Torsional Series Elastic Actuator for Precise Robotic Torque Control
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Solution Overview
Problem
Position-controlled robots with gear reduction are limited in precise force control due to nonlinearities like friction and stiction, lacking 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 to measure deflection, enabling precise control of rotational force (torque) through a feedback control loop, using disc-shaped torsional springs and an internal mechanism to amplify deflection for accurate torque measurement.
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 nonlinearities like friction and stiction
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 that directly measures the force applied to the environment, bypassing the nonlinearities of the gear transmission. The spring's deflection is proportional to the applied force, providing accurate force measurement despite friction and stiction in the gear system.
Solution Approach 2:
The patent implements a feedback control loop where the force measured by the spring (through deflection sensing) is fed back to the controller. This feedback enables the controller to adjust the actuator's output to achieve precise force control, compensating for the nonlinearities in the gear transmission system.
2Force
If gear transmission assembly is used to increase output force, then force capability is improved, but stability deteriorates when interacting with rigid environments
Solution Approach 1:
The series elastic element acts as a cushion between the actuator and the environment. When the robot interacts with rigid environments or humans, the spring can compress or extend, absorbing shocks and preventing instability. This elastic element provides inherent stability by decoupling the high-force gear transmission from direct contact with the environment.
3Measurement precision
If sensors are added to measure spring deflection for force feedback, then force control precision is improved, but device complexity increases
Solution Approach 1:
The spring serves multiple functions simultaneously: it acts as both a mechanical element to transmit force and a force sensor to measure the applied force. By measuring the spring's deflection, the system obtains force information without requiring separate sensing mechanisms, thereby reducing overall system complexity while maintaining high force measurement precision.
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 provides enhanced stability, safety, and natural interaction by allowing precise control of rotational force, balancing external and inertial forces, and offering high-resolution torque detection, thus improving robotic performance in force-controlled applications.
Implementation Method 1
The spring assembly may include two torsional springs, a spacer, and an internal mechanism with a sensor that detects the deflection of the springs
Implementation Method 2
an internal mechanism with a sensor that detects the deflection of the springs
Data Source
AI summary
A spring assembly for 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.