Threshold value calculation device and computer-readable storage medium

Abstract

This threshold value calculation device acquires a value of a load applied to an axis of a machine tool, determines whether the value of the load is a value detected in a cutting time zone or a value detected in a non-cutting time zone, calculates an intersection point between a probability density function of the value of the load in the cutting time zone and a probability density function of the value of the load in the non-cutting time zone, and calculates the value of the load of the intersection point, as a threshold value for detecting the breakage of a tool.

Description

Threshold calculation device and computer-readable storage medium

[0001] The present disclosure relates to a threshold calculation device and a computer-readable storage medium.

[0002] [Correction based on Rule 91 01.10.2025] Conventionally, in devices for detecting or predicting breakage of tools used in machine tools, there is a technology that multiplies a feature amount of load during cutting time by a coefficient to calculate a fluctuating threshold value and determine breakage. For example, see Patent Document 1.

[0003] Japanese Patent Application Laid-Open No. 2004-130407

[0004] When a load is used to detect breakage, the accuracy of breakage detection may be poor in machining in which the load fluctuation is small.

[0005] In the field of numerical control devices, there is a demand for improved accuracy in detecting breakage.

[0006] The threshold calculation device includes a data acquisition unit that acquires the value of the load applied to the axis of the machine tool, a determination unit that determines whether the load value acquired by the data acquisition unit is a value detected during a cutting time period or a value detected during a non-cutting time period, and a calculation unit that calculates the intersection between a probability density function of the load value during the cutting time period and a probability density function of the load value during the non-cutting time period, and calculates the load value at the intersection as a threshold for detecting tool breakage.

[0007] 1 is a block diagram of a threshold calculation device. FIG. 2 is a graph showing a change in a command during cutting. FIG. 3 is a graph showing load values. FIG. 4 is a graph showing a probability density distribution of load during cutting time periods and non-cutting time periods. FIG. 5 is a graph showing the relationship between the load value before breakage and the threshold value. FIG. 6 is a graph showing the relationship between the load value after breakage and the threshold value. FIG. 7 is a flowchart explaining the flow of calculating a threshold value. FIG. 8 is a flowchart explaining the procedure for detecting breakage. FIG. 9 is a graph showing an example of a load with a small difference between before and after breakage. FIG. 10 is a graph showing the relationship between the load and the threshold value when the tool is not broken. FIG. 11 is a graph showing the relationship between the load and the threshold value when the tool is broken. FIG. 12 is a block diagram of a threshold calculation device of a second embodiment. FIG. 13 is a hardware configuration diagram of a threshold calculation device.

[0008] First Embodiment A threshold calculation device 100 according to a first embodiment will be described below. The threshold calculation device 100 is realized by an information processing device such as a numerical control device or a PC (personal computer).

[0009] 1 is a block diagram of a threshold calculation device 100. The threshold calculation device 100 includes a data acquisition unit 10, a determination unit 11, a calculation unit 12, a threshold storage unit 13, and a breakage detection unit 14.

[0010] The data acquisition unit 10 acquires at least one of the loads of the spindle or the feed axis. The determination unit 11 determines whether the load value acquired by the data acquisition unit 10 is a value detected during a cutting time period or a value detected during a non-cutting time period. A cutting time period is a time period during which the tool is cutting the workpiece. A non-cutting time period is a time period during which the tool is not cutting the workpiece. One method of determination is to detect a signal. For example, during a cutting time period, a "cutting in progress" command signal is output from the numerical control device. Figure 2 shows an example of a "cutting in progress" command signal. The upper graph in Figure 2 shows the load value, and the lower graph in Figure 2 shows the "cutting in progress" command signal. When the numerical control device analyzes a machining program or the like and executes a cutting command such as G01, the "cutting in progress" command signal turns "ON." This signal can be used to determine whether the time period is a cutting time period or a non-cutting time period.

[0011] The calculation unit 12 calculates a threshold value for determining breakage. The method for calculating the threshold value will be described with reference to the drawings. FIG. 3 is a graph showing load values. The straight line drawn on the graph represents the average load value during the cutting time period. The load during the cutting time period is higher than the load during the non-cutting time period.

[0012] The calculation unit 12 calculates the probability density distribution of the load during the cutting time period and the probability density distribution of the load during the non-cutting time period. In Fig. 4, the solid line is the probability density function during the non-cutting time period, and the dotted line is the probability density function during the cutting time period.

[0013] The calculation unit 12 determines the intersection of the probability density functions. The calculation unit 12 regards the load value at the intersection as a threshold value T. The threshold value storage unit 13 stores the calculated threshold value T.

[0014] The breakage detection unit 14 acquires the load of the spindle or feed axis from the data acquisition unit 10 and detects breakage of the tool. The graph in FIG. 5 shows the load value before breakage. The breakage detection unit 14 calculates the feature value of the load value during the cutting time period and compares it with a threshold value T. In this example, the feature value of the load data during cutting is the average value of the load. The breakage detection unit 14 compares the average value of the load with the threshold value T.

[0015] The graph in Figure 6 shows the load value after breakage. When the tool breaks, the load value during the cutting time period decreases. Therefore, the average load value during the cutting time period also decreases. In Figure 6, the average load value is smaller than the threshold value. The breakage detection unit 14 detects tool breakage when the average load value during the cutting time period falls below the threshold value T.

[0016] 7 is a flowchart illustrating the flow of the threshold value calculation device 100 calculating the threshold value. The threshold value is calculated, for example, when test machining is performed before starting continuous operation. The data acquisition unit 10 acquires at least one of the loads of the main spindle and the feed axis (step S1). The determination unit 11 determines whether the load value acquired in step S1 is cutting time period data or non-cutting time period data (step S2). One method of determination is to make the determination from a command signal.

[0017] The calculation unit 12 calculates the probability density function of the load value during the cutting time period and the probability density function of the load value during the non-cutting time period (step S3). The calculation unit 12 calculates the intersection between the probability density function of the load value during the cutting time period and the probability density function of the load value during the non-cutting time period (step S4). The calculation unit 12 regards the load value at the calculated intersection as the threshold value T (step S5). The threshold value storage unit 13 stores the calculated threshold value T (step S6). At this point, the calculation of the threshold value ends.

[0018] 8 is a flowchart illustrating the procedure for the threshold calculation device 100 to detect breakage. The breakage detection unit 14 reads out a threshold value from the threshold storage unit 13 (step S11). The machine tool starts machining (step S12). The breakage detection unit 14 acquires a load value from the data acquisition unit 10 (step S13). The determination unit 11 determines whether the load value acquired in step S13 is data for a cutting time period or data for a non-cutting time period (step S14). The breakage detection unit 14 calculates an average value of the load values ​​for the cutting time period. It is not necessary to calculate an average value of the load values ​​for the non-cutting time period.

[0019] The breakage detection unit 14 compares the average value of the load during the cutting time period with the threshold value T (step S15). If the average value of the load during the cutting time period is greater than the threshold value T (step S16; No), the breakage detection unit 14 proceeds to step S15 and continues comparing the average value with the threshold value T. If the average value of the load during the cutting time period is smaller than the threshold value T (step S16; Yes), the breakage detection unit 14 detects breakage of the tool (step S17).

[0020] As described above, the threshold calculation device 100 of this embodiment determines cutting time periods and non-cutting time periods, finds the intersection between the probability density function of the load during the cutting time periods and the probability density function of the load during the non-cutting time periods, and calculates the load value at the intersection as the threshold value.

[0021] Conventionally, there is a method for calculating a threshold value using a load feature (such as an average value) and a predetermined coefficient. This method can result in poor breakage detection accuracy in machining where the difference in load between before and after breakage is small. For example, in Figure 9, the dotted line represents the load value before breakage, and the solid line represents the load value after breakage. In Figure 9, the difference in load between before and after breakage is small. Problems that can arise when the difference in load between before and after breakage is small will be described. Figure 10 shows the relationship between the load and the threshold value when the tool is not broken (normal). Since the load is high when the tool is not broken, the load value is higher than the threshold value. Figure 11 shows the relationship between the load and the threshold value when the tool is broken. When the tool breaks, the load decreases, but if the change in load between before and after breakage is small, it does not fall below the threshold value, and breakage cannot be detected. Thus, when the difference in load between before and after breakage is small, breakage may not be detected.

[0022] [Correction based on Rule 91 01.10.2025] The threshold calculation device 100 of this embodiment calculates the threshold using a probability density function. This improves the accuracy of the threshold even in machining where the difference in load before and after breakage is small. Furthermore, by calculating the threshold using a probability density function, the threshold is less susceptible to the machining state, improving the accuracy of the threshold.

[0023] Second Embodiment Next, a threshold calculation device 100 according to a second embodiment will be described. Only the configurations that differ from the threshold calculation device 100 according to the first embodiment will be described below. As shown in FIG. 12 , the threshold calculation device 100 according to the second embodiment includes a status acquisition unit 15 that acquires status information of the numerical control device. The threshold storage unit 13 according to the second embodiment stores thresholds and status information of the numerical control device in association with each other. The status information includes cutting conditions and identification information of the machining program. The cutting conditions include the depth of cut and the type of tool. The load varies depending on the machining method. In the threshold calculation device 100 according to the second embodiment, status information that affects the load value is stored in the threshold storage unit 13 in association with a threshold value.

[0024] The breakage detection unit 14 of the second embodiment acquires status information from the numerical control device. The breakage detection unit 14 reads a threshold value that matches the status information from the threshold value storage unit 13. Once the threshold value is read, the breakage detection unit 14 of the second embodiment operates in substantially the same manner as the breakage detection unit 14 of the first embodiment. That is, the breakage detection unit 14 acquires the load of the spindle or feed axis and calculates a feature value of the load value during the cutting time period (it may also calculate a feature value of the load value during both the cutting time period and the non-cutting time period). The breakage detection unit 14 compares the feature value of the load value with the threshold value T to detect breakage.

[0025] The threshold calculation device 100 of the second embodiment improves the accuracy of the threshold by storing a threshold value and state information that affects the threshold value in association with each other.

[0026] The hardware configuration of a threshold calculation device 100 to which the present disclosure is applied will be described below. Fig. 13 is a hardware configuration diagram of the threshold calculation device 100. As shown in Fig. 13, the threshold calculation device 100 includes a CPU 111 that controls the entire threshold calculation device 100, a ROM 112 that records programs and data, and a RAM 113 for temporarily expanding data. The CPU 111 reads out a system program recorded in the ROM 112 via a bus and calculates a threshold value in accordance with the system program.

[0027] [Correction based on Rule 91 01.10.2025] The nonvolatile memory 114 retains its stored state even when the power to the threshold calculation device 100 is turned off, for example, by being backed up by a battery (not shown). The nonvolatile memory 114 stores various data, such as programs read from the external device 120 via the interfaces 115, 118, and 119 and operation inputs entered via the input unit 30. The nonvolatile memory 114 may also store programs and data for executing the threshold calculation device 100 of this embodiment. In addition, the display unit 70 displays a parent-child relationship setting screen and the like.

[0028] The interface 115 is an interface for connecting the threshold calculation device 100 to an external device 120 such as an adapter. Programs, various parameters, etc. are loaded from the external device 120. The interface 118 is an interface for connecting the threshold calculation device 100 to a display unit 70 such as a liquid crystal display. The display unit 70 displays various data loaded into memory, data obtained as a result of executing programs, etc. The interface 119 is an interface for connecting the threshold calculation device 100 to an input unit 30 such as a keyboard or pointing device. The input unit 30 passes commands, data, etc. based on operations by an operator to the CPU 111 via the interface 119.

[0029] Although the present disclosure has been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the present disclosure or the gist of the present disclosure derived from the claims and their equivalents. Furthermore, these embodiments can also be implemented in combination. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these.

[0030] [Correction based on Rule 91 01.10.2025] The following supplementary notes are further disclosed regarding the above embodiment and modified examples. (Supplementary Note 1) A threshold calculation device (100) includes a data acquisition unit (10) that acquires a load value applied to a machine tool shaft, a determination unit (11) that determines whether the load value acquired by the data acquisition unit is a value detected during a cutting time period or a non-cutting time period, and a calculation unit (12) that calculates an intersection between a probability density function of the load value during the cutting time period and a probability density function of the load value during the non-cutting time period, and calculates the load value at the intersection as a threshold value for detecting tool breakage. (Supplementary Note 2) The determination unit (11) determines whether the time period is a cutting time period or a non-cutting time period based on a command signal for controlling the machine tool. (Supplementary Note 3) The threshold calculation device (100) includes a status acquisition unit (15) that acquires status information of a numerical control device, and a threshold storage unit that stores a threshold value and the status information of the numerical control device in association with each other. (Supplementary Note 4) The system includes a breakage detection unit (14) that calculates a feature amount of the load value acquired from the data acquisition unit (10), compares the feature amount with the threshold value, and detects tool breakage. (Supplementary Note 5) The feature amount is an average value of the load values. (Supplementary Note 6) The computer-readable storage medium (112, 113, 114) stores instructions that cause one or more processors (111) to execute processing to acquire a load value applied to a shaft of a machine tool, determine whether the load value is a value detected during a cutting time period or a value detected during a non-cutting time period, calculate an intersection point between a probability density function of the load value during the cutting time period and a probability density function of the load value during the non-cutting time period, and calculate the load value at the intersection point as a threshold value for detecting tool breakage.

[0031] REFERENCE SIGNS LIST 100 Threshold value calculation device 10 Data acquisition unit 11 Determination unit 12 Calculation unit 13 Threshold value storage unit 14 Breakage detection unit 15 Status acquisition unit 111 CPU 112 ROM 113 RAM 114 Non-volatile memory

Claims

1. A threshold calculation device comprising: a data acquisition unit that acquires load values ​​applied to a shaft of a machine tool; a determination unit that determines whether the load value acquired by the data acquisition unit is a value detected during a cutting time period or a value detected during a non-cutting time period; and a calculation unit that calculates the intersection between a probability density function of the load value during the cutting time period and a probability density function of the load value during the non-cutting time period, and calculates the load value at the intersection as a threshold for detecting tool breakage.

2. [Correction based on Rule 91 01.10.2025] A threshold calculation device as claimed in claim 1, wherein the determination unit determines whether it is a cutting time period or a non-cutting time period based on a command signal for controlling the machine tool.

3. A threshold calculation device according to claim 1, comprising: a status acquisition unit that acquires status information of a numerical control device; and a threshold storage unit that stores the threshold value and the status information of the numerical control device in association with each other.

4. The threshold calculation device according to claim 1, further comprising a breakage detection unit that calculates a feature amount of the load value acquired from the data acquisition unit, compares the feature amount with the threshold value, and detects breakage of the tool.

5. The threshold calculation device according to claim 4, wherein the characteristic amount is an average value of the load values.

6. A computer-readable storage medium storing instructions to cause one or more processors to execute the following process: acquire a load value applied to an axis of a machine tool; determine whether the load value is a value detected during a cutting time period or a non-cutting time period; calculate the intersection point between the probability density function of the load value during the cutting time period and the probability density function of the load value during the non-cutting time period; and calculate the load value at the intersection point as a threshold value for detecting tool breakage.

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