JPH11267948A - Operation control device of machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a highly precise correction by providing a control means for controlling the operating state of a machine tool on the basis of the detection value of a displacement sensor provided in the diameter directional opposite positions on the circumference of a spindle. SOLUTION: The signal showing the difference and sum of signals of both sensors 4a, 4b determined by a computing element 7 are separated to a signal showing the difference and a signal showing the sum by a signal separator 8. Such a signal showing the difference shows the vibration of a spindle. A comparator 9 determines the acceleration of the vibration extending over the radial direction of the spindle on the basis of the signal showing the displacement based on the vibration of the spindle and the signal showing the rotating speed of the spindle, and compares it with a preset reference value. A command is transmitted to an NC device 10 which is a control means to change the working condition of a workpiece by a machine tool in the direction of suppressing the vibration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The machine tool operation control device according to the present invention is incorporated in various precision machine tools to precisely finish the size and shape of a workpiece so that vibration generated during machining can be suppressed. The purpose of the present invention is to prevent the position of a tool supported and fixed at the end of the spindle from being shifted due to a rise in temperature during operation.

[0002]

2. Description of the Related Art A machine tool, such as a machining center, for cutting a workpiece is rotatably supported on a housing by a plurality of rolling bearings on a main shaft. When processing the workpiece, while supporting and fixing a desired tool at the tip of the spindle, and rotating the spindle at high speed,
One or both of the spindle and the table supporting and fixing the workpiece are displaced in three-dimensional directions (X, Y, Z axis directions).

[0003] When such a machine tool is operated, vibration is generated based on the engagement between the tool and the workpiece. If processing is continued while such vibrations have increased to a certain degree or more, good processing cannot be performed, such as deterioration of the surface properties of the processed portion. Further, during machining, the temperature of the spindle increases due to heat generated at a cutting portion of the workpiece by the tool or at the rolling bearing portion, and the overall length of the spindle increases. When the total length of the main shaft is extended due to such a cause, the position of the tool supported and fixed at the tip of the main shaft is changed in the axial direction (Z-axis direction) of the main shaft.
Is displaced. If the machining operation is performed while leaving such a displacement, the size and shape of the workpiece become inaccurate.

For this reason, conventionally, the following method is used.
During the operation of the machine tool, it is possible to prevent the vibration of the spindle supporting and fixing the tool from becoming excessive, or to prevent the position of the tool fixed and supported at the tip of the spindle from being shifted, Some have been implemented. A vibrometer is installed at a fixed part such as the nose of the spindle, and cutting conditions are changed according to the level of vibration detected by the vibrometer to suppress vibration. A temperature sensor is installed on a fixed part such as the nose of the main shaft that rises in temperature with the temperature of the main shaft, and based on an empirical formula showing the relationship between the detected value of this temperature sensor and the actual temperature of the main shaft, the NC device uses: The position of the tip of the spindle is corrected.

[0005]

When the vibration of the main shaft is indirectly detected by the method as described above, the detected value includes a large amount of disturbance, so that it is difficult to perform strict correction. For this reason, if the surface properties of the workpiece cannot be improved, or if the safety factor is increased to improve the surface properties, the processing efficiency deteriorates. Also, when calculating the amount of thermal expansion of the spindle by the method as described above, it is difficult to perform high-precision correction because the influence of aging of the machine tool is large. Is difficult to do. In view of such circumstances, the present invention provides a relatively low-cost machine tool operation control device that is not affected by disturbance, and that can perform high-precision correction regardless of aging of the machine tool. This is what we wanted to achieve.

[0006]

An operation control device for a machine tool according to the present invention is rotatably supported by a housing and a plurality of rolling bearings on the housing and supports a tool for processing a workpiece. It is attached to a machine tool having a fixed main shaft and detects a displacement of the main shaft during operation of the machine tool, and performs control according to the displacement.

In particular, the operation control device for a machine tool according to the first aspect of the present invention is a first operation control device which is provided at a position diametrically opposite the periphery of the main shaft, and each detects a displacement of the outer peripheral surface of the main shaft along the diametric direction. , A second displacement sensor, a calculating means for processing the detected values of the first and second displacement sensors, and based on the detected values of the first and second displacement sensors processed by the calculating means, Control means for controlling the operating state of the machine tool.

[0008] In the case of the operation control device for a machine tool according to the second aspect, the calculating means obtains a value representing the vibration of the main shaft based on the difference between the detection values of the first and second displacement sensors. The control means changes the processing condition of the workpiece by the machine tool in a direction in which the generation of the vibration is suppressed, based on the value representing the vibration of the main shaft.

Further, in the case of the operation control device for a machine tool according to the third aspect, the calculating means determines whether the operation of the spindle is based on the sum of the detection values of the first and second sensors and the rotation speed of the spindle. The thermal expansion is determined, and the control means controls the relative displacement between the tool set in the machine tool and the workpiece in accordance with the thermal expansion of the spindle, regardless of the thermal expansion of the spindle. The processing amount of the workpiece is set to a desired value.

[0010]

According to the machine tool operation control device of the present invention constructed as described above, the vibration of the main shaft or the amount of thermal expansion can be detected with high accuracy, and the operation state of the machine tool can be controlled appropriately and with high accuracy. it can. For example, according to the operation control device for a machine tool described in claim 2, the intensity of vibration of the main shaft can be detected with high accuracy without being greatly affected by disturbance. Because of this,
For example, when the vibration of the main spindle becomes a certain degree or more, the vibration is suppressed by performing control such as reducing the cutting speed of the workpiece by the machine tool supported and fixed to the end of the main spindle. Further, according to the operation control device for a machine tool described in claim 3, the amount of change in the overall length of the main shaft is calculated from the outer diameter change of the main shaft and the amount of elastic deformation of the main shaft based on the centrifugal force,
The position of the tool supported and fixed at the end of the spindle can be accurately determined, and high-precision machining can be performed.

[0011]

1 to 4 show a first embodiment of the present invention, which corresponds to claim 2 of the present invention. A machine tool incorporating the operation control device of the present invention includes a spindle 2 inside a spindle head 1 which is a housing, a ball bearing, a cylindrical roller bearing,
It is rotatably supported via a plurality of rolling bearings 3, 3 such as tapered roller bearings. When cutting a workpiece (not shown), the workpiece is supported and fixed on the upper surface of a table (not shown), and the spindle 2 is rotated at a high speed by a motor (not shown). Then, while moving one or both of the spindle 2 and the table in the three-dimensional direction,
The workpiece is cut by a tool (not shown) supported and fixed to the tip of the main spindle 2 (the left end in FIGS. 1 and 2).

As shown in FIG. 3, non-contact type displacement sensors 4 are provided around the main shaft 2 at diametrically opposite positions.
a and 4b are provided so as to be closely opposed to the outer peripheral surface of the main shaft 2. The two displacement sensors 4a and 4b each use a pair of the same type, each of which can measure a minute displacement. That is, these two displacement sensors 4a, 4b
Does not contact the outer peripheral surface of the main shaft 2 irrespective of the radial vibration of the main shaft 2, but detects the radial vibration as a displacement. Regarding detection of such displacement based on radial vibration, the positive and negative directions of one displacement sensor 4a and the other displacement sensor 4b are reversed at every moment.

The values detected by the pair of displacement sensors 4a and 4b as described above are input to a control device 5 as shown in FIGS. The control device 5 includes the first and second displacement sensors 4.
calculating means for processing the detected values of the first and second displacement sensors 4a and 4b processed by the calculating means; and controlling means for controlling the operating state of the machine tool based on the detected values of the first and second displacement sensors 4a and 4b processed by the calculating means. Is provided. The arithmetic means includes an A / D converter 6 for converting the analog detection signals of the two sensors 4a and 4b into a digital signal, and an A / D converter 6 for converting the signals of the two sensors 4a and 4b, each of which is converted into a digital signal. And an arithmetic unit 7 for calculating the difference and the sum.

The signal representing the difference and the sum of the signals of the two sensors 4a and 4b obtained by the computing unit 7 is separated by a signal separator 8 into a signal representing the difference and a signal representing the sum. Such a signal representing the difference between the signals of the two sensors 4a and 4b represents the vibration of the main shaft 2. Therefore, in the case of this example, only a signal representing this difference is extracted and sent to the comparator 9. The reason why the signal indicating such a difference indicates the vibration of the main shaft 2 will be described.

During operation of the machine tool, the outer peripheral surface of the spindle 2 is displaced in the radial direction due to vibration and thermal expansion.
At this time, of the detection values of the displacement sensors 4a and 4b,
The detection value α _4a of the first displacement sensor 4a is given by the following equation (1):
The detection value α _4b of the second displacement sensor 4b can be similarly expressed by Expression (2). α _4a = β _4a + γ --- (1) α _4b = β _4b --γ --- (2) In these formulas (1) and (2), β _4a and β _4b are the main shaft 2
Is the displacement of the outer peripheral surface of the main shaft 2 based on the thermal expansion of
_4a ≒ β _4b . Γ is the displacement of the outer peripheral surface of the main shaft 2 based on the vibration of the main shaft 2. The difference between the detection values α _4a and α _4b of the two displacement sensors 4a and 4b is given by the following (3)
It becomes an expression. α _4a −α _4b = β _4a + γ− (β _4b −γ) = (β _4a −β _4b ) + 2γ ≒ 2γ (3) Therefore, if 1/2 of the above difference is obtained, the vibration of the main shaft 2 becomes The displacement amount γ of the outer peripheral surface of the main shaft 2 can be obtained based on the above.

The signal representing the displacement γ based on the vibration of the main shaft 2 obtained as described above is compared with the signal representing the rotational speed of the main shaft 2 detected by a separately provided rotation detector (not shown). Input to the container 9. This comparator 9
First, based on the signal representing the displacement amount γ and the signal representing the rotational speed of the main shaft 2, the acceleration of the main shaft 2 in the radial direction is obtained. Then, the acceleration thus obtained is compared with a preset reference value. Then, based on this comparison, a command is sent to the NC device 10 as the control means, and the processing condition of the workpiece by the machine tool is changed in a direction to suppress the occurrence of the vibration. That is, when the acceleration of vibration of the spindle 2 in the radial direction exceeds the reference value, the relative displacement speed (feed speed) between the table on which the workpiece is mounted and the spindle head is reduced. The processing speed of the workpiece by the tool supported and fixed to the end of the main spindle 2 is reduced so that vibrations due to the processing hardly occur. If the vibration still does not stop in this state, the machine tool is stopped, and a display such as a buzzer or a warning light (not shown) is displayed to indicate that the machine tool has been stopped.

In the case of the machine tool operation control apparatus of the present embodiment configured and operated as described above, the vibration of the main shaft 2 can be accurately detected without being affected by disturbance, and the operation control of the machine tool can be performed. . For this reason, it is possible to reliably prevent the operation from continuing while the spindle 2 is in a state of harmful vibration, to secure the processing accuracy of the workpiece, and to effectively prevent the tool and the machine tool from being damaged. .

Next, FIG. 5 shows a second example of the embodiment of the present invention corresponding to claim 3. In this case,
The detection values of the pair of displacement sensors 4a and 4b shown in FIG. 3 are input to the control device 5a. This control device 5
a is a calculating means for processing the detected values of the first and second displacement sensors 4a and 4b, and based on the detected values of the first and second displacement sensors 4a and 4b processed by the calculating means, There is provided control means for controlling the relative displacement between the tool and the workpiece, which are supported and fixed at the end of the spindle 2 (FIGS. 1 to 3). The arithmetic means among them has an A / A for converting the analog detection signals of the two sensors 4a and 4b into digital signals.
A D converter 6 and an arithmetic unit 7 for calculating the difference and the sum of the signals of the two sensors 4a and 4b, each of which is converted into a digital signal, are provided.

The signal representing the difference and the sum of the signals of the two sensors 4a and 4b obtained by the arithmetic unit 7 is separated by a signal separator 8 into a signal representing the difference and a signal representing the sum. Such a signal representing the sum of the signals of the two sensors 4a and 4b represents the displacement of the outer peripheral surface of the main shaft 2 due to thermal expansion. Therefore, in the case of this example,
Only the signal representing the sum is taken out and the second computing unit 1
Send to 1. The reason why a signal representing such a sum represents a displacement amount of the outer peripheral surface of the main shaft 2 based on thermal expansion will be described.

During operation of the machine tool, the outer peripheral surface of the spindle 2 is displaced in the radial direction due to vibration and thermal expansion as described above, and the detection values α _4a and α 4 of the displacement sensors 4a and 4b at this time. _4b can also be expressed by the above-described equations (1) and (2). The two displacement sensors 4a, 4b
The sum of the detected values α _4a and α _4b is given by the following equation (4). _{α 4a + α 4b = β 4a} + γ + β 4b -γ = β 4a + β 4b ≒ 2β 4a ≒ 2β 4b --- (4) Accordingly, by obtaining the sum, the spindle 2 due to thermal expansion
The increase in the outer diameter can be determined. The amount of thermal expansion in the axial direction of the main shaft 2 can be obtained from the increase and the total length of the main shaft 2.

On the other hand, the entire length of the main shaft 2, which rotates at a high speed during operation of the machine tool, tends to shrink due to centrifugal force. As described above, the amount by which the overall length of the main spindle 2 is reduced with the high-speed rotation of the main spindle 2 is obtained by an empirical formula set in advance for each type of the target machine tool. Therefore, based on a signal indicating the rotation speed of the spindle 2 detected by a separately provided rotation detector (not shown), the third computing unit 12 calculates the amount by which the overall length of the spindle 2 is reduced.

The signal indicating the amount of contraction of the main shaft 2 based on the centrifugal force obtained by the third computing unit 12 in this way is calculated by the second computing unit 11.
Together with a signal indicating the amount of displacement of the outer peripheral surface of the fourth computing unit 1
Enter 3 The fourth computing unit 13 calculates the displacement of the outer peripheral surface of the main shaft 2 based on the thermal expansion and the total contraction amount of the main shaft 2 based on the centrifugal force, obtained by the second and third computing units 11 and 12. Based on the above, the axial displacement of the tool supported and fixed to the tip of the main shaft 2 is obtained. Then, based on the displacement amount thus obtained, a command for supporting the position correction is sent to the NC device 10 as the control means. That is, the relative displacement between the tool and the workpiece is performed while adding the amount of displacement of the tool in the axial direction obtained by the fourth computing unit 13 as a correction value.

The detection of the tool displacement based on the thermal expansion based on the detected values of the first and second displacement sensors 4a and 4b and the rotation speed of the main shaft 2 is based on the aging of the machine tool. Regardless, it can be performed stably for a long time. Therefore, cutting of various workpieces can be stably performed with high accuracy over a long period of time. When the present invention is applied to an actual machine tool, both the tool position correction based on the thermal expansion shown in this example and the operation control based on the vibration detection in the first example described above must be performed. Can also.

[0024]

The operation control device for a machine tool according to the present invention is constructed and operates as described above, so that the surface property of the workpiece can be reduced without using a complicated structure that makes the processing complicated. In addition to protecting the machine tool while improving the quality, the workpiece can be machined with high accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a spindle head portion and a control device of a machine tool showing an example of an embodiment of the present invention.

FIG. 2 is a schematic side view showing a rotation support portion of a main shaft taken out.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a block diagram of a control system of a device that changes the operating state of a machine tool based on the magnitude of vibration.

FIG. 5 is a block diagram of a control system of a device that changes an operation state of a machine tool based on thermal expansion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Spindle head 2 Spindle 3 Rolling bearing 4a, 4b Displacement sensor 5, 5a Control device 6 A / D converter 7 Computing unit 8 Signal separator 9 Comparator 10 NC device 11 Second computing unit 12 Third computing unit 13 Fourth arithmetic unit

Claims (3)

[Claims] 1. A machine tool comprising a housing and a main shaft rotatably supported by the housing via a plurality of rolling bearings and supporting and fixing a tool for processing a workpiece. An operation control device for a machine tool that detects a displacement of the main shaft during operation of the machine and performs control in accordance with the displacement, provided at diametrically opposite positions around the main shaft. First and second displacement sensors for detecting displacement in the diametric direction of the surface, and arithmetic means for processing detection values of these first and second displacement sensors;
A machine tool operation control device comprising: control means for controlling the operation state of the machine tool based on the detected values of the first and second displacement sensors processed by the arithmetic means. 2. The calculating means calculates a value representing the vibration of the main shaft based on the difference between the detection values of the first and second displacement sensors, and the control means calculates a value representing the vibration of the main shaft. The operation control device for a machine tool according to claim 1, wherein a machining condition of the workpiece by the machine tool is changed based on the direction in which the generation of the vibration is suppressed. 3. The arithmetic means determines thermal expansion of the main shaft based on the sum of the detection values of the first and second sensors and the rotational speed of the main shaft. The relative displacement between the tool set in the machine tool and the workpiece is controlled in accordance with the expansion amount, and the processing amount of the workpiece is set to a desired value regardless of the thermal expansion of the spindle. Claim 1
The operation control device for a machine tool described in the above item.