Design of a passive alternative for long stroke linear aerostatic stages based on ferrofluid bearings

Design of a passive alternative for long stroke linear aerostatic stages based on ferrofluid bearings

van den Toorn, S.W.M. (TU Delft Support Precision and Microsystem Engineering)
Spronck, J.W. (TU Delft Mechatronic Systems Design)
van Ostayen, R.A.J. (TU Delft Mechatronic Systems Design)
Lampaert, S.G.E. (TU Delft Mechatronic Systems Design)

2021

The objective of this research is to demonstrate the capability of a long stroke linear ferrofluid (FF) stage. This stage is a passive alternative to existing linear aerostatic stages and can be used in low loaded CNC devices, pick and place machines, microscopy or scanner applications. To compete with aerostatic stages the bearing must be repeatable and achieve sufficient stiffness for the application. The effects of ferrofluid trail formation are countered with the use of a ferrofluid reservoir located on the mover. To increase stiffness a specially designed magnet configuration is used. A linear guidance was built with outer dimensions of 180x600x80 mm (WxLxH), a mover of 1.8 kg without actuator and payload having a 430 mm stroke. The load capacity of the stage was measured to be 120 N, with a stiffness of 0.4 N/μm. The maximum height delta after a stroke with 1 kg payload and a mover velocity of 0.25 m/s was measured to be less than ±3μm, and with 1.75 kg payload and a velocity of 0.5 m/s the height delta was within ±7μm. Using a rheometer, it was shown that the effects of evaporation in ferrofluid can be reversed, within certain limits of mass loss, by adding carrier fluid. The damping is shown to be a function of payload and velocity and was measured to be between 2 and 4 N⋅s/m for velocities between 0.2 and 0.5 m/s. In comparison to a linear aerostatic stage it can be concluded that while the linear ferrofluid stage is outperformed in stiffness and out-of-plane repeatability, the ferrofluid stage does not require a continuous supply of air and has lower fabrication tolerances due to the higher fly height. Thus, the linear ferrofluid stage is a cost-effective alternative to a linear aerostatic stage when the stiffness and straightness are of less importance.

Air bearing alternative
Ferrofluid design
Ferrofluid linear stage
Magnetic fluid
Passive bearing

http://resolver.tudelft.nl/uuid:023a42c0-0c22-4f34-aafe-1d951fe7cf61

https://doi.org/10.1016/j.precisioneng.2020.09.021

0141-6359

Precision Engineering, 67, 428-437

Institutional Repository

journal article

© 2021 S.W.M. van den Toorn, J.W. Spronck, R.A.J. van Ostayen, S.G.E. Lampaert