Prosthetic Limb Torque Control via Variable Drag
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Solution Overview
Problem
Conventional prosthetic limbs using hydraulic or spring cylinders require excessive hip joint muscle effort due to uneven resistance distribution during walking, leading to poor walk-following properties and discomfort, especially when the toe is lifted from the ground.
Innovation Solution
A prosthetic limb with a multiple-link mechanism and adjustable drag generating means, such as a hydraulic or spring cylinder, where the torque is minimized at initial knee bending and maximized at larger angles, reducing the burden on the hip joint and improving walk-following properties without increasing costs by varying the lever arm length and attachment positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a hydraulic cylinder or spring cylinder is used to produce large force, then the prosthetic limb size can be reduced, but the burden on the hip joint muscle increases
Solution Approach 1:
The patent applies dynamics by making the drag force variable rather than constant. The drag coefficient changes according to the knee joint angle, being smaller at initial bending angles (reducing hip joint burden) and larger at larger bending angles (maintaining compact size). This dynamic adjustment resolves the contradiction between force magnitude and burden distribution.
Solution Approach 2:
The patent changes the parameter of drag coefficient based on knee joint angle. By varying this parameter, the system achieves different force characteristics at different stages of movement, allowing compact design while managing muscle burden effectively throughout the walking cycle.
2Force
If a pneumatic cylinder is used to reduce initial resistance, then the burden on hip joint muscle is reduced, but the force produced is insufficient requiring larger size
Solution Approach 1:
The patent makes the drag coefficient dynamic, varying it with knee joint angle. This allows the system to provide appropriate force at each stage without requiring a uniformly large cylinder, resolving the size-force trade-off that plagues pneumatic systems.
3Ease of operation
If the drag force is increased to improve walk-following properties, then the prosthetic limb control is improved, but the burden on hip joint muscle increases
Solution Approach 1:
The patent changes the drag coefficient parameter according to knee joint angle, providing higher drag when needed for walk-following control and lower drag when the hip joint would be overburdened. This parameter variation optimizes both control performance and user comfort.
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 solution reduces the initial torque at knee joint bending, minimizing the burden on the hip joint and enhancing walk-following properties, making the prosthetic limb feel more comfortable and efficient, similar to those using pneumatic cylinders.
Implementation Method 1
The hydraulic cylinder uses oil that is an incompressible fluid and therefore, it can produce a force larger than that of the pneumatic cylinder
Implementation Method 2
The spring cylinder can also produce a force larger than that of the pneumatic cylinder in compliance with the spring constant
Implementation Method 3
since pneumatic pressure is compressed, the force produced by the pneumatic cylinder is smaller than that produced by the hydraulic cylinder or the spring cylinder
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
A technology for making the sensation at use of prosthetic limbs utilizing a hydraulic cylinder and a spring cylinder as comfortable as at use of those utilizing a pneumatic cylinder and further for improving walk following properties. In particular, the arrangement of drag generating means, such as a hydraulic cylinder and a spring cylinder, per se is specified. Accordingly, the resistance produced by the drag generating means in accordance with an increase of knee angle is increased. The first torque T1 at the first stage of initial period of bend of knee joint is made small, while the second torque T2 at the second stage of final period of the further advanced bend of knee joint is made large, thereby satisfying a relation of T1 ≤ T2, as different from conventional ones.