JPH07237069A - Static pressure bearing spindle - Google Patents

Abstract

PURPOSE:To enable the coaxial disposition of a displacement sensor to a hollow spindle and heighten the detecting accuracy of displacement by thrust of the spindle. CONSTITUTION:A contactless displacement sensor 20 of hollow cylindrical shape for detecting the displacement by thrust of a spindle 2 is disposed in a position coaxial with the spindle 2 and opposed to the rear end face of the thrust plate 5 provided at the spindle 2. The tip of a push rod 12 for moving a collet chuck 9 longitudinally pierces the hollow part of the contactless displacement sensor 20 so as to be inserted into the through hole 2a of the spindle 2. The contactless displacement sensor 20 is an eddy current type sensor formed of a cylindrical sensor core 20a formed of insulating material such as synthetic resin material, and a coil 20b formed of conductive material and mounted to the outer diameter of the sensor core 20a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle having a hollow main shaft such as a spindle with an automatic tool changing mechanism,
The present invention relates to means for detecting a displacement of the hollow main shaft due to a thrust force.

[0002]

2. Description of the Related Art In machining a small-diameter hole, there is a problem that the diameter of the tool is small and the tool is easily broken during machining. For this reason,
Conventionally, attempts have been made to detect or predict tool breakage by constantly monitoring the machining state.As one means of this, a displacement sensor is incorporated in the spindle to detect machining reaction force by the thrust displacement of the spindle. There is something to do. In particular, when the main shaft is supported by a static pressure gas bearing in a non-contact manner, vibration during rotation due to the bearing is very small, so even a minute machining reaction force can be detected as a thrust displacement of the main shaft. .

In order to detect such thrust displacement of the spindle with a displacement sensor with high accuracy, it is necessary to avoid the influence of the spindle shape error and whirling, and for that purpose, the displacement for detecting the displacement. The sensor is preferably arranged coaxially with the main axis.

[0004]

By the way, many spindles used in NC drilling machines and the like are provided with an automatic tool changing mechanism so that tools such as drills can be changed accurately and automatically. For example, the spindle shown in FIG. 9 (only the main spindle portion is shown) has a main spindle 31
Taper hole 3 provided at the tip (tool side) of the through hole 31a
The collet chuck 32 is attached to 1a1 so as to be movable back and forth, the tip of the push rod 33 is inserted from the rear end (counter tool side) of the through hole 31a, and the collet chuck 32 is pushed through the draw bar 34 connected to the rear end. By moving the rod 33 back and forth, the tool 35 can be held and released freely. That is, when the push rod 33 is moved forward by receiving compressed air pressure or the like, the collet chuck 32 is pushed forward through the draw bar 34 and the tool 35 is opened. On the other hand, the push rod 33
When is retracted, the collet chuck 32 is pulled backward by the elastic force of the elastic body 36 via the draw bar 34, and the tool 35 is gripped.

In the spindle having the automatic tool changing mechanism as described above, a pressing force is applied to the member (draw bar 34 in FIG. 9) arranged in the through hole of the main shaft from the side opposite to the tool (rear side). It is essential that the means (the push rod 33 in FIG. 9, but compressed air or the like may be used) is coaxially arranged behind the main shaft. Therefore, in such a spindle, a commonly used displacement sensor cannot be coaxially arranged with the spindle, and therefore,
The thrust displacement of the spindle could not be detected accurately.

Therefore, an object of the present invention is to enable the spindle having the hollow main shaft as described above to be coaxially arranged with the main shaft of the displacement sensor and to improve the detection accuracy of the displacement due to the thrust force of the main shaft. Is.

[0007]

SUMMARY OF THE INVENTION A hydrostatic bearing spindle of the present invention detects a hollow main shaft supported by a hydrostatic bearing in a housing in a radial direction and a thrust direction in a non-contact manner, and a displacement of the hollow main shaft due to a thrust force. And a non-contact displacement sensor for making a non-contact displacement sensor in the shape of a hollow cylinder, which is arranged coaxially with the hollow main shaft and opposite to the part of the hollow main shaft that is the target of detection. It was done.

As the non-contact displacement sensor, an eddy current type sensor having a hollow cylindrical sensor core made of an insulating material and a coil made of a conductive material and attached to the outer diameter of the sensor core may be used. it can.

The non-contact displacement sensor may be integrally provided with a dummy sensor and a dummy target. In this case, the dummy sensor is made of an electrically conductive material, and is an eddy current type equipped with a dummy coil attached to the outer diameter of the sensor core (of the non-contact displacement sensor) on the side opposite to the hollow main shaft side, and the dummy target is It may be formed of a conductive material and mounted on the end face of the sensor core on the side opposite to the hollow main shaft.

The sensor core of the non-contact displacement sensor can be formed of a synthetic resin material or a ceramic material.

Further, a collet chuck mounted in a taper hole portion provided in a part of the through hole of the hollow main spindle so as to be movable back and forth, a draw bar arranged in the through hole and connected to the collet chuck, and a draw bar opposed to the draw bar. In a hydrostatic bearing spindle including a push rod capable of applying a pressing force from the collet chuck side, the push rod may be configured to be guided back and forth on the inner diameter surface of the sensor core.

Further, a bearing surface of a thrust bearing that supports the hollow main shaft in a non-contact manner with respect to the housing in a thrust direction is communicated with a throttle hole of the thrust bearing, and a circumferential groove or a portion shallower than a thrust bearing gap under no load is provided. A circumferential groove may be formed.

[0013]

By making the non-contact displacement sensor a hollow cylinder, the non-contact displacement sensor can be arranged coaxially with the main shaft even in the case of a hollow main shaft. Therefore, the shape error of the main shaft, the shake, etc. do not affect the output of the non-contact displacement sensor, and the thrust displacement of the main shaft due to the thrust force applied from the outside can be accurately detected. Also,
As the non-contact displacement sensor, an eddy current type sensor including a hollow cylindrical sensor core formed of an insulating material and a coil formed of a conductive material and attached to the outer diameter of the sensor core is used. Since it can be composed of a simple sensor core and coil, it is easy to make it compact and hollow.

Generally, an eddy current displacement sensor may have a sensor output drift due to a temperature change in the sensor section and the detection circuit section. However, a non-contact displacement sensor is integrally provided with a dummy sensor and a dummy target. By taking the output difference between the contact displacement sensor and the dummy sensor, the influence of drift can be eliminated.

By forming the sensor core of the non-contact displacement sensor from a synthetic resin material or a ceramic material, the inner diameter of the sensor core can be used as a guide surface for other members.

The push rod capable of applying a pressing force from the side opposite to the collet chuck is guided to the draw bar connected to the collet chuck by the inner diameter surface of the sensor core so as to be movable back and forth, thereby simplifying the structure. it can.

By providing the bearing surface of the thrust bearing with the circumferential groove communicating with the throttle hole, most of the compressed gas flowing from the throttle hole into the thrust bearing gap flows along the circumferential groove,
Since the hollow main shaft is supported over the entire circumference, the load capacity in the thrust direction is significantly increased as compared to when there is no load. If air hammer is predicted to occur due to conditions such as the bearing area of the thrust bearing and the groove depth of the circumferential groove, it is necessary to reduce the volume of the entire groove by providing an independent partial circumferential groove for each throttle hole. This can be prevented.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the outer diameter surface of the main shaft 2 rotatably inserted in the housing 1 opposes the inner diameter surfaces of the bearing sleeves 3 and 4 through the journal bearing gap, and the main shaft 2 The end surface of the thrust plate 5 provided at the rear end of the bearing 2 faces the end surface of the bearing sleeve 4 and the bearing surface of the thrust bearing 6 via a thrust bearing gap.
When compressed gas (compressed air or the like) is supplied from the bearing air supply port 7 provided in the housing 1, the compressed gas passes through the air supply passage 8 provided in the housing 1 and the bearing sleeves 3 and 4 and the thrust bearing. From the throttle holes 3a, 4a and 4b, 6a of No. 6 into the journal bearing gap and the thrust bearing gap, the main shaft 2 is supported with respect to the housing 1 in the radial direction and the thrust direction in a non-contact manner. The bearing exhaust flowing out from the journal bearing gap and the thrust bearing gap is discharged to the outside of the spindle via an exhaust passage (not shown) provided in the housing 1.

The main shaft 2 is hollow and has a through hole 2a at the center thereof. The tip of the through hole 2a is a tapered hole portion 2a1, and the collet chuck 9 is attached to the inner diameter of the tapered hole portion 2a1 so as to be movable back and forth. The tip of the collet chuck 9 is divided into a plurality of parts by a plurality of slits (not shown) along the axis, and its outer diameter surface is a tapered surface 9 that matches the inner diameter surface of the tapered hole 2a1.
It is a. Therefore, when the collet chuck 9 is pulled rearward, the collet chuck 9 is pressed from the inner diameter surface of the tapered hole 2a1 and its tip portion is reduced in diameter, and when it is pushed forward along the tapered hole portion 2a1, its tip portion is enlarged. The collet chuck 9 is normally urged rearward by the elastic force of an elastic body 11 such as a disc spring via a draw bar 10 connected to the rear end thereof, and is drawn into the tapered hole 2a1 portion.

The rear end of the through hole 2a of the main shaft 2 is open, and the tip of the push rod 12 penetrates through this opening and enters the through hole 2a. Push rod 12
Is normally biased rearward by the elastic force of the compression spring 13, and is held at a position where its tip does not come into contact with the rear end of the drawbar 10. When compressed gas is supplied from the air supply port 14 provided at the rear end of the housing 1, the push rod 12 moves forward against the elastic force of the compression spring 13 to come into contact with the rear end of the drawbar 10, and the compression spring The collet chuck 9 is pushed forward through the drawbar 10 by advancing against the elastic force of the elastic body 13 and the elastic body 11. As a result, the diameter of the collet chuck 9 is expanded, and the tool 15 gripped by the collet chuck 9 is released and becomes detachable. When the supply of the compressed gas from the air supply port 14 is stopped, the push rod 12 is pushed by the elastic force of the compression spring 13 to the drawbar 10.
Retreat to a position where it does not come into contact with. Then, the collet chuck 9 is pulled rearward through the drawbar 10 by the elastic force of the elastic body 11. As a result, the collet chuck 9 is reduced in diameter and the tool 15 is gripped.

Further, a squirrel cage rotor 16 is integrally provided on the main shaft 2, and a stator 17 is fixed to the inner diameter of the housing 1 so as to face the rotor 16. Stator 17
Spindle 2 rotates at high speed when an electric current is applied to
The collet chuck 9, the tool 15, the draw bar 10, and the elastic body 11 rotate together at high speed with the main shaft 2.

The hollow cylindrical non-contact displacement sensor 20 for detecting the displacement of the main shaft 2 due to the thrust force is disposed coaxially with the main shaft 2 and at a position facing the rear end surface of the thrust plate 5 provided on the main shaft 2. Has been done. The tip of the push rod 12 that moves the collet chuck 9 back and forth penetrates the hollow portion of the non-contact displacement sensor 20 and is inserted into the through hole 2 a of the main shaft 2. In this embodiment, as the non-contact displacement sensor 20, a cylindrical sensor core 20a made of an insulating material such as a synthetic resin material and a sensor core 20 made of a conductive material are used.
An eddy current type coil including a coil 20b mounted on the outer diameter of a is used. The sensor core 20a is fixed to the housing 1 with screws or the like. By using such a non-contact displacement sensor 20, it is possible to arrange the non-contact displacement sensor 20 coaxially with the main shaft 2 even in the case of the hollow main shaft 2 (the push rod 12 is inserted from the rear end). Becomes Therefore, the shape error such as the inclination of the thrust plate 5 with respect to the thrust bearing 6 and the runout of the main shaft 2 do not affect the output of the non-contact displacement sensor 20, and the thrust displacement of the main shaft 2 due to the thrust force applied from the outside is accurately detected. can do. Further, by using the eddy current type sensor as described above as the non-contact displacement sensor 20, the sensor unit can be composed of the simple sensor core 20a and the coil 20b, so that it is easy to be compact and hollow.

In the embodiment shown in FIG. 2, the circumferential surface of the thrust bearing 6 shown in FIG. 1 has a circumferential groove 6b communicating with the throttle hole 6a.
Is provided. The reason why the circumferential groove 6b is provided is as follows. Generally, when the output of the displacement gauge is used to detect the thrust force, the resolution for the thrust force is determined by (rigidity of thrust bearing x resolution for displacement of the displacement gauge).
In order to detect the thrust force with high accuracy, the rigidity of the thrust bearing (thrust rigidity) should be small. To reduce the thrust rigidity, reduce the diameter of the throttle hole,
A means for reducing the number of throttle holes and increasing the thrust bearing gap may be considered. However, if the diameter of the throttle holes is reduced or the number thereof is reduced, the load capacity may be reduced more than necessary, and the spindle force and the thrust bearing may come into contact with each other due to the thrust force during processing. Further, if the thrust bearing gap is made too large, there is a problem in that the consumption of compressed air increases. Therefore, in this embodiment, by providing the circumferential groove 6b on the bearing surface of the thrust bearing 6, it is possible to reduce the thrust rigidity without causing a decrease in load capacity during machining and an increase in compressed air consumption. It was done. The groove depth of the circumferential groove 6b is made shallower than the thrust bearing gap under no load, and the thrust bearing gap is defined by the ratio of thrust rigidity (resolution of necessary force) / (resolution for displacement of displacement gauge). Is also set to a value that is small. Aperture 6a
Is about 3 to 6 (4 in this embodiment), which is less than normal (about 7 to 8). When there is no load, the circumferential groove 6b has a smaller groove depth than the thrust bearing gap, so the influence of the circumferential groove 6b is small. However, when thrust force is applied from the outside to reduce the thrust bearing gap, the circumferential groove 6b is less affected. Since the groove depth of 6b becomes relatively larger than the thrust bearing gap, the effect of the circumferential groove 6b becomes remarkable. That is, most of the compressed gas flowing from the throttle hole 6a of the thrust bearing 6 into the thrust bearing gap flows along the circumferential groove 6b, and the thrust plate 5 is supported over the entire circumference, so that there is no load capacity in the thrust direction. Significantly increased compared to under load. On the other hand, since the number of the throttle holes 6a is smaller than usual, the increase in gas consumption is small. Therefore, according to the configuration of this embodiment, a minute thrust force can be accurately detected by reducing the thrust rigidity, and there is no fear of causing adverse effects such as a decrease in load capacity and an increase in gas consumption.

3 to 5 show the effect of the above-mentioned circumferential groove 6b by calculation results. 3 to 5, A is a product of this embodiment (circumferential groove: provided, throttle hole: 4),
B and C show the results of the comparative product, respectively.
Comparative product B (circumferential groove: none, throttle hole: 4), comparative product C
Is (circumferential groove: none, throttle hole: 24). The thrust bearing clearances under no load are all S.

As shown in FIG. 3, the thrust load capacity of the product A of the present embodiment rapidly increased from the vicinity of the thrust bearing gap being smaller than the predetermined value, and showed a value equal to or higher than that of the comparative product C. . Further, as shown in FIGS. 4 and 5, the thrust rigidity and gas consumption of the product A of this example were slightly larger than those of the comparative product B, and were considerably smaller than those of the comparative product C.

The number of the throttle holes 6a is reduced so that the circumferential groove 6
If b is provided, unstable self-excited vibration (air hammer) may easily occur. When the occurrence of the air hammer is predicted depending on the conditions such as the bearing area of the thrust bearing 6 and the groove depth of the circumferential groove 6b, as shown in FIG. 6, an independent partial circumferential groove 6b ′ is provided for each throttle hole 6a. This can be prevented by providing the groove and reducing the volume of the entire groove.

In the embodiment shown in FIG. 7, a separate sensor target 21 is integrally mounted on the rear end surface of the thrust plate 5 of the main shaft 2, and the non-contact displacement sensor 20 is replaced by the dummy sensor 2.
0'and the dummy target 22 are integrally provided. The sensor target 21 is a material having physical properties suitable as a target of an eddy current displacement sensor, for example, SU.
It is formed of S310S material or the like. The dummy sensor 20 ′ has the same sensor core 2 as the non-contact displacement sensor 20.
0a and a dummy coil 20b 'mounted on the outer diameter of the rear end of the sensor core 20a. The dummy target 22 is made of the same material as the sensor target 21, and is attached to the rear end surface of the sensor core 20a. The sensor core 2
A hollow cylindrical guide 25 for guiding the push rod 12 back and forth is attached to the inner diameter of 0a.

The main shaft 2 must be made of a magnetic material in order to integrally provide the squirrel cage rotor 16, but this is not necessarily suitable as a target of the eddy current displacement sensor.
There is a concern that the sensor output may fluctuate due to the unevenness of the material, or the electric resistance may be large and the sensitivity of the displacement sensor may decrease. The sensor target 21 is a separate part from the spindle 2,
By making the material freely selectable, the sensitivity of the non-contact displacement sensor 20 can be increased. Further, in the eddy current type displacement sensor, the sensor output may drift due to the temperature change of the sensor unit and the detection circuit unit, but the detection circuit is connected to each of the non-contact displacement sensor 20 and the dummy sensor 20 ′, and the output difference between them By taking, it is possible to eliminate the influence of the drift.

In the embodiment shown in FIG. 8, the push rod 12 is guided by the inner diameter surface of the sensor core 20a so as to be movable back and forth. In this case, the material of the sensor core 20a needs to be an insulator and has excellent wear resistance and slidability, and ceramics, nylon, synthetic resin such as fluororesin and polyacetal are suitable.

The present invention can be applied to a general spindle having a hollow main shaft (having means for applying a pressing force from the opposite tool side to a member arranged in a through hole of the main shaft). It is not limited to the configuration of the embodiment. For example, it can be similarly applied to a spindle or the like having a configuration in which compressed air or the like is used instead of the push rod 12 (a configuration in which compressed air or the like is supplied to the through hole of the main shaft from the opposite tool side to operate the drawbar). Further, as a supporting means for the housing of the main shaft, a non-contact supporting means such as a hydrostatic bearing or a magnetic bearing, or a spindle using contact supporting means such as a general bearing can be similarly applied.
And in these cases, the same effects as the above can be obtained.

[0032]

The present invention has the following effects.

(1) Since the non-contact displacement sensor has a hollow cylindrical shape, the non-contact displacement sensor can be arranged coaxially with the main shaft even in the case of the hollow main shaft. Therefore, the shape error of the main shaft, the shake, etc. do not affect the output of the non-contact displacement sensor, and the thrust displacement of the main shaft due to the thrust force applied from the outside can be accurately detected. (2) By using, as the non-contact displacement sensor, an eddy current type sensor including a hollow cylindrical sensor core made of an insulating material and a coil made of a conductive material and attached to the outer diameter of the sensor core. Since the sensor unit can be composed of a simple sensor core and coil, it is easy to make it compact and hollow.

(3) The influence of drift can be eliminated by integrally providing the non-contact displacement sensor with the dummy sensor and the dummy target and taking the output difference between the non-contact displacement sensor and the dummy sensor.

(4) By forming the sensor core of the non-contact displacement sensor from a synthetic resin material or a ceramic material, the inner diameter of the sensor core can be used as a guide surface for other members. (5) The structure can be simplified by adopting a structure in which a push rod capable of applying a pressing force from the side opposite to the collet chuck is guided to the draw bar connected to the collet chuck by the inner diameter surface of the sensor core so as to be movable back and forth. it can.

(6) By reducing the load capacity by communicating with the throttle hole on the bearing surface of the thrust bearing and providing a circumferential groove or partial circumferential groove shallower than the thrust bearing gap when there is no load,
It is possible to accurately detect a minute thrust force by reducing thrust rigidity without causing an adverse effect such as an increase in gas consumption. When air hammer is predicted to occur due to conditions such as the bearing area of the thrust bearing and the groove depth of the circumferential groove, an independent partial circumferential groove is provided for each throttle hole to reduce the volume of the entire groove. This can be prevented.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a spindle according to an embodiment of the present invention.

FIG. 2 is a plan view showing a thrust bearing surface of a spindle according to another embodiment of the present invention.

3 is a diagram showing the results of a comparative test of the relationship between thrust bearing gap and thrust load capacity in the spindle shown in FIG.

4 is a diagram showing the results of a comparative test of the relationship between thrust bearing clearance and thrust rigidity in the spindle shown in FIG.

5 is a diagram showing the results of a comparative test of the relationship between thrust bearing gap and gas consumption in the spindle shown in FIG.

FIG. 6 is a plan view showing a thrust bearing surface of a spindle according to another embodiment of the present invention.

FIG. 7 is a sectional view showing a spindle according to another embodiment of the present invention.

FIG. 8 is a sectional view showing a spindle according to another embodiment of the present invention.

FIG. 9 is a cross-sectional view showing a main shaft portion in a conventional spindle device.

[Explanation of symbols]

 1 housing 2 hollow main shaft 3 bearing sleeve 4 bearing sleeve 5 thrust plate 6 thrust bearing 6a throttle hole 6b circumferential groove 6b 'partial circumferential groove 20 non-contact displacement sensor 20a sensor core 20b coil 20' dummy sensor 20b 'dummy coil 22 dummy target

Claims (6)

[Claims] 1. A hollow main shaft supported by a hydrostatic bearing in a housing in a non-contact manner in a radial direction and a thrust direction,
A non-contact displacement sensor for detecting the displacement of the hollow main shaft due to the thrust force, wherein the non-contact displacement sensor is a hollow cylinder, which is coaxial with the hollow main shaft and which is hollow. A hydrostatic bearing spindle, which is arranged so as to face a detection target portion of a main shaft. 2. The eddy current type non-contact displacement sensor comprises a hollow cylindrical sensor core made of an insulating material and a coil made of a conductive material and attached to the outer diameter of the sensor core. The hydrostatic bearing spindle of claim 1, wherein: 3. The hydrostatic bearing spindle according to claim 2, wherein the non-contact displacement sensor is integrally provided with a dummy sensor and a dummy target, wherein the dummy sensor is made of a conductive material, and the hollow hollow of the sensor core. It is an eddy current type equipped with a dummy coil mounted on the outer diameter of the spindle side,
The hydrostatic bearing spindle, wherein the dummy target is made of a conductive material and is mounted on the end surface of the sensor core on the side opposite to the hollow main shaft. 4. The hydrostatic bearing spindle according to claim 2, wherein the sensor core of the non-contact displacement sensor is formed of a synthetic resin material or a ceramic material. 5. A collet chuck mounted in a tapered hole portion provided in a part of the through hole of the hollow spindle so as to be movable back and forth, and a draw bar arranged in the through hole and connected to the collet chuck. The hydrostatic bearing spindle according to claim 4, further comprising: a push rod capable of applying a pressing force to the draw bar from the side opposite to the collet chuck, and the push rod is guided by an inner diameter surface of the sensor core so as to be movable back and forth. . 6. The bearing surface of a thrust bearing that supports the hollow main shaft in a non-contact manner in the thrust direction with respect to the housing, communicates with a throttle hole of the thrust bearing, and has a circumferential groove shallower than a thrust bearing gap under no load or 2. The hydrostatic bearing spindle according to claim 1, wherein a partial circumferential groove is formed.