Bow Pulley Cam String Segmentation for Powerstroke
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Solution Overview
Problem
Conventional bows face challenges in achieving a lightweight, compact design with increased powerstroke, speed, and reduced draw weight, as reducing bow length or sweeping the risers rearward often sacrifices powerstroke and increases draw weight.
Innovation Solution
A bow design featuring a pair of limbs with a pulley and cam configuration, where a first string is coupled between the pulley and cam, and a second string is located on the side of the pulley and cam closest to the riser, allowing for increased powerstroke and speed with reduced draw effort by drawing the second string from the forward portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the bow length is reduced or risers are swept rearward to make the bow compact and lightweight, then the bow size and weight are reduced, but the powerstroke is reduced and draw weight increases
Solution Approach 1:
The bowstring system is segmented into two separate strings: a first string coupled between the pulley and cam, and a second string located on the side of the pulley and cam closest to the riser. This segmentation allows independent optimization of draw weight and powerstroke characteristics
Solution Approach 2:
A cam mechanism is introduced as an intermediary between the pulley and the second string. The cam modifies the mechanical advantage curve during the draw cycle, enabling reduced draw weight while maintaining or increasing powerstroke. The cam acts as a mediator that transforms the force application characteristics
2Volume of moving object
If the bow length is reduced or risers are swept rearward to make the bow compact, then the bow size is reduced, but the powerstroke is reduced and arrow speed decreases
Solution Approach 1:
The bowstring system is segmented into two separate strings with distinct functions. The second string, drawn from the forward portion of the cam and pulley, is specifically configured to maximize powerstroke length, directly contributing to increased arrow speed despite compact bow dimensions
Solution Approach 2:
The mechanical advantage parameters are changed through the cam profile design. The cam alters the relationship between draw position and force required, extending the powerstroke phase of the draw cycle. This parameter change enables increased arrow speed from a compact bow by optimizing the energy transfer profile
3Reliability
If a single cam arrangement with a pulley is used to reduce synchronization problems, then lateral travel of the arrow is reduced, but the powerstroke is limited
Solution Approach 1:
The single cam arrangement is segmented into a pulley-cam system with two separate strings. The first string handles the mechanical advantage function while the second string, drawn from the forward portion, extends the powerstroke. This segmentation allows the stability function to be maintained while the powerstroke function is enhanced
Solution Approach 2:
The system transitions from a single-dimension cam operation to a two-dimensional string arrangement. By positioning the second string on the side of the pulley and cam closest to the riser and drawing it from the forward portion, the system adds a spatial dimension that extends the powerstroke while maintaining the stabilizing effect of the cam-pulley synchronization
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 design results in a lightweight, compact bow that increases arrow speed while decreasing the effort required to launch it, maintaining performance in challenging environments like thick woods.
Implementation Method 1
cams on the bow to increase the mechanical advantage associated with the draw of the bowstring
Data Source
AI summary
A bow having an increased powerstroke allowing for reduced draw weight and increased speed. The bow is provided with a riser and a pair of limbs. A pulley is coupled to one limb and a cam is coupled to the other at a first journal point and second journal point respectively. The powerstroke is increased by locating the bowstring on the pulley and cam between the riser and the journal points.