Abnormality detection system for machine tool

Abstract

To provide an abnormality detection system for a machine tool that is robust and highly resistant to change in the operating state of the machine tool.SOLUTION: The abnormality detection system for a machine tool includes: a sensor for detecting an abnormality signal; initial threshold setting means for determining an abnormality based on the sensor information; and threshold updating means for updating an initial threshold based on change in the sensor information.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a system for detecting abnormalities in a tool or the machining state of a workpiece when a machine tool continuously machines the workpiece. [Background technology]

[0002] In the field of machine tools, workpieces are continuously machined using various tools. In this case, in order to prevent defective machining of the workpiece, if an abnormality occurs in the spindle that controls and holds the rotation of the workpiece, the tool spindle that controls the rotation of the tool, or the tool, etc., the abnormality is detected and an alarm is issued or machining is stopped.

[0003] For example, Patent Document 1 discloses a cutting system in which an acceleration sensor and a strain sensor are attached to the shaft portion of a milling tool, and the state of the milling tool is determined based on information from these sensors. In this case, a predetermined threshold is set for determining the state of the milling tool. However, when machine tools are operated continuously, the machining temperatures of the machine tools and workpieces change due to heat generated by the workpiece's processing and the various drive parts, and changes in machining conditions due to NC programs can reduce the accuracy of abnormality detection using the thresholds initially set. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7260077 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide an abnormality detection system for a machine tool that is robust and resistant to changes in the operating state of the machine tool. [Means for solving the problem]

[0006] The machine tool abnormality detection system according to the present invention is characterized by having a sensor for detecting an abnormal signal, an initial threshold setting means for determining an abnormality based on the sensor information, and a threshold update means for updating the initial threshold based on changes in the sensor information.

[0007] Here, the initial threshold value is used to determine whether or not there is an abnormality as the machine tool operates. However, since the sensor information tends to become unstable in the early stages of machine tool operation, it is preferable to detect changes in the sensor information by differential analysis, and use the threshold value for determining whether or not the information is good once the state has stabilized. Therefore, in the present invention, it is preferable to update the threshold value based on the most recent data when determining whether the sensor information is good or bad based on changes in the sensor information. For example, the initial threshold setting means may be based on initial processing data, and the threshold updating means for updating the threshold may be based on the latest processing data after the initial processing data is obtained. In the field of machine tools, temperature and other factors are prone to change over time during machining due to heat generated by drive motors and the like and heat generated during processing of workpieces. Therefore, the threshold value can be updated based on changes in sensor information, and can also be updated based on changes over time.

[0008] In the present invention, the sensor information may be any one of a driving current value, an acceleration change, a vibration change, a sound change, and a temperature change, but is not limited to these. [Effects of the Invention]

[0009] The present invention sets predetermined thresholds based on various sensors attached to the machine tool, and detects abnormalities in the operating status of the machine tool based on the most recent sensor information to determine whether or not there is an abnormality, thereby improving the accuracy of the judgment and making the detection system robust to changes in the operating conditions and environment of the machine tool. [Brief explanation of the drawings]

[0010] [Figure 1] 1 shows a detection chart according to the present invention. [Figure 2] 1 shows a conventional detection chart. DETAILED DESCRIPTION OF THE INVENTION

[0011] First, an example of a conventional anomaly detection system will be described with reference to FIG. In FIG. 2, the horizontal axis indicates a data plot (time series plot) for anomaly detection based on sensor information, and the vertical axis indicates the signal strength of the sensor information. Conventionally, a pass / fail judgment threshold 2a is set based on the signal strength 1a of the initial sensor information (initial data). However, this meant that the sensor information changed over time, and if the initially set threshold value 2a was left unchanged, there would be a large gap between the actual pass / fail judgment threshold value during processing, and there was a high risk of overlooking an abnormality.

[0012] In contrast, the anomaly detection system of the present invention detects initial, unstable changes in sensor information using differential analysis, etc., sets an initial threshold value 2s for determining pass / fail when the changes in sensor information are stable and steady, and further updates it to threshold value 2 based on changes in sensor information 1 and uses it to determine pass / fail.

[0013] In this case, the threshold value may be updated at time intervals, or the threshold value may be updated based on the magnitude of the change by differentially analyzing the displacement of the sensor information. In addition, in accordance with the case where the machining conditions are changed by the NC program, the initial threshold value may be set based on the initial machining data and then updated based on the latest machining data, or threshold value 2 may be updated based on the most recent sensor information, or threshold value 2 may be updated based on the temperature change of the machine tool in combination with other sensor information such as thermal change information of the machine tool. This improves the accuracy of the threshold for detecting an abnormality, making it possible to reduce detection errors. Examples of sensor information used in the present invention include current sensors, acceleration sensors, vibration sensors, sound sensors, strain sensors, etc., of motors used to drive the rotating spindles of machine tools, or vibration sensors and sound sensors attached to the tool rests of machine tools, etc. Furthermore, for example, a temperature sensor may be attached to the tool rest or the like, and the threshold value may be updated in combination with temperature changes.

[0014] For example, if a current sensor is attached to a motor or the like and abnormalities are detected by fluctuations in the current flowing through the motor, the current flowing through the motor will fluctuate greatly depending on the machining program when the motor accelerates or decelerates, so a threshold can be set to detect abnormalities excluding the acceleration / deceleration range.

[0015] In the case of NC-controlled machine tools, various sensor information can be connected to the NC control unit via communication, and a subprogram that monitors macro variables can be incorporated into the main machining program.When an abnormality is detected in the sensor information and the macro variables are rewritten, this subprogram can be called using an M-code for auxiliary functions, and the automatic operation of the machine tool can be stopped or an alarm can be issued. [Explanation of symbols]

[0016] 1. Sensor information 2. Threshold

Claims

1. a sensor for detecting an abnormal signal; an initial threshold setting means for determining an abnormality based on the sensor information; A machine tool anomaly detection system comprising: a threshold value update means for updating the initial threshold value based on a change in the sensor information.

2. the initial threshold value setting means is based on initial processing data; 2. The machine tool abnormality detection system according to claim 1, wherein the threshold updating means updates the threshold based on the latest machining data obtained after the initial machining data is obtained.

3. 2. The machine tool abnormality detection system according to claim 1, wherein the change in the sensor information is due to a change over time.

4. 4. The machine tool abnormality detection system according to claim 1, wherein the sensor information is any one of a drive current value, an acceleration change, a vibration change, a sound change, and a temperature change.

5. A machine tool comprising the machine tool abnormality detection system according to any one of claims 1 to 4.

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