JPH03184743A - Heat displacement compensator - Google Patents

Abstract

PURPOSE:To secure such a heat displacement compensator as making the extent of heat displacement surely compensable by measuring the expansion or contraction of a reference scale supported on a headstock by a displacement sensor attached to a tool rest, and compensating the relative displacement between the headstock and the tool rest. CONSTITUTION:One end of a horizontal reference scale 6 is fixed to the peripheral surface of a headstock 2 and other end is set free the other way whereby this scale 6 is overhangingly supported, and it is constituted of an umber material or the like of 1/10 of general steel in a linear expansion factor. Next, a displacement sensor 7 reading graduations of the scale 6 is attached to a spot nearest to a tool rest 5 of a carriage 12, measuring the displacement and slippage of the scale 6 to the command value of a numerical control system. In this slippage, a positioning error of the carriage 12 due to heat expansion in a driving ball screw 9 of the carriage 12 and the relative displacement with the carriage due to heat displacement of the headstock 2 are included. Accordingly, the measured value of the sensor 7 is inputted into the NC system, and it is subjected to feedback to a command value for axial movements, so that heat displacement between the headstock 2 and the carriage 12 can be compensated.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a thermal displacement correction device for a machine tool.

<Prior Art> Conventional thermal displacement correction devices do not directly measure the relative displacement between the headstock and the tool post, but instead measure the displacement of the tool post itself from its reference position. For example, a conventional thermal displacement correction device will be explained using an NG lathe shown in FIG. 2 as an example. As shown in the figure, on the bed 13, the carriage 12 is screwed onto a ball screw 9 arranged in the horizontal direction Connected.

Further, on the carriage 12, the tool rest 3 is screwed onto a ball screw 11 arranged in the vertical direction Z in the figure, and one end of the ball screw 11 is rotatably supported, and the other end is connected to the motor 10. There is. Therefore, the carriage 13 can move on the bed 13 in the horizontal direction X in the figure, and the tool rest 3
can further be moved in the vertical direction Z in the figure on the carriage 13. A cutter 5 is attached to the cutter rest 3 via cutlery 4.

On the other hand, a headstock 2 is installed on the bed 13, and a workpiece (not shown) is gripped by a chuck I on the headstock 2.

Here, the relative distance in the vertical direction Z in the figure between the axis of the chuck 1 that grips the workpiece and the cutting tool 5 that cuts the workpiece determines the machining accuracy of the workpiece.

However, since the headstock 2 has a built-in rotating body,
The rotational motion generates heat, causing thermal deformation of the headstock 2 and the carriage I2.

Therefore, in the past, a displacement sensor 7 was attached to the tool post 3, and a scale 6 was disposed on the carriage 12 along the vertical direction Z in the figure. Then, the measurement error between the value read by the displacement sensor 7 and the command value commanded for actually cutting the workpiece is added or subtracted from the command value as a correction amount to perform correction including thermal displacement. was.

<Problems to be Solved by the Invention> However, although the above method can correct thermal displacement between the carriage I2 and the tool rest 3, the bed 13 supporting the carriage 12
There was a problem that the error due to thermal deformation could not be fully corrected.

The present invention has been made in view of the above-mentioned prior art,
It is an object of the present invention to provide a thermal displacement correction device that can reliably correct thermal displacement.

<Means for Solving the Problems> The configuration of the present invention to solve the above object is that in a machine tool having an NC control device, a headstock for holding a workpiece, a tool rest having a cutting tool for cutting the workpiece, A reference scale cantilevered from the headstock, a displacement sensor attached to the tool post, and the displacement sensor measures expansion and contraction of the reference scale, and corrects relative displacement between the headstock and the tool post. It is characterized by

Effect〉 The value measured by the displacement sensor of the expansion and contraction of the reference scale and N
When determining the error in the value commanded by the C control device, the error includes not only the thermal displacement of the tool rest and the carriage on which it is mounted, but also the heat of the headstock and the bed on which it is mounted. It also includes displacement, etc. Therefore, this error is
By importing the command values into the device and correcting the command values, the precision of the workpiece can be improved.

<Example> Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows an embodiment of the present invention. As shown in the figure, a reciprocating table 12 is screwed onto a ball screw 9 disposed on the bed 13 in the horizontal direction is connected to.

On the carriage I2, a tool post 3 is screwed onto a ball screw 11 arranged in the vertical direction Z in the figure, and the ball screw 1
One end of 1 is rotatably supported, and the other end is connected to the motor IO.
is connected to. , Therefore, the carriage 13 is
In addition to being able to move in the horizontal direction X in the figure, the tool rest 3 can further move in the vertical direction Z in the figure on the carriage 12. A cutter 5 is attached to the cutter rest 3 via cutlery 4.

On the other hand, a headstock 2 is installed on the bed 13, and a workpiece (not shown) is gripped by a chuck I on the headstock 2.

Further, one end of the horizontal reference scale 6 is fixed to the outer peripheral surface of the headstock 2, and the other end is left free.
is cantilevered.

This standard scale 6 has a linear expansion coefficient of l/10 of that of general steel.
The rope is made of, for example, umber material. A displacement sensor 7 that reads the scale of this reference scale 6 is
It is attached to the position closest to the cutting tool 5 on the carriage 12. This displacement sensor 7 measures the deviation between the displacement of the reference scale 6 and the command value from the NC device. This deviation includes a positioning error of the carriage 12 due to thermal expansion of the ball screw 9 that drives the carriage 12 and a relative displacement of the carriage 12 due to thermal displacement of the headstock 2 with respect to the carriage. Therefore, by taking the measured value of the displacement sensor 7 into the NC device and feeding it back to the axis movement command value, the headstock 2 and the carriage I
It is possible to correct the thermal displacement between 2 and 2.

Moreover, since the displacement sensor 7 is attached as close as possible to the cutting tool 5, the influence of thermal displacement of the carriage 12 is minimized. Furthermore, since the coefficient of thermal expansion of the reference sensorf is small, there is little measurement error due to its own influence.

In the above embodiment, the reference scale 6 is made of amber material having a relatively small coefficient of linear expansion, but other materials having a small coefficient of linear expansion may be used.

<Effects of the Invention> As described above in detail based on the examples, the present invention has the following effects.

(1) Misalignment in positioning due to thermal expansion of the ball screw that drives the carriage of a machine tool can be corrected, improving the machining accuracy of the workpiece.

(2) Furthermore, since the reference scale is fixed to the headstock, it is possible to directly measure and correct deviations in relative displacement due to thermal displacement between the headstock and the carriage due to heat generation in the headstock.

(3) If a material with a low coefficient of linear expansion, such as amber or glass, is used for the reference scale, errors due to thermal displacement of the scale itself will be reduced and measurement accuracy will be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a thermal displacement correction device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional thermal displacement correction device. In the drawing, ■ is the chuck, 2 is the headstock, 3 is the tool post, 4 is the tool head, 5 is the cutting tool, 6 is the reference scale, 7 is the displacement sensor, 8.10 is the motor, 9.11 is the ball screw, 12 is the The carriage, 13, is a bed.

Claims (1)

[Claims] In a machine tool having an NC control device, a headstock that holds a workpiece, a toolrest that has a cutting tool that cuts the workpiece, a reference scale that is cantilevered from the headstock;
A thermal displacement correction device comprising: a displacement sensor attached to the tool rest; and a displacement sensor that measures expansion and contraction of the reference scale to correct relative displacement between the headstock and the tool rest.