JPH0463659A - Main spindle temperature control method for machine tool - Google Patents

Abstract

PURPOSE:To prevent the stable thermal distortion state of a main spindle established by the previous operation from being disturbed by over-cooling by stopping the feed of a cooling liquid to the main spindle only when the stop period of the main spindle exceeds a preset value while the rotation of the main spindle is temporarily stopped to perform the required work during the operation of a machine tool. CONSTITUTION:When a main spindle is once stopped, the circulation of a cooling liquid to bearings 2 of a main spindle device 1 is continued as it is for a preset period, and normal feedback control is continued. If the stop period of the main spindle is prolonged beyond the preset period, the feedback control by a control unit 11 is interrupted, a stop command is sent to a refrigerating compressor 9 and a pump 5, and the circulation of the cooling liquid to bearings 2 of the main spindle device 1 is also interrupted. The stable thermal expansion state of the main spindle is prevented from being disturbed by over-cooling, and high-precision machining can be performed immediately after the rotation of the main spindle is restarted without undergoing the thermal distortion transient state.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is aimed at stabilizing the distortion caused in the main shaft of a machine tool due to the heat generated during the operation of a liquid temperature controller, thereby improving machining accuracy. This invention relates to a method for cooling the main shaft of a machine.

[Conventional technology]

Generally, in a machine tool, heat is mainly generated in the bearing portion due to the rotation of the spindle, resulting in a temperature difference between the spindle head and the machine base that supports it. This causes the spindle to elongate relative to the machine base, resulting in a reduction in machining accuracy.To prevent this, a cooling liquid is circulated around the spindle head to absorb the heat generated.
A cooling system is provided to maintain the difference between the spindle temperature and the machine stand temperature at a constant value.

An example of a cooling system for this machine tool is shown in FIG. In the area of the bearing 2 of the spindle 1 of the machine tool, a circulation path 3 is provided, in which the coolant in the tank 4 is circulated by means of a pump 5 . A cooler 6 is disposed in the middle of this circulation path 3, and supplies the refrigerant gas cooled by the refrigeration compressor 9 to the heat exchanger 8 through the refrigerant gas circulation path 10, and the coolant in the circulation path 3 passing through it. It is configured to cool it by exchanging heat between the two. The temperature of the coolant, which has cooled the bearing area of the main shaft and has been raised to the same temperature as the main shaft, is detected by a temperature detector 7 provided in the return circuit 3 and is continuously input to the control unit 11 . and,
The difference between the temperature of the machine base and the reference temperature is calculated, and feed puncture control is performed in which the control unit 11 issues an on/off command to the cooler 6 so that this difference matches the target value. ing.

(Problem to be solved by the invention) When the main spindle of a machine tool is operated for a long time, it expands due to thermal expansion, but this elongation becomes a constant value with respect to the machine base, resulting in stable precision. Good processing is done.

However, while machining a workpiece with a machine tool, it may be necessary to temporarily stop the rotation of the spindle. For example, this applies to manual tool replacement or workpiece inspection, which requires the spindle to be stopped for about 2 to 10 minutes. In this case, even if the spindle stops rotating, the spindle temperature remains high due to the heat that has previously accumulated in the machine base, so the cooling system will continue to cool the spindle for a while. It operates to maintain a constant temperature difference with the machine base. As a result, the entire machine cools down, the spindle contracts, and the stable conditions established as a result of previous operation are disturbed. Then, after the rotation of the spindle is restarted, the machining accuracy deteriorates until a stable state is obtained again.

The present invention solves the problems of the prior art, and provides a machine tool that can maintain stable elongation of the spindle due to heat, even when the rotation of the spindle is temporarily stopped. The purpose of this invention is to provide a method for cooling the spindle.

[Means to solve the problem]

The purpose of this is to circulate cooling fluid through the liquid temperature controller in the spindle device of the machine tool, and to feedback-control the cooling capacity of the liquid temperature controller based on the difference between the detected spindle temperature and the reference temperature. In a method for controlling the spindle temperature of a machine tool in which the temperature is maintained at a target value, when the rotation of the spindle stops for more than a predetermined time, the feedback control is performed only during the period when the spindle is stopped. This is achieved by a method for controlling the temperature of a spindle of a machine tool, characterized in that the temperature control method for the spindle of a machine tool is characterized in that the circulation of the coolant to the spindle device is stopped at the same time as the cooling liquid is stopped.

[For production]

While the spindle continues to rotate, the machine tool performs feedback control on the spindle temperature, such as by turning on and off the liquid temperature controller, so that the difference between the detected spindle temperature and the reference temperature remains constant. being driven while being

Once the main shaft stops, the circulation of the coolant to the main shaft continues for a predetermined period of time, and normal feedback control continues. However, if the stop time of the main shaft exceeds this, the feedback control is stopped and the circulation of the coolant to the main shaft is also stopped.

This prevents the stable thermal elongation state of the spindle from being disturbed by excessive cooling, and enables high-precision machining immediately without going through a transient state of thermal strain even after the spindle resumes rotation.

Hereinafter, the present invention will be explained in more detail based on preferred embodiments shown in the drawings.

〔Example〕

As described above, the present invention prevents the stable thermal strain state of the spindle from being disturbed due to excessive cooling when the spindle of a machine tool in operation is stopped midway.

The control procedure for this will be explained based on FIG. 1.

The method of the present invention can be directly applied to the conventional spindle cooling system shown in FIG. 3, so this figure will also be referred to in the following description.

As shown in step 1, first, the control unit 11 issues a spindle stop command to the spindle drive motor 12.

When the spindle has completely stopped, the signal is sent to the control unit 11.
, and the built-in time counter starts counting time, as shown in step 2.

When this count reaches a predetermined value T that is preset in the time counter, the control unit 11 issues a stop command to the refrigeration compressor 9 and pump 5 of the cooling system, as shown in step 3. The cooling of the coolant as well as the supply of coolant to the area of the bearing 2 is discontinued.

In this way, as a daily routine for machine tools,
When stopping the rotation of the spindle during machining of a workpiece,
For example, there are cases such as automatic tool replacement by ATC and reversal of tool rotation during tapping operations, which involve relatively short rotation interruption times of about 2 to 20 seconds. Operations that require a longer stop time include manual tool replacement and mid-work inspection, which require interruptions of rotation for about 1 to 10 minutes. It is desirable that the present invention is directed to the latter type of work that involves a relatively long spindle rotation stop time,
The former case, in which the rotation of the spindle is restarted in a short time, is not so preferred. This is because frequent on/off operations tend to adversely affect the function of the pump as well as the refrigeration compressor and shorten their lifespan. Therefore, the predetermined value T set in the time counter must be determined to be an appropriate value, taking into consideration such problems that may occur if the time is too short, and the amount of contraction due to excessive cooling of the main shaft that may occur if the time is too long. . Of course, it is desirable that this value can be changed arbitrarily.

The effects of the present invention will be apparent from the graph shown in FIG. 2, which shows the experimental results of examining the change over time in the amount of thermal displacement of the spindle when the spindle, which had been rotating at 3000 rpm and stopped, was stopped.

In this graph, the three-dot chain line indicates the case of the conventional method in which feedback control is performed to maintain the spindle temperature at a predetermined value by continuing to circulate the coolant even when the spindle stops rotating. According to this, the main shaft contracts by about 5 μm in 3 minutes after stopping rotation.
It reached 8 μm or more in 6 minutes.

In contrast, in the case of the present invention, the solid line indicates that the circulation of the coolant is stopped immediately after the rotation of the spindle stops, and the dotted line, -dotted chain line, and two-dot chain line indicate that the circulation of the coolant is stopped after 5 seconds, 10 seconds, and 20 seconds, respectively. The case of the present invention is shown below. In the case of the solid line where the circulation of the coolant was immediately stopped, a slight expansion of the main axis was observed over time, but it converged to about 0.5 μm;
When the circulation of the coolant is stopped after a predetermined period of time has elapsed, the shrinkage in all cases converges to about 1 μm. This level of expansion and contraction is fully tolerable since it does not have a substantial adverse effect on processing accuracy.

Judging from this experimental result, - for example, the predetermined value T is 2
By setting it to 0 seconds, during operations that occur frequently on a daily basis, such as tool changes using ATC or tapping operations, the circulation of the coolant will continue even if the spindle rotation stops, allowing the refrigeration compressor to This eliminates the need for excessive on/off operations, and on the other hand, during other operations that occur relatively infrequently but require long spindle downtimes, the coolant circulation is stopped and the thermal strain state of the spindle is stabilized. can be maintained.

〔Effect of the invention〕

As described in detail above, according to the present invention, when the rotation of the spindle is temporarily stopped during operation of a machine tool to perform a necessary work, only when the spindle stop time exceeds a predetermined value is Since the supply of cooling liquid to the spindle is stopped, the stable thermal strain state of the spindle established by the previous operation is prevented from being disturbed by excessive cooling of the spindle. This makes it possible to perform highly accurate machining immediately after restarting the rotation of the spindle.

In addition, a predetermined waiting time is provided between when the spindle stops rotating and when the coolant circulation stops, reducing excessive on/off operations of the refrigeration system's refrigeration compressor and pump that would otherwise occur during this time. be able to.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing the procedure for implementing the method for cooling the main spindle of a machine tool according to the present invention; FIG. 2 is a graph showing changes over time in the amount of displacement due to heat of the main spindle, showing the effects of the present invention; FIG. 3 is a schematic diagram showing a system configuration for controlling the temperature of the main shaft of a machine tool. 1 - Main shaft device 2 - Bearing coolant circulation path - Tank pump - Cooler temperature detector - Heat exchanger Refrigeration compressor 〇 - Refrigerant gas circulation path l - Control unit

Claims (1)

[Claims] 1. Circulate cooling fluid through the liquid temperature controller in the spindle device of the machine tool, feedback control the cooling capacity of the liquid temperature controller based on the difference between the detected spindle temperature and the reference temperature,
In a spindle temperature control method for a machine tool that maintains the temperature of the spindle at a target value, if the rotation of the spindle stops for more than a predetermined time, the feedback is applied only during the period when the spindle is stopped. In addition to discontinuing control,
A method for controlling the temperature of a main spindle of a machine tool, comprising stopping circulation of a coolant to the main spindle device.