Cutting load calculation device and computer-readable storage medium

Abstract

A cutting load calculation device according to the present disclosure chronologically collects a spindle load during a spindle rotation period from the start to the end of spindle rotation, extracts a non-cutting period which is included in the spindle rotation period and in which a spindle speed is constant and cutting is not performed, calculates a representative value of the spindle load during the non-cutting period, and calculates a cutting load by subtracting the representative value from the spindle load during the spindle rotation period.

Description

Cutting load calculation device and computer-readable storage medium

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

[0002] In a machine tool, a method of acquiring the spindle load during spindle rotation as a cutting load and determining abnormalities such as tool damage and wear is known. However, since the spindle load includes mechanical variations such as wear of the ball screw, its product accuracy, product accuracy of the linear guide, and assembly state, it does not represent the load due to pure cutting.

[0003] Also, lubricating grease affects the spindle load. When the machine tool is in a low-temperature state, the lubricating grease cools and solidifies, increasing the spindle load. After the operation of the machine tool starts, the lubricating grease softens, so the resistance due to the lubricating grease decreases.

[0004] Thus, the spindle load includes factors other than cutting, which becomes noise for monitoring the cutting load. Conventionally, there is a technique of removing components other than cutting using data during idling. For example, Patent Document 1.

[0005] Japanese Patent Laid-Open No. 10-286743

[0006] When monitoring the cutting load, it is desired to exclude the load caused by factors other than cutting from the spindle load.

[0007] The cutting load calculation device according to the present disclosure includes a spindle load collection unit that collects the spindle load in a time series during the spindle rotation time period from the start to the end of spindle rotation, a non-cutting time period extraction unit that extracts a non-cutting time period in which the spindle speed is constant and no cutting is being performed during the spindle rotation time period, a representative value calculation unit that calculates a representative value of the spindle load in the non-cutting time period, and a cutting load calculation unit that calculates a cutting load obtained by subtracting the representative value from the spindle load in the spindle rotation time period.

[0008] This is a block diagram of the cutting load calculation device of the first embodiment. This diagram illustrates the non-cutting time period in milling and drilling. This diagram illustrates the non-cutting time period in tapping. This diagram illustrates an example in which there are multiple non-cutting time periods in the spindle rotation time period. This diagram illustrates the cutting load when the representative value of each non-cutting time period is subtracted. This is a block diagram of the cutting load calculation device of the second embodiment. This is a flowchart illustrating the collection of spindle load. This is a flowchart illustrating the identification of the machining type and the extraction of non-cutting time periods in tapping. This is a flowchart illustrating the extraction of non-cutting time periods in milling or drilling. This diagram illustrates the determination of abnormalities using thresholds. This is a block diagram of the cutting load calculation device of the third embodiment. This is a hardware configuration diagram of the cutting load calculation device.

[0009] Embodiments of this disclosure will be described below with reference to the drawings. In the following description, components having the same or similar functions will be denoted by the same reference numerals. Duplication of these components may be omitted.

[0010] In this application, "based on XX" means "based on at least XX," and includes cases where it is based on another element in addition to XX. Furthermore, "based on XX" is not limited to cases where XX is used directly, but also includes cases where it is based on something that has been calculated or processed. "XX" is any element (for example, any information).

[0011] The cutting load calculation device 100 of this embodiment can be applied to information processing devices such as numerical control devices and industrial PCs (personal computers). In the numerical control device, the calculated cutting load is applied to detecting abnormalities during machining by monitoring the spindle load. Furthermore, the calculated cutting load can be applied to simulations, data analysis, machine learning, and the like.

[0012] [First Embodiment] Figure 1 is a block diagram of the cutting load calculation device 100 according to the first embodiment. The cutting load calculation device 100 comprises a spindle load collection unit 11, a non-cutting time period extraction unit 12, a representative value calculation unit 13, and a cutting load calculation unit 14.

[0013] The spindle load collection unit 11 detects the start of spindle rotation. The spindle load collection unit 11 collects the spindle load during the spindle rotation period from the start of rotation to the end of rotation. The start of spindle rotation can be detected by an increase in rotation speed from a stopped state (rotation speed "0"). The end of spindle rotation can be detected by a transition from a rotating state (rotation speed ≠ 0) to a stopped state (rotation speed "0").

[0014] The spindle load can be obtained from the servo motor's control current. However, the obtained spindle load contains noise that is unnecessary for detecting cutting abnormalities. Examples of noise include variations in the precision of the machine tool's products and aging of parts. Also, slight changes in the tool's mounting position can affect the spindle load. Furthermore, the temperature of the machine tool also affects the spindle load. The temperature of the machine tool rises after operation begins. If the machine tool is at a low temperature, the lubricating grease cools and solidifies, resulting in a higher spindle load. The room temperature of the factory can also affect the temperature of the machine tool.

[0015] The non-cutting time period extraction unit 12 extracts non-cutting time periods. Non-cutting time periods are periods when the spindle speed is constant and no cutting is being done; these are idle periods. The cutting load calculation device 100 considers the spindle load during non-cutting time periods to be a load caused by factors other than cutting.

[0016] The non-cutting time period extraction unit 12 extracts the time periods during which the spindle is not being accelerated or decelerated, the spindle is not being reversed, and no cutting is being performed, as non-cutting time periods. For example, speed control before and after cutting is excluded from the non-cutting time period because the spindle is accelerating or decelerating. Spindle reversal (tap reversal) is also excluded from the non-cutting time period.

[0017] The non-cutting time period will be explained with reference to Figures 2 and 3. The non-cutting time period in milling and drilling will be explained with reference to Figure 2. At point (I), the spindle speed begins to accelerate, and at point (II), it reaches the rotational speed or cutting speed (called the commanded speed) commanded by the machining program. Cutting begins at point (III). From (III) to (IV) is the cutting feed. When cutting ends at point (IV), the speed is maintained and the spindle rotates freely until point (V). Then, cutting begins at point (V). The feed during cutting is the cutting feed. Cutting ends at point (VII), and the spindle speed begins to decelerate. At point (VIII), the spindle rotation ends.

[0018] In Figure 2, the non-cutting time periods, when the cutting edge of the tool is not in contact with the workpiece, the spindle speed is constant, and the spindle rotates in the forward direction, are the time periods from (II) to (III), from (IV) to (V), and from (VI) to (VII). Contact or non-contact of the tool cutting edge can be determined by the cutting signal. When the cutting signal is active, the tool feed becomes the cutting feed. Non-cutting time periods in milling and drilling can be said to be the time periods when the cutting signal is ON (the time periods of cutting feed).

[0019] Tapping is a process for forming male threads. In tapping, after forming the male threads, the tap is reversed and the tool is removed. During the time when the tap is reversed, the cutting feed is active, but no cutting is actually taking place. In tapping, the non-cutting time is determined by whether the tool is rotating forward or reversed.

[0020] Refer to Figure 3 to explain the extraction of non-cutting time periods in tapping. In the example in Figure 3, at time (I), the cutting feed begins and the spindle starts accelerating. At time (II), the command speed is reached. At time (III), the cutting edge of the tool makes contact with the workpiece and cutting begins. At time (IV), cutting is completed, and at time (V), the spindle is reversed and the tap is pulled out of the screw hole. In tapping, the non-cutting time period, when the cutting edge of the tool is not in contact with the workpiece, the spindle speed is constant, and the spindle is rotating in the forward direction, is from (II) to (III).

[0021] The representative value calculation unit 13 calculates representative values ​​of the spindle load during non-contact periods. Representative values ​​include maximum value, minimum value, average value, etc. Referring to Figure 4, the method for calculating representative values ​​of non-cutting periods in milling and drilling will be explained. In the graph of Figure 4, there are three non-cutting periods: the first, second, and third spindle rotation periods. The first non-cutting period is before the temperature rises, and the spindle load during the non-cutting period is high. The spindle loads during the second and third non-cutting periods are approximately the same. When the machining time is long, the temperature of the machine tool rises, and the spindle load during the non-cutting period decreases.

[0022] The representative value calculation unit 13 calculates representative values ​​(maximum value, minimum value, average value, etc.) of the spindle load during the first non-cutting period, and representative values ​​of the spindle load during the second and third non-cutting periods, respectively.

[0023] Referring to Figure 3, the method for calculating the representative value of tapping is explained. As mentioned above, in tapping, the cutting feed is active from the first (I), so there is no clear non-cutting period. Therefore, in the case of tapping, the non-cutting period of the spindle rotation time is just before threading, where the tool is not in contact with the workpiece and the spindle load is at its minimum. Thus, without strictly calculating the non-cutting period, the minimum value of the spindle load (point A in Figure 3) may be used as the representative value of the spindle load.

[0024] The cutting load calculation unit 14 calculates the cutting load by subtracting the spindle load during non-cutting periods from the spindle load during cutting periods. Non-cutting periods are defined as the state in which the cutting edge of the tool is not in contact with the workpiece (no cutting is occurring), the spindle speed is constant (no acceleration or deceleration load is applied), and the tool is rotating in the forward direction. Non-cutting periods are the state in which the tool is spinning freely without cutting or acceleration or deceleration. The spindle load during non-cutting periods is considered to be a load caused by factors other than cutting, and by subtracting the spindle load during non-cutting periods from the spindle load during cutting periods, loads caused by factors other than cutting are excluded from the spindle load.

[0025] Furthermore, loads caused by factors other than cutting can change over time. For example, the machine temperature gradually rises after operation begins, reducing the resistance of lubricating grease. Therefore, if there are multiple non-cutting periods within a single spindle rotation cycle, a representative value is calculated for each non-cutting period to address the temporal changes in load caused by factors other than cutting. Specifically, in Figure 4, the representative value for the first non-cutting period is greater than the representative values ​​for the other non-cutting periods. If a representative value is calculated from the spindle load during the first non-cutting period and subtracted from the spindle load during the first cutting period, the result is as shown in Figure 5. In Figure 5, by subtracting the representative value for each non-cutting period from the spindle load, the effect of temperature on the spindle is eliminated, and the cutting load for the first, second, and third cutting periods becomes approximately the same.

[0026] [Second Embodiment] Figure 6 shows the cutting load calculation device 100 of the second embodiment. The cutting load calculation device 100 of the second embodiment includes an abnormality determination unit 15. The abnormality determination unit 15 calculates the cutting load during the operation of the machine tool and compares the cutting load with a predetermined threshold to determine an abnormality in the cutting load. The same configuration as the first embodiment will be omitted below, and the cutting load calculation device 100 of the second embodiment will be described.

[0027] In the cutting load calculation device 100 of the second embodiment, in order to perform machining and abnormality detection simultaneously, the collection of spindle load, extraction of non-cutting time periods, calculation of cutting time periods, calculation of representative values, calculation of cutting load, and abnormality determination are performed in parallel. Figures 7 to 9 are flowcharts illustrating the operation of the cutting load calculation device 100.

[0028] In Figure 7, spindle load is collected. At this time, spindle load during acceleration / deceleration and tap reversal is not collected as it is not needed. The spindle load collection unit 11 waits for the start of spindle rotation. The start of spindle rotation can be detected by the increase in spindle speed from zero. If the start of spindle rotation is not detected (step S11; No), monitoring continues.

[0029] In step S12, the non-cutting time extraction unit 12 determines whether the spindle rotation is accelerating or decelerating or tap reversing. Acceleration can be detected from fluctuations in spindle speed, and tap reversing can be detected from the sign of the spindle speed. If the spindle rotation is accelerating or decelerating or tap reversing (step S12; Yes), the non-cutting time extraction unit 12 proceeds to step S14 without collecting spindle load. If the spindle rotation is neither accelerating or decelerating nor tap reversing (step S12; No), the spindle load collection unit 11 collects the spindle load (step S13) and proceeds to step S14.

[0030] In step S14, the spindle load collection unit 11 determines whether or not the spindle rotation has finished. The end of spindle rotation can be detected from the cessation of spindle rotation (spindle speed = 0).

[0031] Figure 8 is a flowchart illustrating the identification of the type of machining and the extraction of non-cutting time periods in tapping. The non-cutting time period extraction unit 12 determines whether the spindle rotation immediately preceding the collected spindle load was for tapping. Tapping can be determined by one of the following two methods. The first is to use the presence or absence of a tapping operation. A tapping operation is the operation in which the spindle rotates forward at a constant speed to cut threads, then reverses direction to withdraw the tool. By observing the spindle load, if a tapping operation is detected, it is determined to be tapping. The second is the signal from the numerical control device. If the tapping signal is ON, it is determined to be tapping.

[0032] If the previous spindle rotation was for tapping (step S21; Yes), the non-cutting time period extraction unit 12 extracts the time when the spindle load is at its minimum as the non-cutting time period (step S22), and then terminates the extraction of the non-cutting time period.

[0033] If the previous spindle rotation was not for tapping (step S21; No), the non-cutting time period extraction unit 12 starts extracting non-cutting time periods for milling or drilling (step S23).

[0034] Referring to Figure 9, the extraction of non-cutting time periods in milling or drilling operations will be explained. The following process is performed if tapping is not performed in step S21. The non-cutting time period extraction unit 12 acquires a cutting signal (step S31). The cutting signal is an output signal of the numerical control device. When the cutting signal switches from a cutting feed to something other than a cutting feed (step S32; Yes), the non-cutting time period extraction unit 12 records the time of the switch as the start time of the non-cutting time period (step S33) and proceeds to step S34. If the cutting signal does not switch from a cutting feed to something other than a cutting feed (step S32; No), proceeds to step S34. In step S34, it is determined whether a switch has occurred from something other than a cutting feed to a cutting feed. If a switch has occurred from something other than a cutting feed to a cutting feed (step S34; Yes), the non-cutting time period extraction unit 12 records the time of the switch as the end time of the non-cutting time period (step S35). The non-cutting time zone extraction unit 12 repeats the process from step S31 to step S35 until the spindle rotation is completed.

[0035] When a non-cutting period is extracted, the representative value calculation unit 13 calculates a representative value of the spindle load for the extracted non-cutting period. The representative value calculation unit 13 calculates the representative value sequentially from the start to the end of the spindle rotation.

[0036] The abnormality detection unit 15 determines tool abnormalities by comparing a threshold value with the cutting load, or a threshold value with the spindle load. The graph in the upper section of Figure 10 shows the relationship between the conventional threshold value and the spindle load, and the relationship with the representative value calculated by the cutting load calculation device 100. The graph in the middle section of Figure 10 shows that an abnormality is determined by subtracting the representative value from the spindle load and comparing the cutting load with the threshold value. In the case of the graph in the lower section of Figure 10, an abnormality is determined by adding the representative value to the threshold value and comparing the spindle load with the threshold value (new threshold value). The abnormality detection unit 15 determines an abnormality if the cutting load or spindle load exceeds the threshold value.

[0037] [Third Embodiment] Figure 11 shows the cutting load calculation device 100 of the third embodiment. The cutting load calculation device 100 of the third embodiment includes a machine learning unit 16. As a preprocessing step for machine learning, the cutting load calculation device 100 eliminates loads caused by factors other than cutting. The machine learning unit 16 uses the cutting components from which unnecessary components have been removed to perform analysis and learning of the load on the tool. By eliminating loads on the spindle caused by factors other than cutting, the cutting load calculation device 100 can improve the quality and effectiveness of learning.

[0038] The hardware configuration of the cutting load calculation device 100 to which this disclosure is applied will be described below. Figure 12 is a hardware configuration diagram of the cutting load calculation device 100. As shown in Figure 12, the cutting load calculation device 100 includes a CPU 111 that controls the cutting load calculation device 100 as a whole, a ROM 112 that records programs and data, and a RAM 113 for temporarily expanding data. The CPU 111 reads the system program recorded in the ROM 112 via a bus.

[0039] The non-volatile memory 114 is backed up, for example, by a battery (not shown), so that its stored state is maintained even when the power to the cutting load calculation device 100 is turned off. Various data such as programs read from external devices 120 via interfaces 115, 118, and 119, and operation inputs input via input device 20 are stored in the non-volatile memory 114. Programs and data for running the cutting load calculation device 100 of this embodiment may also be stored in the non-volatile memory 114.

[0040] Interface 115 is an interface for connecting the cutting load calculation device 100 to an external device 120 such as an adapter. Programs and various parameters are read from the external device 120. Interface 118 is an interface for connecting the cutting load calculation device 100 to a display device 30 such as a liquid crystal display. The display device 30 displays data read into memory, data obtained as a result of executing programs, etc. Interface 119 is an interface for connecting the cutting load calculation device 100 to an input device 20 such as a keyboard or pointing device. The input device 20 passes commands, data, etc. based on operator operations to the CPU 111 via interface 119.

[0041] While embodiments of this disclosure have been described in detail above, this disclosure is not limited to the individual embodiments described above. These embodiments can be added, replaced, modified, partially deleted, etc., in any way that does not depart from the spirit of the invention or from the idea and intent of this disclosure derived from the claims and their equivalents. For example, the order of operations and processes in the embodiments described above are shown as examples only and are not limited thereto. The same applies when numerical values ​​or mathematical formulas are used in the description of the embodiments described above.

[0042] The following are annotations relating to embodiments of the present disclosure. (Annotation 1) A cutting load calculation device (100) according to one aspect of the present disclosure includes: a spindle load collection unit (11) that collects spindle loads in a time series during spindle rotation time from the start to the end of spindle rotation; a non-cutting time period extraction unit (12) that extracts non-cutting time periods during the spindle rotation time when the spindle speed is constant and no cutting is being performed; a representative value calculation unit (13) that calculates a representative value of the spindle load during the non-cutting time period; and a cutting load calculation unit (14) that calculates the cutting load by subtracting the representative value from the spindle load during the spindle rotation time period. (Annotation 2) The representative value is one of the maximum, minimum, or average value of the spindle load during the non-cutting time period. (Annotation 3) The non-cutting time period extraction unit (12) extracts time periods when no cutting is being performed as non-cutting time periods based on cutting signals. (Note 4) If there are multiple non-cutting time periods in the spindle rotation time period, the representative value calculation unit (13) calculates a representative value for each non-cutting time period. (Note 5) The non-cutting time period extraction unit (12) extracts the time period in the spindle rotation time period when the spindle load is at its minimum value as a non-cutting time period. (Note 6) In the case of milling or drilling, the non-cutting time period extraction unit (12) extracts the time period when no cutting is being performed based on the cutting signal as a non-cutting time period, and in the case of tapping, extracts the time period in the spindle rotation time period when the spindle load is at its minimum value as a non-contact time period. (Note 7) The non-cutting time period extraction unit (12) extracts non-cutting time periods in the spindle rotation time period when the spindle speed is constant, no cutting is being performed, and no reversal is occurring. (Note 8) The system includes an abnormality determination unit (15) that determines an abnormality by comparing a threshold value obtained by adding the representative value to the spindle load, or a threshold value obtained by subtracting the representative value to the cutting load. (Note 9) The cutting load calculation device (100) includes a machine learning unit (16) that performs machine learning using the cutting load.(Note 10) The storage media (112, 113, 114) readable by the computer (111) record a program that causes the computer (111) to operate as a spindle load collection unit (11) that collects spindle load in a time series for the spindle rotation time period from the start to the end of spindle rotation, a non-cutting time period extraction unit (12) that extracts non-cutting time periods in the spindle rotation time period when the spindle speed is constant and no cutting is being performed, a representative value calculation unit (13) that calculates a representative value of the spindle load during the non-cutting time period, and a cutting load calculation unit (14) that calculates the cutting load by subtracting the representative value from the spindle load during the spindle rotation time period.

[0043] 100 Cutting load calculation device 11 Spindle load collection unit 12 Non-cutting time period extraction unit 13 Representative value calculation unit 14 Cutting load calculation unit 15 Anomaly detection unit 16 Machine learning unit 111 CPU 112 ROM 113 RAM 114 Non-volatile memory

Claims

1. A cutting load calculation device comprising: a spindle load collection unit that collects spindle load in a time series during the spindle rotation period from the start to the end of spindle rotation; a non-cutting period extraction unit that extracts non-cutting periods during the spindle rotation period when the spindle speed is constant and no cutting is being performed; a representative value calculation unit that calculates a representative value of the spindle load during the non-cutting period; and a cutting load calculation unit that calculates the cutting load by subtracting the representative value from the spindle load during the spindle rotation period.

2. The cutting load calculation device according to claim 1, wherein the representative value is one of the maximum, minimum, or average values ​​of the spindle load during the non-cutting period.

3. The cutting load calculation device according to claim 1, wherein the non-cutting time period extraction unit extracts the time period during which cutting is not being performed as a non-cutting time period based on the cutting signal.

4. The cutting load calculation device according to claim 3, wherein, if there are multiple non-cutting time periods within the spindle rotation time period, the representative value calculation unit calculates a representative value for each non-cutting time period.

5. The cutting load calculation device according to claim 1, wherein the non-cutting time period extraction unit extracts the time period in which the spindle load during the spindle rotation time period is at its minimum value as the non-cutting time period.

6. The cutting load calculation device according to claim 1, wherein the non-cutting time period extraction unit extracts the time period during which cutting is not performed as a non-cutting time period based on the cutting signal in the case of milling or drilling, and in the case of tapping, extracts the time period during which the spindle load during the spindle rotation time period is at its minimum as a non-contact time period.

7. The cutting load calculation device according to claim 1, wherein the non-cutting time period extraction unit extracts non-cutting time periods during the spindle rotation time period in which the spindle speed is constant, no cutting is performed, and no reversal is performed.

8. The cutting load calculation device according to claim 1, further comprising an abnormality determination unit that determines an abnormality by comparing a threshold obtained by adding the representative value with the spindle load, or a threshold obtained by subtracting the representative value with the cutting load.

9. The cutting load calculation device according to claim 1, further comprising a machine learning unit that performs machine learning using the cutting load.

10. A computer-readable storage medium containing a program that causes the computer to operate as: a spindle load collection unit that collects spindle load in a time series for the spindle rotation time period from the start to the end of spindle rotation; a non-cutting time period extraction unit that extracts non-cutting time periods during the spindle rotation time period when the spindle speed is constant and no cutting is being performed; a representative value calculation unit that calculates a representative value of the spindle load during the non-cutting time period; and a cutting load calculation unit that calculates the cutting load by subtracting the representative value from the spindle load during the spindle rotation time period.

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