Gait Assist Control Using Thigh Phase Angle Estimation
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Solution Overview
Problem
Conventional gait motion assisting devices face challenges in accurately identifying gait states due to noise components and time delays, particularly when users with paralysis or stroke attempt to perform gait motions, leading to inadequate assisting force delivery.
Innovation Solution
A gait motion assisting device that utilizes a thigh phase angle calculating method replicating leg movement as pendulum movement, employing a state estimator like a Kalman filter to estimate hip joint angles and angular velocities, and calculates torque values for assisting force based on these estimates, reducing noise and time delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If differential processing is used to obtain hip joint angular velocity from hip joint angle, then the thigh phase angle can be calculated, but noise components are emphasized and measurement precision deteriorates
Solution Approach 1:
The patent introduces a state estimator as an intermediary component that processes the hip joint angle signal to derive both hip joint angle and angular velocity. The state estimator uses a dynamic model of the thigh-leg system to filter noise while calculating derivatives, acting as a mediator between the raw sensor signal and the final phase angle calculation, thereby avoiding direct differentiation of noisy signals
Solution Approach 2:
The state estimator implements feedback by continuously comparing the measured hip joint angle with the estimated angle from the dynamic model, and using the difference (error) to correct the estimates of both angle and angular velocity. This feedback mechanism allows the system to maintain accurate estimates while suppressing noise effects
2Measurement precision
If low-pass processing is applied to remove noise components, then measurement precision improves, but time delay occurs and productivity deteriorates
Solution Approach 1:
The state estimator serves as an intermediary that simultaneously achieves noise filtering and real-time response. By using a dynamic model-based estimation approach rather than simple low-pass filtering, it removes noise components while maintaining the temporal characteristics of the signal, thus avoiding the time delay associated with traditional low-pass filters
Solution Approach 2:
The patent replaces the mechanical low-pass filtering approach with a model-based state estimation system. Instead of using a passive filter that inherently introduces phase lag, the system uses an active computational model that can estimate the true state in real-time without the time delays characteristic of passive filtering methods
3Device complexity
If lower leg angle sensor is used to detect gait motion state, then device complexity is reduced, but reliability deteriorates when lower leg cannot perform normal gait motion
Solution Approach 1:
The patent inverts the conventional approach by detecting thigh motion (hip joint angle) instead of lower leg motion to identify gait state. Since the thigh can perform relatively normal gait motion even when the lower leg is paralyzed, this inversion allows reliable gait state detection and subsequent provision of appropriate assisting force to the lower leg
Solution Approach 2:
The system uses feedback from thigh motion detection to control actuator operation on the lower leg. By monitoring the thigh's natural movement and using this information to trigger and modulate assisting force, the system achieves reliable operation even when the lower leg cannot provide feedback through normal motion
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
Enables precise and timely delivery of assisting force in response to gait states, effectively addressing the limitations of conventional devices by improving accuracy and reducing noise and time delays.
Implementation Method 1
replicates movement of a user's leg including a thigh and a lower leg around a hip joint in gait motion by pendulum movement of a rod-like rigid body
Data Source
AI summary
The gait motion assisting device according to the present invention replicates movement of user's leg including thigh and lower leg around hip joint by pendulum movement of a rod-like rigid body, estimates hip joint angle and hip joint angular velocity of thigh calculated based on equation of motion of the pendulum movement by a state estimator using angle-related signal received from a thigh orientation detecting means as the observation, calculates the thigh phase angle using the estimated hip joint angle and the estimated hip joint angular velocity, and outputs assisting force having torque value calculated based on the thigh phase angle.