JPS63308263A - Pre-load adjusting device for ball screw - Google Patents

Abstract

PURPOSE:To secure necessary rigidity by interposing a piezo-electric actuator between double nuts screw-engaged with a screw shaft through balls to adjust pre-load to the balls in a ball screw for a XY table or the like. CONSTITUTION:When a motor 5 of a ball screw mechanism A is driven, a screw shaft 1 is rotated through gears 6, 4 and nuts 9, 10 are rectilinearly moved through balls 8, so that a work table 16 is transferred in the direction of an arrow X along a track table 18. When a designated voltage is applied to a piezo-electric actuator 11 interposed between the nuts 9, 10, the actuator is elongated in the axial direction to urge both nuts 9, 10 in the separating directions, whereby pre-load is given to the balls 8. Thus, the necessary rigidity of the ball screw mechanism can be secured to improve the working accuracy. At the time of no-load feeding, pre-load is cancelled to prevent the occurrence of disadvantages such as lowering of the life, generation of heat and so on.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a ball screw used in a driving part of an X-Y table for a machine tool, etc. It is characterized by being adjustable.

(Prior art) This type of ball screw mechanism is one in which a nut is screwed onto a long screw shaft via a ball, and the nut is moved in the longitudinal direction of the screw shaft by rotationally driving the screw shaft. ,
In this case, even if there is some backlash in the direction of nut movement, especially when this ball screw mechanism is applied to a machine tool, it will cause play in the axial direction, making it impossible to achieve high-precision machining. be.

Therefore, to eliminate the axial play of such a ball screw mechanism,
Alternatively, in order to increase the rigidity of the constituent members, a method has been adopted in which a preload is applied to the ball screw mechanism. There is a method of applying this preload by interposing a spacer between two nuts and adjusting the thickness of this spacer.

(Problems to be Solved by the Invention) However, according to the conventional method of applying preload described above, it is not possible to arbitrarily change the preload m in accordance with changes in load during cutting, etc. Not only does the lack of positioning accuracy reduce positioning accuracy, making it impossible to perform high-precision machining, but also a cutting reaction force acts on the work table, causing problems such as chatter on the cutting surface. On the other hand, if an excessive amount of preload is applied to increase the rigidity, the work table not only cannot be moved rapidly due to an abnormal increase in the jH dynamic resistance, but also causes problems such as heat generation and shortened service life.

Therefore, the present invention was made in view of the above circumstances, and its purpose is to enable preload to be adjusted arbitrarily depending on the usage conditions, thereby improving positioning accuracy and ensuring the necessary rigidity, and making it easy to use. The object of the present invention is to provide a ball screw mechanism that can perform rapid traverse.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a piezoelectric actuator that is interposed between a double nut that is screwed onto a screw shaft via a ball, and that the actuation of the piezoelectric actuator causes the double nut and the screw to be connected to each other. The preload applied to the ball between it and the shaft can be adjusted.

(Function) In the present invention having the above-mentioned configuration, if a unidirectional electric field is applied to the piezoelectric actuator interposed between the double nut, the piezoelectric actuator will expand due to the piezoelectric reverse effect. The required amount of preload can be applied to the ball. In this case, since the voltage applied to the electrodes of the piezoelectric actuator and the amount of displacement of the piezoelectric element are in a proportional relationship, the amount of preload can be adjusted steplessly by controlling the amount of applied voltage.

(Example) An example of the present invention will be described below based on the accompanying drawings.

Fig. 1 is a vertical sectional side view of the main part of a ball screw mechanism according to the present invention, Fig. 2 is a partially cutaway side view of a one-way table that employs the same ball screw mechanism, and Fig. 3 is a side view of an x-y table. FIG.

In FIG. 2 showing a state in which the ball screw mechanism according to the present invention is applied to a one-way table of a machine tool, reference numeral 1 denotes a screw shaft installed horizontally between side walls 2a and 2b of the housing body 2, and the screw The shaft 1 is rotatably supported by the side walls 2a, 2b by ball bearings 3.3. A gear 4 is connected to one end of the screw shaft 1.
The gear 4 meshes with a gear 6 connected to the end of the output shaft of a motor 5.

By the way, as shown in FIG. 1, the screw shaft 1 has a continuous spiral groove 7 formed therein, and the screw shaft 1 has a plurality of balls 8 that engage with the spiral groove 7. Two nuts 9 and 10 are movably screwed together at a predetermined interval. A single or halved annular piezoelectric element 11 is interposed between both double nuts 9 and 10. Since this piezoelectric element has a characteristic that it expands and contracts when a voltage is applied to it, in the present invention, the piezoelectric element is configured as a piezoelectric actuator (displacement element) that utilizes this characteristic. Note that the piezoelectric actuator may be formed by a plurality of rod-shaped piezoelectric elements arranged parallel to the screw axis l. A ball screw mechanism A is formed by the screw shaft 1, double nuts 9 and 10, and piezoelectric actuator 11 described above.

Further, as shown in FIG. 2, both nuts 9 and 10 are held by a bracket 15 hanging from a work table 16, and this work table 16 has slide guides 17...
The work table 16 is configured to be movable in the lateral direction along a pair of front and rear tracks 18 and 18 that are laid parallel to each other in the direction perpendicular to the plane of the paper, and a workpiece W is set on the work table 16. In FIG. 2, reference numeral 19 denotes a tool such as a milling cutter that is rotationally driven by a drive source (not shown) to machine the upper surface of the workpiece W.

Next, the effect on this ball screw mechanism will be explained.

For example, when the motor 5 of the ball screw mechanism A is driven, the rotational force of the motor 5 is transmitted to the screw shaft 1 through the gear 6.4, and the screw shaft 1 is rotated at a fixed position. and,
This rotation of the screw shaft 1 causes the nut 9.10 to tighten the screw shaft 1.
This movement transports the work table 16 along the track 18.18 in the XX direction.

Thus, for example, the nut 9 constituting the ball screw mechanism A
．． When an electric field is applied to the piezoelectric actuator 11 interposed between the piezoelectric actuators 10 and 10, the piezoelectric actuator 11 expands in the axial direction due to piezoelectric reverse effect, biasing both nuts 9 and 10 in the direction of separating them from each other, and the ball screw mechanism. Increase the preload of △. This not only eliminates the axial backlash of the work table 16 along the XX direction, but also increases the rigidity of the ball screw mechanism A.

Furthermore, the ball screw mechanism according to the present invention can be used in the X-Y direction of a machine tool.
In FIG. 3 showing a state in which it is applied to a table, the same components as those in the embodiment shown in FIG. 2 are given the same reference numerals. Directly below the first ball screw mechanism A (exactly the same as the ball screw mechanism A in Fig. 2) to be transferred in the X-X direction along the table 18. The second ball screw mechanism B
are provided, and the work table 16 is moved along the tracks 18', 18' in the YY direction orthogonal to the XX direction. Like the first ball screw mechanism A, this second ball screw mechanism B is also composed of a screw shaft, a double nut, and a piezoelectric actuator, and the housing body 2 that holds the first ball screw is connected to the track base 18. By moving the table in the Y-Y direction along the lines ' and 18', the table is moved in the Y-Y direction. In the X-Y table shown in FIG. 3, the method of applying preload to the ball mechanism A and B is exactly the same as in the embodiment shown in FIG.

Next, the mode of preload adjustment will be explained.

(A) In the case of a ball screw mechanism applied to a one-way table, for example, the work table 16 is moved in the direction of arrow a shown in FIG.
When cutting the workpiece W with the tool 19 in a fixed position without transporting the workpiece W, if the preload of the ball screw mechanism A is increased by the operation of the piezoelectric actuator, the workpiece table 16
Since it is fixed in the X-X direction, it is possible to eliminate play in the axial direction and at the same time ensure rigidity, which eliminates the chatter phenomenon on the cutting surface of the workpiece W and allows the workpiece W to be machined with high precision. obtain. (If the amount of preload is eliminated or reduced by reducing the amount of voltage applied to the piezoelectric actuator after shallow area machining is completed, the work table 16 can be easily fast-forwarded without jU dynamic resistance, and the ball screw mechanism concerned Problems such as heat generation and shortened lifespan of A do not occur.

(B) In the case of a ball screw mechanism applied to an The work table 16 is fixed or released in the X direction by applying or releasing preload to the ball screw mechanism A, as in FIG. 2. By the way, when cutting the work W while moving the work table 16 in the x-X direction, the work table 1
6, since the load is acting not only in the X-X direction but also in the direction of the cutting reaction force along the Y-Y direction, Y -
If the backlash in the Y direction is not eliminated and the work table 16 is not rigid, the work table 16 may vibrate in the Y-Y direction, resulting in poor machining accuracy.

Therefore, when applied to an X-Y table as shown in Figure 3, it is necessary to eliminate axial play in the Y-Y direction and improve rigidity by adjusting the preload of the ball screw mechanism B. There is.

Incidentally, when the work table 16 is moved f-heavy in the Y-Y direction, the amount of preload may be reduced as necessary.

(Effects of the Invention) As is clear from the above description, according to the present invention, a piezoelectric actuator is interposed between a double nut that is screwed onto a screw shaft via a ball to configure a ball screw. By expanding and contracting the piezoelectric actuator due to the effect, the preload of the Hall net can be changed arbitrarily according to the usage conditions, thereby ensuring the necessary stiffness. The effect is that the problem can be solved.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional side view of a ball screw mechanism according to the present invention, Fig. 2 is a cutaway side view of a one-way work table of a machine tool incorporating the same ball screw mechanism, and Fig. 3 is a cutaway side view of a one-way work table of a machine tool incorporating the same ball screw mechanism. FIG. 3 is a plan view of the XY work table. Explanation of symbols 1...Screw shaft 8...Ball 9.10...
・Nut 11...Piezoelectric actuator A, B...
・Ball screw mechanism (Fig. 1) Exported by Teitouri Neho Seisho) November 5, 1986

Claims (1)

[Claims] A double nut is screwed onto the screw shaft through a ball, and a piezoelectric actuator is interposed between the two nuts, and the preload applied to the ball between the double nut and the screw shaft is applied by the operation of the piezoelectric actuator. A ball screw preload adjustment device characterized by being adjustable.