Rotary Series Elastic Actuator With Reconfigurable Nonlinear Stiffness
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Solution Overview
Problem
Conventional series elastic actuators (SEAs) face limitations due to fixed stiffness, compromising force control performance and adaptability in assistive robots, as they struggle to achieve a balance between force fidelity, bandwidth, and impedance, especially in human-robot interaction (HRI).
Innovation Solution
A reconfigurable rotary series elastic actuator (RSEA) with nonlinear stiffness is introduced, utilizing ordinary tension springs and adjustable configurations, such as pretension length and offset angles, to generate various stiffness profiles, enabling modular designs suitable for different assistive robots and tasks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a soft spring is used in conventional SEA, then force control fidelity is improved and output impedance is reduced, but force range and force bandwidth are limited
Solution Approach 1:
The patent applies dynamics by making the spring stiffness adjustable rather than fixed. The elastic element's stiffness can be dynamically changed based on task requirements, allowing the system to achieve both high force control fidelity (when soft spring is needed) and large force bandwidth (when stiff spring is needed) at different operating conditions.
Solution Approach 2:
The patent changes the physical parameter of spring stiffness from a fixed value to an adjustable parameter. By modifying the stiffness parameter of the elastic element, the system can optimize performance for different tasks - using softer springs for precision force control and stiffer springs for broader force bandwidth requirements.
2Productivity
If a stiff spring is used in conventional SEA, then force bandwidth is increased, but force control fidelity and intrinsic compliance are reduced
Solution Approach 1:
The system dynamically adjusts spring stiffness to match task requirements. When high force bandwidth is needed, the spring is configured to be stiffer; when precise force control is needed, the spring is configured to be softer, thus resolving the contradiction between bandwidth and fidelity.
Solution Approach 2:
The spring stiffness parameter is made variable rather than fixed. This allows the system to change the stiffness parameter according to operational needs, achieving both high force bandwidth and high force control fidelity at different times as required by different tasks.
3Adaptability or versatility
If variable stiffness actuators with secondary motors and stiffness adjustment mechanisms are used, then stiffness adaptability is improved, but device complexity and weight increase
Solution Approach 1:
The patent extracts the complex secondary motor and stiffness adjustment mechanism from the actuator design. Instead of using active control systems, it employs a passively adjustable elastic element that can change stiffness through simple mechanical reconfiguration, thereby reducing device complexity while maintaining stiffness adaptability.
Solution Approach 2:
The elastic element is designed to provide stiffness adaptation through its own mechanical properties rather than requiring external active control systems. The structure itself enables stiffness variation through passive mechanical means, eliminating the need for additional motors and control mechanisms.
4Adaptability or versatility
If nonlinear stiffness is achieved with specially designed cam shapes, then stiffness adjustment is possible, but adaptability to different applications is reduced
Solution Approach 1:
The patent employs a universal elastic element design that can be configured for different stiffness characteristics through simple parameter adjustments rather than requiring application-specific cam shapes. This single versatile mechanism can serve multiple applications by changing its configuration, not its fundamental structure.
Solution Approach 2:
Instead of changing the geometric shape of cams for different applications, the patent achieves different stiffness profiles by changing parameters of the same elastic element structure - such as pre-tension, mounting positions, or connection points - making the system adaptable to different applications without redesigning the core mechanism.
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 RSEA achieves a balance of low output impedance, high force control fidelity, and large force bandwidth, providing improved adaptability and performance in HRI by allowing adjustable stiffness profiles, which are validated through simulations and experimental results.
Implementation Method 1
Series elastic actuator (SEA) is one such compliant actuator, in which the physical elastic element is intentionally introduced in series between the stiff actuator and the external load
Implementation Method 2
making it difficult to achieve satisfactory control performance in the pHRI
Data Source
AI summary
Disclosed is a reconfigurable rotary series elastic element (RSEE) comprising: an inner tension spring mount: an outer tension spring mount; and a plurality of tension springs connected between the inner tension spring mount and outer 5 tension spring mount. A position at which each spring connects to one or both of the inner tension spring mount and outer tension spring mount: can be changed to adjust a relationship between an output torque and deflection angle of the RSEE; and is configured such that, during relative rotation of the inner tension spring mount and outer tension spring mount, an amount of tension in 10 at least one said tension spring differs from an amount of tension in at least one other said tension spring.