Control device for machine tool

Abstract

Provided is a control device for a machine tool, which is capable of performing thread cutting while reducing the load on the machine tool due to a swing operation without prolonging the cycle time, and which is capable of reliably chopping chips when executing a non-swing operation in the current path after the swing operation in the previous path. A control device for a machine tool includes: a swing operation execution determination unit that determines whether or not to execute a swing operation that swings a cutting tool in a radial direction of a workpiece; a swing command generation unit that generates a swing command on the basis of the determination result; and a control unit that generates a drive command by superimposing a swing command on a position command of the feed shaft, a swing operation execution determination unit that determines that a swing operation is executed intermittently, and a swing command generation unit that generates a swing command such that a non-swing cutting portion of a current path includes a swing cutting completed portion of a previous path. Or the swing cutting part of the current path comprises the non-swing cutting completion part of the previous path.

Description

[0001] This application is a divisional application of the patent application filed on September 28, 2020, with application number 2020110421163 and invention name “Machine Tool Control Device”. Technical Field

[0002] The invention relates to a control device for a machine tool. Background Art

[0003] At present, there is a known technique for performing thread cutting while crushing the chips. For example, during a predetermined multiple cutting process, the workpiece and the cutting tool are reciprocated and vibrated, and the vibration mode during each cutting process accompanied by the reciprocating vibration is set so that the cutting process portion during the predetermined cutting process partially includes the portion that has been cut by other cutting processes (for example, refer to Patent Document 1).

[0004] However, in the technology of Patent Document 1, since the reciprocating vibration (hereinafter also referred to as swinging motion) between the workpiece and the cutting tool is always performed during the thread cutting process, the reciprocating vibration places a heavy burden on the machine tool. Therefore, a control device for a machine tool is desired, which can perform thread cutting while reducing the burden on the machine tool caused by the swinging motion without extending the important cycle time during the processing of the machine tool.

[0005] In addition, in the technology of Patent Document 1, due to response delay and the like, the deviation between the position command and the actual position, i.e., the position deviation, is large during the swing operation, thereby causing incomplete cutting (see the following description). Figure 7 ). Therefore, it is currently difficult to achieve chip crushing in the final path finish machining, and a machine tool control device is desired that can effectively crush the chips when performing a non-swinging action of the current path after the swinging action of the previous path, such as in the final path finish machining of thread cutting.

[0006] Patent Document 1: International Publication No. 2016 / 056526 Summary of the invention

[0007] One aspect of the present disclosure is a control device for a machine tool that causes at least one spindle and at least one feed axis to cooperate, and performs thread cutting while the cutting tool radially cuts into the workpiece multiple times. The at least one spindle rotates the cutting tool relative to the workpiece, and the at least one feed axis relatively moves the cutting tool relative to the workpiece. The control device of this machine tool includes: a swing motion execution determination unit that determines whether to execute a swing motion that causes the cutting tool to swing in the radial direction of the workpiece; a swing command generation unit that generates a swing command for the swing motion based on the determination result of the swing motion execution determination unit; and a control unit that overlaps the swing command on the position command of the feed axis to generate a drive command for the feed axis. The swing motion execution determination unit determines to intermittently execute the swing motion, and the swing command generation unit generates a swing command such that the non-swing cutting portion in the current cutting action includes the completed portion of the swing cutting in the previous cutting action, or such that the swing cutting portion in the current cutting action includes the completed portion of the non-swing cutting in the previous cutting action.

[0008] According to the present disclosure, it is possible to provide a control device for a machine tool that can perform thread cutting while reducing the burden on the machine tool caused by the swing motion without extending the cycle time. In addition, it is possible to provide a control device for a machine tool that can effectively break chips when performing a non-swing motion in the current path after a swing motion in the previous path, such as in finish machining in the final path of thread cutting. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a functional block diagram showing the structure of a control device for a machine tool according to one aspect of the present disclosure.

[0010] Figure 2 It shows a screw made by thread cutting.

[0011] Figure 3 It shows a workpiece in thread cutting.

[0012] Figure 4 It is used to explain the operation of thread cutting performed by the control device for a machine tool according to one aspect of the present disclosure.

[0013] Figure 5 It is used to explain the operation of thread cutting performed by the control device for a machine tool according to one aspect of the present disclosure.

[0014] Figure 6 It is used to explain the operation of thread cutting performed by the control device for a machine tool according to one aspect of the present disclosure.

[0015] Figure 7Indicates the finish machining in the final path of the existing thread cutting process.

[0016] Figure 8 Indicates the finish machining in the final path of the thread cutting process performed by the control device of the machine tool according to one aspect of the present disclosure. Detailed Description of the Invention

[0017] Hereinafter, one aspect of the present disclosure will be described in detail with reference to the accompanying drawings.

[0018] The control device of the machine tool according to one aspect of the present disclosure causes at least one main shaft and at least one feed shaft to cooperate with each other, and performs thread cutting by causing a cutting tool to cut into the workpiece multiple times in the radial direction. The at least one main shaft rotates the cutting tool relative to the workpiece, and the at least one feed shaft relatively moves the cutting tool with respect to the workpiece.

[0019] Figure 1 It is a functional block diagram showing the structure of the control device 100 of the machine tool according to one aspect of the present disclosure. As Figure 1 shown, the control device 100 outputs drive commands for causing these shafts to cooperate with each other to the motors 120 that drive at least one main shaft and at least one feed shaft. The at least one main shaft rotates the cutting tool relative to the workpiece, and the at least one feed shaft relatively moves the cutting tool with respect to the workpiece.

[0020] Before describing the structure of the control device 100, refer to Figure 2 and Figure 3 to describe the thread cutting process. Here, Figure 2 indicates the screw 12 formed by the thread cutting process. Figure 3 indicates the workpiece 14 in the thread cutting process.

[0021] As Figure 2 shown, the screw 12 formed by the thread cutting process has a thread groove 10 with a sufficient depth spirally formed on its outer peripheral surface. The control device 100 of the machine tool according to one aspect of the present invention rotates the cutting tool relative to the workpiece and relatively moves the cutting tool with respect to the workpiece to perform cutting, thereby forming the thread groove 10.

[0022] As Figure 3 shown by the arrow P in, the cutting tool 16 performs cutting of the thread groove 10 of the workpiece 14 multiple times on a predetermined trajectory 10a (i.e., the position of the thread groove 10) on the workpiece 14. The trajectory 10a spirally exists on the entire outer peripheral surface of the workpiece 14. Figure 3 is the state just starting the cutting process, and the depth of the thread groove 10 is still shallow. By repeating the cutting process multiple times, the Figure 2 shown deep thread groove 10 is formed, and the final screw 12 is completed.

[0023] In Figure 3 this, the workpiece 14 is mounted on the main shaft 18 and is controlled to rotate in the rotational direction shown by the arrow C. The rotational coordinate axis shown by the arrow C is called the C axis. That is, the C axis is an angular coordinate representing the angle around the main shaft 18.

[0024] The cutting tool 16 moves on the locus 10a on the surface of the rotating workpiece 14 to perform the cutting process of the thread groove 10. Therefore, the cutting tool 16 is controlled to move along the coordinate axis in the length direction of the workpiece 14, that is, the Z axis, synchronously with the rotation of the workpiece 14 in the C axis direction.

[0025] In addition, in each cutting process, the cutting tool 16 gradually moves in the direction perpendicular to the surface of the workpiece 14, that is, in the X axis direction which is the radial coordinate axis. Therefore, the cutting tool 16 is controlled to perform the cutting process at a gradually deeper position relative to the workpiece 14.

[0026] Next, the structure of the control device 100 of the machine tool according to an embodiment of the present disclosure will be described. As Figure 1 shown, the control device 100 includes a swing motion execution determination unit 102, a swing condition calculation unit 104, a swing command generation unit 106, an adder 108, and a control unit 110.

[0027] As the control device 100, for example, a numerical control device is used. This control device 100 is realized, for example, by causing a computer having a CPU, a memory, etc. to read the program of the present embodiment.

[0028] The swing motion execution determination unit 102 determines whether to execute a swing motion that causes the cutting tool 16 to swing in the radial direction (X axis direction) of the workpiece 14. This determination is made based on a machining program input from the outside. The swing motion execution determination unit 102 according to an embodiment of the present disclosure is characterized in that it determines to intermittently execute this swing motion. That is, the swing motion execution determination unit 102 determines the execution of an intermittent swing motion such that a swing motion that causes the cutting tool 16 to reciprocate relative to the workpiece 14 and a non-swing motion that does not perform this reciprocating vibration are alternately repeated. Thereby, within the same machining path, the swing motion and the non-swing motion are alternately repeated.

[0029] Preferably, the swing motion execution determination unit 102 determines the execution of the swing motion such that the swing cutting process is performed at a position different from the completed part of the swing cutting process in the previous cutting-in motion in the current cutting-in motion. Thereby, in the current cutting process, the completed part of the previous cutting process can be more reliably included, so-called idle swings are reliably generated, and the chipping of the chips becomes more reliable.

[0030] In addition, it is preferable that the swing motion execution determination unit 102 determines that after performing the plunge cut based on the swing motion intermittently, a plunge cut without a swing motion is performed in the next path. Thereby, for example, when non-swing cutting is performed in the final path after performing swing cutting, etc., the chips can be reliably shredded. This will be described in detail later.

[0031] In addition, it is preferable that the swing motion execution determination unit 102 determines that in the non-swing cutting unit based on the intermittent swing motion, non-swing cutting is performed until the deviation between the position command and the actual position, that is, the position deviation, becomes equal to or less than a predetermined threshold value. Thereby, in the non-swing cutting unit based on the intermittent swing motion, the chips can be reliably shredded. This will be described in detail later.

[0032] The swing condition calculation unit 104 calculates the conditions for the swing motion output to the swing command generation unit 106 based on at least one of the machining program, machining parameters, and feedback values from the machine tool. For example, as Figure 1 shown, the swing condition calculation unit 104 calculates the interval of the swing motion (the distance between adjacent vertices in the swing waveform described later Figure 4 shown), amplitude, period, and other conditions based on the machining program input from the outside.

[0033] It is preferable that the swing condition calculation unit 104 changes the interval of the above-described swing motion. More specifically, the swing condition calculation unit 104 can change the interval of the swing motion between different machining paths. In addition, the swing condition calculation unit 104 can also change the interval of the swing motion within the same machining path. Alternatively, the swing condition calculation unit 104 can change the interval of the swing motion between different machining paths and change the interval of the swing motion within the same machining path.

[0034] In addition, the swing condition calculation unit 104 can also change the interval of the swing motion according to the diameter of the workpiece 14. For example, the smaller the diameter of the workpiece 14 becomes, that is, the more the number of cutting operations increases, the longer the interval of the swing motion is made. Or conversely, the smaller the diameter of the workpiece 14 becomes, that is, the more the number of cutting operations increases, the shorter the interval of the swing motion is made. The setting of the interval of this swing motion will be described in detail later.

[0035] The swing command generation unit 106 generates a swing command for the swing motion based on the determination result of the swing motion execution determination unit 102. Additionally, the swing command generation unit 106 generates a swing command for the swing motion according to the swing conditions calculated by the swing condition calculation unit 104. The swing command generation unit 106 in one embodiment of the present disclosure generates a swing command such that the non-swing cutting portion in the current plunge motion includes the completed swing cutting portion in the previous plunge motion. Alternatively, the swing command generation unit 106 generates a swing command such that the swing cutting portion in the current plunge motion includes the completed non-swing cutting portion in the previous plunge motion. Thereby, so-called idle swings can be more reliably generated, and the chips can be more reliably shredded.

[0036] The adder 108 calculates the position deviation, which is the difference between the position feedback obtained from the position detection of an encoder (not shown) provided in the motor 120 and the position command of the feed axis. The position command of the feed axis and the position deviation are input to the control unit 110 described later.

[0037] The control unit 110 generates a drive command for the motor 120 used to drive the feed axis by superimposing the swing command generated by the swing command generation unit 106 on the position command of the feed axis and the position deviation. Additionally, in one embodiment of the present disclosure, a position command for the transfer axis is temporarily generated, and the generated position command is superimposed with the swing command. However, it is not limited thereto, and the position command of the feed axis may also be generated by superimposing the swing command in advance.

[0038] Next, Figures 4 - 6 The operation of thread cutting of the control device 100 of the machine tool according to one embodiment of the present disclosure will be described in detail. Here, Figures 4 - 6 is used to illustrate the operation of thread cutting performed by the control device 100 of the machine tool according to one embodiment of the present disclosure. These figures correspond to observing part A in the Z-axis direction from the cutting start side. Figure 3 More specifically, Figure 4 shows an example when the interval of the swing motion of each machining path (hereinafter simply referred to as the path) is fixed. Figure 5 shows an example where the smaller the diameter of the workpiece 14, the longer the interval of the swing motion. Figure 6 shows an example when the swing motion of each path is not in the direction of plunging into the workpiece 14 but in the direction of moving away from the workpiece 14.

[0039] Additionally, the C-axis, Z-axis, and X-axis in Figure 3 are used with the same definitions as the C-axis, Z-axis, and X-axis in Figures 4 - 6 Additionally, in Figures 4 - 6In the figure, the part circled by a dotted line is the part that includes the completed part of the previous cutting process in the current cutting process, indicating the part where so-called idle running occurs to break the chip into pieces.

[0040] In Figure 4 In the illustrated operation example, any one of the first path to the fourth path performs an intermittent swinging operation, alternately repeating a linear non-swinging cutting process and a curved deep-cutting swinging cutting process. In addition, in any one of the first path to the fourth path, the Figure 4 interval L of the illustrated swinging operation is set to be fixed. Regarding the final path, since it is a finishing process, it is only a non-swinging cutting process without swinging, and all become linear cutting processes.

[0041] Here, regarding the interval L of the swinging operation, that is, Figure 4 the distance between adjacent vertices in the illustrated swinging waveform, it can be set according to the allowable length of the chip. The allowable length of the chip is set to a length that does not cause the chip to entangle the cutting tool 16 or the like and does not interfere with the cutting process. Thus, the chip can be broken into pieces within the range that does not interfere with the cutting process. Regarding the allowable chip length, it can be specified by G-code or parameters, etc., and thus the interval L of the intermittent swinging operation can be specified.

[0042] In Figure 5 the illustrated operation example, similar to the Figure 4 illustrated operation example, any one of the first path to the fourth path performs an intermittent swinging operation, alternately repeating a linear non-swinging cutting process and a curved deep-cutting swinging cutting process. However, as Figure 5 shown, the interval of the swinging operation is made different between each of the first path to the fourth path. Regarding the final path, since it is a finishing process, it is only a non-swinging cutting process without swinging, and all become linear cutting processes.

[0043] Specifically, the smaller the diameter of the workpiece 14 becomes, that is, as the cutting process progresses, the interval of the swinging operation is set to be longer. Therefore, as Figure 5 shown, the interval L2 of the swinging operation of the fourth path is set to be longer than the interval L1 of the swinging operation of the first path. Thus, the more the number of cutting processes increases, the shorter the circumference of the workpiece 14 becomes, and by extending the interval of the swinging operation, the length of the chip can be kept fixed.

[0044] In Figure 6 the illustrated operation example, similar to the Figure 4Similarly to the illustrated operation example, any one of the first to fourth paths performs an intermittent swinging operation, alternately repeating linear non-swinging cutting and curvilinear swinging cutting. Further, in any one of the first to fourth paths, the interval L of the swinging operation is set to be fixed. However, the swinging operation of any one of the first to fourth paths is in the direction away from the workpiece 14 rather than the direction of cutting into the workpiece 14. That is, the direction of swinging is opposite to that of the operation example of Figure 4 Similarly to the illustrated operation example, the interval L of the swinging operation is set to be fixed. However, the swinging operation of any one of the first to fourth paths is in the direction away from the workpiece 14 rather than the direction of cutting into the workpiece 14. That is, compared with the operation example of Figure 4 or Figure 5 , the direction of swinging is reversed.

[0045] Here, as shown in Figure 4 and Figure 5 , in the case of performing a swinging operation in the direction of cutting into the workpiece 14, in order to determine the swinging amplitude so that the cutting completion part of the current path is included in the cutting of the next path, since the cutting depth of the next path depends on the swinging amplitude of the current path, it is necessary to pre-read the machining program by a control device 100 such as a numerical control device. In contrast, as in the operation example of Figure 6 , the direction of swinging is reversed, so that the swinging amplitude of the next path does not depend on the swinging amplitude of the current path, and thus it is not necessary to pre-read the machining program by a control device 100 such as a numerical control device.

[0046] Next, with reference to Figure 7 and Figure 8 , the finish machining in the final path of the thread cutting performed by the control device 100 of the machine tool according to an aspect of the present disclosure will be described in detail. Here, Figure 7 represents the finish machining in the final path of the existing thread cutting. Figure 8 represents the finish machining in the final path of the thread cutting performed by the control device 100 of the machine tool according to an aspect of the present disclosure. Further, the C-axis, Z-axis, and X-axis in Figure 3 are used with the same definitions as the C-axis, Z-axis, and X-axis in Figure 7 and Figure 8 . Further, the portion circled by the dashed line in Figure 8 is the portion that includes the cutting completion part of the previous cutting in the current cutting, and represents the portion where a so-called idle swing occurs to break the chips.

[0047] In the existing thread cutting, when a swinging cutting-in operation is performed in the path immediately before the final path and then a non-swinging cutting-in operation is performed in the final path, originally as in Figure 7As shown by the dashed line 72 in [reference], there are places where the machined part in the final path includes the machined completed part in the previous path of the final path (i.e., where the dashed line 72 overlaps with the straight line of the final path. The trough part of the dashed line 72, which is the so-called idle swing part.), and the chips should be chopped. However, in reality, as Figure 7 shown by the solid line 71 in [reference], since there are no places where the machined part in the final path includes the machined completed part in the previous path of the final path (i.e., where the solid line 71 overlaps with the straight line of the final path.), sometimes the chips cannot be chopped. This is caused by the deviation between the position command and the actual position during the swing motion, i.e., the position deviation.

[0048] In contrast, in one aspect of the present disclosure, ideally, as Figure 8 shown by the dashed line 82 in [reference], there are places where the machined part in the final path includes the machined completed part in the previous path of the final path, and in fact, as Figure 8 shown by the solid line 81 and the dashed line surrounded by a circle in [reference], there are places where the machined part in the final path includes the machined completed part in the previous path of the final path, and the chips are chopped. This is because by setting the swing motion and the non-swing motion within the same path, the position deviation converges during the non-swing motion. Thus, the chips can be chopped effectively in the final path.

[0049] In addition, it is also possible to simply use a value determined in advance by time or distance to determine the period of the non-swing motion, or it can also be determined based on whether the above-mentioned position deviation is below a predetermined threshold. In the above description, the finish machining in the final path of the thread cutting process is taken as an example, but it is not limited thereto, and it can be said to be the same for all cases where a non-swing cutting action is performed in the next path after a cutting action with swing.

[0050] In summary, according to one aspect of the present disclosure, the following effects are achieved.

[0051] (1) The control device 100 of the machine tool causes at least one spindle 18 to cooperate with at least one feed axis, and performs thread cutting while cutting into the workpiece 14 multiple times in the radial direction (X direction) with the cutting tool 16. The at least one spindle 18 rotates the cutting tool 16 relative to the workpiece 14, and the at least one feed axis relatively moves the cutting tool 16 relative to the workpiece 14. In this machine tool control device 100, there are provided: a swing motion execution determination unit 102 that determines whether to execute a swing motion for swinging the cutting tool 16 in the radial direction (X direction) of the workpiece 14; a swing command generation unit 106 that generates a swing command for the swing motion based on the determination result of the swing motion execution determination unit 102; and a control unit 110 that overlaps the swing command with the position command of the feed axis to generate a drive command for the feed axis. Moreover, the swing motion execution determination unit 102 determines to intermittently execute the swing motion, and the swing command generation unit 106 is configured to generate a swing command such that the non-swing cutting part in the current cutting-in motion includes the completed part of the swing cutting in the previous cutting-in motion, or the swing cutting part in the current cutting-in motion includes the completed part of the non-swing cutting in the previous cutting-in motion.

[0052] Thus, by intermittently performing the swing motion, it is possible to surely break up the chips without extending the cycle time compared with the prior art. In addition, the number of swing motions can be reduced, so the burden on the machine tool caused by the swing motion can be alleviated.

[0053] In addition, in the prior art, due to a large position deviation generated during the swing motion due to response delay or the like, there may be a case where incomplete cutting occurs and the chips cannot be broken up. However, according to the present disclosure, since the position deviation converges during the non-swing motion, the chips can be surely broken up when the non-swing motion of the current path is executed after the swing motion of the previous path.

[0054] (2) The swing motion execution determination unit 102 is configured to determine the execution of the swing motion such that the swing cutting is performed at a position different from the completed part of the swing cutting in the previous cutting-in motion in the current cutting-in motion.

[0055] Thus, in the current cutting process, the completed part of the previous cutting process can be more surely included, so-called idle swings can be more surely generated, and the chips can be more surely broken up.

[0056] (3) A swing condition calculation unit 104 is further provided. The swing condition calculation unit 104 calculates the conditions for the swing motion output to the swing command generation unit 106 based on at least one of the machining program, machining parameters, and feedback values from the machine tool, and the swing condition calculation unit 104 changes the interval of the swing motion.

[0057] Accordingly, conditions such as the interval, amplitude, and period of the swinging motion can be calculated, and the chips can be chopped more effectively. In particular, by changing the interval of the swinging motion, the length of the chips can be adjusted.

[0058] (4) The swinging condition calculation unit 104 is configured to change the interval of the swinging motion between different machining paths. Accordingly, the chips can be chopped more effectively, and the length of the chips can be adjusted.

[0059] (5) The swinging condition calculation unit 104 is configured to change the interval of the swinging motion within the same machining path. Accordingly, the chips can be chopped more effectively, and the length of the chips can be adjusted.

[0060] (6) The swinging condition calculation unit 104 is configured to change the interval of the swinging motion according to the diameter of the workpiece 14.

[0061] Accordingly, as the number of cutting operations increases, the circumference of the workpiece 14 becomes shorter, the diameter of the workpiece 14 becomes smaller, and the interval of the swinging motion is made longer, so that the length of the chips can be kept constant, and thus smooth thread cutting can be performed more efficiently.

[0062] (7) The swinging motion execution determination unit 102 is configured to determine that after the plunge cut based on the swinging motion is intermittently performed, a plunge cut without the swinging motion is performed in the next path.

[0063] Accordingly, when non-swing cutting is performed in the next path after the swing cutting, the chips can be chopped effectively. For example, in the finish machining of the final path, the chips can also be chopped effectively.

[0064] (8) The swinging motion execution determination unit 102 is configured to determine that in the non-swing cutting unit based on the intermittent swinging motion, non-swing cutting is performed until the position deviation becomes equal to or less than a predetermined threshold.

[0065] Accordingly, in the non-swing cutting unit based on the intermittent swinging motion, the chips can be chopped more effectively.

[0066] In addition, the present invention is not limited to the above-described embodiments, and includes variations and improvements within the scope that can achieve the object of the present invention.

[0067] Description of reference numerals

[0068] 10: Thread groove; 12: Screw; 14: Workpiece; 16: Cutting tool; 18: Spindle; 100: Control device; 102: Swing action execution determination unit; 104: Swing condition calculation unit; 106: Swing command generation unit; 108: Adder; 110: Control unit; 120: Motor; X: X-axis; Z: Z-axis; C: C-axis; L, L1, L2: Intervals of swing actions.

Claims

1. A control device for a machine tool, wherein at least one spindle and at least one feed axis cooperate to perform thread cutting by a cutting tool while cutting into a workpiece multiple times in a radial direction, wherein the at least one spindle causes the cutting tool and the workpiece to rotate relative to each other, and the at least one feed axis causes the cutting tool to move relative to the workpiece, It is characterized in that The control device of the machine tool includes a swing operation execution determination unit for determining whether to execute a swing operation for swinging the cutting tool in a radial direction of the workpiece. The swing operation execution determination unit determines that, after the cutting by the swing operation is intermittently performed, the cutting without the swing operation is performed in the next path.

2. The control device for a machine tool according to claim 1, It is characterized in that The oscillation operation execution determination unit determines that the non-oscillation cutting process is to be executed in the non-oscillation cutting process unit based on the intermittent oscillation operation until the position deviation becomes equal to or smaller than a predetermined threshold value.

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