Variable Stiffness Actuator With Rotational Contactor Flexure
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Solution Overview
Problem
Current variable stiffness actuators lack a sufficient range of stiffness and are too slow in adjusting their stiffness, making them inadequate for many applications, particularly in unstructured environments where robots need to comply with changing surroundings.
Innovation Solution
A selectable-rate spring with a flexure bar and rotational contactors connected to a motor, allowing for continuous variable stiffness across a full range of motion and rapid changes between minimum and maximum stiffness, achieved by varying the connection stiffness between a rotatable shaft and a link member through the rotation of the contactors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If current variable stiffness actuators are used, then some degree of stiffness adjustment is achieved, but the range of stiffness is insufficient and adjustment speed is too slow
Solution Approach 1:
The patent implements a dynamic stiffness adjustment mechanism where rotational contactors can continuously change their position along the arched flexure bar, enabling real-time variation of stiffness from minimum to maximum. This dynamic reconfiguration allows the actuator to adapt stiffness rapidly (within 0.12 seconds) across a wide range (1200:1 ratio), resolving the contradiction between adequate stiffness range and fast adjustment speed.
Solution Approach 2:
The patent changes the physical parameter of contact position along the flexure bar to control stiffness. By varying the distance between the rotational contactor and the flexure bar's pivot point, the effective lever arm changes, directly controlling the stiffness parameter. This parameter-based control enables continuous stiffness adjustment from soft (contactor near pivot) to stiff (contactor far from pivot) states, achieving both wide range and rapid transition.
2Measurement precision
If high stiffness actuators are used for positioning accuracy, then absolute positioning accuracy is achieved, but contact instability and noise increase
Solution Approach 1:
The patent employs dynamic stiffness adjustment to match the actuator's stiffness to the task requirements. During positioning operations requiring accuracy, stiffness can be increased; during interactions with unknown environments or when compliance is needed, stiffness can be reduced. This dynamic adaptation eliminates the need for continuously high stiffness, thereby reducing contact instability and noise while maintaining positioning accuracy when needed.
Solution Approach 2:
The patent varies the stiffness parameter in response to operational conditions. By adjusting the contactor position along the flexure bar, the system can transition between soft and stiff states, optimizing the balance between positioning precision and contact stability. This parameter modulation allows high positioning accuracy when stiff contact is acceptable, while avoiding the harmful effects of high stiffness during sensitive operations.
3Adaptability or versatility
If variable stiffness actuators are used for force control in unstructured environments, then compliance with surroundings is improved, but the maximum stiffness is insufficient for full range of motion
Solution Approach 1:
The patent implements a dynamic stiffness mechanism that can adapt to varying environmental requirements. In unstructured environments, the actuator can operate in a compliant state (low stiffness) for safe interaction with unknown objects. When full range of motion or high force is required, the stiffness can be increased to maximum levels, ensuring both compliance when needed and sufficient strength for complete motion capability.
Solution Approach 2:
The patent modulates the stiffness parameter across a wide range (1200:1 ratio) to match environmental demands. By adjusting the contactor position on the flexure bar, the system achieves low stiffness for compliant force control in unstructured environments, while maintaining the capability to reach high stiffness levels when maximum strength or full range of motion is required, thus resolving the contradiction between compliance and strength.
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 solution provides a wide range of operating stiffness, up to 1200 times greater than minimum stiffness, enabling safe and effective performance in complex tasks with rapid adjustments from zero to maximum stiffness in 0.12 seconds, enhancing safety and functionality in dynamic environments.
Implementation Method 1
a flexure bar connected to a rotatable shaft, the flexure bar having at least one arched portion. The selectable-rate spring also includes at least one rotational contactor connectable to a link member, wherein the rotational contactor rotates about an axis while maintaining contact with the arched portion of the flexure bar
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
In one embodiment a selectable-rate spring comprises a flexure bar connected to a rotatable shaft, the flexure bar having at least one arched portion. The selectable-rate spring also includes at least one rotational contactor connectable to a link member, wherein the rotational contactor rotates about an axis while maintaining contact with the arched portion of the flexure bar. As the rotational contactor rotates, it changes the connection stiffness between the rotatable shaft and the link member.