Underactuated Shoulder Exoskeleton With Hyper-Redundant Joint Alignment
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Solution Overview
Problem
Existing exoskeletons face challenges in accurately aligning the axes of active robotic joints with human body joints, particularly at the shoulder joint, leading to misalignment issues that cause unwanted arm movements and stresses due to hyperstatic properties, and they fail to compensate for the movement of the shoulder center of rotation.
Innovation Solution
An underactuated mechanism with a proximal passive rotoidal joint and a distal active rotoidal joint connected via a hyper-redundant mechanism, allowing the exoskeleton to self-align and compensate for misalignments, ensuring the distal joint remains aligned with the shoulder's flexion-extension axis, and transferring reaction forces to the torso without constraining movements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the axes of active robotic joints are aligned with human body joints, then the exoskeleton can accurately determine posture and torques at human joints, but misalignment occurs due to movement of the shoulder center of rotation causing unwanted arm movements and stresses
Solution Approach 1:
The patent applies dynamics by making the exoskeleton joint axes movable rather than fixed. The mechanism allows the joint axes to dynamically adapt and move with the shoulder center of rotation during arm movements, ensuring continuous alignment accuracy while preventing misalignment-induced harmful effects.
Solution Approach 2:
The patent changes the parameter of joint axis position from static to dynamic. By allowing the joint axes to change their position and orientation in response to shoulder center of rotation movement, the system maintains accurate alignment throughout the range of motion, eliminating unwanted arm movements and stresses.
2Measurement precision
If the exoskeleton has kinematics isomorphous to the human arm with multiple connection points, then posture and torques can be accurately determined, but the device complexity increases due to the need to adjust link lengths to arm segment lengths
Solution Approach 1:
The patent applies universality by designing the exoskeleton with a standardized kinematic structure that can serve multiple functions. The mechanism provides both accurate posture determination through multiple connection points and automatic adaptation to different users without requiring complex manual adjustments, making the system universally applicable.
Solution Approach 2:
The patent applies self-service by enabling the exoskeleton to automatically adapt its configuration to match the user's arm dimensions. The system self-adjusts its link lengths and joint positions through its inherent mechanical design, eliminating the need for external adjustment mechanisms and reducing device complexity.
3Device complexity
If a single motor is used to actuate the shoulder joint, then the device complexity is reduced, but the system must be underactuated which may limit control precision
Solution Approach 1:
The patent applies dynamics by designing an underactuated mechanism where the single motor actuates one joint while other joints move passively in response. The dynamic coupling between joints, achieved through the hyper-redundant connection mechanism, ensures that the passive joints follow the appropriate motion trajectories, maintaining control precision despite the reduced number of actuators.
Solution Approach 2:
The patent applies the intermediary principle by introducing a hyper-redundant connection mechanism as a mediator between the actuated and passive joints. This intermediary mechanism transfers motion and forces in a controlled manner, enabling the single motor to indirectly control multiple joints with sufficient precision for rehabilitation tasks.
Data Source
AI summary
An underactuated mechanism has a first rotoidal joint connected to a human torso and rotating about a first joint rotation axis, a hyper-redundant connection mechanism connected to the first rotoidal joint, and a second rotoidal joint rotating about a second joint rotation axis, coplanar with the first joint rotation axis. The second rotoidal joint is remotely actuated by a driven pulley and Bowden cables or by a direct drive actuation system with co-located motor, and is fixed to the hyper-redundant connection mechanism on one side and to a human arm on the other side. The hyper-redundant connection mechanism has at least three members. Two members of the at least three members are rigidly fixed to one of the rotoidal joints, respectively. All members are connected together by rotation joints with axes parallel to one another and arranged to connect one member to a successive member to form a rotation constraint.