Balanced Pulley Assembly for Compound Archery Bows
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Solution Overview
Problem
Compound archery bows often suffer from imbalance in pulley operation, leading to uneven force application on the bow string, which compromises accuracy and energy storage during the draw cycle.
Innovation Solution
The Libra pulley assembly, featuring uniquely configured pulleys with cable controllers that adjust the effective length of bow cables during the draw cycle, ensuring self-balancing operation and optimizing the force/draw profile by varying the rate of cable shortening and lengthening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional pulley systems are used in compound bows, then the bow can store mechanical energy, but the pulleys operate out of balance causing uneven force application on the bow string
Solution Approach 1:
The cable controller employs an asymmetric cam profile with varying radius of curvature that is specifically designed to compensate for the asymmetric forces generated during the draw cycle. The cam's eccentric geometry creates a mechanical advantage that balances the pulley system by applying differential cable length adjustments at different points in the draw cycle, thereby resolving the imbalance while maintaining energy storage capability
Solution Approach 2:
The invention changes the geometric parameters of the cable controller cam profile to optimize pulley balance. By varying the cam radius, eccentricity, and profile curvature throughout the draw cycle, the system dynamically adjusts cable tension distribution to maintain balanced pulley operation while preserving the force/draw profile characteristics necessary for energy storage
2Use of energy by moving object
If the bow string is drawn to full extension, then maximum energy is stored, but uneven forces compromise accuracy
Solution Approach 1:
The cable controller acts as a mechanical feedback device that continuously monitors and adjusts cable length distribution based on the instantaneous position and force state of the bow during the draw cycle. This feedback mechanism ensures that energy is stored efficiently while maintaining balanced forces that preserve shooting accuracy
3Speed
If cable length is reduced to store energy, then velocity increases, but the rate of cable shortening must be controlled to maintain balance
Solution Approach 1:
The cable controller is directly driven by the pulley rotation itself, eliminating the need for external control mechanisms. As the pulley rotates during the draw cycle, the cam profile automatically translates this rotation into the appropriate cable length adjustments, making the system self-regulating and reducing overall complexity while maintaining the ability to control cable shortening rates for optimized velocity and balance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The Libra system maintains balanced operation, allowing for increased energy storage and improved accuracy by synchronizing pulley rotation and moderating the rate of cable shortening and lengthening, ensuring the bow remains 'in tune' throughout the draw and release cycles.
Implementation Method 1
the pulleys (also termed cams) are configured so that when the bow string is drawn, the cables are wound into grooves on the pulleys, thereby decreasing their effective length, and storing energy in the bow
Implementation Method 2
The cable controller of each of said pulleys is operative so as to cause the first end of the cable attached thereto to move relative to its respective pivot axis, in a direction running at least in part, from said handle, towards said respective pivot axis and thence towards said bow string
Data Source
AI summary
A compound bow includes a first and second pulley, each of which is operative, when the bow is drawn, to unwind a portion of a bow string from a bow string groove and to take up a portion of a bow cable so as to decrease its effective length. At least one of the pulleys includes a cable controller which operates to modify the rate at which the effective length of the bow cable is decreasing so that during an initial portion of the draw of the bow, the rate is greater than it would be in the absence of the controller, and during a second portion of the draw, the rate is less than it would be in the absence of the controller. Use of the controller provides a bow which has an inherently balanced draw.