Working machinery

Abstract

To provide a machine tool capable of precisely determining gripping defects. [Solution] An NC lathe 1 is equipped with a first spindle 4 having a collet chuck 48 for gripping a rod-shaped material W1, and by repeatedly performing machining operations, it is equipped with a determination means 23 that performs a determination regarding a gripping defect of the first spindle 4 based on at least one of the following pieces of information: machining timing information, which indicates the timing of the machining operation; gripping force history information, which is information on the gripping force when the collet chuck 48 gripped the material W1 in previous machining operations; and current gripping force information, which is information on the gripping force when the collet chuck 48 gripped the material W1 in the current machining operation.

Description

Technical Field

[0001] The present invention relates to a machine tool for processing a workpiece held by a spindle.

Background Art

[0002] A machine tool for processing a bar-shaped workpiece held by a spindle is known (see, for example, Patent Document 1). The spindle is rotatably supported by a spindle headstock. The spindle is provided with a gripping portion that changes its state between a gripping state for gripping the workpiece and a gripping release state for releasing the gripping of the workpiece. In addition, a safety monitoring system has also been proposed that determines a gripping failure in the gripping portion by attaching a sensor to the gripping portion (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the safety monitoring system of Patent Document 2, since the abnormality determination is made only based on the output of the sensor attached to the gripping portion, there is a problem that only a uniform determination can be made and it is difficult to accurately determine a gripping failure in the gripping portion.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a machine tool capable of accurately determining a gripping failure.

Means for Solving the Problems

[0006] The machine tool of the present invention for solving the above problems is A machine tool equipped with a spindle having a gripping portion for gripping a rod-shaped material, which repeatedly performs a machining operation to process the material gripped by the gripping portion and manufacture multiple products of the same shape, The device is characterized by having a determination means that performs a determination regarding the gripping failure of the spindle based on at least one of the following pieces of information: processing timing information, which indicates the timing of the processing operation; gripping force history information, which is information about the gripping force when the gripping part gripped the material in previous processing operations; and current gripping force information, which is information about the gripping force when the gripping part gripped the material in the current processing operation.

[0007] According to this machine tool, the determination means performs a determination regarding gripping defects based on at least one of the processing timing information and the gripping force history information and the current gripping force information, so that gripping defects can be determined precisely.

[0008] Here, the machine tool may execute multiple cycles, with one cycle being the machining operation that produces one product. The determination means may classify and determine the type of gripping defect. Alternatively, the determination means may classify and determine the gripping defect according to its cause.

[0009] In this machine tool, The determination means may determine that a gripping defect has occurred due to a setup error if the gripping force in the current gripping force information is outside a predetermined range when the processing timing information is information indicating the first processing operation.

[0010] This machine tool allows for the identification of setup errors as the cause of insufficient gripping force, making it easier to address the defect.

[0011] In this machine tool, A material feeder is connected to which multiple materials are stored and which sequentially supplies the stored materials to the main spindle. The determination means may determine that a gripping failure has occurred due to an abnormal material diameter of the material supplied by the material feeder if the gripping force in the current gripping force information is outside a predetermined range when the processing timing information indicates the processing operation immediately after the material feeder has newly supplied the material to the spindle.

[0012] This machine tool allows us to identify that poor gripping force is caused by an incorrect material diameter, making it easier to address the defect.

[0013] In this machine tool, The determination means may determine that a gripping failure has occurred if the amount of change in the gripping force in the current gripping force information relative to the gripping force in the gripping force history information exceeds a threshold.

[0014] By doing so, for example, it is possible to determine that a small foreign object has become caught in the gripping part as a gripping failure.

[0015] Furthermore, in this machine tool, The determination means may classify the type of gripping failure based on whether the gripping force in the current gripping force information has increased or decreased relative to the gripping force in the gripping force history information, if the amount of change exceeds the threshold.

[0016] This allows for accurate classification of the types of gripping failures.

[0017] Furthermore, in this machine tool, If the amount of change exceeds the threshold, and the gripping force in the current gripping force information is increasing relative to the gripping force in the gripping force history information, the device may be equipped with a control device that causes the device to perform a removal operation to remove foreign matter that has become stuck in the gripping part.

[0018] When the change amount exceeds the threshold value and the gripping force in the current gripping force information has increased with respect to the gripping force in the gripping force history information, it is highly likely that foreign matter such as chips has bitten into the gripping part. By performing the removal operation, it is possible to reduce the risk that the material will be damaged by the foreign matter that has bitten into the gripping part. In addition, it is possible to reduce the risk of stopping the processing operation due to poor gripping.

[0019] Here, the removal operation may include an operation of releasing the gripping of the material by the gripping part. Further, the removal operation may include an operation of releasing the gripping of the material by the gripping part and moving the main spindle. Furthermore, the removal operation may include an operation of releasing the gripping of the material by the gripping part and discharging fluid toward the gripping part.

[0020] Furthermore, in this machine tool, the determination means may classify the type of poor gripping based on a combination of whether the gripping force in the current gripping force information is outside a predetermined range and whether the change amount of the gripping force in the current gripping force information with respect to the gripping force in the gripping force history information exceeds a threshold value.

[0021] According to this machine tool, the type of poor gripping can be determined more precisely.

[0022] In addition, in this machine tool, a tool rest on which a tool for processing the material is mounted and which moves together with the tool, a storage means in which a movement correction value for correcting a designated movement position designated in a machining program is stored, and a correction value rewriting means for rewriting the movement correction value stored in the storage means are provided. The correction value rewriting means may rewrite the movement correction value stored in the storage means when the determination means determines that the gripping force in the current gripping force information is outside a predetermined range and the change amount of the gripping force in the current gripping force information with respect to the gripping force in the gripping force history information does not exceed a threshold value.

[0023] When the gripping force of the gripping portion gradually changes due to thermal displacement or the like, the correction value rewriting means rewrites the movement correction value to an appropriate value in accordance with the change, so that the processing accuracy is improved.

Advantages of the Invention

[0024] According to the present invention, it is possible to provide a machine tool capable of accurately determining gripping failure.

Brief Description of the Drawings

[0025] [Figure 1] It is a plan view schematically showing the internal configuration of the NC lathe according to the present embodiment. [Figure 2] It is a cross-sectional view seen from above, obtained by cutting the first spindle headstock and the first spindle shown in FIG. 1 with a horizontal plane passing through the axis of the first spindle. [Figure 3] It is a perspective cross-sectional view showing the first spindle headstock and the first spindle by cutting a part of the first spindle headstock shown in FIG. 1. [Figure 4] It is a control block diagram of the NC lathe shown in FIG. 1. [Figure 5] It is a flowchart showing the first machining operation using the first spindle shown in FIG. 1. [Figure 6] It is a flowchart showing the first machining operation using the first spindle shown in FIG. 1. [Figure 7] It is a graph showing an example of the gripping force for each gripping operation of the first spindle 4 from the first machining operation to the last machining operation. [Figure 8] It is a flowchart showing the second machining operation using the second spindle shown in FIG. 1. [Figure 9] It is a flowchart showing the second machining operation using the second spindle shown in FIG. 1.

Embodiments for Carrying Out the Invention

[0026] Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, the present invention will be described using an example in which it is applied to a Swiss-type NC (Numerical Control) lathe. That is, the NC lathe described below corresponds to an example of a machine tool.

[0027] Figure 1 is a simplified plan view showing the internal configuration of the NC lathe 1 according to this embodiment. The material feeder 10 is also shown in Figure 1.

[0028] As shown in Figure 1, the NC lathe 1 contains a control device 2, a first headstock 3, a first spindle 4, a guide bush 5, a first tool post 6, a second headstock 7, a second spindle 8, and a second tool post 9. A material feeder 10 is also connected to the NC lathe 1. These NC lathe 1 and material feeder 10 form an NC lathe system. This NC lathe system is an example of a machine tool system. The control device 2 is a computer that operates the first headstock 3, first spindle 4, first tool post 6, second headstock 7, second spindle 8, and second tool post 9 according to an NC program. In addition to operation using an NC program, the NC lathe 1 can also be operated by directly inputting commands to the control device 2 from the operation unit 11 (see Figure 4).

[0029] The first headstock 3 moves in the Z1 axis direction together with the first spindle 4 in response to a signal from the control device 2. The Z1 axis direction is horizontal, and in Figure 1, it is the left-right direction. The first spindle 4 is rotatably supported on the first headstock 3. A first spindle motor 31 (see Figure 2) is also provided between the first headstock 3 and the first spindle 4. When the first spindle motor 31 rotates in response to a signal from the control device 2, the first spindle 4 rotates around the first axis CL1. The direction of the first axis CL1 coincides with the Z1 axis direction.

[0030] The first spindle 4 changes state between a gripping state in which it grips the long rod-shaped material W1 inserted inside it, and a release state in which it releases the material W1. This first spindle 4 is an example of a spindle. The material W1 gripped by the first spindle 4 rotates together with the first spindle 4 around the first axis CL1 as the first spindle 4 rotates. The configuration of the first headstock 3 and the first spindle 4 will be described in detail later. A collet chuck 48, which will be described in more detail later, is provided at the tip of the first spindle 4. This collet chuck 48 is an example of a gripping part.

[0031] The guide bush 5 is fixed inside the NC lathe 1. The guide bush 5 slidably supports the tip portion of the material W1 protruding from the first spindle 4 in the Z1 axis direction. The portion of the guide bush 5 that supports the material W1 is rotatable around the first axis CL1 in synchronization with the first spindle 4. In other words, the first axis CL1 is also the axis of rotation of the portion of the material W1 supported by the guide bush 5. The presence of the guide bush 5 suppresses the deflection of the material W1 during machining, allowing for high-precision machining of particularly long and slender materials W1.

[0032] The first tool post 6 is movable in the X1 axis direction, which is perpendicular to the Z1 axis direction and oriented horizontally, and in the Y1 axis direction, which is oriented vertically. This first tool post 6 is an example of a tool post. The first tool post 6 moves in the X1 axis direction and the Y1 axis direction in response to signals from the control device 2. In Figure 1, the vertical direction is the X1 axis direction, and the direction perpendicular to the plane of the paper is the Y1 axis direction. The first spindle tool T1 for machining the material W1 is mounted on the first tool post 6. Figure 1 shows the first spindle tool T1 mounted on the first tool post 6. Multiple types of first spindle tools T1, including cutting tools for outer diameter machining and cutting tools, are mounted on the first tool post 6 in a row along the Y1 axis direction. When the first tool post 6 moves in the Y1 axis direction, any first spindle tool T1 is selected from these multiple types of first spindle tools T1. Then, as the first tool post 6 moves in the X1 axis direction, the selected first spindle tool T1 cuts into the material W1 held by the first spindle 4 and processes the material W1. The first tool post 6 is also provided with a first coolant discharge section 61 that discharges coolant towards the first spindle tool T1 and the material W1.

[0033] The second headstock 7 moves together with the second spindle 8 in the X2 axis direction and the Z2 axis direction in response to signals from the control device 2. The X2 axis direction is the same direction as the X1 axis direction described above, and the Z2 axis direction is the same direction as the Z1 axis direction described above. The second headstock 7 is equipped with a second spindle motor (not shown), such as a built-in motor. When this second spindle motor receives a signal from the control device 2 and rotates, the second spindle 8 rotates around the second axis CL2. The direction of the second axis CL2 coincides with the Z2 axis direction.

[0034] The cut material W2, which has been cut by a parting tool after machining using the first spindle 4, is transferred to the second spindle 8. The second spindle 8 changes state between a gripping state, in which it grips the cut material W2 transferred from the first spindle 4, and a released state, in which it releases the cut material W2. This second spindle 8 corresponds to an example of a spindle. The cut material W2 gripped by the second spindle 8 rotates together with the second spindle 8 around the second axis CL2 as the second spindle 8 rotates. A second collet chuck 81 is provided at the tip of the second spindle 8. When the second spindle 8 is used as a spindle, this second collet chuck 81 corresponds to an example of a gripping part.

[0035] The second tool post 9 moves in the Y2 axis direction in response to a signal from the control device 2. This Y2 axis direction is the same direction as the Y1 axis direction described above, i.e., perpendicular. Multiple second spindle tools T2 for machining the cut material W2 held by the second spindle 8 are mounted on the second tool post 9. Figure 1 shows the second spindle tools T2 mounted on the second tool post 9. Multiple types of second spindle tools T2, such as drills and end mills, are mounted on the second tool post 9. The second spindle tools T2 are mounted in a row not only in the X2 axis direction but also in the Y2 axis direction. By moving the second headstock 7 in the X2 axis direction and the second tool post 9 in the Y2 axis direction, any second spindle tool T2 is selected from these multiple types of second spindle tools T2. Then, when the second headstock 7 moves in the Z2 axis direction, the cut end portion of the cut material W2 held by the second spindle 8 is machined. Furthermore, the second tool post 9 is provided with a second coolant discharge section 91 that discharges coolant towards the second spindle tool T2, the cut material W2, or the second spindle 8.

[0036] The material feeder 10 is a device that supplies long, rod-shaped material W1 to the NC lathe 1. The material feeder 10 is installed alongside the NC lathe 1, at the rear end of the first spindle 4. Multiple pieces of material W1 are stored in the material feeder 10. The material feeder 10 has a built-in material feed control device 101 (see Figure 4) that controls the material feeder 10. The material feed control device 101 operates the material feeder 10 according to commands from the control device 2 of the NC lathe 1. Status information of the material feeder 10 is also transmitted to the control device 2 as needed. The material feeder 10, according to commands from the control device 2, pulls out and discharges the remaining material W1, which has been shortened by the machining operation of the NC lathe 1. After discharging the remaining material, the material feeder 10 sequentially feeds and supplies new material W1 to the NC lathe 1. The operation of removing this remaining material from the NC lathe 1, discharging it, and sending new material W1 to the NC lathe 1 corresponds to the material W1 replacement operation.

[0037] Figure 2 is a cross-sectional view of the first headstock 3 and first spindle 4 shown in Figure 1, taken from above by cutting them through a horizontal plane passing through the first axis CL1. Note that the drawings used to describe this embodiment do not include hatching to indicate cross-sections.

[0038] As shown in Figure 2, the first spindle 4 is generally cylindrical in shape and has its axis in the direction of the first axis CL1. The first spindle 4 is rotatably supported on the first headstock 3 by a bearing 39. The first spindle 4 includes a spindle body 41, a shifter 42, a jaw member 43, an adjustment nut 44, a push sleeve 45, a chuck sleeve 46, a coil spring 47, a collet chuck 48, and a spindle cap 49.

[0039] The spindle body 41 is a cylindrical body extending in the Z1 axis direction, serving as the base of the first spindle 4. The shifter 42 is located at the rear end of the first spindle 4. In Figure 2, the left side of the figure is the rear end of the first spindle 4, and the right side of the figure is the front end of the first spindle 4. The shifter 42 is generally cylindrical and is attached to the spindle body 41 so as to be slidable in the Z1 axis direction by sliding its inner circumferential surface against the outer circumferential surface of the spindle body 41. As shown in Figure 2, a cam surface 42a is formed on the outer circumferential surface of the shifter 42. The cam surface 42a consists of a small-diameter surface with the smallest and constant outer diameter, a changing surface with a gradually increasing outer diameter, and a large-diameter surface with the largest and constant outer diameter, in order from the rear end of the first spindle 4. This shifter 42 slides in the Z1 axis direction by driving the air cylinder 32. Figure 2 shows the shifter 42 in its position closest to the front end of the first spindle 4.

[0040] Two claw members 43 are attached to the spindle body 41 so as to be pivotable around the claw shaft 431. The tip portion of each claw member 43 has a claw tip portion 43b which acts as a cam follower that contacts the cam surface 42a of the shifter 42. As the shifter 42 slides, the claw tip portion 43b moves closer to or further away from the first axis CL1 along the cam surface 42a, causing the claw member 43 to pivot around the claw shaft 431 as the pivot point. The claw member 43 has a sleeve pressing portion 43a which contacts the rear end of the pressing sleeve 45.

[0041] The adjustment nut 44 is screw-connected to the spindle body 41 at the rearmost end of the first spindle 4. An internal female thread is formed on the inside of the adjustment nut 44, which engages with an external male thread formed on the rear end of the spindle body 41. By rotating the adjustment nut 44 in the tightening direction, the jaw member 43, push sleeve 45, and chuck sleeve 46 move together with the adjustment nut 44 toward the tip of the first spindle 4. This relatively reduces the inner diameter of the collet chuck 48 in the gripping state, increasing the gripping force of the first spindle 4 on the material W1 (see Figure 1). Conversely, by rotating the adjustment nut 44 in the loosening direction, the jaw member 43, push sleeve 45, and chuck sleeve 46 move together with the adjustment nut 44 toward the rear end of the first spindle 4. This relatively increases the inner diameter of the collet chuck 48 in the gripping state, decreasing the gripping force of the first spindle 4 on the material W1. In other words, the gripping force of the material W1 in the gripping state of the first spindle 4 is adjusted by the adjustment nut 44. The adjustment nut 44 is C-shaped with a notch that runs radially when viewed from the rear end to the front end of the first spindle 4, and the width of the notch can be changed by a screw (not shown). After the adjustment of the gripping force using the adjustment nut 44 is completed, the adjustment nut 44 is fixed to the spindle body 41 in the adjusted position by narrowing the width of the notch with the screw.

[0042] The push sleeve 45 is a cylindrical body positioned inside the spindle body 41, and its tip is in contact with the rear end portion of the chuck sleeve 46. The push sleeve 45 and the chuck sleeve 46 move in the opposite direction to the shifter 42 as the shifter 42 moves in the Z1 axis direction. Specifically, as the shifter 42 slides toward the rear end of the first spindle 4, the tip portion 43b of the jaw member 43 is pushed up by the cam surface 42a of the shifter 42 and moves toward the front end of the first spindle 4. As a result, the push sleeve 45 and the chuck sleeve 46 are pushed by the sleeve push portion 43a of the jaw member 43 and move toward the front end of the first spindle 4, causing the collet chuck 48 to shrink in diameter, and the first spindle 4 to grip the material W1.

[0043] Conversely, as the shifter 42 slides toward the tip of the first spindle 4, the tip portion 43b of the jaw member 43 moves along the cam surface 42a of the shifter 42 toward the first axis CL1. As a result, the push sleeve 45 and the chuck sleeve 46 move toward the rear end of the first spindle 4, the collet chuck 48 expands in diameter, and the first spindle 4 releases gripping of the material W1.

[0044] The coil spring 47 constantly pushes the chuck sleeve 46 toward the rear end and the collet chuck 48 toward the front end. As a result, the push sleeve 45 is also pushed toward the rear end via the chuck sleeve 46, and the push sleeve 45 pushes the sleeve push portion 43a toward the rear end.

[0045] The inner circumferential surface of the tip of the chuck sleeve 46 is a tapered surface, with the diameter increasing towards the tip. The outer circumferential surface of the tip of the collet chuck 48 is also a tapered surface, with the diameter increasing towards the tip. The collet chuck 48 has three continuous slots formed at 120° intervals in the circumferential direction, extending from the tip to a hole formed near the center in the Z1 axis direction. These holes and slots allow the collet chuck 48, especially the tip side, to expand and contract in the radial direction. In the gripping release state shown in Figure 2, the chuck sleeve 46 is located at the rear end, so there is almost no force from the inner circumferential surface of the tip of the chuck sleeve 46 pushing radially inward against the outer circumferential surface of the tip of the collet chuck 48, and the collet chuck 48 expands in diameter due to its own elasticity. Conversely, in the gripping state, the chuck sleeve 46 is located towards the tip, and the inner circumferential surface of the tip of the chuck sleeve 46 pushes the outer circumferential surface of the tip of the collet chuck 48 radially inward, causing the collet chuck 48 to contract in diameter.

[0046] The spindle cap 49 is bowl-shaped with a circular through-hole formed in its center in the Z1 axis direction. The collet chuck 48's tip surface contacts the bottom of the bowl-shaped part of the spindle cap 49, restricting the collet chuck 48's movement toward the tip. The collet chuck 48 is constantly pressed against the spindle cap 49 by a coil spring 47. The spindle cap 49 is fixed to the spindle body 41 by a female thread formed on the inside of its bowl-shaped rim engaging with a male thread formed on the tip of the spindle body 41.

[0047] The first headstock 3 includes a first spindle motor 31, an air cylinder 32, and a shifter lever 33. The first spindle motor 31 is a built-in motor provided in the first headstock 3. As described above, by rotationally driving the first spindle motor 31, the first spindle 4, which is supported by the first headstock 3 via the bearing 39, rotates about the first axis CL1.

[0048] The air cylinder 32 comprises a cylinder tube 321, a piston 322, and a piston rod 323. The cylinder tube 321 is the housing of the air cylinder 32 and is cylindrical in shape. The piston 322 is positioned inside the cylinder tube 321, in contact with the inner circumferential surface of the cylinder tube 321, and is movable to one side and the other. The piston rod 323 is a rod-shaped object with one end fixed to the piston 322. The other end of the piston rod 323 is connected to the shifter lever 33. By supplying air to the air cylinder 32, the piston 322 moves, causing the piston rod 323 to advance or retract relative to the cylinder tube 321. Figure 2 shows the state where the piston 322 has moved furthest to the other side and the piston rod 323 has advanced furthest.

[0049] The shifter lever 33 is pivotable around the lever shaft 331 as the pivot point. One end of the shifter lever 33 is rotatably connected to the other end of the piston rod 323 by a connecting pin 332. The other end of the shifter lever 33 is connected to the shifter 42. By driving the air cylinder 32, the shifter lever 33 pivots, and this pivoting motion causes the shifter 42 to slide in the Z1 axis direction. The air cylinder 32, shifter lever 33, shifter 42, claw member 43, push sleeve 45, chuck sleeve 46, and coil spring 47 described above form a collet expansion and contraction mechanism that expands and contracts the collet chuck 48.

[0050] Figure 3 is a perspective cross-sectional view showing the first headstock 3 and the first spindle 4, obtained by cutting off a portion of the first headstock 3 shown in Figure 1.

[0051] As shown in Figure 3, the shifter lever 33 is roughly U-shaped when viewed from the rear end towards the front end. A strain detection means 333 is attached to the side of the rear end of the shifter lever 33. The strain detection means 333 is a so-called strain gauge that detects the strain that occurs in the shifter lever 33 when the driving force of the air cylinder 32 is transmitted from the air cylinder 32 to the collet chuck 48 (see Figure 2). A signal line 334 is connected to the strain detection means 333. The strain signal detected by the strain detection means 333 is transmitted to the control device 2 (see Figure 1) through the signal line 334. This strain detection means 333 detects the strain of the shifter lever 33 that occurs at the part to which it is attached.

[0052] The configuration of the second spindle 8 for gripping and releasing the cut material W2 shown in Figure 1 is the same as that of the first headstock 3 and the first spindle 4, so a detailed explanation is omitted. The second headstock 7 has a second shifter lever (not shown), and a second strain detection means (not shown) for detecting strain occurring in the second shifter lever is attached to it. The second spindle 8 is also provided with a known air blow device that blows air from the rear end to the front end of the second spindle 8 along the outer circumferential surface of the cut material W2 inside the second spindle 8. The operation of the air blow device is controlled by the control device 2. In this second spindle 8, the cut material W2 is an example of a material.

[0053] Figure 4 is a control block diagram of the NC lathe 1 shown in Figure 1. Note that Figure 4 shows only the control configurations that are particularly relevant to this embodiment.

[0054] As shown in Figure 4, the NC lathe 1 is equipped with an operation unit 11 and a display unit 12 as an interface with the operator. The operation unit 11 is an input device for operating the NC lathe 1. The operation unit 11 consists of a number of buttons, keys, etc. that accept input operations from the operator of the NC lathe 1. The operation unit 11 may also be a touch panel integrated with the display unit 12. The display unit 12 is a display that shows various information related to the NC lathe 1, such as the NC program, various setting values, and error details.

[0055] The control device 2 includes a storage means 21, a gripping force derivation means 22, a determination means 23, and a correction value rewriting means 24. The storage means 21 stores control programs, NC programs, and various information, and is composed of non-volatile memory and volatile memory. The storage means 21 also includes a machining timing information storage unit 211, a first gripping force information storage unit 212, a second gripping force information storage unit 213, a movement correction value storage unit 214, and a counter 215.

[0056] The NC lathe 1 manufactures multiple products of the same shape by repeatedly executing one machining cycle according to the NC program. One product is manufactured each time this machining cycle is executed. In most cases, one machining cycle includes a first machining operation using the first spindle 4 and a second machining operation using the second spindle. However, depending on the product shape, a product may be manufactured using only the first machining operation. At the beginning of the first machining operation, a gripping command is executed to grip the material W1. Similarly, at the beginning of the second machining operation, a gripping command is executed to grip the cut material W2.

[0057] The machining timing information storage unit 211 stores information about the timing of the current machining operation, from the start of the first machining operation to the completion of the last machining operation. This information about the timing of the current machining operation is an example of machining timing information. Specifically, the machining timing information storage unit 211 stores information indicating that it is the first machining operation, or information indicating that it is a machining operation immediately after the material W1 has been replaced and a new material W1 has been supplied to the first spindle 4.

[0058] The first gripping force information storage unit 212 stores information on the gripping force of the material W1 each time the collet chuck 48 grips the material W1, starting from the beginning of the first machining operation. The gripping force of the material W1 by the collet chuck 48 is derived by the gripping force derivation means 22, which will be described later. The gripping force information stored in the first gripping force information storage unit 212 also includes information on the time when the gripping force was stored. Note that the information attached to the gripping force information may be other time information or sequential information such as the order in which the gripping occurred. Of the gripping force information stored in the first gripping force information storage unit 212, the information on the gripping force when the collet chuck 48 gripped the material W1 in the previous machining operation will be referred to as the first gripping force history information in the following description. This first gripping force history information is an example of gripping force history information. Furthermore, among the gripping force information stored in the first gripping force information storage unit 212, the gripping force information when the collet chuck 48 gripped the material W1 during the current machining operation will be referred to as the first current gripping force information in the following description. This first current gripping force information is an example of current gripping force information. In addition, among the gripping force information stored in the first gripping force information storage unit 212, the average value information of the gripping force when the collet chuck 48 gripped the material W1 during multiple machining operations prior to the previous one (for example, a total of two operations, the previous and the one before that) may be referred to as the first gripping force history information.

[0059] The second gripping force information storage unit 213 stores information on the gripping force of the cut material W2 each time the second collet chuck 81 grips the cut material W2, starting from the beginning of the initial processing operation. The gripping force of the cut material W2 by the second collet chuck 81 is also derived by the gripping force derivation means 22. The gripping force information stored in the second gripping force information storage unit 213 also includes information on the time when the gripping force was stored. The information attached to the gripping force information may be other time information, or sequential information such as the order in which the gripping occurred. Of the gripping force information stored in the second gripping force information storage unit 213, the gripping force information from when the second collet chuck 81 gripped the cut material W2 in the previous processing operation will be referred to as the second gripping force history information in the following description. This second gripping force history information is an example of gripping force history information. Furthermore, among the gripping force information stored in the second gripping force information storage unit 213, the gripping force information when the second collet chuck 81 gripped the cut material W2 during the current processing operation will be referred to as the second current gripping force information in the following description. This second current gripping force information is an example of current gripping force information. In addition, among the gripping force information stored in the second gripping force information storage unit 213, information such as the average value of the gripping force when the second collet chuck 81 gripped the cut material W2 during multiple processing operations prior to the previous one may be referred to as the second gripping force history information.

[0060] The movement correction value storage unit 214 stores movement correction values ​​for correcting the movement position of the first tool post 6. The NC control device 2 corrects errors caused by wear of the first spindle tool T1, wear of structural members of the NC lathe 1, and thermal displacement of each member by moving the first tool post 6 to a position that takes the movement correction values ​​into account, as specified in the NC program. This improves machining accuracy and allows the first machining operation to be performed. The movement correction value storage unit 214 also stores second movement correction values ​​for correcting the movement position of the second headstock 7. The NC control device 2 improves machining accuracy and allows the second machining operation to be performed by moving the second headstock 7 and the second tool post 9 to a position that takes the second movement correction values ​​into account.

[0061] The counter 215 stores the number of times a specific operation of the NC lathe 1 is performed. These specific operations include the number of machining operations (number of products machined), the number of foreign matter removal operations in the first spindle 4, the number of foreign matter removal operations in the second spindle 8, and the number of rework operations. The details of these removal and rework operations will be described later. Hereinafter, the counter showing the number of machining operations will be called the production count counter, the counter showing the number of removal operations in the first spindle 4 will be called the first removal count counter, the counter showing the number of removal operations in the second spindle 8 will be called the second removal count counter, and the counter showing the number of rework operations will be called the rework counter.

[0062] The gripping force derivation means 22 derives the gripping force of the collet chuck 48 on the material W1 based on the strain of the shifter lever 33 detected by the strain detection means 333 during the period from when the first spindle 4 starts gripping until the material W1 is gripped. The gripping force derivation means 22 has relationship data between the maximum value of the strain generated in the strain detection means 333 when the shifter lever 33 swings and the gripping force of the collet chuck 48 on the material W1. Using this relationship data, the gripping force of the collet chuck 48 on the material W1 is derived each time the collet chuck 48 grips the material W1. Similarly, the gripping force derivation means 22 derives the gripping force of the cut material W2 on the second spindle 8 each time the second spindle 8 grips the cut material W2.

[0063] The determination means 23 performs a determination regarding gripping defects in the collet chuck 48 based on at least one of the processing timing information stored in the processing timing information storage unit 211 and the first gripping force history information stored in the first gripping force information storage unit 212, as well as the first current gripping force information stored in the first gripping force information storage unit 212. The determination means 23 also performs a determination regarding gripping defects in the second collet chuck 81 based on at least one of the processing timing information stored in the processing timing information storage unit 211 and the second gripping force history information stored in the second gripping force information storage unit 213, as well as the second current gripping force information stored in the second gripping force information storage unit 213. The operation of these determinations will be explained in detail later using flowcharts.

[0064] The correction value rewriting means 24 rewrites the movement correction value stored in the movement correction value storage unit 214 when predetermined conditions are met. These predetermined conditions are when the determination means 23 determines that the gripping force in the second current gripping force information is outside a predetermined range and that the amount of change in the gripping force in the second current gripping force information relative to the gripping force in the second gripping force history information does not exceed a predetermined threshold. Details of these predetermined conditions will be further explained later with reference to Figures 8 and 9.

[0065] Figures 5 and 6 are flowcharts showing the first machining operation using the first spindle shown in Figure 1. The operations shown in these flowcharts are performed under the control of the control device 2. Figure 7 is a graph showing an example of the gripping force for each gripping operation of the first spindle 4 from the first machining operation to the last machining operation.

[0066] The operator of NC lathe 1 performs setup work, such as adjusting each component of NC lathe 1, before starting the machining operation. Then, using the control unit 11, they select the NC program to be executed and specify the number of products to be machined (number of cycles), and then input a machining start command. As a result, NC lathe 1 starts continuous machining, repeating the machining operation according to the selected NC program a number of times corresponding to the number of products. In the explanation of the machining operation, the first machining operation will be explained first, followed by the second machining operation, in the same order as the machining operations that are actually performed.

[0067] As shown in Figure 5, when the first processing operation is started, the control device 2 determines whether the length of the material W1 is equal to or greater than the length required to manufacture the product (step S11). If the length of the material W1 is shorter than the length required to manufacture the product (NO in step S11), the control device 2 issues a command to the material feeder 10 to perform the material W1 replacement operation described above (step S12).

[0068] If the length of material W1 is greater than or equal to the length required to manufacture the product (YES in step S11) or if the material W1 replacement operation in step S12 is completed, the control device 2 reads the production quantity counter on counter 215 to determine whether the processing of the specified number of products has been completed (step S13). The production quantity counter is zero at the start of the first processing operation and is counted up each time a processing operation is completed. If the processing of the specified number of products has been completed (YES in step S13), the first processing operation is terminated.

[0069] If it is determined that the specified number of products have not been processed (NO in step S13), the control device 2 stores in the processing timing information storage unit 211 information indicating whether the current processing operation is the first processing operation and information indicating whether the processing operation is immediately after the material W1 has been replaced and a new material W1 has been supplied to the first spindle 4 (step S14).

[0070] In step S14, if the value of the production count counter is zero, the control device 2 stores an "initial" flag in the processing timing information storage unit 211 to indicate that this is the first processing operation. If the value of the production count counter is not zero, the control device 2 deletes the initial flag from the processing timing information storage unit 211. Alternatively, instead of the initial flag, other information that can distinguish whether this is the first processing operation or not, such as the value of the production count counter itself, may be stored. Furthermore, if the control device 2 determined in step S11 that the length of the material W1 is shorter than the length to which the product can be manufactured, it stores a "just after replacement" flag in the processing timing information storage unit 211. If it determined that the length is longer than or equal to the length to which the product can be manufactured, it deletes the "just after replacement" flag. Alternatively, instead of the "just after replacement" flag, other information that can distinguish whether this is a processing operation immediately after new material W1 has been supplied to the first spindle 4, such as information on whether step S12 was executed in the current cycle, may be stored.

[0071] Next, the NC lathe 1 executes a gripping operation of the first spindle 4 according to the gripping command of the NC program (step S15). In step S15, the gripping force derivation means 22 derives the gripping force of the material W1 by the collet chuck 48 based on the strain of the shifter lever 33 detected by the strain detection means 333. The gripping force derived by the gripping force derivation means 22 is then linked to the stored time information and stored in the first gripping force information storage unit 212. The gripping force information stored at this time becomes the first current gripping force information.

[0072] Once the gripping operation is complete, the determination means 23 determines whether the gripping force in the first current gripping force information stored in the first gripping force information storage unit 212 is outside a predetermined range and outside the machining continuation range (step S16). As shown in Figure 7, the machining continuation range has a larger upper limit and a smaller lower limit than the predetermined range. These predetermined ranges and machining continuation ranges are set by the manufacturer of the NC lathe 1, but may be changed by operator input. The predetermined range is the range in which machining operations can be continued without problems. Outside the predetermined range but within the machining continuation range is the range in which machining operations can be continued, although a warning will be issued. Outside the machining continuation range is the range in which machining operations will be interrupted. The machining continuation range may be made to coincide with the predetermined range. If it is determined that the gripping force in the first current gripping force information is not outside the predetermined range (within the predetermined range) (NO in step S16), the process proceeds to step S21, which will be described later.

[0073] If the gripping force in the first current gripping force information is outside a predetermined range (YES in step S16), the determination means 23 reads whether or not the first-time flag is stored in the processing timing information storage unit 211 and determines whether or not the current processing operation is the first processing operation (step S17). The determination means 23 determines that if the first-time flag is stored in the processing timing information storage unit 211, the current processing operation is the first processing operation, and if the first-time flag is not stored, it determines that it is the second or subsequent processing operation.

[0074] If it is the first machining operation (YES in step S17), the determination means 23 determines that a gripping failure has occurred due to a setup error and displays this fact on the display unit 12. Also, if in step S16 it is determined that the gripping force in the first current gripping force information is outside the machining continuation range, the control device 2 stops the NC lathe 1 with an error. On the other hand, if in step S16 it is determined that the gripping force in the first current gripping force information is outside the predetermined range but within the machining continuation range, the display unit 12 displays that a gripping failure has occurred due to a setup error and proceeds to step S21, which will be described later.

[0075] If it is the second or subsequent machining operation (NO in step S17), the determination means 23 reads from the machining timing information storage unit 211 whether or not the "immediately after replacement" flag is stored therein, and determines whether or not the current machining operation is the one immediately after the material W1 is newly supplied to the first spindle 4 (step S18). That is, if the "immediately after replacement" flag is stored in the machining timing information storage unit 211, the determination means 23 determines that the current machining operation is the one immediately after the material feeder 10 has newly supplied the material W1 to the first spindle 4, and if the "immediately after replacement" flag is not stored therein, it determines that the machining operation is not the one immediately after supply.

[0076] If the machining operation occurs immediately after a new material W1 has been supplied (YES in step S18), the determination means 23 determines that a gripping failure has occurred due to an abnormal material diameter in the supplied material W1, and displays this fact on the display unit 12. As illustrated in Figure 7, the supply of material W1 is performed when the material W1 has become too short after manufacturing multiple products. Figure 7 shows an example in which material W1 is supplied every 12 products (12 cycles). Furthermore, if in step S16 the gripping force in the first current gripping force information is determined to be outside the machining continuation range, the control device 2 stops the NC lathe 1 with an error. On the other hand, if in step S16 the gripping force in the first current gripping force information is determined to be outside the predetermined range but within the machining continuation range, the display unit 12 displays that a gripping failure has occurred due to an abnormal material diameter, and the process proceeds to step S21, which will be described later.

[0077] If the machining operation is not performed immediately after a new material W1 has been supplied (NO in step S18), as shown in Figure 6, the determination means 23 determines whether the change in gripping force in the first current gripping force information relative to the gripping force in the first gripping force history information exceeds a predetermined threshold (step S19). This threshold is set by the manufacturer of the NC lathe 1, but it may be changeable by operator input. As shown in Figure 7, the determination using this threshold is performed by comparing the difference between the gripping force in the first gripping force history information and the gripping force in the first current gripping force information with the threshold, regardless of the predetermined range and the machining continuation range.

[0078] As shown in Figure 6, if the change in gripping force in the first current gripping force information relative to the gripping force in the first gripping force history information exceeds a threshold (YES in step S19), the process proceeds to step S22. If the change in gripping force in the first current gripping force information relative to the gripping force in the first gripping force history information does not exceed a threshold (NO in step S19), the determination means 23 then determines whether the gripping force in the first current gripping force information is stronger than the upper limit of a predetermined range (step S20).

[0079] If the gripping force in the first current gripping force information is stronger than the upper limit of a predetermined range (YES in step S20), the determination means 23 determines that the gripping failure is due to an unexpected cause. In this case, the control device 2 displays this fact on the display unit 12 and stops the NC lathe 1 due to an error. If the gripping force in the first current gripping force information is not stronger than the upper limit of a predetermined range (NO in step S20), the determination means 23 determines that the gripping failure is caused by wear of sliding parts such as the cam surface 42a of the shifter 42 and the tip portion 43b of the claw member 43, and displays this fact on the display unit 12. Also, if in step S16 it was determined that the gripping force in the first current gripping force information is outside the machining continuation range, the control device 2 stops the NC lathe 1 due to an error. On the other hand, if in step S16 it was determined that the gripping force in the first current gripping force information is outside the predetermined range but within the machining continuation range, the display unit 12 displays that the gripping failure is due to wear of sliding parts and proceeds to step S25, which will be described later.

[0080] If, in step S16, it is determined that the gripping force in the first current gripping force information is not outside a predetermined range (NO in step S16), the determination means 23 determines whether the amount of change in the gripping force in the first current gripping force information relative to the gripping force in the first gripping force history information exceeds a predetermined threshold (step S21). As described above, the determination in step S21 may also be performed via step S17 or step S18.

[0081] If the amount of change in the gripping force in the first current gripping force information relative to the gripping force in the first gripping force history information exceeds a threshold (YES in step S19 or YES in step S21), the determination means 23 then determines whether the gripping force in the first current gripping force information has become stronger relative to the gripping force in the first gripping force history information (step S22).

[0082] If the gripping force in the first current gripping force information is not stronger than the gripping force in the first gripping force history information (NO in step S22), the determination means 23 determines that there is a gripping failure due to an unexpected cause. In this case, the control device 2 displays this fact on the display unit 12 and stops the NC lathe 1 due to an error. If the gripping force in the first current gripping force information is stronger than the gripping force in the first gripping force history information (YES in step S22), the determination means 23 reads the first removal counter provided on the counter 215 to determine whether the number of removal operations described later is n or less (step S23). This n is a value set by the operator.

[0083] If the number of removal operations exceeds n (NO in step S23), the determination means 23 determines that the gripping failure is due to an unexpected cause. In this case, the control device 2 displays this information on the display unit 12 and stops the NC lathe 1 due to an error. If the number of removal operations is n or less (YES in step S23), there is a high possibility that foreign matter such as chips has become jammed between the collet chuck 48 and the material W1. In this case, if the foreign matter can be removed, machining can continue, so the control device 2 performs a removal operation (step S24).

[0084] In the removal operation of step S24, the control device 2 expands the diameter of the collet chuck 48 to release the grip of the first spindle 4, and then moves the first spindle 4 back and forth in the Z1 axis direction. As a result, the first spindle 4 and the material W1 move relative to each other, which may remove foreign matter caught in the collet chuck 48. In particular, foreign matter between the collet chuck 48 and the material W1 is highly likely to be removed by this removal operation. Once the execution of step S24 is complete, the control device 2 increments the first removal counter and returns to step S15 shown in Figure 5 to restart the gripping operation.

[0085] If, in step S21, it is determined that the change in gripping force does not exceed a predetermined threshold (NO in step S21), the NC lathe 1 executes the first actual machining operation, which is the manufacturing operation of the leading edge portion of the product using the first spindle 4, according to the NC program (step S25), as shown in Figure 5. Step S25 also includes the operation of transferring the cut material W2 to the second spindle 8. In step S25, the control device 2 also resets the first removal count counter. As mentioned above, the first actual machining operation in step S25 may also be executed via step S20. The NC lathe 1 executes these steps S11 to S25 until the product count counter reaches the specified number of products.

[0086] Figures 8 and 9 are flowcharts illustrating the second machining operation using the second spindle 8 shown in Figure 1. These flowcharts also show operations that are performed under the control of the control device 2.

[0087] As shown in Figure 8, the control device 2, similar to step S13, reads the production quantity counter on the counter 215 to determine whether the processing of the specified number of products has been completed (step S31). If the processing of the specified number of products has been completed (YES in step S31), the second processing operation using the second spindle 8 is terminated. If it is determined that the processing of the specified number of products has not been completed (NO in step S31), the control device 2 performs master bar measurement (step S32). In this master bar measurement, a cylindrical master bar, which is pre-installed in the NC lathe 1 and manufactured with high precision using a material that is resistant to thermal deformation, is gripped by the second spindle 8, and the gripping force derivation means 22 derives the gripping force at that time using the detection result of the second strain detection means. Since the gripped portion of the cut material W2 gripped by the second spindle 8 is often the portion that has been processed using the first spindle 4, the gripping force of the second spindle 8 when gripping the cut material W2 is affected by the precision of the processing using the first spindle 4. In contrast, by measuring the gripping force using a master bar with a known outer diameter, the gripping force of the second spindle 8 can be accurately measured without being affected by the precision of machining using the first spindle 4.

[0088] Once the master bar measurement is complete, the determination means 23 determines whether the gripping force obtained from the master bar measurement is outside a predetermined range and outside the machining continuation range (step S33). These predetermined ranges and machining continuation ranges for the second spindle 8 are common to those of the first spindle 4, but ranges specific to the second spindle 8 may also be set.

[0089] If the gripping force measured in step S32 is determined to be outside the predetermined range (YES in step S33), the determination means 23 then determines whether the measured gripping force is weaker than the lower limit of the predetermined range (step S34). If the measured gripping force is stronger than the lower limit of the predetermined range (NO in step S34), the determination means 23 determines that the gripping failure is due to an unexpected cause. In this case, the control device 2 displays this fact on the display unit 12 and stops the NC lathe 1 due to an error. If the measured gripping force is weaker than the lower limit of the predetermined range (YES in step S34), the determination means 23 determines that the gripping failure is due to wear of sliding parts such as the cam surface 42a of the shifter 42 and the tip portion 43b of the claw member 43, and displays this fact on the display unit 12. Furthermore, if the measured gripping force was determined to be outside the processing continuation range in step S33, the control device 2 stops the NC lathe 1 due to an error. On the other hand, if in step S33 the measured gripping force is determined to be outside the predetermined range but within the processing continuation range, the display unit 12 will display that a gripping failure has occurred due to wear of the sliding part, and the process will proceed to step S42, which will be described later.

[0090] If the gripping force measured in step S32 is determined to be within a predetermined range (NO in step S33), the NC lathe 1 performs a gripping operation to grip the cut material W2 processed by the first machining operation with the second spindle 8 (step S35). In step S35, the gripping force derivation means 22 derives the gripping force of the cut material W2 by the second collet chuck 81. The gripping force derived by the gripping force derivation means 22 is then linked to the saved time information and stored in the second gripping force information storage unit 213. The gripping force information stored at this time becomes the second current gripping force information.

[0091] Once the gripping operation is complete, the determination means 23 determines whether the gripping force in the second current gripping force information stored in the second gripping force information storage unit 213 is outside a predetermined range (step S36). In step S36, both whether it is outside the predetermined range and whether it is outside the processing continuation range are determined. If it is determined that the gripping force in the second current gripping force information is not outside the predetermined range (within the predetermined range) (NO in step S36), the process proceeds to step S42, which will be described later.

[0092] If step S36 is YES, the determination means 23 reads whether the first-time flag is stored in the machining timing information storage unit 211 and determines whether the current machining operation is the first machining operation (step S37). If it is the first machining operation (YES in step S37), the determination means 23 determines that a gripping failure has occurred due to a setup error and displays this fact on the display unit 12. Also, if in step S36 it is determined that the gripping force in the second current gripping force information is outside the machining continuation range, the control device 2 stops the NC lathe 1 with an error. On the other hand, if in step S36 it is determined that the gripping force in the second current gripping force information is outside the predetermined range but within the machining continuation range, the display unit 12 displays that a gripping failure has occurred due to a setup error and proceeds to step S42, which will be described later.

[0093] If it is the second or subsequent machining operation (NO in step S37), the determination means 23 determines, as shown in Figure 9, whether the amount of change in the gripping force in the second current gripping force information relative to the gripping force in the second gripping force history information exceeds a predetermined threshold (step S38). This threshold is common to the first spindle 4, but a threshold specific to the second spindle 8 may be set.

[0094] If the change in gripping force in the second current gripping force information relative to the gripping force in the second gripping force history information exceeds a threshold (YES in step S38), the process proceeds to step S43. If the change in gripping force in the second current gripping force information relative to the gripping force in the second gripping force history information does not exceed a threshold (NO in step S38), the determination means 23 then reads the rework counter and determines whether or not the rework described later has been performed (step S39). The rework counter is zero at the start of the first machining operation and is counted up when the rework is completed. In this embodiment, the upper limit for the number of reworks is set to 1, but the upper limit may be set to multiple times. The upper limit is set by the manufacturer of the NC lathe 1, but it may be changeable by operator input. If the upper limit is set to multiple times, in step S39 the determination means 23 will determine whether or not the rework counter has reached the upper limit.

[0095] If rework has already been performed (YES in step S39), the determination means 23 then determines whether the gripping force in the second current gripping force information is weaker than the lower limit of a predetermined range (step S40). If the gripping force in the second current gripping force information is stronger than the upper limit of a predetermined range (YES in step S40), it is considered that the cause is that the diameter of the gripping portion of the cut material W2 held by the second spindle 8 has changed by a small amount and become thicker than the desired diameter. For this reason, the determination means 23 determines that the gripping is poor due to thermal displacement of the first tool post 6 or wear of the first spindle tool T1, and displays this on the display unit 12 and stops the NC lathe 1 with an error. Conversely, if the gripping force in the second current gripping force information is not stronger than the upper limit of a predetermined range (NO in step S40), it is considered that the cause is that the diameter of the gripping portion of the cut material W2 held by the second spindle 8 has changed by a small amount and become thinner than the desired diameter. Therefore, the determination means 23 determines that the gripping is poor due to thermal displacement of the first tool post 6, etc., and displays this information on the display unit 12, causing the NC lathe 1 to stop due to an error.

[0096] If reprocessing has not been performed (YES in step S39), the correction value rewriting means 24 rewrites the movement correction value of the first tool post 6 stored in the movement correction value storage unit 214. The correction value rewriting means 24 has a relationship formula or relationship data between the gripping force in the second current gripping force information and the movement correction value, and rewrites the movement correction value so that the gripping force in the second current gripping force information becomes the median value of a predetermined range. At the same time, the control device 2 executes control to cut off and discard the processed portion of the material W1 gripped by the first spindle 4. After the rewriting by the correction value rewriting means 24 is completed, the control device 2 restarts the first machining operation using the first spindle 4 from step S11 with the rewritten movement correction value. The control device 2 also discards the cut material W2 gripped by the second spindle 8 to increment the reprocessing counter and restarts the second machining operation using the second spindle 8 from step S35 (end of step S41). In step S41, the first machining operation, which is re-executed from step S11, and the second machining operation, which is re-executed from step S35, become re-machining operations.

[0097] If, in step S36, it is determined that the gripping force in the second current gripping force information is not outside a predetermined range (NO in step S36), the determination means 23 determines whether the amount of change in the gripping force in the second current gripping force information relative to the gripping force in the second gripping force history information exceeds a predetermined threshold (step S42). As described above, the determination in step S42 may also be performed via step S37 or step S34.

[0098] If the amount of change in the gripping force in the second current gripping force information relative to the gripping force in the second gripping force history information exceeds a threshold (YES in step S38 or YES in step S42), the determination means 23 then determines whether the gripping force in the second current gripping force information has become stronger relative to the gripping force in the second gripping force history information (step S43).

[0099] If the gripping force in the second current gripping force information is not stronger than the gripping force in the second gripping force history information (NO in step S43), the determination means 23 determines that there is a gripping failure due to an unexpected cause. In this case, the control device 2 displays this fact on the display unit 12 and stops the NC lathe 1 due to an error. If the gripping force in the second current gripping force information is stronger than the gripping force in the second gripping force history information (YES in step S43), the determination means 23 reads the second removal counter provided in the counter 215 to determine whether the number of removal operations described later is n or less (step S44). This n is the same as the n in step S23, which is the number of removal operations of the first spindle 4, but a value specific to the second spindle 8 may be set.

[0100] If the number of removal operations exceeds n (NO in step S44), the determination means 23 determines that the gripping is faulty due to damage to the first spindle tool T1. In this case, the control device 2 displays this information on the display unit 12 and stops the NC lathe 1 due to an error. If the number of removal operations is n or less (YES in step S44), there is a high possibility that foreign matter such as chips has become jammed between the second collet chuck 81 and the cut material W2. In this case, if the foreign matter can be removed, machining can continue, so the control device 2 performs a removal operation (step S45).

[0101] In the removal operation of step S45, the control device 2 expands the diameter of the second collet chuck 81 to release the grip of the second spindle 8, and then discharges coolant from the second coolant discharge unit 91 toward the second spindle 8. Subsequently, the control device 2 blows air from the rear end to the front end of the second spindle 8 using the air blow device on the second spindle 8. These actions allow foreign matter caught in the second collet chuck 81 to be washed away or blown away. In particular, foreign matter between the second collet chuck 81 and the cut material W2 is highly likely to be removed by this removal operation. Note that in this removal operation, either the second coolant discharge unit 91 or the air blow device may be operated alone, or both the second coolant discharge unit 91 and the air blow device may be operated simultaneously. Once the execution of step S45 is complete, the control device 2 increments the second removal counter and returns to step S35 shown in Figure 8 to restart the gripping operation.

[0102] If, in step S42, it is determined that the change in gripping force does not exceed a predetermined threshold (NO in step S42), the NC lathe 1 executes the second actual machining operation, which is the manufacturing operation of the rear end portion (cut end portion) of the product using the second spindle 8, according to the NC program (step S46), as shown in Figure 8. Step S46 also includes the ejection of the manufactured product upon completion of one machining cycle. In step S46, the control device 2 resets the second removal count counter and increments the production count counter. The NC lathe 1 executes these steps S31 to S46 until the product count counter reaches the specified number of products.

[0103] According to the NC lathe 1 of this embodiment described above, the determination means 23 determines whether a gripping failure has occurred in the first spindle 4 based on at least one of the information stored in the machining timing information storage unit 211 regarding the timing of the current machining operation and the first gripping force history information, as well as the first current gripping force information. If necessary, it classifies and determines the type of gripping failure according to its cause. Therefore, gripping failures can be determined with precision. Similarly, the determination means 23 determines whether a gripping failure has occurred in the second spindle 8 based on at least one of the information stored in the machining timing information storage unit 211 regarding the timing of the current machining operation and the second gripping force history information, as well as the second current gripping force information. If necessary, it classifies and determines the type of gripping failure according to its cause. Therefore, gripping failures can be determined with precision. Furthermore, since the determination means 23 classifies the type of gripping failure according to its cause, it becomes easier for the operator to address the failure.

[0104] Furthermore, since the determination means 23 compares the change in gripping force with a threshold, it can determine that a change in gripping force caused by a small foreign object getting caught in the collet chuck 48 or the second collet chuck 81 is a gripping failure. This helps to prevent the manufacture of products damaged by such foreign objects. In addition, in this determination, the increase or decrease in the current gripping force is compared to the past gripping force, and if it increases, it is determined that a gripping failure due to foreign object jamming has occurred, thus accurately determining the type of gripping failure. Moreover, since the foreign object removal operation is performed when there is a high probability that a foreign object has jammed, the risk of the processing operation stopping due to a gripping failure can be reduced.

[0105] In addition, if the gripping force in the second current gripping force information is outside a predetermined range and the change in gripping force in the second spindle 8 does not exceed a threshold, the correction value rewriting means 24 rewrites the movement correction value to an appropriate value and performs rework, thereby improving machining accuracy and reducing the risk of the machining operation stopping due to poor gripping.

[0106] The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims. For example, although the description of this embodiment shows an example of applying the present invention to a so-called Swiss-type NC lathe 1 equipped with a guide bush 5, the present invention may also be applied to other machine tools such as lathes or machining centers that are not equipped with a guide bush 5. Furthermore, the second headstock 7, second spindle 8, and second tool post 9 may be omitted.

[0107] Furthermore, even if a constituent element is included only in the description of each of the modified examples described above, that constituent element may be applied to other modified examples. [Explanation of symbols]

[0108] 1 NC Lathe (Machine Tool) 4 1st spindle (main spindle) 8 2nd spindle (main spindle) 23 Judgment means 48. Collet chuck (gripping part) 81. Second collet chuck (gripping part) W1 Material W2 Cut Material (Material)

Claims

1. A machine tool equipped with a spindle having a gripping portion for gripping a rod-shaped material, which repeatedly performs a machining operation to process the material gripped by the gripping portion and manufacture multiple products of the same shape, A machine tool characterized by having determination means that performs a determination regarding a poor grip of the spindle based on at least one of the following pieces of information: processing timing information, which indicates the timing of the processing operation; gripping force history information, which is information about the gripping force when the gripping part gripped the material in previous processing operations; and current gripping force information, which is information about the gripping force when the gripping part gripped the material in the current processing operation.

2. The machine tool according to claim 1, characterized in that the determination means determines that a gripping defect has occurred due to a setup error if the gripping force in the current gripping force information is outside a predetermined range when the processing timing information is information indicating the first processing operation.

3. A material feeder is connected to which multiple materials are stored and which sequentially supplies the stored materials to the main spindle. The machine tool according to claim 1, characterized in that the determination means determines that a gripping failure has occurred due to an abnormal material diameter of the material supplied by the material feeder when the gripping force in the current gripping force information is outside a predetermined range when the processing timing information is information indicating the processing operation immediately after the material feeder has newly supplied the material to the spindle.

4. The machine tool according to claim 1, characterized in that the determination means determines that a gripping failure has occurred when the amount of change in the gripping force in the current gripping force information relative to the gripping force in the gripping force history information exceeds a threshold.

5. The machine tool according to claim 4, characterized in that the determination means classifies the type of gripping failure based on whether the gripping force in the current gripping force information has increased or decreased relative to the gripping force in the gripping force history information when the amount of change exceeds the threshold.

6. The machine tool according to claim 4, characterized in that, when the amount of change exceeds the threshold, and the gripping force in the current gripping force information is increasing relative to the gripping force in the gripping force history information, the machine tool is provided with a control device that causes a removal operation to be performed to remove foreign matter that has become stuck in the gripping part.

7. The machine tool according to claim 1, characterized in that the determination means classifies the type of gripping failure based on a combination of whether the gripping force in the current gripping force information is outside a predetermined range and whether the amount of change in the gripping force in the current gripping force information relative to the gripping force in the gripping force history information exceeds a threshold.

8. A tool holder on which a tool for processing the aforementioned material is mounted and which moves together with the tool, A storage means that stores a movement correction value for correcting a specified movement position specified in a machining program, The system includes a correction value rewriting means for rewriting the movement correction value stored in the storage means, The machine tool according to claim 1, wherein the correction value rewriting means rewrites the movement correction value stored in the storage means when the determination means determines that the gripping force in the current gripping force information is outside a predetermined range and the amount of change in the gripping force in the current gripping force information with respect to the gripping force in the gripping force history information does not exceed a threshold.

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