JPH0680023U - Variable bearing diameter air bearing - Google Patents

Abstract

(57) [Abstract] [Object] The present invention relates to a variable bearing diameter type air bearing, which prevents the rotational center position of the rotating shaft from changing while keeping the bearing rigidity constant, and prevents the rotating shaft and the bearing from being seized. An object of the present invention is to provide a variable bearing diameter type air bearing capable of preventing the occurrence of the above. [Structure] A plurality of pads 13 provided on the outer peripheral portion of the rotary shaft 4 so as to face the rotary shaft 4 and divided along the circumference of the rotary shaft 4, and provided on the plurality of pads 13, respectively. ,
A drive mechanism for moving the pads 13 in the radial direction of the rotary shaft 4 is provided.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a variable bearing diameter type air bearing, and more particularly to a variable bearing diameter type air bearing in which the diameter of the bearing can be varied according to the rotation speed of a rotating shaft.

[0002]

[Prior art]

 Generally, an air bearing rotates by supplying compressed air from a compressed air source to a very narrow (20 to 30 μm) space formed between the rotating shaft and a bearing that rotatably supports the rotating shaft. The rotating shaft therein is supported by the compressed air in a non-contact manner.

By the way, since this rotating shaft expands under the influence of heat and centrifugal force generated during high-speed rotation, the gap between the bearing and the bearing becomes small, and a seizure accident or the like may occur due to contact with the bearing. It may happen. In order to eliminate such problems, it is possible to increase the clearance between the rotary shaft and the bearing in a perfect circular bearing, but if this clearance is large, not only the performance will decrease, but also due to whirling phenomenon. The stable rotation limit is reduced, making it difficult to use at higher speeds.

As a means for avoiding the whirling phenomenon and enabling rotation at a higher speed in this way, for example, a partial arc dynamic pressure bearing in which the bearing is divided into three along the radial direction of the rotating shaft has been proposed. . This bearing supports a divided partial arc bearing (hereinafter simply referred to as a pad) so that it can be tilted, and a pad that is located in the vertical direction of the rotating shaft is supported by a spring so that it can move in the semi-radial direction of the rotating shaft. Has become.

In this bearing, when the rotating shaft expands, the pads incline and the pads in the vertical direction move against the biasing force of the spring to increase the allowable diameter. It is possible to prevent seizure due to contact between the rotating shaft and the bearing.

[0006]

[Problems to be solved by the device]

 However, in such a conventional partial circular arc dynamic pressure bearing, the divided pads are supported so as to be tiltable, and the pads located in the vertical direction of the rotary shaft can be moved in the radial direction of the rotary shaft. Since it was supported by springs, it was possible to allow the rotation shaft to expand, but in the process the center of the rotation shaft changed.

Therefore, when this method is applied to a spindle of a processing machine, the rotational center position of a tool or a grindstone attached to the spindle changes with the expansion of the rotary shaft, and the workpiece is accurately machined to a predetermined size. There was a problem that I could not do it. Therefore, according to the invention of claim 1, the diameter of the bearing is varied so that the distance between the rotary shaft and the bearing becomes constant according to the expansion of the rotary shaft, so that the rigidity of the rotary shaft can be kept constant while keeping the bearing rigidity constant. It is an object of the present invention to provide a variable bearing diameter air bearing that can prevent the rotation center position from changing and also prevent the seizure accident of the rotating shaft and the bearing from occurring.

[0008]

[Means for Solving the Problems]

 In order to achieve the above object, a device according to claim 1 has a fixed case, a rotary shaft rotatably housed in the fixed case, a cylindrical motor rotor mounted on an inner circumference of the rotary shaft, and one end. Part is attached to the end of the fixed case, and the other end is provided on the fixed shaft inserted through the inner circumference of the rotating shaft and the outer circumference of the fixed shaft facing the motor rotor. A motor stator that constitutes a built-in motor that rotates the rotating shaft, a plurality of bearings that are provided on the outer peripheral portion of the rotating shaft so as to face the rotating shaft, and that are divided along the circumference of the rotating shaft, and the plurality of bearings. Are installed on the fixed case, the drive mechanism, and the bearing by moving these bearings along the radial direction of the rotating shaft to change the distance between the outer peripheral part of the rotating shaft and the inner peripheral part of the bearing. Formed, A compressed air from a constant air source is supplied to the space between the outer peripheral portion of the rotating shaft and the inner peripheral portion of the bearing to provide an air hole capable of supporting the rotating rotating shaft. I am trying.

[0009]

[Action]

 In the invention according to claim 1, a plurality of bearings, which are provided on the outer peripheral portion of the rotary shaft so as to face the rotary shaft and are divided along the circumference of the rotary shaft, and the plurality of bearings are provided respectively. Further, a drive mechanism is provided which can change the distance between the outer peripheral portion of the rotating shaft and the inner peripheral portion of the bearing by moving these bearings in the radial direction of the rotating shaft.

Therefore, when the rotating shaft expands during high-speed rotation, the bearing is moved outward in the radial direction of the rotating shaft, so that the distance between the rotating shaft and the bearing is kept constant. For this reason, the center position of the rotating shaft does not change during the expansion process, the shaft is supported stably, and no accidental seizure of the rotating shaft and bearing occurs. As a result, when this bearing is applied to the spindle of a machine tool, the work is accurately machined to a predetermined size.

Further, during machining of the work, the gap between the bearing and the rotary shaft is controlled to be optimal, and the gap between the bearing and the rotary shaft is slightly widened to prevent wind loss except during machining. Then, the rotating shaft can be controlled so as not to easily generate heat.

[0012]

【Example】

 Hereinafter, the present invention will be described with reference to the drawings. 1 and 2 are views showing an embodiment of a variable bearing diameter type air bearing according to the invention described in claim 1, and showing an example in which the invention is applied to a spindle of a machine tool. First, the configuration will be described. 1 and 2, reference numeral 1 denotes a cylindrical main body case, and a front side plate 2 and a rear side plate 3 are fixed to the front end and the rear end of the case 1, respectively. Closed by 3. The body case 1 and the front and rear side plates 2 and 3 form a fixed case.

A rotary shaft 4 is housed inside the fixed case 1, and a grinding tool 5 is screwed and fixed to a tip end portion of the rotary shaft 4, and the grinding tool 5 extends outward from the front plate 2. Along with protruding, a grinding wheel 6 is attached to the tip. A concave portion 4a is formed inside the rotary shaft 4, and a cylindrical motor rotor 7 is attached to the concave portion 4a, that is, on the inner peripheral portion of the rotary shaft 4. The tip (the other end) of the fixed shaft 8 is inserted into the recess 4a, and the end (one end) of the fixed shaft 8 is fixed to the rear side plate 3.

A motor stator 9 is attached to the outer periphery of the tip of the fixed shaft 8 so as to face the motor rotor 7 and form a built-in motor in combination with the motor rotor 7. The motor stator 9 is not shown in the drawings. As a result of being energized via the wiring 10, the rotating shaft 4 is rotated by the electromagnetic interaction generated with the motor rotor 7.

Further, a flange portion 4b is formed on the rotary shaft 4 on the front side plate 2 side. The flange portion 4b is inserted into the thrust bearing 11, and a narrow space is provided between the bearing 11 and the flange portion 4b. A space 12 is formed. A supply hole 11a is formed in the thrust bearing 11, and the supply hole 11a communicates with the supply hole 1a formed in the main body case 1. The supply hole 1a communicates with a compressed air source (not shown), and compressed air is supplied to the supply hole 11a via the supply hole 1a.

Therefore, compressed air from the compressed air source is supplied to the narrow space 12 between the flange portion 4b and the bearing 11, and the rotating shaft 4 in rotation does not contact the thrust bearing 11 by this compressed air. It is axially supported in the thrust direction. Further, an exhaust hole 1b communicating with the space 12 is formed in the main body case 1, and the exhaust hole 1b is adapted to discharge the compressed air supplied to the space 12 to the outside.

On the other hand, a plurality of tilting pads 13 as bearings are provided on the outer peripheral portion of the rotary shaft 4 so as to face the rotary shaft 4, and the pads 13 extend along the circumference of the rotary shaft 4. It is divided. The tip of a shaft member 14 is attached to the pad 13, and the shaft member 14 is screwed and supported by a support member 15 and a nut 16. The support member 15 is slidably inserted into the opening 1c formed in the main body case 1, and the support member 15 is attached to the main body case 1 by a leaf spring 17 so as to be outside the radial direction of the rotary shaft 4. Is urged towards Further, an eccentric cam 18 is in contact with the base end of the shaft member 14, and the eccentric cam 18 is housed in a storage case 19 fixed to the main body case 1, and is mounted on a bearing 20 fixed to the storage case 19. A cam shaft 18a is pivotally supported.

The cam shaft 18 is connected to a control means (not shown), and the control means rotates the cam shaft 18 a according to the number of rotations of the rotary shaft 4, and the shaft member 14 is main body via the eccentric cam 18. It is adapted to slide with respect to the case 1. The pad 13 moves along the radial direction of the rotary shaft 4 as the shaft member 14 slides, and the distance between the outer peripheral portion of the rotary shaft 4 and the inner peripheral portion of the pad 13 is made variable. There is. The shaft member 14, the support member 15, the leaf spring 17, the eccentric cam 18 and the control means constitute a drive mechanism.

A supply hole (air hole) 13 a is formed in the pad 13, and the supply hole 13 a is a narrow space portion 21 formed between the outer peripheral portion of the rotary shaft 4 and the inner peripheral portion of the pad 13. Is in communication with. Further, the shaft member 14 and the support member 15 are also provided with supply holes (air holes) 14a and 15a, respectively, and these supply holes 14a and 15a communicate with the supply hole 13a of the pad 13.

Further, the supply hole 15a of the support member 15 communicates with the supply hole 1d formed in the main body case 1, and the supply hole 1d communicates with the above-mentioned compressed air source not shown. Therefore, the compressed air from the compressed air source is supplied to the space portion 21 via the supply holes 1d, 15a, 14a and 13a, and the rotating shaft 4 in rotation is padded by the static pressure bearings by this compressed air. Is supported in the radial direction without contact.

Next, the operation will be described. When the motor stator 9 is energized, a rotational driving force is applied to the rotary shaft 4 by electromagnetic interaction between the stator 9 and the rotor motor 7, and the rotary shaft 4 rotates. At this time, the grinding wheel 6 of the polishing tool 5 is pressed against a work (not shown) to perform a predetermined grinding process on the work.

At this time, compressed air is supplied from the compressed air source to the space portion 12 through the supply holes 1a and 11a, and compressed air is supplied to the space portion 21 through the supply holes 1d, 15a, 14a and 13a. Then, the rotary shaft is supported by the compressed air in the thrust bearing 11 and the pad 13 in a non-contact manner in the thrust direction and the radial direction, so that the rotary shaft 4 can be stably rotated.

Further, while the rotating shaft 4 is rotating at a low speed, since the rotating shaft 4 is at a low temperature and a large centrifugal force is not generated, the outer peripheral portion of the rotating shaft 4 and the inner peripheral portion of the pad 13 are. The control means are activated to maintain the distance between the parts at about 20-30 μm. That is, when the control means detects that the rotation speed of the rotation shaft 4 is lower than the predetermined rotation speed, the control means rotates the cam shaft 18a in the predetermined direction.

At this time, the eccentric cam 18 moves the shaft member 14 and the support member 15 inward in the radial direction of the rotary shaft 4 against the biasing force of the leaf spring 17, and the outer peripheral portion of the rotary shaft 4 and the pad 13 are moved. The distance between the inner circumference is maintained at about 20-30 μm. Therefore, the rotational center position of the rotary shaft 4 does not change during low-speed rotation, the shaft is stably supported, and the accidental burning of the rotary shaft 4 and the pad 13 does not occur.

On the other hand, as the rotation speed of the rotating shaft 4 increases, the rotating shaft 4 becomes hot and a large centrifugal force is generated. Therefore, the rotating shaft 4 expands, and the amount of expansion of the centrifugal force is several tens μm. Can be reached and even exceeded. At this time, when the control means detects that the rotation speed of the rotation shaft 4 is higher than the predetermined rotation speed, the control means rotates the cam shaft 18a in the predetermined direction according to the expansion amount of the rotation shaft 4. At this time, the shaft member 14 and the support member 15 are moved outward in the radial direction of the rotary shaft 4 urged by the leaf springs 17 so that the distance between the outer peripheral portion of the rotary shaft 4 and the inner peripheral portion of the pad 13 is reduced by about 10. It is maintained at 20-30 μm.

Therefore, the rotation center position of the rotary shaft 4 does not change when shifting from the low rotation speed to the high speed rotation, and the rotation shaft 4 is stably supported, and the burning accident of the rotation shaft 4 and the pad 13 occurs. Does not occur. As a result, the work can be accurately machined to a predetermined size. As described above, in this embodiment, a plurality of pads 13 provided on the outer peripheral portion of the rotary shaft 4 so as to face the rotary shaft 4 and divided along the circumference of the rotary shaft 4, and the plurality of pads 13 are provided. A drive mechanism that is provided in each pad 13, and that moves the pads 13 in the radial direction of the rotary shaft 4 to change the distance between the outer peripheral portion of the rotary shaft 4 and the inner peripheral portion of the pad 13, Since the pad 13 is provided, it is possible to maintain a constant distance between the rotary shaft 4 and the pad 13 by moving the pad 13 radially outward of the rotary shaft 4 when the rotary shaft 4 expands at high speed. it can.

Therefore, the center position of the rotary shaft 4 can be prevented from changing, the bearing rigidity can be made constant, and the shaft can be stably supported, and the rotary shaft 4 and the pad 13 can be stably supported. It is possible to prevent a burning accident from occurring. As a result, the work can be accurately machined to a predetermined size. Also, when machining the workpiece, the gap between the pad 13 and the rotary shaft 4 is controlled to be optimal, and the gap between the pad 13 and the rotary shaft 4 is slightly widened to prevent wind loss except during machining. Then, the rotating shaft 4 can be controlled so as not to easily generate heat.

Although the eccentric cam 18 and the like are provided as the drive mechanism in this embodiment, the invention is not limited to this, and the piezoelectric actuator may be used or the pad 13 may be moved by using the wedge mechanism. good. Further, a plurality of sensors for measuring the gap between the pad 13 and the rotary shaft 4 are provided, and by detecting the eccentricity of the rotary shaft with respect to an external force by the sensors, the pad 13 is controlled so as to cancel it. Is also good. By doing so, the apparent rigidity of the rotary shaft 4 can be improved.

[0029]

According to the first aspect of the invention, when the rotating shaft expands at the time of high speed rotation, the bearing is moved outward in the radial direction of the rotating shaft so that the distance between the rotating shaft and the bearing is constant. Can be maintained at. Therefore, the center position of the rotating shaft can be prevented from changing, the bearing rigidity can be kept constant, the shaft can be stably supported, and the seizure accident of the rotating shaft and the bearing can be prevented. Can be prevented. As a result, when this bearing is applied to a spindle of a machine tool, a work can be accurately machined to a predetermined size. When machining a workpiece, the clearance between the bearing and the rotating shaft is controlled to be optimal, and when not machining, the clearance between the bearing and the rotating shaft is slightly widened to prevent wind loss. Can be controlled so as not to generate heat easily.

[Brief description of drawings]

FIG. 1 is a sectional view of a spindle of a machine tool body having a variable bearing diameter type air bearing according to a first aspect of the present invention.

FIG. 2 is a sectional view taken along line AA in FIG.

[Explanation of symbols]

 1 Body case (fixed case) 1d, 13a, 14a, 15a Supply hole (air hole) 2 Front plate (fixed case) 3 Rear plate (fixed case) 4 Rotating shaft 7 Motor rotor 9 Motor stator 13 Pad (bearing) 14 Shaft member (Drive mechanism) 15 Support member (Drive mechanism) 17 Leaf spring (Drive mechanism) 18 Eccentric cam (Drive mechanism) 21 Space

Claims (1)

[Scope of utility model registration request] 1. A fixed case, a rotary shaft rotatably housed in the fixed case, a cylindrical motor rotor mounted on the inner circumference of the rotary shaft, and one end portion mounted on an end portion of the fixed case. At the same time, the other end of the fixed shaft is inserted into the inner peripheral portion of the rotating shaft, and the motor stator is provided on the outer peripheral portion of the fixed shaft facing the motor rotor and constitutes a built-in motor that is combined with the motor rotor to rotate the rotating shaft. And provided on the outer peripheral portion of the rotary shaft so as to face the rotary shaft,
A plurality of bearings divided along the circumference of the rotary shaft, and the plurality of bearings respectively provided on the plurality of bearings. By moving these bearings in the radial direction of the rotary shaft, the outer peripheral portion of the rotary shaft and the bearing A drive mechanism that changes the distance of the inner circumference, a fixed case, a drive mechanism, and a bearing that are formed to supply compressed air from a specified air source to the space between the outer circumference of the rotating shaft and the inner circumference of the bearing. And an air hole capable of supporting the rotating shaft during rotation, and a variable bearing diameter type air bearing.