Walking Assist Device Asymmetric Force Control
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Solution Overview
Problem
Conventional walking assist devices apply unintended forces to users due to differences in the bending/stretching state between legs when ascending or descending slopes or stairs, as they control assist forces solely based on the ratio of right and left treading forces, leading to vertical and backward or forward components in the resultant force.
Innovation Solution
A walking assist device with a control unit that differentiates assist forces based on the bending/stretching state variable between legs, using ground sensors and treading force sensors to adjust forces only when both feet are on the ground, and increasing assist forces with greater bending/stretching and treading forces to minimize unintended force directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If assist forces are controlled only based on the ratio between right-leg side treading force and left-leg side treading force, then the control system is simple, but unintended forces are applied to the user in directions not intended by the user when ascending or descending slopes or stairs
Solution Approach 1:
The control unit receives feedback from bending/stretching state sensors that detect the bending/stretching state of each leg link, and adjusts the assist force distribution accordingly. This feedback mechanism enables the system to detect when a user is ascending or descending slopes or stairs and modify the assist force ratio to prevent unintended forces, resolving the contradiction by adding sensing and control complexity while improving user comfort
Solution Approach 2:
The system dynamically adjusts the assist force distribution ratio based on the detected bending/stretching state of the leg links. When the system detects asymmetric bending/stretching patterns indicative of slope or stair walking, it dynamically modifies the assist force allocation between left and right legs to counteract unintended force components, thereby maintaining user comfort without requiring a completely redesigned control system
2Device complexity
If the same assist force is applied to both legs when the user is in an ascending walking state, then the control logic is simple, but a resultant force with backward components is applied to the user
Solution Approach 1:
The system applies asymmetric assist forces to the left and right legs based on the detected bending/stretching state. When ascending slopes or stairs are detected through asymmetric leg link states, the control unit applies different assist force magnitudes to each leg, creating a balanced resultant force that prevents backward components and aligns with the user's intended motion direction
3Device complexity
If the same assist force is applied to both legs when the user is in a descending walking state, then the control logic is simple, but a resultant force with forward components is applied to the user
Solution Approach 1:
The system implements asymmetric assist force distribution during descending walking states by detecting the bending/stretching state of each leg link. When descent is detected, the control unit applies differentiated assist forces to counterbalance the forward component that would otherwise result from symmetric force application, ensuring the resultant force aligns with the user's intended descending motion
Data Source
AI summary
Provided is a walking assist device independent of a deviation of a bending/stretching state between user's legs and applying a force to a user in a direction intended by the user. The walking assist device performs control so that the larger the deviation of a value of a bending/stretching state variable representing the bending/stretching state of each of a pair of right and left legs of a user P is, the larger the deviation between the assist forces Fr and Fl acting on the user P from each of the leg links 2 is.