Variable Rate Coil Spring for Body Weight Support
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Solution Overview
Problem
Conventional body weight support devices with knee flexion coil springs face challenges in generating sufficient support force when the user stands up from a half-sitting or crouching posture, interfering with walking due to the proportional increase in biasing force with knee angle flexion.
Innovation Solution
A body weight support device with a leg link system featuring a biasing member that applies a first biasing force to prevent flexion decrease and a second, larger biasing force to assist in extending the knee, allowing for adjustable support force based on flexion extent, utilizing a variable rate coil spring for efficient structure and cost reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the biasing force of the knee flexion coil spring is increased to generate sufficient support force when the user stands up from a half-sitting posture or a crouching posture, then the support force is improved, but the user must lift the lower limb with a large force against the biasing force during the swing phase, significantly interfering with walking
Solution Approach 1:
The patent applies a variable rate coil spring that dynamically changes its biasing force characteristics based on the knee flexion angle. The spring has different spring constants for different compression ranges: a first spring constant for small compressions (when knee flexion is small) and a second, larger spring constant for large compressions (when knee flexion is large). This dynamic adjustment allows the system to provide appropriate support force at different stages of knee movement, resolving the contradiction between providing sufficient support force and preventing interference with walking.
Solution Approach 2:
The patent changes the physical parameter of the coil spring by using a variable rate spring with different spring constants for different compression ranges. The spring constant is not fixed but varies based on the compression amount, allowing the biasing force to adapt to different operational conditions. This parameter change enables the system to provide high support force when needed (during standing up from half-sitting or crouching) while maintaining ease of movement during walking.
2Force
If the biasing force increases substantially proportionally with an increase of knee angle flexion, then the support force is improved, but the user experiences burden during walking
Solution Approach 1:
The variable rate coil spring dynamically adjusts its stiffness characteristic based on the compression range. In the first compression range (small compressions corresponding to small knee angles), the spring uses a first spring constant that provides gentle biasing force, allowing easy knee flexion during walking. In the second compression range (large compressions corresponding to large knee angles), the spring switches to a second spring constant that provides strong biasing force for support during standing up. This dynamic adjustment resolves the contradiction between providing sufficient biasing force and maintaining ease of knee flexion.
Solution Approach 2:
The patent changes the spring constant parameter of the coil spring based on the compression amount. By using a variable rate spring, the system transitions from a soft spring characteristic at small compressions to a stiff spring characteristic at large compressions. This parameter change allows the biasing force to be proportional to the knee angle only when necessary (at large angles), while remaining minimal at small angles, thus resolving the contradiction between biasing force magnitude and knee flexion ease.
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 provides sufficient support force without interfering with walking, allowing users to stand up from half-sitting or crouching postures with reduced effort, and is simplified in structure and cost through the use of a variable rate coil spring.
Implementation Method 1
a biasing member (coil spring) that applies, to the joint, a biasing force for preventing the extent of flexion of the leg link from decreasing due to gravity acting on the body weight support device, or a biasing force for decreasing the extent of flexion
Implementation Method 2
the biasing member is a coil spring having characteristics that a change rate of elasticity with respect to a change of a compression amount is different between a first compression range in which the compression amount is not more than a predetermined amount and a second compression range in which the compression amount exceeds the predetermined amount
Data Source
AI summary
A coil spring 14 is provided in a leg link 3. In the case where an extent of flexion of the leg link 3 is not more than a predetermined extent, the coil spring 14 applies, to a third joint 8, a first biasing force for preventing the extent of flexion of the leg link 3 from decreasing due to gravity acting on a body weight support device A. In the case where the extent of flexion of the leg link 3 exceeds the predetermined extent, the coil spring 14 applies, to the third joint 8, a second biasing force for decreasing the extent of flexion, where the second biasing force is larger than the first biasing force and increases with an increase of the extent of flexion. This enables a sufficient support force to be generated when standing up from a half-sitting posture or a crouching posture, without significantly interfering with walking.