JPH04171101A - Continuous variable pre-load type spindle unit - Google Patents

Abstract

PURPOSE:To accurately regulate the quantity of pre-load in a spindle unit for a machine tool or the like by insertedly providing an axially movable bearing case for supporting a spindle inside an outer sleeve and an axially expansible piezoelectric element between the outer sleeve and the bearing case, and changing voltage applied to the piezoelectric element according to the change of the number of revolutions of the main spindle. CONSTITUTION:In establishing heavy pre-load in a low speed rotational domain, high voltage is applied to a piezoelectric element 11 to elongate it to the maximum, and oil is thereby drawn from a left hydraulic chamber 23, and supplied to a right hydraulic chamber 24 for its pressurization. A middle ring 10 is thereby moved left to make a regulating member 16 abut on the end face 1a of an outer sleeve 1 for fixing the member 16, and a functioning member 9 abut on stepped parts 20,22 for giving pre-load P1 to bearings 4-7. A voltage applying device 13 computes the quantity of pre-load on informations given by a revolution detector 14 and a temperature detector 15 as the number of revolutions of the spindle 2 increases to obtain the movement quantity of a bearing case 8, and the dimensions of the piezoelectric element 11 are therefore determined for the control of the applied voltage.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is used for spindles of machine tools, etc.
It is used in a continuously variable preload type spindle unit that continuously changes the preload on the bearing.

[Conventional technology and its problems]

-a. Machine tools are operated with a preload applied to the spindle, and in this case, in order to obtain sufficient rigidity and precision in both the low and high speed rotational ranges of the spindle, it is necessary to respond to changes in the rotational speed. A preload method is used in which the amount of preload is changed based on the amount of preload.

Conventionally, a variable preload type spindle unit that changes the preload applied to the spindle bearing according to the rotation speed has been proposed in Japanese Utility Model Application No. 1-155102 and Japanese Patent Application No. 1-101039 filed by the present applicant. There is something.

However, with these proposed structures, the amount of preload on the bearing is changed by moving the pusher or bearing box inside the spindle until it comes into contact with a stopper, etc., so when changing the preload during rotation, the amount of preload applied to the bearing is changed. The preload changes from front to back, and as a result, the support status and rotational accuracy of the spindle tend to fluctuate dramatically, and machining accuracy becomes unstable due to chatter occurring during cutting and tool position fluctuations. There was a fear that this would happen.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a variable preload spindle unit that can continuously change the amount of preload and accurately adjust the amount of preload to a set value. It's about doing.

[Means to solve the problem]

In order to solve the above problems, the present invention movably provides a bearing box that presses the bearing supporting the main shaft in the axial direction inside the outer cylinder through which the main shaft is inserted, and between the bearing box and the outer cylinder. ,
It has a structure in which the piezoelectric element that expands and contracts in the axial direction is incorporated, and a voltage application device that changes the applied voltage according to changes in the rotational speed of the main shaft is connected to the piezoelectric element.

In the above structure, a moving member that can slide in the axial direction is provided between the piezoelectric element and the outer cylinder, and high-pressure fluid is introduced and discharged between the moving member and the outer cylinder via the pressure control means. It is also possible to have a structure in which a pressure chamber is provided.

[Effect]

In the above structure, when the main shaft rotates at low speed, a high voltage is applied to the piezoelectric element to cause it to expand greatly and press the bearing box.
Apply weight pressure to the bearing. Conversely, when the rotational speed of the main shaft increases, the voltage applied to the piezoelectric element is reduced, causing the piezoelectric element to contract and reducing the amount of preload on the bearing.

By continuously adjusting the expansion and contraction of the piezoelectric element in response to changes in the rotational speed, the preload amount can be continuously and smoothly switched.

In this case, since the amount of expansion and contraction of the piezoelectric element is determined with high precision in proportion to the applied voltage, the amount of preload can be made to match the set value accurately by adjusting the applied voltage.

[Example] Hereinafter, an example of the present invention will be described based on the accompanying drawings.

As shown in FIG. 1, the main shaft 2 inserted through the outer cylinder 1 is rotatably supported at both ends by bearings 4.5 and 6.7 arranged in parallel with a spacer 3 interposed therebetween. ing. The pair of bearings 4.5 and 6.7 are angular contact ball bearings, and are arranged back-to-back when installed! be done.

The bearing 4.5 on the one end side is directly assembled into the outer cylinder 1, and the main shaft end on the bearing side becomes the side on which the workpiece is attached in the use state.

On the other hand, the bearing 6.7 at the other end has an inner ring fixed to the outer diameter surface of the main shaft 2, and an outer ring installed inside a bearing box 8 inserted between the outer cylinder 1.

In this structure, when the bearing box 8 moves in the axial direction, the spacer 3
presses on the outer ring of bearing 6 and a preload is applied to each bearing 4.5.6.7.

On one end side of the bearing box 8, an operating member 9 and an intermediate ring 1 are provided.
0, and both of them are inserted into the bearing box 8 and the outer cylinder 1 inside the outer cylinder 1 so that they can move independently in the axial direction.

Furthermore, a plurality of piezoelectric elements 11 are installed between the opposing surfaces of the actuating member 9 and the bearing box 8 at predetermined intervals in the circumferential direction. This piezoelectric element 11 is arranged so that its expansion and contraction direction coincides with the axial direction of the spindle, and is set so that a gap 12 is formed between the actuating member 9 and the bearing box 8 in the most contracted state. There is.

Further, each piezoelectric element 11 is connected to a voltage application device 13 that can change the applied voltage. This voltage application device 13 receives signals from a rotation detector 14 that detects the rotation speed of the main shaft 2 and a temperature detector 15 that detects the bearing temperature, and based on the input signals, The amount of expansion and contraction of the piezoelectric element 11 to give the amount of preload is calculated, and the voltage corresponding to the calculated amount of expansion and contraction is applied to the piezoelectric element 1.
1.

Further, the voltage application device 13 is configured to receive a signal from a hydraulic control device 26, which will be described later, to indicate the preload setting state of the control device.

On the other hand, an adjustment member 16 that is inserted into the inner diameter side of the intermediate ring 10 and the actuating member S is incorporated in the inner end surface 1a of the outer cylinder 1. This adjustment member 16 is composed of a flange portion 17 for positioning, and a ring portion 18 inserted into the inner diameter side of the intermediate ring 10 and the actuating member 9.
7 is engaged with a summer fixing pin 19 that protrudes from the outer cylinder 1.

The ring portion 18 also includes a stepped portion 22 that limits the movement of the actuating member S, and a stepped portion 21 that limits the movement of the intermediate ring 10.
The operating member 9 is provided with a stepped portion 22 corresponding to the stepped portion 20 . In the above shape, the gap δ1 between the step portion 22 of the actuating member 9 and the step portion 20 of the ring portion 18 is equal to the gap δ2 between the intermediate ring 10 and the step portion 21.
It is set to be thicker ((δ1>δ2)).

In addition, when the adjusting member 16, the intermediate ring 10, and the actuating member 9 are assembled as described above, between the adjusting member 16 and the intermediate ring 10, and between the intermediate ring 10 and the actuating member 9,
Hydraulic chambers 23 and 24 are formed in each hydraulic chamber 23 and 24, and a tm on-off valve 2 is installed in each hydraulic chamber 23 and 24, respectively.
A hydraulic control device 26 is connected via 5.

This hydraulic control device 26, like the voltage application device 13,
A signal indicating the rotation speed of the main shaft 2 is input from the rotation detector 14, and a function is provided to switch the introduction and discharge of hydraulic oil to each hydraulic chamber 23, 24 based on this signal. ing. Furthermore, when switching between introducing and discharging the hydraulic oil is performed, a signal is outputted to the voltage application device 13 each time the switching is performed, as described above, and the piezoelectric element 11 is operated in conjunction.

Further, a spiral groove 27 is formed on the inner peripheral surface of the outer cylinder 1, and a hydraulic control device 26 is connected to this spiral groove 27 via a switching valve. When this is applied, the bearing box 8 contracts to facilitate axial movement.

Such a spiral groove 27 may be provided on the outer periphery of the bearing box 8, and is not limited to a spiral groove.
Any material may be used as long as it facilitates the movement of the bearing box, for example,
There is also a method of incorporating a ball slide between the fitting surfaces of the bearing box 8 and the outer cylinder 1.

The spindle unit of this embodiment has the structure as described above, and its operation will be explained next.

In the second embodiment, the magnitude of the preload (■) on the bearing is set by the amount of movement of the bearing box 8.
The amount of movement can be adjusted by adjusting the adjustment member 16, the actuating member 9 and the intermediate +
) The movement of the bearing box 8 is determined by the size of the gap that exists between the rings 10, and the movement of the bearing box 8 is determined by the pressure generated by introducing and discharging high pressure oil into each hydraulic chamber 23, 24, and the expansion and contraction of the piezoelectric element 11. It is carried out by

First, when setting the weight pressure in the low speed rotation range, apply a high voltage to the piezoelectric element 11 and extend the piezoelectric element to the maximum, and then drain oil from the left hydraulic chamber 23 as shown in Fig. 2. Then, supply oil to the right hydraulic chamber 24 and apply pressure. As a result, the intermediate ring 10 moves to the left, and the adjustment member 1
6 is pressed against the end surface 1a of the outer cylinder and is fixed, and the actuating member 9 moves to a position where the stepped portions 20 and 22 abut. Therefore, as shown in Fig. 4, the bearing has δ1
A preload P corresponding to , is applied, resulting in a heavy weight state.

In this state, when the rotation of the main shaft 2 is increased, the preload amount gradually increases as shown by the broken line in Fig. 4 due to the expansion of the bearing due to increasing centrifugal force and heat generation. Absorption is controlled by shrinking the dimensions of the element 11.

This control is performed by using the voltage application device 13 to calculate the increase in the amount of preload from the information on the rotational speed of the main shaft and the bearing temperature, and determining the amount of movement of the bearing box 8 to prevent the increase from occurring from the calculated value. This is carried out by determining the amount of expansion and contraction of the piezoelectric element 11 in order to apply the amount of movement to the bearing box 8, and then applying a voltage to the piezoelectric element 11 corresponding to the obtained amount of expansion and contraction.

By continuously controlling the voltage applied to the piezoelectric element 11 according to changes in the rotation of the main shaft, the increase in preload can be absorbed by the expansion and contraction of the piezoelectric element 11, as shown by the solid line in FIG. As shown, a constant preload condition can always be obtained.

When the rotational speed of the main shaft 2 increased and the preload increase approached the maximum contraction amount of the piezoelectric element, the spindle was switched to the core pressure setting state, and a high voltage was applied to the piezoelectric element 11 to expand the piezoelectric element to the maximum. In this case, as shown in FIG. 3, oil is drained from the right hydraulic chamber 24, oil is supplied to the left hydraulic chamber 23, and the intermediate ring 10 is moved until it comes into contact with the stepped portion 21. . As a result, the bearing has δ2
A preload corresponding to P1 is applied, and the preload at the time of the switched rotational speed is set to match the initial preload P1.

After this preload switching, the increase in preload that occurs as the rotation of the main shaft increases can be absorbed by controlling the voltage applied to the piezoelectric element 11, as described above, and the preload can be maintained constant.

On the other hand, the rotation of the main shaft 2 further increases, and the piezoelectric element converges to 1I.
When the II field approaches, the setting is switched to a light preload state, and a high voltage is applied to the piezoelectric element 11 to make the piezoelectric element maximally expanded. In this case, both hydraulic chambers 23.
Drain the oil from 24 and reduce the hydraulic pressure to zero. This results in
The intermediate ring 10 and the actuating member 9 move to the left, and the bearing box 8
returns to the state shown in FIG. 1, and a light preload is applied to each bearing.

The preload increase after this switching is caused by the piezoelectric element 1 as described above.
This can be prevented by changing the amount of shrinkage.

As described above, by switching the preload setting state by moving the intermediate ring 10 and the actuating member 9, and absorbing the increase in preload due to the increase in rotation by controlling the voltage of the piezoelectric element 11, as shown by the solid line in FIG. As such, the preload can always be maintained constant regardless of changes in the rotational speed, and stable preload can be performed at a fixed position.

Further, when changing the preload at each stage, oil is supplied to the spiral groove 27 to contract the bearing box 8, thereby allowing smooth movement.

On the other hand, when the rotational speed of the main shaft 2 is decreased from N3, oil may be supplied to and discharged from each hydraulic chamber 23, 24 in a manner opposite to that described above.

In the above example, the piezoelectric element 11 was contracted by the increase in preload due to the increase in rotation, but if the piezoelectric element 11 is contracted by more than the increase in preload, as shown in FIG. It is possible to control the preload to become gradually lighter as the preload increases.

Furthermore, if the piezoelectric element 11 has a sufficient amount of expansion and contraction to apply a preload from heavy weight pressure to light preload to the bearing, it is possible to apply an arbitrary amount of preload to the bearing simply by expanding and contracting the piezoelectric element. , continuous preload variable control can be performed. In this case, the adjustment member 16 and the intermediate ring 10 can be omitted, and the structure of the spindle can be simplified.

Further, in the above embodiment, the bearings 6, 7 are installed inside the bearing box 8, but they may not be installed inside the bearing box in this way, but the outer ring of the bearing may be pressed by both sides of the bearing box.

Furthermore, in the above example, the bearing box 8 and the intermediate ring 10 are used, and the preload is switched in three stages by the two gaps δ1 and δ: with respect to the adjustment member 16, but the number of intermediate rings and the stage of the adjustment member are By increasing the number of sections, it is possible to increase the number of preload changes.

〔Effect of the invention〕

As described above, this invention incorporates a piezoelectric element between the outer cylinder and the bearing box, and expands and contracts the piezoelectric element in response to changes in the rotational speed of the main shaft. The amount of preload can be continuously changed over the period of time, and smooth preload switching can be performed.

Furthermore, since the amount of preload is set by the expansion and contraction of the piezoelectric element, the preload can be accurately adjusted to the set value, resulting in stable spindle rigidity and improved rotation accuracy.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIGS. 2 and 3 are sectional views showing the same operating state, and FIGS. 4 and 5 are graphs showing the preload switching process, respectively. . 1...Outer cylinder, 2...Main shaft, 4.5.6.7...Bearing, 8...
Bearing box, 9... Operating member, 10...
...Middle ring, 11...Piezoelectric element,
13... Voltage application device, 16...
Adjustment member, 23.24... Hydraulic chamber, 26
・・・・・・Hydraulic control device.

Claims (2)

[Claims] (1) A bearing box that presses the bearing supporting the main shaft in the axial direction is movably provided inside the outer cylinder through which the main shaft is inserted, and a piezoelectric element that expands and contracts in the axial direction is placed between the bearing box and the outer cylinder. A continuously variable preload spindle unit that incorporates a piezoelectric element and connects a voltage application device that changes the applied voltage according to changes in the spindle rotation speed. (2) A moving member that can slide in the axial direction is provided between the piezoelectric element and the outer cylinder, and a pressure chamber into which high-pressure fluid is introduced and discharged via a pressure control means between the moving member and the outer cylinder The continuously variable preload spindle unit according to claim 1, further comprising: