Variable Stiffness Spring Mechanism for Augmented Running
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Solution Overview
Problem
Current running exoskeletons with fixed-stiffness springs are limited in reducing metabolic cost and increasing running speed due to energy requirements for leg movement and inefficient energy transfer, and they cannot surpass 65% of the air resistance speed limit, as they require continuous ground contact and intermittent energy supply.
Innovation Solution
A variable stiffness mechanism in an augmented running device that includes a spring with adjustable stiffness and a clutch for intermittent coupling, allowing energy storage during the swing phase and release during ground contact, mimicking the energy transfer efficiency of cycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If fixed-stiffness springs are used in parallel with the legs to support the body, then collision energy losses are prevented, but the top speed remains limited to below 65% of the air resistance speed limit due to reduced ground contact time
Solution Approach 1:
The patent applies variable stiffness springs that can dynamically adjust their stiffness parameter during the running cycle. The springs transition from a compliant state during swing phase to a stiff state during ground contact, enabling both energy conservation and high-speed performance. This dynamic adjustment resolves the contradiction by allowing the system to optimize for different functional requirements at different times.
Solution Approach 2:
The invention changes the physical parameter of spring stiffness from fixed to variable. By controlling the stiffness parameter k(t) to vary with time, the system can prevent collision energy losses when compliant and achieve higher speeds when stiff, directly addressing the trade-off between energy conservation and speed limitation.
2Speed
If the ground contact time is reduced to 0.1 s at top speed of natural running, then running speed increases, but the amount of energy the legs can supply while pushing against the ground is limited
Solution Approach 1:
The variable stiffness spring mechanism pre-stores energy during the swing phase by compressing the spring when stiffness is low. This preliminary energy storage action allows the legs to supply energy in the air instead of only during ground contact, mimicking the continuous energy supply capability of cycling and resolving the limitation imposed by short ground contact time.
Solution Approach 2:
The invention enables continuous energy supply by maintaining spring compression throughout the swing phase and releasing it continuously during ground contact. This continuous action eliminates the intermittency of natural running where energy is only supplied during brief ground contact periods, thereby increasing both speed and energy supply capability.
3Loss of energy
If exoskeleton mass is added to support the body, then metabolic cost reduction is achieved, but the energy required to swing the legs with the added mass increases
Solution Approach 1:
The variable stiffness spring system provides self-service by automatically adjusting its stiffness to match the phase of the running cycle without requiring active control or additional energy input. The mechanism uses the natural motion of the legs to compress and expand the springs, making the exoskeleton energy-neutral or even energy-positive by recovering collision losses.
Solution Approach 2:
By changing the stiffness parameter dynamically, the system reduces the effective mass that needs to be accelerated during swing phase. When the spring is compliant, it reduces the inertial load on the legs; when stiff during ground contact, it provides structural support. This parameter change resolves the contradiction between support function and swing energy requirement.
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 device enhances running speed by amplifying force and power output beyond human capability, reducing metabolic cost and allowing faster running speeds by efficiently storing and releasing energy, similar to cycling, without the need for large motors or batteries.
Implementation Method 1
The spring is compressed by the user during the swing phase of user's running cycle and is released when the user impacts a running surface to propel the user forward
Implementation Method 2
a variable stiffness mechanism that can selectively modify the stiffness of the spring
Data Source
AI summary
Provided are apparatuses for augmenting human speed, human-driven compliant mechanisms, artificial limbs to augment human movement, and the like. The apparatuses can include variable stiffness mechanisms including springs that can be configured to selectively store and subsequently release energy generated by human movement. The apparatuses can selectively release the captured energy supplied by the human to provide force and power output beyond the physical capability of the human.