Crank Arm Assembly With Threaded Removal for Friction-Fit Disassembly
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Solution Overview
Problem
Conventional exercise machines face difficulties in efficiently disassembling crank arms from crankshafts due to strong frictional engagement, even after the fastener is removed.
Innovation Solution
A crank assembly design featuring a threaded crank arm bore and a removal tool with a larger diameter than the crankshaft bore, allowing the removal tool to disengage the crank arm mounting surface from the crankshaft mounting surface by axial contact and rotation, breaking the frictional engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a fastener is used to secure the crank arm to the crankshaft with frictional engagement, then the connection strength is improved, but the disassembly difficulty increases
Solution Approach 1:
A removal tool acts as an intermediary component between the user and the crank arm-crankshaft assembly. The tool engages with the crank arm through a removal tool engagement feature and applies leverage to overcome the frictional engagement, enabling disassembly without damaging the original fastener or components.
Solution Approach 2:
The disassembly function is segmented from the original fastening system. Instead of requiring the fastener to handle both tightening and loosening, the design separates these functions: the fastener provides secure connection during operation, while the dedicated removal tool engagement feature enables controlled disassembly when needed.
2Manufacturing precision
If the crank arm bore diameter is reduced to accommodate smaller fasteners, then the fastener engagement is improved, but the removal tool application becomes difficult
Solution Approach 1:
The crank arm bore exhibits local quality variation: the majority of the bore maintains a first diameter optimized for fastener engagement, while a specific portion features a second, larger diameter that accommodates the removal tool. This localized dimensional change allows both fastening and removal functions to be satisfied without compromising either.
Solution Approach 2:
The bore diameter parameter is changed locally within the crank arm structure. By providing a portion of the bore with a larger second diameter compared to the first diameter, the design enables the removal tool to be applied with sufficient leverage while maintaining precise fastener engagement in the smaller diameter portion.
3Ease of operation
If a larger diameter removal tool is used to disengage the crank arm, then the removal capability is improved, but the tool size and complexity increase
Solution Approach 1:
The crank arm is pre-configured with a removal tool engagement feature and a bore portion with increased diameter during manufacturing. This preliminary preparation eliminates the need for field modification or complex adaptive tools, allowing a relatively simple removal tool to effectively disengage the crank arm by applying force through the pre-designed geometric advantage.
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
Facilitates easy and efficient removal of crank arms from crankshafts, overcoming the challenge of residual frictional engagement.
Implementation Method 1
The threaded crank arm bore is configured for threaded engagement by the removal tool such that removal of the fastener and insertion and rotation of the removal tool in the threaded crank arm bore causes the removal tool to move in a first axial direction through the threaded crank arm bore
Implementation Method 2
a crank arm having a threaded crank arm bore and a crank arm mounting surface that is frictionally engaged with the crankshaft mounting surface
Data Source
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AI summary
An exercise machine has a crankshaft having a crankshaft mounting surface, a landing surface, and a crankshaft bore, a crank arm having a threaded crank arm bore and a crank arm mounting surface that is frictionally engaged with the crankshaft mounting surface, and a fastener that axially extends through the threaded crank arm bore and into engagement with the crankshaft bore to fasten the crank arm to the crankshaft. The threaded crank arm bore is configured for threaded engagement by a removal tool such that removal of the fastener and insertion and rotation of the removal tool in the threaded crank arm bore causes the removal tool to disengage the crank arm mounting surface from the crankshaft mounting surface and thus facilitates removal of the crank arm from the crankshaft. Methods of disassembling an exercise machine having a crank arm are also provided.