JP3756793B2 - Machine tool thermal displacement compensation device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermal displacement correction apparatus for machine tools such as NC lathes and machining centers.
[0002]
[Prior art]
In general, a machine tool is provided with a rolling bearing of a main shaft, for example, as a heat source in each part due to the characteristics of the machine, and heat generated by the heat source is transmitted to surrounding machine parts, thereby causing thermal deformation of the machine body. Since the thermal deformation of the airframe greatly affects the processing accuracy, as a preventive measure, there is a conventional method of cooling the heat generating part, or a method of processing by estimating and correcting the thermal deformation amount from the airframe temperature information. Widely adopted. For example, as the latter prior art, Japanese Examined Patent Publication No. 61-59860 discloses the relationship between the difference between the temperature of the spindle head of a machine tool and the temperature of the machine part having a relatively small temperature change and the elongation of the spindle. A method is disclosed in which a function expression of a temperature difference-thermal displacement amount is stored in a program memory, a thermal displacement amount is calculated based on an immediate value detected by temperature, and a correction amount is given to a servo output.
Japanese Patent Laid-Open No. 10-296586 discloses a correction command for obtaining a correction axis movement amount per unit time, that is, a correction speed based on the calculated thermal displacement correction amount, a preset correction speed processing method, and a set value. The method of value is shown.
[0003]
[Problems to be solved by the invention]
However, according to the method described in Japanese Examined Patent Publication No. 61-59860, the axis movement for correcting the thermal displacement is performed at regular intervals determined by the normal setting. There was a case where a large displacement change occurred, streaks appeared on the machined surface, and the machined surface quality deteriorated.
In the invention described in Japanese Patent Laid-Open No. 10-296586, correction is performed regardless of the axial movement state of the machine and the follow-up performance. Therefore, even a stick slip generated due to a shape change due to the correction or poor follow-up performance. The processed surface will be rough.
[0004]
[Means for Solving the Problems]
Therefore, in the present invention according to claim 1, a temperature detection unit that measures the temperature of each part of the machine that is a heat generation source of the machine tool that processes the generating surface on the work, and the temperature measured by the temperature detection unit Thermal displacement correction comprising: a correction amount estimation unit that estimates a thermal displacement correction amount; and a machining control unit that calculates axis correction coordinates based on the thermal displacement correction amount from the correction amount estimation unit and outputs a correction command to the correction target axis A device,
The machining control unit compares an influence amount calculating unit for calculating an influence amount on the generating surface by the correction command output to the correction target axis, and compares the calculated influence amount with a preset value. A thermal displacement correction device for a machine tool, comprising: an influence amount determination unit that outputs a correction command if the value is small and does not output a correction command if the value is large.
As a result, it is possible to determine the case where the target axis that moves by the correction amount by the correction command has a large influence on the generating surface, and thus it is possible to prevent the occurrence of streaking that deteriorates the machining surface quality as in the conventional case.
During rapid traverse, the cutter is not in contact with the creation surface, and position control based on the correction command does not affect the creation surface.
Next, during the cutting command, even when the blade is in contact with the generating surface, the correction amount itself may be small and the effect on the generating surface may be small. It is possible to perform the correction process until the value is exceeded, and not to perform the correction process when the set value is exceeded.
[0005]
Moreover, in this invention which concerns on Claim 2, it respond | corresponds to the temperature measured by the temperature detection part which measures the temperature of each machine part used as the heat generation source of the machine tool which processes a generating surface to a workpiece | work, and this temperature detection part Thermal displacement correction comprising: a correction amount estimation unit that estimates a thermal displacement correction amount; and a machining control unit that calculates axis correction coordinates based on the thermal displacement correction amount from the correction amount estimation unit and outputs a correction command to the correction target axis A device,
The machining control unit outputs a correction command when a fast feed command is issued to the correction target axis, and a correction output target axis and a machining amount by which the correction command is output during cutting feed. By having an influence amount calculation unit that is calculated from an angle with the normal of the surface and an influence amount determination unit that outputs a correction command if the calculated influence amount is smaller than a preset value, the influence amount is determined in advance. A thermal displacement correction device for a machine tool, wherein a correction command is not output when the value is larger than a set value.
Thus, the influence amount prevent quality degradation that occurs when greater than a preset value, thereby enabling a high-quality pressure Engineering.
Here, Formula 1 described later is preferable as the calculation formula for calculating the influence on the generating surface from the angle between the correction output target axis and the normal of the machining surface. Thereby, how much the locus of the blade obtained from the machining data of the workpiece is shifted before and after the correction, the displacement absolute amount or the distance at the correction point of the two locus straight lines is calculated and digitized, The amount of influence on the surface roughness can be objectively evaluated.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an NC lathe embodying the present invention will be described with reference to the drawings.
FIG. 1 is an explanatory view showing the NC lathe from the axial direction of the main shaft.
The headstock 1 of the NC lathe is placed on the horizontal surface 2a of the slant bed 2, and the tool post 3 is installed on the inclined surface 2b so as to be slidable in the respective axial directions. Then, the workpiece 9 is gripped by the hydraulic chuck 8 attached to the spindle 4, the spindle 4 is rotated by a motor, and the workpiece 9 is turned by the cutter 10 of the tool post 3 whose position is controlled in each axial direction. Yes. The NC device 14 that controls the position of the tool post 3 in the direction of each axis controls the movement coordinates and the movement speed of the servo motor 15 of each axis based on the cutting work values input in advance.
[0007]
A first temperature sensor 5 is attached to the spindle 4 of the headstock 1, a second temperature sensor 6 is attached to the tool post 3, and a third temperature sensor 7 is attached to the slant bed 2 to measure the respective temperatures. ing. The temperature sensors 5 to 7 are connected to the temperature measuring device 11, and each measured temperature value is converted from an analog signal to a digital signal to be digitized, and the temperature data and thermal displacement determined and stored in advance in the storage device 13. Based on the correction parameter related to the amount, the thermal displacement estimation calculator 12 estimates the thermal displacement amount from the temperature data, calculates the correction amount by a known method, and the NC device 14 determines the position of each axis according to the correction amount. A movement command is output to the servo motor 15.
[0008]
Next, the thermal displacement correction process will be described.
FIG. 2 is a drawing for explaining the feed operation of the cutter 10 that performs taper machining on the workpiece 9. The cutter 10 is moved from the initial position to the cutting start position with fast feed 1, and the workpiece 9 is machined with the cutting feed 1 to fast feed 2 shows the movement to return from the cutting end position to the initial position. As described above, the command axis for the thermal displacement correction has three types of axis movement states, that is, a stopped state like the initial position, a fast-feed state where the blade 10 does not contact the workpiece 9, and a cutting state where the workpiece 10 contacts. Depending on the shape, the rapid feed state and the cutting state may be repeated.
The thermal displacement is generated by the operation or machining of the NC lathe. FIG. 4 shows an example of a thermal displacement change curve A, a temporal change B in which a thermal displacement amount is discretely estimated at regular intervals, and a correction command value is output from the estimated amount, and a correction error transition C. At the beginning, the correction command value is large, and as time passes, the change in thermal displacement becomes smaller and the correction amount for thermal displacement becomes smaller.
[0009]
FIG. 3 shows a flowchart of the thermal displacement correction control in the thermal displacement estimation calculator 12 and the NC device 14.
First, a surface roughness value required for processing accuracy is set in advance. Temperature measurement is performed in step S-1 with each of the temperature sensors 5, 6 and 7 attached to the airframe, and based on this result, the amount of thermal displacement is calculated by a known method in step S-2.
Here, if there is no command to correct the thermal displacement and the movement of the target axis is in a stopped state, the correction command calculated in step S-2 is not processed without performing steps S-3 and S-5 described later. No reflection is performed, and the process waits without being performed (step S-8). Thereby, stick-slip does not occur.
During the waiting time, it becomes the update time of the thermal displacement correction calculation. If the thermal displacement correction is continued, the process returns to step S-1, and the update of the thermal displacement calculation calculated in step S-2 is preferentially performed (step S-9). .
[0010]
Next, when the axis movement status of the command target axis to be subjected to thermal displacement correction is not in a stopped state, it is determined whether or not the axis movement status of the thermal displacement correction command target axis is rapid feed in step S-3. For example, a command for reflecting the correction amount calculated in step S-2 is output (step S-4).
[0011]
Further, when the axis movement status of the command target axis to be subjected to thermal displacement correction is neither a stopped state nor a rapid feed, it is determined in step S-5 whether or not the axis movement status of the thermal displacement correction command target axis is a cutting feed. . In the case of the cutting feed operation, the influence amount E on the surface roughness is obtained by Equation 1 described later in Step S-6, and in Step S-7, the obtained influence amount E is obtained in advance in Step S-0. It is determined whether or not correction is performed in comparison with the input value of the surface roughness required for the set machining accuracy.
[0012]
When the amount of influence E on the surface roughness is larger than the set value (step S-7, No), the correction command calculated in step S-2 is not reflected and is left unexecuted ( Step S-8) When the thermal displacement correction calculation time is reached during standby, if the thermal displacement correction is continued, the process returns to Step S-1 to preferentially update the next thermal displacement calculation (Step S-9). As a result, conventionally, as shown in FIG. 5, when a shaft movement command is input during cutting, the amount of movement and speed of the shaft change abruptly.
[0013]
On the other hand, if the influence amount E on the surface roughness is smaller than the set value (step S-7, YES), a command for reflecting the correction amount calculated in step S-2 is output even at the time of cutting. (Step S-4). Thus, when there is no effect on the machined surface also be sent in cutting speed, accurate cutting by executing the correction to the thermal displacement Ru is executed. Incidentally, conventionally, the correction has been performed in any state during the cutting.
[0014]
Note that the comparison between the influence amount E on the surface roughness E and the set value in the step S-7 is not strict, and in the case of almost the same value, either processing may be performed, and the set value in consideration of the case of the same value. It is also possible to determine.
[0015]
Here, the influence amount E on the surface roughness calculated and obtained in step S-6 will be described.
FIG. 6 shows, as an example, the trajectory of the blade at the time of correction when a correction amount in the X-axis direction is entered when cutting into the XZ plane with the combined two axes of the X-axis and the Z-axis. A value E for taking into account the influence on the generating surface at the correction point P1 is calculated by Equation 1. θ is an angle formed by an X axis that is a correction reflection axis and a normal line that passes through the correction point P1 of the generating surface.
[0016]
E = δ · cos θ Equation 1
E: Amount of influence on surface roughness δ: Correction amount θ: Angle between correction reflection axis and normal of generating surface
This calculates the influence amount E on the surface roughness based on how much the locus of the blade obtained from the machining data of the workpiece is shifted before and after the correction. And in process S-7, it determines with the determination formula of Formula 2.
[0018]
IF threshold setting value <E THEN No correction execution Equation 2
[0019]
For example, when the correction target axis is a single axis, when machining is started only by moving the axis that needs to reflect the correction amount, the influence amount E on the surface roughness is determined not to affect the machining surface. If it is, the correction amount is transferred as it is and correction processing is performed.
In the case of machining points P0 to P1 or P2 to P3 where machining is performed with two or more combined axes of the axis reflecting the correction amount and other axes as in the machining from the machining points P0 to P3, XZ It divides | segments into the corrected amount to an axis | shaft, After calculating the influence amount E to a generating surface about each axis | shaft, it is determined whether correction | amendment is reflected. The threshold setting value is determined by the machining operator based on the required machining accuracy and empirical rule of the workpiece, and is input to the influence amount determination unit of the machining control unit before machining. Alternatively, a thermal displacement correction device that stores a correspondence table between the required machining accuracy of a workpiece and a threshold setting value considering empirical rules in a machining control unit and is automatically selected based on machining data may be used.
[0020]
【The invention's effect】
According to the present invention , high- quality machining can be realized because the correction reflection is effectively suppressed in consideration of the influence on the machining surface of the workpiece processed by the machine tool.
That is, in the present invention according to claim 1, the machining control unit of the thermal displacement correction device includes an influence amount calculation unit that calculates an influence amount on the generating surface by the correction command output to the correction target axis, and the calculated amount Since it is a thermal displacement correction device for a machine tool having an influence amount determination unit that compares the influence amount with a preset value and outputs a correction command if the influence on the generating surface is small and outputs a correction command if large. Since it is possible to determine the case where the target axis moving by the correction amount has a large influence on the generating surface by the correction command, it is possible to prevent the occurrence of streaking that deteriorates the quality of the machined surface as in the conventional case.
[0021]
Further, in the present invention according to claim 2, the machining control unit of the thermal displacement correction device outputs a fast feed discriminating unit that outputs a correction command when there is a fast feed command for the correction target axis, and outputs a correction command at the time of cutting feed. The influence amount calculation unit that calculates the influence amount on the created surface from the angle between the correction output target axis and the normal of the machining surface, and the influence that the correction command is output if the calculated influence amount is smaller than a preset value Since this is a thermal displacement correction device for a machine tool that does not output a correction command when the influence amount is larger than a preset value, a streak that deteriorates the quality of the generating surface by the correction command is provided. It enables cutting by accurate positioning while preventing the generation of eyes.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an NC lathe from the axial direction of a main shaft.
FIG. 2 is an explanatory view showing a feed operation of a cutter for performing taper machining on a workpiece.
FIG. 3 is a flowchart showing thermal displacement correction control.
FIG. 4 is an explanatory diagram showing a change with time of a thermal displacement amount and a correction amount.
FIG. 5 is an explanatory diagram showing a change over time in the amount of axial movement for which correction processing is performed.
FIG. 6 is an explanatory diagram showing the trajectory of a cutter that cuts into an XZ plane.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Spindle base 2 Slant bed 3 Tool post 4 Spindle 5-7 Temperature sensor 8 Hydraulic chuck 9 Workpiece 10 Cutting tool 11 Temperature measuring device 12 Thermal displacement estimation calculator 13 Storage device 14 NC device 15 Servo motor

Claims (2)

A temperature detection unit that measures the temperature of each part of the machine that is a heat generation source of a machine tool that processes a generating surface on a workpiece, and a correction amount estimation unit that estimates a thermal displacement correction amount corresponding to the temperature measured by the temperature detection unit And a processing control unit that calculates an axis correction coordinate based on the thermal displacement correction amount from the correction amount estimation unit and outputs a correction command to the correction target axis,
The machining control unit compares an influence amount calculating unit for calculating an influence amount on the generating surface by the correction command output to the correction target axis, and compares the calculated influence amount with a preset value . A thermal displacement correction device for a machine tool, comprising: an influence amount determination unit that outputs a correction command if the value is small and does not output a correction command if the value is large. A temperature detection unit that measures the temperature of each part of the machine that is a heat generation source of a machine tool that processes a generating surface on a workpiece, and a correction amount estimation unit that estimates a thermal displacement correction amount corresponding to the temperature measured by the temperature detection unit And a processing control unit that calculates an axis correction coordinate based on the thermal displacement correction amount from the correction amount estimation unit and outputs a correction command to the correction target axis,
The machining control unit outputs a correction command when a fast feed command is issued to the correction target axis, and a correction output target axis and a machining amount by which the correction command is output during cutting feed. By having an influence amount calculation unit that is calculated from an angle with the normal of the surface and an influence amount determination unit that outputs a correction command if the calculated influence amount is smaller than a preset value, the influence amount is determined in advance. A thermal displacement correction device for a machine tool, wherein a correction command is not output when the value is larger than a set value.

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