KR20190068797A - Preloading device of machine tool spindle - Google Patents

Abstract

A spindle bearing for rotatably supporting a spindle of the machine tool; a plurality of springs and a plurality of hydraulic cylinders provided in the circumferential direction on the bearing body to press the outer ring of the rear end bearing in an axial direction; And a displacement sensor for detecting an axial gap therebetween.
When the value detected from the displacement sensor is greater than a predetermined value, the hydraulic pressure is supplied to the hydraulic cylinder to maintain the main-shaft bearing state in the pre-position pre-load state. When the value is smaller than the predetermined value, the hydraulic pressure does not act on the hydraulic cylinder Only the spring controls the main shaft bearing state of the static pressure preloaded state in which the outer ring of the rear stage bearing is pressed in the axial direction.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preloading device for a machine tool spindle,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preload apparatus for a main shaft bearing of a machine tool and more particularly to a preload apparatus for applying a constant preload to a main shaft bearing even when a back boring pressure is applied to the main shaft in a direction opposite to a normal machining direction .

By applying a constant preload to the main spindle bearing of the machine tool, accuracy in the axial and radial directions of the main spindle can be maintained to maintain machining accuracy of the workpiece, and vibration of the spindle can be suppressed and rigidity of the bearing can be maintained.

The conventional pre-pressurizing apparatuses of the main spindle bearings of the machine tool have been introduced with a fixed preloading method, a static pressure preloading method, and a variable preloading method.

First, as shown in Fig. 1, a pre-position pre-pressurizing method generates a preload in the bearing by adjusting the step difference between the inner ring and the outer ring of the main shaft bearing using an adjusting nut in the axial direction. This method is simple in structure, has small tip displacement, and has a high rigidity. However, if the main shaft rotates at high speed, the centrifugal force of the bearing ball suddenly increases and the preload applied to the bearing increases, There is a problem of increasing.

In addition, the static pressure preloading method is a complement to the fixed position preloading method as shown in Fig. 2. In addition to adjusting the step between the inner ring and the outer ring of the main shaft bearing by adjusting nuts, pressure is applied to the outer ring of the bearing in the direction opposite to the adjusting nut And a spring was added to adjust the preload. This method maintains a certain preload applied to the bearing even if the centrifugal force is varied in the entire region of the rotating region during high-speed rotation of the main shaft. However, in order to keep the preload constant, the axial displacement of the spring occurs, which is more disadvantageous than the fixed preload method in terms of stiffness. In particular, when the spindle is pulled in the direction of compression of the spring, such as back boring, when the bearing is subjected to a pulling force greater than the preload set by the spring, the unloading, So that it becomes more vulnerable to stiffness, and a serious processing error occurs in the workpiece.

The variable preload method as shown in FIG. 3 is to supplement the problems of the prior art. When the rotational speed of the main shaft is changed, the spring and the hydraulic pressure are simultaneously applied to the outer ring of the bearing so that the preload of the main shaft bearing is changed accordingly Method. However, there are several considerations in its application. That is, in order to finely control the proper pressure according to the spindle rotational speed, it is necessary to perform real-time control. To do so, an expensive hydraulic valve having excellent performance should be used. In addition, this method can cause the displacement of the tip of the main shaft due to the pressure fluctuation of the spring and the hydraulic pressure, thereby generating a step on the machined end face of the work. Furthermore, this method increases the preload more than the allowable value when an external force is applied during machining, which may cause a step to be larger on the machined section of the workpiece or damage of the bearing. Due to such a problem, there is a problem that this method must be accompanied by a separate means for correcting the axial displacement of the main shaft.

As described above, the present invention overcomes the problems of the prior art, and avoids the unloading state of the bearing when the spindle is pulled in the axial direction, such as back boring, There is a need to provide a preload apparatus for a machine tool main shaft bearing capable of applying a proper preload to the main shaft bearing to maintain the rigidity of the bearing and to minimize the machining error of the workpiece.

More specifically, it is an object of the present invention to provide a preload apparatus for a main spindle of a machine tool, which is automatically switched between a constant-pressure spindle system and a fixed-spindle system in accordance with machining conditions of a machine tool.

It is another object of the present invention to provide a preload device for a machine tool spindle in which a worker can arbitrarily select a preloading condition between a constant pressure spindle type and a fixed position spindle type.

It is still another object of the present invention to provide a preload device for a main spindle of a machine tool, which improves machining accuracy of a spindle, suppresses vibration, and maintains rigidity of a bearing by applying a preload conforming to the working conditions.

In order to achieve the above object, a pre-pressurizing device for a machine tool main spindle according to the present invention comprises a main shaft rotatably supported in a body of a machine tool, a ball between the inner and outer rings for rotatably supporting the main shaft, The inner ring is fixed to the outer diameter of the main shaft and rotates together with the main shaft, and the outer ring has a leading end bearing and a trailing end bearing supported by the housing.

In addition, the present invention is also characterized in that it comprises: a plurality of springs circumferentially installed on the bearing body and applying a constant pressure in the axial direction to the outer ring of the rear end bearing; And a plurality of hydraulic cylinders which apply a constant pressure to the outer ring of the rear stage bearing in the same direction as the hydraulic cylinder.

Further, the present invention has a displacement sensor installed at one side in the circumferential direction inside the bearing body and detecting an axial gap between the bearing body and the bearing housing.

Further, according to the present invention, when the interval detected by the displacement sensor is greater than a predetermined interval, a predetermined pressure of hydraulic pressure is supplied to the hydraulic cylinder, and when the interval detected by the displacement sensor is smaller than a predetermined interval, So as not to operate.

The control unit may further include a mode selection switch for selecting the automatic mode or the manual mode. When the mode selection switch is set to the manual mode, it is determined whether the rotational speed of the main shaft is within a predetermined rotational speed range And controls the hydraulic cylinder so that the hydraulic pressure is not supplied to the hydraulic cylinder when the rotational speed of the main shaft is higher than a predetermined rotational speed and controls the hydraulic cylinder so that the hydraulic pressure is supplied to the hydraulic cylinder when the rotational speed of the main shaft is slower than a predetermined rotational speed .

Further, the control unit provides a message informing that the hydraulic pressure is not supplied to the hydraulic cylinder when the mode selection switch is selected as the manual mode and the rotation speed of the main shaft is faster than the predetermined rotation speed.

The control unit may further include an oil pressure selection switch connected in series to the mode selection switch and capable of interrupting a hydraulic pressure supplied to the hydraulic cylinder.

Further, the spring is a static pressure type spring, and the hydraulic cylinder is a stationary hydraulic cylinder in which, when supplied with the hydraulic pressure, the piston moves only by a predetermined distance.

The present invention improves machining accuracy of a machine tool by simultaneously installing both a static pressure preloading method and a fixed position preloading method on the main shaft bearing and applying a preload to the main shaft bearing by automatically or manually switching the optimum preloading method according to machining conditions, Vibration of the main shaft is suppressed, and main shaft bearing can be prevented from being burned.

In particular, when the main spindle is pulled in the backward direction as in the case of back boring, the spindle bearing is unloaded to prevent the burnout from becoming excessive.

In addition, in the case of the fixed-position preloading method of the present invention, since the hydraulic cylinder is moved only by a certain distance and the preload is applied to the bearing using the step between the inner ring and the outer ring, There is an advantage in that it is not necessary to use an expensive hydraulic valve in order to precisely control the hydraulic pressure supplied to the hydraulic cylinder, such as the preload method.

FIG. 1 is a schematic cross-sectional view of a machine tool main shaft bearing showing a static preloading system in the prior art.
2 is a schematic cross-sectional view of a machine tool main shaft bearing showing a static pressure preloading method according to the prior art.
3 is a schematic cross-sectional view of a machine tool main shaft bearing showing a variable preload method in the prior art.
4 is a cross-sectional view showing a spring for a static preload in a machine tool main shaft bearing of a combination of a fixed position and a static pressure preloading method according to an embodiment of the present invention.
5 is a cross-sectional view showing a hydraulic cylinder for a fixed position preload in a machine tool main shaft bearing of a combination of a fixed position and a static pressure preloading method according to an embodiment of the present invention.
Fig. 6 is a sectional view taken along the line AA in Fig. 5, according to an embodiment of the present invention.
7 is a partial sectional view of a leading end bearing of a machine tool spindle equipped with a displacement sensor according to an embodiment of the present invention
8 is a control flowchart for controlling the preloading method of the machine tool main shaft bearing according to the embodiment of the present invention.

The structure of the preload apparatus of the machine tool main spindle according to the present invention will be described with reference to Figs. 4 to 7. Fig.

4 and 6, the preload apparatus of the machine tool main spindle 11 of the present invention has a main spindle 11 rotatably supported in the bearing body 10. And a ball 14 is provided between the inner ring 12 and the outer ring 13. The inner ring 12 is fixed to the outer diameter of the main shaft 11 and rotates together with the main shaft 11, Has a main shaft bearing (20) supported on the bearing body (10) together with the housing (15).

The main shaft bearing 20 is composed of a front end bearing 21 for rotatably supporting the front side of the main shaft 11 to be machined and a rear end bearing 22 for rotatably supporting the rear side of the main shaft 11. [

The bearing body 10 is provided with an annular shaft 21 which is provided in the bearing body 10 in a direction opposite to the leading end bearing 21 provided at the leading end of the main shaft 11 with respect to the outer ring 13 of the trailing end bearing 22 provided at the rear end of the main shaft 11 in the circumferential direction. A plurality of static-pressure springs 30 are provided so as to apply a constant pressure in the direction of the arrow.

One end of the spring 30 is supported by the spring seat 32 and the other end is supported by the rear end bearing 22 in the spring pocket 31 formed in the circumferential direction of the bearing body 10 And presses the side surface of the outer ring (13) housing (15). The spring 30 is guided in an axial direction inserted into the guide ring 33 provided inside the spring pocket 31.

5 and 6, the bearing body 10 is provided with the outer ring 13 of the rear end bearing 22 in the same direction as the spring 30 between the springs 30 in the circumferential direction. A plurality of hydraulic cylinders (40) are installed to press the housing (15) at a constant pressure.

The hydraulic cylinder 40 has a passage 41 through which hydraulic pressure is supplied or discharged from the outside of the bearing body 10 and a piston 42 which is advanced and retracted in the axial direction is installed in the cylinder. When the hydraulic pressure is supplied through the oil passage 41, the piston 42 advances in the axial direction to press the side surface of the housing 15 of the outer ring 13 of the rear end bearing 22. The hydraulic cylinder (40) is a stationary hydraulic cylinder (40) in which a piston (42) inside the hydraulic cylinder (40) moves only by a predetermined distance when the hydraulic pressure is supplied.

7, a displacement sensor 50 for detecting the axial distance between the bearing body 10 and the housing 15 of the end bearing 21 is installed at one side in the circumferential direction of the bearing body 10 do. The displacement sensor 50 is a precision sensor capable of detecting up to 0.2 mu m. Further, the detection signal of the displacement sensor 50 is transmitted to the control unit 60 through the electric wire.

The present invention further includes a control unit (60) for receiving a signal indicative of an interval detected by the displacement sensor (50) and controlling the hydraulic pressure supplied to the hydraulic cylinder (40) according to the magnitude.

Hereinafter, the control operation of the controller 60 according to the present invention will be described with reference to FIG.

The control unit 60 controls the hydraulic valve 63 to supply a hydraulic pressure of a predetermined pressure to the hydraulic cylinder 40 when the interval detected by the displacement sensor 50 is greater than a predetermined interval, And controls the hydraulic valve (63) so that the hydraulic pressure can be discharged from the hydraulic cylinder (40) when the interval detected by the pressure sensor (50) is smaller than a predetermined interval.

That is, the main spindle 11 normally presses the housing 15 of the rear end bearing 22 with the springs 30 only to maintain the state of the main spindle of constant pressure and then performs the back boring, (22) in the direction of a predetermined load. At this time, a gap is formed between the housing 15 of the leading end bearing 21 and the bearing body 10 surrounding the main shaft 11 in the axial direction. The displacement sensor 50 provided between the housing 15 of the end bearing 21 and the bearing body 10 transmits this interval to the monitoring and control unit 60 in real time. The controller 60 determines that the displacement sensor 50 is gradually increased and the constant pressure type spring 30 pressing the housing 15 of the rear stage bearing 22 loses its force and the main shaft bearing 20 is unloaded And controls the hydraulic valve 63 so that the hydraulic pressure is supplied to the hydraulic cylinder 40 when the hydraulic pressure is close to the unloading state. That is, the hydraulic pressure is supplied to the hydraulic cylinder 40 when the value detected by the displacement sensor 50 reaches a predetermined value. At this time, the main shaft bearing 20 is switched from the static pressure preload main shaft state by the constant pressure spring 30 to the fixed position preload main shaft state to fix the axial displacement.

When the back boring process is completed after the main spindle 11 is operated in the fixed preload state in which the axial displacement is fixed, the displacement sensor provided between the housing 15 of the leading end bearing 21 and the bearing body 10, The value detected from the sensor 50 is gradually decreased. When the value of the displacement sensor 50 becomes smaller than a predetermined value, the control unit 60 stops the supply of the hydraulic pressure to the hydraulic cylinder 40 and at the same time, the hydraulic valve (not shown) is opened to drain the hydraulic pressure remaining in the hydraulic cylinder 40 63 are opened. As a result, the main shaft bearing 20 is released from the forward preloading state and returned to the preloading state of the main shaft preload by the spring 30 in the initial state.

By automatically controlling the preload of the main spindle 11 as described above, it is possible to prevent the main spindle bearing 20 from rotating in the unloading state due to the unmanned operation of the automatic machining line or the like, thereby preventing the bearing from being damaged, The precision machining and the vibration of the main shaft 11 can be suppressed.

In the case of the correct position prevention method, the hydraulic cylinder 40 is moved only by a certain distance, not by the hydraulic pressure to increase the rigidity of the bearing, but by using the step between the inner ring 12 and the outer ring 13, There is an advantage that it is not necessary to finely control the hydraulic pressure by using an expensive hydraulic valve like a variable preload method.

As another embodiment, a mode selection switch 61 for selecting an automatic mode or a manual mode is provided in the control unit 60. In the automatic mode, the mode selection switch 61 is operated as described above. However, Mode is selected, it is determined whether the rotational speed of the main shaft 11 is within a predetermined rotational speed range. If the rotational speed of the main shaft 11 is faster than the predetermined rotational speed, So that the housing 15 of the rear end bearing 22 is pressed only by the spring 30 and the rotational speed of the main shaft 11 is maintained at the predetermined rotational speed The hydraulic cylinder 40 controls the hydraulic pressure valve 63 so that the hydraulic pressure of the constant pressure is maintained in the hydraulic cylinder 40 so that the hydraulic cylinder 40 moves the housing 15 of the rear end bearing 22 by a predetermined distance in the axial direction And maintains the preloaded pre-pressurized state.

That is, in the present embodiment, when the rotational speed of the main shaft 11 is higher than 3000 rpm, the pressure acting on the bearing outer ring 13 increases due to the centrifugal force of the ball 14 of the main shaft bearing 20, The supply of the hydraulic pressure to the hydraulic cylinder 40 is released to stop the pressing of the bearing outer ring 13 and to maintain the static preload main spindle state by the spring 30 only.

When operating in the manual mode as described above, the operator can directly control the hydraulic operation for fixing the axial displacement of the main shaft 11 for the back boring work. This allows the operator to switch to the correct spindle to remove axial clearance in advance of the back boring. When the back boring process is completed, the manual mode is released through the operation of the mode selection switch 61 and the mode is switched to the automatic mode. As described above, according to the size of the gap detected by the displacement sensor 50, ) So as to switch the state of the main shaft 11 to the fixed-position preloading state or the static-pressure preloading state.

In another embodiment of the present invention, it is necessary for the controller 60 to select the mode selection switch 61 as the manual mode and to maintain the constant pressure pre-pressure state because the rotational speed of the main shaft 11 is higher than the predetermined rotational speed It is possible to inform that the hydraulic pressure is not supplied to the hydraulic cylinder 40 through a separate message display device (not shown). That is, the current rotational speed of the main spindle 11 can be informed to the worker that it is in the static pressure preloading state.

According to another embodiment of the present invention, a hydraulic pressure selection switch 62 is additionally connected to the mode selection switch 61 so that an operator can arbitrarily shut off the hydraulic pressure supplied to the hydraulic cylinder 40. Accordingly, in the manual mode, the operator can arbitrarily shut off the hydraulic pressure supplied to the hydraulic cylinder 40, so that the static pressure pre-pressure state by the spring 30 can be maintained regardless of the rotational speed of the main shaft 11. [

Thus, the worker can arbitrarily control the preload of the spindle 11, thereby preventing the spindle bearing 20 from rotating in the unloading state in the machine tool and damaging the bearing. Further, the precision machining of the workpiece and the vibration of the spindle Can be suppressed.

10 bearing body
11 spindle
12 inner ring
13 Outer ring
14 balls
15 Housing
20 spindle bearings
21 leading bearings
22 Back End Bearing
30 spring
31 spring pockets
32 spring seat
33 Guide ring
40 Hydraulic cylinders
41 Euro
42 piston
50 displacement sensor
60 control unit
61 Mode selection switch
62 Hydraulic select switch
63 Hydraulic valves

Claims (7)

A main shaft rotatably supported inside the body of the machine tool;
A bearing disposed between the inner ring and the outer ring so as to rotatably support the main shaft, the inner ring being fixed to the outer diameter of the main shaft and rotating together with the main shaft, the outer ring being supported by the housing;
A plurality of springs circumferentially installed on the bearing body and applying a constant pressure in an axial direction to the outer ring of the rear end bearing;
A plurality of hydraulic cylinders provided between the springs in the circumferential direction of the bearing body and applying a constant pressure to the outer ring of the rear bearing in the same direction as the spring;
A displacement sensor installed at one side in the circumferential direction inside the bearing body and detecting an axial gap between the bearing body and the bearing housing;
Wherein when the interval detected by the displacement sensor is greater than a predetermined interval, a predetermined pressure of hydraulic pressure is supplied to the hydraulic cylinder, and when the interval detected by the displacement sensor is smaller than a predetermined interval, A pre-pressurizing device for the main spindle of the machine tool. 2. The machine tool according to claim 1, wherein the spring and the hydraulic cylinder are provided so as to press the side surface of the bearing housing supporting the outer ring of the rear stage bearing in the axial direction opposite to the front end of the main shaft. Device. 2. The machine tool according to claim 1, wherein the spring is a static pressure spring, and the hydraulic cylinder is a stationary hydraulic cylinder in which a piston inside the hydraulic cylinder is moved by a predetermined distance. Preloading device. 2. The apparatus according to claim 1, wherein the displacement sensor is installed on one side in the circumferential direction of the bearing body so as to detect an axial gap between the bearing body and the bearing housing, . A main shaft rotatably supported inside the body of the machine tool;
A bearing disposed between the inner ring and the outer ring so as to rotatably support the main shaft, the inner ring being fixed to the outer diameter of the main shaft and rotating together with the main shaft, the outer ring being supported by the housing;
A plurality of springs circumferentially installed on the bearing body and applying a constant pressure in an axial direction to the outer ring of the rear end bearing;
A plurality of hydraulic cylinders provided between the springs in the circumferential direction of the bearing body and applying a constant pressure to the outer ring of the rear bearing in the same direction as the spring;
Wherein when the mode selection switch is set to the manual mode, it is determined whether the rotation speed of the main shaft is within a predetermined rotation speed range, and if the rotation speed of the main shaft is within a predetermined range And controls the hydraulic cylinder so that the hydraulic pressure is supplied to the hydraulic cylinder when the rotational speed of the main shaft is slower than the predetermined rotational speed. Preloading device for machine tool spindle. 6. The control apparatus as claimed in claim 5, wherein the control unit provides a message informing that the hydraulic pressure is not supplied to the hydraulic cylinder when the mode selection switch is selected as the manual mode and the rotation speed of the main shaft is faster than a predetermined rotation speed Preloading device of a machine tool spindle. The pre-pressurizing apparatus for a machine tool spindle according to claim 5, wherein the control unit further includes an oil pressure selection switch connected in series to the mode selection switch and capable of interrupting a hydraulic pressure supplied to the hydraulic cylinder.

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