Exoskeleton Sit-to-Stand Control With Virtual Constraint Trajectories
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing exoskeletons face challenges in comfortably and naturally transitioning from a seated to a standing position, as they require adaptation to individual user positions and weight distributions, and current methods are inefficient and cumbersome, especially due to the need for precise synchronization of joint movements and torque management.
Innovation Solution
A method involving data processing means that generates a parameterized trajectory for exoskeleton movement from seated to standing positions, applying virtual constraints parameterized by a phase variable, allowing for actuated degrees of freedom to be controlled to ensure a stable and comfortable transition, with a controller generating commands to comply with these constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If standard controllers following pre-calculated trajectories are used, then the movement can be controlled, but the tracking quality differences between joints cause synchronization problems and make the movement more difficult
Solution Approach 1:
The patent implements a feedback mechanism where the actual positions of hips and knees are continuously measured and used to adjust the trajectory in real-time. This ensures that even if one joint is ahead or behind its trajectory, the system compensates to maintain synchronization and proper kinematic relationships throughout the standing-up movement.
Solution Approach 2:
The patent transitions from static pre-calculated trajectories to dynamic adaptive trajectories that are continuously adjusted based on real-time joint position feedback. This allows the system to adapt to actual performance and maintain synchronization, rather than following a fixed predetermined path that may not account for tracking errors.
2Productivity
If hip and knee motors are activated to stand up, then the exoskeleton can transition from seated to standing, but the moment of weight requires considerable torques and may send the pelvis to the rear
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal trajectories for the standing-up movement that account for weight distribution and torque requirements. These trajectories are designed in advance to minimize peak torques and prevent excessive pelvis rearward movement, rather than reacting to force limitations during the movement itself.
Solution Approach 2:
The patent changes parameters by adjusting trajectory parameters such as movement speed, acceleration profiles, and joint angle sequences to optimize torque distribution. By modifying these parameters, the system reduces the peak torques required while still achieving the standing-up transition, and prevents the pelvis from being sent considerably to the rear.
3Loss of time
If the exoskeleton adapts to patient movement, then training phases become long and tiresome, but patient control and participation are reduced
Solution Approach 1:
The patent implements self-service by having the system automatically adapt to each patient's specific seated and standing positions and weight distribution characteristics. The exoskeleton performs self-calibration and stores personalized parameters, eliminating the need for lengthy manual training phases while maintaining natural and comfortable movement for each individual patient.
Data Source
AI summary
A method for moving an exoskeleton from a seated position to a standing position (and vice versa) in which none of the degrees of freedom of the exoskeleton is non-actuated. The method includes the implementation by a data processor of steps of: (a) generating a trajectory of the exoskeleton from the seated position to the standing position (and vice versa), the trajectory being parameterised as a function of time; (b) applying to the trajectory a set of virtual constraints on the actuated degrees of freedom, the virtual constraints being parameterised by a phase variable; and (c) running a controller of the exoskeleton associated with the set of virtual constraints such that the exoskeleton moves from the seated position to the standing position (and vice versa), the controller being capable of generating commands for the actuators so as to comply with the virtual constraints during the trajectory.