Externally pressurized gas bearing and spindle equipment using this

#1. Field of the Invention

#The present invention relates to an externally pressurized gas bearing incorporated, for example, into a precision processing machine or inspection device to support the main shaft in a non-contact state, and it also relates to a spindle device using this.

#2. Brief Description of the Prior Art

#FIG. 1 is a sectional view showing an embodiment of the invention;

#FIG. 2 is a sectional view taken along the line A—A in FIG. 1;

#FIG. 3 is a sectional view taken along the line B—B in FIG. 1;

#FIG. 1 shows an embodiment of the present invention. In addition, the same portions as in FIG. 9 are given the same reference characters. An externally pressurized gas bearing in this embodiment comprises bearing sleeves 4, 5 and 6 fixed to a housing 3 by a suitable means, a main shaft 1 radially supported in a non-contact state through a fine bearing clearance by journal bearing sections 7 and 8 formed by the two bearing sleeves 4 and 5, the main shaft 1 being also axially supported in a non-contact state through a fine bearing clearance by a pair of thrust bearing sections 9 and 10 formed in that a thrust plate 2 integral with the main shaft 1 is held at its opposite surfaces between the two bearing sleeves 5 and 6.

#A spindle device having this externally pressurized gas bearing is provided with a drive source 22 coaxial with the main shaft 1, said drive source 22 having a motor rotor 11 integrally attached to the main shaft 1, thus rotating the main shaft 1 by a driving force produced by an electromagnetic force acting between it and a motor stator 12. As the motor, use is made of a brushless motor, such as a synchronous or inductive AC motor in order to make the best use of the feature of the externally pressurized gas bearing supporting the main shaft 1 in a non-contact state. In addition, in the case of using an AC servomotor, a sensor is required for detecting the angle of rotation of the main shaft 1, and a rotary encoder (not shown) is attached as by extending the main shaft 1 rightward in the drawing.

#The bearing sleeves 4 and 5 constituting the journal bearing sections 7 and 8 are provided with two gas feed rows 41a, 41b and 41c, 41d having pluralities of circumferentially equispaced fine gas feed holes 31a, 31b and 31c, 31d, respectively, that open to the bearing surface opposed to the main shaft 1. Further, the outer surface of the main shaft 1 is provided with circumferential grooves 18 in positions where they are opposed to the two gas feed rows 41a, 41b and 41c, 41d formed in the bearing sleeves 4 and 5, respectively. Such relatively simple construction increases the static stiffness of the journal bearing sections 7 and 8.