Exoskeleton with admittance control
Inventors
Corrigan, Madeline • Foulds, Richard
Assignees
New Jersey Institute of Technology
Publication Number
US-11337881-B2
Publication Date
2022-05-24
Expiration Date
2038-08-21
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Abstract
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.
Core Innovation
The invention provides an exoskeleton control system and method that utilizes the admittance control paradigm to enable users to manipulate an exoskeleton with minimal applied force. By retrofitting a passive arm support with force/torque sensors and servo motors, the exoskeleton offers motorized assistance for users with upper extremity weakness or other disabilities. The disclosed control system incorporates both admittance and impedance control, allowing for intuitive and precise trajectory control with reduced physical effort from the user.
Existing devices, such as passive arm supports, have limitations in gravity compensation and often require users to exert strength to overcome the system's inertia. Other exoskeletons and robotic manipulators use unintuitive user interfaces, such as joysticks or push buttons, which are difficult for users with muscle weaknesses. There is also an issue of time delay in these systems' control loops, which contributes to instability and poor user experience.
The core innovation addresses these problems by providing a modular exoskeleton system that combines passive supports with motorization, enabled through an admittance control loop that achieves a control loop time delay of 10 ms or less. The system can be tailored with more sensors and motors as user needs change, including in the context of progressive conditions. Gravity compensation is precisely managed through programmable parameters, and the user can intuitively control arm movement with only minimal physical input required.
Claims Coverage
The patent contains two independent claims that describe the core inventive features regarding an exoskeleton system and its method of use.
Integrated admittance and impedance control for a passive-motorized exoskeleton
An exoskeleton system combining a passive arm support with at least one joint, a forearm cuff, force/torque sensors attached between the cuff and the arm support, and a plurality of motors mounted at each joint to create a passive-motorized hybrid. The system integrates an admittance control loop and impedance control to control the position and orientation of the arm support based on detected forces and torques from the user. The admittance control loop is configured for a fully motorized three degree of freedom (3 DOF) system and achieves a time delay of 10 ms or less.
Antigravity force mechanism using virtual mass and damping coefficient
An antigravity force mechanism applies a constant upward force equal and opposite to the force of gravity on a user's arm. The mechanism incorporates a virtual mass (set at 0.5 kg) and a damping coefficient (set at 25 N*sec/m) that oppose only minimal inertia during user motion. The user controls the forearm cuff’s motion while being opposed only by inertia of the virtual mass and the damping. Both the virtual mass and damping coefficient are programmable to adjust for user medical condition changes, without replacing system components.
Direct drive system via motor horns to eliminate backlash
Motors include motor horns that directly drive the exoskeleton's joints, translating shaft motion to external physical motion. This direct drive eliminates backlash or play that can lead to motor and position errors, improving system fidelity.
Modular and adaptable exoskeleton mounting and control
The exoskeleton can be mounted on various locations including wheelchairs, tables, or desks. It can be tailored to support and direct a user’s arm through residual strength, with joint angles calculated and converted to motor positions for controlled movement each iteration of the control loop based on user-applied force and torque. The system allows for modular adaptation, adding sensors and motors over time as the user’s strength and mobility change.
Method for retrofitting passive supports with sensors, motors, and control loop
A method for providing an exoskeleton system by retrofitting a passive arm support with a force or force/torque sensor and motor(s), and implementing an admittance control loop within the motor to motorize the passive support.
The inventive features cover a hybrid passive-motorized exoskeleton system with integrated admittance and impedance controls, programmable gravity compensation using virtual mass and damping, direct motor drive, modular adaptability, and methods for retrofitting and operation tailored to user needs.
Stated Advantages
Provides more precise gravity compensation compared to conventional passive arm supports using springs or bands.
Minimizes the amount of force required by the user to control the exoskeleton, supporting users with diminished muscle strength.
Admittance and impedance control enables intuitive and safe user interaction, with rapid loop times (10 ms or less) reducing latency for stable control.
Modular design allows for individualized configuration and the system can adapt over time as user strength changes due to progressive conditions.
Direct drive implementation eliminates backlash and improves fidelity in motion control.
Motorized antigravity assistance enables increased independence in activities of daily living for users.
Dynamic and programmable virtual mass and damping coefficient allow system tuning without hardware changes to accommodate user condition changes.
Documented Applications
Medical support for individuals with upper extremity weakness or disabilities, such as Duchenne muscular dystrophy.
Assistance in activities of daily living by supporting and directing arm movement based on a user's residual strength.
Stroke rehabilitation device to assist post-stroke individuals in regaining lost upper extremity function, including use with virtual reality games.
Potential usage in military and civilian applications involving robotic or exoskeleton assistance.
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