On the Design of a Diaphragm Valve for Aerostatic Bearings

Abstract

Because of their almost zero friction, cleanness and long life, aerostatic bearings are commonly used in many applications where high precision of positioning is required, e.g. machine tools, measuring machines, semiconductor manufacturing and power board testing. However, air bearings suffer from low relative stiffness and poor damping. Active and passive compensation are two effective methods to enhance the static and dynamic performance of these kinds of bearings. Despite their higher performance, active compensation solutions are too expensive to be used in industrial applications, as a consequence of the costs related to their controllers, actuators and sensors. This paper presents the design and performance of a passive compensation method that exploits a diaphragm valve. Thanks to its ease of integration, satisfactory performance and relatively low cost, this method could be a valuable solution to increasing the stiffness of aerostatic bearings. This work provides a procedure to design diaphragm valves depending on the type of the integrated pad and the desired nominal air gap height. Results demonstrate that, once correctly designed, the diaphragm valve makes it possible to obtain bearings with quasi-static infinite stiffness at the selected air gap height.

Design and Analysis of an Aerostatic Pad Controlled by a Diaphragm Valve

“…This paper presents a design procedure for a circular and centrally fed aerostatic pad controlled by a diaphragm As demonstrated by previous numerical and experimental works [29][30][31]33], this kind of compensation method makes it possible to significantly increase the static stiffness of air pads up to quasi-static infinite stiffness. Here, a design procedure is proposed to suitably select the geometry of this kind of passively compensated pad depending on the values of a desired air gap height at which the system has to work.…”

“…Chen and Lin [28] proposed an aerostatic pad with a disk spring compensator to increase the bearing damping. Ghodsiyeh et al [29,30] and Colombo et al [31,32] proposed a novel prototype of an aerostatic pad controlled by means of a diaphragm valve. It was found that this kind of passive compensation makes it possible to obtain quasi-static infinite stiffness and high damping in a low frequency range.…”

Theoretical Efficiency Study of Output Lubricant Flow Rate Regulating Principle on the Example of a Two-Row Aerostatic Journal Bearing with Longitudinal Microgrooves and a System of External Combined Throttling

“…It is convenient to calculate the constant static pressure P k0 at the outlet of the damping feeders and the corresponding pressure P p0 in the inter-throttling chambers using the normalized coefficients [18,21,28]…”

“…Figure 5 shows the dependences of the compliance K on the adjustment factor χ for different values of the membrane elasticity coefficient K e for L = 1.5, λ 1 = L 1 /L = 0.2, λ 3 = L 3 /L = 0.15, P s = 5 and the recommended value of the weighting factor for the SECT adjustment ς = 0.15 [18,21]. For an absolutely rigid membrane (K e = 0), the K(K e ) dependence has a unimodal character, with a minimum compliance at χ ≈ 0.45.…”

“…To improve the static characteristics of radial bearings, two-row feeding systems and longitudinal microgrooves made in the inter-row zone are used, which practically exclude circumferential air leakage, and contributes to a significant increase in the load capacity [15][16][17]. To reduce compliance, aerostatic bearings with active air flow compensation are used, where inlet flow compensators; membrane regulators of the nozzle-damper type with throttles in the form of diaphragms with sharp edges and in the form of flat slots [18][19][20][21][22] or Laub elastic orifices, are used [23][24][25]. The use of inlet membrane or elastic regulators makes it possible to reduce the static compliance to zero and even negative values (in the latter case, the increments of the load and the bearing gap have the same signs).…”