Machine tool and method for controlling machine tool

Abstract

Provided are a machine tool with which it is possible to know the degree of axial misalignment during friction joining, and a method for controlling the machine tool. A machine tool (exemplarily illustrated as an automatic lathe 1) according to the present invention includes: a first main shaft 10 that holds a first workpiece (exemplarily illustrated as a workpiece W1) so as to allow rotation thereof; a second main shaft 20 that is opposed to the first main shaft and holds a second workpiece (exemplarily illustrated as a workpiece remainder W2) so as to allow rotation thereof; and a control unit 40a that relatively moves the first main shaft and the second main shaft toward each other while rotating at least one of the first workpiece and the second workpiece and causes the rear end section of the second workpiece to be pressed against the front end section of the first workpiece to join the workpieces together by friction. The control unit includes an axial-misalignment-degree detection means that detects the degree of axial misalignment s of the second workpiece with respect to the first workpiece during friction joining.

Description

[Technical field]

[0001] The present invention relates to a machine tool that joins two workpieces to form one workpiece, and a method for controlling the machine tool. [Background technology]

[0002] In machine tools, there are cases where materials are left over without being processed. When materials are left over, it becomes difficult to reduce material costs and also makes it difficult to contribute to environmental conservation. Therefore, it is considered to make the most effective use of materials by frictionally joining a specified workpiece with the remaining workpiece material. When a workpiece and a residual workpiece are friction-welded, misalignment between the workpiece and the residual workpiece may occur. For this reason, for example, Patent Documents 1 and 2 disclose techniques for detecting whether or not there is misalignment during friction welding. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-208281 [Patent Document 2] Japanese Patent Application Publication No. 7-195183 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the techniques described in Patent Documents 1 and 2 above can detect the presence or absence of misalignment during friction welding, but cannot tell the extent of the misalignment during friction welding.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a machine tool and a method for controlling the machine tool that are capable of detecting the degree of misalignment during friction welding. [Means for solving the problem]

[0006] First, the present invention provides a machine tool including a first spindle which rotatably holds a first workpiece, a second spindle which is disposed opposite to the first spindle and which rotatably holds a second workpiece, and a control unit which moves the first spindle and the second spindle relatively so as to approach each other while rotating at least one of the first workpiece held by the first spindle or the second workpiece held by the second spindle, thereby pressing a rear end portion of the second workpiece against a front end portion of the first workpiece to frictionally join them, wherein the control unit has misalignment amount detection means which detects an amount of misalignment of the second workpiece with respect to the first workpiece during the frictional joining. The misalignment amount detection means determines the amount of misalignment of the second workpiece relative to the first workpiece based on a load applied to a motor that moves the second spindle in a direction intersecting a rotation axis of the second spindle. It is characterized by:

[0007] Secondly, the present invention is characterized in that it has a second spindle moving means for moving the second spindle in a direction intersecting the rotation axis of the second spindle during the friction welding, based on the amount of misalignment of the second workpiece relative to the first workpiece detected by the misalignment detection means.

[0008] Thirdly, the timing at which the second spindle is moved in a direction intersecting the rotation axis of the second spindle is immediately after the first spindle stops rotating, or immediately before the first spindle stops rotating, or while the rotation speed of the first spindle is gradually decreasing.

[0009] Fourthly, the control unit is characterized in having a misalignment direction detection means that detects the misalignment direction of the second workpiece relative to the first workpiece during the friction joining by comparing the amount of misalignment of the second workpiece relative to the first workpiece detected by the misalignment amount detection means with the rotational phase of the first spindle.

[0010] Fifth, the second spindle moving means moves the second spindle in a direction intersecting the rotation axis of the second spindle so as to reduce the amount of misalignment of the second work relative to the first work, based on the amount of misalignment of the second work relative to the first work detected by the misalignment amount detection means and the direction of misalignment of the second work relative to the first work detected by the misalignment direction detection means.

[0011] Sixth, The control unit has a misalignment direction detection means for detecting a misalignment direction of the second workpiece relative to the first workpiece during the friction welding by comparing the amount of misalignment of the second workpiece relative to the first workpiece detected by the misalignment amount detection means with the rotation phase of the first spindle. It is characterized by:

[0013] No. 7 a control method for a machine tool including a first spindle that rotatably holds a first workpiece, a second spindle that is disposed opposite to the first spindle and rotatably holds a second workpiece transferred from the first spindle, and a control unit that controls operations of the first spindle and the second spindle, the method including the steps of: moving the first spindle and the second spindle relatively so as to approach each other while rotating at least one of the first workpiece held by the first spindle or the second workpiece held by the second spindle, thereby bringing a rear end portion of the second workpiece into contact with and rubbing against a front end portion of a newly supplied first workpiece; and while pressing the rear end portion of the second workpiece against the front end portion of the first workpiece to frictionally join them, Based on a load applied to a motor that moves the second spindle in a direction intersecting a rotation axis of the second spindle, The method includes the steps of: detecting an amount of misalignment of the second workpiece relative to the first workpiece; detecting a direction of misalignment of the second workpiece relative to the first workpiece while the friction welding is being performed; and moving the second spindle in a direction intersecting a rotation axis of the second spindle so as to reduce the amount of misalignment of the second workpiece relative to the first workpiece based on the detected amount of misalignment of the second workpiece relative to the first workpiece and the detected direction of misalignment of the second workpiece relative to the first workpiece while the friction welding is being performed. Effect of the Invention

[0014] The present invention can achieve the following effects. The misalignment amount detection means detects the degree of misalignment between the first workpiece and the second workpiece during friction welding of the first workpiece and the second workpiece. Therefore, a desired operation (e.g., elimination of the misalignment) can be performed before the friction welding is completed, and there is no need to check the welding misalignment or correct the misaligned joined workpieces after the friction welding is completed. Furthermore, for example, deburring of the joint can be started immediately. As a result, it is possible to reduce the manufacturing cost of the product and stabilize the quality. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic configuration diagram of an automatic lathe which is a first embodiment of a machine tool according to the present invention. [Diagram 2] 11 is a flowchart showing an operation including the correction of misalignment. [Diagram 3] 10 is a diagram illustrating the rotation phase of a first spindle and the value of a current supplied to an X2-axis motor in friction joining. FIG. [Figure 4] 11A and 11B are diagrams illustrating runout of a workpiece residue due to misalignment. [Diagram 5] 13 is a diagram illustrating the rotation phase of the first spindle and the current value supplied to the X2-axis motor in the upset process. FIG. [Figure 6A] 11A and 11B are diagrams illustrating misalignment of a remaining workpiece with respect to a joined workpiece. [Figure 6B] 13A to 13C are diagrams illustrating an operation for aligning the misalignment direction to the X2 axis direction. [Figure 6C] 11A and 11B are diagrams illustrating an operation for eliminating misalignment. [Figure 7] FIG. 2 is a schematic configuration diagram of an automatic lathe which is a second embodiment of a machine tool according to the present invention. [Figure 8] 13A to 13C are diagrams illustrating runout of a workpiece residue due to misalignment in the second embodiment. [Figure 9] 13A to 13C are diagrams illustrating the rotation phase of the first spindle and the fluctuation in the distance between the laser sensor and the peripheral side surface of the remaining workpiece in the upset process of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0016] A machine tool and a method for controlling the machine tool according to a first embodiment of the present invention will be described below with reference to the drawings. As shown in Fig. 1, an automatic lathe (machine tool) 1 includes a first spindle 10 and a tool table 31. The first spindle 10 can grip (hold) a workpiece W1 via a chuck. This chuck is configured concentrically with the first spindle 10 and can rotate freely together with the first spindle 10.

[0017] The workpiece W1 is a long, round bar material, and is fed from the rear end of the first spindle 10 by using a pushing arrow of a bar feeder. A finger chuck is provided at the tip of the pushing arrow, and the finger chuck grips the rear end of the workpiece W1. The first spindle 10 is rotatably supported by a headstock 12 with its axis in the Z1-axis direction shown in Fig. 1 as its axis, and is rotationally driven by the power of a spindle motor 13 provided on the headstock 12. The headstock 12 is mounted on a Z1-axis feed mechanism 14 and is movable in the Z1-axis direction.

[0018] The Z1-axis feed mechanism 14 is fixed to the bed 1a and has a Z1-axis rail 14a extending in the Z1-axis direction. A Z1-axis slider 14b that slides along the Z1-axis direction by a Z1-axis motor 14c is attached to the Z1-axis rail 14a. The headstock 12 is installed on the Z1-axis slider 14b.

[0019] A guide bush 18 that maintains the cutting position is provided in front of the headstock 12. The guide bush 18 is supported by a support table 17, which is fixed to the bed 1a. The workpiece W1 is supported by the guide bush 18 so as to be rotatable around the Z1 axis, and is sent to the front side of the support table 17. In this way, when the guide bush 18 is provided in front of the first spindle 10, the material from near the tip of the first spindle 10 to the guide bush 18 becomes workpiece waste W2 that cannot be cut. However, by joining this workpiece waste W2 to a newly supplied workpiece W1, the material can be used effectively, thereby reducing material costs.

[0020] A movable table 32 is provided on the front side of the support table 17. The movable table 32 moves the tool table 31 in the X1-axis direction perpendicular to the Z1-axis direction and in the Y1-axis direction perpendicular to the Z1-axis and X1-axis directions. A tool 30 with its tip facing in the X1-axis direction is attached to the tool table 31. The workpiece W1 can be machined with the tool 30 by moving the first spindle 10 in the Z1-axis direction and moving the tool table 31 in the X1-axis direction or the Y1-axis direction.

[0021] The automatic lathe 1 is equipped with a second spindle 20 at a position opposite to the first spindle 10. The second spindle 20 can grip (hold) the workpiece W2 via a chuck. This chuck is configured concentrically with the second spindle 20 and can rotate freely together with the second spindle 20. The workpiece residue W2 is, for example, a round bar having the same diameter as the workpiece W1, and is a remaining material that cannot be machined by the first spindle 10. The workpiece residue W2 is, for example, transferred from the first spindle 10 to the second spindle 20 and held by the second spindle 20.

[0022] The second spindle 20 is rotatably supported by a headstock 22 with its axis in the Z2-axis direction parallel to the Z1-axis direction, and is rotationally driven by the power of a spindle motor 23 provided on the headstock 22. The headstock 22 is mounted on a Z2-axis direction feed mechanism 24 and an X2-axis direction feed mechanism 25, and is movable in the Z2-axis direction and the X2-axis direction. The Z2-axis feed mechanism 24 is, for example, disposed on the X2-axis feed mechanism 25 and has a Z2-axis rail 24a extending in the Z2-axis direction. A Z2-axis slider 24b that slides along the Z2-axis direction by a Z2-axis motor 24c is attached to the Z2-axis rail 24a. The headstock 22 is installed on the Z2-axis slider 24b.

[0023] The X2-axis feed mechanism 25 is fixed to, for example, the bed 1a and has an X2-axis rail 25a parallel to the X1-axis direction. An X2-axis slider 25b that slides along the X2-axis direction by an X2-axis motor 25c is attached to the X2-axis rail 25a. The Z2-axis rail 24a of the Z2-axis feed mechanism 24 is provided on the X2-axis slider 25b. The X2-axis feed mechanism 25 corresponds to the second spindle moving means of the present invention, and the X2-axis motor 25c corresponds to the motor of the present invention.

[0024] The rotation of the first spindle 10 and the second spindle 20, and the movements of the first spindle 10, the second spindle 20, and the moving table 32 are controlled by a control device 40. The control device 40 has a control unit 40a and an input unit 40b, which are connected via a bus. The control unit 40a is made up of a CPU, a memory, etc., and loads various programs and data stored in, for example, a ROM into a RAM and executes the programs, thereby controlling the operation of the automatic lathe 1 based on the programs.

[0025] The rotation of the first spindle 10 and the second spindle 20, the movements of the first spindle 10, the second spindle 20 and the moving table 32, etc. can be set by a program or by inputting to the input section 40b. The control unit 40a also functions as misalignment amount detection means 40c, current value detection means 40d, misalignment direction detection means 40e, and rotation angle detection means 40f. The current value detection means 40d detects the load applied to the X2-axis motor 25c as a current value. The misalignment amount detection means 40c determines the misalignment amount s of the remaining workpiece W2 with respect to the joined workpiece W1 based on the load detected by the current value detection means 40d while the rear end portion of the remaining workpiece W2 is pressed against the front end portion of the workpiece W1 to be joined together (upset process U in FIG. 3).

[0026] Meanwhile, the rotation angle detection means 40f detects the rotation phase of the first spindle 10. The misalignment direction detection means 40e determines the misalignment direction of the remaining workpiece W2 relative to the joined workpiece W1 by comparing the misalignment amount s determined by the misalignment amount detection means 40c with the rotation phase of the first spindle 10 detected by the rotation angle detection means 40f while the rear end portion of the remaining workpiece W2 is pressed against the front end portion of the workpiece W1 to be joined together (upset process U in FIG. 3).

[0027] FIG. 2 is an operation flowchart including misalignment correction, and FIG. 3 is a diagram explaining the rotation speed S1 and rotation phase P1 of the first spindle 10 and the current value I2 supplied to the X2-axis motor 25c during friction joining (including the friction process M and the upset process U). In an automatic lathe 1 as shown in Fig. 1, the length of the workpiece W1 shortens with each cut-off. As machining of the workpiece W1 progresses, when the total length of the workpiece W1 held by the first spindle 10 shortens to about the length from near the tip of the first spindle 10 to the guide bush 18, this shortened portion becomes a workpiece residue that cannot be cut. In order to make effective use of this workpiece residue, the automatic lathe 1 transfers the short workpiece held by the first spindle 10 to the second spindle 20.

[0028] In detail, first, the axis of the first spindle 10 and the axis of the second spindle 20 are arranged concentrically, and, for example, the second spindle 20 is brought close to the first spindle 10. Next, the chuck of the first spindle 10 is opened, and a new workpiece W1 is supplied from the rear of the first spindle 10. Then, this newly supplied workpiece W1 is held by the first spindle 10. When this new workpiece W1 is supplied to the first spindle 10, the short workpiece (which will eventually become the remaining workpiece W2) held by the first spindle 10 is pushed out from the guide bush 18 to the front side of the support table 17. Then, the remaining workpiece W2 is held by the second spindle 20.

[0029] Next, for example, while the first spindle 10 rotates but the second spindle 20 stops rotating (step S10 in FIG. 2), for example, the second spindle 20 is brought close to the first spindle 10 and the rear end portion of the workpiece residue W2 is pressed against the front end portion of the new workpiece W1 so that a predetermined pressure is applied (step S11: start of friction process M). As a result, frictional heat is generated at the contact point between the workpiece residue W2 and the workpiece W1 due to the difference in rotation speed between the first spindle 10 and the second spindle 20, and the contact point is softened.

[0030] In this example, only the first spindle 10 is rotated, but since the first spindle 10 and the second spindle 20 only need to rotate with a speed difference, the second spindle 20 may also be rotated. In this case, the first spindle 10 may be rotated in the same direction as the rotation direction of the second spindle 20 or in the opposite direction. Alternatively, only the second spindle 20 may be rotated. In this example, only the second spindle 20 is moved in the Z2 axis direction, but it is also possible to move only the first spindle 10 in the Z1 axis direction, or to move both the first spindle 10 and the second spindle 20 so that the rear end portion of the workpiece residue W2 comes into contact with the front end portion of the workpiece W1.

[0031] Next, when the contact points between the workpiece residue W2 and the workpiece W1 have softened to a necessary degree, the second spindle 20 applies stronger pressure to bring the workpiece residue W2 closer to the first spindle 10, and presses the workpiece residue W2 against the workpiece W1 (step S12: end of friction process M, start of upset process U). At the same time, the control unit 40a outputs a rotation stop command to the first spindle 10. As a result, the rotation speed S1 of the first spindle 10 gradually decreases, as shown in FIG. 3. In this embodiment, an example has been described in which the rotation stop command and the application of stronger pressure to press the remaining workpiece W2 against the workpiece W1 are simultaneous, but this timing may be different. The degree of softening can be confirmed, for example, by detecting a decrease in the current value (shown as I2' in FIG. 3) of the Z2-axis motor 24c. Alternatively, the conditions until the contact points are softened may be determined in advance through a preliminary experiment, and friction may be applied to the contact points between the workpiece residue W2 and the workpiece W1 based on these conditions. Then, when the rotation of the first spindle 10 is stopped while the second spindle 20 is pressed against the first spindle 10, the rear end portion of the workpiece W2 presses against the front end portion of the workpiece W1 and is joined, so that the workpiece W2 and the workpiece W1 are integrated together.

[0032] Here, the workpiece residue W2 and the workpiece W1 may be integrated in a misaligned state. However, even if the workpiece residue W2 is misaligned with respect to the workpiece W1, it has been found that the workpiece residue W2 can be moved in a direction intersecting the axis of the workpiece residue W2 because the temperature of the contact point between the workpiece residue W2 and the workpiece W1 is high in the upset process U. Therefore, the centers are aligned during the friction welding (until the welding phenomenon is completed) as described below.

[0033] Specifically, after pressing the remaining workpiece W2 against the rotating workpiece W1 (step S11 in FIG. 2), when the first spindle 10 holds the workpiece W1 and the second spindle 20 holds the workpiece W2, the first spindle 10 alone is rotated. The rotation of the first spindle 10 is transmitted to the second spindle 20 via the workpiece W1 and the remaining workpiece W2, so the second spindle 20 also rotates. When misalignment occurs between the remaining workpiece W2 and the workpiece W1, the second spindle 20 vibrates in the X2-axis direction with respect to the axis C1 of the first spindle 10 with an amplitude twice the amount of misalignment (the distance between the axis C1 of the workpiece W1 and the axis C2 of the remaining workpiece W2) s, as shown by the solid line and the two-dot chain line in FIG. 4, respectively.

[0034] On the other hand, the position of the second spindle 20 in the X2-axis direction is held by the X2-axis motor 25c, and the X2-axis motor 25c is controlled by the control unit 40a to hold the position of the second spindle 20 in the X2-axis direction (the X2-axis motor 25c is in a rotationally driven state). Therefore, when vibration due to misalignment is applied to the X2-axis motor 25c, the current value I2 supplied from the control unit 40a to the X2-axis motor 25c increases or decreases according to the rotation phase of the second spindle 20.

[0035] Specifically, when vibration with an amplitude twice the misalignment amount s is applied to the X2-axis motor 25c, the current value I2 supplied to the X2-axis motor 25c fluctuates with an amplitude equivalent to twice the amplitude of the misalignment amount s during the upset process U, as shown by the solid line in the graph of the X2-axis position (vertical axis) and time (horizontal axis) in Figure 5. Therefore, the current value detection means 40d detects the fluctuation range (difference between the maximum and minimum values) of the current value I2 supplied to the X2-axis motor 25c, for example, over a predetermined period of time. Then, the misalignment detection means 40c calculates, for example, the average value of the fluctuation range of this current value I2, and assumes that half of this average value corresponds to the misalignment amount s, thereby detecting the misalignment amount s of the workpiece remainder W2 relative to the integrally joined workpiece W1 (step S13 in FIG. 2).

[0036] In this way, the misalignment amount detection means 40c allows the degree of misalignment between the workpiece W1 and the remaining workpiece W2 to be known during friction welding of the workpiece W1 and the remaining workpiece W2. Therefore, as described later, a desired operation (e.g., elimination of misalignment) can be performed before the friction welding is completed, so there is no need to check the welding misalignment or correct the misaligned workpieces after the friction welding is performed, and further, for example, deburring can be started immediately. As a result, it is possible to reduce the manufacturing cost of the product and stabilize the quality.

[0037] Furthermore, by using the load applied to the X2-axis motor 25c, the amount of misalignment s of the remaining workpiece W2 relative to the workpiece W1 can be easily and accurately obtained. In this embodiment, the load on the X2-axis motor 25c is calculated from the average value of the fluctuation range of the current value I2, but the present invention is not limited to this example. For example, the fluctuation range of the current value I2 only at a specific timing or a reference value of the fluctuation of the current value I2 may be set, and the increase or decrease amount relative to this reference value may be used. Also, other parameters based on the current value I2 may be used.

[0038] On the other hand, the fluctuations (maximum and minimum values) of the current value I2 supplied to the X2-axis motor 25c occur at approximately the same position during one rotation of the workpiece W1. Therefore, by comparing the fluctuations of the current value I2 with the rotation phase P1 of the first spindle 10, the misalignment direction of the workpiece remaining material W2 with respect to the workpiece W1 can be determined. In detail, as shown in FIG. 5, the rotation phase P1 (indicated by a dashed line in the figure) of the first spindle 10 and the current value I2 (indicated by a solid line in the figure) supplied to the X2-axis motor 25c are in such a relationship that, for example, the X2-axis motor 25c rotates approximately once while the spindle motor 13 rotates twice. When the misalignment direction of the workpiece residue W2 with respect to the workpiece W1 occurs in the positive direction of the X2 axis, the current value I2 supplied to the X2-axis motor 25c increases in the positive direction. Also, when the rotation phase P1 of the first spindle 10 is, for example, 270°, the current value I2 supplied to the X2-axis motor 25c is at a maximum value. Therefore, it can be seen that the misalignment of the workpiece residue W2 occurs in the direction connecting the axis C1 of the first spindle 10 and the position of the rotation phase 270°.

[0039] 2 (upset step U in FIG. 3), the misalignment direction detection means 40e detects the misalignment direction of the remaining workpiece W2 relative to the workpiece W1 by comparing the misalignment amount s of the remaining workpiece W2 relative to the workpiece W1 detected by the misalignment amount detection means 40c with the rotation phase P1 of the first spindle 10 detected by the rotation angle detection means 40f. In this way, the misalignment direction detection means 40e determines the misalignment direction of the remaining workpiece W2 relative to the workpiece W1 during frictional joining of the workpiece W1 and the remaining workpiece W2.

[0040] Next, the control unit 40a judges whether the misalignment amount s detected by the misalignment amount detection means 40c is equal to or greater than a predetermined value that requires misalignment correction (step S14 in FIG. 2). If the misalignment amount s detected by the misalignment amount detection means 40c is equal to or greater than the predetermined value (YES in step S14), the process proceeds to step S15 to correct the misalignment. On the other hand, if the misalignment amount s detected by the misalignment amount detection means 40c is less than the predetermined value (NO in step S14), the process proceeds to step S17.

[0041] When the misalignment needs to be corrected (YES in step S14), the control unit 40a outputs a drive signal to the spindle motor 13 to align the misalignment direction of the workpiece remainder W2 with respect to the workpiece W1 to the X2 direction (step S15). In detail, as shown in Fig. 6A, when the misalignment direction of the workpiece remainder W2 with respect to the workpiece W1 (the direction connecting the axis C1 of the workpiece W1 and the axis C2 of the workpiece remainder W2) is not parallel to the X2 axis, the first spindle 10 is rotated to align the misalignment direction with the X2 axis direction.

[0042] Next, the control unit 40a outputs a drive signal to the X2-axis motor 25c immediately after the first spindle 10 stops rotating (indicated by time T3 in FIG. 3), and moves the second spindle 20 in the X2-axis direction in a direction in which the amount of misalignment s decreases, as shown by an arrow in FIG. 6B (step S16 in FIG. 2). More specifically, the second spindle 20 is moved in a direction in which the distance from the axis C2 of the workpiece residual material W2 to the axis C1 of the workpiece W1 becomes shorter, for example, by half the average value of the fluctuation width of the current value I2, to align the centers of the workpiece residual material W2 and the workpiece W1 (FIG. 6C). This makes it possible to eliminate the misalignment of the workpiece residual material W2 during frictional joining of the workpiece W1 and the workpiece residual material W2.

[0043] Next, the control unit 40a outputs a drive signal to the Z2-axis motor 24c to further press the rear end portion of the remaining workpiece W2 against the front end portion of the workpiece W1 to finish the friction welding (step S17 in FIG. 2). The timing for moving the second spindle 20 in the X2-axis direction (step S16) may be any timing when the temperature of the contact point between the workpiece residue W2 and the workpiece W1 is high and the workpiece residue W2 can move in a direction intersecting the axis of the workpiece residue W2. For this reason, in addition to the above-mentioned time T3, the timing may be, for example, immediately before the first spindle 10 stops rotating (indicated by time T2 in FIG. 3) or while the rotation speed S1 of the first spindle 10 is gradually decreasing (indicated by time T1).

[0044] Thereafter, the burrs generated at the joint between the workpiece residue W2 and the workpiece W1 are cut by the tool 30. This is done by releasing the second spindle 20 from holding the workpiece W2 while keeping the workpiece W1 held by the first spindle 10. The tool 30 is, for example, positioned closer to the second spindle 20 than the joint between the workpiece residue W2 and the workpiece W1, and a predetermined cutting depth is set. Then, while rotating the first spindle 10, the tool 30 is moved closer to the first spindle 10 than the joint between the workpiece residue W2 and the workpiece W1 to remove the burrs.

[0045] In this way, the tip portion of the workpiece W1 and the rear end portion of the remaining workpiece W2 are friction-joined using the first spindle 10 and the second spindle 20 arranged opposite each other, and the automatic lathe 1 which combines joining and cutting (integrates the joining and cutting processes) can reduce the manufacturing costs of the product.

[0046] In the above embodiment, an example has been described in which the misalignment amount detection means 40c calculates the misalignment amount s. However, the present invention is also applicable to a case in which the amount of misalignment of the workpiece remainder W2 relative to the workpiece W1 is detected by, for example, photographing the joint between the workpiece W1 and the workpiece remainder W2 with a camera and processing the image, or by measuring with a laser as described later. Furthermore, in the above embodiment, an example has been described in which the misalignment amount s is eliminated (eliminated), but the present invention is also applicable to a case in which the misalignment amount s is reduced without eliminating the misalignment.

[0047] In the above embodiment, the guide bush 18 is provided between the first spindle 10 and the second spindle 20. However, in the present invention, since it is sufficient to detect the amount of misalignment s during friction welding, the guide bush 18 can be omitted. The workpiece W1 may be made of a material different from that of the residual workpiece W2. The workpiece W1 and the residual workpiece W2 may have different diameters. Furthermore, in the above embodiment, the workpiece W1 and the residual workpiece W2 are friction-welded to each other, but the present invention is not limited to the example of joining the residual workpiece W2, and can also be applied to the case of joining new materials together.

[0048] Furthermore, the present invention is not limited to the configurations of the embodiments as long as at least the first spindle 10 is rotatable around the Z1 axis, the second spindle 20 is rotatable around the Z2 axis, either the first spindle 10 or the second spindle 20 is movable in the Z1 axis direction or the Z2 axis direction, and either the first spindle 10 or the second spindle 20 is movable in the X1 axis direction or the X2 axis direction. In the above embodiment, the movement is in the X2 axis direction perpendicular to the Z2 axis, but in the present invention, the direction can be changed in various ways as long as it is a direction that intersects with the Z2 axis. EXAMPLES

[0049] Next, a machine tool and a method for controlling the machine tool according to a second embodiment of the present invention will be described with reference to the drawings. The automatic lathe (machine tool) 2 of the second embodiment is an automatic lathe in which the method of detecting the amount of center misalignment s of the workpiece remaining material W2 with respect to the workpiece W1 in the automatic lathe 1 of the first embodiment is changed. Furthermore, many of the elements of the automatic lathe 2 of the second embodiment are common to the automatic lathe 1 of the first embodiment, so detailed explanations of the common points will be omitted.

[0050] As shown in Fig. 7, the automatic lathe 2 has a laser sensor 50, which is a type of optical sensor controlled by the control device 40, on the bed 1a. As shown in Fig. 8, this laser sensor 50 irradiates the workpiece residue W2 with laser light L parallel to the X2 axis, and detects the distance D in the X2 axis direction between the laser sensor 50 and the peripheral side surface of the workpiece residue W2.

[0051] Next, detection of the amount of misalignment s of the remaining workpiece W2 relative to the workpiece W1 by the automatic lathe 2 of the second embodiment will be described. For example, when vibrations with an amplitude twice the misalignment amount s are applied to the workpiece residue W2, the distance D between the laser sensor 50 and the peripheral side of the workpiece residue W2 fluctuates with an amplitude twice the misalignment amount s during the upset process U, based on the distance O in the X2 axis direction between the laser sensor 50 and the peripheral side of the workpiece W1, as shown by the solid line in the graph of distance (vertical axis) versus time (horizontal axis) in Figure 9. Therefore, during the upset process U, the misalignment detection means 40c detects the maximum value of the fluctuation value in the X2 axis direction of the peripheral side of the workpiece remainder W2 relative to the axis C1 of the workpiece W1, i.e., the misalignment amount s of the workpiece remainder W2 relative to the integrally joined workpiece W1, based on the output value D of the laser sensor 50 (the distance in the X2 axis direction between the laser sensor 50 and the peripheral side of the workpiece remainder W2).

[0052] Next, detection of the misalignment direction of the workpiece remaining material W2 relative to the workpiece W1 by the automatic lathe 2 of the second embodiment will be described. In the second embodiment, the fluctuations (maximum and minimum values) of the output value D of the laser sensor 50 occur at approximately the same positions during one rotation of the workpiece W1. Therefore, by comparing the fluctuations of the output value D with the rotation phase P1 of the first spindle 10, the misalignment direction of the workpiece remainder W2 relative to the workpiece W1 can be determined. Specifically, as shown in FIG. 9, the rotation phase P1 (indicated by a dashed line in the figure) of the first spindle 10 and the output value D (indicated by a solid line in the figure) of the laser sensor 50 are in such a relationship that, for example, the workpiece residue W2 rotates approximately once while the spindle motor 13 (i.e., the workpiece W1) rotates twice. When the misalignment direction of the workpiece residue W2 with respect to the workpiece W1 occurs in the positive direction of the X2 axis, the output value D of the laser sensor 50 increases in the positive direction. Also, when the rotation phase P1 of the first spindle 10 is, for example, 270°, the output value D of the laser sensor 50 is at a maximum value. Therefore, it can be seen that the misalignment of the workpiece residue W2 occurs in the direction connecting the axis C1 of the first spindle 10 and the position of the rotation phase of 270°.

[0053] Therefore, in the upset process U, the misalignment direction detection means 40e detects the misalignment direction of the workpiece remaining material W2 relative to the workpiece W1, by comparing the misalignment amount s of the workpiece remaining material W2 relative to the workpiece W1 detected by the misalignment amount detection means 40c with the rotation phase P1 of the first spindle 10 detected by the rotation angle detection means 40f, as in the first embodiment. In this way, in the automatic lathe 2 of the second embodiment as well, the misalignment direction detection means 40e can detect the misalignment direction of the workpiece remaining material W2 relative to the workpiece W1 during frictional joining of the workpiece W1 and the workpiece remaining material W2.

[0054] As described above, in the second embodiment, the automatic lathe 2 is equipped with a laser sensor 50 that measures the distance to the workpiece residue W2, and the misalignment detection means 40c determines the misalignment amount s of the workpiece residue W2 relative to the workpiece W1 based on the output value D of the laser sensor 50. Therefore, the misalignment amount s is directly detected from the shape of the peripheral side surface of the workpiece residue W2. Therefore, the misalignment amount s can be detected more accurately than in the first embodiment, where the misalignment amount s is indirectly detected based on the load applied to the X2-axis motor.

[0055] In this embodiment, as shown in Figure 8, the laser sensor 50 irradiates the workpiece residue W2 with a laser parallel to the X2 axis to detect the misalignment amount s and misalignment direction of the workpiece residue W2 relative to the workpiece W1. However, as long as the misalignment amount s can be calculated by the misalignment amount detection means 40c, any direction may be used, and the irradiation direction of the laser on the workpiece residue W2 is not limited to parallel to the X2 axis.

[0056] In addition, in this embodiment, a laser sensor 50 using laser light L has been used as an example of an optical sensor, but the optical sensor is not limited to a laser sensor and may be appropriately selected depending on the measurement accuracy, and may be, for example, an optical sensor using emitted light such as LED light. [Explanation of symbols]

[0057] 1 Automatic lathe (machine tool) 1a Bed 10... 1st spindle 12 ... Headstock 13 Spindle motor 14 Z1 axial feed mechanism 14a Z1 axis rail 14b Z1 axis slider 14c Z1 axis motor 17... Support stand 18 Guide bush 20 ... 2nd spindle 22 ... Headstock 23 Spindle motor 24 Z2 axial feed mechanism 24a Z2 axis rail 24b Z2 axis slider 24c ··· Z2 axis motor 25 X2 axial feed mechanism (second spindle moving means) 25a ··· X2 axis rail 25b X2 axis slider 25c ··· X2 axis motor (motor) 30... tools 31 ... tool stand 32 Mobile stand 40 Control device 40a... Control section 40b Input section 40c: Means for detecting misalignment 40d Current value detection means 40e: Means for detecting misalignment direction 40f Rotation angle detection means 50 ··· Laser sensor (optical sensor) W1: Work (first work) W2: Remaining workpiece (second workpiece) M... Friction process U ··· Upset process S1: Rotational speed P1: Rotation phase I2: Current value T1: Time T2: Time T3: Time s: Misalignment amount D: Distance between the laser sensor and the peripheral side of the remaining workpiece in the X2 axis direction L: Laser light

Claims

1. a first spindle that rotatably holds a first workpiece; a second spindle that is disposed opposite to the first spindle and rotatably holds a second workpiece; and a control unit that moves the first spindle and the second spindle relatively so as to approach each other while rotating at least one of the first workpiece held by the first spindle or the second workpiece held by the second spindle, thereby pressing a rear end portion of the second workpiece against a front end portion of the first workpiece to frictionally join them, the control unit has a misalignment amount detection means for detecting a misalignment amount of the second workpiece relative to the first workpiece during the friction joining, The misalignment detection means determines the amount of misalignment of the second workpiece relative to the first workpiece based on a load applied to a motor that moves the second spindle in a direction intersecting a rotation axis of the second spindle.

2. 2. The machine tool according to claim 1, further comprising second spindle moving means for moving the second spindle in a direction intersecting a rotation axis of the second spindle during the friction welding, based on an amount of misalignment of the second workpiece relative to the first workpiece detected by the misalignment amount detection means.

3. 3. The machine tool according to claim 2, wherein a timing at which the second spindle is moved in a direction intersecting a rotation axis line of the second spindle is immediately after the first spindle stops rotating, or immediately before the first spindle stops rotating, or while a rotation speed of the first spindle is gradually decreasing.

4. 4. The machine tool according to claim 2 or 3, wherein the control unit has misalignment direction detection means that detects a misalignment direction of the second workpiece relative to the first workpiece during the friction joining by comparing the amount of misalignment of the second workpiece relative to the first workpiece detected by the misalignment amount detection means with a rotational phase of the first spindle.

5. 5. The machine tool according to claim 4, wherein the second spindle moving means moves the second spindle in a direction intersecting a rotation axis of the second spindle so as to reduce the amount of misalignment of the second workpiece relative to the first workpiece, based on the amount of misalignment of the second workpiece relative to the first workpiece detected by the misalignment amount detection means and the direction of misalignment of the second workpiece relative to the first workpiece detected by the misalignment direction detection means.

6. A machine tool as described in claim 1, wherein the control unit has a misalignment direction detection means for detecting the misalignment direction of the second workpiece relative to the first workpiece during the friction joining by comparing the amount of misalignment of the second workpiece relative to the first workpiece detected by the misalignment amount detection means with the rotational phase of the first spindle.

7. A control method for a machine tool including a first spindle that rotatably holds a first workpiece, a second spindle that is disposed opposite to the first spindle and rotatably holds a second workpiece transferred from the first spindle, and a control unit that controls operations of the first spindle and the second spindle, the method comprising: a step of moving the first spindle and the second spindle relatively so as to approach each other while rotating at least one of the first workpiece held by the first spindle and the second workpiece held by the second spindle, thereby causing a rear end portion of the second workpiece to come into contact with and rub against a front end portion of a newly supplied first workpiece; detecting an amount of misalignment of the second workpiece with respect to the first workpiece based on a load applied to a motor that moves the second spindle in a direction intersecting a rotation axis of the second spindle while the rear end portion of the second workpiece is pressed against the front end portion of the first workpiece to be friction-welded; detecting a misalignment direction of the second workpiece relative to the first workpiece during the friction joining; moving the second spindle in a direction intersecting a rotation axis of the second spindle so that the amount of misalignment of the second workpiece with respect to the first workpiece is reduced based on the detected amount of misalignment of the second workpiece with respect to the first workpiece and the detected direction of misalignment of the second workpiece with respect to the first workpiece during the friction joining; A method for controlling a machine tool, comprising:

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