Abstract:
The present invention provides a target illuminating and sighting apparatus for a bow. A frame for attachment to the bow supports two vertically spaced pivoting mounts, each of mounts supports a laser oriented to illuminate a target when the bow is aimed. Cams abut the pivotal mounts and allow for setting an angle of vertical convergence between the light beams so that the lasers intersect at ranges of between about 10 and 50 yards. An inclination cam, working synchronously with the convergence cam controls the inclination of the beams relative to the initial path of an arrow to be shot from the bow. The inclination cam may be calibrated to adjust for the particular bow and arrow combination.

Description:
This is a continuation-in-part application of application Ser. No. 09/267,036 filed Mar. 12, 1999, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to archery and more particularly to bow sights. Still more particularly the invention relates to a dual beam laser targeting aid providing synchronized control of convergence and inclination of the beams for guiding bow elevation prior to shooting. 
     2. Description of the Problem 
     Arrow flight is an example of ballistic dynamics. Pure ballistic dynamics deals with the trajectory of projectiles which generate no lift and have no continuing source of thrust. Ballistics considers the effects of gravitational fields and allows for aerodynamic drag. Under these conditions projectiles follow a decaying parabolic trajectory with the rate of velocity decay being highest where the velocity is greatest. Accordingly, bow archery has never been a matter of simply taking careful aim directly at a target and loosing the bowstring to send an arrow toward its mark. As long as the archer is not shooting vertically, the archer must estimate the range to the mark in order to give the arrow an initial upward velocity relative to his or her line of sight to the mark. The archer does this by elevating the bow to aim the arrow above the mark. 
     The degree to which the archer elevates the bow is complicated by a number of factors. An archer is trained to shoot from a full draw. For a given bow, a fill draw transfers a fixed amount of energy to the bow which is transferred to the arrow upon loosing the bowstring. Thus, a heavier (more massive) arrow will accelerate less than a lighter (less massive) arrow. An arrow with a larger arrowhead or fetching another arrow will generate correspndingly more drag at a given velocity, contributing to a greater decay in velocity. An archer compensates for all of these factors when elevating a bow for a shot. 
     Archers have long used sights to help aim arrows. Given the differing flight characteristics of arrows and the different energy capacity of different bows, a bowsight will typically be matched to a bow and arrow combination. Lasers have been extensively applied to improve the effectiveness of sights, particularly with respect to estimating the proper elevation of the bow. U.S. Pat. No. 5,782,002 to Reed and U.S. Pat. No. 5,495,675 to Huang are good examples. Both patents teach bowsights incorporating a laser. The laser is oriented to emit its light beam in the direction of arrow flight from the bow. In both patents the laser is positioned above the arrow rest and the inclination of the laser can be adjusted so that the beam illuminates the desired mark when the archer has elevated the bow to compensate for the archer&#39;s estimated range to target. Reed provides a cam based adjustment mechanism for setting laser inclination. However, the effectiveness of the Reed and Huang devices depends upon the archer&#39;s correct in situ estimation of the range to the mark and a correct estimation of the arrow&#39;s trajectory. 
     Laser sights exist for actually measuring range, such as Hines et al., U.S. Pat. No. 4,753,528. The Hines&#39; device is an electronic range finder incorporating a laser and a photosensitive detector for sampling reflected light. Such devices are illegal for hunting in several States and are not permitted at contests under applicable archery competition rules. It remains a problem to supply a bow sight which will guide an archer in correctly elevating his or her bow for hitting a mark without actively measuring the range to the target. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a laser bowsight aid which guides an archer in correctly elevating the bow to hit a mark with an arrow shot from the bow. 
     It is another object of the present invention to provide an adjustable bowsight aid which may be calibrated for arrows of differing flight characteristics and bows of differing energy capacities. 
     It is still another object of the present invention to provide bowsight aid which is light, robust and compact. 
     The present invention provides a sighting aid for use primarily with a short range, low projectile velocity weapon, preferably an archery bow. The sight comprises projectors for light beams, preferably provided by two lasers. In the preferred embodiment, both lasers are positioned, vertically aligned, above the arrow rest of the bow. The lasers are oriented to direct their beams in the general direction of flight of an arrow to be shot from the bow. The lasers are mounted on pivoting arms, diverging slightly outwardly from the vertical plane of the bow. The arms pivot on axes perpendicular to the plane of the bow, allowing the inclination of the lasers relative to the direction of arrow flight, and relative to one another, to be adjusted. The levers ride on the perimeter cam surfaces of a rotatable cam wheel. Convergence of the lasers is controlled by giving one of the perimeter cam surfaces a variable radius, while the second lever rides against a constant radius cam surface. Thus the angle of convergence of the lasers changes as the cam wheel rotates. The range to convergence of the beams is a fixed function of cam wheel position. The inclination of the two lasers is synchronously controlled by raising and lowering the cam wheel. This is done by providing a second, variable radius cam mounted on the cam wheel which rides against a brace fixed to a frame supporting the wheel. As the cam wheel rotates, the height of the cam wheel varies as a function of its radial position as different sections of the variable radius cam come into position on the fixed brace. The second variable radius cam, or declination control cam, is user adjustable, so that the degree of declination of the lasers for a given cam wheel position may be changed and may be calibrated with the range to convergence of the beams for the cam wheel position. 
     In use, the laser sighting aid produces two horizontally aligned illuminated dots on the target when the bow is correctly elevated. To effect this result, the convergence of the laser beams and the declination of the laser beams is calibrated. As described above, the trajectory of an arrow shot from a bow is a decaying parabola. Every point in the trajectory of the arrow will lie below a straight line projection of the arrow&#39;s initial direction of flight. Lasers positioned with one above the other, and with both lasers above, but vertically aligned with, an arrow resting in the bow, can be oriented (with a declination) to intercept one another (converge) to intercept the arrow&#39;s trajectory at a single point. With the ranges to convergence of the laser beams fixed as a function of cam wheel position, the declination of the lasers for each cam wheel position is adjusted to intercept the expected trajectory for an arrow by adjusting the declination control cam. 
     Typically, declination of the beams is calibrated for the ranges to convergence of the beams by trial and error. The declination control cam is step wise adjustable, based on a series of radially spaced, independently adjustable allen screws. An archer calibrates the system for a particular bow and arrow combination by taking aim at a series of targets, spaced to correspond to the changes in range to convergence for each available step in the declination control cam. Declination is adjusted at each range until the archer achieves consistent hits at the proper height for the range to target. 
     Additional effects, features and advantages will be apparent in the written description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of the principal of the invention applied to a ballistic trajectory for an arrow; 
     FIGS. 2A and 2B are schematic illustrations of a preferred embodiment of the invention; 
     FIG. 3 is a side cross sectional view of a preferred embodiment of the invention; 
     FIG. 3A is a partial section view taken along section lines - 3 A- in FIG. 3; 
     FIG. 4A is a cross sectional view of a first embodiment of the invention viewed from the front; 
     FIG. 4B is a cross sectional view of a first embodiment of the invention viewed from the rear; 
     FIG. 5 is a perspective view of a first embodiment of the invention mounted to an archery bow; 
     FIG. 6 is a side elevation of an alternative, preferred cam wheel; and 
     FIG. 7 is a cross sectional view taken along section lines  7 — 7  of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in which like numerals refer to like objects in different views, FIG. 1 schematically illustrates the environment of application of the invention. An arrow  10  shot from bow  12  has a ballistic trajectory  22 . For a non-vertical shot, trajectory  22  is a roughly parabolic track, bending downwardly due to gravity, with the downward tract accentuated by the effects of drag on the forward velocity of the arrow. For an archer  30  to hit mark  20 , arrow  10  must be launched with an upward velocity component, compared to the line of sight  32  to the mark, to compensate for gravity and drag. Archer  30  does this by elevating bow  12 , relative to the line of sight  32 , before loosing bowstring  13 . The present invention guides the archer in correctly elevating bow  12  for hitting mark  20  without actively measuring the range to the mark. 
     Target illuminating apparatus  11  comprises first and second lasers  16  and  18 , positioned with respect to bow  12  to be vertically aligned with arrow rest  14 . Lasers  16  and  18  are oriented to project beams  24  and  26  toward mark  20 . Lasers  16  and  18  are oriented so that beams  24  and  26  vertically converge at the range to mark  20  and have a declination with respect to the initial arrow trajectory  22  that the point of convergence corresponds to the point that arrow  10  will hit, assuming no cross wind condition exists. The range to convergence of beams  24  and  26  and the relative inclinations of the beams to the rest inclination of arrow  10  on arrow rest  14  are controlled by archer  30 . Convergence and inclination are synchronously adjusted by a cam mechanism of the preferred embodiment, in which the inclinations of lasers  16  and  18  are pre-calibrated for the anticipated trajectory of the arrow  10  for a plurality of ranges to convergence. In use, an archer  30  aligns and elevates bow  12  along a line of sight  32  established through a simple sight  28  while synchronously adjusting the inclination and convergence of lasers  16  and  18  until beams  24  and  26  are horizontally aligned on mark  20 . 
     FIGS. 2A and 2B are schematic illustrations of the principals of operation of a cam mechanism  34  used to implement a preferred embodiment of the invention. Cam mechanism  34  is shown at the ends of its travel, with FIG. 2A corresponding to positioning of the cam for distant targets, up to a range of 45 to 50 yards, and FIG. 2B illustrating positioning of the cam for near ranges of about 10 yards. The precise ranges available will depend upon the ballistic trajectory characteristics of the arrow, the energy capacity of the bow and the dimensions of the cam mechanism. Nothing in principal limits the application of the invention to bows or to ranges under 50 yards, but the use of bows at greater ranges is not generally recommended. 
     Cam mechanism  34  is based on a frame  41  adapted for mounting on a bow (shown in FIG.  5 ). A cam wheel  36  is rotatably mounted on an axis  38  which in turn is set in a vertical slot  39  in frame  41 . Cam wheel  36  can, accordingly, rotate on axis  38  as indicated by double arrow “A” as well as move upwardly and downwardly as indicated by double arrow “B”. The mechanism for synchronizing rotation with up and down movement of cam wheel  36  is discussed below. For distant targets cam wheel  36  is rotated clockwise to the maximum extent of its travel and raised. For near targets cam wheel  36  is rotated counterclockwise to the maximum extent of its travel and lowered. 
     Cam wheel  36  has an upper cam surface  40  and a lower cam surface  42 , against which upper lever  44  and lower lever  46  ride. At least one of cam surfaces  40  and  42  has a radially varying radius on axis  38 . As a result, when cam wheel  36  is rotated, the pitch of one of levers  44  and  46  changes as a result of riding on a cam surface which has a varying radius. In the preferred embodiment, upper cam surface  40  varies between a maximum radius and a minimum radius on axis  38 , while the radius of lower cam surface  42  is constant. By varying the radius of only one cam surface machining costs are reduced and greater tolerances are obtained. In the preferred embodiment, the maximum and minimum radii of upper cam surface  40  are both greater than the constant radius of lower cam surface  42 . The radii of the laser cam surface is sufficiently large to assure that levers  44  and  46  assure relative pitches which assures that beams from lasers  16  and  18  converge. The largest, or most open, convergence angle between beams emitted by lasers  16  and  18  occurs when cam wheel  36  is rotated so that upper cam surface  40  abuts lever  44  along its minimum radius  52 . This cam wheel  36  position is used for the maximum effective range for the bow and correspondents FIG.  2 A. The smallest, or most closed convergence angle, used for near marks, is obtained when upper cam surface  40  abuts lever  44  at the point of its greatest radius  54  as illustrated in FIG.  2 B. The ranges to convergence of the beams is a function of the radial position of cam wheel  36 . 
     Where both lasers are to be positioned above the arrow, and levers  44  and  46  are essentially identical, the greater radii for upper cam surface  40  assure that the upper more laser  16  has a greater declination to the horizontal than laser  18 . Cam wheel  36  can be constructed to provide a setting where there was no convergence of the beams. Such a setting would be advantageous where the sight is to be used for vertical shots. The variation in the radii for upper cam surface  40  is less than 2% of the average diameter of cam wheel  36 . The precise measurements depend on the absolute magnitude of the diameter of cam wheel  36 . 
     The pitches of levers  44  and  46  are also changed by the upward and downward movement of cam wheel  36 . In the preferred embodiment, cam mechanism  34  is positioned on a bow above the arrow rest  14 . Thus both laser  16  and  18  are above the arrow, relative to gravity, and both must point downwardly relative to the initial path of the arrow in order to intercept the anticipated trajectory of the arrow. As an arrow&#39;s trajectory will follow a increasingly downward arc, relative to the horizontal distance being traversed, the arrow is fired above a target which is at substantially the same level as the archer. The inclination, or more precisely speaking, declination of lasers  16  and  18  relative to the initial path of an arrow is set by the upward and downward movement of the axis  39  of cam wheel  36  in slot  38 . As described below, the position of axis  38  in slot  39  automatically changes with rotation of cam wheel  36 , synchronizing changes in laser declination with changes in the convergence angle between lasers  16  and  18 . 
     Upper lever  44  is mounted to pivot on axis  48  and lower lever  46  is mounted to pivot on axis  50 , both of which axes extend from frame  41  and are located at the opposite end of where the levers contact the cam wheel  36 . Lasers  16  and  18  are mounted on upper lever  44  and lower lever  46 , respectively, and are oriented to cast their beams in the forward direction indicated generally by arrow “C”. As cam wheel  36  rotates, upper lever  44  pitches relatively up or down as generally indicated by double arrow “D” stemming from both movement up and down of cam wheel  36  and the change in radius of cam surface  40  while lower lever  46  pitches as indicated by double arrow “E” movement of cam surface  42  up and down with movement of the cam wheel. Axes  48  and  50  may be spring biased (not shown) to assure that levers  44  and  46  ride snugly against cam wheel  36 . Levers  44  and  46  are substantially identical otherwise. Under zero wind conditions, and as long as changes in atmospheric density have a negligible effect on aerodynamic drag of the arrow, an arrow shot from a properly drawn and elevated bow will cross the level of the mark when it reaches the range to the mark. If a laser guide mounted to the bow has the correct declination, the beam from the laser will strike the mark at the correct level for a correctly elevated bow. By synchronizing and calibrating the declinations of beams from lasers  16  and  18  with the changing range to convergence of the beams, the archer will no longer have to estimate the range to the target or mark. By rotating cam wheel  36  until the beams converge on the target, he or she will automatically have set the declination of the lasers to the correct angle to illuminate the target when the bow is elevated to the proper degree. 
     FIG. 3 is a side cross section of the preferred embodiment particularly illustrating the mechanism of synchronizing control of cam wheel  36  elevation with rotational position of the cam wheel  36  on frame  41 . A lever  56  is centered and rotationally mounted on a pin  58  extending downward from frame extension  60 . When frame  41  is correctly aligned and mounted on a bow (shown in FIG. 5) lever  56  is positioned so that an archer can reach and move the lever from its lower end  62  in the directions indicated by double arrow “F”. Lever  56  extends behind frame  41  and is attached to cam wheel  36  by a semi-rigid guide wire  64 . Guide wire  64  passes through an opening  63  from the back to front side of frame  41  and attaches to cam wheel  36  at a point on the cam wheel spaced from the central axis  38 . Movement of lever  56  causes tension or pressure to be applied to cam wheel  36  along guide wire  64 , resulting in cam wheel  36  rotating on axis  38 . 
     Cam wheel  36  includes a height control cam  68 , which is positioned in an arc located partway between the central axis  38  of the cam wheel and the fixed radius cam surface  42 . Height control cam  68  rides on a free wheeling pinion  70  mounted on frame  41 . Since axis  38  can move up and down in slot  39 , cam wheel  36  has a maximum elevation on frame  41  when the radius of height control cam  68  is at its maximum and, similarly, the cam wheel has a minimum elevation on frame  41  when the radius of the height control cam is at its minimum. 
     Height control cam  68  comprises a plurality of allen screws  71  set along the arc of a fixed radius arch  76  in cam wheel  36 . Allen screws  71  are independently adjustable to provide a series of step height adjustments particular rotational positions of cam  36 . As previously discussed, the convergence angle between lasers  16  and  18  will be greatest (i.e. most open) at a maximum allowed range for the bow. For shots at the maximum range for a bow, the greatest bow elevation will be required, guided by bringing the declination of lasers  16  and  18  to a relative maximum. Accordingly, the height of cam wheel  36  will be set for its highest relative position for the rotational position of cam wheel  36  which brings the minimum radius portion  52  of cam surface  40  into contact with upper lever  44 . That is, the rotational position of cam wheel  36  which pushes convergence of the beams from lasers  16  and  18  out to the maximum allowed range also sets the declination for both lasers to a maximum. Correspondingly, the allen screws  71  at the position radially corresponding to the maximum radius portion  54  of cam surface  40  will be set at a relative minimum to minimize the declination of lasers  16  and  18 . The precise settings for each allen screw  71  are determined by trial and error. To calibrate height control cam  68  an archer uses a target at each of a plurality of desired ranges. For each target, cam wheel  36  is positioned to bring the twin light beams into convergence for the range to the target. The declination of the lasers is then adjusted by adjusting the alien screw  71  which rides on free wheeling pinion  70  for the rotational angle of cam wheel  36  which produces convergence. The declination setting is correct when the archer consistently obtains the correct bow elevation for hitting the target. Setting the alien screw  71  at end  74  of height control cam  68  higher than all of the remaining allen screws will give cam  68  its maximum radius at end  74  and the greatest declination to the lasers for distant targets. For a nearby target, where the range to convergence of the beams from lasers  16  and  18  is at its minimum, introduced by declination control  21  cam  68 , the declination of the lasers is minimized. 
     Lasers  16  and  18  may be actuated by a three position switch  78  and a replaceable battery (not shown). Switch  78  (will include) includes off and on settings, and may include an “automatic” setting which activates the lasers only when bow  12  is substantially fully drawn. Providing an automatic setting may be provided by use of a strain gauge (not shown) or other device attached to the bow for detecting drawing of the bow string  13 . A site  28  extends from the bottom of frame  41 . 
     FIG. 3A illustrates arch  76  in greater detail. Openings  80  for allen screws  71  are set in two staggered rows. The radial displacement of the screws  71  around the arch is about 3 degrees, corresponding to approximately 2 yard intervals in range. 
     FIGS. 4A and 4B illustrate additional details of construction of the dual beam targeting aid of the present invention, particularly details of the mounting of cam wheel  36  on frame  41 . Additionally, the mounting of lasers  16  and  18  and their relative positioning to sight  14  are shown. Lasers  16  and  18  are held in substantially identical mounts  88  which depend from levers  44  and  46 . Mounts  88  are locked by screws  90  once the desired degree of horizontal divergence has been introduced to the lasers  16  and  18 . The vertical convergence of lasers  16  and  18  may is adjusted by the positioning of screws  84  and  86 , which pass through the ends of levers  44  and  46  respectively to ride on the cam surfaces of cam wheel  36 . 
     Lastly, FIG. 5 is a perspective view illustrating positioning of frame  41  and the cam mechanism  34  on bow  12 . As described above, lasers  16  and  18  as well as sight  14  are vertically aligned with arrow  10 . Frame  41  is positioned on bow  12  above arrow  10  to bring cam adjusting lever  56  within easy reach of the fingers of the hand gripping bow  12 . This allows the archer to adjust the declination of lasers  16  and  18  while simultaneously changing the elevation of bow  12 . 
     FIGS. 6 and 7 illustrate an alternative, preferred embodiment of the invention incorporating an improved cam wheel  100 . The declination adjustment apparatus is unchanged and illustration of that aspect of the mechanism is omitted for the sake of brevity. A height control cam  68  may be attached between arms  108 A and  108 B using mounting points  107  through the arms. 
     Cam wheel  100  is rotatable on axis  105  which is centered in the cam wheel. Levers  44  and  46  are attached to the rim sections  101  and  103 , respectively, of the cam wheel by pin studs  110  and  112 . The free end of lever  44  is inserted into a slot  109  cut into rim section  101  for the outside perimeter. Lever  44  is positioned by a pin stud  110  which is positioned through lever  44  to engage outside slot  102  in the outside walls. Slots  102  are arcs which are centered on axis  105  but which have a varying radius on the axis as a fraction of radial position. The variable radius slots  102  allow changing the angle of convergence of levers  44  and  46 . 
     Similarly, lever  46  is inserted in a slot  113  formed by the art walls of rim section  103 . A stud pin  112  inserted through lever  46  perpendicular to its direction of elongation engages parallel circular section slots  104  cut in through the outer walls  115 . Pin studs  110  and  112  fit snugly in the slots to provide highly controlled positions of levers  44  and  46 . 
     The present invention provides a bowsight with a laser targeting aid which guides an archer&#39;s elevation of a bow to illuminate a target when the bow is held at the correct elevation. The device may be readily calibrated to compensate for arrows of differing mass and air resistance. The bowsight aid itself is light weight, robust and compact. While the preferred embodiment uses two laser sources, those skilled in the art will now realize that a single laser, a beam splitter and other appropriate optics could be substituted for using laser sources. 
     While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.