JP2023106207A - Machine tool main shaft diagnosis method and main shaft diagnosis system - Google Patents

Abstract

To enable a cause of occurrence of an abnormality relating to a bearing of a main shaft to be diagnosed all the time without overlooking.SOLUTION: An NC system executes, as a diagnosis method of a main shaft, vibration determination steps (S11 and S12) of, when vibration of the main shaft detected by a vibration sensor exceeds a predetermined normal range, determining whether the vibration is vibration attributable to a bearing, and occurrence cause diagnosis steps (S13 to S17) of, when the vibration of the main shaft is the vibration attributable to the bearing, diagnosing a cause of occurrence according to whether a condition change relevant to the bearing is present.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a spindle diagnostic method and a spindle diagnostic apparatus for determining the cause of an abnormality related to a bearing of a spindle in a machine tool that processes a workpiece while rotating a tool or workpiece attached to the spindle.

In a machine tool that processes a workpiece while rotating the tool or workpiece attached to the spindle, bearing wear due to deterioration over time can cause loss of preload, contamination with foreign matter, poor lubrication, etc., resulting in damage. It may cause malfunctions such as deterioration of operation accuracy and abnormal noise during operation. In such a state, processing defects such as a defective shape of the workpiece and poor processing surface quality occur, which adversely affects production. In addition, when a failure such as seizure of the spindle occurs, the spindle cannot rotate, and in some cases the machine tool cannot even be operated.
For this reason, machine tools are equipped with a diagnostic device that monitors the vibration of the machine tool and diagnoses the state of lubrication. It also has a built-in monitoring device that stops it from working.
For example, Patent Literature 1 discloses a device for diagnosing the state of lubrication by measuring the vibration of a rotating rolling bearing with a sensor. Further, in Patent Document 2, each of the characteristic frequency output resulting from damage to the bearing calculated by envelope analysis of the acceleration of bearing vibration and the acceleration signal is compared with a threshold, and each of the acceleration and the characteristic frequency output is greater than the threshold. A bearing condition monitoring method is disclosed that diagnoses that the bearing is abnormal at times, and diagnoses that it is a sign of abnormality when only the characteristic frequency output is greater than a threshold.

JP 2019-203753 A JP 2020-153875 A

When the invention of Patent Document 1 is applied to a machine tool, machining has a large impact on the vibration and load of the machine tool even during normal operation, and the non-machining area where diagnosis can be performed takes a shorter time than the machining area. , there is a problem that it is difficult to constantly monitor the state because it is distributed, and an oversight occurs.
The invention of Patent Literature 2 can diagnose a sign of abnormality based on the vibration state, but there is a problem in that even when the same sign of abnormality is determined, the time period until repair is different depending on the reason for the change in the bearing state. If the condition of the bearing changes due to fatigue failure or overload due to an accident during use, there is a relatively long period of time before the bearing changes to an abnormal condition. The lubrication path may be blocked by foreign matter, the amount of lubricating oil may be extremely reduced, and the bearing may seize.

Accordingly, the present disclosure has been made in view of such problems, and an object of the present disclosure is to provide a spindle diagnosis method and a spindle diagnosis apparatus for a machine tool that can constantly diagnose the cause of an abnormality related to a bearing of a spindle without overlooking it. and

In order to achieve the above object, a first configuration of the present disclosure rotates a tool or work attached to a spindle, processes the work while driving a moving body with a feed shaft, and detects vibration of the spindle. A method for diagnosing the cause of an abnormality related to a bearing of a main shaft in a machine tool equipped with vibration detection means for
a vibration determination step of determining whether or not the vibration of the main shaft detected by the vibration detection means is caused by the bearing when the vibration exceeds a predetermined normal range;
and a cause diagnosis step of diagnosing the cause of the occurrence according to the presence or absence of a state change related to the bearing when the vibration of the main shaft is caused by the bearing.
In another aspect of the first configuration, in the above configuration, in the occurrence cause diagnosis step, it is determined whether or not there is a history of occurrence of an overload of the main shaft as the state change,
It is characterized in that, when there is a history of occurrence of the overload, it is diagnosed that the cause of the occurrence is the overload of the spindle.
In another aspect of the first configuration, in the above configuration, in the occurrence cause diagnosis step, it is determined whether or not there has been a decrease in speed during constant rotation of the main shaft as the state change,
If there is a history of speed reduction during the constant rotation, it is diagnosed that the cause of the occurrence is a poor supply of lubricating oil.
In order to achieve the above object, a second configuration of the present disclosure is a machine tool that rotates a tool or work attached to a spindle and processes the work while driving a moving body with a feed shaft, wherein a bearing for the spindle is provided. A device for diagnosing the cause of an abnormality related to
vibration detection means for detecting vibration of the main shaft;
vibration determining means for determining, when the vibration of the main shaft detected by the vibration detecting means exceeds a predetermined normal range, whether or not the vibration is caused by the bearing;
and cause diagnosis means for diagnosing the cause of the occurrence according to the presence or absence of a state change related to the bearing when the vibration of the main shaft is caused by the bearing.
In another aspect of the second configuration, in the configuration described above, the occurrence cause diagnosis means determines whether or not there is a history of occurrence of an overload of the main shaft as the state change,
It is characterized in that, when there is a history of occurrence of the overload, it is diagnosed that the cause of the occurrence is the overload of the spindle.
In another aspect of the second configuration, in the configuration described above, the occurrence cause diagnosis means determines whether or not there is a decrease in speed during constant rotation of the main shaft as the state change,
If there is a history of speed reduction during the constant rotation, it is diagnosed that the cause of the occurrence is a poor supply of lubricating oil.

According to the present disclosure, the cause of occurrence of an abnormality in the bearing is diagnosed when the state of the bearing of the spindle changes. Therefore, it is possible to constantly diagnose the cause of occurrence of an abnormality related to the bearing without overlooking it, and to appropriately respond to the abnormality of the bearing.

1 is a block configuration diagram showing an example of a machine tool including a spindle diagnostic device; FIG. 4 is a flowchart of a spindle diagnosis method;

Embodiments of the present disclosure will be described below with reference to the drawings.
FIG. 1 is a block configuration diagram showing an example of a machine tool including a spindle diagnostic device. A spindle housing 1 of a machine tool comprises a spindle 2 rotatable by a spindle motor. A tool 3 is attached to the tip of the main shaft 2 and is movable in the Z-axis direction by a feed shaft including a servomotor and a ball screw (not shown). A work 5 is fixed on a table 4, which is an example of a moving body. The table 4 is movable on the bed 6 in X-axis and Y-axis directions which are orthogonal to each other by feed shafts (not shown). The workpiece 5 is machined by relatively moving the tool 3 and the workpiece 5 . Further, the spindle 2 is provided with a vibration sensor 7 (an example of vibration detection means) for measuring vibration.

The NC unit 10 of the machine tool includes a program interpreting section 11, a machine operation commanding section 12, a machine operation monitoring section 13, and a monitor . The program interpreting unit 11 interprets a program input by an operator through input means (not shown) into a spindle rotation command and a feed axis operation command. The machine operation command unit 12 controls the spindle motor and each feed axis based on commands sent from the program interpretation unit 11 .
The machine motion monitoring unit 13 receives the detected value of the vibration sensor 7, and information related to control such as motion commands and loads for each feed axis such as the spindle 2, X-axis, Y-axis, and Z-axis generated by the machine motion command unit 12. Integrate and diagnose. When it is determined that there is an abnormality in the machine tool, the contents of the detected abnormality are notified to the monitor 14, or the like. The machine operation monitoring unit 13 constantly performs a process of monitoring vibration of the spindle 2 and a process of monitoring the operation of the spindle 2 . The NC device 10 is an example of the spindle diagnosis device of the present disclosure, and the machine operation monitoring unit 13 is an example of the vibration determination means and cause diagnosis means of the present disclosure.

Next, a method for diagnosing the spindle 2 by the machine operation monitoring unit 13, which is an example of the second configuration of the present disclosure, will be described based on the flowchart of FIG.
First, it is determined whether or not the vibration detected by the vibration sensor 7 is greater than the normal range (S11). Here, if the vibration is larger than the normal range, it is determined whether or not the cause is the vibration caused by the bearing (rolling bearing) of the main shaft 2 (S12). On the other hand, if the vibration is smaller than the normal range, or if the vibration is not caused by the bearing, the process returns to S11. S11 and S12 are vibration determination steps of the present disclosure.
If the vibration is greater than the normal range and the cause is the vibration caused by the bearing, it is determined whether there is a history of spindle overload (S13) and whether there is a history of spindle speed reduction (S14). and If it is determined in S13 that there is a history of occurrence of spindle overload, it is determined in S15 that the bearing is defective due to overload. If it is determined in S13 that there is no history of spindle overload occurrence, but it is determined in S14 that there is a history of slowing down the spindle speed, it is determined in S16 that the bearing is defective due to poor supply of lubricating oil. On the other hand, if the history of the spindle speed reduction is not confirmed in the judgment of S14, it is judged in S17 that the bearing has an unknown cause. Each determination result is displayed on the monitor 14 . S13 to S17 are the cause diagnosis steps of the present disclosure.

The details of the method of monitoring the main shaft vibration in S11 will be described. The monitoring of the spindle vibration is performed by interpreting the information of the machine operation command unit 12 and using the detection value of the vibration sensor 7 when the operation is considered to be the same as the operation used to set the normal state. The same operation means, for example, performing diagnostic operations such as idle operation of the spindle 2 at a predetermined rotational speed on the same machine multiple times, or using multiple machines with the same specifications to obtain information on the normal state. When this is done, the spindle 2 rotates at the same rotation speed as the diagnostic operation after acquiring information on the normal state, and it is determined that machining is not being performed. Further, as described above, whether or not the feature amount extracted from the detection value of the vibration sensor 7 as the normal state is greater than the threshold value is used as a judgment as to whether the vibration is greater than the normal range. In setting the threshold value, an abnormality is often judged as a value with a margin for the obtained normal state. Set the margin to be as small as possible. In addition, the feature amount extracted from the detection value of the vibration sensor 7 may be the amplitude value or RMS value (rms value) in the time domain waveform of the measured vibration. , the state is determined by paying attention to the vibration component caused by the bearing.

A method of calculating the vibration component caused by the bearing in S12 will be described. Fourier transform the vibration data to obtain the frequency analysis result. It is known that the frequency of vibration that occurs during bearing operation can be calculated using a geometric formula. A judgment is made. Therefore, by comparing the frequency component of the vibration determined to be larger than the normal range in S11 with the frequency component of the damaged portion of the bearing, it is possible to determine whether or not the vibration is caused by the bearing.
Equations (1) to (3) below show calculation equations for the vibration frequency generated when the bearing is damaged.

Next, the details of the spindle load monitoring process will be described. The occurrence of spindle overload is determined by monitoring the spindle load and determining that the spindle overload has occurred when the spindle 2 load reaches the upper limit of the motor's maximum torque while the spindle is in operation, excluding when spindle 2 is accelerating or decelerating. do. When it is determined that the spindle overload has occurred, the history of occurrence is stored in a recording device (not shown) of the NC unit 10 and confirmed in S13.
A decrease in the spindle speed is determined by monitoring the spindle speed, and when the rotation speed of the spindle 2 falls below a predetermined amount while the spindle is operating at a constant speed, excluding when the spindle 2 is accelerating or decelerating. to decide. When it is determined that the spindle speed has decreased, the occurrence history is stored in a recording device (not shown) of the NC unit 10 and confirmed in S14.

As described above, the NC device 10 of the above-described embodiment is used as a method of diagnosing the main shaft 2 when the vibration of the main shaft 2 detected by the vibration sensor 7 exceeds a predetermined normal range. and a vibration determination step (S11, S12) for determining whether the vibration of the spindle 2 is caused by the bearing, and the cause of occurrence is diagnosed according to the presence or absence of a state change related to the bearing. Diagnosis steps (S13 to S17) are executed.
According to this configuration, since the cause of bearing abnormality is diagnosed when the state of the bearing of the main shaft 2 changes, the cause of bearing abnormality can always be diagnosed without overlooking it. Therefore, it is possible to take appropriate measures against the abnormality of the bearing.

In the above embodiment, if the spindle overload occurrence history is recorded once, the overload is assumed to be the cause, and if the spindle speed decrease history is recorded once, the lubricating failure is assumed to be the cause. has reached a preset number of times, the cause of the occurrence may be identified.
Further, according to the present disclosure, even in a machine tool having a spindle that grips and rotates a workpiece, it is possible to diagnose the cause of an abnormality related to the bearing of the spindle.
In the above embodiment, the NC device is used as the spindle diagnosis device, but a spindle diagnosis device having a machine operation monitoring unit may be installed separately from the NC device. In this case, a single spindle diagnosis device may be used to diagnose the cause of the abnormality related to the bearing of the spindle in a plurality of machine tools.

1 Spindle housing 2 Spindle 3 Tool 4 Table 5 Work 6 Bed 7 Vibration sensor 10 NC unit 11 Program interpreter 12... Machine operation command part, 13... Machine operation monitoring part.

Claims (6)

A machine tool that rotates a tool or a work attached to a spindle, processes the work while driving a moving body with a feed shaft, and is provided with vibration detection means for detecting vibration of the spindle, wherein: A method for diagnosing the cause of an abnormality, comprising:
a vibration determination step of determining whether or not the vibration of the main shaft detected by the vibration detection means is caused by the bearing when the vibration exceeds a predetermined normal range;
a cause diagnosing step of diagnosing the cause of occurrence according to the presence or absence of a state change related to the bearing when the vibration of the main shaft is caused by the bearing;
A spindle diagnosis method for a machine tool, characterized by: In the occurrence cause diagnosing step, it is determined whether or not there is a history of occurrence of an overload of the spindle as the state change,
2. The method of diagnosing a spindle for a machine tool according to claim 1, wherein, if there is a history of occurrence of said overload, it is diagnosed that said cause of occurrence is an overload of said spindle. In the occurrence cause diagnosing step, it is determined whether or not there has been a decrease in speed during constant rotation of the main shaft as the state change,
3. The method of diagnosing a spindle for a machine tool according to claim 1, wherein, if there is a history of speed reduction during said constant rotation, it is diagnosed that said cause is a poor supply of lubricating oil. A device for diagnosing the cause of an abnormality related to a bearing of a spindle in a machine tool that rotates a tool or workpiece attached to a spindle and processes the workpiece while driving a moving body with a feed shaft,
vibration detection means for detecting vibration of the main shaft;
vibration determining means for determining, when the vibration of the main shaft detected by the vibration detecting means exceeds a predetermined normal range, whether or not the vibration is caused by the bearing;
cause diagnosis means for diagnosing the cause of occurrence according to the presence or absence of a state change related to the bearing when the vibration of the main shaft is caused by the bearing;
A machine tool spindle diagnosis device comprising: The occurrence cause diagnosing means determines whether or not there is a history of occurrence of an overload of the spindle as the state change,
5. A spindle diagnosis apparatus for a machine tool according to claim 4, wherein when there is a history of occurrence of said overload, it is diagnosed that said cause of occurrence is an overload of said spindle. The occurrence cause diagnosing means determines whether or not there has been a decrease in speed during constant rotation of the main shaft as the state change,
6. A spindle diagnosis apparatus for a machine tool according to claim 4, wherein if there is a history of speed reduction during said constant rotation, it is diagnosed that said cause is a poor supply of lubricating oil.

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