Tool cutting edge position detection device and machine tool

Abstract

In order to detect the position of a cutting edge of a tool in a state in which chips do not adhere, a cutting edge position detection device (30) includes: an ejector rod (22) and a tip receiving part (23) that are disposed inside a back main shaft (20) and that can move so as to press and discharge a workpiece (W); a servo motor (28); a back headstock (70); and a control unit (90) that controls the servo motor (28) on the basis of a detection result of an encoder (28b) of the servo motor (28). The control unit (90) controls the back headstock (70) so as to move the back main shaft (20) toward a cutting edge (51a) of a tool (51) in a state in which the ejector rod (22) and the tip receiving part (23) are moved to a standby position, and detects retraction of the ejector rod (22) when the cutting edge (51a) comes into contact with a front end surface (23a) of the tip receiving part (23), and the control unit (90) detects the position of the cutting edge (51a) on the basis of the position of a distal end surface (20A) of the back main shaft (20).

Description

Tool tip position detection device and machine tool

[0001] The present invention relates to a tool cutting edge position detection device and a machine tool.

[0002] Machine tools use tools to machine workpieces, but the cutting edges of the tools wear over time and can break for various reasons. Furthermore, tools not only shorten in length due to wear or breakage, but also lengthen as workpiece material adheres to the cutting edge during machining, forming a built-up edge.

[0003] Such a change in the length of the tool reduces the dimensional accuracy of the product obtained by machining the workpiece, so the length of the tool is inspected periodically or irregularly.

[0004] Such tool length inspections are performed by detecting the position of the cutting edge of the tool. For example, a mechanical detection device displaces a contact to a position where the cutting edge of the tool is assumed to be, and when the contact mechanically contacts the cutting edge, it is determined that the cutting edge is in an appropriate position and the tool is of normal length (see, for example, Patent Document 1).

[0005] In addition, the optical detection device irradiates light such as laser light at the position where the cutting edge of the tool is assumed to be, and when it detects reflected light from the cutting edge, it determines that the position of the cutting edge is appropriate and that the tool is of normal length.

[0006] Japanese Utility Model Application Laid-Open Publication No. 3-113740

[0007] However, machine tools generate chips when turning or cutting workpieces with tools, and these chips may adhere to contacts, light sources, light detection units, etc., making it impossible to accurately detect the position of the cutting edge.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide a tool cutting edge position detection device that can detect the position of the cutting edge of a tool while reducing the influence of chips, and a machine tool equipped with a tool cutting edge position detection device.

[0009] A first aspect of the present invention provides a method for manufacturing a workpiece ejection machine, the method comprising: a movable body that is disposed inside a spindle that grips a workpiece and is movable in the axial direction of the spindle relative to the spindle so as to press the workpiece inserted inside the spindle and eject the workpiece to the outside of the spindle; a movable body drive mechanism that has a drive unit that moves the movable body and a detection unit that detects the movement of the drive unit; a spindle drive unit that moves the spindle in the axial direction; and a control unit that controls the drive unit based on the detection result of the detection unit, wherein the control unit moves the movable body to a specific position at the tip of the spindle and ejects the workpiece to the outside of the spindle. With the movable body moved to the specific position, the spindle drive unit is controlled to move the spindle in the axial direction toward the cutting edge of the tool that processes the workpiece, the detection unit detects the retraction of the movable body due to the cutting edge of the tool abutting against the tip of the movable body, the control unit detects the position of the cutting edge of the tool based on the movement position of the spindle immediately before the detection unit detects the retraction of the movable body, and determines whether the cutting edge is worn or broken based on the detected position of the cutting edge.

[0010] A second aspect of the present invention is a machine tool comprising a spindle that grips a workpiece, a tool that machines the workpiece gripped by the spindle, a control device that controls the operation of the spindle and the tool, and a tool cutting edge position detection device according to the present invention, wherein the control device functions as a control unit of the tool cutting edge position detection device.

[0011] The tool cutting edge position detection device and machine tool according to the present invention can detect the position of the tool cutting edge in a state where the influence of chips is reduced.

[0012] 1 is a plan view schematically showing the main configuration of an automatic lathe. FIG. 1 is a cross-sectional view showing a cross section taken along a vertical plane including the axis of the back spindle, illustrating a state in which the front end face of the ejector rod has moved to a standby position where it coincides with the tip end face of the back spindle. FIG. 1 is a cross-sectional view showing a cross section taken along a vertical plane including the axis of the back spindle, illustrating a state in which the ejector rod has been pushed back by a workpiece inserted into the back spindle. FIG. 1 is a cross-sectional view showing a cross section taken along a vertical plane including the axis of the back spindle, illustrating a state in which the front end face of the ejector rod has moved to a retracted position away from the insertion end face of the workpiece. FIG. 2 is a block diagram showing the configurations of a workpiece ejection device and a tool cutting edge position detection device. FIG. 2 shows a state in which the back spindle is moving forward (advancing) in the z-axis direction toward the tool, with the front end face of the ejector rod positioned at a specific position. FIG. 3 shows a state in which the front end face of the ejector rod has advanced integrally with the back spindle and is in contact with the (tip) of the tool. FIG. 4 shows a state in which the ejector rod, whose front end face is in contact with the cutting edge of the tool, has retracted relative to the back spindle. FIG. 5 is a flowchart showing an example of the flow of cutting edge position detection processing in an automatic lathe. FIG. 10 is a cross-sectional view showing a cross section taken along a vertical plane including the axis of the back spindle, showing a modified example in which a tip receiving portion of the knockout jig is provided on the front side of the ejector rod, and showing a state in which the ejector rod and knockout jig have been moved to a specific position with the front end face of the tip portion protruding from the tip face of the back spindle.

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A cutting edge position detecting device and a machine tool according to embodiments of the present invention will be described below with reference to the drawings.

[0014] (Basic Configuration of Automatic Lathe) FIG. 1 is a plan view showing a schematic view of the main configuration of an automatic lathe 100. As shown in FIG.

[0015] An automatic lathe 100 is one embodiment of a machine tool according to the present invention. As shown in Figure 1, the automatic lathe 100 includes a front spindle 10, a back spindle 20, a gang tool rest 40, a back tool rest 50, a front headstock 60, a back headstock 70, and a control unit 90 (control device).

[0016] The front spindle 10 grips a workpiece W, which is a bar material that is a long, rod-shaped member, and rotates the workpiece W around an axis C1. The front spindle 10 is fixed to a front headstock 60, and the front headstock 60 moves along the z-axis parallel to the axis C1, thereby allowing the front spindle 10 to move in the z-axis direction. The movement of the front headstock 60 in the z-axis direction is controlled by a control unit 90, causing the front spindle 10 to move as described above. The workpiece W gripped by the front spindle 10 is subjected to predetermined machining by tools provided on the gang tool rest 40.

[0017] The back spindle 20 receives the workpiece W machined while being gripped by the front spindle 10 from the front spindle 10, with the axis C2 of the back spindle 20 being positioned coaxially with the axis C1 of the front spindle 10. The back spindle 20 has the workpiece W inserted therein, grips the inserted workpiece W, and rotates the gripped workpiece W around the axis C2.

[0018] The workpiece W transferred to the back spindle 20 is cut to a predetermined length by a cut-off tool provided on the gang tool rest 40 while also being held by the front spindle 10. Thereafter, the end face (discharge side end face) of the workpiece W held by the back spindle 20 and cut to a predetermined length is machined by tools provided on the gang tool rest 40 and the back tool rest 50.

[0019] The back spindle 20 is fixed to the back headstock 70, and is movable in the z-axis direction by moving the back headstock 70 along the z-axis parallel to axis C2, and is also movable in the x-axis direction by moving the back headstock 70 along the x-axis in a horizontal plane perpendicular to the z-axis. The movement of the back headstock 70 in the z-axis and x-axis directions is controlled by the control unit 90, and the back spindle 20 is moved as described above.

[0020] The control unit 90 controls the operations of the front spindle 10, back spindle 20, gang tool rest 40, back tool rest 50, front headstock 60 and back headstock 70 (spindle drive unit).

[0021] 2, 3, and 4 are cross-sectional views showing a cross section taken along a vertical plane including the axis C2 of the back spindle 20 of the automatic lathe 100, Fig. 2 shows a state in which the front end face 22a of the ejector rod 22 has moved to a standby position where it coincides with the tip end face 20A of the back spindle 20, Fig. 3 shows a state in which the ejector rod 22 has been pushed back by the workpiece W inserted into the back spindle 20, and Fig. 4 shows a state in which the front end face 22a of the ejector rod 22 has moved to a retracted position away from the insertion-side end face W1 of the workpiece W. Fig. 5 is a block diagram showing the configurations of the workpiece discharge device 29 and the tool cutting edge position detection device 30.

[0022] The back spindle 20 is supplied with a workpiece W from the front spindle 10, which is disposed opposite the back spindle 20. As shown in Fig. 2, a collet chuck 21 is provided at the tip of the back spindle 20, which is closer to the front spindle 10. The collet chuck 21 has a sleeve 21a and a collet 21b, and by the control of the control unit 90, the sleeve 21a advances along the axis C2 toward the tip surface 20A of the back spindle 20, thereby reducing the inner diameter of the collet 21b and gripping the workpiece W inserted inside the collet 21b from the outer peripheral surface side.

[0023] The back spindle 20 is equipped with a workpiece discharge device 29. The workpiece discharge device 29 discharges the workpiece W held by the collet chuck 21 to the outside from the tip end surface 20A of the back spindle 20. As shown in Fig. 5, the workpiece discharge device 29 has a control unit 90, a servo motor 28 (moving body drive mechanism), and an ejector rod 22 (moving body). The servo motor 28 and the ejector rod 22 are provided in the back spindle 20, and the control unit 90 is provided in the automatic lathe 100 separately from the back spindle 20.

[0024] As shown in Figures 2 to 4, the ejector rod 22 is disposed inside the back main shaft 20 along the axis C2. The ejector rod 22 is a rod-shaped member extending along the axis C2. The ejector rod 22 is provided so as to be linearly movable along the axis C2 between the standby position shown in Figure 2 and the retracted position shown in Figure 4. The ejector rod 22 does not rotate around the axis C2.

[0025] 2 is a position where the ejector rod 22 is disposed before the back spindle 20 receives the workpiece W from the front spindle 10. When the ejector rod 22 is disposed at the standby position, the front end surface 22a of the ejector rod 22 coincides with the tip end surface 20A of the back spindle 20.

[0026] 2 into the back spindle 20, the insertion side end face W1 of the workpiece W comes into contact with the front end face 22a. As the insertion of the workpiece W progresses, the workpiece W pushes the ejector rod 22 backward, and the ejector rod 22 moves backward (retreats).

[0027] When the workpiece W has been inserted into the back spindle 20 by a predetermined length, the insertion operation of the workpiece W stops, and the collet chuck 21 grips the workpiece W under the control of the control unit 90. Thereafter, the workpiece W is rotated by the back spindle 20, and a parting tool provided on the gang tool rest 40 is pressed against a predetermined position on the workpiece W that protrudes from the back spindle 20, cutting the workpiece W into short pieces, and the workpiece W cut into short pieces is then machined by tools 51, 52, and 53 provided on the back tool rest 50.

[0028] Here, the workpiece W rotates during machining, but the ejector rod 22 cannot rotate, and therefore, before the workpiece W rotates, as shown in Fig. 4, the ejector rod 22 moves rearward (retreats) so that its front end face 22a moves away from the insertion-side end face W1 of the workpiece W. The position shown in Fig. 4 where the ejector rod 22 is positioned rearward and away from the insertion-side end face W1 is the retracted position of the ejector rod 22.

[0029] When machining of the workpiece W is completed, the back spindle 20, under the control of the control unit 90, releases the grip of the collet chuck 21 to release the workpiece W. Thereafter, when discharging the workpiece W, the control unit 90 controls the servo motor 28 of the workpiece discharging device 29 to linearly move the ejector rod 22, which is in the retracted position shown in FIG. 4, along the z-axis toward the workpiece W. The ejector rod 22 moves forward (advances) in the z-axis direction, and the front end surface 22a of the ejector rod 22 comes into contact with the insertion-side end surface W1 of the workpiece W.

[0030] The ejector rod 22 pushes the workpiece W forward and advances to a standby position where the front end surface 22a of the ejector rod 22 coincides with the tip surface 20A of the back spindle 20, and ejects the workpiece W to the outside of the back spindle 20. Therefore, the ejector rod 22 is an example of a movable body that can move in the axial direction of the back spindle 20 relative to the back spindle 20 so as to eject the workpiece W to the outside of the back spindle 20.

[0031] The servo motor 28 includes a drive unit 28a that rotates and an encoder 28b (detector). The encoder 28b detects the rotation of the drive unit 28a and the angle of rotation. The control unit 90 controls the rotation of the drive unit 28a based on the rotation angle (detection result) detected by the encoder 28b.

[0032] The drive unit 28a is connected to the ejector rod 22. The control unit 90 rotates the drive unit 28a to linearly move the ejector rod 22 along the axis C2. The control unit 90 also switches the rotation direction of the drive unit 28a between a forward direction and a reverse direction, thereby switching the ejector rod 22 between moving forward and backward along the axis C2. The control unit 90 also controls the rotation angle of the drive unit 28a to adjust the linear movement length of the ejector rod 22.

[0033] (Tool cutting edge position detection device) The back spindle 20 is equipped with a tool cutting edge position detection device 30 shown in Fig. 5. The tool cutting edge position detection device 30 is one embodiment of the tool cutting edge position detection device according to the present invention. The cutting edge position detection device 30 detects the position of cutting edges 51a, which are the tips of tools 51, 52, 53 that are provided on a back tool rest 50 and extend in the z-axis direction (with their longitudinal directions coinciding with the z-axis). The cutting edge position detection device 30 is configured using a workpiece discharge device 29.

[0034] The cutting edge position detection device 30 detects the cutting edge positions of the tools 51, 52, and 53 by using a servo motor 28 (moving body drive mechanism) in the workpiece discharge device 29 and an ejector rod 22, and by controlling the servo motor 28 with a control unit 90.

[0035] In addition to the control unit 90, servo motor 28, and ejector rod 22, the cutting edge position detection device 30 includes a back headstock 70 as a spindle drive unit, an alarm unit 31, and a program change unit 32. The alarm unit 31 and the program change unit 32 are controlled by the control unit 90.

[0036] 6, the control unit 90 constituting the cutting edge position detection device 30 first controls the driving of the servo motor 28 so as to move the front end surface 22a of the ejector rod 22 to a specific position protruding by a dimension L1 from the tip end surface 20A of the back spindle 20. The specific position of the ejector rod 22 is a position protruding by the dimension L1 from the standby position when the workpiece W is transferred as shown in FIG.

[0037] Next, the control unit 90 controls the driving of the back headstock 70 to move the back spindle 20 in the x-axis direction. Specifically, as shown in Fig. 6, the control unit 90 moves the back headstock 70 in the x-axis direction so that the axis C2 of the back spindle 20 coincides with the axis of the tool 51 mounted on the back tool rest 50 whose cutting edge position is to be detected (the axis of the tool 52 when another tool 52 is the target, or the axis of the tool 53 when tool 53 is the target).

[0038] Thereafter, the control unit 90 moves the back spindle stock 70 forward on the z axis so as to bring the back spindle 20 closer to the tool 51, with the axis C2 of the back spindle 20 aligned coaxially with the axis of the tool 51. The back spindle 20 gradually approaches the tool 51, and eventually, as shown in Fig. 7, the cutting edge 51a, which is the tip of the tool 51, comes into contact with the front end surface 22a of the ejector rod 22 protruding from the tip end surface 20A of the back spindle 20. If the coordinate position on the z axis of the tip end surface 20A of the back spindle 20 at this time is assumed to be z1, then the position of the front end surface 22a of the ejector rod 22 is z1 + L1.

[0039] The control unit 90 stores the initial position of the tip surface 20A before the rear headstock 70 moves, and detects the amount of movement of the rear headstock 70. Therefore, based on the amount of movement of the rear headstock 70, the coordinate position z1 of the tip surface 20A of the rear spindle 20 after movement can be recognized in real time as the coordinate position after movement relative to the initial position.

[0040] Here, the ejector rod 22, which has moved integrally with the back spindle 20, stops moving forward when its front end face 22a comes into contact with the cutting edge 51a of the tool 51, but the back spindle 20 continues to move forward. Therefore, as shown in Fig. 8, the ejector rod 22 moves backward along the z-axis relative to the back spindle 20. At this time, the dimension of the front end face 22a of the ejector rod 22 protruding from the tip end face 20A of the back spindle 20 becomes smaller than the dimension L1 at the specific position (<L1).

[0041] When the ejector rod 22 moves rearward relative to the back spindle 20, the drive unit 28a of the servo motor 28 connected to the ejector rod 22 rotates in accordance with the movement of the ejector rod 22. In other words, the drive unit 28a rotates by an angle corresponding to the amount of rearward movement of the ejector rod 22. When the drive unit 28a rotates, the encoder 28b also rotates in synchronization with the rotation of the drive unit 28a. Therefore, the encoder 28b detects the rotation of the drive unit 28a based on the rearward movement of the ejector rod 22 along the z-axis.

[0042] The amount of backward movement of the ejector rod 22 at which the encoder 28b can detect rotation is, for example, about 5 μm, but the amount of movement of the ejector rod 22 that the encoder 28b can detect is not limited to 5 μm and may be greater than 5 μm or less than 5 μm.

[0043] As described above, the control unit 90 recognizes the position of the tip surface 20A of the back main shaft 20 in real time, and therefore stores the movement position of the tip surface 20A of the back main shaft 20 immediately before the timing when the encoder 28b detects rotation. The timing immediately before the timing when rotation is detected refers to the movement position (coordinate position z1) of the tip surface 20A of the back main shaft 20 recognized at the end of a period when rotation is not detected.

[0044] Here, the coordinate position of the front end surface 22a of the ejector rod 22 that contacts the cutting edge 51a of the tool 51 is a position that protrudes a dimension L1 forward in the z-axis direction from the coordinate position z1 of the tip end surface 20A of the back spindle 20. Therefore, the control unit 90 can calculate the position of the cutting edge 51a of the tool 51 by calculating the coordinate position (=z1+L1) of the value obtained by adding the dimension L1 to the stored coordinate position z1 of the tip end surface 20A.

[0045] The tool cutting edge position detection device 30 of this embodiment can detect the thus calculated position of the actual cutting edge 51a of the tool 51 provided on the rear tool rest 50. Here, since chips are unlikely to adhere to the front end surface 22a of the ejector rod 22, the tool cutting edge position detection device 30 can detect the tool cutting edge position in a state where the influence of chips is reduced.

[0046] Furthermore, in the tool cutting edge position detection device 30 of this embodiment, the control unit 90 stores the cutting edge position of the tool 51 in the initial state when the tool 51 is placed on the rear tool post 50 as the position of the reference cutting edge 51a through the above-mentioned cutting edge position detection operation, and the length of the tool 51 in the initial state can be stored in the control unit 90 in correspondence with the cutting edge position in the initial state.

[0047] In this case, the cutting edge position detection device 30 can calculate the change in length of the tool 51 from the initial state based on the difference between the position of the cutting edge 51 a detected by the cutting edge position detection device 30 after a time has elapsed from the initial state and the position of the cutting edge 51 a in the initial state pre-stored in the control unit 90. In this case, the control unit 90 can also determine breakage or wear of the cutting edge of the tool based on the change in length from the initial state.

[0048] In addition, the tool cutting edge position detection device 30 may use a dedicated reference jig, which is not used as the machining tool 51, installed on the rear tool rest 50 as the reference position for detecting the reference cutting edge 51a instead of the initial cutting edge 51a of the tool 51, and the control unit 90 may store the position of the cutting edge when it comes into contact with the cutting edge of the reference jig as the reference position.

[0049] Furthermore, when the encoder 28b does not detect rotation even after the back spindle 20 has been advanced to a considerable position, the tool cutting edge position detection device 30 can determine that the tool 51 is not installed as designed in the machining program (the tool 51 is not installed). Note that the considerable position is, for example, a position that is 3 mm or more advanced from the position where the front end face 22 a of the ejector rod 22 is expected to contact the cutting edge 51 a of the tool 51 if the tool 51 were installed in the designed position.

[0050] The automatic lathe 100 of this embodiment configured as described above operates, for example, as follows: Fig. 9 is a flowchart showing an example of the flow of a cutting edge position detection process in the automatic lathe 100.

[0051] Between machining of the normal workpiece W, the automatic lathe 100 starts the process of detecting the cutting edge positions of the tools 51, 52, and 53 using the cutting edge position detection device 30, as shown in Figure 9, and detects the placement status of the tools 51, 52, and 53 (whether they are placed or not, whether their lengths are appropriate (worn or broken cutting edge 51a, whether there is a constructed cutting edge, etc.)).

[0052] The cutting edge position detection device 30 selects a tool whose placement state is to be detected, either automatically under the control of the control unit 90 or manually by the user (S1 in FIG. 9 ). Next, the automatic lathe 100 controls the back headstock 70 so that the back spindle 20 is coaxial with the selected tool 51, for example, and after the back spindle 20 is coaxial with the selected tool 51, advances the back spindle 20 toward the tool 51 (S2).

[0053] The cutting edge position detection device 30 determines whether or not the cutting edge 51a of the tool 51 is detected while the back spindle 20 is being moved to a considerable position (S3). When the cutting edge position detection device 30 determines that the cutting edge 51a of the tool 51 is not detected while the back spindle 20 is being moved to a considerable position (NO in S3), the control unit 90 controls the notification unit 31, and the notification unit 31 displays a warning message on the monitor or issues an alarm (S8), and the cutting edge position detection process ends.

[0054] On the other hand, when the cutting edge position detecting device 30 determines that the cutting edge 51a of the tool 51 has been detected while the back spindle 20 has been moved to a considerable position (YES in S3), the control unit 90 calculates the length of the tool 51 based on the position of the detected cutting edge 51a (S4).The control unit 90 then calculates the difference between the calculated length of the tool 51 and the design length of the tool 51 in the machining program (=(calculated length of the tool 51)-(design length of the tool 51)) (S5).

[0055] The control unit 90 of the cutting edge position detection device 30 determines whether the calculated difference is within an appropriate range (S6). The determination of whether the difference is within the appropriate range is made by comparing the absolute value of the difference with a threshold value previously stored in the control unit 90. The control unit 90 determines that the difference is within the appropriate range if the absolute value of the difference is smaller than the threshold value (YES in S6), and determines that the difference is not within the appropriate range if the absolute value of the difference is greater than the threshold value (NO in S6). The threshold value used by the control unit 90 to determine whether the difference is within the appropriate range is a preset value suitable for determining whether the difference is within the appropriate range, and is an extremely small dimensional value (e.g., less than 10 μm) that can be determined to represent normal wear of the tool 51.

[0056] The reason why the control unit 90 compares the absolute value of the difference with the threshold value is that when the tool is worn, the difference becomes a negative value, and conversely, when a built-up cutting edge is formed on the tool, the difference becomes a positive value, so that whether the difference is a negative value or a positive value, it can be appropriately determined whether it is within the appropriate range.

[0057] When the control unit 90 determines that the difference is within the appropriate range (YES in S6), it changes the machining program as necessary, using the difference as a correction value for correcting the cutting edge position in the machining program (S7), and terminates the cutting edge position detection process. "As necessary" means, for example, that in the case of wear of the tool 51 (when the difference is a negative value and the absolute value of the difference is greater than the threshold), the machining program is subject to change, but in the case of a built-up cutting edge formed on the tool 51 (when the difference is a positive value and the absolute value of the difference is greater than the threshold), the machining program is not subject to change and the cutting edge position detection process is terminated.

[0058] When the control unit 90 determines that the difference is not within the appropriate range (NO in S6), the control unit 90 controls the notification unit 31, and the notification unit 31 displays a warning message on the monitor or issues an alarm (S9), and the cutting edge position detection process is terminated.

[0059] The flowchart shown in Figure 9 shows how the machining program is changed (S7) depending on the tool placement status detected by the cutting edge position detection device 30, but the automatic lathe 100 of this embodiment is not limited to changing the machining program, and does not need to change the machining program depending on the detected tool placement status.

[0060] In the automatic lathe 100 of this embodiment, the specific position of the ejector rod 22 before the position of the cutting edge 51 a of the tool 51 is detected is the position where the front end face 22 a projects from the tip end face 20A of the back spindle 20. However, the specific position of the ejector rod 22 in the present invention is not limited to the position where the front end face 22 a projects from the tip end face 20A of the back spindle 20.

[0061] In other words, in the present invention, when the tool 51, the cutting edge position of which is to be detected, has an outer diameter greater than that of the workpiece W and cannot be inserted inside the back spindle 20, the specific position of the ejector rod 22 must be a position where the front end surface 22a protrudes from the tip surface 20A of the back spindle 20.

[0062] However, if the tool 51, the cutting edge position of which is to be detected, is the same thickness as the workpiece W and can be inserted into the back spindle 20, or has an outer diameter smaller than that of the workpiece W, the specific position of the ejector rod 22 may be a position where the front end face 22a coincides with the tip face 20A of the back spindle 20 (standby position), or a position behind the tip face 20A (a position inside the back spindle 20).

[0063] In the automatic lathe 100 of this embodiment, in order to prevent the ejector rod 22 serving as the workpiece ejection device 29 from unintentionally moving, the control unit 90 controls the servo motor 28 to apply a predetermined excitation holding force to the servo motor 28. By holding the servo motor 28 in a stopped state with the predetermined excitation holding force, the ejector rod 22 is held in a predetermined position so as not to move, and unintentional movement can be prevented.

[0064] Unintentional movement does not mean that the ejector rod 22 is moved by driving the servo motor 28 with the purpose of moving the ejector rod 22, but rather that the ejector rod 22 moves even though there is no purpose to move the ejector rod 22, for example, due to vibrations caused by operating the automatic lathe 100.

[0065] As described above, if the servo motor 28 is held in a stopped state by the excitation holding force, there is a possibility that the ejector rod 22 serving as the cutting edge position detection device 30 will be unable to retract from a specific position after coming into contact with the cutting edge 51a of the tool 51.

[0066] Therefore, after the automatic lathe 100 has moved the ejector rod 22 to a specific position, while the cutting edge 51a of the tool 51 contacts the ejector rod 22 and causes the ejector rod 22 to retract, it is preferable that the control unit 90 does not apply an excitation holding force to the servo motor 28, or reduces the excitation holding force applied to the servo motor 28 to an extent that does not interfere with the operation of the tool 51 to push backward the ejector rod 22, which is stopped at a specific position.

[0067] In addition, a low excitation holding force that does not hinder the workpiece W from pushing the ejector rod 22, which is stopped at a specific position, backward means an excitation holding force that is such that when the tool 51 pushes the ejector rod 22 backward, the tool 51 can move the ejector rod 22 backward, even when an excitation holding force is acting on the servo motor 28.

[0068] In the cutting edge position detection device 30 of this embodiment, the ejector rod 22 and the servo motor 28 are provided on the back spindle 20, but the cutting edge position detection device according to the present invention is not limited to one in which the ejector rod 22 and the servo motor 28 are provided on the back spindle 20.

[0069] That is, in the present embodiment, the cutting edge position detection device 30 is described in terms of the back spindle 20 as the side to which the workpiece W is supplied, since the front spindle 10 of the automatic lathe 100 performs the function of supplying the workpiece W.

[0070] However, if the front spindle 10 is a machine tool that receives a workpiece W of a predetermined length that is not a rod-shaped member from the tip surface side, the front spindle 10 may be equipped with a workpiece discharge device 29 having an ejector rod 22 and a servo motor 28. Therefore, when the front spindle 10 is equipped with the workpiece discharge device 29, the ejector rod 22 and servo motor 28 of the workpiece discharge device 29 equipped on the front spindle 10 can be configured as the cutting edge position detection device 30. In this case, the machine tool equipped with the cutting edge position detection device according to the present invention does not need to be equipped with a back spindle.

[0071] Although the cutting edge position detecting device 30 of this embodiment includes the notification unit 31 and the program change unit 32, the cutting edge position detecting device according to the present invention does not necessarily need to include the notification unit 31 or the program change unit 32.

[0072] In the cutting edge position detection device 30 of this embodiment, the encoder 28b of the servo motor 28 detects the rotation angle of the drive unit 28a, but the encoder 28b may also be a linear encoder that directly detects the linear movement length of the ejector rod 22 corresponding to the rotation angle of the drive unit 28a.

[0073] (Modification) FIG. 10 is a cross-sectional view showing a cross section taken along a vertical plane including the axis C2 of the back spindle 20, and is a modification in which the tip receiving portion 23 of the knockout jig 27 is provided on the front side of the ejector rod 22, and shows a state in which the front end surface 23 a of the tip receiving portion 23 protrudes from the tip surface 20A of the back spindle 20, and the ejector rod 22 and the knockout jig 27 have moved to a specific position.

[0074] The automatic lathe 100 of the above-described embodiment is configured such that the ejector rod 22 provided inside the back spindle 20 directly pushes the workpiece W to eject it to the outside of the back spindle 20, but the automatic lathe 100 may also be configured such that a knockout jig 27 is provided in front of the ejector rod 22.

[0075] In other words, when the automatic lathe 100 is configured to have a knockout jig 27 as the workpiece discharge device 29, the knockout jig 27 comes into contact with the workpiece W, and the ejector rod 22 pushes the workpiece W via the knockout jig 27, thereby discharging the workpiece W outside the back spindle 20. This invention can also be applied to the automatic lathe 100, and can be considered a modified example of the embodiment.

[0076] 10 , the knockout jig 27 includes a tip receiving portion 23, a cylindrical portion 24, a base portion 25, and a coil spring 26. The tip receiving portion 23 is disposed forward of the ejector rod 22, and its rear end surface 23b contacts the front end surface 22a of the ejector rod 22. When the ejector rod 22 moves (advances) forward (toward the tip surface 20A of the back main shaft 20), the tip receiving portion 23 is pushed by the ejector rod 22 and advances integrally with the ejector rod 22.

[0077] In addition, when the workpiece W contacts the front end surface 23a of the tip receiving portion 23 from the front, the tip receiving portion 23 is pushed backward, causing it to move backward on the z-axis (retract), and with the rear end surface 23b in contact with the front end surface 22a of the ejector rod 22, it pushes the ejector rod 22 backward and retracts integrally with the ejector rod 22.

[0078] The tip receiving portion 23 is formed with an outer diameter slightly smaller than the inner diameter of the collet chuck 21. The tip receiving portion 23 is connected internally between the rear end face 23b and the front end face 23a, and air is blown through the holes formed through the holes when the workpiece is discharged. Therefore, even if the workpiece W held by the back spindle 20 is machined to be penetrated in the axial direction, or even if the workpiece W originally has a hollow through-hole, the outer periphery of the workpiece W is held by the front end face 23a, and air blown through the through-hole formed in the workpiece W when the workpiece W is discharged prevents chips from entering the inside of the back spindle 20.

[0079] The cylindrical portion 24 is fixed to the rear of the tip receiving portion 23 and moves along the axis C2 integrally with the tip receiving portion 23. The cylindrical portion 24 is formed in a cylindrical shape that surrounds the tip side portion of the ejector rod 22 from the outside in the radial direction centered on the axis C2.

[0080] The base 25 is fixed to the sleeve 21a of the back main shaft 20 and moves integrally with the sleeve 21a. The base 25 is also formed in a cylindrical shape that surrounds the ejector rod 22 from the outside in the radial direction centered on the axis C2. The base 25 is further formed so that the inner diameter of the cylinder is larger than the outer diameter of the cylinder portion 24, and is formed so that the cylinder portion 24 can pass through the inner space when the cylinder portion 24 moves back integrally with the tip receiving portion 23.

[0081] The coil spring 26 is formed to extend in the direction of the axis C2, with one end contacting the tip receiving portion 23 from the rear and the other end contacting the base portion 25 from the front, thereby biasing the tip receiving portion 23 in a direction pushing it forward relative to the base portion 25.

[0082] When the front end surface 22a of the ejector rod 22 comes into contact with the rear end surface 23b of the tip receiving portion 23 and the ejector rod 22 moves forward, the ejector rod 22 pushes the tip receiving portion 23 forward while stretching the coil spring 26. On the other hand, when the tip receiving portion 23 moves rearward, the ejector rod 22 pushes the ejector rod 22 rearward while compressing the coil spring 26.

[0083] Here, because the tip receiving portion 23 can rotate around the axis C2 as a whole of the knockout jig 27, when the tip receiving portion 23 is in contact with the rotating workpiece W, the tip receiving portion 23 rotates along with the workpiece W. However, because the ejector rod 22 does not rotate around the axis C2, the ejector rod 22 retracts to a retracted position where the front end face 22a is separated from the rear end face 23b of the tip receiving portion 23. At this time, the coil spring 26 urges the tip receiving portion 23 forward, preventing the front end face 23a of the tip receiving portion 23 from separating from the insertion-side end face W1 of the workpiece W and preventing chips from entering the interior of the back spindle 20 through the through-hole formed in the workpiece W.

[0084] In the automatic lathe 100 of this modified example, the ejector rod 22 and the knockout jig 27 function as the moving body of the present invention. In the automatic lathe 100, the control unit 90 sets the position where the front end surface 23a of the tip end receiver 23 protrudes by a dimension L1 from the tip end surface 20A of the back spindle 20 as a specific position, as shown in Fig. 10 , and in this state, the control unit 90 advances the back spindle 20 toward the tool 51, and the cutting edge 51a of the tool 51 comes into contact with the front end surface 23a of the tip end receiver 23, and the ejector rod 22 retracts via the tip end receiver 23, and the position of the cutting edge 51a can be detected.

[0085] The modified tool cutting edge position detection device 30 configured in this manner can detect the position of the actual cutting edge 51a of the tool 51 provided on the rear tool post 50, similar to the tool cutting edge position detection device 30 of the above-mentioned embodiment. CROSS-REFERENCE TO RELATED APPLICATIONS

[0086] This application claims priority based on Japanese Patent Application No. 2023-132612, filed with the Japan Patent Office on August 16, 2023, the entire disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A machine tool comprising: a movable body that is disposed inside a spindle that grips a workpiece and is movable in the axial direction of the spindle relative to the spindle so as to press the workpiece inserted inside the spindle and eject the workpiece to the outside of the spindle; a movable body drive mechanism having a drive unit that moves the movable body and a detection unit that detects the movement of the drive unit; a spindle drive unit that moves the spindle in the axial direction; and a control unit that controls the drive unit based on the detection result of the detection unit, wherein the control unit moves the movable body to a specific position at the tip of the spindle, and with the movable body moved to the specific position, controls the spindle drive unit to move the spindle in the axial direction toward the cutting edge of a tool that machines the workpiece; and the detection unit detects the retreat of the movable body caused by the cutting edge of the tool coming into contact with the tip of the movable body, The control unit detects the position of the cutting edge of the tool based on the movement position of the spindle immediately before the detection unit detects the retreat of the movable body, and determines whether the cutting edge is worn or broken based on the detected position of the cutting edge.

2. A tool cutting edge position detection device as described in claim 1, wherein the specific position is a position where the tip of the movable body protrudes from the tip surface of the spindle.

3. A tool cutting edge position detection device as described in claim 1, wherein the movable body drive mechanism is a servo motor, and the control unit reduces the excitation holding force of the servo motor when the cutting edge of the tool abuts against the tip of the movable body.

4. A tool cutting edge position detection device as described in claim 1, further comprising an alarm unit that notifies when the position of the cutting edge of the tool is not within a predetermined range set in advance, and when the position of the cutting edge of the tool detected by the control unit is not within the predetermined range set in advance, the control unit controls the alarm unit to give an alarm.

5. A machine tool comprising: a spindle for gripping a workpiece; a tool for machining the workpiece gripped by the spindle; a control device for controlling the operation of the spindle and the tool; and a tool cutting edge position detection device described in any one of claims 1 to 4, wherein the control device functions as a control unit of the tool cutting edge position detection device.

6. A machine tool as described in claim 5, wherein, when the position of the cutting edge of the tool detected by the control device is not within a predetermined range, the control device changes the machining program that controls the operation of the spindle and the tool.

Images