EP0701681A1

EP0701681A1 - No interference mechanical-magnetic arrow suspension system for archery

Info

Publication number: EP0701681A1
Application number: EP94914550A
Authority: EP
Inventors: Maurizio Maurizi
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-05-31
Filing date: 1994-03-30
Publication date: 1996-03-20
Also published as: ITPE930002A0; ITPE930002A1; WO1994028368A1; IT1268447B1

Abstract

The invention, applicable to all bows existing in the field of archery, eliminates the interference encountered during the initial arrow flight near the bow. The steady flipper rests, presently in use, which sustain the shaft of the arrow are replaced by a mechanical suspension operating in all traction phases which precede the position at maximum elongation status and by a magnetic suspension that replaces mechanical suspension and becomes active in the said final position. Mechanical support is made by appropriate shaping of the clicker that could be retractable after the release. The point insert of the arrow will be in ferromagnetic material since it is designed to support the arrow at the end of its guided run between the pole shoes of a magnet. After the string release, the magnetic effect will cease when the arrow point insert has left the magnetic field of attracting forces: this will allow arrow flight which is free of any interference phenomenon.

Description

NO INTERFERENCE MECHANICAL-MAGNETIC ARROW SUSPENSION SYSTEM FOR ARCHERY

D E S C R I P T I O N

OBJECT AND PURPOSE OF THE INVENTION

The object of the present invention is a new arrow support system for archery.

The purpose of the invention is to eliminate every element that could cause interference between the bow and the arrow during crossing of the latter after the bow string release.

The planned system is usable on bows with a clicker.

Therefore, according to F.I.T.A. (Federation

Internationale de Tir a l'Arc) regulations, the invention is immediately applicable on take-down bows and on compound bows.

WORKING CRITERIUM

The inspiring principle of this invention is to eliminate the mechanical flipper rest for the arrow and replace it with a magnetic suspension device. In theory, a rigid arrow lying on the bow action plane, geometrically set in line with the mark, encounters points of interference with the rest when its axis lies on the plane of symmetry for the bow (geometric centre).

The collision points are due to the lower feather of the arrow fletching during its passage on the rest.

Although it is possible to reduce the collision consequences on shooting by selecting a certain type of arrow, the flexibility of its shaft and the model of the pressure button, and by setting the point of the arrow out of alignment with the mark, it is still convenient to eliminate the systematic error due to the fletching collision against the rest, in order to assure uniformity in the arrow's performance and a consequent uniformity in the shot.

In theory, the new suspension system will not change the trajectory of the arrow, since the bearing is obtained by magnetic forces whose field ends immediately after the departure of the arrow. In fact there is no influence on initial arrow flight even in the case of a centre-shot set on a geometrical centre. Since the arrow shafts, in paramagnetic or diamagnetic material (aluminium X7, XX75 alloy, carbon fibre, metal-nonmetal composite A.C.E., A.C.C., and so forth), are assembled with ferromagnetic point inserts, the forces produced by a permanent magnet could only hold up the arrow if its force lines have the chance to create a circuit through the high magnetic permeability of the point insert material. This also occurs if there is the thickness of a diamagnetic wall of the shaft across the magnetic flow.

The holding up of the arrow by magnetic forces can only occur, therefore, when the maximum elongation status of the bow is achieved, that is, when the pole shoes of the magnet meet the point insert.

Immediately after the string release and before the separation of the nock from the string, support of the arrow forepart which was due to magnetic action will come away. This will happen during the initial flight of the arrow, when the forepart of the shaft with the ferromagnetic point insert has left the magnetic force field. To eliminate any interference with the transiting arrow, the pole shoes of the magnet will be appropriately moulded according to the type of fletching. For this reason the pole shoes will be cut so that they can offer a tran- sversal obstruction less than the angular space between two consecutive feathers of the arrow tail (120° in three feathers setting).

THE SYSTEM ELEMENTS

Since the magnetic bearing operates only near the maximum elongation status, that is when the magnetic force lines can cross the ferromagnetic point insert, the system is designed to transfer to another element the task of supporting, sliding and guiding the arrow during the development of all the phases executed before the "anchorage" position of the archer (aim position at own maximum stretching elongation). The basic criterium of the system is, therefore, to separate the arrow bearing requirements: initially, during the development of the alignment and traction phases carried out in the archer's movements, the arrow bearing is obtained by a mechanical supporting guide, and finally, when the aim position is achieved, the bearing requirement is assigned to a magnetic field of forces.

Now, safe reliability of a mechanical support can be obtained by giving an appropriate form to the clicker tip (hook) . The supporting action of this clicker ends when it clicks. In other words, the clicker of the system will thence bear and steadily guide the slide of the arrow shaft during the execution of traction phases before the maximum elongation status. During the last drawing back of the arrow, when the archer is about to reach the fixed position at his own maximum elongation status, the steady guide of the clicker correctly brings the ferromagnetic point insert of the arrow between the pole shoes of the magnet.

So, in the pre-final phase, the supporting action is jointly made by the mechanical and the magnetic elements and, in the final phase, the arrow forepart support is transferred to the magnetic forces. This happens at the sound of the clicker. In this condition the clicker can disappear inside a special hole provided in the handle riser of the bow (retractable clicker), or lean against the wall of the riser window (see drawings on sheet no.3/7), hiding its moulded tip behind the pole shoes of the magnet. In accordance with the functions performed by the two elements of the system, they will be called "bearing clicker" and "magnetic rest" (or "mag-rest" for simplicity) respectively. MANUFACTURING CONFIGURATIONS

Given the functional criteriu , the choice of the configuration of the magnetic rest for manufacturing will vary widely in terms of design and materials.

Consequently, the positioning of one or more magnets, or otherwise moulding and/or housing of the magnet differently can be contemplated.

These considerations could also be for the clicker shaping or its placing.

In other words and without any prejudice to the original designs or protection of the ownership of the invention, the components of the system could be manufactured in different shapes and/or arranged in different places.

The choice of design could vary as a consequence of a wide spectrum that goes from solutions which do not alter the architecture of the two components' housing zone to radical modifications on the geometrical shape of the handle riser.

The enclosed drawings show various manufacturing solutions.

Drawings on sheet no. 1/7 illustrate the system designed in such a way as not to alter the handle riser configuration so that the traditional clicker and flipper rest can easily be replaced by the components of the system. Drawings on sheet no. 2/7 illustrate the system applied to a bow planned with an unbroken frame window. This choice, in which the magnet could be laid along the symmetrical axis of the bow appears an appropriate solution when a string releaser is in use. In fact, with this unhooking device, there are no arrow shaft vibrations so that it will be possible to have a coincidence between the centre shot and the geometrical centre.

The symmetry of the riser related to the central vertical plane allows a better distribution of elastic bending stresses and totally erases every torsional stress.

Handle risers designed with the unbroken frame window and equipped with a mag-rest in the middle for lifting the arrow vertically and with a horizontal layout for the clicker could be the best solution for compound bows.

5. INVENTION TESTING

To test the system a traditional recurve take-down bow was used.

The first idea was to install the magnet in the pressure button hole and to shape the clicker tip as a hook without changing its original position. The need to eliminate every interference between the clicker in the resting position and the flying arrow feather set led us to design a special hole in the wall of the riser window in which the tip could hide (Fig. 6 on sheet no. 3/7) .

Clicker point suspension adjustment allowed us to obtain the exact level of its hooking end and, therefore, the exact arrow height for guiding its point insert between the magnet pole shoes. To eliminate every crossing interference, the magnet pole shoes were shaped in such a way as to be inscribed inside an elliptical cone surface with the greatest axis set parallel to the arrow axis.

Magnetic flow was perpendicular to arrow axis. In the vertical plane, the angular obstruction of the magnet pole shoes was restricted to 60°. For arrow contact purposes, the tips of the pole shoes were shaped in such a way as to assure a stable arrow shaft setting.

Retractable bearing clicker and rigid magnetic rest testing results revealed the excellent operating mode of the two system components oy observing the initial flight of the arrows. The arrow impact zone was, however, reiterated on the left side of the target centre. This phenomenon supplied confirmation on the expected systematic error due to uncompensated arrow flexibility caused by the stiffness of the mag-rest arrangement.

Another critical element of the first experimental model was the lack of a supporting force due to the magnetic field which sometimes did not allow arrow support especially during nock movements caused by unstable anchorage as a result of muscle stress.

Consequently, initial test results on the system suggested the following requirements:

A magnetic rest with a lateral shock absorber to obtain a pressure button action;

An adequate magnetic force to assure good bearing during nocking point swings. To fulfil the first requirement, a new prototype was built which allowed a laterally elastic magnetic rest to cushion the shock effects due to initial deformation of arrow shaft (which, in practice, occurs as an effect of the arrow nock deviation beside the action plane of the bow when manual releases are applied) and, in the meantime, gave the opportunity to obtain its lateral adjustment to vary the centre-shot position. To fulfil the second requirement, a larger magnetic ferrite core was used; consequently the increased magnetic field held up a double vertical load compared to the previous one. The table of drawings on sheet no. 4/7, in which the longitudinal and transverse sections are represented, highlights the adjustment solutions used for varying the centre-shot position and for regulating the spring preloading against the magnetic core to obtain a proper action under lateral shocks caused by arrow shaft deflections.

Swinging motion laws make it, however, evident that shock absorbing behaviour will be proportionally better with a lesser magnetic element mass (inertial mass). This mass, on the other hand, could be reduced by utilizing new magnetic materials replacing the traditional magnetite or ferrite core. In any case an intensity of magnetic field must be sufficient to allow the bearing of the arrow in every disturbed situation that could occur in shooting. Using ferrite the need for lightness brings about a reduction of mass of the moulded plates set on both sides of the magnetic core. Reference marks and convenient graduation scales could be drawn on this model to allow simplification of the system tuning. Test results, obtained from this new magnetic rest system, proved the best and came up to expectations.

In fact, the effects on shooting due to centre-shot and inertial stiffness of magnetic shell adjustments (by wheeling the internal threaded bush for the former and by loading the spring by the screw, for the latter) were checked and revealed correct behaviour.

6. EVOLUTION OF THE SYSTEM

The replacement of magnetic ferrite with rare earths magnets which have much more power was a further evolution of the system. ith these new magnetic materials, it is possible to minimize the magnetic core mass according to the swinging motion law requirements.

The very small dimensions of these powerful magnets could allow us to realize some mag-rest arrangements replacing the screwing tephlon tip head of the pressure button shaft. An appropriate tooled shell made for housing the little rare earths magnetic core and for repla¬ cing the pressure button tephlon head, appears the best solution for a shock absorber mag-rest. The enclosed drawing on sheet no. 5/7 shows this arrangement in which polydirectional magnetization is utilized as a magnetic source. Tests on a rare earths polydirectional magnetic source revealed the same vertical load capacity produced by a 15 times bigger ferrite core mass. The bearing clicker, too, became simpler than the prototype by shaping its tip like a horizontal hook (drawing on sheet no. 3/7, Fig. 7).

In such a way the arrow shaft can be supported because its sliding position is found between the pushing horizontal hook of the bearing clicker and the pole, shoes of the mag-rest. Since the hooking tip of the clicker can hide behind the obstruction of the mag-rest, it was found unnecessary to tool the hand-riser window to build it retractable.

During testing, arrows with ferromagnetic point inserts embedded in the shafts (aluminium X7 alloy, carbon fibre, A.C.E.) and arrows with specially designed ferromagnetic point inserts to allow the best contact with the magnetic pole shoes were used.

By these latter inserts it was possible to eliminate paramagnetic material through the magnetic flow due to the wall of the foreward arrow shaft: in fact the thickness of the shaft aluminium wall (14 - 16/1000 inchs) brings a consequently reduced attraction force. On the contrary, by utilizing these special inserts, the lines of magnetic force can circuit through these elements of highly magnetic permeability. Since the commercially available point inserts of the carbon fibre or A.C.E. arrows have a bulging shape, it was essential to replace them by some special tooled point inserts to allow external diameter uniformity in the arrow (drawings on sheet no. 7/7).

In such a way, a steady guide all through the slide of the arrow was assured.

To reduce the peak level of initial sliding friction, it is advisable to eliminate the direct contact between the specially designed ferromagnetic insert and pole shoes by lubricating the insert.

7. SPECIFICATIONS OF THE DRAWINGS

Where indicated, linear measures on the drawings are in millimetric units and are referred to manufacturing details. Drawings on sheet no. 1/7 illustrate the installation of the system on the handle riser of a take-down bow in use in the "free style category".

Lateral view evidences the two conditions "A" and "B" of the holding up of the arrow: these conditions are shown in Fig.2 and Fig.3 rear view pictures. Condition "A" is when the arrow is supported by the clicker; condition "B" is when the arrow is supported only by magnetic forces between mag-rest and ferromagnetic point after the clicker release.

Rear view "A" of Fig. 2 illustrates the form of the clicker when it is in use as a mechanical bearing.

Rear view "B" of Fig. 3 illustrates the clicker in its non-working position and the contour of the shock absorbing rare earths mag-rest.

Drawings on sheet no.2/7 demonstrate a vertical magnetic bearing system applied to an all round frame window compound bow. In this case, the clicker pushes the arrow up against the pole shoes of the magnet. Drawings on sheet no. 3/7 illustrate the lateral and frontal views of a retractable bearing clicker (Fig. 6) and those of a horizontal pushing bearing clicker (Fig. 7).

Drawings on sheet no. 4/7 illustrate the assembled design of the mag-rest in its first shock absorbing arrangement.

The details of the device. identified by numbers, are described below. 1.- Threaded brass block for bearing and adjusting the magnetic cell located inside. The block is pressed into the transverse hole of the handle riser window.

Its internal thread allows centre-shot adjustment by rotating n. 8 brass bush.

2. Grub screw for fixing the n. 8 bush;

This last is called upon to work as a round tail shoulder of the magnetic cell.

3. Dowel for magnetic cell sliding without rotation.

4. Magnetic ferrite inside core.

5. Half round profile (circular sector section) iron for the upper plate of the magnet with a "U" shaped groove in the middle. In the. longitudinal view, the forward end of the plate produces one of the two pole shoes and the other end the shoulder. 6. Iron lower plate of the magnet, shaped like the upper one; it may be without the "U" groove.

7. Epoxy resin or similar substance filling to cement the iron plates with the magnetic core.

8. Threaded brass bush for adjusting the longitudi¬ nal position of the magnetic cell.

9. Brass counter-bush for pressure button screwing.

10. ordinary pressure button.

11. Shaft aluminium wall section.

12. Ferromagnetic point insert of the arrow.

13. Aluminium alloy handle-riser section.

Drawing on sheet no. 5/7 illustrates the longitudinal section of a shock absorbing rare earths mag-rest device.

The components, identified by numbers, are:

1. Mag-rest plug tooled to house a rare earths magnetic source.

2. Pressure button tooled in such a way as to eliminate any transversal movement of the shaft. The drilled hole crossing the shaft at its forward end behind the screw is for housing a pin tool to grip the mag-rest plug.

3. Aluminium alloy handle-riser section. Drawings on sheet no. 6/7 illustrate the orthogonal projections and the longitudinal section of the mag-rest plug configuration designed to replace the tephlon head of an ordinary pressure button.

The details of the plug, suitable for an A.C.E. arrow shaft, are identified by numbers and described below:

Inner rare earths magnetic core.

The cylindrical tablet core has a polydirectio¬ nal magnetization on its surfaces so that it has to be housed to face one of these towards the arrow.

Aluminium case for housing the rare earths magnetic core.

The tip of the shell is moulded to guide a sliding arrow.

The semi-cylindrical cavity drilled at the forward end of the shell is sized according to the external diameter of the arrow. Iron rear stopper.

The stopper has a horizontal threaded hole to tighten the mag-rest plug to the screwed end of a pressure button shaft.

Drilled vertical crossing hole to accomodate a pin tool for gripping the plug. In the mag-rest plugs, free to rotate jointly with the pressure button shaft, the upper position of the hole view may be used as a reference mark to verify the correct horizontal position of the semi-cylindrical cavity at the tip of the mag-rest.

Drawings on sheet no. 7/7 show some specially designed ferromagnetic point inserts manifactured to obtain a direct contact with the pole shoes of the magnet.

The first insert shown in Fig. 14 is suitable for aluminium arrow shafts, size 1916, and planned for the standard 125 grains weight. The second insert shown in Fig. 15 is suitable for A.C.E. arrow shafts and planned for varying its weight from 80 grains to 90 grains. Weight change is achieved by increasing the number of lead bullets housed in the appropriate tip cavity after removing the screwed point cap.

SUBSTITUTE

Claims

C A I M S

1. Clicker form designed to assure the mechanical support and slide of the arrow during the phases of the cycle that precede the maximum stretching elongation status of the archer.

2. Magnetic bearing at the forward end of the arrow, activated in the maximum elongation position, carried out by a sliding magnetic element with an adjustable shock absorber, acting on the ferromagnetic point insert of the arrow.