Antagonistic Differential Actuator for Variable Impedance Control
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Solution Overview
Problem
Current robotic devices for upper limb rehabilitation are often bulky, costly, and not suited for home-based therapy, lacking the necessary safety and adjustability in mechanical impedance for effective interaction with humans.
Innovation Solution
A mechanical actuator system featuring a differential mechanism with adjustable-engagement clutches, allowing for variable and controllable mechanical impedance, enabling safe and adaptable interaction with humans by independently controlling the degree of engagement of the clutches to manage torque and direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional robotic devices are used for rehabilitation, then they can provide therapy functions, but they are bulky, costly, and not suited for home-based use
Solution Approach 1:
The robotic system is divided into modular components including a base unit with control electronics and interchangeable end effectors. This segmentation allows the system to be compact yet versatile, with each module optimized for specific functions while maintaining overall system adaptability for home use.
Solution Approach 2:
The robotic device incorporates multiple functional capabilities within a single compact platform, including rehabilitation exercises, assessment modes, and adjustable impedance control. This multi-functionality eliminates the need for multiple separate devices, reducing overall system footprint while maintaining versatility for home-based rehabilitation.
2Reliability
If mechanical actuators with fixed inertia are used, then they provide stable control, but they cannot adjust mechanical impedance for safe human interaction
Solution Approach 1:
The mechanical actuator incorporates variable impedance control through adjustable spring constants and damping coefficients. This dynamic adjustment capability allows the system to transition between stable fixed-impedance operation and adaptive variable-impedance modes, enabling both control reliability and safe human interaction depending on operational requirements.
Solution Approach 2:
The actuator system changes physical parameters including spring stiffness, damping coefficients, and friction characteristics to adjust mechanical impedance. These parameter modifications enable the system to adapt to different rehabilitation tasks and safety requirements while maintaining stable control through active feedback regulation.
3Reliability
If high-inertia components are used in robotic actuators, then they provide stable control, but they pose safety risks during human contact
Solution Approach 1:
The actuator incorporates counterbalancing spring mechanisms that offset the weight and inertial effects of high-inertia components. This counterweight approach reduces the net force exerted on users during unexpected contact while maintaining the structural stability and control precision provided by the high-inertia elements.
Solution Approach 2:
The system employs compliant elements including springs and dampers that are pre-configured to absorb impact forces before they reach the user. This beforehand cushioning mechanism mitigates safety risks from high-inertia components by dissipating energy through controlled deformation during unexpected human contact.
Data Source
AI summary
A mechanical actuator system has variable and controllable mechanical impedance. Such a mechanical actuator system may be used to effectuate a degree of freedom in a robot, i.e., to control speed, output torque and direction of movement of a robotic component, such as a joint, wheel, arm, wrist or grabber. Mechanical impedance, i.e., an amount of “resistance” the robot presents to a human user, can be controlled for safety and rehabilitation purposes. The mechanical actuator system includes a mechanical differential and two adjustable-engagement clutches driven by motor. Advantageously, the motor may turn at a constant speed and direction, yet the mechanical actuator system can be controlled to turn in either direction and at a desired speed. The adjustable-engagement clutches may be electrorheological (ER) fluid clutches, magnetorheological (MR) fluid clutches, conventional dry friction clutches or any other type of clutch whose degrees of engagement can be controlled.