Eccentric Pulleys for Compound Bow Timing and Vibration Control
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Solution Overview
Problem
Compound archery bows face challenges in maintaining synchronized pulley rotation and adjusting draw length without compromising arrow flight accuracy, leading to issues like erratic nocking point travel and excessive vibration.
Innovation Solution
The development of 'Cam&½' bows with pulley assemblies that combine the synchronization and forgiveness of dual cam systems with the high let-off of single cam systems, allowing for adjustable draw length without changing nocking point travel or draw force curve, using a single cable reference anchor and slaving pulley rotation to maintain timing and reduce vibration through resilient elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dual cam systems are used, then synchronization and forgiveness are improved, but device complexity increases
Solution Approach 1:
The patent merges the synchronization benefits of dual cam systems with the simplicity of single cam systems by integrating a single cam mechanism that incorporates timing enforcement features. The cam is designed with asymmetric geometry that inherently maintains proper timing between pulleys while using fewer components than traditional dual cam arrangements.
Solution Approach 2:
The single cam mechanism performs multiple functions: it provides the mechanical advantage for draw force let-off, enforces timing between pulleys through its asymmetric geometry, and maintains synchronization without requiring separate timing mechanisms. This multi-functional design reduces overall system complexity while maintaining reliability.
2Adaptability or versatility
If draw length is adjusted, then adaptability is improved, but nocking point travel stability deteriorates
Solution Approach 1:
The cam mechanism is designed with dynamic geometry that allows the nocking point to maintain a substantially straight travel path regardless of draw length adjustments. The cam profile is specifically shaped to compensate for changes in draw length, ensuring that the nocking point follows a consistent trajectory from brace to full draw position.
Solution Approach 2:
The patent utilizes changes in cam geometry parameters to maintain stable nocking point travel. By carefully designing the cam profile with specific curvature and radius variations, the system compensates for draw length changes and maintains consistent nocking point motion characteristics across different draw lengths.
3Reliability
If pulley rotation is enslaved to maintain timing, then synchronization is improved, but device complexity increases
Solution Approach 1:
The cam employs asymmetric geometry where the cam follower on one pulley interacts with an asymmetrically shaped cam surface. This asymmetric design inherently enforces proper timing between the pulleys as the cam rotates, eliminating the need for additional timing mechanisms or complex synchronization systems.
Solution Approach 2:
The cam acts as an intermediary mechanism that couples the rotation of the two pulleys. Through its asymmetric profile and interaction with the cam follower, it mediates the rotational motion between pulleys, ensuring they remain synchronized without requiring direct mechanical coupling or complex control systems.
4Stability of the object's composition
If resilient elements are used to reduce vibration, then arrow flight stability is improved, but device complexity increases
Solution Approach 1:
Resilient elements are strategically positioned at locations where vibration and shock occur during the shooting cycle. These elements provide cushioning and vibration dampening before excessive vibrations can develop, protecting the arrow flight path from disturbances while using simple, passive components rather than active vibration control systems.
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 solution provides stable arrow flight with adjustable draw length, maintaining accuracy and reducing vibration, while allowing for adjustments without requiring a bow press and minimizing changes in pulley timing or draw force curve.
Implementation Method 1
reducing vibration through resilient elements
Implementation Method 2
employ a pulley system with bow string rigging arranged to provide a mechanical advantage to deflect flexible bow limbs, and to provide a draw force let-off at full draw
Implementation Method 3
An eccentric defines a groove, or string track, in which to receive a rigging element, that is spaced by a variable radius from the axis of rotation of the eccentric
Data Source
AI summary
A pulley arrangement for a compound archery bow (100) that combines the forgiveness and symmetry of a “dual cam” system with the positive draw stop (hard wall), enforced synchronization (or built-in timing) between opposite pulley assemblies, and high let-off associated with “single cam” systems. The pulley rigging (112) includes only a single cable reference anchor to a limb (104, 106). Certain pulleys (108, 110) include rotating module portions (183, 214) effective to change the wrapped lengths of power and control cables (270, 272) to change draw length (LD) while the bow (100) is strung, and at a brace condition with the drawstring (116) under full tension, and without changing the timing of the pulley members (108, 110), or changing the lengths of rigging members (112). Certain embodiments include a resilient element (196) in a positive draw stop (194) to reduce noise as the draw stop (194) engages a rigging element (270). A resilient element (206) adapted to reduce drawstring vibration may further be included, in one or more pulleys, and arranged to contact the drawstring (116) as the pulleys (108, 100) over-rotate. A preferred mounting arrangement employs a flanged bearing assembly (200) to resist bearing walk relative to the pulley on which the bearing assembly (200) is installed. Certain preferred embodiments of pulleys (108, 110) include a spiral cam shape at a let-off portion of the string cams (150, 210).