JP2001054803A - Preload control type spindle unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately control preload even in a fixed position with simple structure with a bearing part made compact. SOLUTION: A thermoelement 9 with a Peltier effect is fitted along an outer spacer 7 provided between outer rings 2b, 3b of a pair of rolling bearings 2, 3 for supporting a rotating shaft 1. The heat absorbing side of the thermoelement 9 is disposed along the surface of the outer spacer 7, and the heat generating side of the thermoelement 9 is provided with a cooling route 13 allowing the flow of cooling oil of constant temperature. The specified amount of current flows to the thermoelement 9 by controlling a current regulator 10 by a control device 12 according to the rotating speed of the rotating shaft. The temperature of the outer spacer 7 is thereby lowered according to the rotating speed of the rotating shaft 1, and the length of the outer spacer 7 is shortened to control preload.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle unit used in a machine tool or the like, and more particularly to an improvement in a preload control type spindle unit.

[0002]

2. Description of the Related Art A spindle unit receives a thrust load such as an angular ball bearing for the purpose of increasing the rotational speed of the bearing, increasing the rigidity of the bearing, and preventing vibration or noise of the bearing. It is common practice to apply a preload to a rolling bearing that can be used, and there are two types of preload: fixed position preload and constant pressure preload.

In general, fixed position preload is used for cutting in a machine tool. However, during high-speed rotation, a thrust load generated inside the bearing due to centrifugal force causes heavy preload, resulting in a rise in temperature. There is a possibility that seizure of the bearing based on the friction may occur. In addition, constant pressure preload has low rigidity,
Since it cannot be used for cutting work that needs to withstand a large tensile load, it is used exclusively for high-speed light cutting.

[0004] Therefore, in response to the demand for high-speed machine tool spindles and a wide range of machining requirements, low-speed to ultra-high-speed cutting or grinding is required.
A preload control type spindle unit that switches a preload according to the number of rotations is used in order to realize a single spindle.

A conventional preload control type spindle unit is:
In many cases, the length of an outer spacer provided between outer rings of a pair of rolling bearings is changed using a hydraulic pressure or a piezoelectric element. There are two types that use hydraulic pressure: a cylinder type that applies hydraulic pressure in the thrust direction,
There is a method in which hydraulic pressure acts on the peripheral surface of a thin cylindrical portion in the radial direction.

[0006]

The method of changing the length of the outer spacer by using hydraulic pressure has a complicated structure such as requiring a hydraulic device. In particular, a cylinder type has a complicated structure of a bearing portion. As a result, the spindle unit becomes large.
Further, this cylinder type has an advantage that it can cope with a large load and relatively accurately perform preload control. However, since an O-ring for preventing oil leakage is used, accuracy in assembly is ensured. It becomes difficult.

Further, in the cylinder type, since the cylinder and the piston are arranged between the pair of rolling bearings, the span between the rolling bearings becomes longer. If the span is long, the change in span due to the thermal expansion of the spindle due to rotation also increases, and the inner ring of the rolling bearing on the tip end side (front side) of the pair of rolling bearings is fixed to suppress changes in the tip position of the spindle. Even if this is done, the inner race of the rear rolling bearing will move, so that a preload deviation occurs at the fixed position preload.

Further, in the system using a piezoelectric element, there is no element that can withstand the axial pressure due to thermal expansion. In addition, there is a method of adjusting the length of the outer spacer by heating with a heater and cooling with oil, but the response of control is poor and is not practical.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a spindle unit having a simple structure, a compact bearing portion, and capable of accurately controlling the preload even at a fixed position preload.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides a rolling bearing having a pair of rolling bearings. In a preload control type spindle unit for controlling a preload acting on the rolling bearing by relatively changing a height, a thermoelectric element having a Peltier effect in which a heat absorbing side is attached along at least one surface of the inner spacer and the outer spacer. Power supply means for supplying a desired amount of current to the thermoelectric element, and cooling means provided on the heat generation side of the thermoelectric element. That is, the present invention reduces the temperature of at least one of the inner spacer and the outer spacer by a thermoelectric element having a Peltier effect, thereby adjusting the length and controlling the preload. The thermoelectric element having the Peltier effect is compact, can be incorporated without enlarging the bearing part, and is easy to assemble, while not deteriorating the assembly accuracy of the inner spacer and the outer spacer, Power supply to the thermoelectric element is simpler in structure than hydraulic pressure, and furthermore, excellent controllability and high control accuracy can be obtained.

It is preferable that the power supply means is configured to flow a current of a predetermined amount corresponding to the number of rotations of the rotating shaft, and that an inner spacer or an outer spacer along the thermoelectric element is provided. The spacer is preferably formed of a material having a larger coefficient of thermal expansion than the outer spacer or the inner spacer, which is not along the thermoelectric element, in order to increase the change in length due to temperature change.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. Reference numeral 1 denotes a rotary shaft, which is rotatably supported on a casing 4 by angular ball bearings 2 and 3 as rolling bearings capable of receiving a thrust load. Angular contact ball bearings 2 and 3 are inner rings 2a and 3
a, the outer rings 2b, 3b face each other, that is, the outer ring 2b faces leftward in FIG. 1, and the outer ring 3b pairs with each other so as to receive rightward thrust load in FIG.
The so-called back side is arranged.

The left side of the inner ring 2a in FIG.
The inner ring 3a is pressed against the inner ring 2a via the inner spacer 5, and the right end of the inner ring 3a is fixed to the rotating shaft 1 by a stepped sleeve 6
Has been taken by On the other hand, the right end of the outer ring 3b in FIG. 1 is pressed against the step portion 4a of the casing 4, the outer ring 2b is pressed against the outer ring 3b via the outer spacer 7, and the left end of the outer ring 2b is Is pressed and fixed by a holding plate 8 attached to the base plate.

The inner spacer 5 has a coefficient of thermal expansion of 1
1.3 × 10 ^-6 / ° C rolled steel for general structures: SS40
0 (JIS G 3101 (1995)), whereas the outer spacer 7 has a thermal expansion coefficient of 23.9.
It is formed of an aluminum alloy having a coefficient of thermal expansion of × 10 ⁻⁶ / ° C. and larger than that of the inner spacer 5. Also,
The relative lengths of the inner spacer 5 and the outer spacer 7 are adjusted so that the preload of the angular ball bearings 2 and 3 becomes the rated preload when assembled.

A ring-shaped thermoelectric element 9 having a Peltier effect is fitted on the casing 4 so as to contact the outer peripheral surface of the outer spacer 7 with the heat absorbing side as the inner periphery and the heat generating side as the outer periphery. A power supply 11 is connected to the thermoelectric element 9 via a current regulator 10, for example, by detecting the rotation speed of the rotation shaft 1 or the actual rotation speed of the rotation shaft 1 given to the control device 12 as an operating condition. , A predetermined current is supplied according to the rotation speed of the rotating shaft 1.

A cooling path 13 is provided on the outer periphery of the thermoelectric element 9 on the heat generation side. Cooling oil controlled to a predetermined temperature by a cooling oil circulating device (not shown) is supplied from a supply port 14 and discharged from a discharge port 15. By doing so, the outer periphery of the thermoelectric element 9 is maintained at a predetermined temperature.

Next, the operation of the present apparatus will be described. When the rotating shaft 1 rotates at a relatively low speed, the angular ball bearings 2 and 3 generate relatively little heat and the thrust load generated by centrifugal force is also small. Rotate.

On the other hand, when the rotating shaft 1 is rotated at a high speed, the calorific value of the angular ball bearings 2 and 3 increases, and the thrust load generated by thermal expansion and centrifugal force of each part increases, which may result in heavy preload. In addition, since the heat generation increases even at the rated preload, if the rotating shaft 1 is rotated at a high speed, a current of a predetermined amount according to the number of rotations of the rotating shaft 1 is increased.
The power is supplied from the power supply 11 to the thermoelectric element 9 via the current regulator 10 by the control device 12.

In the thermoelectric element 9, the temperature of the inner periphery on the heat absorbing side is reduced by the Peltier effect due to the flow of current, and the temperature of the outer spacer 7 in contact with the thermoelectric element 9 is reduced. At this time, the temperature of the outer periphery of the thermoelectric element 9 on the heat generation side tends to rise, but is kept at a constant temperature by the cooling oil flowing through the cooling passage 13.

Due to the temperature drop of the outer spacer 7, a temperature difference is generated between the inner spacer 5 and the outer spacer 7, and the length of the outer spacer 7 is relatively shorter than that of the inner spacer 5.
As a result, the force for pushing the outer ring 2b and the outer ring 3b away from each other is reduced, and the preload is reduced. Due to the decrease in the preload, the angular ball bearings 2 and 3 can smoothly rotate at high speed.

At this time, if the outer spacer 7 is formed of a material having a larger coefficient of thermal expansion than the inner spacer 5 as in this embodiment, the sensitivity of the preload change to the current value flowing through the thermoelectric element 9 can be increased. it can.

In the above-described embodiment, the pair of angular ball bearings 2 and 3 are arranged on the so-called rear surface, and the outer spacer 7 is provided.
Although the example of reducing the temperature by the Peltier effect of the thermoelectric element 9 to reduce the preload has been described, the present invention is not limited to this, and the arrangement of the angular ball bearings 2 and 3 may be the reverse of the rear arrangement. In this case, the temperature of the inner spacer 5 may be lowered, and both the inner and outer spacers 5 may be used.
The temperature of both spacers 5 and 7 may be reduced at a predetermined rate so that the lengths of both spacers are relatively changed while suppressing the thermal expansion of. Further, the present invention is not limited to the angular ball bearings 2 and 3, but is applicable to a rolling bearing capable of receiving various thrust loads such as a tapered roller bearing and a thrust ball bearing.

Furthermore, in the above-described embodiment, an example in which a predetermined amount of current is supplied to the thermoelectric element 9 in accordance with the number of rotations of the rotating shaft 1 has been described. The temperature of the outer or inner spacer 7 or 5 is detected by a temperature sensor (not shown), and the temperature is set to a predetermined value.
The current value supplied to the thermoelectric element 9 may be controlled.

[0024]

As described above, according to the present invention, there is provided a simple structure in which a thermoelectric element having a Peltier effect is attached along at least one of the inner spacer and the outer spacer between a pair of rolling bearings. Since the part can be made compact and the temperature of the inner or outer spacer can be controlled accurately and responsively by this thermoelectric element,
The effect that the preload control in the fixed position preload can be accurately performed is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rotating shaft 2, 3 Angular contact ball bearing (rolling bearing) 2a, 3a Inner ring 2b, 3b Outer ring 4 Casing 5 Inner spacer 6 Stepped sleeve 7 Outer spacer 8 Holding plate 9 Thermoelectric element 10 Current regulator 11 Power supply 12 Control device 13 Cooling Road 14 Inlet 15 Outlet.

Claims (3)

[Claims] 1. A preload acting on a rolling bearing by relatively changing the lengths of an inner spacer and an outer spacer provided between an inner ring and an outer ring of a pair of rolling bearings supporting a rotating shaft. A thermoelectric element having a Peltier effect whose heat-absorbing side is attached along at least one surface of the inner spacer and the outer spacer; and a flowr for flowing a desired amount of current to the thermoelectric element. A preload control type spindle unit comprising: a power supply unit; and a cooling unit provided on a heat generation side of the thermoelectric element. 2. The preload control type spindle unit according to claim 1, wherein said power supply means is configured to flow a current of a predetermined amount corresponding to the rotation speed of said rotary shaft. . 3. An inner spacer or an outer spacer along which the thermoelectric element is formed is made of a material having a larger coefficient of thermal expansion than an outer spacer or an inner spacer which is not formed along the thermoelectric element. 3. The preload control type spindle unit according to 1 or 2.