JPH0796180B2 - Thermal expansion compensator for lead screw - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compensating device for thermal expansion of a feed screw in a machine tool in which a driven body is position-controlled by a feed screw.

Conventional technology When a machine tool is operated for a long time, the feed screw that feeds the driven body generates heat due to friction with the nut and expands in the axial direction.Therefore, when the driven body is fed to the target position commanded in NC control, In the case where the current position is detected by rotating the feed screw, an error due to the thermal expansion actually occurs.

Problems to be solved by the invention Therefore, in the case of aiming for highly accurate position control, environmental conditions are maintained so that the positioning error is within an allowable range during long-time operation, or products are frequently inspected to compensate the feed amount. Care is required.

Means for Solving the Problems In a machine tool in which a driven body is moved and positioned by rotation of a feed screw, a nut screwed with the feed screw and a nut fitted to such an extent that the nut can move in an axial direction. A first piezoelectric element axially interposed between the housing and a reference side end of the feed screw; and a nut housing fitted to the driven body so as to be movable in the axial direction with the first piezoelectric element interposed. A second piezoelectric element axially interposed between the driven body and the opposite end of the nut housing, and a displacement sensor for detecting a displacement of the length of the feed screw at a shaft end which is not the reference side of the feed screw. A voltage that changes corresponding to the displacement of the feed screw is applied to the first and second piezoelectric elements based on a signal from the displacement sensor, and a voltage is applied to each of the first and second piezoelectric elements in advance. By returning the voltage to zero And rising remove the effect of hysteresis of the process, first, those comprising a voltage control means for controlling a voltage in a direction that acts only extension of the second piezoelectric element during use.

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

In a machine tool such as a well-known NC lathe, a turret tool rest 4 is provided on the upper surface of a center table 3 mounted on a guide surface 2 in the X-axis direction on a saddle 1 which is guided in the Z-axis direction and position-controlled. It is provided. A ball screw nut unit 5 is provided on the lower surface of the center table 3, and the ball screw nut unit 5 is rotated via a gear group 7 from a servomotor 6 provided at the rear portion of the saddle 1, and is supported at one end by a bearing 8. It is screwed with a ball screw 9 which is axially restricted and supported only for rotation. And the ball screw nut unit 5
A nut that is screwed onto the ball screw 9 and has a flange 10 on the end surface.
11 and backlash removing nut 12 together with nut housing 14
Is mounted on the flange of the nut 11 on the side opposite to the flange 10.
A nut housing 14 having 13 is fitted to a bracket 15 attached to the lower surface of the middle table 3. Then, the nut 11 is tightly fitted into the hole 14a of the nut housing 14 so as to be movable in the axial direction, and the flange 10 and the end surface of the nut housing 14 are united with the bolt 17 via the piezoelectric element assembly 16 so as to integrally shaft the both. It is fixed in the direction.

For the piezoelectric element, for example, the product name Piezo Stack manufactured by Nippon Tokuyo can be used. When such a ceramic piezoelectric element is used alone, there is a large hysteresis regarding the applied voltage and the amount of displacement, especially in the rising process, as shown in FIG. Therefore, even if the applied voltage is zero, the displacement does not return to zero. For this reason, a prescribed voltage is once applied to each of the first and second piezoelectric element assemblies in advance, and the voltage is returned to zero to eliminate the effect of the initial rising hysteresis. Further, a plurality of piezoelectric treatments are laminated to form an assembly so that a predetermined displacement amount can be obtained with a low applied voltage. However, since a tensile force cannot be applied to the laminated piezoelectric element assembly,
Two sets of piezoelectric element assemblies are used so that they are extended only by being extended by an applied voltage, and a displacement amount for compensating the displacement of the coating driving body with respect to expansion and contraction of the feed screw is secured.

The nut 12 is slid into the hole 14a of the nut housing 14 and the key 1
The backlash is removed by a spring 19 which is fitted in the key groove 14b and is prevented from rotating, and which is inserted between the nut 8 and the nut 11. Further, the nut housing 14 is tightly fitted in the hole 15a of the bracket 15 so as to be movable in the axial direction, and is integrally formed in the axial direction by the bolt 21 via the piezoelectric element assembly 20 between the flange 13 and the end surface of the bracket 15. It is fixed to. A displacement sensor 22 that outputs a signal having a magnitude corresponding to the amount of displacement of the ball screw 9 that has detected thermal expansion is mounted in the saddle 1 on the axis of the ball screw 9 so as to correspond to the shaft end.
As the displacement sensor 22, for example, an analog sensor AH series manufactured by Reed Electric Co., Ltd. is used, and an output voltage inversely proportional to the distance (gap) is obtained by combining the controller with the AS-440 series in a non-contact manner. Each piezoelectric element assembly 16 and 20 is connected to a switch 23, a DC power source 24, and a variable resistor 25 in series by another circuit, and the variable resistor 25 is controlled by returning to the output of the displacement sensor 22 to apply the piezoelectric element. The voltage is changed to change the displacement amount of the element.

That is, when the clearance between the ball screw 9 and the displacement sensor 22 decreases due to thermal expansion, the output of the displacement sensor 22 increases. In order to retract the turret 4 by the amount of the extended displacement, the piezoelectric element assembly 20 is subjected to the same displacement + expansion amount of the ball screw, and when the ball screw contracts and the gap with the displacement sensor 22 increases, the displacement sensor The respective applied voltages are determined so that the output of 22 becomes small and the piezoelectric element assembly 16 is displaced in the extension direction by the same amount as the contraction amount of the ball screw.

Before starting the operation, first, the switch 23 is turned on to sequentially apply the specified voltage to the piezoelectric element assembly 16 or 20 to give the maximum displacement, and the voltage is returned to zero to eliminate the hysteresis in the rising process. Then run continuously nuts 11,1
The ball screw 9 is thermally expanded by heat generated by friction with 2. The variable resistor 25 is controlled by the output of the displacement sensor 22 corresponding to the clearance at the ball screw end, the applied voltage of the piezoelectric element assembly 20 is adjusted, and the constant number is set so that a product with stable dimensions can be obtained by trial cutting. Set. Ball screw 9
Operation is stopped in the state of thermal expansion of the ball screw and the amount of shrinkage of the ball screw due to cooling is detected by the displacement sensor, and the output controls the variable resistor 25 to adjust the applied voltage of the piezoelectric element assembly 16 to the shrinkage amount. The constant is set so that the corresponding amount of elongation is obtained.

After the adjustment of the compensation device including the characteristics of the element and the characteristics of the mechanism is completed in this way, the respective switches 23 of the piezoelectric element assemblies 16 and 20 are continuously turned on to start the actual operation.

As the ball screw 9 thermally expands, the gap between the ball screw 9 and the displacement sensor 22 becomes smaller, and the output from the displacement sensor continuously increases in accordance with the expansion. This output enables piezoelectric element assembly
The variable resistor 25 of 20 acts to increase the applied voltage and deforms the piezoelectric element so as to stretch accordingly. Therefore, the center table 3 is retracted by the ball screw 9 by the amount of thermal expansion with respect to the feed amount, and the blade T is correctly positioned at the commanded target position.

After lunch, etc., the operation is temporarily stopped, the temperature of the ball screw drops, and the gap between the displacement sensor and the ball screw becomes large.
The output of the sensor becomes small, and the piezoelectric element assembly 16 is given a corresponding displacement to extend the amount of contraction and move the intermediate platform 3 forward.

Effect As described in detail above, according to the present invention, the length is displaced by the applied voltage between the nut screwed with the feed screw and the driven body.
The first and second piezoelectric element assemblies are axially fixed via a nut housing, a displacement sensor for detecting the thermal expansion of the feed screw is provided, and a circuit for changing the applied voltage by the signal output of the displacement sensor is provided in advance. 1, After the specified voltage is applied to the 2nd piezoelectric element assembly, it is used so that only the extension works when the voltage is returned to zero, so the hysteresis of the first rising of the piezoelectric element is eliminated and the characteristics are improved. Displacement due to expansion can be continuously and accurately compensated instead of stepwise compensation, which has the effect of contributing to unmanned long-term operation.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of the present apparatus, FIG. 2 is an explanatory sectional view of a ball screw nut unit, and FIG. 3 is a characteristic diagram of a relationship between an applied voltage applied to a single piezoelectric element and a displacement amount. 3 …… Middle base 5 …… Ball screw nut unit 9 …… Ball screw, 11,12 …… Nut 14 …… Nut housing, 15 …… Bracket 16,20 …… Piezoelectric element assembly, 22 …… Displacement sensor 24 …… DC power supply, 25 …… Variable resistor

Claims (1)

[Claims] 1. A machine tool in which a driven body is moved and position-controlled by the rotation of a feed screw, and a nut that is screwed with the feed screw and a nut housing in which the nut is fitted to such an extent that the nut can move in an axial direction are fed. A first piezoelectric element axially interposed between a screw and a reference side end of the screw, and a nut housing in which the nut housing is fitted to a driven body so as to be movable in the axial direction and the first piezoelectric element is interposed. A second piezoelectric element that is axially external to the driven body at the opposite end, a displacement sensor that detects the length displacement of the feed screw at the shaft end that is not the reference side of the feed screw, and the displacement sensor A voltage that changes corresponding to the displacement of the feed screw is applied to the first and second piezoelectric elements based on the signal of 1., and a voltage is applied to each of the first and second piezoelectric elements in advance, and the voltage is set to zero. By returning to 1. A thermal expansion compensating device for a feed screw, comprising: voltage control means for removing the effect of sterisis and controlling the voltage in a direction in which only the expansion of the first and second piezoelectric elements acts when in use.