JP2876614B2 - Ball screw device and method for adjusting preload of ball screw device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a ball screw device frequently used for devices requiring precise positioning, such as machine tools and robots.
In particular, the present invention relates to an improvement of a variable preload type ball screw device which can adjust the preload state freely from the outside.

[Conventional technology]

Generally, when performing high-precision positioning with a ball screw device, preload is applied to the ball screw as a means to reduce the axial clearance of the ball screw to zero and further reduce the amount of elastic displacement with respect to the axial load to increase rigidity. give.

As such a preloading method, there is, for example, a spacer preloading method. As shown in FIG.
There are two types of methods in which a metal annular spacer C is inserted between the nuts A and B to apply a preload. One method is to insert a spacer between nuts that is thicker by the preload amount to apply preload (tensile preload), and the other is to insert a spacer that is thinner by the preload amount between the nuts and tighten both nuts together by tightening means. This is a method of applying preload (compression preload).

However, the first prior art spacer preloading method is used when the initial set preload state changes due to wear, temperature change, or the like,
It is not possible to cope with intentionally changing the preload to change the torque and rigidity of the screw shaft.

As a countermeasure, a variable preload ball screw device has been proposed in which the preload state can be freely adjusted from the outside.

As a conventional ball screw device of this type, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 61-95757 (second conventional example). This second conventional example includes a means for regulating the relative rotation between the first nut and the second nut screwed to the screw shaft, and a means (spacing) for controlling the axial distance between both nuts. Have. As means for controlling the nut interval, for example, a ring-shaped piezoelectric element as a micro-displacement actuator and a ring-shaped piezoelectric element as a repulsive force detecting device are incorporated between the nuts, and a screw is formed by utilizing the piezoelectric effect of the piezoelectric element. The preload amount of the shaft and the nut is detected as a repulsive force or a fluctuation of the repulsive force of the screw shaft, and the preload amount is variably controlled as necessary.

That is, when the ball screw device is started, the preload amount of the nut is set to zero, and the preload is applied when the predetermined positioning control is started, so that the starting torque at the start of rotation can be reduced. After the preload is applied, if the feedback control is performed to keep the preload constant while detecting the repulsive force or its fluctuation with the repulsive force detector, the torque fluctuation during steady rotation of the ball screw device can be suppressed. There are benefits that can be.

[Problems to be solved by the invention]

In the variable ball screw device of the second conventional example, as means for restricting the relative rotation while allowing the relative displacement of the first nut and the second nut in the feed axis direction,
An elastic member that is connected to both nuts with screws and that can expand and contract in the feed axis direction.The outer cross-section of both nuts is formed in a shape other than circular, and it is formed according to the shape of both nuts and put on both nuts. An axial key groove is provided on the outer surfaces of the fixed sleeve and the nuts, and a parallel key or the like is inserted into the key groove and fixed to one of the nuts.

However, these nut rotation restricting means have a large frictional resistance acting between the nuts due to the tight fit so that no play occurs between the nuts. There is a problem in that a malfunction occurs when adjusting the gap between the nuts by changing the thickness of the spacer.

Also, if an external load exceeding the set value is applied to the nut from the reverse direction (compression direction) in the state where the spacer is thickened, for example, by the voltage control of the piezoelectric element and a tensile preload is applied, a negative preload will result and play will occur. There was a problem that it was easy.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and the purpose thereof is to be able to variably control the preload state from the outside, and to cause a malfunction when adjusting the nut interval, It is an object of the present invention to provide a ball screw device provided with a preload means that does not cause play due to a negative preload.

[Means for solving the problem]

In order to achieve the above object, the present invention according to claim 1 is:
A first nut and a second nut screwed onto the screw shaft;
The relative rotation between the first nut and the second nut is prevented by the key means, and a spacer is interposed between the nuts, and the preload adjustment is performed by variably controlling the axial thickness of the spacer. In the ball screw device described above, the spacer is elastically attached to the spacer when the piezoelectric sheet is stuck alternately on the surface facing the first nut and the surface facing the second nut and strongly clamped by both nuts. It is characterized in that it is configured to cause deformation.

Further, the present invention according to claim 2 has a first nut and a second nut screwed to the screw shaft, and the first nut and the second nut
A ball screw device that prevents relative rotation of the nut by key means, inserts a spacer between the nuts, and variably controls the axial thickness of the spacer to perform preload adjustment. The spacer is characterized in that a piezoelectric element is attached to at least one surface facing the nut, and an AC voltage is applied to the piezoelectric element for a short time immediately before adjusting the preload of both nuts.

[Action]

According to the first aspect of the present invention, when the piezoelectric sheet is stuck alternately on the surface facing the first nut and the surface facing the second nut of the spacer for adjusting the preload amount, the distance between the two nuts is increased. When the spacer is strongly pinched, the spacer is deformed into a waveform and elastically deforms. That is, the spring force due to the elastic deformation of the spacer is applied between both nuts. Even if an external load greater than the set value is applied to the nut from the opposite direction in the elastically deformed state of the spacer, the preload is spring, so the elastic displacement of the spacer does not result in negative preload, thus preventing backlash. Can be.

According to the second aspect of the present invention, immediately before the preload adjustment is performed by supplying a predetermined (DC) voltage to the piezoelectric element and controlling the axial thickness, an AC voltage is temporarily applied to the piezoelectric element. When the spacer is vibrated in the screw axis direction, the large static friction force between the nuts, the key means for regulating the relative rotation thereof, and the spacer is changed to a smaller dynamic friction force. Therefore, the subsequent preload adjustment operation can be performed smoothly, and it is possible to prevent poor preload adjustment due to the static friction force.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1 to 4 show an embodiment of the present invention. A flange-matched double nut structure for providing a predetermined preload by inserting a spacer thicker by a preload amount between two nut flanges. It is a ball screw device. A first nut 3 having a flange 2 on a screw shaft 1;
And a second nut 5 having a flange surface 2A
And 4A are screwed together so that they face each other, and both flange surfaces
The spacer 6 is interposed between 2A and 4A and is integrally connected by a plurality of bolts 7. In addition, 8 is a steel ball circulation tube.

Both sides of spacer 6, that is, surface 6A facing flange surface 2A
As shown in FIGS. 3 and 4, a piezoelectric sheet 10 having a size and shape obtained by dividing an annular body corresponding to the flange surfaces 2A and 4A into a plurality of fan-shaped parts is provided on a surface 6B opposed to the flange surface 4A. It is stuck alternately. The ends of the piezoelectric sheets 10 on both sides 6A and 6B are separated by an interval H so that they do not overlap in the axial direction of the spacer 6. The spacer 6 configured in this manner is the first
Between the nut 3 and the second nut 5 and the bolt 7
When the is tightened, the spacer 6 has a wavy shape, generating spring properties.

A piezoelectric sheet 13 serving as preload detecting means for outputting a voltage corresponding to a change in the interval L between the first nut 3 and the second nut 5 is attached to the outer peripheral surface of the spacer 6. It is.

A keyway 12A is formed in the flanges 2 and 4 of each of the first and second nuts.
Are fitted. The preload fixing key 12 is a means for preventing the relative rotation between the first nut 3 and the second nut 5.

One end of the key 12 is locked to the flange 2 by a screw 15, and the other end is also locked to the flange 4 by a screw 15.

The groove 12B provided in the spacer 6 is an escape for loosely fitting to the key 12. The output voltage of the piezoelectric sheet 13 for detecting the preload of the spacer 6 is received by the detecting device 20. The detecting device 20 detects the voltage generated by the piezoelectric sheet 13 for detecting the preload according to the magnitude of the axial compressive stress of the spacer 6 corresponding to the change in the distance between the first and second nuts 3 and 5. And the drive device as the nut relative displacement signal
Output to 30.

The driving device 30 applies a voltage that compensates for a change in the distance L between the first nut 3 and the second nut based on the nut relative displacement signal input from the detection device 20. And the thickness of the piezoelectric sheet 10 is controlled.

 Next, the operation will be described.

When the spacer 6 in which a plurality of fan-shaped piezoelectric sheets 10 are alternately attached to both sides 6A and 6B is inserted between the first nut 3 and the second nut 5, and the bolt 7 is tightened, the ball A predetermined amount of preload is applied to the screw device. In this case, however, the spacer 6 has a wavy shape at the same time, which causes "springiness", and thus acts as a spring preload. Therefore, even if the first nut 3 or the second nut 3
Even if a load in a direction opposite to the preload direction is applied to the nut 5 from the outside, the preload is prevented by the action of the spring preload. That is, it is possible to prevent a phenomenon in which the screw is loosened due to the negative preload due to the load in the opposite direction.

The amount of preload initially set by the spacer 6 changes due to a temperature change of the ball screw, a lead error of the screw shaft 1, or a wear of the screw or the steel ball. As a result, the torque and rigidity of the ball screw change slightly, which affects high-precision positioning. When such a small change in the preload amount occurs, the interval L between the first nut 3 and the second nut 5 slightly changes. Then, the compressive stress in the spacer 6 changes according to the minute fluctuation of the nut interval L. In response to this stress change, the detection device 20 feeds back a voltage change generated based on the piezoelectric effect of the piezoelectric sheet 13 to the drive device 30. The driving device 30 outputs a predetermined driving voltage based on the feedback signal so as to recover the minute variation of the nut interval L, and applies the driving voltage to the piezoelectric sheet 10 of the spacer 6.

In this manner, by adjusting the thickness of the piezoelectric sheet 10, the amount of preload can be adjusted to prevent fluctuations in the torque and rigidity of the ball screw.

When adjusting the preload amount, the key 12 and the flange of each nut
The static friction force between 2 and 4 may cause resistance and hinder operation. Therefore, in the present embodiment, the spacer 6
A predetermined (DC) drive voltage is output from the driving device 30 to the piezoelectric sheet 10 to adjust the thickness of the piezoelectric sheet 10 and
Immediately before the preload amount is changed, in other words, in a preparation stage of the preload amount adjustment, an AC voltage is temporarily applied from the driving device 30 to the piezoelectric sheet 10 of the spacer 6.

Thus, the piezoelectric sheet 10 and the spacer 6 are finely vibrated in the screw axis direction according to the cycle of the applied AC voltage, and the static friction between the key 12 and the flanges 2 and 4 of each nut is previously reduced to dynamic friction with a small frictional force. On the other hand, it is possible to prevent a malfunction of the preload amount adjustment caused by excessive friction.

Applying a DC voltage to the piezoelectric sheet 10 and adjusting the variation of the preload amount by adjusting the thickness of the piezoelectric sheet 10, the initial preload amount adjustment operation in the ball screw device has changed with time or the like. In this case, the torque and rigidity of the screw shaft can be intentionally changed.

For example, when the ball screw device is used as a feed device for a blade table of an automatic machine tool or the like, the thickness of the spacer 6 such that the preload amount becomes almost zero during teaching work in which a processing reaction force is not applied to the screw shaft. During the actual processing operation, a voltage is applied from the drive unit 30 to the piezoelectric sheet 10 of the spacer 6 to increase the sheet thickness, and a preload having a magnitude corresponding to the processing reaction force is applied. Thus, during the teaching operation, a low torque and low rigidity state is set to facilitate the manual feed of the blade table. On the other hand, at the time of machining, it is possible to achieve high positioning by giving high rigidity that can withstand the machining reaction force.

Also, when the table is rapidly traversed, the spacer 30 from the driving device 30 is moved.
The voltage applied to the piezoelectric sheet 10 in the direction of decreasing the thickness of the piezoelectric sheet 10 can be used to reduce the preload amount and suppress the temperature increase of the screw shaft 1.

Alternatively, in the high acceleration state of rising, the voltage applied from the driving device 30 to the piezoelectric sheet 10 of the spacer 6 is applied to the piezoelectric sheet 10.
The amount of preload is reduced as the direction in which the thickness of the screw 10 is reduced, and the load on the rotary drive motor (not shown) of the screw shaft 1 is reduced. On the other hand, for damping and braking at the time of stop, the voltage applied to the piezoelectric sheet 10 can be controlled by increasing the preload amount in the direction of increasing the thickness of the piezoelectric sheet 10.

 5 and 6 show another embodiment of the present invention.

This embodiment is different from the first embodiment in that an annular piezoelectric sheet 40 as an example of a piezoelectric element is attached to both surfaces 6A and 6B of the spacer 6 (12B is a key groove). I have.

In this case, the annular body is divided into a plurality of fan-shaped
As in the case where the piezoelectric sheets 10 having different shapes are stuck to each other, even if the spacers 6 are inserted between the first nut 3 and the second nut 5 and the bolts 7 are tightened, the spacers 6 It does not strike and produce springiness.

Therefore, unlike the first embodiment, there is no function of "preventing the loss of the preload by the action of the spring preload and preventing the occurrence of screw play due to the load in the opposite direction".

However, when a small change occurs in the preload amount initially set in the spacer 6, a function of adjusting the preload amount by applying a DC voltage to the piezoelectric sheet 40 and adjusting the thickness of the piezoelectric sheet 40, and Immediately before the preload adjustment, a function of temporarily applying an AC voltage to the piezoelectric sheet 40 of the spacer 6 and causing it to vibrate slightly to change static friction into dynamic friction in advance to prevent malfunction of the preload adjustment is described. This is the same as in the first embodiment. In the figure, the annular piezoelectric sheet 40 is attached to both sides of the spacer 6.
6A and 6B are attached, but may be attached to only one side.

In each of the above-described embodiments, the piezoelectric sheet, which is a piezoelectric element, is attached to at least one surface of the spacer, and the preload adjustment by applying the DC voltage and the operation failure prevention of the preload adjustment by applying the AC voltage immediately before are described. Is
It goes without saying that the present invention is also applicable to a variable preload type in which the piezoelectric element itself is used as a spacer.

Although the above-described embodiment has described the ball screw device having the flange-matched double nut structure, the present invention is not limited to this.
It is also applicable to the one flange double nut structure.

Further, if a predetermined amount of initial preload is applied to the piezoelectric sheets 10 and 40 of the spacer 6 by applying a bias voltage from the driving device 30 in advance, the feedback signals from the piezoelectric sheets 10 and 40 of the spacer 6 can be used. By increasing or decreasing the bias voltage, the preload can be controlled to both positive and negative.

The number of keys 12 is not limited to one, but may be plural.

 The piezoelectric sheet may be attached to the key 12.

〔The invention's effect〕

As described above, according to the first aspect of the present invention, the piezoelectric sheets are stuck alternately on both surfaces of the spacer interposed between the two nuts engaged with the screw shaft, and the two nuts are strongly attached. Since the spacer is elastically deformed when pinched, the spacer can be provided with a spring property, and as a result,
When an external load in the preload direction and the reaction direction is applied to the nut, an effect is obtained that a negative preload can be prevented and a play can be prevented.

According to the second aspect of the present invention, in the ball screw device in which the preload adjustment is performed by variably controlling the thickness of the piezoelectric element, the (DC) voltage is applied to the piezoelectric element to perform the preload adjustment. Immediately before that, if an AC voltage is temporarily applied and vibrated, the static friction existing between the two nuts and the detent key can be changed into dynamic friction, and as a result, the preload caused by excessive friction The effect of preventing malfunction of adjustment can be obtained.

[Brief description of the drawings]

1 is a side view showing a main part of one embodiment of the present invention, FIG. 2 is a front view of the one shown in FIG. 1, FIG. 3 is a front view of a spacer shown in FIG. 1, and FIG. Is a side view of the same spacer, FIG. 5 is a front view of another example of spacer, FIG. 6 is a side view thereof, and FIG.
The figure is a longitudinal sectional view of a conventional spacer preloading type ball screw device.

Claims (2)

(57) [Claims] A first nut and a second nut screwed to a screw shaft, wherein relative rotation of the first nut and the second nut is prevented by key means, and a spacer is provided between the nuts; In the ball screw device in which the preload adjustment is performed by variably controlling the thickness of the spacer in the axial direction, the spacer has a surface facing the first nut and a second nut. A ball screw device characterized in that the spacer is elastically deformed when the piezoelectric sheet is alternately stuck to the facing surface and strongly sandwiched between both nuts. A first nut and a second nut screwed to the screw shaft, wherein relative rotation of the first nut and the second nut is prevented by key means, and a spacer is provided between the nuts; In a ball screw device in which preload adjustment is performed by variably controlling the axial thickness of the spacer, the spacer has a piezoelectric element attached to at least one surface facing a nut, A preload adjusting method for a ball screw device, wherein an AC voltage is applied to the piezoelectric element for a short time immediately before adjusting the preload of the nut.