Abstract: A novel Delta mechanism with three translational degrees of freedom in space is proposed to realize the spatial three-dimensional low-frequency vibration isolation.A parallel mechanism with negative stiffness is deduced from the Delta mechanism. Then a three-DOF parallel quasi-zero stiffness vibration isolation platform is constructed by connecting the parallel mechanism with a vertical spring with positive stiffness.The statics and dynamics models of the vibration isolation platform are established to analyze the stiffness characteristics and natural frequencies of the vibration isolation platform in different spatial coordinates.The result shows that the static characteristic of the vibration isolation platform is linear in the horizontal direction and is only related to the horizontal displacement. In the vertical direction，it has quasi-zero stiffness characteristic，which can obtain a lower natural frequency，and is only related to the vertical displacement. When the vibration isolation platform deviates from the equilibrium position，the zero-stiffness characteristic is no longer obvious. The vertical natural frequencies of the vibration isolation platform with the parallel mechanisms with and without negative stiffness were test. The test results show that the vibration isolation platform with the parallel mechanism with negative stiffness can greatly reduce the vertical natural frequency of the system.

Key words: Deltamechanism, vibrationisolationplatform, quasi-zero-stiffness, negativestiffnessmechanism