Binary Variable Stiffness Joint Using Modular Clutch-Spring Bits
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Solution Overview
Problem
Existing variable stiffness joints for robotic applications face challenges such as complex stiffness tuning mechanisms, bulky size, and non-ideal stiffness curves, which hinder their application in robotic arms and increase control complexity, especially in wearable robotics and haptic devices.
Innovation Solution
A passive binary controlled variable stiffness joint (BpVSJ) is designed with a plurality of stiffness bits, each comprising an elastic element connected to a clutch, utilizing torsional springs and electromagnetic friction clutches, and a gear train mechanism to achieve 2m stiffness levels by selectively engaging or disengaging clutches to alter joint stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive compliant elements are added to achieve variable stiffness, then safety and energy absorption are improved, but device complexity and control difficulty increase
Solution Approach 1:
The variable stiffness mechanism is segmented into multiple independent stiffness bits, each controlled by its own clutch. This allows independent control of each stiffness element, simplifying the overall control architecture while achieving complex variable stiffness behavior through combination of simple units.
Solution Approach 2:
The system transitions from static stiffness to dynamic variable stiffness by enabling real-time switching between different stiffness levels through clutch engagement/disengagement, allowing the robotic joint to adapt its mechanical properties during operation for both safety and performance.
2Adaptability or versatility
If continuous stiffness tuning mechanisms are used, then adaptability is improved, but device size and complexity increase
Solution Approach 1:
The continuous stiffness tuning mechanism is replaced by segmented discrete stiffness levels achieved through binary combination of stiffness bits. This provides sufficient adaptability for robotic applications while dramatically reducing the mechanical complexity and size compared to continuous tuning mechanisms.
Solution Approach 2:
The system achieves variable stiffness by changing the engagement state of clutches rather than physically adjusting mechanical parameters. This allows stiffness variation through binary state changes (engaged/disengaged) rather than continuous mechanical parameter adjustment, reducing size and complexity.
3Measurement precision
If motor-based control is used for stiffness variation, then control precision is improved, but energy consumption increases
Solution Approach 1:
The patent replaces motor-based active control with passive mechanical control using springs and clutches. The stiffness is determined by the mechanical configuration of engaged springs rather than active motor control, dramatically reducing energy consumption while maintaining precise stiffness levels through binary clutch states.
Solution Approach 2:
The variable stiffness mechanism uses passive elastic elements (springs) that automatically provide the required stiffness force without active energy input. The system serves itself by utilizing the inherent elastic properties of springs rather than requiring continuous energy input from motors to maintain stiffness.
4Adaptability or versatility
If complex stiffness tuning mechanisms are used, then stiffness range is improved, but ease of manufacture decreases
Solution Approach 1:
The stiffness tuning mechanism is divided into identical, modular stiffness bits that can be manufactured using standard components (springs, clutches, gears). This modularity simplifies manufacturing compared to custom complex mechanisms, as each bit is a repeatable unit that can be produced independently and assembled systematically.
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 BpVSJ enables efficient and flexible alteration of stiffness levels, providing a wide range of stiffness variations with low switching time, enhancing safety and adaptability in robotic interactions while reducing energy consumption and control complexity.
Implementation Method 1
electromagnetic friction clutches
Implementation Method 2
electromagnetic friction clutches
Implementation Method 3
torsional springs
Implementation Method 4
torsional springs
Data Source
AI summary
A variable stiffness joint and method to alter the stiffness of the joint with multiple stiffness levels is described wherein a plurality of stiffness bits (m) are used for enabling 2 m stiffness level variations for the joint. Each stiffness bit comprises an elastic element in mechanical connection with a clutch (21, 22, 23). The joint revolves with zero stiffness level when all the clutches (21, 22, 23) are disengaged whereas a clutch (21, 22, 23) involves one of the elastic elements which alter the stiffness of the joint. Engaging other clutches (21, 22, 23) involve more elastic elements for altering the joint stiffness and the resultant joint stiffness is determined by adding the stiffness values of all the involved springs (6, 7, 8).