JPH04336935A - NC machining device with automatic thermal displacement correction means - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides a motor with a built-in structure.
The present invention relates to an NC machining device having means for correcting the amount of displacement due to thermal expansion of a main shaft for a machine tool having a rotor.

0002

2. Description of the Related Art As shown in FIG. 5, in a conventional NC machining device having a main spindle 1 having a built-in motor 30, the rotor 2 of the motor 30 is directly attached to the center of the main spindle 1. A stator 7 of a motor 30 is attached to the inside of a case 6 that holds the motor 1. Further, a tool 4 is attached to one end of the main spindle 1 via a chuck 3, and a workpiece 19 on a table 18 is processed by the tool 4. The entire case 6 of the main shaft 1 can be moved in the thrust direction of the main shaft 1 by driving a ball screw 9 screwed into a ball screw nut 8 attached to the lower surface of the case 6 with a servo motor 10. This servo motor 10 is numerically controlled via a positioning control means 15 based on a position command from a numerical control device 20. Further, a speed command for the spindle 1 is output from the numerical control device 20, and the rotational speed of the spindle 1 is numerically controlled via the spindle motor control means 12. Temperature detection means 11 is built into the stator 7 inside the main shaft case 6, and the motor 3
0 temperature is detected, and when the temperature exceeds a certain level, the motor 3
0 protection means 13 is activated to protect the motor.

0003

[Problem to be solved by the invention] Built-in structure model
In the main shaft 1 having a motor 30, the main shaft 1 and the motor 30 are integrated and compact, but since the rotor 2 and stator 7 of the motor 30 are arranged around the main shaft 1, the Heat is transmitted to the main shaft 1 and the main shaft 1 thermally expands. As shown in FIG. 5, when the main shaft 1 thermally expands in the thrust direction as shown by the broken line, the actual required movement amount is Z' compared to the preset movement amount Z when the motor 30 is normally at room temperature. Therefore, an error of Z-Z' is generated, and the machining accuracy is deteriorated.

[0004] In this way, the heat generated by the stator 7 and rotor 2 is transmitted to the main shaft 1 of the built-in motor, and the error in the movement amount due to thermal expansion of the main shaft 1 will deteriorate machining accuracy unless corrected. There is a challenge to make it happen.

[0005] The present invention takes into account these problems with conventional NC machining equipment having a built-in motor spindle, functions easily without adding any special equipment, and therefore achieves stable workpiece machining accuracy at low cost. Moreover, since thermal correction is performed automatically, it is also effective for unmanned operation.
The purpose is to provide C machining equipment.

[0006]

[Means for Solving the Problems] The present invention includes automatic thermal displacement correction means for inputting a temperature signal detected by a temperature detection means of a motor and correcting a position command from a main control means based on the input temperature signal. This is an NC machining device with automatic thermal displacement correction means.

[0007]

[Operation] In the present invention, the automatic thermal displacement correction means
When inputting the temperature of the motor and outputting the position correction value, for example, input the room temperature as a parameter in advance, find the difference between the room temperature and the temperature of the spindle to obtain the position correction value, and output it from the main control means. The corrected position command is added to the position command, and the position of the main shaft is corrected by the positioning control means using the corrected position command as input.

[0008]

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

FIG. 1 is a schematic cross-sectional view of an embodiment of an NC machining device with automatic thermal displacement correction means according to the present invention, viewed from the front. That is, the rotor 2 of a motor 30 is attached to the center of the main shaft 1, and the tool 4 is attached to one end via a chuck 3. The main shaft 1 is attached to a case 6 via a bearing 5 so as to rotate together with a rotor 2, a chuck 3, and a tool 4. Also, a stator 7 of a motor 30 is attached to the inside of the case 6, and the built-in motor 30 The main shaft 1 has the following structure. The case 6 is movable in the thrust direction of the main shaft 1, and a ball screw 9 screwed into a ball screw nut 8 attached to the case 6 is connected to a servo motor 10.
It is driven by Further, the stator 7 has a built-in temperature detection means 11 such as a thermistor to detect the temperature of the stator 7 and, by extension, the temperature of the rotor 2 and the main shaft 1. The main shaft motor control means 12 inputs the detected stator temperature, and when a certain temperature is exceeded, a built-in protection means 13 protects the motor 30 by reducing the drive voltage to 0, etc. . The main control means 14 is a means for sending a speed command to the spindle motor control means 12 to control the rotational speed of the spindle 1. The main control means 14 also sends a position command to the positioning control means 15 via a position correction value adder 17. The positioning control means 15 controls the servo motor 1 according to the position command from the main control means 14.
Based on the position feedback signal of 0, servo motor 1
This is a means for controlling the position of the main shaft 1 based on 0.

The output signal of the temperature detection means 11 is also input to an automatic thermal displacement correction means 16 built in the main control means 14. The automatic thermal displacement correction means 16 calculates a position correction value based on the thermal displacement of the main shaft 1 based on the detected temperature of the stator 7 . The position correction value due to this thermal displacement is added to the tool length correction value and is input to the adder 17 as a position correction value. The adder 17 adds the position command output from the main control means 14 and the position correction value inputted to the adder 17, and adds the corrected position command to the positioning control means 15.
It is designed to output to . Further, a workpiece 19 to be processed is held on a table 18.

FIG. 2 is a block diagram for explaining the calculation contents of the automatic thermal displacement correction means 16. The room temperature θr is input as a parameter in advance. The stator temperature θs is the stator temperature detected by the temperature detection means 11 in FIG. The temperature difference Δθ between the room temperature θr and the stator temperature θs input as a parameter is the transfer function G(s)21
The temperature difference Δθ' between the spindle 1 and the room temperature θr is converted into a temperature difference Δθ′, which is input to the validity/invalidity determination circuit 22. The validity/invalidity determination circuit 22 determines whether the absolute value of the temperature difference Δθ' between the spindle 1 and the room temperature θr is greater than or less than a certain constant value, and if it is greater, it outputs a valid signal, and if it is smaller, it outputs an invalid signal. 2
Send to 4. Further, the temperature difference Δθ' between the main shaft 1 and the room temperature θr is input to a certain function f(Δθ') 23 and converted into the relative thermal expansion amount ΔZ of the main shaft 1. The correction execution control unit 24 determines the value of the relative thermal expansion amount ΔZ of the main shaft based on the valid/invalid signal.
It is a means for outputting a position correction value based on thermal displacement, with the value of ΔZ as it is in the case of a valid signal, and 0 in the case of an invalid signal.

Next, the operation of the present invention will be explained.

[0013] Initially, it is assumed that information necessary for machining is input to the main control means 14. At this time, the parameters of the automatic thermal displacement correction means 16 are set to room temperature θr. Next, it is assumed that the workpiece 19 to be machined is mounted on the table 18, and that machining is started using the NC machining device equipped with automatic thermal displacement correction means. When the NC machining device with automatic thermal displacement correction means starts operating,
The main control means 14 outputs a speed command to the spindle motor control means 12. This main shaft motor control means 12 outputs a driving voltage to the stator 7 of the motor 30. Then, the rotor 2 of the motor 30 rotates, and the main shaft 1 integrated with the rotor 2 also rotates. The tool 4 attached to the main shaft 1 via the chuck 3 also rotates. Also, suppose that the temperature of the stator 7 exceeds a certain value for some reason while the motor 30 is in operation. At this time, the stator temperature detected by the temperature detection means 11 built in the stator 7 is input to the protection means 13, so that the protection means 13 controls the spindle motor control means 12 based on the detected stator temperature. outputs a signal to protect the motor. The main shaft motor control means 12 protects the motor 30 by, for example, reducing the drive voltage output to the motor 30 to zero. Further, the main control means 14 outputs a position command to the positioning control means 15. Positioning control means 1 that receives a position command
5 controls the drive voltage of the servo motor 10 based on the position feedback signal of the servo motor 10. When this servo motor 10 is driven and the ball screw 9 rotates,
The ball screw nut 8 screwed onto the ball screw 9 moves in the thrust direction of the main shaft 1. Then, since this ball screw nut 8 is attached to the case 6,
The spindle 1 and the tool 4 also move in the same way. At this time, the distance required for the tool 4 to move to the workpiece 19 is defined as Z.

In this way, the N
When operating the C machine tool, the stator 7 of the motor 30
temperature is rising. Then, the temperature of the rotor 2 and the main shaft 1 which are close to the stator 7 also rises, and the main shaft 1 expands as shown by the broken line in FIG. Therefore, since the position of the tool 4 attached to one end of the spindle 1 also changes, the tool 4
The true distance required to move to workpiece 19 is Z'
It is.

At this time, the stator temperature θs detected by the temperature detection means 11 built in the stator 7 of the motor 30 is input to the automatic thermal displacement correction means 16. Then, the automatic thermal displacement correction means 16 calculates from the detected stator temperature θs and the initially set parameter room temperature θr,
Output the position correction value based on the calculated thermal displacement. The tool length correction value is added to the position correction value due to this thermal displacement to obtain a position correction value, which is input to the adder 17. The adder 17 adds the position command output from the main control means 14 and the position correction value to correct the position command. Next, the positioning control means 15 controls the drive voltage of the servo motor 10 based on this corrected position command. and servo motor 1
0 rotates the ball screw 9, and the ball screw 9 moves the ball screw nut 8. Then, since the ball screw nut 8 is attached to the case 6, the main spindle 1 attached to the case 6 and the tool 4 attached to the main spindle 1 also move. In this way, the tool 4 is moved by the corrected distance Z'.

Next, the operation of the automatic thermal displacement correction means 16 is shown in FIG.
This is explained by Automatic thermal displacement correction means 1 as described above
6, the room temperature θr is input as a parameter in advance. When the motor 30 is operated, the stator temperature θs detected by the temperature detection means 11 is input to the automatic thermal displacement correction means 16, which calculates the temperature difference Δθ=θs−θr between the stator temperature θs and the parameter room temperature θr.

Next, with Δθ as input, the temperature difference Δθ between the principal axis temperature and the room temperature θr is
Find ′.

[0018] Usually, G(s) is It is a first-order lag element represented by .

This Δθ' is input to the validity/invalidity determination circuit 22, and it is determined whether the absolute value of Δθ' is larger or smaller than a certain constant value. It is sent to the control unit 24. This is because if the value is small, it may be better not to make the correction in terms of control delays.

[0020] Also, let Δθ' be a certain function f(Δθ')23
and calculate the relative thermal expansion amount ΔZ of the main axis.
Usually, f(Δθ') is ΔZ=f(Δθ')=k
・Represented by Δθ′ (∵k is a time constant).
(ΔZ≒Z−Z′) Next,
Based on the valid/invalid signal, the correction execution control unit 24 outputs the value of ΔZ as it is in the case of a valid signal, and outputs the value of 0 in the case of an invalid signal as a position correction value based on thermal displacement.

When the valid/invalid judgment circuit 22 outputs a valid signal, the adder 17 adds the tool length to the position command outputted by the main control means 14 and the position correction value based on thermal displacement outputted by the correction execution control unit 24. Add the position correction value obtained by adding the correction value (see Figure 1) to eliminate the error between the movement amount Z when the room temperature is θr and the movement amount Z' when the stator temperature of the main shaft 1 is θs. The corrected position command is output to the positioning control means 15.

The positioning control means 15 outputs a drive signal to the servo motor 10 based on the corrected position command,
The servo motor 10 corrects the error in thermal displacement of the movement amount of the case 6 and therefore the tool 4 attached to one end of the main shaft 1, and drives the tool 4 correctly.

Furthermore, the position correction value may not be added to the tool length correction value, but may be added to another correction value, such as a workpiece coordinate system shift value.

Transfer function G(s
), and the function f(Δθ') that converts the temperature difference Δθ' into the relative thermal expansion amount ΔZ of the main axis may be other than those in the embodiment.

It is also conceivable to eliminate the validity/invalidity determination circuit 22 and perform position correction even in the case of a minute temperature difference.

[0026] In order to prevent the positional correction value from becoming extremely large, an upper limit value may be determined, and if the upper limit value is exceeded, correction may be performed using the upper limit correction value.

Note that the cooling effect of cutting oil or the like may be added to the temperature difference Δθ' as a correction factor. That is, FIG. 3 is a part of a block diagram of the automatic thermal displacement correction means 16 when correcting the effect of cooling action by cutting oil or the like. The transfer function G1(s)25 is the transfer function G(s)21 of the above embodiment.
is the same as A correction function f(n) 26 for the cooling effect by cutting oil etc. is generated for the temperature difference Δθ' which is the output of the transfer function G1(s) 25, inputted to the transfer function G2(s) 27, and its output Δθ1 is added. Δθ2 is input to the validity/invalidity determination circuit 22.

[0028] Furthermore, a temperature detecting means may be separately provided in the room to detect the room temperature. At this time, as shown in FIG. 4, a part of the block diagram of the calculation of the automatic thermal displacement correction means 16 is changed, and the detected room temperature θg is expressed by the transfer function G3(s) 28 between the temperature of the workpiece, etc. and the parameter θr. is converted into a temperature difference Δθ2, and a correction value ΔZ in the thrust direction of the main shaft is calculated using a certain function f(Δθ2)29.
Output as 1. The output correction value ΔZ1 is added to the spindle expansion amount ΔZ to become ΔZ2, and the correction execution control unit 24
is input.

Furthermore, in order to determine the temperature of the main shaft, for example, the temperature of the main shaft may be directly detected instead of the temperature of the stator.

The parameter initially input to the automatic thermal displacement correction means 16 may be other than the room temperature, such as the temperature of the NC machining device itself, or a certain fixed value.

[0031] Furthermore, the NC with automatic thermal displacement correction means of the present invention
The machine tool may, of course, be realized in software form using a microcomputer, in addition to a dedicated hardware circuit having the above-mentioned functions.

[0032]

[Effects of the Invention] As explained above, the NC machining device with automatic thermal displacement correction means according to the present invention inputs the temperature signal detected by the temperature detection means, and corrects the position command from the main control means based on the temperature signal detected by the temperature detection means. Equipped with an automatic thermal displacement correction means, it prevents the spindle from expanding due to the heat generated by the motor, causing errors in the travel amount and deteriorating machining accuracy, and eliminates the need for special equipment. It works easily and at a low cost,
It has the advantage of being effective in unmanned operation because the machining accuracy is stable and correction is performed automatically.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an embodiment of an NC machining device with automatic thermal displacement correction means according to the present invention.

FIG. 2 is a block diagram of the calculation contents of the automatic thermal displacement correction means of the same embodiment.

FIG. 3 is a block diagram of part of the calculation contents of the automatic thermal displacement correction means of another embodiment.

FIG. 4 is a block diagram of part of the calculation contents of the automatic thermal displacement correction means of another embodiment.

[Figure 5] N with a main shaft of a conventional built-in motor structure
It is a schematic cross-sectional view of the C machining device.

[Explanation of symbols]

1 Main shaft 11 Temperature detection means 12 Spindle motor control means 13. Protective measures 14 Main control means 15 Positioning control means 16 Automatic thermal displacement correction means 30 Motor

Claims (1)

[Claims] 1. Main control means for commanding the rotational speed of a main shaft and the position of the main shaft having a built-in motor, and a main shaft motor for controlling the speed of the motor based on the rotational speed command. a control means, a positioning control means for controlling the position of the spindle based on the position command, a temperature detection means for detecting the temperature of the motor, and protecting the motor based on the detected temperature signal. The NC machining device has a protection means for controlling the temperature, and is characterized by comprising an automatic thermal displacement correction means for inputting a temperature signal detected by the temperature detection means and correcting a position command from the main control means based on the temperature signal detected by the temperature detection means. NC machining device with automatic thermal displacement correction means.