Abstract:
A device is provided for releasing a spear shaft of a spear gun for scuba diving or the like. The shaft has a latch element formed on a first lever pivotally connected at its front end to a screw attached to and integrally with a frame of the gun, the lever being maintained elastically in a resting position. The gun has a trigger with an abutment portion forced elastically against the front end of the first lever extending forward of a convex upper surface. The convex upper surface intersects 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. This causes the second lever 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 a screw, such that the first lever may be variably displaced, thereby adjusting the force applied by the second lever to the trigger.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to underwater activities and, more particularly, to spear guns for use in fishing, underwater hunting and the like.. 
   BACKGROUND OF THE INVENTION 
   Conventional spear guns, such as those utilized in scuba diving, typically comprise a frame having a longitudinally elongated body mounting, at a rear end, a grip and a trigger. A shaft of a spear is mounted to a front end of the frame, the shaft being mounted slidingly on the elongated body of the frame. The spear is then launched toward a desired target, e.g., a fish, by pulling the trigger. 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. 
   The force for propelling the spear is provided by a pair of cables, made of an elastic material, that are stretched and hooked to the shaft of the spear when the diver loads the gun. Once the trigger is pulled, the spear is released, effecting conversion of the elastic energy accumulated by the elastic cables into kinetic energy in the spear shaft, and propelling the spear outwardly along the longitudinal axis of the gun. 
   The kinematic trigger mechanism that enables the diver to launch or shoot the spear generally comprises a lever hingedly mounted to the frame with a latch element at one end for engaging a notch at a proximal end of the spear&#39;s shaft when the spear is loaded on the gun so as to withstand a pulling force exerted on the shaft by the elastic cables. During loading, the proximal end of the shaft abuts a radial appendage on the lever, thereby inducing its rotation, Such rotation results not only in engagement of the latch member with the notch on the shaft, but also of the opposite end of the lever elastically within a seat in the trigger formed on the side opposite its operating arm. Disengagement of the lever from the trigger, induced when a diver&#39;s finger pulls on the operating arm, causes the shaft to be released from the latch element and the propulsive force of the elastic cables prevails. 
   The kinematic chains often used to operate spear guns, though useful, do not permit adjustment of the stroke of the trigger nor of the force necessary to pull it. If the stroke of the trigger is short, and the spear gun is operated by an inexperienced scuba diver who lacks a feel for the trigger, or in the event of other circumstances such as a diver&#39;s use of very thick gloves, the spear may be accidentally released. Simply put, adjustments of the trigger&#39;s stroke and/or graduating the effort required for a diver to pull the trigger has been found difficult and has yet to provide a solution that is both safe and simple. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   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 operating stroke of the trigger and/or the effort necessary to pull the trigger to be graduated in accordance with a selected diver&#39;s characteristics and needs. 
   Another object of the present invention is to provide a device for releasing a spear shaft of a spear gun that provides for quick and easy adjustment of the trigger&#39;s stroke and/or of the force necessary to pull the trigger through use of a kinematic chain that is neither complicated to manufacture nor to assemble. 
   According to one apsect of the present invention, there is provided a device for releasing the spear shaft of a spear gun for scuba divers. The gun comprises a frame having a longitudinally elongated body for supporting the shaft, terminating with a grip portion and an underlying trigger connected pivotally to the frame. Elastically opposed operation of the trigger is configured so as to release a latch element engaged with a shaped recess formed in a rear end of the shaft so as to withstand a pulling force exerted axially along the shaft by an elastic member connected to the frame that provides a propulsive force for launching the spear. The latch element is formed on a first lever pivotally connected at its front end to a stem attached to the frame and generally parallel to the longitudinal axis. The elastic member maintains the first lever in a resting position, at which the gun is not loaded. The latch element abuts a first shoulder attached to and integrally with the frame and is aligned axially relative to the shaft when it is ready for loading a spear in the elongated body of the frame. The trigger comprises an abutment portion biased elastically against the front end of the first lever and extends forward of a convex upper surface intersecting a concave surface at an edge which, upon rotation of the trigger, traces a first circular trajectory. A second lever is pivotally connected to the frame at a point generally behind the latch element and below the front end of the first lever, the front end of the second lever being displaceable along a second circular trajectory that intersects the first. An arm of the second lever extends so as to intersect the trajectory of the shaft as it is loaded in the gun, whereupon axial movement in loading the spear, the spear shaft first abuts the latch element, thus moving the first lever away from its resting position, and then comes to a loaded position, wherein the latch element engages the shapes recess and abuts the arm of the second lever, causing it to rotate until it abuts the first lever at the latch element, simultaneously raising its front end up to and against the convex surface of the trigger. The front end of the lever is slidingly connected to the stem such that the first lever is adjustably displaceable in the direction of the longitudinal axis so as to vary the point at which the first lever rests against the second lever, and thereby adjust the force with which the front end of the second lever rest against the convex surface of the trigger. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       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; 
       FIG. 2  is a side view of the device illustrated in  FIG. 1 , in an intermediate position with the spear shaft being loaded; 
       FIG. 3  shows the device of  FIG. 2  in a further intermediate position, with the spear shaft in a more advanced phase of loading; 
       FIG. 4  shows the device of  FIG. 2  with the spear shaft in a fully loaded position; 
       FIG. 5  shows the device of  FIG. 2  with the spear shaft in a position immediately after the trigger is pulled; and 
       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. 
   

   The same numerals are used throughout the drawing figures to designate similar elements. 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 
   As set forth herein, illustration of spear guns for scuba divers is restricted generally to the elements that comprise a device for releasing a spear shaft of the spear gun, according to various apsects of the present invention. Consequently, swivel pins for articulation of the various component parts, and abutment elements for the moving parts, are shown schematically only. The pins and abutment elements are attached integrally to the frame of the gun, which is not shown in its entirety, the remaining structural and functional aspects of spear guns being known by those skilled in the art. As their further description is considered unnecessary for illustration of the present invention, the foregoing discussion is not intended to limit the environment. 
   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. In one embodiment, illustrated in  FIG. 1 , there is shown a cross-sectional view of two bushings S 1  and S 2 , respectively, attached to and integrally with the frame. Abutment elements S 4 , S 5 , S 6 , S 7  and S 8  are also attached to and integrally with the frame, and are thus in a fixed position as well. In this manner, motion of movable parts or elements of the device is contained. Generally speaking, the movable elements include a first lever L 1 , a second lever L 2  and a trigger L 3  articulated, respectively, about pins C 1 , C 2  and C 3 , attached to and integrally with the frame. 
   More particularly, second lever L 2  and trigger L 3  have a flattened shape and lie substantially in a vertical plane of symmetry of the gun, passing through its longitudinal axis X. First lever L 1 , on the other hand, comprises two symmetrical elements (only one of which is shown), lying parallel to the plane of symmetry of the gun, the distance between them corresponding to at least the thicknesses of second lever L 2  and of trigger L 3  so that the latter two elements can move without interfering with movement of lever L 1 . 
   In general, the terms “front” and “rear”, as set forth herein, are intended to refer to orientation of the gun to the left and right ends, respectively, as the spear gun appears, for instance, in  FIGS. 1-6 , The words “upper” and “lower” are intended to make reference, for example, to the axis of longitudinal symmetry of the gun. More specifically, the shaft and spear point are located in an upper part of the gun, i.e., above its axis of symmetry, whereas the trigger is typically positioned in alower part of the gun. 
   Bushings S 1  and S 2  support a freely-revolving longitudinal threaded stem  10 . The rear end of the stem (facing the right-hand side in the drawings) is threaded inside and screws into a corresponding threaded hole in a transverse hub  11  from either side of which two transverse, symmetrical pins C 1  project (only one of which is shown) about which the two parallel and adjacent elements forming first lever L 1  are integrally articulated. 
   For simplicity, alternatively or concurrently, reference is made hereinafter to C 1  as a single pin as if first lever L 1  comprises a single element. 
   Preferably, the axis of threaded stem  10  lies substantially along the vertical plane of symmetry of the gun. Between bushings S 1  and S 2 , threaded stem  10  has a ring-shaped ribbing  12 , the knurled lateral surface of which extends from the bushings and enables the scuba diver to turn the threaded stem, thereby screwing or unscrewing its end into and out of, respectively, the threaded hole in hub  11 . This, in turn, effects displacement of the axial position of transverse pin C 1  in the two directions indicated by double line F 1 . As shown in  FIGS. 1-5 , for instance, the tranverse pin occupies its rearward most position, whereas in  FIG. 6  the pin is at an end of its forward stroke. 
   While first lever L 1  is hinged about tranverse pin C 1  at its front end (on the left-hand side of the drawing), it is mounted at its rear end by a freely-revolving wheel  14 . The upper side of the rear end of the first lever terminates with a surface  13  designed to be pushed up against a shoulder S 6 , which is attached integrally to the gun frame. When surface  13  and shoulder S 6  are in contact with one another, they define the end of a stroke of the first lever in its counterclockwise or leftward-turning angular displacement, such corresponding to a starting or resting position of the lever , when the gun is not loaded. 
   The rear end of the second lever L 2  is connected to swivel pin C 2 , located to the rear of wheel  14  and on a slightly lower level than transverse pin C 1 . Counterclockwise rotation of the second lever is limited by a shoulder S 4 . The swivel pin is wrapped within the turns of a spring M 2 , which terminate with lower and upper arms  15  and  16 , respectively. Lower arm  15  is retained by a pair of fixed striker plates S 5 , while upper arm  16  rests up against wheel  14  of first lever L 1 , thereby pushing lever surface  13  toward shoulder S 6 . In addition, upward-facing bracket  20  extends from the rear end of second lever L 2 . 
   The front of trigger L 3 , which rotates about pin C 3 , has a front concave surface  51 , against which the scuba diver&#39;s finger bears, a convex, cylindrical surface  39 , having an axis coincident with that of pin C 3 , and an upper-rear concave, circular surface  38  with a radius of curvature equal to the distance between the axis of swivel pin C 2  and front end  18  of second lever L 2 . At a suitable angle of counterclockwise rotation of the trigger, concave circular surface  38  overlaps a trajectory T 2  traced by end  18  of second lever L 2  as it moves to the right. In the position of the trigger, an edge  40  common to surfaces  38 ,  39 , which edge traces trajectory T 3 , coincides with point T, where trajectories T 2  and T 3  intersect one another. 
   Clockwise rotation of the trigger is limited by a ledge  19  thereof resting up against hub  11 . A spring M 3  is wrapped around pin C 3 , with a lower arm  21  pushing trigger L 3  to turn clockwise toward its end of stroke, wherein the ledge rests up against the hub. An upper arm  22  of spring M 3  rests elastically against a lower edge of first lever L 1 , co-operating with the spring in pushing the first lever into its endmost counterclockwise position, at which surface  13  is in contact with shoulder S 6 . 
   A lower end  23  of a stem  24  is housed, with looseness or play angularly, in a seat  41  in second lever L 2 , upper end  25  of the stem being retained between striker plates S 7  and S 8 . When the device, according to the invention, is in the resting position, as shown in  FIG. 1 , stem  24  is withdrawn, i.e., it does not extend beyond striker plates S 7  and S 8 , whereas upon loading the gun with a spear, as shown in  FIG. 4 , the stem projects beyond the striker plates. Upper end  25  serves as a transmission element for a string line (not shown) that links rear end  31  of spear shaft  30  to the gun frame through a hole  32  in the shaft to which one end of the line is attached. On the underside of rear end  31 , an elongated recess  33  is formed, the recess having tapered sides  34 . 
   To load the gun, the spear shaft is pushed along the gun, in the direction of arrow F 2 , its rear end  31  rests up against wheel  14  of lever L 1 , illustrated generally in  FIG. 2 . At the point shown, levers L 1  and L 2 , trigger L 3 , stem  24  and springs M 2  and M 3  are still in the positions shown in  FIG. 1 . 
   As movement of spear shaft  30  continues along the loading trajectory, generally in the direction of arrow F 2 , best seen in  FIG. 3 , it rides over the wheel, which is thus pushed downwardly, overcoming the elastic force of springs M 2  and M 3  and causing first lever L 1  to rotate to the right. In this position of shaft  30 , its rear end  31  rests against, but does not displace, the end of bracket  20  on second lever L 2 . Second lever L 2 , trigger L 3 , and stem  24  are still in the positions shown in  FIGS. 1 and 2 , while the angle coming between the arms of springs M 2  and M 3  is reduced due to the effect created upon lowering first lever L 1  to the end of its clockwise rightwardly turning stroke. 
   With reference to  FIG. 4 , as displacement of the shaft continues further in the direction of arrow F 2 , the shaft is forced against bracket  20 , effecting rotation of second lever L 2  to the right until it reaches the end of its stroke. Notably, as also shown in  FIG. 6 , in its endmost position, the shaft does not necessarily remain in contact, at its rear end, with the bracket. 
   As best seen in  FIG. 4 , in the final position of shaft  30 , wheel  14  rises inside recess  33  due to the effect of spring M 2 , reaching an intermediate position relative to the terminal or endmost position illustrated in  FIG. 1 , so that first lever L 1  rotates partially to the left, albeit without reaching the initial position shown in  FIG. 1 . 
   As second lever L 2  turns to the right, driven by the rear end of the shaft, its front end  18  slides along upper rear surface  38  of trigger L 3  causing the trigger to turn in a counterclockwise direction, overcoming the force of spring M 3 , until the front end passes beyond point  40 , thus enabling trigger L 3 , through the biasing force of spring M 3 , to return to the position shown in  FIGS. 1 - 4 . Upon completion of this rightward rotation, toward the initial position of trigger L 3  (See  FIG. 1 ), front end  18  of second lever L 2  rests up against surface  39  and occupies a position substantially parallel to the longitudinal axis of the gun, with its upper surface  50  coming up against wheel  14 . 
   A leftwardly acting axial tensile force, as come to bear on shaft  30  in its loaded position (See  FIG. 4 ), is transmitted via surface  34  interfacing with the recess to the wheel and through its upper surface  50  to second lever L 2 . This force generates a lever or moment arm b 1 , balanced by lever or moment arm b 2  generated by the force with which end  18  of lever L 2  rests against surface  39  of the trigger. The force needed to turn the trigger clockwise, or to the left, must, therefore, generate a torque capable of exceeding that created by the force of friction at the point of contact between end  18  of lever L 2  and surface  39  of the trigger. It is considered particularly noteworthy that clockwise rotation of the second lever results in upward displacement of stem  24 , an upper end  25  of the stem extending above striker plates S 7  and S 8 . This enables the string line that joins end  25  to the shaft of the spear to be hooked. 
   Turning now to  FIG. 5 , the end of a stroke of trigger L 3  is shown under the effect of a force R 4  exerted by the scuba diver&#39;s finger on trigger surface  51 . Exertion of this force causes first lever L 1  to release spear shaft  30 , the tensile stress exerted by the elastic cables, which are now disengaged, causes a leftward stroke of the first lever, thereby restoring the first lever and wheel  14  to the positions illustrated in  FIG. 3 . As the shaft continues its displacement to the left, the movable elements of the device return to the positions shown generally in  FIG. 1 . As set forth above, force R 4  overcomes the force of friction at the point of contact between end  18  of second lever L 2 , and surface  39  of trigger L 3 , effecting counterclockwise rotation of the trigger and releasing the second lever, which lever also rotates in a counterclockwise direction through the biasing force of spring M 2 , until the lever abuts shoulder S 4 . 
   To adjust the device, i.e., the effort necessary to pull the trigger initially, as shown in  FIG. 4 , the upper rear portion of ledge  19  rests against hub  11  at point P 1 . As also illustrated in  FIGS. 2 and 5 , the hub is in its rearward most position. 
   If threaded stem  10  is then screwed down into the threaded hole in the hub - by acting on knurled ring  12  - until the hub reaches its forward most position, (See  FIG. 6 ), the point of contact between the hub and the ledge changes to P 2 . Hence, moving the position of tranverse pin C 1  to the left increases the torque necessary to pull trigger L 3 , namely, by overcoming the frictional torque generated by the force with which end  18  of second lever L 2  presses against surface  39  of the trigger. 
   Moreover, since the upper rear portion of ledge  19  is convex, displacement of the point of contact to the left involves clockwise angular displacement of second lever L 2  such that the angular displacement of the trigger required to release shaft  30  also increases. 
   Upon exertion of a force R by shaft  30  on wheel  14 , where R 1  is the force component applied to second lever L 2 , the resulting moment M 1  is determined by the expression M 1 =R 1 *b 1 , where b 1  is the lever arm corresponding to the distance of the line of action of force R 1  from the axis of rotation of swivel pin C 2 . Moment M 1  is, in turn, balanced by a second moment M 2  according to the expression M 2 =R 2 *b 2 , where R 2  is the force applied by end  18  of second lever L 2  on surface  39 , and b 2  is the corresponding lever arm relative to the axis of the swivel pin. 
   For trigger L 3  to be turn or rotated, it is necessary to overcome a torque M 3  determined by the expression M 3 =R 3 *b 3 =f*R 2 *b 3 , where f is the coefficient of friction between elements  18  and  39 , and b 3  is the radius of curvature of circular surface  39  concentric to the axis of pin C 3 . In other words, the scuba diver must exert a torque M 4  on the trigger in order to make it turn, calculated from the expression M 4 =R 4 *b 4 , where R 4  is the force applied by the scuba diver&#39;s finger on front surface  51  of the trigger and b 4  is the lever arm of the force relative to the axis of pin C 3 . Hence, R 4 =R 1 *f*b 1 *b 3 /(b 2 *b 4 ), where the only variable is lever arm b 1 , which increases when hub  11  is shifted to the left, as seen in the drawings, i.e., toward the front end of the gun, when threaded stem  10  is screwed into the threaded hole in the hub. 
   Accordingly, it is now possible to vary the force required to pull the trigger, between a minimum (See  FIG. 4 ) and a maximum (See  FIG. 6 ). Moreover, when the force necessary to pull the trigger has been increased, the angular displacement required for the trigger to release shaft  30  also increases, given the greater extent of sliding action needed of end  18  over surface  39  before such end reached edge  40  of the trigger. 
   Overall, the present invention is especially advantageous in providing a device for releasing a spear shaft of a spear gun that allows the operating stroke of the trigger and/or the effort needed to pull the trigger to be graduated in accordance with a selected diver&#39;s charateristics and needs. It also provides for quick and easy adjustment of the trigger&#39;s stroke and of the force necessary to pull the trigger by using a kinematic chain that is neither complicated to manufacture nor assemble. The effect of this adjustment is not only beneficial in that it is maximized when the spear shafts associated with a particular gun are used, but also in allowing different shafts to be used, even if elongated recess  33  of such a shaft differs slightly in shape or position. 
   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.