Researchers Develop 'Smart Cushion' to Suppress Low-Frequency Vibrations
Motor-actuated isolators automatically adjust to weight variations, solving a key limitation in isolating equipment from vibration.
At a Glance
- Quasi-zero stiffness isolators combine high static and low dynamic stiffness for better vibration control.
- Electric actuators modulate horizontal spring pretension to achieve zero-stiffness conditions automatically.
- Hybrid control strategy addresses both payload matching and resonance problems in a single system.
Vibration isolators aim to protect systems and assemblies in used in high precision manufacturing, aerospace, vehicles, and other industrial equipment from vibration damage. Traditional solutions involve using springs and dampers between the load and the vibration source to absorb vibrations. Researchers at Pusan National University in South Korea, however, may have identified an alternative approach: a "smart cushion."
Typical isolators are usually linear, suppressing low-frequency vibration through low static stiffness. But researchers fear this compromises the system’s capability for supporting static loads.
A research team led by Professor Seunghun Baek from the School of Mechanical Engineering at Pusan National University explored non-linear isolators with quasi-zero stiffness (QZS), which have high static and low-dynamic stiffness properties. They 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, they reported in a news release.
These devices aim to address the limitations of conventional linear vibration isolators and support both static payloads and low-frequency vibration isolation, but they have two critical limitations, the researchers pointed out. 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, it was reported.
The team's solution was to create a hybrid control strategy for a QZS isolator. “We have developed a controllable QZS isolator that utilizes motor actuation to address both payload variations and vibrations associated with the residual resonant peak,” explained Baek, in the release. The team’s 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 team’s rhombus-shaped QZS consists of four identical links, two fixed vertical springs, and a horizontal spring. In its passive configuration, the system is highly sensitive to payload variations. To solve this, the researchers modified the structure by integrating electric actuators at the joints to which the horizontal spring is connected. The actuators are employed to modulate the horizontal spring’s pretension, changing its effective initial length, which serves as the control parameter, they reported.
To achieve a zero-stiffness condition with this system, the researchers devised a hybrid control strategy. Read about their experiments to validate the strategy here. “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,” stated 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.”