Threshold calculation device and computer-readable storage medium

Abstract

This threshold calculation device receives a value of a load applied to an axis of a machine tool, determines whether the load value is a value acquired during a cutting period or a value acquired during a non-cutting period; calculates an intersection point between a probability density function of the load values ​​during the cutting period and a probability density function of the load values ​​during the non-cutting period, and calculates the load value of the intersection point as a threshold for detecting tool breakage.

Description

[Technical field]

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

[0002] Typically, devices for detecting or predicting breakage of a tool used in a machine tool employed technologies for multiplying a set of characteristics of a load during a cutting time by a coefficient, calculating a variable threshold, and determining a breakage. See, for example, patent specification 1. [Reference list][Patent specification]

[0003] Patent specification 1: Japanese patent application disclosure no.: 2004 - 130 407 [Summary of the invention][Technical problem]

[0004] When a load is used to detect fractures, the fracture detection accuracy may be affected when machining under less variable loads.

[0005] In the field of numerical control devices, an improvement in fracture detection accuracy is desired. [Solution to the problem]

[0006] A threshold calculation device comprises: a data acquisition unit that receives a value of a load applied to a shaft of a machine tool; a determination unit that determines whether the load value obtained by the data acquisition unit is a value acquired during a cutting period or a value acquired during a non-cutting period; and a calculation unit that calculates an intersection point of a probability density function of load values ​​during the cutting period and a probability density function of load values ​​during the non-cutting period, and calculates a load value at the intersection point as a threshold value used to detect tool breakage. [Brief description of the drawings] [ Fig. 1] Fig. Figure 1 is a block diagram of a threshold calculation device. [ Fig. 2] Fig. Figure 2 is a graph illustrating a change in instructions during cutting. [ Fig. 3] Fig. Figure 3 is a graph illustrating values ​​of a load. [ Fig. 4] Fig. Figure 4 is a graph illustrating a probability density function of the load during a cutting period and a non-cutting period. [ Fig. 5] Fig. Figure 5 is a graph illustrating a pre-fraction relationship between the value of the load and a threshold value. [ Fig. 6] Fig. Figure 6 is a graph illustrating a relationship after the fraction between the value of the load and a threshold value. [ Fig. 7] Fig. Figure 7 is a flowchart illustrating the flow of calculating a threshold. [ Fig. 8] Fig. Figure 8 is a flowchart illustrating the process of detecting a fraction. [ Fig. 9] Fig. Figure 9 is a graph illustrating an example of a load that has a small difference between the loads before and after the break. [ Fig. 10] Fig. Figure 10 is a graph illustrating a relationship between the load when a tool is not broken and the threshold. [ Fig. 11] Fig. Figure 11 is a graph illustrating a relationship between the stress when the tool breaks and the threshold. [ Fig. 12] Fig. Figure 12 is a block diagram of a threshold calculation device of a second embodiment. [ Fig. 13] Fig. Figure 13 is a hardware configuration diagram of the threshold calculation device. [Detailed Description][First Design]

[0007] A threshold calculation device 100 of the first embodiment is described below. The threshold calculation device 100 is equipped with an information processing device, such as a numerical control device, a personal computer (PC), or the like.

[0008] Fig. Figure 1 is a block diagram of the threshold calculation device 100. The threshold calculation device 100 has a data acquisition unit 10, a determination unit 11, a calculation unit 12, a threshold storage unit 13 and a fraction detection unit 14.

[0009] The data acquisition unit 10 receives the load on a spindle and / or a pull shaft.

[0010] The determination unit 11 determines whether the load value obtained by the data acquisition unit 10 is a value recorded during a cutting period or a value recorded during a non-cutting period. The cutting period is the time during which a tool is cutting a workpiece. The non-cutting period is the time during which the tool is not cutting a workpiece.

[0011] A signal detection method can be used as a determination method. For example, a signal indicating a "cut in progress" instruction is issued by the numerical control device during the cutting period. Fig. Figure 2 illustrates an example of the signal for the "cut in aisle" instruction. The upper graph in Fig. Figure 2 represents values ​​of a load, and the lower graph in Fig. 2 represents a signal for a "cut in process" instruction. When the numerical control device analyzes a machining program or similar and executes a cutting instruction such as G01, the "cut in process" instruction signal is switched "ON". This signal allows the determination of whether the value is acquired during the cutting period or the non-cutting period.

[0012] The calculation unit 12 calculates a threshold value for breakage detection. A threshold calculation method is described with reference to the drawings. Fig. Figure 3 is a graph illustrating the values ​​of a load. The straight line drawn in the graph represents the average load during the cutting period. Loads during the cutting period are higher than loads during the non-cutting period.

[0013] The calculation unit 12 finds a probability density distribution of the load during the cutting period and a probability density distribution of the load during the non-cutting period. In Fig. 4 The solid line represents a probability density function for the non-intersection period and the dashed line represents a probability density function for the intersection period.

[0014] The calculation unit 12 finds the intersection point of the probability density functions. The calculation unit 12 defines the value of the load at the intersection point as a threshold value T. The threshold storage unit 13 stores the calculated threshold value T.

[0015] The breakage detection unit 14 receives a load signal on the spindle or the draw shaft from the data acquisition unit 10 and detects a breakage of the tool. The graph in Fig. Figure 5 illustrates pre-fracture stress values. The fracture detection unit 14 calculates a set of features representing the stress values ​​for the cutting period and compares this set of features to the threshold value T. In this example, the set of features representing the stress during cutting is a mean stress value. The fracture detection unit 14 compares this mean stress value to the threshold value T.

[0016] The graph in Fig. Figure 6 illustrates the stress values ​​after breakage. When the tool breaks, the stress value during the cutting period decreases. Therefore, the average stress value during the cutting period also decreases. Fig. 6. The mean load is less than the threshold value. The breakage detection unit 14 detects a tool breakage if the mean load during the cutting period falls below the threshold value T.

[0017] Fig. Figure 7 is a flowchart illustrating the process by which the threshold calculation device 100 calculates a threshold value. The threshold calculation is performed, for example, when test machining is carried out before continuous operation or the like is started. The data acquisition unit 10 receives the load on a spindle and / or a drawbar (step S1). The determination unit 11 determines whether the load value obtained in step S1 represents data from a cutting period or data from a non-cutting period (step S2). A determination method based on a signal, instruction, or the like can be used.

[0018] The computation unit 12 calculates a probability density function of the load values ​​during the cutting period and a probability density function of the load values ​​during the non-cutting period (step S3). The computation unit 12 then calculates the intersection point of the probability density function of the load values ​​during the cutting period and the probability density function of the load values ​​during the non-cutting period (step S4). The computation unit 12 defines the load value at the calculated intersection point as the threshold value T (step S5). The threshold storage unit 13 stores the calculated threshold value T (step S6). The threshold calculation ends here.

[0019] Fig. Figure 8 is a flowchart illustrating the process by which the threshold calculation device 100 detects a fracture. The fracture detection unit 14 reads a threshold value from the threshold storage unit 13 (step S11). The machine tool starts machining (step S12). The fracture detection unit 14 receives stress values ​​from the data acquisition unit 10 (step S13). The determination unit 11 determines whether the stress values ​​obtained in step S13 are data from the cutting period or data from the non-cutting period (step S14). The fracture detection unit 14 calculates the mean of the stress values ​​during the cutting period. The mean of the stress values ​​for the non-cutting period may or may not be calculated.

[0020] The fracture detection unit 14 compares the mean load value for the cutting period with the threshold value T (step S15). If the mean load value during the cutting period is greater than the threshold value T (step S16; No), the fracture detection unit 14 begins step S15 and continues comparing the mean value with the threshold value T. If the mean load value for the cutting period is less than the threshold value T (step S16; Yes), the fracture detection unit 14 detects a tool fracture (step S17).

[0021] As described above, the threshold calculation device 100 of the present embodiment identifies the cutting period and the non-cutting period, finds the intersection of the probability density function of the load for the cutting period and the probability density function of the load for the non-cutting period and calculates the value of the load at the intersection as the threshold.

[0022] Typically, a method is used to calculate a threshold value by employing a set of features (such as a mean value) of a load and a predetermined coefficient. With such a method, the fracture detection accuracy during processing can be compromised if the difference between the loads before and after fracture is small. For example, the dashed line in Fig. Figure 9 represents the value of a load before a fracture, and the solid line represents the value of the load after the fracture. Fig. 9. The difference between the loads before and after the fracture is small. A problem that can arise when the difference between the loads before and after the fracture is small is described below. Fig. Figure 10 illustrates the relationship between the load when the tool is not broken (normal) and the threshold value. Since the load is higher when the tool is not broken, the load value is higher than the threshold value. Fig. Figure 11 illustrates the relationship between the stress at the point of tool breakage and the threshold value. The stress is lower when the tool breaks; however, if the change from the pre-breakage stress to the post-breakage stress is small, the stress value will not fall below the threshold, and thus the breakage will not be detected. In this way, if the difference between the pre-breakage and post-breakage stresses is small, the breakage may go undetected.

[0023] In the threshold calculation device 100 of the present embodiment, a probability density function is used to calculate a threshold value. This improves the accuracy of the threshold value, even during machining when the difference between the loads before and after fracture is small. Furthermore, when using a probability density function to calculate a threshold value, the threshold value is less likely to be affected by the machining condition, and the accuracy of the threshold value is improved. [Second embodiment]

[0024] Next, the threshold calculation device 100 of the second embodiment is described. It should be noted that only those designs that differ from those of the threshold calculation device 100 of the first embodiment are described below.

[0025] As in Fig. Figure 12 illustrates that the threshold calculation device 100 of the second embodiment includes a state detection unit 15 that receives state information from the numerical control device. The threshold storage unit 13 of the second embodiment stores the threshold and the state information of the numerical control device in relation to each other. The state information may include cutting conditions, identification information of a machining program, or the like. The cutting conditions may include a cutting depth, a tool type, or the like. The load varies according to the machining operation. In the threshold calculation device 100 of the second embodiment, the state information that influences the load values ​​is stored in the threshold storage unit 13 in relation to the threshold.

[0026] The breakage detection unit 14 of the second embodiment receives the status information from the numerical control device. The breakage detection unit 14 reads a threshold value corresponding to the status information from the threshold storage unit 13. In response to reading the threshold value, the breakage detection unit 14 of the second embodiment operates essentially in the same way as the breakage detection unit 14 of the first embodiment. That is, the breakage detection unit 14 receives a load on the spindle or the drawbar and calculates a feature set of the load value for the cutting period (or can calculate both feature sets of the load value for the cutting period and the non-cutting period). The breakage detection unit 14 compares the feature set of the load value with the threshold value T to detect a break.

[0027] The threshold calculation device 100 of the second embodiment stores a threshold value and state information that influences the threshold value in relation to each other, thereby improving the accuracy of the threshold value.

[0028] The hardware configuration of the threshold calculation device 100 used in the present disclosure is described below. Fig. Figure 13 is a hardware configuration diagram of the threshold calculation device 100. As in Fig. Figure 13 illustrates that the threshold calculation device 100 has a CPU 111, which controls the threshold calculation device 100 as a whole, a ROM 112, which stores programs or data, and a RAM 113, into which data is temporarily loaded, and the CPU 111 reads a system program stored in the ROM 112 via a bus and calculates a threshold according to the system program.

[0029] The non-volatile memory 114, which is buffered, for example, by a battery (not illustrated) or the like, retains its memory state even when the threshold calculation device 100 is switched off. The non-volatile memory 114 stores programs loaded via interfaces 115, 118, 119 from an external device 120, and various data, such as operator input entered via an input unit 30. The non-volatile memory 114 can store a program and data used to implement the threshold calculation device 100 of the present embodiment. Furthermore, windows, such as a settings window for a master-slave relationship, are displayed on a display unit 70.

[0030] Interface 115 is used to connect the threshold calculation device 100 and the external device 120, such as an adapter. Programs, various parameters, or the like are loaded from the external device 120.

[0031] Interface 118 is an interface for connecting the threshold calculation device 100 and the display unit 70, such as a liquid crystal display. Data loaded into a memory, data such as that obtained as a result of executing a program, or the like, are displayed on the display unit 70.

[0032] Interface 119 is used to connect the threshold calculation device 100 and the input unit 30, such as a keyboard, pointing device, or the like. Based on an operator action, the input unit 30 transmits instructions, data, or the like to the CPU 111 via interface 119.

[0033] Although the present disclosure has been described, it is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial omissions, or the like may be made to these embodiments within the scope of protection without deviating from the essence of the present disclosure and without deviating from the spirit of the present disclosure, as derived from the content specified in the claims and their equivalents. Furthermore, these embodiments may be implemented in combination. For example, the sequence of respective actions or the sequence of respective processes in the embodiments described above is illustrated by way of example and is not limited thereto.

[0034] Additional remarks on the embodiments of the present disclosure are set out below. (Supplementary Note 1)

[0035] A threshold calculation device (100) comprises: a data acquisition unit (10) designed to obtain a value of a load applied to a shaft of a machine tool; a calculation unit (11) designed to determine whether the load value obtained by the data acquisition unit is a value acquired during a cutting period or a value acquired during a non-cutting period; and a calculation unit (12) designed to calculate an intersection point of a probability density function of load values ​​during the cutting period and a probability density function of load values ​​during the non-cutting period, and to calculate a load value at the intersection point as a threshold value used to detect tool breakage. (Supplementary Note 2)

[0036] The determination unit (11) is designed to identify the cutting period and the non-cutting period based on a signal from an instruction used to control the machine tool. (Supplementary Note 3)

[0037] A threshold calculation device (100) comprises a state detection unit (15) designed to obtain state information of a numerical control device; and a threshold storage unit designed to store the threshold and state information of the numerical control device in relation to each other. (Supplementary Note 4)

[0038] A threshold calculation device (100) includes a breakage detection unit (14) designed to calculate a set of features of the load value obtained from the data acquisition unit, compare the set of features with the threshold value, and detect a breakage of the tool. (Supplementary Note 5)

[0039] The set of characteristics is an average of the values ​​of the load. (Supplementary Note 6)

[0040] A computer-readable storage medium (112, 113, 114) is designed to store an instruction designed to cause one or a plurality of processors (111) to perform the following processes: acquiring a value of a load applied to a shaft of a machine tool; determining whether the value of the load is a value acquired during a cutting period or a value acquired during a non-cutting period; and calculating an intersection point of a probability density function of values ​​of the load during the cutting period and a probability density function of values ​​of the load during the non-cutting period, and calculating a value of the load at the intersection point as a threshold value used to detect tool breakage. [List of reference symbols] 100 Threshold Calculation Device 10 Data acquisition unit 11 Unit of determination 12 units of calculation 13 Threshold storage unit 14 fracture detection units 15 Data acquisition unit 111 CPU 112 ROM 113 RAM 114 Non-volatile memory QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2004 - 130 407

[0003]

Claims

[1] Threshold calculation device comprising the following: a data acquisition unit designed to obtain a value of a load applied to a shaft of a machine tool; a unit of determination designed to determine whether the load value obtained by the data acquisition unit is a value acquired during a cutting period or a value acquired during a non-cutting period; and a computation unit designed to calculate an intersection point of a probability density function of values ​​of the load during the cutting period and a probability density function of values ​​of the load during the non-cutting period, and to calculate a value of the load at the intersection point as a threshold value used to detect the breakage of a tool. [2] Threshold calculation device claim 1, wherein the determining unit is designed to identify the cutting period and the non-cutting period based on a signal of an instruction used to control the machine tool. [3] Threshold calculation device according to claim 1 further comprising: a state detection unit designed to obtain state information from a numerical control device; and a threshold storage unit designed to store the threshold and state information of the numerical control device in relation to each other. [4] Threshold calculation device according to claim 1, further comprising a breakage detection unit designed to calculate a feature set of the value of the load obtained from the data acquisition unit, to compare the feature set with the threshold and to detect a breakage of the tool. [5] Threshold calculation device according to claim 4, wherein the set of features is an average of values ​​of the load. [6] A computer-readable storage medium that stores an instruction designed to cause one or a plurality of processors to perform the following operations: Obtaining a value of a load applied to a shaft of a machine tool; Determine whether the load value is a value recorded during a cutting period or a value recorded during a non-cutting period; and Calculating an intersection point of a probability density function of values ​​of the load during the cutting period and a probability density function of values ​​of the load during the non-cutting period, and calculating a value of the load at the intersection point as a threshold value used to detect the breakage of a tool.

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