Transtibial Prosthesis Resistance Control for Downhill Gait
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Solution Overview
Problem
Existing methods for controlling lower leg prostheses struggle to maintain a natural and safe gait pattern when navigating various terrains, particularly stairs and uneven surfaces, due to inaccurate determination of resistance adjustment based on foot inclination, which is unreliable on non-level surfaces.
Innovation Solution
A method for controlling a lower leg prosthesis that adjusts resistance using predetermined ankle and lower leg angles, determining the wearer's direction of movement (uphill or downhill) by calculating height differences and gradient angles between stance phases, independent of local ground inclination, with sensors and an electrical control system to ensure safe and natural gait.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If resistance is significantly increased midway through the stance phase to imitate natural gait, then natural gait pattern is achieved, but further rotation of the foot element becomes impossible or significantly difficult
Solution Approach 1:
The resistance device transitions from a static high-resistance state to a dynamic system that can adjust resistance levels based on gait phase detection. The control system dynamically modifies the resistance characteristic midway through the stance phase, allowing initial rotation followed by controlled limitation, thereby achieving natural gait while managing rotation appropriately.
2Difficulty of detecting and measuring
If foot inclination sensors are used to determine terrain slope, then gradient detection is simplified, but reliable determination fails on uneven surfaces and stairs where foot inclination does not reflect actual terrain slope
Solution Approach 1:
The patent introduces intermediate parameters (height difference and gradient angle calculated from consecutive foot positions) as mediators between the raw sensor data and terrain classification. Instead of directly using foot inclination to determine terrain, the system uses position tracking over time to calculate these intermediate values, which more reliably indicate whether the wearer is moving uphill, downhill, or on level ground, even on stairs and uneven surfaces.
Solution Approach 2:
The system transitions from a single-dimension measurement (foot inclination angle) to a two-dimension approach by tracking foot position changes between consecutive stance phases. By analyzing the vertical height difference and calculating the gradient angle from position data, the system gains additional dimensional information that enables more accurate terrain classification independent of local foot orientation.
3Device complexity
If switching angle is determined solely by ankle angle sensor, then control is simplified, but incorrect resistance adjustment occurs on inclined surfaces where ankle angle does not reflect actual gait phase
Solution Approach 1:
The control system implements feedback by continuously monitoring the calculated gradient angle from consecutive foot positions and using this information to adjust the switching angle criterion dynamically. When moving uphill or downhill, the system modifies when resistance should be increased based on the detected gradient, ensuring that resistance adjustment occurs at the appropriate point in the gait cycle regardless of the incline, thereby maintaining reliable control.
Data Source
Figure 1~2d
AI summary
The invention relates to a method for controlling a transtibial prosthesis comprising a foot element, a transtibial element pivotally arranged thereon and an adjustable resistance device for applying a resistance against a pivoting of the foot element relative to the transtibial element, wherein a first flex angle is defined as a predetermined ankle angle value between the transtibial element and the foot element, a second flex angle is defined as a predeterimined transtibial angle value of the absolute angle of the lower leg, wherein, in the method, is it determined whether the wearer of the transtibial prosthesis is travelling downhill at least also from the height difference between the position of the foot element in a step cycle and the position of the foot element in a previous step cycle, and the resistance of the resistance device is increased to a predetermined resistance value if a blocking criterion is fulfilled, wherein the blocking criterion is fulfilled if it is determined that the wearer is not going downhill, and the second flex angle is achieved, or if it is determined that the wearer is going downhill and the flex angle achieved later in the step cycle is achieved.