Analysis system of current flowing through motor and tool breakage detection system using the same, and machine tool

Abstract

To provide an analysis system in which, by the size of variation (amplitude) of current flowing through a motor, ranges of a stop state and an acceleration / deceleration state of the motor can be removed, thereby improving analysis accuracy, and to provide a detection system capable of predicting breakage of a tool using the analysis system, and a machine tool.SOLUTION: An analysis system of current flowing through a motor comprises: a current sensor that detects current flowing through the motor; variation detection means that detects a variation width of the current detected by the current sensor; and threshold setting means provided in the variation detection means. An analysis range of the current is set by using the threshold.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an analysis system for analyzing the state of a motor being driven by using the current flowing through the motor. The present invention also relates to a system and machine tool incorporating this system for detecting tool damage. Tool damage also includes signs of damage. [Background technology]

[0002] For example, in the field of machine tools, motors are used to rotate and drive various tools to machine workpieces. In addition, in the field of lathes, motors are used to grip a workpiece and control its rotation. The rotation of these motors is controlled by an NC program built into the NC control device, and fluctuations in the current flowing through the motor are obtained using a current sensor or other device to analyze whether machining is being performed normally. In this case, the current flowing through the motor fluctuates not only due to the load when machining the workpiece, but also when the rotation of the motor is accelerated or decelerated. Therefore, if one were to analyze whether or not the workpiece is being machined normally based solely on fluctuations in the current flowing through the motor, there is a risk of making an erroneous judgment.

[0003] Therefore, for example, Patent Document 1 proposes a system that has a motor and a drive circuit for rotating and moving a tool that processes a workpiece and the workpiece relative to each other, determines whether the NC program command is for speed control or position control, and if it is for position control, calculates acceleration information by performing double differentiation, determines whether the motor is accelerating or decelerating, and excludes that part. However, the method disclosed in the publication is based on the premise that the rotations of a first motor that controls the rotation of a tool and a second motor that controls the relative position of the tool and the workpiece are synchronized and controlled, and therefore the range of applicability is limited. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7035875 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide an analysis system that can eliminate the range of motor stopped states and acceleration / deceleration states by measuring the magnitude (amplitude) of fluctuations in the current flowing through the motor, thereby improving analysis accuracy, and a detection system and machine tool that utilizes the same and can predict tool damage. [Means for solving the problem]

[0006] The analysis system for the current flowing through a motor according to the present invention comprises a current sensor that detects the current flowing through the motor, a fluctuation detection means that detects the fluctuation range of the current detected by the current sensor, and a threshold setting means provided in the fluctuation detection means, and is characterized in that the analysis range of the current is set using the threshold.

[0007] Here, a known sensor can be used as the current sensor, and for example, the sensor can detect fluctuations in the current flowing through the motor as fluctuations in the current waveform, and detect the width of the fluctuations as fluctuations in the amplitude. This will result in a chart such as that shown in Figure 1.

[0008] In the chart shown in FIG. 1, the horizontal axis represents the elapsed time t, and the vertical axis represents the change in current as an amplitude of ±f relative to the center line f0. It should be noted that the present invention is not limited to the above-mentioned change in amplitude, as long as it can detect a change in the fluctuation width of the current. In the chart in Figure 1, the motor is stopped. <m0>For amplitude f0=0, the motor rotation speed is accelerating. <m1>, the rotation speed is steady <m2>,The rotation speed is decelerating <m3>and the subsequent suspension <m0>The range where In this case, various noise filters may be combined to suppress the influence of noise when detecting changes in the fluctuation range of the current. Examples of noise filters include a mean filter and a median filter.

[0009] Here, the motor to be analyzed may be a motor for driving a workpiece or tool of a machine tool.

[0010] In the present invention, by excluding the acceleration range and the stop range before that, and the deceleration range and the stop range after that from the analysis range during idle operation when the workpiece is not being machined, one idle operation is performed in accordance with the NC program and the range to be removed at that time is determined, and during the subsequent workpiece machining process, only the period during which the motor is rotating at a generally steady state is monitored, making it possible to detect abnormalities in the rotation of the workpiece or the rotation of the tool. This reduces losses and tool wear caused by test machining of the workpiece. Furthermore, since the accuracy of the analysis range of the current flowing through the motor is improved, when the change in current within this analysis range is applied to detect signs of possible damage to a tool or the actual damage, the accuracy of detecting such signs or damage is improved. [Effects of the Invention]

[0011] In the analysis system according to the present invention, when a workpiece is machined using an NC program, the NC program is called up in advance, and the detection range of the data flowing through the motor can be grasped by a single idle run after a machining start command is issued. Therefore, in the subsequent machining process of the workpiece, changes in the motor current can be detected based only on data in the steady state of rotation of the tool, etc., or the range in which the rotation speed gradually changes, improving the accuracy of abnormality determination of the tool, etc. When such an analysis system is incorporated into a machine tool, there is a risk that the machining start signal generated by the NC program will have a time lag each time. However, with the present invention, the analysis range can be narrowed down based on the actual current waveform at the start of machining by the immediately preceding NC program, thereby improving the accuracy of the analysis. [Brief explanation of the drawings]

[0012] [Figure 1] 1 shows an example of a chart showing fluctuations in current flowing through a motor. [Figure 2] 1 shows a flow diagram of an analysis system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] An example of a system for analyzing a current flowing through a motor according to the present invention will be described below with reference to the drawings. The analysis system of the present invention includes a current sensor that detects the current flowing through the motor, a fluctuation detection means that detects fluctuations in the amplitude of the current waveform acquired based on the current sensor, and a means for setting a threshold value for the fluctuation range.

[0014] FIG. 2 shows an example of a flow diagram of workpiece machining by a machine tool using the analysis system according to the present invention. The operator calls up an NC program that will process the target workpiece (step S1). Next, or when the NC program is called, a threshold value f1 of the fluctuation range of the current for detecting the acceleration range and deceleration range of the rotation of the motor is set (step S2).

[0015] Next, an idle run is performed using an NC program without using a workpiece (step S3). This will result in a chart of amplitude (f) vs. time (t), where f is the fluctuation range of the current change, as shown in Figure 1. When the amplitude of the motor is stopped, f0=0, and the fluctuation range is measured, the motor is stopped. <m0>Acceleration of motor rotation from <m1>A large amplitude occurs at <m2>When this happens, the amplitude decreases and the motor rotation slows down. <m3>It can be seen that the amplitude increases again when In this embodiment, the threshold value f1 is set to a value that is approximately 1 / 3 of the amplitude in the accelerating state. In addition, various noise filters may be combined to suppress the effects of noise. This allows the range where the amplitude exceeds the threshold value f1 to be removed as the acceleration / deceleration range (t1, t3), and the part before acceleration begins from the machining start command to be the motor stopped state, and the part after the motor rotation has slowed down to be the motor stopped part, and these ranges can be removed in advance from the monitoring range (step S5). Thereafter, actual machining of the workpiece is repeatedly performed while monitoring fluctuations in the current flowing through the motor in a range t2 where the rotation of the motor is generally in a steady state (step S6). In machine tools, NC machining programs are switched each time depending on the machining specifications, but the trigger signals that start machining in NC programs vary. Therefore, by using the analysis system according to the present invention, it is possible to narrow down the analysis range based on the current waveform of the NC program that is actually used. If an abnormality occurs in the tool or the like, it can be detected with high accuracy based on the magnitude of this current fluctuation. For example, if a change occurs in the cutting edge of the tool, the load during actual machining of the workpiece increases, and the current value fluctuates in the increasing direction. Furthermore, even if the tool wears, the machining load increases, and this change can be detected.

Claims

1. An analysis system for a current flowing through a motor, comprising: a current sensor for detecting a current flowing through the motor; a fluctuation detection means for detecting a fluctuation range of the current detected by the current sensor; a threshold setting means provided in the fluctuation detection means, A system for analyzing a current flowing through a motor, wherein the threshold value is used to set an analysis range of the current.

2. 2. The system for analyzing a current flowing through a motor according to claim 1, wherein the threshold value is used to exclude an acceleration range and a deceleration range of the motor from an analysis range.

3. 3. The system for analyzing a current flowing through a motor according to claim 2, wherein the motor is a motor for driving a workpiece or a tool of a machine tool.

4. 4. The system for analyzing the current flowing through a motor according to claim 3, wherein the acceleration range and the stop range before that, and the deceleration range and the stop range after that are excluded from the analysis range when the motor is running idle and not machining a workpiece.

5. Using the analysis system for the current flowing through the motor according to any one of claims 1 to 4, A tool breakage detection system that detects the risk of tool breakage or breakage based on changes in the current flowing through a motor within an analysis range.

6. A machine tool comprising an analysis system for current flowing through a motor according to any one of claims 1 to 4.

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