Machining system and manufacturing method of workpiece

Abstract

A machining system includes: a tool for machining a workpiece; a motor for rotating the tool or the workpiece; a controller for controlling the motor; and a measuring device for acquiring the load current of the motor. If the Mahalanobis distance exceeds a threshold, the controller changes the rotational speed of the motor. The Mahalanobis distance is a value calculated using parameters based on the load current, which is acquired by the measuring device within a specific machining range of the workpiece. The parameters based on the load current include parameters obtained by performing a Fourier transform on the load current and a measured value of the load current.

Description

Technical Field

[0001] This disclosure relates to a processing system and a method for manufacturing a workpiece.

[0002] This application claims priority based on Japanese Patent Application No. 2021-033931, filed on March 3, 2021, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Patent document 1 discloses the machining of sintered parts. The machining uses cutting tools and grinding tools.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2006-336078 Summary of the Invention

[0007] The machining system disclosed herein comprises: a tool for machining a workpiece; a motor for rotating the tool or the workpiece; a controller for controlling the motor; and a measuring device for acquiring the load current of the motor. If the Mahalanobis distance exceeds a threshold, the controller changes the rotational speed of the motor. The Mahalanobis distance is a value calculated using parameters based on the load current, which is acquired by the measuring device within a specific machining range of the workpiece. The parameters based on the load current include parameters obtained by performing a Fourier transform on the load current and a measured value of the load current.

[0008] The method for manufacturing a workpiece disclosed herein includes a step of machining the workpiece with the tool while rotating a tool or workpiece by a motor and measuring the load current of the motor with a measuring instrument. In the machining step, if the Mahalanobis distance exceeds a threshold, the rotational speed of the motor is changed. The Mahalanobis distance is a value obtained using parameters based on the load current, which is acquired by the measuring instrument within a specific machining range of the workpiece. The parameters based on the load current include parameters obtained by performing a Fourier transform on the load current and the measured value of the load current. Attached Figure Description

[0009] Figure 1 This is an explanatory diagram showing the processing system of the embodiment.

[0010] Figure 2 This is an explanatory diagram showing the tools included in the machining system of the embodiment and the workpiece being machined using the tools.

[0011] Figure 3It is a graph showing the waveform of the motor load current obtained by the processing system of the embodiment.

[0012] Figure 4 This is a graph showing the waveform of the Fourier spectrum after performing a Fourier transform on the load current of the motor obtained by the processing system of the embodiment.

[0013] Figure 5 This is a flowchart illustrating the processing procedure of the controller in the processing system of the embodiment.

[0014] Figure 6 This is an explanatory diagram showing the tools included in the machining system of Modified Example 1 and the workpiece machined by the tools.

[0015] Figure 7 This is an explanatory diagram showing the machining system of Modified Example 2. Detailed Implementation

[0016] [The technical problem this disclosure aims to solve]

[0017] Tools can sometimes be damaged during the machining process. When a tool is damaged, it cannot perform the intended machining on the subsequent workpiece, resulting in defective products that have not been machined as intended.

[0018] One of the purposes of this disclosure is to provide a processing system and a method for manufacturing processed products that can suppress the production of defective products.

[0019] [The Effects of This Disclosure]

[0020] The processing system and the method for manufacturing the processed product disclosed herein can suppress the production of defective products.

[0021] [Description of embodiments of this disclosure]

[0022] First, the contents of the embodiments of this disclosure will be described.

[0023] (1) A processing system according to one aspect of the present disclosure comprises: a tool for processing a workpiece; a motor for rotating the tool or the workpiece; a controller for controlling the motor; and a measuring device for acquiring the load current of the motor, wherein the controller changes the rotational speed of the motor when the Mahalanobis distance exceeds a threshold value, the Mahalanobis distance being a value obtained using parameters based on the load current, the load current being acquired by the measuring device within a specific processing range in the workpiece, the parameters based on the load current including parameters obtained by performing a Fourier transform on the load current and a measured value of the load current.

[0024] The aforementioned machining system can suppress the production of defective products due to non-standard processing by the tools. The system can immediately change the motor speed if the Mahalanobis distance exceeds a threshold. In this specification, the Mahalanobis distance is sometimes referred to as the MD value. As detailed later, an MD value exceeding a threshold indicates the production of defective products. That is, if the aforementioned machining system produces defective products, it can immediately change the motor speed.

[0025] (2) In the above processing system, the parameters obtained by performing a Fourier transform on the load current may also include: the effective value of the load current after performing a Fourier transform; the amplitude value of the peak in the Fourier spectrum after performing a Fourier transform on the load current; the centroid of the amplitude of the peak; and the centroid of the amplitude of the peak in a specific frequency range of the Fourier spectrum.

[0026] The above methods can prevent the production of defective products.

[0027] (3) In the above processing system, the measured value of the load current may also include: the maximum value of the load current; and the effective value of the load current.

[0028] The above methods can prevent the production of defective products.

[0029] (4) In the above processing system, the number of parameters based on the load current may be seven parameters, from the first parameter to the seventh parameter. The first parameter to the fifth parameter are parameters obtained by performing a Fourier transform on the load current, and the sixth parameter and the seventh parameter are the measured values ​​of the load current.

[0030] The above methods can prevent the production of defective products.

[0031] (5) In the processing system described in (4) above, the first parameter may be the effective value of the load current after Fourier transform, the second parameter is the amplitude value of the peak in the Fourier spectrum after Fourier transform of the load current, the third parameter is the centroid of the amplitude of the peak, the fourth parameter is the centroid of the amplitude of the peak in the range of 28Hz to 30Hz of the Fourier spectrum, the fifth parameter is the centroid of the amplitude of the peak in the range of 31Hz to 33Hz of the Fourier spectrum, the sixth parameter is the maximum value of the load current, and the seventh parameter is the effective value of the load current.

[0032] The above methods can prevent the production of defective products.

[0033] (6) In the above processing system, the specific processing range may also include the range of the parts where the processing conditions of the tool change.

[0034] During the machining process of a workpiece, if the machining conditions of the tool change at a certain point, the load current measured by the measuring instrument will exhibit a specific change. By observing this specific change, it is easy to determine whether the MD value exceeds the threshold. Therefore, by focusing on this specific change, it is possible to detect defective products with high precision. The locations where the machining conditions of the tool change will be described later.

[0035] (7) In the above-mentioned machining system, the machining system may also have a multi-axis lathe, and the tool is the turning tool of the multi-axis lathe.

[0036] In multi-axis lathes, since multiple workpieces are essentially machined simultaneously, vibrations generated during the machining of other workpieces propagate as interference to the vibration meter. Therefore, relying solely on vibration-based MD values ​​can sometimes fail to adequately identify whether defective products have been produced. In contrast, the motor load current generated during the machining of each workpiece is measured by separate measuring instruments. Furthermore, unlike vibration, the load currents of each motor are independent of each other. Therefore, the aforementioned machining system, by using MD values ​​derived from the first to seventh parameters based on the load current to determine whether defective products have been produced, can adequately identify defective products even on multi-axis lathes.

[0037] (8) The method for manufacturing a workpiece disclosed herein includes a step of machining the workpiece with the tool while rotating the tool or workpiece by a motor and measuring the load current of the motor with a measuring instrument. In the machining step, if the Mahalanobis distance exceeds a threshold, the rotation speed of the motor is changed. The Mahalanobis distance is a value obtained using parameters based on the load current, which is obtained by the measuring instrument within a specific machining range in the workpiece. The parameters based on the load current include parameters obtained by performing a Fourier transform on the load current and the measured value of the load current.

[0038] The above-described method for manufacturing processed products can suppress the production of defective products. This is because, similar to the above-described processing system, the method for manufacturing processed products can immediately change the motor speed in the event of defective products being produced.

[0039] Details of the embodiments disclosed herein

[0040] Hereinafter, details of embodiments of the present disclosure will be described with reference to the accompanying drawings. The same reference numerals in the drawings denote components with the same names.

[0041] Implementation Method

[0042] [Machining System]

[0043] Reference Figures 1 to 5 The processing system 1 of the embodiment will be described below. Figure 1 As shown, the machining system 1 of this embodiment includes a tool 2, a motor 3, a measuring device 4, and a controller 5. The tool 2 processes the workpiece 10. The motor 3 rotates either the tool 2 or the workpiece 10. The measuring device 4 acquires the load current of the motor 3. The controller 5 controls the motor 3. One feature of the machining system 1 of this embodiment is that when the MD value of the currently processed workpiece 10 exceeds a threshold, the controller 5 changes the rotation speed of the motor 3. The machining system 1 of this embodiment processes multiple workpieces 10 sequentially. That is, the machining system 1 of this embodiment processes multiple workpieces 10 one by one in sequence.

[0044] [Workpiece]

[0045] Workpiece 10 is the object to be processed by tool 2. Figure 1 The workpiece 10 is shown in simplified form. The material, type, and shape of the workpiece 10 are not particularly limited and can be appropriately selected. The material of the workpiece 10 is typically metal, resin, or ceramic. Examples of metals include pure iron, ferroalloys, or non-ferrous metals. Examples of non-ferrous metals include copper, copper alloys, aluminum, or aluminum alloys. The type of workpiece 10 is, for example, a powder-molded body, a sintered body, a molten material, or a resin-molded body. A powder-molded body is obtained by pressing raw material powder into shape. A sintered body is obtained by sintering a powder-molded body. A molten material is obtained by solidifying a raw material melt. A resin-molded body is obtained by solidifying molten resin. The shape of the workpiece 10 can be, for example, a simple shape such as a single plate or column, or a complex shape such as a combination of multiple plates and columns.

[0046] The workpiece 10 in this embodiment is a sintered metal body. The workpiece 10 in this embodiment has a recess 10a. For example... Figure 2 As shown, the recess 10a is composed of a wall surface 11, a bottom surface 12, and a corner portion 13. The corner portion 13 connects the wall surface 11 and the bottom surface 12. In this embodiment, the wall surface 11 and the bottom surface 12 within the recess 10a are finished using a tool 2. Alternatively, the recess 10a may be rough-machined, unlike in this embodiment.

[0047] [tool]

[0048] Tool 2 is used to machine workpiece 10. The type of tool 2 can be appropriately selected depending on the type of machining. For example, the type of machining is turning or rotary machining. In the case of turning, tool 2 is a turning tool. A turning tool is, for example, a lathe tool. In the case of rotary machining, tool 2 is a rotary tool. Rotary tools are, for example, drills, reamers, taps, end mills, side mills, T-slot cutters, and hobs.

[0049] Tool 2 is mounted on a machine tool. In the case of turning, the machine tool is, for example, a multi-axis lathe. A multi-axis lathe is, for example, a parallel two-axis lathe or a opposed two-axis lathe. In the case of turning, the machine tool is, for example, a machining center. The machine tool can also be a composite machining center capable of performing both turning and turning operations. Known multi-axis lathes and machining centers can be used.

[0050] like Figure 1 As shown, the machine tool in this embodiment is a parallel two-axis lathe. The parallel two-axis lathe is a lathe in which the first spindle 101 and the second spindle 102 are parallel. The parallel two-axis lathe includes the first spindle 101 and the second spindle 102, the first chuck 111 and the second chuck 112, the first tool post and the second tool post, and a conveyor. Illustrations of the first tool post, the second tool post, and the conveyor are omitted.

[0051] A first chuck 111 is mounted at the front end of the first spindle 101. A second chuck 112 is mounted at the front end of the second spindle 102. The first chuck 111 and the second chuck 112 hold the workpiece 10. A first tool post is mounted with a first tool 21. A second tool post is mounted with a second tool 22. The first tool 21 processes the workpiece 10 held by the first chuck 111. The second tool 22 processes the workpiece 10 held by the second chuck 112. The first tool 21 and the second tool 22 can be appropriately selected according to the type of processing, as described above. The first tool 21 and the second tool 22 can be the same or different. In this embodiment, as... Figure 1 As shown, the first tool 21 and the second tool 22 are identical cutting tools with interchangeable tool tips. The first tool 21 and the second tool 22 perform finishing on corresponding areas of different workpieces 10 under the same machining conditions. The first spindle 101 and the second spindle 102, the first chuck 111 and the second chuck 112, the first tool post and the second tool post are identical in configuration. The following description will focus on the first spindle 101, the first chuck 111, and the first tool post.

[0052] The first spindle 101 is rotated by the first motor 31 (described later). The rotation of the first spindle 101 causes the workpiece 10, held by the first chuck 111, to rotate. The first spindle 101 is driven by a drive mechanism (not shown in the figure). Figure 1 The arrows indicate forward and backward movement in the up and down directions. Through this drive mechanism, the first main shaft 101 can also be further... Figure 1 The left and right arrows indicate horizontal movement. The first tool holder moves horizontally via a drive mechanism (not shown in the diagram). Figure 1 The arrows indicate forward and backward movement in the up and down directions. Through this drive mechanism, the first tool holder can also be further... Figure 1The arrows indicate horizontal movement in the left and right directions. Moving forward means bringing workpiece 10 closer to tool 2. Moving backward means moving workpiece 10 away from tool 2. Horizontal movement refers to moving in a direction perpendicular to both the forward and backward directions.

[0053] The conveyors transport workpiece 10 from outside the parallel two-axis lathe to the first chuck 111 and the second chuck 112 respectively, and from the first chuck 111 and the second chuck 112 to the outside of the parallel two-axis lathe respectively. There can be multiple conveyors. For example, there can be only two conveyors: a first conveyor and a second conveyor. The first conveyor transports workpiece 10 from outside the parallel two-axis lathe to the first chuck 111 and from the first chuck 111 to the outside of the parallel two-axis lathe. The second conveyor transports workpiece 10 from outside the parallel two-axis lathe to the second chuck 112 and from the second chuck 112 to the outside of the parallel two-axis lathe.

[0054] The process of machining workpiece 10 using the first tool 21 is as follows: Workpiece 10 is conveyed from outside the parallel twin-axis lathe to the first chuck 111 via a conveyor and held by the first chuck 111. While workpiece 10 is held by the first chuck 111, the first spindle 101 is rotated by the motor 3. This rotation causes workpiece 10 held by the first chuck 111 to rotate. The rotating workpiece 10 approaches the first tool 21, and the first tool 21 machines the recess 10a of workpiece 10. The conveyor unloads the workpiece 10, which has been machined by the first tool 21, from the first chuck 111. The unloaded workpiece 10 is then conveyed to the outside of the parallel twin-axis lathe. The process of machining workpiece 10 using the second tool 22 is the same as that of machining workpiece 10 using the first tool 21. The machining of workpiece 10 held by the first chuck 111 and the machining of workpiece 10 held by the second chuck 112 are essentially performed simultaneously. The first tool 21 and the second tool 22 repeatedly process the workpiece 10. Therefore, the first tool 21 and the second tool 22 each process a plurality of workpieces 10 in sequence.

[0055] [Electric motor]

[0056] Motor 3 is a spindle motor that rotates the workpiece 10 or tool 2. In the case of turning operations as described in this embodiment, as above, motor 3 rotates the workpiece 10 via chuck 110 by rotating the spindle 100. In the case of a parallel two-axis lathe as described in this embodiment, the number of motors 3 is two: a first motor 31 and a second motor 32. The first motor 31 rotates the first spindle 101. The second motor 32 rotates the second spindle 102. Figure 1In the diagram, the double-dotted line connecting the first motor 31 and the first spindle 101, and the double-dotted line connecting the second motor 32 and the second spindle 102, virtually represent the rotation axes of each spindle 100 that rotates via each motor 3. The workpiece 10 rotates around these rotation axes. Unlike this embodiment, in the case of rotary machining, the motor 3 causes the tool 2 to rotate.

[0057] [Measuring instrument]

[0058] Measuring device 4 acquires the load current of motor 3. Measuring device 4 is, for example, a current sensor. In the case where the machine tool is a parallel two-axis lathe as in this embodiment, the number of measuring devices 4 is two: a first measuring device 41 and a second measuring device 42. The first measuring device 41 acquires the load current of the first motor 31. The second measuring device 42 acquires the load current of the second motor 32. That is, the load currents measured by the first measuring device 41 and the second measuring device 42 are independent of each other without affecting each other.

[0059] [Controller]

[0060] Controller 5 controls motor 3. Controller 5 changes the rotation speed of motor 3. The rotation speed of motor 3 is set to a speed corresponding to the machining conditions before machining workpiece 10. Typically, the rotation speed of motor 3 is changed based on whether the MD value of the currently machined workpiece 10 exceeds a threshold. The MD value of the currently machined workpiece 10 will be described later. In the case where the machine tool is a parallel two-axis lathe as in this embodiment, controller 5 controls the first motor 31 and the second motor 32 separately. Here, the first tool 21 and the second tool 22 perform finishing on different corresponding ranges of different workpieces 10 under the same machining conditions. That is, the basic control process of controller 5 controlling the first motor 31 and controller 5 controlling the second motor 32 is common. Therefore, the following description will be based on the case where controller 5 controls the first motor 31. Controller 5 also controls the operation of the drive mechanism of the first spindle 101, the drive mechanism of the second spindle 102, the drive mechanism of the first tool post, the drive mechanism of the second tool post, and the conveyor.

[0061] Typically, the controller 5 is configured as a computer. The computer, for example, includes a processor and a memory. The memory stores a program for causing the processor to execute the control process described later. The processor reads and executes the program stored in the memory. The program includes program code related to processing whether the calculation result of the arithmetic unit 52 satisfies a threshold, and processing to change the rotation speed of the motor 3 based on the determination. The controller 5 has a storage unit 51 and an arithmetic unit 52.

[0062] (Storage Department)

[0063] Storage unit 51 stores a threshold. The threshold is, for example, a preset value as follows.

[0064] Multiple qualified products are produced by processing workpiece 10 using a normal, undamaged tool 2. The more qualified products there are, the easier it is to improve the reliability of the threshold. While the number of qualified products depends on the type of workpiece being processed, it can be, for example, 500 or more, further exceeding 650, and particularly exceeding 800. The load current of motor 3 is obtained in advance when producing each qualified product.

[0065] The unit space is created using the MT (Massaurus Taguchi) method. The unit space is created using parameters based on the load current of motor 3 obtained when producing multiple qualified products. In the MT method, these parameters are sometimes referred to as monitoring objects or characteristic quantities. This load current utilizes the load current obtained during machining of a specific machining range of workpiece 10.

[0066] In workpiece 10, the aforementioned specific machining range is a defined range that is continuously machined by the first tool 21. For example, if... Figure 2 In the case of the workpiece 10 with the recess 10a shown, the cutting edge of the first tool 21 may act only on the wall surface 11, only on the bottom surface 12, or simultaneously on both the wall surface 11 and the bottom surface 12. The cutting edge of the tool 2 acts simultaneously on both the wall surface 11 and the bottom surface 12 because it is machining the corner 13 formed by the wall surface 11 and the bottom surface 12. The specific machining range described above may also be the range constituting the wall surface 11, the range constituting the bottom surface 12, or the range constituting the corner 13, etc.

[0067] The aforementioned specific processing range can also include the range where the processing conditions of the first tool 21 change. The processing conditions of the tool 2 include, for example, the feed rate of the cutting edge of the first tool 21, the depth of cut, the revolutions of the first tool 21 or the workpiece 10, the feed direction, and the processing time. For example, if the workpiece 10 has a recess 10a, the aforementioned specific processing range is the range constituting the corner 13. The range constituting the corner 13 includes the corner 13 and the area near the corner 13. The area near the corner includes both the wall surface 11 and the bottom surface 12. When processing the corner 13, the feed direction of the cutting edge of the first tool 21 changes from the wall surface 11 to the bottom surface 12. When the feed direction changes in this way, the portion of the cutting edge of the first tool 21 that contacts the workpiece 10 changes. Specifically, when processing the corner 13, the cutting edge of the first tool 21 acts on both the wall surface 11 and the bottom surface 12 simultaneously. Within the range constituting the corner 13, the processing resistance of the first tool 21 increases. Figure 3The graph shown illustrates the waveform of the load current of the motor 3, as measured by the measuring device 4, during the sequential machining of wall 11, corner 13, and bottom 12. The horizontal axis of the graph represents time, and the vertical axis represents the load current. Along the horizontal axis are thick arrows indicating the areas machined on wall 11 and bottom 12. The two thick arrows partially overlap. Thin arrows indicate the areas machined on corner 13 within the overlapping areas. The vertical axis of the graph uses + (positive) to represent positive and - (negative) to represent negative. Due to the increased machining resistance of the first tool 21 machining corner 13, the current... Figure 3 As shown, the load current at corner 13 has a larger waveform compared to the load current at wall 11 and bottom 12.

[0068] The parameters based on the load current include parameters obtained by performing a Fourier transform on the load current and the measured value of the load current. The parameters obtained by performing a Fourier transform on the load current can be appropriately selected, for example, depending on the type of processing and processing conditions. If the parameters obtained by performing a Fourier transform on the load current are parameters focusing on a certain frequency band of the Fourier spectrum, that frequency band can be appropriately selected based on the rotational speed of motor 3.

[0069] The parameters obtained by performing a Fourier transform on the load current include, for example, the effective value of the Fourier transform of the load current, the amplitude of the peak in the Fourier spectrum of the load current, the centroid of the amplitude of the peak, and the centroid of the amplitude of the peak within a specific frequency range of the Fourier spectrum. The effective value of the Fourier transform is the root mean square of the Fourier transform. The peak of the Fourier spectrum refers to the entire mountain-shaped curve including the maximum amplitude value. The amplitude of the peak in the Fourier spectrum is the largest amplitude value in the aforementioned curve. The centroid of the amplitude of the peak in the Fourier spectrum is the amplitude of the centroid of the lower part of the aforementioned curve. The centroid of the amplitude of the peak within a specific frequency range is the amplitude of the centroid of the lower part of the curve within that specific frequency range.

[0070] Figure 4 The graph shown illustrates the waveform of the Fourier spectrum after performing a Fourier transform on the load current. Figure 4 The graph of the Fourier spectrum is Figure 3 The graph is obtained by performing a Fourier transform on the load current. Figure 4 The horizontal axis of the chart represents frequency, and the vertical axis represents amplitude. Figure 4 In the chart, the peak refers to the entire mountain-shaped curve extending from inflection point x1 to inflection point x2. Figure 4 In the equation, the amplitude value at the peak is the maximum amplitude value within the range from inflection point x1 to inflection point x2, i.e., the amplitude value y1. Figure 4In the equation, the centroid of the peak's amplitude is the centroid of the lower part of the curve within the range from inflection point x1 to inflection point x2, expressed as amplitude value g1. In other words, the centroid of the peak's amplitude is the centroid of the area enclosed by the horizontal axis, the straight line from inflection point x1 along the vertical axis, the straight line from inflection point x2 along the vertical axis, and the curve within the range from inflection point x1 to inflection point x2, expressed as amplitude value g1. Figure 4 In this context, for example, the centroid of the amplitude of the peak in a specific frequency range above x3 and below x4 is the centroid of the lower part of the curve in the range above x3 and below x4, which is the amplitude value g2. In other words, the centroid of the amplitude of the peak in the range above x3 and below x4 is the centroid of the area enclosed by the horizontal axis, the straight line from the inflection point x1 along the vertical axis, the straight line from the inflection point x2 along the vertical axis, and the curve in the range above x3 and below x4.

[0071] The measured values ​​of load current include, for example, the maximum value and the effective value (RMS) value of the load current. The maximum value is the largest absolute value of the load current. The RMS value is the maximum value divided by the square root of 2. Figure 3 In this context, the maximum value of the load current is current value a1. Figure 3 In this context, the effective value of the load current is the current value a2.

[0072] The number of parameters can be appropriately selected based on the required detection accuracy, specifically, according to the probability of the chi-square distribution described later. In this embodiment, the number of parameters is seven, from the first parameter to the seventh parameter. The first to fifth parameters are obtained by performing a Fourier transform on the load current. The sixth and seventh parameters are the measured values ​​of the load current.

[0073] Specifically, the first parameter is the effective value of the Fourier transform of the load current. The second parameter is the amplitude of the peak in the Fourier spectrum of the load current after its Fourier transform. The third parameter is the centroid of the amplitude of the peak in the Fourier spectrum. The fourth parameter is the centroid of the amplitude of the peak in the range of 28Hz to 30Hz in the Fourier spectrum. The fifth parameter is the centroid of the amplitude of the peak in the range of 31Hz to 33Hz in the Fourier spectrum. The sixth parameter is the maximum value of the load current. The seventh parameter is the effective value of the load current. The above Fourier transform can be performed using the High-Speed ​​Fourier Transform (HST). The HST is an algorithm that calculates the Discrete Fourier Transform at high speed. That is, the HST has a short computation time.

[0074] The MD value of each qualified product is calculated using the created unit space. Then, the square root of the chi-square distribution of the MD values ​​of the qualified products is calculated. This is because the square of the MD value follows a chi-square distribution. The probability of the chi-square distribution can be appropriately chosen, for example, based on the number of processed products produced each month. When the number of processed products produced each month is N, this probability is, for example, greater than {1-(1 / N)}. The probability is, for example, greater than {1-(1 / 1.5N)}, further greater than {1-(1 / 2N)}, and especially greater than {1-(1 / 2.5N)}. For example, let this probability be {1-(1 / 1000000)}, which is 0.999999. Let the degrees of freedom of the chi-square distribution be "n-1". n is the number of parameters. Since there are 7 parameters in this embodiment, the degrees of freedom are 6. With a probability of 0.999999 and 6 degrees of freedom, the square root of the chi-square distribution is 6.2. This value is rounded to the second decimal place. The square root of the calculated chi-square distribution is used as the threshold. In this case, statistically, it means that 99.9999% of the acceptable MD values ​​are below the threshold. That is, if the MD value exceeds the threshold, the processed product with that MD value is considered unacceptable.

[0075] (Computation Department)

[0076] The calculation unit 52 calculates the MD value of the currently being processed workpiece 10. This MD value is obtained using parameters based on the load current, which is acquired by the first measuring instrument 41 during processing of a specific processing range within the currently being processed workpiece 10. The specific processing range is as described above. As mentioned above, at locations where the processing conditions of the first tool 21 change, the load current acquired by the first measuring instrument 41 will exhibit a particular change. By observing this particular change, it is easy to determine whether the MD value exceeds a threshold. The parameters based on the load current are the same as those used when setting the aforementioned threshold. That is, the parameters based on the load current include the parameters obtained by performing a Fourier transform on the aforementioned load current and the measured value of the load current. In this embodiment, the MD value is obtained using the aforementioned first to seventh parameters. The Fourier transform used to calculate the MD value can be a high-speed Fourier transform. As mentioned above, the calculation time of the high-speed Fourier transform is short. Therefore, during the processing of workpiece 10, it is possible to determine almost in real time whether a qualified product or a defective product has been produced. The calculation result can also be stored in the storage unit 51.

[0077] If the calculated MD value exceeds a threshold, the controller 5 sets the rotation speed of the first motor 31 to zero. If the rotation speed of the first motor 31 becomes zero, the rotation of the workpiece 10 stops in this embodiment. If the calculated MD value exceeds the threshold, a defective product is produced. That is, the workpiece 10 is processed using the damaged first tool 21. By setting the rotation speed of the first motor 31 to zero via the controller 5, the rotation of the workpiece 10 stops. Therefore, after rotation stops, the workpiece 10 is no longer processed using the damaged first tool 21. Thus, the continued production of defective products for which the prescribed processing was not performed is prevented.

[0078] If the calculated MD value is below the threshold, the controller 5 does not change the rotation speed of the first motor 31. In this case, the next workpiece 10 is processed by the first tool 21 that processed the previous workpiece 10 while the first motor 31 is rotating at the same speed as the previous workpiece 10.

[0079] [Control Process]

[0080] Reference Figure 5 The control process of controller 5 will be explained.

[0081] The workpiece 10 is rotated by the motor 3, and the workpiece 10 is processed by the first tool 21.

[0082] In step S1, the first measuring device 41 acquires the load current of the first motor 31.

[0083] In step S2, the calculation unit 52 calculates the MD value of the workpiece 10 currently being processed. This MD value is obtained using the first to seventh parameters based on the acquired load current. Here, the load current acquired during processing of a specific processing range of the workpiece 10 currently being processed is used. In this embodiment, the specific processing range includes the range where the processing conditions of the tool 2 change, i.e., the range constituting the corner 13.

[0084] In step S3, it is determined whether the calculated MD value exceeds the threshold. In this embodiment, the Fourier transform used to calculate the MD value is the High-Speed ​​Fourier Transform.

[0085] If the threshold is exceeded in step S3, in step S4, the controller 5 sets the rotation speed of the first motor 31 to zero. Then, the control ends. The threshold exceeding in step S3 refers to the production of a defective product. That is, the threshold exceeding in step S3 refers to the processing of the workpiece 10 using the damaged first tool 21.

[0086] If the determination in step S3 is negative, the controller 5 does not change the rotation speed of the first motor 31. A negative determination in step S3 indicates that a qualified product has been produced. That is, it means that the workpiece 10 has been processed using a normal first tool 21 without damage. Therefore, the next workpiece is processed by the first tool 21 that processed the previous workpiece 10 at the same rotation speed of the first motor 31. Then, the processing of the next workpiece 10 and steps S1 to S3 are repeated until it is determined that the MD value exceeds the threshold.

[0087] The machining system 1 of this embodiment can immediately reduce the rotation speed of the motor 3 to zero when the MD value exceeds a threshold, i.e., when a defective product is produced, thus suppressing the production of defective products. In particular, since the machining system 1 of this embodiment uses the MD value calculated using the first to seventh parameters based on the load current of the motor 3 to determine whether a defective product has been produced, even a multi-axis lathe can appropriately identify whether a defective product has been produced.

[0088] [Method for manufacturing processed products]

[0089] In the manufacturing method of the processed object in this embodiment, multiple workpieces are processed sequentially using a tool. The processing in this embodiment is finish machining. Unlike this embodiment, the processing can also be rough machining. The processing steps will be described in detail below.

[0090] [Processing Steps]

[0091] A machining operation is performed while measuring the load current of the motor that rotates the tool or workpiece. During this machining operation, if the MD value exceeds a threshold, the motor speed is changed. Specifically, if the MD value exceeds the threshold, the motor speed is set to zero. As described above, the MD value is obtained using the first to seventh parameters based on the load current, which is acquired by the measuring instrument during machining of a specific machining range of the currently being machined workpiece.

[0092] Once the motor stops rotating, the damaged tool is replaced with a new one. Once a new tool is used, the machining of the next workpiece is repeated until the MD value exceeds the threshold. Conversely, if the MD value is below the threshold, the motor speed remains constant. In this case, the next workpiece is machined by the tool that machined the previous workpiece at the same speed as the previous workpiece. The machining of the next workpiece is then repeated until the MD value exceeds the threshold.

[0093] Similar to processing system 1, the processing method of this embodiment can suppress the production of defective products because it can immediately reduce the motor speed to zero when the MD value exceeds the threshold, i.e., when a defective product is produced.

[0094] Variation Example 1

[0095] like Figure 6 As shown, the machining system of Variation 1 differs from the machining system 1 of the above-described embodiment in that the type of machining is rotary machining. Other configurations are the same as those of the machining system 1 of the embodiment. The following description focuses on the differences. Descriptions of identical configurations are omitted. This is also the case in Variation 2, which will be described later. Rotary machining is, for example, milling. The first tool 21 rotates via a first motor (not shown). In this example, the first tool 21 is an end mill. The first tool 21 is driven by a drive mechanism as shown... Figure 6 The arrows indicate forward, backward, and horizontal movement in the up / down and left / right directions. In this machining system, the rotation of the first motor is stopped when the MD value of the load current of the first motor that rotates the first tool 21 exceeds a threshold.

[0096] Variation Example 2

[0097] like Figure 7 As shown, the machining system 1 of Modified Example 2 differs from the machining system 1 of the above-described embodiment in that the machine tool is a two-axis opposed lathe.

[0098] A opposed-axis lathe is a lathe in which a first spindle 101 and a second spindle 102 are opposite to each other. In this example, the rotation axes of the first spindle 101 and the second spindle 102 are offset from each other. In this example, the first tool 21 and the second tool 22 perform the same finishing on different areas of the workpiece 10.

[0099] In this example, the conveyor transports workpiece 10 from the outside of the opposed two-axis lathe to the first chuck 111, from the first chuck 111 to the second chuck 112, and from the second chuck 112 to the outside of the opposed two-axis lathe.

[0100] The machining process for workpiece 10 is as follows. Workpiece 10 is conveyed from outside the opposed twin-axis lathe to the first chuck 111 via a conveyor and held by the first chuck 111. Once workpiece 10 is held by the first chuck 111, the first spindle 101 is rotated by the motor 3. This rotation causes the workpiece 10 held by the first chuck 111 to rotate. The rotating workpiece 10 approaches the first tool 21, and the first tool 21 processes the first recess 10b of the workpiece 10. The first recess 10b is the same as the recess 10a described in Embodiment 1.

[0101] The workpiece 10, processed by the first tool 21, is unloaded from the first chuck 111 via a conveyor. The unloaded workpiece 10 is then conveyed to the second chuck 112 and held there. Then, similarly to the processing of the first recess 10b of the workpiece 10, the second recess 10c of the workpiece 10 held by the second chuck 112 is processed by the second tool 22. The second recess 10c is a recess in the workpiece 10 located opposite to the first recess 10b. The second recess 10c is identical to the first recess 10b. The workpiece 10, processed by the second tool 22, is unloaded from the second chuck 112 via a conveyor and conveyed to the outside of the opposing twin-axis lathe.

[0102] From the moment the workpiece 10, processed by the first tool 21, is unloaded from the first chuck 111 via the conveyor until it is processed by the second tool 22, the next workpiece 10 is conveyed to and held by the first chuck 111 via the conveyor. Then, the processing of the workpiece 10 held by the first chuck 111 and the processing of the workpiece 10 held by the second chuck 112 are performed substantially simultaneously. By repeating the above process, multiple workpieces 10 are processed sequentially.

[0103] In this machining system 1, the rotation of the first motor 31 can be stopped when the MD value of the load current of the first motor 31 that causes the first tool 21 to rotate exceeds a threshold.

[0104] Trial Production Examples

[0105] The threshold is determined as follows. Multiple qualified products are produced by machining the workpieces using normal tools that do not cause damage. Here, the number of qualified products is set to be more than 800 and less than 850. During the machining of a specific machining range for each workpiece, the motor load current is obtained by a measuring device. The specific machining range is set as the range constituting the corner as described above. When creating the unit space, 31 parameters based on the aforementioned load current are selected.

[0106] The first parameter is the effective value of the load current after performing a high-speed Fourier transform.

[0107] The second parameter is the amplitude value of the peak in the Fourier spectrum after performing a high-speed Fourier transform on the above-mentioned load current.

[0108] The third parameter is the peak factor in the Fourier spectrum. The peak factor is the ratio of the amplitude of the peak to the effective value (amplitude of the peak / effective value).

[0109] The fourth parameter is the centroid of the amplitude of the peak in the Fourier spectrum mentioned above.

[0110] The fifth parameter is the centroid of the amplitude of the peak in the range of 10 Hz to 15 Hz of the aforementioned Fourier spectrum.

[0111] The sixth parameter is the centroid of the amplitude of the peak in the range of 15 Hz to 20 Hz of the aforementioned Fourier spectrum.

[0112] The seventh parameter is the centroid of the amplitude of the peak in the range of 22 Hz to 24 Hz of the aforementioned Fourier spectrum.

[0113] The eighth parameter is the centroid of the amplitude of the peak in the range of 25 Hz to 27 Hz of the aforementioned Fourier spectrum.

[0114] The ninth parameter is the centroid of the amplitude of the peak in the range of 28 Hz to 30 Hz of the aforementioned Fourier spectrum.

[0115] The tenth parameter is the centroid of the amplitude of the peak in the range of 31 Hz to 33 Hz of the aforementioned Fourier spectrum.

[0116] The eleventh parameter is the centroid of the amplitude of the peak in the range of 34 Hz ​​to 36 Hz of the aforementioned Fourier spectrum.

[0117] The twelfth parameter is the centroid of the amplitude of the peak in the range of 37 Hz to 39 Hz of the aforementioned Fourier spectrum.

[0118] The thirteenth parameter is the centroid of the amplitude of the peak in the range of 40 Hz to 42 Hz of the aforementioned Fourier spectrum.

[0119] The fourteenth parameter is the centroid of the amplitude of the peak in the range of 79 Hz to 93 Hz of the aforementioned Fourier spectrum.

[0120] The fifteenth parameter is the maximum value of the aforementioned load current.

[0121] The sixteenth parameter is the minimum value of the aforementioned load current.

[0122] The seventeenth parameter is the effective value of the load current mentioned above.

[0123] The eighteenth parameter is the skewness of the load current. Skewness is an indicator of the left-right symmetry of the load current histogram, representing the degree to which the load current histogram deviates from a normal distribution.

[0124] The nineteenth parameter is the kurtosis of the load current. Kurtosis is an indicator of the sharpness of the peaks and the extent of the tail extension of the histogram of the load current; it is a value that indicates how sharp the histogram of the load current is relative to a normal distribution.

[0125] The twentieth parameter is the quantity of the aforementioned load current, 1.

[0126] The twenty-first parameter is the quantity of the aforementioned load current, 2.

[0127] The twenty-second parameter is the quantity of the aforementioned load current, 3.

[0128] The twenty-third parameter is the quantity of the aforementioned load current, 4.

[0129] The twenty-fourth parameter is the presence of the aforementioned load current, 5.

[0130] The twenty-fifth parameter is the quantity of the aforementioned load current, 6.

[0131] The twenty-sixth parameter is the change in the load current mentioned above.

[0132] The twenty-seventh parameter is the change in the load current, 2.

[0133] The twenty-eighth parameter is the change in the load current, which is 3.

[0134] The twenty-ninth parameter is the change in the load current, which is 4.

[0135] The thirtieth parameter is the change in the load current, which is 5.

[0136] The thirty-first parameter is the change in the load current, which is 6.

[0137] The aforementioned quantity refers to the number of data points where the load current exceeds a certain value during the processing time of a specific processing range. For example, if the load current evolves to 7.2A, 7.4A, 7.6A, 7.4A, 7.2A, and a certain value is 7.5A, the number of data points is 1. The number of data points is the total number of data points for each workpiece. For example, in... Figure 3 In this diagram, we assume the processing time for a specific processing range is the time from the left end to the right end of the graph. With a current value of a3, there are 15 data points. With a current value of a4, there are 4 data points. Quantity 1 is the number of data points with a load current exceeding 7.5A. Quantity 2 is the number of data points with a load current exceeding 8A. Quantity 3 is the number of data points with a load current exceeding 8.5A. Quantity 4 is the number of data points with a load current exceeding 9.0A. Quantity 5 is the number of data points with a load current exceeding 9.5A. Quantity 6 is the number of workpieces with a load current exceeding 10A. That is, quantity 1 includes quantities 2 to 6. Similarly, quantity 2 includes quantities 3 to 6. Quantity 3 includes quantities 4 to 6. Quantity 5 includes quantity 6.

[0138] The aforementioned change refers to the number of times the load current crosses a certain value within a specific processing range. For example, the number of times the load current evolves from less than 7.5A to more than 7.5A and the number of times it evolves from more than 7.5A to less than 7.5A are each counted as 1. That is, if, as described above, the number of data points where the load current evolves to 7.2A, 7.4A, 7.6A, 7.4A, 7.2A and the load current exceeds 7.5A is 1, then the number of times the load current crosses 7.5A is 2. For example, in... Figure 3 In this diagram, we assume the processing time for a specific processing range is the time from the left end to the right end of the graph. With a current value of a3, the number of times the current crosses the current threshold is 30. With a current value of a4, the number of times the current crosses the current threshold is 8. Change 1 represents the number of times the load current crosses the current threshold of 7.5A. Change 2 represents the number of times the load current crosses the current threshold of 8A. Change 3 represents the number of times the load current crosses the current threshold of 8.5A. Change 4 represents the number of times the load current crosses the current threshold of 9A. Change 5 represents the number of times the load current crosses the current threshold of 9.5A. Change 6 represents the number of times the load current crosses the current threshold of 10A.

[0139] A unit space for the MT method is created using 31 parameters. The MD value of each acceptable item is then calculated using this unit space. Next, the square root of the chi-square distribution of the MD values ​​of the acceptable items is calculated. The probability of the chi-square distribution is assumed to be 0.999999. The degrees of freedom of the chi-square distribution are 30. The square root of the chi-square distribution, calculated based on this probability and degrees of freedom, is 9.1. This value is rounded to two decimal places. This value is used as the threshold.

[0140] Workpieces are produced by sequentially processing 850 to 900 workpieces using a single tool. These workpieces include both acceptable and unacceptable pieces. The minimum density (MD) value of each workpiece is calculated using the aforementioned 31 parameters. Workpieces are categorized into those with MD values ​​below a threshold and those with MD values ​​exceeding a threshold. As a result, unacceptable pieces were found among the workpieces with MD values ​​below the threshold. Furthermore, acceptable pieces were found among the workpieces with MD values ​​exceeding the threshold.

[0141] Therefore, the process of selecting parameters from 31 parameters, creating unit spaces, setting thresholds, recalculating MD values ​​using the selected parameters, and grouping the processed items based on the thresholds was repeated.

[0142] Specifically, the number of parameters is set to 14. These 14 parameters are the first, second, fourth, fifth, seventh, ninth, tenth, fifteenth, seventeenth, twentieth, twenty-first, twenty-second, twenty-fifth, and thirtieth parameters mentioned above. These 14 parameters are used to create unit space, set thresholds, and group processed items based on the thresholds. The probability of the chi-square distribution is set to 0.999999. The degrees of freedom of the chi-square distribution are 13. The square root of the chi-square distribution, calculated based on this probability and degrees of freedom, is 7.3. This value is rounded to two decimal places. This value is used as the threshold. Even when grouping based on this threshold, similar to the case with 31 parameters, it is impossible to accurately group qualified and unqualified items using the threshold.

[0143] Therefore, the number of parameters is set to 7. These 7 parameters are the first, second, fourth, ninth, tenth, fifteenth, and seventeenth parameters mentioned above. The 7 parameters are used to create unit space, set thresholds, and group processed items based on these thresholds. The probability of the chi-square distribution is set to 0.999999. The degrees of freedom of the chi-square distribution are 6. The square root of the chi-square distribution, calculated based on this probability and degrees of freedom, is 6.2. This value is rounded to the second decimal place. This value is used as the threshold. Grouping based on this threshold reveals that all processed items with an MD value below the threshold are qualified, and all processed items with an MD value exceeding the threshold are unqualified. That is, unqualified items with an MD value below the threshold and qualified items with an MD value exceeding the threshold were not detected.

[0144] The invention is not limited to these examples, but is shown in the claims and is intended to include all modifications with the same meaning and scope as the claims. For example, the above-described processing system and method of manufacturing the workpiece can also be adapted for grooving processes.

[0145] Explanation of reference numerals in the attached figures

[0146] 1: Machining system; 2: Tool; 21: First tool; 22: Second tool; 3: Motor; 31: First motor; 32: Second motor; 4: Measuring device; 41: First measuring device; 42: Second measuring device; 5: Controller; 51: Storage unit; 52: Calculation unit; 10: Workpiece; 10a: Recess; 10b: First recess; 10c: Second recess; 11: Wall surface; 12: Bottom surface; 13: Corner; 100: Spindle; 101: First spindle; 102: Second spindle; 110: Chuck; 111: First chuck; 112: Second chuck.

Claims

1. A processing system comprising: Tools are used to process workpieces; An electric motor that causes the tool or the workpiece to rotate; Controller, controlling the motor; and The measuring device acquires the load current of the motor. If the Mahalanobis distance exceeds a threshold, the processed product with that Mahalanobis distance is determined to be a defective product, and the controller changes the speed of the motor. The Mahalanobis distance is a value calculated using parameters of the motor's load current obtained in advance when producing multiple qualified products by machining the workpiece with the undamaged, normal tool. This load current is acquired by the measuring device within a specific machining range of the workpiece, which includes the areas where the tool's machining conditions change. The parameters based on the load current include parameters obtained by performing a Fourier transform on the load current and the measured value of the load current.

2. The processing system according to claim 1, wherein, The parameters obtained by performing a Fourier transform on the load current include: The effective value of the load current after performing a Fourier transform; The amplitude value of the peak in the Fourier spectrum after performing a Fourier transform on the load current; The centroid of the amplitude of the peak; and The centroid of the amplitude of the peak in a specific frequency range of the Fourier spectrum.

3. The processing system according to claim 1 or 2, wherein, The measured values ​​of the load current include: The maximum value of the load current; and The effective value of the load current.

4. The processing system according to claim 1 or 2, wherein, The number of parameters based on the load current is seven, from the first parameter to the seventh parameter. The first to the fifth parameters are obtained by performing a Fourier transform on the load current. The sixth and seventh parameters are the measured values ​​of the load current.

5. The processing system according to claim 4, wherein, The first parameter is the effective value of the Fourier transform of the load current. The second parameter is the amplitude value of the peak in the Fourier spectrum after performing a Fourier transform on the load current. The third parameter is the centroid of the amplitude of the peak. The fourth parameter is the centroid of the amplitude of the peak in the range of 28 Hz to 30 Hz of the Fourier spectrum. The fifth parameter is the centroid of the amplitude of the peak in the range of 31 Hz to 33 Hz of the Fourier spectrum. The sixth parameter is the maximum value of the load current. The seventh parameter is the effective value of the load current.

6. The processing system according to claim 1 or 2, wherein, The machining system has a multi-axis lathe. The tool is the turning tool provided by the multi-axis lathe.

7. A method for manufacturing a processed product, The method for manufacturing the workpiece includes a step of machining the workpiece with the tool while rotating the tool or workpiece using a motor and measuring the load current of the motor using a measuring instrument. During the processing step, if the Mahalanobis distance exceeds a threshold, the processed product with that Mahalanobis distance is determined to be a defective product, and the motor speed is changed. The Mahalanobis distance is a value calculated using parameters of the motor's load current obtained in advance when producing multiple qualified products by machining the workpiece with the undamaged, normal tool. This load current is acquired by the measuring device within a specific machining range of the workpiece, which includes the areas where the tool's machining conditions change. The parameters based on the load current include parameters obtained by performing a Fourier transform on the load current and the measured value of the load current.

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