Abstract
We propose a spiral-groove aerodynamic thrust bearing functioning as a viscous vacuum pump in a laser scanner motor to reduce the windage power loss of a polygon mirror. The proposed bearing pumps out the air in the scanner housing using the pumping effect of the spiral-groove thrust bearing, reducing the inner pressure of the housing. The pumping performances and the static characteristics of the spiral-groove thrust bearings were investigated numerically and experimentally. Two numerical calculation methods were used to study the pumping characteristics of the spiral-groove thrust bearing. It was found that a bearing with 15 spiral grooves reduced the inner pressure of the housing to <0.01 MPa at 20,000 rpm and at bearing clearance of 2.5 μm, and this has sufficient load-carrying capacity to support the rotating shaft and the mirror.
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Abbreviations
- D :
-
shaft diameter
- e :
-
rotor displacement in the axial direction from the center position
- G m :
-
mass of air in the sealed housing
- h :
-
bearing clearance
- h d :
-
groove depth
- h r0 :
-
average bearing clearance in the ridge region
- h g0 = h r0 + h d :
-
average bearing clearance in the groove region
- h g and h r :
-
bearing clearances at the groove and ridge regions, respectively
- H 0 = h g0 /h r0 :
-
the ratio of the bearing clearances
- l w :
-
length of land region
- n :
-
number of grooves
- p :
-
pressure
- p a :
-
ambient pressure
- p i :
-
pressure in the sealed housing
- P i = p i /p a :
-
dimensionless pressure in the sealed housing
- P u :
-
ultimate pressure
- q :
-
mass flow rate in the bearing clearance
- r 0 :
-
shaft radius
- t :
-
time
- V i :
-
inner volume of the sealed housing
- r and θ :
-
radial and circumferential coordinates, respectively
- α :
-
ratio of the groove width to the (ridge + groove) width
- β :
-
groove angle
- ε = e/h r0 :
-
dimensionless axial displacement of the rotor
- λ = paλa/p :
-
molecular mean free path
- λa :
-
molecular mean free path at atmospheric pressure (= 0.064 μm)
- \( \Lambda = 6\mu \omega r^{2}_{0} /p_{a} h^{2}_{{r0}} \) :
-
bearing number
- μ :
-
viscosity of air
- ρ :
-
density of air
- ω :
-
rotational angular velocity
- ξ and η :
-
boundary-fitted coordinates
- r :
-
ridge region
- g :
-
groove region
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Yoshimoto, S., Miyatake, M., Iwasa, T. et al. A method of reducing the windage power loss in a laser scanner motor using spiral-groove aerodynamic thrust bearings functioning as a viscous vacuum pump. Microsyst Technol 13, 1123–1130 (2007). https://doi.org/10.1007/s00542-006-0327-4
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DOI: https://doi.org/10.1007/s00542-006-0327-4