Dual Differential Semi-Active Actuator for Low Impedance Control
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Solution Overview
Problem
Modern robotic systems face limitations in tasks requiring safe and versatile interactions due to high output impedance and non-collocation of sensing and actuating transducers, which hinder their performance in applications like grinding, polishing, and complex assembly, despite advancements in interaction control theory.
Innovation Solution
A dual differential semi-active actuator is developed, utilizing two semi-active actuators coupled with mechanical differentials to control output force in both directions, achieving high force or torque density, sufficient bandwidth, low output impedance, and high-fidelity force display capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If classic actuators are used for robotic systems, then high force or torque density is achieved, but output impedance becomes high which prevents safe and versatile interactions
Solution Approach 1:
The actuator is divided into two independent semi-active sub-actuators (brakes) that operate in opposition to each other. Each brake independently controls one direction of force, allowing the system to achieve high force density while maintaining low output impedance through the differential mechanism that combines their effects.
Solution Approach 2:
A mechanical differential mechanism is introduced as an intermediary between the two semi-active brakes and the output. This differential acts as a mediator that combines the forces from both brakes while isolating the high impedance characteristics of individual brakes from the output, thereby achieving low output impedance with high force capability.
2Measurement precision
If classic actuators with force feedback are implemented, then force control capability is improved, but non-collocation of sensing and actuating transducers occurs which limits performance
Solution Approach 1:
Each semi-active brake is equipped with its own sensing transducer that directly measures the force it generates. This self-service approach eliminates the need for separate sensing and actuating transducers, achieving collocation where the sensing element is integrated with the actuating element, thereby simplifying the overall system architecture.
3Object-affected harmful factors
If semi-active actuators are used to reduce output impedance, then safe interactions are enabled, but force bandwidth becomes insufficient for fast motion tasks
Solution Approach 1:
Two semi-active brakes are merged in an opposed configuration within the differential mechanism. This combination allows the system to simultaneously achieve the low output impedance characteristic of semi-active actuators and the high force bandwidth of active systems, as the two brakes work together to provide both safety and speed capabilities.
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
This configuration enables precise force and velocity control, ensuring safe and versatile robotic interactions with low natural impedance and high bandwidth, suitable for complex tasks that previous actuators struggled with.
Implementation Method 1
The actuator makes use of two magnetorheological (MR) brakes
Data Source
Figure 1~2
Figure 3~4
Figure 5a~5b
AI summary
The present invention regards a mechanical differential actuator for interacting with a mechanical load, comprising a first semi-active sub-actuator; a second semi-active sub-actuator; a velocity source; a first mechanical differential having three interaction ports, including a first interaction port coupled to the velocity source, a second interaction port and a third interaction port coupled to the first semi-active sub-actuator; and a second mechanical differential having three interaction ports, including a first interaction port coupled to the velocity source, a second interaction port and a third interaction port coupled to the second semi-active sub-actuator; wherein the second interaction port of the first mechanical differential and the second interaction port of the second mechanical differential are coupled together to form an output which is configured so as to be coupled to the load. According to the present invention, the first and second mechanical differentials include respective first and second speed reducer mechanisms for implementing a mechanical differential function, the velocity source being coupled to the first and second speed reducer mechanisms.