JPH0373205A - Preload variable spindle - Google Patents

Abstract

PURPOSE:To uniformly provide a preload to bearings in accordance with the temperature change of a main spindle housing by circulating cooling fluid, whose temperature and flow rate have been controlled in accordance with the rotating speed, to the outer circumference of an outer-ring spacer, and also by circulating cooling fluid of room temperature to the outer circumference of a main shaft housing. CONSTITUTION:Cooling fluid of room temperature is circulated to outer cylinder cooling grooves 20 in the operating condition to restrain the thermal displacement of an outer cylinder 2. The distance L2 between the outer rings of bearings 3, 4 depends on the length of an outer-ring spacer 6, and cooling fluid is circulated to outer-ring spacer cooling grooves 15 by setting the temperature and flow rate in such a way that the outer-ring spacer 6 can be maintained at room temperature at the time of low-speed heavy-cutting, so that the temperature rise of the outer-ring spacer 6 due to heat generation can be prevented. When it is changed over to light-cutting high-speed rotation, the temperature and flow rate of the cooling fluid to be supplied to the outer-ring spacer cooling grooves 15 are changed over to the values which have been previously obtained on experiment in accordance with the rotating speed detecting signal of a spindle shaft 1 for preventing the increase in preload caused by the thermal expansion of the outer-ring spacer 6 due to high-speed rotation. When the length of the outer-ring spacer 6 is shortened than an initially set length by the intensified cooling of the outer-ring spacer 6 to produce a clearance between the spacer and the outer ring 3B, the outer ring 3B is elastically pressed by the energizing force of a spring 11 of a bolt 12 for fitting a front cover 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a variable preload spindle that is capable of changing the amount of preload applied to a bearing that supports the spindle.

[Conventional technology]

The preload of the bearing that supports the main shaft of a machine tool is set by adjusting the length of the spacer inserted between the bearings in advance so as to provide high rigidity during low-speed rotation during heavy cutting.

However, during high-speed rotation, the preload on the bearing generally becomes excessive due to expansion of the shaft or bearing due to heat generation, which causes the problem of premature seizure. Therefore, a variable preload type spindle is used in which the preload is changed when necessary in accordance with the rotational speed.

As a conventional variable preload spindle of this type, there is one disclosed in, for example, Japanese Patent Laid-Open No. 64-34602.

This spindle includes first and second bearings spaced from each other that rotatably support the spindle in a housing, and a piezoelectric element or an electrostrictive element is provided on both sides of at least one of the bearings, By operating these elements and causing one of the bearings to reciprocate in the axial direction, a predetermined preload load is generated on the bearing (
1st conventional example).

Further, Japanese Utility Model Application Publication No. 63-97440 discloses a device for maintaining a constant preload on a main shaft bearing of a machine tool using temperature-controlled oil. This oil pan is made of a material with a high coefficient of thermal expansion and has an oil chamber, and is interposed between the outer ring of the main shaft bearing of a machine tool. is the temperature sensor that detects the temperature of the member, the oil receiver calculated from the temperature detected by the temperature sensor is the member length, and the oil receiver that can apply the optimal preload amount calculated from the spindle rotation speed is compared with the member length. The optimal oil receiver is equipped with an oil supply device that supplies oil at a temperature that allows the length of the member to be obtained through a passage to the oil chamber (second conventional example).

[Problem to be solved by the invention]

However, in the first conventional example using a piezoelectric element or an electrostrictive element, a plurality of elements each having somewhat different characteristics are arranged at intervals in the circumferential direction, and the bearing reciprocates in the axial direction. Because of the movement of the bearing, there was a problem in that it was difficult to apply a preload load evenly over the entire circumference of the bearing.

Further, in the second conventional example, the oil receiver serving as a spacer for regulating the spacing between a pair of bearings is calculated from the current length of the member, and the oil receiver detected by a temperature sensor is calculated from the temperature of the member. On the other hand, the oil receiver at the current spindle rotation speed calculates the target length of the member. The two calculated values are then compared, and the temperature of the oil supply device is controlled to make the difference zero, and the oil receiver attempts to maintain a constant preload by thermally displacing the length of the member.

However, the preload of the oil receiver, which is a spacer, is affected not only by temperature changes in the members, but also by elongation of the main shaft housing due to temperature rise. Therefore, even if the oil pan only controls the temperature of the members, there is a problem in that it is difficult to perform accurate preload control unless displacement due to temperature changes in the main shaft housing is dealt with.

Therefore, the present invention has been made by focusing on the above-mentioned conventional problems, and its purpose is to apply a preload load evenly and to accurately adjust the preload in response to temperature changes in the spindle housing. The object of the present invention is to provide a variable preload spindle whose size can be controlled to solve the above-mentioned conventional problems.

[Means to solve the problem]

A pair of bearings is arranged between the spindle shaft and the outer cylinder at a predetermined distance in the axial direction via a spacer, and the bearing is created by controlling the thermal displacement of the outer ring spacer made of a material with a large coefficient of thermal expansion. The variable preload spindle is configured to adjust the preload of the spindle, comprising means for controlling the temperature and flow rate of the cooling fluid in accordance with the rotational speed of the spindle shaft, and a means for controlling the temperature and flow rate of the cooling fluid on the outer circumferential surface of the outer ring spacer. The cooling device is characterized in that it includes a first cooling path through which a cooling fluid of approximately the same temperature as room temperature flows, and a second cooling path through which a cooling fluid having approximately the same temperature as room temperature flows on the outer circumferential surface of the outer cylinder.

[Effect]

An initial preload is set in advance for the bearing. Since this preload is applied via the cylindrical outer ring spacer 6 that abuts the entire circumference of the end surfaces of the outer rings 3B and 4B of the bearings 3 and 4, it is not uniform, for example, when conventional piezoelectric elements are used. It is applied evenly without the risk of it becoming a problem.

The initial preload is applied between the outer ring interposed between the bearings so that the optimal size of fixed position preload is applied to the bearing when the spindle shaft rotates at low speed and performs heavy cutting when the temperatures of both spacers are the same. This is done by setting the length of the seat and the inner ring spacer.

A cooling fluid at room temperature is constantly supplied to the second cooling path during operation. This prevents the distance between the outer rings between the bearings from changing due to thermal displacement of the outer cylinder and affecting the preload.

On the other hand, a cooling fluid that is controlled separately from the fluid in the first cooling path is caused to flow in the first cooling path under predetermined conditions depending on the rotational speed. Here, the predetermined conditions are the type of cooling fluid that can be used for the spindle of the type, ranging from low speed heavy cutting to high speed light cutting, and that provides the length of the outer ring spacer that provides the optimum amount of preload; These are conditions such as temperature and flow rate, and the relationship with the rotation speed may be determined in advance through experiments.

In this way, even when switching to high-speed rotation, it is only necessary to send the cooling fluid to the first cooling path in response to the rotation speed detection signal of the spindle shaft (in the case of an NC machine tool, the speed signal is transmitted as a pulse signal). There is no need to take the trouble to detect the temperature of the outer ring spacer and calculate the length of the outer ring spacer, and therefore no temperature sensor is required.

〔Example〕

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

FIG. 1 shows an embodiment of the present invention.

A pair of bearings 3.4 are spaced apart from each other by a predetermined distance in the axial direction between the spindle shaft 1 and an outer cylinder 2, which is a housing, via a cylindrical inner ring spacer 5 and a cylindrical outer ring spacer 6. It is arranged. Each of the bearings 3 and 4 is a combination bearing formed by combining, for example, two rolling bearings such as angular contact ball bearings in parallel.

The outer diameter of the spindle 1 is the largest at the front end (left @).
From the stepped portion 1a onward, the portion becomes thinner. A bearing 3 is inserted from the left end side of this spindle 1, and the end surface of the inner ring 3A of the front bearing is locked to the step portion 1a. The inner ring spacer 5 and the outer ring spacer 6 for applying preload are also inserted from the left end side of the spindle 1, and the bearing 4 is further inserted, and the nut 7 is screwed onto the spindle 1, and the inner ring 4 behind the bearing 4 is inserted.
The end face of A is pressed. Thus, the distance Ll between the inner rings between the bearings 3 and 4 is regulated by the length of the inner ring spacer 5.

On the other hand, the end surface of the outer ring 4B at the rear of the bearing 4 is engaged with the inner step 2a of the outer cylinder 2, and the end surface of the outer ring 3B at the front of the bearing 3 is pressed by the front cover 8. This front cover 8 is fitted into the outer cylinder 5 so as to be movable in the axial direction with a certain gap 10 between it and the front end surface of the outer cylinder 5, and has a hexagonal socket with a disc spring 11 as a washer. It is attached by tightening the bolt 12. Thus, the distance L2 between the outer rings of the bearing 3 and the bearing 4 is regulated by the length of the outer ring spacer 6.

The length Ll of the inner ring spacer 5 and the length L2 of the outer ring spacer 6 are set to lengths that provide an initial preload amount to the bearings 3 and 4 at the same temperature (room temperature in this case). . Normally, this initial preload amount is set to a value that can maintain the necessary rigidity during heavy cutting at low speeds.

The outer ring spacer 6 is made of a material with a large coefficient of thermal expansion, such as stainless steel 5US304 or free-cutting brass C3604. A spiral outer ring spacer cooling groove 15 as a first cooling path and a sealing groove 17 for a sealing material 16 to prevent external leakage of the cooling fluid flowing therethrough are formed on the outer circumferential surface.

The outer cylinder 2 is provided with an outer ring spacer cooling fluid inlet 18 and an outer ring spacer cooling flow exit loe 9, which communicate with the outer ring spacer cooling groove 15. These outer ring spacer cooling fluid inlets and outlets 18, 19 are connected to a spacer cooling fluid supply device (not shown). On the outer peripheral surface of the outer cylinder 2, a spiral outer cylinder cooling groove 20 as a second cooling path and a seal groove 22 for a sealing material 21 to prevent external leakage of the cooling fluid flowing therein are formed. ing.

An outer sleeve 23 is further fitted on the outer peripheral surface of the outer sleeve 2, and an outer sleeve cooling fluid 24 is fitted to the outer sleeve 23.
and an outer cylinder cooling fluid outlet 25 are provided, which communicate with the outer cylinder cooling groove 20. These outer cylinder cooling fluid inlets and outlets 24 and 25 are connected to an outer cylinder cooling fluid supply device (not shown) that supplies cooling fluid maintained at approximately the same temperature as room temperature.

The spacer cooling fluid supply device described above is different from the outer tube cooling fluid supply device in that it supplies cooling fluid whose temperature and flow rate are controlled to correspond to the rotational speed of the spindle shaft 1.

When using this spindle, place the right side of the flange 2F provided on the outer cylinder 2 against the machine surface and attach it with bolts inserted into the bolt holes 2B.

Therefore, the outer sleeve 23 is exposed to the outside air.

Therefore, the heat generated by the spindle has almost no effect on the machine, so it can be easily controlled.

Next, we will discuss the effect.

The initial preload set in advance on the bearings 3 and 4 that support the spindle shaft 1 is set to an optimum value that ensures the rigidity necessary for low-speed heavy cutting of the workpiece with the tool attached to the spindle shaft 1. be. Since this preload is applied via the cylindrical outer ring spacer 6 that is in uniform contact with the end faces of the outer rings 3B and 4B of the bearings 3 and 4, it is not possible to use the preload, for example, when conventional piezoelectric elements are used. There is no risk of it becoming uniform, and it is applied uniformly.

Cooling fluid at room temperature is constantly supplied to the outer cylinder cooling groove 20, which is the second cooling path, in the spindle operating state, thereby suppressing thermal displacement of the outer cylinder 2. As a result, the length of the spacing L2 between the outer rings of the bearing 3.4 depends on the length of the outer ring spacer 6. On the other hand, a cooling fluid whose temperature and flow rate are set so that the outer ring spacer 6 can maintain the room temperature is passed through the outer ring spacer cooling groove 15, which is the first cooling path, when the rotation speed is low and heavy cutting. This is to prevent the temperature of the outer ring spacer 6 from rising due to heat generated by the rotating bearing. This prevents the preload from exceeding an appropriate amount due to thermal expansion of the outer ring spacer 6 even if low-speed heavy cutting continues.

When the tool is changed to high-speed rotation for light cutting such as hole drilling, the pulse signal representing the rotation of the spindle shaft l changes. Based on this change in the rotational speed of the spindle shaft 1, conditions such as the temperature and flow rate of the cooling fluid supplied to the outer ring spacer cooling groove 15 are switched to values set in advance according to the rotational speed. In other words, at high speed rotation, bearings 3 and 4
Since the amount of heat generated increases, the preload tends to increase due to thermal expansion of the outer ring spacer 6. On the other hand, in order to keep the preload smaller than during low-speed heavy cutting, the cooling of the outer ring spacer 6 is strengthened. As a result, the length of the outer ring spacer 6 is shorter than the length at the time of initial preload, and the preload is reduced.

The cooling enhancement of the outer ring spacer 6 when switching to high-speed rotation is experimentally determined in advance according to the rotation speed detection signal of the spindle shaft 1 (a speed signal transmitted as a pulse signal in the case of an NC machine tool). It is only necessary to send the cooling fluid to the outer ring spacer cooling groove 15 under certain conditions. It is not necessary to take the trouble of detecting the temperature of the outer ring spacer 6 to calculate the length of the outer ring spacer 6, as in the conventional case, and therefore a temperature sensor is also unnecessary.

In addition, by strengthening the cooling of the outer ring spacer 6, the length of the outer ring spacer 6 is shortened from the initial setting length, and a gap is created between the outer ring spacer 6 and the outer ring 3B of the bearing 3. However, since a gap 10 is provided between the outer cylinder 2 and the front lid 8, the elastic biasing force of the disc spring 11 of the hexagon socket head bolt 12 that attaches the front lid 8 acts, and the front lid 8 follows the shortening of the outer ring spacer 6 and presses the outer ring 3B of the bearing 3 so that no clearance is generated.

Thus, depending on the change in the rotational speed of the spindle shaft 1,
With a simple configuration, it is possible to easily and automatically change the magnitude of preload.

〔Effect of the invention〕

As explained above, according to the present invention, in a variable preload spindle in which the fixed position preload by the spacer is adjusted by controlling the thermal displacement of the outer ring spacer made of a material with a large coefficient of thermal expansion, A first cooling path is provided on the outer circumferential surface of the seat, through which a cooling fluid whose temperature and flow rate are controlled in accordance with the rotational speed of the spindle shaft flows, and a cooling passage at approximately the same temperature as room temperature is provided on the outer circumferential surface of the spindle housing. The structure includes a second cooling path through which fluid flows. Therefore, it is possible to provide a variable preload spindle that can uniformly apply a preload load to the bearings and can accurately control the magnitude of preload in response to temperature changes in the spindle housing.

[Brief explanation of drawings]

FIG. 1 is a half-longitudinal sectional view of an embodiment of the present invention. In the figure, 1 is the spindle shaft, 2 is the outer cylinder, 3.4 is the bearing, and 5
is an inner ring spacer, 6 is an outer ring spacer, 15 is a first cooling path, 20
is the second cooling path.

Claims (1)

[Claims] (1) A pair of bearings are arranged between the spindle shaft and the outer cylinder at a predetermined distance in the axial direction via a spacer to control thermal displacement of the outer ring spacer made of a material with a large coefficient of thermal expansion. The variable preload spindle adjusts the preload of the bearing by adjusting the preload of the bearing. A variable preload spindle comprising: a first cooling passage through which cooling fluid flows, and a second cooling passage through which a cooling fluid having a temperature substantially the same as room temperature flows on the outer circumferential surface of the outer cylinder.