JPS6159860B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to correction of thermal displacement of a machine tool, and particularly to a numerical control device having a function of correcting elongation in the direction of the main axis.

Various countermeasures have been proposed for thermal displacement of machine tools. In particular, since machining centers have a three-dimensional structure, various measures are being actively taken to address the problem of thermal displacement. To summarize these countermeasures, for example, (a) Methods to reduce heat generation itself (b) Removal of heat through heat exchange (c) Implementation of warming-up (d) Adoption of thermally symmetrical structure (e) Thermal displacement There are various methods such as adoption of correction devices (f), atmosphere control (for example, by showering), and the above (a), (b), (c), and (d) have been widely adopted, but regarding (e), The current situation is that it is almost never implemented.

This means that displacement in the X-Y coordinate direction has been reduced by taking measures (a) to (d), but in general, as for the elongation in the Z-axis, that is, the principal axes, as much precision is not required as compared to the X and Y-axis directions. It seems that there was also a situation.

However, the required machining accuracy in the Z-axis direction is gradually increasing, and countermeasures are also becoming necessary in response to unmanned systems.

The present invention assumes that the thermal displacement in the Z-axis direction is caused by the temperature gradient of the structural members constituting the machine, and that the temperature of the spindle head nose, which is the largest heat generating part in the Z-axis direction, and other parts where the temperature changes are relatively small. The purpose of this method is to find a relational expression between the temperature difference with the temperature of the spindle head and the thermal displacement of the nose portion of the spindle head, and correct the thermal displacement according to the measured temperature difference.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 is a side view of the horizontal machining center MT, and Figure 11 is a column bed.
A column 12 is mounted on the column 1 so as to be slidable in the Z direction. Also, the left end of the column bed 11 is the bed 11 on which the saddle 13 and table 14 are mounted.
A is provided.

Reference numeral 15 denotes a spindle head nose constituting the tip of the spindle head which is housed in the column 12 and moved in the Y direction, and has a spindle bearing section built therein. Sho 1
6 is a tool magazine used for automatic tool exchange.

A temperature detection sensor t1 is attached to the spindle head nose 15 at a sensor position S1, and another sensor t2 is attached at a sensor position S1 near the right end of the column bed 11. This machining center is the location of sensor position S2.
It is preferable that the temperature of the MT body is relatively stable and maintained at a substantially constant temperature during operation.
Therefore, the distance between the sensor positions S1 and S2 in the Z direction does not have any direct meaning in this case.

Figure 2 shows a graph of data showing an example of a temperature rise test.The horizontal axis shows the spindle rotation speed (rpm) and the elapsed time during which the same rotation speed is maintained, and the vertical axis shows the temperature (°C). and sensor position S
1. Temperature change in S2 and sensor type
Shows temperature changes using IC sensor and alcohol thermometer.

Figures 3A and 3B show the displacement in the Z-axis direction (Figure 3A) and temperature change (Figure 3B) over time when the spindle was driven at 3150 rpm for 3.5 hours.

Figure A shows the displacement of the tip of the test bar, the displacement of the end face of the main shaft, and the displacement between the column and column bed, respectively.

Figure B shows temperature changes due to the IC sensor and alcohol thermometer at the spindle bearing built into the spindle head nose (sensor position S1), and temperature changes due to the IC sensor and room temperature changes at the column bed position (sensor position S2). shows.

FIG. 4 is a graph showing the transition of thermal displacement of the spindle end face measured by an IC sensor and an alcohol thermometer, respectively, and the abscissa axis indicates the temperature difference Δt=t1−t2 at the sensor positions S1 and S2. The graph from each sensor is 3.5 when the main shaft is driven at 3150 rpm.
This corresponds to the case where the spindle rotation is stopped after almost reaching a thermal equilibrium state over time, and the graph part where the displacement increases up to points P1 and P2 as shown by the arrow corresponds to when the spindle is being driven. .

The reason why there is hysteresis as shown in the figure is due to the presence of thermal inertia of mechanical members such as columns and beds.

The straight line L in the same figure is the temperature (difference) Δt obtained based on experimental data to represent each of the above-mentioned graph curves.
One approximate straight line for , and its empirical formula is constructed as follows.

ZCOMP=ZTMPA/100・(t1−t2)・24/1000+ZTMPB −(1) Here, ZCOMP; Z-axis direction thermal displacement correction amount (microns) t1; Spindle head nose temperature (IC sensor temperature) t2; Column bed temperature ( IC sensor temperature) ZTMPA; System parameter 0≦ZTMPA≦999 ZTMPB; System parameter -200≦ZTMPB≦200 When the constants ZTMPA and ZTMPB in the above equation (1) are determined by experimental data, ZCOMP638/100 (t1-t2 )−26 (2).

FIG. 5 shows a circuit configuration in which temperature signals detected by each sensor are input to the numerical control device CNC in the present embodiment shown in FIG. The same sensor 101 installed at sensor positions S1 and S2,
The detected temperatures t1, t2, t1, t2 are converted into electrical signals and provided to amplifiers 103, 104.

105 is a selector and the sensors 101, 10
Amplifier 1 to incorporate 2 into the numerical control device CNC
03 and 104 sequentially.

106 is an analog-to-digital converter (A/D converter), and 107A is a buffer unit that represents the output of the A/D converter 106 as a binary number and holds it.

Reference numeral 107 denotes an I/O unit which includes the buffer unit 107A, and a switching command to the selector 105 is given from the I/O unit 107 to the selector 105. 108 is an arithmetic processing unit CPU of the numerical control device CNC, and 109 and 110 are data memory and program memory, respectively.

FIG. 6 is a flowchart showing the process of making the thermal displacement correction amount involved in the amount of movement when a movement command is given in the X, Y, and Z axis directions.
This is a part of the program memory (P/M) 110 shown in the figure.

In the same figure, program step STj-2 is the servo command value for each axis (now Z) at the next sampling time.
If only the axis is considered, calculate ΔZ).
Next, pitch error correction processing is performed in STj-1, and ΔZP is added to the calculation result ΔZ in STj-2. Next, the program moves to step STj for thermal displacement correction, and in STj1, the temperature t1 detected by the sensor t1 is loaded into the data memory 109, and then
At STj2, the temperature t2 detected by the sensor t2 is taken in. Next, in STj3, the difference Δt=t1−t2 is calculated.

Next, in STj4, ZCOMP=ZCOMP/100×(t1−t2)×24/1000+ZTMPB is calculated. ZTMPA and ZTMPB are stored in the data memory 109 in advance.

In STj5, the difference ΔZCOMP(n) between the previous correction amount calculation value (n-1) and the current correction amount calculation value (n) is calculated as ΔZCOMP(n)=ZCOMP(n)−ZCOMP(n−1).

Next, in STj6, the output ΔZCOMP of STj5
(n) is added to the output ΔZ+ΔZP at STj-1, resulting in ΔZ=ΔZ+ΔZP+ΔZCOMP.

STj+1 is a backlash correction process and Z
The backlash correction amount ΔZB of the shaft drive system is applied to the output ΔZ of Tj6 and then applied to the servo system.

Note that the steps STj1 to STj6 may be performed before the pitch error correction processing STj-1, but they must be performed before the pitch error correction processing STj+1.
Of course, it must be in front of.

Figure 7 A, B, and C are part program Z-axis movement command contents (sequence numbers N001 and N002)
Z-axis movement Z = 1000, F = 100 and sensor t
1 and t2 and the timing at which correction is made. The horizontal axis of each signal indicates the coordinate value in the Z-axis direction.

FIG. 7 shows an example in which the correction operation is actually performed for each program block.

Figure 8 A, B, and C show more general correction operations, and while one movement command is valid, the program flow STj1 to STj6 in Figure 6 is the servo output ΔZ (STj-2). ΔZCOMP(1), ΔZCOMP(2), ΔZCOMP(3)...ΔZCOMP(n) are given one after another. If Δt=t1−t2 does not change at each sample time i, ΔZCOMP
(i) is zero.

In order to improve the detection accuracy of the temperature difference Δt=t1−t2, sampling is performed 10 times (by switching the selector), and the average value obtained by removing the maximum value and minimum value is set as Δt. That is, It is.

FIG. 9 is a plot of data when thermal displacement correction is performed, and it can be seen that the displacement of the spindle end face position is significantly reduced compared to the case where no correction is made.

In the above explanation, only the Z-axis was explained, but it goes without saying that the explanation is also applicable to the other moving axes in the X and Y directions. For that purpose, X, Y
It is sufficient to simply provide sensors t1X and t2X in the axial direction. Also, although the function is shown as a linear equation for correction, the system parameters ZTMPA and ZTMPB should be selected to other values as appropriate depending on the range of t1-t2.
Moreover, it is also easy to modify the above parameters as appropriate, taking into account the current temperature state of the machining center MT and to which side the arrow in Fig. 4 corresponds from the previous spindle drive state. It is possible.

As explained above, according to the present invention, it is possible to compensate for thermal displacement associated with spindle drive simply by installing two sensors in the machine and providing a temperature compensation program in the numerical controller CNC. As shown in the flowchart of FIG. 6, if there is a change in Δt during a movement command, the displacement accompanying this change can be constantly corrected, so that machining can be performed with high accuracy.

In addition, since most of the thermal displacement in the spindle direction (Z) occurs near the spindle head nose, in the present invention, the correction amount can be determined for the correction operation regardless of the current position of the Z-axis or the movement amount commanded by the part program. Therefore, the programming process is simple and the correction amount can be incorporated for each servo output (ΔZ).

[Brief explanation of the drawing]

Figure 1 is a side view of the machining center, Figure 2
Figure 3 is a graph showing the temperature rise test, Figure 3 is a graph showing the state of temperature and displacement when the spindle is driven at 3150 rpm, Figure 4 is a graph showing the displacement of the spindle end face with respect to the temperature difference between each sensor, and Figure 5 The figure is a block diagram showing the connection between the sensor and the numerical control device, and Figure 6 is a flowchart showing the process of thermal displacement correction.
Figure 7 A, B, and C are explanatory diagrams when the correction is performed every time a movement command is given. Figure 8 A, B, and C are explanatory diagrams when the correction is performed almost continuously. Figure 9 is a graph showing the thermal displacement of the spindle end face when correction is performed. 11... Column bed, 12... Column, 13
... Saddle, 14 ... Table, 15 ... Spindle head nose, 16 ... Tool magazine, S1, S2 ...
sensor position.

Claims (1)

[Claims] 1. In a numerical control device for correcting thermal displacement of a machine tool, a first sensor detects the temperature of the spindle head of the machine tool, and a second sensor detects the temperature of a body part of the machine tool where temperature changes are relatively small. A temperature difference-thermal displacement function expression representing the relationship between the temperature difference (Δt) at two locations detected using the sensor and the amount of elongation of the main shaft is stored in the program memory, and the axial direction relative to the main shaft is stored in the program memory. Stores a program step that gives a thermal displacement correction amount (ΔZCOMP) obtained from the above functional formula to the servo output (ΔZ) outputted as a result of interpolation calculation in the numerical control device when a movement command is given. Numerical control device with thermal displacement correction function and program memory.