Stride Emulator Lever Mechanism for Continuous Power Transfer
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Solution Overview
Problem
Existing mechanisms for converting linear motion into rotary motion, such as bicycle cranks, are inefficient at lower input RPM and cannot effectively emulate the asymmetrical leg movements of walking or climbing, leading to inefficient power transfer and reliance on inertia for efficiency.
Innovation Solution
A lever mechanism with a power cycle longer than the travel cycle, utilizing two slider cranks joined by a chain or gears, allowing for continuous power transfer by mimicking the motion of walking or climbing, with cam tracks and offset crank arms to ensure efficient energy transfer throughout more than half of the rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a traditional bicycle crank is used to convert linear motion to rotary motion, then the mechanism is simple and easy to manufacture, but power transfer efficiency deteriorates at lower input RPM due to intermittent power stroke and reliance on inertia
Solution Approach 1:
The mechanism divides the power transfer function into two separate slider cranks (first and second slider cranks) that operate in alternating phases. Each crank handles a portion of the power stroke, ensuring that while one crank is in its power phase, the other is in its travel phase, thereby maintaining continuous power transfer and eliminating the intermittent power delivery characteristic of traditional single-crank systems.
Solution Approach 2:
The invention merges two slider crank mechanisms into a unified system where both cranks are connected to a common output gear. This combination allows the system to leverage the complementary motion cycles of both cranks, creating a continuous power transfer mechanism that overcomes the limitations of individual single-crank systems while maintaining mechanical simplicity.
2Adaptability or versatility
If a traditional crank mechanism is used, then the structure is simple, but it cannot emulate the asymmetrical leg movements of walking or climbing, resulting in inefficient power transfer at lower cadences
Solution Approach 1:
The mechanism incorporates asymmetrical cam tracks on the levers that replicate the natural asymmetry of human leg movements during walking or climbing. The cam tracks are designed with different profiles for the power stroke versus the travel stroke, allowing the levers to follow motion paths that closely match biological locomotion patterns, thereby enabling efficient power transfer at lower cadences while maintaining structural feasibility.
Solution Approach 2:
The lever mechanism employs dynamic cam tracks that allow the geometry of the motion path to change during the cycle. The cam profiles are designed to vary the lever arm length and angle throughout the stroke, dynamically adapting the mechanical advantage to match the varying force requirements of walking or climbing motions, thus achieving both motion emulation and efficient power transfer.
3Speed
If high RPM is used with a traditional crank to maintain efficiency, then power transfer efficiency is maintained, but applications requiring lower RPM (such as hill climbing) become inefficient
Solution Approach 1:
The dual slider crank mechanism ensures continuous useful action by maintaining overlapping power strokes. As one crank completes its power phase and enters the travel phase, the other crank is simultaneously in its power phase, creating a continuous chain of power delivery to the output gear. This continuity eliminates the need for high RPM to maintain efficiency, as power is transferred smoothly across the full range of lower cadences required for applications like hill climbing.
Solution Approach 2:
The mechanism utilizes periodic action through the alternating cycles of the two cranks. Each crank operates in a repeating cycle of power stroke and travel stroke, with the timing arranged so that the cycles are out of phase by approximately half a rotation. This periodic coordination ensures that power delivery is continuous while allowing the system to operate efficiently at lower RPM without relying on inertial effects.
4Force
If a crank mechanism relies on inertia from high speed and high RPM to pass dead spots, then efficiency is maintained at high cadence, but efficiency deteriorates when inertia is not available (such as when climbing hills)
Solution Approach 1:
The mechanism performs preliminary action by maintaining positive mechanical drive throughout the entire cycle through the cam track design. The cam profiles are shaped to ensure that the levers are always actively driven during their power phases, eliminating the presence of dead spots where inertia would be required to carry the mechanism through non-power portions of the cycle. This preliminary structuring of the motion paths ensures continuous force transmission independent of inertial effects.
Data Source
AI summary
A stride emulator device for efficiently utilizing human leg power for transference to a rotary drive system including a pair of levers, at least two gears, at least two crankshafts having crank arms, and where each lever includes a cam and cam track.