Robotic Manipulandum with Passive Wrist for 3D Workspace Motion
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Solution Overview
Problem
Existing robotic devices for upper-limb rehabilitation, such as manipulanda and exoskeletons, fail to fully regulate patient arm posture, allow non-planar movements, and provide inadequate gravity compensation, leading to mechanical constraints and high costs.
Innovation Solution
An electromechanical manipulandum device with a drive system, arm, capstan transmission, and end-effector providing three degrees-of-freedom motion, controlled by a system to apply forces and compensate for gravity, allowing for a large workspace and ease of setup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If exoskeleton devices are used to produce 3D arm motion, then spatial movement capability is improved, but device complexity and cost increase
Solution Approach 1:
The device segments the motion control into two independent parts: a passive spherical wrist mechanism that provides 3D spatial movement capability without actuation, and a separate planar parallel manipulator that provides actuated control in the horizontal plane. This segmentation allows the device to achieve 3D motion capability while keeping the actuated mechanism simple and cost-effective.
Solution Approach 2:
The invention adds a passive spherical wrist mechanism that operates in the vertical dimension without requiring actuators. This allows the device to provide 3D spatial movement capability while the actuation system remains confined to the simpler planar horizontal dimension, reducing overall device complexity.
2Adaptability or versatility
If exoskeleton kinematics are used to conform to skeletal system, then anatomical matching is improved, but mechanical constraint and setup complexity increase
Solution Approach 1:
The device separates the anatomical conforming function (passive spherical wrist) from the actuated control function (planar parallel manipulator). The passive wrist naturally conforms to the user's arm anatomy without requiring complex adjustment mechanisms, while the actuated planar mechanism uses standard parallel manipulator kinematics that are simpler to configure.
Solution Approach 2:
The passive spherical wrist mechanism self-adapts to the user's arm anatomy through its inherent degrees of freedom, eliminating the need for complex adjustment mechanisms. The mechanism automatically conforms to the user's posture requirements without requiring therapist intervention for mechanical adjustments.
3Strength
If high gear ratio is introduced to address motor inertia, then static load capability is improved, but backdriveability deteriorates
Solution Approach 1:
The device applies actuation forces partially, only in the horizontal plane where they are most effective for rehabilitation exercises. The vertical dimension relies on passive gravity compensation and user effort, eliminating the need for high gear ratios that would compromise backdriveability in the actuated directions.
Solution Approach 2:
The device uses passive gravity compensation mechanisms to counteract the weight of the manipulator arms, eliminating the need for high gear ratios to provide static load capability. This allows the use of direct-drive or low-gear-ratio motors that maintain good backdriveability.
4Ease of operation
If planar manipulandum design is used, then transparency is improved, but 3D workspace capability deteriorates
Solution Approach 1:
The device segments the workspace capability into a passive 3D spherical wrist mechanism that provides full spatial movement without affecting transparency, and an actuated planar parallel manipulator that maintains mechanical transparency while providing controlled forces in the horizontal plane.
Solution Approach 2:
The invention adds 3D workspace capability through a passive spherical wrist mechanism that operates in the vertical dimension without introducing mechanical constraints that would reduce transparency. The actuated planar mechanism maintains transparency while the passive wrist extends capability to 3D space.
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
The device offers a large 3D workspace, ease of setup, high transparency, and effective gravity compensation, minimizing mechanical constraints and reducing the impact on user movements, while maintaining a cost-effective design.
Implementation Method 1
a capstan transmission for transmitting actuating force from the drive system to the arm
Implementation Method 2
a drive system comprising a plurality of electrical motors
Data Source
AI summary
An electromechanical manipulandum device can include: a drive system having a plurality of electrical motors; an arm driveable by the drive system and having three degrees-of-freedom of motion; a capstan transmission for transmitting actuating force from the drive system to the arm; an end-effector coupled to the arm, the end-effector configured to engage a user and having at least three degrees-of-freedom of rotational motion; and a control system for controlling the drive system such as to provide a force to the end-effector in a selected direction.