Numerical control device, numerical control method, and numerical control program

Abstract

A numerical control device (1) controls a machine tool (10) so as to perform machining, in a state in which a pressing part (41) of the machine tool (10) is pressed against a machining target (W) along a predetermined axis (X) by torque control, while moving the machining target (W) in a direction along the axis (X). The numerical control device (1) is provided with at least one memory (3) and at least one processor (4). The memory (3) stores an allowable range of a relative physical quantity relating to relative movement in the axis (X) direction of the pressing part (41) with respect to the machining target (W). The processor (4) acquires a first physical quantity relating to movement in the axis (X) direction of the machining target (W) and a second physical quantity relating to movement in the axis (X) direction of the pressing part (41), and compares a difference between the first physical quantity and the second physical quantity with the allowable range.

Description

Numerical control device, numerical control method, and numerical control program

[0001] The present disclosure relates to a numerical control device, a numerical control method, and a numerical control program.

[0002] There is known a machine tool that performs machining by rotating a workpiece around its axis while pressing a tailstock against the workpiece supported by a spindle that can rotate about its axis from the opposite side of the spindle with a constant force (see, for example, Patent Document 1).This type of machine tool detects an abnormality in the contact point between the workpiece and the tailstock due to deformation of the workpiece, wear of the tailstock, etc., by determining whether the position of the tailstock during machining is deviated from the position of the tailstock before machining.

[0003] Japanese Patent Application Laid-Open No. 2000-153431

[0004] However, when a tailstock such as the above is used on a machine tool such as an automatic lathe that processes a workpiece by not only rotating it around its axis but also moving it in the axial direction, the tailstock must also follow the axial movement of the workpiece, and therefore the above-mentioned method of detecting an abnormality in the contact point between the workpiece and the tailstock based on the deviation of the tailstock position during processing from the position of the tailstock before processing cannot be applied.

[0005] Therefore, even when a member such as a tailstock is pressed along the axis of a workpiece being machined while it is moved in a predetermined axial direction, it is desirable to be able to accurately detect abnormalities in the contact point between the workpiece and the member pressed against the workpiece.

[0006] One aspect of the present disclosure is a numerical control device that controls a machine tool so that a pressing part of the machine tool is pressed against a workpiece along a predetermined axis by torque control, and the workpiece is machined while being moved in a direction along the axis, the numerical control device comprising at least one memory and at least one processor, wherein the memory stores an allowable range of a relative physical quantity related to the relative axial movement of the pressing part with respect to the workpiece, and the processor acquires a first physical quantity related to the axial movement of the workpiece and a second physical quantity related to the axial movement of the pressing part, and compares a difference between the first physical quantity and the second physical quantity with the allowable range.

[0007] 5 is a schematic diagram showing the configuration of a numerical control device according to an embodiment of the present disclosure, and a machine tool to which the numerical control device is applied. FIG. 1 is a diagram showing information stored in a memory of the numerical control device shown in FIG. 1. FIG. 2 is a block diagram conceptually dividing the configuration of the numerical control device shown in FIG. 1 based on each function. FIG. 3 is a flowchart explaining a numerical control method using the numerical control device shown in FIG. 1. FIG. 4 is a schematic diagram showing a state in which a workpiece set on the machine tool shown in FIG. 1 is deformed. FIG. 5 is a graph showing the positions of the workpiece and center in the state of FIG. 5, and the relative position of the center with respect to the workpiece. FIG. 6 is a schematic diagram showing a state in which the center has separated from the workpiece set on the machine tool shown in FIG. 1. FIG. 7 is a graph showing the positions of the workpiece and center in the state of FIG. 7, and the relative position of the center with respect to the workpiece. FIG. 8 is a schematic diagram showing a state in which the tip of the workpiece set on the machine tool shown in FIG. 1 is worn.

[0008] A numerical control device 1, a numerical control method, and a numerical control program according to an embodiment of the present disclosure will be described below with reference to the drawings. The numerical control device 1 according to this embodiment is, for example, a device for controlling the operation of a machine tool 10, such as an automatic lathe, that processes a workpiece (a workpiece) W, as shown in FIG.

[0009] 1 , machine tool 10 includes a bed 20, a headstock 30, a tailstock 40, and a tool unit 50. The headstock 30 is disposed on the upper surface of the bed 20, and includes a chuck 31 that grips the outer peripheral surface of a cylindrical workpiece W, and a spindle 32 that rotates the workpiece W gripped by the chuck 31 about axis X. The headstock 30 also includes a spindle moving unit 33 that supports the spindle 32 so that it can move in a direction along axis X. In other words, the headstock 30 supports the workpiece W so that it can rotate about axis X and move translationally in the direction of axis X.

[0010] The tailstock 40 is disposed on the upper surface of the bed 20 on the opposite side of the headstock 30 with the workpiece W in between. The tailstock 40 includes a conical center (pressing portion) 41 having an apex, and a movable portion 42 to which the center 41 is attached, with the apex facing the tip of the workpiece W. The tailstock 40 also includes a linear motion mechanism 43 that moves the movable portion 42 to which the center 41 is attached along the direction of the axis X.

[0011] The linear motion mechanism 43 includes a servo motor 43 a, a ball screw 43 b connected to the rotation shaft of the servo motor 43 a and supported rotatably about an axis parallel to the axis X, and a nut (not shown) fixed to the movable part 42. The ball screw 43 b is engaged with the nut, and rotation of the ball screw 43 b about its axis causes the movable part 42 to which the nut is fixed to move linearly along the axis X. In other words, the movable part 42 supports the center 41 so that the apex of the center 41 moves on the axis X.

[0012] Furthermore, the servo motor 43a is torque controlled by the numerical control device 1, which will be described later, to cause the movable part 42 to follow the movement of the workpiece W in the direction of the axis X, and press the apex of the center 41 with a predetermined force against the tip of the workpiece W. As a result, the workpiece W being machined is supported by being pressed from both sides in the direction of the axis X by the spindle 32 and the apex of the center 41, thereby stabilizing the rotation of the workpiece W about the axis X.

[0013] The tool unit 50 is supported on the bed 20 by a support member (not shown), and includes a main body 51 that is movable in the radial direction of the workpiece W, and a tool 52 attached to the tip of the main body 51. The operation of the main body 51 causes the tip of the tool 52 to come into contact with the outer peripheral surface of the workpiece W that is rotating around the axis X, thereby cutting the workpiece W.

[0014] 1 and 2, the numerical control device 1 includes an input device 2, a memory 3 having a volatile storage medium 3a such as RAM and a non-volatile storage medium 3b such as ROM, HDD, or SSD, and at least one processor 4 such as a CPU. In addition, a display device 5, which is an external device, is connected to the numerical control device 1.

[0015] The input device 2 is configured by, for example, a keyboard, a touch panel, a serial interface such as USB, or a combination of these, and accepts input of various information by a user. Specifically, the input device 2 accepts input for setting a machining program P for numerically controlling the machine tool 10 and performing predetermined machining on the workpiece W. The input device 2 also accepts input of an allowable range A for the relative position (relative physical quantity) between the position (first physical quantity) of the tip of the workpiece W moving in the direction of the axis X and the position (second physical quantity) of the apex of the center 41 that follows the movement of the workpiece W.

[0016] 2, for example, the volatile storage medium 3a of the memory 3 stores the machining program P and the tolerance range A received by the input device 2. On the other hand, the non-volatile storage medium 3b of the memory 3 stores a system program p1, an application program p2, a torque control program p3, and an abnormality detection program (numerical control program) p4 in advance.

[0017] The machining program P is a numerical control program in which a plurality of operation commands are arranged in order of execution to control the operation of each part of the machine tool 10 required to machine the workpiece W. The system program p1 and the application program p2 are core programs that perform the basic functions of the numerical control device 1.

[0018] The torque control program p3 is a program for controlling the torque of the servo motor 43a of the tailstock 40. Specifically, the torque control program p3 is a program for causing the servo motor 43a that controls the center 41 to output a predetermined torque.

[0019] The abnormality detection program p4 is a program for detecting an abnormality in the contact point between the workpiece W and the center 41 that is pressed against the workpiece W by torque control. The abnormality detection program p4 acquires the position of the tip of the workpiece W moving in the direction of the axis X and the position of the apex of the center 41 that follows the workpiece W by torque control. In this case, the position of the tip of the workpiece W can be acquired from a control command that operates the workpiece W by the machining program P. In addition, the position of the apex of the center 41 can be acquired based on feedback information from an encoder (not shown) provided on the servo motor 43a. Furthermore, the abnormality detection program p4 calculates the relative position of the center 41 with respect to the workpiece W based on the acquired positions of the workpiece W and the center 41, and determines whether the relative position exceeds the tolerance range A.

[0020] The processor 4 reads and executes a machining program P from the volatile storage medium 3a of the memory 3 in accordance with a system program p1 and an application program p2 stored in the nonvolatile storage medium 3b of the memory 3. In conjunction with the execution of the machining program P, the processor 4 also executes a torque control program p3 and an abnormality detection program p4.

[0021] 3 shows a block diagram in which the numerical control device 1 is conceptually subdivided based on the contents of various programs stored in the memory 3 and executed by the processor 4. The control contents of the numerical control device 1 will be explained in more detail below using the block diagram shown in FIG.

[0022] First, the numerical control device 1 can be considered to include the input device 2, a torque control unit 61, a workpiece information acquisition unit 62, a center information acquisition unit 63, and a determination unit 64. In this case, the torque control unit 61 is a conceptual functional block based on the function achieved by the processor 4 executing the torque control program p3. The torque control unit 61 causes the servo motor 43a to output a predetermined torque.

[0023] The workpiece information acquisition unit 62 is a conceptual functional block based on the function achieved by executing the abnormality detection program p4 by the processor 4. The workpiece information acquisition unit 62 analyzes the operation commands for the workpiece W included in the machining program P and acquires time-series data on the position of the workpiece W during machining.

[0024] The center information acquisition unit 63 is a conceptual functional block based on the function achieved by executing the abnormality detection program p4 by the processor 4. The center information acquisition unit 63 acquires the position of the center 41 during machining of the workpiece W based on information fed back at a predetermined sampling period from an encoder provided on the servo motor 43 a of the tailstock 40. In other words, the center information acquisition unit 63 acquires the position of the center 41 at each sampling period of the encoder.

[0025] The determination unit 64 is a conceptual functional block based on the function achieved by the processor 4 executing the abnormality detection program p4. The determination unit 64 compares the positions of the workpiece W and the center 41 at corresponding times and calculates the relative position of the center 41 with respect to the workpiece W. The determination unit 64 also compares the calculated relative position with the allowable range A stored in the memory 3, and if the relative position deviates from the allowable range A, determines that there is an abnormality at the contact point between the workpiece W and the center 41. The determination unit 64 then transmits a signal according to the determination result to the display device 5.

[0026] The display device 5 is, for example, a monitor device, and displays text or the like based on the signal sent from the determination unit 64. That is, the display device 5 notifies the user whether or not there is an abnormality in the contact point between the work W and the center 41.

[0027] A numerical control method using the numerical control device 1 according to this embodiment configured as described above will be described below. The following describes the abnormality detection program p4 that is executed when the numerical control device 1 executes the machining program P and the torque control program p3 and causes the machine tool 10 to machine the workpiece W. The following description will also be made using the block diagram shown in FIG. 3 and the flowchart shown in FIG. 4.

[0028] First, the user operates the input device 2 to input the machining program P along with the tolerance A, and stores them in advance in the memory 3. In this state, when the machining program P is executed by the numerical control device 1, the servo motor 43a of the tailstock 40 is torque-controlled, and the apex of the center 41 is pressed against the tip of the workpiece W with a predetermined force. Next, the numerical control device 1 controls the spindle 32 to rotate the workpiece W around the axis X. Furthermore, the numerical control device 1 controls the main body 51 of the tool unit 50 to press the tip of the tool 52 against the outer peripheral surface of the workpiece W, while controlling the spindle moving unit 33 to move the workpiece W in the direction of the axis X. This starts cutting the workpiece W in accordance with the machining program P.

[0029] At this time, the numerical control device 1 executes the abnormality detection program p4 simultaneously with the execution of the machining program P. This causes the workpiece information acquisition unit 62 to extract control commands for the operation of the spindle movement unit 33 in accordance with the machining program P. Then, the workpiece information acquisition unit 62 acquires time-series data on the position of the tip of the workpiece W in the direction of the axis X based on the extracted control commands (step S1).

[0030] The center information acquisition unit 63 also acquires, at every predetermined sampling period, information indicating the rotational position of the servo motor 43 a, which is fed back from an encoder provided in the servo motor 43 a of the tailstock 40. Then, every time the center information acquisition unit 63 acquires feedback information from the encoder of the servo motor 43 a, it calculates the position of the apex of the center 41 in the direction of the axis X based on the feedback information (step S2).

[0031] Next, every time the center information acquisition unit 63 acquires the position of the apex of the center 41, the determination unit 64 extracts the corresponding position of the tip of the workpiece W from the time-series data acquired by the workpiece information acquisition unit 62 and calculates the difference between the two. That is, the determination unit 64 calculates the relative position of the apex of the center 41 with respect to the tip of the workpiece W for each sampling period of the encoder provided in the servo motor 43a (step S3).

[0032] Furthermore, the determination unit 64 compares the calculated relative position with the allowable range A stored in the memory 3, and determines whether the calculated relative position deviates from the allowable range A (step S4). If the result of the determination is that the calculated relative position does not deviate from the allowable range A, the execution of the machining program P and the torque control program p3 continues.

[0033] On the other hand, if it is determined that the relative position is outside the allowable range A, the determination unit 64 determines that the center 41 is not pressed against the workpiece W at an appropriate position and that there is an abnormality in the contact point between them. Then, the determination unit 64 stops the machining program P and torque control program p3 that are being executed, and interrupts machining (step S5).

[0034] The determination unit 64 then determines whether the relative position exceeds the upper limit of the allowable range A or falls below the lower limit of the allowable range A. That is, the determination unit 64 determines the direction in which the center 41 deviates from the allowable range A (step S6). For example, if the direction in which the center 41 is pressed against the workpiece W is defined as the positive direction, and the relative position exceeds the upper limit of the allowable range A, it is determined that the center 41 is pressed too far against the workpiece W. On the other hand, if the relative position falls below the lower limit of the allowable range A, it is determined that the center 41 is separated from the workpiece W. The determination unit 64 then transmits a signal to the display device 5 according to the determined direction in which the center 41 deviates from the allowable range A.

[0035] The display device 5 displays different text on the display screen depending on the type of signal received from the determination unit 64. For example, if it is determined that the center 41 is pressed too hard against the workpiece W, the display device 5 displays text indicating that the workpiece W may be buckled or that the workpiece W or the center 41 may be worn (step S7). On the other hand, if the center 41 deviates from the allowable range A in the direction away from the workpiece W, the display device 5 displays text indicating that the center 41 is away from the workpiece W (step S8).

[0036] Here, the determination of an abnormality in the contact point between the workpiece W and the center 41 by the determination unit 64 will be described in more detail using the abnormal states illustrated in Figures 5 to 8. For example, when the workpiece W buckles in the direction of the axis X as shown in Figure 5, the position of the tip of the workpiece W becomes closer to the spindle 32 than it should be. Therefore, the position of the apex of the torque-controlled center 41 also becomes closer to the spindle 32.

[0037] 6, the workpiece information acquisition unit 62 acquires the position of the tip of the workpiece W based on the machining program P, which differs from the actual position of the tip of the workpiece W. Meanwhile, the center information acquisition unit 63 acquires the actual position of the apex of the center 41, which has been brought closer to the spindle 32 due to buckling of the workpiece W. Therefore, the relative position of the center 41 with respect to the workpiece W calculated by the determination unit 64 increases sharply at the time when the workpiece W buckles, and deviates from the upper limit of the allowable range A. As a result, the determination unit 64 determines that the center 41 being machined is pressed against the workpiece W more than it should be, and detects that there is an abnormality in the contact point between the workpiece W and the center 41.

[0038] On the other hand, as shown in Fig. 7, if the workpiece W and the center 41 become separated during machining, the position of the apex of the center 41 acquired by the center information acquisition unit 63 will be farther from the workpiece W than it should be. Therefore, as shown in Fig. 8, the relative position of the center 41 calculated by the determination unit 64 will suddenly decrease and fall below the lower limit of the allowable range A at the time the center 41 becomes separated from the workpiece W. As a result, the determination unit 64 determines that the center 41 is separated from the workpiece W during machining, and detects an abnormality in the contact point between the workpiece W and the center 41.

[0039] According to this embodiment, even when machining is performed while moving the workpiece W pressed against the center 41 along the axis X in a direction along the axis X, it is possible to accurately detect whether or not there is an abnormality in the relative position of the two in the direction of the axis X. If an abnormality is detected, the machining program P and torque control program p3 being executed are interrupted, thereby preventing machining from continuing while there is an abnormality in the contact point between the workpiece W and the center 41. This prevents unexpected excessive force from acting on the machine tool 10, damaging the machine tool 10, or continuing machining while the workpiece W is not properly supported.

[0040] Furthermore, according to this embodiment, if an abnormality in the contact point between the workpiece W and the center 41 is detected, the display device 5 displays the cause of the abnormality, that is, whether the center 41 is pressed too hard against the workpiece W or is too far away. Therefore, if there is an abnormality in the contact point between the workpiece W and the center 41, the user can easily understand the cause of the abnormality and can take appropriate measures, such as stopping or resetting the machine tool 10.

[0041] In this embodiment, the numerical control device 1 detects an abnormality in the contact point between the workpiece W and the center 41 based on information on the positions of the workpiece W and the center 41. Alternatively, the numerical control device 1 may detect an abnormality in the contact point between the workpiece W and the center 41 based on the speed (first physical quantity) of the workpiece W and the speed (second physical quantity) of the center 41 during machining. In this case, the memory 3 may store an allowable range A corresponding to the relative speed (relative physical quantity) of the center 41 with respect to the workpiece W.

[0042] Alternatively, the numerical control device 1 may detect an abnormality in the contact point between the workpiece W and the center 41 using both the positions and speeds of the workpiece W and the center 41. In this case, it is possible to distinguish between a deviation from the allowable range A due to buckling of the workpiece W as shown in FIG. 5 and a deviation from the allowable range A due to wear of the workpiece W as shown in FIG. 9. In the case of FIG. 5, when the workpiece W buckles, the position of the tip of the workpiece W suddenly deviates from its intended position, and the speed of the center 41, which follows the tip of the workpiece W through torque control, also increases significantly. Therefore, in the case of FIG. 5, it is highly likely that both the position and speed of the center 41 will exceed the allowable range A. On the other hand, in the case of FIG. 9, the relative position of the center 41 with respect to the workpiece W gradually deviates as the workpiece W wears, so even if the position of the center 41 exceeds the allowable range A, it is highly likely that the speed will not exceed the allowable range A.

[0043] Based on the above phenomenon, the determination unit 64 can estimate the cause of the abnormality, which is that the center 41 is being pressed too hard against the workpiece W. Then, by displaying text or the like based on this estimated cause on the display device 5, it is possible to notify the user of more detailed information regarding the abnormality in the contact point between the workpiece W and the center 41.

[0044] Furthermore, according to the present embodiment, the numerical control device 1 is provided with the input device 2, but instead, the numerical control device 1 may be configured without the input device 2. For example, if the machine tool 10 is a dedicated machine for performing a predetermined machining operation, the machining program P and tolerance range A required for that machining may be stored in advance in the memory 3 of the numerical control device 1. This allows the input device 2 to be omitted from the numerical control device 1, making the numerical control device 1 more simply configured and facilitating the setting work performed by the user.

[0045] Furthermore, in this embodiment, the numerical control device 1 obtains the position of the center 41 based on feedback information from the encoder provided in the servo motor 43a, but the position of the center 41 may be obtained based on other information. For example, if the position of the movable part 42 is controlled by execution of the machining program P, similar to the headstock 30, rather than by torque control, the position of the center 41 may be obtained based on an operation command (command information) for the center 41 in the machining program P.

[0046] Furthermore, according to this embodiment, the numerical control device 1 stops the machining program P and the torque control program p3 when it determines that the relative position of the center 41 with respect to the workpiece W exceeds the allowable range A. Alternatively, the numerical control device 1 may execute the torque control program p3 to reduce or stop the current value (output) supplied to the servo motor 43a when it determines that the relative position of the center 41 with respect to the workpiece W exceeds the allowable range A. Even in this case, the torque control of the tailstock 40 is limited when an abnormality in the contact point between the workpiece W and the center 41 is detected, thereby preventing the center 41 from being pressed excessively against the workpiece W. This prevents damage to the workpiece W and the tailstock 40.

[0047] In this embodiment, as shown in FIG. 4 , when the numerical controller 1 detects a contact abnormality between the workpiece W and the center 41, it stops the machining program P and the torque control program p3 and then notifies the operator of the contact abnormality. Alternatively, when the numerical controller 1 detects a contact abnormality, it may first notify the operator of the contact abnormality on the display device 5 and then stop the machining program P and the torque control program p3. Alternatively, it may notify the operator of the contact abnormality and stop the various programs simultaneously. Furthermore, in cases where an operator constantly monitors the operation of the machine tool 10, the numerical controller 1 may simply display an alarm screen indicating the abnormality on the display device 5 without stopping the various programs when it detects a contact abnormality. In this case, the operator can interrupt the various programs as needed.

[0048] Furthermore, in this embodiment, the present invention is exemplified as being applied to a machine tool 10 that moves the workpiece W in the direction of axis X together with the chuck 31 and spindle 32. Alternatively, the present invention may be applied to a machine tool that performs machining by changing the length of the portion of the workpiece W that protrudes from the tip of the chuck 31 while keeping the spindle 32 fixed.

[0049] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible to these embodiments without departing from the gist of the invention or the concept and spirit of the present invention derived from the content of the claims and their equivalents. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these.

[0050] The following supplementary notes are further disclosed regarding the above-described embodiments and modified examples. (Supplementary Note 1) A numerical control device controls a machine tool so as to machine a workpiece while moving it in a direction along a predetermined axis, with a pressing unit of the machine tool pressed against the workpiece along the axis by torque control, the numerical control device comprising: at least one memory and at least one processor, wherein the memory stores an allowable range of a relative physical quantity related to relative movement of the pressing unit in the axial direction relative to the workpiece, and the processor acquires a first physical quantity related to the movement of the workpiece in the axial direction and a second physical quantity related to the movement of the pressing unit in the axial direction, and compares a difference between the first physical quantity and the second physical quantity with the allowable range. (Supplementary Note 2) The numerical control device according to Supplementary Note 1, wherein the processor accepts input of the allowable range. (Supplementary Note 3) The numerical control device according to Supplementary Note 1 or Supplementary Note 2, wherein the first physical quantity is at least one of a position and a velocity of the workpiece during the movement, and the second physical quantity is at least one of a position and a velocity of the pressing unit during the movement. (Supplementary Note 4) The numerical control device according to any of Supplementary Note 1 to Supplementary Note 3, wherein the processor acquires the second physical quantity based on feedback information from the pressing unit during the movement. (Supplementary Note 5) The numerical control device according to any of Supplementary Note 1 to Supplementary Note 3, wherein the processor acquires the second physical quantity based on command information for moving the pressing unit. (Supplementary Note 6) The numerical control device according to any of Supplementary Note 1 to Supplementary Note 5, wherein the processor reduces or stops the output of the torque control when the relative physical quantity deviates from the allowable range. (Supplementary Note 7) The numerical control device according to any one of Supplementary Note 1 to Supplementary Note 6, wherein, when the relative physical quantity deviates from the allowable range, the processor determines whether the relative physical quantity exceeds the allowable range in the pressing direction of the pressing unit, or whether the relative physical quantity exceeds the allowable range in the direction opposite to the pressing direction, and determines a cause of an abnormality in the contact point between the workpiece and the pressing unit. (Supplementary Note 8) The numerical control device according to any one of Supplementary Note 1 to Supplementary Note 7, wherein the processor outputs a signal according to the result of the comparison to a display device.(Supplementary Note 9) A numerical control method for controlling a machine tool so as to machine a workpiece while moving it in a direction along a predetermined axis with a pressing unit of the machine tool pressed against the workpiece along the axis by torque control, the numerical control method comprising: acquiring a first physical quantity related to the movement of the workpiece in the axial direction and a second physical quantity related to the movement of the pressing unit in the axial direction, and comparing a difference between the first physical quantity and the second physical quantity with an allowable range. (Supplementary Note 10) A numerical control program for controlling the machine tool so as to machine the workpiece while moving it in a direction along the axis with a pressing unit of the machine tool pressed against the workpiece along a predetermined axis by torque control, the numerical control program causing a computer to execute the following steps: acquiring a first physical quantity related to the movement of the workpiece in the axial direction and a second physical quantity related to the movement of the pressing unit in the axial direction, and comparing a difference between the first physical quantity and the second physical quantity with an allowable range.

[0051] 1 Numerical control device 3 Memory 4 Processor 10 Machine tool 41 Center (pressing part) A Tolerance range W Work (machining object) X Axis

Claims

1. A numerical control device that controls a machine tool so that a pressing part of the machine tool is pressed against a workpiece along a predetermined axis by torque control, and the workpiece is machined while being moved in a direction along the axis, the numerical control device comprising at least one memory and at least one processor, wherein the memory stores an allowable range of a relative physical quantity related to the relative axial movement of the pressing part relative to the workpiece, and the processor acquires a first physical quantity related to the axial movement of the workpiece and a second physical quantity related to the axial movement of the pressing part, and compares the difference between the first physical quantity and the second physical quantity with the allowable range.

2. The numerical control device according to claim 1, wherein said processor accepts an input of said tolerance range.

3. A numerical control device according to claim 1 or claim 2, wherein the first physical quantity is at least one of the position and speed of the workpiece during the movement, and the second physical quantity is at least one of the position and speed of the pressing part during the movement.

4. The numerical control device according to any one of claims 1 to 3, wherein the processor acquires the second physical quantity based on feedback information from the pressing unit during the movement.

5. The numerical control device according to any one of claims 1 to 3, wherein the processor acquires the second physical quantity based on command information for moving the pressing unit.

6. A numerical control device according to any one of claims 1 to 5, wherein the processor reduces or stops the output of the torque control when the relative physical quantity deviates from the allowable range.

7. A numerical control device according to any one of claims 1 to 6, wherein, when the relative physical quantity deviates from the allowable range, the processor determines whether the relative physical quantity exceeds the allowable range in the pressing direction of the pressing unit, or whether the relative physical quantity exceeds the allowable range in the direction opposite to the pressing direction, and determines the cause of the abnormality in the contact point between the workpiece and the pressing unit.

8. A numerical control device according to any one of claims 1 to 7, wherein the processor outputs a signal according to the result of the comparison to a display device.

9. A numerical control method for controlling a machine tool so that a pressing part of the machine tool is pressed against a workpiece along a predetermined axis by torque control, and the workpiece is machined while being moved in a direction along the axis, the numerical control method comprising: obtaining a first physical quantity related to the movement of the workpiece in the axial direction and a second physical quantity related to the movement of the pressing part in the axial direction; and comparing a difference between the first physical quantity and the second physical quantity with an allowable range.

10. A numerical control program for controlling a machine tool to process an object to be processed while moving the object in a direction along a predetermined axis while pressing a pressing part of the machine tool against the object to be processed along the axis by torque control, the numerical control program causing a computer to acquire a first physical quantity related to the movement of the object to be processed in the axial direction and a second physical quantity related to the movement of the pressing part in the axial direction, and compare a difference between the first physical quantity and the second physical quantity with an allowable range.

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