Exoskeleton Sit-to-Stand Control With Virtual Constraints
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Solution Overview
Problem
Current exoskeletons face challenges in comfortably and naturally transitioning from a sitting to a standing position due to varied chair shapes, user-specific initial positions, and the need for synchronized movement of the body and legs, leading to complex and painful training phases.
Innovation Solution
A method involving data processing means to generate a trajectory for the exoskeleton from a sitting to a standing position, applying virtual stresses parameterized by a phase variable, and using a controller to execute this trajectory, ensuring that all actuated degrees of freedom respect the virtual stresses, allowing for a universal, comfortable, and natural lifting motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If a pre-calculated trajectory in time is used to move the exoskeleton from sitting to standing position, then the movement can be executed automatically, but the tracking quality of joints may be inconsistent causing one joint to be ahead or late of its path, which aggravates the movement difficulty and creates excessive moments on joints
Solution Approach 1:
The patent implements feedback control by continuously monitoring the actual positions of joints during trajectory execution and adjusting control commands to maintain accurate tracking. The controller compares desired joint positions with actual positions and generates corrective control signals to ensure all joints follow their respective trajectories synchronously, preventing any joint from being ahead or late of its path.
2Speed
If the hips move too fast compared to the knees during the lifting movement, then the standing position can be reached faster, but the basin is sent widely backwards and exercises a very important moment on the knees, making the movement more difficult
Solution Approach 1:
The patent employs dynamic trajectory optimization that adjusts the motion profile of each joint based on the current system configuration and dynamics. The controller dynamically modifies the trajectory of hip and knee joints during execution to maintain optimal coordination, ensuring that when the hip moves forward, the knee moves forward as well to prevent excessive backward displacement of the basin and reduce moments on the knee joint.
3Ease of operation
If the exoskeleton uses a simplistic approach with ground contact detection and standard controllers, then the system is easier to control, but it is far from allowing comfortable movement and natural sensations
Solution Approach 1:
The patent changes control parameters dynamically during the lifting movement based on the exoskeleton's configuration and the user's needs. The controller adjusts trajectory parameters, velocity profiles, and coordination parameters to optimize both comfort and naturalness of movement. This allows the system to adapt to different users, chair types, and initial positions while maintaining comfortable and natural sensations during the transition.
4Adaptability or versatility
If the starting and arrival positions of the exoskeleton are adapted to each patient and each case of utilization, then the movement becomes more personalized and comfortable, but finding a movement from one position to another by respecting the kinematic constraint on the feet becomes non-trivial
Solution Approach 1:
The patent segments the trajectory planning into multiple independent phases: first determining the sitting position, then determining the standing position, and finally generating the trajectory between them. Each phase can be optimized independently, and the feet kinematic constraint is respected throughout by coordinating hip and knee movements. This segmentation reduces the overall complexity while maintaining adaptability to different users and situations.
Data Source
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AI summary
The present invention relates to a method for moving an exoskeleton (1) accommodating a human operator, from a seated position to a standing position (and vice versa), the seated and standing positions being such that the exoskeleton (1) has in these seated and standing positions a plurality of degrees of freedom, each actuated by an actuator controlled by data processing means (11) in such a way that no degree of freedom is non-actuated, the method being characterised in that the following steps are implemented by the data processing means (11): (a) generating a trajectory of the exoskeleton (1) from the seated position to the standing position (and vice versa), with time-dependent parameters; (b) applying to the trajectory a set of virtual constraints of the actuated degrees of freedom, the virtual constraints being parameterised with a phase variable; (c) running a controller of the exoskeleton (1) associated with the set of virtual constraints such that the exoskeleton (1) 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.