JPH048452A - Smoothing method of thermal displacement compensation value - Google Patents

Abstract

PURPOSE:To reduce the extent of step difference on a work machined surface being produced by thermal displacement compensation by calculating the predictive temperature range of a thermal straight line found out of plural pieces of temperature data, comparing the inputted thermometric value with the predictive temperature range, and correcting the thermometric value. CONSTITUTION:A temperature intermittent reading part 13 reads a thermometric value at each specified time, while a temperature data storage part 14 stores these data successively, and when the measured value is reaches the specified number, these values are outputted to a straight line operating part 15 as adjacent continuous temperature data making these value into one block, and when a new thermometric value is read, the first measured point is discharged and memory contents are renewed. The straight line operating part 15 seeks a thermal straight line, while a predictive temperature range setting part 16 sets a predictive temperature range and stores it, and a temperature comparison correcting part 17 corrects the existing thermometric value to a boundary temperature nearest to the predictive temperature range when it comes off this predictive temperature range. A compensation value operating part 18 calculates the thermal displacement from the existing temperature, and a compensating shaft driving control part 19 adds or subtracts the compensation value, driving a Z-axis servomotor 9.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a thermal displacement correction method for preventing machining accuracy from deteriorating due to thermal displacement caused by local temperature changes caused by the operation of a machine tool. be.

Conventional technology Conventionally, there is a method for correcting thermal displacement caused by a temperature rise in the spindle and its surroundings due to rotation of the spindle of a machine tool, such as a machining center, by directly measuring the amount of displacement and feeding back the correction amount in real time. However, since the equipment is large-scale, in most cases, for example, as shown in the diagram of a machining center in Figure 1, the temperature at positions a and b of the spindle head, which is susceptible to heat, and the environmental temperature of the bed are controlled. Measure the temperature at position C shown, calculate the displacement amount from the temperature rise value at positions a and b with respect to the temperature at position C, using an experimental or empirical coefficient, and feed this back to the Z-axis command value. A commonly used method is to perform correction.

Problems to be Solved by the Invention In the method of calculating the amount of thermal displacement from the temperature rise value described in the conventional technique, the displacement position is calculated based on the input temperature measurement value. As shown in Fig. 2, when an error occurs in the temperature measurement value due to disturbance, etc., the correction value changes each time, and a step is created on the machined surface. Therefore, when the workpiece is a mold or the like, there is a problem in that subsequent manual surface finishing takes time.

The present invention has been made in view of the problems of the prior art, and its purpose is to provide a smoothing method for reducing the level difference on the machined surface of a workpiece caused by thermal displacement correction. It is something to do.

Means for Solving the Problems In order to achieve the above object, the smoothing method of the thermal displacement correction value of the present invention is a thermal displacement correction method that calculates a correction value by calculation based on the temperature measurement value of the heat generating part. The temperature data of the immediately preceding block is stored as a block containing a plurality of input temperature measurement values, and a temperature straight line passing through the center of the measurement points of the temperature data is calculated, and the temperature line is centered around this extension line. When a new temperature measurement value is input, it is compared with the value of the expected temperature range, and when the measured value deviates from the expected temperature range, it is corrected to the nearest boundary expected temperature value, and this correction is performed. A thermal displacement correction value is obtained by calculation from the input temperature value or the input temperature measurement value, and the content of the stored temperature data is updated with the newly input temperature measurement value to prepare for the next time.

In addition, in the thermal displacement correction method that calculates the correction value by calculation based on the temperature measurement value of the heat generating part, the temperature data of the immediately preceding consecutive blocks is stored, with multiple temperature measurement values that are intermittently input as a - block. Then, calculate a temperature straight line that passes through the center of each measurement point group of each temperature data, calculate the expected temperature straight line from the rate of change in the slope angle of each temperature straight line, and set the expected temperature straight line as the center. The expected temperature range is set, and when a new temperature measurement value is input, it is compared with the corresponding value in the expected temperature range, and when the measured value is outside the expected temperature range, it is corrected to the value of the nearest boundary expected temperature, and this A thermal displacement correction value is calculated from the corrected temperature value or the input temperature measurement value, and the contents of a plurality of temperature data are stored when the newly input temperature measurement value reaches a predetermined configuration point of the block. This is to update.

Operation claim 1 stores the temperature data of the immediately preceding block of a plurality of input temperature measurement values, and calculates the expected temperature with a width above and below the extension line of the 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. If the temperature deviates from the expected temperature range due to disturbance etc., it is corrected to the upper or lower limit of the expected temperature range and the newly input temperature is According to a second aspect of the present invention, the temperature data is characterized by inputting measured values, and the temperature data of a plurality of consecutive blocks immediately before a plurality of input temperature measurement values are set as a -block is stored;
This sets the expected temperature range, and when one measurement value is entered, this prediction is compared with the value at the corresponding position in the temperature range, and when it deviates from the expected temperature range, the value at the upper limit or the lower limit at the corresponding position. At the same time, when the input measurement value reaches the number of blocks configured, the contents of the temperature data are updated.

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

In a known portal type machining center, a table 2 is placed on a guide in the X-axis direction provided on a bed 1 so as to be movable and positionable, and columns 3 are erected on the floor on both sides of the bed 1. Top beam 4 is tightened. A cross rail 5 having a guide in the Y-axis direction is provided on the guide 3a in the X-axis direction cut in the column 3 so as to be movable and positionable, and the spindle head 6 can be movably positioned on this guide in the Y-axis direction. It is on a shelf. Quill 7 is attached to spindle head 6
The main shaft 8 is rotatably supported on the quill 7 by a plurality of bearings (not shown), and the quill 7
, the main shaft 8 is moved and positioned by an NC-controlled servo motor 9.

The spindle head 6 has two thermocouples 1) a and b that are susceptible to the heat generated by the bearing due to the rotation of the spindle 8, and thermocouples 1) a and b.
A thermocouple 1)C is attached at a position C that exhibits a value close to the ambient temperature of the bed 1.

Next, the servo system for correcting thermal displacement based on the temperature measurement values of thermocouples 1) A to IIC will be explained using the Bronk diagram in FIG.
2, when the output signal of each thermocouple is input, based on the output T3 of thermocouple 1) C at position C, from the output TI and T2 of thermocouple 1) A, 1) B at positions a and b. This is where the respective temperature differences (referred to as temperature measurements) are calculated. The temperature intermittent reading section 13 reads the temperature measurement value every minute for a set fixed period of time, for example, in the first embodiment, and the temperature data storage section 14 sequentially stores the temperature measurement value as it is read intermittently. When the number of measured values (measurement points) reaches a predetermined number, for example six, as shown in FIG. Then, when a new temperature measurement value is read, the first measurement point is released and the stored contents are updated. The linear calculation section 15 is a section that calculates a temperature straight line using the least squares method from the input temperature data, and the expected temperature range setting section 16 adds a predetermined width above and below the extension line of the temperature straight line to set the expected temperature. This is the part that sets and stores the range. The temperature comparison correction unit 17 compares the current temperature measurement value inputted via the temperature storage unit with the expected temperature range,
This is the part that corrects the current temperature measurement value to the closest boundary temperature of the expected temperature range when it deviates from the expected temperature range.

The correction amount calculation unit 18 calculates the amount of thermal displacement by multiplying the corrected temperature or the uncorrected current temperature input via the temperature comparison correction unit 17 by a coefficient determined by experiment or experience,
The part that outputs this as a correction value, correction axis drive control section 1
Reference numeral 9 denotes a part that, when a correction value is input, adds or subtracts this correction value to the Z-axis position command value of the NC to drive the Z-axis servo motor 9.

Next, the operation of the first embodiment will be explained according to the flowchart shown in FIG.

In step S1, when a new temperature measurement value is read from the temperature intermittent reading unit 13, it is checked in step S2 whether the number of measurement points read into the temperature data storage unit 14 has reached six, which is the number of blocks, and the start Immediately after, the answer is NO, and the process returns to step S1. If the answer is YES in step S2, then in step S3 the temperature data constituted by the read six measurement points is read by the linear calculation section 15, and in step S4, the temperature data is calculated by the least squares method. Calculate.

Next, in step S5, an expected temperature range is calculated from the extension line of the obtained temperature straight line, and in step S6, a new current temperature measurement value is read, and in step S7, the current temperature measurement read by the temperature comparison correction unit 17 is The value is checked to see if it is within the expected temperature range, and if no, in step S8 it is corrected to the value of the boundary temperature of the expected temperature range that is closest to the current temperature measurement value, and in step S9
At this time, the current temperature measurement value is taken into the temperature data storage section 14 as a new measurement point, and the temperature data is updated. If the answer is YES in step S7, the current temperature measurement value read in step S9 is output as is, and this temperature measurement value is taken in as a new measurement point, discarding one old measurement point, and updating the temperature data. do. Then, in step SIO, the correction value performance section 1
A Z-axis correction value is calculated by calculation based on the temperature measurement value as read in step 8 or the corrected temperature value corrected by the temperature comparison correction section, and the Z-axis correction value is calculated by the output from the correction axis drive control section 19 in step Sll. The Z-axis servo motor 9 is driven and thermal displacement correction is executed.Next, in step S12, it is confirmed whether a machine operation stop command has been issued, and if no, the process returns to step S1, and if yes, the process returns to step S1. It will be the end.

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

Note that FIG. 1 shows the first embodiment and a vehicle, and in order to avoid duplication of explanation, only the parts that are different from the first embodiment will be explained and the rest will be omitted.

The temperature data storage unit 14 is stored at a temperature faster than the first embodiment, e.g.
Temperature measurement values are read at a pitch of 0 seconds, and as shown in Figure 4, for example, each temperature data of three blocks adjacent to each other, where six measurement points constitute one block, is calculated as the consecutive temperature immediately before the - group. This part stores the temperature data as data and outputs it to the linear calculation section 15, and also discards the oldest block when the number of newly input measurement points reaches six, thereby updating a set of temperature data in three blocks. Linear calculation section 15
is a part that calculates the temperature straight line of each temperature data, and the expected temperature range setting unit 16 calculates the expected temperature straight line from the rate of change of the slope angle of each temperature straight line, and sets the width above and below the expected temperature straight line as the center. This is the part where the expected temperature range is set and stored as a parameter. Here, an example of the measurement formula for calculating the expected temperature line from three temperature lines is shown in Figures 4 and 5.
The respective differences in the slope angles A-C of the temperature lines I to ■ shown in the figure are C-B and B-A, and the difference E in the slope angle of the expected temperature line ■ with respect to the slope angle A is estimated from this. (C-
B) - (B-A), then D = (B-A) - E, and the slope angle of the expected temperature straight line ■ is given by the following formula D = 3A-38
It can be determined by +C.

The temperature comparison and correction section 17 is a section that compares the current temperature measurement value with a corresponding value in the expected temperature range, and corrects the current temperature measurement value to the nearest boundary temperature when it deviates from the expected temperature range. The same expected temperature range is used here until the number of new current temperature measurement values input reaches six, which is the number of elements in one block.

Next, the operation of this embodiment will be explained with reference to the flowchart shown in FIG.

In step 5101, the measured temperature value is read, and in step S102, the third block (
It is checked whether there are 6 measurement points read in block 1 in Fig. 4. Immediately after startup, the result is NO, and step 510
Return to 1. If the result in step S102 is YES, then in step 5103, each temperature line of the three blocks is calculated by the least squares method.Next, in step 5104, each slope of each calculated temperature line is The angle is calculated, and in step S105, an expected temperature straight line for the next block is calculated from the rate of change of each slope angle, and in step 5106, a predetermined width is provided above and below this expected temperature straight line to calculate an expected temperature range. Then, in step 5107, the current temperature measurement value is read, and in step 310B, it is checked whether the read current temperature measurement value is within the expected temperature range, and if no, in step 5109, the correspondence of the expected temperature range is determined. The current temperature measurement value before the correction is stored in the temperature data storage unit 14 as the measurement point of the next block.

If the answer is YES in step 3108, the current temperature measurement value is stored as a measurement point, and step 51)
At step 0, it is checked whether the number of read measurement points for the next block has reached 6, and if yes, at step 51)1, the next block is inserted and the old block is discarded.
Update the contents of temperature data made up of three blocks. Then, in step S1)2, a correction value is calculated based on the read current temperature measurement value or the corrected temperature value, and in step S1)3, Z-axis correction is executed.

Next, in step 51)4, it is confirmed whether a machine operation stop command has been issued, and if no, step 51) is performed.
Go back to 07, and if yes, it's over.

Effects of the Invention Since the present invention is configured as described above, it produces the following effects.

The method for smoothing the thermal displacement correction value according to claim 1 is to obtain a temperature straight line by calculation from the temperature data of the immediately preceding block, which is a block containing a plurality of temperature measurement values that are intermittently input, and to calculate an extension line of this temperature straight line. Calculate the expected temperature range centered on Since the temperature measurement value is now corrected using the new expected temperature range, even if the temperature measurement value fluctuates due to external disturbances, it is no longer reflected in the correction amount. The difference in level on the machined surface due to displacement correction is reduced, and the number of subsequent manual finishing steps 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 set as a block, and calculates the temperature of each temperature data. The expected temperature range is set by finding a straight line and calculating the expected temperature line from the rate of change of the slope angle of each temperature line, and when a new temperature measurement value is input, it is compared with the corresponding value in the expected temperature range. When a new temperature measurement reaches a predetermined number of blocks, it updates the stored temperature data and updates the temperature measurement with a new expected temperature range. Since the correction is made, as in claim 1, there is no difference in level on the finished cut surface due to thermal displacement correction, and the number of steps for subsequent manual finishing can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 shows a block diagram of a machining center including a partial block diagram common to the first and second embodiments, and the block diagram of a machining center in this figure is also cited in the conventional technical description. Second
The figure is a graph for explaining the process from inputting the temperature measurement value to setting the expected temperature range in the first embodiment.
FIG. 4 is a flowchart diagram for explaining the operation of the embodiment; FIG. 4 is a graph diagram for explaining the process from inputting the temperature measurement value to setting the expected temperature range in the second embodiment; J is a supplementary table of FIG. 4, FIG. 6 is a flowchart for explaining the operation of the second embodiment, FIG. 7 is a bluff diagram showing an example of variation in conventional temperature measurement points, and FIG. 8 is also a diagram of conventional temperature measurement points. It is a bluff diagram showing an example of variation in measurement points. 6... Main shaft U 8... Main shaft 9... Servo motor 1) A~IIC... Thermocouple

Claims (2)

[Claims] (1) In a thermal displacement correction method that calculates a correction value by calculation based on the temperature measurement value of a heat generating part, temperature data of the immediately previous block is stored, where one block consists of multiple temperature measurement values that are intermittently input. , calculates a temperature straight line passing through the center of the measurement point group of the temperature data, calculates the expected temperature range centered on this extension line, and when a new temperature measurement value is input, the value of the expected temperature range is calculated. When the measured value deviates from the expected temperature range, it is corrected to the nearest boundary expected temperature value, and a thermal displacement correction value is calculated by calculation from this corrected temperature value or the input temperature measurement value, and A method for smoothing a thermal displacement correction value, characterized in that the content of the stored temperature data is updated with a newly input temperature measurement value and prepared for the next time. (2) In a thermal displacement correction method that calculates a correction value by calculation based on the temperature measurement value of a heat generating part, the temperature data of the immediately preceding consecutive blocks is defined as one block of multiple temperature measurement values that are intermittently input. , and calculate a temperature straight line that passes through the center of each measurement point group of each temperature data,
An expected temperature straight line is calculated from the rate of change in the slope angle of each temperature straight line, an expected temperature range centered on this expected temperature straight line is set, and when a new temperature measurement value is input, the corresponding value in the expected temperature range is calculated. When the measured value deviates from the expected temperature range, it is corrected to the nearest boundary expected temperature value, and a thermal displacement correction value is calculated by calculation from this corrected temperature value or the input temperature measurement value, and A method for smoothing thermal displacement correction values, comprising updating the contents of a plurality of stored temperature data when the number of newly input temperature measurement values reaches a predetermined number forming one block.