Variable Stiffness Actuator with Spiral Cam for Gait Assistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing powered exoskeletons and prosthetic devices require complex motors and transmissions for ankle flexion and extension, which are power-intensive and lack efficient variable stiffness adjustment for different gait phases.
Innovation Solution
A variable stiffness actuator assembly comprising a main cam, connecting pin, spiral cam, housing, and cantilever subassembly, which adjusts stiffness profiles by rotating the spiral cam to alter the distance between supports, allowing for high stiffness during stance phase and low stiffness during swing phase, using a cam follower trajectory curve and spiral cam slot for efficient energy storage and release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If complex motors and transmissions are used for ankle flexion and extension, then the actuator can provide sufficient power, but the device becomes power-intensive and structurally complex
Solution Approach 1:
The patent replaces complex motor-transmission systems with a cam-based mechanical system. The main cam and spiral cam convert rotational motion into controlled linear and rotational movements of the cantilever beam, eliminating the need for motors, gears, and other transmission components while maintaining sufficient power output for ankle actuation
Solution Approach 2:
The patent implements variable stiffness through the spiral cam mechanism that allows dynamic adjustment of the cantilever beam's support position. By rotating the spiral cam, the distance between supports changes, enabling the system to adapt its stiffness profile in real-time to match different gait phases, thereby reducing overall structural complexity while maintaining performance
2Adaptability or versatility
If fixed stiffness is used in the actuator, then the structure is simple, but the actuator cannot efficiently assist during different gait phases
Solution Approach 1:
The spiral cam mechanism enables dynamic adjustment of the cantilever beam's support position, transforming the fixed stiffness system into a variable stiffness system. As the spiral cam rotates, it continuously changes the distance between supports, allowing the actuator to adapt its stiffness profile to different gait phases without requiring complex active control systems
Solution Approach 2:
The patent changes the physical parameter of support distance in the cantilever beam system by incorporating a spiral cam. This geometric parameter change directly modifies the stiffness characteristics of the beam, enabling the system to provide high stiffness during stance phase and low stiffness during swing phase through passive mechanical means
3Reliability
If high stiffness is maintained throughout the gait cycle, then structural stability is improved, but energy consumption increases and mobility assistance deteriorates during swing phase
Solution Approach 1:
The cam mechanism is designed to periodically adjust stiffness in sync with the gait cycle. During stance phase, the cam configuration provides high stiffness for stability and energy storage; during swing phase, it reduces stiffness to minimize energy consumption and allow natural foot movement. This periodic variation in stiffness matches the physiological requirements of walking
Solution Approach 2:
The system dynamically changes the stiffness parameter by altering the support distance of the cantilever beam through the spiral cam mechanism. This parameter change allows the structure to be stiff when needed for stability during stance phase and compliant when needed for energy efficiency during swing phase, eliminating the need to maintain high stiffness throughout the entire cycle
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 actuator provides enhanced gait assistance by dynamically adjusting stiffness based on gait phase, minimizing energy consumption and improving mobility assistance for elderly and individuals with gait disorders, with stiffness ratios varying significantly between dorsiflexion and plantarflexion directions.
Implementation Method 1
Some VSAs can adjust elastic element response to the environment-especially during energy storage and release
Implementation Method 2
The spiral cam is rotatable about the rotary axis between a first setting and a second setting such that the spiral cam is configured to adjust the distance
Data Source
AI summary
A variable stiffness actuator including a main cam, connecting pin, spiral cam, housing, a cantilever subassembly, and a spiral cam pin. The main cam has a main cam surface and is configured for rotation about a rotary axis. The connecting pin is coupled to the main cam. The spiral cam defines a spiral cam slot. The main cam is positioned within the housing and the housing includes a housing connector. The cantilever subassembly includes a cantilever beam, a first support coupled to the housing, a roller in contact with the main cam surface, and a second support spaced a distance from the first support. The spiral cam pin is positioned within the spiral cam slot for movement upon rotation of the spiral cam. The spiral cam is rotatable between a first setting and second setting to adjust the distance and a corresponding stiffness profile of the actuator.