Dynamic Analysis of a Motorized Spindle With Externally Pressurized Air Bearings

Abstract

The purpose of this paper is to investigate the dynamic characteristics of a motorized spindle with externally pressurized air bearings. The externally pressurized air bearings consist of a journal bearing and a double pad thrust bearing with orifice restrictors. The equations of motion for the rotor-bearing system are established considering five degrees-of-freedom (DOF). The perturbation method and the finite difference method are introduced to calculate the static and dynamic characteristics of the air bearings; and the effects of the rotating speed and tilt angle of the rotor on the dynamic characteristics of the air bearings are analyzed. With the dynamic coefficients of the air bearings and the 5DOF rotor-dynamic model obtained, the stability, the unbalance response, and the forced response of the rotor-bearing system are investigated. Finally, the static and dynamic characteristics of the spindle are verified by an experimental study.

Dynamics characteristics of a rotary table motorized spindle with externally pressurized air bearings

“…where is the radius of the journal bearing, h is the gas film thickness, is the dynamic viscosity of air, and is the angular velocity of rotor. The static Reynolds equation and the perturbation equations are obtained by the perturbation method [13][14][15][16][17][18][19] and solved by the finite difference method [20][21][22]. Taking the thrust bearing as an example, the nondimensional static Reynolds equation can be written as:…”

“…2) The rotor of the rotary table is a rigid body, and the unbalance of the rotor is in the crosssection passing the mass center. Thus, the motion equations for the rotary table spindle are as follows [14]:…”

“…The analysis method of forced response of the rotary table spindle under grinding force refers to [14]. Table 4 shows the maximum values of the displacement and tilt angle of the rotary table spindle under the grinding force.…”

“…(3) is mounted on the test stand (4). The spring-loaded method [14] consists of the upper load-applying block (6), the lower load-applying block (9), the load-applying bolt (1), the guide bar (2), and the spring (7). The test force is measured by the force sensor (8), and the axial displacement Δ of spindle top due to the air film deformation is measured by the micrometer (5).…”

“…The bearing bush (5) consists of the lower pad thrust bearing and the journal bearing. The journal bearing has one row of the orifice restrictors (14) uniformly distributed along circumference to supply compressed air to the bearing clearance, and each pad of the thrust bearing has one row of orifice restrictors (16). A framed DC brushless type motor, including the motor stator (8) and the motor rotor (13), is controlled by the revolver (9) to drive the rotary table spindle; this motor has high power density, low temperature rises and good speed regulation performance.…”