Thermal displacement correction device for machine tool

Abstract

In order to improve correction accuracy with respect to thermal displacement in a thermal displacement correction device for a machine tool, a thermal displacement correction device (100) is provided with: temperature sensors (Si) provided at a plurality of locations of an automatic lathe (200); a storage unit (30) that stores a plurality of data tables (31) set in accordance with each of a plurality of different environmental conditions as a correspondence relationship between a temperature distribution of the automatic lathe (200), which is detected by the temperature sensor (Si) in accordance with machining performed under the machining conditions, and a thermal displacement amount of the position of a tool of the automatic lathe (200); a comparison selection unit (20) that selects, from among the plurality of data tables (31) stored in the storage unit (30), a data table (31) having a temperature distribution close to the temperature distribution detected by the automatic lathe (200) during on-site machining; a thermal displacement estimation unit (40) that estimates the amount of thermal displacement on the basis of the selected data table (31) and the detected temperature distribution; and a correction command unit (50) that outputs a thermal displacement correction amount for correcting the position of the tool, said thermal displacement correction amount offsetting the estimated thermal displacement amount.

Description

Technical Field

[0001] The present invention relates to a thermal displacement correction device for a machine tool. Background Art

[0002] In a machine tool, a drive source operates to cause displacement such as rotation and movement of a workpiece and a tool, thereby generating heat in the drive source, a sliding portion, etc. In addition, heat is also generated at the contact portions between the machine tool and the workpiece and the tool. Moreover, these heats cause displacement of various parts of the machine tool through thermal expansion, etc., so that the position of the tool relative to the workpiece changes, which affects the dimensional accuracy of the product obtained by machining the workpiece.

[0003] Therefore, the machine tool is provided with a thermal displacement correction device for suppressing the influence of the displacement caused by this heat. The thermal displacement correction device includes: temperature sensors provided at various parts of the machine tool; a thermal displacement estimation unit that estimates the displacement amount of the position of the tool relative to the position of the workpiece undergoing displacement based on the temperatures respectively detected by these temperature sensors; and a correction instruction unit that outputs a correction instruction to the control unit of the machine tool for correcting the position of the tool in a manner that cancels out the displacement amount estimated by the thermal displacement estimation unit.

[0004] Here, the thermal displacement estimation unit stores the correspondence relationship between the detected temperatures Ti (i = 1, 2, 3,...) and the measured displacement amount (thermal displacement amount) ΔA of the position of the workpiece and the tool as the following multiple regression equation (1), where the detected temperatures Ti (i = 1, 2, 3,...) are the temperatures detected by the respective temperature sensors under various machining conditions (for example, conditions related to the machining process such as the cutting depth, the rotational speed of the workpiece, the feed speed of the tool, etc.) when machining the workpiece in advance.

[0005] ΔA = α1×T1 + α2×T2 + α3×T3 +... (1) The αi (i = 1, 2, 3,...) in formula (1) are coefficients (thermal displacement coefficients) corresponding to the detected temperatures Ti detected by the respective temperature sensors, and are preset to satisfy formula (1) corresponding to various machining conditions.

[0006] Then, the thermal displacement estimation unit estimates the thermal displacement amount ΔA based on the detected temperatures Ti detected by the respective temperature sensors when actually using the machine tool to manufacture a product and the stored formula (1). The output unit of the thermal displacement correction device outputs a correction instruction to the control unit of the machine tool for correcting in a manner that cancels out the thermal displacement amount estimated by the thermal displacement estimation unit. The control unit of the machine tool controls the tool in a manner that corrects the position of the tool relative to the position of the workpiece to cancel out the thermal displacement amount based on the correction instruction output from the correction instruction unit of the thermal displacement correction device, thereby reducing the influence of the thermal displacement on the dimensions of the product obtained by machining with the machine tool (for example, refer to Patent Document 1).

[0007] Prior art documents Patent documents Patent Document 1: Japanese Patent Laid-Open No. 2004-154907 Summary of the invention Problems to be solved by the invention However, the thermal displacement coefficient αi in formula (1) stored in the thermal displacement estimation unit of the thermal displacement correction device is a coefficient set in a state where the machine tool is arranged in a specified environment as a reference. On the other hand, the machine tool is actually installed and used at the site where products are manufactured, so the environment in which the machine tool is installed varies greatly and is sometimes different from the specified environment as a reference.

[0008] Therefore, in order to manufacture products with higher dimensional accuracy in the environment where the machine tool is installed, it is required to improve the correction accuracy of the machine tool for thermal displacement.

[0009] The present invention is proposed in view of the above situation, and its object is to provide a thermal displacement correction device for a machine tool that can improve the correction accuracy for thermal displacement.

[0010] Means for solving the problems The present invention is a thermal displacement correction device for a machine tool, comprising: temperature sensors respectively provided at a plurality of parts of the machine tool; a storage unit storing a plurality of corresponding relationships respectively set corresponding to a plurality of different environmental conditions, as the corresponding relationship between the temperature distribution of the machine tool detected by the temperature sensors corresponding to machining under a preset specified machining condition and the thermal displacement amount of the position of the tool with respect to the workpiece machined by the tool of the machine tool; a comparison and selection unit comparing the temperature distribution of the machine tool detected by the temperature sensors when machining under the environmental conditions where the machine tool is installed with the temperature distribution of the machine tool in the plurality of corresponding relationships stored in the storage unit, and selecting one corresponding relationship closest to the temperature distribution of the machine tool detected under the environmental conditions where the machine tool is installed from the plurality of corresponding relationships stored in the storage unit; a thermal displacement estimation unit estimating the thermal displacement amount under the environmental conditions where the machine tool is installed based on one corresponding relationship selected by the comparison and selection unit and the temperature distribution of the machine tool detected under the environmental conditions where the machine tool is installed; and a correction instruction unit outputting a thermal displacement correction amount for correcting the position of the tool in a manner that cancels the thermal displacement amount estimated by the thermal displacement estimation unit.

[0011] Advantages of the invention According to the thermal displacement correction device for a machine tool of the present invention, the correction accuracy for thermal displacement can be improved. Description of the drawings

[0012] Figure 1is a block diagram showing the structure of the thermal displacement correction device.

[0013] Figure 2 is a perspective view of a lathe in which thermal displacement correction is performed by the thermal displacement correction device.

[0014] Figure 3 is an example showing the correspondence between the elapsed time t and the temperature Ti of each part under the first machining condition K1 shown in Table 1.

[0015] Figure 4 is a flowchart explaining the operation process of the thermal displacement correction device. Detailed Embodiment

[0016] As described below, embodiments of the thermal displacement correction device for a machine tool of the present invention will be described with reference to the accompanying drawings.

[0017] <Structure> Figure 1 is a block diagram showing the structure of the thermal displacement correction device 100, Figure 2 is a perspective view of a lathe 200 in which thermal displacement correction is performed by the thermal displacement correction device 100. The illustrated thermal displacement correction device 100 is an embodiment of the thermal displacement correction device for a machine tool of the present invention, and the lathe 200 is an embodiment of a machine tool to which the thermal displacement correction device for a machine tool of the present invention is applied.

[0018] (Lathe) The lathe 200 is an NC (numerical control) lathe controlled by a computer that operates by reading a prescribed program. As Figure 2 shown, the lathe 200 has a front spindle 210, a rear spindle 220, a turret tool post 230, and a control unit 240 on a base 250. The rear spindle 220 is arranged facing the front spindle 210. The front spindle 210 and the rear spindle 220 can each individually hold a workpiece to be machined and rotate it around an axis, and can also transfer the workpiece to each other.

[0019] The front spindle 210 is provided on a spindle stand 260 provided on the base 250. The rear spindle 220 is provided on a carriage 270 provided on the base 250.

[0020] A plurality of tools for machining a workpiece are provided on the outer peripheral surface of the rotating turret of the turret tool post 230. The turret tool post 230 selects a tool by rotating the turret. And, for the lathe 200, while rotating the workpiece around an axis by the front spindle 210 or the rear spindle 220, the tool selected by the turret tool post 230 is brought into contact with the workpiece, thereby performing machining such as cutting and drilling on the workpiece. The turret tool post 230 is provided on a slide support table 280.

[0021] The control unit 240 controls the positions, movements, speeds, etc. of the front spindle 210, the rear spindle 220, the turret tool rest 230, the carriage 270, and the slide support table 280 by a computer that reads a prescribed program. In addition, the control unit 240 corrects the positions of the front spindle 210, the rear spindle 220, the turret tool rest 230, the carriage 270, and the slide support table 280 according to a correction instruction output from a correction instruction unit 50 of a thermal displacement correction device 100 described later. Further, the automatic lathe 200 has a coolant cooling system (not shown), and the control unit 240 also controls the operation of this cooling system.

[0022] (Thermal Displacement Correction Device) The automatic lathe 200 is provided with a thermal displacement correction device 100. The thermal displacement correction device 100 suppresses the influence of displacement (thermal displacement) caused by heat generated by the automatic lathe 200, and outputs a correction instruction to the control unit 240 of the automatic lathe 200, and this correction instruction is an instruction for correcting the machining point position in a manner that cancels the thermal displacement at the machining point (the point where the tool contacts the workpiece) in the automatic lathe 200.

[0023] As Figure 1 shown, the thermal displacement correction device 100 includes temperature sensors Si (i = 1, 2,..., 8), a storage unit 30, a comparison and selection unit 20, a thermal displacement estimation unit 40, and a correction instruction unit 50.

[0024] As Figure 2 shown, the temperature sensors Si are provided at multiple locations on the automatic lathe 200 (in this embodiment, for example, at 8 locations (i = 1, 2,..., 8)). Specifically, the temperature sensor S1 is provided on the front spindle 210, the temperature sensor S2 is provided on the rear spindle 220, the temperature sensor S3 is provided on the turret tool rest 230, the temperature sensor S4 is provided on the spindle support 260, the temperature sensor S5 is provided on the carriage 270, the temperature sensor S6 is provided on the slide support table 280, the temperature sensor S7 is provided at a position on the base 250 close to the spindle support 260, and the temperature sensor S8 is provided at a position on the base 250 close to the carriage 270, and the temperature of the respective installed locations is detected.

[0025] In addition, when the individual temperature sensors S1, S2,..., S8 are not distinguished in the following description, they are sometimes collectively referred to as the temperature sensor Si.

[0026] The comparison and selection unit 20 compares the temperature distribution (thermal balance) of the automatic lathe 200 detected by eight temperature sensors Si when the automatic lathe 200 actually operates for manufacturing a product with multiple temperature distributions respectively measured when the automatic lathe 200 performs a specified machining operation under a plurality of preset environmental conditions and stored in the storage unit 30 described later, and selects the temperature distribution closest to the temperature distribution when the automatic lathe 200 actually operates from the stored multiple temperature distributions.

[0027] The storage unit 30 stores the above temperature distribution as a data table 31. Specifically, first, the automatic lathe 200 is operated to machine a preset specified workpiece under a plurality of preset machining conditions Kp (p = 1, 2...: for example, conditions related to the machining process of the automatic lathe 200 such as the cutting depth, the rotational speed of the workpiece, the feed speed of the tool, etc.) to manufacture a product with a preset specified shape.

[0028] At this time, the elapsed time t (seconds) from the start of machining of the automatic lathe 200 and the temperature Ti (T1, T2... T8) of each part of the automatic lathe 200 detected by each temperature sensor Si (S1, S2... S8) when machining the workpiece under each machining condition Kp are detected and recorded, and the thermal displacement amount ΔA of the machining point position where the tool of the turret tool rest 230 contacts the workpiece is recorded at this time.

[0029] For example, if the elapsed time t (seconds), the detected temperature Ti (T1, T2... T8) of each part, and the measured thermal displacement amount ΔA of the machining point position when machining the workpiece under the first machining condition K1 are associated, it is as shown in Table 1.

[0030] [Table 1]

[0031] Figure 3 is an example showing the correspondence relationship between the elapsed time t and the temperature Ti of each part under the first machining condition K1 shown in Table 1. The elapsed time t and the temperature Ti of each part under the above first machining condition K1 are, for example, as Figure 3 shown. In addition, Figure 3 is a schematic diagram for simply explaining the relationship between the elapsed time t and the temperature Ti of each part, and does not show the relationship between the actually measured elapsed time t and the temperature Ti of each part.

[0032] In this way, in such a manner that the temperature Ti (T1, T2... T8) of each part and the thermal displacement amount ΔA of the machining point position at each elapsed time t under the first machining condition K1 satisfy the following multiple regression equation (1), the thermal displacement coefficient αi (i = 1, 2, 3...) corresponding to the temperature sensor Si is calculated.

[0033] ΔA = α1×T1 + α2×T2 + …… + α8×T8 (1) The calculation results are shown in Table 2. The set (α1, α2, ……, α8) of the thermal displacement coefficients αi (i = 1, 2, ……, 8) of the temperature sensor Si is associated with the elapsed time t under the first processing condition K1.

[0034] [Table 2]

[0035] Then, using the same workpiece, similarly under other processing conditions Kp (the second processing condition K2, the third processing condition K3, ……), the elapsed time t (seconds), the temperatures Ti (T1, T2, ……, T8) of the detected parts, and the thermal displacement amount ΔA of the measured machining point position are respectively associated, and the thermal displacement coefficient αi (i = 1, 2, 3, ……) corresponding to the temperature sensor Si is calculated in a manner that satisfies the multiple regression equation (1). Similar to Table 2, under each processing condition Kp, the set (α1, α2, ……, α8) of the thermal displacement coefficients αi (i = 1, 2, ……, 8) of the temperature sensor Si is associated with the elapsed time t.

[0036] In the present embodiment, the number p of the processing conditions is, for example, 10 (p = 1, 2, ……, 10), and it can be 1 or more and 9 or less, or 11 or more.

[0037] Next, the environmental conditions Mq corresponding to the on-site environment where the automatic lathe 200 is installed are changed. Under multiple environmental conditions Mq, the temperature Ti and the thermal displacement amount ΔA at each elapsed time t are measured under each of the above processing conditions Kp. Under each processing condition Kp corresponding to each environmental condition Mq, the set (α1, α2, ……, α8) of the thermal displacement coefficients αi (i = 1, 2, ……, 8) of the temperature sensor Si is associated with each elapsed time t.

[0038] Here, the environmental conditions Mq are the conditions assuming the actual on-site environment where the automatic lathe 200 is installed except for the above processing conditions Kp, and in particular, the conditions that affect the thermal displacement of the machining point position of the tool. Specifically, the environmental conditions Mq are the conditions that can change the temperature of the automatic lathe 200, such as the ambient gas temperature (room temperature) at the site where the automatic lathe 200 is installed, local sunlight, and the positional relationship with surrounding heat sources.

[0039] The number q of the preset environmental conditions Mq is, for example, 10, but as long as it is multiple (2 or more), it can be 9 or less, or 11 or more.

[0040] Thus, before the automatic lathe 200 is set in an environment where products are actually manufactured, the automatic lathe 200 is experimentally set in various assumed environmental conditions Mq. The correspondence relationship (as an example, Table 1) between the temperature Ti distribution and the thermal displacement amount ΔA at each part under each of the multiple environmental conditions Mq, under each machining condition Kp obtained by machining the workpiece under various machining conditions Kp, and at each elapsed time t is stored in the storage unit 30 as the data table 31.

[0041] In addition, each data table 31 may also have the correspondence relationship (as an example, Table 2) between the temperature Ti distribution at each part under each of the multiple environmental conditions Mq, under each machining condition Kp obtained by machining the workpiece under various machining conditions Kp, and at each elapsed time t, and the group (α1, α2... α8) of thermal displacement coefficients αi.

[0042] As described above, before the automatic lathe 200 is set at the site where products are actually manufactured, for each environmental condition Mq assuming the site where the automatic lathe 200 is set, multiple data tables 31 are stored in the storage unit 30. When the automatic lathe 200 is set at a specific site for machining the workpiece in order to manufacture products, the comparison selection unit 20 compares the temperature Ti (temperature distribution) of each part of the automatic lathe 200 detected by the 8 temperature sensors Si at a specified elapsed time t with the temperature distribution in the temperature distribution data table 31.

[0043] Then, the comparison selection unit 20 selects from the multiple data tables 31 stored in the storage unit 30 one temperature distribution data table 31 that is closest to the temperature Ti (temperature distribution) actually detected from the automatic lathe 200 set at the specific site, and outputs it together with the actually detected temperature Ti (temperature distribution) to the thermal displacement estimation unit 40.

[0044] The thermal displacement estimation unit 40 uses the group (α1, α2... α8) of thermal displacement coefficients αi of the data table 31 input from the comparison selection unit 20 and the temperature Ti of each part actually detected during operation at the specific site, and uses the multiple regression equation (1) to estimate the thermal displacement amount ΔA of the machining point position in this temperature distribution by calculation, and outputs the estimated thermal displacement amount ΔA to the correction instruction unit 50.

[0045] The correction instruction unit 50 calculates the thermal displacement correction amount for correcting the machining point position of the tool of the automatic lathe 200 to a position that cancels out the thermal displacement amount ΔA input from the thermal displacement estimation unit 40, and outputs this thermal displacement correction amount to the control unit 240 of the automatic lathe 200.

[0046] <Operation> Figure 4is a flowchart showing the operation process of the thermal displacement correction device 100. The thermal displacement correction device 100 of the present embodiment uses Figure 4 The flowchart operates as follows.

[0047] After the automatic lathe 200 is actually installed at the site where products are manufactured by machining workpieces with tools, the automatic lathe 200 is started to operate for machining. The comparison selection unit 20 acquires a specified elapsed time t since the start of machining of the automatic lathe 200 and the temperatures Ti (temperature distribution) of respective parts of the automatic lathe 200 detected by eight temperature sensors Si provided in the automatic lathe 200 (#1).

[0048] The comparison selection unit 20 compares the temperature Ti (temperature distribution) of the automatic lathe 200 at the acquired elapsed time t with the temperature Ti distributions at respective elapsed times t in a plurality of data tables 31 stored in the storage unit 30, and selects a data table with the closest temperature distribution (#2).

[0049] Here, "the closest temperature distribution" can be defined, for example, as follows: among the temperature sensors Si in the data table 31, the number of temperature sensors Si corresponding to temperatures within an approximate range of, for example, ±5 (%) of the acquired respective temperatures Ti is equal to or more than a preset number.

[0050] The approximate range for the acquired respective temperatures Ti is not limited to the above-mentioned ±5 (%) range, and can be a ±10 (%) range, or other preset ranges can also be used. In addition, the number of temperature sensors Si in the approximate range when defining "the closest temperature distribution" can be, for example, 3 or more, and can also be appropriately set to 4 or more, 5 or more, etc.

[0051] In addition, for "the closest temperature distribution", for example, when there is an order of temperature sensors Si regarding the degree of influence of the temperature Ti on the thermal displacement amount ΔA, weighted calculation can be performed in the calculation of the number of temperature sensors Si with a large degree of influence. The specific degree of weighting can be changed according to the on-site environmental conditions where the automatic lathe 200 is installed, etc.

[0052] Based on the group of thermal displacement coefficients αi (α1, α2... α8) of the data table 31 selected by the comparison selection unit 20 and the temperature Ti (temperature distribution) of the automatic lathe 200 at the acquired elapsed time t, the thermal displacement estimation unit 40 estimates the thermal displacement amount ΔA in the state where the automatic lathe 200 is actually used using the multiple regression equation (1) (#3).

[0053] The correction instruction unit 50 calculates a thermal displacement correction amount for correcting the machining point position of the tool of the automatic lathe 200 to a position that cancels out the thermal displacement amount ΔA based on the thermal displacement amount ΔA estimated by the thermal displacement estimation unit 40, and outputs the calculated thermal displacement correction amount to the control unit 240 of the automatic lathe 200 (#4).

[0054] As described in detail above, for the thermal displacement correction device 100 of the automatic lathe 200 of the present embodiment, a data table 31 of thermal displacement coefficients αi and temperatures Ti (temperature distributions) is stored for each of a plurality of environmental conditions assumed for the on-site environment where the automatic lathe 200 is actually installed. The data table 31 with the temperature Ti (temperature distribution) closest to the temperature Ti (temperature distribution) obtained at the actual installation site is used to correct the thermal displacement amount at the site.

[0055] Therefore, it is possible to correct the thermal displacement amount suitable for the on-site environment where the automatic lathe 200 is installed, and it is possible to improve the correction accuracy for thermal displacement.

[0056] For the thermal displacement correction device 100 of the present embodiment, the comparison selection unit 20 selects the data table 31 with the closest temperature distribution, but there may be no data table 31 with a temperature distribution close to the specified one. Therefore, the storage unit 30 stores a set (αs1, αs2... αs8) of reference thermal displacement coefficients αsi (i = 1, 2... 8) corresponding to a preset reference environmental condition K0 as a reference data table. Then, the comparison selection unit 20 selects this reference data table (#2).

[0057] The thermal displacement estimation unit 40 estimates the thermal displacement amount ΔA in the actual use state of the automatic lathe 200 based on the set (αs1, αs2... αs8) of reference thermal displacement coefficients αsi of the reference data table and the obtained temperature Ti (temperature distribution) of the automatic lathe 200 over time t, using the multiple regression equation (1) (#3). The correction instruction unit 50 calculates a thermal displacement correction amount for correcting the machining point position of the tool of the automatic lathe 200 to a position that cancels out the thermal displacement amount ΔA based on the thermal displacement amount ΔA estimated by the thermal displacement estimation unit 40, and outputs the calculated thermal displacement correction amount to the control unit 240 of the automatic lathe 200 (#4).

[0058] When there is no data table 31 with a temperature distribution close to the specified one, the thermal displacement correction device 100 can correct the thermal displacement amount corresponding to the reference environmental condition by applying the set (αs1, αs2... αs8) of thermal displacement coefficients αsi of the reference data table. For a wide variety of environmental conditions, although it may not be the best correction, it is possible to perform a standard correction.

[0059] The thermal displacement correction device 100 of the present embodiment has eight temperature sensors Si (i = 1, 2,..., 8). However, the number of temperature sensors Si is not limited to eight, and may be two or more and seven or less, or may be nine or more. In addition, the location where the temperature sensors Si are provided is not limited to the location of the automatic lathe 200 described in the present embodiment, and may be provided at other locations.

[0060] The thermal displacement correction device 100 of the present embodiment is applied to an automatic lathe 200 having a front spindle 210, a rear spindle 220, and a turret tool rest 230 as an example of a machine tool. However, as the automatic lathe 200, the spindle may be one (only the front spindle), the spindle may also be three or more, and in addition, a comb-type tool rest may be provided instead of the turret tool rest 230.

[0061] The thermal displacement correction device 100 of the present embodiment is applied to the automatic lathe 200 as an example of a machine tool. However, the thermal displacement correction device of the machine tool of the present invention is not limited to being applicable to an automatic lathe, and can be applied to machine tools other than automatic lathes that perform various plastic working on workpieces.

[0062] Cross-reference to related applications This application claims priority based on Japanese Patent Application No. 2022-202074 filed with the Japan Patent Office on December 19, 2022, the entire disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A thermal displacement correction device for a machine tool, characterized in that, comprising: temperature sensors respectively disposed at a plurality of parts of the machine tool; a storage unit storing a plurality of corresponding relationships respectively set corresponding to a plurality of different environmental conditions, as a corresponding relationship between the temperature distribution of the machine tool detected by the temperature sensor corresponding to machining performed under a predetermined machining condition and the thermal displacement amount of the position of the tool with respect to the workpiece machined by the tool of the machine tool; a comparison and selection unit that compares the temperature distribution of the machine tool detected by the temperature sensor when machining is performed under the environmental conditions set in the machine tool with the temperature distribution of the machine tool in the plurality of corresponding relationships stored in the storage unit, and selects one corresponding relationship that is closest to the temperature distribution of the machine tool detected under the environmental conditions set in the machine tool from the plurality of corresponding relationships stored in the storage unit; a thermal displacement estimation unit that estimates the thermal displacement amount under the environmental conditions set in the machine tool based on one corresponding relationship selected by the comparison and selection unit and the temperature distribution of the machine tool detected under the environmental conditions set in the machine tool; and a correction instruction unit that outputs a thermal displacement correction amount for correcting the position of the tool in a manner that cancels the thermal displacement amount estimated by the thermal displacement estimation unit.

2. The thermal displacement correction device for a machine tool according to claim 1, wherein the environmental condition is a condition that affects the temperature of the machine tool in the environment where the machine tool is disposed.

3. The thermal displacement correction device for a machine tool according to claim 1 or 2, wherein the storage unit stores a reference corresponding relationship set corresponding to a reference environmental condition as one of the plurality of corresponding relationships respectively set corresponding to a plurality of different environmental conditions, when there is no corresponding relationship closest to the temperature distribution of the machine tool detected under the environmental conditions set in the machine tool among the plurality of corresponding relationships stored in the storage unit, the comparison and selection unit selects the reference corresponding relationship.

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