Combined effect of recess shape and fluid film thickness on the performance characteristics of hydrostatic guideways

Hydrostatic guideways, meant for linear motion are used in high-precision machine tools, to reduce vibration and improve the damping characteristics. The hydrostatic pad in the guideway is provided with a recess, to facilitate the formation of fluid film for supporting the load acting on it. The objective of this work is to study the influence of recess shape in the hydrostatic pad, on the load-bearing capacity and static pressure inside the recess. A numerical model of the hydrostatic pad with recess is analyzed to obtain the pressure distribution of fluid in the recess under operating conditions. Among the various recess shapes analyzed, the newly proposed full rounded rectangular recess is observed to have better load carrying capacity and recess pressure. A comparative analysis has been performed on various recess shapes, having a constant ratio of recess area to fluid film area. Further, the influence of constant flow resistance restrictors using a capillary compensator is included, to study the bearing capability. The static pressure developed in the recess for supporting the externally applied load is determined by making the inlet pressure to the restrictor and the fluid film thickness as constant. The other performance characteristics including variation in mass flow rate and stiffness of the fluid are also studied. Later, the influence of fluid film thickness on the performance characteristic is investigated. The recess shape having better performance characteristics in terms of load bearing capacity, static pressure, mass flow rate, and stiffness is proposed.