Ferrofluid linear long stroke stage

Abstract

Stick-slip friction is the resulting effect of the transition between the dynamic and static friction coefficient. This effect determines the minimal sustained speed and minimal incremental motion of a movement system, limiting the performance in precise positioning systems. Available bearing types without stick-slip suffer from complexity, high cost, energy storage (for example in flexures) or need for active components (for example in magnetic bearings). The ferrofluid bearing has none of these issues. This makes it a potential alternative for current bearings in precise positioning systems. Ferrofluid is a colloidal suspension of magnetic particles in a carrier liquid. This gives the unique property of a fluid that is drawn towards the highest magnetic field intensity. The ferrofluid can be used in two ways to construct a bearing; the pocket bearing and pressure bearing arrangements. This research focuses on the latter, as the pocket bearing has shown bad repeatability. The pressure bearing consists of a ferrofluid in a magnetic field in between bearing surfaces. As a load is applied, the space between bearing surfaces decreases. This results in the ferrofluid being displaced from the least energetic configuration in the magnetic field which induces a normal force on the bearing surfaces. The objective of this study is to improve the performance of the ferrofluid pressure bearing by removing or improving the limitations in stroke length and repeatability. This is done by the creation of a longstroke linear ferrofluid demonstrator stage. The challenges in the creation of this stage are primarily focused on limiting the effects of trail formation, addressing the evaporation of the ferrofluid, and achieving a sufficient load capacity and stiffness to be a feasible alternative to other bearing types.