Hydraulic quad sticks

Abstract

A device for supporting a rifle comprises four members 1A, 1B, 1C, 1D. Each member 1A, 1B, 1C, 1D has an upper and lower portion. The members 1A, 1B, 1C, 1D are connected in pairs at upper pivot poin

Description

The present invention relates to the field of shooting-aids. Background to the Invention As a sport which requires skill, rather than physical superiority, Target Shooting has been hailed as offering a great degree of inclusivity; since participants can compete together regardless of their sex or physical fitness, and across a wide range of ages. Furthermore it is one of the most inclusive sports available to differently abled participants. When operating a rifle, particularly over longdistance, it is essential for accuracy that the rifle be adequately supported to minimize unwanted movement caused by factors such as wind, muscle tremor, breathing, the user’s pulse etc. In a prone position, the user typically has a small sandbag on which to rest the stock of the rifle, which offers resistance to movement by transmitting a reactive force into the ground. The sandbag allows for deliberate movement while removing much of the unwanted and unintentional movement by utilizing the natural damping properties offered by the internal friction of sand. When a prone position cannot be adopted as is often the case - due perhaps to vegetation or other low-level obstructions, it may be necessary for the user to shoot from a sitting or standing position. In this case, although it is possible to operate the rifle free-hand, it is generally accepted that much better accuracy can be achieved by again using a supportive structure upon which to rest the rifle. Additionally, some elderly, disabled, or very young users may find itdifficult to support the weight of a rifle without aid. To address these issues, various portable shooting aids which lend themselves to elevated shooting positions have been in use for well over a century. Typical examples of popular modern shooting rests include Bipods, Tripods, and Quad-sticks. Ideally a shooting rest should remove certain degrees of freedom between the rifle and ground, while only damping other degrees of freedom. Degrees of freedom which may be removed entirely include cant (rotation in an axis parallel to the bore axis), and translational movement in all x,y, and z planes. Meanwhile degrees of freedom which ideally should only be damped, include those in the elevation and azimuth axes which allow the user to point the rifle at a target. Ideally the structure of the shooting rest should provide enough stiffness that there is minimal freedom due to elasticity of the structure. In reality, few devices actually meet this criteria and those which do tend not to be portable enough to carry on one’s person. Quad sticks are generally considered to be the best portable option available and are superior to tripods and bipods on account of their vastly improved stiffness. The inherently high stiffness of quad-sticks can be attributed to their triangulated structure which promotes compressive loading rather than bending stresses. Tripods and bipods by contrast, can only resist azimuth rotation by transmitting a bending force into their legs. A long slender member such as the leg of a tripod or quad stick will tend to deflect many orders of magnitude more under bending than it will in compression or tension, given the same load force. Primitive quad sticks consist of four sticks connected together using wire or string to form flexible pivotal connections, with the top pivots far enough down the sticks that vee-shapes are formed, in which to securely rest the rifle. This setup will entirely remove all but one degree of freedom - that being elevation, which is not ideal since it gives the user no freedom to alter azimuth, making it difficult to aim the rifle without repositioning the entire structure. In a sense this traditional quad-sticks design is too stable to be practical. To introduce freedom in the azimuth axis, more advanced quad-sticks have been developed in which one of the V-shapes is replaced with a horizontal flat plinth, allowing one end of the rifle to slide left and right. This plinth must be kept level by means of some mechanism - often a geared twin-pivot system, which introduces complexity and cost to the manufacturing process. The horizontal plinth also increases the width of the device even in the folded configuration. Reducing the width of the plinth narrows the scope of adjustability in the azimuth axis. Typical plinths are long enough to offer an angular adjustability within the scope of around 10-15 degrees. The plinth is often coated in a rubberized material to increase the friction at the point of contact with the gun stock and reduce unintentional sliding - moving the gun therefore requires forcefully overcoming this friction and some compensation must be made by the user to address the difference between static and dynamic friction, making precise aiming somewhat difficult. DK201771025A1 (VIPER FLEX APS) 2019-05-13, is entitled ‘Stabilizing support stand’; In this disclosure a set of quad sticks is provided which have a horizontal plinth and height adjustability. Another requirement of shooting rests in a commercial context is that they must be height-adjustable to suit the various heights of potential users. Many tripods, bipods, and quad sticks feature legs which comprise telescopically arranged tubes with a sliding interface to allow height adjustability. In such designs there must be locking mechanisms at each telescopic interface on each leg. These mechanisms which tend to feature lever or screw-actuated collets or clamps, again add significant cost and complexity to the design. Another practical consideration is that in the event that the quad sticks have to be deployed on a hill or uneven ground plane, requiring that one of the feet must be positioned higher than the other, the weight distribution between the feetwill be compromised. On a steep enough hill there could potentially be little to no weight on one of the feet, making the structure unstable. Additionally, in designs which feature a horizontal plinth and mechanisms to keep the plinth parallel with the ground plane, the plinth will naturally be tilted if the ground is uneven. A solution to this is to have each leg individually length-adjustable, which often comes as a byproduct of the mechanism for overall height adjustability. This allows the rifle supports to be positioned centrally between the feet, however in practice adjusting the legs individually can be quite tedious and time-consuming. Typically the user has to adjust each leg several times since the height of each leg effects the angle of the other legs. Summary of the Invention The object of the present invention is to provide an improved quad-stick type shooting rest, which utilizes a hydraulic mechanism to satisfy the requirements of having a damped yet smooth degree of freedom in the azimuth axis while also offering a simple solution to adjustability of height, and weight distribution. According to the first aspect of the invention a portable device for supporting and stabilizing a rifle, comprises: four members (1A, 1B, 1C, 1D), each providing an upper and lower portion, interconnected such that there is one member connected at each of the two opposing portions of each member; and wherein each connection between members is a pivoting connection, providing two upper pivots (14) and two lower pivots (23); and wherein the device is configurable to have at least one of the members at each lower pivot form a point of contact with the ground at its lower portion, while at least one of the members at each upper pivot forms a point of contact with a rifle at its upper portion; and wherein at least two of the members are hydraulic members which each feature a hydraulic piston (5) and cylinder (2) arrangement providing a chamber(10), such that the length of each hydraulic member changes with a change in the volume of its respective chamber; and wherein at least two of the hydraulic members form a hydraulically communicative pair (13A, 13B) by means of a flexible or articulated transferpassage (18) configurable to allow the flow of hydraulic fluid between their respective chambers (10), which when filled with incompressible fluid become otherwise volumetrically constrained, such that the shortening of one member in the hydraulically communicative pair results in the lengthening of the other member in the hydraulically communicative pair. Preferably all four members are hydraulic members, providing two sets of hydraulically communicative pairs. Preferably the transfer-passage (18) features a valve (20) configurable to modulate the restriction of flow of fluid between the chambers (10) in the hydraulically communicative pair. Preferably the transfer-passage (18) is integrated into one of the upper pivots (14). Preferably each member has an extended portion which extends past its upper pivotal connection; such that when two members connected by an upper pivotal connection are at an angle to each other a vee-shape (28A, 28B) configurable to support a rifle is formed by their extended portions. Preferably each extended portion features an area of a high friction rubberized material (3) which presents as the inside of the vee-shape (28A, 28B) such that a rifle resting in the vee-shape is in contact with the rubberized material. Preferably removable feet (30) are provided, which affix to the end of the lower portion of at least two of the members. Preferably at least two of the members incorporate integrated magnets (32) which cause the members to become magnetically attracted to each other when the device is articulated such that all four members are parallel. Preferably the scope of angular freedom of the lower pivots is limited by means of a flexible cord (34) tethering at least two of the members together. Preferably the flexible cord (34) is connected at each end to a member via a detachable clip (35). Optionally, an additional detachable member is connected to the device on some form of hinge, deployable to provide a third point of contact with the ground plane, allowing the device to become freestanding. Brief description of drawings Figure 1 shows an isometric view of the device in a folded configuration such that all four members are parallel. Figure 2 shows an isometric view of the device in the deployed configuration, without the cord attached. Figure 3 shows an isometric view of the device in the deployed configuration, complete with a cord attached and a rifle resting in the V-supports. Figure 4 shows a birds-eye view of the device deployed and supporting a rifle, with the rifle rotated clockwise about the azimuth axis. Figure 5 shows a birds-eye view of the device deployed and supporting a rifle, with the rifle rotated anticlockwise about the azimuth axis. Figure 6 shows the device deployed on a flat ground-plane, with a rifle resting in the V-supports. Figure 7 shows the device deployed on an inclined ground-plane and adapting to uneven ground, with a rifle resting in the V-supports, demonstrating the adjustability of weight distribution. Figure 8 shows a full length cross section view of a hydraulically communicative pair. Figure 9 shows a full length cross section view of two members connected at the lower pivot. Figure 10 is a more detailed view of part of figure 4, showing the connected chambers of a hydraulically communicative pair. Figure 11 shows a detailed cross section view of the components which make up an upper pivot, transfer passage and valve arrangement. Figure 12 shows a cross section through a plane perpendicular to the axis of the pivot valve pins, and intersect!ng the transfer valves, demonstrating the operation of the transfer valves, showing two transfer valves - one in the open position and one in the closed position. Figure 13 shows a cross section through a plane perpendicular to the axis of the pivot valve pins, and intersecting the transfer passage, demonstrating how the groove in one side of the pin prevents the transfer-passage and transfer hole from forming an unwanted valve. Detailed description of Embodiments In the following description numerous specific details are set forth in order to provide a clear understanding of examples of embodiments of the invention. It will be apparent however, to one skilled in the art, that the present invention may be practiced without limitation to some of these specific details. In other instances, intricate details of well-known methodsand structures have been omitted so as not to unnecessarily obscure the description. To improve the smoothness of the azimuth axis in a set of quad-sticks, the preferred embodiment of the present invention comprises four hydraulic members (1 A, 1 B,1C,1 D). Each hydraulic member comprises the following: A seamless aluminum tube (2) (hereby referred to as the “cylinder tube”) which forms the walls of a hydraulic cylinder. The tube features a pivot hole towards one end which is a through-hole and approximately half the diameter of the cylinder tube. A small section of the cylinder tube (of length roughly 100mm) overhangs the pivot hole. This section has a rubberized sleeve (3) on the outside surface to increase friction. A carbon fiber composite tube (4) (hereby referred to as the “piston rod”) sized to fit inside the cylinder tube (2) with a clearance, to create a telescopic arrangement. A piston endcap (5) (hereby referred to as the “piston”) which attaches to the end of the piston rod (4) and features an o-ring seal (6) retained within a groove, which slides inside the cylinder tube (2) to form a hydraulic piston. A plastic bushing (7) fixed to the end of the cylinder tube (2) which has a bore slightly smaller than that of the cylinder tube but still big enough for the piston rod (4) to slide freely through, which serves to prevent the end of the cylinder tube from scratching the piston rod during sliding. Ideally the plastic used is softer than the matrix of the carbon fiber composite tube. A valve housing (8) which is positioned towards the end of the cylinder tube (2) opposing the piston, and also features an o-ring seal (9) retained in a groove which seals statically against the bore of the cylinder tube to create a hydraulic chamber (10) with the piston such that by sliding the piston rod (4) with respect to the cylinder tube, the member can be extended resulting in an increase in the volume of the chamber (10), or the member can be shortened resulting in a decrease in the volume of the chamber (10). The valve housing (8) also has a small axial “transfer hole” (11) which leads from the hydraulic chamber to intersect a large perpendicular pivot-hole. The pivot hole in the valve housing lines up with the pivot hole in the cylinder tube such that with a pin present in the holes, the two are locked together. A lower-endcap (12) which is fixed to the opposing end of the piston rod (4) to the piston end cap (5), made from aluminum, and featuring a through-hole (hereby referred to as the “bolt hole”) perpendicularto the axis of the piston rod. The four hydraulic members are connected in two hydraulically communicative pairs (13A, 13B), hereby also referred to as “hydraulic pairs”. Each hydraulic pair (13A,13B) comprises two hydraulic members connected by a pivot valve pin (14). The pivot valve pin is of a length over twice the diameter of the cylinder tube, featuring an axial hole connecting two perpendicular radial holes which have been drilled through the side of the pin. The axial hole is otherwise sealed to the environment using a plug (17). These three holes together form a “transfer-passage”(18), along which fluid may pass. Each of the two radial holes has at either side of it, an o-ring seal (19) retained in a groove such that each hole has a dedicated pair of O-ring seals. The pin is sized to fit snugly through the pivot holes in the cylinder tube and the valve housing. The pivot valve pin (14) is used to connect two members while forming a pivot between them. The radial holes (of the transfer-passage (18)) in the side of the pin are spaced such that when in situ there is one inside each of the two valve housings (8) in the hydraulic pair and each hole is near the center of the valve housing. The o-ring seals (19) at either side of each radial hole seal against the bore of the pivot hole in their respective valve housing. When two members are connected by one pin, their respective chambers (10) are in communication since fluid may pass from one chamber, through the transfer hole (11) in the valve housing, through the transfer-passage (18) in the pin, through the transfer hole (11) in the othervalve housing and into the other chamber (10). The fluid however may not otherwise escape and therefore, when filled with an incompressible liquid, the pair of chambers becomes hydraulically constrained to a fixed volume. Since the volume of a chamber is dependent on piston position, the result is that compressing one member in the hydraulic pair will result in the other member extending by an equal amount. To further functionality, one of the two radial holes in the pin forms a valve (20), which allows the passage of fluid easily when it lines up with the transfer hole (11) in its respective valve housing. Rotating the pin until these two holes do not align will result in the valve closing and preventing the passage of fluid, causing the volume of both chambers in the hydraulic pair to become locked. The other radial hole on the pin must not function as a valve - since the angle between the two connected members is adjustable by the user, while the angle between the radial holes on the pin is fixed. To prevent the second radial hole in the pin from acting as a valve, the hole intersects a groove (21), which allows liquid to pass into the respective transfer hole regardless of the relative orientation of the radial hole. To prevent the pivot valve pin from escaping and provide an easy way to open and close the valve, a brass thumb-stick (22) screws into the end of the pin perpendicularly. To form the complete set of quad-sticks, two hydraulic pairs are connected together by lower pivots (23). These pivotal connections, of which there are two, are formed by connecting the lower endcaps (12) together in pairs with a single bolt (24) through their respective bolt holes and a nylon-insert type nut (25) to secure. It may be necessary to provide washers (26) between each pair of alloy endcaps to reduce frictional wear from pivotal motion. The pairing of the members at the lower pivotal connections is inverse to the pairing of the members at the hydraulic connections: If the hydraulic pairs are (1A)&(1 B), (1C)&(1 D), then the lower pivotal pairing will be (1 A)&(1 C), (1 B)&(1 D). The present invention provides a structure which in appearance is very similar to traditional cane-type quad sticks. In each hydraulic pair, the sections of the cylinder tubes which overhangs the pivot, can form a vee-shaped support, hereby referred to as a “V-support” (28A, 28B). When deployed, the structure has two such V-supports in which the front and rear parts of the rifle stock can rest respectively. The rubberized sleeves (3) on the V-supports resists cant of the rifle. A degree of freedom in the elevation axis is naturally present - like in traditional quadstick designs. With at least one of the two fluid-transfer valves open, the user can also freely move the respective V-support left and right allowing the rifle to rotate in the azimuth axis. The limited cross-sectional area of the fluid transfer-passage resists fluid flow to some degree resulting in some damping of the movement. This damping can be adjusted by the user by alteringthe degree to which the fluid transfer valve is open. Closing both fluid transfer valves results in locking of the azimuth axis. With both fluid transfer valves (20) open, the scope of movement offered in the azimuth axis can exceed 40 degrees - a vast improvement on typical designs, and yet since no horizontal plinth is present, the width of the device when folded will be little more than twice the width of the cylinder tube; in practice easily less than 45mm. The preferred embodiment of the device can also adapt quickly and easily to uneven ground. Opening both the transfer valves will allow lateral movement of the V-supports, allowing them to be shifted for optimal weight distribution between the feet, even on an inclined ground-plane. This process takes only a few seconds, during which the user simply manipulates the rifle into a comfortable position, which passively adjusts the length of all four legs simultaneously. Height adjustability is inherently offered by altering the total volume of fluid in the chambers (10). It is conceivable for an abundant fluid such as water to be used as the hydraulic fluid, allowing the user freedom to empty the device of fluid for storage and re-fill to their desired height when in use. The plug (17) on each pivot valve pin is designed to unscrew for this purpose. To fill the device, the plugs (17) are unscrewed with the device in the folded configuration and the valves (20) open, the valved end of the device is then submerged in a body of water such as a bucket or lake, and then the members extended, drawing fluid into the chambers (10) through the transfer-passage (18). Once the chambers are filled, the device is positioned upright to allow air bubbles to float to the top of the chambers, then the members compressed slightly to achieve the desired height and to purge air from the system through the transfer-passage (18), before re-securing the plugs (17). One of the more subtle challenges in creating any set of quad sticks is accommodating for the requirement of various degrees of freedom in the pivotal connections which are necessary for articulation of the structure, which in turn is necessary for it to be adjustable / collapsable. Many quad sticks on the market do so crudely by incorporating week fixtures which simply flex to add artificial axial freedom in each leg in absence of a true joint. This approach requires necessarily week material which then compromises the integrity of the device under non-design conditions such as drops or unexpected loading. The preferred embodiment of the present invention however, can utilize much stronger material in the pivoting joints since it inherently accommodates all the degrees of freedom required to allow full articulation of the members. This is thanks to the fact that the piston rod (4) in each member can rotate relative to its respective cylinder tube (2). In the folded state, all four members are free to assume a parallel position allowing the device to be very compact. There are certain other practical considerations for the implementation of the invention: The device may need to operate in sub-zero temperatures, and the hydraulic fluid should therefore be suitably selected to have an appropriately low freezing or solidification point. The viscosity of the chosen fluid will ultimately affect the damping of the movement therefore a high viscosity index may be preferable, however the ability to modulate the opening of the fluid transfer valves will assist in compensating for varying viscosity. Another consideration for selecting an appropriate hydraulic fluid is that traces of the fluid are likely to come into contact with the users hands - the fluid should therefore be non-irritant. The forces on the members during operation are typically only compressive, however the bore of the cylinder / piston diameter should be sized to provide a piston surface area big enough that the vacuum effect on the piston (5) prevents the piston rod (4) from being pulled out of the cylinder (2) by other forces likely to be encountered during its lifetime. For simplicity of disassembly, the plastic bushings (7) should ideally have a minimum bore which is still large enough for a piston (5) and piston o-ring seal (6) to be removed through - in the case of the piston o-ring seal there will necessarily be significant interference when being removed through this bore, however experimentation has proven that by selecting a soft enough o-ring seal with a thick enough section, it is possible. This allows a hydraulic member to be disassembled to access and change a worn piston o-ring seal. The pivot hole in the cylinder tubes is naturally arc-shaped from the side profile, since it is a circular hole intersecting a cylindrical wall. This means that when the cylinder tubes in a hydraulic pair are pivoted to a relative angle, they can move closer to each other along the axis of the pivot, than when they are parallel. The same applies to the thumb-stick. This may interfere with the alignment of the valve holes. To prevent this from happening plastic washers (29) can be added in the pivot valve pin, at either side of each cylinder tube. These also create a healthy clearance between the members to prevent the cylinder tubes from colliding, and provide a bearing surface to prevent wear. The addition of interchangeable feet (30) may be useful to accommodate various types of terrain, and to allow worn feet to be replaced. Interchangeable feet can be provided by having a thread in the lower end caps, and then a screw-hole through the feet and a screw (31) to secure. Only one foot is necessary for each lower pivot to provide 2 points of contact with the ground. The feet should be attached to the inner set of endcaps to promote ground clearance of the outer endcaps. The endcaps which end up on the inside will depend on which way the device is deployed, which in turn will depend on the users preference of left or right handed operation. Therefore all four lower endcaps should be threaded. To help prevent the device from unfolding unintentionally while in the folded state, it may be useful to provide magnets (32) at the top and bottom of each member, which can be retained within end-caps (33,12) at the end of each tube. Since at each end of the device the four members are connected into two pairs by pivots, the magnets must be oriented to ensure one pair is attracted to the other. In the folded position, the pivots at the top of the device, are at 90 degrees to the pivots at the bottom of the device. The magnets at the top of the device will therefore be at 90 degrees to the magnets at the bottom of the device. It may be useful for a piece of cord (34) to be added which limits the extent to which the two V-supports can move apart from each other by tethering them together- this stops the front pair of members from falling on the floor during deployment. It may be useful to have the tether attach to the piston tube by means of clips (35) for ease of adjustment and removal. Sliding these tether connection clips up and down the members will allow the user to adjust the constrained distance between the V-supports to suit a particular rifle.

Claims

1. A portable device for supporting and stabilizing a rifle, comprising: four members (1 A, 1B, 1C, 1D), each providing an upper and lower portion, interconnected such that there is one member connected at each of the two opposing portions of each member; and wherein each connection between members is a pivoting connection, providing two upper pivots (14) and two lower pivots (23); and wherein the device is configurable to have at least one of the members at each lower pivot form a point of contact with the ground at its lower portion, while at least one of the members at each upper pivot forms a point of contact with a rifle at its upper portion; and wherein at least two of the members are hydraulic members which each feature a hydraulic piston (5) and cylinder (2) arrangement providing a chamber (10), such that the length of each hydraulic member changes with a change in the volume of its respective chamber; and wherein at least two of the hydraulic members form a hydraulically communicative pair (13A, 13B) by means of a flexible or articulated transfer-passage (18) configurable to allow the flow of hydraulic fluid between their respective chambers (10), which when filled with incompressible fluid become otherwise volumetrically constrained, such that the shortening of one member in the hydraulically communicative pair results in the lengthening of the other member in the hydraulically communicative pair.

2. A device according to claim 1, wherein all four members are hydraulic members, providing two sets of hydraulically communicative pairs.

3. A device according to claim 1, wherein the transfer-passage (18) in at least one of the hydraulically communicative pairs features a valve (20) configurable to modulate the restriction of flow of fluid between the chambers (10) in the hydraulically communicative pair.

4. A device according to claim 1, wherein the transfer-passage (18) is integrated into one of the upper pivots (14).

5. A device according to claim 1, wherein each member has an extended portion which extends past its upper pivotal connection; such that when two members connected by an upper pivotal connection are at an angle to each other, a vee-shape (28A, 28B) configurable to support a rifle is formed by their extended portions.

6. A device according to claim 5, wherein each extended portion features an area of a high friction rubberized material (3) which presents as the inside of the vee-shape, such that a rifle restingin the vee-shape (28A, 28B) is in contact with the rubberized material (3).

7. A device according to claim 1, wherein removable feet (30) are provided, which attach to the end of the lower portion of at least two of the members.

8. A device according to claim 1, wherein at least two of the members incorporate integrated magnets (32), which cause the members to become magnetically attracted to each other when the device is articulated such that all four members are parallel.

9. A device according to claim 1, wherein the scope of angular freedom of the lower pivots is limited by means of a flexible cord (34) tethering at least two of the members together.

10. A device according to claim 9, wherein the flexible cord (34) is connected at each end to a member via a detachable clip (35).

11. A device according to claim 1, with an additional detachable member connected to it on some form of hinge, deployable to provide a third point of contact with the ground plane, allowing the device to become freestanding.

12. A device for supporting and stabilizing a rifle as described by any preceding claim, wherein the hydraulic chambers (10) of each hydraulically communicative pair (13A, 13B) are provided with a hydraulic fluid contained within.

13. A device according to claim 12, wherein the hydraulic fluid comprises Polydimethylsiloxane-based oil.

14. A device according to claim 12, wherein the hydraulic fluid comprises Polyalphaolefinbased oil.

15. A device according to claim 12, wherein the hydraulic fluid comprises Propylene Glycol.

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