Abstract:
A device is provided for releasing a spear shaft of a spear gun for scuba diving or the like. A latch element of the shaft is formed on a first lever pivotally connected at its front end to a screw attached to and integrally with a frame of the gun, and is elastically maintained in a resting position. A trigger of the gun includes an abutment portion forced elastically against the front end of the first lever extending forward of a convex upper surface intersecting a concave surface at an edge that traces a first circular trajectory when the trigger is rotated. A second lever is rotatably connected to the frame, the front end of the second lever being movable along a second circular trajectory intersecting the first circular trajectory. An arm of the second lever extends so as to intersect the trajectory of the spear shaft when it is loaded in the gun, such that the shaft abuts the latch element first, thereby moving the first lever away from its resting position, until it engages a shaped cavity of the shaft, and subsequently abuts the arm of the second lever, causing it to turn until it abuts the first lever in line with the latch element, simultaneously raising its front end up to and against the convex surface of the trigger. The front end of the first lever is slidingly connected to the screw, such that the first lever may be adjustably displaced, thereby varying the force applied by the second lever on the trigger.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to underwater activities and, more particularly, to spear guns for use in fishing and underwater hunting.  
       BACKGROUND OF THE INVENTION  
       [0002]     Conventional spear guns, such as those utilized in scuba diving, typically comprise a frame having a longitudinally elongated body fit at a rear end with a grip and a trigger. The trigger is pulled to launch a spear attached to a front end of a shaft, mounted slidingly on the elongated body of the frame. The rear end of the shaft is usually connected to a string line for retrieval of the spear and any prey that may have been snagged by the diver.  
         [0003]     The propulsive force of the spear is provided by a pair of cables made of an elastic material that are stretched and hooked onto the shaft of the spear when the diver loads the gun, then the spear is released when the trigger is pulled, converting the elastic energy accumulated by the elastic cables into kinetic energy in the spear shaft.  
         [0004]     The kinematic mechanism that enables the diver to shoot the spear by means of the trigger generally comprises a lever hinged onto the frame and presenting a latch element at one end that engages in a notch at the proximal end of the spear shaft when the spear on the gun is loaded so as to withstand the pulling force exerted on the shaft by the elastic cables. During the movement used to load the spear gun, the proximal end of its shaft abuts against a radial appendage on the lever, thereby inducing its rotation, as a result of which, in addition to the latch element engaging in the notch on the shaft, the opposite end of the lever elastically engages within a seat in the trigger formed on the side opposite its operating arm. The disengagement of the lever from the trigger, which is induced by a finger pulling on its operating arm, causes the shaft to be released from the latch element on the lever and the propulsive force of the elastic cables prevails. A kinematic chain of this type is shown, for instance, in U.S. Pat. No. 5,904,132.  
         [0005]     In the spear fishing guns of the known type, the kinematic chains used to operate them, such as the one described above, do not allow for any adjustment of the stroke of the trigger and of the effort needed to pull it. In the event of the scuba diver&#39;s finger being scarcely sensitive due to limited experience, or for contingent reasons such as the use of very thick gloves, the spear may be released by accident if the stroke of the trigger is short. In other words, the problem of graduating the effort required to pull the trigger and/or adjusting the trigger&#39;s stroke is strongly felt and has yet to find a simple and safe solution.  
       OBJECTS AND SUMMARY OF THE INVENTION  
       [0006]     Accordingly, it is an object of the present invention to provide a device for releasing a spear shaft of a spear gun for scuba diving or the like that allows the effort required to pull the trigger and/or the operating stroke of the trigger to be graduated in accordance with a selected diver&#39;s characteristics and needs.  
         [0007]     A particular object of the invention is to provide a device of the aforementioned type wherein the force required to pull the trigger and/or the trigger&#39;s stroke can be adjusted quickly and easily by means of a kinematic chain that is not particularly complex from the point of view of its manufacture and assembly.  
         [0008]     These objects are achieved with a device for releasing the spear shaft of a fishing gun for scuba divers according to the present invention, wherein the latch element is formed on a first lever, the front end of which is pivotally connected to a threaded stem fixedly attached to the frame of the gun and lying parallel to its longitudinal axis and elastic means are provided for keeping the first lever in a resting position, corresponding to the situation when the gun is not loaded, wherein the latch element abuts against a first shoulder integrally attached to the frame and is axially aligned with the spear shaft when it is prepared for loading on the elongated body of the frame. The trigger comprises an elastically-tensioned abutment portion for the front end of the first lever and extending forward from a convex upper surface intersecting a concave surface at an edge that traces a first circular trajectory as the trigger is rotated. A second lever pivotally connected to the frame at a point situated behind the latch element and below the front end of the first lever is also provided, the front end of the second lever being movable along a second circular trajectory intersecting the first circular trajectory. An arm of the second lever extends to intersect the trajectory of the spear shaft when the gun is loaded, whereby during the axial movement to load the spear, the spear shaft abuts against the latch element first, displacing the first lever from its resting position and occupying a loaded position wherein the latch element engages in the shaped recess in the shaft, and then it abuts against the arm of the second lever, making the latter rotate until it abuts against the first lever on at the latch element, simultaneously bringing its front end up against the convex surface of the trigger. The front end of the first lever is slidingly connected to the threaded stem, whereby the first lever is adjustably displaceable in the longitudinal axis direction to enable a variation in the point where the first lever rests on the second lever and the consequent force with which the front end of the second lever rests against the convex surface of the trigger. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     A specific, illustrative device for releasing a spear shaft of a spear gun, according to the present invention, is described below with reference to the accompanying drawings, in which:  
         [0010]      FIG. 1  shows schematically a longitudinal section of a device for releasing a spear shaft of a spear gun, according to one aspect of the present invention, in a resting position, ready for loading with a spear;  
         [0011]      FIG. 2  is a side view of the device illustrated in  FIG. 1  in an intermediate position with the spear shaft being loaded;  
         [0012]      FIG. 3  shows the device of  FIG. 2  in a further intermediate position, with the spear shaft in a more advanced phase of loading;  
         [0013]      FIG. 4  shows the device of  FIG. 2  with the spear shaft in a fully loaded position;  
         [0014]      FIG. 5  shows the device of  FIG. 2  with the spear shaft in a position immediately after the trigger is pulled; and  
         [0015]      FIG. 6  shows the device in a similar condition to that in  FIG. 4 , but with a different degree of adjustment to the effort necessary for a user to pull the trigger. 
     
    
       [0016]     Still other objects and advantages of the present invention will become apparent from the following description of the preferred embodiments.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     Hereinafter, the adjectives “front” and “rear” refer to the orientation of the gun and refer to the left and right ends, respectively, as the spear gun appears in the figures. The adjectives “upper” and “lower” are used in an absolute sense and refer to the axis of longitudinal symmetry of the gun: the shaft and spear point are placed in the upper part of the gun, i.e. above its axis of symmetry, while the trigger is conventionally positioned in the lower part of the gun.  
         [0018]     The illustration of the fishing gun for scuba divers is restricted to the elements comprising the release device according to the invention. The swivel pins for the articulation of the various component parts and the abutment elements for the moving parts are consequently only shown schematically, said pins and abutment elements being integrally attached to the gun frame, which is not shown in its entirety because it is structurally well-known to a person skilled in the art.  
         [0019]     Referring now to the drawings and, more particularly, to  FIGS. 1-6 , there is shown generally a specific, illustrative device for releasing a spear shaft of a spear gun for scuba diving or the like, according to various aspects of the present invention. Illustrated in  FIG. 1  is a cross-sectional view of two bushings S 1  and S 2 , respectively, attached to and integrally with the frame, according to one embodiment. Abutment elements S 4 , S 5 , S 6 , S 7  and S 8  are also attached to and integrally with the frame and, consequently, are in a fixed position. In this manner, motion of moving parts or elements of the device is contained. Generally speaking, the movable elements of the device include a first lever L 1 , a second lever L 2  and a trigger L 3  articulated, respectively, around pins C 1 , C 2  and C 3 , which are attached to and integrally with the frame.  
         [0020]     In particular, the lever L 2  and the trigger L 3  have a flattened shape and lie substantially in the vertical plane of symmetry of the gun, passing through its longitudinal axis X, while the lever L 1  comprises two symmetrical elements (only one of them shown in the figures), lying parallel to the plane of symmetry of the gun, the distance between them corresponding to at least the thicknesses of the lever L 2  and of the trigger L 3  so that the latter two elements can move without interfering with the movement of the lever L 1 .  
         [0021]     The bushes S 1  and S 2  support a freely-revolving longitudinal threaded stem  10 , the rear end of which (facing towards the right in the figure) is threaded inside and screws into a corresponding threaded hole in a transverse hub  11  from either side of which there project two transverse, symmetrical pins C 1  (only one of which is shown in the figures) around which the two parallel and adjacent elements forming the first lever L 1  are integrally articulated.  
         [0022]     For the sake of simplicity, reference is made hereinafter to a single pin C 1  as if the lever L 1  consisted of a single element, a condition which may in fact constitute an alternative embodiment of the invention.  
         [0023]     The axis of the threaded stem  10  lies substantially along the vertical plane of symmetry of the gun. Between the two bushes S 1  and S 2 , the threaded stem  10  is provided with ring-shaped ribbing  12 , the knurled lateral surface of which extends from the bushes S 1  and S 2  and enables the scuba diver to turn the threaded stem  10 , thereby screwing or unscrewing its end in the threaded hole in the hub  11  and consequently displacing the axial position of the transverse pin C 1  in the two directions indicated by the double line F 1 . In FIGS.  1  to  5 , for instance, the pin C 1  occupies its rearmost position, whereas in  FIG. 6  the pin C 1  is at the end of its forward stroke.  
         [0024]     The lever L 1  is hinged around the pin C 1  at its front end (on the left in the figure), whereas it is fitted at its rear end with a freely-revolving wheel  14 . The upper side of the rear end of the lever L 1  terminates with a surface  13  designed to be pushed up against a shoulder S 6 , which is integrally attached to the gun frame. When in contact with one another, the surface  13  and the shoulder S 6  define the end of the stroke of the lever L 1  in its leftward-turning angular displacement, corresponding to the resting position of the lever L 1 , when the gun is not loaded.  
         [0025]     The rear end of the second lever L 2  is connected to the swivel pin C 2 , which is positioned to the rear of the wheel  14  and on a slightly lower level than the pin C 1 . The anticlockwise rotation of the second lever L 2  is restricted by a shoulder S 4 . The pin C 2  is wrapped with the turns of a spring M 2 , which terminate with two arms  15  and  16 . The lower arm  15  is retained by a pair of fixed striker plates S 5 , while the upper arm  16  rests up against the wheel  14  of the lever L 1 , consequently pushing the surface  13  towards the shoulder S 6 . An upward-facing bracket  20  extends from the rear end of the second lever L 2 , the purpose of which will be explained with reference to the subsequent figures.  
         [0026]     The front of the trigger L 3 , revolving around the pin C 3 , has a front concave surface  51 , on which the scuba diver&#39;s finger comes to bear, a cylindrical and convex surface  39 , whose axis coincides with that of the pin C 3 , and an upper-rear concave circular surface  38  with a radius of curvature equal to the distance between the axis of the pin C 2  and the front end  18  of the lever L 2 . At a suitable angle of leftward rotation of the trigger L 3 , the concave circular surface  39  overlaps the trajectory T 2  traced by the end  18  of the lever L 2  as it moves rightwards. In said position of the trigger L 3 , the edge  40  common to the surfaces  38  and  39 , which traces the trajectory T 3 , coincides with the point T, where the trajectories T 2  and T 3  intersect each other.  
         [0027]     The clockwise rotation of the trigger L 3  is restricted by a ledge  19  thereof resting up against the hub  11 . There is also a spring M 3  wrapped around the pin C 3 , with a lower arm  21  that pushes the trigger L 3  to turn clockwise towards its end of stroke, wherein the ledge  19  rests up against the hub  11 . The upper arm  22  of the spring M 3  rests elastically against the lower edge of the lever L 1 , co-operating with the spring M 2  in pushing the lever L 1  into its endmost anticlockwise position, at which the surface  13  lies in contact with the shoulder S 6 .  
         [0028]     The lower end  23  of a stem  24  is housed, with an angular slack, in a seat  41  in the lever L 2 , the upper end  25  of said stem being retained between striker plates S 7  and S 8 . When the device according to the invention is in the resting position, shown in  FIG. 1 , said stem  24  is withdrawn, i.e. it does not extend beyond the striker plates S 7  and S 8 , whereas it does project therefrom when spear is loaded on the gun, as shown in  FIG. 4 . Said upper end  25  serves as a transmission element for a string line (not shown) that links the rear end of the spear shaft  30  to the frame of the gun by means of a hole  32  in the shaft to which one end of the line is attached.  
         [0029]     On the underside of the rear end  31  of the shaft  30  an elongated recess  33  with tapered sides  34  is formed, the purpose of which will be explained later on.  
         [0030]     To load the gun, the shaft  30  is pushed along the gun in the direction of the arrow F 2  so that its rear end  31  rests up against the wheel  14  of the lever L 1 , as shown in  FIG. 2 . In the condition shown in said figure, the levers L 1  and L 2 , the trigger L 3 , the stem  24  and the springs M 2  and M 3  are still in the positions shown in  FIG. 1 .  
         [0031]     As shown in  FIG. 3 , as the shaft  30  proceeds in its displacement along the loading trajectory in the direction of the arrow F 2 , it rides over the wheel  14 , which is thus pushed downwards, overcoming the elastic force of the springs M 2  and M 3  and making the lever L 1  rotate towards the right. In this position of the shaft  30 , its rear end  31  rests against, but does not displace end of the bracket  20  on the lever L 2 . The lever L 2 , the trigger L 3 , and the stem  24  are still in the positions shown in  FIGS. 1 and 2 , while the angle coming between the two arms of the springs M 2  and M 3  is reduced due to the effect of the lever L 1  being lowered to the end of its rightward turning stroke.  
         [0032]     As it continues in its displacement in the direction of the arrow F 2 , the shaft  30  forces against the bracket  20 , inducing the rightward rotation of the lever L 2  until it reaches the end of its stroke, shown in  FIG. 4 . It should be noted that, in its endmost position, the shaft  30  does not necessarily remain in contact, at its rear end, with the bracket  20 , as shown clearly with reference to the subsequent  FIG. 6  too.  
         [0033]     In the final position of the shaft  30 , shown in  FIG. 4 , the wheel  14  rises inside the recess  33  due to the effect of the spring M 2 , reaching an intermediate position with respect to the terminal position of  FIG. 1 , so the lever L 1  rotates partially leftwards, albeit without reaching the initial position shown in  FIG. 1 .  
         [0034]     As the lever L 2  turns to the right, driven by the rear end of the shaft  30 , its front end  18  slides along the upper rear surface  38  of the trigger L 3  making the trigger turn anticlockwise and overcoming the force of the spring M 3 , until the front end  18  of the lever L 2  passes beyond the point  40 , thus enabling the trigger L 3  to return to the position shown in  FIGS. 1, 2 ,  3  and  4 , due to the effect of the spring M 3 . At the end of this rightward rotation towards the initial position of the trigger L 3  ( FIG. 1 ), the front end  18  of the lever L 2  rests up against the surface  39  and occupies a position substantially parallel to the longitudinal axis of the gun, with its upper surface  50  coming up against the wheel  14 .  
         [0035]     The leftward axial tensile force coming to bear on the shaft  30  in its loaded position ( FIG. 4 ) is transmitted via the surface  34  interfacing with the recess  33  to the wheel  14  and via its upper surface  50  to the lever L 2 . Said force generates an arm moment b 1 , balanced by the arm moment b 2  generated by the force with which the end  18  of the lever L 2  rests against the surface  39  of the trigger L 3 . The force needed to turn the trigger leftwards must consequently generate a torque capable of exceeding the one due to the force of friction at the point of contact between the end  18  of the lever L 2  and the surface  39  of the trigger L 3 .  
         [0036]     It should be noted that the rightward rotation of the lever L 2  results in an upward displacement of the stem  24 , the upper end  25  of which extends above the striker plates S 7  and S 8 , thus enabling the string line connecting the shaft of the spear to the gun to be hooked to said end  25 .  
         [0037]      FIG. 5  shows the end of the stroke of the trigger L 3  under the effect of the force R 4  exerted by the scuba diver&#39;s finger on its surface  51 , as a result of which the shaft  30  is released by the lever L 1  and begins its leftward stroke due to the effect of the tensile stress exerted by the elastic cables, which are now no longer retained, restoring the lever L 1  and the wheel  14  to the positions already shown in  FIG. 3 . As the shaft  30  continues in its leftward displacement, the movable elements of the device return to the positions shown in  FIG. 1 . As mentioned previously, the force R 4  overcomes the force of friction existing at the point of contact between the end  18  of the lever L 2  and the surface  39  of the trigger L 3 , enabling the anticlockwise rotation of the trigger L 3  and releasing the lever L 2  that also turns anticlockwise, due to the effect of the spring M 2 , until it abuts against the shoulder S 4 .  
         [0038]     To adjust the device, i.e. to adjust the effort needed to pull the trigger L 3 , reference is made to the positions shown in  FIGS. 4 and 6 . In the position shown in  FIG. 4 , the upper rear portion of the ledge  19  rests against the hub  11  at the point P 1 . In the position shown in  FIG. 4 , as in  FIGS. 2 and 5 , the hub  11  is in its rearmost position.  
         [0039]     Supposing now that the threaded stem  10  is screwed down into the threaded hole in the hub  11 , by means of an action taken on the knurled ring  12 , until the hub  11  reaches its forwardmost position, as shown in  FIG. 6 , the point of contact between the hub  11  and the ledge  19  changes to P 2 .  
         [0040]     It is easy to demonstrate that, moving the position of the pin C 1  leftwards increases the torque needed to pull the trigger L 3  by overcoming the torque of the friction generated by the force with which the end  18  of the lever L 2  presses against the surface  39  of the trigger L 3 .  
         [0041]     Moreover, since the upper rear part of the ledge  19  is convex, the leftward displacement of the point of contact entails a clockwise angular displacement of the lever L 3  so the angular displacement required for the trigger to release the shaft  30  also increases.  
         [0042]     Let R be the force exerted by the shaft  30  on the wheel  14  and R 1  the component applied to the lever L 2 , the resulting moment will be M 1 =R 1 *b 1 , where b 1  is the lever arm consisting of the distance of the line of action of the force R 1  from the axis of rotation of the pin C 2 .  
         [0043]     The moment M 1  is balanced by the moment M 2 =R 2 *b 2 , where R 2  is the force applied by the end  18  of the lever L 2  on the surface  39 , and b 2  is the corresponding lever arm with respect to the axis of the pin C 2 .  
         [0044]     To make the trigger L 3  turn, it is consequently necessary to overcome the torque M 3 =R 3 *b 3 =f*R 2 *b 3 , where f indicates the coefficient of friction between the elements  18  and  39 , and b 3  is the radius of curvature of the circular surface  39  concentric to the axis of the pin C 3 . In other words, the torque that the scuba diver needs to exert on the trigger to make it turn is M 4 =R 4 *b 4 , where R 4  indicates the force applied by the scuba diver&#39;s finger on the front surface  51  of the trigger L 3  and b 4  indicates the arm of said force with respect to the axis of the pin C 3 .  
         [0045]     Thus, R 4 =R 1 *f*b 1 *b 3 /(b 2 *b 4 ), where the only variable is the arm b 1 , which increases when the hub  11  is shifted leftwards, as seen in the figure, i.e. towards the front end of the gun, when the threaded stem  10  is screwed into the threaded hole in the hub  11 .  
         [0046]     It is consequently possible to vary the force required to pull the trigger, between a minimum ( FIG. 4 ) and a maximum ( FIG. 6 ).  
         [0047]     It should also be noted that, when the force needed to pull the trigger is increased, the angular displacement required for the trigger to succeed in releasing the shaft  30  also increases because the extent of the sliding action of the end  18  over the surface  39  before it reaches the edge  40  of the trigger L 3  is also greater.  
         [0048]     The effect of the above-mentioned adjustment is obviously maximized when the spear shafts associated with a given gun are used, but it also allows for different shafts to be used, even if their cavity  33  differs slightly in shape or position.  
         [0049]     Various modifications and alterations to the present invention may be appreciated based on a review of this disclosure. These changes and additions are intended to be within the scope and spirit of the invention as defined by the following claims.