Rotary Series Elastic Actuator for Precise Torque Feedback
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Solution Overview
Problem
Position-controlled robots with gear reduction are limited in precise force control due to force nonlinearities like friction and stiction, lacking precise force feedback, which can lead to instability when interacting with rigid environments or humans.
Innovation Solution
A rotary series elastic actuator (SEA) is designed with a motor, gear transmission, and a spring assembly with sensors, where the spring deflection is proportional to applied torque, allowing for precise force control through a feedback control loop, enhancing stability and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If position-controlled actuators with gear reduction are used, then output force is increased, but force control precision deteriorates due to friction and stiction nonlinearities
Solution Approach 1:
A series elastic element (spring) is introduced as an intermediary between the actuator and the environment. This spring serves as a force sensor by deflecting proportionally to the applied force, enabling precise force measurement without being affected by gear friction and stiction. The spring acts as a mediator that decouples the force sensing function from the power transmission system.
Solution Approach 2:
The patent implements force feedback control by measuring the spring deflection and using this information to control the actuator output force. The feedback loop continuously adjusts the actuator to maintain the desired force level, compensating for disturbances and nonlinearities in the gear transmission system.
2Productivity
If position-controlled robots interact with rigid environments, then task completion is achieved, but stability deteriorates due to lack of compliance
Solution Approach 1:
The series elastic element provides beforehand cushioning by being pre-loaded and compliant. When the robot interacts with the environment, the spring can compress or extend to absorb shocks and accommodate position errors, preventing instability and damage while maintaining task completion.
3Reliability
If force-controlled robots interact with humans, then safety is improved, but device complexity increases due to force feedback requirements
Solution Approach 1:
The spring serves as a passive safety intermediary that inherently limits the force the robot can exert on humans. Even if the actuator fails or receives incorrect commands, the spring's mechanical compliance prevents dangerous force transmission, providing intrinsic safety without complex control systems.
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 SEA enables precise control of rotational force (torque) and improves stability and safety by providing inherent force feedback, allowing for natural interaction with humans and environments.
Implementation Method 1
The elastic element is usually a spring or a set of springs whose deflection is proportional to the force applied to itself
Data Source
AI summary
A rotary-type series elastic actuator (SEA) for use in robotic applications. The SEA including a motor, gear transmission assembly, spring assembly, and sensors. In one example, a robotic joint may include the SEA as well as two links coupled with each other at the joint assembly. The two links may be designated as input and output links. Each link may have a joint housing body which may be concentrically connected via a joint bearing so that they freely rotate against each other. The housing frame of the SEA may be fixed at the joint housing body of the input link while the output mount of the spring assembly of the SEA may be concentrically coupled with the joint housing body of the output link. The rotation of the motor rotor causes the rotation of the output link with respect to the input link plus spring deflection of the spring assembly. When an external force or torque are applied between the two links, a control action of a control loop may cause a rotation and motive force of the motor that lead to the deflection of the spring assembly to balance with the external force/torque and inertial force from body masses moving together with the links.