Archery is a sport which, especially when pursued competitively, demands high accuracy. Sophisticated compound bows have been developed for the shooting of an arrow toward a target. However, one particular reoccurring problem that is generally encountered by archers in accurately aiming an arrow is the difficulty to determine reliably when the arrow has been drawn back on the bow string to the most desirable position providing the proper tension in the bow string for an accurate firing of the arrow. An arrow's trajectory is determined by the initial velocity and angle of firing. The initial velocity is directly dependent on the accelerating force exerted on the arrow by the bow string when both are released. The accelerating force in turn depends on how far the bow string has been drawn back from the center of the bow. A skilled archer will use a bow which he is able to draw completely, since the greater the draw, the larger the accelerating force and the straighter the arrow's trajectory will be. However, unless the bow is drawn to the same extent on every shot, the individual arrow trajectories will be different resulting in a low shooting accuracy.
Most archers use draw checks, usually of the audible clicker type, to indicate when they have reached full bow string draw which enables them to have the bow string apply the same propelling force to the arrow each time, thereby improving their shooting accuracy. U.S. Pat. Nos. 3,499,414 to Frydenlund; 3,518,959 to Bunker; 3,669,059 to Stuart and 4,061,107 to Smith are examples of known devices which produce an audible signal when the arrow head or point reaches the arrow guide or rest and the bow string has been retracted a uniform distance for each arrow and is ready for release. However, most of these clicker devices include mounts or brackets which extend into the flight path of the stabilizing feathers or vanes or other portions of the arrow and, thus, affect shooting accuracy. Furthermore, none of these clicker devices will warn the archer of overdraw which is a common reason for shooting inaccuracy and occurs when after the audible signal has been released the arrow is drawn back further than the desired draw.
Other arrow actuated devices designed to signal full draw are described in U.S. Pat. No. 3,450,122 by Diamond which discloses a signal light actuated by closing an electric circuit through magnetic material incorporated into special arrows; U.S. Pat. No. 3,867,920 by Westphal wherein the electric signal light circuit is closed through an electric conductor close to the arrow's tip; and U.S. Pat. No. 4,179,613 by Koren which discloses a photoelectric sensor for detecting the tip of the arrow at full draw. However, all of these devices require the use of special arrows or arrows of constant length, cannot be used with some large arrow tips such as hunting type broadheads, and cannot detect overdraw.
Draw indicators which operate independently of the type of arrow used are disclosed by Bergquist in U.S. Pat. No. 3,097,624 wherein the bending of the bow structure itself is used to operate a cricket snapper device; by Flood in U.S. Pat. No. 4,134,383 who teaches the closing of a signal light circuit by a switch that is operated by a cord connected to the bow string; by Christopher in U.S. Pat. No. 4,368,719 disclosing a cable guard mounted clicker device actuated by the rearward moving bow cables upon bending of the bow; by Troncoso in U.S. Pat. No. 4,542,732 and Wiard in U.S. Pat. No. 4,741,320 who teach cable guard mounted electric signal light actuating switches which are operated by a bow cable mounted contact block; and by MacPherson in U.S. Pat. No. 4,572,153 who teaches the use of an electric signal light actuating switch mounted in and protruding from a hollow cable guard, whereby the switch is operated by a bow cable passing thereover during bending of the bow. Of all the devices disclosed in these patents, only two indicate overdraw, namely the Flood and MacPherson devices. However, both these indicators are rather crude since they are operated by the movement of the bow cables in relation to the bow upon bending of the bow which movement is small compared to the corresponding difference in draw of the bow string. Furthermore, the indicators are operated by mechanical interaction between the movable bow string or bow cables and a stationary structure of the bow, which may affect accuracy. Thus, a more accurate draw check is desired which indicates both under and over draw and preferably does not operate on the basis of a mechanical interaction between the indicator and movable parts of the bow.