JP3615779B2 - Hydrostatic bearing spindle - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a means for detecting a displacement due to a thrust force of a hollow main shaft in a spindle having a hollow main shaft such as a spindle with an automatic tool change mechanism.
[0002]
[Prior art]
In small diameter drilling, there is a problem that the tool is easily broken because of the small diameter of the tool. For this reason, attempts have been made to detect or predict tool breakage by constantly monitoring the machining state. As one means, a displacement sensor is incorporated in the spindle, and machining reaction force is applied to the thrust of the spindle. Some are detected by displacement. In particular, when the main shaft is supported in a non-contact manner by a static pressure gas bearing or the like, vibration during rotation caused by the bearing is very small, so even a small machining reaction force can be detected as a thrust displacement of the main shaft. .
[0003]
In order to accurately detect the thrust displacement of the main shaft with the displacement sensor, it is necessary to avoid the influence of the main shaft shape error, run-out, etc. For this purpose, the displacement sensor for detecting the displacement is the main shaft. Are preferably arranged coaxially with each other.
[0004]
[Problems to be solved by the invention]
By the way, many spindles used for NC drilling machines are equipped with an automatic tool changing mechanism so that a tool such as a drill can be exchanged accurately and automatically. For example, in the spindle shown in FIG. 9 (only the main shaft portion is shown), the collet chuck 32 is mounted in a tapered hole portion 31a1 provided at the tip (tool side) of the through hole 31a of the main shaft 31 so as to be movable back and forth. The tip of the push rod 33 is inserted from the rear end (on the opposite tool side) of the through hole 31a, and the collet chuck 32 is moved back and forth by the push rod 33 via the draw bar 34 connected to the rear end, thereby holding the tool 35・ Open freely. That is, when the push rod 33 is advanced by receiving compressed air pressure or the like, the collet chuck 32 is pushed forward via the draw bar 34 and the tool 35 is released. On the other hand, when the push rod 33 is retracted, the collet chuck 32 is pulled backward through the draw bar 34 by the elastic force of the elastic body 36, and the tool 35 is gripped.
[0005]
In a spindle equipped with an automatic tool change mechanism as described above, a pressing means for applying a pressing force from the side opposite to the tool (rear side) to a member (drawbar 34 in FIG. 9) disposed in the through hole of the main shaft (see FIG. 9). In FIG. 9, the push rod 33 is used, but compressed air or the like may be used. Therefore, with such a spindle, a displacement sensor that is normally used cannot be coaxially arranged with the main shaft, so that the thrust displacement of the main shaft cannot be accurately detected.
[0006]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to allow a spindle having a hollow main shaft as described above to be arranged coaxially with the main shaft of a displacement sensor and to increase the detection accuracy of displacement due to the thrust force of the main shaft.
[0007]
[Means for Solving the Problems]
The hydrostatic bearing spindle of the present invention is movable back and forth in a hollow main shaft that is supported in a radial and thrust non-contact manner by a hydrostatic bearing on a housing, and a tapered hole provided at the tip of a through hole of the hollow main shaft. The collet chuck mounted on the through hole, the draw bar disposed in the through hole and connected to the rear end of the collet chuck, and inserted into the through hole from the rear end opening of the through hole, can apply a pressing force to the draw bar from the rear. A push rod and a non-contact displacement sensor for detecting displacement due to the thrust force of the hollow main shaft, wherein the non-contact displacement sensor is selected from nylon, fluororesin, and polyacetal A hollow cylindrical sensor core made of a material or a ceramic material, and a coil formed of a conductive material and attached to the outer diameter of the sensor core. The eddy current type non-contact displacement sensor is arranged coaxially with the hollow main shaft and facing the detection target portion of the hollow main shaft, and moves the push rod back and forth on the inner diameter surface of the sensor core. It will guide you freely.
[0008]
The non-contact displacement sensor may be integrally provided with a dummy sensor and a dummy target. In this case, the dummy sensor is formed of a conductive material, and is an eddy current type including a dummy coil attached to the outer diameter of the rear end of the sensor core (of the non-contact displacement sensor), and the dummy target is formed of a conductive material. is formed, it may be deemed to have been attached to the end plane of the sensor core.
[0009]
Furthermore, the circumferential surface of the thrust bearing that supports the hollow main shaft in a non-contact manner in the thrust direction with respect to the housing is communicated with the throttle hole of the thrust bearing, and the circumferential groove or partial circumferential groove is shallower than the thrust bearing clearance at no load. May be formed.
[0010]
[Action]
By making the non-contact displacement sensor have a hollow cylindrical shape, the non-contact displacement sensor can be arranged coaxially with the main shaft even in the case of a hollow main shaft. Therefore, the main shaft shape error, vibration, and the like do not affect the output of the non-contact displacement sensor, and the main shaft thrust displacement due to the thrust force applied from the outside can be detected with high accuracy.
[0011]
Further, as a non-contact displacement sensor, a hollow cylindrical sensor core made of a synthetic resin material or ceramic material selected from nylon, fluororesin, and polyacetal, and a conductive material, the outer diameter of the sensor core By using an eddy current type composed of a mounted coil, the sensor unit can be composed of a simple sensor core and coil, so that it is easy to make it compact and hollow. In addition, the push rod can be moved back and forth smoothly on the inner surface of the sensor core made of the above-mentioned synthetic resin material or ceramic material, which has excellent wear resistance and slidability. The operation can be made possible, and at the same time, the structure can be simplified.
[0012]
In general, an eddy current type displacement sensor may cause the sensor output to drift due to temperature changes in the sensor unit and the detection circuit unit. However, a non-contact displacement sensor is provided with a dummy sensor and a dummy target as a unit. By taking the output difference between the sensor and the dummy sensor, the influence of drift can be eliminated.
[0013]
By providing a circumferential groove communicating with the throttle hole on the bearing surface of the thrust bearing, most of the compressed gas flowing from the throttle hole into the thrust bearing gap flows along the circumferential groove and supports the hollow main shaft over the entire circumference. Therefore, the load capacity in the thrust direction is remarkably increased as compared with the no load state. If air hammer is expected to occur depending on 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, and the volume of the entire groove is reduced. This can be prevented.
[0014]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0015]
As shown in FIG. 1, the outer diameter surface of the main shaft 2 that is rotatably inserted into the housing 1 faces the inner diameter surfaces of the bearing sleeve 3 and the bearing sleeve 4 via a journal bearing gap. The end face of the thrust plate 5 provided at the end is opposed to the end face of the bearing sleeve 4 and the bearing face of the thrust bearing 6 through a thrust bearing gap. When compressed gas (compressed air or the like) is supplied from a bearing air supply port 7 provided in the housing 1, the compressed gas passes through an air supply passage 8 provided in the housing 1 and the bearing sleeves 3 and 4 and the thrust bearing. 6 flows into the journal bearing gap and the thrust bearing gap from the throttle holes 3a, 4a and 4b, 6a, and supports the main shaft 2 in a radial and thrust direction with respect to the housing 1 in a non-contact manner. Bearing exhaust flowing out from the journal bearing gap and the thrust bearing gap is discharged outside the spindle through an exhaust passage (not shown) provided in the housing 1.
[0016]
The main shaft 2 has a hollow shape with a through hole 2a at the center of the shaft. The tip of the through hole 2a is a tapered hole 2a1, and a collet chuck 9 is attached to the inner diameter of the tapered hole 2a1 so as to be movable back and forth. The tip portion of the collet chuck 9 is divided into a plurality of portions by a plurality of slits (not shown) along the axis, and the outer diameter surface thereof is a tapered surface 9a adapted to the inner diameter surface of the tapered hole portion 2a1. Yes. Therefore, when the collet chuck 9 is pulled backward, the collet chuck 9 is pressed from the inner diameter surface of the tapered hole portion 2a1 to reduce its tip portion, and when it is pushed forward along the tapered hole portion 2a1, its tip portion expands. The collet chuck 9 is normally urged rearward by the elastic force of an elastic body 11 such as a disc spring through a draw bar 10 connected to the rear end thereof, and is drawn into the tapered hole 2a1.
[0017]
The rear end of the through hole 2a of the main shaft 2 is open, and the tip of the push rod 12 enters the through hole 2a through the opening. The push rod 12 is normally urged rearward by the elastic force of the compression spring 13 and is held at a position where its tip does not contact the rear end of the draw bar 10. When compressed gas is supplied from an 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 and comes into contact with the rear end of the draw bar 10. The collet chuck 9 is pushed forward through the draw bar 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 increased, and the tool 15 held by the collet chuck 9 is released and can be detached. When the supply of compressed gas from the air supply port 14 is stopped, the push rod 12 is retracted to a position where it does not come into contact with the draw bar 10 by the elastic force of the compression spring 13. Then, the collet chuck 9 is pulled backward via the draw bar 10 by the elastic force of the elastic body 11. Thereby, the diameter of the collet chuck 9 is reduced and the tool 15 is gripped.
[0018]
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. When an electric current is passed through the stator 17, the main shaft 2 rotates at a high speed. As a result, the collet chuck 9, the tool 15, the draw bar 10, and the elastic body 11 rotate integrally with the main shaft 2.
[0019]
A hollow cylindrical non-contact displacement sensor 20 that detects displacement due to the thrust force of the main shaft 2 is arranged 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. . The tip of the push rod 12 that moves the collet chuck 9 back and forth passes through 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, the non-contact displacement sensor 20 includes a cylindrical sensor core 20a formed of an insulating material such as a synthetic resin material, and a coil 20b formed of a conductive material and attached to the outer diameter of the sensor core 20a. An eddy current type 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, the non-contact displacement sensor 20 can be arranged 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). It becomes. Therefore, the shape error such as the inclination of the thrust plate 5 with respect to the thrust bearing 6 and the deflection 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. In addition, by using the eddy current type sensor as described above as the non-contact displacement sensor 20, the sensor unit can be configured by a simple sensor core 20a and a coil 20b, so that it is compact and easy to be hollow.
[0020]
In the embodiment shown in FIG. 2, a circumferential groove 6b communicating with the throttle hole 6a is provided on the bearing surface of the thrust bearing 6 in FIG. The reason why the circumferential groove 6b is provided is as follows. Generally, when the output of a displacement meter is used to detect thrust force, the resolution for thrust force is determined by (stiffness of thrust bearing x resolution for displacement of displacement meter), so in order to detect thrust force accurately, thrust bearing It is better that the rigidity (thrust rigidity) is smaller. As means for reducing the thrust rigidity, means for reducing the diameter of the throttle hole, reducing the number of throttle holes, and further increasing the thrust bearing gap may be considered. However, when the diameter of the throttle hole is reduced or the number is reduced, the load capacity decreases more than necessary, and the main shaft 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 too large, an increase in the amount of compressed air consumed becomes a problem. 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 reduction in load capacity and an increase in compressed air consumption during processing. It is a thing.
[0021]
The groove depth of the circumferential groove 6b is made shallower than the thrust bearing gap at the time of no load, and the thrust bearing gap has a thrust rigidity ratio (required force resolution) / (resolution with respect to displacement of the displacement meter). Is set to a value that also decreases. The number of apertures 6a is about 3 to 6 (4 in this embodiment), which is smaller than usual (about 7 to 8). At no load, the groove depth of the circumferential groove 6b is relatively small compared to the thrust bearing gap, so that the influence of the circumferential groove 6b is small. However, when the thrust bearing gap is reduced by applying a thrust force from the outside, the circumferential groove 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 into the thrust bearing gap from the throttle hole 6a of the thrust bearing 6 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. Increased significantly compared to load. On the other hand, since the number of throttle holes 6a is smaller than usual, the increase in gas consumption is also 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.
[0022]
3 to 5 show the effect of the circumferential groove 6b as a result of calculation. 3 to 5, A shows the results of the product of this example (circumferential groove: there are four throttle holes), and B and C show the results of the comparative product. Comparative product B is (circumferential groove: none, throttle holes: 4), and comparative product C is (circumferential groove: none, throttle holes: 24). The thrust bearing clearance at no load is S.
[0023]
As shown in FIG. 3, the thrust load capacity of the product A of this example rapidly increased from the vicinity where the thrust bearing gap became smaller than a 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.
[0024]
If the number of throttle holes 6a is reduced and the circumferential groove 6b is provided, unstable self-excited vibration (air hammer) may be easily generated. When the occurrence of an air hammer is predicted depending on 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, the partial circumferential groove 6b ′ independent for each throttle hole 6a. This can be prevented by reducing the volume of the entire groove.
[0025]
In the embodiment shown in FIG. 7, a separate sensor target 21 is integrally attached to the rear end surface of the thrust plate 5 of the main shaft 2, and the non-contact displacement sensor 20 is integrally provided with a dummy sensor 20 ′ and a dummy target 22. It has been made. The sensor target 21 is formed of a material having physical properties suitable as a target of an eddy current displacement sensor, such as a SUS310S material. The dummy sensor 20 ′ includes a sensor core 20a common to the non-contact displacement sensor 20, and a dummy coil 20b ′ attached to 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. A hollow cylindrical guide 25 that guides the push rod 12 to be movable back and forth is mounted on the inner diameter of the sensor core 20a.
[0026]
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 type displacement sensor, and fluctuations in the sensor output due to unevenness of the material or electrical resistance There is a concern that the sensitivity of the displacement sensor is greatly reduced. The sensitivity of the non-contact displacement sensor 20 can be increased by making the sensor target 21 a separate component from the main shaft 2 and allowing the material to be freely selected. In addition, the sensor output of the eddy current type displacement sensor may drift due to the temperature change of the sensor unit and the detection circuit unit. By taking, the effect of drift can be eliminated.
[0027]
The embodiment shown in FIG. 8 is configured to guide the push rod 12 so as to be movable back and forth on the inner diameter surface of the sensor core 20a. In this case, the material of the sensor core 20a needs to be an insulator and excellent in wear resistance and slidability, and synthetic resins such as ceramic, nylon, fluororesin, and polyacetal are suitable.
[0028]
The present invention can be applied to general spindles having a hollow main shaft (having means for applying a pressing force from the side opposite to the tool to a member arranged in the through hole of the main shaft). The configuration is not limited. For example, the present invention 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 side opposite to the tool to operate the draw bar). Further, the present invention can be similarly applied to a spindle using a non-contact support means such as a hydrostatic fluid bearing and a magnetic bearing, or a contact support means such as a general bearing as a support means for the housing of the main shaft. In these cases, the same effects as described above are obtained.
[0029]
【The invention's effect】
The present invention has the following effects.
[0030]
(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 a hollow main shaft. Therefore, the main shaft shape error, vibration, and the like do not affect the output of the non-contact displacement sensor, and the main shaft thrust displacement due to the thrust force applied from the outside can be detected with high accuracy.
[0031]
(2) As a non-contact displacement sensor, a hollow cylindrical sensor core formed of a synthetic resin material or ceramic material selected from nylon, fluororesin, and polyacetal, and an outer diameter of the sensor core formed of a conductive material By using an eddy current type composed of a coil mounted on the sensor, the sensor unit can be composed of a simple sensor core and coil, so that it is easy to make it compact and hollow. In addition, the push rod can be moved back and forth smoothly on the inner surface of the sensor core made of the above-mentioned synthetic resin material or ceramic material with excellent wear resistance and slidability. The operation can be made possible, and at the same time, the structure can be simplified.
[0032]
(3) A dummy sensor and a dummy target are integrally provided in a non-contact displacement sensor, and the influence of drift can be eliminated by taking an output difference between the non-contact displacement sensor and the dummy sensor.
[0033]
(4) Disadvantages such as reduction of load capacity and increase of gas consumption by providing a circumferential groove or partial circumferential groove that is shallower than the thrust bearing gap at the time of no load, and is connected to the throttle hole on the bearing surface of the thrust bearing. It is possible to reduce the thrust rigidity without causing the occurrence of a small thrust force with high accuracy. If the occurrence of an air hammer is predicted depending on 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 overall volume of the groove. This can be prevented.
[Brief description of the drawings]
[1] Ru Ah a 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 a result of a comparative test of a relationship between a thrust bearing gap and a thrust load capacity in the spindle shown in FIG. 2. FIG.
4 is a diagram showing the results of a comparative test of the relationship between thrust bearing clearance and thrust stiffness in the spindle shown in FIG. 2;
5 is a diagram showing a result of a comparative test of a relationship between a thrust bearing gap and a gas consumption amount in the spindle shown in FIG. 2. FIG.
FIG. 6 is a plan view showing a thrust bearing surface of a spindle according to another embodiment of the present invention.
[7] Ru Ah a sectional view showing a spindle according to another embodiment of the present invention.
[8] Ru Ah 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]
DESCRIPTION OF SYMBOLS 1 Housing 2 Hollow main shaft 3 Bearing sleeve 4 Bearing sleeve 5 Thrust board 6 Thrust bearing 6a Throttling 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 (3)

A hollow main shaft supported non-contactingly in a radial direction and a thrust direction by a hydrostatic bearing in a housing; a collet chuck mounted in a taper hole provided at a tip of a through hole of the hollow main shaft so as to be movable back and forth; A draw bar disposed in the through hole and connected to the rear end of the collet chuck; a push rod inserted into the through hole from the rear end opening of the through hole, and capable of applying a pressing force to the draw bar from behind; A non-contact displacement sensor for detecting displacement due to a thrust force of the hollow main shaft,
The non-contact displacement sensor is formed of a hollow cylindrical sensor core made of a synthetic resin material or ceramic material selected from nylon, fluororesin, and polyacetal, and a conductive material, and is attached to the outer diameter of the sensor core. Eddy current type consisting of a coil,
The non-contact displacement sensor is arranged coaxially with the hollow main shaft and opposed to a detection target portion of the hollow main shaft, and guides the push rod to move back and forth on the inner diameter surface of the sensor core. A hydrostatic bearing spindle. 2. The hydrostatic bearing spindle according to claim 1, wherein the non-contact displacement sensor is integrally provided with a dummy sensor and a dummy target, wherein the dummy sensor is formed of a conductive material and is attached to a rear end outer diameter of the sensor core. A hydrostatic bearing spindle, wherein the hydrostatic bearing spindle is of an eddy current type provided with a dummy coil, wherein the dummy target is formed of a conductive material and is mounted on the rear end surface of the sensor core. On 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, a circumferential groove or a partial circumferential groove that is communicated with the throttle hole of the thrust bearing and is shallower than the thrust bearing gap at no load is provided. 2. The hydrostatic bearing spindle according to claim 1, wherein the hydrostatic bearing spindle is formed.

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