Researchers have developed a novel hybrid control strategy to achieve payload compensation and resonance elimination in quasi-zero stiffness isolators
BUSAN, South Korea, July 27, 2026 /PRNewswire/ — Vibration isolators are essential in applications like high precision manufacturing, aerospace, automobiles, and sensitive scientific equipment, where vibration can significantly degrade performance and reduce operational lifespan. Conventional vibration isolators apply springs and dampers between the load and the vibration source to absorb vibrations. However, these isolators are linear and face an inherent trade-off: achieving low-frequency vibration suppression requires a low static stiffness, that is, a very soft spring, but this compromises the system’s capability for supporting static loads.
This trade-off has prompted researchers to explore non-linear isolators with high static and low-dynamic stiffness properties, known as quasi-zero stiffness (QZS) isolators. QZS isolators can decouple static and dynamic behaviors by implementing a positive stiffness element, like a linear spring, that bears the static load combined with a parallel negative stiffness element that enables effective isolation of low-frequency vibrations. Despite their advantages, QZS isolators have two critical limitations. Their performance is dependent on precise parameter tuning for a specific payload, meaning that any change in payload can lead to a significant degradation or even complete loss of isolation performance. Second, these systems do not eliminate the residual resonant peak, which can result in large-amplitude oscillations and, under certain conditions, even chaotic motion.
To address these limitations, a research team led by Professor Seunghun Baek from the School of Mechanical Engineering at Pusan National University in South Korea has developed an innovative hybrid control strategy for a QZS isolator. “We have developed a controllable rhombus QZS isolator that utilizes motor actuation to address both payload variations and vibrations associated with the residual resonant peak,” explains Prof. Baek. Their study was made available online on June 10, 2026, and published in Volume 257 of Mechanical Systems and Signal Processing on August 1, 2026.
The study examines a rhombus-shaped QZS system made of four identical links, two vertical springs, and a horizontal spring. To address payload sensitivity, the researchers added actuators to adjust the horizontal spring’s pretension and effective length. Using a hybrid control strategy, one control law shifts the equilibrium point to compensate for payload changes, while the other adjusts the system in real time to suppress the residual resonant peak.
Experiments using a prototype validated the strategy. The first control law allowed the system to adapt to payloads ranging from 1.01 kg to 1.21 kg, successfully maintaining low-frequency isolation under conditions where passive systems would have failed. The second law demonstrated strong suppression of residual ultra-low-frequency resonance under a 1.11 kg payload.
“Our hybrid control strategy effectively addresses the static payload-matching problem and the dynamic resonance problem as two coupled aspects of a single control challenge,” remarks Prof. Baek. “By expanding the capabilities of QZS isolators, our ‘smart cushion’ could inspire isolators that automatically sense a change in weight and re-tune themselves in seconds. This will be crucial for fields like chip manufacturing where precision is paramount, and even for robots carrying fragile goods.”
Overall, this innovative strategy brings QZS isolators a step closer to becoming adaptive, intelligent systems that respond smartly to their physical environment.
Reference
Title of original paper: Active equilibrium control of a rhombus QZS isolator: A hybrid strategy for payload compensation and resonance elimination
Journal: Mechanical Systems and Signal Processing
DOI: https://doi.org/10.1016/j.ymssp.2026.114561
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SOURCE Pusan National University