Crossbow Spanning Device Linkage Mechanism
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Solution Overview
Problem
Conventional crossbows require significant effort to span the string, and if the string is not successfully pulled to the cocked position, it can bounce back and potentially harm the user.
Innovation Solution
A spanning device for a crossbow that utilizes a pull rod, pivotal rod, and first link mechanism to leverage the action unit within the barrel, allowing the string to be easily pulled with reduced effort, featuring a slide with a slot, hook member, recovery spring, and safety mechanism to facilitate smooth operation and safe string release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the string is pulled backward to a cocked position manually, then the crossbow can be cocked, but it requires a lot of effort and may cause injury if the string bounces back
Solution Approach 1:
A spanning device is introduced as an intermediary mechanism between the user and the string. The spanning device includes a spanning element that engages with the string and a triggering mechanism that controls the spanning action. This intermediary device reduces the direct force requirement by providing mechanical advantage through levers and linkages, while also controlling the string movement to prevent dangerous bouncing back.
Solution Approach 2:
The spanning device transitions from a static manual pulling action to a dynamic controlled mechanism. The triggering mechanism allows the spanning element to move along a controlled path, converting a static high-force requirement into a dynamic low-force operation. The mechanism includes moving parts that guide the string through a controlled cocking motion, reducing the peak force needed.
2Ease of operation
If a spanning device is introduced to reduce effort, then the ease of operation improves, but the device complexity increases
Solution Approach 1:
The spanning device is segmented into distinct functional components: a spanning element that engages the string, a triggering mechanism that controls the spanning action, and a release mechanism. This segmentation allows each component to perform its specific function efficiently, reducing overall complexity compared to a monolithic design. The modular structure also facilitates easier manufacturing and maintenance.
Solution Approach 2:
The spanning device is designed to perform multiple functions: it spans the string, controls the cocking motion, and can be integrated with the trigger mechanism for firing. This multi-functionality reduces the need for separate dedicated components, thereby reducing overall device complexity while maintaining ease of operation.
3Reliability
If the string is pulled to cocked position, then the energy is stored, but the string may bounce back and hurt the user
Solution Approach 1:
The spanning device incorporates safety features that preemptively prevent the harmful bouncing back of the string. The triggering mechanism controls the release of the spanning element in a predetermined safe manner, and the design includes features that guide the string along a controlled path during both cocking and firing. This preliminary anti-action eliminates the dangerous uncontrolled rebound that could injure the user.
Solution Approach 2:
The spanning device includes safety mechanisms that are in place before the spanning action occurs. These mechanisms ensure that if the string does attempt to rebound, it is constrained by pre-positioned guides and stops that prevent it from reaching the user. The design anticipates potential failures and provides protective measures in advance.
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
Enables the string to be easily pulled with less force, ensuring safe and efficient cocking of the crossbow, reducing the risk of injury from a recoiling string.
Implementation Method 1
A recovery spring is located between the action rod and the operation member. The recovery spring is biased between the hook member and the slide. The recovery spring provides a force to return the hook member.
Data Source
Figure 1
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AI summary
A spanning device of a crossbow includes a barrel (1), an action unit and an spanning unit. A space is defined in the barrel. A limb (5) is connected close to the front end of the barrel. A string is connected between two ends of the limb. The action unit slidably located in the space and has a portion exposed from the space. The action unit has a slide (21), a restriction member (22), a safety member (23) , a hook member (24) and a trigger (25). The restriction member, the safety member, the hook member and the trigger are connected to the slide which is slidably engaged with the space. The spanning unit has a pull rod, a pivotal rod and a first link. The spanning unit drives the action unit to move in the space, so that when the hook member hooks the string, the string is easily pulled with less effort.