Machine tool and control method for machine tool

Abstract

To provide a machine tool and a control device for the machine tool capable of correctly determining success or failure of cut-off machining.SOLUTION: An NC lathe 1 executes separating movement for moving a second main shaft 61 in a direction separating from a first main shaft 31 after executing cut-ff machining of a workpiece W held in a state where the shared workpiece W is held by the first main shaft 31 movable in an axial direction and the second main shaft 61 facing the first main shaft 31, and includes: a movement control unit 211 which performs control to stop the first main shaft 31 at a command position in the separating movement; and a cut-off success or failure determination unit 213 which monitors a position deviation being a difference between the command position and an actual position of the first main shaft 31 in the separating movement, and determines success or failure of the cut-off machining on the basis of the positional deviation.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a machine tool that performs parting machining on a workpiece held in a state where a first spindle movable in the axial direction and a second spindle facing the first spindle hold a common workpiece, and then performs a separation movement of moving the second spindle in a direction away from the first spindle, and a control method for a machine tool including a first spindle movable in the axial direction and a second spindle facing the first spindle and movable in a direction away from the first spindle.

Background Art

[0002] A machine tool is known that includes a first spindle and a second spindle facing the first spindle, and cuts a workpiece by parting machining in a state where the first spindle and the second spindle hold a common workpiece (see, for example, Patent Document 1). The machine tool described in Patent Document 1 performs a separation movement of moving the second spindle in a direction away from the first spindle after the parting machining, and determines the success or failure of the parting machining based on whether or not the position deviation of the second spindle in the separation movement exceeds a predetermined threshold value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the machine tool described in Patent Document 1, since the position deviation is monitored while the second spindle is moved away, even when the plunge cutting is successful, a minute position deviation occurs due to the movement. Moreover, depending on the machine body of the machine tool, the frictional load or the like in the movement of the second spindle may vary, and there is also a possibility that a position deviation caused by the variation may occur. And if the threshold value for determining the success or failure of the plunge cutting is increased in consideration of the occurrence of these position deviations, there may be a possibility that the failure cannot be determined even though the plunge cutting has failed.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a machine tool and a control device for a machine tool that can accurately determine the success or failure of plunge cutting.

Means for Solving the Problems

[0006] The machine tool of the present invention for solving the above object is a machine tool that performs a plunge cutting of a workpiece held in a state where a first spindle movable in the axial direction and a second spindle facing the first spindle hold a common workpiece, and then performs a separation movement of moving the second spindle in a direction away from the first spindle. In the machine tool, a movement control unit that performs control to stop the first spindle at a commanded position in the separation movement; and a plunge cutting success / failure determination unit that monitors a position deviation that is a difference between the commanded position and the actual position of the first spindle in the separation movement, and determines the success or failure of the plunge cutting based on the position deviation.

[0007] According to this machine tool, when the plunge cutting is successful, the success or failure of the plunge cutting is determined based on the position deviation of the first spindle that remains stopped even when the second spindle moves. Therefore, compared with the case where the success or failure of the plunge cutting is determined based on the position deviation of the second spindle, the success or failure of the plunge cutting can be accurately determined.

[0008] Here, the direction in which the second main shaft moves away from the first main shaft during the separation movement may be a direction along the axial direction of the first main shaft. Further, the separation movement may be an operation performed while one and the other of the workpieces separated by the piercing process are gripped by the first main shaft and the second main shaft, respectively. Furthermore, a position deviation acquisition unit for acquiring the position deviation may be provided. In addition, the position deviation acquisition unit may acquire the position deviation based on the output of an encoder of a motor that moves the first main shaft in the separating direction. Still further, a display unit that displays a warning when the piercing success / failure determination unit determines that the piercing process has failed may be provided.

[0009] In this machine tool, the piercing success / failure determination unit may use the position deviation immediately before the separation movement as a reference deviation, and determine that the piercing process has failed when the amount of change from the reference deviation exceeds a predetermined amount.

[0010] By doing so, the influence of the position deviation that occurred immediately before the separation movement can be excluded, so that it is possible to more accurately determine the success or failure of the piercing process.

[0011] Further, a control method for a machine tool according to the present invention for solving the above object is a control method for a machine tool including a first main shaft movable in the axial direction and a second main shaft facing the first main shaft and movable in a direction away from the first main shaft, a piercing step of performing a piercing process on a workpiece held in a state where the first main shaft and the second main shaft hold a common workpiece; a separation movement step of stopping the first main shaft at a commanded position and moving the second main shaft in a direction away from the first main shaft after the piercing step; and a piercing success / failure determination step of monitoring a position deviation that is the difference between the commanded position and the actual position of the first main shaft during the execution of the separation movement step, and determining the success or failure of the piercing process based on the position deviation.

[0012] According to the control method of this machine tool, when the plunge cutting is successful, the success or failure of the plunge cutting is determined based on the position deviation of the first spindle that basically does not change even when the second spindle moves. Therefore, the success or failure of the plunge cutting can be accurately determined.

[0013] Also, in the control method of this machine tool, a process that is executed before the plunge cutting process, in which the first spindle and the second spindle hold a common workpiece, the first spindle is stopped, and the second spindle is moved in a direction away from the first spindle, and a gripping force pre-determination process for monitoring the position deviation and determining whether the gripping force of the workpiece on the second spindle is sufficient based on the position deviation may be provided.

[0014] Whether the gripping force of the workpiece on the second spindle is set to a gripping force that can determine the success or failure of the plunge cutting in the plunge cutting success or failure determination process can be easily confirmed by executing the gripping force pre-determination process.

[0015] Here, the separation movement process may be a process of gripping the workpiece on the second spindle with the gripping force determined to be sufficient by the gripping force pre-determination process and moving the second spindle.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide a machine tool and a control device for a machine tool that can accurately determine the success or failure of plunge cutting.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, an example in which the present invention is applied to an NC (Numerical Control) lathe will be used for the description.

[0019] FIG. 1 is a front view showing the appearance of the NC lathe according to this embodiment. In FIG. 1, the operation unit and the display unit are not shown.

[0020] As shown in FIG. 1, the NC lathe 1 includes a cutting chamber 11 formed on the legs and a headstock chamber 12. This NC lathe 1 corresponds to an example of a machine tool. The cutting chamber 11 is arranged on the right side of the NC lathe 1 when viewed from the front side of the NC lathe 1. Hereinafter, in the description using this FIG. 1, the right side of the NC lathe 1 when viewed from the front side of the NC lathe 1 will be simply referred to as the right side, and the left side of the NC lathe 1 when viewed from the front side will be simply referred to as the left side. On the front side of the cutting chamber 11, three sliding door-type cutting chamber doors 110 are provided. FIG. 1 shows a state in which the cutting chamber 11 is closed by the three cutting chamber doors 110. These three cutting chamber doors 110 are interlocking doors that move in conjunction. Among the three cutting chamber doors 110, cutting door handles 111 are attached to each of the cutting chamber doors 110 arranged on the left side and the right side.

[0021] When the user of the NC lathe 1 grasps the cutting door handle 111 on the left side and slides the cutting chamber door 110 to the right, the central cutting chamber door 110 also moves to the right little by little in conjunction. As a result, approximately two-thirds of the left side of the cutting chamber 11 can be maximally released. Similarly, when the user of the NC lathe 1 grasps the cutting door handle 111 on the right side and slides the cutting chamber door 110 to the left, the central cutting chamber door 110 also moves to the left little by little in conjunction. As a result, approximately two-thirds of the right side of the cutting chamber 11 can be maximally released. Also, by sliding both the right cutting chamber door 110 and the left cutting chamber door 110 simultaneously toward the central cutting chamber door 110, it is also possible to release approximately one-third of the left and right sides of the cutting chamber 11 at most.

[0022] On the left side of the cutting chamber 11 of the NC lathe 1, a first door sensor 113 and a first door locking device 114 are provided. The first door sensor 113 detects whether the left cutting chamber door 110 is in the closed position. Also, the first door locking device 114 is for locking the left cutting chamber door 110 in the closed position in response to a command from a control device 2 (see FIG. 2) described later. Further, on the right side of the cutting chamber 11 of the NC lathe 1, a second door sensor 115 and a second door locking device 116 are provided. The second door sensor 115 detects whether the right cutting chamber door 110 is in the closed position. Also, the second door locking device 116 is for locking the right cutting chamber door 110 in the closed position in response to a command from the control device 2. Note that the first door sensor 113 and the first door locking device 114 may be an integrated unit. Similarly, the second door sensor 115 and the second door locking device 116 may also be an integrated unit.

[0023] The control device 2 (see FIG. 2) controls the operations of the first door lock device 114 and the second door lock device 116 based on the outputs from the first door sensor 113 and the second door sensor 115. Specifically, when the control device 2 outputs a signal indicating that both the first door sensor 113 and the second door sensor 115 are in the closed position, it sets the first door lock device 114 and the second door lock device 116 to the unlocked state. That is, in a state where the cutting chamber 11 is closed by the three cutting chamber doors 110, the left and right cutting chamber doors 110 can slide in the opening direction respectively. However, since the first door lock device 114 and the second door lock device 116 also function as door interlocks, the left and right cutting chamber doors 110 are locked in a state where the three cutting chamber doors 110 are in the closed position while the machining unit 10 (see FIG. 2) of the NC lathe 1 is operating. Also, when the control device 2 outputs a signal indicating that at least one of the first door sensor 113 and the second door sensor 115 is not in the closed position, it also sets the first door lock device 114 and the second door lock device 116 to the unlocked state. Thereby, when the left and right sides of the cutting chamber 11 are each opened, the left and right cutting chamber doors 110 can move to the closed position.

[0024] On the other hand, when one of the first door sensor 113 and the second door sensor 115 outputs a signal indicating that it is in the closed position and the other outputs a signal indicating that it is not in the closed position, after a predetermined time has elapsed since the combination of these signal outputs, the control device 2 locks the cutting chamber door 110 in the closed position with the first door lock device 114 or the second door lock device 116. The predetermined time is, for example, 1 second, but it may be other than that and may be configured to be arbitrarily settable. If both the first door sensor 113 and the second door sensor 115 output signals indicating the same open / closed state within the predetermined time from the start of the above-mentioned signal output, the control device 2 leaves the first door lock device 114 and the second door lock device 116 in the unlocked state.

[0025] When one of the left and right cutting chamber doors 110 is closed and the other is open, if the other door is forcefully closed, the force will be transmitted through the central cutting chamber door 110 to the one cutting chamber door 110 that is interlocked therewith, and there is a case where the closed cutting chamber door 110 may be opened. As in this embodiment, by locking one of the left and right cutting chamber doors 110 when one of them is closed and the other is open, even if the other cutting chamber door 110 is forcefully closed, it is possible to surely prevent the one cutting chamber door 110 from being unintentionally opened.

[0026] The headstock chamber 12 is arranged on the left side of the NC lathe 1. On the front side of the headstock chamber 12, three sliding door type headstock chamber doors 120 are provided. FIG. 1 shows a state where the headstock chamber 12 is closed by the three headstock chamber doors 120. These three headstock chamber doors 120 are interlocking doors that move in conjunction. Among the three headstock chamber doors 120, spindle door handles 121 are attached to each of the headstock chamber doors 120 arranged on the left side and the right side. Since the movement of the headstock chamber door 120 in closing and opening the headstock chamber door 120 is the same as that of the cutting chamber door 110, detailed description is omitted.

[0027] On the left side of the spindle headstock chamber 12 of the NC lathe 1, a third door sensor 123 and a third door locking device 124 are provided. The third door sensor 123 detects whether the left spindle headstock door 120 is in the closed position. Also, the third door locking device 124 is for locking the left spindle headstock door 120 in the closed position in response to a command from the control device 2 (see FIG. 2). Further, on the right side of the spindle headstock chamber 12 of the NC lathe 1, a fourth door sensor 125 and a fourth door locking device 126 are provided. The fourth door sensor 125 detects whether the right spindle headstock door 120 is in the closed position. Also, the fourth door locking device 126 is for locking the right spindle headstock door 120 in the closed position in response to a command from the control device 2. Note that the third door sensor 123 and the third door locking device 124 may be an integrated unit. Similarly, the second door sensor 115 and the fourth door locking device 126 may also be an integrated unit.

[0028] The control device 2 (see Fig. 2) controls the operations of the third door locking device 124 and the fourth door locking device 126 based on the outputs from the third door sensor 123 and the fourth door sensor 125. Specifically, when the control device 2 outputs a signal indicating that both the third door sensor 123 and the fourth door sensor 125 are in the closed position, it sets the third door locking device 124 and the fourth door locking device 126 to the unlocked state. That is, in a state where the spindle headstock chamber 12 is closed by the three spindle headstock chamber doors 120, the left and right spindle headstock chamber doors 120 can slide in the opening direction respectively. However, since the third door locking device 124 and the fourth door locking device 126 also function as door interlocks, while the machining part 10 (see Fig. 2) of the NC lathe 1 is operating, the left and right spindle headstock chamber doors 120 are locked in a state where the three spindle headstock chamber doors 120 are in the closed position. In addition, when at least one of the first door sensor 113, the second door sensor 115, the third door sensor 123, and the fourth door sensor 125 outputs a signal indicating that the cutting chamber door 110 or the spindle headstock chamber door 120 is not in the closed position, the control device 2 does not operate the machining part 10 of the NC lathe 1. Also, when the control device 2 outputs a signal indicating that both the third door sensor 123 and the fourth door sensor 125 are not in the closed position, it also sets the third door locking device 124 and the fourth door locking device 126 to the unlocked state. Thereby, when each of the left and right sides of the spindle headstock chamber 12 is opened, the left and right spindle headstock chamber doors 120 can move to the closed position.

[0029] On the other hand, when one of the third door sensor 123 and the fourth door sensor 125 outputs a signal indicating that it is in the closed position and the other outputs a signal indicating that it is not in the closed position, after a predetermined time has elapsed since the combination of these signal outputs occurred, the control device 2 locks the spindle headstock chamber door 120 on the side in the closed position with the third door locking device 124 or the fourth door locking device 126. The predetermined time is, for example, 1 second, but it may be other than that and may be configured to be arbitrarily settable. In addition, when both the third door sensor 123 and the fourth door sensor 125 output signals indicating the same open / closed state within the predetermined time from the start of the output of the above-mentioned signals, the control device 2 leaves the third door locking device 124 and the fourth door locking device 126 in the unlocked state.

[0030] When one of the left and right main spindle housing doors 120 is closed and the other is open, if the other door is forcefully closed, the force is transmitted to one of the main spindle housing doors 120 that is interlocked via the central main spindle housing door 120, and the closed main spindle housing door 120 may be opened. As in this embodiment, when one of the left and right main spindle housing doors 120 is closed and the other is open, by locking one of the main spindle housing doors 120, even if the other main spindle housing door 120 is forcefully closed, it is possible to surely prevent the one cutting chamber door 110 from being unintentionally opened.

[0031] FIG. 2 is a plan view simply showing the machining part of the NC lathe shown in FIG. 1. Also, the control device 2 is shown in this FIG. 2. Further, in FIG. 2, the ranges of the cutting chamber 11 and the main spindle housing 12 are shown by thin two-dot chain lines.

[0032] Inside the NC lathe 1, a machining part 10 is formed. As shown in FIG. 2, the machining part 10 includes a first main spindle base 3, a guide bush 4, a first tool post 5, a second main spindle base 6, and a second tool post 7. The operation of the machining part 10 is controlled by the control device 2. The control device 2 stores an NC program and operation information and the like corresponding to various commands used in the NC program. The control device 2 is a computer that numerically controls the first main spindle base 3, the first tool post 5, the second main spindle base 6, and the second tool post 7 according to the NC program. Also, the control device 2 controls the rotation of the first main spindle 31 and the second main spindle 61. In addition, when a rotary tool is attached to the first tool post 5 or the second tool post 7, the control device 2 also controls the rotation of the rotary tool.

[0033] A first spindle head 3 is equipped with a first spindle 31. The first spindle head 3 is movable in the Z1-axis direction together with the first spindle 31. These first spindle head 3 and first spindle 31 are arranged in the spindle head chamber 12. The Z1-axis direction is a horizontal direction and is the left-right direction in FIG. 2. This Z1-axis direction corresponds to the axial direction of the first spindle 31. The first spindle 31 has a first gripping portion such as a collet chuck. The first spindle 31 releasably grips a long bar-shaped workpiece W inserted therein with the first gripping portion. The first spindle 31 can rotate about the first spindle center line CL1 while gripping the workpiece W. The direction of the first spindle center line CL1 coincides with the Z1-axis direction. The first spindle 31 is provided with a first spindle motor (not shown) such as a built-in motor. By receiving a command from the control device 2 and rotating, the first spindle 31 rotates about the first spindle center line CL1. Thereby, the workpiece W gripped by the first spindle 31 rotates about the first spindle center line CL1.

[0034] The guide bush 4 is fixed to the leg which is the base of the NC lathe 1 by a guide bush support base 41. The end face of the guide bush 4 on the side opposite to the side where the first spindle 31 is arranged is exposed in the cutting chamber 11. The guide bush 4 slidably supports the tip-side portion of the workpiece W penetrating through the inside of the first spindle 31 in the Z1-axis direction. The portion of the guide bush 4 that supports the workpiece W can rotate about the first spindle center line CL1 in synchronization with the first spindle 31. That is, the first spindle center line CL1 is also the rotation center line of the portion of the workpiece W supported by the guide bush 4. Since the guide bush 4 suppresses the deflection of the workpiece W during machining, particularly long and slender workpieces W can be machined with high precision.

[0035] The first tool rest 5 is movable in the X1-axis direction orthogonal to the Z1-axis direction and facing the horizontal direction, and in the Y1-axis direction facing the vertical direction. In FIG. 2, the vertical direction is the X1-axis direction, and the direction orthogonal to the paper surface is the Y1-axis direction. A tool T1 for machining the workpiece W is mounted on the first tool rest 5. FIG. 2 shows a state in which the tool T1 is mounted on the first tool rest 5. This tool T1 is disposed in the cutting chamber 11. A plurality of types of tools T1 including a tool for outer diameter machining, a tool for plunge cutting, etc. are mounted side by side in the Y1-axis direction on the first tool rest 5. By moving the first tool rest 5 in the Y1-axis direction, any one of these plurality of types of tools T1 is selected. Then, by moving the first tool rest 5 in the X1-axis direction, the selected tool T1 cuts into the workpiece W gripped by the first spindle 31 to machine the tip portion of the workpiece W.

[0036] The second spindle head 6 is disposed within the cutting chamber 11. A second spindle 61 is mounted on the second spindle head 6. The second spindle head 6 is movable together with the second spindle 61 in the X2-axis direction and the Z2-axis direction. The X2-axis direction is the same direction as the above-described X1-axis direction, and the Z2-axis direction is the same direction as the above-described Z1-axis direction. This Z2-axis direction corresponds to the axial direction of the second spindle 61. FIG. 2 shows a state where the second spindle 61 is positioned to face the first spindle 31 with the guide bush 4 therebetween. At this position, a second spindle center line CL2, which is the rotation center of the second spindle, is arranged on the same line as the first spindle center line CL1. The direction of the second spindle center line CL2 coincides with the Z2-axis direction. The tip portion of the workpiece W that has been machined using the first spindle 31 and cut by a tool for cutoff machining is delivered to the second spindle 61. Hereinafter, after being cut, the tip portion of the workpiece W delivered to the second spindle 61 is referred to as the cut workpiece, and the workpiece W remaining on the first spindle 31 side is referred to as the workpiece material. The second spindle 61 has a second gripping portion such as a collet chuck. In the cutoff machining, the second spindle 61 grip-releases a portion of a predetermined length from the tip of the workpiece W by the second gripping portion. Further, the second spindle 61 grip-releases the cut workpiece delivered from the first spindle 31 after the cutoff machining by the second gripping portion. The second spindle head 6 is provided with a second spindle motor such as a built-in motor. When the second spindle motor rotates in response to a command from the control device 2, the second spindle 61 rotates about the second spindle center line CL2. As a result, the cut workpiece gripped by the second spindle 61 rotates about the second spindle center line CL2.

[0037] The second tool rest 7 is disposed within the cutting chamber 11. The second tool rest 7 is movable in the Y2-axis direction, which is the same direction as the above-described Y1-axis direction. A plurality of types of tools T2, such as drills and end mills, for machining the cut workpiece gripped by the second spindle 61 are attached to the second tool rest 7. FIG. 2 shows a state in which the tool T2 is mounted on the second tool rest 7. Although not shown in FIG. 2, the tools T2 are arranged side by side not only in the X2-axis direction but also in the Y2-axis direction. By the movement of the second spindle base 6 in the X2-axis direction and the movement of the second tool rest 7 in the Y2-axis direction, any one of these plurality of tools T2 is selected. Then, by the movement of the second spindle base 6 in the Z2-axis direction, the cut end side portion of the cut workpiece gripped by the second spindle 61 is machined.

[0038] FIG. 3 is a block diagram showing the hardware configuration of the NC lathe shown in FIG. 1. In FIG. 3, only the configuration highly relevant to the present invention among the hardware configurations of the NC lathe 1 is shown, and other configurations are omitted from the illustration. Further, the description of other configurations is also omitted.

[0039] As shown in FIG. 3, in addition to the above-described first spindle base 3 and second spindle base 6, the machining unit 10 includes a Z1-axis motor 32 and a Z2-axis motor 62. The Z1-axis motor 32 is a motor for moving the first spindle base 3 in the Z1-axis direction in response to a command from the control device 2. A Z1-axis encoder 321 that outputs the rotation direction, rotation angle, etc. thereof is provided on the Z1-axis motor 32. Based on the output from the Z1-axis encoder 321, the control device 2 grasps the actual position of the first spindle base 3 in the Z1-axis direction. The Z2-axis motor 62 is a motor for moving the second spindle base 6 in the Z2-axis direction in response to a command from the control device 2. A Z2-axis encoder 621 that outputs the rotation direction, rotation angle, etc. thereof is provided on the Z2-axis motor 62. Based on the output from the Z2-axis encoder 621, the control device 2 grasps the actual position of the second spindle base 6 in the Z2-axis direction.

[0040] The control device 2 includes a CPU 21, an operation unit 22, a display unit 23, and a storage unit 24. The CPU 21 executes processing according to a processing program stored in the storage unit 24. The processing program is a list of various instructions. The CPU 21 sequentially executes processing corresponding to those instructions. The operation unit 22 includes a plurality of buttons, keys, etc. that receive input operations by the user of the NC lathe 1. Note that the operation unit 22 may be a touch panel integrated with the display unit 23. The user of the NC lathe 1 can store the processing program in the storage unit 24 using the operation unit 22 or an external computer. Also, the user of the NC lathe 1 can modify the processing program using the operation unit 22 and store the modified processing program in the storage unit 24. Further, a threshold value described later is also stored in the storage unit 24. The display unit 23 is a display that displays the processing program stored in the storage unit 24, various setting values of the NC lathe 1, and various information regarding the NC lathe 1, etc.

[0041] Figure 4 is a functional block diagram showing the functional configuration of the control device shown in Figure 3. In this Figure 4, the processing unit 10 is also shown in a simplified manner. Note that in Figure 4, only the functional configuration highly relevant to the present invention is shown, and other functional configurations of the control device 2 are omitted from the illustration. Also, the description of other functional configurations is omitted.

[0042] As shown in FIG. 4, the control device 2 includes a movement control unit 211, a position deviation acquisition unit 212, and a plunge cutting success / failure determination unit 213. These movement control unit 211, position deviation acquisition unit 212, and plunge cutting success / failure determination unit 213 are functional configurations mainly achieved by the CPU 21 and the storage unit 24 shown in FIG. 3. The movement control unit 211 controls the power supply to various motors such as the Z1-axis motor 32 and the Z2-axis motor 62. More specifically, the movement control unit 211 performs feedback control by receiving the output of the encoder provided in each motor, thereby controlling the rotation speed and stop angle of each motor. As a result, the movement control unit 211 moves the first spindle base 3 and the second spindle base 6 shown in FIG. 3 at the speed commanded in the machining program and stops them at the commanded position. In addition, the movement control unit 211 may apply a holding torque to the Z1-axis motor 32, the Z2-axis motor 62, etc. in order to maintain the stopped first spindle base 3, second spindle base 6, etc. at the stop position.

[0043] The position deviation acquisition unit 212 acquires a position deviation, which is the difference between the commanded position for the first spindle base 3 (see FIG. 3) and the actual position of the first spindle base 3, based on the commanded position specified by the NC program and the output from the Z1-axis encoder 321. The movement control unit 211 controls the Z1-axis motor 32 to reduce the position deviation based on this position deviation. Although not shown in the figure, the movement control unit 211 similarly performs control based on the position deviation for other motors such as the Z2-axis motor 62. By the way, if the cutting tool for plunge cutting is damaged or severely worn, the plunge cutting may fail and the workpiece W may not be cut. The plunge cutting success / failure determination unit 213 determines the success or failure of the plunge cutting based on the position deviation of the first spindle base 3 that has stopped after the execution of the plunge cutting. The plunge cutting process including these plunge cutting and determination operations will be described in detail below with reference to FIG. 5 while referring to FIGS. 2 to 4.

[0044] FIG. 5 is a flowchart showing the operations related to the plunge cutting process of the NC lathe shown in FIG. 1.

[0045] When the machining using the first spindle 31 and the first tool rest 5 on the workpiece W is completed, the control device 2 (the movement control unit 211) moves the second spindle 61 to a position facing the first spindle 31. Then, the control device 2 moves the second spindle base 6 in the direction approaching the first spindle 31 along the Z2 axis direction until a portion of a predetermined length from the tip of the workpiece W is inserted into the second spindle 61. Next, the control device 2 causes the second gripping portion provided on the second spindle 61 to grip the portion of the predetermined length of the workpiece W inserted into the second spindle 61 (step S11). By this step S11, the first spindle 31 and the second spindle 61 are in a state of gripping the common workpiece W. Thereafter, the control device 2 moves the first tool rest 5 along the X1 axis while synchronously rotating the first spindle 31 and the second spindle 61 to cut a cutting tool for parting off into the axis of the workpiece W, and executes a parting off process for separating the tip portion of the workpiece W that has been machined using the first spindle 31 (step S12). This step S12 corresponds to an example of the parting off process.

[0046] When the plunge cutting process in step S12 is completed, the control device 2 acquires the position deviation in the Z1-axis direction of the first spindle 31 at that time by the position deviation acquisition unit 212, and stores it in the storage unit 24 as data A1 indicating the reference deviation (step S13). Next, the control device 2 starts a separation movement for moving the second spindle 61 in a direction away from the first spindle 31 (step S14). Then, the control device 2 acquires the position deviation in the Z1-axis direction of the first spindle 31 by the position deviation acquisition unit 212, for example, every 4 msec, and stores the acquired position deviation in the storage unit 24 as data B1 (step S15). Further, each time the data B1 is stored, the plunge cutting success / failure determination unit 213 determines whether the plunge cutting process has been successful (step S16). Specifically, the plunge cutting success / failure determination unit 213 determines whether the data B1 is equal to or less than the maximum value obtained by adding the threshold value to the data A1 and equal to or greater than the minimum value obtained by subtracting the threshold value from the data A1. This step S16 corresponds to an example of the plunge cutting success / failure determination process. As described above, the threshold value is a value stored in advance in the storage unit 24. When the data B1 is equal to or less than the maximum value and equal to or greater than the minimum value (YES in step S16), the plunge cutting success / failure determination unit 213 repeats the processes of steps S15 and S16 until the movement of the second spindle 61 is completed (loop of NO in step S17). When the separation movement of the second spindle 61 is completed (YES in step S17), the plunge cutting success / failure determination unit 213 determines that the plunge cutting process has been successful. Further, the control device 2 ends the plunge cutting process. Note that the movement amount of the second spindle 61 from step S14 to S17 is preferably a minute movement amount within a range in which it can be determined whether the plunge cutting process has been successful, such as 0.1 mm, for example.

[0047] On the other hand, if the data B1 exceeds the maximum value or becomes smaller than the minimum value before the movement of the second main shaft 61 is completed, the cut-through determination unit 213 determines that the cut-through process has failed (NO in step S16). In other words, when the change amount of the position deviation of the first main shaft 31 exceeds a predetermined amount, the cut-through determination unit 213 determines that the first main shaft 31 has moved due to the movement of the second main shaft 61 via the workpiece W because the tip portion of the workpiece W has not been separated from the workpiece material. When the cut-through determination unit 213 determines the failure of the cut-through process, the control device 2 forcibly terminates the movement of the second main shaft 61 and displays on the display unit 23 an indication of the failure of the cut-through process (step S18). These steps from step S14 to step S18 correspond to an example of the separation movement process. That is, during the separation movement process, the cut-through determination process is executed multiple times.

[0048] The movement control unit 211 executes control to apply a holding torque to the Z1-axis motor 32 so as to stop the first main shaft 31 at a predetermined position until the separation movement is completed after the cut-through process. However, the movement control unit 211 may perform control to reduce the holding torque of the Z1-axis motor 32 to be lower than normal or stop the holding torque from before or after step S13 until the separation movement is completed. By doing so, the position deviation of the first main shaft 31 is likely to occur, so that the failure of the cut-through process can be determined more sensitively and quickly.

[0049] Next, the test cut-through process executed during the setup operation will be described with reference to FIGS. 2 to 4 and using FIG. 6. The setup operation is an operation performed before processing such as cutting or cut-through processing when changing to workpieces W with different diameters. FIG. 6 is a flowchart showing operations related to the test cut-through process of the NC lathe shown in FIG. 1. This test cut-through process does not necessarily have to be executed, but by executing it, it is possible to easily determine whether the gripping force of the second main shaft 61 is appropriate. In this test cut-through process, the cut-through determination unit 213 acts as a gripping force determination unit.

[0050] Prior to the test cutting process, with the workpiece W gripped by the first spindle 31, the control device 2 projects the workpiece W to the second spindle 61 side beyond the guide bush 4 and moves the second spindle 61 to a position facing the first spindle 31. Thereafter, the test cutting process shown in FIG. 6 is started. First, the control device 2 moves the second spindle head 6 in a direction approaching the first spindle 31 along the Z2-axis direction until a portion of a predetermined length from the tip of the workpiece W is inserted into the second spindle 61. Next, the control device 2 causes the second gripping portion provided on the second spindle 61 to grip a portion of the predetermined length of the workpiece W inserted into the second spindle 61 (step S21). By this step S21, the first spindle 31 and the second spindle 61 are in a state of gripping the common workpiece W.

[0051] Thereafter, the control device 2 acquires the position deviation of the first spindle 31 in the Z1-axis direction at that time by the position deviation acquisition unit 212, and stores it in the storage unit 24 as data A2 (step S22). Next, the control device 2 starts the movement of the second spindle 61 in the direction away from the first spindle 31 (step S23). Then, the control device 2 acquires the position deviation of the first spindle 31 in the Z1-axis direction by the position deviation acquisition unit 212, for example, every 4 msec, and stores it in the storage unit 24 as data B2 (step S24). Further, the piercing success / failure determination unit 213 (holding force determination unit) determines whether the data B2 is less than or equal to the maximum value obtained by adding the threshold value to the data A2 and greater than or equal to the minimum value obtained by subtracting the threshold value from the data A2 every time the data B2 is stored (step S25). Note that the threshold value used here is preferably a value larger than the threshold value used in step S16 described above. By doing so, the holding force of the second spindle 61 can be set to an appropriate holding force suitable not only for determining the success or failure of the piercing process but also for machining. Conversely, the threshold value used in step S16 described above is preferably set to the smallest possible value within a range where no false determination occurs due to external disturbances or the like. Thereby, the success or failure of the piercing process can be determined more accurately. When the data B2 is less than or equal to the maximum value and greater than or equal to the minimum value (YES in step S25), the piercing success / failure determination unit 213 repeats the processes of step S24 and step S25 until the movement of the second spindle 61 is completed (loop of NO in step S26). When the movement of the second spindle 61 is completed (YES in step S26), the piercing success / failure determination unit 213 determines that the second spindle 61 has insufficient holding force. Then, the control device 2 displays on the display unit 23 that the second spindle 61 has insufficient holding force (step S27). Note that the movement amount of the second spindle 61 from step S23 to S26 is preferably the same as the movement amount from step S14 to S17 described above, but may be a movement amount longer than that from step S14 to S17.

[0052] On the other hand, if the data B2 exceeds the maximum value or becomes smaller than the minimum value before the movement of the second spindle 61 is completed (NO in step S25), the piercing success / failure determination unit 213 determines that the gripping force of the second spindle 61 is sufficient. That is, when the position deviation of the first spindle 31 exceeds the predetermined range, even due to the movement of the second spindle 61, no slippage occurs between the second gripping portion of the second spindle 61 and the workpiece W, and it is determined that the second spindle 61 firmly grips the workpiece W to such an extent that the success or failure of the piercing process can be determined. Then, the control device 2 forcibly ends the movement of the second spindle 61 (step S28) and causes the display unit 23 to display that the gripping force is sufficient (step S29).

[0053] When insufficient gripping force is displayed, the user of the NC lathe 1 adjusts the gripping force of the second spindle 61 and executes the test piercing process shown in FIG. 6 again. Then, the user of the NC lathe 1 repeats the test piercing process and the adjustment of the gripping force of the second spindle 61 until the gripping force of the second spindle 61 is sufficient. Thereby, the gripping force of the second spindle 61 can be easily set to an appropriate gripping force. Also, in the piercing process shown in FIG. 5, the piercing success / failure determination unit 213 can make an accurate determination. Note that the movement control unit 211 stops the first spindle 31 at a predetermined position during the test piercing process shown in FIG. 6.

[0054] As described above, in this embodiment, after the piercing process is completed, the second spindle 61 is moved while the first spindle 31 is stopped. In the movement of the second spindle 61, when the piercing process is successful, the workpiece W is cut off, so the position deviation of the first spindle 31 basically does not change regardless of the movement of the second spindle 61. Therefore, according to the NC lathe 1 and the control method of the NC lathe 1 described above, by determining the success or failure of the piercing process based on the position deviation of the first spindle 31, compared with the case of determining the success or failure of the piercing process based on the position deviation of the second spindle 61, the success or failure of the piercing process can be determined with higher accuracy. Further, in step S13, the position deviation of the first spindle 31 is saved, and using this position deviation as a reference deviation, it is determined that the piercing process has failed when the change amount of the position deviation from the reference deviation exceeds a predetermined amount, and the influence of the position deviation that occurred before the start of the separation movement can be excluded. Thereby, the success or failure of the piercing process can be determined with higher accuracy.

[0055] The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope described in the claims. For example, in the description of this embodiment, an example of applying the present invention to the NC lathe 1 is shown, but the present invention may also be applied to other machine tools such as machining centers. Further, the piercing success / failure determination unit 213 of this embodiment uses the data A1 as a reference deviation and determines whether or not the change amount of the position deviation from the reference deviation exceeds a predetermined amount as a determination criterion. However, without using the data A1, it may be used as a determination criterion simply whether or not the data B1 or the absolute value of the data B1 exceeds a threshold value.

[0056] Note that even constituent elements included only in the description of each of the above-described modification examples may be applied to other modification examples.

Explanation of Reference Numerals

[0057] 1 NC lathe (machine tool) 31 First spindle 61 Second spindle 211 Movement control unit 213 Piercing success / failure determination unit W Workpiece

Claims

1. In a machine tool that performs a parting operation on a workpiece held in a state where a first spindle movable in the axial direction and a second spindle facing the first spindle grip a common workpiece, and then performs a separation movement of moving the second spindle in a direction away from the first spindle, a movement control unit that performs control to stop the first spindle at a commanded position during the separation movement; a machine tool characterized by including a parting success / failure determination unit that monitors a position deviation, which is the difference between the commanded position and the actual position of the first spindle during the separation movement, and determines the success or failure of the parting operation based on the position deviation.

2. The machine tool according to claim 1, wherein the parting success / failure determination unit uses the position deviation immediately before the separation movement as a reference deviation, and determines that the parting operation has failed when the amount of change from the reference deviation exceeds a predetermined amount.

3. In a control method for a machine tool including a first spindle movable in the axial direction and a second spindle facing the first spindle and movable in a direction away from the first spindle, a parting step of performing a parting operation on a workpiece held in a state where the first spindle and the second spindle grip a common workpiece; a separation movement step of stopping the first spindle at a commanded position after the parting step and moving the second spindle in a direction away from the first spindle; a control method for a machine tool characterized by including a parting success / failure determination step of monitoring a position deviation, which is the difference between the commanded position and the actual position of the first spindle during the execution of the separation movement step, and determining the success or failure of the parting operation based on the position deviation.

4. A step performed before the parting step, in which, in a state where the first spindle and the second spindle grip a common workpiece, the first spindle is stopped, the second spindle is moved in a direction away from the first spindle, the position deviation is monitored, and a gripping force pre-determination step of determining whether the gripping force of the workpiece on the second spindle is sufficient based on the position deviation is provided. The control method for a machine tool according to claim 3 is characterized by this.

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