JPH0432202Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Application Field] The present invention relates to a thermal deformation prevention device that prevents thermal deformation that reduces machining accuracy in a machine tool. [Prior art] Generally, when a workpiece is machined using a machine tool, thermal expansion due to temperature rise in the vicinity of the spindle bearing causes the relative position of the tool attached to the spindle end and the workpiece to change at the start of machining. It fluctuates with respect to the position of , which has a negative effect on machining accuracy. Therefore, a cooling cylinder is installed around the above-mentioned bearing, and a cooling liquid is circulated through this cooling cylinder. Through heat exchange with the cooling liquid, heat is released to the outside, preventing deterioration of machining accuracy due to thermal expansion. Trying to. In this case, the temperature rise in the spindle bearing is determined by calculating the difference between the temperature of the returned liquid after cooling and the atmospheric temperature (room temperature) or the temperature of a part of the machine tool, and The temperature of the coolant is controlled depending on the temperature (for example, Japanese Patent Laid-Open No. 112748/1983). Here, in order to clarify the gist of the present invention, the content of the above-mentioned conventional technology will be explained from a different perspective using mathematical formulas. That is, the relationship between the amount of thermal deformation ΔL of the object and the temperature rise Δt is expressed by the following equation. ΔL=β×Δt×L ₀ However, β: Coefficient of linear expansion of the object L ₀ : Representative length at the initial temperature of the object (temperature at the start of machining work) Also, Δt=T−T ₁ T: Current temperature (This temperature is in direct proportion to the cooling return liquid temperature, and both can be considered to be almost the same temperature.) T ₁ ; Initial temperature of the heat generating part As is clear from the above, the amount of thermal deformation ΔL is: Since it is a function of the temperature difference Δt, thermal deformation of the heat generating part can be prevented by controlling the temperature of the coolant using a cooler etc. so that the temperature difference Δt is below a certain value, for example 0°C. It is possible to prevent deterioration of processing accuracy. [Problem that the invention attempts to solve] However, the above-mentioned atmospheric temperature (room temperature)
The temperature of a part of a machine tool actually fluctuates greatly even during machining work, depending on the presence or absence of sunlight, environmental conditions around the machine installation location, operating conditions, etc. For this reason, if the temperature of the coolant is controlled by regarding the atmospheric temperature as the initial temperature of the heating element, for example, even though the heating element is actually generating heat, the Due to the rise in the air temperature itself, the temperature difference Δt apparently falls below a predetermined value, making it impossible to prevent heat generation, resulting in problems such as insufficient temperature control performance and failure to sufficiently prevent thermal deformation. Ta. Another method is to set the initial temperature as a constant value of 10°C or 15°C using a setting circuit, and to control the coolant temperature when the temperature difference Δt with respect to this constant value exceeds a reference value. I can think of it, too. However, the room temperature inside factories in Japan usually rises and falls by about 15 degrees Celsius per year. ) actually rises and falls within a range of about 15°C.
In other words, the relationship is [room temperature at the start of processing]≒[actual initial temperature of the heat generating part]. As mentioned above, since the actual initial temperature changes variously throughout the year, controlling the temperature of the coolant based on a preset constant value as the reference temperature and the difference in temperature from this value will cause heat generation. It is clear that sufficient temperature control performance cannot be obtained for the part. Of course, by measuring the actual initial temperature, the constant value or
Although the reference value for the temperature difference Δt may be reset at the start of work, there is a problem that this is too complicated. Therefore, the inventors of the present invention actually measured the temperature changes in various parts of the machine tool installation location, and as a result, as shown in Figure 7, the temperature underground near the ground surface is stable compared to room temperature or machine tool temperature. I found out.
Figure 7 is an actual measurement example showing the change over time when the main shaft is rotated at 3000 rpm. The machine temperature is shown respectively. Furthermore, when we measured the soil temperature inside the factory throughout the year, we found that, as shown in Table 1 and Figure 8 below, the soil temperature changes continuously, closely following the room temperature, based on the year. It turned out to be going. It was also found that the difference between soil temperature and room temperature is almost constant throughout the year, and is small.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a heat exchange device that circulates coolant around a bearing, a first temperature detector that detects the temperature of the returned coolant after cooling,
This device includes a second temperature detector that detects the temperature underground, and a temperature control device that compares the outputs of the temperature detectors and controls the temperature of the coolant based on the difference. [Operation] In the thermal deformation prevention device of the present invention, the temperature of the return coolant detected by the first temperature sensor and the underground temperature detected by the second temperature sensor are controlled by the temperature control device. Based on the difference, the temperature of the coolant is controlled to suppress changes in the temperature of the heat generating part. [Embodiment] Hereinafter, an embodiment of the present invention will be described based on FIGS. 1 to 4. 1 in the figure is the base of the machine tool 2. A column 3 is provided on this base 1, and this column 3 is driven by a servo motor 4 for driving the column installed at the end of the base 1. It is configured to move in the Z-axis (left and right in FIG. 1) direction. The column 3 is also provided with a spindle head 5, which is moved in the Y-axis (up and down in FIG. 1) direction by a servo motor 6 installed at the top of the column 3. It's becoming like that. The spindle head 5 is provided with a spindle 8 rotated by a spindle motor 7, and a tool for machining a workpiece 10 on a table 9 is inserted into the spindle 8. ing. Further, the table 9 has a pair of guide rails 11 on the base 1.
The table base 12 is placed on a table base 12 fitted into the ) direction. A cooling cylinder 14 is installed around the bearing for the main shaft 8 in the main spindle head 5, and a cooling liquid tank in the temperature control device 17 is connected to the cooling cylinder 14 via circulation pipes 15 and 16. 18 and a circulation pump (not shown). Inside this cooling liquid tank 18, there is a first temperature detector 19 for detecting the temperature of the cooling liquid.
is arranged. Further, as shown in FIG. 3, a recess 21 is formed at an appropriate position on the concrete floor 20 on which the machine tool 2 is installed.
1, a second temperature detector 22 is disposed for detecting the underground temperature near the ground surface, which is used as a reference temperature. The recess 21 that accommodates the second temperature sensor 22 is filled with a conductive material 23 having good thermal conductivity, such as copper, and the upper surface of the recess 21 is filled with a conductive material 23 that covers the recess 21. A heat insulating material 24 is provided. The first and second temperature detectors 19 and 22 are electrically connected to a subtraction circuit 27 via amplifiers 25 and 26 of the temperature control device 17. This subtraction circuit 27 is configured to combine the output of the first temperature detector 19 with the output of the second temperature detector 19.
The difference (temperature difference) Δt from the output of the temperature detector 22 is calculated, and this temperature difference Δt is input to the comparison circuit 28. The comparison circuit 28 compares the temperature difference Δt with a target value Δt ₀ preset in the target value setting circuit 29.
The results of this comparison are input to the determination circuit 30,
Size is now being determined. That is, when the temperature difference Δt exceeds the target value Δt ₀ , the determination circuit 30
operates the cooler 31 that cools the coolant in the coolant tank 18, and the temperature difference Δt reaches the target value Δt ₀
When the temperature falls below, the operation of the cooler 31 is stopped. In the machine tool 2 configured as described above,
The main shaft motor 7 is operated to rotate the main shaft 8,
The workpiece 1 is
0, as the spindle 8 rotates, the bearings for the spindle 8 generate heat, causing the spindle head 5 to
temperature begins to rise. The heat generated inside the spindle head 5 is transmitted to the cooling fluid flowing within the cooling cylinder 14, increasing the temperature of the cooling fluid. Next, the coolant whose temperature has increased by cooling the spindle head 5 returns to the coolant tank 18 via the circulation pipe 16. At this time, the coolant temperature is set at the coolant tank 18.
The temperature of the ground surface, which is the reference temperature, is detected by the second temperature detector 22. The detected value is
5 and 26 to the subtraction circuit 27, the temperature of the coolant increases and
7 (the difference between the coolant temperature and the underground temperature near the ground surface) Δt is set in advance by the target value setting circuit 29.
When the target value Δt ₀ set in is exceeded, the judgment circuit 3
0 operates the cooler 31 to cool the coolant. Therefore, the cooled liquid cools the spindle head 5.
By being supplied to the inner cooling cylinder 14, a temperature rise due to heat generation within the spindle head 5 is suppressed, and thermal deformation (thermal expansion) of the spindle and mechanical parts in its vicinity is prevented. As a result, the relative positions of the tool inserted into the spindle 8 and the workpiece 10 placed on the table 9 do not shift, and the machining accuracy does not deteriorate. Further, when the temperature of the coolant returning to the coolant tank 18 decreases due to the action of the cooler 31 and the temperature difference Δt becomes equal to or less than the target value Δt ₀ , the determination circuit 30 stops the operation of the cooler 31. Therefore, the temperature of the coolant is maintained near a predetermined temperature difference (target value) Δt ₀ with respect to the underground temperature, which is stable and difficult to change, and thermal deformation of the machine tool due to temperature changes of the coolant is prevented. Therefore, the machining accuracy of the workpiece 10 is not adversely affected. The above effect is shown in the target value Δt ₀ in Figure 4.
This is a time change diagram of the amount of thermal displacement when = 0°C. In this figure, the amount of displacement A in the Y-axis direction and the amount of displacement A in the Z-axis direction based on the temperature of the machine tool (for example, the temperature of the base) are shown. Compared to the displacement amount B, the displacement amount C in the Y-axis direction of this example based on the underground temperature
It can be seen that the displacement amount D in the Z-axis direction is clearly small, and the temperature control performance during machining work is extremely good. In the above embodiment, the case where the second temperature detector 22 is installed near the ground surface has been described, but as shown in FIG.
1, a detection hole 40 deeper than the recess 21 is bored, and the second temperature sensor 22 and a good conductive member 23 covering the second temperature sensor 22 are installed below the detection hole 40. In addition, the upper part of the detection hole 40 may be covered with a heat insulating material 42 via an air layer 41, or as shown in FIG. A configuration may also be provided in which a filling member 43 made of a material or a heat insulating material is provided. Furthermore, to explain the advantage of the device of this example, if the reference temperature for calculating the temperature difference t ₀ is set to a constant value using a setting circuit, the There was an inconvenience that the reference temperature had to be reset by measuring the room temperature or the initial temperature of the heating element, which was cumbersome, but according to the device of this embodiment, the temperature changes according to the room temperature over the year. Since we use the ground temperature as the reference temperature, even if the room temperature changes significantly over the year, the reference temperature can be continuously adjusted according to the change without any resetting or temperature measurement work. This allows good temperature control of the coolant. Moreover, this eliminates the need to provide a setting circuit, which has the advantage of simplifying the device. Further, although the above embodiment has been described using the cooler 31, a heater may be provided if necessary. Furthermore, in the above embodiment, the case where the cooling tube 14 is provided near the main shaft 8 has been explained, but the thermal deformation prevention device of the present invention can also be used when cooling other heat generating parts of the machine tool 2. Needless to say. [Effects of the invention] As explained above, the present invention includes a heat exchange device that circulates cooling fluid around a bearing, a first temperature detector that detects the temperature of the returned cooling fluid after cooling, and a temperature detector that detects the temperature underground. A temperature control device that compares the outputs of the respective temperature detectors and controls the temperature of the coolant based on the difference. By comparing the temperature of the returned coolant detected with the underground temperature detected by the second temperature sensor using a temperature control device, and controlling the temperature of the coolant based on the difference, the temperature of the coolant is controlled. Temperature changes in the heat generating part of the machine can be easily suppressed without being affected by the environmental conditions around the machine installation location or the operating conditions of the machine during machining work, and thermal deformation of the machine tool can be reliably prevented. Therefore, since the relative position between the workpiece and the tool inserted into the machine tool does not change, the machining accuracy of the workpiece can be maintained in a good condition and no defective products are produced.
It has the excellent effect of improving product yield. Furthermore, in this invention, the ground temperature, which changes according to the room temperature during the year, is used as the reference temperature, so even if the room temperature changes over the year, that is, the actual initial temperature of the heat generating part is large, It is possible to continuously change the reference temperature in accordance with this change without any reset work or temperature measurement work, and thereby perform good temperature control of the coolant. I can do it. Further, there is an advantage that there is no need to provide a setting circuit for keeping the reference temperature constant, and the device can be simplified.

[Brief explanation of drawings]

Figures 1 to 4 show an embodiment of the present invention; Figure 1 is a schematic configuration diagram, Figure 2 is a block diagram of the electric circuit, and Figure 3 is the installation state of the second temperature detector. 4 is a characteristic diagram illustrating temporal changes in the amount of thermal displacement, FIG. 5 is a sectional view showing another installation state of the second temperature detector, and FIG. 6 is a diagram showing the second temperature detector. Figure 7 is a characteristic diagram showing temporal changes in temperature at various parts of the place where the machine tool is installed, and Figure 8 is a characteristic diagram showing continuous changes in soil temperature over the year. . 5... Spindle head, 8... Main shaft, 14... Cooling cylinder,
15, 16...Environmental piping, 17...Temperature control device, 18...Cooling liquid tank, 19...First temperature detector, 22...Second temperature detector, Δt...Temperature difference.

Claims (1)

[Scope of utility model registration request] a heat exchange device that circulates coolant around the bearing;
A first temperature detector that detects the temperature of the return coolant after cooling the surroundings of the bearing, a second temperature detector that detects the underground temperature, and the outputs of each of the temperature detectors are compared, and the A thermal deformation prevention device for a machine tool, comprising: a temperature control device that controls the temperature of the coolant based on the difference.