Exoskeleton Admittance Control Gravity Compensation
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Solution Overview
Problem
Current robotic and exoskeleton devices for individuals with Duchenne muscular dystrophy and similar conditions face limitations such as inexact gravity compensation, requiring significant user strength, unintuitive interfaces, and a time delay in control loops, which hinder independence in daily activities and stability in arm movements.
Innovation Solution
A motorized exoskeleton system utilizing admittance control with a force sensor and motors, reducing the time delay to 10 ms or less, allowing users to control their arm movements based on residual strength, providing intuitive and stable interaction by translating user force into precise motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If passive arm supports with springs or rubber bands are used to support the arm against gravity, then the active range of motion is increased, but the gravity compensation is inexact and users lack sufficient strength to overcome the inertia of the support itself
Solution Approach 1:
The patent replaces the passive mechanical spring-based support system with an active motorized exoskeleton system. Motors are integrated into the exoskeleton structure to actively generate forces that compensate for gravity and inertia, eliminating the reliance on passive elastic elements and providing precise, controllable support forces.
Solution Approach 2:
The exoskeleton system uses force sensors to detect user intent and automatically generates the necessary compensatory forces through its motors. The system serves itself by sensing the user's residual strength and independently calculating the required assistance without external control input, enabling intuitive operation.
2Ease of operation
If exoskeletons with motors are used to support and direct arm movement, then the active range of motion is greatly improved, but complex and unintuitive user interfaces such as joysticks and push buttons are required
Solution Approach 1:
The force sensor acts as an intermediary between the user and the motorized exoskeleton system. Instead of requiring complex interfaces, the sensor directly captures the user's natural force application and translates it into control signals, serving as a natural mediator that bridges human intent and machine response.
Solution Approach 2:
The system interfaces with the user through their natural residual strength without requiring learned control strategies. The force sensor detects user intent and the control system automatically translates this into appropriate motor commands, making the interface as intuitive as natural arm movement itself.
3Productivity
If traditional user interfaces with push buttons or joysticks are used, then task completion is achieved, but significant time is required and a time delay of 310 ms causes instability
Solution Approach 1:
The patent replaces traditional mechanical or software-based control interfaces (joysticks, push buttons) with a direct force-sensing interface. This substitution eliminates the multi-step processing required by traditional interfaces and enables direct, real-time control with a response time of 10 ms or less.
Solution Approach 2:
The patent changes the fundamental control parameter from position-based control (joystick movement) to force-based control (user applied force). This parameter change enables direct mapping between user intent and system response, eliminating the time delays inherent in traditional interfaces and achieving stable control with 10 ms or less latency.
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 system enhances independence in daily activities and rehabilitation by enabling users to perform tasks with diminished muscle strength, offering precise antigravity assistance and adaptable support as muscle capacity changes over time.
Implementation Method 1
The sensor determines a desired movement direction and magnitude based on the user's applied force
Implementation Method 2
Motors could be mounted at each joint to control the position and orientation of the forearm cuff
Implementation Method 3
The exoskeleton supports the arms against gravity using residual strength
Data Source
AI summary
A control system and method for an exoskeleton is provided. The control system utilizes the admittance control paradigm to provide a system and method for manipulating the exoskeleton using minimal force from the user. A force/torque sensor and servo motors are fitted onto a passive arm support, enabling motorized support for a user with upper extremity weaknesses. The exoskeleton may be used on any extremity. The admittance control paradigm includes an impedance control and an admittance control to allow a user with upper extremity weakness and limited independence to intuitively and with minimal force control the precise trajectory of their arms to achieve a greater degree of independence in activities of daily living. Unlike existing passive arm supports that utilize springs or rubber bands to balance the user's arm against gravity, this system provides more precise gravity compensation and minimizes the amount of force required to control the exoskeleton.