to enter said mated concavity space; and, allowing the spring to cause the arms to return to the home position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is an exploded view of a device of the present invention, showing essential principal parts which include opposing side housings and mating arms with jaw-lower ends.

[0016] FIG. 2 is a front view of a device of the present invention, namely, an assembly comprised of the parts shown in FIG. 1.

[0017] FIG. 3 is a right side view of the device shown in FIG. 2.

[0018] FIG. 4 is a right side cross section view of the device of FIG. 1 with the locking pin and bushing absent.

[0019] FIG. 4A is a side, partial cross-sectioned, view of a modification of the device shown in FIG. 2.

[0020] FIG. 5 is front view of one of the two arms of the device of FIG. 2.

[0021] FIG. 6 is a front view of the first arm of FIG. 5 as it mates with a mirror-like second arm, along with a compression spring to thereby hold a rod. A pin in the holes 66B, 66A is implied in the Figure.

[0022] FIG. 7 is a horizontal plane cross section of the assembly of FIG. 6, looking along vertical axis CL, showing how the spring runs at an angle to the plane between the arms.

[0023] FIG. 7A is a cross section like that of FIG. 7, shown an embodiment of tool which lacks housings.

[0024] FIG. 8 is a front view like FIG. 6, showing the arms of a sister hook tool and the jaws as they are separated from each other while engaging an object with relative longitudinal axis motion.

[0025] FIG. 9 illustrates a prior art generic object having a handle which can be engaged for lifting by a sister hook of the present invention.

[0026] FIG. 10 is a partial front view of the lower end of a sister hook of the present invention, like the view of FIG. 2, showing the lower end of the sister hook as it is being pushed (stabbed) toward an off-center object to engage it.

[0027] FIG. 11 is an exploded view of portions of an alternate embodiment device, like the device shown in FIG. 2, but having a different locking mechanism.

[0028] FIG. 12A and FIG. 12B are side views of the device shown in FIG. 11, illustrating respectively how the device opens to receive an article and how the device closes and locks.

[0029] FIG. 13 is a partial side view of a tool like that shown in FIG. 11, with a locking button.

DESCRIPTION

[0030] The present invention tool/device is said to be capable of being stab connectable to an object, then to hold it in sister-hook fashion. By that jargon is meant that the device can be thrust toward an object such as the bar shape handle 60 of a fitting 62, which for example is secured to a stationary object 64, as shown in FIG. 9 as assembly 55. As a result of such stabbing the jaws of the invention sister hook will become engaged with the object, for lifting or pulling of the object.

[0031] FIG. 1 is an exploded view of device 20 (also called here tool 20), an embodiment of the present invention. Assembled tool 20 is shown in front view in FIG. 2, in side view in FIG. 3, and in vertical cross section in FIG. 4. In FIG. 4 some elements in the other Figures are absent, for clarity. The tool is described in terms of its orientation in the pictures of the Figures, but terms such as top, bottom, lower, etc. shall not be limiting since it will understood the tool may be used of stored in any orientation.

[0032] The tool embodiment 20 is comprised of opposing side housings 22, 24 that are preferably made of a strong thermoset plastic, optionally a metal alloy or a carbon fiber epoxy composite. With reference particularly to FIG. 1, each housing has (a) an upper end called the pivot end which has a pivot hole 66C, 66D respectively that is centered on transverse axis 52; (b) a mid-boy portion, (c) a lower end comprised of spaced apart forks 54C, 54D respectively that define between them a U shape opening 65; and (d) a central portion with a through hole 61C, 61D respectively that is centered on transverse axis 50; and (d) a locking pin hole 67C, 67D respectively that is centered on transverse axis 48 which axis runs through the mid-body portion of the housing. The axes 48, 50, 52 are parallel to each other and intersect vertical axis CL of tool 20 when the tool is assembled.

[0033] The housings are nearly mirror-identical, but for optional parts such as shield portions, any reciprocal male-female portions, and features that might be associated with a locking mechanism, such as described below. The arms, described next, have mirror shapes. Sometimes reference herein is made to a feature having a number that lacks a suffix letter. Such should be construed as a reference to all features which have the same number with a suffix letter.

[0034] Arms 26, 28, which are also shown in FIGS. 5 and 6, have mirror shapes. Each arm, as exemplified by FIG. 5 and arm 26, has an upper pivot end 33A where is the aforementioned pivot hole, a descending shank 35A that connects to a C shape portion 37A, at the bottom of which is the lower terminal end and jaw 42A. Each arm has a tab 44A, 44B respectively which descends from the bottom of the shank and is a portion of that which defines the C shape interior concavity of the arm. The shank and tabs and nubs mentioned below are features which generally extend in the lengthwise axis direction of the tool.

[0035] The arms are preferably made of a strong steel, preferably a corrosion resisting (stainless) steel, such as AISI type 316 steel or 17-4PH steel. Optionally, alternative use may be made of a copper base alloy such as admiralty brass or bronze, or of high-strength engineered plastics and composite materials, including carbon-fiber reinforced plastics.

[0036] In the assembled tool, spacer 84 and spacer 30 help space the housings relative to each other, for good cooperation with the arms. Arms 26, 28 have certain holes that in the assembled tool 20 mate with holes in the housings. As best shown in FIG. 1, each arm has an upper end (the pivot end) having pivot hole 66A, 66B that in the assembly lies along axis 52. Thus, a pin, such as the pin 70 of a shackle 54 shown in phantom in FIG. 3, can be inserted along axis 52 to keep the upper ends of the four parts 22, 24, 26, 28 aligned in pivotable fashion. The motion of the arms in the assembly may also be referred to as partial-rotation or part-rotation.

[0037] Alternatively, use may be made of an optional hollow rivet 72, shown in FIG. 1 and FIG. 4A. Other pin-like means or fasteners, for holding the four principal parts 22, 24, 26, 28 together, may be used. For example, use may be made of a threaded bolt, a solid rivet, or a pintle affixed to some other device. While for simplicity a pin or fastener is not shown on axis 52 in some assembly figures here, the presence of a pin should be implied by the artisan/reader. In still other embodiments one or more of the housing or arms may have an integral transverse portion, such as an integral axle stub to fulfil the aforementioned pin or fastener function.

[0038] When the arms 26, 28 are in their closed or home position, as shown in FIG. 2, the concavities of the arms partially overlap and the curved upper surfaces of the respective jaws 42A, 42B mate with each other in overlapping fashion, to provide a curved surface which defines the lower bound of space 68, which space is between the arms and is where an object such as handle 60 will be held during use of the tool 20.

[0039] Tool 20 also has a locking mechanism comprised of locking pin holes 67A, 67B respectively in arms 26, 28. When the arms are in home position, the locking pin holes lie along axis 48 and align with housing pin holes 67C, 67D, thus enabling pin 36 to be inserted, thereby holding the arms in the home position, as suggested/shown by FIG. 2 and FIG. 3. In other embodiments there is no locking pin; tool 20 nonetheless will be functional, since holding an object which is exerting sufficient lengthwise CL axis force will prevent the arm jaws from opening. See FIG. 6. FIG. 8 and FIG. 9 show another configuration of locking mechanism, as discussed below. As discussed below,

[0040] With reference to FIG. 2, a user can with one hand grasp the tool 20 and squeeze the arms 26, 28 above the vertical mid-point of the tool where the outer edges of the arms extend laterally from the opposing side housings. Thus, the user optionally can squeeze the arms to open the jaws sufficiently to allow them to close around an object such as handle 60 without the user applying the thrusting force associated with the aforementioned stabbing.

[0041] FIG. 4A is a side view like FIG. 4, with partial cross sectioning, showing device 20A which is like device 20 except for having a hollow rivet 72 as fastener at axis 52 to hold the housings together, and having a hollow rivet 74 at axis 50, which keeps in place spacer 30.

[0042] FIG. 6 is a view of an assembly 21 that comprises arms 26, 28 in their home positions with the housings not pictured, for clarity. FIG. 7 is a horizontal plane cross section looking down along axis CL of the assembly 21. FIG. 6 and FIG. 7 (and FIG. 1) show compression coil spring 40 that is captured by the integral pins 38A, 38B respectively and is captured within the space between the arms. Spring 40 pushes on the arms so that jaws 42A, 42B move toward each other. With reference to FIG. 7, the length of spring 40 runs at an angle to the plane between the mated arms. When the jaws are in their home position, the terminal or pointed top end of each jaw presses against the interior surface of one of the forks of a housing. Generally, coil spring 40 is one of several spring force means which may be used, for applying pivoting force to the arms, to cause their jaws to move apart from each other. be used. In a variation of spring means, not shown but within ordinary skill, spring force may be applied to the arms by one or more torsion springs which circumscribe axis 52, for instance running around a solid or hollow pin or rivet that runs through holes 66A, 66B. In another variation of spring means, one or more leaf springs may be used in to apply the desired pivoting force to the arms; for example a V shape leaf spring may replace the coil spring. Other known resilient devices may be used in substitution of coil spring 40 or for the other kinds of springs. For example, rubber or elastic polymer springs may be used. One or more than one spring means may be used cooperatively in a device.

[0043] The lower/terminal end surfaces of the jaws may be nominally perpendicular to the length of the tool, or as shown in FIG. 2, preferably curved so that when the jaws are in the home position, the lower end of the tool comprises a (curved) V shape contour surface 70. Such. end shape helps the user engage the tool with an object. FIG. 8 is a side view like FIG. 6, showing how, when tool 20 is forced (stabbed) against an object 60 (as shown by the arrow along the CL axis), contact of the object the V shape curved surface 70 thrusts the jaws 42A, 42B outwardly and away from each other as indicated by arrows A. Alternatively, a user may squeeze the arms toward each other in proximity to the coil spring location, thereby to open the jaws and engage an object.

[0044] That may be useful where the object being engaged is non-rigid, such as a cable or a rope which is not taut, etc.

[0045] FIG. 8 also illustrates how the extent of opening (outward motion) of the arms will be desirably limited, due to engagement of tabs 44A and 44B of the respective arms with bushing 30 which lies along axis 50. The spacer and forks comprise a preferred feature combination. As illustrated by the FIG. 1 exploded view along with FIG. 2 and FIG. 3, spacer 30 is held in place along axis 50 by screw 32 and nut 34 which act both as fastener and as a shaft running through the spacer. Alternatively, other means for mounting spacer 50 may be used, including a solid or hollow rivet, or some other sort of shaft. In other alternatives: the spacer may be mounted on one only of the housings; and, the spacer may comprise an integral feature projecting from one or both of the housing inward facing surfaces. In terms of the arm-limiting-function of a fastener or a fastener with surrounding spacer, there is no appreciable difference and a claim reference to one shall comprise a reference to the other.

[0046] FIGS. 2, 3, and 6 illustrate how locking pin 36 may optionally be used to keep the arms (and thus the jaws) from opening when they are in their home position. Use of the locking pin can help prevent inadvertent release of an engaged object such as handle 60.

[0047] Tool 221 is an embodiment comprised of arms held together by a fastener at axis 52; there are no housing parts. Tool 221 has features for limiting the closing and opening of the jaws to an extent comparable to that described for tool 20 where the limiting is achieved by using portions of the tool that are associated with the housings.

[0048] FIG. 7A is a cross section like FIG. 7, showing a portion of tool 221. Tool 221 is largely configured like tool 21 of FIG. 6 and comprises arms 226, 228 that are like arms 26, 28. The spring of tool 221 is omitted for clarity of illustration. Tool 221 comprises features which act as stop means and thereby limit the relative arm motion and associated relative jaws opening. More specifically, arm 226 has integral pin 238A which has a laterally projecting portion that is hit by integral pin 238B of arm 228 when arm 228 moves sufficiently close, thereby limiting jaw opening. And tool 221 comprises changeable length linking means, connecting the arms. More specifically, arm 228 is connected to arm 226 by lanyard 231, thereby limiting the separation distance of the arms and the of related jaw closing. Other linkages of equivalent function may be used in substitution of a lanyard. For example, use may be made a slotted rigid link that extends pivotably from one arm to a pin on the other arm, with the pin within the slot. Tool 221 may further comprise a pair of housings, not shown, having pivot ends and pivot holes lying along the pivot axis, between which the mated arms 226, 227 are contained.

[0049] FIG. 11 is an exploded view of portions of an alternate embodiment device 120 which is much like the device 20 shown in FIG. 2, but which has a different locking mechanism. FIG. 12A and FIG. 12B are side views of the device shown in FIG. 11, illustrating respectively how the device opens to receive an article and how the device closes and locks. Parts which correspond to those of FIG. 1 and other illustrations of device 20 have the same last two digits. Referring to the several Figures showing device 120, housings 122, 124 capture arms 126, 128 by means of a not-shown fastener passing through the housing and arm holes on axis 50. Spacer 184 is interposed between the housing on axis 52, and a not-shown fastener may run within spacer.

[0050] Instead of a locking mechanism which comprises a pin that fits into aligned holes, for locking the arms the home position, device 120 has a locking mechanism which comprises bar 76 that is guided for vertical CL axis motion (indicated by an arrow in FIG. 12B) by fitting in slots 78 in the opposing side housings. Bar 76 is urged downwardly along the slot lengths by spring 80. Bar 76 preferably has a round end, shaped to press-fit receive rectangular shape button 86, to make it easier for a user to move the bar vertically against the spring bias. Each arm has a first nub, 182A, 182B respectively on the upper surface of the curved C shape portion, near the shank that runs to the pivot end; and each arm has a second nub 188A, 188B respectively, on the shank.

[0051] As illustrated by comparing FIG. 12A and FIG. 12B, when the jaws of tool 120 are maximally opened, their spacing is determined by contact of tabs 144A, 144B with spacer 130, similar to how tool 20 works. Thus from the full open position, the jaws can only move inwardly as indicated by arrows M. When the arms are moved inwardly and the jaws come to their home position, thereafter the jaws can only more outwardly as indicated by arrows P in FIG. 12B. At the home position, the bias of spring 80 moves the bar downwardly, so that the motions P are prevented because first nubs 182A, 182B hit the bar. See FIG. 12B. If a user then raises the bar, that allows the first nubs to move left-right, allowing the jaws to open. In an alternate embodiment, there is no spring and the bar is moved manually to lock and unlock the arms and jaws.

[0052] FIG. 13 is a partial side view of tool 120 showing button 86 and, by the arrow. its vertical motion which moves bar 76. Latching means, to hold button 86 in a particular position may be provided.

[0053] A slide button 86 may be present on both ends of the locking bar 76, pressed of screw-fastened onto the end of the bar. With reference to FIG. 13, an embodiment of button 80 will have, on its left-right sides, molded resilient latch portions (e.g., small protrusions) that fit into detents in the edge of the housing depression that holds the button against the spring force, when the button is in uppermost position, as shown. (The latches and detents are not shown but are within ready comprehension of the artisan.)

[0054] The engagement of the latches with the housing will keep the button, and thus the bar 76, in the upmost or unlock position, with the spring compressed. When the bar is released, as by a user pressing the button(s) downward with force sufficient to overcome the detent engagement, the spring then urges the button to lock the arms, because the bar engages first nubs 182, as already described. See FIG. 12B.

[0055] When an object is stabbed to engage it, provided the button/bar are in upward position (where the button will be held manually or by the latches just described), the force from contact with the object causes either or both of the jaws to move outwardly. That action pivots the arms so the shank portions come closer to each other. See FIG. 12A. When the shank portions sufficiently move toward each other and the centerline of the tool, as shown in FIG. 12A one or both second nubs 188 contacts bar 76, pushing it downwardly with sufficient force to pull the button(s) free of latch engagement with the housing. Then, the spring urges the bar 76 down until it engages the space between first nubs 182, as shown in FIG. 12B, automatically locking the arms, so the object desirably cannot be removed from space 68 without manual intervention, to move the button, then to press inwardly on the shanks of the arms. The button configuration and means of latching may be carried out in different ways within the scope of invention. For example, the button could be on the exterior of the housing and not in a recess, and the latching feature could be interior of the housing and associated with the bar and not the button.

[0056] FIG. 10 illustrates another feature of the invention which enables engagement and capture of an object even though it is not being stabbed or contacted by relative motion along the central CL axis of tool 20. As suggested by FIG. 10, an off-center object 60 will push on the angle-curved terminal surface of arm jaw 42B and cause the jaw to move away from contact with the U shape opening at the lower end of the housing. In addition, the lower end of each housing comprises forks which have angled tips 56 that help guide tool 20 in engaging off-center object 60.

[0057] It will be appreciated that the assembly 21 of FIG. 6 is an embodiment which could be utilized for grasping a load, notwithstanding the absence of the opposing side housings, and the resultant absence of features of exemplary tool 20. Modifications might be made to the assembly 21 to compensate for some of those missing features, for example, to limit the travel toward each other of the jaws 42A, 42B.

[0058] While the invention has been described in terms of a user grasping the sister hook tool manually, the invention may attached to mechanical members and machine controlled, and used in other ways where there is absence of manual contact. For example. a tool of the present invention may be fastened to the arm of a robotic device by means of a pin like pin 70.

[0059] Thus the invention tool fulfils objects of the invention. The tool can be engaged with a load by stabbing at the engagement point on an object, either manually or mechanically. The tool will not disengage when the load applied to an object fluctuates or goes to zero. The tool further optionally has a safety lock to inhibit inadvertent release of a load. The tool is compact and there is little tendency for snagging of a disengaged tool with extraneous objects. The tool enables easier one-hand manual engagement or disengagement. The tool can be manufactured on an economic mass basis.

[0060] The invention, with explicit and implicit variations and advantages, has been described and illustrated with respect to several embodiments. Those embodiments should be considered illustrative and not restrictive. Any use of words such as optional and preferred and variations suggest a feature or combination which is desirable but which is not necessarily mandatory. Thus embodiments lacking any such preferred feature or combination may be within the scope of the claims which follow. Persons skilled in the art may make various changes in form and detail of the invention embodiments which are described, without departing from the spirit and scope of the claimed invention.