JPH0736976B2 - Smoothing method for thermal displacement correction value - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal displacement correction method for preventing deterioration of machining accuracy due to thermal displacement due to a partial temperature change generated by operation of a machine tool. is there.

2. Description of the Related Art Conventionally, there is a method of correcting a thermal displacement caused by a temperature rise of a spindle and its surroundings due to rotation of a spindle of a machine tool, such as a machining center, etc., by measuring a linear displacement amount, and feeding back the correction amount in real time. However, since the equipment becomes large in size, in most cases, for example, as shown in the drawing of the machining center in Fig. 1, the temperatures a, b of the spindle bearing part of the spindle head, which are easily affected by heat, and the ambient temperature of the bed are Measure the temperature at the indicated position c, and
A general method is to calculate the displacement amount from the temperature rise values at the a and b positions using an experimental or empirical coefficient, and feed back this to the Z-axis command value for correction.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the method of calculating the thermal displacement amount from the temperature rise value described in the related art, the displacement amount is calculated based on the input temperature measurement value. When an error occurs in the temperature measurement value due to a disturbance or the like as shown in, the correction value fluctuates each time and a step is formed on the machined surface. Therefore, when the workpiece is a mold or the like, there is a problem that it takes time to finish the surface by manual work thereafter.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a smoothing method for reducing a step difference of a workpiece processed surface caused by thermal displacement correction. It is a thing.

Means for Solving the Problems In order to achieve the above object, a method for smoothing a thermal displacement correction value of the present invention is a thermal displacement correction method for obtaining a correction value by calculation based on a temperature measurement value of a heat generating portion, and intermittently. The temperature data of a block immediately before a plurality of input temperature measurement values are stored as one block, a temperature straight line passing through the center of the measurement point group of the temperature data is obtained by calculation, and this extension line is used as the center. When a new temperature measurement value is input, it is compared with the value of the expected temperature range and corrected to the closest boundary expected temperature value when the measured value deviates from the expected temperature range. The thermal displacement correction value is calculated by calculation from the input temperature value or the input temperature measurement value, and the contents of the temperature data stored by the newly input temperature measurement value are updated and provided next. is there.

Further, in a thermal displacement correction method for obtaining a correction value by calculation based on a temperature measurement value of a heat generating portion, temperature data of a plurality of consecutive blocks immediately before a plurality of intermittently input temperature measurement values are stored is stored. Then, a temperature straight line passing through the central portion of each measurement point group of each temperature data is obtained by calculation, and an expected temperature straight line is calculated from the rate of change of the inclination angle of each temperature straight line. When the expected temperature range is set and a new temperature measurement value is input, it is compared with the corresponding value of the expected temperature range and corrected to the closest boundary expected temperature value when the measured value deviates from the expected temperature range. A thermal displacement correction value is obtained by calculation from the corrected temperature value or the input temperature measurement value, and a plurality of temperature data to be stored when the newly input temperature measurement value reaches a predetermined configuration point in one block. It is to the content update.

Action Claim 1 stores temperature data of a block immediately before a plurality of input temperature measurement values are made into one block, and an expected temperature having a width above and below an extension line of a temperature straight line calculated from this temperature data. When the range is set and a new measured value is input, it is compared with the expected temperature range, and when it is out of the expected temperature range due to disturbance, etc., it is corrected to the upper limit value or lower limit value of the expected temperature range and the newly input temperature Enter the measured value and update the temperature data.

According to a second aspect of the present invention, temperature data of a plurality of consecutive blocks immediately before a plurality of input temperature measurement values are set as one block is stored,
The expected temperature range is set by this, and when one measured value is input, it is compared with the value of the corresponding position of this expected temperature range, and when it deviates from the expected temperature range, it becomes the upper limit value or the lower limit value of the corresponding position. In addition to the correction, the content of the temperature data is updated when the input measured value reaches the number of constituents of one block.

First Embodiment A first embodiment will be described with reference to FIGS. 1 to 3.

In a well-known portal machining center, a table 2 is movably positioned on a guide provided in the X-axis direction on a bed 1, columns 3 are erected on both floors of the bed 1, and a column 3 is installed on the column 3. The top beam 4 is fastened. A cross rail 5 having a guide in the Y-axis direction is movably positioned on a guide 3a in the Z-axis direction cut in the column 3, and a spindle head 6 can be moved and positioned on the guide in the Y-axis direction. It is placed. Quill 7 on the spindle head 6 is Z
The quill 7 is rotatably supported, and the quill 7 has a main shaft 8 rotatably supported by a plurality of bearings (not shown).
The spindle 8 is moved and positioned by an NC controlled servo motor 9.

The thermocouples 11A and 11B are attached to the spindle head 6 at two positions a and b that are easily affected by the heat generation of the bearing due to the rotation of the spindle 8, and the thermocouples 11A and 11B are close to the environmental temperature of the bed 1. A thermocouple 11c is attached to c.

Next, the servo system for performing thermal displacement correction based on the temperature measurement values of the thermocouples 11A to 11C will be described with reference to the block diagram of FIG. When the output signal is input, thermocouple 11C at C position
With reference to the output T3 of the above, the temperature difference (called a temperature measurement value) between the outputs T1 and T2 of the thermocouples 11A and 11B at the positions a and b is calculated. The temperature intermittent reading unit 13 reads the temperature measurement value at a set fixed time, for example, every 1 minute in the first embodiment, and the temperature data storage unit 14 sequentially stores the temperature measurement value when it is read intermittently. As shown in FIG. 2, when the number of measured values (measurement points) reaches a predetermined number, for example, six, the six measurement points are stored as continuous temperature data immediately before being made into one block and output to the linear calculation unit 15. Then, when a new temperature measurement value is read, the first one measurement point is released and the stored content is updated. The straight line calculation unit 15 is a unit for obtaining a temperature straight line by the method of least squares by calculation from the input temperature data, and the predicted temperature range setting unit 16 adds a predetermined width above and below the extension line of the temperature straight line to predict the temperature. This is a part for setting and storing a temperature range. The temperature comparison correction unit 17
This is a part that compares the current temperature measurement value input via the temperature storage unit with the expected temperature range, and when the current temperature measurement value deviates from the expected temperature range, corrects the boundary temperature closest to the expected temperature range.

The correction amount calculation unit 18 calculates the thermal displacement amount by multiplying the corrected temperature or the uncorrected current temperature input via the temperature comparison correction unit 17 by a coefficient obtained by experiment or experience, and corrects this. The portion that outputs as a value, the correction axis drive control unit 19,
When the correction value is input, this correction value is added or subtracted from the NC Z-axis position command value to drive the Z-axis servomotor 9.

Next, the operation of the first embodiment will be described with reference to the flowchart of FIG.

When a new temperature measurement value is read from the temperature intermittent reading unit 13 in step S1, it is confirmed whether or not the number of measurement points read in the temperature data storage unit 14 in step S2 is six, which is the number of blocks, and the operation is started. Immediately afterwards no
The process returns to step S1. If the answer in step S2 is YES, the value 6 read in step S3 is read.
The temperature data composed of individual measurement points is calculated by the linear calculation unit 15
And the temperature straight line is calculated by the method of least squares in step S4. Next, in step S5, the expected temperature range is calculated from the extended line of the obtained temperature straight line, in step S6, the new current temperature measurement value is read, and in step S7, the current temperature measurement read by the temperature comparison and correction unit 17 is measured. It is confirmed whether the value is within the expected temperature range, and in the case of No, in step S8, it is corrected to the boundary temperature value of the expected temperature range closest to the current temperature measurement value, and in step S9 the current temperature at this time is corrected. The measured value is taken into the temperature data storage unit 14 as a new measuring point and the temperature data is updated. In step S7, if the result is YES, the current temperature measurement value read in step S9 is output as it is, and this temperature measurement value is taken in as a new measurement point, and one old measurement point is discarded, and the temperature data is updated. To do. Then, in step S10, the correction value calculation unit 18
A Z-axis correction value is calculated by calculation based on the temperature measurement value read as it is or the correction temperature value corrected by the temperature comparison / correction unit, and the Z-axis correction value is output by the correction-axis drive control unit 19 in step S11. The axis servo motor 9 is driven and thermal displacement correction is executed. Next, in step S12, it is confirmed whether or not a machine operation stop command has been issued, and if no, the process returns to step S1, and if yes, the process ends.

Next, a second embodiment will be described with reference to FIGS. 1 and 4 to 6.

Note that FIG. 1 is also used for the first embodiment, and in order to avoid duplication of description, only the portions different in content from the first embodiment will be described and the others will be omitted.

The temperature data storage unit 14 reads temperature measurement values at a pitch of, for example, 20 seconds earlier than in the first embodiment, and as shown in FIG. 4, for example, three blocks adjacent to each other having six measurement points as one block. Each temperature data of is stored as a set of immediately preceding continuous temperature data and output to the linear calculation unit 15, and when the number of newly input measurement points reaches 6, the oldest one block is discarded and three blocks are Is a part for updating a set of temperature data. The straight line calculation unit 15 is a part for calculating a temperature straight line of each temperature data, the expected temperature range setting unit 16 obtains an expected temperature straight line from the rate of change of the inclination angle of each temperature straight line, and the expected temperature straight line is the center, This is a part for setting an expected temperature range having a width above and below and storing it as a parameter. Here, an example of a calculation formula for obtaining an expected temperature straight line from three temperature straight lines will be described. The difference between the inclination angles A to C of the respective temperature straight lines I to III shown in FIGS.
B, B-A, which is the expected temperature line IV
The difference E of the inclination angle D with respect to the inclination angle A of (C−B) − (B
-A), D = (BA) -E, and the inclination angle D of the expected temperature straight line IV can be obtained by the following equation D = 3A-3B + C.

The temperature comparison / correction unit 17 is a unit that compares the current temperature measurement value with the corresponding value in the expected temperature range and corrects the boundary temperature to the closest boundary temperature when the current temperature measurement value deviates from the expected temperature range. The predicted temperature range used here is such that the same predicted temperature range is used until the number of inputs of the new current temperature measurement value reaches 6 which is the number of constituents of one block.

Next, the operation of this embodiment will be described with reference to the flowchart of FIG.

In step S101, the measured temperature value is read, and in step S102, it is confirmed whether or not there are six measurement points read in the third block (one block in FIG. 4). Return to step S101. If YES in step S102, step
In S103, the temperature straight lines of the three blocks are calculated by the least square method by calculation. Then, in step S104, each tilt angle of each calculated temperature straight line is calculated, in step S105, the expected temperature straight line of the next block is calculated from the change rate of each tilt angle, and in step S106, this predicted temperature straight line is calculated. The expected temperature range is calculated by giving a certain width above and below. Next, in step S107, the current temperature measurement value is read, and in step S108, it is confirmed whether or not the read current temperature measurement value is within the expected temperature range. If not, in step S109, the corresponding value of the expected temperature range is determined. The boundary temperature value closest to the temperature measurement value is corrected, and the current temperature measurement value before correction is stored as the measurement point of the next block in the temperature data storage unit 14.
If yes in step S108, the current temperature measurement value is stored as a measurement point, and in step S110, it is confirmed whether the number of read measurement points in the next block has reached six, and if yes, in step S111. , Insert the next block, discard the old block, and update the contents of the temperature data composed of three blocks. Then, in step S112, a correction value is calculated based on the read current temperature value or the corrected temperature value,
In S113, Z-axis correction is executed. Then step
In S114, it is confirmed whether or not a machine operation stop command is issued. If NO, the process returns to step S107, and if YES, the process ends.

EFFECTS OF THE INVENTION Since the present invention is configured as described above, it has the following effects.

The smoothing method of the thermal displacement correction value according to claim 1 obtains a temperature straight line by calculation from temperature data of a block immediately before which a plurality of intermittently input temperature measurement values are made into one block, and an extension line of this temperature straight line. The expected temperature range centered on is calculated, and when a new temperature measurement value is input, the temperature measurement value is compared with the expected temperature range and the temperature measurement value is corrected.The temperature data content is updated with the new temperature measurement value. Since it is corrected with a new expected temperature range, even if the temperature measurement value fluctuates due to disturbances etc., it will not be reflected in the correction amount, and this will prevent heat from being generated during finish cutting such as die machining. The step difference on the machined surface due to the displacement correction is reduced, and the number of steps for subsequent hand finishing can be significantly reduced.

The smoothing method of the thermal displacement correction value according to claim 2 stores temperature data of a plurality of consecutive blocks immediately before a plurality of intermittently input temperature measurement values are made into one block, and calculates the temperature of each temperature data by calculation. Obtain the straight line, calculate the expected temperature line from the rate of change of the inclination angle of each temperature line, and set the expected temperature range.When a new temperature measurement value is input, it is compared with the corresponding value of the expected temperature range. When the new temperature measurement value reaches the specified number of components in one block, the contents of the multiple temperature data to be stored are updated and the temperature measurement value is updated according to the new expected temperature range. Since the correction is made, as in the first aspect, there is no step on the finish-cutting surface due to the thermal displacement correction, and the number of man-hours required for subsequent hand-finishing can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a diagram of a machining center including a partial block diagram common to the first and second embodiments, and the diagram of the machining center in this figure is also cited in the conventional technical description. Second
FIG. 3 is a graph for explaining the process from the input of the temperature measurement value to the setting of the expected temperature range in the first embodiment, and FIG. 3 is the first graph.
FIG. 4 is a flow chart for explaining the operation of the embodiment, FIG. 4 is a graph for explaining the process from the input of the temperature measurement value to the setting of the expected temperature range of the second embodiment, and FIG. 5 is a supplementary table of FIG. 6, FIG. 6 is a flow chart for explaining the operation of the second embodiment, FIG. 7 is a graph showing an example of variations in the conventional temperature measurement points, and FIG. 8 is a graph showing an example of variations in the conventional temperature measurement points. It is a figure. 6 ... Spindle head, 8 ... Spindle 9 ... Servo motor 11A-11C ... Thermocouple

Claims (2)

[Claims] 1. A thermal displacement correction method for obtaining a correction value by calculation based on a temperature measurement value of a heat generating part, wherein temperature data of a block immediately before a plurality of intermittently input temperature measurement values are regarded as one block. Storing and calculating the temperature straight line passing through the central part of the measurement point group of the temperature data, calculating the expected temperature range centered on this extended line, and when a new temperature measurement value is input, the expected temperature range is calculated. When the measured value deviates from the expected temperature range by comparing with the value of the above, it is corrected to the closest boundary expected temperature value, and the thermal displacement correction value is calculated by calculation from this corrected temperature value or the input temperature measurement value. At the same time, the content of the temperature data to be stored is updated by the newly input temperature measurement value, and the method is further provided with the following, and a thermal displacement correction value smoothing method is provided. 2. A thermal displacement correction method for obtaining a correction value by calculation based on a temperature measurement value of a heat generating part, wherein a plurality of intermittently input temperature measurement values are treated as one block and a plurality of consecutive blocks immediately before the temperature measurement value are treated as one block. The temperature data is stored, a temperature straight line passing through the central portion of each measurement point group of each temperature data is calculated, and an expected temperature straight line is calculated from the rate of change of the inclination angle of each temperature straight line. Set the expected temperature range centered on, and when a new temperature measurement value is entered, it will be compared with the corresponding value of the expected temperature range to the closest boundary expected temperature value when the measured value deviates from the expected temperature range. A plurality of correction values are stored, which are corrected and a thermal displacement correction value is obtained by calculation from the corrected temperature value or the input temperature measurement value, and when the newly input temperature measurement value reaches a predetermined number of constituents in one block. Smoothing method of temperature compensation values and updates the contents of degree data.