Lathe and method for detecting breakage of cut-off tool

Abstract

To provide a lathe which eliminates a need to increase the processing time during continuous processing and enables improvement of accuracy of detecting damage of a cutting-off tool.SOLUTION: A lathe 1 includes: a spindle 11; an opposing spindle 16; a cutter holder 30; a control unit 70; and a contact type damage detection part 40. The control unit 70 performs processing to determine whether or not a cutting-off tool TO3 is damaged based on control parameters for controlling at least one of the spindle 11 and the opposing spindle 16 at a first detection timing (ST3) immediately after cutting-off operation is performed in such a state that the opposing spindle 16 holds a bar B1 held by the spindle (11). Further, the control unit (70) performs processing to determine whether or not the cutting-off tool TO3 is damaged according to a detection result of the contact type damage detection part 40 at a second detection timing (ST6) different from the first detection timing (ST3).SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a lathe equipped with a means for detecting breakage of a cut-off tool, and a method for detecting breakage of the cut-off tool. [Background technology]

[0002] A well-known type of lathe is the NC (numerically controlled) lathe, which repeatedly cuts off workpieces from a bar stock supplied by a material feeder to continuously form products. NC lathes perform front machining of the tip of the bar stock held in the front spindle using a tool attached to a tool post, then grip the tip of the bar stock after front machining with the back spindle and cut off the bar stock with a cut-off bit attached to the tool post. This separates the front-machined workpiece held in the back spindle from the bar stock. NC lathes also perform back machining of the workpiece using a tool attached to the tool post and discharge the resulting product.

[0003] If the cut-off bit breaks, it becomes impossible to separate the workpiece from the bar material. Therefore, NC lathes are equipped with a means to detect breakage of the cut-off bit.

[0004] The dual-spindle opposed lathe disclosed in Patent Document 1 is equipped with a position deviation detection means that detects the position deviation, which is the difference signal between the position command from the NC device and the position feedback signal detected by a pulse encoder or the like of the headstock feed motor of the moving headstock. The dual-spindle opposed lathe issues a command to slowly separate the fixed headstock and the moving headstock, and if the position deviation detected at this time exceeds a set value, it determines that the workpiece has not been separated, issues an alarm, and stops the machine. If the cut-off bit is damaged, the position deviation will increase, causing an alarm to be issued and the machine to stop. The above-described cut-off tool breakage detection means can be said to be a non-mechanical breakage detection means because it does not use a detector that comes into contact with the tip of the bar material remaining after the cut-off operation when advancing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-245740 Summary of the Invention [Problem to be solved by the invention]

[0006] When a new bar is supplied to the front spindle from the material feeder or when continuous machining is resumed, a top cut operation may be performed to position the bar, in which the tip of the bar is cut off using a cut-off bit while the back spindle is not gripping the tip of the bar. In this case, if the cut-off bit is damaged, the tip of the bar that should have been cut off remains, affecting subsequent machining operations. However, the non-mechanical breakage detection means described above cannot detect breakage in the cut-off bit when the cut-off operation is performed while the back spindle is not gripping the bar currently gripped by the front spindle. Even when top cutting is not performed, there are cases where the back spindle is not gripping the bar that is being held by the front spindle when continuous machining begins. In this case, too, the non-mechanical breakage detection means described above cannot detect breakage in the cut-off bit.

[0007] Here, instead of the non-mechanical breakage detection means, we will assume that a mechanical breakage detection means equipped with a detector that contacts the tip of the bar material when advancing if the tip remains after the cut-off operation. The mechanical breakage detection means can detect breakage of the cut-off bit even immediately after the top cut process. However, the mechanical breakage detection means requires time to move the detector, which results in a longer continuous machining time.

[0008] The present invention discloses a lathe that can improve the accuracy of detecting breakage of a cut-off bit without the need to extend the machining time during continuous machining, and a method for detecting breakage of the cut-off bit. [Means for solving the problem]

[0009] The lathe of the present invention is a main shaft that releasably grips the bar; an opposing main shaft that releasably grips a tip end of the bar extending forward from the main shaft; a tool rest to which a cut-off tool is attached that cuts through the bar material held by the spindle; a control unit that controls operations of the main spindle, the counter spindle, and the tool rest; a contact-type breakage detection unit having a detector that can be advanced and retracted to an advanced position where it comes into contact with the tip of the bar material if the tip of the bar material remains after the cut-off operation in which the cut-off tool cuts through the bar material, and that detects that the cut-off tool is broken when the detector that has advanced to the advanced position comes into contact with the tip of the bar material, The control unit performing a process of determining whether or not the cut-off tool is damaged based on a control parameter for controlling at least one of the main spindle and the counter spindle at a first detection timing immediately after the cut-off operation is performed in a state in which the counter spindle holds the bar held by the main spindle; At least one of the timing immediately after the cut-off operation is performed in a state in which the bar material gripped by the main spindle is not gripped by the counter main spindle, and the timing at which continuous machining of the bar material is started. Second detection timing Limited and performing a process to determine whether or not the cut-off tool is broken based on the detection result by the contact-type breakage detection unit.

[0010] Further, the method for detecting breakage of a cutting tool of a lathe according to the present invention comprises the steps of: a main shaft that releasably grips the bar; an opposing main shaft that releasably grips the tip end of the bar extending forward from the main shaft; a tool rest to which a cut-off tool is attached that cuts through the bar material held by the spindle; a contact-type damage detection unit having a detector that can advance and retreat to an advanced position where it contacts the tip of the bar material if the tip remains after the cut-off operation in which the cut-off bit cuts through the bar material, and that detects that the cut-off bit is broken when the detector that has advanced to the advanced position contacts the tip of the bar material, a first step of determining whether or not the cut-off tool is damaged based on a control parameter for controlling at least one of the main spindle and the counter spindle at a first detection timing immediately after the cut-off operation is performed in a state in which the counter spindle holds the bar held by the main spindle; At least one of the timing immediately after the cut-off operation is performed in a state in which the bar material gripped by the main spindle is not gripped by the counter main spindle, and the timing at which continuous machining of the bar material is started. Second detection timing Limited and a second step of determining whether or not the cut-off tool is broken based on the detection result by the contact-type breakage detection unit. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a lathe and a method for detecting breakage of a cut-off bit that improve the accuracy of detecting breakage of a cut-off bit without requiring an increase in the machining time during continuous machining. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a front view schematically illustrating an example of the configuration of a lathe to which a guide bush is attached. [Figure 2] FIG. 1 is a front view schematically illustrating an example of the configuration of a lathe from which a guide bush has been removed. [Figure 3] 1 is a diagram schematically illustrating an example of a tool rest provided with a contact-type breakage detection unit that detects breakage of a cut-off tool bit. FIG. [Figure 4] 10 is a plan view schematically showing an example of a cut-off operation in which a cut-off tool cuts through a bar material during continuous machining. FIG. [Figure 5] 10 is a plan view schematically showing an example of a cut-off operation in which a cut-off tool cuts through a bar material during a top cut process. FIG. [Figure 6] FIG. 2 is a block diagram illustrating a configuration example of an electrical circuit of a lathe. [Figure 7] FIG. 2 is a block diagram illustrating an example of a control system for a headstock. [Figure 8] 10 is a flowchart schematically illustrating an example of processing. [Figure 9]10 is a flowchart schematically illustrating an example of a mechanical damage detection process. [Figure 10] 10 is a flowchart schematically illustrating an example of a non-mechanical damage detection process. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes embodiments of the present invention. Of course, the following embodiments are merely examples of the present invention, and not all of the features shown in the embodiments are necessarily essential to the solution of the invention.

[0014] (1) Overview of the technology included in this invention: First, an overview of the technology included in the present invention will be described with reference to the examples shown in Figures 1 to 10. Note that the figures in this application are diagrams showing schematic examples, and the magnifications in the directions shown in these figures may differ, and the figures may not be consistent. Of course, each element of the present technology is not limited to the specific example indicated by the symbol.

[0015] [Aspect 1] As illustrated in FIGS. 1 to 3 , a lathe 1 according to one aspect of the present technology includes a spindle (e.g., a front spindle 11), an opposing spindle (e.g., a back spindle 16), a tool rest 30, a control unit (e.g., an NC device 70), and a contact-type breakage detection unit 40. The spindle (11) releasably grips a bar B1. The opposing spindle (16) releasably grips a tip end B1a of the bar B1 protruding forward from the spindle (11). A cut-off tool TO3 is attached to the tool rest 30, and the cut-off tool TO3 cuts through the bar B1 gripped by the spindle (11). The control unit (70) controls the operation of the spindle (11), the opposing spindle (16), and the tool rest 30. The contact-type breakage detection unit 40 has a detector 41 that can advance to and retreat from an advance position P1 where it contacts the tip B1a of the bar B1 if the tip B1a remains after the cut-off operation in which the cut-off tool TO3 cuts through the bar B1, and detects that the cut-off tool TO3 is broken when the detector 41 that has advanced to the advance position P1 contacts the tip B1a of the bar B1. The control unit 70 performs processing to determine whether the cut-off tool TO3 is broken or not based on a control parameter (e.g., position deviation SG2 shown in FIG. 7) for controlling at least one of the main spindle 11 and the counter spindle 16 at a first detection timing (e.g., state ST3 shown in FIG. 4) immediately after the cut-off operation is performed with the counter spindle 16 gripping the bar B1 held by the main spindle 11. The control unit (70) performs a process to determine whether the cut-off tool TO3 is broken or not in accordance with the detection result by the contact-type breakage detection unit 40 at a second detection timing (for example, state ST6 shown in FIG. 5) different from the first detection timing (ST3).

[0016] At a first detection timing (ST3) immediately after a cut-off operation is performed while the counter spindle (16) is gripping the bar B1 held by the main spindle (11), it is determined whether the cut-off bit TO3 is broken based on control parameters (SG2) for controlling at least one of the main spindle (11) and the counter spindle (16). In this case, the detector 41, which moves back and forth, is not used to detect breakage of the cut-off bit, so the machining time during continuous machining is not extended. At a second detection timing (ST6), which is different from the first detection timing (ST3), it is determined whether the cut-off bit TO3 is broken based on the detection results of the contact-type breakage detector 40. As a result, breakage of the cut-off bit can be detected even at the second detection timing (ST6), when breakage of the cut-off bit cannot be detected based on the control parameters (SG2). As described above, the above-mentioned first aspect can provide a lathe that improves the accuracy of detecting breakage of the cut-off tool without the need to lengthen the machining time during continuous machining.

[0017] Here, "immediately after the cut-off operation is performed while the counter spindle is gripping the bar material held by the main spindle" means the time from the time when the cut-off bit cuts through the bar material if the cut-off bit is normal to the time when at least one of the main spindle and the counter spindle starts to move along the center line of the main spindle. In this application, the terms "first" and "second" are terms for distinguishing between two components that have similarities, and do not imply an order. The above remarks also apply to the following aspects.

[0018] [Aspect 2] As shown in Figure 5, the second detection timing may be timing (ST6) immediately after the cut-off operation is performed while the counter spindle (16) is not gripping the bar B1 held by the spindle (11). If the cut-off bit TO3 is damaged immediately after the top cut process, in which the counter spindle (16) is not gripping the bar B1 held by the spindle (11), the tip B1a of the bar B1 that should have been cut off remains, affecting subsequent machining operations. This mode makes it possible to detect breakage of the cut-off bit even immediately after the top cut process. The second detection timing may also be the timing at which continuous machining of the bar B1 begins. Even if top cutting is not performed at the start of continuous machining, the tip B1a of the bar B1 that should have been cut off may remain due to damage to the cut-off bit TO3. This embodiment makes it possible to detect breakage of the cut-off bit even at the start of continuous machining.

[0019] An embodiment in which the second detection timing is at least one of immediately after the top cut process and at the start of continuous machining can provide a suitable example for improving the accuracy of detecting breakage of the cut-off bit. Here, "immediately after a cut-off operation is performed when the bar held by the main spindle is not held by the counter main spindle" means the time from when the cut-off bit cuts through the bar to when the main spindle starts moving along the main spindle center line if the cut-off bit is normal.

[0020] [Aspect 3] Here, one of the main spindle (11) and the counter main spindle (16) is designated as a first main spindle (e.g., front main spindle 11), and the other is designated as a second main spindle (e.g., back main spindle 16). As illustrated in FIGS. 7 and 10, the control parameter may be a position deviation SG2, which is a difference signal between a position command CM1 and a position feedback signal SG1 for the first main spindle (11). The control unit (70) may determine that the cut-off tool TO3 is damaged if the position deviation SG2 exceeds a predetermined amount (e.g., threshold value Td1) due to control to separate the second main spindle (16) from the stopped first main spindle (11) at the first detection timing (ST3). The control unit (70) may determine that the cut-off tool TO3 is not damaged if the position deviation SG2 does not exceed the predetermined amount (Td1).

[0021] If the cut-off bit TO3 is damaged, the second spindle 16, which is moving away from the first spindle 11, applies a pulling force to the first spindle 11 via the bar B1, increasing the positional deviation SG2 for controlling the first spindle 11. If the cut-off bit TO3 is not damaged, the bar B1 is broken, so the second spindle 16 does not apply force to the first spindle 11, and the positional deviation SG2 for controlling the first spindle 11 does not increase. Therefore, if the positional deviation SG2 exceeds a predetermined amount (Td1) due to control to move the second spindle 16 away from the stopped first spindle 11, it can be determined that the cut-off bit TO3 is damaged, and if the positional deviation SG2 does not exceed the predetermined amount (Td1), it can be determined that the cut-off bit TO3 is not damaged. Furthermore, since the position deviation SG2 for determining breakage of the cut-off bit is a control parameter for controlling the stopped first spindle (11), there is no fluctuation in the position deviation SG2 due to movement of the first spindle (11). As described above, the third aspect can improve the accuracy of detecting breakage of the cut-off tool during continuous machining.

[0022] Although not included in the above-mentioned mode 3, the detection of breakage of the cut-off bit at the first detection timing may be performed by the following means a1 to a7, etc. Here, it is assumed that the first spindle is mounted on a first headstock, the first headstock feed motor moves the first headstock, and the first spindle rotation motor rotates the first spindle, the second spindle is mounted on a second headstock, the second headstock feed motor moves the second headstock, and the second spindle rotation motor rotates the second spindle. (a1) A means for determining whether or not the actual position of the first spindle in the spindle center line direction deviates from the commanded position by more than a predetermined amount due to control for moving the second spindle away from the stopped first spindle. (a2) A means for determining whether or not the torque generated in the first headstock feed motor by controlling the second spindle to move away from the stopped first spindle exceeds a predetermined amount. (a3) A means for determining whether or not the position deviation exceeds a predetermined amount due to control for separating the first spindle from the stopped second spindle. (a4) A means for determining whether or not the actual position of the first spindle in the spindle center line direction deviates from the command position by more than a predetermined amount due to control for separating the first spindle from the stopped second spindle. (a5) A means for determining whether or not the torque generated in the first headstock feed motor by controlling the first spindle to move away from the stopped second spindle exceeds a predetermined amount. (a6) A means for determining whether or not the actual rotation position of the first main spindle deviates from the commanded rotation position by more than a predetermined amount due to control for rotating the second main spindle relatively to the first main spindle. (a7) A means for determining whether or not the torque generated in the first main spindle rotating motor by controlling the second main spindle to rotate relatively to the first main spindle exceeds a predetermined amount.

[0023] [Aspect 4] As illustrated in FIG. 3 , the contact-type breakage detection unit 40 may include a detector drive unit (e.g., a cylinder 42) that moves the detector 41 in a direction (e.g., the X-axis direction) that intersects with the center line (e.g., the spindle center line AX1) of the spindle (11). The contact-type breakage detection unit 40 may also include a contact detection unit (e.g., a position sensor 43) that detects whether the detector 41, which has advanced toward the center line (AX1), has come into contact with the tip end B1a of the bar B1. The contact-type breakage detection unit 40 may detect that the cut-off bit TO3 is broken when the contact detection unit (43) detects that the detector 41, which has advanced toward the center line (AX1), has come into contact with the tip end B1a of the bar B1. This embodiment can provide a suitable example for detecting breakage of the cut-off bit immediately after top-cut processing or at the start of continuous machining.

[0024] [Aspect 4'] As one example of the above-mentioned fourth aspect, the contact-type breakage detection unit 40 may include a cylinder 42 that holds the detector 41 so that it can be retracted in a direction (e.g., the X-axis direction) perpendicular to the center line (e.g., the spindle center line AX1) of the spindle (11). The contact-type breakage detection unit 40 may include a position sensor 43 that detects the position of the detector 41 relative to the cylinder 42. The contact-type breakage detection unit 40 may detect that the cut-off bit TO3 is broken when the position sensor 43 detects that the detector 41, which has been advanced toward the center line (AX1), does not reach the center line (AX1). This aspect can provide a more suitable example for detecting breakage of the cut-off bit immediately after top cutting or at the start of continuous machining.

[0025] Although not included in the above-mentioned mode 4', the contact-type damage detection unit may be the following means b1 to b3, etc. Here, the tool post feed motor moves the tool post, and the tool post servo amplifier issues a torque command to the tool post feed motor. (b1) A means for detecting whether the detector, which is swung toward the center line of the spindle by a rotation drive unit (an example of a detector drive unit), has reached the center line of the spindle using a sensor (an example of a contact detection unit) that detects the stopping position of the detector. (b2) A means for determining whether the torque generated by the tool post servo amplifier (an example of a contact detection unit) in the tool post feed motor (an example of a detector drive unit) by controlling the advancement of the detector provided on the tool post toward the center line of the spindle exceeds a predetermined amount. In the above-mentioned means b2, when the torque exceeds a predetermined amount, it is determined that the detector has come into contact with the tip of the bar material, and the cut-off tool is broken. (b3) A tool post provided with a swingable detector and a sensor (an example of a contact detection unit) that detects the swing of the detector is moved by a tool post feed motor (an example of a detector drive unit) so that the detector advances toward the center line of the spindle. This means detecting whether the detector has swung or not by the sensor. In the above-mentioned means b3, when the detector swings, it means that it has come into contact with the tip of the bar material, and therefore, when the sensor detects the swing of the detector, it is detected that the cut-off tool bit has been damaged.

[0026] [Aspect 5] Furthermore, a method for detecting breakage of a cut-off bit of a lathe 1 according to one aspect of the present technology is a method for detecting breakage of a cut-off bit of a lathe 1 equipped with a main spindle (11), an opposing main spindle (16), a tool post 30, and a contact-type breakage detection unit 40, and includes the following steps (A1) and (A2). (A1) A first step (e.g., step S120 shown in FIG. 8 and FIG. 10) of determining whether or not the cut-off tool TO3 is damaged based on control parameters (SG2) for controlling at least one of the main spindle (11) and the counter spindle (16) at a first detection timing (ST3) immediately after the cut-off operation is performed while the counter spindle (16) is gripping the bar B1 gripped by the main spindle (11). (A2) A second step (e.g., step S112 shown in FIG. 8 and FIG. 9) of determining whether the cut-off tool TO3 is broken or not in accordance with the detection result by the contact-type breakage detection unit 40 at a second detection timing (ST6) different from the first detection timing (ST3).

[0027] The above-mentioned fifth aspect can provide a method for detecting breakage of a cut-off tool in a lathe, which improves the accuracy of detecting breakage of the cut-off tool without requiring an increase in the machining time during continuous machining.

[0028] (2) Specific examples of lathe configuration: FIG. 1 is a front view showing a schematic example of the configuration of a lathe 1 with a guide bush 14 attached. FIG. 2 is a front view showing a schematic example of the configuration of a lathe 1 with the guide bush 14 removed. FIG. 3 shows a tool post 30 equipped with a contact-type breakage detector 40 for detecting breakage of the cut-off bit TO3, together with the guide bush 14 and a bar B1. In FIG. 3, the bar B1 is shaded for clarity. FIG. 4 is a plan view showing a schematic example of the cut-off bit TO3 cutting through the bar B1 during continuous machining. FIG. 5 is a plan view showing a schematic example of the cut-off bit TO3 cutting through the bar B1 during top-cut processing.

[0029] 1 to 5, etc., symbol D81 indicates the upward direction, symbol D82 indicates the downward direction, symbol D83 indicates the leftward direction, symbol D84 indicates the rightward direction, symbol D85 indicates the forward direction, and symbol D86 indicates the rearward direction. These directions are based on the direction in which the lathe 1 shown in FIG. 1 is viewed. The control axes of the lathe 1 include an X-axis indicated by "X," a Y-axis indicated by "Y," and a Z-axis indicated by "Z." The Z-axis direction is a horizontal direction along the spindle center line AX1, which is the rotation center of the bar B1. The X-axis direction is a horizontal direction perpendicular to the Z-axis. The Y-axis direction is a vertical direction perpendicular to the Z-axis. The Z-axis and the X-axis do not have to be perpendicular as long as they intersect, and the Z-axis and the Y-axis do not have to be perpendicular as long as they intersect. Furthermore, the drawings referred to in this specification merely show examples for explaining the present technology and do not limit the present technology. The explanation of the positional relationship of each part is merely an example. Therefore, the present technology also includes reversing the left and right sides, reversing the direction of rotation, etc. The identity of the direction, position, etc. is not limited to exact agreement, and includes deviation from exact agreement due to error.

[0030] The lathe 1 is an NC lathe equipped with a headstock 10, a headstock drive unit 13, a back headstock 15, a back headstock drive unit 18, a support stand 25, a tool rest 30, a tool rest drive unit 31, a contact-type breakage detection unit 40, an NC (numerical control) unit 70, and the like. Here, the NC unit 70 is an example of a control unit. The headstock 10 incorporates a front spindle 11, which is an example of a spindle that releasably grips a bar B1 inserted from the rear by a material feeder 20. A front end 11a of the front spindle 11 faces the back spindle 16, and a rear end 11b of the front spindle 11 faces the material feeder 20. The front spindle 11 has a through-hole 11h that passes through along a spindle center line AX1. The bar B1 is inserted from the rear into the through-hole 11h. The back spindle stock 15 incorporates a back spindle 16, an example of an opposing spindle, which releasably grips the tip B1a of the bar B1 protruding forward from the front end 11a of the front spindle 11. The front end 16a of the back spindle 16 faces the front end 11a of the front spindle 11. That is, the front spindle 11 and the back spindle 16 face each other. Note that the "forward" direction of the front spindle 11 refers to the direction in which the bar B1 is pushed out from the front spindle 11, which is the rightward direction D84 in the example shown in FIG. 1. The "rearward" direction of the front spindle 11 refers to the direction from the front spindle 11 toward the material feeder 20, which is the leftward direction D83 in the example shown in FIG. 1. The "forward" direction of the back spindle 16 refers to the direction in which the back spindle 16 faces the front spindle 11, which is the leftward direction D83 in the example shown in FIG. 1. The mounting holes 26 of the support base 25 can be fitted with the guide bush 14 as shown in Fig. 1, and the front part of the front spindle 11 can be inserted therein as shown in Fig. 2. Therefore, the lathe 1 is a moving spindle type lathe that can be switched between the presence and absence of the guide bush 14.

[0031] The front spindle 11 has a gripping section 12 that releasably grips the bar B1 at a portion including the front end 11a. The gripping section 12 releasably grips the bar B1 and is rotatable together with the bar B1 around the spindle center line AX1. The NC device 70 controls the gripping state of the gripping section 12 by driving a gripping actuator 12a, as shown in FIG. 6. The gripping section 12 can be configured, for example, by a collet. The NC device 70 controls a servo motor (e.g., a built-in motor) (not shown) to rotate the front spindle 11. The front headstock drive section 13 moves the front headstock 10, to which the front spindle 11 is attached, in the Z-axis direction in accordance with commands from the NC device 70.

[0032] The back spindle 16 includes a gripper 17 that releasably grips the front end 16a of the bar B1 after front machining. The gripper 17 releasably grips the front end B1a of the bar B1 and can rotate together with the bar B1 around the spindle center line AX1. The workpiece W1, which becomes the final product, is the portion of the bar B1 that includes the front end B1a and is separated from the bar B1 by a cut-off tool TO3. The NC unit 70 controls the gripping state of the gripper 17 by driving a gripping actuator 17a, as shown in FIG. 6. The gripper 17 can be configured, for example, with a collet. The NC unit 70 controls a servo motor (e.g., a built-in motor) (not shown) to rotate the back spindle 16. The back headstock drive unit 18 moves the back headstock 15, to which the back spindle 16 is attached, in the Z-axis direction according to commands from the NC unit 70. The back headstock drive unit 18 may move the back headstock 15 incorporating the back spindle 16 in at least one of the X-axis direction and the Y-axis direction. The workpiece W1 separated from the bar B1 is turned into a product by back machining.

[0033] The material feeder 20 that supplies the bar B1 to the front spindle 11 includes, for example, a rail (not shown) along the spindle center line AX1 and a drive unit (not shown) that moves the bar B1 on the rail toward the front spindle 11 (rightward D84). The material feeder 20 inserts the bar B1 into the through-hole 11h of the front spindle 11 from the rear. The material feeder 20 detects whether the bar B1 to be supplied to the front spindle 11 has run out and transmits a bar shortage signal to the NC device 70 indicating that the bar B1 has run out. The material feeder 20 may be a finger-type bar feeder that grips the bar and feeds it to the front spindle, or a push-pull-type bar feeder that feeds the bar to the front spindle simply by pushing it from behind. The bar B1 is not limited to a solid material such as a long cylindrical material, but may also be a hollow material such as a long cylindrical material.

[0034] The support base 25 is located between the front headstock 10 and the back headstock 15 in the Z-axis direction and has a mounting hole 26 that penetrates in the Z-axis direction. When a guide bush is used as shown in FIG. 1, the guide bush 14 is inserted into the mounting hole 26 and removably attached to the support base 25. The guide bush 14 supports the bar B1 that protrudes forward from the through hole 11h of the front spindle 11 so that it can slide in the Z-axis direction. The portion of the bar B1 that protrudes from the guide bush 14 toward the back spindle 16 (rightward D84) is machined by the tool TO1. When a guide bush is not used as shown in FIG. 2, the front part of the front spindle 11 is inserted into the mounting hole 26. The portion of the bar B1 that protrudes forward from the front spindle 11 (rightward D84) is machined by the tool TO1.

[0035] The tool rest 30 is equipped with multiple tools TO1 for machining the bar B1 and is movable in the X-axis and Y-axis directions. The tool rest driver 31 moves the tool rest 30 in the X-axis and Y-axis directions according to commands from the NC device 70. The tool rest driver 31 may also move the tool rest 30 in the Z-axis direction. The tool rest 30 may be a comb tool rest as shown in FIG. 3 or a turret tool rest. The lathe 1 may also be equipped with a back-machining tool rest for back-machining the workpiece W1 held by the back spindle 16. The multiple tools TO1 include tools TO2 including a cut-off tool TO3, rotary tools such as a rotary drill or end mill, and the like. The tool rest 30 shown in FIG. 3 includes a tool rest 30A equipped with a cut-off tool TO3 and a tool rest 30B equipped with a contact-type breakage detector 40. The tool post 30A is equipped with a plurality of cutting tools TO2, including the cut-off tool TO3 located at the bottom, protruding toward the spindle center line AX1 (rearward direction D86). As shown in Fig. 4, the cut-off tool TO3 cuts through the bar B1 between the front spindle 11 and the back spindle 16, thereby separating the workpiece W1, including the tip B1a of the bar B1 held by the back spindle 16, from the bar B1. The tool post 30B shown in Fig. 3 is provided with a contact-type breakage detection unit 40, with a detector 41 protruding toward the spindle center line AX1 (forward direction D85).

[0036] The tool rests 30A, 30B may be integrated and movable in the X-axis and Y-axis directions by a single tool rest drive unit 31, or may be movable independently of each other at least in the X-axis direction by separate tool rest drive units. Also, the cut-off tool TO3 may be attached to the tool rest 30B instead of the tool rest 30A, and the contact-type breakage detection unit 40 may be attached to the tool rest 30A instead of the tool rest 30B.

[0037] Figure 4 shows the cut-off operation in which cut-off tool TO3 separates workpiece W1 from bar B1 during continuous machining. In Figure 4, the "closed" state of grippers 12, 17 indicates that grippers 12, 17 are tightened by gripping actuators 12a, 17a shown in Figure 6 to grip bar B1. Figure 4 shows the cut-off operation when a guide bush is not used, but when a guide bush is used, the cut-off operation is performed with guide bush 14 holding bar B1.

[0038] In state ST1 shown in FIG. 4, the gripper 12 of the front spindle 11 grips a bar B1, and the gripper 17 of the back spindle 16 grips a workpiece W1 including a tip B1a of the bar B1. While the front spindle 11 and the back spindle 16, which are gripping the bar B1, are rotating, the NC device 70 controls the movement of the tip TO3a of the cut-off tool TO3 together with the tool rest 30 in the X-axis direction (rearward direction D86) until it crosses the spindle center line AX1 between the front spindle 11 and the back spindle 16. This results in state ST2, in which the bar B1 has been cut off between the front spindle 11 and the back spindle 16, i.e., the workpiece W1 gripped by the back spindle 16 has been separated from the bar B1. Next, the NC device 70 controls the retraction of the cut-off tool TO3 together with the tool rest 30 from between the workpiece W1 and the bar B1. A state ST3 shown in FIG. 4 is an example of the first detection timing immediately after a cut-off operation is performed in a state in which the back spindle 16 is gripping the bar B1 gripped by the front spindle 11.

[0039] If the cut-off bit TO3 breaks, it becomes impossible to separate the workpiece W1 from the bar B1. Therefore, it is desirable to detect breakage of the cut-off bit TO3. The lathe 1 of this example is equipped with a non-mechanical breakage detection means that determines whether the cut-off bit TO3 is broken based on control parameters for controlling the front spindle 11 during continuous machining. By using the control parameters for cut-off bit breakage detection, cut-off bit breakage can be detected quickly during continuous machining. Cut-off bit breakage detection by the non-mechanical breakage detection means is limited to immediately after a cut-off operation is performed while the counter spindle 16 is gripping the bar B1 held by the front spindle 11.

[0040] As shown in FIG. 5, the cut-off operation is also performed immediately after the top-cut process, in which the cut-off tool TO3 cuts off the tip B1a of the bar B1 while the back spindle 16 is not gripping the tip B1a of the bar B1. The tip surface of the new bar B1 supplied from the feeder 20 is chamfered to facilitate passage through the front spindle 11 and guide bush 14. Furthermore, when continuous machining is resumed after the bar B1 has been partially used, the tip surface of the bar B1 is expected to change over time. The top-cut process is performed to cut the tip surface of the bar B1 to achieve precise dimensions or to position the bar B1 when a new bar B1 is supplied from the feeder 20 to the front spindle 11 or when continuous machining is resumed. State ST4 shown in FIG. 5 is a state in which the gripper 12 of the front spindle 11 grips the bar B1, but the gripper 17 of the back spindle 16 does not grip the bar B1. While rotating the front spindle 11 gripping the bar B1, the NC device 70 controls the movement of the tip TO3a of the cut-off tool TO3 together with the tool rest 30 in the X-axis direction (rear direction D86) until it passes the front spindle center line AX1 of the front spindle 11. This brings the bar B1 into a state ST5 where it has been cut off in front of the front spindle 11, i.e., where the tip B1a has been separated from the bar B1. Next, the NC device 70 controls the cut-off tool TO3 together with the tool rest 30 to retract from the front spindle center line AX1 of the front spindle 11. State ST6 shown in FIG. 5 is an example of the second detection timing immediately after the cut-off operation is performed when the back spindle 16 is not gripping the bar B1 gripped by the front spindle 11.

[0041] If the cut-off bit TO3 is broken even immediately after the top cut process, the tip B1a of the bar B1 that should have been cut off will remain, affecting subsequent machining operations. Also, even if the top cut process is not performed, there are cases where the back spindle 16 is not gripping the bar B1 that is being gripped by the front spindle 11 when continuous machining begins. In this case, too, the non-mechanical breakage detection means cannot detect breakage in the cut-off bit. The lathe 1 of this example is provided with a contact-type breakage detection unit 40 for detecting breakage of the cut-off tool, in addition to the non-mechanical breakage detection means, as shown in FIG.

[0042] The contact-type damage detection unit 40 shown in FIG. 3 includes a detector 41 protruding from the tool post 30B toward the spindle center line AX1 (frontward direction D85), a cylinder 42 incorporated in the tool post 30B, and a position sensor 43 incorporated in the tool post 30B. Here, the cylinder 42 is an example of a detector drive unit, and the position sensor 43 is an example of a contact detection unit. The detector 41 is held relative to the cylinder 42 so that it can move forward and backward in the X-axis direction, which is perpendicular to the spindle center line AX1. The cylinder 42 holds the detector 41 so that it can be retracted in the X-axis direction, and applies a force to the detector 41 in the frontward direction D85. The position sensor 43 detects the position of the detector 41 relative to the cylinder 42. When cut-off bit breakage detection is performed, with the spindle center line AX1 oriented in the direction of projection of the detector 41, if the tip B1a of the bar B1 does not remain, the tool post 30B moves forward in the front direction D85 until the tip 41a of the detector 41 passes the spindle center line AX1. Therefore, the detector 41 can advance to and retreat from an advanced position P1 where it comes into contact with the tip B1a of the bar B1 if the tip B1a of the bar B1 remains after the cut-off operation in which the cut-off bit TO3 cuts through the bar B1. The contact-type breakage detection unit 40 detects that the cut-off bit TO3 is broken when the detector 41, which has advanced to advanced position P1, comes into contact with the tip B1a of the bar B1. From the above, when the position sensor 43 detects that the detector 41 has reached the spindle center line AX1 immediately after movement, it is determined that the cut-off bit TO3 is not broken. When the position sensor 43 detects that the detector 41 has hit the tip B1a of the bar B1 and has not reached the spindle center line AX1 immediately after movement, it is determined that the cut-off bit TO3 is broken. Because the contact-type breakage detection unit 40 moves the detector 41, it can be said to be a mechanical breakage detection means.

[0043] The contact-type breakage detection unit 40 takes longer to detect breakage in a cut-off bit than non-mechanical breakage detection means because it is necessary to move the detector 41 together with the tool post 30. For this reason, if the contact-type breakage detection unit 40 is used to detect breakage in a cut-off bit during continuous machining, the continuous machining time will be longer. Therefore, in the lathe 1 of this example, cut-off bit breakage detection is performed by the contact-type breakage detection unit 40 only at the second detection timing when cut-off bit breakage cannot be detected by the non-mechanical breakage detection means. This eliminates the need to extend the machining time during continuous machining, and improves the accuracy of detecting cut-off bit breakage.

[0044] FIG. 6 shows a schematic diagram of the electrical circuit configuration of a lathe 1 equipped with an NC device 70. The NC device 70 is connected to an operation unit 80, a material feeder 20, a headstock drive unit 13, a rotation drive unit (not shown) for the headstock 11, a gripping actuator 12a, a backheadstock drive unit 18, a rotation drive unit (not shown) for the backspindle 16, a gripping actuator 17a, a tool rest drive unit 31, a position sensor 43 for the contact-type breakage detection unit 40, and the like. The gripping actuator 12a drives the gripping unit 12 of the headspindle 11 shown in FIGS. 1 and 2. The gripping actuator 17a drives the gripping unit 17 of the backspindle 16 shown in FIGS. 1 and 2. The NC device 70 includes a CPU 71, which is a processor, a ROM 72, which is a semiconductor memory, a RAM 73, which is a semiconductor memory, a clock circuit 74, an I / F (interface) 75, and the like. In FIG. 6, the interfaces for the operation unit 80, material feeder 20, headstock drive unit 13, gripping actuator 12a, backheadstock drive unit 18, gripping actuator 17a, tool rest drive unit 31, position sensor 43, etc. are collectively referred to as I / F 75. A control program PR1 for interpreting and executing a machining program PR2 is written in ROM 72. ROM 72 may be a rewritable semiconductor memory. The machining program PR2 created by an operator is rewritably stored in RAM 73. The machining program is also called an NC program. The CPU 71 uses RAM 73 as a work area and executes the control program PR1 recorded in ROM 72 to realize the functions of the NC device 70.

[0045] The operation unit 80 includes an input unit 81 and a display unit 82, and functions as a user interface for the NC device 70. The input unit 81 is configured, for example, by buttons or a touch panel for receiving operation inputs from an operator. The display unit 82 is configured, for example, by a display for displaying the contents of various settings received as operation inputs from the operator and various information related to the lathe 1. The operator can store the machining program PR2 in the RAM 73 using the operation unit 80 or an external computer (not shown).

[0046] The headstock drive unit 13 includes a servo amplifier 51 connected to the NC device 70 and a servo motor 52 connected to the servo amplifier 51 in order to move the headstock 10 including the head spindle 11 along the Z axis. The servo motor 52 is an example of a first headstock feed motor. The servo amplifier 51 controls the position and movement speed of the headstock 10 in the Z axis direction in accordance with commands from the NC device 70. The servo motor 52 includes an encoder 53 and rotates in accordance with commands from the servo amplifier 51, moving the headstock 10 in the Z axis direction via a feed mechanism and guide (not shown). A ball screw mechanism or the like can be used as the feed mechanism, and a linear guide or the like can be used as the guide.

[0047] The back headstock drive unit 18 includes a servo amplifier 61 connected to the NC device 70 and a servo motor 62 connected to the servo amplifier 61 in order to move the back headstock 15 including the back spindle 16 along the Z axis. The servo motor 62 is an example of a second headstock feed motor. The servo amplifier 61 controls the position and movement speed of the back headstock 15 in the Z axis direction in accordance with commands from the NC device 70. The servo motor 62 includes an encoder 63 and rotates in accordance with commands from the servo amplifier 61, moving the back headstock 15 in the Z axis direction via a feed mechanism and guide (not shown). A ball screw mechanism or the like can be used as the feed mechanism, and a linear guide or the like can be used as the guide. Furthermore, the back headstock driving unit 18 may include a servo amplifier (not shown) connected to the NC device 70 and a servo motor (not shown) connected to the servo amplifier in order to move the back headstock 15 along at least one of the X-axis and Y-axis.

[0048] The tool post drive unit 31 includes a servo amplifier (not shown) connected to the NC device 70 and a servo motor (an example of a tool post feed motor) (not shown) connected to the servo amplifier in order to move the tool post 30 along the X-axis and Y-axis. The servo motor rotates in accordance with commands from the servo amplifier, and moves the tool post 30 in the X-axis and Y-axis directions via a feed mechanism and guide (not shown).

[0049] FIG. 7 shows a schematic example of a control system for the headstock 10. The NC device 70 can output a position command CM1 for the front spindle 11 to the servo amplifier 51. The subtractor 54 of the servo amplifier 51 inputs the position command CM1 from the NC device 70, inputs a position feedback signal SG1 based on the output from the encoder 53 of the servo motor 52, and outputs a position deviation SG2 to the position gain. The position deviation SG2 is a difference signal between the position command CM1 for the front spindle 11 and the position feedback signal SG1. The servo amplifier 51 can output the position deviation SG2 to the NC device 70. The position gain inputs the position deviation SG2 from the subtractor 54 and outputs a speed command to the subtractor 55 based on the position deviation SG2. The subtractor 55 inputs a speed command from the position gain, inputs a speed feedback signal based on the output from the encoder 53, corrects the speed command based on the speed feedback signal, and inputs it to the speed gain. The speed gain inputs the corrected speed command from the subtractor 55 and outputs a torque command to the servo motor 52 based on the corrected speed command. Since the torque of the servo motor 52 is proportional to the current flowing through the servo motor 52 , the torque command corresponds to the value of the current flowing through the servo motor 52 .

[0050] The NC device 70 of this example acquires the position deviation SG2 from the servo amplifier 51 and performs processing to determine whether the cut-off tool TO3 is damaged or not based on the position deviation SG2 during continuous machining. The position deviation SG2 is an example of a control parameter for controlling the front spindle 11. The control system of the back headstock 15 is the same as the control system of the front headstock 10. The control system of the tool rest 30 is the same as the control system of the front headstock 10.

[0051] (3) Examples of processing: Fig. 8 shows a schematic example of the machining process performed when the machining program PR2 shown in Fig. 6 is executed. The machining process is performed by the NC device 70 executing the control program PR1. As a prerequisite for the machining process, the NC device 70 prepares in the RAM 73 a mechanical execution flag indicating whether or not to use the contact-type damage detection unit 40, and sets this mechanical execution flag to ON (for example, 1).

[0052] When the machining process starts, the NC device 70 determines whether to perform the first machining of the continuous machining (step S102). Hereinafter, the term "step" will be omitted. The first machining of the continuous machining occurs immediately after the lathe 1 is turned on or when continuous machining is resumed after being stopped with the power on. In these cases, the front spindle 11 side stops with the tip TO3a of the cut-off bit TO3 beyond the spindle center line AX1, as shown in state ST2 in FIG. 4, and the back spindle 16 side retracts to the rear origin position (not shown), as shown in state ST5 in FIG. 5. The gripper 17 of the back spindle 16 retracted to the origin position either grips the workpiece W1 or is open and does not grip the workpiece W1. When the bar B1 gripped by the front spindle 11 abuts the cut-off bit TO3, the bar B1 is positioned, so top cutting is not necessary. When performing the first machining of the continuous machining, the NC device 70 turns on the mechanical execution flag (S104) and then proceeds to S106, and when performing the second or subsequent machining of the continuous machining, the NC device 70 proceeds to S106 without changing the process.

[0053] In S106, the NC device 70 determines whether or not the top cut process (see FIG. 5) has been performed. As described above, the top cut process is performed to create a reference for the position of the bar B1 when a new bar B1 is supplied to the front spindle 11 from the material feeder 20 or when continuous machining is resumed. The top cut process may be performed when a top cut command written in the machining program PR2 at a location before continuous machining is executed. During continuous machining, the position of the bar B1 is determined by the cut-off operation, so there is no need to perform the top cut process. A top cut command is not written in the machining program PR2 at a location during continuous machining. If the top cut processing has been performed, the NC device 70 turns on the mechanical execution flag (S108) and then proceeds to S110, and if the top cut processing has not been performed, the NC device 70 proceeds to S110 as is.

[0054] In S110, if the mechanical execution flag is on, the NC device 70 performs the processes of S112 to S114 and then proceeds to S116; if the mechanical execution flag is off, the NC device 70 proceeds directly to S116. In S112, the NC device 70 performs a mechanical breakage detection process using the contact-type breakage detection unit 40 to determine whether the cut-off tool TO3 is broken. The mechanical breakage detection process is performed at a second detection timing different from the first detection timing (state ST3 shown in FIG. 4) immediately after the cut-off operation is performed while the back spindle 16 is gripping the bar B1 gripped by the front spindle 11. At this second detection timing, the back spindle 16 is retracted backward, as in state ST6 shown in FIG. 5. After the mechanical breakage detection process, the NC device 70 turns the mechanical execution flag off (e.g., to 0) (S114) and proceeds to S116.

[0055] FIG. 9 shows a schematic example of the mechanical damage detection process performed in S112 of FIG. When the mechanical breakage detection process begins, the NC device 70 performs a process of moving the tool post 30B in the front direction D85 until the tip 41a of the probe 41 passes the spindle center line AX1 (S202) if the tip B1a of the bar B1 does not remain, with the probe 41 extending in the direction of the spindle center line AX1 as shown in FIG. 3. At this time, the NC device 70 drives the tool post driver 31 to move the tool post 30B. In S202, the probe 41 advances toward the spindle center line AX1.

[0056] Next, the NC device 70 acquires the position of the detector 41 detected by the position sensor 43, and determines whether or not the detector 41 has reached the spindle center line AX1 based on this detected position (S204).

[0057] If the cut-off bit TO3 is normal, i.e., if the cut-off bit TO3 is not broken, the tip B1a of the bar B1 does not remain, and the detector 41 reaches the spindle center line AX1 without contacting the tip B1a. When the position sensor 43 detects that the detector 41 has reached the spindle center line AX1, the NC device 70 determines that the cut-off bit TO3 is normal and proceeds to S206. In S206, the NC device 70 moves the tool post 30B in a direction that retracts the detector 41 from the movement path of the bar B1, thereby ending the mechanical breakage detection process. Thereafter, in S114 shown in FIG. 8, the mechanical execution flag is turned off, and the process from S116 onward shown in FIG. 8 is performed.

[0058] If the cut-off bit TO3 is broken, the tip B1a of the bar B1 remains, so the detector 41 comes into contact with the tip B1a and does not reach the spindle center line AX1. If the position sensor 43 detects that the detector 41 is not positioned to reach the spindle center line AX1, the NC device 70 determines that the cut-off bit TO3 is broken and proceeds to S208. In S208, the NC device 70 outputs an alarm indicating the breakage of the cut-off bit TO3 and stops the machining process. The alarm output can be displayed on the display unit 82, output an alarm sound from a speaker (not shown), or output an alarm to a computer (not shown) connected to the NC device 70. In this case, the operator can replace the broken cut-off bit with an undamaged one and resume the machining process from S102 in FIG. 8.

[0059] As described above, the contact-type breakage detection unit 40 detects that the cut-off bit is normal if the detector 41 that has advanced to the advance position P1 does not come into contact with the tip B1a of the bar B1, and detects that the cut-off bit is broken if the detector 41 that has advanced to the advance position P1 comes into contact with the tip B1a of the bar B1. The NC device 70 performs processing to determine whether the cut-off bit TO3 is broken or not according to the detection result by the contact-type breakage detection unit 40.

[0060] 8 continues, in S116, the NC device 70 performs a process of performing front surface machining on the tip portion B1a of the bar B1 held by the front spindle 11. If the back spindle 16 is holding a workpiece W1 that has already been front surface machined, the NC device 70 performs a process of performing back surface machining on the workpiece W1 held by the back spindle 16 and ejects the product. In S116, the NC device 70 drives the front headstock drive unit 13 to move the front headstock 10, drives a rotation drive unit (not shown) to rotate the front spindle 11, drives the back headstock drive unit 18 to move the back headstock 15, drives a rotation drive unit (not shown) to rotate the back spindle 16, and drives the tool rest drive unit 31 to move the tool rest 30.

[0061] After the front surface machining of the bar B1, the NC device 70 causes the back spindle 16 to grip the tip portion B1a of the bar B1 held by the front spindle 11, thereby performing a bar cut-off process (S118). First, the NC device 70 causes the back headstock drive unit 18 to move the back headstock 15, and causes the gripping unit 17 of the back spindle 16 to grip the tip portion B1a of the bar B1 protruding forward from the front headstock 10. This state is state ST1 shown in FIG. 4. Next, the NC device 70 causes the front spindle 11 and the back spindle 16 to rotate at the same rotational speed, and causes the tool rest drive unit 31 to move the tool rest 30 so that the workpiece W1, including the tip portion B1a of the bar B1, is cut off from the bar B1 by the cut-off tool TO3. The cut-off tool TO3 operates to cut through the bar B1, i.e., to separate the workpiece W1 from the bar B1. The state in which the operation of separating the workpiece W1 by the cut-off tool TO3 is completed is state ST2 shown in FIG.

[0062] After the bar cut-off process, the NC device 70 moves the cut-off tool TO3 away from the bar B1 by using the tool post driver 31 to move the tool post 30 in the X-axis direction (state ST3 shown in FIG. 4), and then performs non-mechanical breakage detection (S120). The non-mechanical breakage detection process is performed at a first detection timing (state ST3 shown in FIG. 4) immediately after the cut-off operation is performed while the back spindle 16 is holding the bar B1 held by the front spindle 11. The non-mechanical breakage detection process may be performed when a non-mechanical breakage detection command written in the machining program PR2 at a point during continuous machining is executed. Before continuous machining, a cut-off operation is not performed while the back spindle 16 is holding the bar B1 held by the front spindle 11, so a non-mechanical breakage detection command is not written in the machining program PR2 at a point before continuous machining.

[0063] FIG. 10 shows a schematic example of the non-mechanical damage detection process performed in S120 of FIG. When the non-mechanical damage detection process begins, the NC device 70 begins control in the Z-axis direction to move the back spindle 16 (back spindle 15) away from the stopped front spindle 11 (front spindle stock 10) (S302). At this time, the NC device 70 issues a position command to the servo amplifier 61 of the back spindle drive unit 18 to move the back spindle 16 away from the front spindle 11. The NC device 70 also issues a position command CM1 to the servo amplifier 51 of the front spindle drive unit 13 shown in FIG. 7 to maintain the current position of the front spindle 11. If the cut-off bit TO3 is normal, the workpiece W1 is separated from the bar B1, and the back spindle 16 moves in a direction away from the front spindle 11. If the cut-off bit TO3 is damaged, the back spindle 16 is connected to the front spindle 11 via the bar B1, and therefore movement of the back spindle 16 is hindered. In this case, a pulling force toward the back headstock 15 is applied from the bar B1 to the headstock 10 on which the head spindle 11 is mounted. The servo amplifier 51 supplies a position feedback signal SG1 to a subtraction unit 54 based on the output from the encoder 53 of the servo motor 52 so as to maintain the head spindle 11 at the position indicated by the position command CM1 against the pulling force. The generated position feedback signal SG1 indicates a position that is rearward (leftward D83) from the position indicated by the position command CM1. As a result, the head spindle 11 is maintained at approximately the position indicated by the position command CM1 in the Z-axis direction.

[0064] After the process of S302, the NC device 70 acquires a position deviation SG2 from the servo amplifier 51 of the headstock drive unit 13 (S304). The position deviation SG2 is a difference signal between the position command CM1 and the position feedback signal SG1. The NC device 70 acquires a position deviation value d1, which is the absolute value of the position deviation SG2, and performs a process of determining whether or not the cut-off tool TO3 is damaged based on the position deviation value d1 from S306 onwards.

[0065] If the cut-off bit TO3 is normal, i.e., if the cut-off bit TO3 is not damaged, no pulling force toward the back headstock 15 is applied to the headstock 10, so even if the control amount of the separation control of the back spindle 16 increases, the position deviation value d1 does not increase. If the cut-off bit TO3 is damaged, a pulling force toward the back headstock 15 is applied to the headstock 10, so as the control amount of the separation control of the back spindle 16 increases, the position deviation value d1 increases. Therefore, after acquiring the position deviation value d1, the NC device 70 determines whether the position deviation value d1 exceeds a predetermined threshold value Td1 (S306). Note that the NC device 70 issues a position command CM1 to the servo amplifier 51 to maintain the current position of the head spindle 11 in the Z-axis direction, so even if the position deviation value d1 increases, the head spindle 11 will hardly move from the position indicated by the position command CM1.

[0066] If the position deviation value d1 does not exceed the threshold value Td1, the NC device 70 determines whether the control amount of the separation control of the back spindle 16 has reached a predetermined control amount (S308). If the control amount of the separation control has not reached the predetermined control amount, the NC device 70 returns the process to S306. If the control amount of the separation control has reached the predetermined control amount, the NC device 70 determines that the cut-off tool TO3 is normal and ends the non-mechanical damage detection process. Thereafter, the process from S122 onwards shown in FIG. 8 is carried out.

[0067] If the position deviation value d1 exceeds the threshold value Td1, the NC device 70 determines that the cut-off bit TO3 is damaged, and proceeds to S310. In S310, the NC device 70 outputs an alarm indicating damage to the cut-off bit TO3 and stops the machining process. The process of outputting the alarm can be a process of displaying the alarm on the display unit 82, a process of outputting an alarm sound from a speaker (not shown), a process of outputting an alarm to a computer (not shown) connected to the NC device 70, or the like. In this case, the operator can replace the damaged cut-off bit with an undamaged cut-off bit and resume the machining process from S102 shown in FIG. 8.

[0068] As described above, in state ST3 shown in FIG. 4, the NC device 70 determines that the cut-off bit is broken if the position deviation SG2 exceeds a predetermined amount due to control to move the back spindle 16 away from the stopped front spindle 11, and determines that the cut-off bit is normal if the position deviation SG2 does not exceed the predetermined amount.

[0069] When the processing shown in FIG. 8 continues, in S122, the NC device 70 determines whether or not it has received a material shortage signal from the material feeder 20 indicating that the bar B1 has run out. If the NC device 70 does not receive the material shortage signal, the process returns to S102, whereby the machining process is repeated and non-mechanical damage detection process is performed during continuous machining.

[0070] When the NC device 70 receives a stockout signal, it turns on the mechanical execution flag (S124), performs a bar replacement process in which the remaining bar is discharged and a new bar B1 is supplied from the material feeder 20 to the front spindle 11 (S126), performs a top cut process (see FIG. 5) (S128), and returns the process to S102. In this case, a mechanical breakage detection process is performed in S112. Therefore, immediately after the cut-off operation is performed while the back spindle 16 is not gripping the bar B1 held by the front spindle 11, a process is performed to determine whether the cut-off tool TO3 is damaged or not based on the detection result by the contact-type breakage detection unit 40. When a top cut command is written in the machining program PR2 at a position before continuous machining, the processes of S124 and S128 may be omitted.

[0071] As described above, at the first detection timing (state ST3 shown in FIG. 4 ) immediately after the cut-off operation is performed while the back spindle 16 is gripping the bar B1 held by the front spindle 11, it is determined whether the cut-off bit TO3 is broken or not based on the position deviation SG2, which is a control parameter for controlling the front spindle 11. In this case, the detector 41, which moves back and forth, is not used to detect breakage of the cut-off bit, so the machining time during continuous machining is not extended. On the other hand, at the timing when continuous machining of the bar B1 is started or immediately after the cut-off operation is performed while the back spindle 16 is not gripping the bar B1 held by the front spindle 11 (state ST6 shown in FIG. 5 ), it is determined whether the cut-off bit TO3 is broken or not based on the detection result of the contact-type breakage detector 40. As a result, breakage of the cut-off bit can be detected even at the second detection timing, when breakage of the cut-off bit cannot be detected based on the control parameters. As described above, this example does not require an increase in the machining time during continuous machining, and can improve the accuracy of detecting breakage of the cut-off tool.

[0072] (4) Variation: The present invention can be modified in various ways. For example, the second detection timing for performing the mechanical breakage detection process shown in FIG. 9 may be only the timing immediately after the top cut process is performed, or only the timing when continuous processing of the bar B1 is started.

[0073] 8, the NC device 70 may perform processing to determine whether or not the cut-off bit TO3 is broken, based on a position deviation that is a difference signal between a position command and a position feedback signal in the back spindle 16, in addition to the position deviation SG2 in the front spindle 11. For example, the NC device 70 may determine that the cut-off bit is broken if, at a first detection timing, the position deviation SG2 in the front spindle 11 exceeds a first predetermined amount or the position deviation in the back spindle 16 exceeds a second predetermined amount. Furthermore, the NC device 70 may perform processing to determine whether or not the cut-off bit TO3 is damaged based on the position deviation in the back spindle 16, without using the position deviation SG2 in the front spindle 11. In this case, the NC device 70 may determine that the cut-off bit is damaged when the position deviation exceeds a predetermined amount due to control to move the front spindle 11 away from the back spindle 16, which is stopped in the Z-axis direction, in state ST3 shown in Fig. 4, and may determine that the cut-off bit is normal when the position deviation does not exceed the predetermined amount.

[0074] Of course, non-mechanical damage detection processing may be performed by the above-mentioned means a1 to a7, etc. For example, the control parameter for controlling at least one of the front spindle 11 and the back spindle 16 may be a torque (for example, a torque command shown in FIG. 7) that the speed gain outputs to the servo motor, like the torque of means a2 and a5. The NC device 70 may determine that the cut-off bit is damaged if the torque exceeds a predetermined amount, and may determine that the cut-off bit is normal if the torque does not exceed the predetermined amount. Furthermore, the control parameters are not limited to the position deviation and torque in the Z-axis direction, but may also be parameters for controlling the speed in the Z-axis direction, parameters for controlling the rotation of at least one of the front spindle 11 and the back spindle 16 as in means a6 and a7, etc.

[0075] The mechanical breakage detection process in S112 shown in FIG. 8 may be performed by the above-mentioned means b1 to b3, etc. For example, when the tip 41 shown in FIG. 3 is fixed so as not to move forward or backward relative to the tool post 30B, the mechanical breakage detection process may be performed by means b2. In this case, when the spindle center line AX1 is present in the protruding direction of the tip 41, the NC device 70 may control the tool post 30B to advance the tip 41 to an advanced position P1 where the tip 41a of the tip 41 contacts the tip B1a of the bar B1 if the tip B1a remains toward the spindle center line AX1. At this time, a tool post servo amplifier (an example of a contact detection unit) connected to the NC device 70 issues a torque command to a tool post feed motor (an example of a tip drive unit) and outputs a torque value corresponding to this torque command to the NC device 70. If the tip B1a of the bar B1 remains, the tip 41a of the probe 41 comes into contact with the tip B1a, and the torque value exceeds a predetermined value. If the tip B1a of the bar B1 does not remain, the probe 41 does not come into contact with the tip B1a, and the torque value does not exceed the predetermined value. Therefore, the tool post servo amplifier, which outputs the torque value, detects whether the probe 41, which has advanced toward the spindle center line AX1, has come into contact with the tip B1a of the bar B1. The NC device 70 may acquire the torque value from the servo amplifier of the tool post driver 31, and determine that the cut-off bit is damaged if the torque value exceeds the predetermined value, or that the cut-off bit is normal if the torque value does not exceed the predetermined value.

[0076] Furthermore, if a torque limit can be applied to the movement of the tool post 30, it is possible to determine whether the cut-off tool TO3 is damaged by detecting the position of the tool post 30 on which the probe 41 is advanced toward the spindle center line AX1. In this case, a tool post servo amplifier (an example of a contact detection unit) connected to the NC device 70 outputs the position of the tool post 30 to the NC device 70. If the tip B1a of the bar B1 remains, the probe 41 advanced toward the spindle center line AX1 will be in a position that does not reach the spindle center line AX1, and this position will be detected by the tool post servo amplifier. If the tip B1a of the bar B1 does not remain, the probe 41 will be in a position that reaches the spindle center line AX1, and this position will be detected by the tool post servo amplifier. Therefore, the tool post servo amplifier that outputs the detected position of the tool post 30 detects whether the probe 41 advanced toward the spindle center line AX1 has come into contact with the tip B1a of the bar B1. The NC device 70 acquires the detected position of the tool post 30 from the servo amplifier of the tool post drive unit 31, and determines that the cut-off bit is broken if the detected position does not reach the spindle center line AX1, and determines that the cut-off bit is normal if the detected position reaches the spindle center line AX1.

[0077] Furthermore, if the tool post 30 is provided with a swingable detector and a proximity sensor (an example of a contact detection unit) that detects the swing of the detector, a mechanical breakage detection process may be performed by means b3. The proximity sensor reacts when the detector moves relative to the tool post 30 and does not react when the detector does not move relative to the tool post 30. The tool post feed motor is an example of a detector drive unit that moves the detector in a direction intersecting with the spindle center line AX1. If the tip B1a of the bar B1 remains toward the spindle center line AX1, the NC device 70 may control the tool post 30 to advance the detector to an advanced position where the detector comes into contact with the tip B1a. If the tip B1a of the bar B1 remains, the detector comes into contact with the tip B1a, causing the detector to move and the proximity sensor to react. If the tip B1a of the bar B1 does not remain, the detector does not come into contact with the tip B1a, so the detector does not move and the proximity sensor does not react. The NC device 70 may determine that the cut-off bit is broken when the proximity sensor reacts, i.e., when the proximity sensor detects the oscillation of the detector, and may determine that the cut-off bit is normal when the proximity sensor does not react, i.e., when the proximity sensor does not detect the oscillation of the detector.

[0078] If a rotation drive unit (an example of a detector drive unit) that swings the detector and a sensor (an example of a contact detection unit) that detects the stop position of the detector swung toward the spindle center line AX1 are provided near the spindle center line AX1 instead of on the tool post 30, mechanical breakage detection processing may be performed by means b1. If the tip B1a of the bar B1 remains, the detector will come into contact with the tip B1a, and the NC device 70 can determine that the cut-off bit is broken if the sensor's detection position does not reach the spindle center line AX1. If the tip B1a of the bar B1 does not remain, the detector will not come into contact with the tip B1a, and the NC device 70 can determine that the cut-off bit is normal if the sensor's detection position reaches the spindle center line AX1.

[0079] Furthermore, the detector 41 may be moved by an electric single-axis linear motion robot or the like.

[0080] (5) Conclusion: As explained above, according to various aspects of the present invention, it is possible to provide a technology for a lathe or the like that improves the accuracy of detecting breakage of a cut-off bit without the need to extend the machining time during continuous machining. Of course, even a technology consisting only of the constituent features of the independent claims can achieve the basic functions and effects described above. Furthermore, it is possible to implement configurations in which the components disclosed in the above examples are substituted with each other or the combination is changed, or configurations in which the components disclosed in the publicly known techniques and the above examples are substituted with each other or the combination is changed, etc. The present invention also includes these configurations. [Explanation of symbols]

[0081] 1...Lathe, 10...Front headstock, 11...Front spindle (example of spindle), 12...Gripping part, 13...Front headstock drive unit, 15... rear headstock, 16... rear spindle (example of opposing spindle), 17... gripping part, 18... Rear headstock drive unit, 20...material feeding machine, 30, 30A, 30B... Tool rest, 31... Tool rest drive unit, 40...contact type damage detection unit, 41...detector, 42... Cylinder (example of detector drive unit), 43... Position sensor (example of contact detection unit), 51...Servo amplifier, 52...Servo motor, 53...Encoder, 61...Servo amplifier, 62...Servo motor, 63...Encoder, 70...NC device (example of control unit), AX1…Spindle center line, B1...bar material, B1a...tip part, CM1...Position command, P1...Advance position, SG1: Position feedback signal, SG2: Position deviation, TO1...Tool, TO2...Bit, TO3...Cut-off Bit, TO3a...Tip, W1...Work.

Claims

1. a main shaft that releasably grips the bar; an opposing main shaft that releasably grips a tip end of the bar extending forward from the main shaft; a tool rest to which a cut-off tool is attached that cuts through the bar material held by the spindle; a control unit that controls operations of the main spindle, the counter spindle, and the tool rest; a contact-type breakage detection unit having a detector that can be advanced and retracted to an advanced position where it comes into contact with the tip of the bar material if the tip of the bar material remains after the cut-off operation in which the cut-off tool cuts through the bar material, and that detects that the cut-off tool is broken when the detector that has advanced to the advanced position comes into contact with the tip of the bar material, The control unit performing a process of determining whether or not the cut-off tool is damaged based on a control parameter for controlling at least one of the main spindle and the counter spindle at a first detection timing immediately after the cut-off operation is performed in a state in which the counter spindle holds the bar held by the main spindle; a second detection timing that is at least one of a timing immediately after the cut-off operation is performed in a state where the bar material held by the main spindle is not held by the counter main spindle, and a timing when continuous machining of the bar material is started, and determines whether or not the cut-off bit is broken in accordance with the detection result by the contact-type breakage detection unit.

2. when one of the main spindle and the counter main spindle is designated as a first main spindle and the other is designated as a second main spindle, the control parameter is a position deviation which is a difference signal between a position command and a position feedback signal for the first main spindle, 2. The lathe according to claim 1, wherein the control unit determines that the cut-off bit is damaged if the positional deviation exceeds a predetermined amount due to control of moving the second spindle away from the stopped first spindle at the first detection timing, and determines that the cut-off bit is not damaged if the positional deviation does not exceed the predetermined amount.

3. The contact type damage detection unit is a detector driving unit that moves the detector in a direction intersecting a center line of the main shaft; a contact detection unit that detects whether the detector advanced toward the center line has come into contact with the tip end of the bar material, 3. The lathe according to claim 1, wherein the contact detection unit detects that the detector, advanced toward the center line, has come into contact with the tip of the bar, thereby detecting that the cut-off bit is broken.

4. a main shaft that releasably grips the bar; an opposing main shaft that releasably grips a tip end of the bar extending forward from the main shaft; a tool rest to which a cut-off tool is attached that cuts through the bar material held by the spindle; a contact-type damage detection unit having a detector that can advance and retreat to an advanced position where it contacts the tip of the bar material if the tip remains after the cut-off operation in which the cut-off bit cuts through the bar material, and that detects that the cut-off bit is broken when the detector that has advanced to the advanced position contacts the tip of the bar material, a first step of determining whether or not the cut-off tool is damaged based on a control parameter for controlling at least one of the main spindle and the counter spindle at a first detection timing immediately after the cut-off operation is performed in a state in which the counter spindle holds the bar held by the main spindle; and a second step of determining whether or not the cut-off bit is broken in accordance with a detection result by the contact-type breakage detection unit, limited to a second detection timing which is at least one of the timing immediately after the cut-off operation is performed in a state where the bar material held by the main spindle is not held by the counter main spindle, and the timing when continuous machining of the bar material is started.

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