Variable Stiffness Isolator Layout for Large Seismic Displacements
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Solution Overview
Problem
Existing passive variable stiffness devices for vibration isolation are bulky and occupy significant space, especially when designed to accommodate large isolator displacements, which is a challenge in compact installations like higher floors of buildings where seismic activity amplifies horizontal ground motion.
Innovation Solution
A passive variable stiffness device with variable diameter cylinders and constant force springs, where the diameter changes along the length of the cylinders, allowing for a compact design that adjusts restoring force with displacement, using a combination of gear trains and pulleys to amplify force and accommodate large displacements without increasing device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a passive variable stiffness device is designed to accommodate large isolator displacements, then vibration isolation effectiveness is improved, but device size and occupied floor space increase significantly
Solution Approach 1:
The patent employs a nested configuration where the variable stiffness mechanism is integrated within a compact housing structure. The isolator components are arranged concentrically and in overlapping configurations, allowing the device to accommodate large displacements without proportionally increasing the external footprint. The nested arrangement enables internal components to move through large ranges while maintaining a small overall device envelope.
Solution Approach 2:
The patent transitions from a linear displacement accommodation approach to a multi-dimensional configuration. By arranging isolator elements in three-dimensional space with vertical and lateral components, the device accommodates large displacements through spatial distribution rather than linear extension. This dimensional reconfiguration reduces the horizontal footprint while maintaining the capacity for large isolator movements.
2Reliability
If zero stiffness isolation is used to reduce payload accelerations, then vibration isolation performance is improved, but isolator displacements increase significantly
Solution Approach 1:
The patent implements a variable stiffness mechanism that dynamically adjusts the isolator stiffness based on displacement magnitude. At small displacements, the stiffness is high to limit travel; at large displacements, the stiffness reduces to near-zero to provide effective vibration isolation. This dynamic stiffness variation allows the system to achieve both displacement control and effective isolation performance without requiring permanently high displacements.
Solution Approach 2:
The patent changes the stiffness parameter as a function of displacement through a mechanical mechanism. The variable stiffness isolator transitions from a constant stiffness state to a displacement-dependent stiffness state, where the restoring force coefficient varies with the isolator displacement. This parameter change enables the system to achieve zero stiffness isolation at large displacements while maintaining compact dimensions through high stiffness at small displacements.
3Adaptability or versatility
If installation is performed on higher floors where free space is available, then installation flexibility is improved, but isolator displacements are amplified due to floor acceleration amplification
Solution Approach 1:
The variable stiffness mechanism dynamically adapts to the amplified excitations encountered on higher floors. When subjected to larger accelerations from floor amplification, the isolator automatically transitions to a lower stiffness state to accommodate the increased displacement demands without requiring pre-designed oversized travel capacity. This dynamic adaptation enables effective isolation on higher floors while maintaining a compact device footprint.
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 device achieves positive tangential stiffness at small and large displacements and zero tangential stiffness in between, effectively isolating vibrations while maintaining a compact footprint, reducing payload accelerations and floor space requirements.
Implementation Method 1
an assembly of two constant force springs that resides in the space between the variable diameter cylinders
Implementation Method 2
restoring force characteristics that can be optimized for different ranges of isolator displacements
Implementation Method 3
variable diameter cylinders and constant force springs, where the diameter changes along the length of the cylinders, allowing for a compact design that adjusts restoring force with displacement, using a combination of gear trains and pulleys to amplify force
Implementation Method 4
zero tangential stiffness in between [small and large displacements]. This results in a variable restoring force that ensures stability of the system under service loading, limits excessive displacements under extreme seismic loading, and allows for zero stiffness isolation at the design level earthquake
Data Source
AI summary
Described and shown are passive variable stiffness devices, which are of compact design and configured to produce a restoring force that varies optimally with the isolator displacement when subjected to vibration-inducing loading.