Machine tool, control method of machine tool

Abstract

The present invention provides a machine tool capable of knowing the degree of eccentricity in frictional engagement and a control method for the machine tool. The machine tool of the present invention (illustrated by an automatic lathe (1)) includes: a first spindle (10) that rotatably holds a first workpiece (illustrated by a workpiece (W1)); a second spindle (20) that is disposed opposite to the first spindle and rotatably holds a second workpiece (illustrated by a workpiece blank (W2)); and a control unit (40a) that relatively moves the first spindle and the second spindle closer to each other while rotating at least any one of the first workpiece and the second workpiece, and presses the rear end portion of the second workpiece against the front end portion of the first workpiece to perform frictional engagement. The control unit has an eccentricity amount detection unit, and the eccentricity amount detection unit detects the eccentricity amount (s) of the second workpiece relative to the first workpiece during frictional engagement.

Description

Technical Field

[0001] The present invention relates to a machine tool for joining two workpieces into one workpiece and a control method for the machine tool. Background Art

[0002] In a machine tool, there are cases where the material remains unprocessed. If the material remains, it is difficult to reduce the material cost, and it is also difficult to contribute to environmental protection. Therefore, it can be considered to maximize the effective use of materials by frictionally joining a specified workpiece and a workpiece remnant.

[0003] When frictionally joining a workpiece and a workpiece remnant, eccentricity between the workpiece and the workpiece remnant sometimes occurs. Therefore, for example, techniques for detecting whether there is eccentricity during friction joining are disclosed in Patent Documents 1 and 2.

[0004] Patent Document 1: Japanese Patent Laid-Open No. 5-208281

[0005] Patent Document 2: Japanese Patent Laid-Open No. 7-195183

[0006] However, in the techniques described in Patent Documents 1 and 2 above, although it is possible to detect whether there is eccentricity during friction joining, it is not possible to know to what extent there is deviation during friction joining. Summary of the Invention

[0007] The present invention has been made in view of the above actual situation, and an object thereof is to provide a machine tool and a control method for the machine tool that can know the degree of eccentricity during friction joining.

[0008] First, the present invention is 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; and a control unit that rotates at least either the first workpiece held by the first spindle or the second workpiece held by the second spindle, and relatively moves the first spindle and the second spindle closer to each other, and presses the rear end portion of the second workpiece against the front end portion of the first workpiece to perform friction joining. The machine tool is characterized in that the control unit has an eccentricity amount detection unit that detects the eccentricity amount of the second workpiece with respect to the first workpiece during the friction joining.

[0009] Second, it is characterized in that it has a second spindle moving unit that moves the second spindle in a direction intersecting the rotation axis of the second spindle during the friction joining based on the eccentricity amount of the second workpiece with respect to the first workpiece detected by the eccentricity amount detection unit.

[0010] Third, it is characterized in that the timing of moving the second main shaft in a direction intersecting with the rotation axis of the second main shaft described above is after the rotation of the first main shaft has just stopped, before the rotation of the first main shaft is about to stop, or during the period when the rotation speed of the first main shaft is gradually decreasing.

[0011] Fourth, it is characterized in that the control unit has an eccentricity direction detection unit, and the eccentricity direction detection unit detects the eccentricity direction of the second workpiece relative to the first workpiece during the frictional engagement by comparing the eccentricity amount of the second workpiece relative to the first workpiece detected by the eccentricity amount detection unit and the rotation phase of the first main shaft.

[0012] Fifth, it is characterized in that the second main shaft moving unit moves the second main shaft in a direction intersecting with the rotation axis of the second main shaft in such a way that the eccentricity amount of the second workpiece relative to the first workpiece is reduced based on the eccentricity amount of the second workpiece relative to the first workpiece detected by the eccentricity amount detection unit and the eccentricity direction of the second workpiece relative to the first workpiece detected by the eccentricity direction detection unit.

[0013] Sixth, it is characterized in that the eccentricity amount detection unit obtains the eccentricity amount of the second workpiece relative to the first workpiece based on the load applied to the motor, and the motor moves the second main shaft in a direction intersecting with the rotation axis of the second main shaft.

[0014] Seventh, it is characterized in that the eccentricity amount detection unit obtains the eccentricity amount of the second workpiece relative to the first workpiece based on the output value of the optical sensor, and the optical sensor measures the distance to the second workpiece.

[0015] Eighth, a control method for a machine tool, the machine tool comprising: 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 the operations of the first spindle and the second spindle. The control method for the machine tool is characterized by including the following steps: while rotating at least either one of the first workpiece held by the first spindle or the second workpiece held by the second spindle, moving the first spindle and the second spindle relatively closer to each other, bringing the rear end portion of the second workpiece into contact with and frictionally engaging it with the front end portion of a newly supplied first workpiece; during the frictional engagement of pressing the rear end portion of the second workpiece against the front end portion of the first workpiece, detecting the amount of eccentricity of the second workpiece relative to the first workpiece; during the frictional engagement, detecting the direction of eccentricity of the second workpiece relative to the first workpiece; and during the frictional engagement, based on the detected amount of eccentricity of the second workpiece relative to the first workpiece and the detected direction of eccentricity of the second workpiece relative to the first workpiece, moving the second spindle in a direction intersecting the rotational axis of the second spindle in such a way that the amount of eccentricity of the second workpiece relative to the first workpiece is reduced.

[0016] The present invention can achieve the following effects.

[0017] Through the eccentricity detection unit, it is possible to know the degree of eccentricity between the first workpiece and the second workpiece during the frictional engagement of the first workpiece and the second workpiece. Therefore, it is possible to perform a desired operation (such as eliminating eccentricity) before the end of the frictional engagement. Thus, after the frictional engagement is performed, it is not necessary to confirm engagement deviation, correct the deviated engaged workpieces, etc. Also, for example, it is possible to quickly start deburring operations on the engaged portion. As a result, it is possible to reduce the manufacturing cost of the product and stabilize the quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic structural diagram of an automatic lathe as a first embodiment of the machine tool according to the present invention.

[0019] Figure 2 is a flowchart of operations including eccentricity correction.

[0020] Figure 3 is a diagram for explaining the rotational phase of the first spindle and the current value supplied to the X2-axis motor during frictional engagement.

[0021] Figure 4 is a diagram for explaining the vibration of the workpiece residue caused by eccentricity.

[0022] Figure 5It is a diagram for explaining the rotation phase of the first main shaft in the upset process and the current value supplied to the X2-axis motor.

[0023] Figure 6A It is a diagram for explaining the eccentricity of the workpiece remnant with respect to the joined workpiece.

[0024] Figure 6B It is a diagram for explaining the operation of aligning the eccentricity direction with the X2-axis direction.

[0025] Figure 6C It is a diagram for explaining the operation of eliminating the eccentricity.

[0026] Figure 7 It is a schematic structural diagram of an automatic lathe as a second embodiment of the machine tool according to the present invention.

[0027] Figure 8 It is a diagram for explaining the vibration of the workpiece remnant caused by eccentricity in the second embodiment.

[0028] Figure 9 It is a diagram for explaining the rotation phase of the first main shaft in the upset process of the second embodiment and the change in the distance between the laser sensor and the circumferential side of the workpiece remnant. Detailed Embodiment

[0029] Embodiment 1

[0030] Hereinafter, with reference to the drawings, a machine tool and a control method of the machine tool according to the first embodiment of the present invention will be described.

[0031] As Figure 1 shown, an automatic lathe (machine tool) 1 includes a first main shaft 10 and a tool table 31. The first main shaft 10 can hold (retain) a workpiece W1 via a chuck. The chuck is configured to be concentric with the first main shaft 10 and rotatable integrally with the first main shaft 10.

[0032] The workpiece W1 is a round bar-shaped long bar, and is supplied from the rear end of the first main shaft 10 by a pusher of a bar feeder. A finger chuck is provided at the front end of the pusher, and the finger chuck holds the rear end of the workpiece W1.

[0033] The first main shaft 10 Figure 1 is rotatably supported by a spindle head 12 with the Z1-axis direction shown as the axis, and is rotationally driven by the power of a spindle motor 13 provided on the spindle head 12. The spindle head 12 is mounted on a Z1-axis direction feed mechanism 14 and is movable in the Z1-axis direction.

[0034] The Z1-axis feed mechanism 14 has a Z1-axis guide rail 14a which is fixed to the machine bed 1a and extends in the Z1-axis direction. A Z1-axis slider 14b is mounted on the Z1-axis guide rail 14a, and the Z1-axis slider 14b slides along the Z1-axis direction by a Z1-axis motor 14c. A spindle table 12 is provided on the Z1-axis slider 14b.

[0035] A guide bushing 18 for holding the cutting position is provided in front of the spindle table 12. The guide bushing 18 is supported by a support table 17, and the support table 17 is fixed to the machine bed 1a. The workpiece W1 is supported by the guide bushing 18 so as to be rotatable about the Z1-axis and fed toward the front side of the support table 17.

[0036] In this way, if the guide bushing 18 is provided in front of the first spindle 10, the amount of material of the length from the vicinity of the front end of the first spindle 10 to the guide bushing 18 becomes the workpiece residue W2 that cannot be cut. However, if the workpiece residue W2 and the newly supplied workpiece W1 are joined, the material can be effectively utilized, so that the reduction of the material cost can be achieved.

[0037] A moving table 32 is provided on the front side of the support table 17. The moving table 32 moves the tool table 31 in the X1-axis direction orthogonal to the Z1-axis direction and in the Y1-axis direction orthogonal to the Z1-axis direction and the X1-axis direction.

[0038] A tool 30 with its front end facing the X1-axis direction is mounted on the tool table 31. 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, the workpiece W1 can be machined with the tool 30.

[0039] The automatic lathe 1 is provided with a second spindle 20 at a position opposite to the first spindle 10. The second spindle 20 can hold (retain) the workpiece residue W2 via a chuck. The chuck is configured to be concentric with the second spindle 20 and rotatable integrally with the second spindle 20.

[0040] The workpiece residue W2 is, for example, a round bar having the same diameter as the workpiece W1 and is the 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.

[0041] The second spindle 20 is rotatably supported by a spindle table 22 with 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 spindle table 22. The spindle table 22 is mounted on a Z2-axis feed mechanism 24 and an X2-axis feed mechanism 25 and is movable in the Z2-axis direction and the X2-axis direction.

[0042] The Z2-axis feed mechanism 24 is disposed, for example, on the X2-axis feed mechanism 25 and has a Z2-axis guide rail 24a extending in the Z2-axis direction. A Z2-axis slider 24b is mounted on the Z2-axis guide rail 24a, and the Z2-axis slider 24b slides along the Z2-axis direction by a Z2-axis motor 24c. A spindle head 22 is provided on the Z2-axis slider 24b.

[0043] The X2-axis feed mechanism 25 has, for example, an X2-axis guide rail 25a, and the X2-axis guide rail 25a is fixed to the bed 1a and is parallel to the X1-axis direction. An X2-axis slider 25b is mounted on the X2-axis guide rail 25a, and the X2-axis slider 25b slides along the X2-axis direction by an X2-axis motor 25c. The Z2-axis guide rail 24a of the Z2-axis feed mechanism 24 is provided on the X2-axis slider 25b. In addition, the X2-axis feed mechanism 25 corresponds to the second main spindle moving unit of the present invention, and the X2-axis motor 25c corresponds to the motor of the present invention.

[0044] The rotation of the first main spindle 10 and the second main spindle 20, and the movement of the first main spindle 10, the second main 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.

[0045] The control unit 40a is composed of a CPU, a memory, etc. For example, various programs and data stored in the ROM are loaded into the RAM, and the program is executed. Thereby, the operation of the automatic lathe 1 can be controlled based on the program.

[0046] The rotation of the first main spindle 10 and the second main spindle 20, and the movement of the first main spindle 10, the second main spindle 20, the moving table 32, etc. can be set by a program or by input to the input unit 40b.

[0047] In addition, the control unit 40a functions as an eccentricity detection unit 40c, a current value detection unit 40d, an eccentricity direction detection unit 40e, and a rotation angle detection unit 40f.

[0048] The current value detection unit 40d detects the load applied to the X2-axis motor 25c by detecting the current value. The eccentricity detection unit 40c calculates the eccentricity s of the workpiece stock W2 with respect to the integrally joined workpiece W1 based on the load detected by the current value detection unit 40d during the upsetting process U in which the rear end portion of the workpiece stock W2 is pressed against the front end portion of the workpiece W1 and integrally joined. Figure 3 The rotation angle detection unit 40f detects the rotation phase of the first main spindle 10. The eccentricity direction detection unit 40e, during the period in which the rear end portion of the workpiece stock W2 is pressed against the front end portion of the workpiece W1 and integrally joined (

[0049] On the other hand, the rotation angle detection unit 40f detects the rotation phase of the first main spindle 10. The eccentricity direction detection unit 40e, during the period in which the rear end portion of the workpiece stock W2 is pressed against the front end portion of the workpiece W1 and integrally joined ( Figure 3In the upsetting process U), the eccentricity direction of the workpiece residue W2 with respect to the integrally joined workpiece W1 is obtained by comparing the eccentricity s obtained by the eccentricity detection unit 40c and the rotation phase of the first main shaft 10 detected by the rotation angle detection unit 40f.

[0050] Figure 2 is a flowchart of operations including eccentricity correction. Figure 3 is a diagram illustrating the rotational speed S1, the rotation phase P1, and the current value I2 supplied to the X2-axis motor 25c during friction joining (including the friction process M and the upsetting process U) of the first main shaft 10.

[0051] In Figure 1 In such an automatic lathe 1, each time a cutting process is performed, the length of the workpiece W1 becomes shorter. If, as the machining of the workpiece W1 progresses, the overall length of the workpiece W1 held by the first main shaft 10 becomes shorter to the extent from near the front end of the first main shaft 10 to the guide bushing 18, the shortened portion becomes a workpiece residue that cannot be machined. In order to effectively utilize this workpiece residue, in the automatic lathe 1, the workpiece with a shorter length held by the first main shaft 10 is handed over to the second main shaft 20.

[0052] Specifically, first, the axes of the first main shaft 10 and the second main shaft 20 are arranged concentrically, for example, by bringing the second main shaft 20 closer to the first main shaft 10. Next, the chuck of the first main shaft 10 is opened, and a new workpiece W1 is supplied from the rear of the first main shaft 10. Then, the first main shaft 10 holds the newly supplied workpiece W1. When the new workpiece W1 is supplied to the first main shaft 10, the workpiece with a shorter length held by the first main shaft 10 (eventually becoming the workpiece residue W2) is pushed out from the guide bushing 18 to the front side of the support table 17. Therefore, the second main shaft 20 holds the workpiece residue W2.

[0053] Next, for example, in a state where the first main shaft 10 is rotating but the second main shaft 20 is stopped from rotating ( Figure 2 step S10), for example, the second main shaft 20 is brought closer to the first main shaft 10, and the rear end portion of the workpiece residue W2 is pushed against the front end portion of the new workpiece W1 while applying a predetermined pressure (step S11: start of the friction process M). As a result, the contact portion between the workpiece residue W2 and the workpiece W1 is softened by the frictional heat generated due to the rotational speed difference between the first main shaft 10 and the second main shaft 20.

[0054] In addition, in this example, only the first main shaft 10 is rotated, but as long as the first main shaft 10 and the second main shaft 20 rotate with a speed difference, the second main shaft 20 can also be rotated. In this case, the first main shaft 10 can rotate in the same direction or in the opposite direction with respect to the rotation direction of the second main shaft 20. Alternatively, only the second main shaft 20 can be rotated. Further, in this example, only the second main shaft 20 is moved in the Z2-axis direction, but it is also possible to move only the first main shaft 10 in the Z1-axis direction or to move both the first main shaft 10 and the second main shaft 20, so that the rear end portion of the workpiece remnant W2 contacts the front end portion of the workpiece W1.

[0055] Next, when the contact portion between the workpiece remnant W2 and the workpiece W1 is softened to a necessary degree, a stronger pressure is applied to press the workpiece remnant W2 against the workpiece W1 in such a manner that the second main shaft 20 is further brought closer to the first main shaft 10 (step S12: end the friction process M and start the upsetting process U). Further, at the same time, the control unit 40a outputs a rotation stop command to the first main shaft 10. As a result, as Figure 3 shown, the rotational speed S1 of the first main shaft 10 gradually decreases.

[0056] In addition, in the present embodiment, an example has been described in which the rotation stop command and the timing of applying a stronger pressure to press the workpiece remnant W2 against the workpiece W1 are simultaneous, but the timing may be different.

[0057] Further, as a method for confirming the degree of softening, for example, it can be understood by detecting a decrease in the current value of the Z2-axis motor 24c ( Figure 3 shown as I2' in ). Further, it is also possible to predetermine the conditions until the contact portion is softened through a preliminary experiment, and to apply friction to the contact portion between the workpiece remnant W2 and the workpiece W1 based on the conditions.

[0058] Then, when the first main shaft 10 stops rotating while the second main shaft 20 is pressed against the first main shaft 10, the rear end portion of the workpiece remnant W2 pushes the front end portion of the workpiece W1 and they are joined together, and the workpiece remnant W2 and the workpiece W1 become integral.

[0059] Here, there is a case where the workpiece remnant W2 and the workpiece W1 become integral in an eccentric state. However, it is known that even if the workpiece remnant W2 is eccentric with respect to the workpiece W1, since the temperature of the contact portion between the workpiece remnant W2 and the workpiece W1 is high in the upsetting process U, the workpiece remnant W2 can be moved in a direction intersecting the axis of the workpiece remnant W2. Therefore, as follows, in the friction joining (during the period until the joining phenomenon is completed) for the core.

[0060] Specifically, after the workpiece remnant W2 is pushed against the rotating workpiece W1 ( Figure 2In step S11), when the workpiece W1 is held by the first spindle 10 and the workpiece residue W2 is held by the second spindle 20 respectively, if only the first spindle 10 is rotationally driven, the rotation of the first spindle 10 is transmitted to the second spindle 20 via the workpiece W1 and the workpiece residue W2, so the second spindle 20 is also driven to rotate. If eccentricity occurs between the workpiece residue W2 and the workpiece W1, the second spindle 20 vibrates in the X2-axis direction with an amplitude twice the eccentricity amount s (the distance between the axis C1 of the workpiece W1 and the axis C2 of the workpiece residue W2) with respect to the axis C1 of the first spindle 10, as shown by solid lines and double-dot dash lines respectively in Figure 4 .

[0061] On the other hand, the position of the second spindle 20 in the X2-axis direction is maintained by the X2-axis motor 25c, and the X2-axis motor 25c is controlled by the control unit 40a to maintain the position of the second spindle 20 in the X2-axis direction (the X2-axis motor 25c is in a rotationally driven state). Therefore, if vibration caused by eccentricity 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 and decreases corresponding to the rotation phase of the second spindle 20.

[0062] Specifically, when vibration caused by an amplitude twice the eccentricity amount s is applied to the X2-axis motor 25c, the current value I2 supplied to the X2-axis motor 25c varies with an amplitude equivalent to twice the eccentricity amount s in the upsetting 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 .

[0063] Therefore, the current value detection unit 40d detects, for example, the variation range (the difference between the maximum value and the minimum value) of the current value I2 supplied to the X2-axis motor 25c throughout the entire specified period. Then, the eccentricity amount detection unit 40c obtains, for example, the average value of the variation range of the current value I2, assumes that half of the average value corresponds to the eccentricity amount s, and detects the eccentricity amount s of the workpiece residue W2 with respect to the integrally joined workpiece W1 ( Figure 2 step S13).

[0064] In this way, through the eccentricity amount detection unit 40c, the eccentricity degree between the workpiece W1 and the workpiece residue W2 can be known during the friction joining of the workpiece W1 and the workpiece residue W2. Therefore, as described later, a desired operation (such as eliminating eccentricity) can be performed before the end of this friction joining. Thus, after this friction joining is performed, it is not necessary to confirm joining deviation, correct the workpiece joined deviantly, etc., and, for example, the deburring operation can be started quickly. As a result, the manufacturing cost of the product can be reduced and the quality can be stabilized.

[0065] In addition, by using the load applied to the X2-axis motor 25c, the eccentricity amount s of the workpiece residue W2 with respect to the workpiece W1 can be easily and accurately obtained.

[0066] Furthermore, in the present embodiment, an example is given and described as follows, that is, the load applied to the X2-axis motor 25c is obtained based on the average value of the variation range of the current value I2. However, the present invention is not limited to this example. For example, the variation range of the current value I2 only at a specified timing and the reference value of the variation of the current value I2 may be preset, and the increase or decrease amount with respect to this reference value may be used. In addition, other parameters based on the current value I2 may also be used.

[0067] On the other hand, the variation (maximum value, minimum value) of the current value I2 supplied to the X2-axis motor 25c occurs at substantially the same position during one rotation of the workpiece W1. Therefore, if the variation of the current value I2 and the rotation phase P1 of the first spindle 10 are compared, the eccentricity direction of the workpiece residue W2 with respect to the workpiece W1 can also be known.

[0068] Specifically, as Figure 5 shown, the rotation phase P1 of the first spindle 10 (shown by a one-dot chain line in the figure) and the current value I2 supplied to the X2-axis motor 25c (shown by a solid line in the figure) are in the following relationship, for example, during two rotations of the spindle motor 13, the X2-axis motor 25c rotates approximately one week. Moreover, when the eccentricity direction of the workpiece residue W2 with respect to the workpiece W1 is in the positive direction of the X2-axis, the current value I2 supplied to the X2-axis motor 25c increases in the positive direction. In addition, when the rotation phase P1 of the first spindle 10 is 270°, for example, the current value I2 supplied to the X2-axis motor 25c is the maximum value. Therefore, it can be known that the eccentricity 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°.

[0069] Therefore, in Figure 2 step S13 ( Figure 3 upsetting process U), the eccentricity direction detection unit 40e compares the eccentricity amount s of the workpiece residue W2 with respect to the workpiece W1 detected by the eccentricity amount detection unit 40c and the rotation phase P1 of the first spindle 10 detected by the rotation angle detection unit 40f to detect the eccentricity direction of the workpiece residue W2 with respect to the workpiece W1. In this way, through the eccentricity direction detection unit 40e, the eccentricity direction of the workpiece residue W2 with respect to the workpiece W1 can be known during the frictional engagement between the workpiece W1 and the workpiece residue W2.

[0070] Next, the control unit 40a determines whether the eccentricity amount s detected by the eccentricity amount detection unit 40c is equal to or greater than a specified value that requires eccentricity correction ( Figure 2Step S14). Then, when the eccentricity amount s detected by the eccentricity detection unit 40c is equal to or greater than a specified value (YES in step S14), the process proceeds to step S15 to correct the eccentricity. On the other hand, when the eccentricity amount s detected by the eccentricity detection unit 40c is less than the specified value (NO in step S14), the process proceeds to step S17.

[0071] When eccentricity correction is required (YES in step S14), the control unit 40a outputs a drive signal to the main spindle motor 13 so that the eccentricity direction of the workpiece residue W2 with respect to the workpiece W1 coincides with the X2 direction (step S15). Specifically, as Figure 6A shown, when the eccentricity direction of the workpiece residue W2 with respect to the workpiece W1 (the direction connecting the axis C1 of the workpiece W1 and the axis C2 of the workpiece residue W2) is not parallel to the X2 axis, the first main spindle 10 is rotated to make this eccentricity direction coincide with the X2 axis direction.

[0072] Next, the control unit 40a outputs a drive signal to the X2-axis motor 25c, for example, immediately after the rotation of the first main spindle 10 stops ( Figure 3 shown by time T3), and as shown by the arrow in Figure 6B , the second main spindle 20 is moved in the X2-axis direction and in the direction in which the eccentricity amount s decreases ( Figure 2 step S16). More specifically, the second main spindle 20 is moved in the direction in which the distance from the axis C2 of the workpiece residue W2 to the axis C1 of the workpiece W1 becomes shorter, for example, by half of the average value of the variation range of the moving current value I2, so that the cores of the workpiece residue W2 and the workpiece W1 are aligned ( Figure 6C ). Thereby, eccentricity of the workpiece residue W2 can be removed during the friction joining of the workpiece W1 and the workpiece residue W2.

[0073] Next, the control unit 40a outputs a drive signal to the Z2-axis motor 24c to further press the rear end portion of the workpiece residue W2 against the front end portion of the workpiece W1 to complete the friction joining ( Figure 2 step S17).

[0074] In addition, regarding the timing of moving the second main spindle 20 in the X2-axis direction (step S16), it is sufficient that the temperature of the contact portion between the workpiece residue W2 and the workpiece W1 becomes high and the workpiece residue W2 can move in a direction intersecting the axis of the workpiece residue W2. Therefore, in addition to the above time T3, for example, it may also be immediately before the rotation of the first main spindle 10 stops ( Figure 3 shown by time T2), or during the period when the rotational speed S1 of the first main spindle 10 gradually decreases (shown by time T1).

[0075] After that, a burr generated at the joint portion between the workpiece remnant W2 and the workpiece W1 is machined by the tool 30. For this purpose, while the workpiece W1 is held by the first spindle 10, the holding of the workpiece remnant W2 by the second spindle 20 is released. The tool 30 is arranged, for example, closer to the second spindle 20 than the joint portion between the workpiece remnant W2 and the workpiece W1, and a prescribed cutting amount is set. Then, while rotating the first spindle 10, the tool 30 is moved to a position closer to the first spindle 10 than the joint portion between the workpiece remnant W2 and the workpiece W1 to remove the burr.

[0076] In this way, by using the automatic lathe 1 with the first spindle 10 and the second spindle 20 arranged opposite to each other, the front end portion of the workpiece W1 and the rear end portion of the workpiece remnant W2 are frictionally joined, and joining and cutting (integrating the joining process and the cutting process) are combined, it is possible to reduce the manufacturing cost of the product.

[0077] In addition, in the above-described embodiment, an example is given in which the eccentricity detection unit 40c calculates the eccentricity s. However, the present invention can also be applied to a case where, for example, the joint portion between the workpiece W1 and the workpiece remnant W2 is photographed with a camera and image processing is performed, or the eccentricity of the workpiece remnant W2 with respect to the workpiece W1 is detected by measurement using a laser as described later.

[0078] In addition, in the above-described embodiment, an example of eliminating (removing) the eccentricity s is given, but the present invention can also be applied to a case where the eccentricity is not eliminated but the eccentricity s is reduced.

[0079] In addition, in the above-described embodiment, an example is given in which the guide sleeve 18 is provided between the first spindle 10 and the second spindle 20. However, since the present invention only needs to be able to detect the eccentricity s during frictional joining, the guide sleeve 18 can be omitted. In addition, the workpiece W1 and the workpiece remnant W2 may be made of different materials. In addition, the workpiece W1 and the workpiece remnant W2 may have different diameters. And, in the above-described embodiment, an example of frictionally joining the workpiece remnant W2 and the workpiece W1 is given, but the present invention is not limited to the example of joining the workpiece remnant W2, and can also be applied to a case of joining new materials to each other.

[0080] In addition, for the present invention, as long as at least the first spindle 10 can rotate around the Z1 axis, the second spindle 20 can rotate around the Z2 axis, either the first spindle 10 or the second spindle 20 can move in the Z1 axis direction or the Z2 axis direction, and either the first spindle 10 or the second spindle 20 can move in the X1 axis direction or the X2 axis direction, it is not limited to the structure of the embodiment.

[0081] In addition, in the above-described embodiment, it moves in the X2-axis direction orthogonal to the Z2-axis. However, for the present invention, as long as it is a direction intersecting the Z2-axis, this direction can be variously changed.

[0082] Embodiment 2

[0083] Next, with reference to the drawings, a machine tool and a control method of the machine tool according to a second embodiment of the present invention will be described.

[0084] An automatic lathe (machine tool) 2 according to the second embodiment is an automatic lathe in which a method for detecting the eccentricity amount s of the workpiece residue W2 with respect to the workpiece W1 in the automatic lathe 1 of the first embodiment is changed.

[0085] Moreover, a large number of elements of the automatic lathe 2 according to the second embodiment are also common to the automatic lathe 1 according to the first embodiment, and thus detailed descriptions of the common matters are omitted.

[0086] As Figure 7 shown, the automatic lathe 2 has a laser sensor 50, which is a kind of optical sensor, on the bed 1a and is controlled by the control device 40. As Figure 8 shown, the laser sensor 50 irradiates the workpiece residue W2 with a laser L in a direction parallel to the X2-axis, and detects the distance D in the X2-axis direction between the laser sensor 50 and the circumferential surface of the workpiece residue W2.

[0087] Next, the detection of the eccentricity amount s of the workpiece residue W2 with respect to the workpiece W1 performed by the automatic lathe 2 according to the second embodiment will be described.

[0088] For example, when vibration caused by an amplitude twice the eccentricity amount s is added to the workpiece residue W2, the distance D between the laser sensor 50 and the circumferential surface of the workpiece residue W2 is as shown by the solid line in the graph of the distance (vertical axis) and time (horizontal axis) in Figure 9 . In the upsetting process U, it varies with an amplitude twice the eccentricity amount s with reference to the distance O in the X2-axis direction between the laser sensor 50 and the circumferential surface of the workpiece W1.

[0089] Therefore, in the upsetting process U, the eccentricity detection unit 40c detects the maximum value of the variation value in the X2-axis direction of the circumferential surface of the workpiece residue W2 with respect to the axis C1 of the workpiece W1, that is, the eccentricity amount s of the workpiece residue W2 with respect 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 circumferential surface of the workpiece residue W2).

[0090] Next, the detection of the eccentricity direction of the workpiece residue W2 with respect to the workpiece W1 performed by the automatic lathe 2 according to the second embodiment will be described.

[0091] In the second embodiment, changes (maximum value, minimum value) in the output value D of the laser sensor 50 also occur at substantially the same positions during one rotation of the workpiece W1. Therefore, by comparing the changes in the output value D and the rotation phase P1 of the first spindle 10, the eccentricity direction of the workpiece remnant W2 with respect to the workpiece W1 can also be known.

[0092] Specifically, as Figure 9 shown, the rotation phase P1 of the first spindle 10 (shown by a one-dot chain line in the figure) and the output value D of the laser sensor 50 (shown by a solid line in the figure) are in the following relationship, for example. During two rotations of the spindle motor 13 (i.e., the workpiece W1), the workpiece remnant W2 rotates approximately one week. Moreover, when the eccentricity direction of the workpiece remnant W2 with respect to the workpiece W1 is in the positive direction of the X2 axis, the output value D of the laser sensor 50 increases in the positive direction. Additionally, 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 its maximum. Therefore, it can be known that the eccentricity of the workpiece remnant W2 occurs in the direction connecting the axis C1 of the first spindle 10 and the position of the rotation phase 270°.

[0093] Therefore, in the upsetting process U, the eccentricity direction detection unit 40e, in the same manner as in the first embodiment, compares the eccentricity amount s of the workpiece remnant W2 with respect to the workpiece W1 detected by the eccentricity amount detection unit 40c and the rotation phase P1 of the first spindle 10 detected by the rotation angle detection unit 40f to detect the eccentricity direction of the workpiece remnant W2 with respect to the workpiece W1. Thus, in the automatic lathe 2 of the second embodiment, the eccentricity direction detection unit 40e can also know the eccentricity direction of the workpiece remnant W2 with respect to the workpiece W1 during the frictional engagement between the workpiece W1 and the workpiece remnant W2.

[0094] As described above, in the second embodiment, the automatic lathe 2 is provided with the laser sensor 50 that measures the distance to the workpiece remnant W2. The eccentricity amount detection unit 40c calculates the eccentricity amount s of the workpiece remnant W2 with respect to the workpiece W1 based on the output value D of the laser sensor 50, and thus directly detects the eccentricity amount s according to the shape of the circumferential surface of the workpiece remnant W2. Therefore, compared with the case of indirectly detecting the eccentricity amount s based on the load applied to the X2 axis motor as in the first embodiment, the eccentricity amount s can be detected more accurately.

[0095] Furthermore, in the present embodiment, as Figure 8 shown, the laser sensor 50 irradiates the workpiece remnant W2 with laser in a direction parallel to the X2 axis to detect the eccentricity amount s and the eccentricity direction of the workpiece remnant W2 with respect to the workpiece W1. However, as long as the eccentricity amount s can be calculated by the eccentricity amount detection unit 40c, it can be in any direction, and the irradiation direction of the laser on the workpiece remnant W2 is not limited to being parallel to the X2 axis.

[0096] In addition, in this embodiment, the laser sensor 50 using the laser L is described as an example of the optical sensor. However, the optical sensor is not limited to the laser sensor and can be appropriately selected according to the measurement accuracy. For example, it can also be an optical sensor using emitted light such as LED light.

[0097] Description of Reference Numerals

[0098] 1... Automatic lathe (machine tool); 1a... Bed; 10... First spindle; 12... Spindle headstock; 13... Spindle motor; 14... Feed mechanism in the Z1-axis direction; 14a... Z1-axis guide rail; 14b... Z1-axis slider; 14c... Z1-axis motor; 17... Support table; 18... Bush; 20... Second spindle; 22... Spindle headstock; 23... Spindle motor; 24... Feed mechanism in the Z2-axis direction; 24a... Z2-axis guide rail; 24b... Z2-axis slider; 24c... Z2-axis motor; 25... Feed mechanism in the X2-axis direction (second spindle moving unit); 25a... X2-axis guide rail; 25b... X2-axis slider; 25c... X2-axis motor (motor); 30... Tool; 31... Tool table; 32... Moving table; 40... Control device; 40a... Control unit; 40b... Input unit; 40c... Eccentric amount detection unit; 40d... Current value detection unit; 40e... Eccentric direction detection unit; 40f... Rotation angle detection unit; 50... Laser sensor (optical sensor); W1... Workpiece (first workpiece); W2... Workpiece residue (second workpiece); M... Friction process; U... Upsetting process; S1... Rotation speed; P1... Rotation phase; I2... Current value; T1... Time; T2... Time; T3... Time; s... Eccentric amount; D... Distance in the X2-axis direction between the laser sensor and the circumferential side of the workpiece residue; L... Laser.

Claims

1. A machine tool, comprising: 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 rotates at least one of the first workpiece held by the first spindle and the second workpiece held by the second spindle, and relatively moves the first spindle and the second spindle closer to each other to press a rear end portion of the second workpiece against a front end portion of the first workpiece for frictional engagement. The machine tool is characterized in that the control unit includes an eccentricity amount detection unit that detects an eccentricity amount of the second workpiece relative to the first workpiece during the frictional engagement. The eccentricity amount detection unit obtains the eccentricity amount 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 with the rotation axis of the second spindle.

2. The machine tool according to claim 1, characterized in that it includes a second spindle movement unit that moves the second spindle in a direction intersecting with the rotation axis of the second spindle during the frictional engagement based on the eccentricity amount of the second workpiece relative to the first workpiece detected by the eccentricity amount detection unit.

3. The machine tool according to claim 2, characterized in that the timing of moving the second spindle in a direction intersecting with the rotation axis of the second spindle is after the first spindle has just stopped rotating, before the first spindle is about to stop rotating, or during a period when the rotational speed of the first spindle is gradually decreasing.

4. The machine tool according to claim 2 or 3, characterized in that the control unit includes an eccentricity direction detection unit that detects an eccentricity direction of the second workpiece relative to the first workpiece during the frictional engagement by comparing the eccentricity amount of the second workpiece relative to the first workpiece detected by the eccentricity amount detection unit with the rotational phase of the first spindle.

5. The machine tool according to claim 4, characterized in that the second spindle movement unit moves the second spindle in a direction intersecting with the rotation axis of the second spindle in such a way that the eccentricity amount of the second workpiece relative to the first workpiece is reduced based on the eccentricity amount of the second workpiece relative to the first workpiece detected by the eccentricity amount detection unit and the eccentricity direction of the second workpiece relative to the first workpiece detected by the eccentricity direction detection unit.

6. The machine tool according to claim 1, characterized in that the control unit includes an eccentricity direction detection unit that detects an eccentricity direction of the second workpiece relative to the first workpiece during the frictional engagement by comparing the eccentricity amount of the second workpiece relative to the first workpiece detected by the eccentricity amount detection unit with the rotational phase of the first spindle.

7. A control method for a machine tool, the machine tool comprising: 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 the operations of the first spindle and the second spindle. The control method for the machine tool is characterized by including the following steps: While rotating at least one of the first workpiece held by the first spindle and the second workpiece held by the second spindle, relatively move the first spindle and the second spindle toward each other so that the rear end portion of the second workpiece contacts and rubs against the front end portion of the newly supplied first workpiece. During the friction engagement by pressing the rear end portion of the second workpiece against the front end portion of the first workpiece, detect the amount of eccentricity of the second workpiece relative to the first workpiece based on the load applied to the motor that moves the second spindle in a direction intersecting the rotation axis of the second spindle. During the friction engagement, detect the direction of eccentricity of the second workpiece relative to the first workpiece. And During the friction engagement, move the second spindle in a direction intersecting the rotation axis of the second spindle so that the amount of eccentricity of the second workpiece relative to the first workpiece decreases based on the detected amount of eccentricity of the second workpiece relative to the first workpiece and the detected direction of eccentricity of the second workpiece relative to the first workpiece.

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