lathe

Abstract

The present invention provides a lathe capable of shortening the cycle time of workpiece processing. The lathe (1) comprises: a first spindle (12) capable of holding a workpiece (W0) and rotating around a spindle centerline (AX1); a second spindle (22) opposite to the first spindle (12) and capable of holding the workpiece W0 and rotating around the spindle centerline (AX1); a tool holder 31 provided with a cutting tool T1 for cutting the workpiece W0 held on the two spindles (12, 22); and a control unit (U1) for controlling the rotation of the two spindles (12, 22) and the relative movement of the two spindles (12, 22) and the tool holder 31 for cutting the workpiece (W0). The control unit (U1) causes the two spindles (12, 22) holding the workpiece W0 to rotate synchronously, then changes the rotation speed V1 of the first spindle (12) and detects the rotation speed V2 of the second spindle (22). If the detected change (ΔV2) of the rotation speed V2 is within a specific range, it is determined that the cutting of the workpiece (W0) is normal.

Description

Technical Field

[0001] The present invention relates to a lathe for judging whether the cutting of a workpiece held on two main spindles facing each other is normally performed. Background Art

[0002] As a lathe, there is a known NC (numerical control) lathe that performs front processing on a workpiece held on a front spindle and delivers the workpiece after front processing to a back spindle for back processing. When this NC lathe delivers the workpiece after front processing from the front spindle to the back spindle, it rotates the workpiece held on the front spindle and the back spindle facing each other while performing cutting processing using a cutting tool. Here, if the cutting tool is damaged, there is a possibility that the cutting of the workpiece is not completed. If the cutting of the workpiece is not completed, the next processing such as back processing cannot be performed normally, so the next processing is performed after judging whether the cutting of the workpiece is performed normally.

[0003] The discrimination process is performed by allowing the workpiece detection pin to enter between the front spindle and the back spindle after the cutting process to confirm that the workpiece detection pin does not contact the workpiece. A contact-action switch is installed on the workpiece detection pin. If the switch does not operate, it is determined that the cutting of the workpiece is normal and the next processing is performed. If the switch operates, it is determined that the cutting of the workpiece is abnormal and the operation of the machine is stopped. Here, because the workpiece will rotate at a high speed just after the cutting process, the rotation of the front spindle and the back spindle must be slowed down before the workpiece detection pin is entered to prevent the high-speed rotating workpiece from contacting the workpiece detection pin. In the next processing, there is a situation where the rotation of the front spindle and the back spindle becomes high speed.

[0004] In addition, Patent Document 1 discloses a method for cutting a workpiece of a dual-spindle opposing lathe having a phase synchronization control unit between a first spindle and a second spindle facing each other on the same axis. The phase synchronization control unit comprises: a phase difference detection unit for detecting the phase difference between the rotating first spindle and the second spindle; and a correction instruction unit for correcting the speed instruction given to the spindle motor from the NC device based on the detected phase difference. After the lathe performs cutting of the workpiece by operating the first spindle and the second spindle synchronously, different rotation speed instruction values ​​are given to the first spindle motor and the second spindle motor while blocking the feedback output of the correction instruction unit. If the phase difference output from the phase difference detection unit exceeds the set value, the next processing is performed.

[0005] Background Art Literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Laid-Open No. 5-138404 Summary of the invention

[0008] [Problems to be solved by the invention]

[0009] When using a workpiece detection pin, after the cutting process, at least the rotation of the front spindle and the back spindle must be decelerated to allow the workpiece detection pin to move in and out, so the discrimination process takes time accordingly, resulting in a longer cycle time for workpiece processing. In addition, when using a phase difference between the first spindle and the second spindle, the rotation speeds of the first spindle and the second spindle must also be changed after the cutting process, so the discrimination process takes time accordingly, resulting in a longer cycle time for workpiece processing.

[0010] Furthermore, the problems as described above exist in various lathes.

[0011] The invention discloses a lathe capable of shortening the cycle time of workpiece processing.

[0012] [Technical means to solve the problem]

[0013] The lathe of the present invention has the following form, and comprises: a first spindle capable of holding a workpiece and rotating around a spindle centerline;

[0014] A second spindle, opposite to the first spindle, capable of holding the workpiece and rotating around the spindle centerline;

[0015] a tool holder provided with a cutting tool for cutting the workpiece held on the first spindle and the second spindle; and

[0016] a control unit that controls the rotation of the first spindle and the second spindle, and the relative movement of the first spindle, the second spindle and the tool holder for cutting the workpiece; and

[0017] The control unit rotates the first spindle and the second spindle holding the workpiece synchronously, changes the rotation speed of the first spindle, and detects the rotation speed of the second spindle. If the detected rotation speed change is within a specific range, it is determined that the workpiece is cut normally.

[0018] [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a lathe capable of shortening the cycle time for machining a workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a diagram schematically showing a configuration example of a lathe.

[0021] Figure 2 This is a block diagram schematically showing a configuration example of a circuit of a lathe.

[0022] Figure 3This is a diagram schematically showing an example of normal cutting processing.

[0023] Figure 4 It is a diagram schematically showing an example of abnormal cutting processing.

[0024] Figure 5 This is a diagram schematically showing an example of a time change in the rotation speed of the main spindle when the cutting process is normal.

[0025] Figure 6 This is a diagram schematically showing an example of a temporal change in the rotation speed of the main spindle when a cutting process is abnormal.

[0026] Figure 7 This is a flowchart showing an example of a cutting process performed by a numerical control device.

[0027] Figure 8 This is a flowchart showing another example of the cutting process performed by the numerical control device.

[0028] Fig. 9 It is a diagram schematically showing a state of detecting whether or not cutting processing is normal in a comparative example.

[0029] Fig.10 It is a diagram schematically showing the time change of the rotation speed of the main shaft in the comparative example. DETAILED DESCRIPTION

[0030] The following embodiments of the present invention will be described. Of course, the following embodiments are merely examples of the present invention, and all features disclosed in the embodiments are not necessarily essential to the solution means of the invention.

[0031] (1) Overview of the technology included in the present invention:

[0032] First, refer to Figures 1 to 10 The examples shown illustrate the outline of the technology included in the present invention. In addition, the figures of this case are schematic diagrams of examples, and the magnifications of the directions shown in these figures are sometimes different, and the figures sometimes do not match. Of course, the elements of this technology are not limited to the specific examples shown by the symbols.

[0033] In addition, in the present case, the numerical range "Min to Max" means a range from a minimum value Min to a maximum value Max.

[0034] [Form 1]

[0035] A lathe according to one form of the present technology includes a first spindle (e.g., a front spindle 12), a second spindle (e.g., a back spindle 22), a tool rest 31, and a control unit U1. The first spindle 12 is capable of holding a workpiece W0 and rotating around a spindle center line AX1. The second spindle 22 is opposite to the first spindle 12, and is capable of holding the workpiece W0 and rotating around a spindle center line AX2 aligned with the spindle center line, e.g., the spindle center line AX1. The tool rest 31 is provided with a cutting tool T1 for cutting the workpiece W0 held on the first spindle 12 and the second spindle 22. The control unit U1 controls the rotation of the first spindle 12 and the second spindle 22, and the relative movement of the first spindle 12 and the second spindle 22 and the tool rest 31 for cutting the workpiece W0. The control unit U1 causes the first spindle 12 and the second spindle 22 holding the workpiece W0 to rotate synchronously, then changes the rotation speed V1 of the first spindle 12 and detects the rotation speed V2 of the second spindle 22. If the change in the detected rotation speed V2 (for example, the change amplitude ΔV2) is within a specific range (for example, does not reach the threshold TH), it is determined that the cutting of the workpiece W0 is normal.

[0036] If the rotation speed V1 of the first spindle 12 is changed after the first spindle 12 and the second spindle 22 holding the workpiece W0 are rotated synchronously, the workpiece W0 is connected between the first spindle 12 and the second spindle 22, and the rotation speed V2 of the second spindle 22 also changes. If the cutting of the workpiece W0 is completed, the change in the rotation speed V1 of the first spindle 12 will not affect the rotation speed V2 of the second spindle 22. Therefore, if the change in the rotation speed V2 of the second spindle 22 is within a specific range, it can be determined that the cutting of the workpiece W0 is normal. In the above-mentioned form 1, if the rotation speed V2 of the second spindle 22 is detected and the change (ΔV2) of the detected rotation speed V2 is within a specific range, it is determined that the cutting of the workpiece W0 is normal, so the normality of the cutting is determined just after the workpiece W0 is cut. Therefore, this form can provide a lathe that shortens the cycle time of workpiece processing.

[0037] Here, the first main axis may be the front main axis and the second main axis may be the back main axis, or the first main axis may be the back main axis and the second main axis may be the front main axis.

[0038] The relative movement of the first and second spindles and the tool holder includes the first and second spindles not moving and the tool holder moving, the tool holder not moving and the first and second spindles moving, and the first and second spindles and the tool holder both moving.

[0039] When the control unit determines whether the workpiece cutting is normal or not at the time point when the variation of the rotation speed of the second spindle is outside the specific range, if the variation of the detected rotation speed is within the specific range, then the workpiece cutting can be determined to be normal. Of course, at the time point of determining whether the workpiece cutting is normal or not, if the variation of the rotation speed of the second spindle is within the specific range, the control unit can also immediately determine that the workpiece cutting is normal.

[0040] [Form 2]

[0041] In addition, the control unit U1 can change the rotation speed V1 of the first spindle 12 and detect the rotation speed V2 of the second spindle 22 while moving the tool rest 31 to the position where the cutting of the workpiece W0 is completed (for example, the position X=+Xe). The control unit U1 can determine that the cutting of the workpiece W0 is normal when the change (ΔV2) of the detected rotation speed V2 is within the specific range. This form does not need to move the first spindle 12 and the second spindle 22 in the direction intersecting the spindle centerline AX1 (for example, the X-axis direction) during the cutting process, so the structure of the lathe can be simplified.

[0042] (2) Specific example of the structure of a lathe:

[0043] Figure 1 The configuration of a spindle-moving type NC (numerical control) lathe 1 in which a front spindle 12 moves is schematically illustrated as an example of a lathe. Figure 1 The present invention is merely an example simplified for the purpose of explaining the present invention, and does not limit the present invention. In addition, the description of the positional relationship of each part is merely an example. Therefore, changing the left-right direction to the up-down direction or the front-to-back direction, or changing the up-down direction to the left-right direction or the front-to-back direction, or changing the front-to-back direction to the left-right direction or the up-down direction, or changing the rotation direction to the opposite direction, etc. are also included in the present invention. In addition, the same direction or position, etc. is not limited to strict consistency, and includes situations where the strict consistency is deviated due to errors.

[0044] Figure 1 The lathe 1 shown includes an NC device 70, a front spindle head 11 provided on a fixed base 10, a rear spindle head 21 provided on a fixed base 20, a tool rest 31 provided on a fixed base 30, etc. The NC device 70 controls the operation of the above-mentioned components 11, 21, 31, etc.

[0045] The front spindle table 11 is provided to be movable in the Z-axis direction along the spindle centerline AX1. Figure 2The position of the front spindle stage 11 in the Z-axis direction is controlled by a driving unit such as the Z1-axis motor MZ1 shown as an example. The front spindle 12 provided on the front spindle stage 11 has a holding unit 13 such as a collet, and the holding unit 13 is used to releasably hold the cylindrical (rod-shaped) workpiece W1 inserted in the Z-axis direction. The NC device 70 rotates the front spindle 12 around the spindle center line AX1 along the length direction of the workpiece W1 via a driving unit such as a rotary motor 15. As a result, the front spindle 12 rotates the workpiece W1 around the spindle center line AX1.

[0046] like Figure 1 As shown by the double-dotted line, a guide sleeve 18 may also be arranged in front of the front spindle 12. In this case, the guide sleeve 18 is arranged in front of the front spindle 12, supports the long workpiece W1 passing through the front spindle 12 so that it can slide in the Z-axis direction, and is driven to rotate synchronously with the front spindle 12 around the spindle centerline AX1.

[0047] The back spindle table 21 is provided to be movable in the Z-axis direction along the spindle center line AX2 and in the Y-axis direction perpendicular to (intersecting) the Z-axis direction. Figure 2 The illustrated driving units such as the Z2-axis motor MZ2 or the Y2-axis motor MY2 control the position of the back spindle stage 21 in the Z-axis direction and the Y-axis direction. The back spindle 22 provided on the back spindle stage 21 has a holding unit 23 such as a collet, and the holding unit 23 is used to releasably hold the front-processed workpiece W2 inserted in the Z-axis direction in a state where the spindle center lines AX1 and AX2 are aligned with each other. The NC device 70 rotates the back spindle 22 around the spindle center line AX2 via a driving unit such as a rotary motor 25. As a result, the back spindle 22 rotates the workpiece W2 around the spindle center line AX2. The back spindle 22 is sometimes referred to as an opposing spindle in the sense of being opposite to the front spindle.

[0048] In addition, the workpiece W1 before front processing and the workpiece W2 after front processing are collectively referred to as workpiece W0, and the workpiece held by the holding portions 13 and 23 of the two spindles 12 and 22 along the spindle center line AX1 for cutting processing is referred to as workpiece W0.

[0049] The tool rest 31 is provided with a plurality of tools T0 for machining the workpiece W0, and is configured to be movable in the X-axis direction and the Z-axis direction. Here, the X-axis direction is a direction perpendicular to (intersecting with) the Z-axis direction and the Y-axis direction. Figure 2The illustrated driving units such as the X3-axis motor MX3 or the Z3-axis motor MZ3 control the position of the tool rest 31 in the X-axis direction and the Z-axis direction. The plurality of tools T0 include a cutting tool T1 for cutting the workpiece W0 held by the holding parts 13 and 23 of the two spindles 12 and 22. The tool rest may be a turret tool rest, a comb tool rest, etc. A variety of tool rests may also be provided on the lathe. In addition, the moving directions of the parts 11, 21, 31, etc. are not limited to Figure 1 direction shown.

[0050] Figure 2 The circuit configuration of the NC lathe 1 is schematically illustrated. Figure 2 In the lathe 1 shown, the NC device 70 is connected to an operation panel 80, a Z1-axis motor MZ1, a Y2-axis motor MY2, a Z2-axis motor MZ2, an X3-axis motor MX3, a Z3-axis motor MZ3, a rotary motor 15 for rotating and driving the front spindle 12, a rotary motor 25 for rotating and driving the back spindle 22, an actuator 14 for opening and closing the holding portion 13 of the front spindle 12, an actuator 24 for opening and closing the holding portion 23 of the back spindle 22, etc. The NC device 70 is a computer having a CPU (Central Processing Unit) 71, a ROM (Read Only Memory) 72 as a semiconductor memory, a RAM (Random Access Memory) 73 as a semiconductor memory, a timer circuit 74, an I / F (interface) 75, etc. Figure 2 In the figure, the I / Fs of the operation panel 80, the servo motors MZ1, MY2, MZ2, MX3, MZ3, the rotary motors 15, 25, and the actuators 14, 24 are collectively represented as I / F 75. The interpretation execution program P1 for interpreting and executing the processing program P2 is written in ROM72. The processing program P2 created by the user is rewritably stored in RAM73. The processing program is also called an NC program. CPU71 uses RAM73 as a work area to execute the interpretation execution program P1 recorded in ROM72, thereby making the computer function as an NC device 70. Of course, part or all of the functions realized by the interpretation execution program P1 can also be realized by other units such as ASIC (Application Specific Integrated Circuit).

[0051] The operation panel 80 includes an input unit 81 and a display unit 82, and functions as a user interface of the NC device 70. The input unit 81 includes, for example, a button or a touch panel for accepting operation input from an operator. The display unit 82 includes, for example, a display for displaying the contents of various settings accepted from the operator or various information related to the NC lathe 1. The operator can store the machining program P2 in the RAM 73 using the operation panel 80 or an external computer.

[0052] The Z1-axis motor MZ1 moves the front spindle table 11 in the Z-axis direction according to the command from the NC device 70. The Y2-axis motor MY2 moves the back spindle table 21 in the Y-axis direction according to the command from the NC device 70. The Z2-axis motor MZ2 moves the back spindle table 21 in the Z-axis direction according to the command from the NC device 70. The X3-axis motor MX3 moves the tool rest 31 in the X-axis direction according to the command from the NC device 70. The Z3-axis motor MZ3 moves the tool rest 31 in the Z-axis direction according to the command from the NC device 70.

[0053] The rotary motor 15 has an encoder 16 that generates reference angle pulses at intervals corresponding to the rotation speed of the front spindle 12, and rotates the front spindle 12 according to the command from the NC device 70. The rotary motor 25 has an encoder 26 that generates reference angle pulses at intervals corresponding to the rotation speed of the back spindle 22, and rotates the back spindle 22 according to the command from the NC device 70. In addition, the rotation speed is also called the number of revolutions, which means the number of revolutions per unit time.

[0054] The actuator 14 opens and closes the holding portion 13 of the front spindle 12 via a power transmission mechanism such as a sleeve member in accordance with the control of the NC device 70. If the holding portion 13 is opened, the workpiece can move in the Z-axis direction, and if the holding portion 13 is closed, the workpiece is held in the holding portion 13. The actuator 24 opens and closes the holding portion 23 of the back spindle 22 via a power transmission mechanism such as a sleeve member in accordance with the control of the NC device 70. If the holding portion 23 is opened, the workpiece can move in the Z-axis direction, and if the holding portion 23 is closed, the workpiece is held in the holding portion 23. The actuators 14 and 24 can use a servo motor including a linear motor, a cylinder, a hydraulic cylinder, etc. The actuators 14 and 24 can also include a speed reduction mechanism such as a ball screw mechanism.

[0055] In this specific example, the front spindle 12 is an example of a first spindle, and the rear spindle 22 is an example of a second spindle. In addition, the NC device 70, the rotary motors 15, 25, and the X3-axis motor MX3 are examples of the control unit U1.

[0056] (3) Specific example of cutting process:

[0057] First, refer to Figure 3, an example of cutting processing when cutting processing is performed normally is described. Figure 3 A normal cutting process using the cutting tool T1 provided on the tool holder 31 is schematically illustrated. Figure 3 2 shows the cutting process of the lathe without using the guide bushing, but the cutting process of the workpiece W0 held by the two spindles 12 and 22 is also performed when the guide bushing is used.

[0058] Figure 3 The left side of the diagram shows that the front spindle 12 has a holding portion 13 holding a workpiece W0 of diameter D, the back spindle 22 approaches the front spindle 12 and the holding portion 23 holds the workpiece W0, and the tip of the cutting tool T1 moves in the +X direction to the position X=-D / 2. If the tool holder 31 further moves in the +X direction while the two spindles 12 and 22 rotate at the speed of cutting, the workpiece W0 is cut, and if there is no error, the workpiece W0 is cut at the center position X=0 of the workpiece W0. In fact, if Figure 3 As shown on the right side of , the tool holder 31 is moved to the cutting completion position X=+Xe (Xe>0) passing through the center position X=0.

[0059] Figure 4 The cutting process is schematically illustrated in the case where the cutting tool T1 is damaged during the cutting process. Figure 4 On the left side, the damaged part of the cutting tool T1 is indicated by a double-dashed line. In this case, the cutting process cannot be performed normally. Figure 4 As shown on the right side of , the workpiece W0 is connected between the two spindles 12 and 22. If the cutting of the workpiece W0 is not completed, the next processing such as back processing cannot be performed normally, so the next processing is performed after the judgment processing of the cutting of the workpiece W0 has been performed normally.

[0060] Fig. 9 The following schematically shows the detection of normality of the cutting process of the workpiece W0 in the comparative example. Fig. 9 The lathe shown is equipped with a detection device 900 for detecting whether the cutting process is normal or not. The detection device 900 comprises: a workpiece detection pin 901, which is arranged on a tool holder (not shown) that can move in the X-axis direction and can move forward and backward in the direction intersecting the spindle center line AX1 of the two spindles 12 and 22; and a contact action type switch 902, which is installed at the end of the detection pin 901. If the detection pin 901 does not contact the workpiece W0 and the switch 902 does not operate when the detection pin 901 is moved in and out, it is determined that the cutting of the workpiece W0 is normal and the next processing is carried out. If the detection pin 901 contacts the workpiece W0 and the switch 902 is operated when the detection pin 901 is moved in and out, it is determined that the cutting of the workpiece W0 is abnormal and the operation of the machine is stopped.

[0061] Here, since the workpiece W0 rotates at high speed immediately after the cutting process, the rotation of the two spindles 12 and 22 must be decelerated before the detection pin 901 is inserted so as to prevent the workpiece W0 rotating at high speed from contacting the detection pin 901 .

[0062] Fig.10 The following diagram schematically shows the time variation of the rotation speed of the two main shafts 12 and 22 in the comparative example. Fig.10 In FIG. 1 , the horizontal axis represents time t, and the vertical axis represents the rotation speed of the spindles 12 and 22. Fig.10 The upper side of represents the time variation of the rotation speed V1 (rpm; number of revolutions per minute) of the front spindle 12. Fig.10 The lower side of represents the time change of the rotation speed V2 (rpm) of the back spindle 22.

[0063] The first time point t91 indicates the time point when the holding portion 23 of the back spindle 22 holds the workpiece processed on the front side and starts the synchronous operation of the rotation of the two spindles 12, 22. The synchronous operation means the operation to make the command value of the rotation speed V2 of the back spindle 22 consistent with the command value of the rotation speed V1 of the front spindle 12. The next time point t92 indicates the time point when the synchronous operation is completed at a high rotation speed (for example, 1000 to 4000 rpm) during the cutting process. The next time point t93 indicates the time point when the tool holder with the cutting tool is set moves to the cutting completion position X=+Xe. Because the workpiece W0 rotates at a high speed at this time point, the NC device reduces the rotation speed of the spindles 12, 22 to a low rotation speed (for example, 300 to 700 rpm) during the period to the next time point t94. During the period to the next time point t95, the workpiece detection pin 901 moves in and out to detect whether the cutting process of the workpiece W0 is normal or not. When the detection pin 901 is not in contact with the workpiece W0 , the NC device restores the rotation of the spindles 12 , 22 at a high speed until the time point t96 to perform the next machining process.

[0064] Based on the above, after the tool rest reaches the cutting completion position X=+Xe, detection processing at time points t93 to t96 is required each time the workpiece is processed.

[0065] In this specific example, by changing the rotation speed V1 of the front spindle 12 in synchronous operation before the tool holder reaches the cutting completion position, and confirming that the change in the rotation speed V2 of the back spindle 22 is within a specific range, it can be immediately determined that the cutting of the workpiece W0 is normal. In addition, no space is required for the detection device 900.

[0066] Figure 5 The following schematically illustrates the time change of the rotation speed of the main spindle when the cutting process is normal. Figure 5In FIG. 1 , the horizontal axis represents time t, and the vertical axis represents the rotation speed of the spindles 12 and 22. Figure 5 The upper side of represents the time variation of the rotation speed V1 (rpm) of the front spindle 12. Figure 5 The lower side of represents the time change of the rotation speed V2 (rpm) of the back spindle 22.

[0067] The first time point t11 ​​indicates the time point when the holding portion 23 of the back spindle 22 holds the workpiece after the front processing and the synchronous operation of the rotation of the two spindles 12, 22 begins. The synchronous operation in this case means the operation of making the command value of the rotation speed V2 of the back spindle 22 consistent with the command value of the unchanged rotation speed V1 of the front spindle 12. The next time point t12 indicates the time point when the synchronous operation is completed at a high rotation speed (for example, 1000 to 4000 rpm) during cutting processing. If the synchronous operation is completed, the NC device 70 starts to control the tool holder 31 on which the cutting tool T1 is set to move in the +X direction. The time point t13 indicates the time point when the tool holder 31 moves to the position where the rotation change starts, X=-Xs (Xs>0). At the time point t13, the NC device 70 starts to control the rotation speed V1 of the front spindle 12 to change by a change amplitude ΔV1. Since the workpiece W0 is connected between the spindles 12 and 22 , the rotation speed V2 of the back spindle 22 is also changed.

[0068] The variation range ΔV1 means the difference between the maximum and minimum values ​​of the rotation speed, and is twice the amplitude representing the maximum displacement from the center value. Therefore, when the rotation speed is varied by ±A (rpm), the amplitude becomes A (rpm) and the variation range ΔV1 becomes 2A (rpm). The amplitude A is set to be smaller than the rotation speed V1 (rpm) (for example, 1 to 3 digits smaller), for example, it can be set to about 1 to 20 rpm. The frequency f1 of the rotation speed V1 can be set to about 1 to 20 Hz, for example.

[0069] The next time point t14 indicates the time point when the tool holder 31 moves to the cutting tool contact position X=-D / 2. Because the tip of the cutting tool T1 contacts the workpiece W0 at time point t14, the rotation speeds V1 and V2 are reduced due to the load during cutting. The rotation speed V2 of the back spindle 22 is continuously varied. If the workpiece W0 is cut, the rigidity of the cut portion of the workpiece W0 becomes lower, so the variation range ΔV2 of the rotation speed V2 of the back spindle 22 becomes smaller. In addition, because the load during cutting is reduced, the rotation speeds V1 and V2 return to their original state. The next time point t15 indicates the time point when the tool holder 31 moves to the cutting completion position X=+Xe.

[0070] Figure 6 The time variation of the rotation speed of the spindle when the cutting process is abnormal is schematically illustrated. Figure 6In FIG. 1 , the horizontal axis represents time t, and the vertical axis represents the rotation speed of the main shafts 12 , 22 .

[0071] When the cutting process is abnormal, the time variation of the rotation speeds V1 and V2 at time points t11 to t14 is the same as that when the cutting process is normal. However, even when the tool holder 31 reaches the cutting completion position X=+Xe at time point t15, the workpiece W0 is connected between the two spindles 12 and 22, so the variation range ΔV2 of the rotation speed V2 of the back spindle 22 remains.

[0072] like Figure 5 As shown in FIG. 1 , when the cutting of the workpiece W0 is normal, the variation range ΔV2 of the rotation speed V2 of the back spindle 22 becomes smaller. Therefore, as long as the variation range ΔV2 is within a specific range, it can be determined that the cutting of the workpiece W0 is normal. Therefore, it is not necessary to determine that the cutting is normal immediately after the workpiece W0 is cut. Fig.10 The detection process at the time points t93 to t96 is shown. Therefore, the cycle time of workpiece processing can be shortened.

[0073] In addition, the normality of the workpiece cutting is determined immediately after the cutting is performed, so the rotation change start position X=-Xs can also be the position after the cutting tool contacts the position X=-D / 2. Figure 5 , 6 The time point t13 shown may also be after the time point t14 at which X=-D / 2.

[0074] (4) Example of cutting process:

[0075] Figure 7 The following is an example of a cutting process performed by the NC device 70 that interprets and executes the program P1. This process starts when the NC device 70 reads the cutting instruction recorded in the machining program P2. Figure 5 , 6 Therefore, the NC device 70 executing the interpretation and execution program P1 realizes the rotation speed change, which is shown in the example. Figure 7 . Below, also refer to Figures 2 to 6 ,right Figure 7 The cutting process shown is explained.

[0076] If the cutting process is started, the NC device 70 makes Figure 2 The Z2-axis motor MZ2 shown is driven to move the back spindle table 21 toward the front spindle table 11, and the actuator 24 is driven to cause the holding portion 23 of the back spindle 22 to hold the workpiece W0 (step S102).

[0077] Next, the NC device 70 outputs the command value of the rotation speed V1 for cutting processing to the two rotary motors 15 and 25 to start the synchronous drive of the rotary motors 15 and 25, and starts the synchronous operation of the rotation of the two spindles 12 and 22 holding the workpiece W0 (step S104). Here, the front spindle 12 is the active spindle and the back spindle 22 is the driven spindle, and the command value of the rotation speed V2 for the rotary motor 25 for the back spindle is consistent with the command value of the rotation speed V1 for the rotary motor 15 for the front spindle. The start time point of the processing of step S104 is equivalent to Figure 5 , 6 At the time point t11 ​​shown. When the detected values ​​of the rotation speeds V1 and V2 of the two spindles 12 and 22 become the high rotation speed during cutting processing ( Figure 5 , 6 At time point t12), the NC device 70 sends a synchronous operation completion signal.

[0078] Furthermore, the NC device 70 acquires the rotation change start position X=−Xs with respect to the position of the tool rest 31 in the X-axis direction from the machining program P2 (step S106 ).

[0079] Next, the NC device 70 drives the X3-axis motor MX3 to move the tool post 31 together with the cutting tool T1 in the +X direction along the cutting path (step S108 ).

[0080] Next, when the tool holder 31 reaches the rotation change starting position X=-Xs, the NC device 70 applies a variation component of a variation amplitude ΔV1 and a frequency f1 to the command value of the rotation speed V1 of the front spindle rotation motor 15, and starts the variation of the rotation speed V1 of the front spindle 12 (step S110). The process of varying the rotation speed V1 may also be a process of controlling the current value, that is, the torque, applied to the rotation motor 15 in such a way that the rotation speed becomes the rotation speed after applying a variation component of a variation amplitude ΔV1 and a frequency f1 to the rotation speed V1 during cutting processing. No variation component is applied to the command value of the rotation speed V2 of the back spindle rotation motor 25. The start time point of the process of step S110 corresponds to Figure 5 , 6 At time t13 shown, the rotation speed V1 of the front spindle 12 continues to change while the tool rest 31 is moving to the workpiece cutting completion position X=+Xe. The back spindle rotary motor 25 detects the rotation speed V2 of the back spindle 22 based on the generated pulses of the encoder 26 .

[0081] Next, the NC device 70 repeatedly obtains the detection value of the rotation speed V2 from the back spindle rotation motor 25, and determines whether the variation range ΔV2 of the detection value of the rotation speed V2 is less than a specific threshold value TH before the tool holder 31 reaches the cutting completion position X=+Xe (step S112). However, the threshold value TH is a positive value less than the variation range ΔV2 when the variation of the rotation speed V1 of the front spindle 12 starts in step S110. ΔV2<TH means that the variation of the detection value of the rotation speed V2 is within a specific range. In addition, the value of the threshold value TH is stored in the ROM72 or RAM73.

[0082] like Figure 3 As shown, when the cutting of workpiece W0 is normal, Figure 5 As shown, before the tool rest 31 reaches the cutting completion position X=+Xe, the variation amplitude ΔV2 becomes smaller, ΔV2<TH. In this case, it is determined that the cutting of the workpiece W0 is normal, and the NC device 70 drives the Z2-axis motor MZ2 to retract the back spindle table 21, that is, to move the back spindle table 21 away from the front spindle table 11, and continue the continuous processing operation of the workpiece (step S114). The subsequent processing includes the back processing of the workpiece W2 held by the holding portion 23 of the back spindle 22, and the front processing of the workpiece W1 held by the holding portion 13 of the front spindle 12.

[0083] On the other hand, Figure 4 As shown, in the case where the cutting of the workpiece W0 is not normal, even if Figure 6 The tool rest 31 is at the cutting completion position X = +Xe, and the rotation speed V2 of the back spindle 22 remains unchanged, ΔV2≧TH. In this case, it is determined that the cutting of the workpiece W0 is abnormal, and the NC device 70 outputs a warning indicating that the cutting of the workpiece W0 is abnormal, and stops the continuous processing operation of the workpiece (step S116). The output of the warning is included in Figure 2 The display unit 82 shown displays a warning, and a warning sound is output from an audio output device (not shown).

[0084] As described above, one cutting process is completed.

[0085] According to this specific example, the rotation speed V1 of the front spindle 12 is changed before the workpiece W0 is cut. Therefore, if the workpiece W0 is cut normally, the rotation speed V2 of the back spindle 22 is not changed immediately after the cutting. Therefore, by confirming that the change range ΔV2 of the rotation speed V2 does not reach the threshold value TH, it is determined that the cutting is normal immediately after the workpiece W0 is cut. Therefore, this specific example can shorten the time to determine whether the workpiece is cut normally, and shorten the cycle time of workpiece processing.

[0086] In addition, no special device is required to determine whether the cutting is normal or not, so the cost of the lathe can be reduced.

[0087] Furthermore, since the variation range ΔV2 of the rotation speed V2 is used to determine whether the cutting is normal or not, the number of sampling times for data acquisition increases, and the reliability of the determination is improved.

[0088] Furthermore, when the NC device 70 has a function of adding a change to the rotation speed V1 to suppress the resonance caused by the rotation speed V1 of the front spindle 12, it is possible to easily determine whether the cutting is normal or not by utilizing this function.

[0089] (5) Variations:

[0090] The present invention can be conceived of various variations.

[0091] For example, the lathe to which the present technology can be applied is not limited to a mobile spindle type lathe, and may be a fixed spindle type lathe where the front spindle does not move.

[0092] The lathe 1 moves the tool holder 31 in the X-axis direction during cutting, but the cutting process can also be performed by moving the front spindle and the back spindle instead of the tool holder in the X-axis direction, or by moving both the two spindles and the tool holder in the X-axis direction. The lathe 1 performs synchronous operation in which the front spindle 12 is active and the back spindle 22 is driven, but the present technology can also be applied in the case of synchronous operation in which the back spindle is active and the front spindle is driven. In this case, the lathe can also apply a change to the rotation speed of the back spindle during synchronous operation and detect the rotation speed of the front spindle. If the detected change in rotation speed is within a specific range, it is determined that the cutting of the workpiece is normal.

[0093] The above-mentioned processing may be appropriately changed by exchanging the order, for example. Figure 7 In the cutting process of S106, the process of obtaining the rotation change start position X=-Xs can be performed before any of the processes of step S102 and S104. In addition, the time point for starting to judge whether the change of the rotation speed of the second spindle is within a specific range can be set to various time points such as the time point when the machining is considered to be completed in the machining program. Furthermore, the time point for ending the judgment of whether the change of the rotation speed of the second spindle is within a specific range can also be set to various time points.

[0094] Figure 8 Another example of the primary cutting process performed by the NC device 70 is shown. Figure 8 The cutting process shown is similar to Figure 7 Compared with the cutting process shown in FIG. 1 , step S112 is replaced by steps S202 and S204. In addition, for the convenience of illustration, Figure 8The processing of steps S102 to S108 is summarized in . If the NC device 70 starts the change of the rotation speed V1 of the front spindle 12 when the tool rest 31 reaches the rotation change start position X=-Xs during the processing of steps S102 to S110, the processing enters step S202. In step S202, the NC device 70 obtains the cutting completion time of the workpiece from the machining program P2 and determines whether it is the cutting completion time. The cutting completion time can be the time when the tool rest 31 reaches the cutting completion position X=+Xe, or it can be other time points. If it is not the cutting completion time, the NC device 70 repeats the judgment processing of S202.

[0095] When the cutting is completed, the NC device 70 repeatedly obtains the detection value of the rotation speed V2 from the back spindle rotary motor 25 within the specified judgment time, and determines whether the obtained variation range ΔV2 is less than a specific threshold value TH (0<TH<ΔV2) (step S204). In the case where multiple variation ranges are obtained within the judgment time, the NC device 70 can also use the arithmetic average of the multiple variation ranges as the variation range ΔV2 to determine whether the variation range ΔV2 is less than the threshold value TH. In addition, the NC device 70 can also use the arithmetic average after removing the maximum and minimum values ​​from the multiple variation ranges as the variation range ΔV2 to determine whether the variation range ΔV2 is less than the threshold value TH. When the variation range ΔV2 does not reach the threshold value TH, it is determined that the cutting of the workpiece W0 is normal, and the NC device 70 continues the continuous processing operation of the workpiece (step S114). When the variation range ΔV2 is greater than the threshold value TH, it is determined that the cutting of the workpiece W0 is abnormal, and the NC device 70 outputs a warning and stops the continuous processing operation of the workpiece (step S116).

[0096] Since the rotation speed V1 of the front spindle 12 is changed before the workpiece W0 is cut, even if Figure 8 In the cutting process shown, the rotation speed V2 of the back spindle 22 is not changed during the judgment time just after the workpiece is cut. Therefore, it is confirmed that the change range ΔV2 of the rotation speed V2 of the back spindle 22 does not reach the threshold value TH, and thus it is judged that the cutting is normal just after the workpiece W0 is cut. Therefore, the time to judge whether the cutting of the workpiece is normal is shortened, and the cycle time of the workpiece processing is shortened. In addition, the number of sampling times for data acquisition is increased, so the reliability of the judgment is improved.

[0097] In addition, when Figure 7 When the middle knife rest 31 moves to the cutting completion position X=+Xe (step S112), or Figure 8When the cutting is completed (step S202), it is determined whether the variation amplitude ΔV2 is less than a specific threshold value TH, but the time point for ending the determination may also be after a specific time has passed since the tool holder 31 moved to the cutting completion position X=+Xe, or after a specific time has passed since the cutting is completed. By determining that the variation amplitude ΔV2 is less than a specific threshold value TH for a specific period of time, the number of sampling times for data acquisition is further increased, and thus the reliability of the determination is further improved. As an example, the arithmetic average of multiple variation amplitudes obtained during the determination period may be set as the variation amplitude ΔV2 to determine whether the variation amplitude ΔV2 is less than the threshold value TH, or the arithmetic average after removing the maximum and minimum values ​​from multiple variation amplitudes may be used as the variation amplitude ΔV2 to determine whether the variation amplitude ΔV2 is less than the threshold value TH.

[0098] (6) Summary:

[0099] As described above, according to the present invention, various aspects can provide a lathe capable of shortening the cycle time of workpiece machining. Of course, even a technology consisting only of the constituent elements of the independent claims can achieve the above basic functions and effects.

[0100] In addition, it is also possible to implement a configuration in which the configurations disclosed in the above examples are replaced with each other or are modified and combined, a configuration in which the known technology and the configurations disclosed in the above examples are replaced with each other or are modified and combined, etc. The present invention also includes these configurations, etc.

[0101] [Explanation of Symbols]

[0102] 1 Lathe

[0103] 11 Front spindle table

[0104] 12 Front spindle

[0105] 13. Holding part

[0106] 14 Actuator

[0107] 15 Rotary motor

[0108] 16 Encoder

[0109] 18 Guide bushing

[0110] 21 Back spindle table

[0111] 22 Back spindle

[0112] 23. Holding part

[0113] 24 Actuator

[0114] 25 Rotary motor

[0115] 26 Encoder

[0116] 31 Tool holder

[0117] 70 NC device

[0118] AX1, AX2 Spindle centerline

[0119] MX3 X3 axis motor

[0120] T0 Tools

[0121] T1 Cutting Tool

[0122] U1 Control Unit

[0123] W0, W1, W2 workpieces.

Claims

1. A lathe having: A first spindle, capable of holding a workpiece and rotating around a spindle centerline; A second spindle, opposite to the first spindle, capable of holding the workpiece and rotating around the spindle centerline; A tool holder provided with a cutting tool for cutting the workpiece held on the first spindle and the second spindle; as well as a control unit for controlling the rotation of the first spindle and the second spindle, and the relative movement of the first spindle, the second spindle and the tool holder for cutting the workpiece; and The control unit rotates the first spindle and the second spindle holding the workpiece synchronously, controls the rotation speed of the first spindle to change while moving the tool holder to a cutting completion position of the workpiece, and detects the rotation speed of the second spindle. If the variation in the rotation speed of the second spindle detected before the tool rest moves to the cutting completion position is within a specific range, it is determined that the cutting of the workpiece is normal.

2. A lathe having: A first spindle, capable of holding a workpiece and rotating around a spindle centerline; A second spindle, opposite to the first spindle, capable of holding the workpiece and rotating around the spindle centerline; A tool holder provided with a cutting tool for cutting the workpiece held on the first spindle and the second spindle; as well as a control unit for controlling the rotation of the first spindle and the second spindle, and the relative movement of the first spindle, the second spindle and the tool holder for cutting the workpiece; and The control unit causes the first spindle and the second spindle holding the workpiece to rotate synchronously, and controls the tool holder to move to the position where cutting of the workpiece is completed while changing only the rotation speed of the first spindle. If the arithmetic mean of the variation range of the rotation speed of the second spindle obtained by detecting the rotation speed of the second spindle within a specified judgment time starting from the point when cutting of the workpiece is completed is within a specific range, it is judged that the cutting of the workpiece is normal.

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