Porous Air Bearing Load & Stiffness Calculator
Ultra-Precision Machine Design: Determine aerostatic load capacity ($W$), micro-gap air film stiffness ($K_h$), and volumetric compressed air consumption for porous precision bearings.
Bearing Geometry & Air Supply
Load Capacity & Air Film Stiffness Output
Porous Aerostatic Air Bearing Mechanics & Slocum Sizing Models
Aerostatic porous air bearings provide non-contact, friction-free linear motion in coordinate measuring machines (CMMs) and wafer steppers.
1. Aerostatic Load Capacity
W = A_bearing · ( P_supply - P_ambient ) · η_porous [Newtons]
2. Film Stiffness & Flow Rate
K_h = - dW/dh ≈ 1.45 · ( W / h_gap ) [N/μm] Q_air ≈ C · A_bearing · P_supply · h_gap^1.3 [Normal Liters / min]
Frequently Asked Questions
Why are porous carbon air bearings superior to orifice-fed air bearings?
Traditional orifice air bearings inject air through discrete tiny holes, creating localized pressure spikes and risking unstable self-excited acoustic vibrations ("pneumatic hammer"). Porous carbon bearings diffuse air uniformly across millions of sub-micron pores, delivering a flat pressure profile, higher load capacity, superior stiffness ($K_h$), and complete immunity to pneumatic hammer.
What determines the optimal flying air gap h?
Standard precision air bearings operate with flying gaps between $5\,\mu\text{m}$ and $8\,\mu\text{m}$. If the gap is too large ($>15\,\mu\text{m}$), air film stiffness drops and air flow increases cubically ($Q \propto h^3$). If the gap is too small ($<3\,\mu\text{m}$), surface waviness or dust particles risk mechanical contact.
Why are aerostatic bearings essential for semiconductor lithography and CMMs?
Because fluid film thickness separates moving parts completely, aerostatic bearings possess exactly zero static friction (no stick-slip). This permits infinite sub-nanometer positioning resolution and zero wear over decades of operation.